Initial data for the analysis have to be inserted in the Initial and Conditional Data window of Tdyn. This window can be opened by selecting Data > Initial Data menu option.
Initial condition for the X component of the velocity is a uniform field of 1 m/s as shown in Figure 24.
Remark:
As a result of the analysis, (in this or in a different problem) a physical temporal instability in the flow is expected to be found (the weel known von Kármán vortex street in this case). However, depending mainly on the quality of the mesh (i.e. average size of the elements), a spurious steady solution of the flow field may be found (a steady pair of eddies in the wake of the cylinder, whithout initiating the periodical and alternating vortex shedding). This is a “physical”, but unstable solution of the problem. In these cases the unsteady solution (the vortex shedding) can be found by artificially introducing an instability to the problem.
As an example of this artificial destabilization of the flow, we will introduce a variable velocity field in the cylinder, defined by the following function:
if((t>50)&(t<55)&(x>-.01)&(y>.47))then(1)else(0)endif
This funtion have to be inserted in the Data > Initial Data >RANSOLwindow as shown in Figure 24. This will create a perturbation in the OY component of the velocity, between t=50s and t=55s.
Figure 24 Tdyn Initial and Conditional Data window |
|