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Hyperman

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  1. Felipe M Leila liked a post in a topic by Hyperman in BALL JOINT   
    Hi,
     
    you can try to add torque based on BISTOP function to limit joint motion.  Please refer to the attached document (from Hyperworks for MBD 13).
    HyperWorks_for_MBD_v13.pdf
  2. pohan liked a post in a topic by Hyperman in Negative % ERROR IN RADIOSS   
    Hi,
     
    Use the recommended contact parameters for interface Type 7:
    Istf=4
    Igap=2
    Fscale_Gap=0.8
    INACTI=6
    Gap_min=1
    Fric = 0.1
    Iform=2
     
    Another reason for timestep drop and energy error is because Interface type 7 does not deal with edge to edge impact. When the mesh is fine enough, edge to edge penetration is often followed by a node to shell contact. The main problem with edge to edge impact is the locking situations. If there is a change of load after edge penetration, locking is unavoidable since a node to surface contact is detected. This usually leads to high penetration; therefore, the analysis comes to a standstill as time step is reduced. If locking occurs, the use of interface type 11 in this area is necessary to solve the problem.
     

    Share the model file if the issue persists.
  3. pohan liked a post in a topic by Hyperman in Negative % ERROR IN RADIOSS   
    Hi,
     
    Large contact energies relative to total energy can cause large negative Energy Errors because contact energy is not part of the Energy Error equation. If the simulation has friction and a lot of sliding contact, then the large contact energy and resulting energy error can be considered acceptable.

    example-edit_0000.rad
  4. pohan liked a post in a topic by Hyperman in Is it possible to activate boundary condition at certain time?   
    Hi,
     
    it is possible to activate (BCS) or release (BCSR) boundary conditions by using BCS/TRA and BCS/ROT engine cards. 
     
    Refer to the following examples:
    RD-E: 4200 Rubber Ring: Crush and Slide
    RD-E: 5501 Fan Blade Rotation Initialization
    Kinematic Conditions.pdf
  5. Kunal Hirudkar liked a post in a topic by Hyperman in INCOMPATIBLE KINEMATIC CONDITIONS IN MODEL DESCRIPTION :   
    Hi,
     
    the TOP_BCS load collector constrains all DOF, which is incompatible kinematic condition with the imposed displacement in the Y translational direction on the same node of a rigid body. Therefore Y translational DOF has to be free in the TOP_BCS load collector.
    seck_debug_edit_0000.rad
    Check unit consistency: the unit system declared in the BEGIN CARD is kg, m, s however the material parameters used are consistent with tonne, mm, s. 

     

  6. Rahul R liked a post in a topic by Hyperman in Optistruct topology optimization result does not make sense   
    In the model you shared the optimization problem was actually min volume fraction with a constrained frequency of the first mode. The objective and constraint should be switched as you proposed (min 1st frequency s.t. 0.5 VF).
     
    To make sense of topology optimization results it is useful to output ESE- strain energy. 



    I have reduced the order of tetra elements and meshed the design space with hexahedral elements to save computation time. Note however the model is stiffer due to 1st order tetra- the plate should be structured hexahedral meshed for accuracy and efficiency. The minimum and maximum member size were used on topology>parameters. Door_opt_Topo_Opt-edit1.hm

    Refer to a similar example OS-E: 3005 Eigenvalue Maximization for alternative approaches (topography + multi frequency optimization setup).
    OS-E_ 3005 Eigenvalue Maximization.pdf eigenplate.fem
     
  7. SergioV liked a post in a topic by Hyperman in Shells and solid   
    Hi,
     
    there are many techniques to connect shell and solid elements:
     
    -using rigid elements
    -inserting a layer of shell elements inside solid elements
    -inserting a layer of shell elements on the face of solid elements


    shell2solid.fem
  8. Rahul R liked a post in a topic by Hyperman in Composite modeling in HyperMesh   
    Hi,
     
    with the setting Z0=blank, the plies will be arranged symmetrically, i.e. half the laminate thickness on both sides of the surface geometry (see image attached).
    Or have I misunderstood what you are trying to do?

    composite_laminate_edit.hm
  9. Hyperman liked a post in a topic by Imre.F in Composite modeling in HyperMesh   
    Hey Hyperman!
     
    Thanks for your effort, you understand me well.
    I was lame and did not leave the z0 offset blank, I left there a 0 mm value.
     
    Thanks again, you are the real hero, not superman.
     
     
     
  10. Imre.F liked a post in a topic by Hyperman in Composite modeling in HyperMesh   
    Hi,
     
    with the setting Z0=blank, the plies will be arranged symmetrically, i.e. half the laminate thickness on both sides of the surface geometry (see image attached).
    Or have I misunderstood what you are trying to do?

    composite_laminate_edit.hm
  11. Crashphys liked a post in a topic by Hyperman in Determine Equivalent Static Loads in RADIOSS   
    Hi,
     
    there are some modeling errors:
    check elements(F10)>1D>duplicates: there are some duplicate beam elements tools>find connectivity: the Undercarriage beams are not connected with the rest of the model. Equivalence the nodes in edges panel (shift+F3).  You should reconsider the boundary conditions.  There are point supports which cause stress singularities (as the mesh is refined, the stress and strain energy will tend to infinity) and even worse- displacement singularity (displacements will also increase with refinement). Constrain a cluster of nodes to avoid this issue. Consider how the hopper wagon is constrained in real life- the model is only constrained with 4x point support on one end and rely on XZ plane symmetry to constrain the other end. As a result, the wagon is lifting vertically in the symmetry plane. Gravity and lateral loads should probably be applied to the whole model, not just SPH. 
     
    The lateral load was ramped up during settling under gravity stage when kinetic relaxations was still active. It should be ramped up only after this stage instead. I have no explanation about the "Brownian motion", but when I ran settling under gravity it was well behaved.

    The contact forces are actually distributed, but you are only seeing the peaks as the legend contours according to the max value. Contour panel>legend>edit legend...>type:dynamic scale or input small number in the max field. 

    The coarse mesh is stiffer so it is normal to see more deformation with finer mesh. My guess (without h3d it's hard to tell) for the roof is the frame beams are deforming (coming together in the Y direction) imparting compressive forces to the roof which is buckling elastically. This may be because the undercarriage beams were not connected. Use the deformed shape scale factor to magnify deformations. Consider if the beam layout should also be optimized. 
     
    The interface is controlling the timestep in the 2nd run, which may be due to too high AMS imposed timestep. Output the number of AMS iterations per cycle via /DT/AMS/Iflag=2 which may help monitoring convergence quality at no extra CPU cost. Maximum allowed iterations before the divergence stops is 1000. 75 to 100 iteration per cycle is a sign of a poor convergence, 50 still may provide some speedup and 30 iterations or less is considered a good convergence.
  12. Kunal Hirudkar liked a post in a topic by Hyperman in Time Step Less or Equal Zero Error   
    Hi,
     
    From the engine out file we can  review what is causing very low time step.
    It can be an element, a node or an interface.
    •For an element, check the related material (especially its Young modulus and density in case of an elastic-plastic material; and its viscosity in case of a visco-elastic material). There must not be an error in the units system that this data is given in. 
    Check the size of the element, since elemental length is proportional to time step. If some elements are distorting badly during simulation it will lead to very low time step and the run will terminate. In this case use small strain formulation (in the property card).
    •For a node, check the characteristics of connected elements. If the node is on the master side or the slave side of an interface, this interface must be verified.
    •For an interface, the gap of the interface must be verified if some failure happens on the master or the slave side of the interface. Check the interfaces defined in the model for any penetrations.
  13. Joel Rodarte liked a post in a topic by Hyperman in CONTPRM card?   
    Hi,
     
    Ctrl+F search for any keyword (input in the upper right corner).

    Use PREPRT>YES to output .CPR file.
  14. pohan liked a post in a topic by Hyperman in QUASI STATIC RADIOSS   
    Hi,
     
    glad to help.
     
    In the explicit quasistatic analysis it is recommended:
    The loading should be gradually ramped up from zero over a reasonable period (at least 0.3 s). Instantaneous loading (non-zero loading at time zero) causes propagation of a stress wave through the model similar to impact load. The kinetic energy should be bellow 5% internal strain energy throughout the simulation to ensure a quasistatic process without inertial effects. Vibrations should be damped using for instance /DAMP Rayleigh damping.  
    The implicit quasistatic analysis with instantaneous loading has convergence difficulties as the equilibrium solution at initial load is far from the initial position. As a workaround try:
    create two engine files with the first engine ending after the preload is applied using the ramping function and the second simulation starts in the equilibrium condition perform pretension analysis and export deformed shape and stress fields using STATE file. Then initialize the stresses and deformed position in the original solver deck. However, this approach is not tested as I am away from my Hyperworkstation. Implicit and explicit solutions can be compared only if the explicit solution satisfies above recommendations regarding slower loading and damping- both will increase explicit solution CPU  time. The implicit solution could be further optimized for better convergence. Note also that Radioss implicit is only meant to complement explicit (capability to switch during simulation)- otherwise use NLSTAT non-linear quasi-static analysis in Optistruct.
  15. Hyperman liked a post in a topic by tinh in Penetration Issue   
    Rotate the green so its nodes become concide to the blue one.
  16. Crashphys liked a post in a topic by Hyperman in Determine Equivalent Static Loads in RADIOSS   
    Hi,
     
    the first run ended with the -0.7% energy error and the second run starts from 0% energy error. The energy error is reset to zero on restart so there is actually no energy increase. To restart from the previous energy balance a *.ctl file should be created with /STOP defined (similar to the checkpoint CHKPT command in Radioss Solver Run Manager).
     
    The /AMS in the starter is used to declare components on which AMS is applied and is defined only once.
    /KEREL is applied in the engine file.
  17. Crashphys liked a post in a topic by Hyperman in Determine Equivalent Static Loads in RADIOSS   
    Hi,
     
    my bad, sorry for the confusion-  the lateral acceleration was 5 m/s2 indeed.
     
    Consider splitting the simulation into two parts (otherwise kinetic relaxation will be applied throughout):
    1st engine file: settling under gravity with /KEREL for about 0.5s 2nd engine file: lateral loading till peak response + 0.1 or 0.2s margin  
    Looking forward to hearing about the results.
  18. Chris Coker liked a post in a topic by Hyperman in BALL JOINT   
    Hi,
     
    you can try to add torque based on BISTOP function to limit joint motion.  Please refer to the attached document (from Hyperworks for MBD 13).
    HyperWorks_for_MBD_v13.pdf
  19. Hyperman liked a post in a topic by Crashphys in Determine Equivalent Static Loads in RADIOSS   
    Hyperman,
     
    Isn't the load calculated as:
     

     
    With a function value of 9.81 and an FSCALE of -1, I should get an acceleration of -9.81 m/s2 down, and similarily I should get 5 m/s2 lateral, no?
     
    I was not aware that the settling was necessary however it does make sense that it should. The peak response occurs at 0.175 sec because the gravity initially drops the SPH particles onto the hopper, which I have not been able to fix as of yet. The dropping creates the high load you see at 0.175 seconds, which is not of interest as this is a software limitation and not a realistic load. The main interest is the lateral load on the walls. If the particles do not settle until 0.5 seconds, I must run it for at least that. 
     
    Regardless, I have found some more computing power I can use and am getting results soon. I will share here once I get them for the sake of learning for other people. 
  20. Crashphys liked a post in a topic by Hyperman in Determine Equivalent Static Loads in RADIOSS   
    Hi,
     
    The assumption of a rigid body on the walls is not valid, because a high acceleration lateral load (5g) considerably deforms the structure. As can be seen in the image below, the resultant contact forces are nearly equivalent during gravity loading but diverge significantly during lateral acceleration. 

    Below is a comparison (by normalization) between rigid/deformable and deformable AMS/deformable. It can be observed that rigid model overpredicts 3x on spikes and underpredicts 0.5x during peak response. The AMS overpredicts by 1.25x and follows the trend more consistently. The AMS was run with the timestep of SPH elements (3e-5).

    Below is a plot of resultant contact forces and strain energy of components designated for optimization. The peak response occurs at 0.175s so there is no need to run the model for 2.2s during optimization. ESLM needs to capture the peak responses of interest (in case of compliance it is strain energy) and it evaluates only the animation output timesteps. Therefore reduce the total run time and increase the animation output frequency, as the peak response might shift during optimization. 

    There are some other concerns:
    the 5g lateral acceleration is more consistent with F1 car than hopper wagon the lateral load is applied from 0.1s, before the cargo is settled under gravity (it takes approximately 0.5s with /KEREL)
  21. Hyperman liked a post in a topic by Luis Barros in Unable to install any of the programs   
    I solved the unable to execute the desired program error. I simply entered the administrator profile (https://www.howtogeek.com/howto/windows-vista/enable-the-hidden-administrator-account-on-windows-vista/) and it installed normally.
  22. Hyperman liked a post in a topic by cfuser in Problem with Non-linear Direct Transient Analysis of thin metal sheet   
    Hi,
    the shell thickness is supposed to be this thin (0.0004m). And yes, the unit system is N, m, s. I am aware of the warning (thanks for pointing it out anyways). As it does not effect similar analysis I have run with same shell thickness, I don't suppose this will be the source of the oscillations.
     
    Cheers
  23. cfuser liked a post in a topic by Hyperman in Problem with Non-linear Direct Transient Analysis of thin metal sheet   
    Hi,
     
    hopefully, someone from Altair support will look into the issue.
    the unit system is N, m, s and the plate dimensions are 0.05x0.26. In the description above you mentioned the shell thickness is T=0.4 (meters?) but in the model the shell thickness is 0.0004 (0.4mm) resulting in the warning message reported in the out file:
     
     
    While I'm not sure if this might be causing unexpected oscillations, it should at least be checked. Unfortunately, I have no experience with comparable models to give useful tips.
  24. cfuser liked a post in a topic by Hyperman in Problem with Non-linear Direct Transient Analysis of thin metal sheet   
    Hi,
     
    glad to help.
     
    I only added EXPERTNL and it completed without errors in ten minutes- it would solve faster if DTMAX on NLADAPT was not used. I have no explanation why it failed on your end. Which version are you using? I am using version 2019.1 and ran with solver run options: -len 120000 -nt 4
     
    Non-linear_transient_bending_sheet_edit.h3d Non-linear_transient_bending_sheet_edit.out
  25. Crashphys liked a post in a topic by Hyperman in Determine Equivalent Static Loads in RADIOSS   
    Hi,
     
    the reasoning behind the assumption that making the walls rigid will not affect the contact forces significantly because:
    the walls are not deforming too much to alter the orientation or induce stress stiffening the contact stiffness is taken from material properties, according to Istf flag As a consequence of this assumption, it is expected the contact forces due to rigid mesh will only be slightly off the results from the deformable mesh. However, this technique enables extracting better force resolution on a finer mesh, ultimately improving the stress distribution. I won't be able to qualify the validity of this approach myself until next week.
     
    While it is possible to use flexible bodies in Radioss, I am not sure if flexible bodies will deform on contact.
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