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8.7.4 Dynamic versus Steady-State Analyses
FEBio runs fluid analyses in dynamic mode by default, because many fluid flow problems do not have a steady-state solution, since the governing equations are nonlinear. For example, many flows may exhibit vortex shedding as fluid flows across an obstacle, such as a flow constriction or a solid body. Even if some form of periodicity emerges under specific flow conditions, as in the von Karman vortex street, the corresponding solution is not in steady state. However, for some low Reynolds number laminar flows, a steady-state response may exist and FEBio will attempt to find that solution when using analysis type “steady-state” (Section 3.3↑). The user should be aware that, under steady-state analyses, the solution may not necessarily converge as efficiently to the final solution as would a dynamic analysis that allows the solution to reach steady state after a sufficiently long time. The best choice of analysis type for steady-state problems may need to be determined by trial and error.