Towards reliable and survivable ocean wave energy converters

Ocean wave energy is a new and developing field of renewable energy with great potential. The energy contained in one meter of an average wave off the coast of Newport Oregon could supply dozens of homes with electricity. However, ocean waves are usually quite irregular which leads to large bursts and lulls in the power available for extraction. These bursts and lulls generate large cyclic system stresses that will invariably work over time to damage an ocean wave energy converter. Due to the generally remote and extreme conditions of deployment, the reliability and survivability of an Ocean Wave Energy Converter (OWEC) are expected to greatly impact the cost of generated power passed to the consumer. For this reason, it is imperative that OWECs are both highly reliable during operation, and highly survivable through extreme conditions. This thesis is a compilation of three papers relating to the reliability and survivability of OWECs. The first paper broadly addresses the probabilistic design of ocean wave energy converters for real ocean waves. The analysis conducted in this paper used 13 years of data from the Stonewall Banks data buoy off the coast of Newport Oregon (NDBC buoy 46050) to extrapolate probabilistic information that could be used throughout the design process to improve system reliability. The second paper provides a definition and metric for the widely used term survivability. Survivability is often confused with the similar concept of reliability. The paper seeks to highlight differences between the two terms with the intention of clarifying their relation to system design. The final paper presents a method for concept evaluation in the earliest stages of design. A comparative function based failure analysis is conducted during the concept stage to aid in design selection. Selecting concepts that show promising failure traits early in the design process will improve the reliability and survivability of the final system

Avaliação do risco em ativos físicos baseada numa metodologia Fuzzy-FMEA

Trabalho final de mestrado para obtenção do grau de mestre em Engenharia MecânicaNo contexto atual, a sustentabilidade das organizações surge como um aspeto essencial e transcendente aos demais departamentos de uma organização, desde a conceção de produto à responsabilidade social que a organização contribui com esse produto. No âmbito da área industrial da presente era tecnológica, é necessário delinear e construir estratégias de negócio que permitam não só garantir a competitividade do produto, quer em aspetos qualitativos, quer em aspetos monetários, como também eliminar deficiências no desempenho global de uma organização, destacando as deficiências de produção, manutenção e as resultantes das anteriores. A fim de colmatar tais deficiências no sector da Manutenção Industrial, foram desenvolvidas técnicas analíticas que apoiam a tomada de decisão no planeamento das ações de manutenção dos demais ativos físicos. A presente dissertação foca-se na metodologia FMEA e limitações respetivas, propondo uma solução que tenha a capacidade de as mitigar. Esta solução agrega a metodologia FMEA a uma sequência de metodologias de decisão baseada em multicritérios, em concreto o Analytical Hierarchy Process (AHP) e a Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). O enquadramento da lógica Fuzzy na metodologia proposta, permite que seja quantificada a incerteza humana no processo de tomada de decisão. Esta abordagem permite propor uma priorização mais expedita de 110 potenciais modos de falha de um caso de estudo, minimizando perdas na produção e aumentando o conforto e segurança dos colaboradores de uma organização, entre outros aspetos fundamentais ao sucesso da mesma.The sustainability of organizations is an important element to be considered in every department of an organization, from the product design to the organizations’ social responsibility on that product and how it contributes to society. As the present technological industrial sector grows, there’s an urgent need to draw and develop new business strategies which not only ensures product competitiveness, in matters of quality and economy, but also allows identifying the deficiencies in the overall performance of an industrial organization, particularly the deficiencies of the industrial process, of production and maintenance and those resulting from the previous. In order to solve those issues in the field of Industrial Maintenance, were created several analytical techniques which identify and rank the critical events of the equipment. The present dissertation focuses on the FMEA methodology and its limitations, proposing a methodology to mitigate them. This solution proposes one methodology which adds to the FMEA methodology a sequence of multicriteria decision making approaches (MCDM), specifically the Analytical Hierarchy Process (AHP) and the Technique for Order Preference for Similarity to the Ideal Solution (TOPSIS). The framing of Fuzzy Logic in this proposed methodology allows human uncertainty to be quantified in the decision-making process. This approach makes it possible to propose a prioritization of the 110 potential failure modes in a real a case study, minimizing losses in production and increasing the comfort and safety of the employees of the organization, among other aspects essential to its success.N/