The paper proposes an analytical approach to investigate the synchronization of the two coupled exciters in a vibrating system of spatial motion. Introducing the distur- bance parameters for average angular velocity o...The paper proposes an analytical approach to investigate the synchronization of the two coupled exciters in a vibrating system of spatial motion. Introducing the distur- bance parameters for average angular velocity of two excit- ers, we deduce the non-dimensional coupling equations of angular velocities of two exciters, in which the inertia cou- pling matrix is symmetric and the stiffness coupling matrix is antisymmetric in a non-resonant vibrating system. The analysis of the coupling dynamic characteristic shows that the coupled cosine effect of the phase angles will cause the torque acting on two motors to limit the increase of phase difference between two exciters as well as sustain its sym- metry of two exciters during the running process. It physi- cally explains the peculiarity of self-synchronization of two exciters. The cosine effect of phase angles of the vibrations excited by each exciter will decrease its moment of inertia. The residual moment of inertia of each exciter represents its relative moment of inertia. The stability condition of synchro- nization of two exciters is that the relative non-dimensional moments of inertia of two exciters are all greater than zero and four times their product is greater than the square of their coefficient of coupled cosine effect of phase angles, which is equivalent to that the inertia coupling matrix is positive definite and all its elements are positive. The numeric results show that the structure of the vibrating system can ensure the stability condition of synchronous operation.展开更多
We derive the non-dimensional coupling equation of two exciters, including inertia coupling, stiffness coupling and load coupling. The concept of general dynamic symmetry is proposed to physically explain the synehron...We derive the non-dimensional coupling equation of two exciters, including inertia coupling, stiffness coupling and load coupling. The concept of general dynamic symmetry is proposed to physically explain the synehronisation of the two exciters, which stems from the load coupling that produces the torque of general dynamic symmetry to force the phase difference between the two exciters close to the angle of general dynamic symmetry. The condition of implementing synchronisation is that the torque of general dynamic symmetry is greater than the asymmetric torque of the two motors. A general Lyapunov function is constructed to derive the stability condition of synchronisation that the non-dimensional inertia coupling matrix is positive definite and all its elements are positive. Numeric results show that the structure of the vibrating system can guarantee the stability of synchronisation of the two exciters, and that the greater the distances between the installation positions of the two exciters and the mass centre of the vibrating system are, the stronger the ability of general dynamic symmetry is.展开更多
In this paper, the synchronization problem of three homodromy coupled exciters in a non-resonant vibrating system of plane motion is studied. By introducing the average method of modified small parameters, we deduced ...In this paper, the synchronization problem of three homodromy coupled exciters in a non-resonant vibrating system of plane motion is studied. By introducing the average method of modified small parameters, we deduced dimensionless coupling equation of three exciters, which converted the problem of synchronization into that of the existence and stability of zero solutions for the average differential equations of the small parameters. Based on the dimensionless coupling torques and characteristics of the cor- responding limited functions, the synchronization criterion for three exciters was derived as the absolute value of dimensionless residual torque difference between arbitrary two motors being less than the maximum of their dimensionless coupling torques. The stability criterion of its synchronous state lies in the double-condition that the inertia coupling matrix is positive definite and all its elements are positive as well. The synchronization determinants are the coefficients of synchronization ability, also called as the general dynamical symmetry coefficients. The double-equilibrium state of the vibrating system is manifested by numeric method, and the numeric and simulation results derived thereof indicate the indispensable and crucial role the structural parameters of the vibrating system play in the stability criterion of synchronous operation. Besides, by adjusting its structural parameters, the elliptical motion of the vibrating system successfully met the requirements in engineering applications.展开更多
For the electro-hydraulic servo vibrating system（ESVS） with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control（ILC）, is proposed on the basis of tradition...For the electro-hydraulic servo vibrating system（ESVS） with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control（ILC）, is proposed on the basis of traditional PID control. By using memory ability of computer, the method keeps last time＇s tracking error of the system and then applies the error information to the next time＇s control process. At the same time, a forgetting factor and a D-type learning law of feedforward fuzzy-inferring referenced displacement error under the optimal objective are employed to enhance the systemic robustness and tracking accuracy. The results of simulation and test reveal that the algorithm has a trait of high repeating precision, and could restrain the influence of nonlinear factors like leaking, external disturbance, aerated oil, etc. Compared with traditional PID control, it could better meet the requirement of nonlinear electro -hydraulic servo vibrating system.展开更多
The theory on synchronization of two exciters is more widely used in engineering, while that of more than two exciters is less considered. So it is of great significant to investigate synchronization of three exciters...The theory on synchronization of two exciters is more widely used in engineering, while that of more than two exciters is less considered. So it is of great significant to investigate synchronization of three exciters. Firstly by introducing the average method of modified small parameters, the dimensionless coupling equations(DCE) of three exciters are derived, which convert the problem of synchronization into that of existence and stability of zero solutions for the DCE and lead to the construction on criterions of synchronization and stability in the simplified form for three exciters. Then the synchronization criterion is discussed numerically, as well as the abilities of synchronization and stability, some results thereof indicate that the synchronization ability increases with the increase of the coupling moment among three exciters, but decreases with that of their phase differences. Finally, an experiment on synchronization with three exciters is carried out. Through the comparison and analysis of experimental data on phase differences among three exciters, responses of system, and phases of three exciters recorded by high-speed camera, the parameters of system satisfying the above two criterions can ensure the synchronous and stable operation of three exciters. As a result, the average method of modified small parameters can be used as a theoretical apparatus studying reasonably the synchronization mechanism of three exciters, it is also proved to be useful and feasible by numeric and experiment. The present research lays the foundation and guidance for the establishment of synchronization theory system with multi-exciter and engineering design.展开更多
In this paper a three degrees of freedom autoparametric system with limited power supply is investigated numerically. The system consists of the body, which is hung on a spring and a damper, and two pendulums connecte...In this paper a three degrees of freedom autoparametric system with limited power supply is investigated numerically. The system consists of the body, which is hung on a spring and a damper, and two pendulums connected by shape memory alloy （SMA） spring. Shape memory alloys have ability to change their material properties with temperature. A polynomial constitutive model is assumed to describe the behavior of the SMA spring. The non-ideal source of power adds one degree of freedom, so the system has four degrees of freedom. The equations of motion have been solved numerically and pseudoelastic effects associated with the martensitic phase transformation are studied. It is shown that in this type system one mode of vibrations might excite or damp another mode, and that except different kinds of periodic vibrations there may also appear chaotic vibrations. For the identification of the responses of the system＇s various techniques, including chaos techniques such as bifurcation diagrams and time histories, power spectral densities, Poincare maps and exponents of Lyapunov may be used.展开更多
Bifurcation problems of a spring-mass system vibrating against an infinite large plane are studied in this paper. It is shown that there exist phenomena of codimension two bifurcations when the ratios of frequencies a...Bifurcation problems of a spring-mass system vibrating against an infinite large plane are studied in this paper. It is shown that there exist phenomena of codimension two bifurcations when the ratios of frequencies are in the neigborhood of the same special values and the coefficient of restitution approach unity. By theory of normal forms, we reduce Poincare maps to normal forms.and find flip bifurcations, Hopf bifurcations of fixed points and that of period two points The theoretical solutions are verified by numerical computations.展开更多
Maintaining the integrity and longevity of structures is essential in many industries,such as aerospace,nuclear,and petroleum.To achieve the cost-effectiveness of large-scale systems in petroleum drilling,a strong emp...Maintaining the integrity and longevity of structures is essential in many industries,such as aerospace,nuclear,and petroleum.To achieve the cost-effectiveness of large-scale systems in petroleum drilling,a strong emphasis on structural durability and monitoring is required.This study focuses on the mechanical vibrations that occur in rotary drilling systems,which have a substantial impact on the structural integrity of drilling equipment.The study specifically investigates axial,torsional,and lateral vibrations,which might lead to negative consequences such as bit-bounce,chaotic whirling,and high-frequency stick-slip.These events not only hinder the efficiency of drilling but also lead to exhaustion and harm to the system’s components since they are difficult to be detected and controlled in real time.The study investigates the dynamic interactions of these vibrations,specifically in their high-frequency modes,usingfield data obtained from measurement while drilling.Thefindings have demonstrated the effect of strong coupling between the high-frequency modes of these vibrations on drilling sys-tem performance.The obtained results highlight the importance of considering the interconnected impacts of these vibrations when designing and implementing robust control systems.Therefore,integrating these compo-nents can increase the durability of drill bits and drill strings,as well as improve the ability to monitor and detect damage.Moreover,by exploiting thesefindings,the assessment of structural resilience in rotary drilling systems can be enhanced.Furthermore,the study demonstrates the capacity of structural health monitoring to improve the quality,dependability,and efficiency of rotary drilling systems in the petroleum industry.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
Two-dimensional phononic crystal(PnC)slabs have shown advantages in enhancing the quality factors Q of piezoelectric laterally vibrating resonators(LVRs)through topology optimization.However,the narrow geometries of m...Two-dimensional phononic crystal(PnC)slabs have shown advantages in enhancing the quality factors Q of piezoelectric laterally vibrating resonators(LVRs)through topology optimization.However,the narrow geometries of most topology-optimized silicon–air 2D PnC slabs face significant fabrication challenges owing to restricted etching precision,and the anisotropic nature of silicon is frequently overlooked.To address these issues,this study employs the finite element method with appropriate discretization numbers and the genetic algorithm to optimize the structures and geometries of 2D silicon–air PnC slabs.The optimized square-lattice PnC slabs,featuring a rounded-cross structure oriented along the`110e directions of silicon,achieve an impressive relative bandgap(RBG)width of 82.2%for in-plane modes.When further tilted by 15° from the (100) directions within the(001)plane,the optimal RBG width is expanded to 91.4%.We fabricate and characterize thin-film piezoelectric-on-silicon LVRs,with or without optimized 2D PnC slabs.The presence of PnC slabs around anchors increases the series and parallel quality factors Q_(s) and Q_(p) from 2240 to 7118 and from 2237 to 7501,respectively,with the PnC slabs oriented along the`110e directions of silicon.展开更多
The ballistic impact identification method for the helicopter Tail Drive Shaft System(TDSS)isn't yet comprehensive,which affects helicopter flight safety.This paper proposes a ballistic impact identification metho...The ballistic impact identification method for the helicopter Tail Drive Shaft System(TDSS)isn't yet comprehensive,which affects helicopter flight safety.This paper proposes a ballistic impact identification method for the TDSS based on vibration response analysis.Based on the Johnson-Cook constitutive model and failure criteria,the ballistic impact finite element simulation model is established,which is verified by the ballistic impact experiment of the Tail Drive Shaft(TDS).Considering the ballistic impact excitation force,the dynamic model of the TDSS with ballistic impact is established,which is verified by finite element commercial software.If a bullet hits the TDS,the bending vibration displacement increases sharply at a certain moment and then significantly increases but remains stable.Meanwhile,the critical speed component appears in the frequency-domain response of bending vibration,and then the speed component significantly increases but remains stable.What's more,the axis trajectory exhibits a sudden,large-scale,and irregular whirling motion at a certain moment,followed by a significant increase but remains stable.Furthermore,if the axial vibration response is small,the bullet core shooting should be considered vertically or at a small incident angle,otherwise,it should be considered at a large incident angle.展开更多
Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to ...Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to investigate the broader model,namely the asymmetric piecewise linear system.The traditional averaging method is frequently used for studying nonlinear systems,particularly symmetric piecewise linear systems,with the harmonic response of the oscillator serving as a key prerequisite for calculating steady-state solutions.However,asymmetric systems inherently exhibit nonharmonic,asymmetric responses,rendering the traditional averaging method inapplicable.To overcome this limitation,this paper introduces an improved averaging method tailored for an oscillator characterized by asymmetric gaps and springs.Unlike the traditional method,which assumes a purely harmonic response,the improved averaging method redefines the system response as a superposition of a direct current(DC)term and a first harmonic component.Herein,the DC term can be regarded as the offset induced by model asymmetry.Furthermore,the DC term is treated as a slow variable function of time,with its time derivative assumed to be zero when calculating the steady-state solution,akin to the amplitude and phase in the traditional averaging method.Numerical validation demonstrates that the responses computed in both time and frequency domains with the improved averaging method exhibit greater accuracy compared with those derived from the traditional method.Leveraging these improved results,the study also examines the parameter effect,stability,and bifurcation phenomena within the amplitude-frequency responses.展开更多
A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state ...A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state of the medium and low speed maglev coupled system by the additional deformation of the maglev track.This study investigated the dynamic properties of the coupled vibration system affected by the subgrade settlement.First,a theoretical coupled vibration model of a maglev train-track-ground girder system with uneven subgrade settlement was proposed and verified.Then,the effect mechanism of the coupled system caused by the uneven subgrade settlement was explored.Finally,settlement types and subgrade support voiding were examined.The analysis showed that the uneven subgrade settlement considerably increased the dynamic responses of the levitation control system and maglev vehicle while having a minor influence on those of the track-ground girder.The influence of a single ground girder settling was the strongest,and adjacent sides’settling of two ground girders was the weakest for the vibration of a maglev train.An extremely large uneven settlement exceeding 6 mm led to active levitation control system instability.The subgrade support voiding enlarged the vehicle-induced vibration of the track ground girder.展开更多
To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibratio...To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibration simulation model of the CHMTS was set up by gear dynamics theory and loaded contact analysis.For better evaluation of the system vibration,a vibration evaluation method for the CHMTS was established by the G1 method-variation coefficient method.A hybrid Gravitational Search Algorithm-Simulated Annealing(GSA-SA)algorithm was combined to balance convergence speed and searching accuracy.The principle test was conducted to prove the accuracy of theoretical method,in which the maximum relative error is16.26%.The optional results show that the vibration of the optimized transmission system decreases significantly,in which the maximum reduction of key vibration indicators reaches more than 20%.The theoretical results have been compared to the experiment to verify the effectiveness of the vibration optimization method.The proposed method could be extended to other fields.展开更多
The gear transmission system directly affects the operational performance of high-speed trains(HST).However,current research on gear transmission systems of HST often overlooks the effects of gear eccentricity and run...The gear transmission system directly affects the operational performance of high-speed trains(HST).However,current research on gear transmission systems of HST often overlooks the effects of gear eccentricity and running resistance,and the dynamic models of gear transmission system are not sufficiently comprehensive.This paper aims to establish an electromechanical coupling dynamic model of HST traction transmission system and study its electromechanical coupling vibration characteristics,in which the internal excitation factors such as gear eccentricity,time-varying meshing stiffness,backlash,meshing error,and external excitation factors such as electromagnetic torque and running resistance are stressed.The research results indicate that gear eccentricity and running resistance have a significant impact on the stability of the system,and gear eccentricity leads to intensified system vibration and decreased anti-interference ability.In addition,the characteristic frequency of gear eccentricity can be extracted from mechanical signals and current signals as a preliminary basis for eccentricity detection,and electrical signals can also be used to monitor changes in train running resistance in real time.The results of this study provide some useful insights into designing dynamic performance parameters for HST transmission systems and monitoring train operational states.展开更多
Background:Due to its high relevance in sports and rehabilitation,the exploration of interventions to further optimize flexibility becomes paramount.While stretching might be the most common way to enhance range of mo...Background:Due to its high relevance in sports and rehabilitation,the exploration of interventions to further optimize flexibility becomes paramount.While stretching might be the most common way to enhance range of motion,these increases could be optimized by imposing an additional activation of the muscle,such as mechanical vibratory stimulation.While several original articles provide promising findings,contradictory results on flexibility and underlying mechanisms(e.g.,stiffness),reasonable effect size(ES)pooling remains scarce.With this work we systematically reviewed the available literature to explore the possibility of potentiating flexibility,stiffness,and passive torque adaptations by superimposing mechanical vibration stimulation.Methods:A systematic search of 4 databases(Web of Science,MEDLINE,Scopus,and Cochrane Public Library)was conducted until December2023 to identify studies comparing mechanical vibratory interventions with passive controls or the same intervention without vibration(sham)on range of motion and passive muscle stiffness in acute(immediate effects after single session)and chronic conditions(multiple sessions over a period of time).ES pooling was conducted using robust variance estimation via R to account for multiple study outcomes.Potential moderators of effects were analyzed using meta regression.Results:Overall,65 studies(acute:1162 participants,chronic:788 participants)were included.There was moderate certainty of evidence for acute flexibility(ES=0.71,p<0.001)and stiffness(ES=-0.89,p=0.006)effects of mechanical vibration treatments vs.passive controls without meaningful results against the sham condition(flexibility:ES=0.20,p<0.001;stiffness:ES=-0.19,p=0.076).Similarly,moderate certainty of evidence was found for chronic vibration effects on flexibility(control:ES=0.64,p=0.043;sham:ES=0.65,p<0.001).Lack of studies and large outcome heterogeneity prevented ES pooling for underlying mechanisms.Conclusion:Vibration improved flexibility in acute and chronic interventions compared to the stand-alone intervention,which can possibly be attributed to an accumulated mechanical stimulus through vibration.However,studies on biological mechanisms are needed to explain flexibility and stiffness effects in response to specific vibration modalities and timing.展开更多
In nuclear power engineering,the quality requirements for concrete are extremely stringent.Concrete structures must exhibit high durability to withstand the effects of nuclear radiation,chemical corrosion,and environm...In nuclear power engineering,the quality requirements for concrete are extremely stringent.Concrete structures must exhibit high durability to withstand the effects of nuclear radiation,chemical corrosion,and environmental changes.In particular,nuclear power projects impose higher design standards and safety requirements regarding concrete density.Traditional manual vibration and visual inspection methods are difficult to ensure the required level of concrete compaction.This paper presents an intelligent vibration technology for concrete in nuclear power engineering to enhance construction quality and efficiency.By integrating intelligent sensors,control systems,and data processing algorithms,the technology enables real-time monitoring and evaluation of the vibration process.Results show that intelligent vibration technology effectively ensures the density and uniformity of concrete in nuclear power engineering,thereby improving structural safety and reliability.展开更多
As a common fault of the aero-engine,the blade-casing rubbing(BCR)has the potential to cause catastrophic accidents.In this paper,to investigate the dynamic responses and wear characteristics of the system,the laminat...As a common fault of the aero-engine,the blade-casing rubbing(BCR)has the potential to cause catastrophic accidents.In this paper,to investigate the dynamic responses and wear characteristics of the system,the laminated shell element is used to establish the finite element model(FEM)of a flexibly coated casing system.Using the shell element,the blade is modeled,and the surface stress of the blade is calculated.The stress-solving method of the blade is validated through comparisons with the measured time-domain waveform of the stress.Then,a dynamic model of a blade-flexibly coated casing system with rubbing is proposed,accounting for the time-varying mass and stiffness of the casing caused by coating wear.The effects of the proposed flexible casing model are compared with those of a rigid casing model,and the stress changes induced by rubbing are investigated.The results show that the natural characteristics of the coated casing decrease due to the coating wear.The flexibly coated casing model is found to be more suitable for studying casing vibration.Additionally,the stress changes caused by rubbing are slight,and the change in the stress maximum is approximately 5%under the influence of the abrasive coating.展开更多
This paper analyzes the nonlinear dynamic characteristics and stability of Aero-Engine Dual-Rotor(AEDR)systems under high-frequency excitation,based on the Adaptive Harmonic Balance with the Asymptotic Harmonic Select...This paper analyzes the nonlinear dynamic characteristics and stability of Aero-Engine Dual-Rotor(AEDR)systems under high-frequency excitation,based on the Adaptive Harmonic Balance with the Asymptotic Harmonic Selection(AHB-AHS)method.A finite element dynamic equation for the AEDR system is introduced,considering complex nonlinearities of the intershaft bearing,unbalanced excitations,and high-frequency excitation.A solving strategy combining the AHB-AHS method and improved arclength continuation method is proposed to solve highdimensional dynamic equations containing complex nonlinearities and to track periodic solutions with parameter variations.The Floquet theory is used to analyze the types of bifurcation points in the system and the stability of periodic motions.The results indicate that high-frequency excitation can couple high-order and low-order modes,especially when the system undergoes superharmonic resonance.High-frequency excitation leads to more combination frequency harmonics,among which N_(f)ω_(1)-2ω_(2)dominates.Furthermore,changing the parameters(amplitude and frequency)of high-frequency excitation widens or shifts the unstable regions of the system.These findings contribute to understanding the mechanism of high-frequency excitation on aero-engines and demonstrate that the proposed AHB-AHS method is a powerful tool for analyzing highdimensional complex nonlinear dynamic systems under multi-frequency excitation.展开更多
A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the p...A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the principle that the Euler beam has a negative stiffness in the critical state,the dynamic stiffness of the loaded QZS vibration isolator in the balance position tends to be close to zero by connecting a vertical spring in parallel.Firstly,the stiffness of the QZS vibration isolation system at the balance position is analyzed statically,and the material parameters and properties of the Euler beam are determined.Then,the dynamic equations are established,and the harmonic equilibrium method is used to solve the dynamic response under sinusoidal excitation to obtain the force transmissibility of the QZS vibration isolation system,and to make a comparison with that of the linear isolation system.Finally,the modal simulation,harmonic response simulation and random vibration simulation of the QZS vibration isolator are carried out through the finite element analysis,and the results show that the QZS vibration isolator has a lower initial isolation frequency and a larger isolation range,and the peak vibration isolation can reach about 11.58 dB.展开更多
基金supported by Liaoning Province College Science and Research(2008S095)the Key Project of the National Natural Science Foundation of China(50535010,50805020)High-tech Research and Development Program of China(2007AA04Z442)
文摘The paper proposes an analytical approach to investigate the synchronization of the two coupled exciters in a vibrating system of spatial motion. Introducing the distur- bance parameters for average angular velocity of two excit- ers, we deduce the non-dimensional coupling equations of angular velocities of two exciters, in which the inertia cou- pling matrix is symmetric and the stiffness coupling matrix is antisymmetric in a non-resonant vibrating system. The analysis of the coupling dynamic characteristic shows that the coupled cosine effect of the phase angles will cause the torque acting on two motors to limit the increase of phase difference between two exciters as well as sustain its sym- metry of two exciters during the running process. It physi- cally explains the peculiarity of self-synchronization of two exciters. The cosine effect of phase angles of the vibrations excited by each exciter will decrease its moment of inertia. The residual moment of inertia of each exciter represents its relative moment of inertia. The stability condition of synchro- nization of two exciters is that the relative non-dimensional moments of inertia of two exciters are all greater than zero and four times their product is greater than the square of their coefficient of coupled cosine effect of phase angles, which is equivalent to that the inertia coupling matrix is positive definite and all its elements are positive. The numeric results show that the structure of the vibrating system can ensure the stability condition of synchronous operation.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50535010 and 10702014)the Project of Liaoning Province Science (Grant No. 2008S095)the National High Technology Research and Development Program of China(Grant No. 2007AA04Z442)
文摘We derive the non-dimensional coupling equation of two exciters, including inertia coupling, stiffness coupling and load coupling. The concept of general dynamic symmetry is proposed to physically explain the synehronisation of the two exciters, which stems from the load coupling that produces the torque of general dynamic symmetry to force the phase difference between the two exciters close to the angle of general dynamic symmetry. The condition of implementing synchronisation is that the torque of general dynamic symmetry is greater than the asymmetric torque of the two motors. A general Lyapunov function is constructed to derive the stability condition of synchronisation that the non-dimensional inertia coupling matrix is positive definite and all its elements are positive. Numeric results show that the structure of the vibrating system can guarantee the stability of synchronisation of the two exciters, and that the greater the distances between the installation positions of the two exciters and the mass centre of the vibrating system are, the stronger the ability of general dynamic symmetry is.
基金supported by the National Key Technology R&D Program (2009BAG12A01-F01-3)the National Natural Science Foundation of China (51075063)
文摘In this paper, the synchronization problem of three homodromy coupled exciters in a non-resonant vibrating system of plane motion is studied. By introducing the average method of modified small parameters, we deduced dimensionless coupling equation of three exciters, which converted the problem of synchronization into that of the existence and stability of zero solutions for the average differential equations of the small parameters. Based on the dimensionless coupling torques and characteristics of the cor- responding limited functions, the synchronization criterion for three exciters was derived as the absolute value of dimensionless residual torque difference between arbitrary two motors being less than the maximum of their dimensionless coupling torques. The stability criterion of its synchronous state lies in the double-condition that the inertia coupling matrix is positive definite and all its elements are positive as well. The synchronization determinants are the coefficients of synchronization ability, also called as the general dynamical symmetry coefficients. The double-equilibrium state of the vibrating system is manifested by numeric method, and the numeric and simulation results derived thereof indicate the indispensable and crucial role the structural parameters of the vibrating system play in the stability criterion of synchronous operation. Besides, by adjusting its structural parameters, the elliptical motion of the vibrating system successfully met the requirements in engineering applications.
文摘For the electro-hydraulic servo vibrating system（ESVS） with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control（ILC）, is proposed on the basis of traditional PID control. By using memory ability of computer, the method keeps last time＇s tracking error of the system and then applies the error information to the next time＇s control process. At the same time, a forgetting factor and a D-type learning law of feedforward fuzzy-inferring referenced displacement error under the optimal objective are employed to enhance the systemic robustness and tracking accuracy. The results of simulation and test reveal that the algorithm has a trait of high repeating precision, and could restrain the influence of nonlinear factors like leaking, external disturbance, aerated oil, etc. Compared with traditional PID control, it could better meet the requirement of nonlinear electro -hydraulic servo vibrating system.
基金supported by National Basic Research Program of China(973 Program, Grant No. 2011CB706504)National Natural Science Foundations of China(Grant No. 51075063)
文摘The theory on synchronization of two exciters is more widely used in engineering, while that of more than two exciters is less considered. So it is of great significant to investigate synchronization of three exciters. Firstly by introducing the average method of modified small parameters, the dimensionless coupling equations(DCE) of three exciters are derived, which convert the problem of synchronization into that of existence and stability of zero solutions for the DCE and lead to the construction on criterions of synchronization and stability in the simplified form for three exciters. Then the synchronization criterion is discussed numerically, as well as the abilities of synchronization and stability, some results thereof indicate that the synchronization ability increases with the increase of the coupling moment among three exciters, but decreases with that of their phase differences. Finally, an experiment on synchronization with three exciters is carried out. Through the comparison and analysis of experimental data on phase differences among three exciters, responses of system, and phases of three exciters recorded by high-speed camera, the parameters of system satisfying the above two criterions can ensure the synchronous and stable operation of three exciters. As a result, the average method of modified small parameters can be used as a theoretical apparatus studying reasonably the synchronization mechanism of three exciters, it is also proved to be useful and feasible by numeric and experiment. The present research lays the foundation and guidance for the establishment of synchronization theory system with multi-exciter and engineering design.
文摘In this paper a three degrees of freedom autoparametric system with limited power supply is investigated numerically. The system consists of the body, which is hung on a spring and a damper, and two pendulums connected by shape memory alloy （SMA） spring. Shape memory alloys have ability to change their material properties with temperature. A polynomial constitutive model is assumed to describe the behavior of the SMA spring. The non-ideal source of power adds one degree of freedom, so the system has four degrees of freedom. The equations of motion have been solved numerically and pseudoelastic effects associated with the martensitic phase transformation are studied. It is shown that in this type system one mode of vibrations might excite or damp another mode, and that except different kinds of periodic vibrations there may also appear chaotic vibrations. For the identification of the responses of the system＇s various techniques, including chaos techniques such as bifurcation diagrams and time histories, power spectral densities, Poincare maps and exponents of Lyapunov may be used.
文摘Bifurcation problems of a spring-mass system vibrating against an infinite large plane are studied in this paper. It is shown that there exist phenomena of codimension two bifurcations when the ratios of frequencies are in the neigborhood of the same special values and the coefficient of restitution approach unity. By theory of normal forms, we reduce Poincare maps to normal forms.and find flip bifurcations, Hopf bifurcations of fixed points and that of period two points The theoretical solutions are verified by numerical computations.
文摘Maintaining the integrity and longevity of structures is essential in many industries,such as aerospace,nuclear,and petroleum.To achieve the cost-effectiveness of large-scale systems in petroleum drilling,a strong emphasis on structural durability and monitoring is required.This study focuses on the mechanical vibrations that occur in rotary drilling systems,which have a substantial impact on the structural integrity of drilling equipment.The study specifically investigates axial,torsional,and lateral vibrations,which might lead to negative consequences such as bit-bounce,chaotic whirling,and high-frequency stick-slip.These events not only hinder the efficiency of drilling but also lead to exhaustion and harm to the system’s components since they are difficult to be detected and controlled in real time.The study investigates the dynamic interactions of these vibrations,specifically in their high-frequency modes,usingfield data obtained from measurement while drilling.Thefindings have demonstrated the effect of strong coupling between the high-frequency modes of these vibrations on drilling sys-tem performance.The obtained results highlight the importance of considering the interconnected impacts of these vibrations when designing and implementing robust control systems.Therefore,integrating these compo-nents can increase the durability of drill bits and drill strings,as well as improve the ability to monitor and detect damage.Moreover,by exploiting thesefindings,the assessment of structural resilience in rotary drilling systems can be enhanced.Furthermore,the study demonstrates the capacity of structural health monitoring to improve the quality,dependability,and efficiency of rotary drilling systems in the petroleum industry.
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.52175552)the National Key RD Program of China(Grant Nos.2022YFB3205400 and 2022YFB3204300).
文摘Two-dimensional phononic crystal(PnC)slabs have shown advantages in enhancing the quality factors Q of piezoelectric laterally vibrating resonators(LVRs)through topology optimization.However,the narrow geometries of most topology-optimized silicon–air 2D PnC slabs face significant fabrication challenges owing to restricted etching precision,and the anisotropic nature of silicon is frequently overlooked.To address these issues,this study employs the finite element method with appropriate discretization numbers and the genetic algorithm to optimize the structures and geometries of 2D silicon–air PnC slabs.The optimized square-lattice PnC slabs,featuring a rounded-cross structure oriented along the`110e directions of silicon,achieve an impressive relative bandgap(RBG)width of 82.2%for in-plane modes.When further tilted by 15° from the (100) directions within the(001)plane,the optimal RBG width is expanded to 91.4%.We fabricate and characterize thin-film piezoelectric-on-silicon LVRs,with or without optimized 2D PnC slabs.The presence of PnC slabs around anchors increases the series and parallel quality factors Q_(s) and Q_(p) from 2240 to 7118 and from 2237 to 7501,respectively,with the PnC slabs oriented along the`110e directions of silicon.
基金co-supported by the National Natural Science Foundation of China(No.52275061)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(No.KYCX24_0562)。
文摘The ballistic impact identification method for the helicopter Tail Drive Shaft System(TDSS)isn't yet comprehensive,which affects helicopter flight safety.This paper proposes a ballistic impact identification method for the TDSS based on vibration response analysis.Based on the Johnson-Cook constitutive model and failure criteria,the ballistic impact finite element simulation model is established,which is verified by the ballistic impact experiment of the Tail Drive Shaft(TDS).Considering the ballistic impact excitation force,the dynamic model of the TDSS with ballistic impact is established,which is verified by finite element commercial software.If a bullet hits the TDS,the bending vibration displacement increases sharply at a certain moment and then significantly increases but remains stable.Meanwhile,the critical speed component appears in the frequency-domain response of bending vibration,and then the speed component significantly increases but remains stable.What's more,the axis trajectory exhibits a sudden,large-scale,and irregular whirling motion at a certain moment,followed by a significant increase but remains stable.Furthermore,if the axial vibration response is small,the bullet core shooting should be considered vertically or at a small incident angle,otherwise,it should be considered at a large incident angle.
基金Project supported by the National Natural Science Foundation of China(Nos.12272242 and U1934201)。
文摘Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to investigate the broader model,namely the asymmetric piecewise linear system.The traditional averaging method is frequently used for studying nonlinear systems,particularly symmetric piecewise linear systems,with the harmonic response of the oscillator serving as a key prerequisite for calculating steady-state solutions.However,asymmetric systems inherently exhibit nonharmonic,asymmetric responses,rendering the traditional averaging method inapplicable.To overcome this limitation,this paper introduces an improved averaging method tailored for an oscillator characterized by asymmetric gaps and springs.Unlike the traditional method,which assumes a purely harmonic response,the improved averaging method redefines the system response as a superposition of a direct current(DC)term and a first harmonic component.Herein,the DC term can be regarded as the offset induced by model asymmetry.Furthermore,the DC term is treated as a slow variable function of time,with its time derivative assumed to be zero when calculating the steady-state solution,akin to the amplitude and phase in the traditional averaging method.Numerical validation demonstrates that the responses computed in both time and frequency domains with the improved averaging method exhibit greater accuracy compared with those derived from the traditional method.Leveraging these improved results,the study also examines the parameter effect,stability,and bifurcation phenomena within the amplitude-frequency responses.
基金National Natural Science Foundation of China under Grant Nos.52478467and 52108417Guangdong Basic and Applied Basic Research Foundation under Grant No.2024A1515012569the Natural Science Basic Research Program of Shaanxi under Grant No.2021JQ-101。
文摘A ground girder is laid on the preprocessed subgrade by gravity compaction and integrally uniformly supported by subgrade in maglev transit.The settlement of the maglev subgrade inevitably affects the vibration state of the medium and low speed maglev coupled system by the additional deformation of the maglev track.This study investigated the dynamic properties of the coupled vibration system affected by the subgrade settlement.First,a theoretical coupled vibration model of a maglev train-track-ground girder system with uneven subgrade settlement was proposed and verified.Then,the effect mechanism of the coupled system caused by the uneven subgrade settlement was explored.Finally,settlement types and subgrade support voiding were examined.The analysis showed that the uneven subgrade settlement considerably increased the dynamic responses of the levitation control system and maglev vehicle while having a minor influence on those of the track-ground girder.The influence of a single ground girder settling was the strongest,and adjacent sides’settling of two ground girders was the weakest for the vibration of a maglev train.An extremely large uneven settlement exceeding 6 mm led to active levitation control system instability.The subgrade support voiding enlarged the vehicle-induced vibration of the track ground girder.
基金funded by the National Natural Science Foundation of China(No.52105060)the Special Transmission Project,China(No.KY-1044-2023-0458)。
文摘To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibration simulation model of the CHMTS was set up by gear dynamics theory and loaded contact analysis.For better evaluation of the system vibration,a vibration evaluation method for the CHMTS was established by the G1 method-variation coefficient method.A hybrid Gravitational Search Algorithm-Simulated Annealing(GSA-SA)algorithm was combined to balance convergence speed and searching accuracy.The principle test was conducted to prove the accuracy of theoretical method,in which the maximum relative error is16.26%.The optional results show that the vibration of the optimized transmission system decreases significantly,in which the maximum reduction of key vibration indicators reaches more than 20%.The theoretical results have been compared to the experiment to verify the effectiveness of the vibration optimization method.The proposed method could be extended to other fields.
基金supported by Sichuan Science and Technology Program(Grant No.2020YFH0080)the National Natural Science Foundation of China(Grant No.51475386)the National Basic Research Project of China(973 Program,Grant No.2015CB654801).
文摘The gear transmission system directly affects the operational performance of high-speed trains(HST).However,current research on gear transmission systems of HST often overlooks the effects of gear eccentricity and running resistance,and the dynamic models of gear transmission system are not sufficiently comprehensive.This paper aims to establish an electromechanical coupling dynamic model of HST traction transmission system and study its electromechanical coupling vibration characteristics,in which the internal excitation factors such as gear eccentricity,time-varying meshing stiffness,backlash,meshing error,and external excitation factors such as electromagnetic torque and running resistance are stressed.The research results indicate that gear eccentricity and running resistance have a significant impact on the stability of the system,and gear eccentricity leads to intensified system vibration and decreased anti-interference ability.In addition,the characteristic frequency of gear eccentricity can be extracted from mechanical signals and current signals as a preliminary basis for eccentricity detection,and electrical signals can also be used to monitor changes in train running resistance in real time.The results of this study provide some useful insights into designing dynamic performance parameters for HST transmission systems and monitoring train operational states.
文摘Background:Due to its high relevance in sports and rehabilitation,the exploration of interventions to further optimize flexibility becomes paramount.While stretching might be the most common way to enhance range of motion,these increases could be optimized by imposing an additional activation of the muscle,such as mechanical vibratory stimulation.While several original articles provide promising findings,contradictory results on flexibility and underlying mechanisms(e.g.,stiffness),reasonable effect size(ES)pooling remains scarce.With this work we systematically reviewed the available literature to explore the possibility of potentiating flexibility,stiffness,and passive torque adaptations by superimposing mechanical vibration stimulation.Methods:A systematic search of 4 databases(Web of Science,MEDLINE,Scopus,and Cochrane Public Library)was conducted until December2023 to identify studies comparing mechanical vibratory interventions with passive controls or the same intervention without vibration(sham)on range of motion and passive muscle stiffness in acute(immediate effects after single session)and chronic conditions(multiple sessions over a period of time).ES pooling was conducted using robust variance estimation via R to account for multiple study outcomes.Potential moderators of effects were analyzed using meta regression.Results:Overall,65 studies(acute:1162 participants,chronic:788 participants)were included.There was moderate certainty of evidence for acute flexibility(ES=0.71,p<0.001)and stiffness(ES=-0.89,p=0.006)effects of mechanical vibration treatments vs.passive controls without meaningful results against the sham condition(flexibility:ES=0.20,p<0.001;stiffness:ES=-0.19,p=0.076).Similarly,moderate certainty of evidence was found for chronic vibration effects on flexibility(control:ES=0.64,p=0.043;sham:ES=0.65,p<0.001).Lack of studies and large outcome heterogeneity prevented ES pooling for underlying mechanisms.Conclusion:Vibration improved flexibility in acute and chronic interventions compared to the stand-alone intervention,which can possibly be attributed to an accumulated mechanical stimulus through vibration.However,studies on biological mechanisms are needed to explain flexibility and stiffness effects in response to specific vibration modalities and timing.
基金The Advanced Civil Design and Construction Technology Joint LAB of Nuclear Engineering(Project No.:KY23015).
文摘In nuclear power engineering,the quality requirements for concrete are extremely stringent.Concrete structures must exhibit high durability to withstand the effects of nuclear radiation,chemical corrosion,and environmental changes.In particular,nuclear power projects impose higher design standards and safety requirements regarding concrete density.Traditional manual vibration and visual inspection methods are difficult to ensure the required level of concrete compaction.This paper presents an intelligent vibration technology for concrete in nuclear power engineering to enhance construction quality and efficiency.By integrating intelligent sensors,control systems,and data processing algorithms,the technology enables real-time monitoring and evaluation of the vibration process.Results show that intelligent vibration technology effectively ensures the density and uniformity of concrete in nuclear power engineering,thereby improving structural safety and reliability.
基金Project supported by the National Science and Technology Major Project(No.J2022-IV-0005-0022)the Aero Science Foundation of China(No.20230015050001)the Shenyang Science and Technology Plan Project of China(No.24-202-6-01)。
文摘As a common fault of the aero-engine,the blade-casing rubbing(BCR)has the potential to cause catastrophic accidents.In this paper,to investigate the dynamic responses and wear characteristics of the system,the laminated shell element is used to establish the finite element model(FEM)of a flexibly coated casing system.Using the shell element,the blade is modeled,and the surface stress of the blade is calculated.The stress-solving method of the blade is validated through comparisons with the measured time-domain waveform of the stress.Then,a dynamic model of a blade-flexibly coated casing system with rubbing is proposed,accounting for the time-varying mass and stiffness of the casing caused by coating wear.The effects of the proposed flexible casing model are compared with those of a rigid casing model,and the stress changes induced by rubbing are investigated.The results show that the natural characteristics of the coated casing decrease due to the coating wear.The flexibly coated casing model is found to be more suitable for studying casing vibration.Additionally,the stress changes caused by rubbing are slight,and the change in the stress maximum is approximately 5%under the influence of the abrasive coating.
基金the financial support from the National Key R&D Program of China(No.2023YFE0125900)National Natural Science Foundation of China(Nos.12372008 and 12102234)+1 种基金Natural Science Foundation of Heilongjiang Province,China(No.YQ2022A008)Taif University,Saudi Arabia,for supporting this work through Project number(TU-DSPP-2024-73).
文摘This paper analyzes the nonlinear dynamic characteristics and stability of Aero-Engine Dual-Rotor(AEDR)systems under high-frequency excitation,based on the Adaptive Harmonic Balance with the Asymptotic Harmonic Selection(AHB-AHS)method.A finite element dynamic equation for the AEDR system is introduced,considering complex nonlinearities of the intershaft bearing,unbalanced excitations,and high-frequency excitation.A solving strategy combining the AHB-AHS method and improved arclength continuation method is proposed to solve highdimensional dynamic equations containing complex nonlinearities and to track periodic solutions with parameter variations.The Floquet theory is used to analyze the types of bifurcation points in the system and the stability of periodic motions.The results indicate that high-frequency excitation can couple high-order and low-order modes,especially when the system undergoes superharmonic resonance.High-frequency excitation leads to more combination frequency harmonics,among which N_(f)ω_(1)-2ω_(2)dominates.Furthermore,changing the parameters(amplitude and frequency)of high-frequency excitation widens or shifts the unstable regions of the system.These findings contribute to understanding the mechanism of high-frequency excitation on aero-engines and demonstrate that the proposed AHB-AHS method is a powerful tool for analyzing highdimensional complex nonlinear dynamic systems under multi-frequency excitation.
文摘A small quasi-zero stiffness(QZS)vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system.By using the principle that the Euler beam has a negative stiffness in the critical state,the dynamic stiffness of the loaded QZS vibration isolator in the balance position tends to be close to zero by connecting a vertical spring in parallel.Firstly,the stiffness of the QZS vibration isolation system at the balance position is analyzed statically,and the material parameters and properties of the Euler beam are determined.Then,the dynamic equations are established,and the harmonic equilibrium method is used to solve the dynamic response under sinusoidal excitation to obtain the force transmissibility of the QZS vibration isolation system,and to make a comparison with that of the linear isolation system.Finally,the modal simulation,harmonic response simulation and random vibration simulation of the QZS vibration isolator are carried out through the finite element analysis,and the results show that the QZS vibration isolator has a lower initial isolation frequency and a larger isolation range,and the peak vibration isolation can reach about 11.58 dB.
