Skip to main content

Defining Ansys Superelement SUB File Manually

Photo by  James Owen  on  Unsplash A surprisingly popular blog-post written here is Exporting Stiffness Matrix from Ansys . A sensible follow up question is what can one do with the exported stiffness matrix? In a recent Xansys Forum post, a question was raised on how we can edit the stiffness matrix of a superelement and use it for our model.  An approach presented below is to first create a superelement that has the same number of DOF and nodal location that will serve as a template. An APDL script can then be written to edit the stiffness matrix entries as desired before exporting to a new superelement *.SUB file for use in future models. The self-contained script below demonstrates this.  /prep7 et ,1, 185 mp , ex, 1, 200e3 mp , prxy, 1, 0.33 w = 0.1 ! single element (note nodal locations) n , 1, w, -w, -w n , 2, w, w, -w n , 3, -w, w, -w n , 4, -w, -w, -w n , 5, w, -w, w n , 6, w, w, w n , 7, -w, w, w n , 8, -w, -w, w e , 1, 2, 3, 4, 5, 6, 7, 8 /solu antype , substr     ! analy

COMBIN40 As Simplified 1D Friction

Spring that Imitates Static/Dynamic Friction

Sometimes, a simple linear spring is not adequate. In tough jobs where a spring with a built-in gap or force saturation is needed, COMBIN40 is the spring of choice. It could behave similarly to a one dimensional friction contact like in Wikipedia:
Static to Dynamic Friction

In the animation above, the spring is actually two COMBIN40 springs in parallel. When done just right, they could imitate the behavior of static to dynamic friction forces:
Spring Forces

To do it in Mechanical, here's the tip! Under Geometry, you'll have to change the Element Control setting to Manual. This allows the spring element to be modified.
Element Control

Next, two identical springs are added (parallel springs). The snippet for the first spring:
Spring #1 Snippet

The second spring snippet:
Spring #2 Snippet

The snippet has two lines of code. The first line changes the element to COMBIN40, the second line defines the stiffness (K1) and the amount of saturation force. A negative value drops the force to zero after the absolute value is reached. In the above example, 200N spring force drops to zero while the 100N saturated force remains.