Print my scalar to .csv file

1

Question: I can print drag for every time steps in FEniCS, but how can I put the data (code is

print(f"drag: {assemble(D)}") )into csv file.

code:

def sigmaVisc(u,mu):
        
    return 2.0*mu*sym(grad(u))

for step in range(0,N_STEPS):
    print("======= Time step "+str(step+1)+"/"+str(N_STEPS)+" =======")
    solve(F==0,up,bcs=bcs)
    
    up_old.assign(up)
    u,p = up_old.split()   
    u.rename("u","u")
    p.rename("p","p")
    ufile << u
    
    n = FacetNormal(mesh)
    viscous_stress = dot(2.0*mu*sym(grad(u)), n)
    D =(viscous_stress[0])*ds(4) 
    print(f"drag: {assemble(D)}")
2

See: