Hi Yves, The answer depends.
About what you should scale, that is a general computational mechanics question and is not specific to DEM, and you should be able to find related readings from textbooks or webpages. If you scale time, then all quantities that involve time must be scaled accordingly. These include velocity, acceleration, Young's modulus etc. However I doubt if it is needed at all. >From what I understand, scaling in computational mechanics is usually used to tackle numerical instability (extremely small numbers etc.), and it does not reduce runtime just like there is no free lunch. If the physics in your DEM problem is driven by some extremely small velocity/acceleration (hence the long simulation time), then you should be able to just use large time step sizes. The quality of DEM simulations depends heavily on whether contact events are resolved sufficiently with at least something like 4 time steps. A typical DEM contact event has a short duration (~1e-5 s), so the step size is usually that small. But a contact event with an impact velocity of 1 m/s resolved with a step size of 1 s, has about the same quality as a contact event with an impact velocity of 100 m/s resolved with a step size of 0.01 s. So if the physics you are trying to resolve is "mild", you can use large step sizes, and this is not scaling; if the physics is not "mild" then even scaling will not make it more numerically feasible. But one may be able to say otherwise if the physics driving the simulation is something I did not expect. Then it depends, whether scaling can help. As for what scaling factor/actual time step size you should choose, again it depends. No one can say without knowing the specific problem, and this is something you need to figure out, and sometimes trial-and-error is needed. Thank you, Ruochun On Sunday, June 26, 2022 at 4:33:25 AM UTC-5 [email protected] wrote: > Hello, > > My plan is to simulate a slowly evolving granular system, with time scales > of days for the frame rendering, and the whole simulation would probably > cover several hundreds of days. > > Since the DEM time step is usually very low (~1e-5s), I was thinking of > scaling down the time. In other words, I would accelerate the process. > > But I have now several questions: > > - First, is it the solution you recommend? > - Since I really do not want to impact the physics of the phenomena in the > system, what should I scale as well? I use material-based properties for > the simulation. I guess the gravity would have to be scaled, what about the > material properties? > - How do I choose the acceleration factor? 1 day could be represented by > 1e-5s, 1s, 10s, etc. What kind of criterion is usually used? > > Thank you, > Yves > -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/f66be60f-d770-46d9-9a0b-d00b8dae82d5n%40googlegroups.com.
