The straight line calm water performance of stepped planing hulls has been studied experimentally, by prediction method, and numerically. A model test was conducted to provide a systematic understanding of the effects that displacement and step location have on the performance of a stepped planing hull. Ten different step configurations were tested at three different displacements and over a range of four different speeds in calm water. Seven of these configurations were tested at two different Longitudinal Center of Gravity (LCG) locations. Of all the configurations tested, the stepped hull configurations showed reduced resistance compared to the unstepped hull. The configurations with the largest step height aft showed the least amount of resistance over the speed range tested. Increasing displacement and shifting LCG had similar effects on craft performance for both stepped and unstepped hulls. The current stepped hull prediction method was expanded to include a three dimension wave profile and the ability for the stagnation line to cross the step. Using previous model test data and existing two dimension wave profile equations, a single equation was developed to predict the three dimension wave profile aft of a step. Formulations were added to Savitsky's planing prediction method to include very high speed craft and chines dry conditions. Lastly, two simulations were performed using two computational fluid dynamics numerical tools, OpenFOAM, and NFA. The results of these simulations were compared to the experimental test results to assess each code's relative strengths and weaknesses for use in detail design of stepped planing craft. / Ph. D.

Yes / The role of lichens as environmental monitors is widely recognised. Not only are they valuable as indicators of habitat stability and enyironmental continuity, but they are also effectiye in monitoring environmental quality. more particularly air and soil (and more recently water) pollution. In the past. the main role of lichens in this context has been to monitor sulphur dioxide air pollution. especially stable and rising levels (Seaward 1993). Howeyer, it has also been shown that lichens arc effective monitors of falling levels of gaseous sulphur dioxide and indeed of other pollutants. some of which are manifesting themselves as a consequence of the reduction in the former; of particular interest in this respect is the use of lichens to detect and determine the extent of qualitative changes in air pollution such as the impact of acid rain and hypertrophication (Seaward 1997: Seaward & Coppins 2(04).

No description available.

In this Ph.D. dissertation research, we lay the mathematical foundations of various fundamental concepts in convex mixed-integer programs (MIPs), that is, optimization problems where all the decision variables belong to a given convex set and, in addition, a subset of them are required to be integer. In particular, we study properties of their feasible region and properties of cutting planes. The main contribution of this work is the extension of several fundamental results from the theory of linear MIPs to the case of convex MIPs. In the first part, we study properties of general closed convex sets that determine the closedness and polyhedrality of their integer hulls. We first present necessary and sufficient conditions for the integer hull of a general convex set to be closed. This leads to useful results for special classes of convex sets such as pointed cones, strictly convex sets, and sets containing integer points in their interior. We then present a sufficient condition for the integer hulls of general convex sets to be polyhedra. This result generalizes the well-known result due to Meyer in the case of linear MIPs. Under a simple technical assumption, we show that these sufficient conditions are also necessary for the integer hull of general convex sets to be polyhedra. In the second part, we apply the previous results to mixed-integer second order conic programs (MISOCPs), a special case of nonlinear convex MIPs. We show that there exists a polynomial time algorithm to check the closedness of the mixed integer hulls of simple MISOCPs. Moreover, in the special case of pure integer problems, we present sufficient conditions for verifying the closedness of the integer hull of intersection of simple MISOCPs that can also be checked in polynomial time. In the third part, we present an extension of the duality theory for linear MIPs to the case of conic MIPs. In particular, we construct a subadditive dual to conic MIPs. Under a simple condition on the primal problem, we are able to prove strong duality. In the fourth part, we study properties of maximal S-free convex sets, where S is a subset of integers contained in an arbitrary convex set. An S-free convex set is a convex set not containing any points of S in its interior. In this part, we show that maximal S-free convex sets are polyhedra and discuss some properties of these sets. In the fifth part, we study some generalizations of the split closure in the case of linear MIPs. Split cuts form a well-known class of valid inequalities for linear MIPs. Cook et al. (1990) showed that the split closure of a rational polyhedron - that is, the set of points in the polyhedron satisfying all split cuts - is again a polyhedron. In this thesis, we extend this result from a single rational polyhedron to the union of a finite number of rational polyhedra. We also show how this result can be used to prove that some generalizations of split cuts, namely cross cuts, also yield closures that are rational polyhedra.

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Due to the interesting financial moment we are living, my motivations to write this Master thesis has mostly been the behavior of interest rates and models that can be used predict them. Thus, in this dissertation I have presented theHull-White model and the way to calibrate it against market data so it can be used to price interest rate derivatives. The reader can find both theoretical and practical presentations and examples along with the code to program them byhim/herself.

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The purpose of this thesis is to advance research in the development of trimaran hullforms and analyze the feasibility of the hullform for a possible naval surface combatant using current hullform design tools. The “Generalized” Trimaran Methodology is a new process that focuses on the manipulation of the three hulled system’s total sectional area curve. The methodology is intended for rapid hull form development during the conceptual design phase, and can analyze an infinite number of trimaran hullforms. The thesis first proposes a new methodology for the design of trimaran hullforms, describes how the process was applied to an existing hullform, presents results of the analysis, and provides validation data from a tow tank resistance experiment.

A cinza da casca do arroz (CCA) é um resíduo rico em sílica amorfa. Um método simples e de baixo consumo energético para extração desta sílica foi pesquisado, obtendo-se um material com baixo teor de impurezas e alta reatividade, adequado para a síntese de zeólitas e wolastonita (CaSiO3). As zeólitas sintéticas, que não possuem estruturas similares na natureza, são cada vez mais valorizadas no mercado devido a pureza e eficiência em aplicações específicas nas áreas de troca iônica, peneira molecular e catálise. A wolastonita com elevado grau de pureza tem várias aplicações na indústria e agricultura. O mineral wolastonita pode ser formado de várias maneiras na natureza. Em geral é aceito que existem dois processos de formação; os quais envolvem o metamorfismo (calor e pressão) do calcário. Neste trabalho, foi desenvolvido um novo processo para a síntese das zeólitas e da wolastonita, ambas a partir da sílica coloidal da CCA; tendo como objetivo um processo de um menor custo energético, menor número de etapas e menor consumo de reagentes. Foram sintetizadas neste trabalho as zeólitas: A, usada em detergentes, e a ZSM-5, empregada na indústria petroquímica, devido a sua alta seletividade em reações catalíticas e grande estabilidade térmica e resistência aos ácidos. A primeira etapa na síntese da wolastonita foi estudada com o objetivo da formação do hidrossilicato de cálcio (CSH). Contudo, onze hidrossilicatos de cálcio diferentes ocorrem no sistema Ca(OH)2-SiO2-H2O que em uma segunda etapa passam por um tratamento térmico para dar formação a fase wolastonita. / Rice hull ash (RHA) is a industry scrap rich in amorphous silica. A simple and low-energy cost method for the extraction of this silica was researched. A low level of impurity and high reactivity material was produced, which is appropriate for the synthesis of zeolites and wolastonite (CaSiO3). The synthetic zeolites, has not similar structures in nature, and they have been more and more valued in the market due to their purity and efficiency in specific applications like ion exchange, molecular sieve and catalysis areas. High purity wolastonite has many applications in manufacturing and agriculture. The mineral wolastonite can be formed in nature in different ways; it is generally accepted two forming processes, both encompassing limestone metamorphism (heat and pressure). In this work, a new process for the synthesis of zeolites and wolastonite from RHA colloidal silica was developed. Moreover, the process is aimed at lower energy costs, fewer stages and fewer reactants consume. In this work, zeolite A used in detergent and zeolite ZSM-5, employed in the petrochemical industry due to its high selectivity in catalytic reactions and its high thermo and acid stability, were synthesized. The first step of the wolastonite synthesis was studied, with the purpose of obtaining calcium hydrosilicate. Eleven different hydrosilicates occur in the system Ca(OH)2-SiO2-H2O, in the second step, it was annealed to form the wolastonite phase.

Na construção de cascos resistentes de submarinos são utilizados, frequentemente, os processos de conformação a frio e de soldagem. Estes processos produzem na estrutura deformações plásticas permanentes originando tensões residuais. A presença das tensões residuais é equivalente a introduzir uma pré-carga inicial na estrutura, o que acelera o processo de plastificação, reduzindo à capacidade de resistência da estrutura à pressão hidrostática. Para quantificar esta redução foi realizado, inicialmente, um estudo considerando a presença das tensões residuais devido à conformação a frio das chapas do casco e do flange das cavernas, para submarinos com 6, 8 e 10 m de diâmetro, em aço HY100. Para isso, um modelo não-linear foi produzido considerando não-linearidades geométricas e de material. Complementarmente, também foi estudada a influência de perfis de tensões residuais definidos a partir de resultados experimentais na redução da pressão de colapso do casco resistente do submarino espanhol S-80. Estes perfis consideram a presença simultânea de tensões residuais de conformação e de soldagem. Em todos os modelos estudados, as tensões residuais foram introduzidas no modelo numérico utilizando o comando INISTATE disponível no software comercial Ansys. Este comando é frequentemente utilizado na literatura em modelos numéricos envolvendo tensões residuais e foi validado utilizando três modelos de referência disponíveis na literatura. Ao final, pôde-se verificar que a presença das tensões residuais acelera a plastificação do casco resistente e reduz a pressão de colapso em até 5%, sendo a tensão residual de conformação a que mais contribuí nesta redução. De qualquer forma, pôde-se concluir que a influência das tensões residuais é pequena quando comparada com a pressão de colapso obtida para cada casco resistente analisado. / During the manufacturing of submarine pressure hull are often applied processes like cold forming and welding. Those processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial pre-load in the structure, which accelerates the plastification process, decreasing hull pressure resistance. To quantify this reduction, a case study that considers residual stresses due to cold forming on hull and flange plates has been performed. The study encompasses hull diameters of 6, 8 and 10 m, made of HY100 steel. A nonlinear model has been done, considering material and geometric non-linearity. Complementarily, the influence of experimental residual stresses profiles on the reduction of collapse pressure of the Spanish S-80 submarine has been studied. These profiles consider the simultaneous presence of residual stresses due to cold forming and welding. In all studied models, the residual stresses have been introduced in the numerical models through INISTATE Ansys software command. This command has been validated using three reference models available in open source literature. In the end, it has been possible to verify that the presence of residual stresses increase the hull plastification and reduces the collapse pressure up to 5%, being the cold forming induced stress which most contributes to this reduction. Finally, it could be concluded, in the end of the study, that the influence of the residual stresses is small when compared with the collapse pressure obtained for the analyzed pressure hulls.