Home
Verification Problems
This manual presents solved verification models including NAFEMS problems.
Rotor Dynamics
OS-V: 1030 Rigid Jeffcott Model
This problem describes the Rigid Jeffcott model for rotor dynamics.

Welcome
What's New
View new features for OptiStruct 2025.
Overview
OptiStruct is a proven, modern structural solver with comprehensive, accurate and scalable solutions for linear and nonlinear analyses across statics and dynamics, vibrations, acoustics, fatigue, heat transfer, and multiphysics disciplines.
Tutorials
Discover OptiStruct functionality with interactive tutorials.
User Guide
This manual provides detailed information regarding the features, functionality, and simulation methods available in OptiStruct.
Reference Guide
This manual provides a detailed list and usage information regarding input entries, output entries, and parameters available in OptiStruct.
Example Guide
The OptiStruct Example Guide is a collection of solved examples for various solution sequences and optimization types and provides you with examples of the real-world applications and capabilities of OptiStruct.
Verification Problems
This manual presents solved verification models including NAFEMS problems.
- Aerospace Verification
  This manual presents solved aerospace verification models including NAFEMS problems.
- NAFEMS Linear Elastic
- NAFEMS Thermo-elastic
- NAFEMS Heat Transfer
- NAFEMS Nonlinear Static Analysis
- NAFEMS Dynamic Response Analysis
- NAFEMS Random Response Analysis
- NAFEMS Normal Modes Analysis
- NAFEMS Composites
- Response Spectrum Analysis
- Elements
- Materials
- Fatigue Analysis
- Rotor Dynamics
  - OS-V: 1000 Complex Eigenvalue Analysis of Rotor Bearing System
    Rotor Bearing system is an excellent example of rotating machines used in mechanical engineering applications.
  - OS-V: 1010 Complex Eigenvalue Analysis of Rotor Bearing System
    Rotor Bearing system is an excellent example of rotating machines used in mechanical engineering applications.
  - OS-V: 1020 Nelson-Mac Vaugh Rotor Model (3D Rotor)
    The Nelson-Mac Vaugh rotor model for rotor dynamics is described to determine the critical speeds at which resonance occurs. The Campbell diagram is used in to review resonance and stability.
  - OS-V: 1030 Rigid Jeffcott Model
    This problem describes the Rigid Jeffcott model for rotor dynamics.
- Frequency Response Analysis
- Explicit Dynamic Analysis
- Aeroelastic Analysis
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding OptiStruct.

View All Altair HyperWorks Help

OS-V: 1030 Rigid Jeffcott Model

This problem describes the Rigid Jeffcott model for rotor dynamics.

Figure 1. Model

Model Files

Before you begin, copy the file(s) used in this problem to your working directory.

jeffcott.fem

Benchmark Model

The model details are as follows:

Unbalanced rigid disc on a massless rigid shaft.
CELAS, CTETRA4 and RBE2 elements defined.
ASYNC Complex Eigenvalue Analysis with Gyroscopic effects.
Rotor speed increments via RSPEED from 0 to 100 Hz, in steps of 10 Hz.

Material

The MAT1 material properties are:

Property: Value
Young's modulus (E): 1.0E+20 ton/s²-mm
Poisson's Ratio (NU): 0.3
Mass Density (RHO): 1.0 ton/mm³

Results

Figure 2. Eigen Mode Contour Plots

Figure 3. OptiStruct Results

The reference results are obtained by:

s = σ + i ω

Where,

\{\begin{cases} ω = \frac{J_{p} Ω \pm \sqrt{J_{p}^{2} Ω^{2} + 4 J_{t} K_{22}}}{2 J_{t}} \\ σ = 0 \end{cases}

$J_{p}$: Inertia moment of polar axis.
$J_{t}$: Inertia moment of transverse axis.
$K_{22}$: Stiffness of the transverse rotation.
$Ω$: Spinning speed [rad/s].
$ω$: Whirling frequency [rad/s].

Table 1. Comparison
RotorSpeed (Hz)	OptiStruct_mode 1*	OptiStruct_mode 2**	Reference_mode 1^¹	Reference_mode 2^¹
0	246	245	245.7213	245.7213
10	255	236	255.254	236.5446
20	265	227	265.1419	227.7231
30	275	219	275.3828	219.2546
40	286	211	285.9728	211.1353
50	297	203	296.9069	203.3599
60	308	196	308.1784	195.9211
70	319	189	319.7799	188.8141
80	331	182	331.7025	182.0274
90	344	175	343.9369	175.5524
100	356	169	356.4728	169.3789

* mode 1 - Forward Whirl Mode

** mode 2 - Backward Whirl Mode

Figure 4. Reference versus OptiStruct Results

¹ Genta, Giancarlo. “Dynamics of Rotating Systems.” Mechanical Engineering Series, 2005, doi:10.1007/0-387-28687-x.