Design and Mechanics of a Composite Wave-driven Soft Robotic Fin for Biomimetic Amphibious Robot

Bionic amphibious robots have important prospects in scientific, commercial, and military fields. Compared with traditional amphibious robots which use propellers/jets for aquatic medium and wheels/tracks for terrestrial medium, bionic propulsion method has great advantages in terms of manoeuvrability, efficiency, and reliability, because there is no need to switch between different propulsion systems. To explore the integrated driving technology of amphibious robot, a novel bio-inspired soft robotic fin for amphibious use is proposed in this paper. The bionic fin can swim underwater and walk on land by the same undulating motion. To balance the conflicting demands of flexibility underwater and rigidity on land, the undulating fin adopts a special combination of a membrane fin and a bending spring. A periodic longitudinal wave in horizontal direction has been found generating passively in dynamic analysis. To find the composite wave-driven mechanics, theoretical analysis is conducted based on the walking model and swimming model. A virtual prototype is built in ADAMS software to verify the walking mechanics. The simulation result reveals that the passive longitudinal wave is also periodical and the composite wave contributes to land walking. Finally, an amphibious robot prototype actuated by a pair of undulating fins has been developed. The experiments show that the robot can achieve multiple locomotion, including walking forward/backward, turning in place, swimming underwater, and crossing medium, thus giving evidence to the feasibility of the newly designed undulating fin for amphibious robot.

Rarefaction Wave Interaction and Shock-Rarefaction Composite Wave Interaction for a Two-Dimensional Nonlinear Wave System

In order to construct global solutions to two-dimensional(2 D for short)Riemann problems for nonlinear hyperbolic systems of conservation laws,it is important to study various types of wave interactions.This paper deals with two types of wave interactions for a 2 D nonlinear wave system with a nonconvex equation of state:Rarefaction wave interaction and shock-rarefaction composite wave interaction.In order to construct solutions to these wave interactions,the authors consider two types of Goursat problems,including standard Goursat problem and discontinuous Goursat problem,for a 2 D selfsimilar nonlinear wave system.Global classical solutions to these Goursat problems are obtained by the method of characteristics.The solutions constructed in the paper may be used as building blocks of solutions of 2 D Riemann problems.

Analysis of Second-Harmonic Generation of Low-Frequency Dilatational Lamb Waves in a Two-Layered Composite Plate

We analyze the effect of second-harmonic generation（SHG） of primary Lamb wave propagation in a two-layered composite plate, and then investigate the influence of interfacial properties on the said effect at low frequency. It is found that changes in the interfacial properties essentially affect the dispersion relation and then the maximum cumulative distance of the double-frequency Lamb wave generated. This will remarkably influence the efficiency of SHG. To overcome the complications arising from the inherent dispersion and multimode natures in analyzing the SHG effect of Lamb waves, the present work focuses on the analysis of the SHG effect of low-frequency dilatational Lamb wave propagation. Both the numerical analysis and finite element simulation indicate that the SHG effect of low-frequency dilatational Lamb wave propagation is found to be much more sensitive to changes in the interfacial properties than primary Lamb waves. The potential of using the SHG effect of low-frequency dilatational Lamb waves to characterize a minor change in the interfacial properties is analyzed.

Effects of Breaking Waves on Composite Backscattering from Ship-Ocean Scene

The existence of the sea surface is bound to affect the electromagnetic （EM） scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories, the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves, a three dimensional geometric model is adopted together with Ufimtsev＇s theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.

In-service Structural Health Monitoring of a Full-scale Composite Horizontal Tail

In-service structural health monitoring（SHM） technologies are critical for the utilization of composite aircraft structures. We developed a Lamb wave-based in-service SHM technology using built-in piezoelectric actuator/sensor networks to monitor delamination extension in a full-scale composite horizontal tail. The in-service SHM technology combine of damage rapid monitoring（DRM） stage and damage imaging diagnosis（DID） stage allows for real-time monitoring and long term tracking of the structural integrity of composite aircraft structures. DRM stage using spearman rank correlation coeffi cient was introduced to generate a damage index which can be used to monitor the trend of damage extension. The DID stage based on canonical correlation analysis aimed at intuitively highlighting structural damage regions in two-dimensional images. The DRM and DID stages were trialed by an in-service SHM experiment of CFRP T-joint. Finally, the detection capability of the in-service SHM technology was verified in the SHM experiment of a full-scale composite horizontal tail. Experimental results show that the rapid monitoring method effectively monitors the damage occurrence and extension tendency in real time; damage imaging diagnosis results are consistent with those from the failure model of the composite horizontal tail structure.

LARGE-TIME BEHAVIOR OF SOLUTIONS TO THE INFLOW PROBLEM OF THE NON-ISENTROPIC MICROPOLAR FLUID MODEL

We investigate the asymptotic behavior of solutions to the initial boundary value problem for the micropolar fluid model in a half line R+:=(0,∞).Inspired by the relationship between a micropolar fluid model and Navier-Stokes equations,we prove that the composite wave consisting of the transonic boundary layer solution,the 1-rarefaction wave,the viscous 2-contact wave and the 3-rarefaction wave for the inflow problem on the micropolar fluid model is time-asymptotic ally stable under some smallness conditions.Meanwhile,we obtain the global existence of solutions based on the basic energy method.

Wave force on composite bucket foundation of an offshore wind turbine

A new analytical expression for calculating the wave force on a composite bucket foundation is obtained. Based on the diffraction theory, the analytical solution of the wave pressure and the wave force on the composite bucket foundation is accurately derived by assigning reasonable boundary conditions. Experiments for the wave pressure on the bucket foundation with a scale of 1：60 under different wave conditions in the wave flume are designed and conducted. The analytical results agree well with the experimental data, and the theoretical approach can accurately predict the wave force on the large-scale structures. The wave pressure distribution on the composite bucket foundation is presented and the influence of the wave height, the water depth and the wave period on the wave force on the composite bucket foundation is investigated. This study provides a quite accurate method to calculate the wave force on a composite bucket foundation, which gives a good framework for future studies of the wave force on other large-scale structures with complex boundaries.

Low frequency ultrasonic multi-mode Lamb wave method for characterizing the ultra-thin transversely isotropic laminate composite: Theory and experiment

A low-frequency multi-mode ultrasonic Lamb wave method suitable for character- izing the thickness, the density and the elastic constants of the ultra-thin transversely isotropic laminate composite is presented. The 'ultra-thin' here means that the thickness of the plate is much less than the wavelength of the ultrasonic wave so that the echoes from the front and back faces of the plate can't be separated in the time domain. The dispersion equations for the low frequency ultrasonic Lamb waves with the propagation directions parallel and vertical to the fiber direction are derived. In conjunction with the least square algorithm method, the secant algorithm is used to estimate the parameters of the ultra-thin fiber-reinforced composite layer. The evaluation errors and the sensitivity of the method to different paramters of the thin composite are analyzed. The technique has been used to characterize the ultra-thin grass fiber reinforced PES composite with thickness down to ten percents of the ultrasonic wavelength. It is observed that the agreement between the nominal and the estimation values is reasonably good.