Array Values Not Changing Within Loop

Question

Thomas Faulkner 2020-3-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/511735-array-values-not-changing-within-loop

评论： Sriram Tadavarty 2020-3-19

Hi everyone,

I am working on a Runge Kutta code for modeling annular flow within a pipe.

I am able to plot graphs for my uR,T and Z as intended in the code, however my arrays for these values do not change from the initial values in the for loops so my graphs are simply straight lines at these values.

I believe there is something wrong with my loops.

Any help would be appreciated,

thanks.

 % Parameters & Boundary Conditions
dTdz=30.12; Ri=0.05; Ro=0.075; Rm=0.0621; hcoeff=100;  To=300; Ti=0; Zo=0; Zi=1.3*Ri*hcoeff*(Ti-To); uRi=0; uRo=0; tawi=4.3465; tawo=3.792; npoints=1000;
h=(Ro-Ri)/npoints;
r=(Ri+h:h:Ro)';
uR= zeros(npoints,1);
T= zeros(npoints,1);
Z = zeros(npoints,1);
%  Runge Kutta Function Fourth Order
for i=1:1:(npoints-1)
     T(1)=Ti;
     Z(1)=Zi;
     uR(1)= uRi;
        
     if r<Rm
         
         k1=h*dUdrI(r(i),uR(i));
         w1=h*dTdr(r(i),T(i));
         f1=h*dZdr(r(i),Z(i));
         
         k2=h*dUdrI((r(i)+h/2),(uR(i)+h*k1/2));
         w2=h*dTdr((r(i)+h/2),(T(i)+h*w1/2));
         f2=h*dZdr((r(i)+h/2),(Z(i)+h*f1/2));
         
         k3=h*dUdrI((r(i)+h/2),(uR(i)+h*k2/2));
         w3=h*dTdr((r(i)+h/2),(T(i)+h*w2/2));
         f3=h*dZdr((r(i)+h/2),(Z(i)+h*f2/2));
         
         k4=h*dUdrI((r(i)+h),(uR(i)+h*k3));
         w4=h*dTdr((r(i)+h),(T(i)+h*w3));
         f4=h*dZdr((r(i)+h),(Z(i)+h*f3));
         
         uR(i+1) = uR(i) + (k1+2*k2+2*k3+k4)/6;
         T(i+1) = T(i) + (w1+2*w2+2*w3+w4)/6;
         Z(i+1) = Z(i) + (f1+2*f2+2*f3+f4)/6;
      end
      
end
 
 for i=(npoints-1):1:1
        T(1)=To;
        Z(1)=Zo;
        uR(1)=uRo;
        if r>=Rm
            k1=h*dUdrO(r(i),uR(i));
            w1=h*dTdr(r(i),T(i));
            f1=h*dZdr(r(i),Z(i));
            
            k2=h*dUdrO((r(i)-h/2),(uR(i)-h*k1/2));
            w2=h*dTdr((r(i)-h/2),(T(i)-h*w1/2));
            f2=h*dZdr((r(i)-h/2),(Z(i)-h*f1/2));
            
            k3=h*dUdrO((r(i)-h/2),(uR(i)-h*k2/2));
            w3=h*dTdr((r(i)-h/2),(T(i)-h*w2/2));
            f3=h*dZdr((r(i)-h/2),(Z(i)-h*f2/2));
            
            k4=h*dUdrO((r(i)-h),(uR(i)-h*k3));
            w4=h*dTdr((r(i)-h),(T(i)-h*w3));
            f4=h*dZdr((r(i)-h),(Z(i)-h*f3));
            
            uR(i+1)=uR(i)+(k1+2*k2+2*k3+k4)/6;
            T(i+1)=T(i)+(w1+2*w2+2*w3+w4)/6;
            Z(i+1)=Z(i)+(f1+2*f2+2*f3+f4)/6;
            
        end
 end
 
figure, plot (r,uR)
xlabel('Radius')
ylabel('Velocity')
title('Velocity vs Radius')
figure, plot (r,T)
xlabel('Radius')
ylabel('Temperature')
title('Temperature vs Radius')
figure, plot (r,Z)
xlabel('Radius')
ylabel('Heat transfer per unit length')
title('Heat transfer per unit length vs Radius')
% Heat Transfer per Unit Length
function [dZdr_] = dZdr (r,rho,Cp,uR,dTdz)
dZdr_ = -r*rho(T)*Cp(T)*uR*dTdz;
end
 % Temperature Profile
function [dTdr_] = dTdr (Z,r,k,rho,epsilon_m)
dTdr_ = Z/(r*(k(T)+rho(T)*Cp(T)*epsilon_m(r,T,Rm,Ri,Ro,tawi,tawo)));
end 
% Velocity Profile
function [dUdrI_] = dUdrI (tawi,mu,rho,epsilon_m,Rm,r,Ri)
dUdrI_= tawi./(mu(T)+rho(T)*epsilon_m(r,T,Rm,Ri,Ro,tawi,tawo))*((Rm^2-r^2)/(Rm^2-Ri^2))*(Ri/r);
end
function [dUdrO_] = dUdrO (tawo,mu,rho,epsilon_m,r,Rm,Ro)
dUdrO_= tawo./(mu(T)+rho(T)*epsilon_m(r,T,Rm,Ri,Ro,tawi,tawo))*((r^2-Rm^2)/(Ro^2-Rm^2))*(Ro/r);
end
%eddy diffusivities of momentum
function [epsilon_m_] = epsilon_m (r,T,rm,ri,ro,tawi,tawo)
      if r<rm
        radratio=(r-ri)/(rm-ri);
        rEpsI=6.516e-4+3.9225e-1*radratio+(-6.0949e-1)*(radratio).^2+(2.3391e-1)*(radratio).^3+(1.410e-1)*(radratio).^4+(-9.6098e-2)*(radratio).^5;
        epsilon_m_=rEpsI*sqrt(tawi./rho(T))*(rm-ri);
      else
        radratio=(ro-r)/(ro-rm);
        rEpsO=6.516e-4+3.9225e-1*radratio+(-6.0949e-1)*(radratio).^2+(2.3391e-1)*(radratio).^3+(1.410e-1)*(radratio).^4+(-9.6098e-2)*(radratio).^5;
        epsilon_m_=rEpsO*sqrt(tawo./rho(T))*(ro-rm);
      end
end
     
function [Cp_]=Cp(T)
Cp_=1010.4755 + 0.1151*(T) + 4.00e-5*(T)^2;
end
function [k_]=k(T)
k_=0.0243+(6.548e-5)*(T) - (1.65e-8)*(T)^2;
end
%Dynamic Viscosity
function [mu_]=mu(T)
mu_=1.747e-5 + 4.404e-8*(T) - 1.645e-11*((T).^2);
end
function [Pr_]=Pr(T)
Pr_=0.7057*10^(2.06e-5*(T));
end
function [rho_]=rho (T)
rho_ =1e5/(287*(T));
end
function [vis_]=vis(T)
vis_=1.380e-5 + (8.955e-8)*(T) - (1.018e-10)*(T)^2;
end

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Thomas Faulkner 2020-3-19

Main_Script.m

Hi Sriram,

thanks for your response.

I have tried changing the functions many times but keep getting 'not enough input arguments' for my dUdrI functoin.

i have attached a copy of my new code.

Kind regards,

Thomas

Sriram Tadavarty 2020-3-19

在 MATLAB Online 中打开

It does complain because, function dUdrl has the following function signature

dUdrI (tawi,mu,rho,epsilon_m,Rm,r,Ri) % Implies there are 7 inputs

But you are passing only two inputs in the for loop code

k1=h*dUdrI(r(i),uR(i)); % Passing only r and uR

This is the issue for your case. You need to either update the function signature for velocity profile or send those many inputs to the function. I am not sure what is intended output with those functions.

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Array Values Not Changing Within Loop

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