We study the effects of mechanical nonlinearity arising from large thickness-shear deformation on the transient process of an AT-cut quartz plate resonator. Mindlin＇s two-dimensional plate equation is used, from whic...We study the effects of mechanical nonlinearity arising from large thickness-shear deformation on the transient process of an AT-cut quartz plate resonator. Mindlin＇s two-dimensional plate equation is used, from which a system of first-order nonlinear differential equations governing the evolution of the vibration amplitude is obtained. Numerical solutions by the Runge-Kutta method show that in common operating conditions of quartz resonators the nonlinear effect varies from noticeable to significant. As resonators are to be made smaller and thinner in the future with about the same power requirement, nonlinear effects will become more important and need more understanding and consideration in resonator design.展开更多
An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current...An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.展开更多
Considering the same initial state error in each repetitive operation in the iterative learning system, a method of arranging the transient process is given. During the current iteration, the system will track the tra...Considering the same initial state error in each repetitive operation in the iterative learning system, a method of arranging the transient process is given. During the current iteration, the system will track the transient function firstly, and then the expected trajectory. After several iterations, the learning system output will trend to the arranged curve, which has avoided the effect of the initial error on the controller. Also the transient time can be changed as you need, which makes the designing simple and the operation easy. Then the detailed designing steps are given via the robot system. At last the simulation of the robot system is given, which shows the validity of the method.展开更多
The 1/3 sub-harmonic solution for the Duffing＇s with damping equation was investigated by using the methods of harmonic balance and numerical integration. The assumed solution is introduced, and the domain of sub-har...The 1/3 sub-harmonic solution for the Duffing＇s with damping equation was investigated by using the methods of harmonic balance and numerical integration. The assumed solution is introduced, and the domain of sub-harmonic frequencies was found. The asymptotical stability of the subharmonic resonances and the sensitivity of the amplitude responses to the variation of damping coefficient were examined. Then, the subharmonic resonances were analyzed by using the techniques from the general fractal theory. The analysis indicates that the sensitive dimensions of the system time-field responses show sensitivity to the conditions of changed initial perturbation, changed damping coefficient or the amplitude of excitation, thus the sensitive dimension can clearly describe the characteristic of the transient process of the subharmonic resonances.展开更多
The 1/3 subharmonic solution for the Duffing’s equation is investigated by using the methods of harmonic balance and numerical integration. The sensitivity of parameter variation for the transient process and the tra...The 1/3 subharmonic solution for the Duffing’s equation is investigated by using the methods of harmonic balance and numerical integration. The sensitivity of parameter variation for the transient process and the transient process for the perturbance initial conditions are studied. Over and above, the precision of numerical integration method is discussed and the numerical integration method is compared with the harmonic balance method. Finally, asymptotical stability of the pure subharmonic oscillations element is inspected.展开更多
This paper investigates the effect of carried-envelope phase on transient process in a cascade-type atomic system, which is driven by two ultrashort laser pulses （probe and signal laser）. It is found that the one- a...This paper investigates the effect of carried-envelope phase on transient process in a cascade-type atomic system, which is driven by two ultrashort laser pulses （probe and signal laser）. It is found that the one- and two-photon processes corresponding to pathway ｜0〉→｜1〉and ｜0〉→｜1〉→｜2〉 can be enhanced or ,suppressed by modulating the carried-envelope phases of probe laser pulse. Our numerical results also show that the transient populations of two excited states can be periodically affected by the carried-envelope phase of probe laser pulse. With certain time, the partial population transfer between two exited states can be realized just by adjusting the carried-envelope phase of probe laser pulse.展开更多
By applying a nonlinear control and arranging a transient process, the initiative error of the pneumatic servo positioning system is reduced largely, and a larger gain of the controller is used to improve the respondi...By applying a nonlinear control and arranging a transient process, the initiative error of the pneumatic servo positioning system is reduced largely, and a larger gain of the controller is used to improve the responding speed of the system at the same damping ratio. Therefore, a compromise is made among the responding speed, overshoot, robustness, adaptability and stability. In addition, a dynamic output feedback controller, including position velocity and acceleration （PVA） feedback, is designed to improve the performance of the system. And a nonlinear controller is reconstructed based on the linear output feedback controller to decrease noises and disturbances. The dynamic responses of the system are simulated and tested. Results show that the error is kept within 0.02 mm under different mass loads and the positioning transient process is smooth, without overshoot and speedy.展开更多
A mathematical model for analysing transient process of AC silent discharge isestablished from its physical model.Then,the breakdown characteristics and the dependence ofdischarge current density on time are calculate...A mathematical model for analysing transient process of AC silent discharge isestablished from its physical model.Then,the breakdown characteristics and the dependence ofdischarge current density on time are calculated theoretically in this kind of AC silent discharge.They are compared with the experimental results and the deviation between the theoretical andexperimental results are discussed briefly.展开更多
The adjustment and the regeneration of the flow field unstructuredmesh as well as the fi- nitelement solutions for the Euler equationsin the transient process of the separation o external stores form anaircraft at a p...The adjustment and the regeneration of the flow field unstructuredmesh as well as the fi- nitelement solutions for the Euler equationsin the transient process of the separation o external stores form anaircraft at a predetermined downward translation and rotation areinvestigated. It is shown that the adjustment or regeneration ofgrids needed for moving store can be confined within a small regionaround the store and the finite element numerical solution method ofEuler equations for fixed grids can also be used for moving grids ifthe conservative fluxes F_k of fixed grids are replaced by E_k ofmoving grids. The relation-ships between F_k and E_k are alsoestablished. The numerical results For practical examples of aircraftwith external stores are shown.展开更多
The annealing time is an important affecting factor in the performance of many furnaces.The present work deals with the transient simulation of annealing process in a cubic furnace in which a solid element is placed i...The annealing time is an important affecting factor in the performance of many furnaces.The present work deals with the transient simulation of annealing process in a cubic furnace in which a solid element is placed in its center.As the working gas can have some radiating features,a set of governing equations including the energy balance with the radiative transfer equation(RTE)for the gray radiating medium and the conduction equation inside the solid product are numerically solved with progressing in time.Numerical results which are validated against both analytical and theoretical findings in the literature demonstrate that during the starting period,a high rate of radiant energy transfers into the solid body even at small optical thickness.This behavior which hastens the rate of heat transfer at low values of the radiation conduction parameter,causes a fast annealing process in which the solid body warms up to its maximum temperature.Moreover,it is revealed that the rate of heat transfer is an increasing function of radiation-conduction parameter.展开更多
The main goal of this paper is to study the characteristics of regression rate of solid grain during thrust regulation process. For this purpose, an unsteady numerical model of regression rate is established. Gas–sol...The main goal of this paper is to study the characteristics of regression rate of solid grain during thrust regulation process. For this purpose, an unsteady numerical model of regression rate is established. Gas–solid coupling is considered between the solid grain surface and combustion gas.Dynamic mesh is used to simulate the regression process of the solid fuel surface. Based on this model, numerical simulations on a H2O2/HTPB（hydroxyl-terminated polybutadiene） hybrid motor have been performed in the flow control process. The simulation results show that under the step change of the oxidizer mass flow rate condition, the regression rate cannot reach a stable value instantly because the flow field requires a short time period to adjust. The regression rate increases with the linear gain of oxidizer mass flow rate, and has a higher slope than the relative inlet function of oxidizer flow rate. A shorter regulation time can cause a higher regression rate during regulation process. The results also show that transient calculation can better simulate the instantaneous regression rate in the operation process.展开更多
With permanent down-hole gauges （PDGs） widely installed in oilfields around the world in recent years, a continuous stream of transient pressure data in real time is now available, which motivates a new round of res...With permanent down-hole gauges （PDGs） widely installed in oilfields around the world in recent years, a continuous stream of transient pressure data in real time is now available, which motivates a new round of research interests in further developing pressure transient processing and analysis techniques. Transient pressure measurements from PDG are characterized by long term and high volume data. These data are recorded under unconstrained circumstances, so effects due to noise, rate fluctuation and interference from other wells cannot be avoided. These effects make the measured pressure trends decline or rise and then obscure or distort the actual flow behavior, which makes subsequent analysis difficult. In this paper, the problems encountered in analysis of PDG transient pressure are investigated. A newly developed workflow for processing and analyzing PDG transient pressure data is proposed. Numerical well testing synthetic studies are performed to demonstrate these procedures. The results prove that this new technique works well and the potential for practical application looks very promising.展开更多
In this study, a two-step heating process is introduced for transient liquid phase ( TLP) diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating ...In this study, a two-step heating process is introduced for transient liquid phase ( TLP) diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9/ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend's strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.展开更多
Unstable operating conditions such as surge could cause damage to both aerodynamic performance and structural integrity of a compression system.This paper addresses the critical issue of aerodynamic instability in com...Unstable operating conditions such as surge could cause damage to both aerodynamic performance and structural integrity of a compression system.This paper addresses the critical issue of aerodynamic instability in compressor design,particularly focusing on an axial-centrifugal combined compressor,a widely used yet underexplored configuration.An experimental investigation was conducted on a three-stage axial and one-stage centrifugal compressor(3A1C),using two pipe systems and employing fast-responding transducers to capture the dynamic instability process from choke condition to deep surge.Results reveal that at the design speed,3A1C enters deep surge directly,whereas at off-design speeds,it experiences rotating stall and mild surge across a wide mass flow range.Some special instability features in the combined compressor can be found in the steady state map and dynamic process.The characteristic curve of the first axial stage keeps a positive slope during the whole mass flow range at an off-design speed.The first stage could work stably on the stall characteristic curve because the centrifugal stage has stronger pressurization and plays a dominant role in global aerodynamic instability.Besides,rotating instability occurs at the first rotor tip and disappears as the back pressure increases,which is also rarely seen in a single-axial compressor.This is also related to the strong pressurization of the centrifugal stage.The findings of this paper will contribute to the understanding of aerodynamic instabilities in combined compressors.展开更多
Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the ra...Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the random code(Rcode)used in traditional UCI will lead to low-frequency noise covering high-frequency information due to its uneven sampling interval,which is a great challenge in the fidelity of large-frame reconstruction.Here,a high-frequency enhanced compressed active photography(H-CAP)is proposed.By uniformizing the sampling interval of R-code,H-CAP capture the ultrafast process with a random uniform sampling mode.This sampling mode makes the high-frequency sampling energy dominant,which greatly suppresses the low-frequency noise blurring caused by R-code and achieves high-frequency information of image enhanced.The superior dynamic performance and large-frame reconstruction ability of H-CAP are verified by imaging optical self-focusing effect and static object,respectively.We applied H-CAP to the spatial-temporal characterization of double-pulse induced silicon surface ablation dynamics,which is performed within 220 frames in a single-shot of 300 ps.H-CAP provides a high-fidelity imaging method for observing ultrafast unrepeatable dynamic processes with large frames.展开更多
基金supported by the Program for New Century Excellent Talents in Universities(No.NCET-12-0625)the Natural Science Foundation for Distinguished Young Scholars of Jiangsu Province(No.SBK2014010134)+2 种基金the Fundamental Research Funds for Central Universities(No.NE2013101)the National Natural Science Foundation of China(No.11232007)a project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘We study the effects of mechanical nonlinearity arising from large thickness-shear deformation on the transient process of an AT-cut quartz plate resonator. Mindlin＇s two-dimensional plate equation is used, from which a system of first-order nonlinear differential equations governing the evolution of the vibration amplitude is obtained. Numerical solutions by the Runge-Kutta method show that in common operating conditions of quartz resonators the nonlinear effect varies from noticeable to significant. As resonators are to be made smaller and thinner in the future with about the same power requirement, nonlinear effects will become more important and need more understanding and consideration in resonator design.
基金Project supported by the National Natural Science Foundation of China （Grant No 0475012） and partially by Technology ＆ Science Foundation of China Academy of Engineering ＆ Physics （Grant No 20040210）.
文摘An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.
文摘Considering the same initial state error in each repetitive operation in the iterative learning system, a method of arranging the transient process is given. During the current iteration, the system will track the transient function firstly, and then the expected trajectory. After several iterations, the learning system output will trend to the arranged curve, which has avoided the effect of the initial error on the controller. Also the transient time can be changed as you need, which makes the designing simple and the operation easy. Then the detailed designing steps are given via the robot system. At last the simulation of the robot system is given, which shows the validity of the method.
基金Project supported by the National Natural Science Foundation of China (No.50275024)
文摘The 1/3 sub-harmonic solution for the Duffing＇s with damping equation was investigated by using the methods of harmonic balance and numerical integration. The assumed solution is introduced, and the domain of sub-harmonic frequencies was found. The asymptotical stability of the subharmonic resonances and the sensitivity of the amplitude responses to the variation of damping coefficient were examined. Then, the subharmonic resonances were analyzed by using the techniques from the general fractal theory. The analysis indicates that the sensitive dimensions of the system time-field responses show sensitivity to the conditions of changed initial perturbation, changed damping coefficient or the amplitude of excitation, thus the sensitive dimension can clearly describe the characteristic of the transient process of the subharmonic resonances.
文摘The 1/3 subharmonic solution for the Duffing’s equation is investigated by using the methods of harmonic balance and numerical integration. The sensitivity of parameter variation for the transient process and the transient process for the perturbance initial conditions are studied. Over and above, the precision of numerical integration method is discussed and the numerical integration method is compared with the harmonic balance method. Finally, asymptotical stability of the pure subharmonic oscillations element is inspected.
文摘This paper investigates the effect of carried-envelope phase on transient process in a cascade-type atomic system, which is driven by two ultrashort laser pulses （probe and signal laser）. It is found that the one- and two-photon processes corresponding to pathway ｜0〉→｜1〉and ｜0〉→｜1〉→｜2〉 can be enhanced or ,suppressed by modulating the carried-envelope phases of probe laser pulse. Our numerical results also show that the transient populations of two excited states can be periodically affected by the carried-envelope phase of probe laser pulse. With certain time, the partial population transfer between two exited states can be realized just by adjusting the carried-envelope phase of probe laser pulse.
基金The National Natural Science Foundation of China (No.50085002)
文摘By applying a nonlinear control and arranging a transient process, the initiative error of the pneumatic servo positioning system is reduced largely, and a larger gain of the controller is used to improve the responding speed of the system at the same damping ratio. Therefore, a compromise is made among the responding speed, overshoot, robustness, adaptability and stability. In addition, a dynamic output feedback controller, including position velocity and acceleration （PVA） feedback, is designed to improve the performance of the system. And a nonlinear controller is reconstructed based on the linear output feedback controller to decrease noises and disturbances. The dynamic responses of the system are simulated and tested. Results show that the error is kept within 0.02 mm under different mass loads and the positioning transient process is smooth, without overshoot and speedy.
基金Supported by National Natural Science Foundation of China
文摘A mathematical model for analysing transient process of AC silent discharge isestablished from its physical model.Then,the breakdown characteristics and the dependence ofdischarge current density on time are calculated theoretically in this kind of AC silent discharge.They are compared with the experimental results and the deviation between the theoretical andexperimental results are discussed briefly.
文摘The adjustment and the regeneration of the flow field unstructuredmesh as well as the fi- nitelement solutions for the Euler equationsin the transient process of the separation o external stores form anaircraft at a predetermined downward translation and rotation areinvestigated. It is shown that the adjustment or regeneration ofgrids needed for moving store can be confined within a small regionaround the store and the finite element numerical solution method ofEuler equations for fixed grids can also be used for moving grids ifthe conservative fluxes F_k of fixed grids are replaced by E_k ofmoving grids. The relation-ships between F_k and E_k are alsoestablished. The numerical results For practical examples of aircraftwith external stores are shown.
文摘The annealing time is an important affecting factor in the performance of many furnaces.The present work deals with the transient simulation of annealing process in a cubic furnace in which a solid element is placed in its center.As the working gas can have some radiating features,a set of governing equations including the energy balance with the radiative transfer equation(RTE)for the gray radiating medium and the conduction equation inside the solid product are numerically solved with progressing in time.Numerical results which are validated against both analytical and theoretical findings in the literature demonstrate that during the starting period,a high rate of radiant energy transfers into the solid body even at small optical thickness.This behavior which hastens the rate of heat transfer at low values of the radiation conduction parameter,causes a fast annealing process in which the solid body warms up to its maximum temperature.Moreover,it is revealed that the rate of heat transfer is an increasing function of radiation-conduction parameter.
基金co-supported by the Innovation Foundation of Beihang University for Ph.D. Graduatesthe National Natural Science Foundation of China (No. 51206007)
文摘The main goal of this paper is to study the characteristics of regression rate of solid grain during thrust regulation process. For this purpose, an unsteady numerical model of regression rate is established. Gas–solid coupling is considered between the solid grain surface and combustion gas.Dynamic mesh is used to simulate the regression process of the solid fuel surface. Based on this model, numerical simulations on a H2O2/HTPB（hydroxyl-terminated polybutadiene） hybrid motor have been performed in the flow control process. The simulation results show that under the step change of the oxidizer mass flow rate condition, the regression rate cannot reach a stable value instantly because the flow field requires a short time period to adjust. The regression rate increases with the linear gain of oxidizer mass flow rate, and has a higher slope than the relative inlet function of oxidizer flow rate. A shorter regulation time can cause a higher regression rate during regulation process. The results also show that transient calculation can better simulate the instantaneous regression rate in the operation process.
基金Science Foundation of China University of Petroleum, Beijing (No.YJRC-2011-02)for the financial support during this research
文摘With permanent down-hole gauges （PDGs） widely installed in oilfields around the world in recent years, a continuous stream of transient pressure data in real time is now available, which motivates a new round of research interests in further developing pressure transient processing and analysis techniques. Transient pressure measurements from PDG are characterized by long term and high volume data. These data are recorded under unconstrained circumstances, so effects due to noise, rate fluctuation and interference from other wells cannot be avoided. These effects make the measured pressure trends decline or rise and then obscure or distort the actual flow behavior, which makes subsequent analysis difficult. In this paper, the problems encountered in analysis of PDG transient pressure are investigated. A newly developed workflow for processing and analyzing PDG transient pressure data is proposed. Numerical well testing synthetic studies are performed to demonstrate these procedures. The results prove that this new technique works well and the potential for practical application looks very promising.
基金supported by the Natural Science Foundation of Henan Province(Grant No.152107000047)
文摘In this study, a two-step heating process is introduced for transient liquid phase ( TLP) diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9/ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend's strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.
基金supported by the National Science and Technology Major Project of China(Nos.2017-II-0004-0016 and J2019-I-0011-0011).
文摘Unstable operating conditions such as surge could cause damage to both aerodynamic performance and structural integrity of a compression system.This paper addresses the critical issue of aerodynamic instability in compressor design,particularly focusing on an axial-centrifugal combined compressor,a widely used yet underexplored configuration.An experimental investigation was conducted on a three-stage axial and one-stage centrifugal compressor(3A1C),using two pipe systems and employing fast-responding transducers to capture the dynamic instability process from choke condition to deep surge.Results reveal that at the design speed,3A1C enters deep surge directly,whereas at off-design speeds,it experiences rotating stall and mild surge across a wide mass flow range.Some special instability features in the combined compressor can be found in the steady state map and dynamic process.The characteristic curve of the first axial stage keeps a positive slope during the whole mass flow range at an off-design speed.The first stage could work stably on the stall characteristic curve because the centrifugal stage has stronger pressurization and plays a dominant role in global aerodynamic instability.Besides,rotating instability occurs at the first rotor tip and disappears as the back pressure increases,which is also rarely seen in a single-axial compressor.This is also related to the strong pressurization of the centrifugal stage.The findings of this paper will contribute to the understanding of aerodynamic instabilities in combined compressors.
基金supported by the National Science Foundation of China(No.12127806,No.62175195 and No.12304382)the International Joint Research Laboratory for Micro/Nano Manufacturing and Measurement Technologies.
文摘Single-shot ultrafast compressed imaging(UCI)is an effective tool for studying ultrafast dynamics in physics,chemistry,or material science because of its excellent high frame rate and large frame number.However,the random code(Rcode)used in traditional UCI will lead to low-frequency noise covering high-frequency information due to its uneven sampling interval,which is a great challenge in the fidelity of large-frame reconstruction.Here,a high-frequency enhanced compressed active photography(H-CAP)is proposed.By uniformizing the sampling interval of R-code,H-CAP capture the ultrafast process with a random uniform sampling mode.This sampling mode makes the high-frequency sampling energy dominant,which greatly suppresses the low-frequency noise blurring caused by R-code and achieves high-frequency information of image enhanced.The superior dynamic performance and large-frame reconstruction ability of H-CAP are verified by imaging optical self-focusing effect and static object,respectively.We applied H-CAP to the spatial-temporal characterization of double-pulse induced silicon surface ablation dynamics,which is performed within 220 frames in a single-shot of 300 ps.H-CAP provides a high-fidelity imaging method for observing ultrafast unrepeatable dynamic processes with large frames.
