def calc_properties(self):
'''Sets the center of mass and inertia of the solid, both with respect
to the fixed human frame.
'''
self.COM = self.pos + self.RotMat * self.relCOM
self.Inertia = inertia.rotate3_inertia(self.RotMat,self.relInertia)
def calc_properties(self):
'''Calculates the segment's center of mass with respect to the
fixed human frame origin (in the fixed human reference frame) and the
segment's inertia in the fixed human frame but about the segment's
center of mass.
'''
# center of mass
self.COM = self.pos + self.RotMat * self.relCOM
# inertia in frame f w.r.t. segment's COM
self.Inertia = inertia.rotate3_inertia(self.RotMat, self.relInertia)
def calc_rel_properties(self):
'''Calculates mass, relative center of mass, and relative/local
inertia, according to formulae in Appendix B of Yeadon 1990-ii. If the
stadium solid is arranged anterior-posteriorly, the inertia is rotated
by pi/2 about the z axis.
'''
D = self.density
h = self.height
r0 = self.stads[0].radius
t0 = self.stads[0].thick
r1 = self.stads[1].radius
t1 = self.stads[1].thick
a = (r1 - r0) / r0
if (t0 == 0):
b = 1.0
else:
b = (t1 - t0) / t0 # DOES NOT WORK FOR CIRCLES!!!
self.Mass = D * h * r0 * (4.0 * t0 * self.F1(a,b) +
np.pi * r0 * self.F1(a,a))
zcom = D * (h**2.0) * (4.0 * r0 * t0 * self.F2(a,b) +
np.pi * (r0**2.0) * self.F2(a,a)) / self.Mass
self.relCOM = np.array([[0.0],[0.0],[zcom]])
# moments of inertia
Izcom = D * h * (4.0 * r0 * (t0**3.0) * self.F4(a,b) / 3.0 +
np.pi * (r0**2.0) * (t0**2.0) * self.F5(a,b) +
4.0 * (r0**3.0) * t0 * self.F4(b,a) +
np.pi * (r0**4.0) * self.F4(a,a) * 0.5 )
Iy = (D * h * (4.0 * r0 * (t0**3.0) * self.F4(a,b) / 3.0 +
np.pi * (r0**2.0) * (t0**2.0) * self.F5(a,b) +
8.0 * (r0**3.0) * t0*self.F4(b,a) / 3.0 +
np.pi * (r0**4.0) * self.F4(a,a) * 0.25) +
D * (h**3.0) * (4.0 * r0 * t0 * self.F3(a,b) +
np.pi * (r0**2.0) * self.F3(a,a)))
# CAUGHT AN (minor) ERROR IN YEADON'S PAPER HERE
Iycom = Iy - self.Mass * (zcom**2.0)
Ix = (D * h * (4.0 * r0 * (t0**3.0) * self.F4(a,b) / 3.0 +
np.pi * (r0**4.0) * self.F4(a,a) * 0.25) +
D * (h**3.0) * (4.0 * r0 * t0 * self.F3(a,b) +
np.pi * (r0**2.0) * self.F3(a,a)))
Ixcom = Ix - self.Mass*(zcom**2.0)
self.relInertia = np.mat([[Ixcom,0.0,0.0],
[0.0,Iycom,0.0],
[0.0,0.0,Izcom]])
if self.alignment == 'AP':
# rearrange to anterior-posterior orientation
self.relInertia = inertia.rotate3_inertia(
inertia.rotate3([0,0,np.pi/2]),self.relInertia)
def calc_properties(self):
'''Calculates the segment's center of mass with respect to the
fixed human frame origin (in the fixed human reference frame) and the
segment's inertia in the fixed human frame but about the segment's
center of mass.
'''
# center of mass
self.COM = self.pos + self.RotMat * self.relCOM
# inertia in frame f w.r.t. segment's COM
self.Inertia = inertia.rotate3_inertia(self.RotMat, self.relInertia)
# an alternative way of calculating absolute inertia tensor,
# implemented for validation purposes.
# inertia in frame f w.r.t. segment's COM
self.Inertia2 = np.mat(np.zeros((3, 3)))
for s in self.solids:
dist = s.COM - self.COM
self.Inertia2 += np.mat(inertia.parallel_axis(
s.Inertia, s.Mass,
[dist[0, 0], dist[1, 0], dist[2, 0]]))
