Guanhao Wu

Novel Method for the Modeling and Control Investigation of Efficient Swimming for Robotic Fish

In this paper, analytical techniques and fuzzy logic method are applied to the dynamic modeling and efficient swimming control of a robotic fish. The bioinspired robotic fish, which follows an exact replica of a live mackerel (Scomber scombrus), is modeled by treating the undulating body and flapping tail independently using analytical methods. Comparing the results of simulations and experiments shows the feasibility of the dynamic model. Using this model, we found that the harmonic control of the Strouhal number and caudal fin angle of attack is a principal mechanism through which the robotic fish can obtain high thrust efficiency while swimming. The fuzzy control method, which is based on the knowledge of the robotic fishs dynamic behavior, has successfully utilized this principal mechanism. By comparing the thrust performance of the robotic fish with different control methods via simulation, we established that the fuzzy controller was able to achieve faster acceleration and smaller steady-state error than what could be achieved from an open-loop and conventional proportional-integral-derivative controller. The thrust efficiency during steady state was superior to that with conventional control methods. We also found that, when using the fuzzy control method, robotic fish can always swim near a “universal” Strouhal number that approximates to the swimming of live fish.

Kinematics, hydrodynamics and energetic advantages of burst-and-coast swimming of koi carps (Cyprinus carpio koi)

SUMMARY Koi carps frequently swim in burst-and-coast style, which consists of a burst phase and a coast phase. We quantify the swimming kinematics and the flow patterns generated by the carps in burst-and-coast swimming. In the burst phase, the carps burst in two modes: in the first, the tail beats for at least one cycle (multiple tail-beat mode); in the second, the tail beats for only a half-cycle (half tail-beat mode). The carp generates a vortex ring in each half-cycle beat. The vortex rings generated during bursting in multiple tail-beat mode form a linked chain, but only one vortex ring is generated in half tail-beat mode. The wake morphologies, such as momentum angle and jet angle, also show much difference between the two modes. In the burst phase, the kinematic data and the impulse obtained from the wake are linked to obtain the drag coefficient (Cd,burst≈0.242). In the coast phase, drag coefficient (Cd,coast≈0.060) is estimated from swimming speed deceleration. Our estimation suggests that nearly 45% of energy is saved when burst-and-coast swimming is used by the koi carps compared with steady swimming at the same mean speed.

Quantitative Thrust Efficiency of a Self-Propulsive Robotic Fish: Experimental Method and Hydrodynamic Investigation

The robotic fish that utilize the body/caudal fin undulatory locomotion has long interested both biologists and engineers. Although a variety of free swimming robotic fish prototypes have already been developed, very few studies addressed the methods for determining quantitative thrust efficiency. In this paper, we propose a novel experimental method that enables the simultaneous measurement of the power, wake flow field, and self-propulsive speed of a robotic fish, which together facilitate a quantitative measurement of its efficiency. Our results show that the optimal thrust efficiency of the robotic swimmer is within the Strouhal number (St) range of 0.3 ≤ St ≤ 0.325 when single-row reverse Karman vortices are produced. Nevertheless, present robotic fish swam at Strouhal numbers outside the optimal region under self-propulsive condition, and produced another type of wake structure: “double-row vortices.” We also show that robotic fish that utilize a low amplitude with a large flapping frequency produce higher self-propulsive speeds, whereas a larger amplitude paired with lower frequency results in higher efficiency. Additionally, a peak efficiency value of 31.6% is recored for the self-propulsive robotic swimmer. The general applicability of this experimental method indicates that broader issues regarding thrust efficiency for biomimetic underwater propulsive robots can be quanlitantively measured.

Hydrodynamic investigation of a self-propelled robotic fish based on a force-feedback control method.

We implement a mackerel (Scomber scombrus) body-shaped robot, programmed to display the three most typical body/caudal fin undulatory kinematics (i.e. anguilliform, carangiform and thunniform), in order to biomimetically investigate hydrodynamic issues not easily tackled experimentally with live fish. The robotic mackerel, mounted on a servo towing system and initially at rest, can determine its self-propelled speed by measuring the external force acting upon it and allowing for the simultaneous measurement of power, flow field and self-propelled speed. Experimental results showed that the robotic swimmer with thunniform kinematics achieved a faster final swimming speed (St = 0.424) relative to those with carangiform (Stxa0=xa00.43) and anguilliform kinematics (St = 0.55). The thrust efficiency, estimated from a digital particle image velocimetry (DPIV) flow field, showed that the robotic swimmer with thunniform kinematics is more efficient (47.3%) than those with carangiform (31.4%) and anguilliform kinematics (26.6%). Furthermore, the DPIV measurements illustrate that the large-scale characteristics of the flow pattern generated by the robotic swimmer with both anguilliform and carangiform kinematics were wedge-like, double-row wake structures. Additionally, a typical single-row reverse Karman vortex was produced by the robotic swimmer using thunniform kinematics. Finally, we discuss this novel force-feedback-controlled experimental method, and review the relative self-propelled hydrodynamic results of the robot when utilizing the three types of undulatory kinematics.

Fuzzy vorticity control of a biomimetic robotic fish using a flapping lunate tail

Vorticity control mechanisms for flapping foils play a guiding role in both biomimetic thrust research and modeling the forward locomotion of animals with wings, fins, or tails. In this paper, a thrust-producing flapping lunate tail is studied through force and power measurements in a water channel. Proper vorticity control methods for flapping tails are discussed based on the vorticity control parameters: the dimensionless transverse amplitude, Strouhal number, angle of attack, and phase angle. Field tests are conducted on a free-swimming biomimetic robotic fish that uses a flapping tail. The results show that active control of Strouhal number using fuzzy logic control methods can efficiently reduce power consumption of the robotic fish and high swimming speeds can be obtained. A maximum speed of 1.17 length specific speed is obtained experimentally under conditions of optimal vorticity control. The St of the flapping tail is controlled within the range of 0.4∼0.5.

A novel method based on a force-feedback technique for the hydrodynamic investigation of kinematic effects on robotic fish

In this paper, techniques of force-feedback control are applied to the hydrodynamic study of a laboratory robotic fish. The experimental apparatus which allows a robotic model to accelerate from rest to a steady speed under self-propelled conditions is clearly described. In the current apparatus, the robotic fish is mounted on a servo guide rail system and the towing speed is not preset but determined by the measured force acting on the body of the fish. Such an apparatus enables the simultaneous measurement of power consumption, thrust efficiency and speed of a robotic model obtained under self-propelled conditions. The thrust efficiency of the robotic fish can be estimated based on a 2-D vortex ring force estimation method. By comparing the thrust performance of carangiform body-shaped robotic swimmer with different typical BCF (body and caudal fin ) swimming modes, i.e. anguilliform, carangiform and thunniform, we show that the robotic swimming fish with the thunniform kinematic movement not only reaches a higher steady swimming speed but is also more efficient than the other two modes However, in the start phase, using the anguilliform kinematic movement, the robotic swimmer accelerates faster among all kinematic movements. Ultimately, we found that the robotic fish always produce a double-row wake structure no matter which swimming mode used.

Routine turning maneuvers of koi carp Cyprinus carpio koi:effects of turning rate on kinematics and hydrodynamics

SUMMARY Spontaneous swimming behaviors of koi carp Cyprinus carpio koi were recorded using a video tracking system. Routine single-beat turns were selected from the recorded image sequences for kinematic and hydrodynamic analysis. As with C-starts, the turns can be divided into two stages (stage 1 and stage 2), based on kinematics. Stage 1 involves a bend to one side forming a C-shaped curve in the body, while stage 2 corresponds to the return flip of the body and tail. The turning angle in stage 1 accounts for the greatest portion of the total turning angle and the mean turning rate in stage 1 reflects the intensity of turn. The effects of the turning rate in stage 1 on both kinematics and hydrodynamics were examined. The duration of stage 1 remained relatively stable over a nearly tenfold change in turning rate. Consequently, the turning angle is dominated by the turning rate in stage 1. The turning radius is not related to the swimming speed. Moreover, except in very fast turns, the turning radius is also not affected by the turning rate. The angle between the side jet and the carps initial orientation of a turn does not change substantially with the turning rate, and it is always close to 90° (94.2±3.1°, N=41), so the orientation of the side jet in the forthcoming turn can be predicted. The angle between the jet and the line joining the center of mass of the carp and the trailing edge of the tail (mean value in stage 1) is also always close to 90° (95.3±1.3°, N=41). It is helpful for the carp to maximize the torque so as to improve the turning efficiency. In stage 1, the impulsive moment obtained from the beat of the body and tail and the mean angular momentum of the carp show an agreement in magnitude. Two types of flow patterns in the wake of routine single-beat turns are revealed. The difference between the two types of wakes is in whether or not a vortex ring and a thrust jet are generated in stage 2. The recoil speed of the tail, the bending amplitude of the turn, and the angle of attack of the tail are three probable factors influencing the flow patterns in stage 2.

Novel method based on video tracking system for simultaneous measurement of kinematics and flow in the wake of a freely swimming fish

A novel method based on video tracking system for simultaneous measurement of kinematics and flow in the wake of a freely swimming fish is described. Spontaneous and continuous swimming behaviors of a variegated carp (Cyprinus carpio) are recorded by two cameras mounted on a translation stage which is controlled to track the fish. By processing the images recorded during tracking, the detailed kinematics based on calculated midlines and quantitative analysis of the flow in the wake during a low-speed turn and burst-and-coast swimming are revealed. We also draw the trajectory of the fish during a continuous swimming bout containing several moderate maneuvers. The results prove that our method is effective for studying maneuvers of fish both from kinematic and hydrodynamic viewpoints.

Measuring the Three-Dimensional Kinematics of a Free-Swimming Koi Carp by Video Tracking Method

A video tracking system for measuring three-dimensional kinematics of a free-swimming fish is presented. The tracking is accomplished by simultaneously taking images from the ventral view and the lateral view of the fish with two cameras mounted on two computer-controlled and mutually orthogonal translation stages. Compared to the previous system we reported, the time resolution is greatly improved. A koi carp is selected for the experiment. By processing the images caught by the video tracking system, the three-dimensional kinematics of the koi carp during a continuous swimming containing several moderate maneuvers are obtained. In particular, the pitching motion of fish body and the tail motion, including lateral excursion, variation in tail height and torsion, are revealed for burst-and-coast swimming and turning maneuver. The error analysis is also provided for the measurement results.

Measuring the Wing Kinematics of a Moth (Helicoverpa Armigera) by a Two-Dimensional Fringe Projection Method

We describe a two-dimensional (2-D) fringe projection method, projecting two groups of comb-fringe patterns with high intensity and sharpness onto the flapping wings of a moth (Helicoverpa armigera) from two directions. The images of distorted fringes are caught by two high speed cameras from two orthogonal views. By three-dimensional reconstruction of the wing, we obtain the wing kinematics of the moth including the flapping angle, torsion angle and camber deformation.