def get_volume_by_element_id(self, element_id=None, xyz_cid0=None, total=False):
"""
Gets the volume for one or more elements.
Parameters
----------
element_id : (nelements, ) int ndarray; default=None
the elements to consider
xyz_cid0 : (nnodes, 3) float ndarray; default=None -> calculate
the GRIDs in CORD2R=0
total : bool; default=False
should the volume be summed
Notes
-----
Volume for a CHEXA is the average area of two opposing faces
times the length between the centroids of those points
"""
nodes = self._get_node_locations_by_element_id(element_id, xyz_cid0)
n1, n2, n3, n4, n5, n6, n7, n8 = nodes
volume = volume8(n1, n2, n3, n4, n5, n6, n7, n8)
if total:
volume = abs(volume).sum()
else:
volume = abs(volume)
return volume
def get_mass_matrix(self, i, model, positions, index0s, is_lumped=True):
nnodes = 8
ndof = 3 * nnodes
pid = self.property_id[i]
rho = self.model.elements.properties_solid.psolid.get_density_by_property_id(pid)[0]
n0, n1, n2, n3, n4, n5, n6, n7 = self.node_ids[i, :]
V = volume8(positions[self.node_ids[i, 0]],
positions[self.node_ids[i, 1]],
positions[self.node_ids[i, 2]],
positions[self.node_ids[i, 3]],
positions[self.node_ids[i, 4]],
positions[self.node_ids[i, 5]],
positions[self.node_ids[i, 6]],
positions[self.node_ids[i, 7]],
)
mass = rho * V
if is_lumped:
mi = mass / 4.
nnodes = 4
M = eye(ndof, dtype='float32')
else:
mi = mass / 20.
M = ones((ndof, ndof), dtype='float32')
for i in range(nnodes):
j = i * 3
M[j:j+3, j:j+3] = 2.
M *= mi
dofs, nijv = self.get_dofs_nijv(index0s, n0, n1, n2, n3, n4, n5, n6, n7)
return M, dofs, nijv