Sediment Transport with Particle Tracking

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Particle Tracking

The TUFLOW Particle Tracking Module (PTM) allows the 2D or 3D simulation of discrete Lagrangian particles as they are transported by the flow field (or other drivers such as wind or waves). Particle behavior such as settling, buoyancy, decay, sedimentation and re-suspension can all be simulated. It can be run in conjunction with the sediment transport module to simulated the fate and age of sediment particles within the hydraulic model.

In this optional exercise we will take the existing FMA2_SED_002 model and add some particle tracking to track the input of particles.

Copy and paste the existing FMA2_SED_003.fvc file and rename as FMA2_SED_002a.fvc.

Under the Sediment Files Block add the following particle tracking block to reference a particle tracking file that we will generate.

Particle Tracking Control File == FMA2_SED_002a.fvptm	

In the output commands block, under the current specification for the XMDF file add the following block to output results to a netcdf file. This will output hydraulic parameters, sediment transport parameters as well as results from the particle tracking module.

output == netcdf
      output parameters == h,v,d, Rhow, Taub, TauC, PTM_1
      output interval == 900.
end output

Save and close the file.

Generate a new file called FMA2_SED_002a.fvptm. This is where we will generate the characteristics of our particle tracking module. We will use the same sediment characteristics that we have already applied to the sediment transport model. Add the following commands

! PTM to assess fate of STP plume - TEST POLYGON SEEDING
! use nodestring definition from HD model to allow particles to leave model domain. 
open boundary nodestring == 2  ! downstream tidal boundary
lagrangian timestep == 120. ! seconds
eulerian timestep == 120. ! seconds
! Sediment Transport COMMANDS (required if a particle group interacts with bed)
bed roughness model == ks
bed roughness parameters == 0.01,0.01	! ksc, ksw
Nscalar == 1
Group == fineSed
d50 == 0.000002
      particle density == 2650
      Settling model == constant
      settling parameters == 0.0002 !(m/s)
      deposition model == ws0
      Erosion Model == Mehta	
      Erosion parameters == 0.1, 0.5, 0.5 !Er, taucr, alpha
      initial scalar mass == 10000
End Group
! This is required due to adding deposition and settling.
Material == 0
      Layer == 1
            dry density == 1890.,1890	
      End layer
end material
seed particles == point,  10780,8292
      particle groups == fineSed
      timeseries file ==  ..\bc_dbase\sediment.csv
      timeseries header == Date,fineSed
end seed
output dir == ..\results\
output == ptm_netcdf
      output groups == all
      output parameters == age, state_age, mass, uvw, uvw_water, depth, water_depth
      output interval == 900.
end output

Save and close the file.

We will use the same FMA2_SED_002.fvsed file as the original model with no particle tracking functionality..

Copy and paste the Sediment.csv from the Module folder to the bc_dbase folder. This contains the time series flux for the fine sediment group with a value of 1000g/s.

Sediment PT.PNG

The number of particles per second is equal to:-

Time Series Mass (g/s)/Initial Scalar Mass (g)

The initial scalar mass defined in our particle group settings is 1000g. Therefore the number of particles released per second is:-

1000/10000=0.1 particles per second. Over the 10 hour release period, this equates to 3600 particles being released in total.

Update the batch file and run FMA2_SED_002a.fvc. Once the simulation is complete, use the instructions below to review the particle tracking outputs:-

Plot and animate the particles against the Net Sediment Rate map we generated here. You'll see that the bulk of the fine sediment gets washed out of the model into the ocean. A few particles are deposited on areas which subsequently become dry. Other sediment particles are deposited onto the bed. The particle tracking module provides additional information to the sediment transport module and provides a different aspect of analysis of sediment transport which is useful for assessing contaminated sediments amongst others.

FMA002 PTa.gif