open TELEMAC-MASCARET The mathematically superior suite of solvers

Now our model works (mine and SEBJAMs) but we are not fully satisfied with the output. The simulated wave heights are not as smooth as the input on the boundary. I have attached both the cas-file and a picture comparing the results and the input boundary data. It seems to get better when I decrease the time step but the computation is taking unreasonable long time if I lower it much more (now 60 s).

We would appriciate any help on this and other tips on how to decrease the computaion time!

Hello,

Sorry it took this long to reply.

I know there are guidelines on how to select a time step in TOMAWAC. Please have a look at post 4323.

Perhaps there is something in the mesh geometry that could be responsible for creating the osculations you are seeing. Do you have elements with steep change in bathymetry? What about mesh size?

I don't know for sure this is a problem, but it is certainly worth investigating.

Pat

Thanks for your reply!

I have tried time steps down to 1 s but it doesn't solve the problem. I have narrowed down the problem to appear when the wind direction changes. I have changed my input wave file to steps in the wind direction instead of constantly varying, and then the instability disappears (whith a time step of 3600 s). I will continue with some more tests and see if I can solve the problem - I will try your idea to smooth the bathymetry along the boundary.

Also I found that it is not possible to set NUMBER OF DIRECTIONS = 360 - why is that so?

Best regards,
Charlotta

Hello,

Just an answer on the number of directions :

If NA is the number of angles, ND the number of directions and NP the number of points in the mesh, the number of unknowns in Tomawac is NA*ND*NP, and several arrays of this size have to be allocated, this is why 360 directions is probably too many.

With best regards,

Jean-Michel Hervouet

Hello ,


I modified the limwac.f routine and although the wave height and peak frequency are
transferred alright to the boundary nodes of my mesh, the direction does not fit the entry from the file. I entered a print*, to my fortran file to check the direction and the calculation is correct. Is there any other subroutine where I can modify the variable TETA1L?
I have attached my fortran file





many thanks

Nikos

Hello,

I'm trying to do the same thing as Nikos but also with spatial varying conditions.

I have begun with a constant in time and space series just to check where it is the best place to hook in the code.

First try : Modification in Limwac.f
Hm0,FPICL and TETA1L just hard coded in Limwac.f. It is the same "spirit" than Pat Prodano's code but simplified.
FPICL is exactly represented. Hm0 seems to be well represented (delta varying around 0.001 between code and results). TETA1L is not well represented at all (in my example, asked 330, represented 187...)

Second try : Modification in Speini.f
Hm0,FPICL and TETA1L just hard coded in Speini.f.
Results are the same than 1st try : it is not satisfying for TETA1L. I just think the second try will be better for space varying (loop on boundary point...)

As a conclusion, even if I have tried another way, I have basically the same issue than Nikos...

Does somebody have an idea ?

Regards

Hello Nicolas

the problem with TETA1L is that the value of direction is multiplied by pi/180.

So when you modify limwac.f routine after all your interpolation just multiply TETA1L with pi/180 and it will read the correct direction.

Regards

Nikos

Hello Nikos,

Thank you for your advise, I have just checked it is working now!

Regards

Hi everyone,

This topic have been discussed what I am doing. There is something that I have not understood clearly. it maybe some stupid questions but I have to ask

1. Why do we have to prescribe initial boundary conditions when we already use wave series at the boundary?

2. Regarding types of boundary conditions in TOMAWAC, there are only two kinds of boundary conditions (P.70 in operational manual V7.1). My 2nd question is (not really related to this topic): in case of coupling with TELEMAC2D using THOMPSON boundary option, do I need to prescribe the boundary condition? and how?

I am confusing this because in the operational manual I don't understand some words, by highlighting here:

"Only two kinds of boundary conditions are available in TOMAWAC.

The first one corresponds to a free boundary i.e. a boundary that fully absorbs the wave energy. It may be a liquid boundary: it is then assumed that the waves propagate beyond the domain and nothing else enters it. It may be a solid boundary: it is then assumed that the shore fully absorbs the wave energy.

The second one corresponds to a boundary with a prescribed value. In this case the wave action spectrum is then strictly imposed at each point along that boundary. This boundary condition allows wave energy to enter the computational domain"

Thank you all for sharing your knowledge and experience!

Best Regards

Huy

I am not sure to well understand your question, but I have tried to answer!

1. When you use wave series and so user program, you choose where you enter in the code and what you modify. Maybe your code overwrite the case file values and you don't "use it". You can check easily putting different values in the wave series and the case file and see the results.

2. Boundary conditions : as you say there is only two types and you define it on the boundary condition file.

Regards