Indentifying Overconstrained Models

Models typically fail due to over constraint caused by pipes lacking a pressure reference at either end. This happens when both connected nodes try to control the flow.

Common problematic configurations include:

• Two flow-defined nodes connected directly

• Known flow node connected to a Design-mode flow control valve

• Design-mode flow control valve connected to a flow orifice

Solution: Ensure that at least one node in each pipe connection provides a pressure reference.

In most cases, models fail to converge due to over constraint. This is typically encountered when one of the pipe component in the model do not have a pressure basis for either its inlet or outlet.

Such a case happen when both nodes connected to the pipe applies flow as a definition.

Example configurations are:

• Connection to both known flow nodes

• Known flow node connected to Design case flow control valve

• Design case flow control valve to size for flow orifice