MTtranslateService/Lib/site-packages/sympy/physics/mechanics/tests/test_kane.py

from sympy.core.backend import (cos, expand, Matrix, sin, symbols, tan, sqrt, S,
                                zeros)
from sympy.simplify.simplify import simplify
from sympy.physics.mechanics import (dynamicsymbols, ReferenceFrame, Point,
                                     RigidBody, KanesMethod, inertia, Particle,
                                     dot)
from sympy.testing.pytest import raises


def test_one_dof():
    # This is for a 1 dof spring-mass-damper case.
    # It is described in more detail in the KanesMethod docstring.
    q, u = dynamicsymbols('q u')
    qd, ud = dynamicsymbols('q u', 1)
    m, c, k = symbols('m c k')
    N = ReferenceFrame('N')
    P = Point('P')
    P.set_vel(N, u * N.x)

    kd = [qd - u]
    FL = [(P, (-k * q - c * u) * N.x)]
    pa = Particle('pa', P, m)
    BL = [pa]

    KM = KanesMethod(N, [q], [u], kd)
    KM.kanes_equations(BL, FL)

    assert KM.bodies == BL
    assert KM.loads == FL

    MM = KM.mass_matrix
    forcing = KM.forcing
    rhs = MM.inv() * forcing
    assert expand(rhs[0]) == expand(-(q * k + u * c) / m)

    assert simplify(KM.rhs() -
                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(2, 1)

    assert (KM.linearize(A_and_B=True, )[0] == Matrix([[0, 1], [-k/m, -c/m]]))


def test_two_dof():
    # This is for a 2 d.o.f., 2 particle spring-mass-damper.
    # The first coordinate is the displacement of the first particle, and the
    # second is the relative displacement between the first and second
    # particles. Speeds are defined as the time derivatives of the particles.
    q1, q2, u1, u2 = dynamicsymbols('q1 q2 u1 u2')
    q1d, q2d, u1d, u2d = dynamicsymbols('q1 q2 u1 u2', 1)
    m, c1, c2, k1, k2 = symbols('m c1 c2 k1 k2')
    N = ReferenceFrame('N')
    P1 = Point('P1')
    P2 = Point('P2')
    P1.set_vel(N, u1 * N.x)
    P2.set_vel(N, (u1 + u2) * N.x)
    kd = [q1d - u1, q2d - u2]

    # Now we create the list of forces, then assign properties to each
    # particle, then create a list of all particles.
    FL = [(P1, (-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2) * N.x), (P2, (-k2 *
        q2 - c2 * u2) * N.x)]
    pa1 = Particle('pa1', P1, m)
    pa2 = Particle('pa2', P2, m)
    BL = [pa1, pa2]

    # Finally we create the KanesMethod object, specify the inertial frame,
    # pass relevant information, and form Fr & Fr*. Then we calculate the mass
    # matrix and forcing terms, and finally solve for the udots.
    KM = KanesMethod(N, q_ind=[q1, q2], u_ind=[u1, u2], kd_eqs=kd)
    KM.kanes_equations(BL, FL)
    MM = KM.mass_matrix
    forcing = KM.forcing
    rhs = MM.inv() * forcing
    assert expand(rhs[0]) == expand((-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2)/m)
    assert expand(rhs[1]) == expand((k1 * q1 + c1 * u1 - 2 * k2 * q2 - 2 *
                                    c2 * u2) / m)

    assert simplify(KM.rhs() -
                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(4, 1)

    # Make sure an error is raised if nonlinear kinematic differential
    # equations are supplied.
    kd = [q1d - u1**2, sin(q2d) - cos(u2)]
    raises(ValueError, lambda: KanesMethod(N, q_ind=[q1, q2],
                                           u_ind=[u1, u2], kd_eqs=kd))

def test_pend():
    q, u = dynamicsymbols('q u')
    qd, ud = dynamicsymbols('q u', 1)
    m, l, g = symbols('m l g')
    N = ReferenceFrame('N')
    P = Point('P')
    P.set_vel(N, -l * u * sin(q) * N.x + l * u * cos(q) * N.y)
    kd = [qd - u]

    FL = [(P, m * g * N.x)]
    pa = Particle('pa', P, m)
    BL = [pa]

    KM = KanesMethod(N, [q], [u], kd)
    KM.kanes_equations(BL, FL)
    MM = KM.mass_matrix
    forcing = KM.forcing
    rhs = MM.inv() * forcing
    rhs.simplify()
    assert expand(rhs[0]) == expand(-g / l * sin(q))
    assert simplify(KM.rhs() -
                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(2, 1)


def test_rolling_disc():
    # Rolling Disc Example
    # Here the rolling disc is formed from the contact point up, removing the
    # need to introduce generalized speeds. Only 3 configuration and three
    # speed variables are need to describe this system, along with the disc's
    # mass and radius, and the local gravity (note that mass will drop out).
    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1 q2 q3 u1 u2 u3')
    q1d, q2d, q3d, u1d, u2d, u3d = dynamicsymbols('q1 q2 q3 u1 u2 u3', 1)
    r, m, g = symbols('r m g')

    # The kinematics are formed by a series of simple rotations. Each simple
    # rotation creates a new frame, and the next rotation is defined by the new
    # frame's basis vectors. This example uses a 3-1-2 series of rotations, or
    # Z, X, Y series of rotations. Angular velocity for this is defined using
    # the second frame's basis (the lean frame).
    N = ReferenceFrame('N')
    Y = N.orientnew('Y', 'Axis', [q1, N.z])
    L = Y.orientnew('L', 'Axis', [q2, Y.x])
    R = L.orientnew('R', 'Axis', [q3, L.y])
    w_R_N_qd = R.ang_vel_in(N)
    R.set_ang_vel(N, u1 * L.x + u2 * L.y + u3 * L.z)

    # This is the translational kinematics. We create a point with no velocity
    # in N; this is the contact point between the disc and ground. Next we form
    # the position vector from the contact point to the disc's center of mass.
    # Finally we form the velocity and acceleration of the disc.
    C = Point('C')
    C.set_vel(N, 0)
    Dmc = C.locatenew('Dmc', r * L.z)
    Dmc.v2pt_theory(C, N, R)

    # This is a simple way to form the inertia dyadic.
    I = inertia(L, m / 4 * r**2, m / 2 * r**2, m / 4 * r**2)

    # Kinematic differential equations; how the generalized coordinate time
    # derivatives relate to generalized speeds.
    kd = [dot(R.ang_vel_in(N) - w_R_N_qd, uv) for uv in L]

    # Creation of the force list; it is the gravitational force at the mass
    # center of the disc. Then we create the disc by assigning a Point to the
    # center of mass attribute, a ReferenceFrame to the frame attribute, and mass
    # and inertia. Then we form the body list.
    ForceList = [(Dmc, - m * g * Y.z)]
    BodyD = RigidBody('BodyD', Dmc, R, m, (I, Dmc))
    BodyList = [BodyD]

    # Finally we form the equations of motion, using the same steps we did
    # before. Specify inertial frame, supply generalized speeds, supply
    # kinematic differential equation dictionary, compute Fr from the force
    # list and Fr* from the body list, compute the mass matrix and forcing
    # terms, then solve for the u dots (time derivatives of the generalized
    # speeds).
    KM = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3], kd_eqs=kd)
    KM.kanes_equations(BodyList, ForceList)
    MM = KM.mass_matrix
    forcing = KM.forcing
    rhs = MM.inv() * forcing
    kdd = KM.kindiffdict()
    rhs = rhs.subs(kdd)
    rhs.simplify()
    assert rhs.expand() == Matrix([(6*u2*u3*r - u3**2*r*tan(q2) +
        4*g*sin(q2))/(5*r), -2*u1*u3/3, u1*(-2*u2 + u3*tan(q2))]).expand()
    assert simplify(KM.rhs() -
                    KM.mass_matrix_full.LUsolve(KM.forcing_full)) == zeros(6, 1)

    # This code tests our output vs. benchmark values. When r=g=m=1, the
    # critical speed (where all eigenvalues of the linearized equations are 0)
    # is 1 / sqrt(3) for the upright case.
    A = KM.linearize(A_and_B=True)[0]
    A_upright = A.subs({r: 1, g: 1, m: 1}).subs({q1: 0, q2: 0, q3: 0, u1: 0, u3: 0})
    import sympy
    assert sympy.sympify(A_upright.subs({u2: 1 / sqrt(3)})).eigenvals() == {S.Zero: 6}


def test_aux():
    # Same as above, except we have 2 auxiliary speeds for the ground contact
    # point, which is known to be zero. In one case, we go through then
    # substitute the aux. speeds in at the end (they are zero, as well as their
    # derivative), in the other case, we use the built-in auxiliary speed part
    # of KanesMethod. The equations from each should be the same.
    q1, q2, q3, u1, u2, u3 = dynamicsymbols('q1 q2 q3 u1 u2 u3')
    q1d, q2d, q3d, u1d, u2d, u3d = dynamicsymbols('q1 q2 q3 u1 u2 u3', 1)
    u4, u5, f1, f2 = dynamicsymbols('u4, u5, f1, f2')
    u4d, u5d = dynamicsymbols('u4, u5', 1)
    r, m, g = symbols('r m g')

    N = ReferenceFrame('N')
    Y = N.orientnew('Y', 'Axis', [q1, N.z])
    L = Y.orientnew('L', 'Axis', [q2, Y.x])
    R = L.orientnew('R', 'Axis', [q3, L.y])
    w_R_N_qd = R.ang_vel_in(N)
    R.set_ang_vel(N, u1 * L.x + u2 * L.y + u3 * L.z)

    C = Point('C')
    C.set_vel(N, u4 * L.x + u5 * (Y.z ^ L.x))
    Dmc = C.locatenew('Dmc', r * L.z)
    Dmc.v2pt_theory(C, N, R)
    Dmc.a2pt_theory(C, N, R)

    I = inertia(L, m / 4 * r**2, m / 2 * r**2, m / 4 * r**2)

    kd = [dot(R.ang_vel_in(N) - w_R_N_qd, uv) for uv in L]

    ForceList = [(Dmc, - m * g * Y.z), (C, f1 * L.x + f2 * (Y.z ^ L.x))]
    BodyD = RigidBody('BodyD', Dmc, R, m, (I, Dmc))
    BodyList = [BodyD]

    KM = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3, u4, u5],
                     kd_eqs=kd)
    (fr, frstar) = KM.kanes_equations(BodyList, ForceList)
    fr = fr.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
    frstar = frstar.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})

    KM2 = KanesMethod(N, q_ind=[q1, q2, q3], u_ind=[u1, u2, u3], kd_eqs=kd,
                      u_auxiliary=[u4, u5])
    (fr2, frstar2) = KM2.kanes_equations(BodyList, ForceList)
    fr2 = fr2.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})
    frstar2 = frstar2.subs({u4d: 0, u5d: 0}).subs({u4: 0, u5: 0})

    frstar.simplify()
    frstar2.simplify()

    assert (fr - fr2).expand() == Matrix([0, 0, 0, 0, 0])
    assert (frstar - frstar2).expand() == Matrix([0, 0, 0, 0, 0])


def test_parallel_axis():
    # This is for a 2 dof inverted pendulum on a cart.
    # This tests the parallel axis code in KanesMethod. The inertia of the
    # pendulum is defined about the hinge, not about the center of mass.

    # Defining the constants and knowns of the system
    gravity = symbols('g')
    k, ls = symbols('k ls')
    a, mA, mC = symbols('a mA mC')
    F = dynamicsymbols('F')
    Ix, Iy, Iz = symbols('Ix Iy Iz')

    # Declaring the Generalized coordinates and speeds
    q1, q2 = dynamicsymbols('q1 q2')
    q1d, q2d = dynamicsymbols('q1 q2', 1)
    u1, u2 = dynamicsymbols('u1 u2')
    u1d, u2d = dynamicsymbols('u1 u2', 1)

    # Creating reference frames
    N = ReferenceFrame('N')
    A = ReferenceFrame('A')

    A.orient(N, 'Axis', [-q2, N.z])
    A.set_ang_vel(N, -u2 * N.z)

    # Origin of Newtonian reference frame
    O = Point('O')

    # Creating and Locating the positions of the cart, C, and the
    # center of mass of the pendulum, A
    C = O.locatenew('C', q1 * N.x)
    Ao = C.locatenew('Ao', a * A.y)

    # Defining velocities of the points
    O.set_vel(N, 0)
    C.set_vel(N, u1 * N.x)
    Ao.v2pt_theory(C, N, A)
    Cart = Particle('Cart', C, mC)
    Pendulum = RigidBody('Pendulum', Ao, A, mA, (inertia(A, Ix, Iy, Iz), C))

    # kinematical differential equations

    kindiffs = [q1d - u1, q2d - u2]

    bodyList = [Cart, Pendulum]

    forceList = [(Ao, -N.y * gravity * mA),
                 (C, -N.y * gravity * mC),
                 (C, -N.x * k * (q1 - ls)),
                 (C, N.x * F)]

    km = KanesMethod(N, [q1, q2], [u1, u2], kindiffs)
    (fr, frstar) = km.kanes_equations(bodyList, forceList)
    mm = km.mass_matrix_full
    assert mm[3, 3] == Iz

def test_input_format():
    # 1 dof problem from test_one_dof
    q, u = dynamicsymbols('q u')
    qd, ud = dynamicsymbols('q u', 1)
    m, c, k = symbols('m c k')
    N = ReferenceFrame('N')
    P = Point('P')
    P.set_vel(N, u * N.x)

    kd = [qd - u]
    FL = [(P, (-k * q - c * u) * N.x)]
    pa = Particle('pa', P, m)
    BL = [pa]

    KM = KanesMethod(N, [q], [u], kd)
    # test for input format kane.kanes_equations((body1, body2, particle1))
    assert KM.kanes_equations(BL)[0] == Matrix([0])
    # test for input format kane.kanes_equations(bodies=(body1, body 2), loads=(load1,load2))
    assert KM.kanes_equations(bodies=BL, loads=None)[0] == Matrix([0])
    # test for input format kane.kanes_equations(bodies=(body1, body 2), loads=None)
    assert KM.kanes_equations(BL, loads=None)[0] == Matrix([0])
    # test for input format kane.kanes_equations(bodies=(body1, body 2))
    assert KM.kanes_equations(BL)[0] == Matrix([0])
    # test for input format kane.kanes_equations(bodies=(body1, body2), loads=[])
    assert KM.kanes_equations(BL, [])[0] == Matrix([0])
    # test for error raised when a wrong force list (in this case a string) is provided
    raises(ValueError, lambda: KM._form_fr('bad input'))

    # 1 dof problem from test_one_dof with FL & BL in instance
    KM = KanesMethod(N, [q], [u], kd, bodies=BL, forcelist=FL)
    assert KM.kanes_equations()[0] == Matrix([-c*u - k*q])

    # 2 dof problem from test_two_dof
    q1, q2, u1, u2 = dynamicsymbols('q1 q2 u1 u2')
    q1d, q2d, u1d, u2d = dynamicsymbols('q1 q2 u1 u2', 1)
    m, c1, c2, k1, k2 = symbols('m c1 c2 k1 k2')
    N = ReferenceFrame('N')
    P1 = Point('P1')
    P2 = Point('P2')
    P1.set_vel(N, u1 * N.x)
    P2.set_vel(N, (u1 + u2) * N.x)
    kd = [q1d - u1, q2d - u2]

    FL = ((P1, (-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2) * N.x), (P2, (-k2 *
        q2 - c2 * u2) * N.x))
    pa1 = Particle('pa1', P1, m)
    pa2 = Particle('pa2', P2, m)
    BL = (pa1, pa2)

    KM = KanesMethod(N, q_ind=[q1, q2], u_ind=[u1, u2], kd_eqs=kd)
    # test for input format
    # kane.kanes_equations((body1, body2), (load1, load2))
    KM.kanes_equations(BL, FL)
    MM = KM.mass_matrix
    forcing = KM.forcing
    rhs = MM.inv() * forcing
    assert expand(rhs[0]) == expand((-k1 * q1 - c1 * u1 + k2 * q2 + c2 * u2)/m)
    assert expand(rhs[1]) == expand((k1 * q1 + c1 * u1 - 2 * k2 * q2 - 2 *
                                    c2 * u2) / m)