Dynamic stress seems less in comparison to the static load!

General Questions
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1

So, I’m running an analysis where, I put two steps:

1.) A static step- with a moment load-A with amplitude (constant with time for 2 seconds)

2.) Another with a dynamic step- with another moment load-B with amplitude (linear variable for 1 sec).

Post running this analysis with both steps I’m getting the resultant max. load comparatively less than the only static-step load analysis.

When trying to propagate the static moment form static-step. there is an error :

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Any suggestion for the resolution of this problem will be very appreciable!

Actually, I’m using first-static step for preloading. and second step-dynamic step for variable load with time. However post result, it found the stress developed is less than only static load analysis…. and that is not correct, (as load is applied at same reference point and direction),

Thought, its not counting the moment-1 from first step so propagated to step2 but got this error. Need the logic of working and resolution

2

Check this post about multistep analyses in CalculiX: Understanding multistep analyses

PrePoMax propagates BCs and loads by default (uses OP=NEW and redefines these features) or they can be propagated manually if automatic propagation wasn’t applied (e.g. because of some changes in the step sequence).

The error simply means that you have two conflicting (due to different amplitudes) loads applied to the same node and degree of freedom.

If you want to modify the load in the second step, you can edit it there to change the magnitude or amplitude. If you want to keep it and add a new one, it should act on different nodes/DOF.

2 Likes
3

Actually I tried with changing the load application point, in second step. And it ran properly, However I noticed, Post the analysis , the result stress is even lesser than the only static load case…. Any logical reason; In case of dynamic load, how can a stress developed be less in compression to the only static load if load applied was in same position and orientation.

4

Going straight from static to dynamic step can be tricky because of a few factors. You introduce inertia effects to the system, but also numerical damping that can be quite significant (check the Alpha parameter). There are also different default load amplitudes (dynamic step applies all loads immediately instead of ramping them linearly throughout the step), but you use custom amplitudes so it shouldn’t be a problem. Deactivation of loads happens with this different amplitude too, though. See the OP=NEW parameter.