def davenport(f, sigma2, **kwargs):
    """ one-side Davenport spectrum, Davenport 1961, adopted in Chinese code

    Args:
        f (1d-ndarray): freqency, unit: Hz
        sigma2 (float): variance, (Iu * vz) ** 2

        **kwargs: spectrum propeteries
        Lu (float): integral scale, unit:m
        v10 (float): mean wind speed at 10m height, unit: m/s

    Returns:
        1d-ndarray: specturm value
    """
    if "Lu" in kwargs:
        Lu = kwargs["Lu"]
    else:
        Lu = 1200.0
    v10 = kwargs["v10"]
    x = f * Lu / v10
    ret = sigma2 * 2.0 * x * x / ((1 + x * x) ** (4.0 / 3.0)) / f / 3.0
    return ret