identifier: Jain, Pankaj <https://research.library.mun.ca/view/creator_az/Jain=3APankaj=3A=3A.html>   (1993) Fixed frequency series-parallel DC/DC resonant converters.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis presents generalized modeling and analysis of constant frequency dc/dc resonant converters taking into account the effect of transformer leakage reactance. Frequency-domain analysis is used to obtain generalized equations to describe the steady-state characteristics of the series-parallel resonant converters with primary and tertiary resonance. Transient analysis using state-space method is also presented for the primary-side resonant converter. Simulation results showing the effect of the leakage reactance of the high frequency transformer on the performance of these converters are presented. Experimental results to verify the model and simulation results are also provided. A model is developed for a series-parallel resonant converter with integrated magnetics which is suggested for further size reduction in the converter. A design example is provided to illustrate the use of the generalized equations and performance curves. -- It is shown  that the transformer leakage inductance has a significant effect on the operation of the converter and hence cannot be  neglected in the design of the converter. It is also shown that a series-parallel resonant converter with tertiary resonance is more suitable for operation at higher frequencies.


identifier: Morey, Bradley J. (Bradley Joseph) <https://research.library.mun.ca/view/creator_az/Morey=3ABradley_J=2E_=28Bradley_Joseph=29=3A=3A.html>   (1998) Floating breakwaters : predicting their performance.  Masters thesis, Memorial University of Newfoundland.

type: Thesis NonPeerReviewed

format: application/pdf application/pdf

abstract: Current environmental and financial restrictions on harbour developments dictate that alternatives to traditional fixed rubble mound and caisson breakwaters are required. The most common solution is the Floating Breakwater, a concept which utilizes reflection, dissipation, and/or transformation to reduce incident wave energy. The design and construction of these for exposed coastal regions present major engineering challenges. -- The primary objective of this thesis was to develop a comprehensive design rationale to enable the designer predict local wave climate (exceedance probabilities, design spectra), optimize a breakwater design  (structural parameters, mooring systems) and estimate costs.  To facilitate this a number of aspects were reviewed including methods utilized in predicting the wind-wave climate in fetch limited regions, design criteria for inner harbour wave climates, and performance prediction techniques. Based on this review the author developed a simplified deterministic approach to performance prediction based on dimensional and regression analysis of model test data. This information was combined into a computer simulation to predict the local wave climate, optimize the floating breakwater size, design the mooring system, and determine the cost effective solution.


identifier: Gowda, Ramdas N. <https://research.library.mun.ca/view/creator_az/Gowda=3ARamdas_N=2E=3A=3A.html>   (1992) Field and laboratory studies of mixing tubes for marine outfalls.  Masters thesis, Memorial University of Newfoundland.

abstract: Increase in land costs due to urbanization has led many coastal communities towards marine outfalls as a convenient means of disposing of domestic and non toxic wastes. It has been common practice to use submerged outfalls for small discharges to take advantage of the immediate dilution available as the effluent rises to the surface. The prime objective of the marine outfall installation is to maximize the total dilution of the waste and to minimize impact on the marine environment. Jet pumps or mixing tubes may be used to improve the initial dilution and to promote plume submergence in small outfalls. Theoretical and experimental studies have been carried out but field trials have been very limited. -- Studies have shown that very limited improvement in dilution is obtained with conventional mixing  tubes. The basic reason for this is that the combination of increased flow and increased diameter of the mixing tube modify the values of density difference, relative depth and densimetric Froude number. Due to these changes less mixing takes place between the end of the mixing tube and the surface than would have taken place in the original jet discharged without a mixing tube. The combination of increased dilution within the mixing tube and decreased dilution in the buoyant jet has been found to limit the improvement factor of overall dilution to a factor of about two. -- In this thesis experiments on a novel shape or mixing tube are described. This was designed to overcome the  problems discussed above and used a transition from a square  section at entry to a two dimensional slot at the exit. The study showed that better performance can be achieved at low values of the Froude number. The improvement of overall dilution with a slot mixing tube compared to the circular mixing tube was however, fairly limited. -- Little information is available to describe the field performance or mixing tubes. This lack was rectified by a field study run parallel to the laboratory work. In this study a circular mixing tube was built and installed on a small outfall located at Spaniards bay on the east coast of the island of Newfoundland. Dye studies were done at this installation to check the dilution achieved in the field. Comparisons were made between the performance of a horizontal jet with and without the mixing tube but little improvement in overall dilution was achieved with the mixing  tube. It was found that the mixing tubes performed better in  the field than was theoretically predicted.


identifier: Bird, Corey D. <https://research.library.mun.ca/view/creator_az/Bird=3ACorey_D=2E=3A=3A.html>   (1996) Investigation and suppression of multipath communication signals with applications to a marine environment.  Masters thesis, Memorial University of Newfoundland.

abstract: An investigation of multipath communication signals with applications to a marine environment is conducted by examining a typical L-Band satellite-to-ship communication system.  In order that this investigation be performed, a numerical stochastic maritime multipath model is constructed.  This model has the ability to calculate the average power contained in a multipath communication signal which is reflected off the ocean surface and received by a ship mounted antenna.  This allows the model to provide signal-to-noise ratios as well as signal fade characteristics for different degrees of sea surface roughness as well as a variety of receiving antenna patterns.  By comparing the results obtained with the stochastic multipath model to those from other models as well as various measurement campaigns, the stochastic maritime multipath model is shown to be a valid and useful tool that can be used in multipath research.  Some of the research carried out in this thesis includes an investigation of how various parameters affect the multipath phenomenon.  These parameters include sea roughness, elevation angle, antenna position aboard the vessel, and antenna directivity.  It was discovered that it may be possible to decrease the amount of multipath fading experienced by a ship mounted receiving system by locating an optimal antenna position aboard the vessel and constructing a low cost antenna stabilization platform that could allow the use of a fairly directive antenna.  Suggestions for the continuation of the research reported here are also presented.


identifier: Soeharno, Agung W. H. <https://research.library.mun.ca/view/creator_az/Soeharno=3AAgung_W=2E_H=2E=3A=3A.html>   (1992) Simulation of hydropower generation for the Citarum multi-reservoir system using synthetic flows.  Masters thesis, Memorial University of Newfoundland.

abstract: The demand for electricity in Java and Bali, Indonesia increases an average of 14% per year.  This condition forces the electrical authority in Indonesia to consider various generation alternatives, including hydroelectric power, to meet the growing demand.  One alternative is improving reservoir operations of existing hydro power systems so that improved production can be achieved. -- One such hydropower system considered in this thesis is the series of three hydroelectric stations, Saguling, Cirata and Jatiluhur, on the Citarum river, West Java.  At present these three hydropower plants are operated by different authorities.  They developed the current reservoir operation guideline (CROG) based on consensus.  An average of assumed normal” years of historical flows are used to obtain the current rule curve.  The estimation of annual energy generated is then obtained based on the series of twelve monthly flows of the average of the assumed normal year flows. -- In this study a simulation of reservoir operations was performed using synthetic inflows into the reservoirs.  The synthetic flows were generated by a stochastic model that on average preserved the statistical characteristics of both historical annual and monthly flows.  An auto-regressive moving average model was used to model the annual flows, and the Method of Fragments and the Two-Tier method were examined to model the monthly flows. -- Two rule curves were applied in the simulation of reservoir operations.  These were the CROG rule curve and the water resources development guideline (WRDG) rule curve proposed by the Water Resources Development project.  Two other limiting rule curves were also examined, one assuming that the reservoirs are kept empty, and the other assuming that the reservoirs are kept full.  The operation of the system was simulated using both historical and synthetic inflow sequences, as well as the different rule curves, to evaluate the performance of the system. -- The results showed that the preferred stochastic model for the annual flows was an ARMA (2,0) model, and for the monthly flows, the Two-Tier model.  The CROG rule curve was more suitable for the system than that based on the WRDG rule curve.  From the reservoir operation simulation it was found that on average the available water in the Citarum River was smaller than the installed capacity of the Saguling, Cirata and Jatiluhur plants.  The results of the simulation using synthetic flows could give more comprehensive analysis than using only historical flows.


identifier: Wang, Chuan <https://research.library.mun.ca/view/creator_az/Wang=3AChuan=3A=3A.html>   (1995) Simulation of viscous fluid flows using a control volume finite element-multigrid method.  Masters thesis, Memorial University of Newfoundland.

abstract: The formulation and implementation of an equal-order colocated control volume finite element-multigrid (CVFE-MG) method for steady, two-dimensional, viscous incompressible flows is presented in this thesis.  In the proposed CVFE-MG, the calculation domain is discretized using three-node triangular elements.  Each element is further divided in such a way that control volumes are formed around each node in the calculation domain.  The proposed method is formulated using the velocity components and pressure as dependent variables, and interpolation functions for these dependent variables are all based on an elemental level.  The pressure and the diffused scalars are interpolated linearly; the convected scalars are interpolated using mass weighted interpolation which guarantees positive contributions to the coefficients in the algebraic discretization equation; and the transporting velocities are interpolated using a linear interpolation of pseudo-velocities and pressure coefficients, in which the pressure gradients appear explicitly.  This feature allows the formulation of an equal-order colocated method valid for incompressible flows.  Using these interpolation functions, the discretized forms of the governing equations are obtained by deriving algebraic approximations to integral conservation equations for each control volume.  These nonlinear, coupled, algebraic equations are then solved by a segregated solution algorithm.  This solution method is implemented in the context of FMV- and V-cycle multigrid algorithms in an attempt to improve its convergence behaviour. -- The proposed CVFE-MG method was found to generate solutions that could capture the physical behaviour of the fluid flows used as test problems.  The multigrid methods were found to accelerate the convergence rate 2.18 to 7.43 times for the outflow and recirculating flow test problems presented.  The effectiveness of the multigrid algorithm was reduced for higher Reynolds numbers, due to the interpolation schemes used in the control volume finite element method (CVFEM). -- The successful implementation of multigrid algorithms in the context of a primitive variables, viscous flow CVFEM is very encouraging.  Further research will be performed to improve the effectiveness of CVFE-MG implementations.


identifier: Banerjee, Tapas <https://research.library.mun.ca/view/creator_az/Banerjee=3ATapas=3A=3A.html>   (1993) Simulation and implementation of pulsed analog neural circuits.  Masters thesis, Memorial University of Newfoundland.

abstract: Conventional simulation of neural networks implemented using our pulsed analog topology is slow.  The commercial circuit simulator HSPICE takes about half a day to simulate even a medium scale network, which is frustrating at the design stage.  A new simulator, PULSE, has been developed to relieve the designer from this problem.  PULSE provides about two orders of speed improvement over HSPICE while predicting the circuit, performance with comparable accuracy.  It uses a macromodeling approach in contrast to the transistor level simulation approach in HSPICE.  Special features of pulsed analog networks are exploited constantly to reduce the simulation time.  The analysis algorithms used are Waveform Gauss-Seidel and Functional iteration.  Circuit equations formulated being very sparse, correct ordering of the equations leads to convergence to the solution in only one Gauss-Seidel iteration.  Using PULSE as the simulation tool, a Matrix Associative Memory has also been designed which is in the process of fabrication.


identifier: Pal, Subarna <https://research.library.mun.ca/view/creator_az/Pal=3ASubarna=3A=3A.html>   (1998) Simulation of current mode control schemes for power factor correction circuits.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis deals with a comparative study of the features of constant frequency and variable frequency current control schemes for power factor correction in AC-DC converter circuits. -- Various current control schemes for achieving nearly unity power factor at the input and to minimize the total harmonic distortion (THD) are in use in various applications such as television, radio receivers, AC-motor drives, DC-motor drives and uninterruptible power supplies (UPS). -- Analytical models of Constant Frequency Continuous Current (CFCC), Constant Frequency Discontinuous Current (CFDC), Zero-Current Zero-Voltage Switching (ZCS-ZVS) and Variable Current Hysteresis Control (VCHC) are developed and used to evaluate the performance of the power factor correction circuit.  The main features of these control schemes are highlighted and the performance characteristics are obtained through computer simulation for the same circuit conditions.  Design examples of each control scheme, and power loss calculation associated with the active switching device are also provided.  It is shown that active current waveshaping through constant and variable frequency control schemes posseses many attractive features.


identifier: Mills, Walter Frederick <https://research.library.mun.ca/view/creator_az/Mills=3AWalter_Frederick=3A=3A.html>   (1991) The effect of approach gradient, weather conditions and queue position on discharge headways at signalized intersections in the city of St. John's.  Masters thesis, Memorial University of Newfoundland.

abstract: This experiment was designed to determine the effect, if any, of approach gradient, weather conditions and queue position on discharge headways at signalized intersections in the City of St. John's. -- Many of the factors that affect vehicle operation at signalized intersections were examined through an extensive search of the existing literature.  These factors were considered during the selection process when the intersection approaches on which data was collected were selected. -- A suitable mathematical model was selected and the appropriate hypotheses were generated. -- Headway data was collected during the Spring of 1986 on five intersection approaches having a range in gradients from -7.2% to +7.2%. -- This data was analyzed using the SPSS/X statistical software package.  It was determined that the headway data that was originally collected did not meet the assumption of Normality.  Accordingly, the data was transformed using a logarithmic transformation to produce a more Normal distribution, and was analyzed again. -- The factorial experiment that was performed indicated a statistically significant interaction between weather conditions and approach gradient.  However, subsequent attempts to formulate equations quantifying the relationship between approach gradient and vehicle headways at each level of the weather factor were not successful.  The regression procedure produced equations with very low values of the coefficients of determination.  At the same time, the significance level of the F-test procedure results gave indications that a strong linear relationship existed between approach gradient and discharge headways. -- It was concluded that the significant result of the F-test procedure was a result of the large number of residual degrees of freedom resulting from the very large database. -- Consequent examination of the data revealed an error in the database that had been used during those regression procedures.  However, when the regression procedures were performed on the corrected database, the results were largely unchanged. -- It was, therefore, concluded that there is no practical quantifiable relationship between approach gradient and discharge headways on the approaches to signalized intersections in the City of St. John's. -- However, a practical and statistically significant relationship was developed between the elapsed time from the start of the green phase, a quantity which is related to discharge headway, and vehicle position in the queue, and an appropriate prediction equation was developed that accounts for 93.5% of the variability in the data.


identifier: Hale, Rodney D. <https://research.library.mun.ca/view/creator_az/Hale=3ARodney_D=2E=3A=3A.html>   (1998) Gesture recognition as a means of human-machine interface.  Masters thesis, Memorial University of Newfoundland.

abstract: The development of a reliable multi-modal human-machine interface has many potential applications.  The interface with a personal computer has become very common yet many disabled users have limited access due to the restrictiveness of the current interface.  An improved interface would improve the quality of life for disabled users and has applications in controlling machinery in an industrial setting.  Many different types of gestures ranging from head gestures, headpointing, hand and arm gestures are being investigated.  A wide variety of classification techniques are available.  These techniques range from simple clustering routines to complex adaptive routines.  This work compares the recognition results of four pattern recognition techniques, the k-nearest neighbor, a Mahalanobis distance classifier, a rule based classifier and hidden Markov models.  The techniques were tested on a set of six hand gestures captured using The Flock of Birds data collection system.  The best average recognition result was 97% obtained from the k-nearest neighbor classifier, the Mahalanobis distance classifier had an average recognition rate at 92%, the rule based classifier had an average recognition rate at 89% and the hidden Markov models had the lowest average recognition results at 83%.  The hidden Markov models are the most complex of the four techniques studied.  Although the average recognition results were lower, they are rich in mathematical structure and can be used to model very complex observations.


identifier: Rajagopal, Narayanan <https://research.library.mun.ca/view/creator_az/Rajagopal=3ANarayanan=3A=3A.html>   (1993) Harmonic analysis of AC/DC converters using the harmonic admittance method.  Masters thesis, Memorial University of Newfoundland.

abstract: Phase control technique used in ac/dc converters results in the generation of harmonics which can disrupt the operation of critical and sensitive loads.  In general, the level of harmonics in the system depends on the interaction between the ac network and the harmonics generated by the converter. -- This thesis develops a technique for the harmonic analysis of phase-controlled ac/dc converters connected to the ac network.  The analysis method is based on the harmonic admittance model, which uses the multi-port network concept to define a relationship between the input ac voltages and currents, and the output dc voltage and current.  The matrix representation of the relationships is expressed in terms of A, B, C, D parameters, which contain the harmonic components of the switching functions of the converter and the admittance of the commutating inductance. -- A single phase model of the harmonic admittance technique is first implemented.  The model is used to determine the harmonics at various nodes in the system.  It is shown that in addition to providing quantitative information about the harmonic levels, the model accurately predicts the operating conditions and harmonic instabilities in the system. -- The method is extended to model a three-phase system.  For simplicity, the operation of the converter with commutating overlap angle less than 60° (i.e. mode-I operation) is considered.  However, based on the procedure described in the thesis, the model for other modes of operation can be developed.  The model is used to study the harmonic interaction in a simple HVDC system.  Specifically, the distortion at the point of common coupling, the effects of ac source harmonics and unbalance in ac network impedance on the system voltages are investigated. -- The harmonic admittance models developed in the thesis are verified by EMTP simulation.  The model accurately predicts the harmonics and system behaviour.  It is shown that the harmonic admittance method provides an alternate tool to study the harmonic interactions in power systems with converters.


identifier: Gu, Kaijun <https://research.library.mun.ca/view/creator_az/Gu=3AKaijun=3A=3A.html>   (1995) High performance dual shaped reflector antennas for earth stations.  Masters thesis, Memorial University of Newfoundland.

abstract: In satellite communications, the earth station antenna plays a major role in the vital link between the satellite and the earth station electronic equipment.  In this thesis, dual shaped reflector antennas for earth stations which can provide a pencil beam toward a geostationary satellite are introduced.  The design and analysis of both Cassegrain and Gregorian antennas are presented as follows. -- (i) The high performance antenna feeds are studied in detail.  Various specific characteristics required in Cassegrain and Gregorian antennas are discussed and it is shown that the corrugated conical horn is the best choice. -- (ii) The computer aided synthesis of subreflector and main reflector are developed by using the geometric optics (GO) approach.  Given the feed radiation pattern and the desired main reflector aperture power illumination, the sub and main reflectors can be shaped to obtain optimal reflector profiles. -- (iii) After having the sub and main reflector profiles, the physical optics (PO) are used to calculate the scattered pattern of the subreflector, the radiation patterns as well as the whole antenna specifications. -- (iv) A number of power distributions on the main reflector aperture are investigated to maximize the boresight gain and at the same time, minimize the sidelobe levels.  A pattern control method is also developed. -- (v) Performance comparison between Cassegrain antenna and Gregorian antenna is also made. -- The major contribution of this thesis is the complete computer aided design tool for a very high performance antenna.


identifier: Rokonuzzaman, Mohd. <https://research.library.mun.ca/view/creator_az/Rokonuzzaman=3AMohd=2E=3A=3A.html>   (1995) Neural network based incipient fault detection of induction motors.  Masters thesis, Memorial University of Newfoundland.

abstract: An incipient fault detection scheme of induction motors through the recognition of frequency spectra of the stator current has been developed in this thesis.  It is based on the adaptive resonance theory of neural networks.  This fault diagnosis scheme is not only capable of detecting a fault but also can report if it cannot identify a particular fault so that necessary preventive steps can be taken to update the underlying neural network to adapt to this undetected fault.  Moreover, it can update itself to cope with this dynamic situation retaining already acquired knowledge without the need of retraining with the old patterns. -- A laboratory experimental set-up using a digital signal processing(DSP) technique has been employed to collect the frequency spectra of the stator current at different fault conditions.  A wound-rotor induction motor has been used as the test motor to create different types of faults making unbalance in the stator and rotor circuits.  A 24-bit high speed DSP board has been used with a personal computer to develop a real-time interactive software to collect the spectra.  A driver for the HP-plotter has also been developed to directly plot the frequency spectra of the stator current. -- Adaptive resonance theory(ART) based network is a recent addition to the neural network family.  A new software has been successfully developed and implemented in the laboratory experiment using ART neural network.  Its performances in training, recalling and dynamic updating have been studied with a set of example patterns.  The incipient faults of a 3-phase wound rotor induction motor have been successfully diagonized by this neural network.


identifier: Li, Yulan <https://research.library.mun.ca/view/creator_az/Li=3AYulan=3A=3A.html>   (1996) Nearfield acoustics of a submerged cantilever plate for fatigue crack detection application.  Masters thesis, Memorial University of Newfoundland.

abstract:
This thesis presents an investigation which examines experimentally the change in modal parameters of a submerged  cantilever due to the existence of fatigue cracks, through vibrational and near field acoustical measurements. The modal behaviour of an uncracked cantilever, in air and in various water submergences was also studied and compared with numerical analysis. -- The modal properties of an uncracked cantilever plate in air, and in an infinite water medium were first estimated by solid structure modelling and  underwater shock analysis using a finite element program called ABAQUS. Ten modes were investigated for the dry cantilever and three bending modes for the submerged one. The effect of the depth of submergence of the cantilever on its modal properties was determined experimentally. It was observed that a maximum lowering in the structure's natural frequency of 33% occurred in the first bending mode. The damping ratios of the submerged cantilever increased one to six times in accordance with the different modes. When the ratio of immersion depth to the span length of the cantilever exceeded 0.4, the modal properties of the submerged structure tended to be independent of the depth of the submergence. -- In the fatigue test, a cantilever plate was subjected to a cyclic loading with constant magnitude in  air. Vibrational and near field acoustical tests were conducted at various fatigue cycles both in air and in water. Modal parameters and normalized acoustic intensities (NAI) were monitored as fatigue cycles accumulated. It was
found that those modal frequencies (bending frequencies in this study), with wave propagation directions perpendicular to the crack propagation direction were sensitive indicators  of structural cracking. When the ratio of crack area to the total cross sectional area of the plate (normalized crack area) assumed 33%, the crack was detectable by a maximum natural frequency change of 3-4% in both the air and the water media. It was about 17% when the normalized crack area  was 57%. 1.5 to 2 times increase in damping ratios and 3 to 6.7 dB decreases in NAI magnitudes were observed when the normalized crack area exceeded 47%. Fatigue results of the submerged cantilever agreed well with that of the dry cantilever for all modal frequencies and the lower modal damping ratios. Modal parameters extracted from the acoustical measurements agreed well with those from the vibrational measurements made on the submerged cantilever, and with most of the parameters noted for the dry cantilever. There were discrepancies of modal damping ratios  for the 2nd and the 6th bending modes of the dry cantilever.  -- The frequency response functions (FRF) and the nearfield acoustical pressure transfer functions (PTF) of the uncracked cantilever in air were simulated by using ABAQUS computer program and compared with the experimental results.  Measured and simulated natural frequencies of the dry cantilever plate have good agreements. The maximum difference was 2.67%. Good agreements were also observed between measured and simulated FRFs for the first four bending modes and PTFs for the 3rd and 4th bending modes. The maximum discrepancy of PTF magnitudes was found to be 5.9 dB for the PTF magnitude of the first bending mode.


identifier: Leung, Arthur Ki-Kit <https://research.library.mun.ca/view/creator_az/Leung=3AArthur_Ki-Kit=3A=3A.html>   (1984) Structural design and analysis of concrete sandwich panels and their practical applications.  Masters thesis, Memorial University of Newfoundland.

abstract: The concept of a concrete sandwich panel originated in the United States in 1906 where a building was constructed with sandwich tilt-up wall panels. Since then sandwich panels have  developed gradually and have continued to improve. -- There are two types of concrete sandwich wall panels: (1) Architectural wall panels (non-composite type), and (2) Load  bearing wall panels (composite and non-composite type). -- In general, the non-composite type of load bearing panel is used more commonly because there are less limitations compared with the composite types. This thesis deals with the structural design and analysis of the non-composite type  of load bearing wall panel. -- In the past, certain problems  besetted architects, engineers, and contractors working with  concrete sandwich panels. These problems are associated with: -- (1) Bonding between concrete and insulation -- (2) Joints in panel -- (3) Panel connections -- (4) Control of cracking. -- This study has been undertaken with the aim of solving some of these problems. Three experiments were conducted accordingly to determine the behavior of concrete sandwich panels. The first experiment was to investigate the  effects of heating and cooling on sandwich panels and to compare the experimental results with theoretical calculations. The principal results of this experiment demonstrated the effects on concrete sandwich panels under varying thermal conditions. These results should serve as a guideline for the design of joints in sandwich panels. The second and third experiments were initiated to investigate and compare the bending stresses, deflections and shear strength in concrete sandwich panels either with or without shear connectors. The panels were subjected to a simulated uniformly distributed load under simply supported conditions. It can be concluded from the experimental results that a well designed anchor system joining the concrete sandwich panel faces through the core insulation is  a fundamental requirement in the future production of sandwich wall panels in order to obtain full shear transfer between the faces. Without these shear connectors, a concrete structural sandwich panel will usually fail by shear of the bond between the core and faces or by shear failure of the core itself. -- The deflection on a sandwich panel is the sum of ordinary bending deflection and an additional deflection associated with shear deformation of the core. Experimental results showed that deflections were mainly associated with shear deformation of the core for panels without shear connectors. -- Deflections measured were less for panels containing shear connectors. For both panels, from theoretical calculations, it was found that the  deflections were mainly associated with shear deformation, with less than 1% due to bending. -- A proper shear connector system transfers all lateral loads including wind forces from the exterior face to the interior structural face of the panel. Hence the sleeve anchor, torsion anchors and connector pins play a very important part in the performance of concrete sandwich panels. Prestressing techniques can also improve the design of such panels and have been widely used in recent developments of sandwich panels. -- For this study, a typical non-composite type of concrete sandwich panel was selected as a design example. For the design of such concrete sandwich panels, the following factors were carefully considered: -- (1) The thickness of both faces of the panel -- (2) The loading conditions -- (3) The fire resistance of the sandwich panel -- (4) The temperature gradient between the faces, and -- (5) The panel anchor system.


identifier: Tiller, Richard W. <https://research.library.mun.ca/view/creator_az/Tiller=3ARichard_W=2E=3A=3A.html>   (1995) Strut-and-tie model for punching shear of concrete slabs.  Masters thesis, Memorial University of Newfoundland.

abstract: The reinforced concrete slab system is an economical and popular structural slab system in building and offshore construction. A major concern of this system is localized punching shear failure at the slab-column interface. Punching shear failure occurs when the column "punches" through the slab. This type of failure is unpredictable and often sudden resulting in cathastrophic failure of the slab system. -- Current North American design codes deal with punching shear in an empirical equation based mainly on test  results. This approach is limited to concrete with a compressive strength generally less than 40 MPa. The strut-and-tie method considers the flow of forces in a reinforced concrete element to consist of a series of compressive struts and tension ties joined at nodes. The strut-and-tie method is a rational approach to structural concrete design which results in a uniform and consistent design philosophy. -- A strut-and-tie model has been developed to model the punching shear behaviour of a concrete slab. This model provides a quick and simple approach to punching shear behaviour. It is applicable for both normal and high strength concrete under symmetric and nonsymmetric loading with and without shear reinforcement. -- The strut-and-tie model for symmetric punching consists of a "bottle shaped" compressive zone in the upper section of the slab depth leading to a "parallel stress" compressive zone in the lower  section depth. Inclined shear cracking develops in the bottle shaped zone prior to failure in the lower zone. Cracking in the bottle shaped zone is related to the diagonal tensile strength of the concrete. Ultimate punching  failure occurs in the parallel stress zone by a high radial compressive stress failure. An equation based failure criteria for the strut-and-tie method is used to model the behaviour in the lower compressive stress zone. The results of the strut-and-tie model for symmetric punching shear behaviour were compared to experimental test results performed and published by others. The results of the strut-and-tie model showed excellent agreement with these test results. -- A strut-and-tie model was also developed to rationally model nonsymmetric punching shear behaviour due to unbalanced moment transfer and symmetric punching behaviour of concrete slabs with shear reinforcement. These models showed excellent agreement with test results performed and published by others. -- The strut-and-tie method presents a unified, consistent, rational behaviour model for structural concrete elements including the punching shear phenomena of concrete slabs.


identifier: Hoque, M. Ashraful <https://research.library.mun.ca/view/creator_az/Hoque=3AM=2E_Ashraful=3A=3A.html>   (1993) Speed and position sensorless permanent magnet synchronous motor drives.  Masters thesis, Memorial University of Newfoundland.

abstract: DC motors have played a crucial rule in drive technology during the last few decades of this century. Recent developments in power converters, digital signal processors and magnetic materials make it possible to use ac motors in a variety of drive applications. Permanent magnet synchronous (PMS) motors are gaining wide recognition over other types of motors in drive systems, mainly due to their inherently advantageous features. For successful operation of PMS motor drives, position and speed sensing are of critical importance. Conventional sensors are expensive and hamper sturdiness of industrial drives. Hence speed and position sensorless PMS drive draws wide attention. In this work, an algorithm is developed which enables the PMS drive to operate successfully at any speed (from zero to twice the  rated value) without any mechanical speed and position sensors while keeping the maximum out put voltage of the inverter constant above the base speed. New expressions have  been derived for the rotor speed and position in terms of the stator voltages and currents. A method has also been suggested to calculate the input voltage of the motor. The present work is an attempt to provide theoretical analysis of speed and position sensorless PMS drives with computer simulations of various drive configurations. Experimental results which are in agreement with the proposed algorithm have been included.


identifier: Lin, Ling <https://research.library.mun.ca/view/creator_az/Lin=3ALing=3A=3A.html>   (1995) Strength characteristics of a modelling silty clay.  Masters thesis, Memorial University of Newfoundland.

abstract: Shear strength is an important soil parameter. Many geotechnical failures have been caused by inadequate shear strength. In order to obtain a high strength modelling silty  clay for use in centrifuge model tests of soil-pipeline interaction, direct shear tests, shear vane tests and cone penetration tests were conducted to investigate its shear strength behaviour. -- This thesis first presents some background on the shear strength of soils and measurement techniques. The details of the direct shear tests, the shear  vane tests, the cone penetration tests and centrifuge modelling are also discussed. The silty clays used in this study were kaolin and a kaolin-silt mixture; the plasticity indices were 30.6% and 19.5% respectively. The kaolin-silt mixture (K-S) was obtained by mixing equal amounts of kaolin  and silt by weight. -- Direct shear and shear vane tests were conducted on both clays at different vertical stresses under various overconsolidation ratios (OCR's). This thesis presents these test procedures and the test results. Cone penetration tests were also conducted in a centrifuge at 50 gravities to verify the results from the direct shear and shear vane tests and to correlate the cone penetration resistance to the undrained shear strength from shear vane and direct shear tests. Centrifuge modelling principles and the current methods to convert cone tip resistance to shear strength are also presented. Test results show that the shear strength of K-S is higher than that of pure kaolin. Shear strengths of heavily overconsolidated clays obtained from the shear vane tests are higher than those obtained from the direct shear tests. A correlation between cone tip resistance and undrained shear strength is presented. The shear strength of K-S interpreted from CPT results was found  to lie between the direct shear and shear vane test results and shows a good correlation in the measurement of shear strength.


identifier: Sen, Debabrata <https://research.library.mun.ca/view/creator_az/Sen=3ADebabrata=3A=3A.html>   (1983) Prediction of wave loads and motions of floating marine structures by three-dimensional flow theory.  Masters thesis, Memorial University of Newfoundland.

abstract: The three-dimensional singularity distribution or boundary integral method has been demonstrated by many investigators to be the most versatile and reliable technique for the calculation of harmonic oscillation of a truly three-dimensional floating marine structure in potential flow field. -- In the present work, a numerical scheme is presented and a computer program has been developed based on the three-dimensional singularity distribution theory.  The program calculates the first order wave exciting forces and moments, hydrodynamic co-efficients and motion responses in six degrees of freedom of any floating marine structure of arbitrary geometry for different angles of heading.  Calculations are performed for a floating rectangular box, a vertical circular cylinder and a 130,000 ton dwt tanker.  The results are compared with available published results based on the same theoretical model.  In general, a good agreement is found between the results. -- To demonstrate the versatility and effectiveness of the program, calculations are also performed for a semi-submersible and the results are presented.


identifier: Paranavitana, Samuel <https://research.library.mun.ca/view/creator_az/Paranavitana=3ASamuel=3A=3A.html>   (1996) Symmetric and asymmetric crack development in tubular T-joints.  Masters thesis, Memorial University of Newfoundland.

abstract: Although many studies on the fatigue behaviour of tubular T-joints have been carried out thus far, the present study is done with the view to evaluating the total fatigue life of a joint in the presence of an asymmetric crack, using the principles of fracture mechanics.  The studies made so far have only analyzed symmetric cracking, which does not generally occur during fatigue cracking, since it is assumed that the cracks at both the hot spot regions grow at the same rate.  Also very few studies address the issue of crack initiation life in tubular T-joints.  D.I. Nwosu (1993) used the stress-strain approach using the Manson-Coffin equation, to evaluate the initiation life.  The elastic life component was used to determine the coefficients.  In this study the author has used both lives (plastic strain life, as well as elastic strain life) to determine the coefficients used in the equation.  The experimental results reported by Iida [1987] on tubular joints have been used to determine them.  The range of obtained coefficients check with the prescribed limits given in earlier studies.  The purpose of the study was to use and compare the results of the numerical model in verifying and correlating the experimental investigation of the tubular T-joints, which is being carried out in the Strength Laboratory of Faculty of Engineering, Memorial University. -- The line spring element was used to model the crack; the reason being that the other known method, viz., that of using singular three dimensional elements would render the problem impractical in the light of computer time and memory space available in the Faculty of Engineering.  Using the stress intensity factors obtained from the line spring model, the through-thickness crack propagation life was obtained using Paris' law.  While the crack initiation compared very well with the experimental value, the crack propagation life compared only favourably with the experimental value.  The procedure required to improve the computed crack propagation life is given in the discussion of results.


identifier: Heale, Donald Gerard <https://research.library.mun.ca/view/creator_az/Heale=3ADonald_Gerard=3A=3A.html>   (1993) Qualitative and quantitative analyses of factors affecting productivity in Canadian construction projects.  Masters thesis, Memorial University of Newfoundland.

abstract: The decline in construction productivity across the North America since the mid 1970's has been reported by many researchers.  Potential exists to affect major cost savings if the factors underlying this decline can be identified and quantified and solutions found.  The issue is complex.  However, it is generally acknowledged that productivity improvement is a management responsibility and that problems are within the control of management to solve. -- This work uses a survey to study the perception of Canadian construction professionals toward factors affecting construction productivity.  Findings for different regions of the country are presented and contrasted.  Factors analyzed are clustered into the following groupings: a) contract environment, b) planning, c) site management, d) working conditions, e) working hours and f) motivation.  Major factors affecting productivity are identified. -- In addition, a weather-related factor model is developed to predict productivity as a function of weather and other site factors.  Significant findings are that a high percentage of the variation in productivity is accounted for by height of worksite above grade and by average temperature, wind and rain.  A method is suggested to allow the calculation of time-location modifiers that would account for local weather conditions and seasonal effects.  They will be of use in more accurate project planning and costing.


identifier: Dawe, Barry John <https://research.library.mun.ca/view/creator_az/Dawe=3ABarry_John=3A=3A.html>   (1988) Radio wave propagation over earth : field calculations and an implementation of the roughness effect.  Masters thesis, Memorial University of Newfoundland.

abstract: Computer programs are developed to calculate radio propagation losses over the ocean surface.  The effects of the ocean surface roughness are evaluated through numerical implementations of modified surface impedance expressions.  The surface roughness is expressed in terms of standard oceanographic models for the directional ocean wave height spectral density.  The modified surface impedance may be used with either a planar earth propagation model, for short propagation distances, or a spherical earth propagation model for long propagation distances. -- The planar earth solution for the electric field distant from the source, is derived using a spatial decomposition method and expressed in the form of the spatial Fourier transform of the electric field.  No assumed boundary conditions are used in the derivation; the method supplies its own boundary conditions.  As well, the surface impedance and the choice of source remains arbitrary.  For a highly conductive surface, such as the ocean surface and an elementary vertical electric dipole source, the expressions reduce to the classical planar earth results. -- For long propagation distances, the effects of radio wave diffraction around the curvature of the earth’s surface are significant.  A computer program has been written using modern compact computer code which implements the classical residue series results for ground wave spherical earth propagation.  The program accounts for rough surface effects using an implementation of the modified surface impedance for a rough ocean surface.  Transmission loss results for a variety of frequencies in the MF and HF bands and a variety of sea states are presented which compare favourably to previous results.


identifier: Cao, Suyun <https://research.library.mun.ca/view/creator_az/Cao=3ASuyun=3A=3A.html>   (1994) On a vibration response of a plate submerged in fluid.  Masters thesis, Memorial University of Newfoundland.

abstract: This study deals with the dynamic characteristics of plates submerged in water using analytical and experimental methods.  The plates considered have two kinds of boundary conditions, one with clamped-free-clamped-free(CFCF) supports, another with simple-free-simple-free(SFSF) supports.  They are submerged in water at different depths. -- For the experimental study, modal testing of the two plates is carried out in air and in water.  The effect of the depth of submergence of the plate is investigated.  The simply supported condition was simulated by using a notched plate with a damped end and the finite element software ABAQUS is used to determine the dimensions of the notch.  The appropriateness of the tested plates as models of the CFCF and SFSF plates is verified.  The added mass factor, which is used to account for the decrease in natural frequencies, and the increase in modal damping ratios for the vibrating plates submerged in water have been evaluated for the first five modes.  The effect of the plate boundary conditions on the vibration of plates in water is also investigated. -- In the analytical study, a thin plate undergoing a flexural bending vibration in a body of homogeneous, incompressible and inviscid fluid whose motion is irrotational, is considered.  The governing equation for the surface displacement of the plate-fluid system is derived.  In the effort to solve the velocity potential, the general linearized fluid free surface boundary condition is applied.  The relationship between the added mass and the depth of submergence above and below the plate is established. -- The analytical solution is applied to the CFCF and SFSF plates submerged in water, and the experimental and analytical studies on the added mass due to the presence of fluid are compared.  The maximum difference between the measured and the predicted added mass factors is found to be within 7.916%.


identifier: Wang, Haiyin <https://research.library.mun.ca/view/creator_az/Wang=3AHaiyin=3A=3A.html>   (1992) On the ground wave propagation over a cliff with finite ground parameters.  Masters thesis, Memorial University of Newfoundland.

abstract: The characteristics of the ground-wave propagation over a cliff are investigated using both the residue and the compensation methods.  The two methods are reviewed and compared.  The theorical analysis for the ground wave propagating from sea to earth is presented in detail.  The residue method employes Fourier transform and Green theorem, while the compensation method employes the surface impedance technique.  The analysis of the two methods are reintroduced in a more clarified way.  The differences between the assumptions of the two methods are identified and comparisons of the relative results are illustrated. -- The flat-cliff approximation is used to obtain the terrain coefficient so that the problem can be solved when the antennas on the cliff top are close to the cliff edge.  The final expressions of terrain coefficient and field distribution over the cliff as well as the sea are presented. -- An approximate analysis expression, called the two terms approximation, is presented in this work to calculate terrain coefficient.  The two terms approximation is based on the flat-cliff approximation of Green theorem method.  It simplifies the numerical calculation of the problem. -- Graphs are shown in this work to describ the fields changing over the ocean and over the cliff for the transmitters on the cliff and on the ocean separately.  The numerical results are in a good agreement with available literature data. -- The expressions and results given in this work can be used to determine the optimum location and height of an antenna over a cliff. -- Presently, a prototype bistatic radar system which uses ground wave propagation for over the horizon target detection is being built on a cliff at Cape Race, Newfoundland.  The radar has a log periodic array antenna as the transmitter and a linear array as a receiver.  The results, data and the program given in this work are very helpful in designing new groundwave radar antennas on the cliff since the program can be used to determine the optimum location and height of the antennas for both the source and the receiver.


identifier: Liu, Bin <https://research.library.mun.ca/view/creator_az/Liu=3ABin=3A=3A.html>   (1994) Numerical modelling of medium scale indentation tests.  Masters thesis, Memorial University of Newfoundland.

abstract: Medium scale indentation tests were conducted at Hobson's Choice Ice Island in 1989 and 1990.  Areas with different degrees of damage were found in the ice close to the indentor in these tests.  It is believed that the fluctuation of the total ice load and local peak pressure is determined by the dynamic behaviour of the ice at the hard spots or the 'critical zones'.  The high confinement pressure at hot spots may have a great effect on the failure process.  A review of the mechanical properties of ice and the damage theory is given.  The effects of hydrostatic pressure on ice deformation and damage development are discussed.  One of the tests from the Hobson's Choice Ice Island experiments is modelled using the finite element method. -- Damage theory and the effects of hydrostatic pressure are considered in the theoretical modelling of the indentation process.  The results of the numerical modelling are compared with the results of the test and good agreement has been found.  Further investigation on the effects of hydrostatic pressure is suggested.


identifier: Krishna, Vikas <https://research.library.mun.ca/view/creator_az/Krishna=3AVikas=3A=3A.html>   (1995) Numerical simulation of vortex shedding in oscillatory flows.  Masters thesis, Memorial University of Newfoundland.

abstract: Viscous forces that act on a body moving in a fluid may form  a significant part of the total force acting on the body. The use of the linear potential-flow theory does not take into consideration the viscous effects that cause flow separation, skin-friction drag, and lift. Various methods have been developed and used to calculate the viscous forces  numerically since Rosenhead's initial calculations. A review  of the earlier work done in the area of vortex shedding and calculation of viscous flows is presented in chapter 1. Some  vortex methods, that are commonly used, are described. One of these, the Discrete Vortex Method, is described in detail  in chapter 2. This is demonstrated for a bluff body with sharp corners using the features of the Clement's model. However, this method does not simulate the effects of vorticity diffusion in the flow. Moreover, the body must also have sharp edges, which are taken to be the separation points. -- Another method, that does not impose such limitations, is the Vortex-In-Cell(VIC) Method. This is developed and first applied to study flows past a circular cylinder in order to validate the method with existing results in chapter 3. Conformal transformations coupled with  this method enable us to study flows past bodies of other cross-sectional shapes. Various mappings are derived and developed to simulate flows past a variety of shapes. A fin was added on to the body contour to simulate the effect of a  skeg in the case of boat-sections. The force coefficients, CD and CM, were calculated at different Keulegan-Carpenter numbers and verified for sections like a circle, a flat plate, and a square, in an oscillatory flow, with the results obtained by other workers. They were also calculated  for a finned-circle, a section of a boat that is rounded and  one that has hard chines. The theory and the method, the necessary modifications to the VIC method, and the simulation results are presented in chapter 4. A conclusion of the work done in the different chapters along with some comments are given in chapter 5.


identifier: Akhmad, Abdul Hanan <https://research.library.mun.ca/view/creator_az/Akhmad=3AAbdul_Hanan=3A=3A.html>   (1993) Regional flood frequency analysis for Aceh Province, Indonesia.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis discusses the development and application of two principal methods of regional flood frequency estimation for the rivers in Aceh Province, Indonesia. -- The first method is based on index-flood approaches and the second method is the regression of flood quantiles on basin characteristics approach. -- For the index-flood approaches, the annual maximum floods at each site were standardized by the mean annual flood of the site.  Five different index-flood methods were used to derive the regional frequency curve.  These are Dalrymple's method, NERC method, the probability weighted moments method, the station year method and the L-moment method. -- For the multiple regression approach, the logarithm of each selected quantile of the annual maximum floods at each site of the nine river basins was regressed on its corresponding catchment variables.  The least squares method was used lo develop the multiple regression equations.  The derived regression equations were corrected for bias caused by the logarithmic transformation. -- The flood estimates obtained using the two regional methods were compared to at-site estimates and to those obtained from a previous study by the Institute of Hydrology (IOH), Wallingford (1983) for basins in Jawa and Sumatra.  The estimates obtained by the various methods were also compared to each other for basins that were not used in the study to show the variability of the results. -- From a comparison of the two regional methods, the findings showed that all index flood approaches provided greater consistency and similarity in the estimation of flood quantile magnitudes.  The L-moment method seemed to give the best compromise estimates, while the regression approach gave lower estimates for most stations and estimates were sometimes inconsistent.  The estimates based on the IOH study gave estimates well above these obtained in this study especially for higher return period floods.


identifier: Wu, Xia <https://research.library.mun.ca/view/creator_az/Wu=3AXia=3A=3A.html>   (1992) Roll motion parameter identification using response in random waves.  Masters thesis, Memorial University of Newfoundland.

abstract: The concept of the random decrement has been used successfully in the damping identification of linear systems.  The formulation of the random decrement existing in the literature is based on the assumptions that the dynamic system is linear, time invariant and subjected to Gaussian, white noise excitation.  Thus, the principle of superposition can be used in formulating the equation for the random decrement. -- In this study, the concept of the random decrement is extended to nonlinear systems.  Using the Fokker-Plank Equation approach, it can be shown that the random decrement formed by calculating the expected value of a stationary random rolling process satisfies the differential equation governing the free roll motion.  It is also shown that, the autocorrelation function for the stationary nonlinear roll motion excited by a zero mean, Gaussian, white noise random process, satisfies a linearized free roll equation.  Thus the random decrement and the autocorrelation function curves can be used for identifying the parameters in the nonlinear equation of free roll motion. -- The validity, accuracy and reliability of the Random Decrement Technique in determining the parameters of the nonlinear equation for roll motion are investigated in this study.  The technique is applied to roll motion obtained from: 1) computer simulation by using a fourth order Runge Kutta routine; 2) experiments of three ship models rolling in a towing tank; 3) full scale tests on a real fishing vessel.  A method for evaluating the parameters in the nonlinear roll equation from free roll decay, the random decrement and the autocorrelation function is developed and presented in this study.  This method is based on the theory of equivalent linearization.  The application of the method provides accurate estimation for the parameters from both simulated and measured data. -- It is shown that the random decrement and the autocorrelation function curves extracted from a history of nonlinear roll response to random excitation closely resemble the measured free roll decay curve.  The predicted natural frequency obtained by either the random decrement or autocorrelation function method can be used to determine the value of the metacentric height for a ship rolling under the action of unknown random excitations.  The damping coefficients estimated by either method are used to generate free roll decay curve which agrees well with the measured free roll decay curve. -- This method does not rely on a model experiment and does not require the measurement of wave height.  In addition, roll response of a ship can be easily measured with the ship underway.  It is expected that the method would be particularly useful for assessing roll stability of a ship sailing in a realistic sea.


identifier: Weng, Chi <https://research.library.mun.ca/view/creator_az/Weng=3AChi=3A=3A.html>   (1995) Roll motion stabilization for small fishing vessels.  Masters thesis, Memorial University of Newfoundland.

abstract: A review of various roll stabilizing systems—bilge keels, active fins, passive bilge fins, rudder stabilization systems, passive anti-roll tanks, active anti-roll tanks, and paravanes—is given, along with a more detailed discussion on their suitability for small fishing vessels. Particular attention was paid to the passive flume tanks and  paravanes, and an experimental study was carried out on these two kinds of stabilizers. -- A flume tank model and a pair of paravanes, as well as an oscillating bench simulating sinusoidal rolling, were designed and then constructed. The tank was tested on the bench for configuring the internal dimensions which give the desired natural frequencies, tuning, and damping. The analysis was carried out by inspecting the phase lags εt of the motion of  tank water to the roll motion. -- Free roll decay tests for a fishing vessel model with the tank and paravanes were carried out for identification of the damping generated by the tank and paravanes. Non-dimensional equivalent linear damping ratios ζE were calculated and discussed. -- The stabilizers were tested in the wave tank at MUN, both in regular and irregular beam waves, to determine their effectiveness. The study of roll responses, roll energy spectra, response amplitude operators (RAO), and resonant and significant roll amplitude reductions at various wave and stability conditions shows that the tank can provide 50%  to 70% roll reductions, which are approximately 30% more than the paravanes can do in the same circumstances. The effects of tuning, liquid level, and internal damping on the  efficiency of the tank are discussed. Comparisons in the behaviors of the stabilizers for different wave conditions are also made. -- Some design considerations are presented, and further work is recommended to develop a systematic method to design passive stabilizing tanks for small fishing  vessels.


identifier: Srivastava, Satish Kumar <https://research.library.mun.ca/view/creator_az/Srivastava=3ASatish_Kumar=3A=3A.html>   (1984) Scattering of high-frequency electromagnetic waves from an ocean surface : an alternative approach incorporating a dipole source.  Doctoral (PhD) thesis, Memorial University of Newfoundland.

abstract: A theoretical analysis of the scattering of High-Frequency (HF), electromagnetic waves from a rough surface such as the ocean surface is proposed.  This is required for an interpretation of the radar signature when using an HF radar for the remote sensing of ocean surface parameters.  The analysis is based on Walsh's (1980b) formulation in the spatial Fourier transform domain for the scattering from a general time invariant surface.  Initially, a two dimensional spatially periodic surface with a high refractive index is considered.  For this surface, a series solution is derived for the surface electric field in the spatial transform domain maintaining the choice of any finite source.  The source then considered is an elementary vertical dipole excited by a pulsed sinusoidal current.  It is assumed that the surface slopes are small compared to unity.  For this source, zero first, and second order approximations of the vertical component of the surface field are inverse spatially transformed in an asymptotic sense.  These solutions are in the form of ground waves with modified surface impedances.  By assuming a narrow beam receiving antenna, the inverse transforms for the first and second order solutions that involve spatial convolution integrals, are evaluated asymptotically for the two orders of the backscattered surface field. -- By modelling the ocean surface as a three dimensional periodic surface in space and time with random Fourier coefficients, the above two orders of the backscattered field are suitably modified to include the time dependency and the statistical variation of the surface.  Based on this model an average first and second order backscattered Doppler spectra and consequently the two orders of the cross section are derived.  The first order cross section is the same as that derived by Barrick (1972b, 1977a) using the Rice perturbation technique.  The second order result contains three parts.  The first part is almost the same as that obtained by Barrick.  The two additional parts result from surface and incident field interaction along the path from transmitter to the primary ocean scattering patch and off-patch double scatter respectively.  The effect of the former may be very pronounced, particularly at the higher Doppler frequencies when the radar is situated in the middle of the ocean.


identifier: Sidhu, Anjana <https://research.library.mun.ca/view/creator_az/Sidhu=3AAnjana=3A=3A.html>   (1995) Seasonal flow forecasting of Newfoundland rivers.  Masters thesis, Memorial University of Newfoundland.

abstract: The general purpose of forecasting is to provide the best estimates of what will happen at specified points in time in the future.  In hydrology, for example, forecasts of riverflows are often used for operational planning of reservoir and flood control systems.  Since, even modest improvements in the operation of a large reservoir system can result in multi-million dollar savings per year, choosing a model which produces reliable and accurate forecasts is therefore essential to the efficient operation of the system.  In this study, monthly and quarterly discharge data of Newfoundland rivers were used to forecast future flows using four different statistical approaches: conventional Box and Jenkins's autoregressive integrated moving average (ARIMA), exponential smoothing, periodic autoregressive (PAR), and Harvey's new structural time series (NSM).  Each monthly riverflow data was divided into three short term series to study forecasting accuracy.  Ten quarterly series were used to predict flows for three forecasting scenarios and thirty monthly series were considered for 3 month, 6 month, 9 month and 12 month ahead forecast horizons.  Forecast performance was assessed using the mean absolute percentage error (MAPE) criterion. -- Based on the MAPE criterion, it is concluded that forecasts using the NSM approach for short term monthly riverflow data in general are better than ARIMA, exponential smoothing and PAR approaches.  For quarterly data, forecasts using the exponential smoothing approach in general are better than NSM, ARIMA and PAR approaches.


identifier: Dunphy, Patricia <https://research.library.mun.ca/view/creator_az/Dunphy=3APatricia=3A=3A.html>   (1989) Second-order steady drift of a floating triangular platform : theory and experiment.  Masters thesis, Memorial University of Newfoundland.

abstract: As ocean industries have grown to demand larger offshore vessels achieving ever increasing levels of performance, the need for a better understanding of the phenomena which govern motions and loading of these structures has been recognized.  These motions and forces are a result of complex environmental conditions including ice, wind, current and waves.  A significant part of the environmental loading is due to waves. -- In general wave loading on a structure is a complex non-linear process of which the first- and second-order (in wave amplitude) components are of main interest.  The steady second-order component of drift force may cause large excursions of the structure and therefore must be seriously considered in the design considerations of mooring and dynamic positioning systems. -- In this thesis second-order mean drift forces on a triangular floating structure in regular waves are calculated utilizing far field potential theory.  These computed forces are compared to those measured during testing of a 1:200 scale model of a moored triangular body.  This is done in an attempt to decide whether mooring forces can be reasonably estimated for such a structure. -- It was concluded that the mean drift forces can be reasonably well predicted using the method presented.  Therefore this method can be used as an aid in the design process.


identifier: Dutton, Catherine Robin <https://research.library.mun.ca/view/creator_az/Dutton=3ACatherine_Robin=3A=3A.html>   (1985) The analytical and experimental studies of the heat transfer around a vertical ice wall in fresh water near its maximum density temperature.  Masters thesis, Memorial University of Newfoundland.

abstract: The analytical as well as experimental investigations of the temperature and velocity distribution in fresh water along a vertical ice wall are carried out.  The analytical investigation involves the simultaneous solution of the continuity equation, the Navier-Stokes equations for fluid motion in two-dimensions and the thermal energy balance equation, by a finite-difference technique.  The general form of these equations can then be solved by the successive-substitution method on a digital computer.  The experimental investigation involves taking temperature and velocity measurements through the boundary layer along the ice surface at various bulk fluid temperatures. -- The analytical and experimental results are compared, for both the temperature and velocity, the local and average heat transfer coefficients and the Nusselt numbers. -- The analytical model is then extended to other bulk fluid temperatures with predictions for the temperature and velocity profiles, the average heat transfer coefficients and the Nusselt numbers.


identifier: Bennett, Peter <https://research.library.mun.ca/view/creator_az/Bennett=3APeter=3A=3A.html>   (1990) The angle dependence of the roll damping moment.  Masters thesis, Memorial University of Newfoundland.

abstract: A new approach to the analysis of the free roll decay curve, the Energy method, is examined in this paper and compared with two commonly accepted methods of analysis, the averaging technique of Krylov-Bogoliubov and the Perturbation method.  The Energy method uses the equality of the rate of change of the total energy of the system to the rate of energy dissipation due to damping.  This method was concluded to be the best method for analysis for three main reasons. 1) It uses the whole roll decay record in its analysis, not just the peak values, allowing for single cycle analysis and analysis of shorter roll decay records.  2) It can separate the influence of the angle and velocity dependent components of the roll damping moment.  3) It can handle non-linear restoring terms which makes it viable for large amplitude motion. -- The Energy method and the Krylov-Bogoliubov method were used to analyze stillwater roll decay test records.  The results of these analyses indicate a strong angle dependence of the roll damping moment.  The quadratic and cubic velocity dependent forms, which are actually functions of the roll angle, of the roll damping moment were shown to be the most viable forms for the roll damping moment.  This supports the findings of a strong angle dependence.  Stillwater roll decay tests with forward speed were performed and also indicate a strong angle dependence of the roll damping moment.  Comparisons of forced roll tests with predictions of forced roll motion using coefficients derived from the stillwater roll decay analyses proved inconclusive.


identifier: Dawe, Byron R. <https://research.library.mun.ca/view/creator_az/Dawe=3AByron_R=2E=3A=3A.html>   (1983) The development of a normalized radar cross section model for icebergs.  Masters thesis, Memorial University of Newfoundland.

abstract: To reliably assess the detection performance of marine radars against iceberg targets a realistic model of the normalized radar cross section is required. Previous research indicates that the radar cross section of an iceberg is directly proportional to the area of an iceberg projected onto a plane normal to the radar beam and that aspect and overall shape are secondary factors. Physical descriptions of the iceberg surface indicate that in the X-band and Ku-band frequency range an iceberg can be modelled as a target composed of a number of large (on the wavelength  scale) slightly rough (on the wavelength scale) surfaces. Empirical fitting of Ku-band scatterometer data (measured normalized radar cross section values) to an average incoherent normalized radar cross section statistical model for a slightly rough surface employing a Gaussian surface height correlation coefficient shows that such a model is applicable to a slightly rough iceberg surface. The model at  9.5 GHZ (horizontal polarization) is shown to give good agreement with independent measurements made by other researchers after making some general assumptions. It predicts that vertical polarization will give higher normalized cross sectional values. Higher frequencies will give higher values for incidence angles less than about 50° from the vertical. Through the use of standard target modelling techniques this normalized radar cross sectional model can be applied in a practical manner to provide a quantitative assessment of the detection capability of icebergs on current commercially available marine radars.


identifier: Reddy, Bhimavarapu Subba <https://research.library.mun.ca/view/creator_az/Reddy=3ABhimavarapu_Subba=3A=3A.html>   (1985) The computer-aided optimal heating schedule of forging ingots using the finite element method.  Masters thesis, Memorial University of Newfoundland.

abstract: This thesis presents the computer simulated thermal stress analysis of forging ingots during the heating and soaking periods.  These results are then used to obtain the optimal heating schedule of these ingots. -- The equations for the transient nonlinear temperature distribution within the ingot due to the convective and radiative heat flux are derived using the nonlinear finite element analysis.  The nonlinearities due to the variation of material properties have been taken into account by calculating the temperature at different time steps first and then at each time step the elemental property matrices are recalculated.  The nonlinear algebraic equations are solved using three techniques and then the best technique is selected from these three for further analysis. -- The mathematical model for the thermal stress analysis has also been formulated using the finite element analysis.  The temperatures obtained from the heat transfer analysis are used to calculate the force vector for the stress analysis.  These finite element models are then used to calculate the effects of axial heat flux, the slenderness ratio of the ingot, and the linearization of the heat flux on the transient temperature and stress distributions within the ingot. -- The optimal heating schedule has been obtained considering two types of constraints; the first type of the constraint is that the stresses developed should not exceed certain value established by some of the commonly known failure theories, and the second type is that the temperature in the ingot during the heating or soaking period does not exceed a specified value for a particular type of material.  The method of optimization of the furnace heating schedule is selected after considering three alternate ways of carrying out the optimization.


identifier: Johnston, Michelle <https://research.library.mun.ca/view/creator_az/Johnston=3AMichelle=3A=3A.html>   (1994) Variation of local pressures during ice-structure interaction.  Masters thesis, Memorial University of Newfoundland.

abstract: Ice-structure interaction is characterized by a nonuniform distribution of pressure across the impact zone.  The interface between the structure and the parent ice consists of a matrix of crushed and sintered ice, throughout which regions of intense pressure are randomly dispersed. -- The variation of localized pressures generated during ice-structure interaction was examined for several sets of data.  Ice indentation tests conducted at Hobson's Choice Ice Island (1989), ship ramming trials of the Louis S. St. Laurent and the CanMar Kigoriak, and one ice event which involved the offshore drilling structure 'Molikpaq' each exhibited rapid fluctuations of pressure in space and in time. -- Small regions of intense pressure are termed critical zones and are identified as important elements in the crushing process.  Fundamental properties of the high pressure zones such as the average size, force and spatial density are quantified.  Critical zones are of the order of 0.10m² and may experience forces ranging from 0.1-4MN.  The analyzed data exhibited a reduction in the average pressure of a critical zone with increasing area of instrumentation.  A decrease in the spatial density of the critical zones (from 0.80 to 0.62 zones/m²) is proposed as a possible explanation for the noted scale effects. -- Due to the random nature of the critical zones, a design methodology which combines the statistical distributions for the zonal force, size, and number is proposed.  Design pressures over small areas may be obtained from a preliminary design curve which is fitted to data from ice interactions with ships and stationary structures.


identifier: Finn, David W. <https://research.library.mun.ca/view/creator_az/Finn=3ADavid_W=2E=3A=3A.html>   (1991) Vertical and inclined edge-indentation of freshwater ice sheets.  Masters thesis, Memorial University of Newfoundland.

abstract: A series of freshwater ice indentation experiments were performed with stiff vertical and downward-breaking inclined indentors in the ice tank at the Institute for Marine Dynamics in the fall of 1989.  Indentor width, indentor angle, indentor velocity and ice sheet thickness were varied for a total of 94 tests.  Three forces, one moment, three accelerations, indentor displacement, and carriage speed were measured.  High sampling rates were used to capture the dynamics of the indentor response.  Crushed ice extruded in front of the indentor was collected and sieved whenever possible. -- Failure modes of crushing, radial cracking, circumferential cracking, spalling and in-plane cleavage were all observed during vertical indentation.  The maximum force on the structure was 29.1 kN.  Analysis of peak pressures revealed good agreement with data collected by previous researchers.  Peak pressures (averaged over the indentor area) ranged from 4 to 11 MPa.  A slight decrease in peak pressures with increasing aspect ratio was observed.  The small range of contact areas used in the test series produced no evidence of a pressure-area relationship.  Peak pressure increased slightly with velocity, up to speeds of 50 mm/s.  At velocities higher than 50 mm/s the indentor began to vibrate steadily and peak pressures dipped slightly.  Significant vibrations were induced in the structure by crushing failure of the ice.  Crushing frequency varied proportionately with velocity at low velocities.  At velocities above 50 mm/s the response became locked at the natural frequency of the structure.  An unusual "double-beat” force-time trace was sometimes observed during this locked-in response, and spectral analysis of the signal revealed the emergence of a higher second frequency in the vibration of the structure. -- For the inclined indentation tests, mixed failure modes of crushing and flexural failure were observed.  For low indentor angles, crushing dominated.  For high indentor angles flexural failure dominated, with crushing still occurring during many tests.  Flexural failure was characterized by the formation of a principal circumferential crack and one or two "subsidiary" circumferential cracks.  The formation of these subsidiary cracks was due to high in-plane forces combined with vertical deflection of the ice sheet to produce shear and buckling failure.  The failure mode underwent transition from bending to crushing as velocity increased, ice thickness increased, and indentor angle decreased.  The maximum horizontal force on the structure was 32.7 kN, produced with a 10° indentor while crushing failure was occurring.  The normalized peak horizontal force exerted on the inclined indentors increased as the indentor approached vertical.  The broken ice pieces produced by flexural failure were between 5% and 40% of the characteristic length of the ice sheet.  The dynamic effect of decreasing broken piece size with increasing velocity was not clearly demonstrated.


identifier: Yetman, Richard D. <https://research.library.mun.ca/view/creator_az/Yetman=3ARichard_D=2E=3A=3A.html>   (1988) Wave attenuation by the deltaport floating breakwater.  Masters thesis, Memorial University of Newfoundland.

abstract: Deltaport is basically a large floating breakwater intended for use in the Hibernia region.  This thesis describes an exploratory investigation into its wave attenuation characteristics.  The breakwater portion of its structure is porous like and consists of a staggered array of tubes.  When wave energy impinges on such a structure, some of it is reflected back, some is transmitted through, under and around the structure, and the rest is dissipated.  Initially, we had hoped to completely isolate the contributions to this energy balance.  However, because of the complex nature of the Deltaport Structure, we found this goal to be extremely difficult, if not impossible, to attain.  To simplify, we decided to consider only two dimensional sections of the structure and concentrate on the effect of porosity.  A two dimensional section of the breakwater structure was installed in the wave tank at Memorial University of Newfoundland, and its attenuation characteristics for several levels of porosity were measured.  As expected, it was found that porosity greatly reduces attenuation. -- Two theoretical procedures were developed for the two dimensional setup.  One, known as Dean's method, assumes the structure to be a nonporous vertical thin plate and is based on a potential flow description of the water motion.  It gives very simple expressions for reflection and transmission and allows one to get a rough but quick look at performance.  The other procedure is basically a finite difference numerical simulation based on the Navier-Stokes equations.  It allows for wave energy dissipation, something not considered in a potential flow formulation.  It also has a feature by which the porous nature of the structure can be accounted for.  We believe we are the first to use this in a study of breakwater performance.  Comparisons of the latter with the experiment show reasonable agreement. -- Numerical schemes are available that can handle three dimensional bodies interacting with waves; however, they can only deal with nonporous structures.  One of these schemes, known as the Panel Method, accounts for wave diffraction and is based on a distribution of potential flow singularities over the wetted surface of the body.  This technique was also applied to the Deltaport geometry.  Obviously, because it ignores porosity, it represents an ideal.  The two dimensional setup suggests that it overpredicts attenuation. -- The report also gives some suggestions for future work.  For example, it might be possible to develop correction factors for the Panel Method based on the two dimensional setup.


identifier: Mir, Saif U. <https://research.library.mun.ca/view/creator_az/Mir=3ASaif_U=2E=3A=3A.html>   (1985) Utilization of microcomputers in the construction industry.  Masters thesis, Memorial University of Newfoundland.

abstract: The use of computers in the construction industry is increasing but the extent and the rate of the growth is minimal considering the availability of this technology.  In an effort to determine the extent to which computers are utilized in the construction industry, a survey was conducted among construction contractors in Atlantic Canada. -- Construction contractors responding to the 1985 computer utilization questionnaire who were using computers indicated that they were generally well satisfied with commercially available software that perform general accounting functions, such as, accounts payable/receivable, job cost, general ledger, and payroll.  Most were not, however, utilizing their computers for tasks that require a great degree of user programming skill.  Nor were they using the commercially available software outside the accounting area because of the non-compatibility of the software with their in-house procedures. -- Among the contractors who did not use computers, it was found that the non-use of computers was mainly due to the contractor's lack of knowledge of computer systems, both hardware and software.  There was also a general misconception about the high cost of computerization. -- In order to expand the use of computers in the construction industry, a data processing system has been developed, which is expected to solve many of the problems of extending computer use outside the traditional accounting areas.  The suggested system makes use of an integrated software package developed for the microcomputer.  Integrated software packages offer computer capability with a minimum amount of effort on the part of the users.  The data processing system is demonstrated by modelling real life construction related tasks such as specifications, estimating, forecasting, design, bidding, cash flow analysis, project control, equipment replacement, and owning & operating cost calculations. -- To facilitate increased use of computer technology in the construction industry, criteria for the selection of computer systems are presented.  The criteria describe the characteristics of and selection procedures for both hardware and software commonly used in the construction industry.  The criteria also outline the pre-implementation procedures and make specific recommendations for computerization. -- It is expected that the suggested data processing system and the guidelines for the selection of a microprocessor-based computer system will enhance computer utilization in the construction industry, especially in small construction firms.


identifier: Harinath, Sivakumar <https://research.library.mun.ca/view/creator_az/Harinath=3ASivakumar=3A=3A.html>   (1995) Performance, fault tolerance and reliability of multistage interconnection networks for broadband packet switch architectures.  Masters thesis, Memorial University of Newfoundland.

abstract: Multistage Interconnection Networks (MINs) are being considered for use in switch fabrics of broadband packet switch architectures.  Most of the MINs considered are based on 2 x 2 switching elements (SEs).  Throughput performance is degraded mainly due to the basic size of the SEs.  In this work, the Balanced Gamma (BG) network, a multipath MIN, which features 4 x 4 SEs has been studied in detail.  Architecture, fault tolerance, reliability and hardware complexity of the BG network are compared with the 2-replicated 2-dilated Banyan (R2D2) networks and the Batcher Banyan (BB) networks.  A new simple routing algorithm has been proposed for the BG network to enhance its fault tolerance capability.  Switching performance is enhanced by increasing the size of the basic SEs and thereby providing multiple paths between each input-output pair of the BG network.  The throughput performance of the BG network is studied under certain idealistic uniform and non-uniform traffic conditions.  These performance results are compared with the R2D2 and the BB networks under the same traffic conditions.  Performance analysis and simulation results have shown high throughput performance of the BG network even in the presence of an SE fault.  It has been found that the fault tolerance properties, reliability and throughput performance of the BG network are much superior to those of the R2D2 and the BB networks.  Due to increased throughput performance of the BG network it may be considered as a potential candidate for use in switch fabrics of broadband packet switch architectures.


identifier: Paulin, Michael J. <https://research.library.mun.ca/view/creator_az/Paulin=3AMichael_J=2E=3A=3A.html>   (1992) Physical model analysis of iceberg scour in dry and submerged sand.  Masters thesis, Memorial University of Newfoundland.

abstract: Ice scour is still a phenomena of great concern in the development of offshore oil and gas fields located in a cold ocean environment.  Ice scour could also create problems for power cables or pipelines which pass through inland waters such as the Great Lakes.  Cables, pipelines, and wellheads are in danger offshore.  Direct impact between ice and a subsea installation will most likely cause damage.  A seabed installation, such as buried pipeline, might be subjected to additional loading or intolerable displacements through close proximity of an ice keel.  The question still remains as to how deep is safe. -- In an attempt to further understand the ice scour process, a series of four physical model tests was carried out at Memorial University's scour tank facility.  The first two tests were conducted in a clean, dry silica sand while the remaining two were conducted in the same sand in a submerged state.  The objectives of this experimental program were to measure forces and pressures on the model, to measure the response of the soil in the testbed, and, most importantly, to measure displacements in the testbed below the scour. -- The measured results compare well with computed values.  The results have also been compared with previous works and models.  The analysed experimental results show that there is seabed response and displacement up to 3 1/2 scour cut depths below the unscoured testbed surface.  Finally, it was observed that the scouring process was similar for tests in both the dry and submerged state; measured forces and loads less for the submerged tests.


identifier: Monahan, Craig C. <https://research.library.mun.ca/view/creator_az/Monahan=3ACraig_C=2E=3A=3A.html>   (1988) The relative severity of natural and synthetic seawaters on fatigue crack growth in cathodically protected steel.  Masters thesis, Memorial University of Newfoundland.

abstract: Two solutions, ASTM substitute ocean water and natural seawater, are used more or less interchangeably to evaluate the fatigue crack growth properties of steels.  There is evidence in the literature to suggest that the mechanism responsible for accelerated fatigue crack growth in cathodically protected steel (i.e. water reduction) can be significantly influenced by bulk solution chemistry.  Experiments were designed to investigate the relative severity of these two solutions when used with cathodically protected steel samples.  The investigation was conducted using three types of specimens: welded T-plates, compact type (CT) specimens and artificial crevices.  Welded T-plates provided data on the initiation and propagation behavior of semi-elliptical cracks.  CT specimens were tested to obtain crack growth rate versus crack tip stress intensity range data, since it is difficult to derive similar curves from welded T-plate data.  The artificial crevice experiments were combined with polarographic and scanning electron microprobe (SEM) analyses to study the chemistry of calcareous deposits and their influence on water reduction kinetics. -- The extent to which calcareous deposits affected the rate for water reduction within the artificial crevices depended on the bulk solution chemistry and electrochemical potential under which they formed.  Magnesium rich deposits were less effective in reducing the rate for water reduction than were calcium rich deposits.  Regions of localized corrosion were evident on several of the specimens.  A theory is presented which explains how localized corrosion is possible within crevices and cracks cathodically protected to potentials more negative than -780 mV SCE, the generally accepted potential for complete protection against corrosion. -- For the intermediate levels of crack tip stress intensity range examined using CT specimens, the two solutions produced similar crack growth rate data.  Crack propagation rates were generally between 2 and 2.5 times faster under cathodic protection in seawater than in air.  Significantly different fatigue behaviors were observed for the welded T-plates.  Fatigue cracks initiated early within the specimens tested in natural seawater, but propagated at rates close to those observed in air.  Synthetic seawater prolonged the initiation phase but gave rise to crack propagation rates that were about 2 times higher than those observed in air.  These results have been explained in terms of the properties and precipitation kinetics of calcareous deposits. -- Key Words: calcareous deposits; cathodic protection; corrosion; fatigue; hydrogen embrittlement; seawater chemistry; steel; water reduction


identifier: Bryant, Donald S. <https://research.library.mun.ca/view/creator_az/Bryant=3ADonald_S=2E=3A=3A.html>   (1994) The problem of detecting small targets using microwave radar : a neural network solution.  Masters thesis, Memorial University of Newfoundland.

abstract: A neural network technique has been applied to the marine radar small target detection problem.  It has been compared to the conventional processing method of scan to scan integration.  The results of the analysis indicate that a neural network is capable of providing performance that is at least as good as, and if the scanning window is optimized for the pulse length being used, much better than the conventional processing technique for small targets embedded in sea clutter.


identifier: Ye, Ying <https://research.library.mun.ca/view/creator_az/Ye=3AYing=3A=3A.html>   (1995) A general purpose Reed-Solomon CODEC simulator and new periodicity algorithm.  Masters thesis, Memorial University of Newfoundland.

abstract: In most digital communication systems, if we can afford to send data below the modem transmission speed, then it is possible to achieve the system bit error rate as small as we desire by using error control codes.  The Reed-Solomon codes are such error control codes, that are widely used for forward error correction due to their optimal characteristics in both Hamming distance and structure, but most of all, their capacity for correcting both random and burst errors. -- Finding a suitable code for a communication channel, or trying to explain how the Reed-Solomon codes work, or comparing various decoding methods is not an easy task, hence this thesis developed a general purpose Reed-Solomon (RS) coding and decoding (codec) simulator for teaching as well as research purposes. -- The RS codec simulator has two versions that can be run under Microsoft Windows and Unix operating system, respectively.  A friendly and easy-to-use graphical user interface (GUI) is provided for PC.  The user can define a code by selecting the symbol length m from 3 to 8 bits and the error correcting capability T of up to 20. -- In the encoder, the systematic code generation and the self-reciprocal generator polynomial are used.  The noisy channel can be modeled by an error pattern.  This error pattern can either be entered by the user with the arbitrary weight or generated by an external program, which generates all possible error positions.  In the decoding process, both the Peterson and Berlekamp-Massey algorithms are available for finding the error locator polynomial.  The simulation results show that the Peterson's direct method is better when T ≤ 6.  However, the Berlekamp-Massey algorithm is much faster when T > 6.  Chien search is used for locating the error position in the received word.  Although the error values can be obtained by using either Gauss-Jordan elimination or Forney's algorithm, Gauss-Jordan elimination is preferred when T is small, i.e. T ≤ 10, but as T increased, i.e. T > 10, the Forney algorithm should be used in order to minimize decoding time. -- It is found that the periodicity algorithm conceived by S.Le-Ngoc and Z.Young [1] [2] is a special case of the LeNgoc-Ye Transformation Algorithm [3].  An improved periodicity algorithm is proposed which can eliminate the division operation required by the LeNgoc-Young algorithm.  The analysis shows that the periodicity algorithm is valid for all values of m.  Furthermore, a new periodicity algorithm is also developed by using direct solution method to eliminate the index table required in the proposed periodicity algorithm.  It is shown that the new periodicity algorithm outperforms the look-up table, Chien search, binary decision (fast Chien search) and Okano-Imai algorithms in terms of optimization of both memory space and decoding time.  The new periodicity algorithm has a simple structure and therefore it is well suited for VLSI implementation.