define mesh material density to get real mass properties

[wenqiushui]

Current BaseMesh.get_mass_properties method can't define the mesh material density. To compute real mesh mass and inertia,the density must be seted. Function compute real mass defined as bellow:

`

def get_mass_properties_with_density(self,density):
    # add density for mesh,density unit kg/m3 when mesh is unit is m
    self.check()

    def subexpression(x):
        w0, w1, w2 = x[:, 0], x[:, 1], x[:, 2]
        temp0 = w0 + w1
        f1 = temp0 + w2
        temp1 = w0 * w0
        temp2 = temp1 + w1 * temp0
        f2 = temp2 + w2 * f1
        f3 = w0 * temp1 + w1 * temp2 + w2 * f2
        g0 = f2 + w0 * (f1 + w0)
        g1 = f2 + w1 * (f1 + w1)
        g2 = f2 + w2 * (f1 + w2)
        return f1, f2, f3, g0, g1, g2

    x0, x1, x2 = self.x[:, 0], self.x[:, 1], self.x[:, 2]
    y0, y1, y2 = self.y[:, 0], self.y[:, 1], self.y[:, 2]
    z0, z1, z2 = self.z[:, 0], self.z[:, 1], self.z[:, 2]
    a1, b1, c1 = x1 - x0, y1 - y0, z1 - z0
    a2, b2, c2 = x2 - x0, y2 - y0, z2 - z0
    d0, d1, d2 = b1 * c2 - b2 * c1, a2 * c1 - a1 * c2, a1 * b2 - a2 * b1

    f1x, f2x, f3x, g0x, g1x, g2x = subexpression(self.x)
    f1y, f2y, f3y, g0y, g1y, g2y = subexpression(self.y)
    f1z, f2z, f3z, g0z, g1z, g2z = subexpression(self.z)

    intg = numpy.zeros((10))
    intg[0] = sum(d0 * f1x)
    intg[1:4] = sum(d0 * f2x), sum(d1 * f2y), sum(d2 * f2z)
    intg[4:7] = sum(d0 * f3x), sum(d1 * f3y), sum(d2 * f3z)
    intg[7] = sum(d0 * (y0 * g0x + y1 * g1x + y2 * g2x))
    intg[8] = sum(d1 * (z0 * g0y + z1 * g1y + z2 * g2y))
    intg[9] = sum(d2 * (x0 * g0z + x1 * g1z + x2 * g2z))
    intg /= numpy.array([6, 24, 24, 24, 60, 60, 60, 120, 120, 120])
    volume = intg[0]
    cog = intg[1:4] / volume
    cogsq = cog ** 2
    vmass=volume*density
    inertia = numpy.zeros((3, 3))

    inertia[0, 0] = (intg[5] + intg[6])*density - vmass * (cogsq[1] + cogsq[2])
    inertia[1, 1] = (intg[4] + intg[6])*density - vmass * (cogsq[2] + cogsq[0])
    inertia[2, 2] = (intg[4] + intg[5])*density - vmass * (cogsq[0] + cogsq[1])
    inertia[0, 1] = inertia[1, 0] = -(intg[7]*density - vmass * cog[0] * cog[1])
    inertia[1, 2] = inertia[2, 1] = -(intg[8]*density - vmass * cog[1] * cog[2])
    inertia[0, 2] = inertia[2, 0] = -(intg[9]*density - vmass * cog[2] * cog[0])

    return volume, vmass,cog, inertia

`

[wolph]

Thank you so much for the suggestion. I will add it to the mesh as an extra function for the next release :)

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[wolph]

Apologies for not merging this sooner, I am (and have been) very busy this year. In any case, I have created a new release and added tests for the methods. Thank you for the help!