Rotordynamic Analysis Research Articles

Design and testing of CFRP sleeve for a high-speed permanent magnet synchronous motor with surface-mounted rotor

A high-speed (HS) permanent magnet (PM) synchronous motor (HSPMSM) with a carbon fiber-reinforced plastic (CFRP) protective sleeve in the surface-mounted rotor was explored in this study. In view of retaining the PMs at HS operations, the high-strength CFRP sleeve was designed on the basis of a process that could be summarized as follows. First, a multi-physics analysis of the rotor was conducted. The requirements to the CFRP sleeve were obtained from electromagnetic analysis, loss analysis, heat flow coupling computational fluid dynamics analysis, structural analysis, and rotor dynamics analysis. Second, the CFRP sleeve was designed by theoretical analysis. From the results, the thickness values of the carbon fibers in the circumferential and helical directions were chosen to be 4 and 1 mm, respectively, while the helical angle of carbon fibers was chosen to be 70°. Then, a plate-shaped CFRP product and a cylindrical CFRP product were fabricated to verify the strength and stiffness of the CFRP sleeve. The performance test results show that the hoop strength and elastic modulus and the axial strength and elastic modulus of the plate-shaped CFRP products at 20 °C are 1963 MPa @ 156 GPa and 550 MPa @ 36 GPa, respectively. The hoop strain and axial strain of the cylindrical CFRP product under 35 MPa are about 3000 and 1900 μe, which meet the design requirements of the HSPMSM.

Analysis of elastic supports and rotor flexibility for dynamics of a cantilever impeller

Turbochargers of modern internal combustion engines experience severe service conditions. In particular the compressor impeller is driven at extremely high angular velocity (30,000 rpm and more). Furthermore the increased requirements for the air intake dictate ever larger dimensions of the rotor disk up to 250 mm. These two factors lead to a pressing problem of stiffness, strength and dynamic stability of the newly designed units. This problem is analyzed with the help of a newly created parametric model of cantilever impeller rotor dynamics. This model accounts for the flexibility of the drive shaft and the impeller disk, quasistatic inertial and aerodynamic loads. The rotordynamics analysis is performed with a specific focus on the support behavior. The effect of initial gap and resilient characteristics of bearings and bushings is taken into account. As a result various components of displacements can be evaluated for different values of the disk diameter and angular velocity. It is critical for the design that neither radial nor axial displacement should not exceed given bounds. Furthermore, critical speeds of the studied rotor system have been determined for the various configurations of the disk and shaft dimensions. The proposed solution is to lower the first one or two eigenfrequencies of the system below the operating domain, so that the rotor becomes stable to any external excitations. Altogether, the developed mechanical analysis tool has proved itself as a useful tool for the engineering practice that allows to eliminate fatal flaws at early design stages.

A Scalable Time-Parallel Solution of Periodic Rotor Dynamics in X3D

A time-parallel algorithm is developed for large-scale three-dimensional rotor dynamic analysis. A modified harmonic balance method with a scalable skyline solver forms the kernel of this algorithm. The algorithm is equipped with a solution procedure suitable for large-scale structures that have lightly damped modes near resonance. The algorithm is integrated in X3D, implemented on a hybrid shared and distributed memory architecture, and demonstrated on a three-dimensional structural model of a UH-60A-like fully articulated rotor. Flight-test data from UH-60A Airloads Program transition flight C8513 are used for validation. The key conclusion is that the new solver converges to the time marching solution more than 50 times faster and achieves a performance greater than 1 teraFLOPS. The significance of this conclusion is that the principal barrier of computational time for trim solution using high-fidelity three-dimensional structures can be overcome with the scalable harmonic balance method demonstrated in this paper.

Effective Rotordynamics Analysis of High Speed Machine Tool Spindle – Bearing System

The work is focused on computation of high speed rotor bearing system using XLrotor. The spindle-bearing system which is considered as the most significant component of machine tool, due to its dynamic behavior at varying speeds affects machining productivity and quality. Therefore at design and development stage it is necessary to know the dynamic forces acting on rotor model that causes resonance. The XLrotor advanced computational method is adopted for analysis to assess, investigate and evaluate the performance of spindle- bearing system. The XLrotor tool performs effectively the complete rotordynamic analysis which determines Undamped Critical Speeds (UCS), Campbell diagrams, Imbalance Response and Load on Bearings at Imbalance. For rotor model, the balance correction masses and locations is calculated from measured vibration signature and balancing is carried out for spindle – bearing system as part of corrective measure using XLrotor.

Vibration analysis of rotor-bearing system using polynomial interpolation for squeeze film damper models

The implementation of numerical squeeze film damper (SFD) models into rotordynamic study is a time-consuming work since it is challenging to efficiently calculate the SFD forces under a variety of different situations. This paper proposes a new scheme to incorporate SFD models into rotordynamic analysis. A polynomial interpolation technique is introduced to solve for SFD forces under different operating conditions. To evaluate the efficiency of the proposed method, a rotor shaft supported by an SFD at either end has been selected for vibration study, where a finite element model is created to describe the system. The transient response of the rotor at a steady state rotational speed is presented for an open SFD application. In addition, the frequency response is evaluated by the slow acceleration scheme. The prediction resulted from the interpolation method shows excellent agreement with that from the direct method. Moreover, the proposed method significantly reduces the simulation time for application using advanced SFD models.

Three-Dimensional Solid Finite Element Contact Model for Rotordynamic Analysis: Experiment and Simulation

Abstract Conventional rotordynamic analyses generally treat the rotor as a continuous body without considering effect of clamped joints. However, in modern rotating machines, rotors are often assembled with multiple complex-shaped parts and joints, which may significantly affect rotordynamic behavior. Several authors have proposed methods for implementing contact effects in rotordynamic analysis, but a more general modeling method for handling arbitrary contact geometries with various levels of surface roughness is needed. The present paper suggests a new contact model for rotordynamic analysis of an assembled rotor-bearing system with multiple parts connected by multiple joints. A contact element formulation is presented using solid finite elements and statistics-based contact theories. A test arrangement was developed to validate the proposed contact model for varying interface surface roughness and preloads. An iterative computation algorithm is introduced to solve the implicit relation between contact stiffness and stress distribution. Prediction results, using the contact model, are compared with measured natural frequencies for multiple configurations of a test rotor assembly. A case study is performed for an overhung type rotor-bearing system to investigate the effect of contact interfaces, between an overhung impeller and a rotor shaft, on critical speeds.

Analyzing and Solving Stability Problems during the Commissioning of the Steam Turbine

The commissioning of the steam turbine in the CCPP of Vlore (Albania) was carried out after a shutdown of about one year. During previous operation of the unit, in particular in a couple of shutdowns, were observed high vibration at bearing MAD 21. Before the restart, the oil deflector of the MAD21 bearing (the bearing located in the front standard, on the inlet side of the steam turbine and adjacent to the clutch) was modified increasing the radial clearance on the part of the oil deflector acting as a thermal shield with the aim of eliminating / preventing the risk of rubbings. Rubs at the location of the above mention oil deflector were considered as the very likely cause of high vibration at bearing MAD 21. A lot of tests were carried out during the recommissioning phase and the data received were analyzed. This paper details the discovery of the problems, initial attempts to address them and the use of the rotor dynamics tools to find a solution of the problem by the optimization of the bearings. The bearings were not optimized as per rotordynamics analysis (RDA) findings, because it was a too expensive solution. The solution was found making some modification on control system of the ST, without affecting the mechanical integrity of the machine.

Rotordynamics analysis of a single helical gear transmission system for high speed applications

Since the non-linear dynamic response under various high-speed conditions can directly affect the life of gear transmission systems. In addition, the transmission error and dynamic mesh force play a key role in noise and harshness analysis of gear bearing coupled systems. So, in this piece of work, a 12 degree of freedom dynamic model is developed to probe the vibration response by using finite element method and taking into account the bearing and flexible shafts in the first part. Subsequently, some meshing gear characteristics such as dynamic and vibration acceleration response under different rotational speeds (1000-9000 rev/minute) were analyzed whereas critical speed appeared at 6500 rev/minute. Then, the stability analysis is performed to investigate the dynamics behind the critical speed by using MASTA. It was observed that natural frequency of 0.45 kHz for a fourth harmonic order is analogous to critical speed which further causes sudden elevation in both dynamic mesh force and transmission error.

Modal Analysis and Rotor-Dynamics of an Interior Permanent Magnet Synchronous Motor: An Experimental and Theoretical Study

This paper investigates mechanical vibrations of an interior permanent magnet (IPM) synchronous electrical motor designed for a wide range of speeds by virtue of the modal and rotordynamic theory. Mechanical vibrations of the case study IPM motor components were detected and analyzed via numerical, analytical and experimental investigation. First, a finite element-based model of the stator assembly including windings was set up and validated with experimental and analytical results. Second, the influence of the presence of the motor housing on the natural frequencies of the stator and windings was investigated by virtue of numerical modal analysis. The experimental and numerical modal analyses were further carried out on the IPM rotor configuration. The results show that the natural frequencies of the IPM rotor increase due to the presence of the magnets. Finally, detailed numerical rotordynamic analysis was performed in order to investigate the most critical speeds of the IPM rotor with bearings. Based on the obtained results, the key parameters related to mechanical vibrations response phenomena, which are important when designing electrical motors with interior permanent magnets, are provided. The main findings reported here can be used for experimental and theoretical mechanical vibration analysis of other types of rotating electrical machines.

EXPERIMENTAL EVALUATION OF PERFORMANCE AND MECHANICAL RELIABILITY FOR HIGH PRESSURE CO2 INTEGRALLY GEARED COMPRESSOR

Energy saving has become a trend as well as a countermeasure for global environmental issues. It can be one of the efficient solutions for reducing energy consumptions by adopting integrally geared compressors instead of inline compressors for industrial plants. The development of key technologies for the design centrifugal compressor such as CFD, FEM, Rotor dynamic Analysis has enabled integrally geared centrifugal compressors for higher pressure applications than ever. A commercial size, 5 stages integrally geared CO2 centrifugal compressor of 20MPaG discharge pressure level was designed, manufactured and evaluated the fluid dynamic performances and rotor stability. It was installed in OEM’s factory and the full load and full pressure test was carried out using real CO2 gas. The actual compressor fluid dynamic performance has shown superior results even at high pressure supercritical gas conditions at the high pressure stages of the compressor. The mechanical performances such as rotor vibration and bearing temperature were also measured and observed that the vibration was substantially low and within safe limits even at high pressure operating conditions above 20MPaG. Also the authors established a novel on Direct Rotor Excitation Method to experimentally investigate the rotor stability even at a high operating pressure level of 20MPaG. With this technique the measurements of the actual rotor natural frequencies and the damping ratios (log decrement) during high pressure operating conditions provided more precise results rather than conventional casing excitation method. The open impeller blade vibration was measured during running condition by using a non-contact blade vibration measurement technique. This measurement results revealed that impeller blades stress against the centrifugal force and the external excitation force was very low compared to the allowable stress value of the impeller material. The fluid dynamic characteristics and mechanical reliability are assessed as acceptable including super critical gas condition of CO2 gas.

Estimation of critical speeds of a rotor supported on ball bearings

In this work study of a rotor supported on ball bearings and containing a fatigue crack is carried out. The primary objective of the work is to obtain the load-distribution of the ball bearings from which the support stiffness in two transverse directions are obtained. The other objective is the rotor-dynamic analysis of a shaftsupported on these bearings. A mathematical model of a rigid rotorsupported on flexible bearings is considered for the purpose. Effects of bearing stiffness, damping and gyroscopic effects are included in the study. The governing equations of motion are obtained. The whirl frequencies of the rotor system are obtainedusing Eigen value formulation of the problem. A Campbell diagram is plotted which is used to obtain the critical speeds of the rotor system. These results are supported with the results from frequency response function plots.

270 MW급 발전용 대형 가스터빈의 로터다이나믹 설계 검증

Since large gas turbines used for power generation are operated in conjunction with the power grid, the operation stability is very important, so it must be fully verified from the design stage to the completion of production. The rotor of the gas turbine is difficult to analyze because it is assembled by fastening dozens of disks using tie rods, unlike the rotors of general rotary machines or steam turbines. DHI(Doosan Heavy Industries) is developing a large-scale 270 MW gas turbine(DGT-300HS1) for power generation. In this process, the rotor dynamic design consistency from the scale model to the actual rotor is reviewed in advance in order to improve the rotor dynamic analysis and design consistency. The final design and fabrication have been completed and the assembly is in progress. In this paper, the progress and verification results have been mentioned based on the final results of the development process.

Multiphysics Design and Multiobjective Optimization for High-Speed Permanent Magnet Machines

This article presents a multiphysics design process considering multiobjective optimization for high-speed permanent magnet machines (HSPMMs) to obtain an optimized design. Based on the initial dimensions, the parameters of the active part of the rotor are further limited through the analysis of rotor stress and dynamics. The multiobjective optimization on the electromagnetic characteristics is conducted under the above ranges of parameters to obtain high efficiency and low thermal load. The design parameters of the cooling system are analyzed and the thermal field is also studied using the coupled fluid-temperature model. A prototype has been fabricated and tested to validate the multiphysics design process including the multiobjective optimization.

Investigation of dynamic properties of the microturbine with a maximum rotational speed of 120 krpm – predictions and experimental tests

Advances in the development of analysis and design methods for fluid-flow machines have enabled both their multi-criteria optimisation and miniaturisation. To decrease the size of such a machine whilst, at the same time, maintaining its output power level, the rotor’s rotational speed needs to be increased. It is the reason for serious difficulties with respect to the rotor dynamics and the selection of a bearing system. This article discusses the simulation analysis and experimental research carried out on a prototypical microturbine, designed for use in a domestic ORC (organic Rankine cycle) cogeneration system. During the design process, the basic assumption was to develop a turbomachine, whose dimensions would have been as small as possible and whose output electric power would have been about 1 kilowatt. A supersonic impulse turbine, with a nominal rotational speed of 100,000 rpm, was used in order to obtain high flow efficiency. The maximum speed of the rotor was determined at a level of 120,000 rpm. The article presents the results of analyses made at the design stage and preliminary results of the experimental research. The numerical simulations covered the bearing system optimisation and the rotor dynamics analysis. Next, based on the outcomes of these analyses, a decision was made to use non-conventional gas bearings which are fed by the low-boiling medium’s vapour that comes from the ORC system. Within the framework of the experimental research, the dynamic behaviour of the turbogenerator was examined in terms of the rotational speed and produced energy. The performed measurements are proof of very good dynamic properties of the tested machine and after the research was over it was concluded that there were absolutely no signs of wear of the turbogenerator’s subassemblies.

Model reduction and dynamic matrices extraction from state-space representation applied to rotating machines

Model reduction is a relevant subject within the field of rotordynamics since low order models are fundamental for control strategies design and implementation, health monitoring, behavior prediction, Fault Detection and Identification (FDI) and stochastic analyses. In this context, this article proposes a complete review of three widely used reduction methods: static or Guyan technique, the System Equivalent Reduction Expansion Process (SEREP) and the modified SEREP. Regarding SEREP, a new approach is presented in which right and left eigenvectors from the undamped original system (with mass and stiffness matrices not symmetric) are used to transform all original system dynamic matrices. To modified SEREP (that contemplates all original system characteristics, including frequency dependent damping and gyroscopic effect) an extraction from the reduced state-space representation is achieved to build rotor and bearings reduced dynamic matrices with physical interpretability. A set of practical recommendations is presented, highlighting key aspects to increase reduction success chances. The methods are applied to two different rotors and results show satisfactory agreement between reduced and complete model responses when analyzing Frequency Response Functions (FRFs) and Campbell diagrams. The computational costs of processing each reduced model and running common rotordynamic analyses with reduced and complete models are compared.

Dynamic characteristics of drilling spindle supported by radial permanent magnet bearings

This paper presents the drilling spindle dynamic and harmonic characteristics supported by radial permanent magnet bearings (PMBs).Initially, multi-ring radial PMB is designed in proportionate to the dimensions of drilling spindle using Coulombain model and vector approach. Dynamic analysis of spindle is carried out for three different combinations between conventional angular contact bearings (ACBs) and PMBs. First, the spindle was supported by only ACBs. Second, ACBs were completely replaced by radial PMBs and one ACB was used in between two PMBs making it as a hybrid bearing set (HBS) in the last case. The effect of bearing preload, bearing span and cutting force on the spindle natural frequency, harmonic frequency and critical speed of drilling spindle system was investigated through rotor dynamic analysis. This analysis focuses on the feasibility of successful usage of HBS in drilling machine spindles with higher critical speeds and maximum amplitudes produced due to chattered vibrations and tangential cutting forces.

Performance analysis of magnetic gear with Halbach array for high power and high speed

In this study, we propose a non-contact 80 kW, 60,000 rpm coaxial magnetic gear (CMG) model for high speed and high power applications. Two models with the same power but different radial and axial sizes were optimized using response surface methodology. Both models employed a Halbach array to increase torque. Also, an edge fillet was applied to the radial magnetized permanent magnet to reduce torque ripple, and an axial gap was applied to the permanent magnet with a radial gap to reduce eddy current loss. The models were analyzed using 2-D and 3-D finite element analysis. The torque, torque ripple and eddy current loss were compared in both models according to the materials used, including Sm2Co17, NdFeBs (N42SH, N48SH). Also, the structural stability of the pole piece structure was investigated by forced vibration analysis. Critical speed results from rotordynamics analysis are also presented.

Rotor Stress and Dynamics Analysis of a High-Speed Permanent Magnet Machine for a Micro Gas Turbine Considering Multiphysics Factors

For high-speed permanent magnet machines (HSPMMs), the precise analysis of rotor stress and rotor dynamics is essential to ensure the stable operation of rotor under high-speed conditions. This work conducts an in-depth research on the rotor of an HSPMM for a micro gas turbine with predetermined geometrical sizes. Firstly, the mechanical and electromagnetic losses are investigated by both, empirical methods and finite element method (FEM) respectively, and then the 3D steady-state temperature distribution of the HSPMM is evaluated on this basis. Then, considering the non-isothermal temperature field of the rotor, the 3D thermal-structural coupling method is adopted to analyze the influence of the carbon fiber wrapping direction and the epoxy resin adhesive between permanent magnets (PMs) and rotor core on the rotor thermal stress. Furthermore, in the steady-state thermal field, considering the change in elastic modulus and the generation of thermal stress caused by temperature rise, the results of the modal analysis are compared with those of room temperature to analyze the effect of temperature on the natural frequency of the rotor. Finally, two prototypes of 80 kW, 60000 rpm HSPMMs are fabricated to test the capability of the HSPMM. The experimental results of back-to-back drag test and modal test verify the accuracy of the temperature characteristics and modal analysis, respectively.

Rotordynamic Analysis of a Dual-Spool Turbofan Engine with Focus on Blade Defect Events

Rotordynamic Analysis of a Dual-Spool Turbofan Engine with Focus on Blade Defect Events

Rotor Vibration Evaluation of Small Supersonic Aerospace Engine during Passing Through Critical Speeds by Steady-State Rotordynamic Analysis

Rotor Vibration Evaluation of Small Supersonic Aerospace Engine during Passing Through Critical Speeds by Steady-State Rotordynamic Analysis