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About Crashphys

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  1. Hi, I found that the best solution might be to extract interface forces and import them to OptiStruct to do either explicit dynamic or a linear static. I have an output request for the contact forces, however I was wondering how I can get the raw data rather than a graph? Edit: I was also wondering if you could specify: is your recommendation to get the interface loads and run OptiStruct EXPDYN? I thought EXPDYN runs already with the ESLMO method? Thanks
  2. Both suggestions were incredibly helpful. I reduced the element size by one half and defined FAIL/TENSSTRAIN as recommended. Simulation runs exactly as expected now, with results showing something more realistic.
  3. Hi, I'm wondering if it's possible to run an optimization to minimize compliance rather than mass in RADIOSS. Should the objective be to minimize strain energy instead in this case? Also, there seems to be a very limited selection of responses. Is there anything for center of gravity like in OptiStruct? Thanks in advance.
  4. I have noticed in various simulations that viscosity can cause your simulation to experience a great deal of energy error. For example, in the two simulations I have attached, the only thing I changed with linear and quadratic bulk viscosity from 2.0 and 1.0 to 2e-30 and 1e-30. In the HighVisc solution, I get proper results. For low visc, there is a sharp decline in energy error and the simulation breaks. You can see the sharp decline in energy error immediately after the first cycle. Can anyone explain why this happens and how to counter it? LowVisc_0000.rad LowVisc_0001.rad HighVisc_0000.rad HighVisc_0001.rad
  5. It will be helpful if you share your model. In RADIOSS, you cannot connect an element of any type to the master node of a rigid set. The nodes that the beam3n are connected to are the master nodes for the rigid set defined by the slave nodes at the edges of your square holes. You connected a beam3n to those master nodes, which caused the error. I believe if you use another RBODY to connect the two nodes rather than a beam, your simulation will run. RBE2 is the optistruct version of a rigid connector, which is effectively the same as RBODY in OptiStruct. Watch the video here from 2:10 onwards to see how to manually create a bolt. https://www.youtube.com/watch?v=zwNIfNfaPWg
  6. Hello, Alternatively, I am wondering why it is that the RADIOSS optimization process gives the results below. It seems that all elements are treated as one design variable rather than each their own. I was hoping I would be able to get a topology for an optimized structure with a map of element densities. Is there something wrong with my radopt? HopperOpt_0001.rad HopperOpt_0000.rad HopperOpt.radopt
  7. Hi, I have two blocks colliding at 200 m/s. The impact causes an insane deformation in the solids, which doesn't make any sense. When I set the velocity low to about 10 m/s, I get something reasonable. I'm wondering how I can simulate for high velocities? Collision_0000.rad Collision_0001.rad
  8. Negative energy error can be reasonable depending on your model. A negative energy error makes sense when you have things like friction or damping. What I think may be happening is your damping is so high it is absorbing all the energy, so double check your values for damping.
  9. Your RBODY master nodes are connected to a 1D Beam3N element. As far as I know, this is a big no-no for RADIOSS. Read up on HM3420 in the Hypermesh tutorials to see how to appropriately make a bolt. Also, when making RBODYs in RADIOSS, make sure you use the "calculate node" option rather than selecting the node.
  10. Can you show your interface details? If you read up on interfaces, you will note there is a value called gapmin. This value defines at which distance your components begin to interact. If your gapmin is higher than the distance between the two components, you will have initial penetrations.
  11. Hi, I am wondering if there is any known way to extract the dynamic loads produced by high velocity interactions and convert them to static loads. For example, for a ball hitting a wall, I would like to determine the loads produced on the wall through the ball hitting it and produce an equivalent static case in OptiStruct. As far as I can tell, this is done by using RADIOSS optimization, but I would prefer to only get the loads and not necessarily optimize the part itself. Edit: More specifically, it seems the load case is an XSTEP. Can anyone help me find where this data is stored and how to simply apply it to an OptiStruct model. Thanks!
  12. Hi, I gave that a try. It appears to work fine on my end too. I suppose my question is why exactly such a random guess for gapmin works (for which you said there's no explanation). Why 4e-5 m? And stranger yet, why does the appropriate gapmin work in the tutorial but not in this simulation? Is it the geometry? As I understand, now that the gapmin is so small, it basically means that the bird is interacting with the plate when it's well within the material, which physically makes no sense? I apologize if I'm getting annoying but I'm more concerned with trying to understand what's going on in the simulation, not specifically how to make it work. Thanks, Ayman
  13. Hyperman, Sorry for the late reply. Just got around to taking a look at this. I still can't understand the instability in this model. I took your model and changed the speed from 80 m/s to 200 m/s, but this caused the energy error to hit 68%. Is there any reason for this? Attached: Test7 - 80 m/s Test8 - 200 m/s What factors could be playing into this? Is it that the speed is so high that the elements are distorting too much? Test8_0001.rad Test8_0000.rad Test7_0000.rad Test7_0001.rad
  14. Hyperman, Thanks for all the help. My mistake, I must have originally given a different file. The thing is, that the qa and qb values seem to be what is causing all the problems... I ran your original test1_edit_0000.rad file,which works just fine, but then changed the values of qa and qb to the very small values, and the simulation hit 99% error. I wasn't able to have a look at your Test2_edit_0000.rad, as it is a 2018 file, though looking through it, it seems that you only changed the qa and qb values. Did it run without divergence on your end? The gapmin being so small is also very confusing. I noticed the same as you, that the gapmin appears to be activating the interface far too early... A gapmin at 0.00075 m is equivalent to the radius of the SPH particles, which means that the contact is activating well "inside" the plate, considering that one half its thickness is 0.003175 m.
  15. Thank you, I will check with them and report back.
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