open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi. I'm newbie for hydrodynamic modelling and the TELEMAC system.

When I first tried to run my model, it seemed like running, but found out to be meaningless. Message such as below shows up all the way.


================================================================================

ITERATION 100 TIME: 16 MN 40.0000 S ( 1000.0000 S)
LIQUID BOUNDARY: SL(1) = 97.609999999999999
LIQUID BOUNDARY: Q(2) = 3.2272499999999997
LIQUID BOUNDARY: Q(2) = 3.2272222222222222

---

ADVECTION STEP

---

DIFFUSION-PROPAGATION STEP
GRACJG (BIEF) : EXCEEDING MAXIMUM ITERATIONS: 100 RELATIVE PRECISION:
NaN

---

K-EPSILON MODEL
GRACJG (BIEF) : EXCEEDING MAXIMUM ITERATIONS: 50 RELATIVE PRECISION:
NaN
GRACJG (BIEF) : EXCEEDING MAXIMUM ITERATIONS: 50 RELATIVE PRECISION:
NaN

---

BALANCE OF WATER VOLUME
VOLUME IN THE DOMAIN : NaN M3
FLUX BOUNDARY 1: NaN M3/S ( >0 : ENTERING <0 : EXITING )
FLUX BOUNDARY 2: NaN M3/S ( >0 : ENTERING <0 : EXITING )
ABSOLUTE ERROR IN VOLUME AT T = 1000. S: NaN

---

FINAL BALANCE OF WATER VOLUME

RELATIVE ERROR CUMULATED ON VOLUME: NaN

INITIAL VOLUME : 634334.8 M3
FINAL VOLUME : NaN M3
TOTAL VOLUME LOST : NaN M3

END OF TIME LOOP

CORRECT END OF RUN

ELAPSE TIME :
6 SECONDS



I'm trying to build a model for the creek flowing into reservoir.
Boundary 1 is for downstream and time-dependent surface elevation(SL) is given. It is impacted by water level of reservoir, so almost constant. Time-dependent flowrate(Q) is given for boundary 2.

I suppose initial condition or boundary condition could be problematic. However I just can't find what the problem is.

Really need some help.
Thanks for your advice in advance.

Hi,
I did a quick analysis of you mesh size and you minimum element area is 0.22 which might be contributing to your problem and the smallest distance between two nodes is 0.147m

I think you need to modify your mesh to avoid such small elements


Regards
Tony C

Thank you so much for your advice Tony!

I have taken care of my mesh, so smallest distance between nodes is around 1.67 meters now. It looks much better than a former one on sight. However, problem keeps going on.

It returns message "GRACJG (BIEF) : EXCEEDING MAXIMUM ITERATIONS: 50 RELATIVE PRECISION: NaN". This happens when I use K-epsilon turbulence model. When I use constant viscosity model, it stucks at the second time-step with advection calculation stage. Using Elder model ends up with same symptom as depicted on the original post.

Have been tinkering with some parameters for several hours, but no sign of improvement. I've attached modified steering file and others. Would you mind checking it for me?

Wish you have a nice day.

in your cas file you call a liq boundary file which you have not posted you might try and see if your initial conditions which I think you have set at 99m are causing your model to crash, also depending on this initial water level some of your boundary condition nodes may be dry or a major jump to the imposed water level at theses nodes at the first time step. You might need to start your model with a false situation of say a high water level and gradually move the simulation towards the conditions you want to impose. But also as Costas has rightly identified you may have to reduce your time step significantly to overcome numerical stability

regards
Tony C

Hello,

Usually this error occurs when your given timestep is too large. Try reducing your timestep, or increase the minimum element size as Tony said.

You can also addin your cas file to get a safe estimate of the appropriate timestep for your computation. Then you can disable it if you need a fixed timestep.

Regards,
Costas

Hi,
your model runs attached please find zip of files
I included a liq file that you can change

regards
TonyC

apologies sorry no it does not run

TonyC

here is a cas file that gets the simulation to work

regards
TonyC

Wow, I'll try it right away!

I had some tryouts and found out that time-step has to be extremely small. The only solution I came up with was removing the levee to ease the mesh.

Tony, you saved my day. Thank you soooo much!!!
I really appreciate your kindness.

Regards
Donny Kim.

Thanks for your advice!
It helped me a lot. I completely forgot about relation between time and mesh size due to courant number. It really was a crucial reminder.
Have a nice day!

Regrads
Donny Kim.