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In vortex streets,the motion state of filaments is closely related to its propulsion performance. Studying the influence of flexibility on the motion state of filaments in vortex streets can provide reference for flexible design of flexible aircraft in formation flight. In this paper,three different flexible distribution modes of filaments are given.The influence of flexibility on the motion state of filaments in different vortex streets(including Karman vortices and reversed Karman vortices)is explored by immersed boundary method,and the variation law of the motion state of filaments changing with flexibility is summarized.The results show that when the flexibility of the filament changes,the motion state of the filament will also change,from flapping between vortex streets to flapping outside vortex streets,or from the latter to the former. Moreover,the variation of the motion state of the filament with the flexibility is affected by the vertical dipole-induced velocity and the vortex transportation speed.

As a kind of bionic robot fish,bionic killer whale played an important role in ocean development and scientific investigation. Based on the flapping wing movement theory,the bionic killer whale’s mechanism was analyzed,its instantaneous load was simulated by MATLAB. Based on the stress-strength interference theory,the bionic killer’s load reliability state function was established,the reliability index and reliability of bionic killer whale was calculated,combined with the reliability sensitivity analysis theory,the dimensionless sensitivity was obtained,analyzed the influence of the bionic killer whale’s design variables to reliability sensitivity gradient. This paper provides the theoretical basis,accurate data support and an effective numerical calculation method for the design and optimization of the bionic underwater robot with flapping wing theory as the propeller,which has important practical engineering significance.

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The study of unsteady flow mechanism and aerodynamics performance of flapping wing is very significant for micro aerial vehicle (MAV) design. In this paper, hybrid dynamic mesh technique and unsteady flow solver are used to study the flapping motion of a seagull wing. Radius basis function (RBF) interpolation approach is adopted to generate the moving mesh. The reduced selection of surface reference points is used to save the time consuming of the RBF interpolation. In order to satisfy the geometric conservation law on the moving mesh, the normal velocity of cell interface is calculated by its 'sweeping volume'. A 3D model of seagull wing is built based on observation data and a simple flapping, and the folding motion is also modeled. Influence of the flapping angle, the folding angle and the folding phase is analyzed. Numerical results show that the folding mechanism can weaken the disadvantage of the upstroke. Therefore, with an increasing folding angle, the averaged lift coefficient increases and both the drag and power consumption decrease. Furthermore, increasing the proportion of folding process and decreasing the unfolding process are helpful to improve the time-averaged aerodynamic performance and reduce the power consuming. [ABSTRACT FROM AUTHOR]

The flapping-wing, inspired by natural flyers> is believed as a new conceptual flight technology with potential valuable applications. However, the unusual features of flappingwings, such as complex strong unsteady low Reynolds number aerodynamics and large number of design variables associated with both large flapping motion and shape geometries, pose great challenges for aerodynamic design/optimization. This paper discusses the development and application of unsteady aerodynamic optimization for flapping wing from the aspects of aerodynamic model, parameterization of design variables and optimizing strategies. The advances are reviewed in aerodynamic optimization techniques for flapping wing the traditional method the modern unsteady adjoint approach. Some remarks and speculations are given on the state-of-lheart of this research field. [ABSTRACT FROM AUTHOR]

Flapping-wing micro air vehicle (FMAV) is one of the most important research directions of future aviation. The bird or insect in nature possess the advanced ability of flying because of thousands of years' evolution, so the study of their flight kinematics as well as flow mechanism can greatly contribute to the development of FMAV. To investigate the unsteady aerodynamic mechanism of flapping wing, simplified plunging/pitching motion of a rigid 2-D S1223 airfoil is firstly taken into consideration. Numerical method is based on the hybrid dynamic mesh technique and unsteady flow solver. To improve the moving ability of dynamic mesh, the radius basis function is used to calculate the displacement of volume nodes. For unsteady flow solver on moving mesh, geometric conservation law is satisfied by constraining the normal velocity of cell surface. Second-order finite volume method is used. Dual-time stepping method and BLU-SGS implicit scheme are adopted for time marching. The unsteady lifts, thrusts as well as power consumptions with different flapping parameters are attained. The flow mechanism for lift and thrust is studied. The influence of down-stroke time ratio and stroke angle is analyzed, which would greatly influence the aerodynamic performance and the power consumption. Numerical results show that the 'static effect' of the airfoil plays the main role for lift generation. Meanwhile, the unsteady flow induced by the plunging/pitching motion can enhance the lift by weakening the flow separation and increasing the equivalent angle of attack. The maximum lift per power consumption can be got when down-stroke time takes about 65%-70% of the whole stroke cycle, which agrees well with observation data. Further, a set of appropriate flapping angles are specified based on these analyses, which would greatly contribute to the realistic 3-D simulations in the future. [ABSTRACT FROM AUTHOR]

Due to the coupling between large prescribed motions and flexible deformation, classical dynamics theory could not be applied in the flapping wing aeroelastic studies. In this paper, a dynamic fluid- structure coupling computational framework is developed which is able to simulate the complex flow around flexible flapping wings and investigate the effects of the wing flexibility on aerodynamic performance. The equations of motion are derived using Hamilton's principle, and a Newmark solution method is used to solve the above equations which takes into account of inertial force and aerodynamic force together. The aerodynamic force is obtained by RANS (Reynolds-Averaged Navier-Stokes) solver. An IPS (Infinite Plate Spline) method is used for data exchange between aerodynamic and structural grids. A loose CFD/CSD coupling method is used, and it only requires 3-4 sub-iterations to get converged. A NACA0012 cross-sectional rectangular wing with prescribed pure plunge motion is investigated. Both rigid and flexible wing results are presented, and good agreements between experiment and computation are shown regarding tip displacement and thrust coefficient. [ABSTRACT FROM AUTHOR]