Vibration isolation is a procedure through which the transmission of oscillating disturbances or forces is reduced. The ideal isolator is one that will support the equipment being isolated without transmitting any dynamic forces. An isolator with infinite static stiffness and zero dynamic stiffness will achieve this goal. Although this ideal isolation cannot be obtained in practice, it can be approximated through a wide range of devices. This approximation occurs over a limited frequency band and methods of increasing this band were investigated. The goal of this thesis was to further our understanding of mechanical systems that can approximate the ideal isolator behaviour. To compare the various devices the blocked transfer dynamic stiffness was defined. This value was found to represent the isolator properties without the additional complication of the equipment being isolated as happens in traditional transmissibility methods. Three classes of devices were distinguished namely isolators, vibration-absorbing isolators (VAl) and amplified vibration-absorbing isolators (AVAI). The last two types exploit nodalisation to reduce the dynamic stiffness over a limited frequency range. The focus of this work is the broadening of the effective low stiffness bandwidth of amplified vibration-absorbing isolators by adapting system characteristics. If the excitation is tonal time-varying these devices can be used successfully. Two novel adaptive amplified vibration-absorbing isolators were introduced and studied in the time and frequency domains. The type I AVAI uses flexible reservoir walls to vary the isolation frequency. The type II device incorporates a heavy metal slug. Both devices use variable pressure air springs to change their stiffness. The use of air springs are convenient, offers low damping and can be used in an application such as a pneumatic rock drill handle to eliminate the need for a control system. Conceptual design methodologies for both damped and un-damped fixed and adaptive isolation frequency AVAls are presented. To determine the effects of tuning the equations were transformed in terms of constant frequency ratios and the variable stiffness ratio. The devices can be controlled using an optimisation approach, but care should be taken since the method could be unsuccessful in some cases. The design was then applied to a pneumatic rock drill. This application was particularly demanding because the stiffness had to be large enough for the operator to remain in control of the drill, yet low enough to offer isolation. Extensive measurements of drill vibration at a test facility found that the maximum acceleration values were 18.72 m/s2. The maximum allowed under the proposed European Union legislation is 10 m/s2 for short durations. The excitation consisted of a large tonal component and wide-band noise. The tonal component contributed ~50% of the total weighted equivalent acceleration experienced by the operator and a vibration absorbing isolator should therefore be an ideal solution. The measurements also showed that the excitation frequency is a function of the supply air pressure. By using the supply air pressure to feed the air spring the device could be made self-¬tuning. Numerical simulation showed that there is only a slight difference between using the supply pressure and forcing coincidence of the excitation and isolation frequencies. It was also found that the vibration levels could be reduced to below 10 m/s2<./sup> in some cases. / Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Orientador: Maria Regina Wolf Maciel / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-12T04:26:21Z (GMT). No. of bitstreams: 1 Ferreira_AnaClelia_D.pdf: 3055436 bytes, checksum: 6cdcc391dbaebe6c4d512b488fcb26ed (MD5) Previous issue date: 2008 / Resumo: O presente trabalho foi desenvolvido integrando dois conceitos tradicionais de pesquisa operacional e engenharia química, respectivamente: a otimização da cadeia logística e a otimização global de processos. O objeto de estudo é a Refinaria de Paulínia, REPLAN, da PETROBRAS, a qual participa do complexo de abastecimento de petróleo e derivados do País. Existem dois trens de produção na Refinaria; os dois têm unidades de destilação atmosférica e a vácuo, craqueamento catalítico, coqueamento retardado e hidrotratamento de diesel, onde cada unidade de processo é uma planta química completa. Cerca de 170 tanques, 3,2 milhões de m3, 48 produtos finais e 12000 alinhamentos são alguns números que ressaltam a complexidade do sistema logístico interno, para transferências, misturas e estocagem de petróleo, insumos químicos, produtos intermediários e finais. As decisões de produção da REPLAN constituem o nível local de uma estrutura hierárquica de decisões corporativa, de abrangência nacional. O nível local é subdividido tradicionalmente em planejamento mensal, programação de produção, detalhamento operacional e controle da produção. O presente trabalho propõe uma modificação na hierarquia de decisões de produção da REPLAN, acrescentando um nível entre as atividades de programação de produção e detalhamento operacional, para otimizar a produção de dois tipos de óleo diesel com horizonte de alguns dias. Etapa crucial da otimização global, o modelo matemático do sistema é descrito detalhadamente. Ele inclui as possibilidades e restrições físicas das transferências, os balanços de quantidades e qualidades, as transformações através dos hidrotratamentos e as competições por frações e correntes intermediárias. Foram desenvolvidos novos modelos empíricos de mistura para predição de duas propriedades do diesel: curva de destilação e número de cetano. O modelo geral foi implementado em MS Excel e GAMS e resolvido com o algoritmo CONOPT. Um aumento na produção média e uma redução de estoques de diesel na Refinaria, medidos no período de fevereiro a outubro de 2007, comparativamente a 2006, estão associados ao uso diário da ferramenta. / Abstract: This work has been developed integrating two traditional concepts of operational research and chemical engineering, respectively: supply chain optimization and global process optimization. The focus of the study is the PETROBRAS' Paulínia Refinery, REPLAN, which integrates the downstream petroleum and derivatives complex of Brazil. There are two production trains in the Refinery; they both have atmospheric and vacuum distillation, fluid catalytic cracking, delayed coker, and diesel hydrotreating units, whereof each process unit is a complete chemical plant. Around 170 tanks, 3.2 million m3, 48 final products and 12000 lineups are some figures that highlight the off-site local complex, for transfer, blending and storage of crude, chemicals, intermediate and final products. The production decisions at REPLAN are the local level of a corporate countrywide decision hierachy. The local level is again divided into sublevels, traditionally: month planning, daily scheduling, operation detailing and production control. This work proposes a change in the production decision hierarchy of REPLAN, adding a level between scheduling and operation detailing, with the purpose of providing an optimization tool for the production of two specifications of diesel oil along a few days horizon. Crucial step for global optimization, the system mathematical model is described in details. This includes the lineups possibilities and physical constraints, volume and property balances, property behavior through the hidrotreating units and the competition for swing-cuts and intermediate streams. It was developed new empirical blending models to predict two of the diesel properties: distillation curve and cetane number. The whole set of equations was implemented using MS Excel and GAMS, and solved with CONOPT algorithm. An increase in the average diesel production and a reduction in the diesel inventory, measured from February to October 2007, compared to 2006, are related to the daily use of the software. / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

M.Ing. / This dissertation deals with the implementation of a Reliability Basis Optimisation Process for Eskom’s fossil fired Power Stations. This study comes about as a result of the situation that Eskom currently finds itself in. Eskom currently has a generating capacity of 41 000MW. It supplies 95% of South Africa’s power requirements and 45% of Africa’s power requirements. With the unprecedented economical growth that South Africa has experienced in the last five years, coupled with the economic recession of 2008/2009, Eskom has found itself in a precarious position in terms of power delivery. Eskom’s request for a 45% tariff increase in its Multi Price Determination (MYPD2) application to NERSA was turned down and a figure of 25% was awarded. Eskom’s current reserve margin is currently lies as less than 10%. With the funding restrains it now becomes difficult to replace machinery as it fails. The focus now shifts of carrying out effective maintenance. Eskom established the Asset Management Department with a view to ensure that the right maintenance was carried out. Within the Asset Management Department the Reliability Basis Optimisation (RBO) Process was established. The aim of the RBO stream is to improve the reliability and availability of the fossil fired Power Station. This dissertation looks at how the RBO process was developed and rolled out to the Power Stations. It also gives a brief overview of the Asset Management Improvement process to which the RBO process is the backbone.

No description available.

La presente tesi inizia con un’analisi dell’aspetto nutrizionale degli alimenti. In particolare, è stato discusso il concetto di dieta equilibrata, con riferimento ai principi della “dieta mediterranea”. Proprio da questo modello alimentare trae ispirazione la “ottimazione”, una tecnica sviluppata e utilizzata per programmare pasti conformi a specifici standard nutrizionali (15/30/55 tra proteine, lipidi e carboidrati sull’apporto energetico totale, proporzioni tipicamente mediterranee). Tali preparazioni alimentari sono state testate anche attraverso metodi di analisi sensoriale. Il passaggio successivo è stato l’estensione del concetto di “ottimizzazione nutrizionale” a quello di “ottimizzazione ambientale”, dovuto all’ipotizzato minor impatto ambientale della dieta mediterranea. Il LCA (Life Cycle Assessment) è la tecnica che è stata utilizzata per valutare l’impatto ambientale di alcuni prodotti alimentari, quali verdure surgelate, un salume e un formaggio. Un ulteriore passaggio è stata la creazione di uno strumento di comunicazione, una nuova etichetta ambientale, realizzata per essere utilizzata dalle aziende per comunicare le loro performance ambientali e quindi il loro impegno al miglioramento continuo, e dai consumatori per ottenere maggiori informazioni sull’impatto ambientale dei prodotti acquistati quotidianamente, al fine di accrescere il proprio senso critico ed effettuare acquisti consapevoli. / The thesis begins with an analysis of the nutritional aspects of foods. In particular, the concept of balanced diet has been discussed, by referring to the principles of "mediterranean diet". Just from this food model, the “optimation” draws inspiration, a technique developed and used to plan meals consistent with specific nutritional standards (15/30/55 between protein, fat and carbohydrate on the total energy intake, typically Mediterranean). These food preparations have been tested through sensory analysis methods. The next step is the extension of "nutritional optimization" concept to the "environmental optimization” one, owing to the presumed lower environmental impact of the Mediterranean diet. LCA (Life Cycle Assessment) is the technique used to assess the environmental impact of various food products, such as frozen vegetables, cured meats, dairy products. A further step is the creation of a communication tool, a new environmental label, designed to be used by companies to communicate their environmental performance and therefore their commitment to continuous improvement, and by consumers to obtain more information on the environmental impact of the foods daily consumed, in order to increase their critical sense and make purchases in a conscious way.