Source code for bladedesigner.camberlines.n2dcamberline

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# ***************************************************************************
# *   Copyright (C) 2011-2012 by Andreas Kührmann [kuean@users.sf.net]      *
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# *   the Free Software Foundation; either version 3 of the License, or     *
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# *   GNU General Public License for more details.                          *
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import numpy as np

import bladedesigner.baseclasses as bcls
import bladedesigner.foundation as fdn


__all__ = ['N2DCamberLine']


class N2DCamberLine(bcls.AnalyticalCamberLine):
    r"""

    The NACA 2-digit camber line is characterized by two attributes :math:`m`
    and :math:`p` where :math:`m` is the maximum camber and :math:`p` is the
    chordwise location of maximum camber. This camber line is formed by two
    parabolic segments that match in value and slope at :math:`p`. The camber
    line equation is:

    .. math::

       y = \Bigg\{ \begin{array}{ll} m p^{-2} x (2 p - x) & \mbox{if } x \leq p
       \\ m (1 - p)^{-2} (1 - 2 p + x (2 p - x)) & \mbox{if } x > p \end{array}

    .. tip::

       Jacobs, Eastman N.; Ward, Kenneth E. and Pinkerton, Robert M.:
       *The Characteristics of 78 Related Airfoil Sections From Tests in the
       Variable-Density Wind Tunnel.* NACA Rep. 460, 1933

       Ladson, Charles L.; Brooks, Cuyler W.; Hill, Acquilla S. and Sproles
       Darrell W.: *Computer Program To Obtain Ordinates for NACA Airfoils*
       NACA TM 4741, 1996.
    """

    def __init__(self):
        super(N2DCamberLine, self).__init__()
        # properties (initialized by user)
        self.__max_camber = fdn.Uninit('max_camber')
        self.__max_camber_position = fdn.Uninit('max_camber_position')
        # add user properties to initialization summary
        self._properties.extend(['max_camber', 'max_camber_position'])

    @property
    def max_camber(self):
        """
        Type: ``int or float``
        """
        return self.__max_camber

    @max_camber.setter
    @fdn.restrict(new_max_camber=(int, float))
    def max_camber(self, new_max_camber):
        if self.__max_camber != new_max_camber:
            self.__max_camber = new_max_camber
            self.update()

    @property
    def max_camber_position(self):
        """
        Type: ``float`` - values between (exclusive) 0 and 1 only
        """
        return self.__max_camber_position

    @max_camber_position.setter
    @fdn.restrict(new_max_camber_position=fdn.OpenInterval(0, 1))
    def max_camber_position(self, new_max_camber_position):
        if self.__max_camber_position != new_max_camber_position:
            self.__max_camber_position = new_max_camber_position
            self.update()

    @fdn.memoize
    def get_derivations(self):
        """
        get_derivations()

        Returns: ``ndarray``

        Calculates camber line derivations and returns them in an array.

        .. note::

           The return value will be cached. Recalling this method returns the
           cached value, if the attribues are unchanged.
        """
        self._check_initialization()
        self._cached = True
        p = self.max_camber_position
        m = self.max_camber
        x = self.distribution(self.sample_rate)
        index = np.where(x <= p)[0]
        if index.size:
            dydx_1 = 2 * m / np.power(p, 2) * (p - x[index])
        index = np.where(x > p)[0]
        if index.size:
            dydx_2 = m / (1 - p) ** 2 * 2 * (p - x[index])
        return np.append(dydx_1, dydx_2)

    @fdn.memoize
    def as_array(self):
        """
        as_array()

        Returns: ``ndarray``

        Calculates camber line coordinates and returns them in an array.

        .. note::

           The return value will be cached. Recalling this method returns the
           cached value, if the attribues are unchanged.
        """
        self._check_initialization()
        self._cached = True
        p = self.max_camber_position
        m = self.max_camber
        x = self.distribution(self.sample_rate)
        index = np.where(x <= p)[0]
        if index.size:
            z = x[index]
            y1 = m / p ** 2 * (z * (2 * p - z))
        index = np.where(x > p)[0]
        if index.size:
            z = x[index]
            y2 = m / (1 - p) ** 2 * (1 - 2 * p + z * (2 * p - z))
        y = np.append(y1, y2)
        return np.reshape(np.append(x, y), (-1, 2), "F")