Page 399 - ExtendSim User Guide
P. 399

Upstream supply/downstream demand
This potential rate is considered when using an advanced mode in the Diverge. Merge, and Sensor blocks. It is described fully in “Upstream supply and downstream demand” on page 455.
Rate sections
A rate section is defined as a network of con- nected blocks, all possessing the same effective rate. Each rate section can include a succession of blocks and connections. A rate section always starts with an outflow connector and ends somewhere downstream with an inflow connector. Thus it will always contain at least two blocks sharing at least one flow connection.
Two rate sections in a model
While some blocks always define the boundary between two rate sections, other blocks never define a new rate section boundary:
• Becausearesidenceblock(ConveyItem,Interchange,orTank)canholdflowforsome period of time, its effective inflow rate can be different from its effective outflow rate. Since the boundaries between rate sections never change, residence blocks always define the boundary between two different sections, even if their effective inflow rate is the same as their effective outflow rate. For example, a Tank’s inflow connection ends one rate section and its outflow connection starts another section.
• Somepassing(non-residence)blocksdefineanewratesectionandothersdon’t.Whileflow is not permitted to be held in a passing block for any length of simulation time, some passing blocks are capable of defining boundaries between sections. For example, a Valve is part of one, and only one, rate section. On the other hand, the Change Units block's effective inflow rate will always be different than its outflow rate because it performs a unit conversion. It therefore defines the boundaries between two rate sections.
☞ All residence blocks, and certain passing blocks, always define the boundary between two dif- ferent rate sections. These boundaries are established internally by ExtendSim at the beginning of the simulation run; they do not change.
The table below lists what role each block in the Discrete Rate library plays in defining the boundaries of a rate section:
Rates, Constraints, and Movement 373
Rates, rate sections, and the LP area
Block Bias
Catch Flow Change Units
Always defines a Comments new rate section?
No The inflow effective rate is the same as the outflow effective rate. The block influences the effective rate
associated with the section it is part of.
No The outflow effective rate is the same as the catch effective rate.
Yes The outflow effective rate is the inflow effective rate multiplied by the conversion factor.
Discrete Rate

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