TELEMAC-MASCARET Forum: Deposition Computation (1/1)

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TOPIC: Deposition Computation

Deposition Computation 12 years 2 months ago #5435

qilong
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Posts: 340
Thank you received: 33

Good morning,

I'm running a sediment transport model with mixed sediment, one class is sand and the other one is muud. But in my model, the mass concentration of both classes are extremly high. For example the mud comcentration reached around 100g/L only after half an hour. Here is the output from my model:

==========================================
 V/H/FA/U*/CHZ       11314   1.03686116819121        8.53478469737897
   1.00000000000000       2.653234570108260E-003   63.0474170925341
 V/H/FA/U*/CHZ       49057   1.06183146812738        8.00067359753974
   1.00000000000000       2.827770333106116E-003   62.5414632323544
 V/H/FA/U*/CHZ       52293   1.17724689022523        7.45632028497513
   1.00000000000000       3.538028952489637E-003   61.9899624981796
   
 PROCESS BOUNDARY DATA AT    3810.00000000000      SECONDS
 
 SKIN FRICTION/CRITICAL SHIELDS PARAMETER       11314  0.286453560802549
  3.906600620159939E-002
 SKIN FRICTION/CRITICAL SHIELDS PARAMETER       49057  0.304114217479070
  3.906600620159939E-002
 SKIN FRICTION/CRITICAL SHIELDS PARAMETER       52293  0.386258737539392
  3.906600620159939E-002
  
 EROSION MUD/SAND       11314  1.596816358033108E-004  6.153156675665108E-004
 EQUILIBRIUM CONCENTRATION       11314  1.892414836291465E-002
 EROSION MUD/SAND       49057  1.784636572769837E-004  6.893855143727737E-004
 EQUILIBRIUM CONCENTRATION       49057  2.119143693729157E-002
 EROSION MUD/SAND       52293  2.729408908330855E-004  1.065772637566038E-003
 EQUILIBRIUM CONCENTRATION       52293  3.268916332574235E-002
 
 T2 IN DEPOT FOR F       49057   8250.12676117276
 T2 IN DEPOT FOR F       11314   9422.59137980616
 T2 IN DEPOT FOR F       52293   5871.86058732067
 DEPOSITION FOR  F       11314  6.153522021662347E-004   385.881719486836
 REFERENCE CONCENTRATION FOR F       11314  1.594665336789106E-006
 DEPOSITION FOR  F       49057  6.894174611610509E-004   337.865983174068
 REFERENCE CONCENTRATION FOR F       49057  2.040505690109278E-006
 DEPOSITION FOR  F       52293  1.065459456602229E-003   240.469268876318
 REFERENCE CONCENTRATION FOR F       52293  4.430751012721852E-006
 
 T2 IN DEPOT FOR T       49057   1.00000000000000
 T2 IN DEPOT FOR T       11314   1.00000000000000
 T2 IN DEPOT FOR T       52293   1.00000000000000
 DEPOSITION FOR  T       11314  7.343790712602957E-011  1.100634146341464E-009
 REFERENCE CONCENTRATION FOR T       11314  6.672326800884661E-002
 DEPOSITION FOR  T       49057  8.690889822173269E-011  1.100634146341464E-009
 REFERENCE CONCENTRATION FOR T       49057  7.896256763486770E-002
 DEPOSITION FOR  T       52293  1.011742873470691E-010  1.100634146341464E-009
 REFERENCE CONCENTRATION FOR T       52293  9.192363119332166E-002
===============================================

As you can see from above, the deposition for mud at node 11314 is 7.343790712602957E-011 but the erosion at the same location is 1.596816358033108E-004.

I looked at the subroutine SUSPENSION_DEPOT and I found T2 is the RATIO BETWEEN REFERENCE CONC. ON BOTTOM AND MEAN CONC. For sand, T2 has very large values but for mud it's just 1. If I use large T2 values for mud I could get lower mud concentration. Why do you assume the UNIFORM SEDIMENT ALONG THE VERTICAL for mud concentration and set T2 to 1?

Kind regards,
Qilong

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Deposition Computation 12 years 2 months ago #5436

qilong
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Expert Boarder
Posts: 340
Thank you received: 33

Hello,

I've tested the other values for T2. This time I let the subroutine SUSPENSION_ROUSE calculate T2 values for mud. It turned out that the calculated T2 values for mud are small. I think it's caused by the characteristic of mud.

T2 IN DEPOT FOR T 49057 1.58023085694677
T2 IN DEPOT FOR T 11314 1.81208874810568
T2 IN DEPOT FOR T 52293 2.15173480889725

So the result didn't change so much and the concentration was still too high.

I also tried to set T2 for mud to 1000. The result still didn't change. Then I found in the subroutine SUSPENSION_DEPOT, T2 doesn't affect the calculation of deposition for mud. Why setting T2 to 1 after the calculation of mud deposition?

Kind regards,
Qilong

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Deposition Computation 12 years 2 months ago #5449

cath OFFLINE Moderator Posts: 52 Thank you received: 24	Hello, just a quick answer to your previous question: the ratio between the mean concentration to the near bed concentration is calculated assuming a Rouse profile. For fine sediments (mud type) the Rouse number ws/ku* is very small so the concentration profile is nearly uniform. That is why it is assumed T2=1. Best regards, Cath
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Deposition Computation 12 years 2 months ago #5450

qilong OFFLINE Expert Boarder Posts: 340 Thank you received: 33	Thanks for your help, Cath! Best regards, Qilong
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