"Matthew" wrote in message <email@example.com>... > I removed the abs and signs by putting a constant low flow rate just to see if it would work. However it doesn't make any change it still stops at the same point.
I solved your problem with another software and it worked without problems.
The problem with ODE15s seems to be the abrupt change of the variables in the time span from t=0.95 to t=1. This is caused by the parameter Av.
A remedy (I also used within my ODE integrator) is to call ODE15s seperately for the time span from t=0 to t=0.05, then from t=0.05 to t=0.95 and then from t=0.95 to t=1. Do it in a loop and set the inital conditions of the variables for a new time span to the final values of the variables from the preceeding time span.