modelFiniteEscapeTime
Extends from NonlinearSolverFailureInitial (Nonlinear system of equations has no solutions).
Information
This model describes a simple hydraulic system with a pump, followed by a valve, which fills a reservoir.
As the reservoir level increase, the flow rate w_pump goes to zero. When it does, the energy balance equation causes the specific enthalpy h1, and thus the temperature T1, to go to infinity. The temperature T1 is the input of a first-order linear system, representing the temperature sensor dynamics. If a variable step-size solver with error control is used, it will try to compute the state trajectory, which also goes to infinity, so the solver eventually gets stuck at time t = 664.
The debugger should identify the state variable (Ts, in this case) whose error estimate is causing the step size to be reduced, then suggest the user to look at how its derivative der(Ts) is computed. It will be shown that it depends on T1, which goes to infinity. T1 in turn depends on h1, which also goes to infinity. Finally, h1 depends on the energy balance equation, which depends on w_pump - at that point it will become apparent that as the flow rate w_pump goes to zero, the model wil become ill-posed. The solution in this case is to change the pump model, by adding to the energy balance some dynamic energy storage and/or some heat transfer to the ambient.