Van Anh Pham

Bio: Van Anh Pham is an academic researcher from Ho Chi Minh City University of Technology. The author has contributed to research in topics: Fish fin & Fish locomotion. The author has an hindex of 2, co-authored 6 publications receiving 13 citations.

Dynamic Analysis of a Robotic Fish Propelled by Flexible Folding Pectoral Fins

Abstract: Biological fish can create high forward swimming speed due to change of thrust/drag area of pectoral fins between power stroke and recovery stroke in rowing mode. In this paper, we proposed a novel type of folding pectoral fins for the fish robot, which provides a simple approach in generating effective thrust only through one degree of freedom of fin actuator. Its structure consists of two elemental fin panels for each pectoral fin that connects to a hinge base through the flexible joints. The Morison force model is adopted to discover the relationship of the dynamic interaction between fin panels and surrounding fluid. An experimental platform for the robot motion using the pectoral fin with different flexible joints was built to validate the proposed design. The results express that the performance of swimming velocity and turning radius of the robot are enhanced effectively. The forward swimming velocity can reach 0.231 m/s (0.58 BL/s) at the frequency near 0.75 Hz. By comparison, we found an accord between the proposed dynamic model and the experimental behavior of the robot. The attained results can be used to design controllers and optimize performances of the robot propelled by the folding pectoral fins.

Modeling and Evaluating Motion Performance of Robotic Fish with a Pair of Non-uniform Pectoral Fins

Abstract: Pectoral fins play an essential role in generating the locomotion and balance for fishes and especially for fish robots. The adaptation to shapes and mechanism structure of pectoral fin types helps to improve the swimming motion of the main body effectively, that results in the high flexibility and maneuverability of locomotion. This paper proposes a hydrodynamic model of a fish robot using a pair of flexible pectoral fins, which can be used to increase the robotic fish motion efficient and reduce the consumed energy. The pectoral fin has the symmetrical shape and varying thickness along the symmetrical axis. The body motion is considered as a rigid body motion. Based on the Lagrange energetic method, Assumed Mode Method (AMM), and Kirchhoff’s equation, the mathematical model of the pectoral fin’s deformation and robot body is described explicitly, where the natural frequency and mode shape of pectoral fins are derived by the Rayleigh-Ritz method. The effect of inertia and damping factors are modeled by the Morison force. The numerical simulations of the fins motion and the main body are conducted to show the effectiveness of the proposed model. This model and the analyses processes are expected to support in optimal issue and controller design for biomimetic robotic fish effectively.

Turning motion direction of fish robot driven by non-uniform flexible pectoral fins

Abstract: Flexible fins own outstanding advantages in robotic fish locomotion, especially in high propulsive efficiency. This paper proposes a mechanism for changing the moving direction of fish robots in two-dimensional planes using flexible pectoral fins. Firstly, a mathematical model of the fish robot equipped with non-uniform flexible pectoral fins is introduced. In this model, the influences of fluid inertia, and drag of the surrounding fluid exerting on the fin surface is considered as the Morison force. Based on the energetic method, the Assume Mode Method (AMM) and Rayleigh-Ritz method, the solution for the body motion and deformation of the points on the flexible fins is derived. Secondly, the mechanism for steering the direction of robot swimming motion is proposed. Due to the complex influence of lift forces which are generated by pectoral fins on the robot orientation, a fuzzy logic controller is designed to stabilize the angle trajectory of the fish robot. Finally, the numerical simulations, the movement performances, and the control effectiveness are illustrated.

Hydrodynamic modeling of pectoral fin having varying thickness for biomimetic fish robot

Abstract: Pectoral fin types of biological fish have an enormous diversity, and they play an essential role in locomotion of fish. The adaptation to shapes and movement mechanism of pectoral fin types helps swimming motion of the main body effectively, that results in the high flexibility and maneuverability of locomotion. This paper proposes a hydrodynamic model of a type of flexible pectoral fin (FPF), which can be used to increase the robotic fish motion efficient and reduce the consumed energy. The pectoral fin has the symmetrical shape and varying thickness along the symmetrical axis. Based on the Lagrange energetic method, Assumed Mode Method (AMM), and Rayleigh-Ritz method, the mathematical model of deformation and estimated thrust of the pectoral fin is described explicitly. The effect of inertia and damping factors are modeled by the Morison force. The numerical simulations and some initial experiments are demonstrated to verify the agreement of theoretical and empirical model. The proposed model is expected to support in issues of modeling whole of robotic fish and control design effectively.

A Study on Controllers Design of a 3-Joint Carangiform Fish Robot in 3D Environment

Abstract: This paper proposes a dynamic analysis to control a 3-joint Carangiform fish robot to swim to the 3D environment by using Newton-Euler and Euler-Lagrange concepts. The fish robot is designed into two parts: the head of fish robot and the tail of fish robot. The tail of fish robot will be analyzed which is quite similar to the analysis of the dynamic model of the manipulator. By controlling the tail of fish robot with respect to the desired profiles and controlling the changing central system, the fish robot can be controlled in the 3D environment. To simplify, the motions of fish robot are assumed to consist of two main motions: the movement of fish robot on the horizontal plane and movement of fish robot to the desired depth. The Fuzzy controller is designed to control the centroid displacements system. The Adaptive Back Stepping controller is developed to control the tail of fish robot.

Guidance And Control Of Ocean Vehicles

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Tunabot Flex: a tuna-inspired robot with body flexibility improves high-performance swimming

Abstract: Tunas are flexible, high-performance open ocean swimmers that operate at high frequencies to achieve high swimming speeds. Most fish-like robotic systems operate at low frequencies (≤ 3 Hz) resulting in low swim speeds (≤ 1.5 body lengths per second), and the cost of transport (COT) is often one to four orders of magnitude higher than that of tunas. Furthermore, the impact of body flexibility on high-performance fish swimming remains unknown. Here we design and test a research platform based on yellowfin tuna (Thunnus albacares) to investigate the role of body flexibility and to close the performance gap between robotic and biological systems. This single-motor platform, termed Tunabot Flex, measures 25.5 centimeters in length. Flexibility is varied through joints in the tail to produce three tested configurations. We find that increasing body flexibility improves self-propelled swimming speeds on average by 0.5 body lengths per second while reducing the minimum COT by 53%. The most flexible configuration swims 4.60 body lengths per second with a tail beat frequency of 8.0 Hz and a COT measuring 18.4 joules/kg/m. We then compare these results in addition to the midline kinematics, stride length, and Strouhal number with yellowfin tuna data. The COT of Tunabot Flex's most flexible configuration is less than a half-order of magnitude greater than that of yellowfin tuna across all tested speeds. Tunabot Flex provides a new baseline for the development of future bio-inspired underwater vehicles that aim to explore a fish-like, high-performance space and close the gap between engineered robotic systems and fish swimming ability.

Exploration of swimming performance for a biomimetic multi-joint robotic fish with a compliant passive joint.

Abstract: In this paper, a novel compliant joint with two identical torsion springs is proposed for a biomimetic multi-joint robotic fish, which enables imitatation of the swimming behavior of live fish. More importantly, a dynamic model based on the Lagrangian dynamic method is developed to explore the compliant passive mechanism. In the dynamic modeling, a simplified Morrison equation is utilized to analyze the hydrodynamic forces. Further, the parameter identification technique is employed to estimate numerous hydrodynamic parameters. The extensive experimental data with different situations match well with the simulation results, which verifies the effectiveness of the obtained dynamic model. Finally, motivated by the requirement for performance optimization, we firstly take advantage of a dynamic model to investigate the effect of joint stiffness and control parameters on the swimming speed and energy efficiency of a biomimetic multi-joint robotic fish. The results reveal that phase difference plays a primary role in improving efficiency and the compliant joint presents a more significant role in performance improvement when a smaller phase difference is given. Namely, at the largest actuation frequency, the maximum improvement of energy efficiency is obtained and surprisingly approximates 89%. Additionally, the maximum improvement in maximum swimming speed is about 0.19 body lengths per second. These findings demonstrate the potential of compliance in optimizing joint design and locomotion control for better performance.

Butterflies fly using efficient propulsive clap mechanism owing to flexible wings

Abstract: Butterflies look like no other flying animal, with unusually short, broad and large wings relative to their body size. Previous studies have suggested butterflies use several unsteady aerodynamic mechanisms to boost force production with upstroke wing clap being a prominent feature. When the wings clap together at the end of upstroke the air between the wings is pressed out, creating a jet, pushing the animal in the opposite direction. Although viewed, for the last 50 years, as a crucial mechanism in insect flight, quantitative aerodynamic measurements of the clap in freely flying animals are lacking. Using quantitative flow measurements behind freely flying butterflies during take-off and a mechanical clapper, we provide aerodynamic performance estimates for the wing clap. We show that flexible butterfly wings, forming a cupped shape during the upstroke and clap, thrust the butterfly forwards, while the downstroke is used for weight support. We further show that flexible wings dramatically increase the useful impulse (+22%) and efficiency (+28%) of the clap compared to rigid wings. Combined, our results suggest butterflies evolved a highly effective clap, which provides a mechanistic hypothesis for their unique wing morphology. Furthermore, our findings could aid the design of man-made flapping drones, boosting propulsive performance.

Reconfigurable Curved Beams for Selectable Swimming Gaits in an Underwater Robot

Abstract: Rowing is a swimming motion employed by a number of animals via tuned passive biomechanics and active gait strategies. This gait generates positive net thrust (or moment) by having a higher drag profile in the power stroke compared with the recovery stroke, which is obtained via faster actuation speed or higher effective area. In this letter, we show that using the preferential buckling of curved beams in swimming robots can, via a passive reduction of effective area in recovery stroke, be used to generate positive net thrust and moment. Additionally, these curved beams can be actively tuned to alter their behavior on demand for use in swimming applications, and can be used in an underwater robot to switch between rowing and flapping gaits. A dynamic model has been developed to model the swimming behavior of a robot using buckling joints. A design optimization has been carried out, using the Covariance Matrix Adaption Evolution Strategy (CMA-ES), to find the design and gait parameters that maximize the robot's forward swimming speed. A series of experimental gait searches have subsequently been conducted on the resulting optimal design, again using CMA-ES with the goal of finding the optimal gait pattern across a number of swimming strategies such as paddling, flapping, and undulation. By actively altering the curved beam's buckling limits, an untethered robot has been developed that maneuvers in water across each of these swimming strategies. The findings suggest that tuning the preferential buckling limits of curved beams can be an effective and potentially advantageous approach for producing directional thrust and moments.