identifier: O'Leary, John Joseph <https://research.library.mun.ca/view/creator_az/O=27Leary=3AJohn_Joseph=3A=3A.html>   (1998) CROBOTS: a CAD based robot simulation tool.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis proposes a new CAD based tool for robot simulation (CROBOTS) that can be used in the design, application, and programming of educational and industrial robots. The software is written using the AutoLisp programming language and runs as a third party application inside AutoCAD R14. CROBOTS combines the impressive graphics  capability of AutoCAD with custom developed tools for revolute robot model creation, robot operation cycle planning, and robot controller simulation. Custom functions enable the automatic creation of a 3D solid model representation of robot geometry given dimensions, the teaching of point positions defining a desired robot trajectory, and the 3D graphical simulation of the manipulator's response to computed torque plus PID generated  drive torques. -- CROBOTS should prove an effective tool in the delivery of robotics related curriculum at both secondary and post-secondary educational institutions. The time required to become proficient in the use of CROBOTS should be less than that required to learn stand alone commercial software packages for robot simulation. AutoCAD's  inquiry tools, for example, may be used to facilitate the teaching of robot design concepts. Furthermore, CROBOTS can assist with the development of robot programs offline and should allow for more efficient use of limited robot hardware resources at educational institutions. -- Future developments of CROBOTS should allow modeling of additional robot mechanical configurations, the recording of significant production data, and a task level programming interface. CROBOTS should also be tested in both industrial and educational settings to determine its robustness and to identify needs for additional functionality.


identifier: Melanson, Paul M. <https://research.library.mun.ca/view/creator_az/Melanson=3APaul_M=2E=3A=3A.html>   (1998) Damage and microstructural change in laboratory grown ice under high pressure zone conditions.  Masters thesis, Memorial University of Newfoundland.

type: Thesis NonPeerReviewed

format: application/pdf application/pdf

abstract: Ice-structure interactions, where crushing is the predominant mode of failure, are characterised by zones of intense high pressure within the ice feature. This work investigates the mechanical and microstructural behaviour within these zones by using triaxial testing on laboratory grown freshwater granular ice. The latest interpretation of the behaviour of ice in high pressure zones during ice-structure interactions is presented, based on previous work at Memorial University of Newfoundland. A review of triaxial  testing on ice is also presented. -- Results of triaxial testing on ice indicate the existence of two separate but overlapping deformation mechanism regimes at high and low confining pressures. High microcrack densities followed by a  reduction in grain size by recrystallisation and restructuring were observed in low hydrostatic pressure tests (p < 30 MPa). At higher pressures (p > 40 MPa) this was replaced by more intense recrystallisation and possible pressure melting at grain boundaries and triple points. -- Triaxial tests were used in the calibration of a pressure-dependent constitutive model for granular ice. The constitutive model is based on continuum damage mechanics and uses the reduction of the standard Burgers body to a single non-linear dashpot to model the response of ice under  high stress and high strain conditions. Results show moderate agreement with test data collected from ice damaged  triaxially at constant deformation rate and loaded axially at high confining pressures,. More work is needed to improve  the calibration of the model further over a wider range of confining pressures.


identifier: Au, Colin L. <https://research.library.mun.ca/view/creator_az/Au=3AColin_L=2E=3A=3A.html>   (1997) Left ventricular volume estimation from radionuclide images using an ellipsoidal model.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis presents a method of left ventricular (LV) volume estimation that is an improvement over existing methods. The author has developed a method of left ventricular volume estimation using an ellipsoidal model. It  is shown, in this thesis, that the volume of an ellipsoid can be estimated from three planar projections (radionuclide  images). Thus, this method can be applied to estimate the volume of the left ventricle from three radionuclide images,  taken at different angles. Left ventricular radionuclide images are formed when a radioactive source is injected into  a patient. Generally, a patient's red blood cells are labelled with technetium ⁹⁹mTc which will emit gamma (γ) rays during radioactive decay. -- Two methods have been developed to estimate left ventricular volumes from these radionuclide images. Count based methods use the principle that the number of γ rays detected over a surface is proportional to the volume of the source located under that surface. Geometric methods rely on the outline of the left ventricle and the accuracy heavily depends upon how well the  geometric model fits the left ventricle. -- To test the accuracy of using this geometric method, hollow ellipsoidal models were constructed. A total of 20 trials were performed  in which the models were arbitrarily located relative to a fixed reference frame. Each image from the γ camera (elliptic in shape) was then analyzed to determine the axes lengths and angle of rotation. The estimated volumes were compared with the theoretical volume and the percentage discrepancies ranged in magnitude from 0.7% to 13.9%. -- One  problem is that it may be difficult to determine the exact location of the left ventricular projection border because of scattering, interference of radiation from other organs, and pixel size (resolution of 6.13 mm/pixel). This problem can be minimized by selecting a certain count threshold to help determine where the left ventricular border is located.  Another problem of using a geometric method of volume estimation is how well the geometric model fits the actual organ. For most cases, an ellipsoidal model does seem to be a relatively accurate model but abnormalities in the left ventricle will affect the accuracy. -- It was discovered that self attenuation caused the observed counts to differ by as much as 33.7% for images within the same trial. If a count based left ventricular volume estimation method was performed on this same set of images, then there would be a relatively large discrepancy among the volume estimates. Because of so many factors such as attenuation, self attenuation, radioactive decay, scattering, and interference  from other organs, it would appear as though count based methods would not be able to estimate accurately the volume of the left ventricle.


identifier: Meaney, Richard Benedict <https://research.library.mun.ca/view/creator_az/Meaney=3ARichard_Benedict=3A=3A.html>   (1991) Localized crushing in ice-structure interaction.  Masters thesis, Memorial University of Newfoundland.

abstract: The National Research Council of Canada conducted a medium-scale ice-indentation test program on Hobson's Choice Ice Island in May, 1990. This test series was performed as an extension to a similar program of the previous year. A description of the 1990 test program along with an extensive  characterization study of the observed failure surface is presented. More specifically, this study included measurements of the pulverized layer thickness, comparative density analysis of ice taken from the pulverized layer to undamaged ice, sieve analysis of ejected particles and microstructural studies of damage and pressure melting. -- Ice samples, both undamaged multi-year sea ice and ice from the pulverized layer, were collected and transported to the Ice-Structures Laboratory of Memorial University of Newfoundland. Uniaxial compression tests, including constant  strain rate tests and creep tests, were conducted. Estimates  of peak stress, elastic strain, delayed elastic strain and permanent viscous creep were determined and comparisons were  made between undamaged, predamaged and pulverized ice. Substantial creep enhancement was observed, that is total creep strain appeared to be heavily influenced by the damage  state. -- Utilizing measured parameters of the uniaxial compression test program, field observations and a damaging viscoelastic material model, finite element simulations were  conducted. This finite element analysis focused on the behaviour of an intermediate layer of highly damaged ice at the ice-structure interface. Indentation test NRC-06 of the 1989 test program was chosen as the verification test.


identifier: Nag, Soumya <https://research.library.mun.ca/view/creator_az/Nag=3ASoumya=3A=3A.html>   (1994) Electromagnetic plane wave scattering by uniformly lossy dielectric prolate spheroids.  Masters thesis, Memorial University of Newfoundland.

abstract: Using modal series expansions of electromagnetic fields in terms of prolate spheroidal vector wave functions, an exact solution is obtained for the scattering by: (a) a single uniformly lossy dielectric prolate spheroid, (b) a system of  two uniformly lossy dielectric prolate spheroids in arbitrary orientation, and (c) as an important special case a system of two uniformly lossy dielectric prolate spheroids   in parallel configuration embedded in free space. In all the   above cases, the excitation being a monochromatic plane electromagnetic wave of arbitrary polarization and angle of incidence. Since the dielectric materials of the scatterers are of complex relative permittivities, complex eigenvalues are evaluated for the spheroidal scalar wave functions of transmitted components of E-field and H-field expansions. Rotational-Translational Addition Theorems and Translational  Addition Theorems for spheroidal vector wave functions are used to study the scattering by a system of two spheroids in  arbitrary configuration and as a special case by a system of  two spheroids in parallel configuration respectively. These theorems are used to transform the outgoing wave from one spheroid into the incoming wave at the other spheroid. The field solution determines the column vector of the unknown coefficients of the series expansions of the scattered and transmitted fields expressed in terms of the column vector of the known coefficients of the series expansions of the incident field and the system matrix which is independent of  the direction and polarization of the incident wave. Numerical results in the form of plots for normalized bistatic and monostatic radar cross sections are given for a  variety of uniformly lossy dielectric prolate spheroids with  resonant or near resonant lengths. Also for two-body scattering, different arbitrary configurations including parallel configurations of the spheroids at different distances of separation have been considered.


identifier: Suripin <https://research.library.mun.ca/view/creator_az/Suripin=3A=3A=3A.html>   (1992) Estuarine hydraulics in a shallow deltaic estuary with reference to the Kali Garang Estuary Semarang, Indonesia.  Masters thesis, Memorial University of Newfoundland.

abstract: Most of the Indonesian rivers are characterized by the formation of deltas at the mouths. The estuaries are usually  shallow and the longitudinal bed slope low. The rivers debouch into an ocean with low to moderate marine energy. The river flow fluctuates seasonally in accordance with the monsoon season. During the wet season, from November to April, floods may occur due to the intense rainfall. The river flow becomes quite small during the hot, dry seasons. -- Naturally, the rivers bring a lot of sediments which originate from volcano ashes and erosion of the catchment basin. Most sediments flow down to the estuaries and near-shore areas during the high river flows of the rainy season.  In most cases, many hydraulics structures have been built along the river systems. They are intended for sediment control, flow regulation and flood control. -- The fluctuation of river flow is considered to be a major factor  in determining estuarine circulation patterns and delta formation. Typically, the circulation pattern shifts from that of a highly stratified estuary during the high river flow of the rainy season to that of a well-mixed estuary during the low river flow of the dry season. Furthermore, the quantity and variation of discharge in association with wave effects results in various delta geometries ranging from river-dominated to wave-dominated deltas. River-dominated deltas are characterized by highly irregular and protruding shorelines and by sediment bars deposited parallel to the direction of river flow. Wave-dominated deltas are characterized by straight shorelines with sediment barriers deposited parallel to the shorelines. -- To understand the contribution of river flow and marine forces to the behaviour of estuaries and the geometry of deltas in Indonesia, the Kali Garang Estuary has been chosen  as a subject of study. The Estuary consists of two branches:  Kali Semarang, and the West Channel. Tidal excursion, salinity distribution and circulation patterns are used to represent the estuarine behaviour. The Discharge Effectiveness Index is used to evaluate the relative contribution of river flow versus marine forces to the development of deltas. Field observations of water level, salinity, temperature, currents, and sediments were made during the dry season of 1991. Existing data sets related to  the study were also collated. -- The study shows that the Kali Garang Estuary experiences a small-diurnal tide-range (≈ 65 cm). In the manmade West Channel the tide propagates up the estuary as far as the weir. The tidal range decreases  landward and the fresh water discharge flows seaward over the saline water that intrudes landward below it. In the Kali Semarang, the tide propagates as far as its mid length.  Fresh water mixes directly with seawater, and a weak vertical stratification is experienced. The saline water moves up and down the estuary due to the flood and ebb tides. -- The coast where the estuary discharges to the sea is subject to a very moderate wave climate. Maximum wave power occurs in phase with maximum river discharge and this results in the formation of a wave-dominated delta. The high  river sediment during the rainy season is spread out by waves generated by the west monsoon. This material is then redistributed along the shoreline by waves generated by the east monsoon during the low freshwater flow of the dry season.


identifier: Jiang, Dajiu <https://research.library.mun.ca/view/creator_az/Jiang=3ADajiu=3A=3A.html>   (1994) Evaluation of shear enhancement for high-strength concrete plates.  Masters thesis, Memorial University of Newfoundland.

abstract: A research program including material investigation, experimental and analytical investigation on high-strength concrete plates are reported in this thesis. -- Material investigation was carried out on the durability of high-strength concrete tensile properties under cold ocean environment (freeze-thaw cycles). Tensile properties of high-strength concrete in terms of modulus of rupture, direct tensile strength and fracture energy were examined up  to 700 freeze-thaw cycles in laboratory simulated environment. -- An experimental investigation on shear enhancement was carried out on seven high-strength concrete slabs to study the punching shear capacity and shear enhancement. Five types of different shear reinforcement, namely single bending, U-stirrup, double bending, shear-stud  and T-headed shear reinforcement were tested and evaluated. The emphasis is placed upon the evaluation of their contribution to punching shear capacity of high-strength concrete plates. Structural behaviours were evaluated in terms of overall load-deflection response, ultimate loading capacity, post-ultimate loading capacity, ductility and energy absorption. Failure patterns and strain distribution were also discussed. -- The analytical investigation was conducted by using the finite element analysis. The finite element analysis reported herein is an application of the nonlinear analysis of reinforced concrete structures using three-dimensional solid finite element. The purpose of this application is based on the fact that employing three-dimensional elements is the only successful way to model out-of-plane shear reinforcement in the slabs. Hence, the three-dimensional twenty node brick element with 2x2x2 Gaussian integration rule over the element faces and a plasticity-based concrete model were employed in a finite element program. Single bending and double bending shear reinforcement were modeled with the smeared layer method, while shear-stud and T-headed shear reinforcement were depicted individually in the mesh. Reasonable agreement has been obtained between the numerically predicted behaviour and experimental test results. Transverse shear stress was evaluated by the finite element analysis in terms of punching shear, and compared with the unfactored punching shear resistance specified by the Canadian building design code.


identifier: Kananto <https://research.library.mun.ca/view/creator_az/Kananto=3A=3A=3A.html>   (1993) Evaluation of techniques for estimating reference evapotranspiration for Jawa-Indonesia.  Masters thesis, Memorial University of Newfoundland.

abstract: Due to the shortage of measured consumptive use of water for  crops (i.e., evapotranspiration, ETc) in Indonesia, estimation of reference evapotranspiration (ETo) using climatological data is necessary in order to determine crop water requirements for irrigation planning and operation. -- The objectives of this study are to compare 24 methods of estimating ETo, and to adjust selected methods to the standard method recommended by the Food and Agricultural Organization (FAO) of the United Nations and to derive new empirical equations using regression analysis of published climatological data. This study uses 4156 monthly data values from 50 stations on Jawa. -- In this study, the methods are classified into 4 categories according to the number of climatic variables (i.e., from one to four) used in the equation. From each category, the most promising method is selected and the possibility of adjusting the method to give results closer to that of the standard method  is investigated. In addition, simpler empirical equations for each category are derived using regression analysis. -- The methods which use a greater number of variables and where solar radiation is the dominant factor in estimating reference evapotranspiration gave the best results. All the non-standard methods required adjusting to give results that  are, on average, equal to the standard method. The new empirical equations derived by regression analysis gave excellent results and are easy to use when compared to both the standard and nonstandard methods.


identifier: Zheng, Wen Jie <https://research.library.mun.ca/view/creator_az/Zheng=3AWen_Jie=3A=3A.html>   (1991) Experimental hydrodynamic study of a novel globe-shaped submersible fish cage system.  Masters thesis, Memorial University of Newfoundland.

abstract: In order to meet the increasing requirement of farming fish in more exposed offshore sites, a novel globe-shaped submersible fish cage system with two tension mooring lines has been proposed. In normal sea conditions the cage remains  on the surface; during storms the cage can be submerged some  distance below the water surface to reduce the wave forces and motions of the cage and hence reduce the forces in the mooring system and the stress on the farmed fish. Since the proposed system is a quite new design concept, few theoretical and experimental results can be found to guide the prototype design. -- To have a better understanding of the hydrodynamic performance of the proposed system, qualitative analyses were conducted and a series of resistance tests and moored tests were carried out with two globe-shaped cage models, one spherical and the other geodesic, to study the resistance forces of the cages in currents and the motion and mooring force responses of the cage system in waves. In the resistance tests, three orientations of the cage axle to the current direction were tested. In the moored tests, three submerged positions and three orientations were tested and the effects of pretension  and axial stiffness of the mooring lines were investigated in both regular waves and irregular waves. -- The study shows that the relationship between the current velocity and  the resultant resistance force can be interpolated very well  with a quadratic equation regressed from the test results. Provided the Reynolds numbers of the cage elements are still  within the range of subcritical flow regime, the regressed equation can also be used to extrapolate the resistance force outside the Reynolds number range tested. -- The study  also shows that the method of submerging the cage below the water surface to reduce the motions of the cage and the forces in the mooring system is very effective in deep water  waves, but becomes less and less effective in intermediate water waves. The pretension of the mooring lines has little effect on the dynamic mooring force and motion responses of the cage system as long as the mooring lines do not go slack. The stiffness of the mooring lines has a significant effect on the responses of mooring force, heave and roll, but has little effect on the responses of surge and sway. When the cage is perpendicular to the wavefront, the vertical displacement and mooring force on one side of the cage may be significantly larger than those on the other side because of the phase difference between the heave and roll motions of the cage.


identifier: Leung, Kirk Sing-Keung <https://research.library.mun.ca/view/creator_az/Leung=3AKirk_Sing-Keung=3A=3A.html>   (1993) Experimental study of the effect of forward speed and heel angle on lift roll damping of small fishing vessels.  Masters thesis, Memorial University of Newfoundland.

abstract: An experimental study was carried out to investigate the effect of forward speed and heel angle on the bare hull lift  component of roll damping. The effect of the presence of a rudder was also studied. Experiments were performed on two ship models with different hull characteristics. One of the models was also tested fitted with a rudder to investigate the effect of the rudder. The experiments were conducted in calm water with the ship model restrained from moving freely in any of the six directions. Models were oriented in different combinations of fixed heel angles and yaw angles, and towed at various forward speeds. The lift force and moment acting on the ship hull were measured and the lift coefficient and moment arm were calculated. -- Experimental results show that the lift coefficient is a nonlinear function of the angle of attack. It is also dependent on heel angle and forward speed. The moment arm was found to be  a nonlinear function of both heel angle and forward speed. Its value decreases as heel angle increases. An empirical formula was derived from the experimental results to determine the equivalent linear damping coefficient for lift  roll damping. The empirical formula shows that the equivalent linear damping coefficient is a nonlinear function of forward speed. The lift roll damping will increase with increasing forward speed. On the other hand, increasing heel angle leads to a decrease in the value of the equivalent linear damping. Comparison between the empirical formula and Ikeda's formula indicates that Ikeda's  formula underestimates the equivalent linear damping. The discrepancy increases with increasing forward speed. Effect of the presence of a rudder is significant only at low speeds. -- Neither Ikeda's formula nor the experimental results consider the sinkage of the ship while moving. This may be covered in future work.


identifier: Zhang, Suimin <https://research.library.mun.ca/view/creator_az/Zhang=3ASuimin=3A=3A.html>   (1993) Experimental study of the effect of forward speed and following waves on roll damping of fishing vessels.  Masters thesis, Memorial University of Newfoundland.

abstract: An extensive experimental program has been carried out to estimate roll damping parameters for three models of fishing  vessels having different hull shapes and moving with forward  speed. Roll damping parameters are determined using a novel method. This method combines the Energy method and the Modulating Function technique. The results show that this method gets better estimates compared with the original Energy method. -- A data processing system was designed to process the experimental data. A parameter Cerror was introduced to measure the error in roll damping identification. A database system was developed using VAX-Pascal to store the analytical results and perform various kinds of analyses. The data management and processing system  in this research work has proved to be very efficient. -- The effect of forward speed, initial angle and natural frequency on roll damping is discussed. The effect of forward speed on roll damping was found to be nonlinear. The  effect of initial angle is strong at zero and low forward speeds and decreases as the forward speed is increased. The effect of natural frequency was found to be weak. -- Ikeda's  method was used to predict the roll damping coefficient. The  results were compared with the experimental data. It was found that Ikeda's method overestimates the roll damping at higher forward speeds for all three models. This method fails in predicting the eddy damping for ship forms with hard chines. It was noticed that as models move with forward  speed, their mean drafts increase. A modification to Ikeda's  formula is proposed, making use of this observation. The values predicted by the modified formula fit the experimental data very well. -- A preliminary experiment has  been done to investigate the effect of following waves on roll damping. It has been found that estimating roll damping  parameters, without allowing for the time variation in the restoring moment, results in overestimating the values of these parameters. Further work is needed in this area.


identifier: So, Brian H. P. <https://research.library.mun.ca/view/creator_az/So=3ABrian_H=2E_P=2E=3A=3A.html>   (1993) Experimental testing of stand-alone digital relay for power transformers.  Masters thesis, Memorial University of Newfoundland.

abstract: The differential protection scheme is one of the most widely  used techniques in power system protection, especially for power transformers. This method extracts harmonic components  from current signals via current transformers using various digital filtering algorithms to make protection decisions. Different researchers reported that they have found the best  algorithms for their transformer differential protection schemes. However, since their test results are usually based  on different equipment, it is difficult to compare the relative performance of the test results. For the protection  of various types of transformers, both the hardware and software of the earlier protection units may have to be changed. -- Presented in this thesis is a stand-alone microprocessor based digital relay that has been designed and implemented. Only the software modification is required to accommodate the protection of different types of transformers. The hardware portion of the design consists of  seven identical scaling circuits, a sixth order Chebyshev anti-aliasing filter, a sample-and-hold circuit, and a multiplexer which is connected to an analog-to-digital converter on the TMS32010 boards. The TMS32010 signal processor is used to compute the power transformer data. The  digital relay is designed in a modular form such that the hardware part is a "black box" to the users. -- The software  has been written in TMS assembler language which includes second and fifth harmonic restraints with ground fault plus internal and external protection. Five digital filtering algorithms are used to extract the harmonic components. These algorithms are: Discrete Fourier Transform, Walsh Functions Algorithm, Rectangular Transform Algorithm, Finite  Impulse Response filtering, and Least Squares Algorithm. The  digital relay was tested extensively in the laboratory using  the five algorithms. By comparing the real time performance of these algorithms, Discrete Fourier Transform (DFT) was found to be the best among the algorithms presented. As a result, a transformer protection test set-up has been developed using DFT. This test set-up can be used for the protection of any kind of three phase transformer with minor  changes on the relay software.


identifier: Davies, Isaac <https://research.library.mun.ca/view/creator_az/Davies=3AIsaac=3A=3A.html>   (1992) Electromagnetic wave propagation in a coaxial waveguide with an annular magnetized ferrite rod.  Masters thesis, Memorial University of Newfoundland.

abstract: The propagation of electromagnetic waves in a coaxial waveguide loaded with ferrite is studied by using the exact analysis approach. The results of the partially filled ferrite case (radii ratio 'So = 0.5') and the approximately fully filled ferrite case (radii ratio 'So = 0.9') are given  for the dipolar modes (n = ±1). The ferrite used is assumed to be lossless and completely magnetized. A review of the electromagnetic wave propagation in an infinite ferrite medium is presented to point out the various wave propagation characteristics in the parametric space diagrams. In the exact analysis method, the general dispersion relations are derived directly from Maxwell's equations. Initially, the cutoff and resonant frequencies are examined analytically to predict all possible modes. By employing numerical root search technique the complete dispersion characteristics are obtained. -- The occuring modes in the different parametric regions are identified and  properly classified to provide a better understanding of the  basic mode structure in these types of waveguides which are filled with anisotropic materials. Also, the effects of the radii ratio and the dc magnetic field on the various modes are discussed. Finally, some applicational aspects of such waveguides are considered, especially, in the design of phase shifters where the characteristics of the pairs of dominant waveguide modes play an important role.


identifier: Appleby, Richard Charles Edward <https://research.library.mun.ca/view/creator_az/Appleby=3ARichard_Charles_Edward=3A=3A.html>   (1993) Equipment replacement analysis for publicly owned fleets.  Masters thesis, Memorial University of Newfoundland.

abstract: The economic life of equipment is the point in time when the sum of all equipment costs are minimum.  The factors associated with equipment costs are operating and maintenance costs, ownership costs, obsolescence costs, parts cost, downtime cost and training costs.  With today's economy, public sector agencies are finding it more and more difficult to acquire the funding necessary to operate, maintain and replace their equipment fleets.  In many cases, equipment is used far beyond its optimum economic life because of this lack of funding.  In these cases, the fleet manager requires some method of prioritizing the equipment replacement list. -- In order to effectively plan equipment replacement purchases, the fleet manager must have the ability to forecast future costs.  In some cases, geographic location has an impact on delivery time of new equipment to the public agency and forecasting future equipment costs can provide the lead time necessary to order the new equipment before the end of its economic life.  In other cases, the timing of budget approval for replacement funding can delay the purchase of new equipment. -- The criteria used for deciding when equipment should be replaced vary from one agency to the next.  There are also some differences in the criteria used depending on whether the agency is public or privately owned. -- There are several fleet replacement techniques available to the fleet owner.  In general terms, the life cycle cost method, interval life method and nomographs are commonly used.  Each method has varying degrees of complexity.  The causes of each method depends on the accuracy of the input information used by the fleet manager. -- Commercially prepared software is available to the fleet manager to assist in the equipment replacement decision.  These software packages perform different types of fleet management functions.  Fleet managers should thoroughly investigate the software being considered to ensure it fulfils their needs. -- Fleet replacement models can be developed in-house or by computer software consultants.  The model should be designed so that it is adaptable and easily modified by the fleet owner.  It should have the ability to compile cost data in a concise and logical format.  It should also have the capability of forecasting future equipment costs and provide the fleet manager with a priority listing of equipment to be replaced.


identifier: Eaton, Norris William <https://research.library.mun.ca/view/creator_az/Eaton=3ANorris_William=3A=3A.html>   (1997) Mini-hydro systems using induction generators.  Masters thesis, Memorial University of Newfoundland.

abstract: This study has focused on developing and documenting a systems approach toward modern electrical design that minimizes the cost of building and operating a grid-connected mini-hydro plant. The thesis applied innovative electrical design to reduce capital costs, lower operating costs, increase efficiency, and maximize revenue. This was achieved by following a multi-diciplined engineering approach, selecting a standard three-phase squirrel cage induction motor as the grid-connected induction generator, automating and remotely controlling the plant to eliminate the cost of a full-time operator, and incorporating an innovative diagnostic expert system to quickly assist in isolating the cause of a plant shutdown. -- It was clearly established that a significant reduction in the capital cost  of electrical equipment is achievable if the squirrel cage induction motor is used as the induction generator. The "off-the-shelf" induction motor and standard solid-state motor starter are relatively inexpensive in comparison to custom induction or synchronous generators. Since standard three-phase, 575V induction motors have ratings less than 200 kVA, the focus was on grid connected mini-hydro developments with an installed capacity of less than 200 kVA. Stand-alone plants, similar to those found in isolated communities and mining sites, were not considered. -- Knowing when to use an induction generator, and the type of control philosophy to implement, is based on the assumption the electrical designer has an understanding of the complete  mini-hydro development process, consequently the thesis also  covered the general design of mini-hydro systems. While this  is not an exhaustive treatment of the subject matter, it is an indication of the level of understanding required for the  electrical design. -- The thesis documents the theory, performance characteristics, and design considerations associated with an induction generator, in an effort to evaluate the appropriateness of installing the induction generator at a grid-connected location. Also, a method was presented for selecting the standard squirrel cage induction  motor to use as an induction generator. Induction generator protection requirements, utility protection, and mechanical systems protection were investigated, and modern solutions proposed. The PLC was used to automate the plant and cost effective remote control options were explored. An innovative and novel diagnostic expert system was developed and demonstrated. Finally, the systems approach and documentation of modern electrical design and operating methods was applied to a practical example, a 150 kW installation proposed for Nipper's Harbour.


identifier: Budipriyanto, Agung <https://research.library.mun.ca/view/creator_az/Budipriyanto=3AAgung=3A=3A.html>   (1993) Modal testing and analysis of uncracked and cracked plates in air and in water.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis has investigated the analytical and experimental   changes that occur in modal parameters (i.e., natural frequency, damping and peak response magnitude) of a vibrating horizontal cantilever plate due to the presence of  a crack and due to immersion in two fluids having different densities. Three plates were investigated, viz., an uncracked plate and two cracked plates with 1/32" and 3/32" crack depths, machined on both sides of the plates. -- From the analycal study, it was found that cracks caused the natural frequencies of plates in air to reduce by a maximum of 3% and also changed the modal vectors slightly. The modal  vector changes were mainly around the region of the cracks. It was also observed that the modal vectors changed from "in  vacuum" to "in air" condition. -- Experiments were carried out in air and at two levels of water submergence. For the experiment in air, it was observed that due to the presence of a 2x1/32" crack, the natural frequencies of the plate were lowered by a maximum of 0.75% than the uncracked one. When the water level was just about the middle of the plate thickness, the natural frequencies reduced by as high as 26.8% and the damping increased by 5 times. For full submergence (where the water level was about 23 cm above the  upper surface of the plate), a maximum natural frequency reduction of 40% and damping increase of about 6 times were observed. -- Experimental and analytical results were compared for plates tested in air. The maximum difference between the measured and the predicted natural frequencies were found to be within 8.6%. The correlation of normalized peak strain response magnitudes were good for modes one, two  and four.


identifier: Lin, Yude <https://research.library.mun.ca/view/creator_az/Lin=3AYude=3A=3A.html>   (1993) Modeling long term serial correlation in flood series.  Masters thesis, Memorial University of Newfoundland.

abstract: The standard assumption in flood frequency analysis is that annual peak flows are independent events. Hydrologists pay little attention to the serial correlation of flood peak series in flood frequency analysis because standard statistical tests for independence usually do not reject the  null hypothesis of serial independence at the 90% or 95% confidence level for most rivers. This study was undertaken to investigate the validity of this assumption with regard to Canadian rivers by statistically analyzing the short-term  and long-term dependence of annual peak flows. Ninety stationary flood series of Canadian rivers were tested by eleven tests for short-term dependence and one test for long-term dependence. The results show that about 18%(at 5% level) - 28%(at 10% level) flood series passed the short-term dependence tests but failed the long-term dependence test. The presence of long term serial correlation in flood series is evident and can not be disregarded in flood risk analysis. -- Modeling annual flow series by considering the effect of both short-term and long-term dependence was then discussed. This study considered two newly developed models:  harmonic analysis of cumulative departures, and the mixed-noise model. These two models were further developed and a comparison between them was made. Finally, the effect of long-term dependence on flood risk analysis is evaluated using Monte Carlo simulations. It was found that neglecting serial correlation could cause considerable uncertainty in the estimated flood risk.


identifier: El-Hawary, Ferial M. <https://research.library.mun.ca/view/creator_az/El-Hawary=3AFerial_M=2E=3A=3A.html>   (1981) Modelling and signal processing for identification of ocean subsurface features from acoustic reflections.  Doctoral (PhD) thesis, Memorial University of Newfoundland.

abstract: This thesis is concerned with aspects of modeling and signal processing for identifying features of the ocean subsurface layered media on the basis of acoustic reflection data. Techniques from communications and signal analysis are combined with estimation and system theory to develop procedures to estimate the properties and characteristics of  underwater sediments and layered strata. -- Models of the response of the subsurface to acoustic or seismic source signals are reviewed and classified. A layer indexed reflection model that accounts for higher order reflections in a systematic manner is detailed. This provides the basis for the estimation task. -- Reflection data are generated and acquired using a towed-body system, the so-called "fish", which  contains the acoustic source and sensors. The  motions of the deep towed system introduce inaccuracies in the reflection data. The fish dynamics exhibit a degree of regularity which is utilized in the design of a Kalman-based  filter for estimating the heave effects. The estimates are then used to remove the heave component from the reflection data. -- The problem of estimating amplitude and delay parameters associated with replicas of the source signal primary and multiple reflections imbedded in the return signal is investigated. Three proposed estimation procedures  are given. The first adopts a sequential algorithm where the delay parameters are estimated first followed by those of the corresponding amplitudes. A second approach developed in this thesis involves the simultaneous evaluation of all the parameters of interest. The third procedure is based on a balance property inherent in the source signal waveforms. -- The proposed procedures are evaluated utilizing simulated return records to provide a basis for comparing the effectiveness of each. The application of the procedures to actual field data obtained in a sea-trial in outer Placentia Bay, off the coast of Newfoundland is given.


identifier: Kennedy, Kurt Patrick <https://research.library.mun.ca/view/creator_az/Kennedy=3AKurt_Patrick=3A=3A.html>   (1990) Dynamic activity and crushed ice behavior in medium-scale ice-structure interactions.  Masters thesis, Memorial University of Newfoundland.

abstract: Experimental procedures and results from ice indentation programs conducted by Mobil Oil Canada at Pond Inlet (1984) and by Memorial University of Newfoundland on Hobson's Choice Ice Island (1989) are detailed. Both field programs utilized a hydraulically powered servo-controlled indentation system with a series of spherical and flat indenters. Nominal contact areas in the experiments ranged from 0.02 m² to 3.0 m². The most significant observation in the testing programs was the development of a dynamic load-time trace, i.e., ice-induced vibrations, with frequencies in the area of 30 Hz. Alternate pulverization of ice and clearing (extrusion) of crushed ice products from the impact  zone is suggested as the primary mechanism for the observed dynamics, consistent with previous research. -- The Pond Inlet and Ice Island data sets are examined with emphasis on  the behavior of crushed ice during the extrusion cycle and its importance to the overall dynamic process, including crushed ice layer thickness, impact area reduction by spalling, and dynamic response spectra. Crushed ice layer thickness is observed to vary across the impact zone and, together with highly variant local pressures, suggests that crushing and extrusion takes place in localized areas. These  high pressure zones, or "hot spots", vary both spatially and  temporally and make it difficult to infer a pressure distribution across the entire impact zone. Rather, the impact area may be thought of as a collection of small hot-spots (high pressure zones) linked by a matrix of highly damaged or pulverized ice under low pressure. -- Loads and pressures observed in the experiments are simulated by treating crushed ice as an incompressible linear viscous fluid during the extrusion cycle. Simulation of load and central pressure for a spherical patch loading case is discussed in greatest detail and a body of data is developed  for an indentation test which exhibited dynamic behavior in both load and central pressure. Examples of a two-dimensional incremental analysis for irregular crushed ice layer thickness profiles and extrusion over a three-dimensional elliptical contact zone are also presented.


identifier: Liu, Liqiang <https://research.library.mun.ca/view/creator_az/Liu=3ALiqiang=3A=3A.html>   (1995) Dynamic behaviour of a cracked shaft on elastic supports.  Masters thesis, Memorial University of Newfoundland.

abstract: This is a simple but comprehensive study of the dynamic behavior of a shaft with a crack on elastic supports. The analysis is restricted to the single span shaft with uniform  circular cross-section. The natural frequency and modes of vibration of a shaft having a transverse crack are investigated using the finite element method. The local flexibility due to the crack is evaluated using the theory of fracture mechanics. The effect of crack depth on the natural behavior is discussed. The results show that an increase in the depth of the of crack magnifies the response  amplitude and decreases the natural frequencies. The effect of elastic supports on the dynamic behavior of the shaft is presented through computation. The range of maximum effect is given. -- The element stiffness matrix of a cracked shaft  considering the longitudinal translation and axial rotation is first presented. This makes it possible to analysize the dynamic response of a practical shaft by FEM. A Fortran-77 program is developed which can be used to calculate the two and three dimensional vibration of a shaft containing more than one transverse crack, concentrated mass and elastic foundation. It can also be used in multi-span shaft with different cross-section and applied to some loads.


identifier: Chen, Yin <https://research.library.mun.ca/view/creator_az/Chen=3AYin=3A=3A.html>   (1992) Dynamic characteristics and modal parameters of a plate with a surface crack.  Masters thesis, Memorial University of Newfoundland.

abstract: A systematic study of the behaviour of a plate with a surface crack is carried out using the finite element method. Static, steady state, resonant and transient responses of the cracked plate are examined. Strain, displacement and acceleration responses without/with the crack are computed. Modal analysis is performed to determine  the natural frequencies, mode shapes and strain/displacement  frequency response functions. Frequency response functions without/with the crack are computed. Strain mode shapes, as well as displacement mode shapes, are obtained. The difference of the strain mode shapes between the uncracked plate and the cracked plate is calculated. Each of the parameters mentioned above is examined to determine the sensitivity of this parameter to the crack that occurs in the structure. -- By using all the methods of analysis mentioned above, and comparing the sensitivity of different parameters to cracking, it is found that the surface crack in the structure will affect most of the dynamic characteristics such as strain/stress field around the crack, natural frequencies of the structure, amplitudes of the response and mode shapes. Some of the most sensitive parameters are the difference of the strain mode shapes and the local strain frequency response functions. By monitoring  the changes in the local strain frequency response functions  and difference of strain mode shapes, the location and severity of the crack that occurs in the structure can be determined. Based on these results, suitable procedures for detecting the crack in real structures are suggested.


identifier: Thangam-Babu, Potti V. <https://research.library.mun.ca/view/creator_az/Thangam-Babu=3APotti_V=2E=3A=3A.html>   (1981) Dynamic fluid-structure interaction analysis of floating platforms.  Doctoral (PhD) thesis, Memorial University of Newfoundland.

abstract: The thesis presents finite element analyses of dynamic fluid-structure interaction effects on the response of floating structures subjected to earthquake forces. -- The transmission of seismic accelerations from the sea bottom to the surface through the water medium is studied using a system of lumped masses, springs and dashpots.  Horizontal accelerations are not transmitted to the surface since the water is a shear-free medium.  Depending on the water depth, vertical accelerations transmitted to the bottom of the floating structure are found to be amplified to about 30 to 40 times compared to those at the sea-bottom.  Cavitation, a non-linear effect of the water medium wherein the fluid detaches from the structure, is a possibility for greater depths and higher accelerations. -- The coupled fluid-structure interaction is studied with finite element modelling.  The resulting unsymmetric coupled equations of motion incorporate surface wave effects, radiation damping effects, fluid-structure interface hydrodynamic interaction, and the structural flexibility. -- A new numerical integration scheme, based on the Wilson-O method, to solve the coupled unsymmetric equations of motion is discussed in detail.  The procedure is illustrated for a floating nuclear plant (FNP) and a liquid petroleum gas (LPG) storage facility subjected to amplified earthquake accelerations.  The results are compared with those obtained by using approximate techniques. -- As an alternative approach, since the principle of superposition is valid for linear analysis, the structure and the fluid are isolated and analyzed separately.  The analysis discussed in the previous paragraph yields the hydrodynamic pressures acting at the interface of the floating structure.  Thus, the floating platform itself is modelled as a thick plate resting on an elastic foundation; the platform is discretised with a newly developed high precision triangular thick plate bending element resting on an elastic foundation.  The hydrodynamic pressures are simulated as external forces acting on the fluid-structure interface, in addition to the earthquake forces, and the response is evaluated using the standard Wilson-O method in the time domain; the frequency domain analysis is also carried out.  Two illustrative numerical examples (the floating nuclear plant and the liquid petroleum gas storage facility) are provided. -- A computer program, FLUSIN, has been developed to perform all the above analyses described.  Its organization is similar to NONSAP, and is very flexible to adapt for other types of offshore structures.


identifier: Yu, Rong <https://research.library.mun.ca/view/creator_az/Yu=3ARong=3A=3A.html>   (1995) Dynamic response of a floating dock in regular and irregular waves.  Masters thesis, Memorial University of Newfoundland.

abstract: As a result of the increasing interest by engineers and port  operators in floating docks to resolve port construction problems, the need for investigating the dynamic response of  such structures increases. Since it is not cost effective to  carry out tests on an actual operating floating dock in the ocean, an alternative solution is to undertake parametric model tests. Very few experiments using a floating dock model have been published. -- To establish the motion response and mooring forces of a typical floating dock in both regular and irregular waves in beam seas, an experimental program using a 1:9 scale model of a moored floating dock has been conducted. For each mooring configuration (free floating, crossed, crossed-connected and  non-crossed), tests were undertaken at a 5:1 mooring ratio (horizontal distance to water depth) with prototype wave periods of 3 to 15 seconds. In all cases roll, heave and sway motion responses were obtained. The experiments were conducted in a wave tank equipped with a pseudo random wave making facility. To obtain the response amplitude operator (RAO) from the ambient response data, spectral analysis techniques were used. -- There is very good agreement between regular and irregular wave data. The RAO curves for roll, heave, sway and mooring forces show that the non-crossed mooring configuration should be employed where the situation permits since it will decrease the roll motion and  mooring forces with respect to crossed and crossed-connected  designs. There appears to be no benefit in either of the mooring designs for heave response. The RAO remains relatively constant regardless of wave height and period. -- Based on the findings of the study, areas for further research have been identified and recommendations made for further work on floating dock designs.


identifier: Ganugapati Seshu Srilakshmi <https://research.library.mun.ca/view/creator_az/Ganugapati_Seshu_Srilakshmi=3A=3A=3A.html>   (1996) Edge detection methods for speckled images.  Masters thesis, Memorial University of Newfoundland.

abstract: Images obtained from coherent imaging systems such as laser,  sonar, radar, synthetic aperture radar (SAR) and ultrasound are often corrupted by a phenomenon known as image speckle. Speckle is characterized as multiplicatively signal dependent and may be spatially highly correlated noise. It differs from other types of noise such as the additive white  Gaussian noise (AWGN) most commonly found in digital images.  Observed from a human or computer vision point of view speckle gives a granular patterned appearance to images, thus obscuring underlying image details. -- Gradient methods  taking differences between pixel values may give inconsistent estimates regarding true edge pixels and therefore are not suited for use with speckled images. By contrast, taking ratios between the pixel values tends to factor out the multiplicative noise effect present in speckled images and to generate meaningful edge maps for these images. But these methods generate thick and ambiguous  edge maps, and may also require gradient information supporting the ratio edge strength values in order to generate better edge maps on speckled images. This thesis investigates methods to improve the performance of existing speckle specific edge detection operators. A ratio edge detector based on maximum strength edge pruning (MSPRoA) which uses both edge strength magnitude and direction is proposed. -- The MSPRoA method is different from previous methods in that it uses the edge orientation information that is implicitly expressed in some other ratio based methods,explicitly, thus enabling the generation of precise and well defined edge maps for speckled images. The MSPRoA method does not require either gradient information or edge thinning operators and hence computational savings are achieved. The use of the MSPRoA at multiple scales in order to extract edge information at both micro and macro levels is also suggested. The MSPRoA and multi-scale MSPRoA methods  are tested using both synthetic and real airborne SAR images  of varying scene contents and business. Test results which confirm the suitability of the method for use on speckled images are presented. The use of the MSPRoA method is recommended for detecting edges images in which speckle phenomena are manifest.


identifier: Bhattacharya, Bibhas <https://research.library.mun.ca/view/creator_az/Bhattacharya=3ABibhas=3A=3A.html>   (1993) Fatigue crack growth characteristics of offshore structural steel in marine environment.  Masters thesis, Memorial University of Newfoundland.

abstract: Corrosion fatigue of a metal is a more severe form of fatigue phenomena in the presence of a corrosive environment like seawater or sour gas. The enhanced fatigue crack growth rate has been attributed in part to the anodic dissolution (oxidation of metal) at the crack tip and to hydrogen embrittlement. Numerous studies have produced a wide variety of results regarding the effect of anodic dissolution and cathodic protection on the corrosion fatigue rate of high strength steel. Anodic dissolution can either cause an enhanced crack growth rate or a crack tip blunting causing a much delayed crack initiation or even a crack arrest. There is, however, some consensus about an optimum range of cathodic protection potential (-830mV SCE), around which the offshore steels achieve the maximum corrosion fatigue life. A more positive potential fails to stop the anodic dissolution. A more negative potential causes a higher crack growth rate, (most possibly by generation of hydrogen and hydrogen embrittlement). Micro-organisms, especially Sulfate Reducing Bacteria have been known to have enhanced metal corrosion fatigue. There are mainly two mechanisms responsible for such enhancement. During the respiration process hydrogen is consumed from the system which causes a cathodic depolarisation. Hydrogen sulphide is produced at the end of the respiration cycle, which is known for its contribution to hydrogen embrittlement. -- It is important to understand more about the corrosion fatique phenomena of offshore structural steel in a marine environment. In the present study corrosion fatigue behavior of CSA G 40.21 M 350 WT steel is investigated. Tests were conducted in air, seawater and seawater with cathodic protection. Compact Tension specimens and ASTM substitute seawater had been used in the present study. Crack growth data was acquired using the Alternating Current Potential Drop technique. The data were then analysed according to the ASTM recommendation E647, 1981. A potential of -830 mV (SCE) was applied during the cathodic protection tests. The loading of frequency was 3Hz in air and 0.167Hz in seawater. The air tests were conducted at room temperature and the seawater tests were conducted at 5ﾟC. The stress ratio for all the tests was 0.05. -- Multiple tests conducted in similar environments produced highly agreeable results. Free corrosion crack growth rate for the intermediate range of ΔK was about 1.5 to 2.0 higher than that in air. However, applying a cathodic protection of -830mV (SCE) reduced the crack growth rate to the level of crack growth rate in air. For all the corrosion fatigue tests (both cathodically protected and freely corroding) ΔKth value was found to be higher than that in air.


identifier: Li, Wali <https://research.library.mun.ca/view/creator_az/Li=3AWali=3A=3A.html>   (1992) Development of high-performance control and parallel processor implementation for induction motor drives.  Masters thesis, Memorial University of Newfoundland.

abstract: Implementations of the most popular scheme of indirect field-oriented control for AC induction motor drives still suffer from difficulties due to the sensitivity of rotor parameters in decoupling torque and flux and control algorithm complexity in meeting real-time control requirements. -- This thesis presents solutions to some of these problems. A new parameter adaptation control scheme, named rotor flux orientation control, is proposed and verified by digital simulations which show a very good result in dynamically correcting the mismatched value in the  slip frequency calculator that usually occur when temperature rises or flux saturates. This method is base on the principle of feedback control which uses the detected rotor flux orientation as a feedback control signal. -- For processing complex control algorithms in real-time, a new parallel processor architecture, using T800 Transputers, is proposed. Implementation results show that with this parallel processing controller complex control algorithms such as field-oriented control and parameter adaptive control together can be handled in very short processing times thus meeting fast dynamic control demands. -- In addition, the design of indirect field-oriented control of AC induction motor is studied. A design method for linear control of AC induction motor control based on the indirect field-oriented control scheme is proposed. Decoupling of torque current and flux current is achieved by applying feed-forward controllers. -- A new control scheme, named extended indirect field-oriented control, is proposed and verified by simulation results which show an excellent control performance that cannot be achieved by a linear control scheme. -- Furthermore the incorporation of fault tolerance for Transputer communication link failures and processor failures is studied and some simulation tests have  been carried out. As a result of the fault tolerance mechanisms incorporated, control system reliability is improved.


identifier: Rivera, Carlos Octavio <https://research.library.mun.ca/view/creator_az/Rivera=3ACarlos_Octavio=3A=3A.html>   (1995) Hydrodynamic loads on underwater robot arms.  Masters thesis, Memorial University of Newfoundland.

abstract: Computed Load and Sliding Mode control strategies for robots make use of the overall equations of motion.  Unfortunately, for robots working in a marine environment, these equations do not provide an accurate control because of a lack of good hydrodynamics data. -- The objective of the thesis is to incorporate the hydrodynamic loads, acting on robot arms working underwater, into the equations of motion.  The thesis describes a two-link robot arm model and experimental setup designed for the purpose of gathering hydrodynamic data. -- The thesis also describes the techniques used to analyze the obtained data.  These include dimensional analysis and a neural network identification program.


identifier: Gao, Longjun <https://research.library.mun.ca/view/creator_az/Gao=3ALongjun=3A=3A.html>   (1991) Ice floe collision under wave action in the marginal ice zone.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis describes a research program to study ice floe collisions under wave action in the Marginal Ice Zone ( MIZ ). The primary objective of this program was to develop a new interpretation approach for the phenomenon of ice floe collisions in the MIZ and to obtain the floe collision frequency. -- The ice floe field was considered to be random  while the floe motion was modelled as a stochastic process. A new concept of floe spacing distributions was developed in  order to study collision behavior by probability theory. From the aerial photographs of the LIMEX'89 field experiments, and by using probability plot test, ice floe edge distance distributions and centre distance distributions were derived. Both were shown to display Lognormal Distributions. -- By analysing water particle displacements in a wave field, a floe collision criterion was obtained. With this criterion, floe collisions were related to floe centre distance, floe edge distance, wave amplitude, and wave period. The floe spacing distributions were introduced into this criterion and the collision probability for a floe during one wave cycle was obtained. Valuable results such as the frequency of collision events within an ice floe field and the number of collisions of one  floe during a time period could be derived from this collision probability. -- The same procedures were repeated to obtain floe spacing distributions and collision probabilities in different horizontal directions. The results showed that in two different horizontal directions only small differences existed between the floe spacing distributions, and between the collision probabilities. Ice floe collisions, as well as wave scattering mechanism, made the ice floe field evenly distributed. Eccentric collisions made the collision events happened without dominant directions. -- The acceleration data from the LIMEX'89 were analysed to find the number of collision events of the measured ice floes. Predictions of collision frequencies from floe-wave conditions and from acceleration data were significantly different. However, the difference became smaller after the dimensional effects of the floes were considered. The influences of winds were discussed and shown  as the primary contribution to the results of higher wave amplitude with smaller collision frequency during a time period obtained from the acceleration data of LIMEX'89.


identifier: Rong, Jiequn <https://research.library.mun.ca/view/creator_az/Rong=3AJiequn=3A=3A.html>   (1991) Icing effects on a horizontal axis wind turbine.  Masters thesis, Memorial University of Newfoundland.

abstract: Freezing precipitation has extremely high incidence in parts  of Atlantic Canada and this condition is expected to severely reduce the energy output from aerogenerators. This project was aimed at the evaluation of effects of freezing precipitation conditions on the output of wind turbine generators. Major achievements have included the simulation of freezing rain events, in particular, glaze icing in a cold room and in field applications; testing of a NASA LS(1)-0417 wing section in the wind tunnel under simulated icing conditions; and theoretical evaluation of performance degradation by icing on blades for two horizontal axis wind turbines, that is, a 2.5 m diameter wind turbine and a Carter-23 wind turbine, by using lifting-line theory. -- An experiment to model the form of ice accumulation on a horizontal axis rotor was done in a cold room. Ice profiles on the blade sections were recorded. Wind tunnel tests for an airfoil used typically for wind turbine blades were done with various simulated glaze and rime ice accretions attached to the leading edge of the airfoil. Lift and drag coefficient data were obtained for angles of attack from -6°  to 90°. A theoretical method was used for estimation of degradation of aerodynamic performance of horizontal axis wind turbines in icing conditions. The theory used was based  on marine-propeller lifting line theory that had been adapted for wind turbine use. This made use of airfoil section data obtained from wind tunnel tests. A simulated icing test on a full scale horizontal axis wind turbine was performed at the Atlantic Wind Test Site. -- The cold room icing test gave a better understanding of the blunt shaped glaze ice accretion on the leading edge of blade sections where the wind speed was relatively high. The theoretical estimations showed that icing events, associated with ambient temperatures close to freezing point and high liquid  water content in the air, could destroy the performance of wind turbines completely. The wind turbine field test showed  that a progressive power reduction occurred during a simulated freezing event and a complete loss of power from the wind turbine generator was encountered after a short time period of freezing precipitation. The wind tunnel tests  for the airfoil with simulated ice accretions on the leading  edge revealed that increase of drag coefficient and decrease  of lift coefficient on the iced blade sections of a wind turbine were the main reasons that caused the power output from a wind turbine to drop.


identifier: Aggarwal, Rajnish <https://research.library.mun.ca/view/creator_az/Aggarwal=3ARajnish=3A=3A.html>   (1995) Identification of parameters and control of robotic manipulators using artificial neural networks.  Masters thesis, Memorial University of Newfoundland.

abstract:
In the present work the estimation of dynamic parameters and  the trajectory control of a two link planar manipulator is carried out. The derivation of system equations involve the kinematic parameters such as joint positions, velocities and   accelerations. For both the dynamic parameter estimation and  the trajectory control an Artificial Neural Networks method called, Linear Programming (LP)-Neuro Method, is used. In this algorithm, the weights are obtained by a combination of  linear programming having a sparse coefficient matrix and a single variable nonlinear optimization routine. -- The training set values required for parameter estimation are generated by the Iterative Newton-Euler Dynamics Algorithm. The Artificial Neural Network is trained to predict the dynamic parameters. The values of the forces and torques are  recomputed based on the estimated dynamic parameters. This method is useful for the on line parameter estimation of the  manipulators having odd mass distribution, which is the case in actual practice. -- For the control problem non-linear optimization method is used to evaluate the gain parameters required for the manipulator to follow the desired trajectory. Then the Linear Programming (LP)-Neuro Method is  used to obtain the weight matrix which relates the input (joint positions and velocities) and the output (gain parameters). This weight matrix, for each point along the trajectory, can be used on-line to evaluate the gain parameters thereby eliminating the time consuming
calculations at each point along the trajectory. Finally, the effect of the variation of the maximum tangential velocity and general control law are studied.


identifier: Sitompul, Adolf Tommy <https://research.library.mun.ca/view/creator_az/Sitompul=3AAdolf_Tommy=3A=3A.html>   (1993) Hydraulic modelling of a sharp crested labyrinth weir.  Masters thesis, Memorial University of Newfoundland.

abstract: A labyrinth weir is an attractive alternative for water level control in flat land where the head is usually limited. It is also useful in a river where the weir width is confined by the topography. The advantages occur because the crest length of a labyrinth weir is significantly longer  than the width of the river. This is achieved by having a plan form which consist of repeating geometric cycles, typically trapezoidal in form. As a result large flows can be released at relatively low heads. Trapezoidal and triangular forms have become the favoured geometric cycles for designers. -- This study on a labyrinth weir was undertaken to confirm the operating parameters as well as to  investigate different plan shapes including rectangular, rectangular with a semi-circular connection and reverse trapezoidal. Experimental and theoretical results confirmed that the trapezoidal shape with the side wall angle, α = 0.68 αmax, and the length magnification, 1/w = 2.65 gave the  best hydraulic performance among other labyrinth weir plan forms which were tested in this study. The effect of varying  the crest width was also investigated in this study. This part of the study focused on the trapezoidal shape. It was shown that increasing the width of the crest up to 10 mm (in this case 10% of weir height, P) was not significant in decreasing the flow despite some frictional losses on the crest. Such a crest is useful when a river has a large quantity of debris. -- The economic advantages of labyrinth weirs were also studied with reference to the Ciwadas trapezoidal labyrinth weir which was constructed in Indonesia in 1988. This labyrinth weir was designed to handle the flood flows of 200 m³/s and control water depths between 1.6 m and 2.35 m. Comparison with a typical weir with gate shows that this labyrinth weir was more than 25% less expensive. -- A computer code for analytical studies was also established. It was shown that for trapezoidal plan  forms, a good agreement between theoretical results and experimental data could be achieved. This also confirms the previous theoretical solution proposed by Hay and Taylor although there is a little difference (0.1) in defining the value of the energy loss coefficient (contraction) at the entry to the weir.


identifier: Sunaryo <https://research.library.mun.ca/view/creator_az/Sunaryo=3A=3A=3A.html>   (1994) Hydraulic modelling of purging in sea outfall.  Masters thesis, Memorial University of Newfoundland.

abstract: The presence of seawater in a sea outfall can reduce the effluent discharge from a land-based treatment plant or domestic and industrial areas. In the longterm, it can damage the sea outfall. To avoid the presence of seawater and to anticipate a varying effluent discharge, a minimum effluent discharge is needed to purge the outfall system. -- The objective of this study was to investigate various ways of decreasing the minimum effluent discharge needed to purge  a sea outfall. The effect of port size and an increase in mixing between saltwater and effluent are considered in this  study. In tests on the effect of port size, three different types of tests were undertaken. There included risers without caps, risers with caps having one port of diameter 2.54 cm (one inch), and risers with caps having two ports of  diameter 2.54 cm (one inch). Attempts were made to increase mixing in the vertical risers using small water jets located  below the risers, water jets located upstream of the risers,  air jets located below the risers and a barrier located at the top of tunnel upstream the risers. -- The maximum reduction in the purging discharge was obtained using water jets (1.001/min) located below all risers. The purging discharge using these jets was only 48% of that without water jets. This is a significant reduction.


identifier: Jiang, Zhi-Jian <https://research.library.mun.ca/view/creator_az/Jiang=3AZhi-Jian=3A=3A.html>   (1992) A study of two-rail totally self-checking circuits.  Masters thesis, Memorial University of Newfoundland.

abstract: In order to overcome the limitations of conventional design techniques of totally self-checking (TSC) circuits and provide simple, convenient, and systematic design techniques, we formalize a new two-element morphic Boolean algebra — strong morphic Boolean algebra Bsm — and propose a  new classification of checkers. Based on these, we have developed three types of universal two-rail (TR) totally self-checking (TSC) basic building blocks (BBB) — EIS BBBs, EISS BBBs, and EIIS BBBs. Besides, a group of TR-TSC multi-function BBBs has also been proposed. These BBBs, like ordinary logic gates in common digital circuits, can be easily used to implement any arbitrary combinational logic using our proposed design rules. The resulting circuit is a TR-TSC circuit. -- A simple interconnection method (SIM) and  an image design method (IDM) for the design of TR-TSC circuits have been proposed. The SIM is suitable for the case that the self-testing property can be easily achieved or verified. The IDM deals with the general case that includes complicated logic functions with a large number of inputs. -- We also present a new method to design a TSC circuit with separate error-input indication (EI) and separate internal fault indication (IF). This objective has been achieved by using a new BBB — a TR-TSC decoupling BBB (DC₂). -- An efficient method of diagnosing relevant error sources has been studied. With the help of decoupling circuits consisting of DC₂'s, the error status of relevant inputs and outputs can be indicated. This greatly improves localizability and enhances maintainability. A totally new circuit concept named error-confining circuit has been introduced. TR-TSC error-confining (ECF) circuits implement given logic functions during fault-free operation. But when any internal fault from a prescribed set of faults occurs, the circuit automatically forms several independent areas which are surrounded by isolation boundaries. Thus, the fault is confined to a special area and indicated. This property enhances localizability, maintainability and availability. A TSC double-input decoupling (DIDC) BBB, which is a key component to be used in constructing the isolation boundaries, has been developed. -- The design problems of TSC sequential BBBs have also been discussed. A scheme for designing TSC D flip-flop has been proposed. -- In addition, we have also developed an efficient combinational TSC checker for l-out-of-3 code. The proposed checker uses less hardware, has fewer gate levels, and possesses a higher test capability.


identifier: Lu, Rong-shen <https://research.library.mun.ca/view/creator_az/Lu=3ARong-shen=3A=3A.html>   (1993) Implementation of loss minimization control for high performance AC motor drives.  Masters thesis, Memorial University of Newfoundland.

abstract: AC motors have been used in a wide range of power ratings to  date and are playing a prominent role in drive applications.  However, their highly non-linear dynamic structure with strong dynamic interactions requires more complex control schemes than dc motors. -- The conventional linear techniques can no longer satisfy the stringent requirement placed on high-performance ac motor drive applications. Modern control techniques, such as optimal control and adaptive control, are applied in motor drive systems. But the realization of these techniques is generally difficult because of large time-critical computation requirements. Typical field-oriented control of ac motors uses current loop sampling rates of 5 to 10 KHz. This implies that the controller must process the control algorithms within 100 to  200 μs. Thus, for high-performance ac drives, some powerful microcomputers, such as Transputers, and parallel processing  techniques are used in ac motor drive systems. On the other hand, reducing the energy losses in adjustable-speed electric motor drives is becoming increasingly important due  to the high cost of energy. -- Transputer-based parallel processing of high performance ac motor drives can be a good  solution for fast dynamic calculation, flexible architecture  and interactive control in order to achieve both requirements of high performance and loss minimization of ac  motor drives. -- The purpose of this study is to investigate  and apply multiple Transputers in parallel processing of indirect field-oriented vector control employing loss minimization for high performance ac motor drives. A new scheme is proposed based on the use of multiple Transputers for real-time parallel processing implementation of the indirect field-oriented control scheme incorporating the loss minimization strategy. Losses in ac motor drives are studied and verified by experiments. Computer simulation results of trials using five Transputers and experimental results of using four Transputers for parallel processing are presented in the thesis. It is shown that high performance as well as significant energy savings for ac motor drives can be achieved by the proposed scheme.


identifier: Chen, Jing <https://research.library.mun.ca/view/creator_az/Chen=3AJing=3A=3A.html>   (1993) Improved propagation loss prediction for land mobile radio communications.  Masters thesis, Memorial University of Newfoundland.

abstract: In land mobile radio communications, it is well known that almost 95% of the radio links between transmitter and receiver are non-line-of-sight. The propagation loss between  transmitter and receiver is heavily dependent on the terrain  features. Hence, this thesis examines and improves the CRC propagation loss prediction in two main aspects. -- One is to create a higher resolution and more accurate digital terrain data base based on the CRC data base. The developed procedure is as follows. For a given area of interest first the complete quadratic two-dimensional interpolation for elevations and the weighted vote method for surface codes are applied to augment the CRC data base from 500 meters spacing to 100 meters spacing. If the contour from the augmented data base is not checked with the topographic map,  then the data of missed critical terrain features are taken directly from the topographic map and are used to correct the augmented data base. In this step, the triangular interpolation scheme is introduced to modify the elevations,  and the weighted vote method is used to modify the surface codes. There are eight surface codes which indicate tree, bare ground, fresh water, suburban, marsh, seawater, urban core and unknown type. As the result of the modified data base, the evaluations of diffraction, reflection, tropospheric scattering, urban, and season losses are more accurate. Thus, the total propagation loss prediction is greatly improved. -- As another major work in this thesis, the modified diffraction loss prediction model is proposed. It involves: (a) for the implementation of the de Assis method, the radius of curvature of rounded obstacles' crest is determined by least-squares parabolic fitting; (b) the Deygout correction factor is first applied to deal with multiple rounded obstacles which are close to each other; (c) based on the availability of much more detailed information from the modified data base, all the defineable obstacles in a path profile are taken into account in the diffration loss prediction. -- It is shown that our propagation loss prediction results are close to CRC results  when the terrain is smooth; but in the irregular terrain, our results provide a substantial improvement.


identifier: Colbourne, D. B.(Douglas Bruce) <https://research.library.mun.ca/view/creator_az/Colbourne=3AD=2E_B=2E=28Douglas_Bruce=29=3A=3A.html>   (1989) A three component method of analyzing icebreaking resistance.  Doctoral (PhD) thesis, Memorial University of Newfoundland.

abstract: This thesis presents a broad based review of current literature in the field of ship icebreaking and ice mechanics relevant to icebreaking. -- A dimensional analysis  of the ship icebreaking problem is presented, leading to a system of non-dimensional numbers based on division of the problem into three independent components; an ice breaking component, an ice clearing component and a viscous drag component. Results from a comprehensive set of model tests are presented, validating the three component analysis method. In addition the method is applied to a number of model scale and full scale data sets with considerable success. It is concluded that testing and analysis of icebreaking by dividing the problem into components is practically feasible and offers an improved method of analysis, presentation and scaling.


identifier: Zaman, Marzia Rabbi <https://research.library.mun.ca/view/creator_az/Zaman=3AMarzia_Rabbi=3A=3A.html>   (1992) Adaptive filters for edge-preserving smoothing of speckle noise in digital images.  Masters thesis, Memorial University of Newfoundland.

abstract: Speckle is a common phenomenon in all types of coherent energy imaging system such as Synthetic Aperture Radar (SAR), laser, ultrasound, acoustics, sonar etc, Speckle is a  multiplicative-convolutional noise and as such is different from other commonly found types of noise such as Additive White Gaussian Noise (AWGN). Hence different methods of processing are required to restore speckled images. Moreover, in many applications, the edge structure of an image is very important, and usual filtering methods are not  well suited for preserving edges particularly in speckled images. In this work, an extensive study has been made to investigate the applicability of different existing nonlinear filtering methods and also a new Quadratic Volterra Filter (QVF) based on speckle-model to solve the problem of speckled image restoration in terms of noise smoothing and edge preservation. Edge detection itself on speckled images is a major problem which has not been addressed by many researchers. This thesis attempts to provide a better approach to the solution of restoring images corrupted by speckle while preserving their edge information.


identifier: Choudhury, Mohammad Ali <https://research.library.mun.ca/view/creator_az/Choudhury=3AMohammad_Ali=3A=3A.html>   (1988) An analysis of delta modulated inverters with applications to submersible motors.  Doctoral (PhD) thesis, Memorial University of Newfoundland.

abstract: This thesis presents an analysis of delta modulated inverters and their applications to submersible motors. Submersible motors are induction motors with unique constructional features. These motors are required to operate in one of the most harsh environmental conditions. The operating characteristics of the submersible motor pump system require soft starting facility and variable speed operation during production. To satisfy both requirements, a  delta modulated inverter supply is proposed for the operation of the submersible motor. Several delta modular schemes have been studied and the rectangular wave delta modulation technique is selected for the switching of the inverter. Rectangular wave delta modulation provides inherent constant voltage/frequency (V/f) characteristic of the supply voltage and current control of the motor. The constant V/f characteristic is provided by the low-pass filter in the feedback loop of the modulator and the current  control is provided by the hysteresis window of the quantizing comparator in the feedforward path of the modulator. -- The modulator and the inverter waveform were studied using discrete Fourier transform (DFT). This is simpler than the conventional Fourier series analysis. It is  suitable for on-line harmonic analysis of the modulated waveforms. It also gives the information about the sub-harmonics of the modulated waveforms. An on-line harmonic minimization technique using a tuned filter in the delta modulator has been implemented. This method uses the continuous tuning of the feedback filter in the modulator to  minimize the low order harmonics of the modulated wave for variable frequency operation of the inverter. -- The steady state and starting characteristics of the submersible motor supplied from the rectangular wave delta modulated inverter have been studied using time-domain analysis. Time domain analysis of inverter-fed submersible motors was found to be more accurate and easier than the conventional frequency domain analysis. The motor was provided with ramp frequency and voltage (RFV) control to reduce its electrical and mechanical starting stresses. A semi-closed loop operation has been chosen to maintain constant slip operation of the motor. For the semi-closed loop operation, motor speed was estimated using the motor terminal voltage, current and the phase angle between them. -- The characteristics of the modulator and the motor fed from the rectangular wave delta modulated inverter were experimentally verified.


identifier: Marshall, Alfred R. <https://research.library.mun.ca/view/creator_az/Marshall=3AAlfred_R=2E=3A=3A.html>   (1990) A theoretical and field study of load transmission through grounded ice rubble.  Masters thesis, Memorial University of Newfoundland.

abstract: Oil exploration from artificial Islands in the Beaufort Sea has shown that grounded ice rubble fields often accumulate around such structures, preventing moving ice from acting directly against the structure. A simple, rigid body model, has commonly been used to estimate the load "seen" by the structure, with the result that no loading is expected until  global rubble sliding occurs. It was realized that such an approach is not entirely realistic and so a collaborative field program was carried out, followed by theoretical modelling. The field work was done at a drilling location in  the southern Beaufort Sea on ESSO's Caisson Retained Island (CRI). The three groups involved were ESSO Resources Canada Ltd., National Research Council of Canada (NRC) and Memorial  University of Newfoundland (M.U.N.). The M.U.N. data and subsequent theoretical work is presented here, with the ESSO  and NRC data summarized in the site description. -- Memorial  University collected data from pressure sensor rosettes, a strain array, thermocouple arrays, rubble profiling, and ice  property measurements. The most important data came from the  pressure sensor rosettes and the thermocouple arrays. These indicated that average sea ice pressures against the rubble reached 350 kPa, and that a substantial and rapidly formed refrozen layer existed within the rubble, with a thickness exceeding 3 m near the rubble field periphery. -- Based on the field measurements, a theoretical model was developed to  investigate the role of the rubble refrozen layer in load transmission through rubble. The rubble field was modelled as a system of springs and dampers to represent the elastic,  frictional, and viscous stiffness of the various load paths.  The deformations and load distributions were calculated using a commercial finite element package called ABAQUS. Each material property was assumed to have a range of values, the limits of which were determined from the literature, theoretical considerations and field measurements. -- The sensitivity of the output to each of the inputs was examined and the following was concluded; -- 1. From the analysis it appears that the elastic response of  the rubble leads to the highest loads on the embedded structure because the transmitted load tends to decrease with time (creep). -- 2. The ice rubble properties that are the most important for further study are the delayed elastic  and shear properties of un-refrozen rubble, as well as their  variability within natural rubble fields. -- 3. Significant loads may be transmitted through ice rubble to a structure before global sliding of the rubble field occurs. -- 4. The presence of the refrozen layer gives the potential for substantial loads to be imposed on the structure during rubble field movement. -- 5. Possible future improvements to  the ABAQUS computer model include the incorporation of; refrozen layer discontinuities, berm slope, non-rigid structure behaviour, kinetic and static friction values (rather than an average), and water and ice mass. Furthur research is also required on ice/rubble failure modes to esablish design pressures at the rubble field boundaries. -- 6. The sample 3D calculations show that viscous deformation may also be important, although it is also clear that the 3D  method presented needs improvement. -- KEY WORDS: Sea ice; sea-ice; ice rubble; ice loads; landfast ice; rubble fields; Kaubvik; artificial islands; Beaufort Sea; pressure sensors; strain array; thermocouple array; refrozen layer; consolidated layer; ABAQUS; computer model.


identifier: Bodapatti, Nageswararao <https://research.library.mun.ca/view/creator_az/Bodapatti=3ANageswararao=3A=3A.html>   (1998) Fuzzy-expert system for voltage stability monitoring and control.  Masters thesis, Memorial University of Newfoundland.

abstract: In recent years, electric power utilities are forced to transmit maximum possible power through existing networks due to environmental, economic and regulatory changes.  Due to these constraints, voltage instability has emerged as one of the most important areas of concern to modern power utilities.  Voltage instability has been responsible for several system collapses in North America, Europe and Asia. -- This thesis presents fundamental concepts of voltage stability.  It describes three traditional voltage stability indices namely singular value decomposition, L index and QV curves.  A simple five bus system is used to highlight the limitations of these traditional methods.  A more widely accepted technique like modal analysis along with continuation power flow is studied and simulations are carried out on the IEEE 30 bus system and the New England 39 bus system.  The test results clearly indicate areas prone to voltage instability and also identify groups of buses and critical bus that participate in the instability and thereby eliminate the problems associated with traditional methods.  Hence, modal analysis technique is not only used as a benchmark tool for the development of the proposed fuzzy-expert system, but also as an important tool for validating its accuracy. -- To understand this new approach, fundamental concepts of fuzzy logic based on the theory of approximate reasoning is dealt in detail.  To get further insight into this alternate approach, a simple method using fuzzy sets for the voltage-reactive power control to improve the system voltage level is presented.  A modified IEEE 30 bus system is used as an example to illustrate this method.  Simulation results of this simple problem is encouraging and has been a useful starting point for the proposed fuzzy-expert system for voltage stability evaluation. -- The proposed fuzzy-expert system consists of two main components.  The knowledge-base and the inference engine.  Here, the key system variables like load bus voltage, generator MVAR reserve and generator terminal voltage which are used to monitor the voltage stability are stored in the database.  Changes in the system operating conditions are reflected in the database.  The above key variables are fuzzified using the theory of uncertainty.  The rulebase comprises a set of production rules which form the basis for logical reasoning conducted by the inference engine.  The production rules are expressed in the form of IF-THEN type, that relates key system variables to stability.  The New England 39 bus system is taken as a case study to illustrate the proposed procedure.  The expert system output is compared with the simulation results of a commercially available software ( VSTAB 4.1 ) output through modal analysis.  The proposed system is fast and more efficient than conventional voltage stability methods.


identifier: Dhar, Deepak <https://research.library.mun.ca/view/creator_az/Dhar=3ADeepak=3A=3A.html>   (1994) Fatigue life estimation of turbine blades due to transient thermal, vibratory, and centrifugal stresses.  Masters thesis, Memorial University of Newfoundland.

abstract: The present work involves the study of the three dimensional  transient heat transfer and vibratory analysis of turbine blades with mixed and non-linear boundary conditions. The equations derived for the heat transfer analysis are general  (three dimensional) in nature and are new contributions in this field. The mathematical model for both the heat transfer and the vibration analysis is formulated using curved, solid, C° continuity, quadratic, serendipity, twenty  noded isoparametric finite elements. -- The equations which are non-linear in nature for the transient temperature distribution within the turbine blade are derived using the finite element analysis. The non-linearities arise due to the radiative heat transfer and also due to the change in the material properties of the turbine blade with temperature. Using a finite difference scheme, the non-linear differential equations are transformed to non-linear algebraic equations in the time domain. The transient temperatures obtained from the heat transfer analysis are used in the calculation of the temperature gradients and transient thermal stresses. The vibratory analysis is done at first for finding the undamped natural frequencies of the  turbine blade. These free vibration studies include the effect of the non-linearity in the stiffness matrix caused by the rotation of the turbine blade. The frequencies arising from the free vibration analysis also change because  of the change in the material properties of the turbine blade as the temperature of the turbine blade changes with time. Thereafter, the stresses due to (a) the nozzle excitation and (b) the centrifugal stresses at different rotor speeds are calculated. The nozzle excitation forces are modelled as a sinusoidal pulse. Finally, the total effect of all the three different types of stresses (transient thermal, centrifugal, and vibratory due to the nozzle excitation) on the fatigue life of the turbine blade is studied.


identifier: Deb, Anindya <https://research.library.mun.ca/view/creator_az/Deb=3AAnindya=3A=3A.html>   (1986) Finite element analysis of stiffened plates using Mindlin's theory.  Masters thesis, Memorial University of Newfoundland.

abstract: Finite element procedures based on Mindlin's theory are computationally advantageous and also have the capability of  accounting for transverse shear deformation in plates. Complementary to Mindlin's theory is Timoshenko's theory that accounts for transverse shear deformation in beams. In the present work, both of these shear distortion theories have been applied to the finite element analysis of stiffened plates subjected to lateral loading. Discrete plate-beam formulations, termed FEM(Ml) and FEM(M2), have been set up illustrating two major approaches in the finite element analysis of stiffened plate structures. A third orthotropic formulation, named ORTHO, has been presented based on the smeared plate approach, and is applicable to the case of closely spaced torsionally soft stiffeners. The performance of the discrete plate-beam formulations, especially of the second viz. FEM(M2), has been found to be quite satisfactory based on a comparison with a number of the available results. For the first time an attempt has been made to estimate theoretically the errors that are likely to result from the use of an orthotropic formulation.  This has been accomplished by comparison between ORTHO and FEM(M2) in the form of a parametric study. Additionally, the  orthotropic formulation has been extended to include geometrically non-linear behaviour. It is recognised that under less demanding conditions this latter formulation may be preferable for the reasons of economy of CPU time and simplicity of input data.


identifier: Xiao, Jing <https://research.library.mun.ca/view/creator_az/Xiao=3AJing=3A=3A.html>   (1991) Finite element modelling of damage process in ice-structure interaction.  Masters thesis, Memorial University of Newfoundland.

abstract: Two field programs were carried out on the Hobson's Choice Ice Island in April, 1989 and May, 1990 using different sizes of spherical and flat indenters. Several cores of multiyear field ice were recovered from the ice island and transported to Memorial University to conduct compressive tests in the laboratory. Both constant strain-rate tests and  constant stress tests were performed with uniaxial stress to  investigate the deformation of multiyear ice and calibrate the material constants for theoretical modelling. -- The spherical indentation tests are modelled using an axisymmetrical finite element model. The ice damage process is related to the growing network of micro-cracks and the ice creep process is also enhanced by the existence of cracks. The damage model is developed in FORTRAN code and implemented as a user subroutine in the ABAQUS finite element analysis program. The analysis results show that most of the ice damage is close to the contact surface, and that the maximum damage occurs at the edge of the interface where shear stress is concentrated. This is in agreement with the test results. The model also provides good results on the total load versus time history.