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Analytical Model of Elastomeric Lag Damper Kinematic Coupling and Its Effect on Helicopter Air Resonance in Hover

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Chinese Journal of aero.autics 2002年第1期15卷 27-32页

作者：胡国才向锦武张晓谷 Institute of Aircraft Design Beijing Univ. of Aero. and Astro. Beijing 100083 China

For an elastomeric lag damper with nonlinear properties and kinematic couplings, its differential equation about equilibrium position was derived in a rotating frame. The equation was then transformed into a non-rotating frame by multi-blade transformation and incorporated into the rotor/airframe differential equations for eigen analysis. The effects of damper steady displacement and kinematic couplings on helicopter air resonance in hover were analyzed. The results demonstrate that the elastomeric damper can increase helicopter dynamic stability; however, its available damping will decrease as its steady displacement increased. For the notional rotor system, the damper steady displacement will decrease when kinematic couplings are introduced, and hence the regressive lag modal damping can be increased.

关键词： Airframes Differential equations Helicopter rotors Kinematics Resonance

Genetic algorithms in bidisciplinary (aero.ynamics/electro-magnetism) optimization

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Science China Technological Sciences 2001年第6期44卷 572-580页

作者：朱自强李海明李津于日新 beijing univ. aero. and astro.aut. Beijing 100083 China

The genetic algorithm(GA) is a non-traditional, probability search and global optimization method similar to natural selection and evolution. The key points and control parameters of this method are briefly discussed. To apply it to a multiobjective and multidisciplinary optimization problem a kind of fitness function is suggested, in which the requirements of multiobjects and multiconstraints are considered and the nondimensional coefficients and panalty coefficients of the constraint function are also introduced . Numerical results of bidisciplinary optimization calculation show that the present method is effective, applicable, and robust.

关键词： genetic algorithm multidisciplinary optimization deterministic optimization.

Gas exchange optimization in aircraft engines using sustainable aviation fuel:A design of experiment and genetic algorithm approach

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Energy and AI 2024年第3期17卷 261-280页

作者： Zheng Xu Jinze Pei Shuiting Ding Longfei Chen Shuai Zhao Xiaowei Shen Kun Zhu Longtao Shao Zhiming Zhong Huansong Yan Farong Du Xueyu Li Pengfei Yang Shenghui Zhong Yu Zhou Hangzhou International Innovation Institute Beihang UniversityHangzhou311115China Research Institute of aero.Engine Beihang UniversityBeijing102206China Civil Aviation univ.rsity of China Tianjin300300China Aircraft/Engine Integrated System Safety beijing Key Laboratory Beijing100083China aero.Engine Academy of China Beijing101304China School of Energy and Power Engineering Beihang UniversityBeijing100083China AVIC Chengdu Aircraft Design and Research Institute Chengdu610091China AVIC Nanjing Engineering Institute of Aircraft Systems Nanjing211106China School of Transportation Science and Engineering Beihang UniversityBeijing100083China Faculty of Science and Engineering University of Nottingham Ningbo ChinaNingbo315100China

The poppet valves two-stroke(PV2S)aircraft engine fueled with sustainable aviation fuel is a promising option for general aviation and unmanned aerial vehicle propulsion due to its high power-to-weight ratio,uniform torque output,and flexible valve ***,its high-altitude gas exchange performance remains unexplored,presenting new opportunities for optimization through artificial intelligence(AI)*** study uses validated 1D+3D models to evaluate the high-altitude gas exchange performance of PV2S aircraft *** valve timings of the PV2S engine exhibit considerable flexibility,thus the Latin hypercube design of experiments(DoE)methodology is employed to fit a response surface model.A genetic algorithm(GA)is applied to iteratively optimize valve timings for varying *** optimization process reveals that increasing the intake duration while decreasing the exhaust duration and valve overlap angles can significantly enhance high-altitude gas exchange *** optimal valve overlap angle emerged as 93°CA at sea level and 82°CA at 4000 m *** effects of operating parameters,including engine speed,load,and exhaust back pressure,on the gas exchange process at varying altitudes are further *** higher engine speed increases trapping efficiency but decreases the delivery ratio and charging efficiency at various *** effect is especially pronounced at elevated *** increase in exhaust back pressure will significantly reduce the delivery ratio and increase the trapping *** study demonstrates that integrating DoE with AI algorithms can enhance the high-altitude performance of aircraft engines,serving as a valuable reference for further optimization efforts.

关键词： Poppet valves two-stroke Design of experiment Genetic algorithm optimization Heavy fuel aircraft engine High altitude gas exchange performance

Hairpin Vortices in the Wake of Grid Fin

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Chinese Journal of aero.autics 2001年第4期14卷 200-204页

作者：陆中荣苏文翰 Fluid Mechanics Institute Beijing Univ. of Aero. and Astro. Beijing 100083 China

The flow patterns of the wake of an oblique honeycombed grid fin were visualized by hydrogen bubbles technique in a water channel. It was found that the hairpin vortices existed in the wake of surfaces in the neighborhood of each crossing of intersecting elements at moderate angles of attack. They shed periodically following the flow separation on surfaces and connected each other into chains. The main features of the flow patterns are presented and the flow mechanism concerned is preliminarily discussed.

关键词： Drag Flow patterns Flow visualization Vortex flow Wakes

Numerical study on influence of protrusion heights on Reynolds stress and viscous stress variations in turbulent vortical structures

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Chinese Journal of aero.autics 2024年第9期37卷 59-71页

作者： Zhiping LI Long HE Jingsai ZHOU Yueren ZUO Yao YIN Peng ZHANG Bo MENG Research Institute of aero.Engine Beihang UniversityBeijing 100191China School of Energy and Power Engineering Beihang UniversityBejing 100191China Institute of Acoustics Chinese Academy of SciencesBeijing 100190China College of aero.autical Engineering Civil Aviation University of ChinaTianjin 300300China AECC Hunan Aviation Powerplant Research Institute Zhuzhou 412002China

Analysing the infuence mechanism of the riblet protrusion height on turbulent drag components is more beneficial in organising the vortical structure over the riblet ***,the Large Eddy Simulation(LES)is used to investigate the vortex structure over the rib-let surface with different protrusion ***,the variations of Reynolds stress and viscous shear stress in a turbulent channel are *** a result,the drag reduction rate increases from 3.4%when the riblets are completely submerged in the turbulent boundary layer to 7.9%when the protrusion height is *** analysis shows that the protrusion height affects the streamwise vortices and the normal diffusivity of spanwise and normal vortices,thus driving the variation of Reynolds *** with the smooth surface,the vorticity strength and the number of streamwise vortices are weakened near the wall but increase in the logarithmic layer with increased protrusion ***,the normal diffusivity of spanwise vorticity decreases with the increase of protrusion height,and the normal diffusivity of normal vorticity is the smallest when the protrusion height is ***,the protrusion height affects the velocity gradient of the riblet tip and riblet valley,thus driving the variation of viscous shear *** the increase of protrusion height,the velocity gradient of the riblet tip increases dramatically but decreases in the riblet valley.

关键词： Riblet Dragreduction Protrusion height Vortical structure Vortexdiffusivity Reynolds stress Viscous stress

Hierarchical Decision Maker in Hybrid Control Systems

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Journal of Systems Engineering and Electronics 1996年第4期7卷 65-84页

作者： He Weidong Hao Jiankang Zhang Minglian & Chen Zongji(305, Dept. of Automatic Control, beijing Uni. of aero. & astro., beijing 100083, P. R. China) 305 Dept. of Automatic Control Beijing Uni. of Aero. & Astro. Beijing 100083 P. R. China

A hybrid control system is composed of three boxes which are analogous box, digital time box and decision maker box. A hierarchical structure of decision maker in hybrid control systems is presented in this paper, which is that decision maker consists of two components, i.e., policy decision and coordination. Policy decision can design coordination and digital time box. And policy decision consists of two parts, i.e., steady policy decision and transient policy decision. In general,steady policy decision corresponds to steady requirements and transient policy decision corresponds to transient requirements in systems. A chemical concentration control system severs an illustrative example to show the features of the hierarchical decision maker.

关键词： Decision maker Hybrid control sysems.

Theoretical and experimental research on static stiffness,performance,and lift-off characteristics of multi-layer gas foil thrust bearings

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Friction 2024年第11期12卷 2458-2479页

作者： Yang HU Pengjing DING Fangling WU Xiaojing WANG Bo LIANG Yonggang MENG School of Mechatronic Engineering and Automation Shanghai UniversityShanghai 200072China Aviation Key Laboratory of Science and Technology on aero.Electromechanical System Integration Nanjing Engineering Institute of Aircraft SystemsNanjing 211106China State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China

In this study,a new comprehensive fully coupled elastic–hydrodynamic model is developed for a multi-layer gas foil thrust bearing(GFTB).The interaction effects among the top foil,back board,middle foil,and bottom foil,as well as the Coulomb friction effect,are *** stiffness and static characteristics obtained by the experimental and theoretical approaches are in good agreement,which verifies the accuracy of the *** contribution of each foil layer to the overall stiffness and the load-carrying mechanism are *** effects of the load,preload,and rotational speed on the static performance are investigated ***,start–stop tests are performed to achieve the lift-off speed,start-up torque,and shut-down torque under various operating conditions.

关键词： multi-layer gas foil thrust bearing(GFTB) load carrying mechanism static performance

Low-Cycle Fatigue Crack Initiation Behavior of Nickel-Based Single Crystal Superalloy

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稀有金属材料与工程 2024年第9期53卷 2458-2467页

作者： Zhang Jingang Liu Xinling Chen Xing Li Zhen Li Leyu Liu Changkui Failure Analysis Center of aero.Engine Corporation of China AECC Beijing Institute of Aeronautical MaterialsBeijing 100095China beijing Key Laboratory of aero.autical Materials Testing and Evaluation Beijing 100095China

Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530℃ was *** show that the behavior of crack initiation is closely related to the maximum *** the maximum strain is 2.0%,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the{111}slip *** defects are observed at the crack initiation *** the maximum strain is lower than 1.6%,the cracks are initiated at the casting defects on sub-surface or at interior of the *** casting defects are located on the{100}slip plane vertical to the axial *** crack is initiated along the{100}slip plane and then expanded along different{111}slip planes after a short stage of *** the maximum strain decreases,the position of crack initiation gradually changes from the surface to the ***,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary *** dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase *** oxide layer of 50‒100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.

关键词： crack initiation low-cycle fatigue single crystal superalloy casting defects dislocation density

NEW METHOD FOR REDUCED RANK STAP—NON CLUTTER CHANNEL METHOD

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Chinese Journal of aero.autics 2000年第4期13卷 228-233页

作者：王玮李少洪毛士艺 Faculty 203 Beijing Univ. Aero. and Astronaut. Beijing 100083 China

For reduced-rank space-time adaptive processing(STAP) in airborne radar, this paper presents a new method — non clutter channel(NCC） method which is easy to implement in real radar systems. The NCC method uses those “channels” located in the non-clutter domain to construct the reduce-rank transformation matrix. This method avoids eigen-decomposition and the computational cost is very low. The performance is compared with that of several other methods; the simulation demonstrates that the NCC method can well approach the optimum performance and even outperform some more complex methods in low rank.

关键词： space-time adaptive processing (STAP) adaptive filtering radar signal processing clutter cancellation