def test_apply_loads_on_multi_degree_freedom_holonomic_system():
"""Example based on: https://pydy.readthedocs.io/en/latest/examples/multidof-holonomic.html"""
W = Body('W') #Wall
B = Body('B') #Block
P = Body('P') #Pendulum
b = Body('b') #bob
q1, q2 = dynamicsymbols('q1 q2') #generalized coordinates
k, c, g, kT = symbols('k c g kT') #constants
F, T = dynamicsymbols('F T') #Specified forces
#Applying forces
B.apply_force(F * W.x)
W.apply_force(k * q1 * W.x, reaction_body=B) #Spring force
W.apply_force(c * q1.diff() * W.x, reaction_body=B) #dampner
P.apply_force(P.mass * g * W.y)
b.apply_force(b.mass * g * W.y)
#Applying torques
P.apply_torque(kT * q2 * W.z, reaction_body=b)
P.apply_torque(T * W.z)
assert B.loads == [(B.masscenter, (F - k * q1 - c * q1.diff()) * W.x)]
assert P.loads == [(P.masscenter, P.mass * g * W.y),
(P.frame, (T + kT * q2) * W.z)]
assert b.loads == [(b.masscenter, b.mass * g * W.y),
(b.frame, -kT * q2 * W.z)]
assert W.loads == [(W.masscenter, (c * q1.diff() + k * q1) * W.x)]
def test_body_add_torque():
body = Body('body')
torque_vector = body.frame.x
body.apply_torque(torque_vector)
assert len(body.loads) == 1
assert body.loads[0] == (body.frame, torque_vector)
raises(TypeError, lambda: body.apply_torque(0))
def test_body_add_torque():
body = Body('body')
torque_vector = body.frame.x
body.apply_torque(torque_vector)
assert len(body.loads) == 1
assert body.loads[0] == (body.frame, torque_vector)
raises(TypeError, lambda: body.apply_torque(0))
def test_remove_load():
P1 = Point('P1')
P2 = Point('P2')
B = Body('B')
f1 = B.x
f2 = B.y
B.apply_force(f1, P1)
B.apply_force(f2, P2)
B.loads == [(P1, f1), (P2, f2)]
B.remove_load(P2)
B.loads == [(P1, f1)]
B.apply_torque(f1.cross(f2))
B.loads == [(P1, f1), (B.frame, f1.cross(f2))]
B.remove_load()
B.loads == [(P1, f1)]
def test_apply_torque():
t = symbols('t')
q = dynamicsymbols('q')
B1 = Body('B1')
B2 = Body('B2')
N = ReferenceFrame('N')
torque = t * q * N.x
B1.apply_torque(torque, B2) #Applying equal and opposite torque
assert B1.loads == [(B1.frame, torque)]
assert B2.loads == [(B2.frame, -torque)]
torque2 = t * N.y
B1.apply_torque(torque2)
assert B1.loads == [(B1.frame, torque + torque2)]
