# Euler 's Method for falling velocity ode..

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James 2020 年 6 月 1 日
コメント済み: James 2020 年 6 月 1 日
Mass = 100/6*pi*0.04^3;
g=9.8;
A=0.25*pi*0.04^2;
U=0.0001;
dt = 0.01;
for t=0:dt:15-dt
Re = 1.25*0.04*U/0.000015;
CD=24./Re+(2.6*Re/5)./(1+(Re/5).^1.52)+(0.411*(Re/263000).^(-7.94))./(1+(Re/263000).^(-8))+(0.25*Re/10^6)./(1+Re/10^6);
dUdt = g - (0.5*1.25*U(end)^2*A*CD)/Mass
U(end+1)=U(end)+dUdt*dt
end
plot(0:dt:15, U)
error occurs in "U(end+1)=U(end)+dUdt*dt" sentence
I can't find any problem... Could you find problem in this code? I think 'Re' and 'CD' also looks doubtful..

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### 採用された回答

Sugar Daddy 2020 年 6 月 1 日
Mass = 100/6*pi*0.04^3;
g=9.8;
A=0.25*pi*0.04^2;
U=0.0001;
dt = 0.01;
for t=0:dt:15-dt
Error is in this line as the U size increase Re size increases so put U(end) here too
% Re = 1.25*0.04*U/0.000015; % Error
Re = 1.25*0.04*U(end)/0.000015; % Correct
CD=24./Re+(2.6*Re/5)./(1+(Re/5).^1.52)+(0.411*(Re/263000).^(-7.94))./(1+(Re/263000).^(-8))+(0.25*Re/10^6)./(1+Re/10^6);
dUdt = g - (0.5*1.25*U(end)^2*A*CD)/Mass
U(end+1)=U(end)+dUdt*dt
end
plot(0:dt:15, U)
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James 2020 年 6 月 1 日
thank you so much for giving me a reason!!

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