Linear perturbation modal analysis with temperature  

Tweet Topic Started: Aug 10 2017, 11:20 PM (53 Views)  
janoo  Aug 10 2017, 11:20 PM Post #1 
Totally new

Hello, I'm trying to perform modal analysis of laminated thick beamlike structure (SOLID186 2 or 3 elements per layer height, 7 layers) with aid of linear perturbation. Problem is, I'm not exactly sure whether I understand Ansys manual correctly. I'm trying to include prestress by applying temperature (tunif) in static analysis, which will cause stress due to mismatch of thermal expansion coefficients. ! ! Analysis settings: ! Static analysis: simply supported beam, temperature, small deformations... ! Perturbation: antype,static,restart,,,perturb perturb,modal,nokeep ! freefree bc solve,elform antype,modal,.... ... solve finish /post1... ! Due to theory (zero total external force), there should be almost none change in natural frequency of let's say 1st (bending) and second (bending perpendicular to 1st) modes, (change between prestressed and nonprestressed modal analysis). Which is what I also get from Ansys results. Manual states: „Thermal loads from the base analysis are ignored in a linear perturbation modal or full harmonic analysis. In addition, you cannot apply thermal loads in the second phase of a linear perturbation modal or full harmonic analysis.“ When I try clamped beam (not laminate) and use temperature to increase tensile stress, there is increase in frequency as it should be. So my understanding is that it ignores thermal loads (in F_perturbed), but it creates tangent stiffness matrix (K_t) with stress from temperature included in both analyses (simply supported + free free and clamped). Is it right? I also get same results by using pstres,on only without perturbation. Sorry for maybe stupid question, by the way, and delete it if you wish. Edited by janoo, Aug 10 2017, 11:37 PM.

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