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Showing posts from November, 2017

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

Modal Assurance Criteria MAC with Ansys for select Measurement Locations

Where should the accelerometers be placed? - Test Person Test People are tough to work with! I was one before so I would know. Have a bit of sympathy for them though as they could be frantically troubleshooting equipment in the middle of no-where or spend countless hours rolling-and-unrolling cables. Goal of Measurement Points Selection OK, we have a model with natural frequencies and mode shapes. If your company is well endowed, this is a simple question with pretest software like  FEMtools  or some other software that optimizes the MAC matrix . This would also help with correlation later. Generally speaking, the software will maximize the diagonal matrix while minimize the off diagonal matrix values. Loosely defined, this means the modes are relatively unique (mathematically speaking) for the chosen measurement locations. Poor Man's Method for Picking Measurement Locations Alternately, we can pick measurement locations by hand based on past experience and liberal use of e

DesignXplorer Design Point Alternative Save

Solving for many cases with small variations using DesignXplorer is quite convenient. After setting up an initial model, a parameter could be defined in SpaceClaim or elsewhere. The solution for multiple design points are then generated as I sip on my beer (legally at home). As shown in this YouTube Video , the output parameters are single values like natural frequency, displacements and other maximum or minimum of available solution results. Unfortunately if you are interested in more complicated items that aren't easily available through the user defined results or *GET commands, how do you capture that output parameter? One way would be to retain all design point results for later post processing but that would be overkill especially since I'll have to go into everyone of them to extract out the information which is a pain. Alternately, a post-processing APDL script could be written to extract out key information at each run. An example would be the mode shape o