The aerodynamic model of propeller,wing,fuselage and vertical tail are established for the tilt quad rotor(TQR)with partial tilt-wing,and then the flight dynamic model is established.Based on the six-degree-of-freedom...The aerodynamic model of propeller,wing,fuselage and vertical tail are established for the tilt quad rotor(TQR)with partial tilt-wing,and then the flight dynamic model is established.Based on the six-degree-of-freedom equation and the small disturbance linearization assumption,the trimming and stability of the tilt quad rotor with partial tilt-wing and the tilt quad rotor without tilt-wing are analyzed.The results show that in the hovering state,due to the existence of tilt-wing,the propeller wake reduces the downwash on the wing,thereby reducing the vertical weight gain of the aircraft.It is beneficial to increase the endurance time and improve the endurance performance.The transition corridor of the TQR with tilt-wing is narrower than that of the TQR without tilt-wing,but the transition corridor of TQR with tilt-wing still has a large space for design.Furthermore,the stability analysis shows that the Dutch roll damping ratio is larger,and in other modes the aircraft has a certain stability.The manipulation response analysis shows that in the transition mode the lateral-directional coupling is strong.展开更多
One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow p...One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow pressure on the leakage characteristics of seal. Computational fluid dynamics (CFD) model for 3D labyrinth seal was built which provides a basis for reducing steam flow excitation. The streamline pattern and the pressure drop characteristics for leakage of steam through a labyrinth seal was investigated. Simulations of internal flow and leakage characteristics had been performed by CFD software and Black-Child model. The results showed that the amount of leakage is directly proportional to the tooth gap and inlet pressure and inversely proportional to the cavity depth and outlet pressure. The proposed CFD model provides a feasible method to predict the leakage characteristics of labyrinth seal in response to the structure of seal and the change in inlet-outlet pressures.展开更多
Hydraulic technology has the outstanding advantages of easy pressure compensation and high power density.It is an indispensable part of subsea equipment,such as deep-sea operations and submersible propulsion.There are...Hydraulic technology has the outstanding advantages of easy pressure compensation and high power density.It is an indispensable part of subsea equipment,such as deep-sea operations and submersible propulsion.There are few studies on electrohydraulic servo valves(EHSVs)in the deep sea.In this work,a novel electro-hydraulic servo rotary valve is designed,and its mathematical model is established.The analysis considers the variations in physical parameters such as temperature,ambient pressure,and oil viscosity resulting from changes in sea depth.This study focuses on the deformation of the rotary valve and the consequent alterations in leakage and friction torque.The findings indicate that at a depth of 12000 m,the fit clearance between the valve spool and the valve sleeve is 0.00413 mm,representing a 17%reduction compared with the clearance in a land environment.Then,the response of the rotary valve to depth is analyzed.The results indicate that the bandwidth of the rotary valve decreases with increasing depth.This study provides a reference for the use of the EHSV in the deep sea.展开更多
In this study, shaking table tests were performed to investigate the dynamic characteristics of a mold transformer. Based on the test results, rotary friction dampers were developed to mitigate the excessive lateral d...In this study, shaking table tests were performed to investigate the dynamic characteristics of a mold transformer. Based on the test results, rotary friction dampers were developed to mitigate the excessive lateral displacement that occurred along the direction of the weak stiffness axis of the mold transformer. In addition, shaking table tests were performed by attaching friction dampers to both sides of the mold transformer. Based on the shaking table test results, the natural frequency, mode vector, and damping ratio of the mold transformer were derived using the transfer function and half-power bandwidth. The test results indicated that the use of friction dampers can decrease the displacement and acceleration response of the mold transformer. Finally, dynamic structural models were established considering the component connectivity and mass distribution of the mold transformer. In addition, a numerical strategy was proposed to calibrate the stiffness coefficients of the mold transformer, thereby facilitating the relationship between generalized mass and stiffness. The results indicated that the analytical model based on the calibration strategy of stiffness coefficients can reasonably simulate the dynamic behavior of the mold transformer using friction dampers with regard to transfer function, displacement, and acceleration response.展开更多
The extreme conditions severely constrain the dynamic characteristics of aircraft landing gear retraction mechanism(ALGRM).This paper proposes a dynamic modeling and analysis method for ALGRM considering the coupling ...The extreme conditions severely constrain the dynamic characteristics of aircraft landing gear retraction mechanism(ALGRM).This paper proposes a dynamic modeling and analysis method for ALGRM considering the coupling effects of extreme conditions such as clearance joints,flexible rods,and salt spray corrosion.Firstly,the mathematical model for clearance joint and flexible rod is established and the dynamic model of ALGRM considering clearance joints and flexible rods is formulated based on Lagrangian equation.Furthermore,the salt spray corrosion model for clearance joint is developed using COMSOL simulation software.Finally,the effects of different temperatures and relative humidities on the corrosion depth of clearance joint and the dynamic characteristics of ALGRM under the coupling effects of extreme conditions are investigated.The results have found that the impact of extreme conditions on dynamics of system cannot be ignored.This study not only provides a theoretical foundation for predicting the dynamic characteristics of ALGRM under extreme conditions but also offers insights for the optimization design and corrosion protection efforts of landing gear.展开更多
Aerodynamic and dynamic interference from trains is a key issue of concern for the safety of road vehicles travelling on single-level rail-cum road bridges.Based on the wind-road vehicle-train-bridge(WRTB)coupled vibr...Aerodynamic and dynamic interference from trains is a key issue of concern for the safety of road vehicles travelling on single-level rail-cum road bridges.Based on the wind-road vehicle-train-bridge(WRTB)coupled vibration system developed herein,this study examines the dynamic characteristics when road vehicles meet trains in this situation.The influence of load combination,vehicle type and vehicle location is analyzed.A method to obtain the aerodynamic load of road vehicles encountering the train at an arbitrary wind speed is proposed.The results show that due to the windproof facilities and the large line distance between the railway and highway,the aerodynamic and dynamic influence of trains on road vehicles is slight,and the vibration of road vehicles depends on the road roughness.Among the road vehicles discussed,the bus is the easiest to rollover,and the truck-trailer is the easiest to sideslip.Compared with the aerodynamic impact of trains,the crosswind has a more significant influence on road vehicles.The first peak/valley value of aerodynamic loads determines the maximum dynamic response,and the quick method is optimized based on this conclusion.Test cases show that the optimized method can produce conservative results and can be used for relevant research or engineering applications.展开更多
Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear ...Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear tests were conducted on the saturated transparent sand composed of fused quartz and refractive index-matched oil mixture. The results reveal that an increase in the initial shear stress ratio significantly affects the shape of the hysteresis loop, particularly resulting in more pronounced asymmetrical accumulation. Factors such as lower relative density, higher cyclic stress ratios and higher initial shear stress ratio have been shown to accelerate cyclic deformation, cyclic pore water pressure and stiffness degradation. The cyclic liquefaction resistance curves decrease as the initial shear stress ratio increases or as relative density decreases. Booker model and power law function model were applied to predict the pore water pressure for transparent sand. Both models yielded excellent fits for their respective condition, indicating a similar dynamic liquefaction pattern to that of natural sands. Finally, transparent sand displays similar dynamic characteristics in terms of cyclic liquefaction resistance and Kα correction factor. These comparisons indicate that transparent sand can serve as an effective means to mimic many natural sands in dynamic model tests.展开更多
The air spring is a non-metallic spring device that utilizes the deformation of flexible materials and the compression of air to generate restoring force, achieving vibration damping and buffering effects. It features...The air spring is a non-metallic spring device that utilizes the deformation of flexible materials and the compression of air to generate restoring force, achieving vibration damping and buffering effects. It features height adjustment and highfrequency vibration isolation. Air springs exhibit significant viscoelastic and memory characteristics. Traditional dynamic models of air springs are complex and unable to accurately describe their viscoelastic properties. This paper introduces fractional calculus theory to study them. Through experimental research on air springs, test data are analyzed to obtain their mechanical properties under different working conditions. A fractional-order nonlinear dynamic model of the air spring is established, and the model parameters are identified using the least squares method. The experimental data are fitted to verify the model's accuracy.展开更多
Transmission towers,serving as the support structure of transmission lines,are significant for the functional-ity of an electric transmission system.Bolt joint loosening is one of the critical factors that can affect ...Transmission towers,serving as the support structure of transmission lines,are significant for the functional-ity of an electric transmission system.Bolt joint loosening is one of the critical factors that can affect the safety and stability of transmission towers.In this study,the effects of bolt joint loosening on the dynamic characteristics of a 220-kV angle steel transmission tower are the main topic of concern.First,the mechanical properties of typical joints subjected to different degrees of bolt loosening are studied by finite solid-element simulation,based on which a finite hybrid-element modeling method is developed for a tower structure suffering varying loose degrees in the joints.Taking a 220-kV angle steel transmission tower as the object,the influence of the position and degree of loosening on the tower’s natural frequencies and mode shapes are simulated and discussed.The results demonstrate that the main-member splice joint and the main diagonal-horizontal member gusset plate joint account for the dominant impact on the dynamic characteristics of the tower.In addition,the dominant joint shifts from the main-member splice joint to the main diagonal-horizontal member gusset plate joint as the considered modal order increases.In the case of double joints loosening simultaneously,the loosening of nondomi-nant joints has nonnegligible effects on the tower as well.展开更多
The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results disp...The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results displayed that the FT damage process of samples can be divided into three stages based on the changes in weight,porosity,and P-wave velocity.The dynamic peak strength,dynamic elastic modulus,and strength ratio decreased with increasing FT cycles,and increased with increasing average strain rate.Moreover,the average strain rate reduced the influence of FT cycles on dynamic peak strength.In general,the incident energy,reflected energy and dissipated energy increased with increasing average strain rate,the transmitted energy was negligibly affected by the average strain rate,and the energy dissipation ratio decreased with increasing average strain rate.In addition,the influence of FT cycles on each type of energy and energy dissipation ratio during sample failure was smaller than that of average strain rate.The average size of fragments can accurately demonstrate the impact of FT damage and average strain rate on dynamic peak strength and failure mode,and quantitatively evaluate the sample’s fragmentation degree.Fractal dimension varies with FT cycles and average strain rate,and the threshold is between 148.30 and 242.57 s^(-1).If the average strain rate is in the threshold range,the relationship between the fractal dimension and dynamic peak strength is more regular,otherwise,it will become complicated.The results reveal the dynamic failure mechanism of white sandstone samples,providing assistance for dynamic rock-breaking and disaster prevention in cold regions.展开更多
The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engin...The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engineering often yield unsatisfactory economic and ecological outcomes.As an environment-friendly soil improvement material,Xanthan gum has broad application prospects and is therefore considered a solidifying agent for enhancing silty soil properties in the Yellow River Basin.In this study,a series of tests is conducted using a scanning electron microscope and a dynamic triaxial testing apparatus to investigate the microstructure and dynamic deformation characteristics of unsaturated silty soil with varying xanthan gum contents during the wetting process.The results show that xanthan gum effectively fills voids between soil particles and adheres to their surfaces,forming fibrous and network structures.This modification enhances the inherent properties of the silty soil and significantly improves its stability under dynamic loading.Specifically,with increasing xanthan gum content,the dynamic shear modulus increases while the damping ratio decreases.During the wetting process,as suction decreases,the dynamic shear modulus decreases while the damping ratio increases.Xanthan gum reduces the sensitivity of the dynamic deformation characteristics of the treated silty soil to changes in suction levels.Finally,based on the modified Hardin-Drnevich hyperbolic model,a predictive model for the dynamic shear modulus and damping ratio of treated silty soil is proposed,considering the xanthan gum content.These research findings provide a theoretical basis for the construction and maintenance of water conservancy,slope stabilization,and roadbed projects in the Yellow River Basin.展开更多
Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and respons...Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.展开更多
Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris fl...Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.展开更多
The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting...The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.展开更多
The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scann...The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.展开更多
Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulat...Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulate the typical gas-liquid two-phase fow patterns.First,validation of the numerical model is conducted and the typical fow patterns are consistent with the Baker chart.Then,the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase fow.The results show that the dynamic response under stratified fow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively.Meanwhile,the dynamic responses induced by slug fow,wave fow and annular fow show obvious periodic fuctuations.Furthermore,the dynamic response characteristics under slug flow condition are maximum;the maximum pipe deformation and equivalent stress can reach 4mm and 17.5 MPa,respectively.The principal direction of total deformation is different under various flow patterns.Therefore,the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe.The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions.展开更多
OaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a ...OaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a semi- insulation （SI） GaAs wafer is investigated by the terahertz （THz） non-destructive testing technology. Using an air biased coherent generation and detection THz time domain spectroscopy system, the THz time domain waveform and spectrum of SI-GaAs are obtained by the time domain spectroscopy module, and its optical- electrical characteristics including complex refractive index, permittivity and dielectric loss angle are calculated. Its carrier lifetime is measured by the optical-pump THz-probe module, and the THz pulse induced intervalley scattering in photo-excited SI-GaAs is discussed.展开更多
Generation of attosecond electromagnetic （EM） pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. ...Generation of attosecond electromagnetic （EM） pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. The inter- action process is found to be so complicated even in the situation of utilizing driving laser pulses of only one cycle. Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the coherent synchrotron emission process whose spectra are found to follow an exponential decay rule. Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the relativistic oscillating mirror mechanism. High harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates in the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.展开更多
This study proposes an effective method to enhance the accuracy of the Differential Quadrature Method(DQM)for calculating the dynamic characteristics of functionally graded beams by improving the form of discrete node...This study proposes an effective method to enhance the accuracy of the Differential Quadrature Method(DQM)for calculating the dynamic characteristics of functionally graded beams by improving the form of discrete node distribution.Firstly,based on the first-order shear deformation theory,the governing equation of free vibration of a functionally graded beam is transformed into the eigenvalue problem of ordinary differential equations with respect to beam axial displacement,transverse displacement,and cross-sectional rotation angle by considering the effects of shear deformation and rotational inertia of the beam cross-section.Then,ignoring the shear deformation of the beam section and only considering the effect of the rotational inertia of the section,the governing equation of the beam is transformed into the eigenvalue problem of ordinary differential equations with respect to beam transverse displacement.Based on the differential quadrature method theory,the eigenvalue problem of ordinary differential equations is transformed into the eigenvalue problem of standard generalized algebraic equations.Finally,the first several natural frequencies of the beam can be calculated.The feasibility and accuracy of the improved DQM are verified using the finite element method(FEM)and combined with the results of relevant literature.展开更多
The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with differen...The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.展开更多
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘The aerodynamic model of propeller,wing,fuselage and vertical tail are established for the tilt quad rotor(TQR)with partial tilt-wing,and then the flight dynamic model is established.Based on the six-degree-of-freedom equation and the small disturbance linearization assumption,the trimming and stability of the tilt quad rotor with partial tilt-wing and the tilt quad rotor without tilt-wing are analyzed.The results show that in the hovering state,due to the existence of tilt-wing,the propeller wake reduces the downwash on the wing,thereby reducing the vertical weight gain of the aircraft.It is beneficial to increase the endurance time and improve the endurance performance.The transition corridor of the TQR with tilt-wing is narrower than that of the TQR without tilt-wing,but the transition corridor of TQR with tilt-wing still has a large space for design.Furthermore,the stability analysis shows that the Dutch roll damping ratio is larger,and in other modes the aircraft has a certain stability.The manipulation response analysis shows that in the transition mode the lateral-directional coupling is strong.
基金Sponsored by the National Natural Science Foundation of China (Grant No.10872054,10872055 and 50903082)
文摘One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow pressure on the leakage characteristics of seal. Computational fluid dynamics (CFD) model for 3D labyrinth seal was built which provides a basis for reducing steam flow excitation. The streamline pattern and the pressure drop characteristics for leakage of steam through a labyrinth seal was investigated. Simulations of internal flow and leakage characteristics had been performed by CFD software and Black-Child model. The results showed that the amount of leakage is directly proportional to the tooth gap and inlet pressure and inversely proportional to the cavity depth and outlet pressure. The proposed CFD model provides a feasible method to predict the leakage characteristics of labyrinth seal in response to the structure of seal and the change in inlet-outlet pressures.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2805703)the Major Training Program of University Research and Innovation Platform of Gansu Provincial Department of Education(Grant No.2024CXPT-09).
文摘Hydraulic technology has the outstanding advantages of easy pressure compensation and high power density.It is an indispensable part of subsea equipment,such as deep-sea operations and submersible propulsion.There are few studies on electrohydraulic servo valves(EHSVs)in the deep sea.In this work,a novel electro-hydraulic servo rotary valve is designed,and its mathematical model is established.The analysis considers the variations in physical parameters such as temperature,ambient pressure,and oil viscosity resulting from changes in sea depth.This study focuses on the deformation of the rotary valve and the consequent alterations in leakage and friction torque.The findings indicate that at a depth of 12000 m,the fit clearance between the valve spool and the valve sleeve is 0.00413 mm,representing a 17%reduction compared with the clearance in a land environment.Then,the response of the rotary valve to depth is analyzed.The results indicate that the bandwidth of the rotary valve decreases with increasing depth.This study provides a reference for the use of the EHSV in the deep sea.
基金Basic Science Research Program of the National Research Foundation of Korea under Grant Nos.NRF-2020R1A6A1A03044977 and NRF2022R1A2C2004351。
文摘In this study, shaking table tests were performed to investigate the dynamic characteristics of a mold transformer. Based on the test results, rotary friction dampers were developed to mitigate the excessive lateral displacement that occurred along the direction of the weak stiffness axis of the mold transformer. In addition, shaking table tests were performed by attaching friction dampers to both sides of the mold transformer. Based on the shaking table test results, the natural frequency, mode vector, and damping ratio of the mold transformer were derived using the transfer function and half-power bandwidth. The test results indicated that the use of friction dampers can decrease the displacement and acceleration response of the mold transformer. Finally, dynamic structural models were established considering the component connectivity and mass distribution of the mold transformer. In addition, a numerical strategy was proposed to calibrate the stiffness coefficients of the mold transformer, thereby facilitating the relationship between generalized mass and stiffness. The results indicated that the analytical model based on the calibration strategy of stiffness coefficients can reasonably simulate the dynamic behavior of the mold transformer using friction dampers with regard to transfer function, displacement, and acceleration response.
基金supported by the National Natural Science Foundation of China(Grant No.51875086)Sichuan Science and Technology Program(Grant No.2023NSFSC0866).
文摘The extreme conditions severely constrain the dynamic characteristics of aircraft landing gear retraction mechanism(ALGRM).This paper proposes a dynamic modeling and analysis method for ALGRM considering the coupling effects of extreme conditions such as clearance joints,flexible rods,and salt spray corrosion.Firstly,the mathematical model for clearance joint and flexible rod is established and the dynamic model of ALGRM considering clearance joints and flexible rods is formulated based on Lagrangian equation.Furthermore,the salt spray corrosion model for clearance joint is developed using COMSOL simulation software.Finally,the effects of different temperatures and relative humidities on the corrosion depth of clearance joint and the dynamic characteristics of ALGRM under the coupling effects of extreme conditions are investigated.The results have found that the impact of extreme conditions on dynamics of system cannot be ignored.This study not only provides a theoretical foundation for predicting the dynamic characteristics of ALGRM under extreme conditions but also offers insights for the optimization design and corrosion protection efforts of landing gear.
基金The Research Project of Southwest Municipal Design&Research Institute of China under Grant No.2023KY-KT-02-I。
文摘Aerodynamic and dynamic interference from trains is a key issue of concern for the safety of road vehicles travelling on single-level rail-cum road bridges.Based on the wind-road vehicle-train-bridge(WRTB)coupled vibration system developed herein,this study examines the dynamic characteristics when road vehicles meet trains in this situation.The influence of load combination,vehicle type and vehicle location is analyzed.A method to obtain the aerodynamic load of road vehicles encountering the train at an arbitrary wind speed is proposed.The results show that due to the windproof facilities and the large line distance between the railway and highway,the aerodynamic and dynamic influence of trains on road vehicles is slight,and the vibration of road vehicles depends on the road roughness.Among the road vehicles discussed,the bus is the easiest to rollover,and the truck-trailer is the easiest to sideslip.Compared with the aerodynamic impact of trains,the crosswind has a more significant influence on road vehicles.The first peak/valley value of aerodynamic loads determines the maximum dynamic response,and the quick method is optimized based on this conclusion.Test cases show that the optimized method can produce conservative results and can be used for relevant research or engineering applications.
基金Project(U2268213) supported by the National Natural Science Foundation of ChinaProject(2024YFHZ0121) supported by the Sichuan Science and Technology Program,China。
文摘Transparent sand is a special material to realize visualization of concealed work in geotechnical engineering. To investigate the dynamic characteristics of transparent sand, a series of undrained cyclic simple shear tests were conducted on the saturated transparent sand composed of fused quartz and refractive index-matched oil mixture. The results reveal that an increase in the initial shear stress ratio significantly affects the shape of the hysteresis loop, particularly resulting in more pronounced asymmetrical accumulation. Factors such as lower relative density, higher cyclic stress ratios and higher initial shear stress ratio have been shown to accelerate cyclic deformation, cyclic pore water pressure and stiffness degradation. The cyclic liquefaction resistance curves decrease as the initial shear stress ratio increases or as relative density decreases. Booker model and power law function model were applied to predict the pore water pressure for transparent sand. Both models yielded excellent fits for their respective condition, indicating a similar dynamic liquefaction pattern to that of natural sands. Finally, transparent sand displays similar dynamic characteristics in terms of cyclic liquefaction resistance and Kα correction factor. These comparisons indicate that transparent sand can serve as an effective means to mimic many natural sands in dynamic model tests.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12072206 and U1934201)Science and Technology Project of Hebei Education Department of Hebei Province, China (Grant No. QN2024254)。
文摘The air spring is a non-metallic spring device that utilizes the deformation of flexible materials and the compression of air to generate restoring force, achieving vibration damping and buffering effects. It features height adjustment and highfrequency vibration isolation. Air springs exhibit significant viscoelastic and memory characteristics. Traditional dynamic models of air springs are complex and unable to accurately describe their viscoelastic properties. This paper introduces fractional calculus theory to study them. Through experimental research on air springs, test data are analyzed to obtain their mechanical properties under different working conditions. A fractional-order nonlinear dynamic model of the air spring is established, and the model parameters are identified using the least squares method. The experimental data are fitted to verify the model's accuracy.
基金The Youth Foundation Project of Jiangsu Province(No.BK20230337)the Natural Science Research of Jiangsu Higher Education Institutions of China(No.22KJB560004)the National Natu-ral Science Foundation of China(No.52278523)。
文摘Transmission towers,serving as the support structure of transmission lines,are significant for the functional-ity of an electric transmission system.Bolt joint loosening is one of the critical factors that can affect the safety and stability of transmission towers.In this study,the effects of bolt joint loosening on the dynamic characteristics of a 220-kV angle steel transmission tower are the main topic of concern.First,the mechanical properties of typical joints subjected to different degrees of bolt loosening are studied by finite solid-element simulation,based on which a finite hybrid-element modeling method is developed for a tower structure suffering varying loose degrees in the joints.Taking a 220-kV angle steel transmission tower as the object,the influence of the position and degree of loosening on the tower’s natural frequencies and mode shapes are simulated and discussed.The results demonstrate that the main-member splice joint and the main diagonal-horizontal member gusset plate joint account for the dominant impact on the dynamic characteristics of the tower.In addition,the dominant joint shifts from the main-member splice joint to the main diagonal-horizontal member gusset plate joint as the considered modal order increases.In the case of double joints loosening simultaneously,the loosening of nondomi-nant joints has nonnegligible effects on the tower as well.
基金Funded by the National Natural Science Foundation of China(Nos.52174088,42277154)the Independent Innovation Research Fund Graduate Free Exploration Project for the Wuhan University of Technology(No.104972024JYS0007)。
文摘The influence of FT(freeze-thaw)cycles and average strain rate on the dynamic impact performance,energy evolution characteristics,and failure behavior of sandstone was studied through dynamic impact tests.Results displayed that the FT damage process of samples can be divided into three stages based on the changes in weight,porosity,and P-wave velocity.The dynamic peak strength,dynamic elastic modulus,and strength ratio decreased with increasing FT cycles,and increased with increasing average strain rate.Moreover,the average strain rate reduced the influence of FT cycles on dynamic peak strength.In general,the incident energy,reflected energy and dissipated energy increased with increasing average strain rate,the transmitted energy was negligibly affected by the average strain rate,and the energy dissipation ratio decreased with increasing average strain rate.In addition,the influence of FT cycles on each type of energy and energy dissipation ratio during sample failure was smaller than that of average strain rate.The average size of fragments can accurately demonstrate the impact of FT damage and average strain rate on dynamic peak strength and failure mode,and quantitatively evaluate the sample’s fragmentation degree.Fractal dimension varies with FT cycles and average strain rate,and the threshold is between 148.30 and 242.57 s^(-1).If the average strain rate is in the threshold range,the relationship between the fractal dimension and dynamic peak strength is more regular,otherwise,it will become complicated.The results reveal the dynamic failure mechanism of white sandstone samples,providing assistance for dynamic rock-breaking and disaster prevention in cold regions.
基金supported by the Postgraduate Education Reform and Quality Improvement Project of Henan Province,China(Grant No.YJS2023AL004)the Graduate Innovation Project of North China University of Water Resources and Electric Power(Grant No.NCWUYC-202315069)the China National Scholarship Fund organized by the China Scholarship Council(Grant No.202208410337).
文摘The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process,leading to the failure of roadbed structures.Commonly used methods for improving silty soils in engineering often yield unsatisfactory economic and ecological outcomes.As an environment-friendly soil improvement material,Xanthan gum has broad application prospects and is therefore considered a solidifying agent for enhancing silty soil properties in the Yellow River Basin.In this study,a series of tests is conducted using a scanning electron microscope and a dynamic triaxial testing apparatus to investigate the microstructure and dynamic deformation characteristics of unsaturated silty soil with varying xanthan gum contents during the wetting process.The results show that xanthan gum effectively fills voids between soil particles and adheres to their surfaces,forming fibrous and network structures.This modification enhances the inherent properties of the silty soil and significantly improves its stability under dynamic loading.Specifically,with increasing xanthan gum content,the dynamic shear modulus increases while the damping ratio decreases.During the wetting process,as suction decreases,the dynamic shear modulus decreases while the damping ratio increases.Xanthan gum reduces the sensitivity of the dynamic deformation characteristics of the treated silty soil to changes in suction levels.Finally,based on the modified Hardin-Drnevich hyperbolic model,a predictive model for the dynamic shear modulus and damping ratio of treated silty soil is proposed,considering the xanthan gum content.These research findings provide a theoretical basis for the construction and maintenance of water conservancy,slope stabilization,and roadbed projects in the Yellow River Basin.
基金National Natural Science Foundation of China under Grant No.52278503。
文摘Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.
基金granted by the National Natural Science Foundation of China(Grant Nos.U2244227 and U2244226)the National Key R&D Program of China(Grant No.2022YFC3004301)China Geological Survey Project(Grant No.DD20230538)。
文摘Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.
基金the continued support of Key Laboratory of Inlet and Exhaust system Technology (Nanjing University of Aeronautics and Astronautics), ChinaMinistry of Education, National Science and Technology Major Project of China (Nos. 2017-V-0004-0054, 2019-II-0007-0027, Y2022II-0005-0008)+6 种基金Defense Industrial Technology Development Program of China (No. JCKY2019605D001)Advanced Jet Propulsion Creativity Center of AEAC of China (No. HKCX2020-02-011)China Postdoctoral Science Foundation (No. 2022M721598)Jiangsu Funding Program for Excellent Postdoctoral Talent of China (No. 2022ZB214)the Youth Fund Project of Natural Science Foundation of Jiangsu Province of China (No. BK20230891)the National Natural Science Foundation of China (No. 12332018)Science Center for Gas Turbine Project, China (P2022-B-I-006-001) and some other related foundations
文摘The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.
基金supported by the National Natural Science Foundation of China under Grants Nos.52165013 and 51565021.
文摘The meso-dynamical behaviour of a high-speed rail ballast bed with under sleeper pads(USPs)was studied.The geometrically irregular refined discrete element model of the ballast particles was constructed using 3D scanning techniques,and the 3D dynamic model of the rail-sleeper-ballast bed was constructed using the coupled discrete element method-multiflexible-body dynamics(DEM-MFBD)approach.We analyse the meso-mechanical dynamics of the ballast bed with USPs under dynamic load on a train and verify the correctness of the model in laboratory tests.It is shown that the deformation of the USPs increases the contact area between the sleeper and the ballast particles,and subsequently the number of contacts between them.As the depth of the granular ballast bed increases,the contact area becomes larger,and the contact force between the ballast particles gradually decreases.Under the action of the elastic USPs,the contact forces between ballast particles are reduced and the overall vibration level of the ballast bed can be reduced.The settlement of the granular ballast bed occurs mainly at the shallow position of the sleeper bottom,and the installation of the elastic USPs can be effective in reducing the stress on the ballast particles and the settlement of the ballast bed.
基金the National Natural Science Foundation of China(No.51779143)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(No.SL2020ZD101)the Cultivation of Scientific Research Ability of Young Talents of Shanghai Jiao Tong University(No.19X100040072)。
文摘Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulate the typical gas-liquid two-phase fow patterns.First,validation of the numerical model is conducted and the typical fow patterns are consistent with the Baker chart.Then,the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase fow.The results show that the dynamic response under stratified fow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively.Meanwhile,the dynamic responses induced by slug fow,wave fow and annular fow show obvious periodic fuctuations.Furthermore,the dynamic response characteristics under slug flow condition are maximum;the maximum pipe deformation and equivalent stress can reach 4mm and 17.5 MPa,respectively.The principal direction of total deformation is different under various flow patterns.Therefore,the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe.The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61575161 and 61427814the National Basic Research Program of China under Grant No 2014CB339800+1 种基金the Foundation of Shaanxi Key Science and Technology Innovation Team under Grant No 2014KTC-13the Special Financial Grant from the China Postdoctoral Science Foundation under Grant No 2013T60883
文摘OaAs has been widely used to fabricate a variety of optoelectronic devices by virtue of its superior performance, and it is very important to accurately measure its electrical and optical properties. In this study, a semi- insulation （SI） GaAs wafer is investigated by the terahertz （THz） non-destructive testing technology. Using an air biased coherent generation and detection THz time domain spectroscopy system, the THz time domain waveform and spectrum of SI-GaAs are obtained by the time domain spectroscopy module, and its optical- electrical characteristics including complex refractive index, permittivity and dielectric loss angle are calculated. Its carrier lifetime is measured by the optical-pump THz-probe module, and the THz pulse induced intervalley scattering in photo-excited SI-GaAs is discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 11674146the National Basic Research Program of China under Grant No 2013CBA01500
文摘Generation of attosecond electromagnetic （EM） pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. The inter- action process is found to be so complicated even in the situation of utilizing driving laser pulses of only one cycle. Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the coherent synchrotron emission process whose spectra are found to follow an exponential decay rule. Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the relativistic oscillating mirror mechanism. High harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates in the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.
基金Anhui Provincial Natural Science Foundation(2308085QD124)Anhui Province University Natural Science Research Project(GrantNo.2023AH050918)The University Outstanding Youth Talent Support Program of Anhui Province.
文摘This study proposes an effective method to enhance the accuracy of the Differential Quadrature Method(DQM)for calculating the dynamic characteristics of functionally graded beams by improving the form of discrete node distribution.Firstly,based on the first-order shear deformation theory,the governing equation of free vibration of a functionally graded beam is transformed into the eigenvalue problem of ordinary differential equations with respect to beam axial displacement,transverse displacement,and cross-sectional rotation angle by considering the effects of shear deformation and rotational inertia of the beam cross-section.Then,ignoring the shear deformation of the beam section and only considering the effect of the rotational inertia of the section,the governing equation of the beam is transformed into the eigenvalue problem of ordinary differential equations with respect to beam transverse displacement.Based on the differential quadrature method theory,the eigenvalue problem of ordinary differential equations is transformed into the eigenvalue problem of standard generalized algebraic equations.Finally,the first several natural frequencies of the beam can be calculated.The feasibility and accuracy of the improved DQM are verified using the finite element method(FEM)and combined with the results of relevant literature.
基金supported by the Beijing Natural Science Foundation,China(Grant No.JQ20039)National Natural Science Foundation of China(Grant No.12172019).
文摘The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.
