I did not understand what the problem is ?
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R=8.314/32;
T0=2930;
a=(12)/((2.027*10^6)^0.45);
rhoP=1920;
Astar=pi*0.25^2;
k=1.35;
n=0.45;
P0=101325;
v0=pi*rp^2*8;
%syms P(t)
%at beginning of the integration set initial values for the persistent variables
rp=0.35; %initial port radius
t1=0; %initial time step
dP=@(t,P)Fun(t,P,R,T0,rp,a,n,Ab,P0,rhoP,Astar,k,v0);%@(t,P)(Ab.*a.*P.^n.*(rhoP-rhoO)-P.*Astar.*sqrt(k/(R.*T0)).*(2/(k+1)).^((k+1)/(2.*(k-1)))).*R.*T0./v0;
[t,P]=ode45(dP, [0,0.1], P0);
figure(1)
plot(t,y)
xlabel("Time (s)")
ylabel("Chamber Pressure (Pa)")
title("Chamber Pressure vs Time (Start-Up)")
dP=@(t1,P)Fun(t,P,R,T0,rp,a,n,t1,Ab,P0,rhoP,Astar,k,v0);%@(t,P)(Ab.*a.*P.^n.*(rhoP-rhoO)-P.*Astar.*sqrt(k/(R.*T0)).*(2/(k+1)).^((k+1)/(2.*(k-1)))).*R.*T0./v0;
[t,P]=ode45(dP, [0,60], P0);
figure(2)
plot(t,y)
xlabel("Time (s)")
ylabel("Chamber Pressure (Pa)")
title("Chamber Pressure vs Time ")
function dP = Fun(t,P,Ab,R,T0,rp,a,n,rhoP,Astar,k)
if t==0
rp=0.35;
end
Ab=2*pi*rp*8;
rhoO=P/(R*T0);
if rp>=0.7
Ab=0;
end
v0=pi*rp^2*8;
t1=t;
rp=min(rp+((a*P^n)*10^-3)*(t-t1),0.7);
Ab=2*pi*rp*8;
dP = (Ab.*a.*P.^n.*(rhoP-rhoO)-P.*Astar.*sqrt(k/(R.*T0)).*(2/(k+1)).^((k+1)/(2.*(k-1)))).*R.*T0./v0;
end
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in HW08A (line 15)
[t,P]=ode45(dP, [0,0.1], P0);
1 个评论
darova
2019-11-3
Try
[t,P]=ode45(@(t1,P)Fun(t,P,R,T0,rp,a,n,t1,Ab,P0,rhoP,Astar,k,v0), [0,60], P0);
Also you can use nested function to get rid of number of arguments
function main
% constants
[t,y] = ode45(@Fun,ts,p0);
% plot ...
function dP = Fun(t,P)
% do stuff
end
end
回答(1 个)
Cris LaPierre
2019-11-4
Not sure there is enough info for us to know either. Some observations, though.
- You use variable rp before you define it. That is causing an error.
- You use the variable Ab as an input to the function, but only define it inside the function. You must consider variable scope.
- You call the function Fun twice but each time you use different input arguments. You must call it with exactly the same inputs that you defined it with.
- You plot t vs y, but y does not exist. Do you mean P?
It appears you are a little unsure of what you are doing. It might be good to find an example in the documentation that you can adapt to fit your needs. It would definitely be a good idea to get some more practice with creating and using functions.
Here's what I could do to get your code to run.
R=8.314/32;
T0=2930;
a=(12)/((2.027*10^6)^0.45);
rhoP=1920;
Astar=pi*0.25^2;
k=1.35;
n=0.45;
rp=0.35; %initial port radius
%at beginning of the integration set initial values for the persistent variables
P0=101325;
t1=0; %initial time step
dP=@(t,P)Fun(t,P,R,T0,rp,a,n,rhoP,Astar,k);
[t,P]=ode45(dP, [0,0.1], P0);
plot(t,P)
xlabel("Time (s)")
ylabel("Chamber Pressure (Pa)")
title("Chamber Pressure vs Time (Start-Up)")
[t,P]=ode45(dP, [0,60], P0);
figure
plot(t,P)
xlabel("Time (s)")
ylabel("Chamber Pressure (Pa)")
title("Chamber Pressure vs Time ")
function dP = Fun(t,P,R,T0,rp,a,n,rhoP,Astar,k)
if t==0
rp=0.35;
end
Ab=2*pi*rp*8;
rhoO=P/(R*T0);
if rp>=0.7
Ab=0;
end
v0=pi*rp^2*8;
t1=t;
rp=min(rp+((a*P^n)*10^-3)*(t-t1),0.7);
Ab=2*pi*rp*8;
dP = (Ab.*a.*P.^n.*(rhoP-rhoO)-P.*Astar.*sqrt(k/(R.*T0)).*(2/(k+1)).^((k+1)/(2.*(k-1)))).*R.*T0./v0;
end
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