Applying concetrated forces in radioss

Viktor Antevski

Hello,

I want to ask how do forces given as a function of time F(t) work? For me they work unexpectedly because, when I make the input for constant force, the model doesn't come to a rest but keeps moving as if the force keeps adding up.


I run it for 500ms 

at 100ms i keep getting increased internal energy when it should come to equilibrium with the internal forces of the model (that's what I assume)

then, at 137 ms the internal energy gets reduced again.

then it starts increasing again.
What is happening?

Thanks in advance,
Viktor

Adriano A. Koga

how did you define the timestep? Is it ok? I see that there's a large mass error, of 5.2 (526%).

Added mass is a large portion of the total mass. This might be affecting your computation, maybe.

 

Do you have gravity or other loads in your model?

Viktor Antevski

Thank You Adriano as always for your fast and concise reply.
No, I haven't added gravity but when I apply the force at a slower gradient (over bigger time period) it starts to act like quasi static, and that is what I want to achieve. But I do not understand why is this happening. For now, I think that it is one of the following:
1. When significant displacement occurs at a relative small time and you use force on the displaced node, the node is further displaced;
2. Or some inertial effect
What do you think, and also do you think that it is suitable to do a quasi-static analysis using Radioss?

Thank you and have a great day!
Viktor

Naresh

Hello Viktor,

Even I noticed such issue but not to this extent. May be once you reduce timestep or fix the mass error its should be quite stable.

But I have seen many paper suggesting to apply the load with longer duration of time to nullify the time effect.

But, Adriano do we have a option to do Implicit analysis in Radioss? We end up using Radioss for such loads only because of convergence and Optistruct's limitations with Contacts. 

If Radioss got good implicit solving capability, then Radioss model we build for Dynamic or transient analysis can be used easily for quasi-static or concentrated loading scenarios.

Regards,

Naresh Kini