Showing papers on "Critical speed published in 2020"

Effects of Design Parameters on the Multiphysics Performance of High-Speed Permanent Magnet Machines

Abstract: In the design of high-speed permanent magnet machines (HSPMMs), comprehensive effects of design parameters on the various properties of electromagnetic loss, rotor stress, rotor critical speed, and temperature distribution must be analyzed to obtain the optimal design. The aim of this paper is to examine the effects of design parameters, such as the pole number, stator slots number, number of conductors per slot, permanent magnet (PM) thickness, PM pole arc coefficient, air gap length, rotor diameter, core length, and sleeve thickness, on multiphysics performance based on a high-power HSPMM. A reasonable design is determined according to the abovementioned analysis that satisfies all specified multiphysics constraints. The theoretical results are confirmed by the experimental results on a prototype in terms of electromagnetic, mechanical, and thermal characteristics such as back electromotive force, no-load loss, full-load current, overspeed experiment, and temperature distribution.

Parameter Design for a High-Speed Permanent Magnet Machine Under Multiphysics Constraints

Abstract: Regarding high-speed permanent magnet machines (HSPMMs), there is a lack of complete and detailed design processes for main parameters under multiphysics constraints, which makes it difficult to obtain high-reliability designs for designers of HSPMMs. This paper presents a detailed and complete design process for the main parameters of an HSPMM under multiphysics constraints. Firstly, the initial sizes are obtained through electromagnetic and mechanical design theory. Then, the influence of design parameters on rotor stress is analyzed in detail, including PM material, rotor temperature, sleeve thickness, PM thickness and rotor diameter. Furthermore, the rotor dynamics have also been studied in detail, including the effects of bearing stiffness, impeller mass, rotor diameter, core length, and gyroscopic effect on critical speed. Afterwards, the comprehensive research on the electromagnetic filed and the loss characteristics is performed. The cooling system is designed and the thermal field is also studied in Ansys-Cfx. Besides, the coupled temperature-stress analysis is established considering the interaction between temperature and mechanical characteristics. Finally, a full-size HSPMM prototype has been fabricated and tested to validate the detailed multiphysics design process.

Vibration suppression of nonlinear rotating metamaterial beams

Abstract: In this paper, we investigate the nonlinear vibration of a metamaterial structure that consists of a rotating cantilever beam attached to a periodic array of spring–mass–damper subsystems deployed for vibration suppression. The full nonlinear model of the system is developed. The nonlinear response due to a primary resonance excitation is investigated, and the capability of the metastructure to suppress vibration is examined. The mass of the resonators (absorbers) comes at the expense of the host structure’s mass itself, which makes the total mass of the system conservative. Free and forced vibration analyses are performed. We first use the method of multiple scales to analyze the nonlinear behavior of rotating beams. The perturbation solutions are validated against their numerical counterparts. Results show the presence of a critical rotational speed at which the beam undergoes bifurcation and starts to flutter. The addition of the absorbers is observed to slightly reduce this critical speed. Nevertheless, the amplitude of limit-cycle oscillations beyond bifurcation is found to decrease when equipping the rotating beam with local absorbers. The results demonstrate the capability of the metamaterial structure as an efficient damping treatment. Furthermore, we show that careful placement of the absorbers along the cantilever beam (close to the tip) enables further vibration mitigation.

Potential well escape in a galloping twin-well oscillator

Abstract: When a bi-stable oscillator undergoes a supercritical Hopf bifurcation due to a galloping instability, intra-well limit cycle oscillations of small amplitude are born. The amplitude of these oscillations grows as the flow speed is increased to a critical speed at which the dynamic trajectories escape the potential well. The goal of this paper is to obtain a simple yet accurate analytical expression to approximate the escape speed. To this end, three different analytical approaches are implemented: (i) the method of harmonic balance, (ii) the method of multiple scales using harmonic and elliptic basis functions, and (iii) the Melnikov criterion. All methods yielded an identical expression for the escape speed with only one key difference which lies in the value of a constant that changes among the different methods. A comparison between the approximate analytical solutions and a numerical integration of the equation of motion demonstrated that the escape speed obtained via the multiple scales method using the elliptic functions and the Melnikov criterion are in excellent agreement with the numerical simulations. On the other hand, the first-order harmonic balance technique and the multiple scales using harmonic functions provide analytical estimates that significantly underestimate the actual escape speed. Using the Melnikov criterion, the influence of parametric and additive noise on the escape speed was also studied.

Theoretical Analysis of the Vibrations in Gas Turbine Rotor

Abstract: Vibration analysis plays an important role in the dynamics of rotors, which can be afflicted by unbalancing forces that, over the long term, can lead to the initiation and growth of cracks at the rotor shaft. To predict cracking, it is necessary to study the vibration parameters of the rotor and existence of expected cracks. In this study, rotor vibration was studied analytically and numerically using a developed ANSYS code. The rotor under consideration is supported by journal bearings, the stiffness and damping coefficients were calculated analytically and then applied to the vibration model of the rotor. The results of the numerical analysis were compared with those obtained analytically. Good agreement was obtained between both solutions, with maximum error of 7.31% for the critical speed. These results show that when the depth of the crack is increased, the orbit size and the response are also increased while the critical speed is reduced.

Nonlinear dynamic analysis of Qom Monorail Bridge considering Soil-Pile-Bridge-Train Interaction

Abstract: Railway tracks experience has shown that considering the effects of Soil-Structure Interaction (SSI) especially for soft soil sites is necessary. These effects can also be important for monorail bridges on soft soil beds. The main aim of this study is to investigate the effects of Soil-Pile-Bridge-Train Interaction (SPBTI) on the Qom Monorail Bridge (QMB) responses. In spite of many studies on the effects of monorail train-bridge (fixed-base structure) interaction, very little information is available in the literature on the effects of monorail trains on SPB systems. In this paper, an advanced three-dimensional (3D) continuum finite element analysis of QMB subjected to train moving loads was developed. The SPBT models have been validated using three case studies (two bridge-monorail train studies and a soil-pile-structure study) available in the literature. The maximum displacements of the guideway beam at the different train speeds were obtained for various SPBT system conditions. The effects of the stiffness and thickness of the soil, the bridge span length, and the amplitude, length, and geometry of the train loading on the critical speed of the SPBT system are discussed in detail. Finally, the results have been synthesized into simple design charts to select the appropriate straddle-type monorail train and determine its critical speed for a particular soil-bridge condition. In addition, a new simple method for simulating the behavior of the finger-bands (as one of the excitation source of vertical bridge vibrations) in commercial software was presented. The results show that the position of a monorail train bogies plays an important role in determining critical speed so that with uniformity the spacing between the bogies decreases the critical speed in the vertical direction.

Free Vibration Characteristics of Rotating Functionally Graded Porous Circular Cylindrical Shells with Different Boundary Conditions

Abstract: The free vibration of rotating functionally graded porous (FGP) circular cylindrical shell with different boundary conditions is presented analytically in this study. The porous material properties are assumed to be graded in the thickness direction of the cylindrical shell according to three types of porosity distributions. By using Love’s shell theory and Hamilton’s principle, the governing equations of the rotating FGP cylindrical shell are derived, in which the effects of the centrifugal and Coriolis forces due to rotation are also taken into account. The natural frequencies of the rotating FGP cylindrical shell structure subjected to different boundary conditions are determined by applying Galerkin’s method together with beam functions of longitudinal mode functions. To validate the present results, comparisons between the results of the present method and previous studies are performed; a very good agreement is achieved. Besides, some influences of porous material properties, boundary conditions, circumferential wave number, geometric parameters, Coriolis acceleration, rotating speed on natural frequency as well as critical speed of the rotating FGP cylindrical shell are given.

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

Abstract: 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.

Detection of a slant crack in a rotor bearing system during shut-down

Abstract: The transient response of a slant-cracked rotor system during shut-down has been analyzed while it is decelerating through the critical speed. Vibration response has been simulated by using finite ...

Magnetization State Selection Method for Uncontrolled Generator Fault Prevention on Variable Flux Memory Machines

Abstract: Permanent magnet (PM) machine drive system is vulnerable to uncontrolled generator fault (UCGF) when all gating signals are removed from inverter during high-speed operation. Due to the PM flux controllability of variable flux memory machine (VFMM), this article proposes a novel magnetization state selection (MSS) method, which can not only extend the machine speed range effectively but also avoid the overvoltage issue during UCGF process. In the proposed MSS method, the VFMM operates at several different magnetization states (MSs) to reduce the MS changing frequency. The critical speed of each MS is determined by a steady-state UCGF model to restrict the maximum voltage within a safety margin. Consequently, the overvoltage issue of the VFMM can be eliminated during the entire UCGF process. On the other side, the proposed scheme can also realize highly efficient flux weakening for speed range extension with a reduced requirement of d -axis current excitation. Finally, the developed control strategy is verified by experimental measurements on a VFMM prototype.

Nonlinear hunting stability of high-speed railway vehicle on a curved track under steady aerodynamic load

Abstract: This paper investigates the nonlinear hunting stability of a high-speed vehicle on a curved track under steady aerodynamic load. We first established a nonlinear dynamic model of high-speed...

Convective transport around two rotating tandem circular cylinders at low Reynolds numbers

Abstract: The convective transport around two rotating circular cylinders kept in a tandem configuration to an unconfined flow of an incompressible fluid (Prandtl number, Pr = 0.717) is investigated through two-dimensional numerical simulation. The flow Reynolds number is considered constant at Re = 100. Four different gap spacings between the tandem cylinders such as 0.2, 0.7, 1.5 and 3.0 are chosen for simulation. The cylinders are rotating about their centroidal axes for a range of dimensionless speed $$ \left( {0 \le \Omega \le 2.75} \right) $$ . The rotation to the objects causes the unsteady periodic flow around them to become stabilized and at some critical rotational speed, the vortex shedding stops completely resulting in a steady flow pattern. The critical speed of rotation at which the vortex shedding completely stops is a function of the cylinder spacing. Overall, it is observed that increasing the gap increases the critical rotation rate. The thermal fields are also strongly stabilized as a result of the cylinder rotation. The rotating cylinders actually create a zone in their proximity which acts like a buffer to the convective transport. The conduction mode of heat transfer predominates in these regions causing the heat transfer rate to assume a decaying pattern with increasing the rotational speed at all cylinder spacings.

An integrated moving element method (IMEM) for hydroelastic analysis of infinite floating Kirchhoff-Love plates under moving loads in a shallow water environment

Abstract: The article introduces a novel integrated moving element method (IMEM) to hydroelastic analysis of infinitely extended floating plates under moving loads in shallow water conditions. The floating plate is modeled via the Kirchhoff-Love theory, while the linearized shallow-water equation is adopted for the hydrodynamic modeling. Both computational domains of fluid and structure are concurrently discretized into “moving elements” whose coordinate system moves along with applied loads. Accordingly, the paradigm can absolutely eradicate the update procedure of force vector owing to the change of contact point with discretized elements not only for the plate but also for the fluid. Furthermore, the IMEM also requires fewer number of discrete elements than the standard finite element method (FEM) due to their independence with the distance of moving load. Results obtained in several numerical examples are compared with those of the Fourier Transform Method (FTM) to validate the accuracy and effectiveness of the proposed methodology. In addition, the influence of water depth, load speed, multiple contact points, as well as the distance between axles on the dynamic amplification factor of plate displacement and the loading's critical speed is also examined in great detail.

Influences of Hydrodynamic Forces on the Identification of the Rotor-Stator-Rubbing Fault in a Rotating Machinery

Abstract: Mechanical failures of a complex machine such as rotor widely used in severe conditions often require specialized knowledge, technical expertise, and imagination to prevent its rupture. In this paper, a model for analyzing excitation of a coupled lateral-torsional vibrations of a shaft system in an inviscid fluid is proposed. The model considers the recurrent contact of the vibrating shaft to a fixed stator. The simplified mathematical model of the rotor-stator system is established based on the energy principle. The dynamic characteristics of the fluid-rotor system are studied, and the features of rub-impact are extracted numerically and validated experimentally under the effects of the unbalance and the hydrodynamic forces. The main contribution of this article is in extraction and identification of the rub features in an inviscid medium which proved to be complex by the obstruction of the fluid and required the use of appropriate signal processing tools. The results through a synchrosqueezing wavelet transform indicated that the exciting fluid force could significantly attenuate the instability and amplitude of rubbing rotor. The experimental results demonstrated that for half the first critical speed, the subharmonic and the irregular orbit patterns provide good indices for rub detection in an inviscid fluid of the rotating shafts. Finally, it is revealed that the instantaneous frequency extraction based on wavelet synchrosqueezing is a useful tool to identify the weak and hidden peak harmonics localised in the time-frequency maps of the fluid-rotor system.

Modeling and Dynamic Characteristics Analysis of Blade-Disk Dual-Rotor System

Abstract: In this paper, a simplified dynamic model of a dual-rotor system coupled with blade disk is built, and the effects of blade parameters of an aircraft engine on the dynamic characteristics of a dual-rotor system are studied. In the methodology, the blade is simplified as a cantilever structure, and the dynamical equations are obtained by the means of a finite element method. The amplitude-frequency response curves and orbits of shaft centre-vibration shape diagram are used to analyze the effects of blade parameters on dynamic characteristics of a dual-rotor system. The results indicate that the properties of the blades have huge impacts on the critical speed and other dynamic characteristics of the system. With an increase of the length of the blade, the second-order critical speed decreases obviously, but the first-order critical speed is almost invariant; this means that the blades attached on the low-pressure compressor do not affect the first-order critical speed of the dual-rotor system. Meanwhile, note that the high-pressure rotor and low-pressure turbine rotor can excite the first-order resonance of the dual-rotor system, while the low-pressure compressor rotor can only excite the second-order resonance, and then the dynamic model of this six-point support dual-rotor system can further be simplified as a relatively independent single-rotor system with one disk and a four-support dual-rotor system with dual disks.

Vibration Control of Tie Rod Rotors With Optimization of Unbalanced Force and Unbalanced Moment

Abstract: This paper proposes a method for optimizing unbalanced force and unbalanced moment of the multistage disk based on sequence quadratic program algorithm to solve the vibration problem of gas turbine tie rod rotor. This method guides the assembly phase of the multistage disks. The influence of unbalanced force and unbalanced moment on the vibration of the tie rod rotor are analyzed based on the characteristics of rotor structure and assembly process. A dynamic model of the unbalanced force and unbalanced moment of the tie rod rotor is established. The sequence quadratic program algorithm is used to optimize multi-dimension of unbalanced force and moment, so the global optimal solution can be obtained. In order to verify the effectiveness of the optimization method proposed in this paper, vibration control experiments are carried out for traditional tie rod rotor and gas turbine tie rod rotor structure. The results show that both unbalanced force optimization and unbalanced moment optimization can control the tie rod rotor vibration effectively, and unbalanced moment optimization is better. Unbalanced moment optimization is used to perform constant speed and speed-up experiment on the gas turbine tie rod rotor structure. At 1200r/min, the maximum vibration reduction of the system is 76.68%. And the vibration has a decrease of 43.3% at the first-order critical speed. The proposed method in this paper can be used not only for the guidance of tie rod rotor assembly of gas turbine, but also for the vibration control during operation.

Analysis of Vibration of the Euler-Bernoulli Pipe Conveying Fluid by Dynamic Stiffness Method and Transfer Matrix

Abstract: The dynamic stiffness method and Transfer method is applied to study the vibration characteristics of the Euler-Bernoulli pipe conveying fluid in this paper. According to the dynamics equation of the pipe conveying fluid, the element dynamic stiffness is established. The vibration characteristic of the single-span pipe is analyzed under two kinds of boundary conditions. The results compared with the literature, which has a good consistency. Based on this method, natural frequency and the critical speed of the two types of multi-span pipe are deserved. This paper shows that the dynamic stiffness method and transfer matrix is an effective method to deal with the vibration problem of pipe conveying fluid.