Product(s):	OpenFlows FLOOD
Version(s):	10.03.XX.XX
Area:	Modeling

Overview

This article describes the setup of OpenFlows FLOOD's MOHID Water engine to simulate a submarine outfall plume dispersion. The 3D coastal hydrodynamics MOHID Water engine can simulate submarine outfall plume dispersion using a near field/far field approach. The near field relates to the initial dilution/mixing of the effluent discharge as it leaves the diffusors forms a plume. The time scale for this process is much smaller (seconds to few minutes). The far field relates to the plume dynamics once initial dilution is achieve and the plume is in equilibrium with the ambient hydrodynamics. The article focus on the setup of the near field module (MOHID Jet) and assumes the user already has successfully setup and computed a 3D hydrodynamic solution and a Lagrangian (far field) simulation. 

Solution

To simulate the submarine outfall plume, first setup the Lagrangian module. Below is a simple example of the setup of an "origin". An origin is the discharge source. You need to set parameters relative to a submarine outfall such as it being a continuous point discharge, its location, its turbulent mixing parameters, the flow rate (fixed or variable), the Lagrangian particles volume and emission rate, etc. You also need to define the temperature and salinity of the effluent. You can also (not shown in this example) set the ambient temperature and salinity either directly in the Lagrangian setup or (if ommited) from the WaterProperties module. 

<BeginOrigin>

ORIGIN_NAME                 : Submarine outfall

EMISSION_SPATIAL        :  Point

EMISSION_TEMPORAL  : Continuous

POSITION_COORDINATES : -9.366 39.343

MOVEMENT                     : SullivanAllen

VARVELHX                       : 0.2

VARVELH                         :  0.05

TURB_V                           : Constant

VARVELVX                       : 0.02

VARVELV                         : 0.005 

DT_EMIT                           : 60 !emission frequency, e.g. every 60 seconds

NBR_PARTIC                    : 10 !number of particles emitted in each emission

FLOW                                : 0.5  !flow in m3/s

...

<<BeginProperty>>

NAME                          : temperature

UNITS                          : degC

CONCENTRATION      : 21

<<EndProperty>>

<<BeginProperty>>

NAME                        : salinity

UNITS                        : psu

CONCENTRATION    : 0.1

<<EndProperty>>

<EndOrigin>

To setup the near field module options, still inside the block <BeginOrigin>/<EndOrigin>.you'll need to define the submarine outfall parameters by adding the following keywords: 

COMPUTE_PLUME           : 1   !activates the near field model (0/1)

JET_DATA_FILE                : ..\General Data\Outfall\Outfall.dat   !path to the outfall characteristics

JET_DT                              : 600.   !run near field model every 600 seconds

Then create a text file in the path defined by the JET_DATA_FILE keyword, and add the following keywords: 

PORT_DIAMETER             : 0.1  -> Diameter of each port (m)

PORT_BOTTOM_DISTANCE      : 0.5      -> Port distance from the bottom (m)

PORT_ANGLE_XY             : 90  -> Port horizontal angle (º)*

PORT_ANGLE_HZ             : 0  -> Port vertical angle (º)**

OUTFALL_LENGTH            : 100       -> Outfall length (m)

OUTFALL_ANGLE             : 180       -> Outfall angle (º)*

PORTS_NUMBER             : 50    -> Number of ports

*Angle with XX axis (0º = East, 90º = North)

** Angle with bottom (0º = parallel to bottom, 90º = perpendicular to bottom)

Then run the simulation and a results file will be written in the "res" folder of your domain. The name of the file is the name of the origin with an extension ".jet". The output file contains the initial dilution, and position of the plume and concentration in the equilibrium with ambient water.