def Moody(Re, eD):
    """Calculates Darcy friction factor using the method in Moody (1947)
    as shown in [1]_ and originally in [2]_.

    .. math::
        f_f = 1.375\\times 10^{-3}\\left[1+\\left(2\\times10^4\\frac{\\epsilon}{D} +
        \\frac{10^6}{Re}\\right)^{1/3}\\right]

    Parameters
    ----------
    Re : float
        Reynolds number, [-]
    eD : float
        Relative roughness, [-]

    Returns
    -------
    fd : float
        Darcy friction factor [-]

    Notes
    -----
    Range is Re >= 4E3 and Re <= 1E8; eD >= 0 < 0.01.

    Examples
    --------
    >>> Moody(1E5, 1E-4)
    0.01809185666808665

    References
    ----------
    .. [1] Winning, H. and T. Coole. "Explicit Friction Factor Accuracy and
       Computational Efficiency for Turbulent Flow in Pipes." Flow, Turbulence
       and Combustion 90, no. 1 (January 1, 2013): 1-27.
       doi:10.1007/s10494-012-9419-7
    .. [2] Moody, L.F.: An approximate formula for pipe friction factors.
       Trans. Am. Soc. Mech. Eng. 69,1005-1006 (1947)
    """
    return 4 * (0.001375 * (1 + (20000.0 * eD + 1000000.0 / Re) ** (1 / 3.0)))
