InitialConditions.py 文件源码

def LambDipole(model, U=.01,R = 1.):

    """ Generate Lamb's dipole vorticity field.

       Parameters
       -----------
        U: float
                Translation speed (dipole's strength).
        R: float
                Diple's radius.

       Return
       -------
        q: array of floats
              Vorticity (physical space).

    """

    N = model.nx
    x, y = model.x, model.y
    x0,y0 = x[N//2,N//2],y[N//2,N//2]

    r = np.sqrt( (x-x0)**2 + (y-y0)**2 )
    s = np.zeros_like(r)

    for i in range(N):
        for j in range(N):
            if r[i,j] == 0.:
                s[i,j] = 0.
            else:
                s[i,j] = (y[i,j]-y0)/r[i,j]

    lam = (3.8317)/R
    C = -(2.*U*lam)/(special.j0(lam*R))
    q = np.zeros_like(r)
    q[r<=R] = C*special.j1(lam*r[r<=R])*s[r<=R]

    return q