Xingbang Yang

Design and Experiment of a Bionic Gannet for Plunge-Diving

A bionic gannet was developed based on the analysis of the body configuration and skeleton structure and the motion pattern of wings of a gannet in plunge-diving. In the current prototype, adjustable sweptback wings were implemented so as to achieve different body shapes for entering water. The impact acceleration in the longitudinal body axis direction and the axial overload on the body were investigated through the falling-down experiments under different conditions including dropping height, water-entry inclination angle, and wing sweptback angle. It is found that when the above three key parameters are 10 m for dropping height, 0° for wing sweptback angle, and 90° for water-entry inclination angle, the maximum peak impact acceleration and overload are −167.20 m·s−2 and 18.06 respectively. Furthermore, the variation of peak impact acceleration with the three key parameters were also analyzed and discussed.

Hydrodynamics of a robotic fish tail: effects of the caudal peduncle, fin ray motions and the flow speed

Recent advances in understanding fish locomotion with robotic devices have included the use of biomimetic flapping based and fin undulatory locomotion based robots, treating two locomotions separately from each other. However, in most fish species, patterns of active movements of fins occur in concert with the body undulatory deformation during swimming. In this paper, we describe a biomimetic robotic caudal fin programmed with individually actuated fin rays to mimic the fin motion of the Bluegill Sunfish (Lepomis macrochirus) and coupled with heave and pitch oscillatory motions adding to the robot to mimic the peduncle motion which is derived from the undulatory fish body. Multiple-axis force and digital particle image velocimetry (DPIV) experiments from both the vertical and horizontal planes behind the robotic model were conducted under different motion programs and flow speeds. We found that both mean thrust and lift could be altered by changing the phase difference (φ) from 0° to 360° between the robotic caudal peduncle and the fin ray motion (spanning from 3 mN to 124 mN). Notably, DPIV results demonstrated that the caudal fin generated multiple wake flow patterns in both the vertical and horizontal planes by varying φ. Vortex jet angle and thrust impulse also varied significantly both in these two planes. In addition, the vortex shedding position along the spanwise tail direction could be shifted around the mid-sagittal position between the upper and lower lobes by changing the phase difference. We hypothesize that the fish caudal fin may serve as a flexible vectoring propeller during swimming and may be critical for the high maneuverability of fish.

Computational simulation of a submersible unmanned aerial vehicle impacting with water

A submersible unmanned aerial vehicle (UAV) is proposed firstly, which is capable of operating in both air and water. One of the outstanding characteristics of the UAV is that the air-water transition imitates that of a gannet, i.e., plunge-diving. In this paper, the plunge-diving process of this UAV is simplified as a water-entry problem with a certain initial velocity, and the impact force is calculated by the method of the computational fluid dynamics (CFD). The Volume of Fluid is coupled with the 3-D Navier-Stokes equations to establish the model of the flow field, and the equations are solved in Fluent 6.3. The phase distribution and the pressure distribution during water-entry are presented and analyzed. Furthermore, the effects of the dropping height and the wings sweptback angle on the impact force are investigated and discussed.

A biorobotic adhesive disc for underwater hitchhiking inspired by the remora suckerfish

A multimaterial biomimetic remora disc attaches to a variety of surfaces and enables underwater hitchhiking. Remoras of the ray-finned fish family Echeneidae have the remarkable ability to attach to diverse marine animals using a highly modified dorsal fin that forms an adhesive disc, which enables hitchhiking on fast-swimming hosts despite high magnitudes of fluid shear. We present the design of a biologically analogous, multimaterial biomimetic remora disc based on detailed morphological and kinematic investigations of the slender sharksucker (Echeneis naucrates). We used multimaterial three-dimensional printing techniques to fabricate the main disc structure whose stiffness spans three orders of magnitude. To incorporate structures that mimic the functionality of the remora lamellae, we fabricated carbon fiber spinules (270 μm base diameter) using laser machining techniques and attached them to soft actuator–controlled lamellae. Our biomimetic prototype can attach to different surfaces and generate considerable pull-off force—up to 340 times the weight of the disc prototype. The rigid spinules and soft material overlaying the lamellae engage with the surface when rotated, just like the discs of live remoras. The biomimetic kinematics result in significantly enhanced frictional forces across the disc on substrates of different roughness. Using our prototype, we have designed an underwater robot capable of strong adhesion and hitchhiking on a variety of surfaces (including smooth, rough, and compliant surfaces, as well as shark skin). Our results demonstrate that there is promise for the development of high-performance bioinspired robotic systems that may be used in a number of applications based on an understanding of the adhesive mechanisms used by remoras.

Numerical analysis of biomimetic gannet impacting with water during plunge-diving

This paper reproduces the plunge-diving process of a biomimetic gannet through the CFD (Computational Fluid Dynamics) simulation. The numerical investigation of impulse force and pressure distribution on the designed biomimetic gannet when interacting with water is also presented. Three-dimensional computational transport equations based on the complete set of Navier-Stokes equations are solved by using the FLUENT 6.2 solver. Numerical simulations have been performed to examine the flow characteristics on the interface between air and water, where the interface is tracked by coupling the VOF (Volumn of Fluid) method. The biomimetic gannet is developed by imitating the natural gannet, the morphology and water-entry posture of which are the same as those of the gannet in nature. For different given dropping heights, the effect of initial water-entry velocity on the axial impact force acting on the gannets body is investigated and numerically examined.

A novel method for investigating the kinematic effect on the hydrodynamics of robotic fish

In this paper, a novel method was presented to investigate the hydrodynamics of a robotic fish at different Reynolds number. The ionic polymer-metal composite (IPMC) was used as the soft actuator for biomimetic underwater propulsion. A hydrodynamic model based on the elongated body theory was developed. Based on image analysis, the kinematic parameters of the robotic fish were identified. To obtain the hydrodynamic thrust performance of the robotic fish, we implemented a novel experimental apparatus. Systematic tests were conducted in the servo towing system to measure the self-propelled speed and thrust efficiency at viscous and inertial flow. The robotic fishs thrust efficiency was compared at different body and caudal fin (BCF) swimming modes, i.e. anguilliform, carangiform and thunniform. The thrust performance of the robotic fish is determined by the kinematics and Reynolds number. We show that at high Reynolds number, thunniform kinematics is the most efficient, while anguilliform kinematics produces relatively poor thrust efficiency. At low Reynolds number, the fish has the highest thrust efficiency with the anguilliform type. It is less efficient with the thunniform type.

Modeling and experiments of a soft robotic gripper in amphibious environments

This article presented the optimization parameter of a bidirectional soft actuator and evaluated the properties of the actuator. The systematic simulation was conducted to investigate the effect of the top wedged angle (the angle for the wedged shape of the actuator structure) of the chamber on the bending extent of the actuator when it is deflated. We also investigated the width of the actuator and the material combinations of the two layers with the relation to the deformation performance. A mathematical model was also built to reveal the deformation of the actuator as a function of the geometrical parameters of the inner chambers and the material properties. We quantitatively measured the bending radius and the actuation time of the actuator both in air and under water. Digital particle image velocimetry experiments were conducted under water to observe the flow patterns around the actuator. We found that the top wedged angle has a significant effect on the outward bending of the actuator when it is deflated, and 15° was found to be optimal for bending into a larger gripping space. The result shows that the actuator can deform much easier with a bigger width. Utilizing a soft gripper that was built by mounting four actuators to a three-dimensional-printed rigid support, we found that the prototype can grip objects of different sizes, shapes, and material stiffness in amphibious environments.

Design, fabrication and kinematic modeling of a 3D-motion soft robotic arm

In this paper, we present the design, fabrication and the mathematical model of an entire soft robotic arm with three-dimensional (3D) locomotion. We first describe the design of the soft arm based on 3D printed channels that were spatially distributed at the interface of two different silicone elastomeric materials which enable complex 3D motion of the soft arm. Then we demonstrate the workspace of motion at different air pressure levels, and the ability of the mathematic model to predict the three-dimensional movement in free space. We further demonstrate that modifying the texture of the surface of the soft arm can constrain the radial expansion. Finally, we estimate the workspace, location repeatability of the soft arm via actual tests.

Experimental kinematics modeling estimation for wheeled skid-steering mobile robots

Skid-steering mobile robots, both wheels and tracked vehicles, are widely used because of their simple mechanism and robust. However, due to the complex wheel-ground interactions and the kinematics constraints, it is a challenge to understand the kinematics and dynamics of such a robotic platform. In this paper, we develop a kinematics modeling estimation scheme to analyze the skid-steering wheeled mobile robot based on the boundedness of the Instantaneous Centers of Rotation (ICRs) of treads on the 2D motion plane, and the parameters of this model are determined based on experimental analysis. We study the relationship between the ICRs of the robot treads and two physical factors, i.e., the radius of the path curvature and the robot speed. Moreover, an ICRs coefficient and a nondimensional variable are introduced. An approximating function is used to describe the relationship. To validate the obtained results, the proposed model has been applied to a popular research robotic platform, Pioneer P3-AT. It is empirically demonstrated that the developed model improves dead-reckoning performance of this skid-steering robot.

Submersible unmanned flying boat: Design and experiment

A real submersible flying boat which is both flight-capable and submersible has hardly been reported yet. In this paper, the Flying Fish created by Beihang University will be introduced to verify the feasibility of this kind of novel aircraft. The Flying Fish achieves its ability to transfer between the air and the water by imitating the flying fish and aquatic birds. The morphological characteristics of the flying fish and the variable density method of the aquatic birds are imitated in the design of this novel aircraft. Moreover, the technological deficiencies of this vehicle have also been concluded through the experiments, which can be referred to by the relative future studies.