2D mesh in ICM - the best minimum element size

• January 21, 2014, 11:22 AM
DObolevics
2D mesh in ICM - the best minimum element size
Hi,

Small elements within 2D mesh slow down the simulation. I have reviewed elements within 2D mesh and simplified geometry of some of voids-polygons to remove all elements that have area of less than 1m2.

What minimum size of the element would you advise to have in the model so it would not really slow down the simulation.

Thanks
• January 23, 2014, 04:54 AM
Duncan Kitts
Quote:

Originally Posted by DObolevics
Hi,

Small elements within 2D mesh slow down the simulation. I have reviewed elements within 2D mesh and simplified geometry of some of voids-polygons to remove all elements that have area of less than 1m2.

What minimum size of the element would you advise to have in the model so it would not really slow down the simulation.

Thanks

Hi,

The minimum size of the element really depends on the size of the area to be meshed. The 2D timestep is calculated based on the Courant-Freidrichs-Lewy condition (this is stated in the help under 'Basic 2D Hydraulic Theory') which suggests that the smaller the space step (a measure of the element area and element shape), the smaller the timestep required to acheive stability. An element area of 1m2 is roughly equivalent to a 0.4 second timestep. This may be appropriate for some scales of modelling but not for others. For a decent city sized model I would consider this adequate.
• January 23, 2014, 05:08 AM
DObolevics
Quote:

Originally Posted by Duncan Kitts
Hi,

The minimum size of the element really depends on the size of the area to be meshed. The 2D timestep is calculated based on the Courant-Freidrichs-Lewy condition (this is stated in the help under 'Basic 2D Hydraulic Theory') which suggests that the smaller the space step (a measure of the element area and element shape), the smaller the timestep required to acheive stability. An element area of 1m2 is roughly equivalent to a 0.4 second timestep. This may be appropriate for some scales of modelling but not for others. For a decent city sized model I would consider this adequate.

Hi Duncan,

Thanks a lot for your reply. The area that is covered by 2D zone is quite extensive, according to ICM it is 32422 ha.
I have used the following parameters for 2D zone: Max triangle area = 600m2; Min element area = 150m2. Also, I have a number of Mesh Zones in the areas where a higher resolution mesh is required and following parameters have been used: Max triangle area = 200m2; Min element area = 15m2.

I do understand, that due to size of this model the run time will be quite long, but still having nothing in the model apart of 2D mesh it runs very very slow almost the same as in real-time.
My concern is that I will need to add river and drainage systems into this model and I am sure I wont be able to run it at all or it will take ages to do so.

I am just trying to understand will it help to reduce the run time, if I, for example, remove all elements with area less than 10m2 or it can make such a little difference that it wont be worth even trying.

Thanks