Help with torsional time response

[joselivera]

I'm trying to do an simulation of the following system:

It's basically a generator/motor coupled to an flywheel by a shaft and I'm interested in the torque transient in the flywheel connection, thanks to the topics:

#1134
#795

I managed to create the following model:

%pip install ross-rotordynamics

import numpy as np
import matplotlib.pyplot as plt
import ross as rs
import plotly.io as pio
pio.renderers.default = "colab"

steel = rs.Material("Steel", E=211e9, G_s=81.2e9, rho=7810)

shaft = rs.ShaftElement(L=1, idl=0.0, odl=0.15, material=steel, shear_effects=True, rotary_inertia=True)

# Bearings at both ends
bearing0 = rs.BearingElement(n=0, kxx=1e6, cxx=100)
bearing1 = rs.BearingElement(n=1, kxx=1e6, cxx=100)

# Disk at node 1
disk = rs.DiskElement.from_geometry(n=2, material=steel, width=0.5, i_d=0.0, o_d=0.10)

coupling = rs.CouplingElement(
    m_l=10,  # Mass on the left station
    m_r=10,  # Mass on the right station
    Ip_l=10,   # Polar moment of inertia on the left station
    Ip_r=10,   # Polar moment of inertia on the right station
    kr_z=1000,  # Torsional stiffness
)
shaft_elements = [coupling, shaft] # Cant insert disk element
rotor = rs.Rotor(shaft_elements, disk_elements=[disk])

rotor.plot_rotor()

t_end = 1.0
n_samples = 5001
t = np.linspace(0, t_end, n_samples)
freq = 20.0  # Hz
torque_amp = 5.0  # N·m

node_input = 0
node_output = 2
global_dof_torque_input = 6 * node_input + 5
global_dof_torque_output = 6 * node_output + 5

F = np.zeros((n_samples, rotor.ndof))
F[:, global_dof_torque_input] = torque_amp * np.sin(2 * np.pi * freq * t)

speed = 0.0
response = rotor.run_time_response(speed, F, t, method="newmark")

# Retrieve angular displacement at node 2 (θ DOF)
theta = response.yout[:, global_dof_torque_output]  # [rad]
dt = t[1] - t[0]

# Angular acceleration via second derivative
theta_ddot = np.gradient(np.gradient(theta, dt), dt)

# Compute theoretical torque = I_p * theta_ddot
Ip_disk = disk.Ip
tau_computed = Ip_disk * theta_ddot

plt.figure(figsize=(10,5))
plt.plot(t, F[:, global_dof_torque_input], label="Applied Torque τ(t)", linewidth=2)
plt.plot(t, tau_computed, "--", label="Iₚ·θ̈(t) (computed)", linewidth=2)
plt.xlabel("Time [s]")
plt.ylabel("Torque [N·m]")
plt.legend()
plt.grid(True)
plt.title("Verification of Torque–Angular Acceleration Relation in ROSS")
plt.show()

But I'm not sure if my model could be used to do that, since my results doesn't make any sense, can someone help me with that?
I don't know if the coupling element is the able to simulate the torsional stiffness of the structure we call "rotor spider".
https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs40430-018-1340-0/MediaObjects/40430_2018_1340_Fig1_HTML.png

Anyway, thanks in advance, I really appreciate the help!

[jguarato]

Hi @joselivera!
I’ll investigate your case to understand what might be happening.