Optimization Study on a Single-cylinder Compressed Air Engine

The current research of compressed air engine（CAE） mainly focused on simulations and system integrations. However, energy efficiency and output torque of the CAE is limited, which restricts its application and popularization. In this paper, the working principles of CAE are briefly introduced. To set a foundation for the study on the optimization of the CAE, the basic mathematical model of working processes is set up. A pressure-compensated valve which can reduce the inertia force of the valve is proposed. To verify the mathematical model, the prototype with the newly designed pressure-compensated intake valve is built and the experiment is carried out, simulation and experimental results of the CAE are conducted, and pressures inside the cylinder and output torque of the CAE are obtained. Orthogonal design and grey relation analysis are utilized to optimize structural parameters. The experimental and optimized results show that, first of all, pressure inside the cylinder has the same changing tendency in both simulation curve and experimental curve. Secondly, the highest average output torque is obtained at the highest intake pressure and the lowest rotate speed. Thirdly, the optimization of the single-cylinder CAE can improve the working efficiency from an original 21.95% to 50.1%, an overall increase of 28.15%, and the average output torque increases also increases from 22.047 5 N · m to 22.439 N · m. This research designs a single-cylinder CAE with pressure-compensated intake valve, and proposes a structural parameters design method which improves the single-cylinder CAE performance.

Cutting Behavior of Cortical Bone in Different Bone Osteon Cutting Angles and Depths of Cut

Cortical bone is semi-brittle and anisotropic,that brings a challenge to suppress vibration and avoid undesired fracture in precise cutting process in surgeries.In this paper,a novel analytical model is proposed to represent cortical bone cutting processes.The model is utilized to predict the chip formations,material removal behavior and cracks propagation under varying bone osteon cutting angles and depths.Series of orthogonal cutting experiments were conducted on cortical bone to investigate the impact of bone osteon cutting angle and depth of cut on cutting force,crack initialization and propagation.The observed chip morphology highly agreed with the prediction of chip formation based on the analytical model.The curly,serrated,grainy and powdery chips formed when the cutting angle was set as 0°,60°,90°,and 120°,respectively.Cortical bone were removed dominantly by shearing at a small depth of cut from 10 to 50μm,and by a mixture of pealing,shearing,fracture and crushing at a large depth of cut over 100μm at different bone osteon angles.Moreover,its fracture toughness was calculated based on measured cutting force.It is found that the fluctuation of cutting force is suppressed and the bone material becomes easy to remove,which attributes to lower fracture toughness at bone osteon cutting angle 0°.When the cutting direction develops a certain angle to bone osteon,the fracture toughness increases then the crack propagation is inhibited to some extent and the fluctuation of cutting force comparatively decreases.There is a theoretical and practical significance for tools design and operational parameters choice in surgeries.

Low-frequency variability of terrestrial water budget in China using GRACE satellite measurements from 2003 to 2010

Mass variations in terrestrial water storage（TWS） obtained from eight years of satellite data from the Gravity Recovery and Climate Experiment（GRACE） are used to describe low frequency TWS through Empirical Orthogonal Function（EOF） analysis. Results of the second seasonal EOF mode show the influence of the Meiyu season. Annual variability is clearly shown in the precipitation distribution over China, and two new patterns of interannual variability are presented for the first time from observations, where two periods of abrupt acceleration are seen in 2004 and 2008. GRACE successfully measures drought events in southern China, and in this respect, an association with the Arctic Oscillation and El Nino-Southern Oscillation is discussed. This study demonstrates the unique potential of satellite gravity measurements in monitoring TWS variations and large-scale severe drought in China.

Rotorcraft flight endurance estimation based on a new battery discharge model

To avoid the numerical complexities of the battery discharge law of electric-powered rotorcrafts,this study uses the Kriging method to model the discharge characteristics of Li-Po batteries under standard conditions.A linear current compensation term and an ambient temperature compensation term based on radial basis functions are then applied to the trained Kriging model,leading to the complete discharged capacity-terminal voltage model.Using an orthogonal experimental design and a sequential method,the coefficients of the current and ambient temperature compensation terms are determined through robust optimization.An endurance calculation model for electric-powered rotorcrafts is then established,based on the battery discharge model,through numerical integration.Laboratory tests show that the maximum relative error of the proposed discharged capacity-terminal voltage model at detection points is 0.0086,and that of the rotorcraft endurance calculation model is 0.0195,thus verifying their accuracy.A flight test further demonstrates the applicability of the proposed endurance model to general electric-powered rotorcrafts.

Optimal Model Average Prediction in Orthogonal Kriging Models

The main objective of this paper is to consider model averaging methods for kriging models.This paper proposes a Mallows model averaging procedure for the orthogonal kriging model and demonstrate the asymptotic optimality of the model averaging estimators in terms of mean square error.Simulation studies are conducted to evaluate the performance of the proposed method and compare it with the competitors to demonstrate its superiority.The authors also analyse a real dataset for an illustration.

No-Load Iron Loss Model for a Fractional-Slot Surface-Mounted Permanent Magnet Motor Based on Magnetic Field Analytical Calculation

The common analytical models for the no-load iron loss of permanent magnet(PM)motors usually neglect the iron loss caused by the rotating magnetic field in the tooth tips and the harmonics of the magnetic fields in the teeth and yokes.This paper presents an analytical model for no-load iron loss of a fractional-slot surface-mounted permanent magnet motor.According to the existing analytical model of the magnetic field distribution in the slotted air gap,the magnetic flux densities considering the harmonics of the stator tooth and yoke are both derived based on the continuity of magnetic flux.Due to the complexity of the magnetic field in the tooth tip,the tangential flux density of the tooth tip is approximated by an equivalent sine wave and the radial component is regarded to be the same as that of the corresponding tooth.After obtaining the magnetic fields in stator different regions,the analytical iron loss is calculated by using the Bertotti model and the orthogonal decomposition model.A 20-pole/24-slot PM synchronous motor is taken as an example.The maximum error between the analytical model and finite element model(FEM)is 5.46%,which verifies the validity of the proposed method.

Finite element modeling of chip separation in machining cellular metals

Cellular metals and metal foams belong to a young material group. Although it is desired to manufac- ture near-net-shape parts of cellular metals by primary shaping processes, additional secondary machining opera- tions are often unavoidable to obtain the required geome- tries and quality demands. Nevertheless, conventional machining of cellular metals leads to undesirable surface damage and poor precision. Furthermore, the chip forma- tion and the mechanism description of the surface damage are still unclear. A mesoscopic finite element model was developed to simulate the chip formation process in machining cellular metals. Experimental data of orthogonal machining tests were used to validate the finite element model. The cutting and thrust forces, as well as the images of the chip formation process of both experiments and simulations were compared and analysed. The model enabled the analysis of the chip formation and the surface defect mechanisms. The rake angle and cutting conditions affected the chip formation process, but the cell arrange- ment was detected as a decisive factor in the chip forma- tion and the resulting surface damage.