Optimization of current carrying multicables

Intense electric currents in cable bundles contribute to hotspot generation and overheating of essential car elements, especially in connecting structures. An important aspect in this context is the influence of the positioning of wires in cable harnesses. In order to find an appropriate multicable layout with minimized maximum temperatures, we formulate an optimization problem. Depending on the packing density of the cable bundle, it is solved via different optimization strategies: in case of loosely packed cable bundles solely by a gradient based strategy (shape optimization), densely packed ones by arrangement heuristics combined with a standard genetic algorithm, others by mixed strategies. In the simulation model, the temperature dependence of electric resistances and different parameter values for the multitude of subdomains are respected. Convective and radiative effects are summarized by a heat transfer coefficient in a nonlinear boundary condition. Finite elements in combination with an interior-point method and a genetic algorithm allow the solution of the optimization problem for a large number of cable bundle types. Furthermore, we present an adjoint method for the solution of the shape optimization problem. The jumps at the interfaces of different materials are essential for the Hadamard representation of the shape gradient. Numerical experiments are carried out to demonstrate the feasibility and scope of the present approach

Optimization of modular wiring harnesses by means of regression models for temperature prediction of wire bundles

Automotive wiring harnesses have become heavier and more complex due to their increasing number of electrical components. It is now desired to reduce their mass of copper. For this purpose, experimentation can be partially replaced by simulation, but it is still impossible to exhaustively simulate all of the combinations of modular wiring harness. This proposed approach consists of carrying out simulations using the FEM method and using their results to create regression models. Polynomial formulae can give the same information as simulations within a clearly reduced time and satisfying accuracy. An optimization algorithm introduced in this study will use them to assign new cable cross-sections of harnesses considering their currents and the ambient temperature.Postprint (author's final draft

Custom integer optimization method for wire bundle dimensioning

Automotive wiring harnesses have gained weight and complexity through the last decades due to the increasing number of electrical components, which has raised the interest on its weight optimization. For this purpose, it is essential to know at least the maximum amount of steady current that either single wires or bundles can carry. However, the large amount of combinations of the customer-speci¿c wire harnesses makes it impossible to exhaustively simulate all of the combinations that would allow for a reliable analysis and optimization of the network. The proposed approach consists of achieving accurate predictions of the wire thermal behaviour using fast on-line polynomial functions, which have been created as regression models using data from off-line worst-case ¿nite element sim- ulations. These regression models provide good accuracy for the critical dimensions of wire bundles in a much shorter time than simulations, so that they can be used on-line in optimiza- tion algorithms. Two different approaches of optimization are presented here in order to assign discrete values of available wire cross-section to the wire bundles: The ¿rst one uses integer linear programming, and the second one consists of a recently created custom algorithm whose objective is to reduce the computation time of the integer linear programming approach. This latter objective is satisfactorily accomplished. Results of both optimization approaches are validated by means of ¿nal ¿nite element simulations, and they promisingly ful¿ll the objectives of this study.Peer ReviewedPostprint (author's final draft

Optimization of current carrying multicables

High currents in cable bundles contribute to hotspot generation and overheating of essential car elements, especially in connecting structures. An important aspect in this context is the influence of the positioning of wires in cable harnesses. In order to find an appropriate multicable layout with minimized maximum temperatures, we formulate a corresponding optimization problem. Depending on the packing density of the cable bundle, it is solved via different optimization strategies: in case of loosely packed cable bundles solely by a gradient-based strategy (shape optimization), densely packed ones by arrangement heuristics combined with a standard genetic algorithm, others by mixed strategies. In the simulation model, temperature dependence of the electric conductor resistances and different parameter values for the multitude of subdomains are respected in the governing semilinear and piecewise defined equation. Convective and radiative effects are summarized by a heat transfer coefficient in a nonlinear boundary condition at the exterior multicable surface. Finite elements in combination with an interior-point method and a genetic algorithm allow the solution of the optimization problem for a large number of cable bundle types. Furthermore, we present an adjoint method for the solution of the shape optimization problem. The jumps at the interfaces of different materials are essential for the Hadamard representation of the shape gradient. Numerical experiments are carried out to demonstrate the feasibility and scope of the present approach

A novel optimization methodology of modular wiring harnesses in modern vehicles : weight reduction and safe operation

The weight of electric and electronic components of cars has been uninterruptedly increasing through the last decades, and thus the weight of their wiring harnesses. This fact has awakened the interest of car manufacturers on the weight and cost optimization of automotive wiring harnesses . For this reason, this dissertation discusses and develops approaches to reduce the amount of copper for the purpose of current conduction, i.e. the cross-sections of all of the wires of the car, without endangering safety. On the one hand, harnesses must withstand continuous operation currents. On account of this, it is necessary to know the characteristic flow of current of the in-vehicle electrical network. Nevertheless. the huge quantity of available combinations of equipment of the car produces a proportional variety of customer-specific wiring hamesses, and makes it unfeasible to simulate all of them. This thesis points attention on specific segments of the wiring harnesses. Sorne of them can have many possible compositions, which are related to the customer's car settings. Since computation time is a limiting factor here, it is proposed to predict the bundle heating behaviors by means of response surfaces, obtained from a set of finite element simulation results and the least squares method. On the other hand, the correct wire sizes must ensure that they are protected by their associated melting fuses, so that their maximum acceptable temperature is not exceeded after short circuits. Since many wires in cars are connected to other wires with splices, or may suffer short-circuits in their electric loads, these short-circuits can flow across different wires. In modular wiring harnesses, each of the wires can have different lengths and different installation ratios, their cross-section affects the cost of the wire harness with different importance, as well as the short circuit and the final temperature of the wire. The finite volume method is used to simulate the short circuit of series-connected wires. Finally, non-linear optimization is used to find the mínimum cross­ sections of wires respecting the constraints of maximum temperature and mínimum short-circuit current. Finally, these two different criteria for optima! wire dimensioning are combined in the analysis of the on-board network of the vehicle in order to make a complete weight and cost minimization of the cable harnesses in a particular vehicle, considering also its modularity of loads.El pes dels components elèctrics i electrònics deis automòbils ha crescut ininterrompudament al llarg de les darreres dècades, i conseqüentment ho han fet també els seus feixos de cables. Aquest fet ha despertat entre els fabricants de turismes un elevat interès en la minimització del pes i dels costos del cablejat del vehicle. Per aquest motiu, aquesta tesi desenvolupa mètodes per reduir la quantitat de coure destinat a la conducció de corrent, és a dir, les seccions de tots els fils elèctrics dins el cotxe, sense posar en risc la seguretat. Per una banda, els feixos han de resistir els corrents d'operació continuada. Per a aquest propòsit, cal conèixer el flux de corrents característic de la xarxa de bord del vehicle. No obstant, la immensa quantitat de combinacions de diferents equipaments del vehicle produeix proporcionalment una enorme varietat de feixos personalitzats per als clients, fet que fa inviable simular totes aquestes combinacions . El primer dels mètodes d'optimització que es proposen en aquesta tesi estudia segments dels feixos de cables per separat un a un. Alguns d'ells poden tenir diferents composicions de fils en funció de la configuració aplicada pel client. Com que el temps de calcul és un factor limitant, es proposa predir el comportament tèrmic dels segments per mitja de superfícies resposta, que s'obtenen a través del mètode deis mínims quadrats i un conjunt de resultats de simulació de feixos pel mètode dels elements finits. Per altra banda, les correctes seccions dels fils han de ser tals que els curtcircuits i les sobrecarregues no puguin malmetre'ls, gracies a la correcta coordinació amb els fusibles destinats a protegir-los. Atès que molts fils estan connectats amb altres fils per mitja d'unions soldades i que molts curtcircuits són provocats directament en bornes de les carregues elèctriques, els curtcircuits poden fluir a través de fils diferenciats connectats en serie. Als feixos modulars, cadascun deis fils té diferents longituds i ratis d'instal·lació. És per aquest darrer motiu que llur secció afecta de diferent manera al cost total del conjunt deis feixos de cables deis cotxes venuts . De la mateixa manera, les seves longituds diferents fan que les variacions en les seccions alterin els curtcircuits resultants amb diferent sensibilitat. És per això que es fa servir optimització no lineal per trobar les seccions separades de cadascun dels fils connectats en serie a través dels quals poden passar curtcircuits. Per a aquesta fi es fan simulacions en volums finits i models energètics dels fusibles integrades dins de l'optimització no lineal. Finalment, aquestes dues vies de dimensionament es combinen dins una anàlisi íntegra de la xarxa de bord per dimensionar de forma òptima cadascun dels fils del vehicle, tenint en compte les interconnexions entre feixos i totes les combinacions d'equipament

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Analysis of a Nonlinear Boundary Value Problem with Application to Heat Transfer in Electric Cables

In der vorliegenden Dissertation werden Verfahren zur kontrollierten Modellreduktion des Wärmetransports in elektrischen Leitern entwickelt. Eine typische Reduktionsmethode besteht darin, das zeitabhängige Wärmeleitungsproblem für große Zeiten durch ein stationäres zu ersetzen. Eine weitere Methode vereinfacht das dreidimensionale Randwertproblem in einem zylindrischen Leiter zu einem Problem auf dem zweidimensionalen Querschnitt des Leiters. Diese Reduktionsmethoden werden jedoch oft ohne eine Kenntnis des auftretenden Fehlers angewendet. Daher untersuchen wir die Konvergenz der Lösung des vollen Wärmeleitungsproblems gegen die Lösung eines stationären auf dem Leiterquerschnitt definierten Randwertproblems. Diese Abschätzungen wenden wir auf ein elektrisches Kabel an und identifizieren die zunächst abstrakt bestimmten Approximationsfehler mit konkreten physikalischen Größen. Danach verwenden wir nichtlineare Randintegralmethoden auf mehrfach zusammenhängenden Gebieten um das reduzierte Modell auszuwerten. Zusätzlich zur kontrollierten Modellreduktion liefern die theoretischen Untersuchungen Ergebnisse von praktischer Relevanz. So implizieren z.B. die Bedingungen für die Existenz und Eindeutigkeit des vollen Wärmeleitungsproblems, dass ab einer hinreichen hohen Stromstärke keine endliche Temperatur mehr erreicht wird. Dies wird durch die Unterscheidung subresonanter und resonanter Zustände semilinearer elliptischer Gleichungen beschrieben. Die Analyse des Querschnittsproblems durch Randintegralgleichungen liefert wiederum eine geometrische Eigenschaft von mehrfach zusammenhängenden Gebieten - die Dämpfungseigenschaft. Diese Eigenschaft kann als eine natürliche Eigenschaft von Isolierungen interpretiert werden und ist wesentlich für die Konvergenz der Fixpunktiteration im mehrfach zusammenhängenden Fall

Anuário Científico – 2011 Resumos de Artigos, Comunicações, Livros e Monografias de Mestrado

Há mais de uma década que o ISEL vem firmando a sua aposta na busca e na divulgação do conhecimento científico na área da Engenharia, assentes na inovação e no desenvolvimento de novas tecnologias, procurando que os resultados alcançados nos projetos de investigação tenham impacto na indústria e na vida dos cidadãos como forma de responder às necessidades cada vez mais complexas e exigentes da sociedade no seu todo. Nesta relação, o ISEL tem contribuído para a evolução da produção e do conhecimento científicos, assumindo, por vezes numa posição de vanguarda, ora em iniciativa própria ora em parceria com diversas instituições, quer de ensino quer do tecido empresarial. Como forma de dar visibilidade ao trabalho desenvolvido pelos docentes (com afiliação ISEL) e alunos do ISEL, o Anuário Científico tornou-se num meio de divulgação privilegiado, estando disponível em acesso livre a toda a comunidade científica mas também a todos os cidadãos, podendo ser consultado em formato eletrónico no sítio institucional do ISEL, bem como no Repositório Científico do Instituto Polítécnico de Lisboa.1 Fazendo uma análise comparativa em relação às publicações referentes a 2009 e a 2010, constata-se que o número de publicações duplicou em 2011