Why solution of this equation is linear in simulink

I have formulated the following equation.

 dP/dt = (-v/V)P..... first order differential equation..

 If i will solve this equation then solution of this equation is as given below

P = Po * exp(-vt/V).. where Po is initial condition at t = 0.

 above differential equation is giving pressure decay in constant volume tank. Hence as per solution of this equation pressure is decreasing exponentially in the tank when valve is open.

 But when i made a model in simulink which represented by above equation then P is decreasing linearly.

 Can anybody tell me why  simulink is giving linear decay in pressure.

Regards Jeevan patil

Answer 1

[Titus Edelhofer]

Hi,

hmm, the answer probably is "because you made an error while implementing the model", but I guess this is something you already know, don't you? Without seeing your model or at least a verbal description of your model it's hard to give advice.

Titus

Answer 2

[bimal raj]

there could be an error in the model..plz check it

if no mistakes , go to the configuration , solver options, change 'type' to 'fixed step' and step size to a lower value (depends on the time constant of you model).