A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adj...A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adjustable geometric configuration via the initial inclination angle.Based on the principle of Lagrangian mechanics,the equation of motion governing the structural dynamics is rigorously derived.The system is modeled as a strongly nonlinear single-degree-of-freedom dynamical system,loaded with a normalized payload and subject to harmonic base excitation.To analyze the steady-state response,the harmonic balance method is employed,providing accurate predictions of the payload's vibration amplitude and displacement transmissibility as functions of both the base excitation amplitude and frequency.The analysis reveals a direct relationship between the isolator's geometric and stiffness parameters and its load-bearing capacity,leading to the identification of three distinct operational regimes.Depending on the unloaded initial inclination angle,the equivalent stiffness ratio,and the payload design configuration,the system can exhibit one of three vibration isolation modes:(i)the quasizero stiffness(QZS)isolation mode,(ii)the zero linear stiffness with controllable nonlinear stiffness,and(iii)the full-band perfect zero stiffness.The vibration isolation performance of the proposed structure is thoroughly discussed for all three oscillation modes in terms of frequency response curves,displacement transmissibility,and time-domain responses.The key novel finding is that this structure can operate as a full-band,high-performance vibration isolator when the initial inclination angle is designed to be a right angle,enabling full isolation of the maximum possible payload.Moreover,the analytical results and numerical simulations demonstrate that the isolator's displacement transmissibility T with the unit dB tends to-∞as the air-damping coefficient approaches zero,enabling ideal vibration isolation across the entire excitation frequency range.These analytical insights are validated through comprehensive numerical simulations,which show excellent agreement with the theoretical predictions.展开更多
The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance...The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.展开更多
Devices on aircraft are subjected to complex environmental excitations that pose risks to their operational safety.Passive vibration isolation techniques are extensively employed due to their advantage of not requirin...Devices on aircraft are subjected to complex environmental excitations that pose risks to their operational safety.Passive vibration isolation techniques are extensively employed due to their advantage of not requiring additional energy sources.This paper introduces a novel metallic vibration isolator based on zigzag structures.The proposed isolator features a compact design and can be manufactured using additive manufacturing techniques,allowing for the integration of structural and functional elements.Firstly,the vibration response of the single-degree-of-freedom(SDOF)system is analyzed.To achieve effective vibration reduction,it is crucial for the isolator's stiffness to be sufficiently low.Secondly,to obtain a structure with high compliance,the traversal algorithm and the finite element method(FEM)are applied.The results confirm that the zigzag structure is a reliable high-compliance configuration.Thirdly,the parametric geometric model of the zigzag structure is developed and its stiffness is calculated.Quasi-static compression experiments validate the accuracy of the calculations.Finally,a specific engineering example is considered,where a zigzag vibration isolator is designed and fabricated.Vibration experiments demonstrate that the zigzag isolator effectively reduces both the stiffness and the fundamental frequency of the vibration system,achieving a vibration isolation efficiency exceeding 60%.展开更多
Seismic wavefields propagate through three-dimensional(3D)space,and their precise characterization is crucial for understanding subsurface structures.Traditional 2D algorithms,due to their limitations,are insufficient...Seismic wavefields propagate through three-dimensional(3D)space,and their precise characterization is crucial for understanding subsurface structures.Traditional 2D algorithms,due to their limitations,are insufficient to fully represent three-dimensional wavefields.The classic 3D Radon transform algorithm assumes that the wavefield's propagation characteristics are consistent in all directions,which often does not hold true in complex underground media.To address this issue,we present an improved 3D three-parameter Radon algorithm that considers the wavefield variation with azimuth and provides a more accurate wavefield description.However,introducing new parameters to describe the azimuthal varia-tion also poses computational challenges.The new Radon transform operator involves five variables and cannot be simply decomposed into small matrices for efficient computation;instead,it requires large matrix multiplication and inversion operations,significantly increasing the computational load.To overcome this challenge,we have integrated the curvature and frequency parameters,simplifying all frequency operators to the same,thereby significantly improving computation efficiency.Furthermore,existing transform algorithms neglect the lateral variation of seismic amplitudes,leading to discrepancies between the estimated multiples and those in the data.To enhance the amplitude preservation of the algorithm,we employ orthogonal polynomial fitting to capture the amplitude spatial variation in 3D seismic data.Combining these improvements,we propose a fast,amplitude-preserving,3D three-parameter Radon transform algorithm.This algorithm not only enhances computational efficiency while maintaining the original wavefield characteristics,but also improves the representation of seismic data by increasing amplitude fidelity.We validated the algorithm in multiple attenuation using both synthetic and real seismic data.The results demonstrate that the new algorithm significantly improves both accuracy and computational efficiency,providing an effective tool for analyzing seismic wavefields in complex subsurface structures.展开更多
Hydro-pneumatic near-zero frequency(NZF)vibration isolators have better performance at isolating vibration with low frequencies and heavy loadings when the nonlinear fluidic damping is introduced and the pressurized g...Hydro-pneumatic near-zero frequency(NZF)vibration isolators have better performance at isolating vibration with low frequencies and heavy loadings when the nonlinear fluidic damping is introduced and the pressurized gas pressure is properly adjusted.The nonlinear characteristics of such devices make their corresponding dynamic research involve chaotic dynamics.Chaos may bring negative influence and disorder to the structure and low-frequency working efficiency of isolators,which makes it necessary to clarify and control the threshold ranges for chaos generation in advance.In this work,the chaotic characteristics for a class of hydro-pneumatic NZF vibration isolators under dry friction,harmonic,and environmental noise excitations are analyzed by the analytical and numerical methods.The parameter ranges for the generation of chaos are obtained by the classical and random Melnikov methods.The chaotic characteristics and thresholds of the parameters in the systems with or without noise excitation are discussed and described.The analytical solutions and the influence of noise and harmonic excitation about chaos are tested and further analyzed through many numerical simulations.The results show that chaos in the system can be induced or inhibited with the adjustment of the magnitudes of harmonic excitation and noise intensity.展开更多
In this study, the three-dimensional non-premixed two-phase kerosene/air rotating detonation engines with different isolator configurations and throat area ratios are simulated by the Eulerian-Lagrangian method. The e...In this study, the three-dimensional non-premixed two-phase kerosene/air rotating detonation engines with different isolator configurations and throat area ratios are simulated by the Eulerian-Lagrangian method. The effects of the divergence, straight, and convergence isolators on the rotating detonation wave dynamics and the upstream oblique shock wave propagation mechanism are analyzed. The differences in the rotating detonation wave behaviors between ground and flight operations are clarified.The results indicate that the propagation regimes of the upstream oblique shock wave depend on the isolator configurations and operation conditions. With a divergence isolator, the airflow is accelerated throughout the isolator and divergence section, leading to a maximum Mach number(~1.8) before the normal shock. The total pressure loss reaches the largest, and the detonation pressure drops. The upstream oblique shock wave can be suppressed within the divergence section with the divergence isolator.However, for the straight and convergence isolators, the airflow in the isolator with a larger ψ_(1)(0.3 and0.4) can suffer from the disturbance of the upstream oblique shock wave. The critical incident angle is around 39° at ground operation conditions. The upstream oblique shock wave tends to be suppressed when the engine operates under flight operation conditions. The critical pressure ratio β_(cr0) is found to be able to help in distinguishing the propagation regimes of the upstream oblique shock wave. Slightly below or above the β_(cr0) can obtain different marginal propagation results. The high-speed airflow in the divergence section affects the fuel droplet penetration distance, which deteriorates the reactant mixing and the detonation area. Significant detonation velocity deficits are observed and the maximum velocity deficit reaches 26%. The results indicate the engine channel design should adopt different isolator configurations based on the purpose of total pressure loss or disturbance suppression. This study can provide useful guidance for the channel design of a more complete two-phase rotating detonation engine.展开更多
Optical isolators,the photonic analogs of electronic diodes,are essential for ensuring the unidirectional flow of light in optical systems,thereby mitigating the destabilizing effects of back reflections.Thin-film lit...Optical isolators,the photonic analogs of electronic diodes,are essential for ensuring the unidirectional flow of light in optical systems,thereby mitigating the destabilizing effects of back reflections.Thin-film lithium niobate(TFLN),hailed as“the silicon of photonics,”has emerged as a pivotal material in the realm of chip-scale nonlinear optics,propelling the demand for compact optical isolators.We report a breakthrough in the development of a fully passive,integrated optical isolator on the TFLN platform,leveraging the Kerr effect to achieve an impressive 10.3 dB of isolation with a minimal insertion loss of 1.87 dB.Further theoretical simulations have demonstrated that our design,when applied to a microring resonator with a Q factor of 5×10^(6),can achieve 20 dB of isolation with an input power of merely 8 mW.This advancement underscores the immense potential of lithium niobate-based Kerr-effect isolators in propelling the integration and application of high-performance on-chip lasers,heralding a new era in integrated photonics.展开更多
Periodic isolator is well known for its wave filtering characteristic.While in middle and high frequencies,the internal resonances of the periodic isolator are evident especially when damping is small.This study propo...Periodic isolator is well known for its wave filtering characteristic.While in middle and high frequencies,the internal resonances of the periodic isolator are evident especially when damping is small.This study proposes a novel aperiodic vibration isolation for improving the internal resonances control of the periodic isolator.The mechanism of the internal resonances control by the aperiodic isolator is firstly explained.For comparing the internal resonances suppression effect of the aperiodic isolator with the periodic isolator,a dynamic model combing the rigid machine,the isolator,and the flexible plate is derived through multi subsystem modeling method and transfer matrix method,whose accuracy is verified through the finite element method.The influences of the aperiodicity and damping of the isolator on the vibration isolation performance and internal resonances suppression effect are investigated by numerical analysis.The numerical results demonstrate that vibration attenuation performances of the periodic isolator and aperiodic isolator are greatly over than that of the continuous isolator in middle and high frequencies.The aperiodic isolator opens the stop bandgaps comparing with the periodic isolator where the pass bandgaps are periodically existed.The damping of the isolator has the stop bandgap widening effect on both the periodic isolator and the aperiodic isolator.In addition,a parameter optimization algorithm of the aperiodic isolator is presented for improving the internal resonances control effect.It is shown that the vibration peaks within the target frequency band of the aperiodic isolator are effectively reduced after the optimization.Finally,the experiments of the three different vibration isolation systems are conducted for verifying the analysis work.展开更多
Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving ...Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving QZS suffer from low stiffness regions and significant nonlinear restoring forces with hardening characteristics,often struggling to withstand excitations with high amplitude.This paper presents a novel QZS vibration isolator that utilizes a more compact spring-rod mechanism(SRM)to provide primary negative stiffness.The nonlinearity of SRM is adjustable via altering the raceway of its spring-rod end,along with the compensatory force provided by the cam-roller mechanism so as to avoid complex nonlinear behaviors.The absolute zero stiffness can be achieved by a well-designed raceway curve with a concise mathematical expression.The nonlinear stiffness with softening properties can also be achieved by parameter adjustment.The study begins with the forcedisplacement relationship of the integrated mechanism first,followed by the design theory of the cam profile.The dynamic response and absolute displacement transmissibility of the isolation system are obtained based on the harmonic balance method.The experimental results show that the proposed vibration isolator maintains relatively low-dynamic stiffness even under non-ideal conditions,and exhibits enhanced vibration isolation performance compared to the corresponding linear isolator.展开更多
Bionic X-shaped vibration isolators have been widely employed in aerospace and other industrial fields,but the stiffness properties of classic X-shaped structures limit the vibration isolation ability for low frequenc...Bionic X-shaped vibration isolators have been widely employed in aerospace and other industrial fields,but the stiffness properties of classic X-shaped structures limit the vibration isolation ability for low frequencies.An innovative bionic quasi-zero stiffness(QZS)vibration isolator(BQZSVI),which can broaden the QZS range of a classic X-shaped isolator and can bring it closer to the equilibrium position,is proposed.The BQZSVI consists of an X-shaped structure as the bone fabric of lower limbs and a nonlinear magnetic loop device simulating the leg muscle.Based on static calculation,the stiffness characteristic of the structure is confirmed.The governing equations of motion of the BQZSVI structure are established in the framework of the Lagrange equation,and the harmonic balance method(HBM)is adopted to obtain the transmissibility responses.The results show that the BQZSVI can provide a more accessible and broader range of QZS.In the dynamic manifestation,the introduction of the BQZSVI can reduce the amplitude of a classic X-shaped vibration isolator by 65.7%,and bring down the initial vibration isolation frequency from 7.43 Hz to 2.39 Hz.In addition,a BQZSVI prototype is designed and fabricated,and the exactitude of the theoretical analysis method is proven by means of experiments.展开更多
Standard bacterial suspensions play a crucial role in microbiological diagnosis.Traditional prepar-ation methods,which rely heavily on manual operations,face challenges such as poor reproducibility,low ef-ficiency,and...Standard bacterial suspensions play a crucial role in microbiological diagnosis.Traditional prepar-ation methods,which rely heavily on manual operations,face challenges such as poor reproducibility,low ef-ficiency,and biosafety concerns.In this study,we propose a high-precision automated colony extraction and separation system that combines large-field imaging and artificial intelligence(AI)to facilitate intelligent screening and localization of colonies.Firstly,a large-field imaging system was developed to capture high-resolution images of 90 mm Petri dishes,achieving a physical resolution of 13.2μm and an imaging speed of 13 frames per second.Subsequently,AI technology was employed for the automatic recognition and localiza-tion of colonies,enabling the selection of target colonies with diameters ranging from 1.9 to 2.3 mm.Next,a three-axis motion control platform was designed,accompanied by a path planning algorithm for the efficient extraction of colonies.An electronic pipette was employed for accurate colony collection.Additionally,a bacterial suspension concentration measurement module was developed,incorporating a 650 nm laser diode as the light source,achieving a measurement accuracy of 0.01 McFarland concentration(MCF).Finally,the system’s performance was validated through the preparation of an Esckerichia coli(E.coli)suspension.After 17 hours of cultivation,E.coli was extracted four times,achieving the target concentration set by the system.This work is expected to enable rapid and accurate microbial sample preparation,significantly reducing de-tection cycles and alleviating the workload of healthcare personnel.展开更多
To improve the seismic performance of unrein-forced masonry(URM)buildings in the Himalayan re-gions,including Western China,India,Nepal,and Paki-stan,a low-cost bonded scrap tire rubber isolator(BSTRI)is proposed,and ...To improve the seismic performance of unrein-forced masonry(URM)buildings in the Himalayan re-gions,including Western China,India,Nepal,and Paki-stan,a low-cost bonded scrap tire rubber isolator(BSTRI)is proposed,and a series of vertical compression and horizontal shear tests are conducted.Incremental dynamic analyses are conducted for five types of BSTRI-supported URM buildings subjected to 22 far-field and 28 near-field earthquake ground motions.The resulting fragility curves and probability of damage curves are presented and utilized to evaluate the damage states of these buildings.The results show that in the base-isolated(BI)URM buildings under seismic ground motion at a peak ground acceleration(PGA)of 1.102g,the probability of exceeding the collapse prevention threshold is less than 25%under far-field earthquake ground motions and 31%under near-field earthquake ground motions.Furthermore,the maximum average vulnerability index for the BI-URM buildings,which are designed to withstand rare earthquakes with 9°(PGA=0.632g),is 40.87%for far-field earthquake ground motions and 41.83%for near-field earthquake ground motions.Therefore,the adoption of BSTRIs can significantly reduce the collapse probability of URM buildings.展开更多
Objective This study aims to investigate the joint associations of sarcopenia and social isolation with mortality risk.Methods Using data from the Chinese Longitudinal Healthy Longevity Survey(CLHLS)and the UK Biobank...Objective This study aims to investigate the joint associations of sarcopenia and social isolation with mortality risk.Methods Using data from the Chinese Longitudinal Healthy Longevity Survey(CLHLS)and the UK Biobank,sarcopenia was diagnosed according to European and Asian Working Groups for Sarcopenia criteria.Social isolation was assessed using standardized questionnaires,including questions on solitude,frequency of social activities,contact with others,and marital status(for the CLHLS only).Results During the follow-up period,8,249 deaths occurred in the CLHLS and 26,670 deaths in the UK Biobank groups.While no significant interaction was observed between sarcopenia and social isolation in predicting all-cause mortality in the CLHLS cohort,the association between social isolation and mortality was stronger among individuals with sarcopenia in the UK Biobank(P-interaction=0.03,relative risk due to interaction:0.23,95%confidence interval[CI]:0.06–0.41).Further joint analyses showed that participants with sarcopenia and high levels of social isolation had the highest mortality risk(hazard ration[HR]:1.99;95%CI:[1.74–2.28]in the CLHLS and 1.69[1.55–1.85]in the UK Biobank)compared to those without either condition.Conclusion The combination of social isolation and sarcopenia synergistically increases the risk of mortality in middle-aged and older adults across diverse populations.展开更多
Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling...Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.展开更多
Natural hybridization is known to play a vital role in speciation;however,the mechanisms underlying the early stages of natural hybridization remain unclear.Where two plant species come into contact,two driving forces...Natural hybridization is known to play a vital role in speciation;however,the mechanisms underlying the early stages of natural hybridization remain unclear.Where two plant species come into contact,two driving forces may balance the dynamic consequences of hybridization:fusion by hybridization-mediated gene flow,and separation by reproductive isolation(RI)(Ma et al.,2010a,b;Chang et al.,2022).展开更多
This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-fiel...This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-field station and roof frame,during a Mw 5.5 magnitude earthquake in Pingyuan,Shandong,in 2023.The H/V spectral ratio method was used to evaluate the structural dynamic response characteristics of the building and analyze the regulatory effect of the base-isolation layer on seismic waves.The results indicate that during the earthquake,the peak frequency of the free-field and the measurement points below the base-isolation layer was stable at 0.17 Hz,whereas the main frequency of the measurement points above the base-isolation layer increased to 0.75–1.18 Hz,which is 4–6 times greater than that of the points below.The amplitude was suppressed by more than 70%,confirming that the base isolation layer effectively isolated the low-frequency energy from the ground and increased the response frequency of the building.When the building was excited by an earthquake,a three-tier frequency gradient was formed throughout the building:“base-isolation layer(0.17 Hz)-main body(1.18 Hz)-roof frame(3.83 Hz)”,which can effectively avoid resonance of the entire building.In addition,the composite base-isolation device changed the dynamic characteristics of the structure.The resonance period was extended from 0.74 s(theoretical value without base isolation)to 5.9 s(calculated value),and the resonance frequency was reduced from 1.35 to 0.17 Hz.This finding indicates that the base-isolation layer can enhance seismic performance by increasing flexibility and damping.展开更多
The traditional payload attaching fitting (PAF) does not provide any vibration isolation, because of its large stiffness. Whole-spacecraft vibration isolation is a direct and effective approach to assure the successfu...The traditional payload attaching fitting (PAF) does not provide any vibration isolation, because of its large stiffness. Whole-spacecraft vibration isolation is a direct and effective approach to assure the successful launching and orbit insertion of a spacecraft. In view of the problems of stiffness and vibration isolation design, for which the designers care most, the study of whole-spacecraft vibration isolator (WSVI) consists of two parts. In the first part, the stiffness feature of the WSVI is studied...展开更多
Based on analysis of the work conditions and structural characteristics of the exterior pipeline of the aero-engine, a kind of cantilever-structure wire-rope isolator fitted to the exterior pipeline of the aero-engine...Based on analysis of the work conditions and structural characteristics of the exterior pipeline of the aero-engine, a kind of cantilever-structure wire-rope isolator fitted to the exterior pipeline of the aero-engine is designed for supporting and damping purposes. By static experiments, the static hysteresis loop, the relationship of stiffness and amplitude, and the relationship between the energy dissipation coefficient and the amplitude are obtained. Analyses show that the wire-rope isolator presents obvious hysteresis characteristics, and the characteristics of the isolator, such as stiffness and damping, behave obviously nonlinearly when the amplitude value of deformation changes. At the same time, by changing the structure parameters of the wire-rope, the wirerope isolators can be made with different functions to satisfy different work conditions. The research results have important reference values for the application of the wire-rope isolator on the exterior pipeline of an aeroengine.展开更多
To analyze the response of the wall pressure fluctuation in an isolator when the shock train is subjected to a periodic motion at a low frequency,the isolator experiment is conducted in a blow-down supersonic wind tun...To analyze the response of the wall pressure fluctuation in an isolator when the shock train is subjected to a periodic motion at a low frequency,the isolator experiment is conducted in a blow-down supersonic wind tunnel at free stream Mach number of 1.98 under asymmetric incoming flow.Experimental results show that：The isolator effectively isolates the periodic back pressure fluctuation from affecting upstream undisturbed flow;The wall pressure fluctuations are due to the propagation of wave fronts with the second acoustic mode,but they are subjected to an oscillating shock train in the most part of the shock oscillation region;The attenuation of wall pressure fluctuations on the lower wall with thick boundary layer accords with the exponential law,but it fluctuates on the upper wall with thin boundary layer in the shock oscillation region.展开更多
基金Project supported by the National Key R&D Program of China(No.2023YFE0125900)。
文摘A novel vibration isolation system designed for superior performance in low-frequency environments is proposed in this work.The isolator is based on a unique hexagonal arrangement of linear springs,allowing for an adjustable geometric configuration via the initial inclination angle.Based on the principle of Lagrangian mechanics,the equation of motion governing the structural dynamics is rigorously derived.The system is modeled as a strongly nonlinear single-degree-of-freedom dynamical system,loaded with a normalized payload and subject to harmonic base excitation.To analyze the steady-state response,the harmonic balance method is employed,providing accurate predictions of the payload's vibration amplitude and displacement transmissibility as functions of both the base excitation amplitude and frequency.The analysis reveals a direct relationship between the isolator's geometric and stiffness parameters and its load-bearing capacity,leading to the identification of three distinct operational regimes.Depending on the unloaded initial inclination angle,the equivalent stiffness ratio,and the payload design configuration,the system can exhibit one of three vibration isolation modes:(i)the quasizero stiffness(QZS)isolation mode,(ii)the zero linear stiffness with controllable nonlinear stiffness,and(iii)the full-band perfect zero stiffness.The vibration isolation performance of the proposed structure is thoroughly discussed for all three oscillation modes in terms of frequency response curves,displacement transmissibility,and time-domain responses.The key novel finding is that this structure can operate as a full-band,high-performance vibration isolator when the initial inclination angle is designed to be a right angle,enabling full isolation of the maximum possible payload.Moreover,the analytical results and numerical simulations demonstrate that the isolator's displacement transmissibility T with the unit dB tends to-∞as the air-damping coefficient approaches zero,enabling ideal vibration isolation across the entire excitation frequency range.These analytical insights are validated through comprehensive numerical simulations,which show excellent agreement with the theoretical predictions.
文摘The failure of liquid storage tanks,one of the most critical infrastructure systems widely used,during severe earthquakes can have direct or indirect impacts on public safety.The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of appropriate seismic design.Hence,seismic isolation,specifically base isolation,has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their vibration period.One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system(FPS)isolator.However,due to its fixed period or frequency,it may be susceptible to resonance effects during long-period earthquakes.This research explores an alternative solution by investigating the variable-curvature friction pendulum isolator(VFPI).This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations.The study proposes optimizing this VFPI,which features a polynomial function termed the Polynomial Friction Pendulum Isolator(PFPI),by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure,thereby improving the dynamic performance of the elevated storage tank.The research utilizes two wellestablished metaheuristic algorithms for optimization.It evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records.Results,particularly under long-period ground motions,indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized PFPI.This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.
基金supported by the National Key Research and Development Program of China(Nos.2023YFB4603900,2023YFB4603901)the National Natural Science Foundation of China(No.52275255)。
文摘Devices on aircraft are subjected to complex environmental excitations that pose risks to their operational safety.Passive vibration isolation techniques are extensively employed due to their advantage of not requiring additional energy sources.This paper introduces a novel metallic vibration isolator based on zigzag structures.The proposed isolator features a compact design and can be manufactured using additive manufacturing techniques,allowing for the integration of structural and functional elements.Firstly,the vibration response of the single-degree-of-freedom(SDOF)system is analyzed.To achieve effective vibration reduction,it is crucial for the isolator's stiffness to be sufficiently low.Secondly,to obtain a structure with high compliance,the traversal algorithm and the finite element method(FEM)are applied.The results confirm that the zigzag structure is a reliable high-compliance configuration.Thirdly,the parametric geometric model of the zigzag structure is developed and its stiffness is calculated.Quasi-static compression experiments validate the accuracy of the calculations.Finally,a specific engineering example is considered,where a zigzag vibration isolator is designed and fabricated.Vibration experiments demonstrate that the zigzag isolator effectively reduces both the stiffness and the fundamental frequency of the vibration system,achieving a vibration isolation efficiency exceeding 60%.
基金supported in part by National Natural Science Foundation of China(NSFC)under grant 42274139in part by the R&D Department of China National Petroleum Corporation(Investigations on fundamental experiments and advanced theoretical methods in geophysical prospecting applications,2022DQ0604-03).
文摘Seismic wavefields propagate through three-dimensional(3D)space,and their precise characterization is crucial for understanding subsurface structures.Traditional 2D algorithms,due to their limitations,are insufficient to fully represent three-dimensional wavefields.The classic 3D Radon transform algorithm assumes that the wavefield's propagation characteristics are consistent in all directions,which often does not hold true in complex underground media.To address this issue,we present an improved 3D three-parameter Radon algorithm that considers the wavefield variation with azimuth and provides a more accurate wavefield description.However,introducing new parameters to describe the azimuthal varia-tion also poses computational challenges.The new Radon transform operator involves five variables and cannot be simply decomposed into small matrices for efficient computation;instead,it requires large matrix multiplication and inversion operations,significantly increasing the computational load.To overcome this challenge,we have integrated the curvature and frequency parameters,simplifying all frequency operators to the same,thereby significantly improving computation efficiency.Furthermore,existing transform algorithms neglect the lateral variation of seismic amplitudes,leading to discrepancies between the estimated multiples and those in the data.To enhance the amplitude preservation of the algorithm,we employ orthogonal polynomial fitting to capture the amplitude spatial variation in 3D seismic data.Combining these improvements,we propose a fast,amplitude-preserving,3D three-parameter Radon transform algorithm.This algorithm not only enhances computational efficiency while maintaining the original wavefield characteristics,but also improves the representation of seismic data by increasing amplitude fidelity.We validated the algorithm in multiple attenuation using both synthetic and real seismic data.The results demonstrate that the new algorithm significantly improves both accuracy and computational efficiency,providing an effective tool for analyzing seismic wavefields in complex subsurface structures.
基金Project supported by the National Natural Science Foundation of China(Nos.12172340 and12411530068)the Shenzhen Science and Technology Program(No.JCYJ20240813114012016)+2 种基金the High-Level Talent Introduction Plan of Guangzhou Citythe Fundamental Research Funds for the Central Universities-China University of Geosciences(Wuhan)(No.G1323524005)the Young Top-Notch Talent Cultivation Program of Hubei Province。
文摘Hydro-pneumatic near-zero frequency(NZF)vibration isolators have better performance at isolating vibration with low frequencies and heavy loadings when the nonlinear fluidic damping is introduced and the pressurized gas pressure is properly adjusted.The nonlinear characteristics of such devices make their corresponding dynamic research involve chaotic dynamics.Chaos may bring negative influence and disorder to the structure and low-frequency working efficiency of isolators,which makes it necessary to clarify and control the threshold ranges for chaos generation in advance.In this work,the chaotic characteristics for a class of hydro-pneumatic NZF vibration isolators under dry friction,harmonic,and environmental noise excitations are analyzed by the analytical and numerical methods.The parameter ranges for the generation of chaos are obtained by the classical and random Melnikov methods.The chaotic characteristics and thresholds of the parameters in the systems with or without noise excitation are discussed and described.The analytical solutions and the influence of noise and harmonic excitation about chaos are tested and further analyzed through many numerical simulations.The results show that chaos in the system can be induced or inhibited with the adjustment of the magnitudes of harmonic excitation and noise intensity.
基金supported by the National Natural Science Foundation of China (Grant No. 12202204)the Natural Science Foundation of Jiangsu Province (Grant No. BK20220953)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Science and Technology Association's Young Talent Nurturing Program of Jiangsu Province (Grant No. JSTJ-2024-004)
文摘In this study, the three-dimensional non-premixed two-phase kerosene/air rotating detonation engines with different isolator configurations and throat area ratios are simulated by the Eulerian-Lagrangian method. The effects of the divergence, straight, and convergence isolators on the rotating detonation wave dynamics and the upstream oblique shock wave propagation mechanism are analyzed. The differences in the rotating detonation wave behaviors between ground and flight operations are clarified.The results indicate that the propagation regimes of the upstream oblique shock wave depend on the isolator configurations and operation conditions. With a divergence isolator, the airflow is accelerated throughout the isolator and divergence section, leading to a maximum Mach number(~1.8) before the normal shock. The total pressure loss reaches the largest, and the detonation pressure drops. The upstream oblique shock wave can be suppressed within the divergence section with the divergence isolator.However, for the straight and convergence isolators, the airflow in the isolator with a larger ψ_(1)(0.3 and0.4) can suffer from the disturbance of the upstream oblique shock wave. The critical incident angle is around 39° at ground operation conditions. The upstream oblique shock wave tends to be suppressed when the engine operates under flight operation conditions. The critical pressure ratio β_(cr0) is found to be able to help in distinguishing the propagation regimes of the upstream oblique shock wave. Slightly below or above the β_(cr0) can obtain different marginal propagation results. The high-speed airflow in the divergence section affects the fuel droplet penetration distance, which deteriorates the reactant mixing and the detonation area. Significant detonation velocity deficits are observed and the maximum velocity deficit reaches 26%. The results indicate the engine channel design should adopt different isolator configurations based on the purpose of total pressure loss or disturbance suppression. This study can provide useful guidance for the channel design of a more complete two-phase rotating detonation engine.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2022YFF0712800 and 2019YFA0308700)。
文摘Optical isolators,the photonic analogs of electronic diodes,are essential for ensuring the unidirectional flow of light in optical systems,thereby mitigating the destabilizing effects of back reflections.Thin-film lithium niobate(TFLN),hailed as“the silicon of photonics,”has emerged as a pivotal material in the realm of chip-scale nonlinear optics,propelling the demand for compact optical isolators.We report a breakthrough in the development of a fully passive,integrated optical isolator on the TFLN platform,leveraging the Kerr effect to achieve an impressive 10.3 dB of isolation with a minimal insertion loss of 1.87 dB.Further theoretical simulations have demonstrated that our design,when applied to a microring resonator with a Q factor of 5×10^(6),can achieve 20 dB of isolation with an input power of merely 8 mW.This advancement underscores the immense potential of lithium niobate-based Kerr-effect isolators in propelling the integration and application of high-performance on-chip lasers,heralding a new era in integrated photonics.
基金supported by the National Key Research and Development Plan of China (Grant No.2023YFB3406302)Guangdong Basic and Applied Basic Research Foundation (Grant No.2024A1515011126)the Key Research and Development Plan of Shanxi (Grant No.2024GH-ZDXM-29)。
文摘Periodic isolator is well known for its wave filtering characteristic.While in middle and high frequencies,the internal resonances of the periodic isolator are evident especially when damping is small.This study proposes a novel aperiodic vibration isolation for improving the internal resonances control of the periodic isolator.The mechanism of the internal resonances control by the aperiodic isolator is firstly explained.For comparing the internal resonances suppression effect of the aperiodic isolator with the periodic isolator,a dynamic model combing the rigid machine,the isolator,and the flexible plate is derived through multi subsystem modeling method and transfer matrix method,whose accuracy is verified through the finite element method.The influences of the aperiodicity and damping of the isolator on the vibration isolation performance and internal resonances suppression effect are investigated by numerical analysis.The numerical results demonstrate that vibration attenuation performances of the periodic isolator and aperiodic isolator are greatly over than that of the continuous isolator in middle and high frequencies.The aperiodic isolator opens the stop bandgaps comparing with the periodic isolator where the pass bandgaps are periodically existed.The damping of the isolator has the stop bandgap widening effect on both the periodic isolator and the aperiodic isolator.In addition,a parameter optimization algorithm of the aperiodic isolator is presented for improving the internal resonances control effect.It is shown that the vibration peaks within the target frequency band of the aperiodic isolator are effectively reduced after the optimization.Finally,the experiments of the three different vibration isolation systems are conducted for verifying the analysis work.
基金supported by the National Natural Science Foundation of China(Grant No.11732006)the“Qinglan Project”of Jiangsu Higher Education Institutions.
文摘Quasi-zero stiffness(QZS)isolators have received considerable attention over the past years due to their outstanding vibration isolation performance in low-frequency bands.However,traditional mechanisms for achieving QZS suffer from low stiffness regions and significant nonlinear restoring forces with hardening characteristics,often struggling to withstand excitations with high amplitude.This paper presents a novel QZS vibration isolator that utilizes a more compact spring-rod mechanism(SRM)to provide primary negative stiffness.The nonlinearity of SRM is adjustable via altering the raceway of its spring-rod end,along with the compensatory force provided by the cam-roller mechanism so as to avoid complex nonlinear behaviors.The absolute zero stiffness can be achieved by a well-designed raceway curve with a concise mathematical expression.The nonlinear stiffness with softening properties can also be achieved by parameter adjustment.The study begins with the forcedisplacement relationship of the integrated mechanism first,followed by the design theory of the cam profile.The dynamic response and absolute displacement transmissibility of the isolation system are obtained based on the harmonic balance method.The experimental results show that the proposed vibration isolator maintains relatively low-dynamic stiffness even under non-ideal conditions,and exhibits enhanced vibration isolation performance compared to the corresponding linear isolator.
基金Project supported by the National Natural Science Foundation of China(No.U23A2066)the Liaoning Revitalization Talents Program of China(No.XLYC2202032)。
文摘Bionic X-shaped vibration isolators have been widely employed in aerospace and other industrial fields,but the stiffness properties of classic X-shaped structures limit the vibration isolation ability for low frequencies.An innovative bionic quasi-zero stiffness(QZS)vibration isolator(BQZSVI),which can broaden the QZS range of a classic X-shaped isolator and can bring it closer to the equilibrium position,is proposed.The BQZSVI consists of an X-shaped structure as the bone fabric of lower limbs and a nonlinear magnetic loop device simulating the leg muscle.Based on static calculation,the stiffness characteristic of the structure is confirmed.The governing equations of motion of the BQZSVI structure are established in the framework of the Lagrange equation,and the harmonic balance method(HBM)is adopted to obtain the transmissibility responses.The results show that the BQZSVI can provide a more accessible and broader range of QZS.In the dynamic manifestation,the introduction of the BQZSVI can reduce the amplitude of a classic X-shaped vibration isolator by 65.7%,and bring down the initial vibration isolation frequency from 7.43 Hz to 2.39 Hz.In addition,a BQZSVI prototype is designed and fabricated,and the exactitude of the theoretical analysis method is proven by means of experiments.
文摘Standard bacterial suspensions play a crucial role in microbiological diagnosis.Traditional prepar-ation methods,which rely heavily on manual operations,face challenges such as poor reproducibility,low ef-ficiency,and biosafety concerns.In this study,we propose a high-precision automated colony extraction and separation system that combines large-field imaging and artificial intelligence(AI)to facilitate intelligent screening and localization of colonies.Firstly,a large-field imaging system was developed to capture high-resolution images of 90 mm Petri dishes,achieving a physical resolution of 13.2μm and an imaging speed of 13 frames per second.Subsequently,AI technology was employed for the automatic recognition and localiza-tion of colonies,enabling the selection of target colonies with diameters ranging from 1.9 to 2.3 mm.Next,a three-axis motion control platform was designed,accompanied by a path planning algorithm for the efficient extraction of colonies.An electronic pipette was employed for accurate colony collection.Additionally,a bacterial suspension concentration measurement module was developed,incorporating a 650 nm laser diode as the light source,achieving a measurement accuracy of 0.01 McFarland concentration(MCF).Finally,the system’s performance was validated through the preparation of an Esckerichia coli(E.coli)suspension.After 17 hours of cultivation,E.coli was extracted four times,achieving the target concentration set by the system.This work is expected to enable rapid and accurate microbial sample preparation,significantly reducing de-tection cycles and alleviating the workload of healthcare personnel.
基金The National Natural Science Foundation of China(No.52208195)the Independent Subject of State Key Laboratory of Disaster Reduction in Civil Engineering of Tongji University(No.SLDRCE19-A-10).
文摘To improve the seismic performance of unrein-forced masonry(URM)buildings in the Himalayan re-gions,including Western China,India,Nepal,and Paki-stan,a low-cost bonded scrap tire rubber isolator(BSTRI)is proposed,and a series of vertical compression and horizontal shear tests are conducted.Incremental dynamic analyses are conducted for five types of BSTRI-supported URM buildings subjected to 22 far-field and 28 near-field earthquake ground motions.The resulting fragility curves and probability of damage curves are presented and utilized to evaluate the damage states of these buildings.The results show that in the base-isolated(BI)URM buildings under seismic ground motion at a peak ground acceleration(PGA)of 1.102g,the probability of exceeding the collapse prevention threshold is less than 25%under far-field earthquake ground motions and 31%under near-field earthquake ground motions.Furthermore,the maximum average vulnerability index for the BI-URM buildings,which are designed to withstand rare earthquakes with 9°(PGA=0.632g),is 40.87%for far-field earthquake ground motions and 41.83%for near-field earthquake ground motions.Therefore,the adoption of BSTRIs can significantly reduce the collapse probability of URM buildings.
基金supported by grants from the National Key Research and Development Program of China(No.2023YFC3606300,No.2022YFC3600300)the National Natural Science Foundation of China(No.82325043)the National Key Research and Development Program of Hubei Province(2022BCA036)。
文摘Objective This study aims to investigate the joint associations of sarcopenia and social isolation with mortality risk.Methods Using data from the Chinese Longitudinal Healthy Longevity Survey(CLHLS)and the UK Biobank,sarcopenia was diagnosed according to European and Asian Working Groups for Sarcopenia criteria.Social isolation was assessed using standardized questionnaires,including questions on solitude,frequency of social activities,contact with others,and marital status(for the CLHLS only).Results During the follow-up period,8,249 deaths occurred in the CLHLS and 26,670 deaths in the UK Biobank groups.While no significant interaction was observed between sarcopenia and social isolation in predicting all-cause mortality in the CLHLS cohort,the association between social isolation and mortality was stronger among individuals with sarcopenia in the UK Biobank(P-interaction=0.03,relative risk due to interaction:0.23,95%confidence interval[CI]:0.06–0.41).Further joint analyses showed that participants with sarcopenia and high levels of social isolation had the highest mortality risk(hazard ration[HR]:1.99;95%CI:[1.74–2.28]in the CLHLS and 1.69[1.55–1.85]in the UK Biobank)compared to those without either condition.Conclusion The combination of social isolation and sarcopenia synergistically increases the risk of mortality in middle-aged and older adults across diverse populations.
文摘Isolation technology can reduce the type of structural damage that earthquakes cause.A new type of composite sliding-rolling friction composite seismic isolation bearing(SRF)with composite sliding friction and rolling friction is proposed.SRF is capable of realizing a parallel arrangement of sliding friction and rolling friction,and the coefficient of dynamic friction shows variability.The proposed static tests on composite bearings were conducted to investigate the effects of the number of shims,loading speed and vertical pressure on the dynamic friction factor.Test results show that the coefficient of dynamic friction first generally decreases and then increases with an increase in sliding speed,prior to again decreasing with an increase in vertical pressure.The dynamic friction factor increases and then decreases with an increase in the number of shims for a four-roll ball.It decreases and then increases with an increase in the number of shims for a five-roll ball.Based on finite element analysis,modeling and analyzing the effects of the coefficient of friction,the number of balls and the number of shims on the hysteresis performance of the support and derive its skeleton curve.The SRF hysteretic performance,dynamic friction factor and the number of rolling balls and shims show significant correlation.
基金supported by the National Natural Science Foundation of China(U23A20160,32360336)Guizhou Provincial Key Technology R&D Program(Qian KeHe ZhiCheng[2023]YiBan035).
文摘Natural hybridization is known to play a vital role in speciation;however,the mechanisms underlying the early stages of natural hybridization remain unclear.Where two plant species come into contact,two driving forces may balance the dynamic consequences of hybridization:fusion by hybridization-mediated gene flow,and separation by reproductive isolation(RI)(Ma et al.,2010a,b;Chang et al.,2022).
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(Grant No.2025ZD005100)by Beijing Geolight Technology Co.,Ltd.under the project“The Impact of Strong Ground Motion on Buildings”(YF-202520).
文摘This study employed tri-component continuous monitoring data from 10 measurement points on both sides of a base isolation layer in the basement of a large-span high-rise building in Beijing,as well as from a free-field station and roof frame,during a Mw 5.5 magnitude earthquake in Pingyuan,Shandong,in 2023.The H/V spectral ratio method was used to evaluate the structural dynamic response characteristics of the building and analyze the regulatory effect of the base-isolation layer on seismic waves.The results indicate that during the earthquake,the peak frequency of the free-field and the measurement points below the base-isolation layer was stable at 0.17 Hz,whereas the main frequency of the measurement points above the base-isolation layer increased to 0.75–1.18 Hz,which is 4–6 times greater than that of the points below.The amplitude was suppressed by more than 70%,confirming that the base isolation layer effectively isolated the low-frequency energy from the ground and increased the response frequency of the building.When the building was excited by an earthquake,a three-tier frequency gradient was formed throughout the building:“base-isolation layer(0.17 Hz)-main body(1.18 Hz)-roof frame(3.83 Hz)”,which can effectively avoid resonance of the entire building.In addition,the composite base-isolation device changed the dynamic characteristics of the structure.The resonance period was extended from 0.74 s(theoretical value without base isolation)to 5.9 s(calculated value),and the resonance frequency was reduced from 1.35 to 0.17 Hz.This finding indicates that the base-isolation layer can enhance seismic performance by increasing flexibility and damping.
基金Commission of Science Technology and Industry for National Defense Project (C4120062301)
文摘The traditional payload attaching fitting (PAF) does not provide any vibration isolation, because of its large stiffness. Whole-spacecraft vibration isolation is a direct and effective approach to assure the successful launching and orbit insertion of a spacecraft. In view of the problems of stiffness and vibration isolation design, for which the designers care most, the study of whole-spacecraft vibration isolator (WSVI) consists of two parts. In the first part, the stiffness feature of the WSVI is studied...
基金The National Natural Science Foundation of China(No50275030)
文摘Based on analysis of the work conditions and structural characteristics of the exterior pipeline of the aero-engine, a kind of cantilever-structure wire-rope isolator fitted to the exterior pipeline of the aero-engine is designed for supporting and damping purposes. By static experiments, the static hysteresis loop, the relationship of stiffness and amplitude, and the relationship between the energy dissipation coefficient and the amplitude are obtained. Analyses show that the wire-rope isolator presents obvious hysteresis characteristics, and the characteristics of the isolator, such as stiffness and damping, behave obviously nonlinearly when the amplitude value of deformation changes. At the same time, by changing the structure parameters of the wire-rope, the wirerope isolators can be made with different functions to satisfy different work conditions. The research results have important reference values for the application of the wire-rope isolator on the exterior pipeline of an aeroengine.
基金Supported by the National Natural Science Foundation of China(10572059)~~
文摘To analyze the response of the wall pressure fluctuation in an isolator when the shock train is subjected to a periodic motion at a low frequency,the isolator experiment is conducted in a blow-down supersonic wind tunnel at free stream Mach number of 1.98 under asymmetric incoming flow.Experimental results show that：The isolator effectively isolates the periodic back pressure fluctuation from affecting upstream undisturbed flow;The wall pressure fluctuations are due to the propagation of wave fronts with the second acoustic mode,but they are subjected to an oscillating shock train in the most part of the shock oscillation region;The attenuation of wall pressure fluctuations on the lower wall with thick boundary layer accords with the exponential law,but it fluctuates on the upper wall with thin boundary layer in the shock oscillation region.
