Set off differential Equations in Simulink

1. Apr 2, 2009

rem88

hi,

I have a problem where i am trying to model a change in X (biomass) over time, its a growth of biomass over time.

I have three equations that are linked

The first for Biomass is

dX/dt = [0.25*S/(0.005 + S)]X - (X/V)*dv/dt

Where dv/dt = 529.68*EXP(0.177t)

and ds/dt = 120.37*EXP(0.177t) - 0.074.

I tried doing the equation for S seperatly, i used a clock and gain into a math function (e^u), then mulitplied by another gain of 529.68. So this gave a change in S over time. I then linked this into the formula for dX/dt.

I did the same for dV/dt. but when i plot the graph all i see is a straight line, when it should be expontenitial growth which levels off.

And to simplify things i kept V constant as 2772.3 for now (for x/v)

I would appreciate any help as i have been stuck on this for ages.

Thanks.