The transport block is not really a block but a sub-system. It is used to automatically generate a chain of compartments for one dimensional transport.
There are three components to a transport block:
When a transport sub-system is created the begin, end and N blocks are added automatically. The transport chain is defined by connecting the begin and end blocks with transfers. The begin block will be duplicated (N-1) times, where N is the number of discretizations.
From the Projects window
From the Model window
From the Blocks window
The transport sub-system is edited the same way as a normal sub-system. You can add expressions, parameters and other blocks to it the same way as you would in an ordinary sub-system.
Consider a vertical transport from a source, via a layered media, to a sink. The model is implemented with a transport sub-system according to the matrix below.
Source | Input | |||
Begin | TC | |||
End | Out | |||
N | ||||
Sink |
Where
The corresponding matrix, during simulation, looks like this:
Source | Input | |||||
Begin | TC | |||||
Begin | TC | |||||
Begin | TC | |||||
Begin | TC | |||||
End | Out | |||||
Sink |
A common use for the transport sub-system is to model vertical transport through a media with advection and diffusion. This example shows transport from a top soil layer (implemented as a compartment), through several layers of soil (implemented as a transport sub-system) to a ground water compartment.
Top soil | Advection\\ \\ Diffusion | |||
Diffusion | Begin | Advection\\ \\ Diffusion | ||
Diffusion | End | Advection\\ \\ Diffusion |
||
N | ||||
Ground water |
Where
The corresponding matrix, during simulation, looks like this:
Top soil | Advection\\ \\ Diffusion | |||||
Diffusion | Begin | Advection\\ \\ Diffusion | ||||
Diffusion | Begin | Advection\\ \\ Diffusion | ||||
Diffusion | Begin | Advection\\ \\ Diffusion | ||||
Diffusion | Begin | Advection\\ \\ Diffusion | ||||
Diffusion | End | Advection\\ \\ Diffusion |
||||
Diffusion | Ground water |
Within the transport, the compartments must be homogenous. This means that each “layer” must have the same size and that all the transfers expressions betweeen layers must be identical.
Another limitation is that only the begin and end compartment are available as outputs or when connecting the transport to other objects of a model.
To calculate the mean or total inventory of each transport layer you can use a Transport operation block.