Different answer using ODE45 and symbolic solve
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I've been working through a problem using 2 different methods to solve the time required to reach 135C. One uses ode45 where I iterate through and find that its roughly 162.6 seconds but when I try a different method using symbolic int and solve I get 170 seconds. I can't figure out what's causing the different results.
tspan = [0:0.1:180]
y_0=25
[t T] = ode45(@odefun,tspan,y_0)
Temp=T(1627,1)
time=t(1627,1) % using ode45
time_2=answer_2() % using symbolic solve
function dtdT = odefun(t,T)
A=0.04;
l=0.007;
V=A*l;
h=10;
q_h=1.25*10^4;
sigma = 5.67*10^-8;
C=900;
p=2800;
e=0.80;
T_i=25;
B=(q_h - h*(T-T_i) - ( e*sigma*(T^4 - T_i^4)));
D=A/(V*C*p);
dtdT = D*B;
end
function A=answer_2()
syms t
A=0.04;
l=0.007;
V=A*l;
h=10;
q_h=1.25*10^4;
sigma = 5.67*10^-8;
C=900;
p=2800;
e=0.80;
T_i=25;
T=135;
B=(q_h - h*(T-T_i) - ( e*sigma*(T^4 - T_i^4)));
D=A/(V*C*p);
Solution = double(solve( T-T_i == (D*int(B,t,0,t)),t));
A=Solution;
end
采纳的回答
Torsten
2018-10-29
0 个投票
What make you think the two problem formulations are equivalent ?
Symbolically you solve an algebraic equation while numerically, you solve an ordinary differential equation.
Use "dsolve" instead of "solve" in the symbolic part.
Best wishes
Torsten.
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