Optimum design of hydrodynamic thrust bearings with rayleigh's pocket profiles

Optimum design problem for hydrodynamic self-aligning acting thrust bearings was considered. Based on results for rectangular region the problem for sector region was solved. As an objective function, the maximum of pressure integral over the lubricant layer surface was used and five geometrical parameters described Rayleigh's pocket shape were used as optimization variables during optimization procedure. The bearing pressure distribution was determined on the basis of the Navier-Stokes equations using the ANSYS / CFX software. Numerically the optimization problem was solved using three different methods: IOSO, SIMPLEX and pilOPT+AFilter SQP realized in two commercial optimization software IOSO and modeFRONTIER. The aim of this investigation was designing the technologically advanced profiles of thrust bearing sector microgeometry ensuring the maximum load capacity

Advanced Numerical Models for Design and Optimization of Thrust Bearing Hydrodynamic Characteristics

Efficiency of hydrodynamic thrust bearings used in a wide range of power machines is characterized by including the load capacity of an oil wedge, which has nonlinear dependence on gap size. In this study we consider the different types of lubricant layer microgeometry profiling with the aim of optimal design of the hydrodynamic bearing characteristics for ensuring the maximum load capacity using advanced numerical models and methods. We enlarge the results of significant research works of J.W. Rayleigh and S. Y. Maday in relation to the hydrodynamic sector self-aligning acting thrust bearings based on advanced numerical methods. Different geometrical parameters which define profile curvature were used as optimization variables. The maximum of pressure integral over the lubricant layer surface as objective function was used. Hydrodynamic problems using Navier-Stocks equations were solved based on numerical approach and commercial CFD code ANSYS/CFX using the St.Petersburg Polytechnic Supercomputer Center

Análise e implementação de modelo constitutivo de viscoplasticidade em regime de deformação finita: aplicação em polímeros termoplásticos

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2014Nas últimas décadas a aplicação de componentes feitos de materiais poliméricos sofre um aumento expressivo. Muitas peças tradicionalmente feitas de metais e cerâmicos foram substituídos por algum tipo de polímero. O aumento de itens fabricados desses materiais se deve à grande versatilidade de propriedades mecânicas e químicas aliadas à baixa densidade dos mesmos. No entanto, do ponto de vista computacional esses materiais são extremamente complexos de serem modelados devido à intrínseca sensibilidade às variações de temperatura e taxa de deformações. Em vista disso, no presente trabalho buscou se estudar e implementar um conjunto de modelos constitutivos viscoplásticos capazes de representar o comportamento de materiais termoplásticos. A abordagem variacional foi adotada para formulação do modelo, assim a atualização das tensões e variáveis internas é realizada através da extremização de um pseudo-potencial termodinamicamente consistente. Para o estudo do comportamento do modelo em geometrias tridimensionais foi escrita uma sub-rotina de material, usermat, no programa comercial de Elementos Finitos de análise implícita ANSYS. Ao se fazer a hipótese de isotropia material, a decomposição espectral foi utilizada implicando na redução do número de equações a serem resolvidas em cada ponto de integração. Curvas de força-deslocamento de três polímeros diferentes, PS, PLA e PC foram obtidas através do ensaio de tração para a realização de ajuste de um modelo. O corpo de prova foi modelado via CAD e uma análise de EF do ensaio de tração foi configurada via ANSYS Workbench 14.5. A minimização do erro quadrático das curvas, simulada e real, foi realizada pelo programa de PIDO (Process Integration and Design Optimization) modeFRONTIER®. As curvas força-deslocamento simuladas, após ajuste de parâmetros, ficaram muito próximas aos resultados de ensaio, mostrando a capacidade da formulação matemática escolhida em representar o comportamento mecânico de materiais poliméricos. Por fim, análises envolvendo contato entre corpos e torção foram executadas a fim de se verificar o comportamento e estabilidade do modelo material implementado em situações mais complexas.Abstract: Demands for light weight and high strength structures lead to polymeric materials as a suitable choice for a large class of engineering applications. In some cases, components traditionally made of metals or ceramics have been replaced by some kind of polymer. This paradigm shift is related to good mechanical properties, low density, corrosion resistance, easy to manufacture, etc. However, computational modeling of such materials has become a challenge in mechanical and material science fields, mainly because of its intrinsic sensitivity with respect to temperature and rate strain variations. In the work reported here, the focus was constitutive modeling and implementation of viscoplastic materials submitted to finite strain kinematics.Variational formulation was adopted for material modeling. Stress and internal variables updates are performed solving a minimization problem for each time increment. Material isotropy was admitted allowing spectral decomposition to describe the set of constitutive equations. User material sub-routine was written in the implicit Finite Element program ANSYS. Given arbitrary combinations of well know potentials as Odgen, Hencky, Perzyna and others, material free parameters were tuned by fitting experimental load-displacement data of PS, PLA and PC. Minimization of Mean Squared Error was performed making use of modeFRONTIER, a commercial Process Integration and Design Optimization (PIDO) software. Experimental and numerical results were very closed showing the ability of our model to represent the mechanical behavior of thermoplastic polymers. Finally, three-dimensional FE Analysis using frictionless contact and torsion is presented in order to verify the stability and applicability of our model in large-scale problems