Traveling Wave Motion Research Articles

Comprehensive Influence of Dimensionless Wave Velocity and Expansion Ratio on Energy Absorption Characteristics of Variable Wavelength Traveling Wave Turbine

Based on the traveling wave motion of fish, this paper introduces a new type of variable wavelength traveling wave turbine that significantly differs from traditional turbine designs in its mechanical structure. By developing a two-dimensional traveling wavy plate model and conducting numerical simulations, this study investigates the relationship between the dimensionless wave velocity, variable wavelength coefficient, and expansion ratio, as well as their combined effects on the energy absorption characteristics of the variable wavelength traveling wave turbine. The results reveal that energy absorption efficiency peaks at an optimal dimensionless wave velocity, which is unaffected by changes in the variable wavelength coefficient. Furthermore, the expansion ratio significantly influences both the dimensionless wave velocity and the variable wavelength coefficient, with an optimal ratio of π* = 2.5 achieving 90.42% efficiency. The energy absorption characteristics of the plate with a larger variable wavelength coefficient are found to be constrained by the expansion ratio. Additional analysis reveals that flow characteristics, such as the pressure distribution, vortex street, and velocity field surrounding the traveling wavy plate, are closely related to its energy absorption performance. These findings provide valuable insights for the design of variable wavelength traveling wave turbine.

Parametric study of traveling wave motion in energy absorption mode

There are two modes of traveling wave motion, traveling wave propulsion and traveling wave energy absorption. In this paper, a two-dimensional flexible traveling wave plate is taken as the research object. The characteristic length and characteristic parameter of traveling wave motion are determined by numerical simulation, and the parametric study of the traveling wave motion in energy absorption mode is conducted. The effects of dimensionless amplitude and dimensionless wave velocity on the energy absorption characteristics of flexible traveling wave plate are analyzed, and the mechanism of traveling wave energy absorption is revealed. The results show that the larger the dimensionless amplitude is, the stronger the work capacity of the traveling wave plate becomes, while the absolute amplitude or absolute wavelength has little effect on the work capacity of the traveling wave plate. Under different waveforms, the work capacity of the traveling wave plate increases first and then decreases as the dimensionless wave velocity increases. Within the parameter range studied in this article, when the dimensionless amplitude is 0.2 and the dimensionless wave velocity is 0.5, the traveling wave plate can achieve an energy absorption efficiency of about 40 %.

Multi-gait snake robot for inspecting inner wall of a pipeline

In the field of pipeline inner wall inspection, the snake robot demonstrates significant advantages over other inspection methods. While a simple traveling wave or meandering motion will suffice for inspecting the inner wall of small-diameter pipes, comprehensively and meticulously inspecting the inner wall of large-diameter pipes requires the snake robot to adopt a helical gait that closely adheres to the inner wall. Our review of existing literature indicates that most research and development on the helical gait of snake robots has focused on the outer surface of cylinders, with very few studies dedicated to developing a helical gait specifically for the inspection of the inner wall of pipes. Therefore, in this study, we propose a helical gait that is suitable for the inner wall of pipes and meets the requirements of gas pipeline engineering. The helical gait is designed using the backbone curve method. First, we create a mathematical model for a circular helix curve with constant curvature and torsion, ensuring it is applicable to a snake robot prototype in a laboratory environment. Subsequently, we calculate the joint angles required for two conical spiral curves with variable curvature and torsion, establish a new model, and define the physical significance of the specific parameters. To ensure the feasibility of the proposed gait, we conduct experiments involving meandering and traveling wave motions to verify the communication and control between the host computer and the snake robot. Building upon this foundation, we further validate the mathematical model of the complex helical motion gait through simulation experiments. Our findings provide a theoretical basis for realizing helical movement with a real snake robot.

Peristaltic transporting device inspired by large intestine structure

A pneumatic large intestine-like soft robot with McKibben muscles is designed based on traveling wave motion. The robot consists of four sections, and each section is controlled by axial and circular muscles independently. The robot can propagate traveling waves inspired by the large intestine’s peristaltic wave, defined by the wavelength and delay of the axial and circular muscles’ supplied air signals. This motion can transport the object in the inner cavity of the robot, making the maximum Transport Capacity Index of 0.069 (with an actual speed of 0.77 mm/s). This study investigates the effect of different parameters of traveling waves generated by axial and circular muscles independently on the ability of a robot to transport the object. Various combinations of traveling waves will lead to different transport directions and speeds of the object and provide more possibilities for selecting control patterns. Furthermore, the proposed robot not only demonstrates effective transportation capabilities for solid objects, but it also has the capacity to transport soft objects. This study can provide new ideas for animal tubular organ bioinspired device design and prototype design references for medical teaching tools.

New Exact Soliton Solutions and Multistability for the Modified Zakharov-Kuznetsov Equation with Higher Order Dispersion

The aim of the present paper is to obtain and analyze new exact travelling wave solutions and bifurcation behavior of modified Zakharov-Kuznetsov (mZK) equation with higher-order dispersion term. For this purpose, the first and second simplest methods are used to build soliton solutions of travelling wave solutions. Furthermore, the bifurcation behavior of traveling waves including new types of quasiperiodic and multi-periodic traveling wave motions have been examined depending on the physical parameters. Multistability for the nonlinear mZK equation has been investigated depending on fixed values of physical parameters with various initial conditions. The suggested methods for the analytical solutions are powerful and beneficial tools to obtain the exact travelling wave solutions of nonlinear evolution equations (NLEEs). Two and three-dimensional plots are also provided to illustrate the new solutions. Bifurcation and multistability behaviors of traveling wave solution of the nonlinear mZK equation with higher-order dispersion will add some value to the literature of mathematical and plasma physics.

Numerical investigation on self-propelled hydrodynamics of squid-like multiple tentacles with synergistic expansion

Cephalopods, such as squids, have versatile swimming mechanisms that allow them to adapt to complex underwater environments. Their primary means of propulsion are funnel jets, whereas coordinating soft wrists are often overlooked. The purpose of this study is to provide tentacles at the end of a squid-like robot with a circular symmetric expansion based on the traveling wave motion law and analyze the effects of the number, frequency and expansion amplitude of tentacles on its self-propelled performance. The geometry of the aquatic squid and flexible posterior segment including three joints are considered to be the key features. Overlapping grids of hole cutting technique are applied to manipulate virtual swimmers and simulate incompressible viscous flow. The results indicate that the three-tentacled squid has the best propulsion performance, and excessive tentacles cannot unilaterally enhance propulsion. The increase in frequency can be effectively mapped as an increase in the steady-state velocity coefficient and propulsion efficiency, whereas the maximum amplitude of the tentacle bending could only be raised within a certain range, and excessive bending may be counterproductive. The corresponding flow structure can indirectly reveal the evolution process of the multi-tentacled expansion performance.

Self-propulsion characteristics of fish-like undulating foil – a numerical investigation

ABSTRACT In this work, the propulsive characteristic of an auto-propelled 2D NACA0015 foil undergoing traveling wave motion is numerically investigated. The effects of typical motion parameters, i.e. traveling amplitude, traveling frequency (f), and geometric parameters (thickness, d) on the propulsive property of auto-propelled foil are systematically investigated. The numerical results reveal that the moving velocity of foil can be significantly enhanced by the enlargement of the traveling amplitude and traveling frequency, while it presents a sharp decrease when the foil thickness increases. As for the propulsive efficiency, the effects of a 1, f and d on the magnitude of η are similar to each other, that is, the magnitude of η will ascend to the peak value and then decrease, and there exists an optimum value corresponding to the highest magnitude of η. The flow structures in the wake of the auto-propelled foil under typical calculation conditions are also analysed.

Measurement of thermal radiative and mass transfer of peristaltic pumping of electrically-conducting bio-bi-phase flow due to metachronal wave: Eukaryotic cells in biological applications

Cilia motion are commonly located in mammalian cells of living organisms which is continually grow and feature conspicuously. The ciliary apparatus is associated to cell cycle movement and proliferation, and cilia show a dynamic part in human and animal growth and in everyday life. The measurement of a solo cilium is one to tenth micrometres and width is less than 1 μm. A large number of varieties is originated such as inner ear, kidney, oviduct, eye, testes, olfactory epithelium and respiratory tract. Protozoa, algae, and several small invertebrates are examples of creatures that frequently exhibit metachronal waves in their cilia and flagella. These waves generate an overall propulsive force that enables the movement of these organisms in fluid settings. Cilia or flagella can provide fluid flow that drives the creature ahead or allows it to move particles or other materials around it by producing a travelling wave motion. Motivation of these applications, Present study is measurement of thermal and mass transfer in beating cilia of multiphase peristaltic pumping of non-Newtonian Ree-Eyring fluid in two- and three-dimensional channel using transvers magnetohydrodynamics in porous medium. Two systems of the governing equations both phases dusty and fluid phase are formulated for the non-Newtonian Ree-Eyring fluid. Calculated exact solutions for fluid phase velocity, particulate phase velocity, temperature, concentration and pressure gradient respectively. Also, physical behaviour is discussed by plotting the graph of different dimensionless parameters on both phases solid-liquid on velocity, thermal and concentration. Trapping phenomenon is visualized by plotting the stream lines of different dimensionless parameters on velocity of Ree-Eyring fluid and magnetic field.

Evaluation of Spiral Pneumatic Rubber Actuator Using Finite Element Analysis for Radial Transportation

Emerging actuators with various soft materials and a traveling wave motion are frequently discussed. Various configurations have been proposed and their resulting performances investigated, but it remains challenging to realize large strokes. This study presents an experimentally validated nonlinear finite element model to predict the deformation produced by a spiral pneumatic rubber actuator to generate a traveling wave motion. The actuator consists of a membrane mounted on a rubber substrate with three air chambers in a spiral configuration. The sequential deformations of the successive chambers interact with each other and produce radial traveling waves on the membrane surface, driving the objects placed on the actuator. Finite element analysis with ANSYS computer software was used to analyze the elastic movement by considering the influence of different initial structural types. The simulation results indicated an optimal structure with specific ratios. A reasonable correlation was obtained during experimental validation; the predicted displacement values were approximately 17% smaller than the experimental values. Finally, the transportation performance of the prototype was tested, and a velocity of 2.28 mm/s in the desired direction was achieved. We expect that our demonstration will expand the range of applications of the spiral pneumatic rubber actuator to include conveying or worm-like robots.

Numerical simulation of performance of traveling wave pump-turbine at different wave speeds in pumping mode

Fish swim by flexing their bodies and energy is transferred from the fish to the water. And the plate which imitates traveling wave motion of fish can absorb the energy of fluid under certain motion parameters. By arranging the traveling wave plate in a vertical rectangular flow channel, the flow mode is changed from external flow mode to internal flow mode. This internal flow device is called traveling wave pump-turbine, and it can operate in both pumping mode and turbine mode. The traveling wave plate is simplified into a two-dimensional plate, and the model of the traveling wave pump-turbine is established. The numerical simulation method is used to study its performance characteristics at different wave speeds when it is in pumping mode. The results show that: although it operates in pumping mode by changing the volume of the working chamber, it can output stable mass flow rate. With the increase of wave speed, the volumetric efficiency increases gradually, the time-averaged efficiency first increases and then decreases, and the maximum time-averaged efficiency can reach 0.9. The instantaneous pressure and power are relatively stable when the wave speed is low, while they fluctuate more sharply with the increase of wave speed.

Influence of lengthways spacing and phase difference on traveling wave energy absorption characteristics of flexible airfoils in a diamond array

Under certain motion parameters, traveling wave motion can absorb energy from incoming flow. In addition to the geometric and motion parameters of each unit, the arrangement also has a great influence on the energy absorption efficiency of traveling wave bodies. Using NACA0012 airfoil as a two-dimensional simplified model, the influence of lengthways spacing and phase difference on energy absorption efficiency of airfoils in the diamond array is studied by numerical calculation in this paper. The results show that with the increase of the lengthways spacing between the midstream airfoils and the downstream airfoil, the transverse interference between the airfoils decreases gradually until disappear. Specifically, with the increase of lengthways spacing, the energy absorption efficiency of the midstream airfoils decreases first and then stays constant, while the downstream airfoil shows a simple harmonic fluctuation with decreasing amplitude. When there exists transverse interference in the array, the energy absorption efficiency of the midstream and downstream airfoils shows a simple harmonic fluctuation concerning the phase difference between the upstream airfoil and the downstream airfoil. When there is no transverse interference in the array, the energy absorption efficiency of the downstream airfoil is a simple harmonic fluctuation concerning the phase difference between the upstream airfoil and the downstream airfoil. Under the optimal arrangement, the energy absorption efficiency of the diamond array is 35% higher than that of a single traveling wave airfoil.

Motion planning of a snake robot that moves in crowded pipes

ABSTRACT We propose two motions for a snake robot to move through crowded pipes. One motion is an S-shaped twisting motion performed by the snake robot as it moves around crowded pipes in parallel to the pipes. To develop the shape of the snake robot, the S-shaped twisting motion creates large and small semicircles alternately. In the S-shaped twisting motion, lateral rolling is used to generate the robot's twisting motion along its body to maneuver among crowded pipes. The other motion is an S-shaped traveling wave motion used by the snake robot to move among crowded pipes perpendicularly to the pipes. The S-shaped traveling wave motion adds a hyperbolic shape to the snake robot by utilizing a hyperbolic function. The shape of the hyperbolic function produces a little wave in the S-shaped traveling wave motion, and the wave is transferred from the tail to the head to move ahead. In this study, we describe the design of these two motions and exhibit the results of trials in simulation and with a real snake robot to validate the effectiveness of our proposed snake robot's motion.

Interplay between traveling wave propagation and amplification at the apex of the mouse cochlea

Sounds entering the mammalian ear produce waves that travel from the base to the apex of the cochlea. An electromechanical active process amplifies traveling wave motions and enables sound processing over a broad range of frequencies and intensities. The cochlear amplifier requires combining the global traveling wave with the local cellular processes that change along the length of the cochlea given the gradual changes in hair cell and supporting cell anatomy and physiology. Thus, we measured basilar membrane (BM) traveling waves in vivo along the apical turn of the mouse cochlea using volumetric optical coherence tomography and vibrometry. We found that there was a gradual reduction in key features of the active process toward the apex. For example, the gain decreased from 23 to 19 dB and tuning sharpness decreased from 2.5 to 1.4. Furthermore, we measured the frequency and intensity dependence of traveling wave properties. The phase velocity was larger than the group velocity, and both quantities gradually decrease from the base to the apex denoting a strong dispersion characteristic near the helicotrema. Moreover, we found that the spatial wavelength along the BM was highly level dependent in vivo, such that increasing the sound intensity from 30 to 90 dB sound pressure level increased the wavelength from 504 to 874 μm, a factor of 1.73. We hypothesize that this wavelength variation with sound intensity gives rise to an increase of the fluid-loaded mass on the BM and tunes its local resonance frequency. Together, these data demonstrate a strong interplay between the traveling wave propagation and amplification along the length of the cochlea.

Traveling wave turbine - An internal flow energy absorption mode based on the traveling wave motion

The plate with traveling wave motion can obtain energy from fluid under certain motion parameters. This energy absorption method, which imitates motion of fish, is called traveling wave energy absorption method. In order to improve the energy absorption efficiency, the traveling wave plate is arranged in the rectangular flow channel and is driven by the high pressure gas coming through the inlet. This internal flow mode is called traveling wave turbine. The traveling wave plate is simplified as a two-dimensional plate. The aerodynamic characteristics of traveling wave turbine are studied by numerical simulation. The results show that: Benefiting from the confinement effects of the rectangular flow channel, the incoming flow can maintain high pressure. Therefore, the time-averaged energy absorption efficiency of traveling wave turbine can reach 62.84%. The pressure of the fluid is high before the traveling wave plate, but it becomes low when the fluid flows through the plate. This means that the energy of the fluid is absorbed by the traveling wave plate. There are vortexes in the traveling wave turbine and the vortexes with opposite rotating directions will accelerate the fluid between them.

Computational analysis on propulsive characteristic of flexible foil undergoing travelling wave motion in ground effect

The numerical simulations are employed to study the propulsive characteristic of travelling wave foil under various ground distances and non-dimensional motion frequencies (St number). This study concentrates on ground wall's effect on travelling wave foil's propulsive property and the research object contains both the two dimensional (2D) and three dimensional (3D) models. A finite-volume method is employed to simulate the flow field by using of the commercial software ANSYS Fluent and the dynamic grid technique, coupled with the User Defined Function (UDF), is utilized to realize the foil's travelling wave motion. The calculation results demonstrate that the ground wall produces great impact on travelling wave foil's fluid dynamics. In specific, the thrust force will be enhanced under high St number and the drag force will be reduced when it comes to low St number. As for the propulsive efficiency, there also exists distinct increase. At the same time, the symmetry along the vertical direction of the flow field is destroyed, leading to the pretty high lift force. Flow analyses have demonstrated that the surface pressure of the travelling wave foil presents sharp increase under the existence of the wall and the vortex structure have also undergone huge change. Insights from current study will be beneficial for the future design of bionic underwater vehicle.

Modeling and Characterization of the Passive Bending Stiffness of Nanoparticle‐Coated Sperm Cells using Magnetic Excitation

AbstractOf all the various locomotion strategies in low‐, traveling‐wave propulsion methods with an elastic tail are preferred because they can be developed using simple designs and fabrication procedures. The only intrinsic property of the elastic tail that governs the form and rate of wave propagation along its length is the bending stiffness. Such traveling wave motion is performed by spermatozoa, which possess a tail that is characterized by intrinsic variable stiffness along its length. In this paper, the passive bending stiffness of the magnetic nanoparticle‐coated flagella of bull sperm cells is measured using a contactless electromagnetic‐based excitation method. Numerical elasto‐hydrodynamic models are first developed to predict the magnetic excitation and relaxation of nanoparticle‐coated nonuniform flagella. Then solutions are provided for various groups of nonuniform flagella with disparate nanoparticle coatings that relate their bending stiffness to their decay rate after the magnetic field is removed and the flagellum restores its original configuration. The numerical models are verified experimentally, and capture the effect of the nanoparticle coating on the bending stiffness. It is also shown that electrostatic self‐assembly enables arbitrarily magnetizable cellular segments with variable stiffness along the flagellum. The bending stiffness is found to depend on the number and location of the magnetized cellular segments.

Electrically-Induced Traveling-Wave Motion for Linear Transportation Using Multi-Balloon Dielectric Elastomer Actuator

Electrically-Induced Traveling-Wave Motion for Linear Transportation Using Multi-Balloon Dielectric Elastomer Actuator

Analysis of the multi-balloon dielectric elastomer actuator for traveling wave motion

Recently, various soft actuators with biologically inspired motions have emerged in the field of robotics. The present study focuses on the development of a multi-balloon dielectric elastomer actuator (DEA) to provide a traveling wave motion for the linear transportation of an object. The multi-balloon actuator is designed on the basis of a pneumatic rubber actuator and a DEA, which itself consists of a dielectric membrane mounted on a silicone air chamber. An actuator that is inflated by pre-charged air pressure induces a rapid response speed and large deformations using only electric power; thus, it does not require the bulky external system which is essential for conventional pneumatic actuators. A multi-balloon actuator made of only soft materials was successfully fabricated by screen printing, rubber casting, and plasma treatment processes. Throughout the experiment, the maximum displacements of the balloon actuator with respect to height and width were obtained at an air pressure of 12.2 kPa. Importantly, the multi-balloon actuator’s components assembled and interacted with each other and could successfully transport an object linearly via a traveling wave. In the object transfer experiment of this study, the linear velocity reached 0.97 mm/s with an initial air pressure and the applied voltage maintained at 13.3 kPa and 7.5 kV, respectively. The potential applicability of this system as a portable robot is demonstrated by replaying the traveling wave motions using a multi-balloon actuator. In the future, this design can be applied to portable small-scale robots and annelid robots with high reliability and body compliance.

Study on energy absorption performance of airfoils with traveling wave motion in different school configurations

The airfoil with traveling wave motion can obtain energy from fluid under certain motion parameters, and the school configurations definitely affect the energy absorption efficiency. In this study, we set three NACA0012 airfoil sections as two-dimensional simplified models of the fishlike body. Based on numerical simulation, the energy absorption efficiency of the airfoils in different school configurations is studied. The results show as follows: when only longitudinal interference (tandem configuration) works, the efficiency of the first airfoil fluctuates slightly with the increase of the longitudinal distance, while the efficiency of the second and third airfoils present a simple and harmonic trend. When only lateral interference (parallel configuration) works, the efficiency of both ends of the airfoils gradually decreases with the increase of the lateral distance, while the efficiency of the middle airfoil increases first and then decreases, having a maximum value. When longitudinal and lateral interferences exist simultaneously (triangular configuration), there are optimal longitudinal and lateral distances so that the efficiency of the three airfoils is the highest. Among these three school configurations, the parallel one is the most advantageous for gaining energy from the flow, followed by the triangular one, then the tandem one. This is a completely new energy harness methodology which could be an innovative approach in the future to provide power source energy for the robotic fish for long-endurance missions. Therefore, this study has important research values and application prospects.

Revealing the actions of the human cochlear basilar membrane at low frequency

The basilar membrane (BM) is the key infrastructure that supports the microstructure of cochlear acoustic function, and its interaction with lymph in the cochlea involves a complex, highly nonlinear coupling motion and energy conversion. In 1928, Nobel Laureate Gordon von Békésy experimented and first discovered the traveling wave motion of the BM, thus uncovering the mystery of BM motion. However, with the further development of experimental technology in recent years, scientists have discovered that the traveling wave motion does not explain many experimental observations and phenomena associated with the detection of low-frequency sounds by the cochlea. Because the cochlea is very small and complex, Békésy could only obtain medium- and high-frequency motion data for the BM but not low-frequency motion data. Based on a theory of mathematical physics and biology combined with data from medical and modern light source imaging experiments, a theoretical model of the spiral cochlea and a numerical model that conforms to the real human ear were established. The results reproduce the known traveling wave motion of the BM. Meanwhile, an exciting new finding has revealed a standing wave motion pattern at low frequencies. This newly discovered motion pattern intrinsically explains many experimental observations that could not be explained by the traveling wave theory. These results not only complement the low-frequency motion characteristics of the BM, but also probably reveal the mechanism of active phonoreceptive amplification in the cochlea, which has been a difficult problem to unravel in otology medicine.