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Lateral Flight Stability of Two Hovering Model Insects

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Journal of Bionic Engineering 2014年第3期11卷 439-448页

作者： Na Xu mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Beihang University Beijing 100191 P. R. China

The longitudinal disturbance motion of different insects at hovering flight has the same modal structure. Here, we consider the case of lateral motion. The lateral dynamic flight stability of two model insects, hoverfly and honeybee, at hovering flight is studied. The method of computational fluid dynamics is applied to compute the stability derivatives. The techniques of eigenvalue and eigenvector analysis are used to solve the equations of motion. Results show that the lateral disturbance motion of the hoverfly has three natural modes of motion： an unstable divergence mode, a stable oscillatory mode and a stable subsidence mode, and the flight is unstable; while the honeybee has a different modal structure （a stable slow subsidence mode, a stable fast subsidence mode, and a nearly neutrally stable oscillatory mode） and the flight is nearly neutrally stable. The change in modal structure between the two insects is due to their roll-moment/side-velocity derivative having different sign, and the sign difference is because that the hoverfly has a relatively small, but the honeybee has a relatively large, distance between the wing roots and the center of mass. Thus, unlike the case of longitudinal motion, for lateral motion, some insects have different modal structures and stability properties from others.

关键词： insect hovering flight dynamic flight stability modal structure

The influence of the wake of a flapping wing on the production of aerodynamic forces

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Acta Mechanica Sinica 2005年第5期21卷 411-418页

作者： Jianghao Wu mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Institute of Fluid Mechanics Beihang University Beijing 100083 China

The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the method of computational fluid dynamics. The wake effect is isolated by comparing the forces and flows of the starting stroke （when the wake has not developed） with those of a later stroke （when the wake has developed）. The following has been shown. （1） The wake effect may increase or decrease the lift and drag at the beginning of a half-stroke （downstroke or upstroke）, depending on the wing kinematics at stroke reversal. The reason for this is that at the beginning of the half-stroke, the wing “impinges” on the spanwise vorticity generated by the wing during stroke reversal and the distribution of the vorticity is sensitive to the wing kinematics at stroke reversal. （2） The wake effect decreases the lift and increases the drag in the rest part of the half-stroke. This is because the wing moves in a downwash field induced by previous half-stroke＇s starting vortex, tip vortices and attached leading edge vortex （these vortices form a downwash producing vortex ring）. （3） The wake effect decreases the mean lift by 6%-18% （depending on wing kinematics at stroke reversal） and slightly increases the mean drag. Therefore, it is detrimental to the aerodynamic performance of the flapping wing.

关键词： Insect. Flapping. Unsteady aerodynamics.Wing/wake interaction. CFD analysis

Unsteady aerodynamic forces and power requirements of a bumblebee in forward flight

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Acta Mechanica Sinica 2005年第3期21卷 207-217页

作者： Jianghao Wu mao Sun Institute of Fluid Mechanics. Beijing University of Aeronautics & Astronautics Beijing 100083 China

Aerodynamic forces and power requirements in forward flight in a bumblebee （Bombus terrestris） were studied using the method of computational fluid dynamics. Actual wing kinematic data of free flight were used in the study （the speed ranges from 0 m/s to 4.5 m/s; advance ratio ranges from 0-0.66）. The bumblebee employs the delayed stall mechanism and the fast pitching-up rotation mechanism to produce vertical force and thrust. The leading-edge vortex does not shed in the translatory phase of the half-strokes and is much more concentrated than that of the fruit fly in a previous study. At hovering and low-speed flight, the vertical force is produced by both the half-strokes and is contributed by wing lift; at medium and high speeds, the vertical force is mainly produced during the downstroke and is contributed by both wing lift and wing drag. At all speeds the thrust is mainly produced in the upstroke and is contributed by wing drag. The power requirement at low to medium speeds is not very different from that of hovering and is relatively large at the highest speed （advance ratio 0.66）, i.e. the power curve is Jshaped. Except at the highest flight speed, storing energy elastically can save power up to 20%-30%. At the highest speed, because of the large increase of aerodynamic torque and the slight decrease of inertial torque （due to the smaller stroke amplitude and stroke frequency used）, the power requirement is dominated by aerodynamic power and the effect of elastic storage of energy on power requirement is limited.

关键词： Insect Forward flight Unsteady aerodynamics Power Numerical flow simulation

Simulation and experimental improvement on a small-scale Stirling thermo-acoustic engine

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Frontiers in Energy 2016年第1期10卷 37-45页

作者： mao CHEN Yonglin JU Institute of Refrigeration and Cryogenics Shanghai Jiao TongUniversity Shanghai 200240 China

Compared with the traditional engines, the thermo-acoustic engines are relatively new and can act as the linear compressors for refrigerators. Many institutes have shown great interest in this kind of machine for its absence of moving mechanical part. In this paper, the influence of the dimensions of the main parts of the small- scale Stifling thermo-acoustic engine was numerically simulated using a computer code called DeltaEC. The resonator and the resonator cavity were found to be the most convenient and effective in improving the perfor- mance of the engine. Based on the numerical simulation, a small-scale Stifling thermo-acoustic engine were constructed and experimentally investigated. Currently, with a resonator length of only 1 m, the working frequency of the engine was decreased to 90 Hz and the onset temperature difference was decreased to 198.2 K.

关键词： thermo-acoustic Stifling engine small-scale simulation experiment

Dynamic flight stability of a bumblebee in forward flight

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Acta Mechanica Sinica 2008年第1期24卷 25-36页

作者： Yan Xiong mao Sun 1 Institute of Fluid Mechanics Beihang University 100083 Beijing China

The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one （or two） unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed Ue = （0-3.5）m s^-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed （Ue = 4.5 m s^-1; J = 0.57）, the flight becomes strongly unstable （initial disturbance double its value in only 3.5 wingbeats）.

关键词： Bumblebee Dynamic stability Forward flight Navier-Stokes simulation Natural modes of motion

Dynamic flight stability of a hovering model insect:lateral motion

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Acta Mechanica Sinica 2010年第2期26卷 175-190页

作者： Yanlai Zhang mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Institute of Fluid Mechanics Beihang University 100191 Beijing China

The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.

关键词： Insect Dynamic flight stability Hovering ·Lateral motion Natural modes of motion

Clinical effects of the combination of Traditional Chinese and Western Medicines on coronavirus disease 2019:a systematic review and Meta-analysis

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Journal of Traditional Chinese Medicine 2021年第4期41卷 499-506页

作者： YAN Lizhao mao Fuwei CAO Yinghao XIE mao Department of Hand Surgery Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China Department of Gastrointestinal Surgery Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China Department of Orthopaedic Surgery Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China

OBJECTIVE:To explore the clinical efficacy of the combination of Traditional Chinese and Western Medicines for the treatment of coronavirus disease2019(COVID-19).METHODS:Studies were identified in six popular medical ***:Thirteen studies were *** results showed that combined treatment with Traditional Chinese and Western Medicines can reduce the probability of progression from mild to severe disease[RR=0.34,95%confidence interval(CI)(0.18,0.65)](P=0.001)and improve the clinical cure rate[RR=0.17,95%CI(0.05,0.28)](P=0.004).The use of an integrated treatment strategy shortened the time to the remission of fever[WMD=-1.27,95%CI(-1.67,-0.92)](P<0.001)and improved the incidences of the disappearance of fever and fatigue[RR=1.25,95%CI(1.06,1.47)(P=0.007);RR=1.49,95%CI(1.13,1.97)(P=0.004)].CONCLUSION:A combined treatment strategy is effective for COVID-19.

关键词： COVID-19 severe acute respiratory syndrome herbal medicine systematic review Meta-analysis

Wing kinematics measurement and aerodynamics of free-flight maneuvers in drone-flies

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Acta Mechanica Sinica 2010年第3期26卷 371-382页

作者： Yanlai Zhang mao Sun Ministry-of-Education Key Laboratory of Fluid Mechanics Institute of Fluid Mechanics Beihang University 100191 Beijing China

The time courses of wing and body kinematics of two free-flying drone-flies, as they performed saccades, were measured using 3D high-speed video, and the morpho- logical parameters of the wings and body of the insects were also measured. The measured wing kinematics was used in a Navier-Stokes solver to compute the aerodynamic forces and moments acting on the insects. The main results are as following. （1） The turn is mainly a 90° change of heading. It is made in about 10 wingbeats （about 55 ms）. It is of interest to note that the number of wingbeats taken to make the turn is approximately the same as and the turning time is only a little different from that of fruitflies measured recently by the same approach, even if the weight of the droneflies is more than 100 times larger than that of the fruitflies. The long axis of body is about 40° from the horizontal during the maneuver. （2） Although the body rotation is mainly about a vertical axis, a relatively large moment around the yaw axis （axis perpendicular to the long axis of body）, called as yaw moment, is mainly needed for the turn, because moment of inertial of the body about the yaw axis is much larger than that about the long axis. （3） The yaw moment is mainly pro- duced by changes in wing angles of attack： in a right turn, for example, the dronefly lets its right wing to have a rather large angle of attack in the downstroke （generally larger than 50°） and a small one in the upstroke to start the turn, and lets its left wing to do so to stop the turn, unlike the fruitflies who generate the yaw moment mainly by changes in the stroke plane and stroke amplitude.

关键词： Drone-fly - Maneuver Wing kinematicsmeasurement Aerodynamics Navier-Stokes simulation

BENDING PROBLEM OF A FINITE COMPOSITE LAMINATED PLATE WEAKENED BY MULTIPLE ELLIPTICAL HOLES

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Acta Mechanica Solida Sinica 2013年第4期26卷 419-426页

作者： Chunjian mao Xiwu Xu State Key Laboratory of Mechanics and Control of Mechanical Structures Nanjing University of Aeronautics and Astronautics

Based on the classical composite laminate theory,the bending problem of a finite composite plate weakened by multiple elliptical holes is studied by means of the complex variable *** present work is intended to express the complex potentials in the form of Faber series aided by the use of the least squares boundary collocation techniques on the finite *** a result,concise and high accuracy solutions are presented for the stress distribution around the ***,numerical examples are presented to discuss the effects of some parameters on the stress concentration around the holes.

关键词： anisotropic plate bending finite plate elliptical holes Faber series least squares method