Hydrodynamic bearings

[nilswagner]

Hi all,

Is it possible to compute the stiffness and damping parameters of hydrodynamic bearings for varying speeds by using ross?
The example is taken from the following paper

Model Reduction of Rotor-Foundation Systems Using the Approximate Invariant Manifold Method
https://doi.org/10.21203/rs.3.rs-2222988/v1

[ViniciusTxc3]

@nilswagner currently, there is the THDCylindrical() function that returns the stiffness and damping coefficients for hydrodynamic bearings, you can pass several speeds as in the example below:

import numpy as np
from ross.fluid_flow.cylindrical import THDCylindrical
from ross.units import Q_  

_frequency = Q_([900], "RPM")
bearing = THDCylindrical(
        axial_length=0.263144,
        journal_radius=0.2,
        radial_clearance=1.95e-4,
        elements_circumferential=11,
        elements_axial=3,
        n_pad=2,
        pad_arc_length=176,
        preload=0,
        geometry="circular",
        reference_temperature=50,
        speed=_frequency,
        load_x_direction=0,
        load_y_direction=-112814.91,
        groove_factor=[0.52, 0.48],
        lubricant="ISOVG32",
        node=3,
        sommerfeld_type=2,
        initial_guess=[0.1, -0.1],
        method="perturbation",
        operating_type="flooded",
        injection_pressure=0,
        oil_flow=37.86,
        show_coef=False,
        print_result=False,
        print_progress=False,
        print_time=False,
    )
print(bearing)

[Pierre-zhu]

when I run my code, I get following error:

File d:\ProgramData\Anaconda3\Lib\site-packages\ross\fluid_flow\cylindrical.py:237 in init
lubricant_properties = lubricants_dict[self.lubricant]

KeyError: 'SEAWATER'

but I already add seawater in D:\ProgramData\anaconda3\Lib\site-packages\ross\fluid_flow\lubricants.py

[ViniciusTxc3]

I believe you are running ross directly with pip. For my example above, you would have to clone our repository and insert it manually.

As a simpler solution, We're uploading an update where it will be possible to insert the lubricant directly as a dictionary in PR #1147 also adding seawater as a new lubricant.

Note: After this update, to import the THDCylindrical class, it will be as follows from ross.bearing.cylindrical import THDCylindrical.

This is an example code that I ran in my tests:

import numpy as np
from ross.bearing.cylindrical import THDCylindrical
from ross.units import Q_  

_frequency = Q_([900], "RPM")
_radial_clarence = 1.2e-3
_lubricant_seawater = {
    "liquid_viscosity1": Q_(1.08e-03, "Pa*s").to_base_units().m,
    "temperature1": Q_(20, "degC").to_base_units().m,
    "liquid_viscosity2": Q_(0.35e-03, "Pa*s").to_base_units().m,
    "temperature2": Q_(100, "degC").to_base_units().m,
    "liquid_density": Q_(1025, "kg/m**3").to_base_units().m,
    "liquid_specific_heat": Q_(3850, "J/(kg*degK)").to_base_units().m,
    "liquid_thermal_conductivity": Q_(0.6, "W/(m*degC)").to_base_units().m,
    "vapour_viscosity": Q_(9.75e-06, "Pa*s").to_base_units().m,
    "vapour_density": Q_(0.597, "kg/m**3").to_base_units().m,
    "vapour_specific_heat": Q_(2010, "J/(kg*degC)").to_base_units().m,
    "vapour_thermal_conductivity": Q_(0.025, "W/(m*degK)").to_base_units().m,
    "saturation_pressure": Q_(101325, "Pa").to_base_units().m,
    "surface_tension": Q_(0.074, "N/m").to_base_units().m,
    "molecular_weight": Q_(18.015, "g/mol").to_base_units().m,
}

bearing = THDCylindrical(
        axial_length=0.263144,
        journal_radius=0.2,
        radial_clearance=_radial_clarence,
        elements_circumferential=11,
        elements_axial=3,
        n_pad=2,
        pad_arc_length=176,
        preload=0,
        geometry="circular",
        reference_temperature=50,
        speed=_frequency,
        load_x_direction=0,
        load_y_direction=-112814.91,
        groove_factor=[0.52, 0.48],
        lubricant=_lubricant_seawater,
        node=3,
        sommerfeld_type=2,
        initial_guess=[0.1, -0.1],
        method="perturbation",
        operating_type="flooded",
        injection_pressure=0,
        oil_flow=37.86,
        show_coef=False,
        print_result=False,
        print_progress=False,
        print_time=False,
    )
print(bearing)

[Pierre-zhu]

OK，thanks , I can use "seawater" now accoring to your guide.
But I try to calculation my example bearing , still some errors as such bearing without arc , full circular. bearing be define as following:
`
bearingCase1 = THDCylindrical(
axial_length=1.175, # m
journal_radius=0.385/2.0, #m
radial_clearance=1.29/2000.0, #m
elements_circumferential=11,
elements_axial=2, #Number of volumes along the Z direction (axial direction).
n_pad=2,
pad_arc_length=360, #Arc length of each pad. The unit is degree.
preload=0,
geometry="circular",
reference_temperature=30,
speed=Q_([153], "RPM"), # rad/s
load_x_direction=0, #N
load_y_direction=-7.5e4, # N
groove_factor=[0.0, 0.0],
lubricant="SEAWATER",
node=3,
sommerfeld_type=2,
initial_guess=[0.1, -0.1], #Array with eccentricity ratio and attitude angle
method="perturbation",
operating_type="flooded",
injection_pressure=0,
oil_flow=57.8, #litre/min
show_coef=False,
print_result=False,
print_progress=False,
print_time=False,
)
print(bearingCase1 )

`

error as following:
d:\ProgramData\Anaconda3\Lib\site-packages\ross\bearing\cylindrical.py:1867: OptimizeWarning: Covariance of the parameters could not be estimated
popt, pcov = curve_fit(viscosity, xdata, ydata, p0=(6.0, 1.0))

[ViniciusTxc3]

Analyzing your case, there are some considerations that should be made:

The element values ​​need to be larger so that an axis of this size can be discretized, suggest:

elements_circumferential=20,
elements_axial=20,

There are 2 pads, the value of pad_arc_length needs to be recalculated:

pad_arc_length=176,

The groove_factor needs to be 0.5:

groove_factor=[0.5, 0.5],

The load_y_direction seems that with this lubricant the eccentricity is high. Maybe it can't support this load. I did some tests with values ​​between -0.5e4 and -0.5e3 and got some results that you can use as a starting point.

I suggest enabling the parameters below so you can track the progress:

print_result=True,
print_progress=True,

[Pierre-zhu]

Thanks ,I will try again following.