Learning Forum

[biokill]

Is it possible to define a distributed mass as directional (only in global X and Y direction) in Modal Analysis. I am trying to avoid getting local mode shapes in the vertical direction in which I have no interest. I am in the process of simplifying my building model by removing some weaker walls which results in some floors getting to "bendy" as loosing some support. I know some programs have that options, where You can define in which DOF the mass is acting (X, Y, Z, RX, RY, RZ), but I don`t seem to find this option in ANSYS.

Thanks for Your answers

[ErKo]

You need a mass21 element.

Look up the mass21 element in the help manual - it has options for mass in different directions.
An example - defines a mass (mass21 element) in x only, at node 102:
---
/prep7
ET,1000,mass21
keyopt,1000,3,0
R,1000,10,0,0,0,0,0
TYPE,1000
REAL,1000
E,102
/solu
---
All the best

Erik

[biokill]

Thank You for Your answer. Geometry of my building model is very "geometrically incorrect" and masses differ widely over the floor plan of each story, so defining point masses won`t work best. Is there no option for defining a mass direction for distributed mass ?

[ErKo]

That is not possible with distributed mass (it only takes density - as we use surf154 elements and that is the material property given - MP,,DENS). Thus the only option is to use mass21 if we need mass in only one direction.

Perhaps something that might be of help is to assign the mass21 to a set of nodes in WB mechanical like when we use point mass from the UI and assign to a face (mass will be distributed amongst nodes belonging to that face). Then we can use commands under the point mass object, to change the behaviour of the mass21 element to have only mass in one direction (use RMODIF to change mass).


ALl the best

Erik