LS Dyna

LS Dyna

Eliminate the reflected stress wave of the boundary in a blasting simulation

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    • Miner
      Subscriber
      Hi all,nNo matter what parameters, *BOUNDARY_NON_REFLECTING could not eliminate the reflected stress wave. Because the boundary in my model must be constrained, *MAT_PML is not suitable for my simulation. Any suggestion to effectively eliminate the reflected wave of boundary?nThanksn
    • Jim Day
      Ansys Employee
      If you constrain the boundary nodes not to translate, any effect of the non_reflecting boundary is negated. What you should do is apply nodal forces to represent the constrained boundary. To do that, see *LOAD_SPCFORC.n
    • Miner
      Subscriber
      Thank you very much for your response. I am doing a blasting simulation with preload. Preload is obtained by implicit solution (*LOAD_SEGMENT_SET), and then do the blasting simulation by including the dynain file in the explicit solution. If the boundary was not constrained during the explicit solution, the preload is not steady as the following figure shows,nnAccording to your suggestions, I added *LOAD_SPCFORC, and removed *BOUNDARY_SPC_SET at the non-reflecting boundary (explicit solution), which could not make the preload steady. Could you please elaborate on this?.Thanks in advance.n
    • Jim Day
      Ansys Employee
      Try this ...Run 1:nUse *boundary_spc to constrain nodes, e.g., on the sides and bottom ofna soil mesh.nApply gravity and solve for static or quasi-static equilibrium.nCan use DR, implicit, explicit with damping... whatever method you prefer.nnRun 2:nDo a full restart where *boundary_spc are removed and replacednwith *boundary_non_reflecting.nAdd *load_spcforc command.nThe code will take spc forces stored in dump file (not spcforc file)nand apply them to the corresponding nodes. These forces arenautomatically held constant with time.n
    • Miner
      Subscriber
      Thank you for the detailed steps. I followed your suggestions but I still didn't make it. Here are my steps,nThis a thin plate model, and displacement along z-direction is constrained in both simulations.nIn the explicit simulation, I added *BOUNDARY_NON_REFLECTING and *LOAD_SPCFORC, and then run the simulation as usual. n
    • Miner
      Subscriber

      Try this ... Run 1:Use *boundary_spc to constrain nodes, e.g., on the sides and bottom ofa soil mesh.Apply gravity and solve for static or quasi-static equilibrium.Can use DR, implicit, explicit with damping... whatever method you prefer.Run 2:Do a full restart where *boundary_spc are removed and replacedwith *boundary_non_reflecting.Add *load_spcforc command.The code will take spc forces stored in dump file (not spcforc file)and apply them to the corresponding nodes.  These forces areautomatically held constant with time.https://forum.ansys.com/discussion/comment/113564#Comment_113564

      I also tried DR for preload, then do a full restart analysis using d3dump01 (*load_spcforc  and *STRESS_INITIALIZATION are added). But it could not maintain the preload steady during dynamic phase.n
    • Miner
      Subscriber

      Try this ... Run 1:Use *boundary_spc to constrain nodes, e.g., on the sides and bottom ofa soil mesh.Apply gravity and solve for static or quasi-static equilibrium.Can use DR, implicit, explicit with damping... whatever method you prefer.Run 2:Do a full restart where *boundary_spc are removed and replacedwith *boundary_non_reflecting.Add *load_spcforc command.The code will take spc forces stored in dump file (not spcforc file)and apply them to the corresponding nodes.  These forces areautomatically held constant with time.https://forum.ansys.com/discussion/comment/113564#Comment_113564

      It works. Array Thank you @jday, . There are some elements near the boundary show oscillations, but its variations are very small and can be neglected. Your suggestions helped me a lot. n
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