This paper deals with the control problems involved in insects' and robots' visually guided piloting. Explicit control schemes are presented which may explain how insects navigate by relying on optic flow cues, without requiring any distance or speed measurements. The concept of the optic flow regulator, a feedback control system based on OF sensors, is presented. We tested our control schemes in simulation, and implemented them on-board two types of miniature aerial robots, a helicopter and a hovercraft. Their electronic OF sensors were inspired by the results of our microelectrode studies on motion sensitive neurons in the housefly's compound eye. The control schemes described do without any conventional avionic sensors like rangefinders or speedometers, and therefore show great potential for safe autonomous control of aerial, underwater and space vehicles in unchartered environments.
Swimming movement of human being is quite distinctive compared to those of the other aquatic animals. Taking such peculiarity into account, the authors recently have developed a simulation model “SWUM” to simulate the human swimming. In this paper, the simulation model itself is firstly described. Next, several examples of applications of the model are presented in order to demonstrate the usefulness of the model. Finally, ongoing research projects are introduced to explain the future tasks for the model.
The objective of the present study is to elucidate the flow mechanism of delaying stall by use of a wavy leading edge. Experiments were carried out to examine the effects of various shapes of wavy leading edges. Numerical simulations were also carried out to investigate the flow around wavy leading edge. It is found that the wavy leading edge can restrain flow separation and delay stall. The shorter wavelength of protuberance is the better for producing large lift force at poststall angles of attack on rectangular wing.
This paper describes flapping behavior in powered flight of some selected insects. Free flight by a pair of wings for a dragonfly, free flights of other insects, and tethered flight of a fly are studied by the high-speed video camera system. The morphology of the wings of these insects is also studied. The relationships between wing morphology and flight mechanisms are considered experimentally.
Burst-and-coast, as a locomotion type in freely routine swimming of koi carps (Cyprinus carpio koi) was studied, using a novel integrated CFD method solving the body-fluid interaction problem. The numerical simulation was incorporated with the tracking experiment. The two burst modes, MT (Multiple Tail-beat) and HT (Half Tail-beat) were investigated. The body locomotion was predicted and the flow physics was visualized, both in good agreement with the corresponding experiments. The energy cost and several critical control mechanisms in burst-and-coast swimming of koi carps are explored. Results on the energetics show that, burst-and-coast swimming does not actually save energy comparing with steady swimming at the same average speed, in that frequently changing of speed leads to decrease of efficiency.
Bacterial motion near a free surface was numerically investigated by use of the boundary element method. The fluid flow around a bacterial cell is approximated as a creeping flow. Boundary conditions on the free surface were satisfied by the basic solution for a half space that provides free shear stresses. The swimming speed and the rotational rate were calculated for a bacterial model with a single flagellum. The motion near a free surface was found to be quite different from the motion near a rigid surface which had been previously analyzed.
The objectives are to make the supporting mechanism of the tail flukes of dolphins clear and to obtain the useful knowledge for developing an artificial fin. The inner structure of the flukes was investigated by dissection of the flukes. The mechanical properties of a ligamentous layer and a dense connective tissue composing the flukes are investigated by the tensile test and compression test. It was found that the ligamentous layer had a high tensile modulus in the spanwise direction; the dense connective tissue had a high compressive modulus in the spanwise direction.
The swimming velocity of fish robots are extremely low in comparison with actual live fishes. To investigate the superior propulsive efficiency of actual fish and find measures to improve the propulsive performance of fish robots, a flexible fish robot was developed. The effects of the flexibility of tail fin on the propulsive force were investigated by using the fish robot and three-dimensional CFD. Consequently, the flexibility of tail fin is very important for fish robots to swim efficiently, because the vortex rings generated from a flexible tail fin is useful to maintain reverse Karman vortices for a long time.
Planarians' locomotion is called ciliary gliding: they secrete mucus on substrata, and glide there by beating ventral cilia in an antiplecticly metachronous manner. A mathematical model for this locomotion consists of the continuity of mass and the Brinkman's equation for the continuity of momentum in the periciliary layer. The reaction of the mucus layer is treated by the Maxwell constituent equation. The boundary layer developed on the back is analysed. The equation of motion, built up by these models, reveals that planarians attain the stable steady-state gliding at 4.7 mm/s by utilising 28 % of the full power of cilia.
A numerical investigation of an oscillating hydrofoil with unequal plunging/pitching frequency is conducted by solving unsteady Navier-Stokes equations. Studies are performed for the impact of different frequency ratio on the wake structure and propulsion parameters over a wide range of plunging amplitude, pitching amplitude and oscillating reduced frequency. Results show that, for pitching oscillates at twice frequency as plunging, there exists a critical St, less than which the thrust coefficient (Ct) is larger than that of equal plunging/pitching oscillation. However, beyond this St, a reduced Ct is obtained compared to equal frequency. The lift induced by unequal oscillating and power consumption are always larger than that of equal motion.
In insect flapping flight, non-equilibrium flight conditions such as takeoffs and uncoordinated turn are difficult to investigate with experiments or quasi-steady analysis. Here we develop a simplified rigid body dynamics solver with 6 degrees of freedom (DOF), by utilizing unit quaternions. A free-flight simulator of an insect flapping flight is then built up by coupling the dynamics solver with an in-house CFD solver, which is specified for simulating unsteady flapping-wing aerodynamics. Simulation of the hovering flight of a fruit fly (Drosophila melanogaster) is achieved by manually manipulating three kinematic parameters, wingbeat amplitude, mean positional angle, and stroke plane angle relative to body (anatomical stroke plane angle).
The dynamic behavior of small shrimp-like creature is analyzed by a digital high speed video camera system. Test small aquatic creature is opossum shrimp, Archaeomysis kokuboi Ii. Some movement models of opossum shrimps are observed. The details of the motion of swimming legs and flow fields are revealed experimentally. Flow visualization around tethered opossum shrimp is also performed by slow shutter photographic technique.
This paper describes the numerical simulations of simple motion and motion control of a biomimetic underwater vehicle equipped with two pairs of mechanical pectoral fins. This biomimetic underwater vehicle is called PLATYPUS, which was developed several years ago in Osaka Univ. Practical and accurate control algorithm is necessary to make sure that the underwater vehicle can carry out the prescribed task successfully. For a long time our team has been developing a CFD-based motion simulator with Fuzzy control algorithm. In this paper, firstly motion simulation without control algorithm in still water is given and then motion simulations with distance control and Point-To-Point (PTP) control using Fuzzy control algorithm were described.
Daphnia magna show strong positive phototaxis to blue light. Here, we investigate the effectiveness of behavior control of D. magna by blue light irradiation for their use as bio-micromachines. D. magna immediately respond by swimming toward blue LED light sources. The behavior of individual D. magna was controlled by switching on the LED placed at 15° intervals around a shallow Petri-dish to give a target direction. The phototaxic controllability of Daphnia was much better than the galvanotactic controllability of Paramecium.
Insects generate sound by their flapping wings as a consequence of spatial and temporal changes of pressures on the wing surface and vortices generated by the wing motion. To clarify the mechanism of sound generation, hybrid method combining CFD techniques and acoustic analysis is incorporated here and detailed characteristics of flapping sound, e.g. directivity of transmission or spectrum distributions, are clarified.
Elastic fins may represent a significant advance over traditional screw propellers for the propulsion of underwater vehicle However, the optimum elasticity of the fin is not constant and changes with the required motion and the environment. To address this, we initially developed a fin with a variable-effective-length spring and documented the thrust characteristics given a simple yawing movement of the fin. In this study, we developed a new propulsion mechanism that allows both swaying and yawing movements of the fin. We evaluated the behavior of the fin and the flow field surrounding the fin.
Purpose of this study is to understand a thrust generation mechanism of a swimming mosquito larva. A quick escaping swimming behaved in their dangerous situations. A time-varying motion of a tail related a thrust was investigated by a motion capture method. Moreover, the velocity fields around the tail were measured by micro Particle Image Velocimetry (PIV) system. It was found that their unique wriggling motion generated the thrust in all sequence whereby an effective utilization of a vortex ring. The convenient way to estimate the thrust according to kinetic energy of the vortex ring was proposed in this paper.