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Hi:
I want to create a file to describe the friction coefficient varies in space, and the user manual of telemac modelling system show that it is necessary to use the STRCHE and/or CORSTR subroutines,also give the example of STRCHE, but which keyword in *.cas should I used to trigger this function?
Else,could I used the text file just like the GEOMETRY FILE to define the value of friction coefficient at each mesh point, and which form it should be?
Thanks!

Hello,

I preffer a little more "graphical" alternative which involves using Bluekenue preprocessor to set the bottom friction coefficient storing the variable as "BOTTOM FRICTION" in the geometry file (along "BOTTOM" and the initial water level/free surface condition..) and mapping the desired values using a polygon.

Don't have a BK installation nearby but the general procedure is:

* Set the polygons of your bottom friction coefficient in a gis package e.g. QGIS or ArcGIS.
*Duplicate the bottom mesh with a constant value with the name "BOTTOM FRICTION" (from the dropdown menu)
*Map the polygon's attributes to the bottom friction's mesh nodes.


Regards,

José Díaz.

Hi Wang,
The simple way is to carry out a selafin file of the friction coefficient rather to use the subroutines you indicated.
Do you have BlueKenue? if yes :
1/ You need a shapefile with coordinates X Y and f which is your friction coefficient (Manning or Strickler). Are you familiar wit GIS (for example QGIS), if not, I can give you 3 tips to carry out the friction shape file using a txt file.
2/ Import your shapefile in bluekenue : FILE - Import - ArcView Shape File
3/ Save this shapefile with this format : XYZ Point Set (*.xyz) , let assume that you name it like friction.xyz
4.1/ Interpolate your firction file over the mesh : FILE - New - 2D Interpolator.
4.2/ Drag your file friction.xyz to the interpolator.
4.3/ Double-click on you mesh, then on data and select Node Type (Apply and Ok)
4.4/ Select you Mesh (by one click) and then TOOLS - Map Object
4.5/ Select NewInterpolator2D and clik on Ok.
4.6/ Name the new attribute F or FRIC or other names : this is the name of your variable (friction) . Click Ok.
4.7/ Save it by clicking on your Mesh (for example Mesh(F)) and then FILE- Save Copy as.
4.8/ Save also the interpolator (for example Friction_Interpolator).
5.1/ Create now the friction file as a selafin object : click on File - New – SELAFIN Object
5.2/ Dragh Mesh(F) in newSelafin : make sure that the attibute of the Mesh must be the name of the attribute you have used for the friction coefficient.
5.3/ select newSelafin (one click) and with the righ botton of the mouse you choose Add variable and select BOTTOM FRICTION in Name (if your steering file is in english) and then tick the box "Copy Node Value from Source" and validate by OK.
5.4/ Right-click on newSelafin and then on Mesh.. and then Remove.
5.5/ Select newSelafin (click one time) - then FILE - SAVE : for example save the newSelafin as FRICTION_MAP.

Hope this help

Hi,mourad:
Thanks for your reply.
Is that the shapefile with coordinates X Y and f you indicated means the shapefile of points with the attributes of X Y and f, which I can import through excel? But how can I get the value of f ? Through the bottom of GEOMETRY FILE I can get the value of X Y for each point, if I have to give the value of f in the shaplefile(for example, could I give the value in EXCEL and then improt into ArcGIS to create the shapefile of points?) and then, could I modify it in BlueKenue?
Thanks again.

Regards
W_D

As in BlueKenue you can interpolate the friction coefficient and other variables (i.e free surface at t=0) you can just give the friction on some points and interpolate it over the mesh.
Yes, you can use the X and Y of your mesh and then in excel you fill 3 columns (X,Y,F) and copy/past your data in text file (or directely save it as csv file).
Import your file in ARCGIS (I use QGIS) and save it as Shapefile. Next, do Waht I mentionned in the previous reply.

I dont know how you did obtain your friction coefficient everywere? I assume that you have divided your domain in few zones (3 or 4) with constant friction based on 1-your experience, 2 - the flow charactersitics and 3- the bottom roughness. For example :
Upper reach (UR): Manning coefficient n = 0.035
Middle reach (MR): n = 0.030
Lower reach (LR) : n = 0.025

You can only give approximate values of the friction coefficient, but through running telemac several times you can calibrate this coefficient to get right values of water depth an velocity.

For Example, based on the experience (the yours or litterature) you can test the following :
UR : n in [0.030 , 0.040]
MR : n in [0.028 , 0.037]
LR : n in [0.020 , 0.350]

I'm not sure that you can modify the friction coefficient in BlueKenue.
Hope this help better.

You can load an ASCII xyz file directly in Blue Kenue.
No need to go through a shape file.
Or as suggested above if you have 3 regions then creating the polygons in Blue Kenue is also easy.

In either case the values associated with the points or polygons can be edited in Blue Kenue.

Hope this helps... Martin

Hi,mourad:

I have successfully tried the method , it's very clearly and helpful for me, but I'm just a new user of telemac, there are various problems I have to study. And next, I have to modify the 'FRICTION COEFFICIENT = 0.03' in cas file to 'FRICTION FILE = 'the name of my fricthion file', it's right? If not, what's the suitable way to modify the cas file?
As to the value of friction coefficient, is it refer to the Manning coefficient, such as I can give it the value about 0.03,0.025,0.035 , but in the user manual of telemac modelling system,page45, the example give the number of 50 or 55, which is the right meaning and data range?
Thank you very much!
Regards
W_D

Dear W_D,

1) You don't have to add anything else to your current cas file. At the beginning of the simulation in some point will say that the "BOTTOM FRICTION" variable was extracted from the geometry file. The value of the 'FRICTION COEFFICIENT' keyword (you should only put one in this keyword) will be "ignored".

2) As the telemac suite has different schemes to modelate friction , the one in the manual is different from Manning hence the different order of magnitude of its coefficient.

Regards,

José Díaz.
.

Hello, josekdiaz,
Is that the telemac choose the suitable mehtod automatically according to the value , that I can give it 0.025,also, I can give it 55?
And is that you mean I have to creat the friction and geometry in one file which I add one line to describe friction coefficient in GEOMETRY FILE, rather than to creat two file that GEOMETRY FILE and FRICTION FILE respectively ? If just one file ,I'm sorry I don't konw how to do it now,can you explain detailedly?
Thanks very much
Regards
W_D

Hello,

The law of friction must be chosen using the keyword "LAW OF BOTTOM FRICTION", for manning has the value "4". (No friction is "0", for Haalands law is "1", for Chézy's is "2"... in the user manual are the rest of the options...). The coefficient keyword value has to be in accordance with the law chosen (there is no "automatic" recognition).

Friction ('BOTTOM FRICTION' variable) should be in the same file (the geometry file) with the topography ('BOTTOM'), so there is only one file that contains both variables.

If you choose to include the friction in the geometry file (which you have already done) there is no need for any additional keywords, files and such...

Hope its helps.

Regards,

José Diaz.