This article presents the optical evaluation of the vibrational behavior of a steel bar,by a non-conventional optoacoustic procedure,the LPD(laser photo deflection)method.On this occasion the bar is located horizontal...This article presents the optical evaluation of the vibrational behavior of a steel bar,by a non-conventional optoacoustic procedure,the LPD(laser photo deflection)method.On this occasion the bar is located horizontal and fixed at both ends.Through our procedure we experimentally find the first 9 Eigen frequencies(21 Hz,60 Hz,116 Hz...)and correlate them using the cantilever theory.展开更多
This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration o...This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration of a cantilever beam.Filtered-X RLS algorithm is used to get faster convergence speed and stronger adaptability (in comparison with LMS algorithm). The results demonstrate the efficiency and adaptability of the ACSV-TD.展开更多
In this work we present the results of the optical evaluation of vibrations of a conventional concrete column with a metal frame.In a previous work[1]we reported the optical evaluation of a pure concrete column,withou...In this work we present the results of the optical evaluation of vibrations of a conventional concrete column with a metal frame.In a previous work[1]we reported the optical evaluation of a pure concrete column,without a metal framework.In this evaluation we expected to obtain a noticeably different result,but that was not the case,then the obtained results are surprisingly similar.From the LPD evaluations,the first 12 vibration resonances were found,which fit very well with the basic applied theory(the cantilever theory).Using known average values,we estimate the corresponding column effective length,obtaining an average value of 2.5 m.As in the former case of the concrete column,we find a discrepancy with respect to the length value,measurable from the ground(1.75 m),which can be explained again by the fact that the column and its base were built on inconsistent terrain.展开更多
A boundary element method is presented for the coupled motionanalysis of structural vibration with small-amplitude fluid sloshingin two-dimensional space. The linearized Navier-Stokes equations areconsidered in freque...A boundary element method is presented for the coupled motionanalysis of structural vibration with small-amplitude fluid sloshingin two-dimensional space. The linearized Navier-Stokes equations areconsidered in frequency domain and transformed into boundary integralequations. An appropriate fundamental solution for the Helmholtzequation with pure imaginary constant is found. The condition ofzero-stress is imposed on the free surface, and non-slip condition offluid particles is Imposed on the walls of the container. For rigidmotion models, the expressions for added mass and Added damping tothe structural motion equations are obtained. Some typical numericalexamples are Presented.展开更多
The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems....The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems. In this paper, studies of several EMD control strategies and bench-scale shaking table tests of a two-story model structure are described. First, two structural models corresponding to uncontrolled and Zeroed cases are developed, and parameters of these models are validated through sinusoidal sweep tests to provide a basis for establishing an accurate mathematical model for further studies. Then, a simplified control strategy for the EMD system based on the pole assignment control algorithm is proposed. Moreover, ideal pole locations are derived and validated through a series of shaking table tests. Finally, three benchmark earthquake ground motions and sinusoidal sweep waves are imposed onto the structure to investigate the effectiveness and feasibility of using this type of innovative active control system for structural vibration control. In addition, the robustness of the EMD system is examined. The test results show that the EMD system is an effective and robust system for the control of structural vibrations.展开更多
This paper attempts to develop a scaling procedure to measure structural vibration caused simultaneously by wall pressure fluctuations and the thermal load of hypersonic flow by a wind tunnel test. However, simulating...This paper attempts to develop a scaling procedure to measure structural vibration caused simultaneously by wall pressure fluctuations and the thermal load of hypersonic flow by a wind tunnel test. However, simulating the effect of thermal load is difficult with a scaled model in a wind tunnel due to the nonlinear effect of thermal load on a structure. In this work, the temperature variation of a structure is proposed to indicate the nonlinear effect of the thermal load,which provides a means to simulate both the thermal load and wall pressure fluctuations of a hypersonic Turbulent Boundary Layer(TBL) in a wind tunnel test. To validate the scaling procedure,both numerical computations and measurements are performed in this work. Theoretical results show that the scaling procedure can also be adapted to the buckling temperature of a structure even though the scaling procedure is derived from a reference temperature below the critical temperature of the structure. For the measurement, wall pressure fluctuations and thermal environment are simulated by creating hypersonic flow in a wind tunnel. Some encouraging results demonstrate the effectiveness of the scaling procedure for assessing structural vibration generated by hypersonic flow. The scaling procedure developed in this study will provide theoretical support to develop a new measurement technology to evaluate vibration of aircraft due to hypersonic flow.展开更多
Localized nature of damage in structures requires local measurements for structural health monitoring. The local measurement means to measure the local, usually higher modes of the vibration in a structure. Three fund...Localized nature of damage in structures requires local measurements for structural health monitoring. The local measurement means to measure the local, usually higher modes of the vibration in a structure. Three fundamental issues about the local measurement for structural health monitoring including (1) the necessity of making local measurement, (2) the difficulty of making local measurement and (3) how to make local measurement are addressed in this paper. The results from both the analysis and the tests show that the local measurement can successfully monitor the structural health status as long as the local modes are excited. Unfortunately, the results also illustrate that it is difficult to excite local modes in a structure. Therefore, in order to carry structural health monitoring into effect, we must (1) ensure that the local modes are excited, and (2) deploy enough sensors in a structure so that the local modes can be monitored.展开更多
With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acous...With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acoustic transfer vector（ATV） technique and coupled boundary element model and finite element model （BEM-FEM） approach.Analyses of vibration exciting loads,computing structural dynamic characteristics and dynamic responses have led to theoretical results,which are tested on an L6 diesel engine to validate this proposed technique in engineering practice.展开更多
-This paper reviews the current methodology for dynamic reanalysis. Rayleigh-Ritz approach and receptance approach are discussed in detail. Based on a general finite element structural analysis program SAPS, an eigenp...-This paper reviews the current methodology for dynamic reanalysis. Rayleigh-Ritz approach and receptance approach are discussed in detail. Based on a general finite element structural analysis program SAPS, an eigenproblem re-analysis prorgram ERP was compiled. With a very small change the program can be implemented readily with any general FEM program. Finally, some numerical examples show that the new algorithm is of high precision and efficiency. In the case of local modification in the offshore platform, the efficiency is raised by 20- 50 times when compared with the re-calculation of the whole model.展开更多
In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic and a sensitivity computation of structural vibration is presented. The vibration equation of a system is transfor...In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic and a sensitivity computation of structural vibration is presented. The vibration equation of a system is transformed to a static problem by using the Newmark method. In order to develop computational efficiency and allow for efficient storage, the Preconditioned Conjugate Gradient method （PCG） is also employed. The PCG is an effective method for solving a large system of linear equations and belongs to methods of iteration with rapid convergence and high precision. An example is given and calculated results are compared to validate the proposed methods.展开更多
Impedance eduction methods have been developed for decades to meet the increasing need for high-quality impedance data in the design and optimization of acoustic liners.To this end,it is important to fully investigate...Impedance eduction methods have been developed for decades to meet the increasing need for high-quality impedance data in the design and optimization of acoustic liners.To this end,it is important to fully investigate the uncertainty problem,to which only limited attention has been devoted so far.This paper considers the possibility of acoustically-induced structural vibration as a nonnegligible uncertainty or error source in impedance eduction experiments.As the frequency moves away from the resonant frequency,with the increase in the value of cavity reactance,the acoustic particle velocity inside liner orifices possibly decreases to the extent comparable to the vibration velocity of liner facing sheet.Thus,the acoustically-induced vibration,although generally being weak except at the inherent structural frequencies,may considerably affect the impedance eduction results near the anti-resonant frequency where the liner has poor absorption.To demonstrate the effect of structural vibration,the vibration velocity of liner facing sheet is estimated from the experimentally educed admittance of the liner samples whose orifices are sealed with tape.Further,a three-dimensional numerical model is set up,in which normal particle velocity is introduced over the solid portion of liner facing sheet to imitate structural vibration,rather than directly solving the acoustic-structural coupling problem.As shown by the results,the vibration of liner facing sheet,whose velocity is as small as estimated by the experiment,can result in anomalous deviation of the educed impedance from the impedance model near the anti-resonant frequency.The trend that the anomalous deviation varies with frequency is numerically captured.展开更多
External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impa...External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact identification.This manuscript proposes a method to identify the impact event.By employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact events.The critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of mechanics.The effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact experiment.Through the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.展开更多
We present a statistical investigation of the degree of influence that assumptions made in relation to the mechanical parameters of a pylon have on its ground-induced vibrations.The study is set up by using as a key k...We present a statistical investigation of the degree of influence that assumptions made in relation to the mechanical parameters of a pylon have on its ground-induced vibrations.The study is set up by using as a key kinematic variable the displacement at the top of a reference,a stand-alone pylon with a uniform cross-section and fixity at its base.Next,statistics are produced using a dimensionless displacement ratio defined between the‘parental’and the‘subsidiary’cases,the latter defined for the pylon(a)resting on compliant soil,(b)having an attached top mass,and(c)being non-uniform with height.Furthermore,two materials are examined,namely,steel and reinforced concrete(R/C).More specifically,this displacement ratio is independent of the excitation and plays the role of a transfer function between the base and the top of the pylon.Both horizontal and vertical motions are considered,and the equations of motion are solved in the frequency domain.The ensuing statistical analysis is conducted for the following parameter combinations:(a)pylon founded on soft,intermediate,and stiff soil;(b)low,intermediate,and high-mass ratios of the attached mass to the pylon′s mass;(c)a constant and quadratic degree of pylon tapering with height.Spearman correlation coefficients are calculated for all the above combinations to arrive at statistical results that establish validity bounds and quantify the degree of influence of each assumption on the pylon′s response.展开更多
The Raman and infrared spectra of all-trans-astaxanthin （AXT） in dimethyl sulfoxide （DMSO） solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict ...The Raman and infrared spectra of all-trans-astaxanthin （AXT） in dimethyl sulfoxide （DMSO） solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ1 band into υ1-1 and υ1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ1 band is very sensitive to the excitation wavelength： resonance excitation stimulates the higher-frequency υ1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4＇=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.展开更多
This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled a...This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a full size offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liquid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the Study investigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incident wave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating results can reasonably match the corresponding experimental results.展开更多
The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cyl...The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cylinder with two free ends,and particularly in this trajectory,where the scanning angleβand rollangle a vary over a broad range between 0°and 180.In this work wind tunnel experiments are firstconducted to learn the effects of Reynolds number and scanning angle on aerodynamic parameters forshort cylinder with aspect ratio L/D=1.Similar to infinite cylinder,for the short cylinder with two freeends,the drag crisis phenomenon still exists in the critical regime 1.7×10^(5)≤Re≤6.8×10^(5).Then 3Dsimulations are performed to demonstrate the aerodynamic characteristics of short cylinder and TSBover a broad range of Re,L/D,a and 6.The sensitivity analysis of time step and grid are presented as well.whenβ3=0,for short cylinder,the drag crisis phenomenon was also observed in the simulation,but notas obvious as in the wind tunnel test.In some attitudes,there is an obvious Karman vortexin the wake ofshort cylinder and TSB.The correlation between time-averaged aerodynamic coefficients and L/D,Re,a&l is discussed.The vortex shedding frequency and shear layer behavior are obtained for quasi-steadyand unsteady flow.Finally,the effect of end's shape on drag reduction and vortex shedding frequency isanalyzed.展开更多
ne purpose of this study is to investigate the effectiveness of multi-tuned mass dampers (MTMD) on mitigating vibration of an offshore oil platform subjected to ocean wave loading. An optimal design method is used to ...ne purpose of this study is to investigate the effectiveness of multi-tuned mass dampers (MTMD) on mitigating vibration of an offshore oil platform subjected to ocean wave loading. An optimal design method is used to determine the optimal damper parameters under ocean wave loading. The force on the structure is determined by use of the linearized Morison equation. Investigation on the deck motion with and without MTMD on the structure is made under design conditions. The results show that MTMD with the optimized parameters suppress the response of each structural mode. The sensitivity of optimum values of MTMD to characteristic wave parameters is also analyzed. It is indicated that a single, TMD on the deck of a platform can have the best performance, and the small the damping value of TMD, the better the vibration control.展开更多
An eigenvalue method considering the membrane vibration of wrinkling out-of-plane deformation is introduced, and the stress distributing rule in membrane wrinkled area is analyzed. A dynamic analytical model of rectan...An eigenvalue method considering the membrane vibration of wrinkling out-of-plane deformation is introduced, and the stress distributing rule in membrane wrinkled area is analyzed. A dynamic analytical model of rectangular shear wrinkled membrane and its numerical analysis approach are also developed. Results indicate that the stress in wrinkled area is not uniform, i.e. it is larger in wrinkling wave peaks along wrinkles and two ends of wrinkle in vertical direction. Vibration modes of wrinkled membrane are strongly correlated with the wrinkling configurations. The rigidity is larger due to the heavier stress in the part of wrinkling wave peaks. Therefore, wave peaks are always located at the node lines of vibration mode. The vibration frequency obviously increases with the vibration of wave peaks.展开更多
With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dy...With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dynamic model displays characteristics of strong coupling with structure/control and nonlinearity.Based on the sloshing mass dynamic simplified as a spring-mass-damping model,a rigid-flexible-sloshing model is constructed.Moreover,the effect on the dynamic performance of the coupled model is analyzed with changing frequency and damping.The results show that propellant sloshing dynamics significantly affects the rigid body motion modes,especially flexible mode and short mode.The right half plane pole(RHP)moves far from the imaginary axis with the consumption of the propellant.The flexible mode attenuates with the increase of the sloshing damping,and the coupling becomes stronger when sloshing frequency is close to the short mode frequency or the flexible frequency of the beam.展开更多
In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whol...In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whole shell-structure is divided into the four subsystems,and the SEA physical model and power flow balance equations among these subsystems are established.The similitude relations of input power, coupling loss factor and modal density of the subsystemsbetween the complex shell-structure and its scaled-down model are analyzed. According to thesimilitude theory and power flow balance equations, when the immerged shell-structures are excited,the similar relations of spatially averaged vibration response and underwater radiating sound powerare established for the complex shell-structure and its scaled-down model.展开更多
文摘This article presents the optical evaluation of the vibrational behavior of a steel bar,by a non-conventional optoacoustic procedure,the LPD(laser photo deflection)method.On this occasion the bar is located horizontal and fixed at both ends.Through our procedure we experimentally find the first 9 Eigen frequencies(21 Hz,60 Hz,116 Hz...)and correlate them using the cantilever theory.
文摘This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration of a cantilever beam.Filtered-X RLS algorithm is used to get faster convergence speed and stronger adaptability (in comparison with LMS algorithm). The results demonstrate the efficiency and adaptability of the ACSV-TD.
文摘In this work we present the results of the optical evaluation of vibrations of a conventional concrete column with a metal frame.In a previous work[1]we reported the optical evaluation of a pure concrete column,without a metal framework.In this evaluation we expected to obtain a noticeably different result,but that was not the case,then the obtained results are surprisingly similar.From the LPD evaluations,the first 12 vibration resonances were found,which fit very well with the basic applied theory(the cantilever theory).Using known average values,we estimate the corresponding column effective length,obtaining an average value of 2.5 m.As in the former case of the concrete column,we find a discrepancy with respect to the length value,measurable from the ground(1.75 m),which can be explained again by the fact that the column and its base were built on inconsistent terrain.
文摘A boundary element method is presented for the coupled motionanalysis of structural vibration with small-amplitude fluid sloshingin two-dimensional space. The linearized Navier-Stokes equations areconsidered in frequency domain and transformed into boundary integralequations. An appropriate fundamental solution for the Helmholtzequation with pure imaginary constant is found. The condition ofzero-stress is imposed on the free surface, and non-slip condition offluid particles is Imposed on the walls of the container. For rigidmotion models, the expressions for added mass and Added damping tothe structural motion equations are obtained. Some typical numericalexamples are Presented.
基金The National Natural Science Foundation of China Under Grant. No.50608026The National Major Foundamental Program (973 Program) of China Under Grant No. 2007CB714204
文摘The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems. In this paper, studies of several EMD control strategies and bench-scale shaking table tests of a two-story model structure are described. First, two structural models corresponding to uncontrolled and Zeroed cases are developed, and parameters of these models are validated through sinusoidal sweep tests to provide a basis for establishing an accurate mathematical model for further studies. Then, a simplified control strategy for the EMD system based on the pole assignment control algorithm is proposed. Moreover, ideal pole locations are derived and validated through a series of shaking table tests. Finally, three benchmark earthquake ground motions and sinusoidal sweep waves are imposed onto the structure to investigate the effectiveness and feasibility of using this type of innovative active control system for structural vibration control. In addition, the robustness of the EMD system is examined. The test results show that the EMD system is an effective and robust system for the control of structural vibrations.
基金support of the Equipment Priority Research Field Foundation of China(No.6140246030216ZK01001)
文摘This paper attempts to develop a scaling procedure to measure structural vibration caused simultaneously by wall pressure fluctuations and the thermal load of hypersonic flow by a wind tunnel test. However, simulating the effect of thermal load is difficult with a scaled model in a wind tunnel due to the nonlinear effect of thermal load on a structure. In this work, the temperature variation of a structure is proposed to indicate the nonlinear effect of the thermal load,which provides a means to simulate both the thermal load and wall pressure fluctuations of a hypersonic Turbulent Boundary Layer(TBL) in a wind tunnel test. To validate the scaling procedure,both numerical computations and measurements are performed in this work. Theoretical results show that the scaling procedure can also be adapted to the buckling temperature of a structure even though the scaling procedure is derived from a reference temperature below the critical temperature of the structure. For the measurement, wall pressure fluctuations and thermal environment are simulated by creating hypersonic flow in a wind tunnel. Some encouraging results demonstrate the effectiveness of the scaling procedure for assessing structural vibration generated by hypersonic flow. The scaling procedure developed in this study will provide theoretical support to develop a new measurement technology to evaluate vibration of aircraft due to hypersonic flow.
文摘Localized nature of damage in structures requires local measurements for structural health monitoring. The local measurement means to measure the local, usually higher modes of the vibration in a structure. Three fundamental issues about the local measurement for structural health monitoring including (1) the necessity of making local measurement, (2) the difficulty of making local measurement and (3) how to make local measurement are addressed in this paper. The results from both the analysis and the tests show that the local measurement can successfully monitor the structural health status as long as the local modes are excited. Unfortunately, the results also illustrate that it is difficult to excite local modes in a structure. Therefore, in order to carry structural health monitoring into effect, we must (1) ensure that the local modes are excited, and (2) deploy enough sensors in a structure so that the local modes can be monitored.
基金Sponsored by the National Natural Science Foundation of China (50505047)Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi
文摘With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acoustic transfer vector（ATV） technique and coupled boundary element model and finite element model （BEM-FEM） approach.Analyses of vibration exciting loads,computing structural dynamic characteristics and dynamic responses have led to theoretical results,which are tested on an L6 diesel engine to validate this proposed technique in engineering practice.
文摘-This paper reviews the current methodology for dynamic reanalysis. Rayleigh-Ritz approach and receptance approach are discussed in detail. Based on a general finite element structural analysis program SAPS, an eigenproblem re-analysis prorgram ERP was compiled. With a very small change the program can be implemented readily with any general FEM program. Finally, some numerical examples show that the new algorithm is of high precision and efficiency. In the case of local modification in the offshore platform, the efficiency is raised by 20- 50 times when compared with the re-calculation of the whole model.
基金supported by National Natural Science Foundation under Grant No.10202016
文摘In this paper, material properties, geometry parameters and applied loads are assumed to be stochastic and a sensitivity computation of structural vibration is presented. The vibration equation of a system is transformed to a static problem by using the Newmark method. In order to develop computational efficiency and allow for efficient storage, the Preconditioned Conjugate Gradient method （PCG） is also employed. The PCG is an effective method for solving a large system of linear equations and belongs to methods of iteration with rapid convergence and high precision. An example is given and calculated results are compared to validate the proposed methods.
基金funded by the National Science and Technology Major Project,China(No.2017-II-0008-0022)。
文摘Impedance eduction methods have been developed for decades to meet the increasing need for high-quality impedance data in the design and optimization of acoustic liners.To this end,it is important to fully investigate the uncertainty problem,to which only limited attention has been devoted so far.This paper considers the possibility of acoustically-induced structural vibration as a nonnegligible uncertainty or error source in impedance eduction experiments.As the frequency moves away from the resonant frequency,with the increase in the value of cavity reactance,the acoustic particle velocity inside liner orifices possibly decreases to the extent comparable to the vibration velocity of liner facing sheet.Thus,the acoustically-induced vibration,although generally being weak except at the inherent structural frequencies,may considerably affect the impedance eduction results near the anti-resonant frequency where the liner has poor absorption.To demonstrate the effect of structural vibration,the vibration velocity of liner facing sheet is estimated from the experimentally educed admittance of the liner samples whose orifices are sealed with tape.Further,a three-dimensional numerical model is set up,in which normal particle velocity is introduced over the solid portion of liner facing sheet to imitate structural vibration,rather than directly solving the acoustic-structural coupling problem.As shown by the results,the vibration of liner facing sheet,whose velocity is as small as estimated by the experiment,can result in anomalous deviation of the educed impedance from the impedance model near the anti-resonant frequency.The trend that the anomalous deviation varies with frequency is numerically captured.
基金supported by the National Natural Science Foundation of China(Grant Nos.12272392 and 11790292)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB22040303)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2022020).
文摘External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact identification.This manuscript proposes a method to identify the impact event.By employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact events.The critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of mechanics.The effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact experiment.Through the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.
基金support of the German Research Foundation (DFG) through Grant SM 281/20-1the Hellenic Foundation for Research and Innovation (HFRI) under the 3rd Call for PhD fellowships (Fellowship Number: 6522)
文摘We present a statistical investigation of the degree of influence that assumptions made in relation to the mechanical parameters of a pylon have on its ground-induced vibrations.The study is set up by using as a key kinematic variable the displacement at the top of a reference,a stand-alone pylon with a uniform cross-section and fixity at its base.Next,statistics are produced using a dimensionless displacement ratio defined between the‘parental’and the‘subsidiary’cases,the latter defined for the pylon(a)resting on compliant soil,(b)having an attached top mass,and(c)being non-uniform with height.Furthermore,two materials are examined,namely,steel and reinforced concrete(R/C).More specifically,this displacement ratio is independent of the excitation and plays the role of a transfer function between the base and the top of the pylon.Both horizontal and vertical motions are considered,and the equations of motion are solved in the frequency domain.The ensuing statistical analysis is conducted for the following parameter combinations:(a)pylon founded on soft,intermediate,and stiff soil;(b)low,intermediate,and high-mass ratios of the attached mass to the pylon′s mass;(c)a constant and quadratic degree of pylon tapering with height.Spearman correlation coefficients are calculated for all the above combinations to arrive at statistical results that establish validity bounds and quantify the degree of influence of each assumption on the pylon′s response.
文摘The Raman and infrared spectra of all-trans-astaxanthin （AXT） in dimethyl sulfoxide （DMSO） solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ1 band into υ1-1 and υ1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ1 band is very sensitive to the excitation wavelength： resonance excitation stimulates the higher-frequency υ1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4＇=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.
基金This research was financially supported partially by the National Science Foundation of Japan under grant No.10555173 This work was partially supported by the Scholarship from Japan Ministry of Education,Science and Culture.
文摘This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a full size offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liquid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the Study investigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incident wave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating results can reasonably match the corresponding experimental results.
基金The authors would like to acknowledge the financial supports from the National Natural Science Foundation of China(Grant No.11372136)the Special fund for basic scientific research of Central University(Grant No.30916011306)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX17_0386).
文摘The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cylinder with two free ends,and particularly in this trajectory,where the scanning angleβand rollangle a vary over a broad range between 0°and 180.In this work wind tunnel experiments are firstconducted to learn the effects of Reynolds number and scanning angle on aerodynamic parameters forshort cylinder with aspect ratio L/D=1.Similar to infinite cylinder,for the short cylinder with two freeends,the drag crisis phenomenon still exists in the critical regime 1.7×10^(5)≤Re≤6.8×10^(5).Then 3Dsimulations are performed to demonstrate the aerodynamic characteristics of short cylinder and TSBover a broad range of Re,L/D,a and 6.The sensitivity analysis of time step and grid are presented as well.whenβ3=0,for short cylinder,the drag crisis phenomenon was also observed in the simulation,but notas obvious as in the wind tunnel test.In some attitudes,there is an obvious Karman vortexin the wake ofshort cylinder and TSB.The correlation between time-averaged aerodynamic coefficients and L/D,Re,a&l is discussed.The vortex shedding frequency and shear layer behavior are obtained for quasi-steadyand unsteady flow.Finally,the effect of end's shape on drag reduction and vortex shedding frequency isanalyzed.
基金by the National Natural Science Foundation of China(Grant No.50179014)
文摘ne purpose of this study is to investigate the effectiveness of multi-tuned mass dampers (MTMD) on mitigating vibration of an offshore oil platform subjected to ocean wave loading. An optimal design method is used to determine the optimal damper parameters under ocean wave loading. The force on the structure is determined by use of the linearized Morison equation. Investigation on the deck motion with and without MTMD on the structure is made under design conditions. The results show that MTMD with the optimized parameters suppress the response of each structural mode. The sensitivity of optimum values of MTMD to characteristic wave parameters is also analyzed. It is indicated that a single, TMD on the deck of a platform can have the best performance, and the small the damping value of TMD, the better the vibration control.
文摘An eigenvalue method considering the membrane vibration of wrinkling out-of-plane deformation is introduced, and the stress distributing rule in membrane wrinkled area is analyzed. A dynamic analytical model of rectangular shear wrinkled membrane and its numerical analysis approach are also developed. Results indicate that the stress in wrinkled area is not uniform, i.e. it is larger in wrinkling wave peaks along wrinkles and two ends of wrinkle in vertical direction. Vibration modes of wrinkled membrane are strongly correlated with the wrinkling configurations. The rigidity is larger due to the heavier stress in the part of wrinkling wave peaks. Therefore, wave peaks are always located at the node lines of vibration mode. The vibration frequency obviously increases with the vibration of wave peaks.
基金supported by the Fundamental Research Funds for the Central Universities(No.NS2015097)
文摘With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dynamic model displays characteristics of strong coupling with structure/control and nonlinearity.Based on the sloshing mass dynamic simplified as a spring-mass-damping model,a rigid-flexible-sloshing model is constructed.Moreover,the effect on the dynamic performance of the coupled model is analyzed with changing frequency and damping.The results show that propellant sloshing dynamics significantly affects the rigid body motion modes,especially flexible mode and short mode.The right half plane pole(RHP)moves far from the imaginary axis with the consumption of the propellant.The flexible mode attenuates with the increase of the sloshing damping,and the coupling becomes stronger when sloshing frequency is close to the short mode frequency or the flexible frequency of the beam.
文摘In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whole shell-structure is divided into the four subsystems,and the SEA physical model and power flow balance equations among these subsystems are established.The similitude relations of input power, coupling loss factor and modal density of the subsystemsbetween the complex shell-structure and its scaled-down model are analyzed. According to thesimilitude theory and power flow balance equations, when the immerged shell-structures are excited,the similar relations of spatially averaged vibration response and underwater radiating sound powerare established for the complex shell-structure and its scaled-down model.
