The concept of marine current turbines was developed by Peter Fraenkel in the early 1970s. Ever since Fraenkel's efforts to modify and test the technology, several worldwide agencies have been exploiting the technology to retrofit the marine current turbine to their particular application. The marine current turbine has evolved from generating a few kilowatts to a few gigawatts. The present study focuses on a megawatt sized turbine to be located offshore the coast of Ft. Lauderdale, Florida. The turbine is to be placed in a similar location as a 20 kW test turbine developed by the Southeast National Marine Renewable Energy Center (SNMREC) at Florida Atlantic University, Dania Beach, FL. Data obtained from the SNMREC is used in the mathematical model. ANSYS FLUENT is chosen as the CFD software to perform wave-current interaction simulation for the present study. The turbine is modeled in SolidWorks, then meshed in ANSYS ICEM CFD, then run in FLUENT. The results obtained are compared to published work by scholarly articles from Fraenkel, Barltrop and many other well known marine energy researchers. The effects of wave height on the turbine operation are analyzed and the results are presented in the form of plots for tip speed ratio and current velocity. / by Amit J. SIngh. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

This thesis presents the development and results of an iterative method for obtaining a minimum weight structural design, called an optimum design. The optimum design iteration is based on a sequence of fully stressed designs, each intermediate design possessing a distinct set of allowable stresses that force the desirable design changes to occur. The test for the optimum state is based on the Kuhn-Tucker conditions, where negative Lagrange multipliers in the set identify element parameters that can be changed to produce a lighter weight structure. Five case studies are presented to demonstrate the algorithm. / M.S.

Orientadora: Fernando de Azevedo Silva / Banca: Erick Siqueira Guidi / Banca: Rosinei Batista Ribeiro / Resumo: O conector bipartido, por sua simplicidade construtiva quando comparado ao conector tipo "collet" se torna um componente mecânico bastante atrativo para unir equipamentos em situações na qual não há carga externa de momento fletor. A proposta desse trabalho foi mostrar em detalhes o projeto de um conector bipartido para operar com 68,9 MPa de pressão interna e travado por quatro parafusos UN 1,25" - 8 FPP submetido ao torque de 762,3 N.m (gerando pré-carga de 221,4 kN em cada um dos quatro parafusos) que foi suficiente para energizar o selo metálico e garantir que as faces dos "hubs" se encostassem durante a montagem. A análise foi considerada em duas situações, mínimo coeficiente de atrito (0,08) e máximo coeficiente de atrito (0,15) nas faces de contato entre os Hubs e Bipartidos. Para a condição de mínimo atrito foi verificado que o nível de tensão gerado nas peças do conector não ultrapassa o limite de aceitação da API 6A e API 17D. Para a condição de máximo atrito, foi comprovado que na pior situação tem-se pressão de contato na região de vedação superior a três vezes o valor da pressão hidrostática referente à lâmina d'água de 3000 metros, garantindo que não haverá entrada de água do mar no sistema, mesmo em uma situação extrema na qual a pressão interna seja nula. Para as análises de elementos finitos, foi utilizado o software Abaqus CAE / Abstract: The clamp connector, due to your built simplicity in comparison to the collet connector is an attractive part to connect equipment where there is no external bending moment. The purpose of this job was show in details the clamp connector design for 68.9 MPa internal working pressure locked by four screws UN 1.25"-8 TPI under torque 762.3 N.m (that created bolt load 221.4 kN at each one of the four screws) that was enough to set the seal and ensure hub face to face during assembly. The analysis was considered in two situations, minimum friction (0.08) and maximum friction (0.15) at the contact faces between the Hubs and Clamps. At the minimum friction condition, was verified the stress level at the parts is acceptable by API 6A and API 17D. At the maximum friction condition, was verified at the worst condition the contact press at sealing area is higher than 3 times the hydrostatic pressure at 3000 meters water depth, and therefore enough to ensure no sea water entering in the system at the extreme situation where there is no internal pressure. For the finite element analysis was used the software Abaqus CAE / Mestre

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Most of the parameters involved in the design and analysis of structures are of stochastic nature. This is, therefore, of paramount importance to be able to perform a fully stochastic analysis of structures both in component and system level to take into account the uncertainties involved in structural analysis and design. To the contrary, in practice, the (computerised) analysis of structures is based on a deterministic analysis which fails to address the randomness of design and analysis parameters. This means that an investigation on the algorithmic methodologies for a component and system reliability analysis can help pave the way towards the implementation of fully stochastic analysis of structures in a computer environment. This study is focused on algorithm development for component and system reliability analysis based on the various proposed methodologies. Truss structures were selected for this purpose due to their simplicity as well as their wide use in the industry. Nevertheless, the algorithms developed in this study can be used for other types of structures such as moment-resisting frames with some simple modi cations. For a component level reliability analysis of structures different methods such as First Order Reliability Methods (FORM) and simulation methods are proposed. However, implementation of these methods for the statistically indeterminate structures is complex due to the implicit relation between the response of the structural system and the load effect. As a result, the algorithm developed for the purpose of component reliability analysis should be based on the concepts of Stochastic Finite Element Methods (SFEM) where a proper link between the finite element analysis of the structure and the reliability analysis methodology is ensured. In this study various algorithms are developed based on the FORM method, Monte Carlo simulation, and the Response Surface Method (RSM). Using the FORM method, two methodologies are considered: one is based on the development of a finite element code where required alterations are made to the FEM code and the other is based on the usage of a commercial FEM package. Different simulation methods are also implemented: Direct Monte Carlo Simulation (DMCS), Latin Hypercube Sampling Monte Carlo (LHCSMC), and Updated Latin Hypercube Sampling Monte Carlo (ULHCSMC). Moreover, RSM is used together with simulation methods. Throughout the thesis, the effciency of these methods was investigated. A Fully Stochastic Finite Element Method (FSFEM) with alterations to the finite element code seems the fastest approach since the linking between the FEM package and reliability analysis is avoided. Simulation methods can also be effectively used for the reliability evaluation where ULHCSMC seemed to be the most efficient method followed by LHCSMC and DMCS. The response surface method is the least straight forward method for an algorithmic component reliability analysis; however, it is useful for the system reliability evaluation. For a system level reliability analysis two methods were considered: the ß-unzipping method and the branch and bound method. The ß-unzipping method is based on a level-wise system reliability evaluation where the structure is modelled at different damaged levels according to its degree of redundancy. In each level, the so-called unzipping intervals are defined for the identification of the critical elements. The branch and bound method is based on the identification of different failure paths of the structure by the expansion of the structural failure tree. The evaluation of the damaged states for both of the methods is the same. Furthermore, both of the methods lead to the development of a parallel-series model for the structural system. The only difference between the two methods is in the search approach used for the failure sequence identification. It was shown that the ß-unzipping method provides a better algorithmic approach for evaluating the system reliability compared to the branch and bound method. Nevertheless, the branch and bound method is a more robust method in the identification of structural failure sequences. One possible way to increase the efficiency of the ß-unzipping method is to define bigger unzipping intervals in each level which can be possible through a computerised analysis. For such an analysis four major modules are required: a general intact structure module, a damaged structure module, a reliability analysis module, and a system reliability module. In this thesis different computer programs were developed for both system and component reliability analysis based on the developed algorithms. The computer programs are presented in the appendices of the thesis. / AFRIKAANSE OPSOMMING: Meeste van die veranderlikes betrokke by die ontwerp en analise van strukture is stogasties in hul aard. Om die onsekerhede betrokke in ontwerp en analise in ag te neem is dit dus van groot belang om 'n ten volle stogastiese analise te kan uitvoer op beide komponent asook stelsel vlak. In teenstelling hiermee is die gerekenariseerde analise van strukture in praktyk gebaseer op deterministiese analise wat nie suksesvol is om die stogastiese aard van ontwerp veranderlikes in ag te neem nie. Dit beteken dat die ondersoek na die algoritmiese metodiek vir komponent en stelsel betroubaarheid analise kan help om die weg te baan na die implementering van ten volle rekenaarmatige stogastiese analise van strukture. Di e studie se fokus is op die ontwikkeling van algoritmes vir komponent en stelsel betroubaarheid analise soos gegrond op verskeie voorgestelde metodes. Vakwerk strukture is gekies vir die doeleinde as gevolg van hulle eenvoud asook hulle wydverspreide gebruik in industrie. Die algoritmes wat in die studie ontwikkel is kan nietemin ook vir ander tipes strukture soos moment-vaste raamwerke gebruik word, gegewe eenvoudige aanpassings. Vir 'n komponent vlak betroubaarheid analise van strukture word verskeie metodes soos die "First Order Reliability Methods" (FORM) en simulasie metodes voorgestel. Die implementering van die metodes vir staties onbepaalbare strukture is ingewikkeld as gevolg van die implisiete verband tussen die gedrag van die struktuur stelsel en die las effek. As 'n gevolg, moet die algoritme wat ontwikkel word vir die doel van komponent betroubaarheid analise gebaseer word op die konsepte van stogastiese eindige element metodes ("SFEM") waar 'n duidelike verband tussen die eindige element analise van die struktuur en die betroubaarheid analise verseker is. In hierdie studie word verskeie algoritmes ontwikkel wat gebaseer is op die FORM metode, Monte Carlo simulasie, en die sogenaamde "Response Surface Method" (RSM). Vir die gebruik van die FORM metode word twee verdere metodologieë ondersoek: een gebaseer op die ontwikkeling van 'n eindige element kode waar nodige verandering aan die eindige element kode self gemaak word en die ander waar 'n kommersiële eindige element pakket gebruik word. Verskillende simulasie metodes word ook geïmplimenteer naamlik Direkte Monte Carlo Simulasie (DMCS), "Latin Hypercube Sampling Monte Carlo" (LHCSMC) en sogenaamde "Updated Latin Hypercube Sampling Monte Carlo" (ULHCSMC). Verder, word RSM tesame met die simulasie metodes gebruik. In die tesis word die doeltreffendheid van die bostaande metodes deurgaans ondersoek. 'n Ten volle stogastiese eindige element metode ("FSFEM") met verandering aan die eindige element kode blyk die vinnigste benadering te wees omdat die koppeling tussen die eindige element metode pakket en die betroubaarheid analise verhoed word. Simulasie metodes kan ook effektief aangewend word vir die betroubaarheid evaluasie waar ULHCSMC as die mees doeltre end voorgekom het, gevolg deur LHCSMC en DMCS. The RSM metode is die mees komplekse metode vir algoritmiese komponent betroubaarheid analise. Die metode is egter nuttig vir sisteem betroubaarheid analise. Vir sisteem-vlak betroubaarheid analise is twee metodes oorweeg naamlik die "ß-unzipping" metode and die "branch-and-bound" metode. Die "ß-unzipping" metode is gebaseer op 'n sisteem-vlak betroubaarheid ontleding waar die struktuur op verskillende skade vlakke gemodelleer word soos toepaslik vir die hoeveelheid addisionele las paaie. In elke vlak word die sogenaamde "unzipping" intervalle gedefinieer vir die identifikasie van die kritiese elemente. Die "branch-and-bound" metode is gebaseer op die identifikasie van verskillende faling roetes van die struktuur deur uitbreiding van die falingsboom. The ondersoek van die skade toestande vir beide metodes is dieselfde. Verder kan beide metodes lei tot die ontwikkeling van 'n parallelserie model van die strukturele stelsel. Die enigste verskil tussen die twee metodes is in die soek-benadering vir die uitkenning van falingsmodus volgorde. Dit word getoon dat die "ß-unzipping" metode 'n beter algoritmiese benadering is vir die ontleding van sisteem betroubaarheid vergeleke met die "branch-and-bound" metode. Die "branch-and- bound" metode word nietemin as 'n meer robuuste metode vir die uitkenning van die falings volgorde beskou. Een moontlike manier om die doeltre endheid van die "ß-unzipping" metode te verhoog is om groter "unzipping" intervalle te gebruik, wat moontlik is vir rekenaarmatige analise. Vir so 'n analise word vier hoof modules benodig naamlik 'n algemene heel-struktuur module, 'n beskadigde-struktuur module, 'n betroubaarheid analise module en 'n sisteem betroubaarheid analise module. In die tesis word verskillende rekenaar programme ontwikkel vir beide sisteem en komponent betroubaarheid analise. Die rekenaar programme word in die aanhangsels van die tesis aangebied.

The objective of this study was to develop and validate practical modeling methods for investigating load paths and system behavior in a realistic, light-frame wood structure. The modeling methods were validated against full-scale tests on subassemblies and an L-shaped house. The model of the L-shaped house was then modified and used to investigate the effects of re-entrant corners, wall openings and gable-end retrofits on system behavior and load paths. Results from this study showed that the effects of adding re-entrant corners and wall openings on uplift load distributions were dependent on the orientation of the trusses with respect to the walls. Openings added to walls parallel to the trusses had the least effect on loads carried by the remaining walls in the building. Varying re-entrant corner dimensions of the L-shaped house under ASCE 7-05 (ASCE 2005) design wind loads caused increasing degrees of torsion throughout the house, depending on the relative location and stiffness of the in-plane walls (parallel to the applied wind loads) as well as the assumed direction of the wind loads. Balancing the stiffness of the walls on either side of the house with the largest re-entrant corner helped to decrease torsion in the structure somewhat. Finally, although previous full-scale tests on gable-end sections verified the effectiveness of the gable-end retrofit that was recently adopted into the 2010 Florida building code, questions remained about the effects of the retrofit on torsion in a full building. The current study found that adding the gable-end retrofits to the L-shaped house did not cause additional torsion. / Graduation date: 2013