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Recent content by Elabbasi

  1. Elabbasi

    Frequency Disappearing for half model

    Even though your structure is symmetric, it has both symmetric and non-symmetric natural frequencies and mode shapes. When you model half or a quarter your model cannot capture these non-symmetric modes. There is a workaround however. You can solve the half model twice, once with symmetry and...
  2. Elabbasi

    Thermal expansion + different materials

    If you have two adjacent materials with different thermal expansion coefficients it makes sense that there would be a stress discontinuity at the interface. The surface tractions on the interface must be equal on both sides due to equilibrium (both normal and tangential components) but not the...
  3. Elabbasi

    Uncertainty in transient simulations

    Drop/impact events introduce very high frequency content in a system. Capturing that response in finite element simulations requires both a fine mesh and a small time step size. The FEA response will include high frequency content that is physical and another part results purely from numerics...
  4. Elabbasi

    Lung modeling

    Interesting observation. The definition of compliance varies between engineering fields. In pneumatic systems compliance is the volume change (or flow rate) divided by pressure drop, and parallel lungs have the same pressure drop. Mechanical springs are the opposite; compliance is the...
  5. Elabbasi

    large strain in ABAQUS

    CAX8R can handle large strains. That does not have to be restricted to large strains in elastomers or other hyperelastic materials. It also includes large plastic strains in elastic-plastic materials and visco-plastic materials as well. Nagi Elabbasi www.veryst.com
  6. Elabbasi

    Single shot impact in Abaqus

    Don't use displacements for loading and unloading since you don't know exactly how the shots will slow down. Use initial velocity instead. That way the rebound velocity of the shot will come out as a result from the simulation. Nagi Elabbasi www.veryst.com
  7. Elabbasi

    Help with modelling problem in abaqus explicit

    You're welcome Jlog50. The restrictions that you mentioned are for transient modal dynamic analysis (Section 6.3.7 in the 6.10 User's Manual). What you need is the Implicit dynamic analysis using direct integration (Section 6.3.2). That allows all three nonlinearities that you mentioned. Nagi...
  8. Elabbasi

    Help with modelling problem in abaqus explicit

    Implicit analysis (Abaqus Standard) is clearly more suitable for this rate of loading. However, that does not mean that inertial effects have to be ignored. You can do an implicit transient dynamic analysis and compare the kinetic energy to the strain energy to make sure that it is negligible...
  9. Elabbasi

    CONTACT STRANGE WARNING

    Good luck. AUTOMATIC TOLERANCES helps with a specific type of contact problem, where nodes are going in and out of contact in successive iterations. If that doesn't help, there are many other advanced contact features in Abaqus. Refer to Section 35.1 titled "Resolving contact difficulties in...
  10. Elabbasi

    CONTACT STRANGE WARNING

    The Abaqus message is indeed confusing. The increment is not yet converged because there are large tensile contact forces. You are using the non-default *CONTACT CONTROLS, AUTOMATIC TOLERANCES setting for dealing with "contact chatter". In general, when a contact force at a node becomes...
  11. Elabbasi

    Time lag in micromechanical viscoelastic model

    How does the applied displacement vary with time? If it is applied too fast or too slow (what constitutes fast and slow depends on your viscoelastic constants) then there would be no significant viscoelastic effects and therefore no time lag. Nagi Elabbasi www.veryst.com
  12. Elabbasi

    Time lag in micromechanical viscoelastic model

    Make sure the analysis type is VISCO not STATIC. Nagi Elabbasi www.veryst.com
  13. Elabbasi

    Two FEA runs and different results for the same model !!!

    The difference in results could be due a difference in the way the pressure is applied by both Contractors. If a constant pressure is applied on all internal surfaces of a closed volume, then there should not be any net force (summed over the whole model) in any direction regardless of the...
  14. Elabbasi

    Error Help

    This Abaqus message tells you that the analysis is not converging. There are so many potential causes for this including insufficient constraints, time step too big, unstable model, material failure, and contact. You should look at the information Abaqus provides in the .msg and .dat files...
  15. Elabbasi

    fluid structure interaction with ansys

    If you have all the loads on a structure and you are only interested in a stress analysis (including fatigue), then there is no benefit from performing a fluid-structure interaction analysis. Nagi Elabbasi www.veryst.com
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