Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of...Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of research has been dedicated to the development of technologies that are able to predict and detect chatter. The purpose of these technologies is to facilitate the avoidance of chatter during cutting processes, which leads to better surface precision, higher productivity,and longer tool life. This paper summarizes the current state of the art in research regarding the problems of how to arrive at stable chatter prediction, chatter identification, and chatter control/-suppression, with a focus on milling processes. Particular focus is placed on the theoretical relationship between cutting chatter and process damping, tool runout, and gyroscopic effect, as well as the importance of this for chatter prediction. The paper concludes with some reflections regarding possible directions for future research in this field.展开更多
Traditional PID controllers are no longer suitable formagnetic-bearing-supported high-speed flywheels with significant gyroscopic effects. Becausegyroscopic effects greatly influence the stability of the flywheel roto...Traditional PID controllers are no longer suitable formagnetic-bearing-supported high-speed flywheels with significant gyroscopic effects. Becausegyroscopic effects greatly influence the stability of the flywheel rotor, especially at highrotational speeds. Velocity cross feedback and displacement cross feedback are used to overcomeharmful effects of nutation and precession modes, and stabilize the rotor at high rotational speeds.Theoretical analysis is given to show their effects. A control platform based on RTLinut and a PCis built to control the active magnetic bearing (AMB) system, and relevant results are reported.Using velocity cross feedback and displacement cross feedback in a closed loop control system, theflywheel successfully runs at over 20000 r/min.展开更多
Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyrosc...Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyroscopic modes decoupling method is used to obtain an equivalent system with decoupled gyroscopic modes having only weak couplings.Taking the axially moving string as an example,the instability boundaries in the vicinity of parametric resonances are detected using both the traditional coupled gyroscopic system and our system with decoupled gyroscopic modes,and the results are compared to show the advantages and disadvantages of each method.展开更多
This study presents a kinematic calibration method for exoskeletal inertial motion capture (EI-MoCap) system with considering the random colored noise such as gyroscopic drift.In this method, the geometric parameters ...This study presents a kinematic calibration method for exoskeletal inertial motion capture (EI-MoCap) system with considering the random colored noise such as gyroscopic drift.In this method, the geometric parameters are calibrated by the traditional calibration method at first. Then, in order to calibrate the parameters affected by the random colored noise, the expectation maximization (EM) algorithm is introduced. Through the use of geometric parameters calibrated by the traditional calibration method, the iterations under the EM framework are decreased and the efficiency of the proposed method on embedded system is improved. The performance of the proposed kinematic calibration method is compared to the traditional calibration method. Furthermore, the feasibility of the proposed method is verified on the EI-MoCap system. The simulation and experiment demonstrate that the motion capture precision is significantly improved by 16.79%and 7.16%respectively in comparison to the traditional calibration method.展开更多
As the nano-motor becomes a mechanical reality, its prototype can be envisaged as nano-sized rotating machinery at a situation,albeit for different purposes, like that in the first half of the 20th century during whic...As the nano-motor becomes a mechanical reality, its prototype can be envisaged as nano-sized rotating machinery at a situation,albeit for different purposes, like that in the first half of the 20th century during which rotor dynamics has contributed toboosting machine power capacity. Accordingly, we take the benefit of hindsight to develop a classical framework of vibrationanalysis. Essentially, the equations of motion are formulated to cope with both the special carbon-nanotube properties and thefirst author’s previously developed spinning beam formalism, establishing a model satisfactorily verified by some availablemolecular dynamics (MD) data and classical spinning beam results extracted from the literature. The model is inexpensivebased on continuum mechanics as an alternative to the less-flexible MD method for simulating wave motion of the spinningsingle-walled carbon nanotube, yielding several interesting phenomena, including the fall-off and splitting of the wave charac-teristic curves and the unexpected gyroscopic phase property. Potential applications are proposed.展开更多
Gyroscopic dynamic system can be introduced to Hamiltonian system. Based on an adjoint symplectic subspace iteration method of Hamiltonian gyroscopic system, an adjoint symplectic subspace iteration method of indefini...Gyroscopic dynamic system can be introduced to Hamiltonian system. Based on an adjoint symplectic subspace iteration method of Hamiltonian gyroscopic system, an adjoint symplectic subspace iteration method of indefinite Hamiltonian function gyroscopic system was proposed to solve the eigenvalue problem of indefinite Hamiltonian function gyroscopic system. The character that the eigenvalues of Hamiltonian gyroscopic system are only pure imaginary or zero was used. The eigenvalues that Hamiltonian function is negative can be separated so that the eigenvalue problem of positive definite Hamiltonian function system was presented, and an adjoint symplectic subspace iteration method of positive definite Hamiltonian function system was used to solve the separated eigenvalue problem. Therefore, the eigenvalue problem of indefinite Hamiltonian function gyroscopic system was solved, and two numerical examples were given to demonstrate that the eigensolutions converge exactly.展开更多
The dynamic response of an axially traveling laminated composite beam is investigated analytically,with special consideration to natural frequencies,complex mode functions and critical speeds of the system.The equatio...The dynamic response of an axially traveling laminated composite beam is investigated analytically,with special consideration to natural frequencies,complex mode functions and critical speeds of the system.The equation of motion for a symmetrically laminated system,which is in the form of a continuous gyroscopic system,is considered;the equation of motion is not discretized — no spatial mode function is assumed.This leads to analytical expressions for the complex mode functions and critical speeds.A parametric study has been conducted in order to highlight the effects of system parameters on the above-mentioned vibration characteristics of the system.展开更多
Rotating machinery is an essential and crucial component of numerous mechanical systems in modern industries,transport vehicles,and in several other applications.Excessive vibrations on rotating equipment due to multi...Rotating machinery is an essential and crucial component of numerous mechanical systems in modern industries,transport vehicles,and in several other applications.Excessive vibrations on rotating equipment due to multiple faults may cause catastrophic failure in machines and lead to hazardous accidents.So,there is a need for perceiving the dynamic nature and identifying the faults for the safe,smooth and effective operation of machines.This paper proposes a novel trial misalignment approach to estimate the misalignment with a similar concept as the trial unbalance in the rotor balancing.Active magnetic bearing(AMB)misalignment with the rotor has been investigated with residual misalignment and additional trial misalignment cases.Additional trial misalignments are provided in addition to the unknown misalignments of the residual misalignment case.For the execution of this methodology,the dynamic model of a four-degree-of-freedom unbalanced and misaligned rigid rotor with two offset discs supported by two active magnetic bearings has been mathematically developed.The offset discs result in the gyroscopic effect at high rotor speeds.Equations of motion of the rotor-AMB system have been derived and solved to generate the time domain rotor displacement and controlling current responses at AMB positions.A fast Fourier transform technique has been utilized to convert the time domain responses into the frequency domain for estimation of unbalance eccentricities and phases together with force-displacement and forcecurrent stiffnesses of misaligned AMBs as well as AMB's constant forces using the developed identification algorithm.Identified values of AMB's parameters for both residual and additional trial misalignment cases are evaluated to estimate the four unknown misalignments.Testing of the algorithm has also been carried out at multiple spin speeds against measurement signal noise in rotor responses and bias errors in rotor system parameters to check its effectiveness and robustness.The algorithm is found to be exhi展开更多
An efficient method is developed to investigate the vibration and stability of moving plates immersed in fluid by applying the Kirchhoff plate theory and finite element method.The fluid is considered as an ideal fluid...An efficient method is developed to investigate the vibration and stability of moving plates immersed in fluid by applying the Kirchhoff plate theory and finite element method.The fluid is considered as an ideal fluid and is described with Bernoulli’s equation and the linear potential flow theory.Hamilton’s principle is used to acquire the dynamic equations of the immersed moving plate.The mass matrix,stiffness matrix,and gyroscopic inertia matrix are determined by the exact analytical integration.The numerical results show that the fundamental natural frequency of the submersed moving plates gradually decreases to zero with an increase in the axial speed,and consequently,the coupling phenomenon occurs between the first-and second-order modes.It is also found that the natural frequency of the submersed moving plates reduces with an increase in the fluid density or the immersion level.Moreover,the natural frequency will drop obviously if the plate is located near the rigid wall.In addition,the developed method has been verified in comparison with available results for special cases.展开更多
This paper presents a theoretical and experimental study on controller design for the AMBs in a small-scale flywheel energy storage system,where the main goals are to achieve low energy consumption and improved rotord...This paper presents a theoretical and experimental study on controller design for the AMBs in a small-scale flywheel energy storage system,where the main goals are to achieve low energy consumption and improved rotordynamic stability.A H-infinity optimal control synthesis procedure is defined for the permanent-magnet-biased AMB-rotor system with 4 degrees of freedom.Through the choice of design weighting functions,notch filter characteristics are incorporated within the controller to reduce AMB current components caused by rotor vibration at the synchronous frequency and higher harmonics.Experimental tests are used to validate the controller design methodology and provide comparative results on performance and efficiency.The results show that the H-infinity controller is able to achieve stable rotor levitation and reduce AMB power consumption by more than 40%(from 4.80 to 2.64 Watts)compared with the conventional PD control method.Additionally,the H-infinity controller can prevent vibrational instability of the rotor nutation mode,which is prone to occur when operating with high rotational speeds.展开更多
The axial fluid-induced vibration of pipes is very widespread in engineering applications.The nonlinear forced vibration of a viscoelastic fluid-conveying pipe with nonlinear supports at both ends is investigated.The ...The axial fluid-induced vibration of pipes is very widespread in engineering applications.The nonlinear forced vibration of a viscoelastic fluid-conveying pipe with nonlinear supports at both ends is investigated.The multi-scale method combined with the modal revision method is formulated for the fluid-conveying pipe system with nonlinear boundary conditions.The governing equations and the nonlinear boundary conditions are rescaled simultaneously as linear inhomogeneous equations and linear inhomogeneous boundary conditions on different time-scales.The modal revision method is used to transform the linear inhomogeneous boundary problem into a linear homogeneous boundary problem.The differential quadrature element method(DQEM)is used to verify the approximate analytical results.The results show good agreement between these two methods.A detailed analysis of the boundary nonlinearity is also presented.The obtained results demonstrate that the boundary nonlinearities have a significant effect on the dynamic characteristics of the fluid-conveying pipe,and can lead to significant differences in the dynamic responses of the pipe system.展开更多
A spinning gyroscope precesses about the vertical due to a torque acting upon the wheel. The torque is generated by the shift of moment of force by gravity and it points to the vertical instead of the tangential direc...A spinning gyroscope precesses about the vertical due to a torque acting upon the wheel. The torque is generated by the shift of moment of force by gravity and it points to the vertical instead of the tangential direction of precession. This intuition offers an alternative and straightforward view of precession dynamics in comparison with the literature. It also presumes a dynamic balance of momentum between circular motions of the wheel spin and precession. Accordingly, the gyroscopic dynamics is then applied to the study of galactic motion of the solar system in space and the Galactic mass is calculated with the inclusion of gyroscopic effect of the solar planets. Results indicate that the gyroscopic effect of Mercury orbiting around the Sun can increase the calculated Galactic mass by 23% in comparison with the result obtained by the classic approach.展开更多
Unusual one-way edge states have been observed in composite structures composed of periodic lattices loaded with gyroscopes.Here, we provide a continuum-mechanics understanding to the one-way edge state by formulating...Unusual one-way edge states have been observed in composite structures composed of periodic lattices loaded with gyroscopes.Here, we provide a continuum-mechanics understanding to the one-way edge state by formulating surface state equations of acoustic gyroscopic mediums with Hermite mass density tensor. We discover that the unidirectional edge effect arises from nontrivial off-diagonal components of Hermite densities, which causes the symmetric breaking of surface wave propagation towards forward and backward directions. Theoretical predictions on the velocity and decay length of surface waves coincide excellently with numerical simulations. The unidirectional edge state in a two-interface gyroscopic medium is also analyzed.Due to the rotational symmetry in geometry, the unidirectional edge state on one interface is able to prevent itself from the coupling to surface waves on the other interface regardless of the slab thickness. With these anomalous effects, surface waves residing on gyroscopic mediums can flow around the edge defects without back-scatterings, or can be split into two beams of equal energy magnitudes. Our findings may make a bridge that would help to reach the design of non-reciprocal composite materials via an effective medium approach.展开更多
This paper gives a dynamic decoupling approach for the analysis of large scale non-classically damped system, in which the complex variable computations were completely avoided not only in solving for the eigenvalue p...This paper gives a dynamic decoupling approach for the analysis of large scale non-classically damped system, in which the complex variable computations were completely avoided not only in solving for the eigenvalue problem but also in the calculation of the dynamic response. The analytical approaches for undamped gyroscopic system, non-classically damped system, including the damped gyroscopic system were unified. Very interesting and useful theoretical results, practical algorithms were obtained which are applicable to both non-defective and defective systems.展开更多
To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validat...To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validated through ground tests.The fake gyroscopic torque is first proposed,which the vector mechanism should overcome besides the inertial torque and the gravitational torque.The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane,appears only when the propeller is rotating and is proportional with the rotation speed.It is a sinusoidal pulse,with a frequency that is twice of the rotation speed.Considering the fake gyroscope torque pulse and aerodynamic efficiency,three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.展开更多
This paper gives a succinct review of dual-spinprojectile stability and some technologies relating to them.It describes how the traditional stability factors from linear projectile theory are modified to better descri...This paper gives a succinct review of dual-spinprojectile stability and some technologies relating to them.It describes how the traditional stability factors from linear projectile theory are modified to better describe a controlled dual-spin projectile.Finally,it reviews works which have investigated how different aspects of a controlled dual-spin design can affect flight stability,primarily airframe structure and canard properties.A conclusion is given,highlighting important guidelines from the enclosed discussions.展开更多
In this paper, the coupled bending-bending-axial-torsional free vibrations of rotating blades are investigated based on the Euler-Bernoulli beam model. The coupled partial differential equations governing flapwisc, ed...In this paper, the coupled bending-bending-axial-torsional free vibrations of rotating blades are investigated based on the Euler-Bernoulli beam model. The coupled partial differential equations governing flapwisc, edgewise, axial and torsional motions are derived by the Hamilton's principle, wherein three types of velocity-dependent terms, namely static centrifugal terms, dynamic centrifugal terms and gyroscopic coupling terms, are focused. The ordinary di& ferential equations are acquired by the Galerkin truncation, and the natural frequencies in all directions and complex mode shapes of the rotating blades are analyzed in detail. It is revealed that the three types of velocity-dependent terms have different effects on the natural frequencies. The natural frequencies are noticeably dependent on the rotating speed and preset angle, except for the axial vibration, which is almost immune to the preset angle. The complex modal motions are displayed by a series of positions of the central line and free-end cross section for different time instants, showing the coupled vibrations among different directions.展开更多
On the basis of controlled Lagrangians,a controller design is proposed for underactuated mechanical systems with two degrees of freedom.A new kinetic energy equation(K-equation)independent of the gyroscopic forces is ...On the basis of controlled Lagrangians,a controller design is proposed for underactuated mechanical systems with two degrees of freedom.A new kinetic energy equation(K-equation)independent of the gyroscopic forces is found due to the use of their property.As a result,the necessary and sufficient matching condition comprises the new K-equation and the potential energy equation(P-equation)cascaded,the regular condition,and the explicit gyroscopic forces.Further,for two classes of input decoupled systems that cover the main benchmark examples,the new K-equation,respectively,degenerates from a quasilinear partial differential equation(PDE)into an ordinary differential equation(ODE)under some choice and into a homogeneous linear PDE with two kinds of explicit general solutions.Benefiting from one of the general solutions,the obtained smooth state feedback controller for the Acrobots is of a more general form.Specifically,a constant fixed in a related paper by the system parameters is converted into a controller parameter ranging over an open interval along with some new nonlinear terms involved.Unlike what is mentioned in the related paper,some categories of the Acrobots cannot be stabilized with the existing interconnection and damping assignment passivity based control(IDA-PBC)method.As a contribution,the system can be locally asymptotically stabilized by the selection of the new controller parameter except for only one special case.展开更多
基金supported by Projects of International Cooperation and Exchanges NSFC (51720105009)the National Natural Science Foundation of China (No. 51575147)the Youth Talent Support Program of Harbin University of Science and Technology (201507)
文摘Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of research has been dedicated to the development of technologies that are able to predict and detect chatter. The purpose of these technologies is to facilitate the avoidance of chatter during cutting processes, which leads to better surface precision, higher productivity,and longer tool life. This paper summarizes the current state of the art in research regarding the problems of how to arrive at stable chatter prediction, chatter identification, and chatter control/-suppression, with a focus on milling processes. Particular focus is placed on the theoretical relationship between cutting chatter and process damping, tool runout, and gyroscopic effect, as well as the importance of this for chatter prediction. The paper concludes with some reflections regarding possible directions for future research in this field.
文摘Traditional PID controllers are no longer suitable formagnetic-bearing-supported high-speed flywheels with significant gyroscopic effects. Becausegyroscopic effects greatly influence the stability of the flywheel rotor, especially at highrotational speeds. Velocity cross feedback and displacement cross feedback are used to overcomeharmful effects of nutation and precession modes, and stabilize the rotor at high rotational speeds.Theoretical analysis is given to show their effects. A control platform based on RTLinut and a PCis built to control the active magnetic bearing (AMB) system, and relevant results are reported.Using velocity cross feedback and displacement cross feedback in a closed loop control system, theflywheel successfully runs at over 20000 r/min.
基金the National Natural Science Foundation of China(Grants 11772009,11672007)the Beijing Municipal Natural Science Foundation(Grant 3172003).
文摘Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyroscopic modes decoupling method is used to obtain an equivalent system with decoupled gyroscopic modes having only weak couplings.Taking the axially moving string as an example,the instability boundaries in the vicinity of parametric resonances are detected using both the traditional coupled gyroscopic system and our system with decoupled gyroscopic modes,and the results are compared to show the advantages and disadvantages of each method.
基金supported by the National Natural Science Foundation of China (61503392)。
文摘This study presents a kinematic calibration method for exoskeletal inertial motion capture (EI-MoCap) system with considering the random colored noise such as gyroscopic drift.In this method, the geometric parameters are calibrated by the traditional calibration method at first. Then, in order to calibrate the parameters affected by the random colored noise, the expectation maximization (EM) algorithm is introduced. Through the use of geometric parameters calibrated by the traditional calibration method, the iterations under the EM framework are decreased and the efficiency of the proposed method on embedded system is improved. The performance of the proposed kinematic calibration method is compared to the traditional calibration method. Furthermore, the feasibility of the proposed method is verified on the EI-MoCap system. The simulation and experiment demonstrate that the motion capture precision is significantly improved by 16.79%and 7.16%respectively in comparison to the traditional calibration method.
基金supported by the National Natural Science Foundation of China (Grant Nos.60936001, 11021262 and 11011120245)the National Basic Research Program of China (Grant No. 2007CB310500)
文摘As the nano-motor becomes a mechanical reality, its prototype can be envisaged as nano-sized rotating machinery at a situation,albeit for different purposes, like that in the first half of the 20th century during which rotor dynamics has contributed toboosting machine power capacity. Accordingly, we take the benefit of hindsight to develop a classical framework of vibrationanalysis. Essentially, the equations of motion are formulated to cope with both the special carbon-nanotube properties and thefirst author’s previously developed spinning beam formalism, establishing a model satisfactorily verified by some availablemolecular dynamics (MD) data and classical spinning beam results extracted from the literature. The model is inexpensivebased on continuum mechanics as an alternative to the less-flexible MD method for simulating wave motion of the spinningsingle-walled carbon nanotube, yielding several interesting phenomena, including the fall-off and splitting of the wave charac-teristic curves and the unexpected gyroscopic phase property. Potential applications are proposed.
基金Project supported by the National Natural Science Foundation of China(No.10372019)the Doctoral Fund of Ministry of Education of China(No.20010141024)
文摘Gyroscopic dynamic system can be introduced to Hamiltonian system. Based on an adjoint symplectic subspace iteration method of Hamiltonian gyroscopic system, an adjoint symplectic subspace iteration method of indefinite Hamiltonian function gyroscopic system was proposed to solve the eigenvalue problem of indefinite Hamiltonian function gyroscopic system. The character that the eigenvalues of Hamiltonian gyroscopic system are only pure imaginary or zero was used. The eigenvalues that Hamiltonian function is negative can be separated so that the eigenvalue problem of positive definite Hamiltonian function system was presented, and an adjoint symplectic subspace iteration method of positive definite Hamiltonian function system was used to solve the separated eigenvalue problem. Therefore, the eigenvalue problem of indefinite Hamiltonian function gyroscopic system was solved, and two numerical examples were given to demonstrate that the eigensolutions converge exactly.
文摘The dynamic response of an axially traveling laminated composite beam is investigated analytically,with special consideration to natural frequencies,complex mode functions and critical speeds of the system.The equation of motion for a symmetrically laminated system,which is in the form of a continuous gyroscopic system,is considered;the equation of motion is not discretized — no spatial mode function is assumed.This leads to analytical expressions for the complex mode functions and critical speeds.A parametric study has been conducted in order to highlight the effects of system parameters on the above-mentioned vibration characteristics of the system.
文摘Rotating machinery is an essential and crucial component of numerous mechanical systems in modern industries,transport vehicles,and in several other applications.Excessive vibrations on rotating equipment due to multiple faults may cause catastrophic failure in machines and lead to hazardous accidents.So,there is a need for perceiving the dynamic nature and identifying the faults for the safe,smooth and effective operation of machines.This paper proposes a novel trial misalignment approach to estimate the misalignment with a similar concept as the trial unbalance in the rotor balancing.Active magnetic bearing(AMB)misalignment with the rotor has been investigated with residual misalignment and additional trial misalignment cases.Additional trial misalignments are provided in addition to the unknown misalignments of the residual misalignment case.For the execution of this methodology,the dynamic model of a four-degree-of-freedom unbalanced and misaligned rigid rotor with two offset discs supported by two active magnetic bearings has been mathematically developed.The offset discs result in the gyroscopic effect at high rotor speeds.Equations of motion of the rotor-AMB system have been derived and solved to generate the time domain rotor displacement and controlling current responses at AMB positions.A fast Fourier transform technique has been utilized to convert the time domain responses into the frequency domain for estimation of unbalance eccentricities and phases together with force-displacement and forcecurrent stiffnesses of misaligned AMBs as well as AMB's constant forces using the developed identification algorithm.Identified values of AMB's parameters for both residual and additional trial misalignment cases are evaluated to estimate the four unknown misalignments.Testing of the algorithm has also been carried out at multiple spin speeds against measurement signal noise in rotor responses and bias errors in rotor system parameters to check its effectiveness and robustness.The algorithm is found to be exhi
基金the National Natural Science Foundation of China(Nos.11922205 and 11672071)the Liaoning Revitalization Talents Program(No.XLYC1807026)the Fundamental Research Funds for the Central Universities(No.N2005019)。
文摘An efficient method is developed to investigate the vibration and stability of moving plates immersed in fluid by applying the Kirchhoff plate theory and finite element method.The fluid is considered as an ideal fluid and is described with Bernoulli’s equation and the linear potential flow theory.Hamilton’s principle is used to acquire the dynamic equations of the immersed moving plate.The mass matrix,stiffness matrix,and gyroscopic inertia matrix are determined by the exact analytical integration.The numerical results show that the fundamental natural frequency of the submersed moving plates gradually decreases to zero with an increase in the axial speed,and consequently,the coupling phenomenon occurs between the first-and second-order modes.It is also found that the natural frequency of the submersed moving plates reduces with an increase in the fluid density or the immersion level.Moreover,the natural frequency will drop obviously if the plate is located near the rigid wall.In addition,the developed method has been verified in comparison with available results for special cases.
基金supported by Thailand Science Research and Innovation and the National Research Council of Thailand under Grant RGU6280014.
文摘This paper presents a theoretical and experimental study on controller design for the AMBs in a small-scale flywheel energy storage system,where the main goals are to achieve low energy consumption and improved rotordynamic stability.A H-infinity optimal control synthesis procedure is defined for the permanent-magnet-biased AMB-rotor system with 4 degrees of freedom.Through the choice of design weighting functions,notch filter characteristics are incorporated within the controller to reduce AMB current components caused by rotor vibration at the synchronous frequency and higher harmonics.Experimental tests are used to validate the controller design methodology and provide comparative results on performance and efficiency.The results show that the H-infinity controller is able to achieve stable rotor levitation and reduce AMB power consumption by more than 40%(from 4.80 to 2.64 Watts)compared with the conventional PD control method.Additionally,the H-infinity controller can prevent vibrational instability of the rotor nutation mode,which is prone to occur when operating with high rotational speeds.
基金supported by the National Natural Science Foundation of China(Nos.12072181 and 12121002)the State Key Laboratory of Mechanical System and Vibration of China(No.MSV202105)。
文摘The axial fluid-induced vibration of pipes is very widespread in engineering applications.The nonlinear forced vibration of a viscoelastic fluid-conveying pipe with nonlinear supports at both ends is investigated.The multi-scale method combined with the modal revision method is formulated for the fluid-conveying pipe system with nonlinear boundary conditions.The governing equations and the nonlinear boundary conditions are rescaled simultaneously as linear inhomogeneous equations and linear inhomogeneous boundary conditions on different time-scales.The modal revision method is used to transform the linear inhomogeneous boundary problem into a linear homogeneous boundary problem.The differential quadrature element method(DQEM)is used to verify the approximate analytical results.The results show good agreement between these two methods.A detailed analysis of the boundary nonlinearity is also presented.The obtained results demonstrate that the boundary nonlinearities have a significant effect on the dynamic characteristics of the fluid-conveying pipe,and can lead to significant differences in the dynamic responses of the pipe system.
文摘A spinning gyroscope precesses about the vertical due to a torque acting upon the wheel. The torque is generated by the shift of moment of force by gravity and it points to the vertical instead of the tangential direction of precession. This intuition offers an alternative and straightforward view of precession dynamics in comparison with the literature. It also presumes a dynamic balance of momentum between circular motions of the wheel spin and precession. Accordingly, the gyroscopic dynamics is then applied to the study of galactic motion of the solar system in space and the Galactic mass is calculated with the inclusion of gyroscopic effect of the solar planets. Results indicate that the gyroscopic effect of Mercury orbiting around the Sun can increase the calculated Galactic mass by 23% in comparison with the result obtained by the classic approach.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11622215, 11572039, and 11521062)the "111" Project (Grant No. B16003)
文摘Unusual one-way edge states have been observed in composite structures composed of periodic lattices loaded with gyroscopes.Here, we provide a continuum-mechanics understanding to the one-way edge state by formulating surface state equations of acoustic gyroscopic mediums with Hermite mass density tensor. We discover that the unidirectional edge effect arises from nontrivial off-diagonal components of Hermite densities, which causes the symmetric breaking of surface wave propagation towards forward and backward directions. Theoretical predictions on the velocity and decay length of surface waves coincide excellently with numerical simulations. The unidirectional edge state in a two-interface gyroscopic medium is also analyzed.Due to the rotational symmetry in geometry, the unidirectional edge state on one interface is able to prevent itself from the coupling to surface waves on the other interface regardless of the slab thickness. With these anomalous effects, surface waves residing on gyroscopic mediums can flow around the edge defects without back-scatterings, or can be split into two beams of equal energy magnitudes. Our findings may make a bridge that would help to reach the design of non-reciprocal composite materials via an effective medium approach.
基金the National Science Foundation of Chinathe Doctoral Training of Education Committee of China
文摘This paper gives a dynamic decoupling approach for the analysis of large scale non-classically damped system, in which the complex variable computations were completely avoided not only in solving for the eigenvalue problem but also in the calculation of the dynamic response. The analytical approaches for undamped gyroscopic system, non-classically damped system, including the damped gyroscopic system were unified. Very interesting and useful theoretical results, practical algorithms were obtained which are applicable to both non-defective and defective systems.
文摘To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validated through ground tests.The fake gyroscopic torque is first proposed,which the vector mechanism should overcome besides the inertial torque and the gravitational torque.The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane,appears only when the propeller is rotating and is proportional with the rotation speed.It is a sinusoidal pulse,with a frequency that is twice of the rotation speed.Considering the fake gyroscope torque pulse and aerodynamic efficiency,three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.
基金sponsored by EPSRC ICASE Grant reference 1700064BAE Systems。
文摘This paper gives a succinct review of dual-spinprojectile stability and some technologies relating to them.It describes how the traditional stability factors from linear projectile theory are modified to better describe a controlled dual-spin projectile.Finally,it reviews works which have investigated how different aspects of a controlled dual-spin design can affect flight stability,primarily airframe structure and canard properties.A conclusion is given,highlighting important guidelines from the enclosed discussions.
基金the National Natural Science Foundation of China (Project Nos. 11672007, 11672189)the Key Laboratory of Vibration and Control of Aero-Propulsion System Ministry of Education, Northeastern University (VCAME201601)Beijing Natural Science Foundation (Project No. 3172003).
文摘In this paper, the coupled bending-bending-axial-torsional free vibrations of rotating blades are investigated based on the Euler-Bernoulli beam model. The coupled partial differential equations governing flapwisc, edgewise, axial and torsional motions are derived by the Hamilton's principle, wherein three types of velocity-dependent terms, namely static centrifugal terms, dynamic centrifugal terms and gyroscopic coupling terms, are focused. The ordinary di& ferential equations are acquired by the Galerkin truncation, and the natural frequencies in all directions and complex mode shapes of the rotating blades are analyzed in detail. It is revealed that the three types of velocity-dependent terms have different effects on the natural frequencies. The natural frequencies are noticeably dependent on the rotating speed and preset angle, except for the axial vibration, which is almost immune to the preset angle. The complex modal motions are displayed by a series of positions of the central line and free-end cross section for different time instants, showing the coupled vibrations among different directions.
文摘On the basis of controlled Lagrangians,a controller design is proposed for underactuated mechanical systems with two degrees of freedom.A new kinetic energy equation(K-equation)independent of the gyroscopic forces is found due to the use of their property.As a result,the necessary and sufficient matching condition comprises the new K-equation and the potential energy equation(P-equation)cascaded,the regular condition,and the explicit gyroscopic forces.Further,for two classes of input decoupled systems that cover the main benchmark examples,the new K-equation,respectively,degenerates from a quasilinear partial differential equation(PDE)into an ordinary differential equation(ODE)under some choice and into a homogeneous linear PDE with two kinds of explicit general solutions.Benefiting from one of the general solutions,the obtained smooth state feedback controller for the Acrobots is of a more general form.Specifically,a constant fixed in a related paper by the system parameters is converted into a controller parameter ranging over an open interval along with some new nonlinear terms involved.Unlike what is mentioned in the related paper,some categories of the Acrobots cannot be stabilized with the existing interconnection and damping assignment passivity based control(IDA-PBC)method.As a contribution,the system can be locally asymptotically stabilized by the selection of the new controller parameter except for only one special case.
