Page 387 - ExtendSim User Guide

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Storage and Units 361
Capacity
Tank
Acts as a source, intermediate storage, or final storage (sink). The block has a capac- ity and can have an initial quantity of flow for the simulation.
Changing the flow unit group
Change Units
Changes the flow unit from one unit to another, resulting in a new flow unit group. The dialog has a field for entering the conversion factor and a popup menu for indicat- ing the direction of the change.
Capacity
The Tank, Interchange, and Convey Flow blocks are considered residence blocks. This means that they have capacity and can hold defined amounts of flow as time advances.
A residence block's maximum capacity can be a specific number or, in the case of the Tank or Interchange blocks, it can be set to infinite.
Full and not-full
When a residence block’s capacity is finite, its status can alternate between the full and not-full states. This change of state has an impact on the model's set of effective rates:
• If a residence block with finite capacity is not full, there is room for the flow level to rise. Consequently, the effective inflow rate can be greater than the effective outflow rate.
• If a residence block with finite capacity is full, the flow level is not permitted to rise; the effective inflow rate will be less than or equal to the effective outflow rate.
Any time a residence block with a finite capacity changes state between full and not-full, ExtendSim will calculate a new set of effective rates.
☞ A residence block with infinite capacity can never be full during the simulation run. In this sit- uation, it is similar to a residence block with finite capacity that is not full; its effective inflow rate can be greater than its effective outflow rate.
Tank block’s capacity
A Tank can be a source of flow, an interme- diate storage for flow, or a final storage for flow (sink). A Tank’s capacity can be infinite, a finite but non-zero number, or zero.
Default setting for Tank’s capacity
• Bydefault,theTankhasaninfinitecapacitytoholdflow,asindicatedbytheMaximum capacity: infinite setting in its dialog. In this state it will never be full.
☞ A blank is the same as checking the infinite setting.
• ATank’smaximumcapacitycanbechangedintheblock’sdialogbyenteringanamountin the Maximum capacity field (which unselects the checkbox). It can also be changed dynamically through the block’s C (capacity) value input connector. If the C connector is used, it overrides any entries made in the dialog. With a non-zero finite capacity, the Tank can be in either the full or not-full state at any point in time.
Discrete Rate
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