coheceive sediment concentration negative error

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gegujang@lycos.co.kr
MOHID User
Posts: 20
Joined: Thu Jan 01, 1970 00:00

coheceive sediment concentration negative error

Postby gegujang@lycos.co.kr » Tue Jun 21, 2005 07:42

It's so hard to define InterfaceSedimentWater and Free vertical movement

My InterfaceSedimentWater.dat

<begin_rugosity>
INITIALIZATION_METHOD : CONSTANT
DEFAULTVALUE : 0.0025
<end_rugosity>

<begin_critical_shear_erosion>
INITIALIZATION_METHOD : CONSTANT
DEFAULTVALUE : 0.05
<end_critical_shear_erosion>

<begin_critical_shear_deposition>
INITIALIZATION_METHOD : CONSTANT
DEFAULTVALUE : 0.02
<end_critical_shear_deposition>

<begin_erosion_rate>
INITIALIZATION_METHOD : CONSTANT
DEFAULTVALUE : 0.00005
<end_erosion_rate>

<beginproperty>
NAME : cohesive sediment
UNITS : kg/m2
DESCRIPTION : cohesive sediment mass
PARTICULATE : 1
WATER_FLUXES : 1
EROSION : 1
DEPOSITION : 1
MASS_LIMITATION : 1
MASS_MIN : 1e-8
INITIALIZATION_METHOD : CONSTANT
DEFAULTVALUE : 10.
TIME_SERIE : 1
BOX_TIME_SERIE : 0
OUTPUT_HDF : 1
<endproperty>


And Free Vertical Movement.dat

<beginproperty>
NAME : cohesive sediment
WS_TYPE : 2
SALTINT : 1
SALTINTVALUE : 3
CHS : 4
KL : .006
KL1 : .01
ML : 4.65
M : 1
FREEVERT_IMPEXP_ADV : 0
WS_VALUE : 0.00001
<endproperty>

Why coheceive sediment conc. negative In 75 116 1 cell error message accur?


I am working model for 1 years.

Model calc Dt = 60sec

Saving Time = 1days

luis_at_mohid.com
MOHID Developer
Posts: 553
Joined: Thu Jan 01, 1970 00:00
Location: Instituto Superior Técnico - Technical University of Lisbon
Contact:

Postby luis_at_mohid.com » Tue Jun 21, 2005 08:15

Hi,

Well, no one has ever said it's easy to model sediment transport :D
The probable cause for your problem is the time step.
What is the horizontal resolution of your model?
What are the maximum velocities in your domain?
Reduce your time step in order to reduce the Courant number for transport. You can also compute cohesive sediment transport (advection-diffusion) using an implicit time discretization (ADVECTION_H_IMP_EXP : 0 in the cohesive sediment property block in WaterProperties input data file) , which can also help.
Also, you should have some idea (from data or calibration) of the critical shear stresses for deposition and erosion, reference rates for erosion, and settling velocity.

Hope this helps,
Luis


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