## General Mechanical

#### Question on Cylindrical Coordinate System

• CMU_engineer7
Subscriber

How can I define a cylindrical coordinate system in ANSYS mechanical where the radial coordinate is the z axis in the cylindrical system? I am trying to model a homogenized composite system where the radial component is lower effective modulus than the z and theta (which are equal). When I try to run the model using the x direction as the radial component (conventional cylindrical system), I get an error for the elasticity matrix not being positive definite. I can make the matrix positive definite by switching z and x, but I do not see a way in mechanical to orient a cylindrical coordinate system such that it considers z to be the radial component. Perhaps this can be done with APDL commands. Alternatively, I'm open to suggestions for making the matrix positive definite with x as the lower modulus direction, but I don't see this as as possibility as this is a more fundamental constraint as opposed to the axis definition which I understand to be arbitrary.

• Bill Bulat
Ansys Employee

What release are you using? There's a feature that started being fully supported in 2022R2 that might work. I'll have to create a test case and send you screen shots of how it works since we're not allowed to send files through the forum.

• Bill Bulat
Ansys Employee

It's called Element Orientation (inserted under the Geometry branch in the tree:Note in the image above the the element coordinate systems have their blue (z) axes pointing radially. There are four 90 degree sectors in the geometry. The four faces that I used as a "surface guide" upon which the resulting z direction is based were the outer four cylindrical surfaces extending a full 360 degrees. The four edges I used as an "edge guide" upon which the resulting x direction is based where four cylindrical edges extending a full 360 degrees. Hope this helps. I did this at 2022R2. In earlier versions of WB you might have to resort to an APDL command object - tedious but doable.

• CMU_engineer7
Subscriber

I am currently in 2021R2 but do have access to 2022R2 through my organization. I just haven't needed to update yet. Thank you for the pointers, I'll get an update going and try out element orientation.