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Specifying initial concentration in RMA4

Doug D

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I would like to start RMA4 with initial concentrations whose values are not the same everywhere on the mesh. Is there a way to edit the mesh (I assume edit the IC card somehow) so that initial concentrations can be selectively input by node, element, or material? I am using SMS 10.0.

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You can use the BLE (Boundary Loading by Element) Card to specify concentrations for each element. Our next version of SMS includes support for the BLE card through the interface. Unfortunatley, in SMS 10.0 you will still need to manually change the initial concentrations.

You can add a BLE card (line) to the .trn file in a text editor such as notepad. The TABS programs (RMA2 and RMA4) refer to the input lines of their parameter files as “cards”. Each card defines a parameter that affects how the model operates. In the “trn” file, an END card signifies the end of input for a single timestep. The BLE card needs to be placed before an END card. The mass, specified in a rate per second, will then be effective for that time step, and will continue at the specified rate until another BLE card is found. The BLE card requires two values as follows:

BLE Element_ID Load_In_Mass_Per_Second

Note: when editing the .trn file, make sure you use spaces between the keword and the values. Using tab characters will cause the program to crash. Also, you must specify a BLE card before the first END card even if the load is 0.0. to begin with. This informs RMA4 that loads will be coming at that element. When a mass loading is provided for RMA4, the model assumes the mass is immediately dissolved into the water contained in the specified element. The geometry of the mesh defines the constant area of the element. They hydrodynamic solution defines the water depth at any time for the element. Together they define the volume of water contained in the element. Therefore, the mass per second becomes a concentration in the element for the specified timestep.

Also, once you edit the .trn file, you won't want to resave it in SMS because SMS will strip out the BLE cards. Again, not very friendly in SMS 10.0, but much improved in our next version.

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I haven't tried using the BLT card (although for your situation it looks like it might be easier). The documentation indicates that it is used as you describe.

The tricky part will be getting the concentration to be equal in all the cells unless your element sizes are about the same and your bathymetry is flat since both these cards specify a mass/sec. I suppose you can have a ramping period at the start and allow the model to smooth out the concentrations.

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