The relative importance of the wing's inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wing's elastic and fluid forces is dynamically similar to that of the actual insect, while the wing's inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wing's elastic forces and the wing's inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wing's elastic and aerodynamic forces, while it will be enhanced by the wing's inertial force.
SUMMARYWe have studied the passive maintenance of high angle of attack and its lift generation during the crane fly's flapping translation using a dynamically scaled model. Since the wing and the surrounding fluid interact with each other, the dynamic similarity between the model flight and actual insect flight was measured using not only the non-dimensional numbers for the fluid (the Reynolds and Strouhal numbers) but also those for the fluid-structure interaction (the mass and Cauchy numbers). A difference was observed between the mass number of the model and that of the actual insect because of the limitation of available solid materials. However, the dynamic similarity during the flapping translation was not much affected by the mass number since the inertial force during the flapping translation is not dominant because of the small acceleration. In our model flight, a high angle of attack of the wing was maintained passively during the flapping translation and the wing generated sufficient lift force to support the insect weight. The mechanism of the maintenance is the equilibrium between the elastic reaction force resulting from the wing torsion and the fluid dynamic pressure. Our model wing rotated quickly at the stroke reversal in spite of the reduced inertial effect of the wing mass compared with that of the actual insect. This result could be explained by the added mass from the surrounding fluid. Our results suggest that the pitching motion can be passive in the crane fly's flapping flight.
Since the electromagnetic-mechanical coupled analysis requires large computation time, development of the parallel processing techniques is inevitable. In this paper, the parallel computing technique with the combination of the domain decomposition method and the domain partitioned conjugate gradient method is proposed. The method to evaluate the parallel performance is presented and discussed for the coupled problem using a workstation cluster. This method is efficient for a large scale coupled problem of a magnetic fusion device component.
In this study, element-quality-based stiffening (EQBS) was developed as a method of maintaining mesh quality in the pseudoelastic mesh-moving technique. The proposed EQBS technique increases the stiffness of the element based on two element quality parameters, the element area and shape; this differs from techniques used in previous studies. Importantly, EQBS includes the previously proposed Jacobian-based stiffening (JBS) and minimum height-based stiffening (MHBS) techniques as a specific case. Therefore, it is quite general scenario of the selective stiffening of the mesh. The proposed EQBS technique was applied to the mesh-moving of a rectangular domain including a structure consisting of a square and a fin that undergo large translations and rotations. The proposed EQBS technique showed better performance than JBS on test problems with large translations and rotations applied to the structure. This is because EQBS considers the shear deformation of the element in addition to the tensile and compressive deformations.
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