×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

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

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

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

(OP)
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?

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

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

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

(OP)
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.

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

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

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

(OP)
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.



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

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources