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Fluidization and Transport of Vibrated Granular Matter:A Review of Landmark and Recent Contributions

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Fluid Dynamics & Materials Processing 2024年第1期20卷 1-29页

作者： Peter Watson Sebastien Vincent Bonnieu Marcello Lappa Department of Mechanical and Aerospace Engineering University of StrathclydeGlasgowUK European Space Agency European Space Research and Technology CentreNoordwijkNetherland

We present a short retrospective review of the existing literature about the dynamics of(dry)granular matter under the effect of vibrations.The main objective is the development of an integrated resource where vital information about past findings and recent discoveries is provided in a single treatment.Special attention is paid to those works where successful synthetic routes to as-yet unknown phenomena were identified.Such landmark results are analyzed,while smoothly blending them with a history of the field and introducing possible categorizations of the prevalent dynamics.Although no classification is perfect,and it is hard to distillate general properties out of specific observations or realizations,two possible ways to interpret the existing results are defined according to the type of forcing or the emerging(ensuing)regime of motion.In particular,first results concerning the case where vibrations and gravity are concurrent(vertical shaking)are examined,then the companion situation with vibrations perpendicular to gravity(horizontal shaking)is described.Universality classes are introduced as follows:(1)Regimes where sand self-organizes leading to highly regular geometrical“pulsating”patterns(thin layer case);(2)Regimes where the material undergoes“fluidization”and develops an internal multicellular convective state(tick layers case);(3)Regimes where the free interface separating the sand from the overlying gas changes inclination or develops a kind a patterned configuration consisting of stable valleys and mountains or travelling waves;(4)Regimes where segregation is produced,i.e.,particles of a given size tend to be separated from the other grains(deep containers).Where possible,an analogy or parallelism is drawn with respect to the companion field of fluid-dynamics for which the assumption of“continuum”can be applied.

关键词： Granular materials vibrations fluidization flowability symmetry breaking

Vibration-Based Fault Diagnosis for Railway Point Machines Using VMD and Multiscale Fluctuation-Based Dispersion Entropy

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Chinese Journal of Electronics 2024年第3期33卷 803-813页

作者： Yongkui SUN Yuan CAO Peng LI Guo XIE Tao WEN Shuai SU National Engineering Research Center of Rail Transportation Operation and Control System Beijing Jiaotong University School of Electronic and Information Engineering Beijing Jiaotong University Shaanxi Key Laboratory of Complex System Control and Intelligent Information Processing Xi'an University of Technology Frontiers Science Center for Smart High-speed Railway System Beijing Jiaotong University

As one of the most important railway signaling equipment,railway point machines undertake the major task of ensuring train operation safety.Thus fault diagnosis for railway point machines becomes a hot topic.Considering the advantage of the anti-interference characteristics of vibration signals,this paper proposes an novel intelligent fault diagnosis method for railway point machines based on vibration signals.A feature extraction method combining variational mode decomposition(VMD) and multiscale fluctuation-based dispersion entropy is developed,which is verified a more effective tool for feature selection.Then,a two-stage feature selection method based on Fisher discrimination and ReliefF is proposed,which is validated more powerful than single feature selection methods.Finally,support vector machine is utilized for fault diagnosis.Experiment comparisons show that the proposed method performs best.The diagnosis accuracies of normal-reverse and reverse-normal switching processes reach 100% and 96.57% respectively.Especially,it is a try to use new means for fault diagnosis on railway point machines,which can also provide references for similar fields.

关键词： Fault diagnosis vibrations Support vector machines Diversity reception Switches Feature extraction Rail transportation

Numerical modeling techniques for noise emission of free railway wheels

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Railway Engineering Science 2024年第2期32卷 144-161页

作者： Linus Taenzer Urs Pachale Bart Van Damme Andrea Bergamini Domenico Tallarico Laboratory of Acoustics/Noise Control EmpaÜberlandstrasse 129DübendorfSwitzerland

In this article,we consider the numerical prediction of the noise emission from a wheelset in laboratory conditions.We focus on the fluid-structure interaction leading to sound emission in the fluid domain by analyzing three different methods to account for acoustic sources.These are a discretized baffled piston using the discrete calculation method(DCM),a closed cylindrical volume using the boundary element method(BEM)and radiating elastic disks in a cubic enclosure solved with the finite element method(FEM).We provide the validation of the baffled piston and the BEM using measurements of the noise emission of a railway wheel by considering ground reflections in the numerical models.Selected space-resolved waveforms are compared with experimental results as well as with a fluid-structure interaction finite element model.The computational advantage of a discretized disk mounted on a baffle and BEM compared to FEM is highlighted,and the baffled pistons limitations caused by a lack of edge radiation effects are investigated.

关键词： Discretized baffled piston Finite element Boundary element Railway noise Acoustic emission vibrations

Convection and Stratification of Temperature and Concentration

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Fluid Dynamics & Materials Processing 2024年第6期20卷 1351-1364页

作者： Alexey Fedyushkin Laboratory of Complex Fluid Mechanics Ishlinsky Institute for Problems in Mechanics RASMoscow119526Russia

This study is devoted to an analysis of natural convection and the emergence of delamination in an incompressible fluid encapsulated in a closed region heated from the side.Weak,medium and intensive modes of stationary laminar thermal and thermo-concentration convection are considered.It is shown that nonlinear flow features can radically change the flow structure and characteristics of heat and mass transfer.Moreover,the temperature and concentration segregation in the center of the square region display a non-monotonic dependence on the Grashof number(flow intensity).The formation of a nonstationary periodic structure of thermal convection in boundary layers and in the core of a convective flow in the closed region is also examined.Details of the formation of countercurrents inside the region with the direction opposite to the main convective flow are given.Finally,the influence of vertical and horizontal vibrations on oscillatory convection is analyzed in detail.

关键词： Natural convection stratification segregation numerical simulation vibrations

Behaviour and mechanisms of molecular vibrations induced by a pulsed voltage in a silicone elastomer used for device encapsulation

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High Voltage 2023年第5期8卷 1020-1029页

作者： Junyu Wei Dongxin He Teng Gao Lin Zhu Haochen Wang Qingquan Li Gilbert Teyssedre Shandong Provincial Key Laboratory of UHV Transmission Technology and Equipment School of Electrical Engineering Shandong UniversityJinanChina School of Materials Science and Engineering Shandong UniversityJinanChina UPS INPTCNRSLAPLACE(Laboratoire Plasma et Conversion d’Energie)University of ToulouseToulouseFrance

Silicone elastomers are widely used to encapsulate power electronic devices.However,such devices may be subjected to square‐wave pulsed voltages with a high rate of change,which can create significant challenges for encapsulation insulation.In this article,the molecular vibration of silicon elastomer at the edge of pulsed electric field is studied.Firstly,the relationship between the intensity of molecular vibration and the parameters of pulsed electric field is explored.The experimental results show that the amplitude of the vibrations decreases as the pulse‐edge time increases,and it increases linearly as the pulseedge slope increases.Furthermore,the amplitude of the vibrations is proportional to the square of the amplitude of the pulsed electric field,and it increases as the space charge density increases.Then,the force analysis of charged molecule at the pulse edges is calculated,and the theoretical change law of molecular vibration intensity with pulse edge slope is deduced.Comparing the theoretical results with the experimental results,it is found that they are highly consistent.Finally,electrically induced mechanical stress caused by molecular vibration was shown to be an important factor in insulation failure.

关键词： pulsed insulation vibrations

The Role of Vanes in the Damping of Bird Feathers

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Journal of Bionic Engineering 2023年第4期20卷 1646-1655页

作者： Kai Deng Hamed Rajabi Alexander Kovalev Clemens F.Schaber Zhendong Dai Stanislav N.Gorb Functional Morphology and Biomechanics Institute of ZoologyKiel University24098KielGermany School of Engineering London South Bank UniversityLondonSE10AAUK Institute of Bioinspired Structure and Surface Engineering Nanjing University of Aeronautics and AstronauticsNanjing210026People’s Republic of China

Bird feathers sustain bending and vibrations during flight.Such unwanted vibrations could potentially cause noise and flight instabilities.Damping could alter the system response,resulting in improving quiet flight,stability,and controllability.Vanes of feathers are known to be indispensable for supporting the aerodynamic function of the wings.The relationship between the hierarchical structures of vanes and the mechanical properties of the feather has been previously studied.However,still little is known about their relationship with feathers’damping properties.Here,the role of vanes in feathers’damping properties was quantified.The vibrations of the feathers with vanes and the bare shaft without vanes after step deflections in the plane of the vanes and perpendicular to it were measured using high-speed video recording.The presence of several main natural vibration modes was observed in the feathers with vanes.After trimming vanes,more vibration modes were observed,the fundamental frequencies increased by 51-70%,and the damping ratio decreased by 38-60%.Therefore,we suggest that vanes largely increase feather damping properties.Damping mechanisms based on the morphology of feather vanes are discussed.The aerodynamic damping is connected with the planar vane surface,the structural damping is related to the interlocking between barbules and barbs,and the material damping is caused by the foamy medulla inside barbs.

关键词： Bird Feather vibrations Damping Bionic

Measurement of vibration frequencies of ties in masonry arches by means of a robotic total station

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Earthquake Engineering and Engineering Vibration 2022年第2期21卷 489-500页

作者： Marco Gatti Dipartimento di Ingegneria University of Ferraravia Saragat 144123 FerraraItaly

Measurement of the vibration frequencies of eight ties set in masonry arches of a church by means of a robotic total station is described.The instrument made continuous recordings(up to ten per second)of the three-dimensional positions of a reflector situated at 1/2 or 1/4 of the length of the tie during vertical oscillation induced by an impulsive load.The recording slips,vibration amplitudes(and their accuracy),hourly diagram and experimental spectra of vibrations,and the corresponding frequencies were calculated.The results were verified by comparing them with the vibration frequencies and indirectly the tension and fixed support constraint calculated from accelerometric measurements.The study provides interesting information on the accuracies of the reflector′s three-dimensional coordinates,but highlighted certain limits in the application of robotized total stations for measuring vibration frequencies of ties in masonry arches.

关键词： RTS frequency vibrations ties arches

Experimental investigation of combined vibrations for a hydrofoil-rod system at low Reynold numbers

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Journal of Hydrodynamics 2019年第3期31卷 512-521页

作者： Ren-feng Wang Ke Chen Francis Nobelesse Yun-xiang You Wei Li State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University Shanghai 200240 China Collaborative Innovation Center far Advanced Ship and Deep-Sea Exploration Shanghai 200240 China

A hydrodynamic tunnel experimental investigation and analysis of vibration characteristics for a hydrofoil in a transient regime is considered. Tests are performed for NACA 0017 models with a non-uniform section at an angle of attack AOA = 5° and Reynolds numbers up to Re = 7.0 x 106. This study is related to a project design of experiments in a complex facility that involves several parameters. The analysis focuses on the vibrations of a hydrofoil for different values of the bracing stiffness kh, the torsional stiffness ka, and the locations of the elastic axis a and of the center of gravity xa . The structural bracing response is investigated via measurements of the displacement of the free tip section of the hydrofoil using a three-axis acceleration sensor, and the torsional response of the structure is analyzed via measurements of displacements with single-axis acceleration sensors. The hydrofoil is made of reinforced plastics without flexibility, and elastic functions are performed by a spring support mechanism combined with a torsional structure. The study shows that an increase of the velocity results in different behaviors of the bracing and torsional amplitudes. Another notable result of the study is that the emergence of transition occurs simultaneously with additional peaks and changes of vibration amplitudes.

关键词： vibrations lifting bodies transition laminar separation bubbles

Free vibrations of beam-mass-spring systems:analytical analysis with numerical confirmation

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Acta Mechanica Sinica 2012年第2期28卷 468-481页

作者： Mohammad A.Darabi Siavash Kazemirad Mergen H.Ghayesh Department of Mechanical Engineering University of GuilanRasht Department of Mechanical Engineering McGill UniversityMontrealQuebecCanada H3A 2K6

Free vibrations of a beam-mass-spring system with different boundary conditions are analyzed both analyt- ically and numerically. In the analytical analysis, the system is divided into three subsystems and the effects of the spring and the point mass are considered as internal boundary con- ditions between any two neighboring subsystems. The par- tial differential equations governing the motion of the sub- systems and internal boundary conditions are then solved us- ing the method of separation of variables. In the numerical analysis, the whole system is considered as a single system and the effects of the spring and point mass are introduced using the Dirac delta function. The Galerkin method is then employed to discretize the equation of motion and the result- ing set of ordinary differential equations are solved via eigen- value analysis. Analytical and numerical results are shown to be in very good agreement.

关键词： beam-mass-spring systems vibrations Para- metric study