thermal - structural analysis on cylinder head using ... - structural analysis on cylinder head...

Thermal - Structural Analysis on Cylinder Head using Workbench Platform as Unique Calculation Environment for Different Vertical Codes R. Gonella, V. Peselli Enginsoft , Italia ABSTRACT The design and verification of a cylinder head historically is the most critical condition for the structural optimisation of the assembly behaviour. Nowadays , because of the company cost , the geometry complexity and different schematisation requirements due to cfd and structural themes were causes of an infinite number of problems; these technical difficulties are mainly related to the different meshing topology and to the single non linearities of each numerical code. The add value of this paper is described by the flexibility of the Workbench Platform; in fact this new technical approach is characterized by its capability to connect the different codes and, in the same time, to technically emphasize the single peculiarities of each code. Synthetically, a cfd analysis using Vectis code was performed; its results, in terms of convection coefficients and bulk temperatures, were mapped on a Fem thermal meshing generated in Ansys Simulation. Then these results were used for the structural non linear analysis performed in Ansys. PROJECT DESCRIPTION A pilot project has been developed in order to verify the efficiency of the Workbench 12.0 platform as an unified environment and all the technical activities were focused on a fluid-dynamic, thermal structural analysis applied on an automotive cylinder head. The analysis has been completely performed on ANSYS Workbench 12.0 platform. It has allowed to take advantage of the Workbench capabilities in: –Multiphysic platform –Tool of integration of different technologies (external fluid dynamic software, Ansys thermal, Ansys mechanical) –Tool of advanced meshing and solving of model of a large number of degrees of freedom. Going into this project details, it concerns the logical flux of analysis on a cylinder head , starting from the cfd results on the combustion chamber and also on the cooling system, obtained by Vectis code, transferring the information for the thermal analysis and then to the structural pre-stressed non-linear analysis in Ansys. The add-value of this project is the customization of the Workbench interface; in fact it realizes an automatic link to the Vectis

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

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results and it ensures the possibility of remapping the fluid dynamic results on the thermal-structural mesh, that is completely different from the cfd one.

Figure 1: Logical flux – from cfd to thermal structural analysis

Figure 2: The simulation tree

Figure 3: The customized interface: link to the remapping macros First step: From cfd results to thermal conditions The historical process of work was to perform a unique mesh for the cfd and thermal-structural analysis in order to have the opportunity of remapping the fluid dynamic results, in terms of bulk temperature and convective coefficient, on the mechanical mesh. So the thermal-structural model had to be created with the same topology of the cfd one, causing long time of modelling.




Furthermore, the softwares used for the fluid-dynamic, thermal and structural analysis were , in a lot of cases, belonging to different families of softwares (Ansys, Nastran, Abaquus, Vectis… ). It involves a considerable increase in costs and in problem of interface and further interpolations. Because of the new realized procedure it’s possible to interpolate, in automatic way, the fluid dynamic results on the mechanical mesh that is completely different, from the topological point of view, to the cfd grid. It implies a severe reduction of the modeling time and of the number of obtained elements (from a fine cfd mesh to a coarse thermo-structural model). The only constraint to permit the proper interpolation of the cfd results is to have a proper spatial positioning of the thermal structural model compared to the fluid dynamic model. In other words the two geometrical models must have the same spatial position.

Figure 4: Thermal-structural coarse mesh-cfd fine mesh Thanks to the new customization realized in j-script and Ansys APDL language, it is possible to apply the correct fluid dynamic loads simply pointing the file of the Vectis results and creating a component with the nodes on which it’s important to make the interpolation. In this way, the same model is used to perform the thermal analysis and the structural prestressed analysis, saving time during the preparation and the solution of the model, and bypassing a further phase of interpolation of the values of temperature to set in the structural model.




Second step: From thermal analysis to structural analysis The results of thermal analysis, performed with bulk temperature e convective coefficient evaluated with cfd method, are transferred to the structural model without any further interpolation thanks to the utilisation of the same fem model for the two analysis. In this specific case, the analysis was carried out in several steps just to take in account of pre-heat stress, and then to model the phase of bolts clamping and of clamping of the valve seat with the head. The last step represent the true loading phase connected to the pressure in the combustion chamber. The non-linearity connected to material yielding is considered as well as the non-linearity related to contacts. This procedure is automatic and requires a limited effort by the user, so it’s very simple to perform another analysis with the same logical flux, but with different geometries or with different fluid-dynamics condition. It’s also possible to utilize the model and/or the results of structural analysis to perform a fatigue evaluation or a creep calculation.

Figure 5: Equivalent Von Mises stress in the last time step




thermal - structural analysis on cylinder head using ... - structural analysis on cylinder head...

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