# How do i write the code for navierstokes equation in matlab/comsol?

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Bartholomew Osegbe on 10 May 2018
Answered: Bartholomew Osegbe on 13 May 2018
The idea is to write the code for the navierstokes equation with the laplacian velocity and pressure term
KSSV on 10 May 2018
You want it in comsol? So this is not the forum. You want in MATLAB? What have you attempted?

Precise Simulation on 10 May 2018
The incompressible Navier-Stokes equations is also available as a built-in pre-defined Navier-Stokes physics mode in the FEATool FEM Matlab toolbox. In this case the equations are in 2D defined as
rho_ns*u' - miu_ns*(2*ux_x + uy_y + vx_y) + rho_ns*(u*ux_t + v*uy_t) + p_x = Fx_ns
rho_ns*v' - miu_ns*(vx_x + uy_x + 2*vy_y) + rho_ns*(u*vx_t + v*vy_t) + p_y = Fy_ns
ux_t + vy_t = 0
the Navier-Stokes equations in axisymmetry (2D cylindrical coordinates) and 3D are defined similarly.

Bartholomew Osegbe on 10 May 2018
I have attempted the weak method fem.equ.weak = { ... { ... {'(-eta*ux)*test(ux)+(-eta*uy)*test(uy)-test(u)*px'} ... {'(-eta*vx)*test(vx)+(-eta*vy)*test(vy)-test(v)*py'} ... {'-test(px)*u-test(py)*v'} ... } ... }; but I have errors and when I sourced online I found a code that uses the poisson equation but just wanted a simple code with a laplacian velocity and pressure term.

Ameer Hamza on 10 May 2018
You may find these FEX submission useful:

Bartholomew Osegbe on 13 May 2018