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Ushay

quasi static test

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Hi,

I have performed tensile test by Quasi static state experimentally and now I am trying to simulate in Radioss. I could able to simulate this, however will I be able to control the number of steps such that I can divide the displacements into very small intervals, as one can do in Ansys. How the solver interprets the timestep from the displacement vs time curve, since we donot give the increment?

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Hi,

For explicit analysis time step is the time required for a shock wave to propagate across the smallest distance of the element. Time step of a model is directly proportional to the length of an element and is inversely proportional to the speed of sound. So, if the material is stiffer (higher modulus of elasticity), the speed of sound increases resulting in a lower solution time step, as both material modulus and density control the speed of sound. 

Please go through https://altairuniversity.com/learning-library/considerations-about-time-step/ which is a webinar showing time step calculation in RADIOSS.

RADIOSS will calculate nodal and elemental time steps of the model and will choose the highest of these to run.

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On 15/11/2017 at 10:56 PM, Ushay said:

Hi,

I have performed tensile test by Quasi static state experimentally and now I am trying to simulate in Radioss. I could able to simulate this, however will I be able to control the number of steps such that I can divide the displacements into very small intervals, as one can do in Ansys. How the solver interprets the timestep from the displacement vs time curve, since we donot give the increment?

Hi,

What I can understand is you need to increase the number of time steps for loading. This methodology is done in optistruct where the no. of time steps  can be provided in quasistatic analysis. In radioss, the steps can be increased by increasing the time of loading from zero to max, to achieve a quasistatic phenomena. You can apply your load within 0.3 sec to get good results with energy in the system , making sure it follows a quasistatic process.

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I think may be the solution time is a problem. Since the velocity of a quasi static tensile test may be 10mm/min, the total test time may be several minutes. But for a explicit analysis, the time step is very small. How to deal this in the simulation?

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Hi Roy,

For an explicit analysis the run time will normally will last for milliseconds only.

For these type of quasi static cases you can try running using the implicit options in RADIOSS.

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On 2017/11/16 at 12:20 PM, George P Johnson said:

Hi,

For explicit analysis time step is the time required for a shock wave to propagate across the smallest distance of the element. Time step of a model is directly proportional to the length of an element and is inversely proportional to the speed of sound. So, if the material is stiffer (higher modulus of elasticity), the speed of sound increases resulting in a lower solution time step, as both material modulus and density control the speed of sound. 

Please go through https://altairuniversity.com/learning-library/considerations-about-time-step/ which is a webinar showing time step calculation in RADIOSS.

RADIOSS will calculate nodal and elemental time steps of the model and will choose the highest of these to run.

Hi George,

Is it possible for you to share the PPT documents which showed in the video you mentioned? Or is it possible to download the video?

https://altairuniversity.com/learning-library/considerations-about-time-step/

 

Roy

 

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Hi Roy,

Unfortunately these ppt files are not available for download now.

I'll check internally and if the document is shareable I'll send you the same.

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On 11/17/2017 at 5:02 PM, Roy Duan said:

Could you help me with foam compression test simulation with implicit algorithm in Radioss. I have uploaded my model to the attachment. Thank you.

2017-11-17_192829.png.755b3a317ecf913ab0247acfc5d2e7a0.png

 

Hi Roy,

 

Implicit Solution is RADIOSS is more to complement the Explicit Solution and we suggest to use it only for specific cases like Spring Back. 
You can run this simulation using RADIOSS explicit with quasi static loading but if you are particular to run for more time I recommend you to use OptiStruct for the same. 

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22 hours ago, George P Johnson said:

 

Hi Roy,

 

Implicit Solution is RADIOSS is more to complement the Explicit Solution and we suggest to use it only for specific cases like Spring Back. 
You can run this simulation using RADIOSS explicit with quasi static loading but if you are particular to run for more time I recommend you to use OptiStruct for the same. 

Hi George,

With explicit method in Radioss, the solution time is unacceptable. So I want to try implicit method in Radioss. Unfortunately, I cannot do the right set up for implicit method in Radioss.

If I use OptiStruct, the same material model cannot be used. The purpose of doing this simulation is to calibrate material parameters for further drop simulation, so the same material model should be used. Could you help me to set up the model for implicit method in Radioss? Thank you in advance.

 

Roy

CompressionTest.zip

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Hi Roy,

 

On 11/21/2017 at 11:24 AM, Roy Duan said:

With explicit method in Radioss, the solution time is unacceptable

Please let us know the reason for this.

Also, I have shared a similar model for /MAT/LAW70 in the other post you have created. Please go through it.

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2 hours ago, George P Johnson said:

Hi Roy,

 

Please let us know the reason for this.

Also, I have shared a similar model for /MAT/LAW70 in the other post you have created. Please go through it.

Hi George,

As we know, the time step of the explicit method is very small, however the total test time is about several minutes. So I think the solution time to  calculate this case with explicit method is not acceptable.

I want to try with implicit method in Radioss. My problem is I don't know how to set the model with implicit method in Radioss. I don't think the material model have very serious problem.

 

Roy

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Hi Roy,

 

quasi-static simulation could be done using Rayleigh damping, kinetic or dynamic relaxation (see Example 16). This way the dynamic effects (inertia forces, vibrations) are neutrailzed so the simulation run time could be reduced. 

 

To control the number of steps I suggest using imposed displacements (instead of velocity) and matching the Time History or animation output intervals with test data points. 

 

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