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An automated approach to calculating the maximum diameters of multiple cutters and their paths for sectional milling of centrifugal impellers on a 4_(1/2)-axis CNC machine

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Chinese Journal of Aeronautics 2019年第4期32卷 1030-1039页

作者： Baohai WU Zezhong C.CHEN Ming LUO Dinghua ZHANG Feiyan HAN School of mechanical engineering Northwestern Polytechnical University Department of mechanical Industrial and Aerospace EngineeringConcordia University College of mechanical engineering Xi'an University of Science and Technology

Power generators and chemical engineering compressors include heavy and large centrifugal impellers. To produce these impellers in high-speed machining, a 4?-axis milling machine(or a 4-axis machine plus an indexing table) is often used in the industry, which is more rigid than a5-axis milling machine. Since impeller blades are designed with complex B-spline surfaces and impeller channels spaces vary significantly, it is more efficient to use multiple cutters as large as possible to cut a channel in sections and a blade surface in patches, instead of only using a small cutter to machine a whole blade and a channel. Unfortunately, no approach has been established to automatically calculate the largest diameters of cutters and their paths, which include the indexing table angles. To address this problem, an automated and optimization approach is proposed. Based on the structure of a 4?-axis machine, a geometric model for a cutter gouging/interfering the impeller is formulated, and an optimization model of the cutter diameter in terms of the indexing table angle is established at a cutter contact(CC) point on a blade surface. Then, the diameters of the tools,their orientations, and the indexing table angles are optimized, and each tool's paths are generated for machining its corresponding impeller section. As a test, an impeller is efficiently machined with these tools section by section; thus, this approach is valid. It can be directly used in the industry to improve efficiency of machining centrifugal impellers.

关键词： Automated path generation 4_(1/2)-Axis CNC machining Centrifugal impeller machining Cutter diameter optimization Sectional machining

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Numerical evaluation of passive control of shock wave/boundary layer interaction on NACA0012 airfoil using jagged wall

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Acta Mechanica Sinica 2016年第5期32卷 792-804页

作者： Mojtaba Dehghan Manshadi Ramin Rabani mechanical and aerospace engineering Department Malek-Ashtar University of TechnologyEsfahan Iran Department of mechanical engineering Yazd University

Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.

关键词： Jagged wall Passive flow control Shock wave/boundary layer interaction Aerodynamic efficiency

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Electrochemical Machining Analysis on Grid Cathode Composed of Square Cells

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Chinese Journal of mechanical engineering 2013年第4期26卷 668-674页

作者： LU Yonghua LIU Kai ZHAO Dongbiao College of mechanical and Electrical engineering Nanjing University of Aeronautics and Astronautics Department of aerospace and mechanical engineering University of Notre Dame

During the electrochemical machining (ECM), the cathodes designed by the existing methods are mainly unitary cathodes, which can be only used to produce the workpieces with the same shapes. However, there are few researches on designing cathodes for machining the different workpieces with the different surfaces. This paper presents the grid cathode composed of the square cells to produce the workpieces with different shapes. Three types of the square cells, 2.5 mm′2.5 mm, 3 mm′3 mm, and 4 mm′4 mm, are utilized to construct the plane, the slant, and the blade cathode. The material of the cathode and the anode is CrNi 18 Ti 9 , and the ingredient of electrolyte is 15% NaCl and 15% NaNO 3 . The machining equilibrium machining current and time are acquired and analyzed, the machining process and the workpiece quality are compared between using the grid cathode and the unitary cathode. Moreover, the machining errors on the workpiece surface are measured and analyzed, and the error reasons are traced and discussed to obtain the better surface quality of the workpiece. The experiment and analysis results show that the grid cathode can be used to manufacture the workpieces with complex shapes in certain range of the error. The workpiece quality improves with the size of the square cell being reduced, and if the square element is small enough, the workpiece quality is almost equal to the one machined by the unitary cathode. The proposed research realizes a single cathode machining the different workpieces with the different surfaces.

关键词： grid cathode square cell equilibrium machining current electrochemical machining (ECM)

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Review on monolayer CBN superabrasive wheels for grinding metallic materials

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Chinese Journal of Aeronautics 2017年第1期30卷 109-134页

作者： Ding Wenfeng Barbara Linke Zhu Yejun Li Zheng Fu Yucan Su Honghua Xu Jiuhua College of mechanical and Electrical engineering Nanjing University of Aeronautics and Astronautics Department of mechanical and aerospace engineering University of California Davis

A state-of-the-art review on monolayer electroplated and brazed cubic boron nitride（CBN） superabrasive wheels for grinding metallic materials has been provided in this article. The fabrication techniques and mechanisms of the monolayer CBN wheels are discussed. Grain distribution, wheel dressing, wear behavior, and wheel performance are analyzed in detail. Sample applications of monolayer CBN wheel for grinding steels, titanium alloys, and nickel-based superalloys are also provided. Finally, this article highlights opportunities for further investigation of monolayer CBN grinding wheels.

关键词： Brazed Cubic boron nitride Electroplated Grinding Monolayer superabrasive wheels

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Development of a novel fabricating thin-walled TA2 titanium tube via high-frequency induction welding

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Progress in Natural Science:Materials International 2024年第2期34卷 314-322页

作者： Yanfeng Liu Qi Chen Jibing Chen Junsheng Yang Shijie Dong School of mechanical engineering Wuhan Polytechnic University Hubei Sanjiang aerospace Jiangbei mechanical engineering Co. Ltd

Due to the problems of low welding efficiency, large heat-affected zone, and poor welding quality in the process of welding thin-walled titanium tubes by argon arc welding, there are few studies on the use of high-frequency induction welding(HFIW) of thin-walled titanium alloy tubes. The evolution law of weld microstructure and mechanical properties of the thin-walled titanium tube needs to be further studied because of rapid welding speed and the small heat-affected zone of HFIW. Therefore, a novel manufacturing method via high-frequency induction welding is proposed in this paper to solve the existing problems. With an industrial-grade titanium TA2 tube(wall's thickness is 0.5 mm) as the research object, a comparative study is conducted in this research to examine the morphology, microstructure, microhardness, and tensile characteristics of welded joints at different welding power. The findings demonstrated a significant efficacy of HFIW in resolving these challenges. The mechanical properties and microstructue of heat-affected zone(HAZ) were characterized. The lowest hardness is measured at202 HV, while the base material was recorded as 184 HV, when the welding speed of HFIW is set at 50 m/***, the heat-affected zone has the highest hardness at 224 HV, a tensile strength of 446.8 MPa and a postfracture elongation of 16%. The results showed that HFIW can not only greatly improve the welding efficiency,significantly improve the microstructure of weld joint and HAZ, and improve the mechanical properties of thinwalled titanium pipe, but also provide a highly feasible welding method for welding ultra-thin-walled pipes.

关键词： Heat-affected zone High-frequency induction welding mechanical property Microstructure TA2 titanium Thin-walled tube

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Fundamental theories and basic principles of triboelectric effect: A review

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Friction 2019年第1期7卷 2-17页

作者： Shuaihang PAN Zhinan ZHANG School of mechanical engineering Shanghai Jiao Tong University School of mechanical & aerospace engineering University of California Los Angeles

Long-term observation of the triboelectric effect has not only proved the feasibility of many novel and useful tribo-devices(e.g., triboelectric nanogenerators), but also constantly motivated the exploration of its mysterious nature. In the pursuit of a comprehensive understanding of how the triboelectric process works, a more accurate description of the triboelectric effect and its related parameters and factors is urgently required. This review critically goes through the fundamental theories and basic principles governing the triboelectric process. By investigating the difference between each charging media, the electron, ion, and material transfer is discussed and the theoretical deduction in the past decades is provided. With the information from the triboelectric series, interesting phenomena including cyclic triboelectric sequence and asymmetric triboelectrification are precisely analyzed. Then, the interaction between the tribo-system and its operational environment is analyzed, and a fundamental description of its effects on the triboelectric process and results is summarized. In brief, this review is expected to provide a strong understanding of the triboelectric effect in a more rigorous mathematical and physical sense.

关键词： triboelectric effect triboelectrification triboelectric nanogenerators(TENGs) interface

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Innovative dual-mode device integrating capacitive desalination and solar vapor generation for high-efficiency seawater desalination

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Journal of Energy Chemistry 2025年第1期100卷 171-179页

作者： Jiacheng Wang Zhaoyu Chen Ruduan Yuan Jiaxin Luo Ben Zhang Keju Ji Meng Li Juanxiu Xiao Kuan Sun National Innovation Center for Industry-Education Integration of Energy Storage Technology MOE Key Laboratory of Low-grade Energy Utilization Technologies and SystemsCollege of Energy & Power Engineering Chongqing University Xuefeng Mountain Energy Equipment Safety National Observation and Research Station CQU-NUS Renewable Energy Materials & Devices Joint Laboratory Chongqing University Southwest Technology and engineering Research Institute Jiangsu Provincial Key Laboratory of Bionic Functional Materials College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and Astronautics State Key Laboratory of Marine Resources Utilization in South China Sea Collaborative Innovation Center of Marine Science and Technology School of Marine Science and Engineering Hainan University

Solar-driven interface evaporation with high solar-to-steam conversion efficiency has shown great potential in seawater ***,due to the influence of latent heat and condensation efficiency,the water yield from solar-driven interface evaporation remains insufficient,posing a significant challenge that requires *** this work,we designed a dual-mode high-flux seawater desalination device that combines solar-driven interface evaporation and capacitive *** utilizing coupled desalination materials exhibiting both photothermal conversion and capacitance activity,the device demonstrated photothermal evaporation rates of 1.41 and 0.97 kg m-2h-1for condensate water yield under one-sun ***,the device exhibited a salt adsorption capacity of up to48 mg g-1and a salt adsorption rate of 2.1 mg *** addition,the salt adsorption capacity increased by approximately 32% under one-sun ***,photo-enhanced capacitive desalination performance was explored through numerical simulations and theoretical *** calculations and characterizations confirmed that the defect energy levels formed by the introduction of sulfur vacancies can effectively widen the light absorption range,improve photothermal conversion performance,and stimulate more photoelectrons to participate in capacitive ***,the electron distribution state of molybdenum disulfide with sulfur vacancies and surface defect sites contributes to ion/electron transport at the solid-liquid *** work provides a novel pathway for integrating solar vapor generation with other low-energy desalination technologies.

关键词： Desalination

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Entropy method of measuring and evaluating periodicity of quasi-periodic trajectories

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Science China(Physics,Mechanics & Astronomy) 2018年第6期61卷 30-49页

作者： Yanshuo Ni Konstantin Turitsyn Hexi Baoyin Junfeng Li School of aerospace engineering Tsinghua University Department of mechanical engineering Massachusetts Institute of Technology

This paper presents a method for measuring the periodicity of quasi-periodic trajectories by applying discrete Fourier transform （DFT） to the trajectories and analyzing the frequency domain within the concept of entropy. Having introduced the concept of entropy, analytical derivation and numerical results indicate that entropies increase as a logarithmic function of time. Periodic trajectories typically have higher entropies, and trajectories with higher entropies mean the periodicities of the motions are stronger. Theoretical differences between two trajectories expressed as summations of trigonometric functions are also derived analytically. Trajectories in the Henon-Heiles system and the circular restricted three-body problem （CRTBP） are analyzed with the indicator entropy and compared with orthogonal fast Lyapunov indicator （OFLI）. The results show that entropy is a better tool for discriminating periodicity in quasiperiodie trajectories than OFLI and can detect periodicity while excluding the spirals that are judged as periodic cases by OFLI. Finally, trajectories in the vicinity of 243 Ida and 6489 Golevka are considered as examples, and the numerical results verify these conclusions. Some trajectories near asteroids look irregular, but their higher entropy values as analyzed by this method serve as evidence of frequency regularity in three directions. Moreover, these results indicate that applying DFT to the trajectories in the vicinity of irregular small bodies and calculating their entropy in the frequency domain provides a useful quantitative analysis method for evaluating orderliness in the periodicity of quasi-periodic trajectories within a given time interval.

关键词： quasi-periodic trajectories entropy quality evaluating

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Verification on Spray Simulation of a Pintle Injector for Liquid Rocket Engine

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Journal of Thermal Science 2016年第1期25卷 90-96页

作者： Min Son Kijeong Yu Kanmaniraja Radhakrishnan Bongchul Shin Jaye Koo Korea aerospace University GoyangRepublic of Korea School of aerospace and mechanical engineering Korea Aerospace UniversityGoyangRepublic of Korea

The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.

关键词： Spray characteristics Pintle injector Simulation Experiment Liquid rocket engine

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Dynamic Stability Analysis of Linear Time-varying Systems via an Extended Modal Identification Approach

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Chinese Journal of mechanical engineering 2017年第2期30卷 459-471页

作者： Zhisai MA Li LIU Sida ZHOU Frank NAETS Ward HEYLEN Wim DESMET School of aerospace engineering Beijing Institute of Technology Department of mechanical engineering KU Leuven

The problem of linear time-varying（LTV） system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the ＂frozen-time＂ assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stabilitypreserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system＇s stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam exper- imental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides anew way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.

关键词： Linear time·varying systems · Extended modal identification · Dynamic stability analysis · Time·varying modes

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