Module Lagrangian
From MohidWiki
Overview
Lagrangian transport models are very useful to simulate localized processes with sharp gradients (submarine outfalls, sediment erosion due to dredging works, hydrodynamic calibration, oil dispersion, etc.). MOHID’s Lagrangian module uses the concept of lagrangian tracers. The most important property of a tracer is its position (x,y,z). For a physicist a tracer can be a water mass, for a geologist it can be a sediment particle or a group of sediment particles and for a chemist it can be a molecule or a group of molecules. A biologist can spot phytoplankton cells in a tracer (at the bottom of the food chain) as well as a shark (at the top of the food chain), which means that a model of this kind can simulate a wide spectrum of processes. The movement of the tracers can be influenced by the velocity field from the hydrodynamic module, by the wind from the surface module, by the spreading velocity from oil dispersion module and by random velocity. At the present stage the model is able to simulate oil dispersion, water quality processes and sediment transport. To simulate oil dispersion the lagrangian module interacts with the oil dispersion module, to simulate water quality the lagrangian module uses the water quality module. Sediment transport can be associated directly to the tracers using the concept of settling velocity. Another feature of the lagrangian transport model is the ability to calculate residence time. This can be very useful when studying the exchange of water masses in bays or estuaries.
Concepts
Like referred above, the Lagrangian module uses the concept of tracer. The tracers are characterized by there spatial coordinates, volume and a list of properties (each with a given concentration). The properties can be the same one like the ones described in the water properties module or coliform bacteria. Each tracer has associated a time to perform the random movement. The tracers are “born” at origins. Tracers which belong to the same origin have the same list of properties and use the same parameters for random walk, coliform decay, etc. Origins can differ in the way they emit tracers.
There are three different ways to define origins in space:
- a Point Origin emits tracers at a given point;
- a Box Origin emits tracers over a given area;
- a Accident Origin emit tracers in a circular form around a point;
There are two different ways in which origins can emit tracers in time:
- a Continuous Origin emits tracers during a period of time;
- a Instantaneous Origin emits tracers at one instant;
- a Moving Origin emits tracers during a period of time along a defined track;
Origins can be grouped together in Groups. Origins which belong to the same group are grouped together in the output file, so it is more easy to analyze the results.
Main processes
Tracer Movement
Turbulent Diffusion
Residence Time
Monitor boxes
Oil spills
Water quality processes
To use the Water Quality processes in the lagrangian module it is necessary to define a WaterQuality.dat file different from the one used for the eulerian calculations. Defining its location by the keyword WQM_DATA_FILE.
The waterquality files need to include the different parameters separately in two files in the case that both waterquality processes are calculated.
Larvae
To model larvae as lagrangian properties it is necessary to configure the properties larvae, age and oxygen in the lagrangian file
<BeginOrigin> ORIGIN_NAME : Generic EMISSION_SPATIAL : Box EMISSION_TEMPORAL : Instantaneous MOVEMENT : NotRandom ADVECTION : 1 BOX_NUMBER : 1 BOXVOLINIC : 10000 OLD : 0 WQM_DATA_FILE : ..\..\Test\data\WaterQuality_3.dat <<BeginProperty>> NAME : larvae UNITS : kg/m3 CONCENTRATION : 10e4 MIN_CONCENTRATION : 0.0 AMBIENT_CONC : 0.0 <<EndProperty>> <<BeginProperty>> NAME : age UNITS : --- CONCENTRATION : 5.6 MIN_CONCENTRATION : 0. AMBIENT_CONC : 0.0 <<EndProperty>> <<BeginProperty>> NAME : oxygen UNITS : mg/l CONCENTRATION : 10. MIN_CONCENTRATION : 0.0 AMBIENT_CONC : 10.0 <<EndProperty>> <EndOrigin>
Ecology
First order decayment (coliform bacteria)
Sediment transport
Contaminants/Partition coefficients
Other features
User manual
Setup
Add in nomfich.dat
PARTIC_DATA : ../../WestIberia_ET2_2K4/Portugal/data/Lagrangian_1.dat PARTIC_HDF : ../../WestIberia_ET2_2K4/Portugal/res/Lagrangian_1.hdf PARTIC_FIN : ../../WestIberia_ET2_2K4/Portugal/res/Lagrangian_1.fin
Add in model.dat
LAGRANGIAN : 1
Create Lagrangian.dat
OUTPUT_TIME : 0 3600 OUTPUT_MAX_TRACER : 1 OUTPUT_CONC : 2 DT_PARTIC : 60 <BeginOrigin> ORIGIN_NAME : Off Vigo GROUP_ID : 1 EMISSION_SPATIAL : Point EMISSION_TEMPORAL : Instantaneous BOTTOM_EMISSION : 0 OLD : 0 POINT_VOLUME : 1 NBR_PARTIC : 8 FLOAT : 1 MOVEMENT : SullivanAllen VARVELHX : 0.1 VARVELH : 0.03 TURB_V : Constant VARVELVX : 0.01 VARVELV : 0.003 POSITION_COORDINATES : -10.0 43 !POSITION_CELLS : 45.5 21.5 DEPTH_METERS : 0. START_PARTIC_EMIT : 2007 04 25 09 33 20 <EndOrigin>
