How to apply a load function in mode-superposition transient analysis

[SameSame123]

Hello,

How to apply a load function (for instance, "sfa, all,1,pres,%load%" where %load% is time-dependent element surface load)in mode-superposition transient dynamic analysis?

 

[meshparts]

Hello,

you will have to define a table with TIME as primary variable. You can read all this in the folowing chapters of the Ansys Help:

3.10.4. Defining and Listing Array Parameters
2.5.14. Applying Loads Using TABLE Type Array Parameters

 

[SameSame123]

Hello,

Thank you for your reply, mihaiupb.

In general, there is no problem for me to apply loads using TABLE type array parameters or function boundary conditions. The issue is that I was not able to get a result in mode-superposition transient dynamic analysis by applying element surface loading (element pressures following the normals of the element faces )which time-dependent.
It is necessary to generate a load vector (in modal step) and then vary the LVSC command to scale this load.


For instance,

/solu
antype ,modal
eqslv ,...
...
nsla ,s,1
sf , all,pres,%tdata%
allsel ,all
solve

/solu
antype ,trans
trnopt ,msup
deltim ,...
lvscale ,1 ! applying the element loads
solve

While the load is a constant - it works, then the load is time-dependent - I'm in troubles.

I tried different scenarios - none of them seems to give that I am looking for. Would anyone know is it possible in ANSYS at all?

I did it easily using ABAQUS and NASTRAN.

 

[meshparts]

Hello,

if you have defined the TIME as primary variable in the table, the it should work in time domain too...

Did you also tried to solve a few steps full transient?

Regards,
Alex

 

[SameSame123]

Hi, Alex.
Full transient analysis with "sf,all,pres,%tdata%" or "sfa,all,pres,%tdata%" gives excellent and predictable results. But while I have turn to mode-superposition transient analysis with the same definition of the time-dependent load(TABLE type or function) I have zero solution.
Strange as it may seem I did not found any example with TIME as primary variable for surface load for mode-superposition transient dynamic analysis.

 

[meshparts]

Okay, then it could be a mathematical problem:

In a modal superposition analysis, the matrices are reduced to modal degrees of freedom. The only possibility to apply loads an a modal reduced model is by forces on nodes.

Surface loads require information about element shape an element faces. This information could be missing in a modal superposition transient analysis.

I suppose, this the reason for SFA not working with modal reduced superposition.

If this kind of analysis worked with Nastran, the is the only way to transform surface load to nodal forces. I don't know how to do it in Ansys. But I would give it a try with SFTRAN before solving. If this is not working, then by APDL programing.

Regards,
Alex