def test_stiffness_matrix():
"""
This function instantiate a bearing using the fluid flow class and test if it matches the
expected results for the stiffness matrix, given the eccentricity ratio.
Taken from example 5.5.1, page 181 (Dynamics of rotating machine, FRISSWELL)
"""
bearing = fluid_flow_short_friswell()
kxx, kxy, kyx, kyy = calculate_short_stiffness_matrix(bearing)
assert math.isclose(kxx / 10**6, 12.81, rel_tol=0.01)
assert math.isclose(kxy / 10**6, 16.39, rel_tol=0.01)
assert math.isclose(kyx / 10**6, -25.06, rel_tol=0.01)
assert math.isclose(kyy / 10**6, 8.815, rel_tol=0.01)
def test_stiffness_matrix_numerical(fluid_flow_short_eccentricity):
"""
This function instantiate a bearing using the fluid flow class and test if it matches the
expected results for the stiffness matrix based on Friswell's book formulas, given the
eccentricity ratio.
Taken from chapter 5, page 179 (Dynamics of rotating machine, FRISSWELL)
"""
bearing = fluid_flow_short_eccentricity
bearing.calculate_pressure_matrix_numerical()
K, C = calculate_stiffness_and_damping_coefficients(bearing)
kxx, kxy, kyx, kyy = K[0], K[1], K[2], K[3]
k_xx, k_xy, k_yx, k_yy = calculate_short_stiffness_matrix(bearing)
assert_allclose(kxx, k_xx, rtol=0.29)
assert_allclose(kxy, k_xy, rtol=0.22)
assert_allclose(kyx, k_yx, rtol=0.15)
assert_allclose(kyy, k_yy, rtol=0.22)
def from_fluid_flow(
cls,
n,
nz,
ntheta,
nradius,
length,
omega,
p_in,
p_out,
radius_rotor,
radius_stator,
visc,
rho,
eccentricity=None,
load=None,
tag=None,
n_link=None,
scale_factor=1,
is_random=None,
):
"""Instantiate a bearing using inputs from its fluid flow.
Parameters
----------
n : int
The node in which the bearing will be located in the rotor.
is_random : list
List of the object attributes to become random.
Possibilities:
["length", "omega", "p_in", "p_out", "radius_rotor",
"radius_stator", "visc", "rho", "eccentricity", "load"]
tag: str, optional
A tag to name the element
Default is None.
n_link: int, optional
Node to which the bearing will connect. If None the bearing is
connected to ground.
Default is None.
scale_factor: float, optional
The scale factor is used to scale the bearing drawing.
Default is 1.
Grid related
^^^^^^^^^^^^
Describes the discretization of the problem
nz: int
Number of points along the Z direction (direction of flow).
ntheta: int
Number of points along the direction theta. NOTE: ntheta must be odd.
nradius: int
Number of points along the direction r.
length: float, list
Length in the Z direction (m).
Input a list to make it random.
Operation conditions
^^^^^^^^^^^^^^^^^^^^
Describes the operation conditions.
omega: float, list
Rotation of the rotor (rad/s).
Input a list to make it random.
p_in: float, list
Input Pressure (Pa).
Input a list to make it random.
p_out: float, list
Output Pressure (Pa).
Input a list to make it random.
load: float, list
Load applied to the rotor (N).
Input a list to make it random.
Geometric data of the problem
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Describes the geometric data of the problem.
radius_rotor: float, list
Rotor radius (m).
Input a list to make it random.
radius_stator: float, list
Stator Radius (m).
Input a list to make it random.
eccentricity: float, list
Eccentricity (m) is the euclidean distance between rotor and stator
centers.
The center of the stator is in position (0,0).
Input a list to make it random.
Fluid characteristics
^^^^^^^^^^^^^^^^^^^^^
Describes the fluid characteristics.
visc: float, list
Viscosity (Pa.s).
Input a list to make it random.
rho: float, list
Fluid density(Kg/m^3).
Input a list to make it random.
Returns
-------
random bearing: srs.ST_BearingElement
A random bearing object.
Examples
--------
>>> import numpy as np
>>> import ross.stochastic as srs
>>> nz = 30
>>> ntheta = 20
>>> nradius = 11
>>> length = 0.03
>>> omega = 157.1
>>> p_in = 0.
>>> p_out = 0.
>>> radius_rotor = 0.0499
>>> radius_stator = 0.05
>>> eccentricity = (radius_stator - radius_rotor)*0.2663
>>> visc = np.random.uniform(0.1, 0.2, 5)
>>> rho = 860.0
>>> elms = srs.ST_BearingElement.from_fluid_flow(
... 0, nz, ntheta, nradius, length,
... omega, p_in, p_out, radius_rotor,
... radius_stator, visc, rho,
... eccentricity=eccentricity, is_random=["visc"]
... )
>>> len(list(iter(elms)))
5
"""
attribute_dict = locals()
size = len(attribute_dict[is_random[0]])
args_dict = {
"kxx": [],
"kxy": [],
"kyx": [],
"kyy": [],
"cxx": [],
"cxy": [],
"cyx": [],
"cyy": [],
}
for k, v in attribute_dict.items():
if k not in is_random:
attribute_dict[k] = np.full(size, v)
else:
attribute_dict[k] = np.asarray(v)
for i in range(size):
fluid_flow = flow.FluidFlow(
attribute_dict["nz"][i],
attribute_dict["ntheta"][i],
attribute_dict["nradius"][i],
attribute_dict["length"][i],
attribute_dict["omega"][i],
attribute_dict["p_in"][i],
attribute_dict["p_out"][i],
attribute_dict["radius_rotor"][i],
attribute_dict["radius_stator"][i],
attribute_dict["visc"][i],
attribute_dict["rho"][i],
eccentricity=attribute_dict["eccentricity"][i],
load=attribute_dict["load"][i],
)
c = calculate_short_damping_matrix(fluid_flow)
k = calculate_short_stiffness_matrix(fluid_flow)
args_dict["kxx"].append(k[0])
args_dict["kxy"].append(k[1])
args_dict["kyx"].append(k[2])
args_dict["kyy"].append(k[3])
args_dict["cxx"].append(c[0])
args_dict["cxy"].append(c[1])
args_dict["cyx"].append(c[2])
args_dict["cyy"].append(c[3])
return cls(
n,
kxx=args_dict["kxx"],
cxx=args_dict["cxx"],
kyy=args_dict["kyy"],
kxy=args_dict["kxy"],
kyx=args_dict["kyx"],
cyy=args_dict["cyy"],
cxy=args_dict["cxy"],
cyx=args_dict["cyx"],
frequency=[fluid_flow.omega],
tag=tag,
n_link=n_link,
scale_factor=scale_factor,
is_random=list(args_dict.keys()),
)
