Learning Forum

[thach-hoang.nguyen]

Hello,

I'm a little bit confused but quasi statics solution. I've read all the explaination on the internet but i can't still understand it. 

Here are some of the explainations:

"Quasi-static implies a condition where we can consider a problem as static at a specific moment in time. The key assumption is that the applied load occurs extremely slowly, with a frequency much lower than that of the structure. As a result, the inertial effects are negligible. This assumption is valid when inertia effects are minimal, and it also aids in simplifying nonlinear problems into linear systems."

" ForQuasiStatic application-based settings, the Backward Euler algorithm is used. In addition, damping energy and the work done by any external loading condition is taken into account. This can be seen through the transient solution optionsTRNOPTcommand."

In quasi-static solution, we are solving F=KU or F=MA + KU? It said that it used Backward Euler to solve so i think it used the formulation F=MA + KU? But some said that it still used F=KU. Can someone please explain this part?

Thank you and have a good day

[Sai Deogekar]

Hi, in quasi-static case we should ideally be solving KU = F.

However, in some highly nonlinear cases, it may be difficult to obtain convergence by using an implicit solver. In such cases, one workaround is to use the explicit solver and solve KU + MA = F (explicit solver cannot be used to solve KU = F, it can only be used to solve KU + MA = F), but ensure that the loading is such that kinetic energy is a very small percentage of the total energy. Then, although you are not solving a static case, because the kinetic energy is low, it can be considered to be quasi-static.

So based on the case and what solver is being used to model the quasi-static case, one can solve either KU=F or KU + MA = F equation.