Learning Forum

[benedikt.wuellner]

Hello everybody,

I have to extract mass properties (per unit length) in a cross sectional area of a model. I have a cdb file of the model that I imported in Ansys Workbench that I use in static structural now. 

The geometry is beam-shaped and the largest part of the model consists of shell elements. There are different "imported layers" that use the imported materials to build a complex composite structure. Each of the imported layers is defined over a different part over the geometry.

My general aim is extract a 6 by 6 matrix with the mass and the mass moments of inertia per unit length in the 6 spatial degrees of freedom (3 translations and 3 rotatoins) in a cross secton of the beam shaped model. In other words I want to reduce the complex model to only a few nodes over the longitudinal direction which all have 6 degrees of freedom. I need the mass information of each cross section for another software. This further programm approximates the complex structure with a set of beams. The beam elements must be defined by cross sectional information. The following picture describes the problem. Left is the finely meshed model and on the right are the cross sectional areas:

My first approach was to export the geometry out of Ansys Mechanical and cut out short parts e.g. with SpaceClaim. I wanted to use one cut out part in Ansys Mechanical again, mesh it and extract the mass and mass moments of inertia by the "selection information" tool. The last step would have been to divide the values by the length of the extracted geometry. But the export of the geometrie does not work. One reason is that all the other necessary information like material assignments get lost. In cause of the complex multilayer composite model I am not able to rebuild it. 

My second approach was to use APDL commands to extract mass information of a selected node set. But although I select only specific nodes I get the mass and moments of inertia of the whole geometry object the nodes lie on. The whole model is build up out of three imported geometries so that one sectional area cuts always all the components. The code I used for this is described in detail here: https://towardsdatascience.com/computing-mass-properties-of-ansys-dynamic-models-f0d8dacb2d7c

Has someone an idea how to extract the mass per unit length of a cross section? All I have is the cdb file and no further geometry or CAD-data.

Mayby it is possible to use general techniques of "model reduction"? Or can I work with the mass matrix that I can output from Ansys, e.g by first reduce it to relevent DoFs and transform it so that it physically represents the 6 DoFs? Mayby it is also possible to extract the information by modal analysis?

Many thanks for your help

[dlooman]

Perhaps you could create remote points at the center of the cross-section at 1 meter intervals and then make the dof of the remote point master dof of a static (non-cms) superelement.  

[benedikt.wuellner]

Hello,

thank you for this hint, that sounds promising to me. But I could solve it in another way: I got the information that the cdb file was created in the past with the classis Ansys (Ansys Mechanical apdl). So I tried to import the file with this programm. Now there are no "geometry" objects that were generated by Ansys workbench with the import of the cdb file.

In this program I am able to select individual elements for output mass information independent of there contribution to some composite layer. So by executing the code I shared in the link above in Ansys classic I could solve my problem.

Anyway thank you for your reply.