def voidage_Benyahia_Oneil_spherical(Dp, Dt):
    """Calculates voidage of a bed of spheres
    packed into a bed or tube of diameter `Dt`, with sphere diameters
    `Dp`. Shown in [1]_, and cited by various authors. Correlations exist
    also for solid cylinders, hollow cylinders, and 4-hole cylinders.
    Based on a series of physical measurements.

    .. math::
        \\epsilon = 0.390+\\frac{1.740}{\\left(\\frac{d_{cyl}}{d_p}+1.140\\right)^2}

    Parameters
    ----------
    Dp : float
        Spherical particle diameter, [m]
    Dt : float
        Diameter of the tube, [m]

    Returns
    -------
    voidage : float
        Void fraction of bed packing []

    Notes
    -----
    Average error 1.5%, 1.5 < ratio < 50.

    Examples
    --------
    >>> voidage_Benyahia_Oneil_spherical(Dp=.001, Dt=.05)
    0.3906653157443224

    References
    ----------
    .. [1] Benyahia, F., and K. E. O’Neill. "Enhanced Voidage Correlations for
       Packed Beds of Various Particle Shapes and Sizes." Particulate Science
       and Technology 23, no. 2 (April 1, 2005): 169-77.
       doi:10.1080/02726350590922242.
    """
    return 0.39 + 1.74 / (Dt / Dp + 1.14) ** 2
