Displacement becomes small after activating LGDISP
Altair EmployeeHi everyone,
Could you help me understand the phenomema that I describe below ?
I conducted a non-linear analysis with activating LGDISP. After comparing the results with and without LGDISP, I found that there is a big difference in displacement.
If I don't activate LGDISP, the displacement of model is very large. Otherwises, the displacement becomes small with LGDISP. I don't understand this phenomena.
Note : In my model, I have plastic material so with small young's modulus , but just linear comportement is taken into account (I don't have informations on parameters for determining its non-linear comportement). I implemented non-linear analysis because of contact phenomena.
Thanks for your helps.
Answers
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Hi,
Are you running a large strain problem with NLSTAT without LGDISP?
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Hi Prakash,
Yes, I ran the analysis with NLSTAT without LGDISP. In this case, the displacement is large. Otherwise, if I activate LGDISP with NLGEOM, the displacement becomes small. I am not sure the problem is qualitified as a large strain problem.
Regards,
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Hi,
I think you are running large strain problem. So without LGDISP some effects like contact status are taken into consideration.
with LGDISP this is taken care.
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Hi Prakash,
Thanks for your helps.
I have one more question: What is the differences between NLSTAT and NLGEOM ? I have read Hyperwork Helps. But it is still not clear for me. As NLSTAT works only for small displacement nonlinear analysis, an analysis with NLSTAT and LGDISP should not be allowed by Solver, not ? however, I can do it with my current model.
That means there are 4 combinations :
- NLSTAT with LGDISP
- NLSTAT without LGDISP
- NLGEOM with LGDISP
- NLGEOM without LGDISP
Furthemore, I didn't found an explanation for NLGEOM anlaysis type under the descriptions of ANALYSIS in Hyperworks helps.
Best regards,
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Hi,
LGDISP is used in combination with NLSTAT to analyze large strain problems.
I think with NLGEOM LGDISP will be ignored.
With NLSTAT it is assumed that the simulated physical phenomenon is not influenced by temporal aspects, in other words that the expected results do not depend on the speed of application of efforts. This makes it possible to satisfy the equation of equilibrium with each step, the effects of inertia being ignored. Therefore, the weakly dynamic problem can be solved as a static (quasi-static) problem.0 -
Will NLSTAT with LGDISP consider the Geometric non-linearity ?
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Hi @Karthic
Yes, solver should consider Geometric non-linearity with LGDISP.
See this from OptiStruct help:
Large Displacement Analysis
Large Displacement Nonlinear Static Analysis (LGDISP) is used for the solution of problems wherein the load response relationship is nonlinear and large structural displacements are involved. The source of this nonlinearity can be attributed to multiple system properties, for example, materials, geometry, nonlinear loading, and constraints. Currently, in OptiStruct the large displacement capabilities include large strain elasto-plasticity (MATS1), hyperelasticity of polynomial form (MATHE), contact with small tangential motion, deformation dependent loads (follower loads), and rigid body constraints.
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Thank you @Prakash Pagadala,
Will all the loads in NLSTAT with LGDISP are follower loads. Or FLLWER card is required along with NLSTAT (LGDISP )
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FLLWER card is required for follower load analysis.
If FLLWER = option is present above the first subcase, it is applied to all large displacement nonlinear static subcases.0 -
Thank you @Prakash Pagadala,
Do I need FLLWER card to specify deformation dependent loads (follower loads) in NLGEOM subcase ?
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Hi Karthic,
Follower force is currently only supported for large-displacement nonlinear static analysis subcases.
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