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modal analysis and Vortex Trajectory Description for Tip Leakage Flow of a Transonic Turbine Cascade

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Journal of Thermal Science 2023年第3期32卷 1105-1123页

作者： YANG Yi MA Hongwei ZHONG Yafei ZHANG Qingdian School of Energy and Power Engineering Beihang UniversityBeijing 100191China Research Institute of Aero-Engine Beihang UniversityBeijing 100191China

Tip leakage vortex(TLV),which develops from the clearance between the turbine blade and casing,has been studied for decades.Nevertheless,some associated phenomena,such as its unsteady behaviors,are still not well understood.In the present work,an unsteady simulation of a transonic turbine cascade was conducted by using a validated unsteady Reynolds averaged Navier-Stokes(URANS)technique with the k-ωshear stress transport(SST)turbulence model.Typical three-dimensional vortical topology in the tip region of this transonic turbine blade was depicted based on the vortex and shock wave identification.Afterwards,quantitative descriptions of TLV transient parameters,including core position,radius,intensity,wandering motion amplitude and their statistical analysis were also provided via an ellipse fitting method.Combined with the turbulent parameters in the tip region,it is recognized that the breakdown of TLV does not occur upstream of the trailing edge,and the TLV wandering,especially the spanwise motion is a dominant unsteady feature as migrating downstream.To mathematically extract underlying flow features of tip leakage flow(TLF),two data-driven modal analysis techniques,namely proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD),are presented to complement one another to reveal underlying flow feature.Observation of modes distribution allowed qualitative identification of shockwaves,vortical cluster and corresponding transient interaction.Results of POD show that the dominant unsteady structures in the tip region exhibit various morphology with moving downstream.In the front part near the leading edge,the oscillation of separation bubble and bifurcation of passage vortex paly a dominant role;while in the middle part of the tip region,the corresponding factors are the wandering of TLV and unsteady interaction between shock waves and TLF/TLV.In the vicinity of the trailing edge,the instability induced by the mixing of large-scale vortices serves as the main factor in the context of flow unsteadines

关键词： transonic turbine cascade tip leakage vortex unsteady behavior modal analysis

Comparison Between modal analysis and Impedance-based Methods for Analysing Stability of Unbalanced Microgrids with Grid-forming Electronic Power Converters

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Journal of Modern Power Systems and Clean Energy 2023年第4期11卷 1269-1281页

作者： Sauro J.Yague Aurelio García-Cerrada Pere Palacín Farré IQS School of Engineering Ramón Llull UniversityVia Augusta 39008017 BarcelonaSpain Institute for Research in Technology ICAI School of EngineeringComillas Pontifical UniversityAlberto Aguilera 2328015 MadridSpain

Stability in unbalanced power systems has deserved little attention in the literature.Given the importance of this scenario in distribution systems with distributed generation,this paper revisits modal analysis techniques for stability studies in power systems,and explains how to tackle unbalanced power systems with voltage-dependent loads.The procedure is described in detail and applied to a low-voltage(LV)simple case study with two grid-forming electronic power converters and unbalanced loads.Results are then compared with those obtained with the popular impedance-based method.While the latter is easier to implement using simulation or field data,the former requires complete information of the system,but gives a better insight into the problem.Since both methods are based on a small-signal approximation of the system,they provide similar results,but they discern different information.A larger second case study based on an LV CIGRE distribution system is also analysed.Results are obtained using a detailed Simulink model of the microgrids with electronic power converters.

关键词： Stability microgrid modal analysis impedancebased method unbalanced distribution system

Seismic bearing capacity of strip footing on partially saturated soil using modal response analysis

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Earthquake Engineering and Engineering Vibration 2022年第3期21卷 641-662页

作者： Abhijit Anand Rajib Sarkar Department of Civil Engineering IIT(ISM)DhanbadDhanbad 826004India

The present study proposes a novel and simplified methodology to assess the seismic bearing capacity(SBC) of a shallow strip footing by incorporating strength non-linearity arising due to partial saturation of a soil matrix. Furthermore, developed methodology incorporates the modal response analysis of soil layers to assess SBC. A constant matric suction distribution profile has been considered throughout the depth of the soil. The Van Genuchten equation and corresponding fitting parameters have been considered to quantify matric suction in the analysis. SBC has been obtained for three different geomaterials;viz. sand, fly ash and clay, based on their predominant grain size and diverse soil water characteristics curve(SWCC) attributes. Variation of SBC with different modes of vibration and damping ratio are reported for ranges of matric suction pertinent to the geomaterials considered in the study. The relative significance of matric suction on SBC has been reported for suction values within the transition zone of each geomaterial. It is observed that the SBC of sand is drastically reduced, with matric suction reaching beyond the residual suction value. The SBC of fly ash remains constant beyond the residual suction value, whereas the SBC of clay shows an increasing trend toward the practical range of matric suction values.

关键词： seismic bearing capacity modal analysis matric suction

FEA-based Geometrical Modification of Switched Reluctance Motor for Radial Force Reduction

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Chinese Journal of Electrical Engineering 2024年第1期10卷 124-135页

作者： Rani S Jayapragash R School of Electrical Engineering Vellore Institute of TechnologyChennai 600127India

Switched reluctance motors(SRMs)are becoming increasingly popular in the automotive sector owing to their robust design.Moreover,SRMs are preferred particularly for EV applications owing to their fault tolerance,magnet-free structure,and high power/torque density.The main concerns of SRM compared to other machines include torque ripple and vibration.The primary cause of vibration is the radial force created by the SRM.A geometry-based modification of the SRM to reduce the radial force without significantly changing the average torque produced is proposed.The primary goal is to design a 4-phase,8/6 SRM with a lower radial force.Two possible geometrical alterations are proposed:one with square windows and the other with circular holes on the rotor core.The windows are sized and positioned to avoid flux saturation.General criteria are developed for the optimal window size and placement.Finite element analysis(FEA)modelling of the SRM is used to validate its performance.The FEA results are compared with the performance parameters obtained using the analytical method.Utilizes the multiphysics design tool ANSYS to obtain the natural frequencies and associated deformations through modal analysis.Compared to the conventional geometry,the radial force is significantly reduced by providing windows.

关键词： 8/6 SRM radial force modal analysis FEA analysis natural frequencies SRM with windows

Research on vibration reduction test and frame modal analysis of rice transplanter based on vibration evaluation

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International Journal of Agricultural and Biological Engineering 2022年第32期15卷 116-122页

作者： Xin Jin Qun Cheng Qing Tang Jun Wu Lan Jiang Chongyou Wu Huankun Wang Nanjing Institute of Agricultural Mechanization Ministry of Agriculture and Rural AffairsNanjing 210014China College of Agricultural Equipment Engineering Henan University of Science and TechnologyLuoyang 471003China Science&Technology Innovation Center for Completed Set Equipment Longmen LaboratoryLuoyang 471000China

The chassis of rice transplanter tends to vibrate severely in the severe working environment,causing a severe effect on the operational performance and driving comfort.In order to avoid this situation,this paper constructs a vibration evaluation system of the rice transplanter and carries out experimental analysis.According to the optimal acceleration sensor placement scheme,a test platform system was designed.Taking the high-speed transplanter chassis as the research object,this study carried out the experiments modal analysis and optimization on the chassis.The three-dimensional model of the transplanting machine chassis established by SolidWorks was imported into ANSYS Workbench for finite element modal simulation analysis.Comparing the two modal analyses,it is found that the results data of the two analysis methods were very close.After optimization,the length x1,the section width x2 and the thickness of the hollow beam x3 of the main load-bearing beam of the frame were as follows:x1=1641.5 mm,x2=26.7 mm,x3=5 mm,respectively.The maximum overshoot of the low-level system was reduced by 28.57%.It has been verified that the vibration of the whole machine has been effectively reduced.

关键词： chassis high-speed rice transplanter vibration evaluation modal analysis

Low-frequency oscillation of train-network system considering traction power supply mode

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Railway Engineering Science 2024年第2期32卷 244-256页

作者： Yuchen Liu Xiaoqin Lyu Mingyuan Chang Qiqi Yang School of Electrical Engineering Southwest Jiaotong UniversityChengdu 610031China

The low-frequency oscillation(LFO)has occurred in the train-network system due to the introduction of the power electronics of the trains.The modeling and analyzing method in current researches based on electrified railway unilateral power supply system are not suitable for the LFO analysis in a bilateral power supply system,where the trains are supplied by two traction substations.In this work,based on the single-input and single-output impedance model of China CRH5 trains,the node admittance matrices of the train-network system both in unilateral and bilateral power supply modes are established,including three-phase power grid,traction transformers and traction network.Then the modal analysis is used to study the oscillation modes and propagation characteristics of the unilateral and bilateral power supply systems.Moreover,the influence of the equivalent inductance of the power grid,the length of the transmission line,and the length of the traction network are analyzed on the critical oscillation mode of the bilateral power supply system.Finally,the theoretical analysis results are verified by the time-domain simulation model in MATLAB/Simulink.

关键词： Low-frequency oscillation Train-network system modal analysis Bilateral power supply Participation factor

modal analysis of Thread off Failure of Oil Round Thread Casing Connection

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Journal of University of Science and Technology Beijing 2001年第4期8卷 277-279页

作者： LiWang, Yong Zang, Zhaoneng Chen, Dechun Tong, Jiaxiang Zou 1) Shanahai Jiaotong University Shanghai 200030 China 2) Mechanical Engineering School. University of Science and Technology Beijing. Beijing 100083. China Shanghai Jiaotong University Shanghai 200030 China Mechanical Engineering School University of Science and Technology Beijing Beijing 100083 China

The dynamic modal model analysis of the oil casing connection is done by finite element method (FEM), and the first nature frequency, the second nature frequency, the vibration mode shape and the time domain of the node displacement and the element stress variation in the thread connection are gotten. The Von.Mises stresses of the connection in the static and dynamic state are also studied. The results of calculation and analysis show: (1) because the maximum of static stress is at the coupling thread end of connection, the connection begins to thread off at the coupling thread end, which is in accord with the results of the thread off experiment in laboratory; (2) because the first nature frequency is very high, the probability of casing connection to be damaged from vibration is little; (3) the shock dynamic load makes casing connection begin to thread off at the tube thread end.

关键词： API round thread casing connection modal analysis

modal analysis of AC quadrupole magnet system for CSNS/RCS

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Chinese Physics C 2013年第8期37卷 60-63页

作者：刘仁洪屈化民康玲张俊嵩王海静 Institute of High Energy Physics Chinese Academy of Sciences University of Chinese Academy of Sciences

The quadrupole magnet of the China Spallation Neutron Source （CSNS） Rapid-cycling Synchrotron （RCS） is operated at a 25 Hz sinusoidal alternating current which causes severe vibration. The vibration will influence the long-term safety and reliable operation of the quadrupole magnet. By taking the quadrupole magnet and girder as specific model system, a method for analyzing and studying the dynamic characteristic of the system is put forward by combining theoretical calculation with experimental testing. The theoretical modal analysis results coincide with the experimental testing results. It shows that the dynamic characteristic parameters of the structure can be obtained by modal analysis which will provide a theoretical basis for the further study and the magnet girder optimal design of CSNS/PtCS.

关键词： quadrupole magnet girder modal analysis testing modal

modal analysis of coupled vibration of belt drive systems

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Applied Mathematics and Mechanics(English Edition) 2008年第1期29卷 9-13页

作者：李晓军陈立群 Shanghai Institute of Applied Mathematics and Mechanics

The modal method is applied to analyze coupled vibration of belt drive systems. A belt drive system is a hybrid system consisting of continuous belts modeled as strings as well as discrete pulleys and a tensioner arm. The characteristic equation of the system is derived from the governing equation. Numerical results demenstrate the effects of the transport speed and the initial tension on natural frequencies.

关键词： belt drive system modal analysis axially moving string coupled vibration frequency