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Technical note Exporting Ansys FEM models into Matlab mass and stiffness matrices How to extract structural matrices (mass,stiffness.

..) from Ansys and import them into Matlab. Obtention of elementary cyclic symmetric matrices from an elementary sector in Ansys. Alain Batailly McGill University Structural Dynamics and Vibration Laboratory May 2008, updated: May

2012 1 Structures featuring cyclic symmetry

2 Introduction The purpose of this note is to explain how to extract stiffness and mass matrices from Ansys. This can be useful for speci?c calculations with other codes such as Matlab. Section one fo- cuses on structures featuring cyclic symmetric where the stiffness and mass matrices of only one elementary sector allow to obtain the global matrices. Section two presents the Ansys com- mands to obtain the binary ?les (.emat and .full ?les) containing the matrices. Section three is devoted to the interpretation of these ?les.

1 Structures featuring cyclic symmetry Structures featuring cyclic symmetry require to modify some parameters in Ansys before the extraction of the matrices. That is the reason why the case of these structures is given in the ?rst chapter. The particularity of cyclic symmetry is the de?nition of boundaries allowing the expansion of the structure around the axis of symmetry. 1.1 De?ning the boundaries : manual procedure This section explains how to manually de?ne the boundaries of cyclic symmetric structures. However, for most of the cyclic symmetric structures, Ansys will be able to automatically de- ?ne these boundaries. In that case, you only need to read the second section of this chapter. Each boundary of the structure must have exactly the same number of nodes. The matrices angle α left boudary right boundary axis of symmetry. Figure

1 C General representation of cyclic symmetric structures with 2π α sectors given by Ansys correspond to a full sector and so are different from the elementary matrices 1.2 De?ning the boundaries : automatic procedure

3 required for a cyclic symmetry study. A reorganization of the dofs must be done depending on their belonging to a boundary or not. In our case we consider cylindrical coordinates which ac- tually makes the study easier because the elementary blocks will be obtained directly from the reorganization the dofs. Any other coordinates systems will require modi?cations of the boun- dary dofs so that the right boundary of sector i is compatible with the left boundary of sector i +1. Ansys can automatically generate the left and right boundaries. But with complex (for instance non planar) boundaries, this option might not include all the nodes. Depending on the orientation of the structure, the terms CYCLIC_M01H and CYCLIC_M01L are alternate if an error message appears when the analysis starts. Right boundary Here are the steps to follow : ? click on Select>

Component Manager...>

Create Component ? quote the line Pick entities ? enter the name CYCLIC_M01H before validation by clicking on OK ? select the nodes on the left boundary (see A and the procedure of nodes selection) ? validate the selection by clicking on Apply ? a new component should appear in the Component Manage Window named CYCLIC_M01H Left boundary Follow the procedure of the previous subsection exchanging CYCLIC_M01H by CYCLIC_M01L. The boundaries of the cyclic symmetry are now set. The other parameters of the cyclic symme- Figure

2 C Window Component Manager try study can be entered using the option user de?ned. 1.2 De?ning the boundaries : automatic procedure With most of the cyclic symmetric structures, the auto-de?ned option allows to obtain auto- matically the boundaries. If not, the ?rst thing to do before using the manual procedure is to 1.3 Linking the boundaries