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Found 6 results

  1. Hello everyone, I would like to ask if there is any special requirement in order to determine the proper timestep for simulation that use ALE Mesh + Free surface. Usually, i calculate my timestep using Courant number = 0.5, but still after sometimes the simulation crash with error: Severe mesh distortion; must reduce time increment. Is there any proper/correct formula to calculate timestep size for these condition? *I am simulating a vibrating cylinder. free stream velocity: X-direction active cylinder motion: Y-direction
  2. Hello everyone, my goal in this calculation is to make the depth of impact greater than 200 micros, and finally I've succeed by using ALE method (with ALE-Grid-Displacment). But here comes the problem: After the impact, these two componant stick together (there's no friction between them). Which have not appeared in the Lagrangien method. And I'm wondering why, and how to avoid it? Grid_Standard_compet_M201_v50.hm
  3. Hi, I am trying to model a transient analysis of a planetary mixer but I do not know how to properly introduce the motion in the model. It consists of a shaft rotating around its axis while also rotating around the central axis. I have tried by defining two fluid regions, one close to the shafts with the a mesh motion (the rotation of the shaft around its own axis) and the rest of the fluid with the rotation around the central axis. As I expected, this resulted in a distorted mesh and AcuSolve stops the simulation. If anyone could point me in the right direction about really appreciate it!
  4. Hello all, I am working on a model with an interface between RDX and a metal. With all Lagrangian it works correctly ! So I was expecting to get better results with RDX ALE and metal LAGRANGIAN, but I am getting negative volumes ERROR very quickly... I tried all the Interfaces Types for ALE/LAGRANGIAN but none of them is working correctly for my model. Did anyone know about this problem ? You can find attached the files of my simulation. Thank you in advance for your help ALE_0001.out ALE_0000.out ALE_0000.rad ALE_0001.rad deto_ALE.hm
  5. Hi, I'd like to model a box floating in open water, that means that wave generation and especially wave absorption should be modelised. I've modeled this on Hypermesh with the solver Radioss In this model, there are 2 sorts of interaction : - fluid/fluid : air with water - fluid/structure : both fluids with the box. First, I've used an ALE model for the fluids. I've tried to use both MAT/LAW51 (multimaterial) and MAT/LAW37 (biphasic material) in order to model this, but everytime there is a leakage and the computation can't run until the end (negative rho error). I've also tried to use MAT/LAW11 (bound) because it doesn't work properly with a biphasic material (negative rho error). Then, I've tried with an SPH model with IN and OUT condition, so that the computaiton doesn't take into account the air/water interaction, the computation also stops because of a leakage. For the fluid/structure interaction, I've used INTER/TYPE18 and INTER/TYPE7 respectively for ALE and SPH model. I have to set a STfval value for the stiffness. I use the formula of the Help page : stfval=rho*v²*A_el/GAP = 66.667avec - rho=rho_water = 0.001g/mm3; - v=10 mm/ms , initial velocity of the box when it is dropped in the water; - A_el = lagragien element surface =500 * 500 mm² ; - GAP= 1.5 * E_el = 1.5 * 250 = 375mm With this value, the box is floating in the air, the only way i've found a value that models reality was by dichotomy.. That's not convenient for further simulation with different initial data.... Should you have any suggestion to model an infinite water volume (so wave absorption) and for the stiffness value, please contact me. Sincerly yours, Emmanuelle
  6. Hi, I'm trying to simulate the interraction between a box and waves in the sea. Thus I'm using the material LAW37 (BIPHAS) in order to model the interface between water and air which are modeled in ALE. The problem is that I don't know how to model the boundary conditions on the transverse faces in order to avoid wave reflexions on the wall (to simplify the computation, all DoFs are fixed on the longitudinal faces). I can't use MAT/BOUND (LAW11) because it doesn't work properly with the LAW37. So i'm trying to model these boundary conditions using a material LAW37 to create an "air outlet" and a "water outlet" with the same initial values as air except for : -the liquid bulk modulus C_Liquid = 0.0 - gamma = 0.0 The computation runs well at the beginning and i get a pressure gradient in the fluid volume, so it's okay. But then an error appears : " STOP : NEGATIVE RHO=-0.1322538772563E-09 FOR 3D-ELEMENT ID=3696 ERROR TERMINATION " In the results file I can see that there is a problem with a really big velocity vector on top of the volume in the air part. I think this is linked, but I don't know how to avoid this. Moreover, to model the interface between the box and the water, I use INTER/TYPE18 but I don't know how to set the right value for the StfVal. Using the formula written in the Hyperworks Help i.e. StfVal=(rho * v² * Sel)/GAP , the box is floating in the air, and not in the water. Do you have any suggestion? Thank you very much in advance, Hereby the .rad file ALE_05a_0000.rad
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