Learning Forum

[valerym.m5]

Dear colleagues,

 

I am solving a dynamics problem (implicit solver).

I set the acceleration on the base of the part, changing according to the harmonic law.

The part should perform harmonic movements, but the part only moves upward.

Below are the graphs of vertical displacement for two points of the part (upper and lower).

I will be glad to receive your advice.

 

You can get the model from the specified link:
https://drive.google.com/file/d/1NlNCRUKt_v8xJjCql4Q8zPmE_34DxscK/view?usp=sharing

Regards Valery

[Reno Genest]

Hello Valery,

How do you apply the accelerationa and in which direction? Could you post the relevant LS-DYNA keyword? For example, the *BOUNDARY_PRESCRIBED_MOTION keyword?

Also, note that Ansys employees are not allowed to upload and download files on the Ansys Forum. Hopefully, other users will be able to look at your model and help you.

 

Reno.

[valerym.m5]

Dear Reno

Yes, you are right - I use two keyword

*BOUNDARY_PRESCRIBED_MOTION

 

See pictures below

 

[Reno Genest]

Hello Valery,

Do you have negative values in curve 3? So that the part moves up and down? Do you have other constraints that would prevent the part from moving down?

 

Reno.

[valerym.m5]

 

Good day Reno,

yes – there are negative values ​​in curve 3.

yes – the part moves up and down, without restrictions on movement in the vertical direction.

I have no other restrictions that prevent the part from moving down.

If we specify displacements instead of acceleration, then the problem is solved “correctly” - i.e. at least the specified/prescribed movements are implemented correctly.

Regards Valery

 

[valerym.m5]

 

This is a version of the model where I specify not acceleration, but displacement!
I use material 318.
I plotted the internal energy graphs for two parts of the model, highlighted in yellow and brown.

I take this opportunity to ask you to explain:
How can the internal energy of the parts of this model be negative?

 

Until now, I still haven’t been able to understand – Where/how can I get information about the absorbed energy for the materials with viscous properties?

 

[Reno Genest]

Hello Valery,

I suggest to create a simple model of a 100mmX100mmX100mm cube with 20mm elements (to run fast) and use *MAT_024 with steel material properties. Apply the acceleration load and check the results. Are you getting what you expect? How is the internal energy?

 

Reno.