TELEMAC-MASCARET Forum: Estimating friction at the free surface (1/1)

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TOPIC: Estimating friction at the free surface

Estimating friction at the free surface 5 years 11 months ago #32350

SDAC

Hello,

I've been testing the effects of overhanging vegetation on the surface of my flow. Now I want to test its representation using a friction equation. I thought to modify the bottom friction code in coefro.f and tfond.f. Using Manning's law my code is:

TIERS  = 1.D0/3.D0
        MN = 0.001D0                    !Mannings coeff
        DO N=1,SIZE(IDOV)              
	    I1 = OVOME(N,1)             !nodes with vegetation present
           HC = Z(I3D)                  !node at the free surface
           IPLAN = NPLAN
           I3D = I1+NPOIN2*(IPLAN-1)
           CF = 2 * MN**2 * GRAV / HC**TIERS         !CF estimation
          UETCAR(I3D)=(UN3%R(I3D)**2+VN3%R(I3D)**2)*0.5D0*CF  !friction estimation
        ENDDO

The last line (UETCAR(I3D)...) is problematic and causes Telemac to exit. I assume that UETCAR is being incorrectly used here.

In order to represent the effect of friction on the free surface, what would be appropriate?

Many thanks!

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Estimating friction at the free surface 5 years 10 months ago #32501

SDAC

Hello,

My friction model almost works!

Everything runs smoothly until 1m 24s into my run when I get the dreaded EXCEEDING MAXIMUM ITERATIONS error. Looking at the results I suddenly get very high velocities at the bank (see image). I don't think this is a mesh error as it has been used successfully for other models.
I assume it is a numerical issue.

My code is:

IF (I1.NE.0) THEN

           TIERS  = 1.D0/3.D0
	    MN = 0.001
       IPLAN = NPLAN !for layers at that node
        I3D = I1+NPOIN2*(IPLAN-1) !get the 3D node IDs
        I3D = UID3+NPOIN2*(NPLAN-1)
        CF = 2.D0*(MN**2)*GRAV/HC%R(I)**TIERS   !calculate coeff CF
	  S1U%R(I3D)=SQRT(CF*((UN3%R(I3D)**2)+(VN3%R(I3D)**2))) !apply friction 
       END IF

It finds the nodes (I1) pertinent for the section on parallel. Then, at the free surface, it applies a skin friction term to affect surface velocities S1U%R. I'm using the coefficient CF as calculated using Manning's n.

I tested this code using a simple drag calculation (i.e. S1U%R(I3D)=0.5D0*A*CD2*NORM) and it worked fine.

Is there something wrong in my equations?

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Estimating friction at the free surface 5 years 10 months ago #32523

SDAC	Just checked again today and I realised I hadn't included the S1V%R term when I CTRL+C'd that part of the code over Seems to work fine for now.
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