Problem with Porosity in BOUSS2D

[Hamid Fanaie 0]

Dear all,

Based on the manual I tried to use damping layer for partial reflection from a breakwater. The harbour is small compared to the long period waves, based on the damping coefficient graph( Figure 5 in manual), I should get 30 meter damping width in order to have 40% reflection.

It seems in damping layer water levels are going to be close to zero, which does not let the waves penetrate into the small entrance of the harbour. I need to use porosity layer but the model become instable with the porosity map that I create in SMS V10.1. I could not find in the manual and tutorial an example to show how we should use porosity properly. Can you please let me know how should I use porosity in BOUSS2D?

Best regards,

Hamid

Edited February 5, 2010 by Hamid Fanaie

[J Schultze 0]

Hamid,

Below you will find some suggestions for model stability using porosity:

Crashes are usually caused by problems related to the grid, the boundary conditions, or model parameters.

Model stability requires a low Courant number throughout the domain. SMS computes an approximate maximum timestep to maintain a Courant number below 0.5. You may want to lower the timestep even more. Additionally, you may want to truncate the computational domain to areas with depth above a specified minimum. Another option is to increase resolution by using smaller computational cells.

Damping layers should be 5-10 cells wide.

Generally, avoid placing damping or porosity layers along structures and shorelines.

Wave makers are more stable on the edges of the domain. Therefore, generally speaking, the wave maker should be placed on the boundary of the domain in constant (or nearly constant) depth water. (The SMS interface offers to extend the grid and transition to constant depth if a wave maker is created in a location with more that 20% variation in depth.) This is especially true in real world applications where reflected waves are of no concern. Also, when simulating large waves, the greater stability of external wavemakers may be required.

Wave makers should be placed far enough from shore to avoid interaction between the wave maker and reflecting waves. This is because the external boundary behind the wave maker is treated as a vertical wall.

Regards,

Josh Schultze

XMS Technical Support

(801) 691-5530

support@aquaveo.com

[Hamid Fanaie 0]

Thanks Josh for the reply,

I had considered all the notes that you mentioned in my model, My courant number is already 0.3 and the model even without any damping layer ( fully reflective boundary) is stable. With damping layer also there is no problem.

As soon as I put in porosity layer the model crashes after 3miniute of run. So I think the problem is the way that porosity have been introduce to the model. I select a cell string along the are of interest and assign it as porosity. Can you please answer the following questions?

1- Does the porosity map that sms generate, need any post processing?

2- Does the solver handle the porosity correctly?

Best regards,

Hamid

Edited February 8, 2010 by Hamid Fanaie

[J Schultze 0]

Hamid,

Perhaps there is a bug is SMS which is causing this crash.

Will you send us your files so we may duplicate it?

If the size is less than 25MB you may email them to support@aquaveo.com.

If they are larger, you will need to upload them to our ftp site. I will provide instruction on how to do this, if necessary.

Thank you for the questions.

Regards,

Josh Schultze

XMS Technical Support

(801) 691-5530

support@aquaveo.com

[Hamid Fanaie 0]

Josh,

I have sent you the files and look forward to hearing from you.

Best regards,

Hamid