This study predicts the characteristics of a compressible polytropic air spring model. A second-order nonlinear autonomous air spring model is presented. The proposed model is based on the assumption that polytropic p...This study predicts the characteristics of a compressible polytropic air spring model. A second-order nonlinear autonomous air spring model is presented. The proposed model is based on the assumption that polytropic processes occur. Isothermal and isentropic compression and expansion of the air within the spring chambers are the two scenarios that are taken into consideration. In these situations, the air inside the spring chambers compresses and expands, resulting in nonlinear spring restoring forces. The MATLAB/Simulink software environment is used to build a numerical simulation model for the dynamic behavior of the air spring. To quantify the values of the stiffnesses of the proposed models, a numerical solution is run over time for various values of the design parameters. The isentropic process case has a higher dynamic air spring stiffness than the isothermal process case, according to the results. The size of the air spring chamber and the area of the air spring piston influence the air spring stiffness in both situations. It is demonstrated that the stiffness of the air spring increases linearly with increasing piston area and decreases nonlinearly with increasing air chamber length. As long as the ratio of the vibration’s amplitude to the air spring’s chamber length is small, there is good agreement in both scenarios between the linearized model and the full nonlinear model. This implies that linear modeling is a reasonable approximation of the complete nonlinear model in this particular scenario.展开更多
To reduce the roll movement of an air spring passenger car, an active anti-roll system is developed, which is constructed with hydraulic and pneumatic units to change spring rate during cornering. For the comparing re...To reduce the roll movement of an air spring passenger car, an active anti-roll system is developed, which is constructed with hydraulic and pneumatic units to change spring rate during cornering. For the comparing research between the passive and active system, a two-track vehicle model and a co-simulation model of air spring system are built. For the simulation research on the linear movement of the actuator, a mathematical model is considered as dynamical subsystem in the co-simulation model. To active control the roll angle of vehicle body, a sliding-mode controller with optimized control parameters for the test vehicle is introduced into the model. The characteristics of sliding-mode controller is discussed and the validation of active antiroll control is proved by comparison with other control methods. The results show that the roll angle of air spring vehicle is reduced obviously with the active anti-roll actuator in comparison with that of the passive system. Compared with other control methods, sliding-mode controller has an advantage of shortest switching times, which leads to a longer lifetime of actuator and valves.展开更多
On the basis of analyzing the result of numerical simulation and that of theoretical analysis,the systematic error of some air spring's theoretical formula is researched. The result shows that the vertical stiffne...On the basis of analyzing the result of numerical simulation and that of theoretical analysis,the systematic error of some air spring's theoretical formula is researched. The result shows that the vertical stiffness's theoretical formula of air spring owes the systematic error. And the systematic error is relative to the three supposed conditions which are used in the process of theoretical deduction. However,the systematic error is small enough so that the supposed conditions of theoretical formula are reasonable. Moreover,with the increase of initial inner pressure,the systematical error increases.展开更多
No-tillage planters need to be equipped with row cleaners to remove post-harvest plant residue from the seedbed.The two-disc row cleaners cannot effectively remove the plant residue at high speed because the working d...No-tillage planters need to be equipped with row cleaners to remove post-harvest plant residue from the seedbed.The two-disc row cleaners cannot effectively remove the plant residue at high speed because the working depth is unstable,which leads to poor seeding quality of the seeder.A straw cleaning unit with double air springs was designed to achieve better straw cleaning performance at high speeds.The analysis of the mechanical characteristics of the double air spring system showed that it enabled separate adjustment of force and stiffness.A dynamic model of the straw cleaning unit was established,and the effectiveness of the double air spring system with adjustable stiffness in stabilizing the working depth of the row cleaners was analyzed.Field experiments were conducted to evaluate the straw cleaning performance and consistency of downforce against the ground of the straw cleaning unit with double air springs at different high speeds.The results showed that the stiffness of the double air spring system for better straw cleaning performance of the straw cleaning unit was different at different working speed,and the required stiffness increased as the working speed increased;When the working speed was 8-12 km/h,the coefficient of variation of cleaned strip width was 6.9%-12.1%,the straw cleaning rate was 81.6%-92.2%and the root mean square error of downforce was 19.93-28.63 N;the coefficient of variation of cleaned strip width was moderately positively correlated with the root mean square error of downforce,and the cleaned strip width consistency was better when the root mean square error of downforce was lower than 25.00 N.展开更多
Quasi-zero stiffness(QZS) device is widely studied for their better performance in low-frequency and micro-vibration isolation due to the high-static and low-dynamic(HSLD) stiffness characteristics.The previous QZS is...Quasi-zero stiffness(QZS) device is widely studied for their better performance in low-frequency and micro-vibration isolation due to the high-static and low-dynamic(HSLD) stiffness characteristics.The previous QZS isolator with determined parameters is not suitable for variable isolated mass.In this study,a novel compound regulative quasi-zero stiffness air spring(CRQSAS)has been proposed and designed by introducing a bidirectional regulator for the horizontal air springs.The CRQSAS could change the quasi-zero region depending on the payload.To identify the parameters of the convoluted air spring(CAS) and novel rubber air spring(NRAS),the air spring testing system is established.The stiffness functions of air springs are obtained by the multi-parameter fitting method.According to the structure of the CRQSAS,the dynamic model of the system is analyzed and simplified by Taylor Expansion.The harmonic balance method(HBM) is applied to calculate the frequency response and absolute displacement transmissibility.An experimental prototype has been set up to verify the theoretical model and simulation.Compared with the single NRAS,CRQSAS performs better in low-frequency and micro-amplitude vibration.The research proves that CRQSAS is a passive device widely applied for improving isolation precision under low-frequency vibration.展开更多
The Northeast United States spring is indicative of major meteorological and biological change though the seasonal boundaries are difficult to define and may even be changing with global climate warming. This research...The Northeast United States spring is indicative of major meteorological and biological change though the seasonal boundaries are difficult to define and may even be changing with global climate warming. This research aims to obtain a synoptic meteorological definition of the spring season through an assessment of air mass frequency over the past 60 years. The validity of recent speculations that the onset and termination of spring have changed in recent decades with global change is also examined. The Spatial Synoptic Classification is utilized to define daily air masses over the region. Annual and seasonal baseline frequencies are identified and their differences are acquired to characterize the season. Seasonal frequency departures of the early and late segments of the period of record are calculated and examined for practical and statistical significance. The daily boundaries of early and late spring are also isolated and assessed across the period of record to identify important changes in the season’s initiation and termination through time. Results indicate that the Northeast spring season is dominated by dry air masses, mainly the Dry Moderate and Dry Polar types. Prior to 1975, more polar air masses are detected while after 1975 more moderate and tropical types are identified. Late spring is characterized by increased variability in all moist air mass frequencies. These findings indicate that, from a synoptic perspective, the season is dry through time but modern springs are also warmer than those of past decades and the initiation of the season is likely arriving earlier. The end of the season represents more variable day-to-day air mass conditions in modern times than detected in past decades.展开更多
An active device using electromagnetic forces was constructed and examined for the purpose of minimizing the resonance in air mounts of clean rooms. The air mounts are vulnerable to low-frequency resonance due to heav...An active device using electromagnetic forces was constructed and examined for the purpose of minimizing the resonance in air mounts of clean rooms. The air mounts are vulnerable to low-frequency resonance due to heavy weight and low stiffness. A hybrid structure of the active device, composed of pneumatic and electromagnetic parts, was developed and tested. The pneumatic parts in the device support heavy weights under the air mounts, and the electromagnetic parts reduce the resonance. The electromagnetic parts are composed of dual stators and an armature, which surround the pneumatic parts. The resonance can decrease when electromagnetic forces are generated in the gaps between the stators and the armature. Four active devices were installed under a 3-ton surface plate for a vibration test apparatus. The vibration was detected by eddy-current sensors. Discrete P Control logic was based on displacement, and embedded in a C6713 DSP. The results from impact tests show that the peak magnitude in the resonance frequency can be reduced to –10 dB.展开更多
文摘This study predicts the characteristics of a compressible polytropic air spring model. A second-order nonlinear autonomous air spring model is presented. The proposed model is based on the assumption that polytropic processes occur. Isothermal and isentropic compression and expansion of the air within the spring chambers are the two scenarios that are taken into consideration. In these situations, the air inside the spring chambers compresses and expands, resulting in nonlinear spring restoring forces. The MATLAB/Simulink software environment is used to build a numerical simulation model for the dynamic behavior of the air spring. To quantify the values of the stiffnesses of the proposed models, a numerical solution is run over time for various values of the design parameters. The isentropic process case has a higher dynamic air spring stiffness than the isothermal process case, according to the results. The size of the air spring chamber and the area of the air spring piston influence the air spring stiffness in both situations. It is demonstrated that the stiffness of the air spring increases linearly with increasing piston area and decreases nonlinearly with increasing air chamber length. As long as the ratio of the vibration’s amplitude to the air spring’s chamber length is small, there is good agreement in both scenarios between the linearized model and the full nonlinear model. This implies that linear modeling is a reasonable approximation of the complete nonlinear model in this particular scenario.
基金Sponsored by German Academic Exchange Service(Deutsche Akademische Austauschdienst)
文摘To reduce the roll movement of an air spring passenger car, an active anti-roll system is developed, which is constructed with hydraulic and pneumatic units to change spring rate during cornering. For the comparing research between the passive and active system, a two-track vehicle model and a co-simulation model of air spring system are built. For the simulation research on the linear movement of the actuator, a mathematical model is considered as dynamical subsystem in the co-simulation model. To active control the roll angle of vehicle body, a sliding-mode controller with optimized control parameters for the test vehicle is introduced into the model. The characteristics of sliding-mode controller is discussed and the validation of active antiroll control is proved by comparison with other control methods. The results show that the roll angle of air spring vehicle is reduced obviously with the active anti-roll actuator in comparison with that of the passive system. Compared with other control methods, sliding-mode controller has an advantage of shortest switching times, which leads to a longer lifetime of actuator and valves.
文摘On the basis of analyzing the result of numerical simulation and that of theoretical analysis,the systematic error of some air spring's theoretical formula is researched. The result shows that the vertical stiffness's theoretical formula of air spring owes the systematic error. And the systematic error is relative to the three supposed conditions which are used in the process of theoretical deduction. However,the systematic error is small enough so that the supposed conditions of theoretical formula are reasonable. Moreover,with the increase of initial inner pressure,the systematical error increases.
基金supported by National Key Research and Development Program of China(Grant No.2023YFD1500404)Jilin Science and Technology Development Plan(Grant No.20220508113RC).
文摘No-tillage planters need to be equipped with row cleaners to remove post-harvest plant residue from the seedbed.The two-disc row cleaners cannot effectively remove the plant residue at high speed because the working depth is unstable,which leads to poor seeding quality of the seeder.A straw cleaning unit with double air springs was designed to achieve better straw cleaning performance at high speeds.The analysis of the mechanical characteristics of the double air spring system showed that it enabled separate adjustment of force and stiffness.A dynamic model of the straw cleaning unit was established,and the effectiveness of the double air spring system with adjustable stiffness in stabilizing the working depth of the row cleaners was analyzed.Field experiments were conducted to evaluate the straw cleaning performance and consistency of downforce against the ground of the straw cleaning unit with double air springs at different high speeds.The results showed that the stiffness of the double air spring system for better straw cleaning performance of the straw cleaning unit was different at different working speed,and the required stiffness increased as the working speed increased;When the working speed was 8-12 km/h,the coefficient of variation of cleaned strip width was 6.9%-12.1%,the straw cleaning rate was 81.6%-92.2%and the root mean square error of downforce was 19.93-28.63 N;the coefficient of variation of cleaned strip width was moderately positively correlated with the root mean square error of downforce,and the cleaned strip width consistency was better when the root mean square error of downforce was lower than 25.00 N.
基金supported by the National Key Research and Development Project (Grant No.2021YFC0122502)the National Natural Science Foundation of China (Grant Nos.52205043 and 52275043)。
文摘Quasi-zero stiffness(QZS) device is widely studied for their better performance in low-frequency and micro-vibration isolation due to the high-static and low-dynamic(HSLD) stiffness characteristics.The previous QZS isolator with determined parameters is not suitable for variable isolated mass.In this study,a novel compound regulative quasi-zero stiffness air spring(CRQSAS)has been proposed and designed by introducing a bidirectional regulator for the horizontal air springs.The CRQSAS could change the quasi-zero region depending on the payload.To identify the parameters of the convoluted air spring(CAS) and novel rubber air spring(NRAS),the air spring testing system is established.The stiffness functions of air springs are obtained by the multi-parameter fitting method.According to the structure of the CRQSAS,the dynamic model of the system is analyzed and simplified by Taylor Expansion.The harmonic balance method(HBM) is applied to calculate the frequency response and absolute displacement transmissibility.An experimental prototype has been set up to verify the theoretical model and simulation.Compared with the single NRAS,CRQSAS performs better in low-frequency and micro-amplitude vibration.The research proves that CRQSAS is a passive device widely applied for improving isolation precision under low-frequency vibration.
文摘The Northeast United States spring is indicative of major meteorological and biological change though the seasonal boundaries are difficult to define and may even be changing with global climate warming. This research aims to obtain a synoptic meteorological definition of the spring season through an assessment of air mass frequency over the past 60 years. The validity of recent speculations that the onset and termination of spring have changed in recent decades with global change is also examined. The Spatial Synoptic Classification is utilized to define daily air masses over the region. Annual and seasonal baseline frequencies are identified and their differences are acquired to characterize the season. Seasonal frequency departures of the early and late segments of the period of record are calculated and examined for practical and statistical significance. The daily boundaries of early and late spring are also isolated and assessed across the period of record to identify important changes in the season’s initiation and termination through time. Results indicate that the Northeast spring season is dominated by dry air masses, mainly the Dry Moderate and Dry Polar types. Prior to 1975, more polar air masses are detected while after 1975 more moderate and tropical types are identified. Late spring is characterized by increased variability in all moist air mass frequencies. These findings indicate that, from a synoptic perspective, the season is dry through time but modern springs are also warmer than those of past decades and the initiation of the season is likely arriving earlier. The end of the season represents more variable day-to-day air mass conditions in modern times than detected in past decades.
文摘An active device using electromagnetic forces was constructed and examined for the purpose of minimizing the resonance in air mounts of clean rooms. The air mounts are vulnerable to low-frequency resonance due to heavy weight and low stiffness. A hybrid structure of the active device, composed of pneumatic and electromagnetic parts, was developed and tested. The pneumatic parts in the device support heavy weights under the air mounts, and the electromagnetic parts reduce the resonance. The electromagnetic parts are composed of dual stators and an armature, which surround the pneumatic parts. The resonance can decrease when electromagnetic forces are generated in the gaps between the stators and the armature. Four active devices were installed under a 3-ton surface plate for a vibration test apparatus. The vibration was detected by eddy-current sensors. Discrete P Control logic was based on displacement, and embedded in a C6713 DSP. The results from impact tests show that the peak magnitude in the resonance frequency can be reduced to –10 dB.
