How to modify icoFoam.C to include source term
 

Hi,

I am a novice in the use of OpenFOAM. I was wondering if anyone might be willing to help me modify icoFoam.C so that I can include a source term f, which has the form:

f = (eta)*(u_n+1 - u_n) / dt

u_n+1 and u_n are the current and previous velocities. eta is a variable defined in setFields and created in create.H. I tried the code below but I don't seem to get good results. Indeed if i choose smaller time steps, the solver crashes.

fvVectorMatrix UEqn
(
fvm::ddt(U)
+ fvm::div(phi, U)
- fvm::laplacian(nu, U)

);

solve(UEqn == -fvc::grad(p)-eta*(fvm::ddt(U)));




Please help, thank you.

try this:

How to modify icoFoam.C to include source term
 

Hi Nima,

Thank you for your prompt reply. I have tried that option but the result i get is really weird...the solver seems to get 'stuck' as can be seen below








Courant Number mean: 0.00944072 max: 0.0228351
DILUmyPBiCG: Solving for Ux, Initial residual = 4.94675e-05, Final residual = 2.71278e-105, No Iterations 22
DILUmyPBiCG: Solving for Uy, Initial residual = 7.4114e-05, Final residual = 5.49146e-105, No Iterations 22
DICPCG: Solving for p, Initial residual = 4.46202e-05, Final residual = 8.4033e-17, No Iterations 97
time step continuity errors : sum local = 7.31098e-19, global = -2.32262e-21, cumulative = 1.11216e-17
DICPCG: Solving for p, Initial residual = 1.64486e-06, Final residual = 9.034e-17, No Iterations 92
time step continuity errors : sum local = 7.20432e-19, global = -1.28127e-21, cumulative = 1.11203e-17
ExecutionTime = 19.94 s ClockTime = 35 s

Time = 0.6035

Courant Number mean: 0.00944072 max: 0.0228347
DILUmyPBiCG: Solving for Ux, Initial residual = 4.94634e-05, Final residual = 2.7106e-105, No Iterations 22
DILUmyPBiCG: Solving for Uy, Initial residual = 7.40934e-05, Final residual = 5.84491e-105, No Iterations 22
DICPCG: Solving for p, Initial residual = 4.46209e-05, Final residual = 8.40861e-17, No Iterations 97
time step continuity errors : sum local = 7.16085e-19, global = 4.24348e-21, cumulative = 1.11246e-17
DICPCG: Solving for p, Initial residual = 1.64556e-06, Final residual = 9.18026e-17, No Iterations 92
time step continuity errors : sum local = 7.14218e-19, global = 3.90334e-21, cumulative = 1.11285e-17
ExecutionTime = 19.96 s ClockTime = 35 s

whats wrong with the result? do u mean high iteration numbers?

yes i get very low residuals as soon as the iterations begin and they do not reduce significantly

i have no idea! i dont think it is a cause of error

Hi,

I am modifying the icoFoam solver to include a momentum source in y direction.

where, the Source is defined as,

This is ok. No error during the compile.

However, when I tried to make the Source time dependent as follows,

The compiler complains that:

Could anyone let me know the reason? Thanks.

as function "cos" is defined in math.h too!, so you should define which one, you want to use, so it would be solve with following structure:

Hi Nima,

Many thanks for your quick reply. The problem is solved.

Now, I would like to see the Source term only exists at a specific area.

if (x y z) in zone (x1 to x2, y1 to y2, z1 to z2)
Source = (0, a, 0)
else
Source = (0, 0, 0)
endif

Can you please enlighten me on how to realize this?

there are two options:
1- define it from Dictionary, for example look at interFoam (dambreak test case) to see how to define a non-uniform internalField

2- you can write a pieces of code, you can use mesh.C() which returns position vector
then you can check it whether your cell is set up in specific area or not

Have you solved your problem? I want to do something like yours. I need some help!

setField or funkySetField
 

funkySetFields or setField utility in can be used to initialize this kind of problems.
Please go through Breaking of dam tutorial.