In this paper, the operating conditions, technical requirements, performance characteristics, design ideas, application experiences and development trends of aerospace engine bearings, including material technology, i...In this paper, the operating conditions, technical requirements, performance characteristics, design ideas, application experiences and development trends of aerospace engine bearings, including material technology, integration design and reliability, are reviewed. The development history of aerospace engine bearing is recalled briefly at first. Then today's material technologies and the high bearing performances of the bearings obtained through the new materials are introduced, which play important roils in the aeroengine bearing developments. The integration design ideas and practices are explained to indicate its significant advantages and importance to the aerospace engine bearings. And the reliability of the shaft-bearing system is pointed out and treated as the key requirement with goals for both engine and bearing. Finally, as it is believed that the correct design comes from practice, the pre-qualification rig testing conducted by FAG Aerospace GmbH & Co. KG is briefly illustrated as an example. All these lead to the development trends of aerospace engine bearings from different aspects.展开更多
Under the assumption of low-dissipation, a unified model of generalized Carnot cycles with external leakage losses is established. Analytical expressions for the power output and efficiency are derived. The general pe...Under the assumption of low-dissipation, a unified model of generalized Carnot cycles with external leakage losses is established. Analytical expressions for the power output and efficiency are derived. The general performance characteristics between the power output and the efficiency are revealed. The maximum power output and efficiency are calculated. The lower and upper bounds of the efficiency at the maximum power output are determined. The results obtained here are universal and can be directly used to reveal the performance characteristics of different Carnot cycles, such as Carnot heat engines, Carnot-like heat engines, flux flow engines, gravitational engines, chemical engines, two-level quantum engines, etc.展开更多
This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of ther...This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.展开更多
DG-MOSFETs are the most widely explored device architectures for na</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="f...DG-MOSFETs are the most widely explored device architectures for na</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">no-scale CMOS circuit design in sub-50 nm due to the improved subthre</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">shold slope and the reduced leakage power compared to bulk MOSFETs. In thin-film (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;"> < 10 nm) DG-MOS structures, charge carriers are affected</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> by</span></span></span><span><span><span style="font-family:""> <i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;">-</span></span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">induced quantum confinement along with the confinement caused by </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">a </span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">very high electric field at the interface. Therefore, quantum confinement effects on the device characteristics are also quite important and it needs to be incorpo</span><span style="font-family:Verdana;">rated along with short channel effects for nano-scale circuit design. In this</span> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">, we analyze</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">d</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a DG-MOSFET structure at </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">20 nm technology node</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> incorporating quantum confinement effects and various short channel effects. The effect of physical parameter variations on performance characteristics of </span><span><span style="font-family:Verdana;">the device such as threshold voltage, subthreshold slope, </span><i><span style="font-family:Verdana;">I</span><sub><span style="font-family:Verdana;">ON</span></sub></i><span style="font-family:Verdana;"> - </span><i><span style="font-family:Verdana;">I</span><sub><span style="font-family:Verdana;">OFF</span></sub></i><span style="font-family:Verdana;"> ratio,</span></span> <i><span style="font-family:Verdana;">DIBL</span></i></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> etc. has been investigated and plotted through extensive TCAD simulations. The physical parameters considered in this </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> are operating temperature </span><span><span style="font-family:Verdana;">(</span><i><span style="font-family:Verdana;">T</span><sub><span style="font-family:Verdana;">op</span></sub></i><span style="font-family:Verdana;">), channel doping concentration (</span><i><span style="font-family:Verdana;">N</span><sub><span style="font-family:Verdana;">c</span></sub></i><span style="font-family:Verdana;">), gate oxide thickness (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">ox</span></sub></i><span style="font-family:Verdana;">) an</span></span><span style="font-family:Verdana;">d Silicon film thickness (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;">). It </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">was</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> observed that quantum confinement of </span><span style="font-family:Verdana;">charge </span><span style="font-family:Verdana;">carriers significantly affect</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">ed</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the performance characteristics (mostly the</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> subth</span><span style="font-family:Verdana;">reshold characteristics) of the device and therefore, it cannot be ignored in</span><span style="font-family:Verdana;"> the </span><span style="font-family:Verdana;">subthreshold region</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">based circuit design like in many previous research</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> works. </span><span><span style="font-family:Verdana;">The ATLAS</span><sup><span style="font-family:Verdana;">TM</span></sup><span style="font-family:Verdana;"> device simulator has been used in this </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> to perform simu</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">lation and parameter extraction. The TCAD analysis presented in the</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> manuscript can be incorporated for device modeling and device</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> matching. It can be used to illustrate exact device behavior and for proper device control.展开更多
The low stress abrasion behaviours of heat treated mild, medium carbon and high C - low Cr steels, which are generally used in making farm implements, have been investigated. The simple heat treatment greatly improves...The low stress abrasion behaviours of heat treated mild, medium carbon and high C - low Cr steels, which are generally used in making farm implements, have been investigated. The simple heat treatment greatly improves the hardness, tensile strength and abrasion resistance of medium carbon and high C - low Cr steels. The results indicate that the material removal during abrasion is controlled by a number of factors, such as hardness, chemical composition, microstructure and heat treatment conditions. The conclusion is that the heat treated high C - low Cr steel and mild steel carburized by using coaltar pitch provide the best hardness and abrasion resistance and thus appear to be the most suitable materials for making agricultural tools.展开更多
To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducte...To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducted by using 7.62 mm armor piercing incendiary(API).Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.展开更多
This study aims to determine the morphometric characteristics and reproductive performance of Pasundan cows which are extensively reared on smallholder farms in the coastal areas of the south(Garut,Cianjur,and Sukabum...This study aims to determine the morphometric characteristics and reproductive performance of Pasundan cows which are extensively reared on smallholder farms in the coastal areas of the south(Garut,Cianjur,and Sukabumi)and North Priangan(Bogor,Purwakarta,and Sumedang).This research is descriptive research with a qualitative approach.Production characterization was carried out using a simple method,namely by measuring the body surface including shoulder height,chest circumference,body length,and bodyweight of Pasundan cattle.Meanwhile,the reproductive characteristics discuss puberty,service per conception(S/C),conception rate(CR),calving rate,postpartum estrus,postpartum mating,days open(DO),calving interval(CI),calving birth weight,calving rate,and calves weight growth.Data were collected by survey,and the location was determined by purposive sampling in the area of the seed source with the largest population and the random sampling of livestock was determined purposively as many as 30 Pasundan cows from each region.Data were analyzed using quantitative descriptive analysis.The results showed that the morphometric characteristics of Pasundan cattle included mean shoulder height of 123.00±3.06a cm VS 121.34±2.82a in males and 110.34±2.78 vs 108.00±2.14a in females.Body length 115.74±3.30 cm VS 115.34±2.97acm in males and 112.67±2.97cm VS 109.67±1.82 cm in females.Chest circumference 145.67±2.97cm VS 142.67±2.67cm bulls and 136.00±2.95cm VS 131.00±2.92cm in females,Bodyweight 268.0±17.00 kg VS 246.00±7.00a for males and 215.0±15.00 kg VS 194.00±54.00kg in females.As for reproductive characteristics,it shows puberty of 20-24 months.,S/C 1.4-1.6,Conception rate 65-70%,calving rate 62.5-65%,Postpartum Estrus 50-60 days,postpartum mating 72-104 days,day-open 94-126 days and a calving interval of 12-14 months.Calves'birth weight was 18.0-18.5 kg and daily body weight gain ranged from 0.48 to 0.50 kg.It was concluded that the morphometric characteristics and reproductive performance of Pasundan cattle in the Pesisir Selatan area were better than North Priangan.展开更多
The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles...The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles. With the commercial computational fluid dynamics (CFD) software NUMECA, the turbulent flow in the tandem axial-flow pump is simulated in various flow conditions. The detail flow structure in the leading edge region of the rear impeller is described, and the influence of the deflection angle of the rear blade on the head performance is studied. According to the simulation, the performance comparison is made between the tandem axial-flow pump and the conventional two-stage axial-flow pump with a uniform impeller size. Results of the study indicate that the tandem axial-flow pump can work in a wider range with high efficiency.展开更多
We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. ...We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.展开更多
Experimental investigation of the passive control on improving the unstable characteristics in axial flow fans is performed. It is confirmed that the air-separator is an excellent equipment for rotating stall suppress...Experimental investigation of the passive control on improving the unstable characteristics in axial flow fans is performed. It is confirmed that the air-separator is an excellent equipment for rotating stall suppression. The air-separator can effectively remove low energy fluid near the fan casing. Further, it can improve the low flow rate range performance and increase stall margin of the axial flow fan.展开更多
Based on a general model of Brownian motors, the Onsager coefficients and generalized efficiency of a thermal Brownian motor are calculated analytically. It is found that the Onsager reciprocity relation holds and the...Based on a general model of Brownian motors, the Onsager coefficients and generalized efficiency of a thermal Brownian motor are calculated analytically. It is found that the Onsager reciprocity relation holds and the Onsager coefficients are not affected by the kinetic energy change due to the particle's motion. Only when the heat leak in the system is negligible can the determinant of the Onsager matrix vanish. Moreover, the influence of the main parameters characterizing the model on the generalized efficiency of the Brownian motor is discussed in detail. The characteristic curves of the generalized efficiency varying with these parameters are presented, and the maximum generalized efficiency and the corresponding optimum parameters are determined. The results obtained here are of general significance. They are used to analyze the performance characteristics of the Brownian motors operating in the three interesting cases with zero heat leak, zero average drift velocity or a linear response relation, so that some important conclusions in current references are directly included in some limit cases of the present paper.展开更多
The growth in computer processing power has made it possible to use time-consuming analysis methods such as incremental dynamic analysis(IDA) with higher accuracy in less time.In an IDA study,a series of earthquake ...The growth in computer processing power has made it possible to use time-consuming analysis methods such as incremental dynamic analysis(IDA) with higher accuracy in less time.In an IDA study,a series of earthquake records are applied to a structure at successively increasing intensity levels,which causes the structure to shift from the elastic state into the inelastic state and finally into collapse.In this way,the limit-states and capacity of a structure can be determined.In the present research,the IDA of a concrete gravity dam considering a nonlinear concrete behavior,and sliding planes within the dam body and at the dam-foundation interface,is performed.The influence of the friction angle and lift joint slope on the response parameters are investigated and the various limit-states of the dam are recognized.It is observed that by introducing a lift joint,the tensile damage can be avoided for the dam structure.The lift joint sliding is essentially independent of the base joint friction angle and the upper ligament over the inclined lift joint slides into the upstream direction in strong earthquakes.展开更多
In this paper,a novel remaining useful life prediction approach considering fault effects is proposed.The Wiener process is used to construct the degradation process of single performance characteristic with the fault...In this paper,a novel remaining useful life prediction approach considering fault effects is proposed.The Wiener process is used to construct the degradation process of single performance characteristic with the fault effects.The first passage time based remaining useful life distribution is calculated by assuming fault occurrence moment is a random variable and follows a certain distribution.Expectation maximization algorithm is employed to estimate model parameters,where the fault occurrence moment is considered as a missing data.Finally,a Copula function is used to describe the dependence between the multiple performance characteristics and derive joint remaining useful life(RUL)distribution of product with the fault effects.The effectiveness of the proposed approach is verified by the experiments of turbofan engines.展开更多
Accurate simulation of characteristics performance and state of health(SOH)estimation for lithium-ion batteries are critical for battery management systems(BMS)in electric vehicles.Battery simplified electrochemical m...Accurate simulation of characteristics performance and state of health(SOH)estimation for lithium-ion batteries are critical for battery management systems(BMS)in electric vehicles.Battery simplified electrochemical model(SEM)can achieve accurate estimation of battery terminal voltage with less computing resources.To ensure the applica-bility of life-cycle usage,degradation physics need to be involved in SEM models.This work conducts deep analysis on battery degradation physics and develops an aging-effect coupling model based on an existing improved single particle(ISP)model.Firstly,three mechanisms of solid electrolyte interface(SEI)film growth throughout life cycle are analyzed,and an SEI film growth model of lithium-ion battery is built coupled with the ISP model.Then,a series of identification conditions for individual cells are designed to non-destructively determine model parameters.Finally,battery aging experiment is designed to validate the battery performance simulation method and SOH estimation method.The validation results under different aging rates indicate that this method can accurately es-timate characteristics performance and SOH for lithium-ion batteries during the whole life cycle.展开更多
The objective of this study was to investigate the possibility of fitting spline regression models for power take-off(PTO)performance characteristics of an agricultural tractor tested with four different fuels,includi...The objective of this study was to investigate the possibility of fitting spline regression models for power take-off(PTO)performance characteristics of an agricultural tractor tested with four different fuels,including diesel fuel(B0)and three biodiesel blends made of canola oil(B10:10%biodiesel+90%petro-diesel blend;B20:20%biodiesel+90%petro-diesel blend;B30:30%biodiesel+90%petro-diesel blend).The performance characteristics evaluated were PTO power,engine torque,engine fuel consumption,and specific fuel consumption.Due to sharp slopes in measured quantities around the nominal engine speed(2200 r/min),compared to the standard regression method,the spline regression models suited well to the experimental data with coefficient of determination R2=0.99 for PTO power and engine torque.R2 varied between 0.97 and 0.99 for fuel consumption and 0.91 and 0.95 for specific fuel consumption.The weaker correlation found for specific fuel consumption could be attributed to profound fluctuations in measured data causing atypical pattern in the corresponding graphs around the nominal engine speed.It was concluded that splines were useful to accurately predict the measured PTO power and engine torque.Neither standard methods nor splines were sufficient to obtain very good regression models for specific fuel consumption.展开更多
The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In orde...The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In order to improve the anti-cavitation performance of the centrifugal pumps, variable-pitch inducers are placed upstream of the impeller. Because the rotational speeds directly affect the flow and the performance of the pump, it is essential to characterize the performance of the pump with a variable-pitch inducer at various rotational speeds. In this paper, the simulations and the experimental tests of a centrifugal pump with a variable-pitch inducer are designed and carried out under various rotational speed conditions. Navier-Stokes equations, coupled with a Reynolds average simulation approach, are used in the simulations. In the experimental tests, the external and anti-cavitation performances of the pump are investigated in a closed system. The following results are obtained from the simulations. Firstly, the velocity in the passage of the inducer rises with the increase of the rotational speed. Secondly, the static pressure escalates on the inducer and the impeller with the increase of the rotational speed. Thirdly, the static pressure distribution on the inducer and the impeller is asymmetric. Fourthly, the anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Additional results are gathered from an analysis of the experiments. H-Q curves are similar parabolas at various rotational speeds, while η-Q curves are similar parabolas only when n ≤6 000 r/min. The anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Finally, the simulation results are found to be consistent with the experimental results.展开更多
Fused deposition modeling (FDM) is an additive manufacturing technique used to fabricate intricate parts in 3D, within the shortest possible time without using tools, dies, fixtures, or human intervention. This arti...Fused deposition modeling (FDM) is an additive manufacturing technique used to fabricate intricate parts in 3D, within the shortest possible time without using tools, dies, fixtures, or human intervention. This article empiri- cally reports the effects of the process parameters, i.e., the layer thickness, raster angle, raster width, air gap, part orientation, and their interactions on the accuracy of the length, width, and thicknes, of acrylonitrile-butadiene- styrene (ABSP 400) parts fabricated using the FDM tech- nique. It was found that contraction prevailed along the directions of the length and width, whereas the thickness increased from the desired value of the fabricated part. Optimum parameter settings to minimize the responses, such as the change in length, width, and thickness of the test specimen, have been determined using Taguchi's parameter design. Because Taguchi's philosophy fails to obtain uniform optimal factor settings for each response, in this study, a fuzzy inference system combined with the Taguchi philosophy has been adopted to generate a single response from three responses, to reach the specific target values with the overall optimum factor level settings. Further, Taguchi and artificial neural network predictive models are also presented in this study for an accuracy evaluation within the dimensions of the FDM fabricated parts, subjected to various operating conditions. The pre- dicted values obtained from both models are in good agreement with the values from the experiment data, with mean absolute percentage errors of 3.16 and 0.15, respectively. Finally, the confirmatory test results showed an improvement in the multi-response performance index of 0.454 when using the optimal FDM parameters over the initial values.展开更多
Biomass derived vegetable oils are quite promising alternative fuels for agricultural diesel engines.Use of vegetable oils in diesel engines leads to slightly inferior performance and higher smoke emissions due to the...Biomass derived vegetable oils are quite promising alternative fuels for agricultural diesel engines.Use of vegetable oils in diesel engines leads to slightly inferior performance and higher smoke emissions due to their high viscosity.The performance of vegetable oils can be improved by modifying them through the transesterification process.In this present work,the performance of single cylinder water-cooled diesel engine using methyl-ester of Jatropha oil as the fuel was evaluated for its performance and exhaust emissions.The fuel properties of biodiesel such as kinematic viscosity,calorific value,flash point,carbon residue and specific gravity were found.Results indicate that B25 has closer performance to diesel and B100 has lower brake thermal efficiency mainly due to its high viscosity compared to diesel.The brake thermal efficiency for biodiesel and its blends was found to be slightly higher than that of diesel fuel at tested load conditions and there was no difference of efficiency between the biodiesel and its blended fuels.For Jatropha biodiesel and its blended fuels,the exhaust gas temperature increased with the increase of power and amount of biodiesel.However,its diesel blends showed reasonable efficiencies,lower smoke,CO_(2),CO and HC emissions.展开更多
文摘In this paper, the operating conditions, technical requirements, performance characteristics, design ideas, application experiences and development trends of aerospace engine bearings, including material technology, integration design and reliability, are reviewed. The development history of aerospace engine bearing is recalled briefly at first. Then today's material technologies and the high bearing performances of the bearings obtained through the new materials are introduced, which play important roils in the aeroengine bearing developments. The integration design ideas and practices are explained to indicate its significant advantages and importance to the aerospace engine bearings. And the reliability of the shaft-bearing system is pointed out and treated as the key requirement with goals for both engine and bearing. Finally, as it is believed that the correct design comes from practice, the pre-qualification rig testing conducted by FAG Aerospace GmbH & Co. KG is briefly illustrated as an example. All these lead to the development trends of aerospace engine bearings from different aspects.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11405032)
文摘Under the assumption of low-dissipation, a unified model of generalized Carnot cycles with external leakage losses is established. Analytical expressions for the power output and efficiency are derived. The general performance characteristics between the power output and the efficiency are revealed. The maximum power output and efficiency are calculated. The lower and upper bounds of the efficiency at the maximum power output are determined. The results obtained here are universal and can be directly used to reveal the performance characteristics of different Carnot cycles, such as Carnot heat engines, Carnot-like heat engines, flux flow engines, gravitational engines, chemical engines, two-level quantum engines, etc.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10765004 and 11065008).
文摘This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.
文摘DG-MOSFETs are the most widely explored device architectures for na</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">no-scale CMOS circuit design in sub-50 nm due to the improved subthre</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">shold slope and the reduced leakage power compared to bulk MOSFETs. In thin-film (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;"> < 10 nm) DG-MOS structures, charge carriers are affected</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> by</span></span></span><span><span><span style="font-family:""> <i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;">-</span></span></span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">induced quantum confinement along with the confinement caused by </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">a </span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">very high electric field at the interface. Therefore, quantum confinement effects on the device characteristics are also quite important and it needs to be incorpo</span><span style="font-family:Verdana;">rated along with short channel effects for nano-scale circuit design. In this</span> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">, we analyze</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">d</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> a DG-MOSFET structure at </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">the </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">20 nm technology node</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> incorporating quantum confinement effects and various short channel effects. The effect of physical parameter variations on performance characteristics of </span><span><span style="font-family:Verdana;">the device such as threshold voltage, subthreshold slope, </span><i><span style="font-family:Verdana;">I</span><sub><span style="font-family:Verdana;">ON</span></sub></i><span style="font-family:Verdana;"> - </span><i><span style="font-family:Verdana;">I</span><sub><span style="font-family:Verdana;">OFF</span></sub></i><span style="font-family:Verdana;"> ratio,</span></span> <i><span style="font-family:Verdana;">DIBL</span></i></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> etc. has been investigated and plotted through extensive TCAD simulations. The physical parameters considered in this </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> are operating temperature </span><span><span style="font-family:Verdana;">(</span><i><span style="font-family:Verdana;">T</span><sub><span style="font-family:Verdana;">op</span></sub></i><span style="font-family:Verdana;">), channel doping concentration (</span><i><span style="font-family:Verdana;">N</span><sub><span style="font-family:Verdana;">c</span></sub></i><span style="font-family:Verdana;">), gate oxide thickness (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">ox</span></sub></i><span style="font-family:Verdana;">) an</span></span><span style="font-family:Verdana;">d Silicon film thickness (</span><i><span style="font-family:Verdana;">t</span><sub><span style="font-family:Verdana;">si</span></sub></i><span style="font-family:Verdana;">). It </span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">was</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> observed that quantum confinement of </span><span style="font-family:Verdana;">charge </span><span style="font-family:Verdana;">carriers significantly affect</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">ed</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the performance characteristics (mostly the</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> subth</span><span style="font-family:Verdana;">reshold characteristics) of the device and therefore, it cannot be ignored in</span><span style="font-family:Verdana;"> the </span><span style="font-family:Verdana;">subthreshold region</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">based circuit design like in many previous research</span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;"> works. </span><span><span style="font-family:Verdana;">The ATLAS</span><sup><span style="font-family:Verdana;">TM</span></sup><span style="font-family:Verdana;"> device simulator has been used in this </span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">paper</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> to perform simu</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">lation and parameter extraction. The TCAD analysis presented in the</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> manuscript can be incorporated for device modeling and device</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> matching. It can be used to illustrate exact device behavior and for proper device control.
文摘The low stress abrasion behaviours of heat treated mild, medium carbon and high C - low Cr steels, which are generally used in making farm implements, have been investigated. The simple heat treatment greatly improves the hardness, tensile strength and abrasion resistance of medium carbon and high C - low Cr steels. The results indicate that the material removal during abrasion is controlled by a number of factors, such as hardness, chemical composition, microstructure and heat treatment conditions. The conclusion is that the heat treated high C - low Cr steel and mild steel carburized by using coaltar pitch provide the best hardness and abrasion resistance and thus appear to be the most suitable materials for making agricultural tools.
基金Funded by the National Natural Science Foundation of China(No.51271036)
文摘To investigate the ballistic performance and damage characteristics of quasi threedimensional(3D) needle-punched Cf/SiC composites prepared by chemical vapor infiltration(CVI),penetration experiments were conducted by using 7.62 mm armor piercing incendiary(API).Macro and micro fracture morphologies were then observed on recycled targets.The results show that the protection coefficient of 3D Cf/SiC composites is 2.54.High porosity and many micro thermal stress cracks may directly lead to the lower ballistic performance.Flat fracture morphology was observed on the crater surface.The low dynamic fracture strength along layer direction may be attributed to the voids and microcracks caused by residual thermal stress.The damage characteristics of Cf/Si C composites include matrix cracking,fiber bundle cracking,interfacial debonding,fiber fracture,and fiber bundle pull-out.And interfacial debonding and fiber fracture may play major roles in energy absorption.
文摘This study aims to determine the morphometric characteristics and reproductive performance of Pasundan cows which are extensively reared on smallholder farms in the coastal areas of the south(Garut,Cianjur,and Sukabumi)and North Priangan(Bogor,Purwakarta,and Sumedang).This research is descriptive research with a qualitative approach.Production characterization was carried out using a simple method,namely by measuring the body surface including shoulder height,chest circumference,body length,and bodyweight of Pasundan cattle.Meanwhile,the reproductive characteristics discuss puberty,service per conception(S/C),conception rate(CR),calving rate,postpartum estrus,postpartum mating,days open(DO),calving interval(CI),calving birth weight,calving rate,and calves weight growth.Data were collected by survey,and the location was determined by purposive sampling in the area of the seed source with the largest population and the random sampling of livestock was determined purposively as many as 30 Pasundan cows from each region.Data were analyzed using quantitative descriptive analysis.The results showed that the morphometric characteristics of Pasundan cattle included mean shoulder height of 123.00±3.06a cm VS 121.34±2.82a in males and 110.34±2.78 vs 108.00±2.14a in females.Body length 115.74±3.30 cm VS 115.34±2.97acm in males and 112.67±2.97cm VS 109.67±1.82 cm in females.Chest circumference 145.67±2.97cm VS 142.67±2.67cm bulls and 136.00±2.95cm VS 131.00±2.92cm in females,Bodyweight 268.0±17.00 kg VS 246.00±7.00a for males and 215.0±15.00 kg VS 194.00±54.00kg in females.As for reproductive characteristics,it shows puberty of 20-24 months.,S/C 1.4-1.6,Conception rate 65-70%,calving rate 62.5-65%,Postpartum Estrus 50-60 days,postpartum mating 72-104 days,day-open 94-126 days and a calving interval of 12-14 months.Calves'birth weight was 18.0-18.5 kg and daily body weight gain ranged from 0.48 to 0.50 kg.It was concluded that the morphometric characteristics and reproductive performance of Pasundan cattle in the Pesisir Selatan area were better than North Priangan.
基金Sponsored bythe National Natural Science Foundation of China(50679001) the Basic Research Foundation of Beijing Institute of Technology(20060342001)
文摘The performance characteristics of an axial-flow pump with tandem blades are studied based on the numerical computations. The arrangement of the pump impellers is established through the analysis of velocity triangles. With the commercial computational fluid dynamics (CFD) software NUMECA, the turbulent flow in the tandem axial-flow pump is simulated in various flow conditions. The detail flow structure in the leading edge region of the rear impeller is described, and the influence of the deflection angle of the rear blade on the head performance is studied. According to the simulation, the performance comparison is made between the tandem axial-flow pump and the conventional two-stage axial-flow pump with a uniform impeller size. Results of the study indicate that the tandem axial-flow pump can work in a wider range with high efficiency.
文摘We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.
文摘Experimental investigation of the passive control on improving the unstable characteristics in axial flow fans is performed. It is confirmed that the air-separator is an excellent equipment for rotating stall suppression. The air-separator can effectively remove low energy fluid near the fan casing. Further, it can improve the low flow rate range performance and increase stall margin of the axial flow fan.
基金supported by the National Natural Science Foundation of China (Grant No 10575084)
文摘Based on a general model of Brownian motors, the Onsager coefficients and generalized efficiency of a thermal Brownian motor are calculated analytically. It is found that the Onsager reciprocity relation holds and the Onsager coefficients are not affected by the kinetic energy change due to the particle's motion. Only when the heat leak in the system is negligible can the determinant of the Onsager matrix vanish. Moreover, the influence of the main parameters characterizing the model on the generalized efficiency of the Brownian motor is discussed in detail. The characteristic curves of the generalized efficiency varying with these parameters are presented, and the maximum generalized efficiency and the corresponding optimum parameters are determined. The results obtained here are of general significance. They are used to analyze the performance characteristics of the Brownian motors operating in the three interesting cases with zero heat leak, zero average drift velocity or a linear response relation, so that some important conclusions in current references are directly included in some limit cases of the present paper.
文摘The growth in computer processing power has made it possible to use time-consuming analysis methods such as incremental dynamic analysis(IDA) with higher accuracy in less time.In an IDA study,a series of earthquake records are applied to a structure at successively increasing intensity levels,which causes the structure to shift from the elastic state into the inelastic state and finally into collapse.In this way,the limit-states and capacity of a structure can be determined.In the present research,the IDA of a concrete gravity dam considering a nonlinear concrete behavior,and sliding planes within the dam body and at the dam-foundation interface,is performed.The influence of the friction angle and lift joint slope on the response parameters are investigated and the various limit-states of the dam are recognized.It is observed that by introducing a lift joint,the tensile damage can be avoided for the dam structure.The lift joint sliding is essentially independent of the base joint friction angle and the upper ligament over the inclined lift joint slides into the upstream direction in strong earthquakes.
基金supported by General Program of National Natural Science Foundation of China(61773080)China Central Universities Foundation(2019CDYGZD001)+1 种基金Scientific Reserve Talent Programs of Chongqing University(cqu2018CDHB1B04)Graduate Research and Innovation Foundation of Chongqing(CYB20065)。
文摘In this paper,a novel remaining useful life prediction approach considering fault effects is proposed.The Wiener process is used to construct the degradation process of single performance characteristic with the fault effects.The first passage time based remaining useful life distribution is calculated by assuming fault occurrence moment is a random variable and follows a certain distribution.Expectation maximization algorithm is employed to estimate model parameters,where the fault occurrence moment is considered as a missing data.Finally,a Copula function is used to describe the dependence between the multiple performance characteristics and derive joint remaining useful life(RUL)distribution of product with the fault effects.The effectiveness of the proposed approach is verified by the experiments of turbofan engines.
基金supported by China Postdoctoral Science Foundation(2021M690740)supported by project of the study on the gradient utilization and industrialization demonstration of lithium-ion power battery(ZH01110405180053PWC).
文摘Accurate simulation of characteristics performance and state of health(SOH)estimation for lithium-ion batteries are critical for battery management systems(BMS)in electric vehicles.Battery simplified electrochemical model(SEM)can achieve accurate estimation of battery terminal voltage with less computing resources.To ensure the applica-bility of life-cycle usage,degradation physics need to be involved in SEM models.This work conducts deep analysis on battery degradation physics and develops an aging-effect coupling model based on an existing improved single particle(ISP)model.Firstly,three mechanisms of solid electrolyte interface(SEI)film growth throughout life cycle are analyzed,and an SEI film growth model of lithium-ion battery is built coupled with the ISP model.Then,a series of identification conditions for individual cells are designed to non-destructively determine model parameters.Finally,battery aging experiment is designed to validate the battery performance simulation method and SOH estimation method.The validation results under different aging rates indicate that this method can accurately es-timate characteristics performance and SOH for lithium-ion batteries during the whole life cycle.
文摘The objective of this study was to investigate the possibility of fitting spline regression models for power take-off(PTO)performance characteristics of an agricultural tractor tested with four different fuels,including diesel fuel(B0)and three biodiesel blends made of canola oil(B10:10%biodiesel+90%petro-diesel blend;B20:20%biodiesel+90%petro-diesel blend;B30:30%biodiesel+90%petro-diesel blend).The performance characteristics evaluated were PTO power,engine torque,engine fuel consumption,and specific fuel consumption.Due to sharp slopes in measured quantities around the nominal engine speed(2200 r/min),compared to the standard regression method,the spline regression models suited well to the experimental data with coefficient of determination R2=0.99 for PTO power and engine torque.R2 varied between 0.97 and 0.99 for fuel consumption and 0.91 and 0.95 for specific fuel consumption.The weaker correlation found for specific fuel consumption could be attributed to profound fluctuations in measured data causing atypical pattern in the corresponding graphs around the nominal engine speed.It was concluded that splines were useful to accurately predict the measured PTO power and engine torque.Neither standard methods nor splines were sufficient to obtain very good regression models for specific fuel consumption.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51406185,51579225)the Third Level 151 Talent Project in Zhejiang Province
文摘The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In order to improve the anti-cavitation performance of the centrifugal pumps, variable-pitch inducers are placed upstream of the impeller. Because the rotational speeds directly affect the flow and the performance of the pump, it is essential to characterize the performance of the pump with a variable-pitch inducer at various rotational speeds. In this paper, the simulations and the experimental tests of a centrifugal pump with a variable-pitch inducer are designed and carried out under various rotational speed conditions. Navier-Stokes equations, coupled with a Reynolds average simulation approach, are used in the simulations. In the experimental tests, the external and anti-cavitation performances of the pump are investigated in a closed system. The following results are obtained from the simulations. Firstly, the velocity in the passage of the inducer rises with the increase of the rotational speed. Secondly, the static pressure escalates on the inducer and the impeller with the increase of the rotational speed. Thirdly, the static pressure distribution on the inducer and the impeller is asymmetric. Fourthly, the anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Additional results are gathered from an analysis of the experiments. H-Q curves are similar parabolas at various rotational speeds, while η-Q curves are similar parabolas only when n ≤6 000 r/min. The anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Finally, the simulation results are found to be consistent with the experimental results.
基金supported by Guangdong Basic and Applied Basic Research Foundation(2019B1515120020)the Creative Research Groups of China(51921001)the National Natural Science Foundation of China(52273280)。
文摘Fused deposition modeling (FDM) is an additive manufacturing technique used to fabricate intricate parts in 3D, within the shortest possible time without using tools, dies, fixtures, or human intervention. This article empiri- cally reports the effects of the process parameters, i.e., the layer thickness, raster angle, raster width, air gap, part orientation, and their interactions on the accuracy of the length, width, and thicknes, of acrylonitrile-butadiene- styrene (ABSP 400) parts fabricated using the FDM tech- nique. It was found that contraction prevailed along the directions of the length and width, whereas the thickness increased from the desired value of the fabricated part. Optimum parameter settings to minimize the responses, such as the change in length, width, and thickness of the test specimen, have been determined using Taguchi's parameter design. Because Taguchi's philosophy fails to obtain uniform optimal factor settings for each response, in this study, a fuzzy inference system combined with the Taguchi philosophy has been adopted to generate a single response from three responses, to reach the specific target values with the overall optimum factor level settings. Further, Taguchi and artificial neural network predictive models are also presented in this study for an accuracy evaluation within the dimensions of the FDM fabricated parts, subjected to various operating conditions. The pre- dicted values obtained from both models are in good agreement with the values from the experiment data, with mean absolute percentage errors of 3.16 and 0.15, respectively. Finally, the confirmatory test results showed an improvement in the multi-response performance index of 0.454 when using the optimal FDM parameters over the initial values.
文摘Biomass derived vegetable oils are quite promising alternative fuels for agricultural diesel engines.Use of vegetable oils in diesel engines leads to slightly inferior performance and higher smoke emissions due to their high viscosity.The performance of vegetable oils can be improved by modifying them through the transesterification process.In this present work,the performance of single cylinder water-cooled diesel engine using methyl-ester of Jatropha oil as the fuel was evaluated for its performance and exhaust emissions.The fuel properties of biodiesel such as kinematic viscosity,calorific value,flash point,carbon residue and specific gravity were found.Results indicate that B25 has closer performance to diesel and B100 has lower brake thermal efficiency mainly due to its high viscosity compared to diesel.The brake thermal efficiency for biodiesel and its blends was found to be slightly higher than that of diesel fuel at tested load conditions and there was no difference of efficiency between the biodiesel and its blended fuels.For Jatropha biodiesel and its blended fuels,the exhaust gas temperature increased with the increase of power and amount of biodiesel.However,its diesel blends showed reasonable efficiencies,lower smoke,CO_(2),CO and HC emissions.