A rotor is a body suspended through a set of cylindrical hinges or bearings that allow it to rotate freely about an axis fixed in space. It is the most critical component of any rotating machine; often operating at high speeds and within a wide speed range (Figure 1). Rotor dynamics is the branch of engineering that studies the lateral and torsional vibrations of rotating shafts. The main purpose of rotor dynamics is to predict the rotor vibrations and keep the vibration level under an acceptable limit. To meet stringent reliability requirements, each step of the rotor design should be based on an accurate rotor dynamics prediction.
A rotor dynamics analysis should accomplish several goals. It should predict critical speeds at which vibration due to rotor unbalance is severe and should be avoided. Relatedly, it should suggest modifications that would allow designers to increase a machine’s critical speeds. Rotor dynamics analysis should also predict natural frequencies of torsional vibration, as well as amplitudes of synchronous vibration caused by rotor unbalance. In addition, the analysis should predict dynamic instability (including oil whip), and suggest design modifications to suppress it. Lastly, the analysis should recommend balance correction masses and locations from measured vibration data.
Real-world rotor dynamic systems are typically too complex for existing models to solve in all but the simplest cases. Still, numerical solutions for simplified 2D and 3D models of rotor dynamic systems are standardly used, as they provide decent data for engineers to go on. The Jeffcott rotor is one example of such a simplified model that is commonly employed
Nevertheless, these numerical solutions do not provide the kind of deep insight that can be had from a step-by-step derivation of an analytical solution. Such a derivation can tell us how the different system response characteristics are interconnected in the final design, and thereby provides higher quality data than 2D / 3D models alone do.
The software provides a comprehensive rotor modeling capability, including shaft design, mass-inertia elements, bearings and supports, couplings, as well as forces and accelerations affecting the rotor stress state and its prestress conditions
Each rotor’s unique features impose strict limitations on the structural finite-element method that engineers use to predict vibration response. This method should be capable of calculating the dynamic characteristics of the rotor auxiliary components, such as bearings, supports, and seals.
Engineers are thus able to analyze a rotor’s safe operation with regard to its stress state, vibration response, stability, transient issues occurring during its operation, and more
Errors in prediction of the peak values of the rotor deflection and stress amplitudes can have severe consequences. If the amplitudes are overestimated, necessary design changes cannot be accurately determined in the early stages of the project. If the amplitudes are underestimated, the safety of the rotor operation would be compromised, risking catastrophic failure. It is also important to account for the influence of rotor components such as bearings and supports, since they too can impact the peak values of the rotor deflection and stress amplitude.
The real dynamics of a machine are difficult to model perfectly. Instead, the calculations engineers often use are based on simplified models that resemble various structural components (lumped parameters models), and on equations obtained both from solving models numerically (Rayleigh-Ritz method), and from the finite element method (FEM).
Siemens Digital Industries Software announced the latest update to Siemens’ Simcenter 3D software, part of Siemens’ Xcelerator portfolio of software and services. Among the new capabilities, Simcenter 3D offers increased support for turbomachinery modeling, a dedicated drop test application for handheld devices, tightly integrated topology optimization with the NX Design environment, and a new acoustic solution method that is up to 10 times faster than standard methods.
Siemens’ Isocenter 3D 2022.1 release focuses on helping engineers overcome challenges in four key areas:
Model the complexity: The ability to model and understand complex physical phenomena is at the forefront of this release. Isocenter 3D’s industry-leading solution for the turbomachinery industry has been extended with additional thermal Multiphysics, rotor dynamics and thermal fatigue capabilities to more accurately capture the complex physics happening within these machines. A new dedicated set of tools to simulate spiral bevel gears, as often found in automotive differentials, enables accurate, system-level NVH analysis on these mechanisms to reduce gear whine. Additionally, a new dedicated application simplifies and streamlines the drop-test simulation process for electronic and other handheld devices for engineers who are not simulation experts.
Explore the possibilities: Acoustics naturalization capabilities allow engineers to not only simulate but also listen to the acoustics/sound within the context of the end-user’s experience. Engineers can now mix all contributing sounds and listen to the combined acoustics results to answer questions such as “What will a loudspeaker sound like when you put it in a car and combine it with background noise from the engine, HVAC, wind and road?” In this release, topology optimization is now more tightly integrated with the NX Design environment so that simulations are ‘repayable’ and become easier for designers to create lightweight, yet structurally capable designs.
Go faster: Two core updates enable our customers to break new ground more quickly than ever before. The new high-performance boundary element method with adaptive order solution (BEMAO) used for acoustics simulation is up to 10 times faster compared to the standard boundary element method, while new load case filtering for aero structures allows engineers to quickly determine the final critical list of load cases from the thousands of load cases experienced in an airframe.
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