Keita Hara

Application of fluid–structure interaction analysis to flapping flight of insects with deformable wings

The aerodynamic advantage of the dragonflys flexible wing during hovering is quantitatively investigated. The flapping flight of insects, which have simple wings compared with those of a bird, is an ideal means of travel for microrobots. For the realization of such microflight, reduction of the wing weight is essential. One of the simplest means of trimming the wing mass is to reduce the thickness. However, a very thin wing cannot hold against an aerodynamic force and will loose lift power. Thus, for the design of a flapping microrobot like a dragonfly, we should investigate the loss and choose flexibility to avoid it. Unfortunately, a complicated interaction between wing deformation and the surrounding airflow has long prevented the elucidation of the effect of the flexibility. We found that finite element analysis based on the arbitrary Lagrangian–Eulerian method can handle the problem accurately. We established customized modeling methods for such a deformable wing and its actuation, and tested its adequacy on actual dragonfly hovering. Then, we compared the aerodynamic performance of the flexible wing with that of an imaginary rigid one, and examined the advantages and disadvantages of the flexible wing.

Detection of the B waves in the oscillation of intracranial pressure by fast Fourier transform

Intracranial pressure (ICP) oscillation consists of a cardiac-induced component, a respiration-induced component and fluctuation of the base level of ICP. Lundberg reported three types of fluctuations of the base level of ICP with increasing ICP which were referred to as A, B and C waves. Computer algorithms for sampling, processing and displaying ICP data were investigated to depict the power spectrum of ICP oscillations by fast Fourier transform (FFT), thus enabling the B wave to be automatically detected. A power peak was found in the ICP power spectrum between 30 and 120 s, which corresponds to the frequency of the B wave. The maximum power, corresponding to the B-wave amplitude was above 0 dB. An appropriate sampling interval for FFT inputs was about 8 s for real-time processing of the ICP data. The mean ICP value was found useful for making the B-wave peak clearer by reducing the cardiac and respiratory components of ICP oscillations; the window function had no effect on B-wave detection in the ICP power spectrum.

Investigation on force transmission of direct-drive thorax unit with four ultrasonic motors for a flapping microaerial vehicle

We fabricated a trial version of a thorax unit with four ultrasonic motors (USMs) to simulate a dragonfly-scale flapping micro aerial vehicle (MAV). Each wing was directly driven by a two-degree-of-freedom (2-DOF) transmission. An in-house tiny standing-wave USM capable of bidirectional rotation, which weighs just 0.13 g, was employed on trial. The transmission of the thorax unit converts the two USM rotations into strokes and flip motions of the wing. By implementing two 70-mm-long wings, we fabricated a prototype of a 4-DOF MAV and tested its performance. In a lift-compensated situation, upward, forward, and backward movements of the MAV were obtained. The flapping angular velocity was discussed based on quasi-static wing aerodynamics and was accountable for the motor power. Although the power of the USM should be improved, the quick wing drivability, adequate power transmission on the thorax unit, and potential of a 0.2 W motor power in a unidirectional-type USM promise the viability of a direct-drive multi-DOF dragonfly-scale MAV. Graphical Abstract

Free-flight analysis of flapping flight during turning by fluid-structure interaction finite element analysis based on arbitrary Lagrangian-Eulerian method

An insects flapping flight is an attractive method of transportation. It shows many useful flight modes such as maneuverable turning and stable hovering. In recent studies, experimental methods and numerical simulations have been successfully applied to solve the mechanism quantitatively. However, it is extremely difficult to accurately estimate the deformation of the wing caused by interaction with airflow. In prior studies, we analyzed this problem using a novel numerical simulation, fluid-structure interaction analysis, in order to represent this interactive behavior accurately, and achieved the quantitative evaluation of dragonfly hovering with flexible wings. As an advanced analysis, we added a solution of the interaction between the body and wings to the method, and realized free-flight simulation. Here, we demonstrate a sharp turn of 10 rad/s in a numerical simulation using a model based on an actual dragonfly.

Free-flight analysis of dragonfly hovering by fluid–structure interaction analysis based on an arbitrary Lagrangian–Eulerian method

A ‘free-flight’ simulation of flapping flight based on fluid–structure interaction analysis, which can treat the large deformation of wings quantitatively, is applied to the hovering of the dragonfly. Recently, experimental methods and numerical simulation have made significant progress in solving the unsteady aerodynamics of flapping flight, and succeeded in quantifying it under a tethered situation. However, to analyze the stability of hovering or acrobatic flight modes, free-flight simulation is essential. Especially, the structural dynamics of a light and resultantly deformable wing may seriously affect the controllability of flight. We implement the interaction between a body and wing in the fluid–structure interaction analysis, and solve the free-flight situation, where the wing lifts the body and the body actuates the wing. Although the modeled dragonfly is artificially designed to have only two wings to avoid needing to consider the problem of contact between wings and it might, therefore, have less controllability than the real dragonfly, the free-flight simulation closely matches the real stable flight of the dragonfly, thus demonstrating of the adequacy of the simulation. In addition, the altitude and pitch angle of the body are confirmed to be recovered by slight artificial tilt of the stroke plane.

Feasibility study of an actuator for flapping flight using fluid-structure interaction analysis

An actuator for a middle-sized flapping flight robot is quantitatively investigated. Flapping flight like that of insects is a potentially useful method of travel for micro robots. Some insect-mimicking robots have been developed, which have actuators with two or more degrees of freedom per wing. For the detailed design of such an actuator, it is necessary to deal with the interaction between the behavior of the actuator and the aerodynamic forces generated by the actuation. In particular, the torque and power requirements of each degree of freedom are essential in the choice of a suitable motor, but it is impossible to determine these without considering the interaction between the driving force of the actuator and the reaction force of the wing from the surrounding airflow. Here, we achieved an analysis of the mechanical aspects of flapping flight, actuator and wing, using finite element analysis based on the arbitrary Lagrangian-Eulerian method, which can treat the fluid-structure interaction problem properly. We worked out the spec of motors for the 2DOF actuator, and investigated the structural tolerance. We developed a useful tool for the design of flapping flight robots