On the basis of expounding the corrosion mechanism of the stator hollow copper conductor in the water-cooling generator, methods of preventing corrosion of the stator hollow copper conductor in the wa-ter-cooling gene...On the basis of expounding the corrosion mechanism of the stator hollow copper conductor in the water-cooling generator, methods of preventing corrosion of the stator hollow copper conductor in the wa-ter-cooling generator through adjusting water quality of its cooling water have been proposed. For internal water cooling systems which are airtight, the corrosion of the hollow copper conductor can be prevented through keeping foreign oxygen and carbon dioxide from entering the system, and the amount of oxygen in the internal water can be lowered by blowing high purity nitrogen. For systems not airtight, the corrosion of the hollow copper conductor can be inhibited through lowering the amount of oxygen to some extent by sealing and increasing pH value by processing part of cooling water with bypass small flow sodium-type mix-bed.展开更多
The slight-alkalization of generator internal cooling water(GICW)is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator.CO_(2) inleakage is increasing...The slight-alkalization of generator internal cooling water(GICW)is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator.CO_(2) inleakage is increasingly identified as a potential security risk for GICW system.In this paper,the influence of CO_(2) inleakage on the slight-alkalization of GICW was theoretically discussed.Based on the equilibriums of the CO_(2)-NaOH-H_(2)O system,CO_(2) inleakage saturation was derived to quantify the amount of the dissolved CO_(2) in GICW.This parameter can be directly calculated with the measured conductivity and the[Na+]of GICW.The influence of CO_(2) inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed.The more severe the inleakage,the narrower the water quality operation ranges of GICW,resulting in the more difficult the slight-alkalization conditioning of GICW.The temperature calibrations of the conductivity and the pH value of GICW show nonlinear correlations with the amount of CO_(2) inleakage and the NaOH dosage.This study provides insights into the influence of CO_(2) inleakage on the slight-alkalization of GICW,which can serve as the theoretical basis for the actual slight-alkalization when CO_(2) inleakage occurs.展开更多
The axial flux permanent magnet(AFPM)generator with double-sided internal stator structure is highly suitable for vertical axis wind turbines due to its high power density.The performance of the AFPM generator with do...The axial flux permanent magnet(AFPM)generator with double-sided internal stator structure is highly suitable for vertical axis wind turbines due to its high power density.The performance of the AFPM generator with double-sided internal stator structure can be improved by the reasonable design of electromagnetic parameters.To further improve the overall performance of the AFPM generator with double-sided internal stator structure,multivariable(coil widthω_(c),permanent magnet thickness h,pole arc coefficient α_(p) and working air gap l_(g))and multi-objective(generator efficiencyη,total harmonic distortion of the voltage THD and induced electromotive force amplitude EMF)functional relationships are innovatively established.Orthogonal analysis,mean analysis and variance analysis are performed on the influence parameters by combining the Taguchi method and response surface methodology to study the influence degrees of each influence parameter on the optimization objectives to determine the most appropriate electromagnetic parameters.The optimization results are verified by 3D finite element analysis.The optimized APFM generator with double-sided internal stator structure exhibits superior economy,stronger magnetic density,higher efficiency and improved power quality.展开更多
This paper focuses on the simulation and test of the switched reluctance starter/generator systems. Through the emulational analysis of the initial starting torque, the optimal turn-on section of the power switches is...This paper focuses on the simulation and test of the switched reluctance starter/generator systems. Through the emulational analysis of the initial starting torque, the optimal turn-on section of the power switches is discovered. The fundamental theory of the generating operation is analyzed with the linearity model, and a new method is presented based on voltage pulse width modulation for the generating mode control. Through the steady-state and optimized emulation of the output power and system efficiency, the optimizational control approach for the generating mode over a wide speed range is introduced. At last, the test of the 3KW prototype system shows that the dynamic and static performance of this system is fine.展开更多
Because of the tire nonlinearity and vehicle's parameters'uncertainties,robust control methods based on the worst cases,such as H_∞,μsynthesis,have been widely used in active front steering control,however,in orde...Because of the tire nonlinearity and vehicle's parameters'uncertainties,robust control methods based on the worst cases,such as H_∞,μsynthesis,have been widely used in active front steering control,however,in order to guarantee the stability of active front steering system(AFS)controller,the robust control is at the cost of performance so that the robust controller is a little conservative and has low performance for AFS control.In this paper,a generalized internal model robust control(GIMC)that can overcome the contradiction between performance and stability is used in the AFS control.In GIMC,the Youla parameterization is used in an improved way.And GIMC controller includes two sections:a high performance controller designed for the nominal vehicle model and a robust controller compensating the vehicle parameters'uncertainties and some external disturbances.Simulations of double lane change(DLC)maneuver and that of braking on split-μroad are conducted to compare the performance and stability of the GIMC control,the nominal performance PID controller and the H_∞controller.Simulation results show that the high nominal performance PID controller will be unstable under some extreme situations because of large vehicle's parameters variations,H_∞controller is conservative so that the performance is a little low,and only the GIMC controller overcomes the contradiction between performance and robustness,which can both ensure the stability of the AFS controller and guarantee the high performance of the AFS controller.Therefore,the GIMC method proposed for AFS can overcome some disadvantages of control methods used by current AFS system,that is,can solve the instability of PID or LQP control methods and the low performance of the standard H_∞controller.展开更多
A torque distribution strategy was designed by using fuzzy logic to realize the optimal control. The vehicle load zones were dynamically divided into several zones by several torque lines to indicate the drivers deman...A torque distribution strategy was designed by using fuzzy logic to realize the optimal control. The vehicle load zones were dynamically divided into several zones by several torque lines to indicate the drivers demand and the high or low efficient operating areas of the diesel engine. The fuzzy logic controller with trapezoid membership function and Mamdani rule reference mechanism was utilized. There are over 100 rules used in this fuzzy-based torque distribution strategy which are sorted into four rule-bases. The fuel economy and acceleration tests were designed to test and validate the integrated starter/generator (ISG) bus perfor-mance using fuzzy-based torque distribution strategy. The fuel economy is improved 7.7% compared with the rule-based strategy. Finally the road test results reveal that there is about 15% improvement of fuel economy. And the 0-50 km/h acceleration time is 9.5% shorter than the original bus.展开更多
More Electrical Aircraft(MEA)which replaces the hydraulic and pneumatic power by electrical power leads to reducing emissions and fuel consumption.The MEA concept has led to a growing use of the starter/generator(S/G)...More Electrical Aircraft(MEA)which replaces the hydraulic and pneumatic power by electrical power leads to reducing emissions and fuel consumption.The MEA concept has led to a growing use of the starter/generator(S/G)system.Permanent magnet(PM)machines have been gaining interests for aircraft S/G system application over the last few years.This is mainly due to the several advantages,including high power density,high efficiency and high speed ability.The shortcoming of the PM machines is the de-excitation problem in case of a failure,which is a main issue for the aircraft application.However,by using a PM machine with high reactance or multiphase configuration,the fault-tolerant ability can be improved.In terms of the aircraft S/G system,this paper is going to present a comprehensive analysis of PM machines.Firstly,the state-of-the-art of PM starter/generator(PMS/G)is summarized and the basic structure of PMS/G system is analyzed.Next,key technologies of the PMS/G system are summarized and analyzed.Finally,a flux weakening fault protection strategy that is used to suppress the turn-to-turn short circuit(SC)current is studied,simulated and verified.With the breakthrough of key technologies based on the development of high temperature electromagnetic material and high temperature power electronics,the PMS/G will be a potential candidate for aircraft S/G system including the embedded power generation system.展开更多
Internal tides generated by a rough sea floor are an important source of mixing in the abyssal ocean. Two linear models are employed to evaluate the conversion rate from barotropic tides to internal tides and the ener...Internal tides generated by a rough sea floor are an important source of mixing in the abyssal ocean. Two linear models are employed to evaluate the conversion rate from barotropic tides to internal tides and the energy distribution in each mode. Considering the periodicity of internal tides, the topography is represented by periodically distributed knife edges and sinusoidal ridges within one wavelength of mode-1 internal tides. The knife edges generate greater internal tides than the sinusoidal ridges due to their sharp shape, which approximates an extremely supercritical condition. Energy flux concentrates in modes whose numbers are multiples of the knife edge or ridge number. Then, a fully nonlinear model that integrates viscosity and diffusion is implemented, and its results are compared with those of the linear model. Internal wave rays generated in the nonlinear model show a distribution similar to the linear models’ prediction. High dissipation rates coincide with the rays, suggesting that nonlinear wave-wave interaction is a domi- nant mechanism for internal tide dissipation in the abyssal ocean.展开更多
Based on the theoretical spectral model of inertial internal wave breaking (fine structure) proposed previ- ously, in which the effects of the horizontal Coriolis frequency component f-tilde on a potential isopycnal...Based on the theoretical spectral model of inertial internal wave breaking (fine structure) proposed previ- ously, in which the effects of the horizontal Coriolis frequency component f-tilde on a potential isopycnal are taken into account, a parameterization scheme of vertical mixing in the stably stratified interior be- low the surface mixed layer in the ocean general circulation model (OGCM) is put forward preliminarily in this paper. Besides turbulence, the impact of sub-mesoscale oceanic processes (including inertial internal wave breaking product) on oceanic interior mixing is emphasized. We suggest that adding the inertial inter- hal wave breaking mixing scheme (F-scheme for short) put forward in this paper to the turbulence mixing scheme of Canuto et al. (T-scheme for short) in the OGCM, except the region from 15°S to 15°N. The numeri- cal results ofF-scheme by usingWOA09 data and an OGCM (LICOM, LASG/IAP climate system ocean model) over the global ocean are given. A notable improvement in the simulation of salinity and temperature over the global ocean is attained by using T-scheme adding F-scheme, especially in the mid- and high-latitude regions in the simulation of the intermediate water and deep water. We conjecture that the inertial internal wave breaking mixing and inertial forcing of wind might be one of important mechanisms maintaining the ventilation process. The modeling strength of the Atlantic meridional overturning circulation (AMOC) by using T-scheme adding F-scheme may be more reasonable than that by using T-scheme alone, though the physical processes need to be further studied, and the overflow parameterization needs to be incorporated. A shortcoming in F-scheme is that in this paper the error of simulated salinity and temperature by using T-scheme adding F-scheme is larger than that by using T-scheme alone in the subsurface layer.展开更多
A self-designed and developed 12/10 switched reluctance motor(SRM)is chosen as the object of study and a prototype of 2.5?kW switched reluctance starter/generator with fly-wheel is designed based on the requirements o...A self-designed and developed 12/10 switched reluctance motor(SRM)is chosen as the object of study and a prototype of 2.5?kW switched reluctance starter/generator with fly-wheel is designed based on the requirements of the selected engine (Changan Aotooc three-cylinder engine wagon) for the starter, generator and drive. The 36?V/42 V DC source system is applied to establishing the simulation-analyzing model of the motor. A finite-element (FE) analysis of its two-dimensional electromagnetic field is conducted to obtain the exact model of the motor. Systematic simulation is carried out combining with its power conversion circuit and control element. Meanwhile the starting process and performance of the system are studied and analyzed with special efforts. Satisfactory result is derived from the testing of the prototype: theoretical analysis is basically matched with the tested data, which proves the rationality and feasibility of the design procedures, systematic modeling and control strategies. Therefore, the new 12/10-structure scheme is put forward based on the development and analysis of various SRM and it meets the requirements of the researched motor in terms of the structural parameters.展开更多
We show how to directly use the generalized Feynman-Hellmann theorem, which is suitable for mixed state ensemble average, to derive the internal energy of Hamiltonian systems. A concrete example, which is a two couple...We show how to directly use the generalized Feynman-Hellmann theorem, which is suitable for mixed state ensemble average, to derive the internal energy of Hamiltonian systems. A concrete example, which is a two coupled harminic oscillators, is used for elucidating our approach.展开更多
According to specific performance requirements,an integrated switched reluctance starter/generator system,which can start the engine and supply electrical energy to the loads,is designed and manufactured for the unman...According to specific performance requirements,an integrated switched reluctance starter/generator system,which can start the engine and supply electrical energy to the loads,is designed and manufactured for the unmanned aerial vehicle.Considering the required starting torque and speed range,the geometrical dimensions of the switched reluctance machine are calculated based on the output equation and further optimized with finite element analysis,and the flux-linkage,inductance and static torque characteristics are illustrated.To verify the performances of the designed system,detailed simulation with the model considering piston engine and experiment using the test bench are carried out.展开更多
The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body.The model incorporates b...The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body.The model incorporates body geometry,propeller forcing,and stratification magnitude of seawater.The generation mechanism and wave properties are discussed based on model results.It was found that the generation of the wave and its properties depend greatly on the body speed.Only when that speed exceeds some critical value,between 1.5 and 4.5 m/s,can the moving body generate wake-collapse internal waves,and with increases of this speed,the time of generation advances and wave amplitude increases.The generated wake-collapse internal waves are confirmed to have characteristics of the second baroclinic mode.As the body speed increases,wave amplitude and length increase and its waveform tends to take on a regular sinusoidal shape.For three linearly temperature-stratified profiles examined,the weaker the stratification,the stronger the wake-collapse internal wave.展开更多
The paper presents constitutive theories for non-classical thermoviscoelastic fluids with dissipation and memory using a thermodynamic framework based on entirety of velocity gradient tensor. Thus, the conservation an...The paper presents constitutive theories for non-classical thermoviscoelastic fluids with dissipation and memory using a thermodynamic framework based on entirety of velocity gradient tensor. Thus, the conservation and the balance laws used in this work incorporate symmetric as well as antisymmetric part of the velocity gradient tensor. The constitutive theories derived here hold in coand contra-variant bases as well as in Jaumann rates and are derived using convected time derivatives of Green’s and Almansi strain tensors as well as the Cauchy stress tensor and its convected time derivatives in appropriate bases. The constitutive theories are presented in the absence as well as in the presence of the balance of moment of moments as balance law. It is shown that the dissipation mechanism and the fading memory in such fluids are due to stress rates as well as moment rates and their conjugates. The material coefficients are derived for the general forms of the constitutive theories based on integrity. Simplified linear (or quasi-linear) forms of the constitutive theories are also presented. Maxwell, Oldroyd-B and Giesekus constitutive models for non-classical thermoviscoelastic fluids are derived and are compared with those derived based on classical continuum mechanics. Both, compressible and incompressible thermoviscoelastic fluids are considered.展开更多
In recent papers, Surana et al. presented internal polar non-classical Continuum theory in which velocity gradient tensor in its entirety was incorporated in the conservation and balance laws. Thus, this theory incorp...In recent papers, Surana et al. presented internal polar non-classical Continuum theory in which velocity gradient tensor in its entirety was incorporated in the conservation and balance laws. Thus, this theory incorporated symmetric part of the velocity gradient tensor (as done in classical theories) as well as skew symmetric part representing varying internal rotation rates between material points which when resisted by deforming continua result in dissipation (and/or storage) of mechanical work. This physics referred as internal polar physics is neglected in classical continuum theories but can be quite significant for some materials. In another recent paper Surana et al. presented ordered rate constitutive theories for internal polar non-classical fluent continua without memory derived using deviatoric Cauchy stress tensor and conjugate strain rate tensors of up to orders n and Cauchy moment tensor and its conjugate symmetric part of the first convected derivative of the rotation gradient tensor. In this constitutive theory higher order convected derivatives of the symmetric part of the rotation gradient tensor are assumed not to contribute to dissipation. Secondly, the skew symmetric part of the velocity gradient tensor is used as rotation rates to determine rate of rotation gradient tensor. This is an approximation to true convected time derivatives of the rotation gradient tensor. The resulting constitutive theory: (1) is incomplete as it neglects the second and higher order convected time derivatives of the symmetric part of the rotation gradient tensor;(2) first convected derivative of the symmetric part of the rotation gradient tensor as used by Surana et al. is only approximate;(3) has inconsistent treatment of dissipation due to Cauchy moment tensor when compared with the dissipation mechanism due to deviatoric part of symmetric Cauchy stress tensor in which convected time derivatives of up to order n are considered in the theory. The purpose of this paper is to present ordered rate constitutive theories for deviatoric Cauchy strain tensor, moment tensor and heat vector for thermofluids without memory in which convected time derivatives of strain tensors up to order n are conjugate with the Cauchy stress tensor and the convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n are conjugate with the moment tensor. Conservation and balance laws are used to determine the choice of dependent variables in the constitutive theories: Helmholtz free energy density Φ, entropy density η, Cauchy stress tensor, moment tensor and heat vector. Stress tensor is decomposed into symmetric and skew symmetric parts and the symmetric part of the stress tensor and the moment tensor are further decomposed into equilibrium and deviatoric tensors. It is established through conjugate pairs in entropy inequality that the constitutive theories only need to be derived for symmetric stress tensor, moment tensor and heat vector. Density in the current configuration, convected time derivatives of the strain tensor up to order n, convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n, temperature gradient tensor and temperature are considered as argument tensors of all dependent variables in the constitutive theories based on entropy inequality and principle of equipresence. The constitutive theories are derived in contravariant and covariant bases as well as using Jaumann rates. The nth and 1nth order rate constitutive theories for internal polar non-classical thermofluids without memory are specialized for n = 1 and 1n = 1 to demonstrate fundamental differences in the constitutive theories presented here and those used presently for classical thermofluids without memory and those published by Surana et al. for internal polar non-classical incompressible thermofluids.展开更多
Background: The availability of an anesthesiologist is often a limiting factor in the number of operations that can be performed by International Medical Surgical Response Teams (IMSuRT). Because emergency physicians ...Background: The availability of an anesthesiologist is often a limiting factor in the number of operations that can be performed by International Medical Surgical Response Teams (IMSuRT). Because emergency physicians (EPs) possess skills in airway control, management of moderate and deep sedation, and ventilator management, we propose that with proper training in general anesthesia, EPs can serve as anesthetists for IMSuRT with anesthesiologist supervision. Methods: During a 10-week period, a board-certified EP administered general anesthesia to 60 patients prior to a surgical medical mission trip. The breakdown of surgical cases was: 11 orthopedic, 2 genitourinary, 20 ear, nose, and throat, 8 obstetrics and gynecological, 13 general surgery, and 6 vascular. A simplified protocol for induction, maintenance, and emergence was adhered to for all cases. Results: Fourteen orthopedic cases using general anesthesia were performed in a one-week period in Haiti. These cases involved open reduction and internal fixation (ORIF), hemiarthoplasty, hardware removal, tendon transfer and external fixation of fractured bone. Conclusion: We demonstrate the feasibility of a model curriculum to train EPs in the basics of anesthesia. The EP can safely and effectively deliver general anesthesia for major cases on surgical medical mission trips under the auspices of an anesthesiologist in an austere environment.展开更多
Artificial general intelligence (AGI) is the ability of an artificial intelligence (AI) agent to solve somewhat-arbitrary tasks in somewhat-arbitrary environments. Despite being a long-standing goal in the field of AI...Artificial general intelligence (AGI) is the ability of an artificial intelligence (AI) agent to solve somewhat-arbitrary tasks in somewhat-arbitrary environments. Despite being a long-standing goal in the field of AI, achieving AGI remains elusive. In this study, we empirically assessed the generalizability of AI agents by applying a deep reinforcement learning (DRL) approach to the medical domain. Our investigation involved examining how modifying the agent’s structure, task, and environment impacts its generality. Sample: An NIH chest X-ray dataset with 112,120 images and 15 medical conditions. We evaluated the agent’s performance on binary and multiclass classification tasks through a baseline model, a convolutional neural network model, a deep Q network model, and a proximal policy optimization model. Results: Our results suggest that DRL agents with the algorithmic flexibility to autonomously vary their macro/microstructures can generalize better across given tasks and environments.展开更多
文摘On the basis of expounding the corrosion mechanism of the stator hollow copper conductor in the water-cooling generator, methods of preventing corrosion of the stator hollow copper conductor in the wa-ter-cooling generator through adjusting water quality of its cooling water have been proposed. For internal water cooling systems which are airtight, the corrosion of the hollow copper conductor can be prevented through keeping foreign oxygen and carbon dioxide from entering the system, and the amount of oxygen in the internal water can be lowered by blowing high purity nitrogen. For systems not airtight, the corrosion of the hollow copper conductor can be inhibited through lowering the amount of oxygen to some extent by sealing and increasing pH value by processing part of cooling water with bypass small flow sodium-type mix-bed.
文摘The slight-alkalization of generator internal cooling water(GICW)is widely used to inhibit the corrosion of hollow copper conductor and thereby ensure the safe operation of the generator.CO_(2) inleakage is increasingly identified as a potential security risk for GICW system.In this paper,the influence of CO_(2) inleakage on the slight-alkalization of GICW was theoretically discussed.Based on the equilibriums of the CO_(2)-NaOH-H_(2)O system,CO_(2) inleakage saturation was derived to quantify the amount of the dissolved CO_(2) in GICW.This parameter can be directly calculated with the measured conductivity and the[Na+]of GICW.The influence of CO_(2) inleakage on the slight-alkalization conditioning of GICW and the measurement of its water quality parameters were then analyzed.The more severe the inleakage,the narrower the water quality operation ranges of GICW,resulting in the more difficult the slight-alkalization conditioning of GICW.The temperature calibrations of the conductivity and the pH value of GICW show nonlinear correlations with the amount of CO_(2) inleakage and the NaOH dosage.This study provides insights into the influence of CO_(2) inleakage on the slight-alkalization of GICW,which can serve as the theoretical basis for the actual slight-alkalization when CO_(2) inleakage occurs.
基金funded by Project Supported by Postdoctoral Science Foundation of Jiangsu Province,Grant No.2019k237.
文摘The axial flux permanent magnet(AFPM)generator with double-sided internal stator structure is highly suitable for vertical axis wind turbines due to its high power density.The performance of the AFPM generator with double-sided internal stator structure can be improved by the reasonable design of electromagnetic parameters.To further improve the overall performance of the AFPM generator with double-sided internal stator structure,multivariable(coil widthω_(c),permanent magnet thickness h,pole arc coefficient α_(p) and working air gap l_(g))and multi-objective(generator efficiencyη,total harmonic distortion of the voltage THD and induced electromotive force amplitude EMF)functional relationships are innovatively established.Orthogonal analysis,mean analysis and variance analysis are performed on the influence parameters by combining the Taguchi method and response surface methodology to study the influence degrees of each influence parameter on the optimization objectives to determine the most appropriate electromagnetic parameters.The optimization results are verified by 3D finite element analysis.The optimized APFM generator with double-sided internal stator structure exhibits superior economy,stronger magnetic density,higher efficiency and improved power quality.
文摘This paper focuses on the simulation and test of the switched reluctance starter/generator systems. Through the emulational analysis of the initial starting torque, the optimal turn-on section of the power switches is discovered. The fundamental theory of the generating operation is analyzed with the linearity model, and a new method is presented based on voltage pulse width modulation for the generating mode control. Through the steady-state and optimized emulation of the output power and system efficiency, the optimizational control approach for the generating mode over a wide speed range is introduced. At last, the test of the 3KW prototype system shows that the dynamic and static performance of this system is fine.
基金Supported by National Natural Science Foundation of China(Grant Nos.11072106,51375009)
文摘Because of the tire nonlinearity and vehicle's parameters'uncertainties,robust control methods based on the worst cases,such as H_∞,μsynthesis,have been widely used in active front steering control,however,in order to guarantee the stability of active front steering system(AFS)controller,the robust control is at the cost of performance so that the robust controller is a little conservative and has low performance for AFS control.In this paper,a generalized internal model robust control(GIMC)that can overcome the contradiction between performance and stability is used in the AFS control.In GIMC,the Youla parameterization is used in an improved way.And GIMC controller includes two sections:a high performance controller designed for the nominal vehicle model and a robust controller compensating the vehicle parameters'uncertainties and some external disturbances.Simulations of double lane change(DLC)maneuver and that of braking on split-μroad are conducted to compare the performance and stability of the GIMC control,the nominal performance PID controller and the H_∞controller.Simulation results show that the high nominal performance PID controller will be unstable under some extreme situations because of large vehicle's parameters variations,H_∞controller is conservative so that the performance is a little low,and only the GIMC controller overcomes the contradiction between performance and robustness,which can both ensure the stability of the AFS controller and guarantee the high performance of the AFS controller.Therefore,the GIMC method proposed for AFS can overcome some disadvantages of control methods used by current AFS system,that is,can solve the instability of PID or LQP control methods and the low performance of the standard H_∞controller.
文摘A torque distribution strategy was designed by using fuzzy logic to realize the optimal control. The vehicle load zones were dynamically divided into several zones by several torque lines to indicate the drivers demand and the high or low efficient operating areas of the diesel engine. The fuzzy logic controller with trapezoid membership function and Mamdani rule reference mechanism was utilized. There are over 100 rules used in this fuzzy-based torque distribution strategy which are sorted into four rule-bases. The fuel economy and acceleration tests were designed to test and validate the integrated starter/generator (ISG) bus perfor-mance using fuzzy-based torque distribution strategy. The fuel economy is improved 7.7% compared with the rule-based strategy. Finally the road test results reveal that there is about 15% improvement of fuel economy. And the 0-50 km/h acceleration time is 9.5% shorter than the original bus.
基金This work was supported in part by National Natural Science Foundation for Excellent Young Scholar of China under Award 51622704Jiangsu Provincial Science Funds for Distinguished Young Scientists under Award BK20150033.
文摘More Electrical Aircraft(MEA)which replaces the hydraulic and pneumatic power by electrical power leads to reducing emissions and fuel consumption.The MEA concept has led to a growing use of the starter/generator(S/G)system.Permanent magnet(PM)machines have been gaining interests for aircraft S/G system application over the last few years.This is mainly due to the several advantages,including high power density,high efficiency and high speed ability.The shortcoming of the PM machines is the de-excitation problem in case of a failure,which is a main issue for the aircraft application.However,by using a PM machine with high reactance or multiphase configuration,the fault-tolerant ability can be improved.In terms of the aircraft S/G system,this paper is going to present a comprehensive analysis of PM machines.Firstly,the state-of-the-art of PM starter/generator(PMS/G)is summarized and the basic structure of PMS/G system is analyzed.Next,key technologies of the PMS/G system are summarized and analyzed.Finally,a flux weakening fault protection strategy that is used to suppress the turn-to-turn short circuit(SC)current is studied,simulated and verified.With the breakthrough of key technologies based on the development of high temperature electromagnetic material and high temperature power electronics,the PMS/G will be a potential candidate for aircraft S/G system including the embedded power generation system.
基金supported by the Project of State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography (No. SOEDZZ1701)the Youth Visiting ‘Ocean-Star Scholarship’ of the State Key Laboratory of Satellite Ocean Environment Dynamics (No. QNHX1602)+2 种基金National Key R&D Program of China (No. 2017YFC0305900)support of NSFC-41576008 and CXZZ20140521161827690Numerical computation is supported by the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (No. U1501501)
文摘Internal tides generated by a rough sea floor are an important source of mixing in the abyssal ocean. Two linear models are employed to evaluate the conversion rate from barotropic tides to internal tides and the energy distribution in each mode. Considering the periodicity of internal tides, the topography is represented by periodically distributed knife edges and sinusoidal ridges within one wavelength of mode-1 internal tides. The knife edges generate greater internal tides than the sinusoidal ridges due to their sharp shape, which approximates an extremely supercritical condition. Energy flux concentrates in modes whose numbers are multiples of the knife edge or ridge number. Then, a fully nonlinear model that integrates viscosity and diffusion is implemented, and its results are compared with those of the linear model. Internal wave rays generated in the nonlinear model show a distribution similar to the linear models’ prediction. High dissipation rates coincide with the rays, suggesting that nonlinear wave-wave interaction is a domi- nant mechanism for internal tide dissipation in the abyssal ocean.
基金The National Natural Science Foundation of China under contract No.41275084the Key Program of National Natural Science Foundation of China under contract No.41030855
文摘Based on the theoretical spectral model of inertial internal wave breaking (fine structure) proposed previ- ously, in which the effects of the horizontal Coriolis frequency component f-tilde on a potential isopycnal are taken into account, a parameterization scheme of vertical mixing in the stably stratified interior be- low the surface mixed layer in the ocean general circulation model (OGCM) is put forward preliminarily in this paper. Besides turbulence, the impact of sub-mesoscale oceanic processes (including inertial internal wave breaking product) on oceanic interior mixing is emphasized. We suggest that adding the inertial inter- hal wave breaking mixing scheme (F-scheme for short) put forward in this paper to the turbulence mixing scheme of Canuto et al. (T-scheme for short) in the OGCM, except the region from 15°S to 15°N. The numeri- cal results ofF-scheme by usingWOA09 data and an OGCM (LICOM, LASG/IAP climate system ocean model) over the global ocean are given. A notable improvement in the simulation of salinity and temperature over the global ocean is attained by using T-scheme adding F-scheme, especially in the mid- and high-latitude regions in the simulation of the intermediate water and deep water. We conjecture that the inertial internal wave breaking mixing and inertial forcing of wind might be one of important mechanisms maintaining the ventilation process. The modeling strength of the Atlantic meridional overturning circulation (AMOC) by using T-scheme adding F-scheme may be more reasonable than that by using T-scheme alone, though the physical processes need to be further studied, and the overflow parameterization needs to be incorporated. A shortcoming in F-scheme is that in this paper the error of simulated salinity and temperature by using T-scheme adding F-scheme is larger than that by using T-scheme alone in the subsurface layer.
文摘A self-designed and developed 12/10 switched reluctance motor(SRM)is chosen as the object of study and a prototype of 2.5?kW switched reluctance starter/generator with fly-wheel is designed based on the requirements of the selected engine (Changan Aotooc three-cylinder engine wagon) for the starter, generator and drive. The 36?V/42 V DC source system is applied to establishing the simulation-analyzing model of the motor. A finite-element (FE) analysis of its two-dimensional electromagnetic field is conducted to obtain the exact model of the motor. Systematic simulation is carried out combining with its power conversion circuit and control element. Meanwhile the starting process and performance of the system are studied and analyzed with special efforts. Satisfactory result is derived from the testing of the prototype: theoretical analysis is basically matched with the tested data, which proves the rationality and feasibility of the design procedures, systematic modeling and control strategies. Therefore, the new 12/10-structure scheme is put forward based on the development and analysis of various SRM and it meets the requirements of the researched motor in terms of the structural parameters.
基金the National Natural Science Foundation of China under
文摘We show how to directly use the generalized Feynman-Hellmann theorem, which is suitable for mixed state ensemble average, to derive the internal energy of Hamiltonian systems. A concrete example, which is a two coupled harminic oscillators, is used for elucidating our approach.
基金This work was supported by the Key Research and Development Plan of Shaanxi Province under Grant 2018GY-185,Xi'an Science and Technology Plan under Grant 2017086CG/RC049(XBGY002)the ASN Innovation Development Fund under Grant ASN-IF2015-3110the Fundamental Research Funds for the Central Universities under Grants 3102017AX007.
文摘According to specific performance requirements,an integrated switched reluctance starter/generator system,which can start the engine and supply electrical energy to the loads,is designed and manufactured for the unmanned aerial vehicle.Considering the required starting torque and speed range,the geometrical dimensions of the switched reluctance machine are calculated based on the output equation and further optimized with finite element analysis,and the flux-linkage,inductance and static torque characteristics are illustrated.To verify the performances of the designed system,detailed simulation with the model considering piston engine and experiment using the test bench are carried out.
基金Supported by the State Key Program of National Natural Science of China(No.60638020)
文摘The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body.The model incorporates body geometry,propeller forcing,and stratification magnitude of seawater.The generation mechanism and wave properties are discussed based on model results.It was found that the generation of the wave and its properties depend greatly on the body speed.Only when that speed exceeds some critical value,between 1.5 and 4.5 m/s,can the moving body generate wake-collapse internal waves,and with increases of this speed,the time of generation advances and wave amplitude increases.The generated wake-collapse internal waves are confirmed to have characteristics of the second baroclinic mode.As the body speed increases,wave amplitude and length increase and its waveform tends to take on a regular sinusoidal shape.For three linearly temperature-stratified profiles examined,the weaker the stratification,the stronger the wake-collapse internal wave.
文摘The paper presents constitutive theories for non-classical thermoviscoelastic fluids with dissipation and memory using a thermodynamic framework based on entirety of velocity gradient tensor. Thus, the conservation and the balance laws used in this work incorporate symmetric as well as antisymmetric part of the velocity gradient tensor. The constitutive theories derived here hold in coand contra-variant bases as well as in Jaumann rates and are derived using convected time derivatives of Green’s and Almansi strain tensors as well as the Cauchy stress tensor and its convected time derivatives in appropriate bases. The constitutive theories are presented in the absence as well as in the presence of the balance of moment of moments as balance law. It is shown that the dissipation mechanism and the fading memory in such fluids are due to stress rates as well as moment rates and their conjugates. The material coefficients are derived for the general forms of the constitutive theories based on integrity. Simplified linear (or quasi-linear) forms of the constitutive theories are also presented. Maxwell, Oldroyd-B and Giesekus constitutive models for non-classical thermoviscoelastic fluids are derived and are compared with those derived based on classical continuum mechanics. Both, compressible and incompressible thermoviscoelastic fluids are considered.
文摘In recent papers, Surana et al. presented internal polar non-classical Continuum theory in which velocity gradient tensor in its entirety was incorporated in the conservation and balance laws. Thus, this theory incorporated symmetric part of the velocity gradient tensor (as done in classical theories) as well as skew symmetric part representing varying internal rotation rates between material points which when resisted by deforming continua result in dissipation (and/or storage) of mechanical work. This physics referred as internal polar physics is neglected in classical continuum theories but can be quite significant for some materials. In another recent paper Surana et al. presented ordered rate constitutive theories for internal polar non-classical fluent continua without memory derived using deviatoric Cauchy stress tensor and conjugate strain rate tensors of up to orders n and Cauchy moment tensor and its conjugate symmetric part of the first convected derivative of the rotation gradient tensor. In this constitutive theory higher order convected derivatives of the symmetric part of the rotation gradient tensor are assumed not to contribute to dissipation. Secondly, the skew symmetric part of the velocity gradient tensor is used as rotation rates to determine rate of rotation gradient tensor. This is an approximation to true convected time derivatives of the rotation gradient tensor. The resulting constitutive theory: (1) is incomplete as it neglects the second and higher order convected time derivatives of the symmetric part of the rotation gradient tensor;(2) first convected derivative of the symmetric part of the rotation gradient tensor as used by Surana et al. is only approximate;(3) has inconsistent treatment of dissipation due to Cauchy moment tensor when compared with the dissipation mechanism due to deviatoric part of symmetric Cauchy stress tensor in which convected time derivatives of up to order n are considered in the theory. The purpose of this paper is to present ordered rate constitutive theories for deviatoric Cauchy strain tensor, moment tensor and heat vector for thermofluids without memory in which convected time derivatives of strain tensors up to order n are conjugate with the Cauchy stress tensor and the convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n are conjugate with the moment tensor. Conservation and balance laws are used to determine the choice of dependent variables in the constitutive theories: Helmholtz free energy density Φ, entropy density η, Cauchy stress tensor, moment tensor and heat vector. Stress tensor is decomposed into symmetric and skew symmetric parts and the symmetric part of the stress tensor and the moment tensor are further decomposed into equilibrium and deviatoric tensors. It is established through conjugate pairs in entropy inequality that the constitutive theories only need to be derived for symmetric stress tensor, moment tensor and heat vector. Density in the current configuration, convected time derivatives of the strain tensor up to order n, convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n, temperature gradient tensor and temperature are considered as argument tensors of all dependent variables in the constitutive theories based on entropy inequality and principle of equipresence. The constitutive theories are derived in contravariant and covariant bases as well as using Jaumann rates. The nth and 1nth order rate constitutive theories for internal polar non-classical thermofluids without memory are specialized for n = 1 and 1n = 1 to demonstrate fundamental differences in the constitutive theories presented here and those used presently for classical thermofluids without memory and those published by Surana et al. for internal polar non-classical incompressible thermofluids.
文摘Background: The availability of an anesthesiologist is often a limiting factor in the number of operations that can be performed by International Medical Surgical Response Teams (IMSuRT). Because emergency physicians (EPs) possess skills in airway control, management of moderate and deep sedation, and ventilator management, we propose that with proper training in general anesthesia, EPs can serve as anesthetists for IMSuRT with anesthesiologist supervision. Methods: During a 10-week period, a board-certified EP administered general anesthesia to 60 patients prior to a surgical medical mission trip. The breakdown of surgical cases was: 11 orthopedic, 2 genitourinary, 20 ear, nose, and throat, 8 obstetrics and gynecological, 13 general surgery, and 6 vascular. A simplified protocol for induction, maintenance, and emergence was adhered to for all cases. Results: Fourteen orthopedic cases using general anesthesia were performed in a one-week period in Haiti. These cases involved open reduction and internal fixation (ORIF), hemiarthoplasty, hardware removal, tendon transfer and external fixation of fractured bone. Conclusion: We demonstrate the feasibility of a model curriculum to train EPs in the basics of anesthesia. The EP can safely and effectively deliver general anesthesia for major cases on surgical medical mission trips under the auspices of an anesthesiologist in an austere environment.
文摘Artificial general intelligence (AGI) is the ability of an artificial intelligence (AI) agent to solve somewhat-arbitrary tasks in somewhat-arbitrary environments. Despite being a long-standing goal in the field of AI, achieving AGI remains elusive. In this study, we empirically assessed the generalizability of AI agents by applying a deep reinforcement learning (DRL) approach to the medical domain. Our investigation involved examining how modifying the agent’s structure, task, and environment impacts its generality. Sample: An NIH chest X-ray dataset with 112,120 images and 15 medical conditions. We evaluated the agent’s performance on binary and multiclass classification tasks through a baseline model, a convolutional neural network model, a deep Q network model, and a proximal policy optimization model. Results: Our results suggest that DRL agents with the algorithmic flexibility to autonomously vary their macro/microstructures can generalize better across given tasks and environments.