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Kaustubh Joshi

Issue with Simulation

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Hello!

I am trying to simulate a crash box and I am also getting results. But the Simulation Shows no movement and Deformation of the crash box. 

Also, the error % varies between 0 and -8%. What can I do to get the Deformation of the crash box? Also, how to reduce the error %? 

I have checked my material and property values as well.

Thank You!

 

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Hi,

 

the initial kinetic energy is not enough to deform the crashbox. The impactor weighs 0.6 kg which is far less than the 100 kg structure so the impactor simply bounces off. Increase the kinetic energy by increasing mass, initial velocity or both.

 

Negative energy error represents energy dissipated from the system and this can be from many sources like plastic deformation, hourglass energy,  contact with friction, damping,... Review the energy balance to identify the source of this error.

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Hi,

I have increased the mass of the impactor and yet the crash box is not deforming as expected.

Also, the Energy error % seems to be within acceptable limits. What can be the issue then?

 

 

 

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Hi, 

 

while you have increased the mass of the impactor the initial kinetic energy is still not enough to plastically deform the crash box. You can load the model with imposed displacement and obtain the energy required to deform the crashbox by plotting the total energy in Hypergraph and observing the corresponding deformation in Hyperview. Then you can use this energy as the initial kinetic energy to calculate the required velocity and mass of the impactor. 


There are modeling errors:

  • the base plate of crashbox is not attached to the fixed supporting structure so it will slide sideways when loaded. 
  • the impactor has a relatively small contact area and it can lose contact during deformation. Provide some friction or use larger impactor plate
  • the mesh quality is bad. Use F10 Check elements>3D to check the solid element quality and remesh accordingly. 
  • the impactor and some other components are meshed inappropriately by double walls, effectively halving the stresses. You have to mesh a single mid surface instead.

imposed_displacement_0000.rad

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Hi!

I have changed the mesh and also fixed the base plate. I cannot change the size of the impactor because this is the same we are going to experiment with.

However, even now the same problem persists. I have also tried with the imposed displacement for my new model and it also does not run properly.

Where am I going wrong? Please help!

 

 

 

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Hi,

 

while the mesh in this model is of good quality, the mesh size is not appropriate for explicit- remember the timestep issue! A 100ms run would take 22 hours on my end.

The 300kg mass added to the impactor should give sufficient kinetic energy. The only issue I can think of is initial velocity should include all the nodes of a rigid body. 

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Hi,

Yes, the simulation takes a bit of time to run..but unfortunately, including all the nodes to  initial velocity is also not working in this case.

I am quite confused as to what the problem with this model is.

 

 

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Hi,

I am simulating the crash box, however, the simualtion stops after a certain point automatically (after 5 Animation files) 

Also, there is no 0001.rad file being generated. Please help!

 

Unbenannt.PNG

 

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Hi,

 

such abrupt termination is unusual. The run is usually prematurely terminated either with an error message or by user intervention. I was able to run the model to the 7th frame, after which I manually stopped the simulation (see attached out file). In your run the Radioss calculation process was probably terminated. You can try restarting:

There is no engine file because the engine file was merged with starter on export. Since you have checked  "Merge starter and engine file" option, the engine control cards defined will be in the starter file (_0000.rad) itself and that's why the engine file was not created separately. Open the _0000.rad file in Textpad or Notepad and ensure that engine control cards are present. 

Capture.PNG

11_11_2edit_0001.out

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