Multi-Shaft and Multi-Component Rotor Systems: Advanced Modeling for Vertical Machines

Rotor systems in modern machinery are becoming increasingly complex, particularly in the case of multi-shaft and multi-component designs. Multi-component rotor systems, which include gas turbines, electric generators, turbochargers, pumps, and other rotating machinery, are vital in power generation, aviation, oil and gas, and other advanced sectors. To ensure their reliability and performance, analyzing rotor dynamics requires precise, advanced modeling tools that account for complex mechanical and aerodynamic interactions.

Given the increasing complexity of these systems, traditional rotor dynamics approaches must evolve to account for multi-shaft and multi-component interactions. Advanced modeling techniques enable engineers to analyze not just individual shafts but also the interconnected components that influence overall system behavior.

 

Features of Multi-Shaft and Multi-Component Rotor Systems

Traditionally, rotor dynamics analysis has focused on individual shafts. However, even a single rotor shaft may consist of multiple interconnected components, such as modular shaft sections, disks, couplings, and flexible segments. To fully understand the dynamic behavior of these systems, each component must be modeled accurately. In more complex systems, multiple shafts are interconnected through gear, hydrodynamic, or electromagnetic couplings, adding an additional layer of complexity.

Moreover, the machine housing plays an essential role in influencing rotor dynamics. It impacts rotor behavior through bearing supports and structural deformations, affecting everything from stability to vibration characteristics [1].

When modeling vertical machines such as pumps, turbines, and compressors, the challenge becomes even greater. Vertical rotors experience additional gravity-induced loads and are more sensitive to misalignments and variations in housing stiffness. Ignoring the housing influence can lead to incomplete rotor dynamics analysis and inaccurate predictions of reliability and performance.

Importance of Housing Modeling

The machine housing is not just a mechanical enclosure; it actively participates in dynamic processes and significantly influences the overall rotor behavior. Housing deformations can alter system stiffness, modify vibration characteristics, and introduce additional resonance effects. The interaction between the rotor and housing through bearing supports affects stability, damping, and the propagation of dynamic loads throughout the system. Failing to account for these interactions can lead to underestimations of system vibrations, misidentification of critical speeds, and unanticipated resonance phenomena, which may ultimately compromise machine reliability.

Key aspects of housing influence in rotor dynamics include:

• Structural Flexibility: Housing deformations can introduce local changes in stiffness and alter the natural frequencies of the system.
• Damping Characteristics: The housing contributes to the dissipation of vibrational energy, affecting overall system stability.
• Coupling Effects: Interaction with the rotor can create additional dynamic forces, leading to complex vibration modes.
• Thermal Expansion and Distortion: Temperature variations can lead to housing deformation, causing misalignment and altering rotor behavior.
• Support Structure Influence: Bearings and mounting elements act as critical interfaces between the housing and rotor, transmitting dynamic forces and affecting response characteristics.

In vertical machines, additional considerations must be made for the direction of gravitational forces, which influence the distribution of loads along the rotor system. It is also essential to account for thrust bearings and axial loads, as these components play a critical role in maintaining system stability and ensuring proper force distribution within the rotor-bearing assembly. Neglecting these aspects can lead to increased wear, improper load transmission, and even premature failure of key components.

Modern rotor dynamics software includes sophisticated models that account for housing flexibility, its modal properties, and complex interactions with the rotor. Applying finite element analysis (FEM) enables:

• Accurate consideration of housing influence on system dynamics
• Determination of critical frequencies and potential resonance phenomena
• Analysis of misalignment effects and thermal deformations
• Improved accuracy in predicting system stability and lifespan
• Enhanced optimization of housing design to reduce unwanted vibrations and stresses
• Precise modeling of axial loads and thrust bearing effects, ensuring realistic boundary conditions
• Simulation of housing components by setting their rotational speed to zero, allowing for accurate modeling of structural interactions

These capabilities are integrated into AxSTREAM RotorDynamics, which allows engineers to simulate complex rotor systems, incorporating boundary conditions such as axial forces, thrust bearings, and gravitational effects. This software enables the creation of multi-component rotor systems, offering a more thorough analysis of rotor performance and stability. The software also enables the creation of complex component structures and their connections, allowing for a more detailed and comprehensive analysis of multi-component rotor systems.

For example, the modeling of a vertical pump in AxSTREAM RotorDynamics (as illustrated in the included diagram) demonstrates how the software can account for housing flexibility, thrust bearings, and axial loads while providing a detailed dynamic assessment of the entire system.

AxSTREAM RotorDynamics Software Solutions

AxSTREAM RotorDynamics provides powerful tools for analyzing multi-shaft and multi-component rotor systems, including:

• Comprehensive modeling of rotor-housing interactions;
• Analysis of vertical machines considering gravitational factors;
• High-precision numerical methods for calculating critical speeds, unbalance response and system stability;
• Integrated consideration of thrust bearings and axial loads, ensuring accurate boundary condition representation in AxSTREAM RotorDynamics;
• Capability to model housing components by assigning a rotational speed of zero, facilitating accurate analysis;
• Support for creating and connecting complex multi-component structures, enhancing design flexibility and accuracy.

By leveraging these tools, engineers can optimize rotor designs, prevent detrimental vibrations, and enhance equipment longevity. With AxSTREAM RotorDynamics, multi-shaft and multi-component rotor systems can operate with maximum efficiency and reliability, ensuring their performance and safety in even the most demanding industrial environments.

References:

[1] Moroz, L, Romanenko, L, Kochurov, R, & Kashtanov, E. “Prediction of Structural Supports Influence on Rotating Machinery Dynamics.” Proceedings of the ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. Volume 7B: Structures and Dynamics. Charlotte, North Carolina, USA. June 26–30, 2017. V07BT33A001. ASME. https://doi.org/10.1115/GT2017-63035

[2] Byung Ok Kim, Sung Jin Yang, Myung Ho Lee “Rotordynamic Transient Analysis of Vertical Sea Water Lift Pump for FPSO Deep Well”, The KSFM Journal of Fluid Machinery, Volume 14 Issue 5 / Pages.69-74 https://doi.org/10.5293/kfma..2011.14.5.069