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Found 17 results

  1. AcuSolve uses a semi-implicit predictor/multi-corrector time integration algorithm that places no stability limits on the time step size. Therefore, the time step size is selected based on the physics of the problem, and not the stability constraints of the numerical method. This allows users to perform transient simulations with ease without the need to iterate on solution settings. When performing unsteady RANS simulations, the timestep should be selected to resolve the transient phenomena of interest in the simulation. For example, in the case of vortex shedding behind a bluff body, the timestep would be set to resolve the shedding frequency. For most cases, resolving the shedding cycle with 30 time steps per period is sufficient to get a good estimate of the magnitude and frequency of the fluctuating forces on the body. When performing LES and DES simulations, the timestep size needs to be set according to the size of the turbulent eddies that you expect to resolve. For LES and DES, the size of the turbulent structure that the model can resolve is closely tied to the local element size. Therefore, the time step size should be related to the element size. Therefore, it is suggested that the following formula be used to determine the appropriate time step size: Δt = CFL* Δx/umean Where: Δt=time step size, Δx=characteristic element size, and umean=mean velocity, CFL = Courant-Friedrichs-Lewy number. The CFL should be set to ~5-10 or less for DES simulations. For LES simulations where very small turbulent structures are of interest, the CFL number should be set to approximately 1 for the highest accuracy. It should be noted that these are only guidelines to use for setting an initial time step size. A time step sensitivity should be done to determine when the solution becomes time step independent.
  2. Hello, I know that Radioss is a solver which has both Implicit and Explicit solving scheme. I want to know when I solve a problem in Radioss which scheme is being used. Is there any way to select the method i.e. implicit or explicit when solving a problem? Thanks, Datta
  3. Hi all, I am working on an implicit case. First I applied a load on a group of nodes. Now I apply an imposed displacement. It worked fine for the first one but I get an error in the engine file for the imposed displacement : MESSAGE ID : 79 ** ERROR : RADIOSS IMPLICIT STOPPED DUE TO LOADING DATA ** ISTOP=0 ERROR TERMINATION Here my imposed displacement input: /IMPDISP/551 IMPOSED DISPLACEMENT ON TOP NODES # func_id dir skew_id sens_id grnod_id frame_id icoor 601 Y 803 # x_scale y_scale t_start t_stop 0 -3.000000e-02 0 I see tstop but what is ISTOP ? Thank you in advance, Alice
  4. Hello All, I am currently running a non linear simulation that requires around 25hrs of computing time on a 16 cores machine. It's got 300000 elements. Radioss adjust the timestep automatically and reduces to something around 4e-4s. I therefore need around 2500 time steps to converge. The problem I am trying to solve is something similar to a beam in bending ( I do need non-linear) and my requirement is to find the static deformed shape (not a dynamic case, it will converge to a steady result). I have tried explicit but timestep is 1e-9s and it would take 175days to converge... Are there any tricks/ideas that could be used to speed up the convergence? Thanks, NR
  5. Hi, I am facing the following error while running nonlinear implicit analysis in Optistruct and run got terminated. How to sort out this? Regards, Arul
  6. Dear sir, I want to analyse a model in radioss implicit which was ran in abaqus for vertical loading (non linear static problem with contacts), what are the basic implicit cards i should use to perfrom non linear implicit analysis (with vertical loading of a plate on roof structure and type 7 contacts , elastic - plastic material also) in radioss and compare the results with abaqus. Is there any tutorial which have executed the run in radioss using implicit cards. Thank you.
  7. Hi all, I have some problems when doing tutorial example about non-linear problem by using optistruct. OS-1500: Nonlinear Implicit Analysis of Bending of a Plate I set up the problem according to the tutorial procedure. However, some error occurred when solving. *** ERROR # 4002 *** Running RADIOSS engine, 1 ERROR and 0 WARNINGs have been detected. They are listed below. ENGINE ERROR: ** ERROR : RADIOSS IMPLICIT STOPPED DUE TO SOLVER ERROR ** ISTOP=-4 NLGEOM subcase 1, engine finished The attachments are the model file and error message. Anyone can help how to solve this problem? Best Wishes Roy Geom_NonLinear.fem Geom_NonLinear.out Geom_NonLinear.hm
  8. Hi, It seems that we cannot use imposed displacement/velocity as loading condition while solving through radioss implicit. I was trying the same but was not working properly. I am using version 13 for the same. Kindly let me know about it. Thank you
  9. Hello, I usually perform Radioss explicit analysis for crash simulations (12 ms). Now I need to perform a quasi-static simulation lasting 75 seconds, which, with the explicit solver, takes way to long to solve. Here my engine input : #RADIOSS ENGINE /RUN/pression_statique_02/1 75000 /VERS/140 /TFILE 5 /PRINT/-50 /ANIM/DT 0 100. #################### # IMPLICIT OPTIONS # #################### #Static linear computation: /IMPL/LINEAR # Printout frequency for linear computation: /IMPL/PRINT/LINEAR/-1 # Linear solver method : /IMPL/SOLVER/3 # Iprec It_max Itol Tol 5 0 3 0.0 However I get an error termination saying : MESSAGE ID : 162 ** ERROR : SINGLE PRECISION IS NOT COMPATIBLE WITH IMPLICIT OPTION Would anyone know what this error means and how it can be solved ? Thanks in advance, Alice
  10. Hi all, How to calculate how much force required as a final output in the implicit nonlinear analysis (Optistruct)?
  11. Hi, Is it possible to apply an incremental load in Non-linear implicit analysis using optistruct? Regards, Arul
  12. Hey! I am trying to perform a structural and transient analysis on a Roller Element Bearing model. I am able to perform simple static analysis but I would like to utilize Hyperworks to simulate the following conditions: Inner race to be rotating with a constant velocity and a fixed radial load is applied. Outer race is fixed. The balls should also be rotating. I wish to know how I can give a constant velocity to the inner race of the bearing while also allowing the balls to rotate. What kind of contact constraint should I apply. Right now I am working with freeze contact only. There is one video but in a different solver which does what I have been trying to do. I wish to do it in Hyperworks. Here is the link: Also please suggest whether optistruct's non linear can be used or whether I should switch over to a different solver module! Cheers
  13. Hi all, Is there any learning resource about implicit method in Radiosss? In other words, how to convert a explicit model to implicit with Radioss? Any relevant video and manual are appreciated. Thank you Roy
  14. Hello, Good Afternoon. Optistruct solver fetches me great result for a non linear quasi static analysis ( non linear solution converged). But when I run the same file with a coupled topology optimization I get error 941: non convergent non linear iterations for subclass 2. Feasible design <All constraints satisfied> Why is this happening and how do I resolve it?? thank you.
  15. Hi Support I am running crash can crushed by a wall with RADIOSS using Implicit option, but the run stopped simply at cycle 0. I suspect it might have to do with my engine file. could you take a look at the engine file and out file? p/s: I will send the starter file if required, but I can't post it here due to confidentiality Thanks try_Run_0000.out try_Run_0001.out try_Run_0001.rad
  16. Hello, I use Radioss for a dynamic impact problem, but also for the moment to validate my model through a quasi-static analysis. A first component compresses a second component with an imposed velocity. The interface between them is of type 7. In dynamic explicit simulation the interface works fine but in the implicit simulation, I get a warning in interface : "NODE ... DE-ACTIVATED FROM INTERFACE". If I make an "initial penetration" (initial gap < gapmin entered into type 7 interface) I do not get this problem (however I get initial constraints I want to avoid). Would anyone know what the problem might be ? Hereunder a part of my engine.out file: -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- CYCLE TIME TIME-STEP ELEMENT ERROR I-ENERGY K-ENERGY T K-ENERGY R EXT-WORK MAS.ERR 0 0.000 0.2000E+05 SOLID 39426 0.0% 0.000 0.000 0.000 0.000 0.000 ANIMATION FILE: pression_statique_07A001 WRITTEN ***** WARNING : ELEMENT FORMULATION ISOLID= 0 IS NOT AVAILABLE FOR STIFFNESS MATRIX BUILDING, USING GENERIC ONE INSTEAD POSSIBLE CONVERGING ISSUE. ***** *--------- STIFFNESS MATRIX SETUP ---------* SYMBOLIC DIM : ND = 155532 NZ = 2897175 NB_MAX = 26 FINAL DIM : ND = 47480 NZ = 761383 NB_MAX = 26 --STIFFNESS MATRIX WILL BE REFORMED AFTER EACH 3 ITERATIONS-- * CONVERGED WITH 0 ITERATIONS, |du|/|u|,|r|/|r0|,|dE|/|E|= 0.1000E+01 0.0000E+00 0.1000E+01 WARNING INTERFACE 701 NODE 13703 DE-ACTIVATED FROM INTERFACE WARNING INTERFACE 701 NODE 13548 DE-ACTIVATED FROM INTERFACE WARNING INTERFACE 701 NODE 13693 DE-ACTIVATED FROM INTERFACE ANIMATION FILE: pression_statique_07A002 WRITTEN * IMPLICIT COMPUTATION TERMINATED WITH TOTAL NONLINEAR ITERATIONS: 0 * TOTAL NUM.OF MATRIX FACTORIZATION AND PCG ITERATION: 0 0 RESTART FILES: pression_statique_07_0001_[0001-0001].rst WRITTEN ------------- ** CPU USER TIME ** #PROC [K]SETUP [M]SETUP IMPL.SOLV IMPL.TOTAL 1 .4862E+02 .0000E+00 .0000E+00 .4930E+02 #PROC CONT.SORT CONT. F ELEMENT KIN.COND. INTEGR. I/O TASK0 ASSEMB. RESOL 1 .5591E-01 .6813E-02 .2678E+00 .2133E-01 .4654E-03 .5012E+00 .9117E-03 .1199E-01 .5030E+02 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Thank you a lot, Kinds regards, Alice
  17. Thank you George for the reply. So for any analysis until we use the control card for Implicit, will it always run an explicit analysis?? Also I have one more question, what is the error and mass error here ? CYCLE TIME TIME-STEP ELEMENT ERROR I-ENERGY K-ENERGY T K-ENERGY R EXT-WORK MAS.ERR 3500 0.3713E-02 0.1048E-05 SHELL 106239 0.1% 0.1060E+07 0.7229E+08 0.1347E+05 -0.2986E+06 0.000 Is it the error, the error of the external force to the internal force?
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