1D Transient Diffusion (MATLAB code)

clear; clc;% clear the screen and memory

Nx=500; %number of space nodes

Nt=10000; %number of time nodes

Lx=0.3; %length of space (m)

Lt=10; %length of physical time (s)

dx=Lx/(Nx-1); %grid spacing

dt=Lt/(Nt-1); %time step

c=0.000097; %speed of wave (constant)

a=c*dt/dx.^2;

u=100*ones(Nx,1); %initialization of matrix for the property under investigation

x=zeros(Nx,1); %initialization of space

for i=1:Nx-1 %space loop

    x(i+1)=x(i)+dx;

end

u(1)=-20; %boundary condition

u(Nx)=50; %boundary condition

for t=0:dt:Lt %time loop

    un=u; %u(i,t)

    for i=2:Nx-1 %solution loop, backward in space forward in time

        u(i)=((1-2*a)*un(i))+a*(un(i+1)+un(i-1)); %discretized equation, u(i,t+1)

    end

    plot(x,u) %plotting

    title({t;'Time Elaplsed (s)'},'FontSize',38.5);

    pause(0.001)

end

 

 

1D non-Linear Convection (MATLAB code)

clear; clc;% clear the screen and memory

Nx=41; %number of space nodes

Nt=82; %number of time nodes

Lx=2; %length of space (m)

Lt=1; %length of time (s)

dx=Lx/(Nx-1); %grid spacing

dt=Lt/(Nt-1); %time step

a=dt/dx;

u=ones(Nx,1); %initialization of solution matrix

x=zeros(Nx,1); %initialization of space

hold on

for i=1:Nx-1 %space loop

    x(i+1)=x(i)+dx;

end

for i=0.5/dx:1/dx %initial conditions

    u(i)=2;

end

for t=1:Nt %time loop

    un=u; %u(i,t)

    for i=2:Nx %solution loop, backward in space forward in time

        u(i)=un(i)-u(i)*a*(un(i)-un(i-1)); %discretized equation, u(i,t+1)

    end

    plot(x,u,'k') %plotting

    pause(0.1)

end

1D Linear Convection (MATLAB code) (Updated with CFL condition)

clear; clc;% clear the screen and memory

Nx=41; %number of space nodes

Nt=82; %number of time nodes

Lx=2; %length of space (m)

Lt=1; %length of time (s)

dx=Lx/(Nx-1); %grid spacing

dt=Lt/(Nt-1); %time step

c=2; %speed of wave (constant)

a=c*dt/dx;

u=ones(Nx,1); %initialization of solution matrix

x=zeros(Nx,1); %initialization of space

hold on

for i=1:Nx-1 %space loop

    x(i+1)=x(i)+dx;

end

for i=0.5/dx:1/dx %initial conditions

    u(i)=2;

end

for t=1:Nt %time loop

    un=u; %u(i,t)

    for i=2:Nx %solution loop, backward in space forward in time

        u(i)=un(i)-a*(un(i)-un(i-1)); %discretized equation, u(i,t+1)

    end

    plot(x,u,'k') %plotting

    pause(0.1)

end



New Code, with the CFL condition satisfied.

clear; clc;% clear the screen and memory

Nx=13; %number of space nodes

Lx=2; %length of space (m)

Lt=1; %length of time (s)

dx=Lx/(Nx-1); %grid spacing

c=2; %speed of wave (constant)

dt=dx*0.1/c; %time step, Courant number = 0.1

Nt=(Lt/dt)+1; %number of time nodes

a=c*dt/dx;

u=ones(Nx,1); %initialization of solution matrix

x=zeros(Nx,1); %initialization of space

t=zeros(fix(Nt),1); %initialization of space

hold on

for i=1:Nt-1

    t(i+1)=t(i)+dt;

end

for i=1:Nx-1 %space loop

    x(i+1)=x(i)+dx;

end

for i=0.5/dx:1/dx %initial conditions

    u(i)=2;

end

for j=0:dt:Lt %time loop

    un=u; %u(i,t)

    for i=2:Nx %solution loop, backward in space forward in time

        u(i)=un(i)-a*(un(i)-un(i-1)); %discretized equation, u(i,t+1)

    end

    plot(x,u,'k') %plotting

    pause(0.1)

end