Simulation help - run time

[Anonymous]

Hi everyone,

trying to run an event simulation to see the affects of a load and velocity pulling a trailer. It says that the run time is too long and will not compute (over 12 hours). I tried increasing the mesh size, but am getting the same error. Any advice on how to get this to solve?

Thanks! 

[John_Holtz]

Hi @Anonymous  

The Event Simulation analysis uses an explicit solver. The time step size of an explicit solver is limited by the smallest element size in the model, so you were taking the correct approach by increasing the mesh size. Is it possible that you can increase the mesh size even more?

The second factor that determines the total analysis run time is how many time steps are needed. You specified a duration in the Settings. Dividing the duration by the time step size gives the total number of steps required in the analysis. An estimation of how long each time step takes to solve will give the total run time. If increasing the mesh size does not reduce the run time sufficiently, the second thing that you can do is decrease the analysis duration.

The time step size required by an explicit solver is generally very small (on the order of 1E-6 seconds). A duration of 1 second would result in 1 million time steps and a long run time. This is why an explicit solver is generally used for highly dynamic events like impact and explosions where the total duration is on the order of 0.001 to 0.01 seconds (1000 to 10,000 calculation steps).

The alternative to the Event Simulation is to approximate the analysis using a static analysis. For example, pulling a trailer at a constant speed does not require a dynamic analysis (if you ignore the roughness of the road). Pulling at a constant acceleration can be analyzed using a static analysis with a gravity/acceleration load. The vibration from the road is normally analyzed using a random vibration/random response analysis (which Fusion does not include; use Inventor Nastran to perform that analysis).

Please feel free to provide more information about the loads and goals of your analysis, and someone will be able to provide some more specific ideas.

[dnaikM5JKG]

Where can I find the time step size?  

[martin_madaj]

Hi everyone,
this topic is quite dated but I have to mention that probably there must be some restriction on an Autodesk's side associated with the total simulation runtime in explicit solver. I have also encountered the same 12 hour limit. Maybe this can serve as prevention against overloading Autodesk's servers but on the other hand, it may devalue the benefits of solving in cloud, especially when you really need a detailed mesh in a highly non-linear simulation.

And btw @dnaikM5JKG , the time step size can be found in Simulation - Manage - Settings window.

Best regards,
Martin Madaj.

[dnaikM5JKG]

Hi,  in the settings window I have the following options: total event duration, number of result intervals, and solve status information interval (Heartbeat). Is either one of these time step size?

@martin_madaj 

[martin_madaj]

Hi @dnaikM5JKG,

for the event simulation, the time step is set automatically based on the mesh size and physical properties of the model. But you can set how often the intermediate results are saved during the analysis (Number of Results Intervals) so that you can view them when the analysis is finished. More precisely, how many results you want to see at the end of the analysis - the number of "colorful images".
The Heartbeat relates to the number of time steps between the solver status outputs.

Best regards,
Martin M.