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Liutex (vortex) core definition and automatic identification for turbulence vortex structures

Journal of Hydrodynamics 2019年第5期31卷 857-863页

作者： Hongyi Xu Xiao-shu Cai Chaoqun Liu Aeronautics and Astronautics Department Fudan UniversityShanghai 200433China School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Department of Mathematics University of Texas at ArlingtonArlington 76019TexasUSA

As a milestone research in vortex identification(VI),the physical quantity of Liutex,including its forms of scalar,vector and tensor,was systematically explored and rigorously obtained as the third-generation(3G)of the vortex definition and identification methods distinguished from the first generation(1G)by vorticity and the second generation(2G)by the vortex identification(VI)criteria solely dependent on the velocity gradient tensor *** on these findings,the vortex-core lines were abstracted from the well-defined Liutex,and for the first time,were automatically generated and massively visualized using *** distinctive characteristics of these vortex cores with the intriguing threshold-independency make them be the uniquely appropriate entity to represent and to depict the vortex structures in *** letter made use of the DNS data for the natural transition in a zero-pressure gradient flat-plate(Type-A turbulent boundary layer(TBL))and the fully-developed turbulence in a square annular duct(Type-B TBL)to demonstrate the vortex structure represented by the vortex-core *** 3G VI approach based on the vortex-core lines is capable of profoundly uncovering the vortex ***,the capability of automatically identifying the vortex cores and massively visualizing the large number of vortex-core behaviors in a transient way will enable the fluid-mechanics and other related-science communities to step into a new era to explore the intrinsic natures of the centennial puzzle of turbulence and other vortex-related phenomena in future.

关键词： Direct numerical simulation turbulence structure vortex core identification and automation

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Galilean invariance of Omega vortex identification method

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Journal of Hydrodynamics 2019年第2期31卷 249-255页

作者： Jian-ming Liu Yi-qian Wang Yi-sheng Gao Chaoqun Liu School of Mathematics and Statistics Jiangsu Normal UniversityXuzhou 221116China Department of Mathematics University of Texas at ArlingtonArlington 76019TexasUSA School of Aerospace Engineering Tsinghua UniversityBeijing 100084China

In the new vortex identification method(Liu et al.2016)to represent the rotation level and capture and visualize the vortices,proposed in our previous study,the independence of the reference frame and the Galilean invariant were not *** the present study,the Galilean invariance of the omega vortex identification method is proved and several examples are presented to verify the conclusion.

关键词： Vortex identification Ωmethod.Galilean invariance turbulence visualization

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Cavitation vortex dynamics of unsteady sheet/cloud cavitating flows with shock wave using different vortex identification methods

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Journal of Hydrodynamics 2019年第3期31卷 475-494页

作者： Chang-chang Wang Ying Liu Jie Chen Fu-yi Zhang Biao Huang Guo-yu Wang School of Mechanical Engineering Beijing Institute of Technology Beijing 100081 China

Cavitation is a complex multiphase flow phenomenon with an abrupt transient phase change between the liquid and the vapor, including multiscale vortical motions. The transient cavitation dynamics is closely associated with the evolution of the cavitation vortex structures. The present paper investigates the cavitation vortex dynamics using different vortex identification methods, including the vorticity method, the Q criterion method, the Omega method (Ω), the method and the Rortex method. The Q criterion is an eigenvalue-based criterion, and in the Ω method, the parameter is normalized, is independent of the threshold value and in most conditions Ω= 0.52 . The Rortex method is based on an eigenvector-based criterion. Numerical simulations are conducted using the implemented compressible cavitation solver in the open source software OpenFOAM for the sheet/cloud cavitating flows around a NACA66 (mod) hydrofoil fixed at a = 6°,= 1.25 and Re = 7.96 × 10^5 . The flow is characterized by the alternate interactions of the re-entrant flow and the collapse induced shock wave. Results include the vapor structures and the vortex dynamics in the unsteady sheet/cloud cavitating flows, with emphasis on the vortex structures in thecavitation region, the cavity interface, the cavity closure, the cavity wakes, and the foil wakes with the shedding cavity. The comparisons of the various methods, including that the vorticity method, the Q criterion method, the Ω method, the λ2 method and the Rortex method, show the performances of different methods in identifying the cavitation vortex structures. Generally, during the attached cavity growth stage, the Q criteria can well predict the vortex structures in the cavitation region and at the foil trailing edge in the pure liquid region, while with the Ω method and the Rortex method, the vortex structures outside the attached cavity and on the foil pressure side can also be predicted. The λ2 method can well predict the vortex structures in t

关键词： Cavitation vortex dynamics vortex identification sheet/cloud cavitating flow re-entrant jet shock wave OpenFOAM

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System identification Method for Evaluating the Effect of Thickness Error on Backcalculated Pavement Layer Moduli

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上海交通大学学报 2004年第Z2期38卷 182-187页

作者： ZHONG Yan-hui WANG Fu-ming ZHANG Bei CAI Ying-chun Dalian University of Technology Dalian116024 P. R. China Zhengzhou University Zhengzhou450002 P. R. China Zhengzhou University Zhengzhou450002 P. R. China Zhengzhou University Zhengzhou450002 P. R. China Chonging University Chongqing400044 P. R. China Dalian University of Technology Dalian116024 P. R. China Zhengzhou University Zhengzhou450002 P. R. China

Based on system identification theory and FWD testing data, the effect of thickness error on backcalculating pavement layer moduli is studied and the method of singular value decomposition (SVD) is presented to solve the morbidity problem of sensitivity matrix in this *** results show that the thickness error has great effects on the backcalculated pavement layer moduli. The error of backcalculated moduli can be controlled within the range of ±15% by limiting the thickness error within the range of ±5%.

关键词： system identification singular value decomposition (SVD) backcalculation pavement falling weight deflectometer (FWD) moduli thickness

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Rapid identification of Rice Samples Using an Electronic Nose

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Journal of Bionic Engineering 2009年第3期6卷 290-297页

作者： John Westbrook W.C.Hoffmann R.E.Lacey USDA-ARS College Station Department of Biological and Agricultural Engineering Texas A&M UniversityCollege Station

Four rice samples of long grain type were tested using an electronic nose (Cyranose-320).Samples of 5 g of each variety of rice were placed individually in vials and were analyzed with the electronic nose unit consisting of 32 polymer *** Cyranose-320 was able to differentiate between varieties of *** chemical composition of the rice odors for differentiating rice samples needs to be *** optimum parameter settings should be considered during the Cyranose-320 training process especially for multiple samples,which are helpful for obtaining an accurate training model to improve identification ***,it is necessary to investigate the E-nose sensor selection for obtaining better classification accuracy.A re- duced number of sensors could potentially shorten the data processing time,and could be used to establish an application pro- cedure and reduce the cost for a specific electronic *** research is needed for developing analytical procedures that adapt the Cyranose-320 as a tool for testing rice quality.

关键词： rice grain identification electronic nose data analysis pattern recognition

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An novel identification method of the environmental risk sources for surfacewater pollution accidents in chemical industrial parks

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Journal of Environmental Sciences 2013年第7期25卷 1441-1449页

作者： Jianfeng Peng Yonghui Song Peng Yuan Shuhu Xiao Lu Han State Key Laboratory of Environmental Criteria and Risk Assessment Chinese Research Academy of Environmental Sciences Department of Urban Water Environmental Research Chinese Research Academy of Environmental Sciences

The chemical industry is a major source of various pollution accidents. Improving the management level of risk sources for pollution accidents has become an urgentdemand for most industrialized countries. In pollution accidents, the released chemicals harm the receptors to some extentdepending on their sensitivity or susceptibility. Therefore, identifying the potential risk sources from such a large number of chemical enterprises has become pressingly urgent. Based on the simulation of thewhole accident process, a novel and expandable identification method for risk sources causingwater pollution accidents is presented. The newlydeveloped approach, by analyzing and stimulating thewhole process of a pollution accident between sources and receptors, can be applied to identify risk sources, especially on the nationwide scale. Three major types of losses, such as social, economic and ecological losses,were normalized, analyzed and used for overall consequence modeling. A specific case study area, located in a chemical industry park （CIP） along the Yangtze River in Jiangsu Province, China,was selected to test the potential of the identification method. The results showed that therewere four risk sources for pollution accidents in this CIP. Aniline leakage in the HS Chemical Plantwould lead to the most serious impact on the surroundingwater environment. This potential accidentwould severelydamage the ecosystem up to3.8 kmdownstream of Yangtze River, and lead to pollution over adistance stretching to 73.7 kmdownstream. The proposed method is easily extended to the nationwide identification of potential risk sources.

关键词： water pollution accident risk source identification grading chemical industry parks

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Investigation of lateral-directional aerodynamic parameters identification method for fly-by-wire passenger airliners

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Chinese Journal of Aeronautics 2014年第4期27卷 781-790页

作者： Wu Zhao Wang Lixin Lin Jiaming Ai Junqiang School of Aeronautic Science and Engineering Beihang University

A new identification method is proposed to solve the problem of the influence on the loaded excitation signals brought by high feedback gain augmentation in lateral-directional aerodynamic parameters identification of fly-by-wire（FBW） passenger airliners. Taking for example an FBW passenger airliner model with directional relaxed-static-stability, through analysis of its signal energy distribution and airframe frequency response, a new method is proposed for signal type selection, signal parameters design, and the appropriate frequency relationship between the aileron and rudder excitation signals. A simulation validation is presented of the FBW passenger airliner＇s lateral-directional aerodynamic parameters identification. The validation result demonstrates that the designed signal can excite the lateral-directional motion mode of the FBW passenger airliner adequately and persistently. Meanwhile, the relative errors of aerodynamic parameters are less than 5%.

关键词： Excitation signal design Flight test Fly-by-wire (FBW)passenger airliner High feedback gain augmentation identification Lateral-directional aerodynamic parameter

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Variational mode decomposition based modal parameter identification in civil engineering

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Frontiers of Structural and Civil Engineering 2019年第5期13卷 1082-1094页

作者： Mingjie ZHANG Fuyou XU School of Civil Engineering Dalian University of TechnologyDalian 116024China

An out-put only modal parameter identification method based on variational mode decomposition (VMD) is developed for civil structure identifications. The recently developed VMD technique is utilized to decompose the free decay response (FDR) of a structure into to modal responses. A novel procedure is developed to calculate the instantaneous modal frequencies and instantaneous modal damping ratios. The proposed identification method can straightforwardly extract the mode shape vectors using the modal responses extracted from the FDRs at all available sensors on the structure. A series of numerical and experimental case studies are conducted to demonstrate the efficiency and highlight the superiority of the proposed method in modal parameter identification using both free vibration and ambient vibration data. The results of the present method are compared with those of the empirical mode decomposition-based method, and the superiorities of the present method are verified. The proposed method is proved to be efficient and accurate in modal parameter identification for both linear and nonlinear civil structures, including structures with closely spaced modes, sudden modal parameter variation, and amplitude-dependent modal parameters, etc.

关键词： modal parameter identification variational mode decomposition civil structure nonlinear system closely spaced modes

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Third generation of vortex identification methods:Omega and Liutex/Rortex based systems

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Journal of Hydrodynamics 2019年第2期31卷 205-223页

作者： Chaoqun Liu Yi-sheng Gao Xiang-rui Dong Yi-qian Wang Jian-ming Liu Yu-ning Zhang Xiao-shu Cai Nan Gui Department of Mathematics University of Texas at ArlingtonArlington 76019TexasUSA College of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China School of Aerospace Engineering Tsinghua UniversityBeijing 100084China School of Mathematics and Statistics Jiangsu Normal UniversityXuzhou 221116China Key Laboratory of Condition Monitoring and Control for Power Plant Equipment(Ministry of Education) School of EnergyPower and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China Institute of Nuclear and New Energy Technology Collaborative Innovation Center of Advanced Nuclear Energy TechnologyKey Laboratory of Advanced Reactor Engineering and Safety of Ministry of EducationTsinghua UniversityBeijing 100084China

A vortex is intuitively recognized as the rotational/swirling motion of fluids,but a rigorous and universally-accepted definition is still not *** tube/filament has been regarded equivalent to a vortex since Helmholtz proposed the concepts of vorticity tube/filament in 1858 and the vorticity-based methods can be categorized as the first generation of vortex identification *** the last three decades,a lot of vortex identification methods,including 0,A,and Aci criteria,have been proposed to overcome the problems associated with the vorticity-based *** of these criteria are based on the Cauchy-Stokes decomposition and/or eigenvalues of the velocity gradient tensor and can be considered as the second generation of vortex identification *** from 2014,the Vortex and Turbulence Research Team at the University of Texas at Arlington(the UTA team)focus on the development of a new generation of vortex identification *** first fruit of this effort,a new Omega(/2)vortex identification method,which defined a vortex as a connected region where the vorticity overtakes the deformation,was published in *** 2017 and 2018,a Liutex(previously called Rortex)vector was proposed to provide a mathematical definition of the local rigid rotation part of the fluid motion,including both the local rotational axis and the rotational ***/Rortex is a new physical quantity with scalar,vector and tensor forms exactly representing the local rigid rotation of ***,a decomposition of the vorticity to a rotational part namely Liutex/Rortex and an anti-symmetric shear part(RS decomposition)was introduced in 2018,and a universal decomposition of the velocity gradient tensor to a rotation part(7?)and a non-rotation part(NR、was also given in 2018 as a counterpart of the traditional Cauchy-Stokes *** in early 2019,a Liutex/Rortex based Omega method called Omega-Liutex,which combines the respective advantages o

关键词： Vortex definition vortex identification Omega Liutex/Rortex direct numerical simulation turbulence

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Dynamic modeling and parameter identification of a gun saddle ring

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Defence Technology（防务技术） 2020年第2期16卷 325-333页

作者： Tong Lin Lin-fang Qian Qiang Yin Shi-yu Chen Tai-su Liu School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing210094China

In this study,a theoretical nonlinear dynamic model was established for a saddle ring based on a dynamic force analysis of the launching process and the structure according to contact-impact *** ADAMS software was used to build a parameterized dynamic model of the saddle ring.A parameter identification method for the ring was proposed based on the particle swarm optimization algorithm.A loading test was designed and performed several times at different elevation *** response histories of the saddle ring with different loads were then *** parameters of the saddle ring dynamic model were identified from statistics generated at a 500 elevation angle to verify the feasibility and accuracy of the proposed *** actual loading history of the ring at a 70°elevation angle was taken as the model *** response histories of the ring under these working conditions were obtained through a *** simulation results agreed with the actual ***,the effectiveness and applicability of the proposed dynamic model were verified,and it provides an effective method for modeling saddle rings.

关键词： Gun saddle ring Dynamic response Parameter identification Particle swarm optimization

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