Wedge Waves Research Articles

Study on aerodynamic force and aerothermal effect of two-dimensional wedge wave rider with different passivation shape of the head

With the rapid development of space technology, hypersonic vehicles flying at altitudes of 20-100 km near space are showing more and more important application value, and how to solve the serious aerodynamic heating problem caused by hypersonic vehicles in the process of flight is the focus of current research. In this paper, the simplified two-dimensional wedge-shaped waveride is treated with the passivation leading edge by the Computational Fluid Dynamics (CFD) method, and the aerodynamic and aerothermal properties of the hypersonic continuous flow basin are numerically simulated. The flow field structure of the model is analyzed, and the law of heat-resistant rise is revealed. The research contents mainly include the characteristics of body head heat flux and body lift-drag ratio under different passivation shapes. Within the research scope: 1. The larger the passivation radius, the more effective it is to reduce the head heat flux. When the passivation radius is 2 mm, the reduction is about 82.5%. 2. The larger the passivation radius, the more serious the lift-drag ratio reduction. When the passivation radius is 2mm, the maximum reduction is about 72.4%; 3. The four passivation leading edge modes have the best thermal protection effect when the passivation radius R is the same, and the lift-drag ratio of the Bezier curve passivation leading edge mode is the largest.

Formation optimization of various spacing configurations for a fleet of unmanned surface vehicles based on a hydrodynamic energy-saving strategy

The purpose of this study is to optimize an energy-saving formation of a fleet of unmanned surface vehicles (USVs) for minimum energy consumption where the wave relies on its own hydrodynamic behavior. This work also provides new insights into the mechanisms of energy-saving formations based on the spacing configurations in terms of longitudinal offset and transverse separation. The numerical model is validated to meet precision demands with a prototype experimental test using a fleet of USVs. The echelon formation is constructed within the aft wedge wave pattern region considering the flow expansion of the Kelvin wave. A body force model is applied to replicate the impact of the propeller, and a mesh progressive refinement is executed to divide the functional zones of the computational domain. Energy consumption equations of formations are proposed to quantify the energy profit relationship between individual vehicles and fleets. The results highlight that the resistance component greatly contributes to the energy consumption, and that the hydrodynamic behavior mechanics impact the energy-saving capacity of the fleet. To achieve minimum energy consumption, the formation configurations are optimized based on the spacing partition to achieve energy-savings for individual vehicles and the whole fleet. These findings can be utilized for future energy-savings when using USV's for a variety of purposes, such as hydrographic surveying, data collection, reconnaissance, and general surveillance.

PARAMETRIC STUDY ON WAVE OVERTOPPING DUE TO WEDGE ANGLE AND FREEBOARD OF WAVECAT WAVE ENERGY CONVERTER

Wave energy presents great potential in many coastal regions. This paper deals with WaveCat, a new wave energy converter (WEC) recently patented by the University of Santiago de Compostela. The WaveCat has two hulls, like a catamaran, and it operates according to the overtopping principle. The higher the overtopping amount collected in the reservoir, the higher the energy generated. The wedge angle and freeboard are two important parameters that contribute to a higher overtopping discharge. However, knowledge on the influence that wedge angle and freeboard have on wave overtopping is limited. Hence, this study aims to extend the borders of available knowledge by investigating the influence that two parameters have on wave overtopping discharge through simulation using computational fluid dynamics (CFD). The WEC was designed in the AutoCAD software. Then, the parameters were simulated using CFD. The parameters of wave height and wave period with a specified range are added and the relationship between wedge angle, freeboard and wave overtopping performance of WaveCat were analysed. The validation results showed good agreement between the simulation and physical experiment, with a percentage error of within 20%. The results are useful for further investigation related to optimising WaveCat parameters for selecting the best performance.

Study of influence of periodic defects on the propagation of wedge waves using laser ultrasound technique and finite element analysis

Study of influence of periodic defects on the propagation of wedge waves using laser ultrasound technique and finite element analysis

Numerical simulation of formation optimization for a fleet of unmanned surface vehicles based on a minimum energy consumption requirement

This study proposes a hydrodynamic optimization strategy focusing on minimum energy consumption to construct the formation of a fleet of unmanned surface vehicles (USVs) by transforming the longitudinal offset and transverse separation. USVs were used instead of Autonomous Underwater Vehicles (AUVs) to fully consider the influence of a wave on energy-savings and to address undersize spacing and limited wake. The numerical model provided reasonably accurate results when compared against a series of experimental prototype results. The body force model was used to replicate the impact of the propeller, and an echelon formation was arranged considering the aft wedge wave pattern region induced by the Kelvin wave. The energy consumption equations of two-, three-, and four-hull formations were denoted by resistance components and used to determine the energy relationship between individuals and collectives. Additionally, an optimization platform was developed to integrate the application programs because the computation times were extensive for numerical simulations of spacing configurations transformation

Anomalous reflection and transmission of surface acoustic waves at a crystal edge via coupling to leaky wedge waves

Surface acoustic waves are propagated toward the edge of an anisotropic elastic medium (a silicon crystal), which supports leaky waves with a high degree of localization at the tip of the edge. At an angle of incidence corresponding to phase matching with this leaky wedge wave, a sharp peak in the reflection coefficient of the surface wave was found. This anomalous reflection is associated with efficient excitation of the leaky wedge wave. In laser ultrasound experiments, surface acoustic wave pulses were excited and their reflection from the edge of the sample and their partial conversion into leaky wedge wave pulses was observed by optical probe-beam deflection. The reflection scenario and the pulse shapes of the surface and wedge-localized guided waves, including the evolution of the acoustic pulse traveling along the edge, have been confirmed in detail by numerical simulations.

Gravitational waves in Kasner spacetimes and Rindler wedges in Regge-Wheeler gauge: Formulation of Unruh effect

We derive the solutions of gravitational waves in the future (F) expanding and the past (P) shrinking Kanser spacetimes as well as in the left (L) and right (R) Rindler wedges in the Regge-Wheeler gauge. The solutions for all metric components are obtained in an analytic form in each region. We identify the master variables, which are equivalent to massless scalar fields, to describe the gravitational degrees of freedom for the odd parity and even parity modes under the transformation in the two-dimensional plane symmetric space. Then, the master variables are quantized, and we develop the quantum field theory of the gravitational waves in the F, P, L, and R regions. We demonstrate that the mode functions of the quantized gravitational waves in the left and right Rindler wedges are obtained by an analytic continuation of the left-moving and right-moving wave modes in Kasner spacetime. On the basis of these analyses, we discuss the Unruh effect of quantized gravitational waves for an observer in a uniformly accelerated motion in Minkowski spacetime.

The fundamental ultrasonic edge wave mode: Propagation characteristics and potential for distant damage detection

Engineering structures are often composed of thin elements containing features such as free edges, welds, ribs, and holes, which makes distant safety inspections based on guided waves difficult due to wave scattering. However, these features can themselves generate so-called ‘feature-guided’ waves, which can potentially be utilised for damage detection. One such example are flexural wedge waves, which have been investigated extensively both theoretically and experimentally in the past. Another example is edge waves. These waves, which are a natural analogue of Rayleigh waves propagating in a finite thickness plate, have received relatively little attention, specifically with respect to their possible use in distant damage inspections and Structural Health Monitoring systems. The current paper is aimed to address this gap, and it is focused on the investigation of the fundamental mode of edge waves (ES0), which is the most promising for practical applications. The features of the transient ES0 mode are investigated experimentally and numerically, and compared with previous theoretical studies. It was demonstrated that the ES0 mode can be effectively excited with the wedge excitation method, and distant damage detection with this wave mode at low frequency-thickness values (FTV < 5) is readily achievable. In particular, in a laboratory environment the ES0 mode propagated several meters with almost no decay. However, at higher frequency-thickness values, a wave amplitude modulation, significant energy decay and strong coupling between the ES0 and S0 wave modes were observed. These phenomena may restrict the defect resolution as well as the range of damage inspections based on the fundamental edge wave mode.

Elastic Waves in Cylindrical Metal Wedges with Different Geometries

The article presents results of numerical simulation and experimental studies of elastic wedge wave propagation in cylindrical wedges with positive and negative curvature in the 100–600 kHz frequency range. It is shown that wedge waves in such structures have dispersion and their localization at the edge of the wedge is stronger than that of straight wedges. The results of a study for cases where the inner surface of the wedge is bounded by fluids with different viscosities (water, SAE 10W-30 motor oil, 86% glycerol aqueous solution) are presented.

Shear Flow‐Interchange Instability in Nightside Magnetotail as Proposed Cause of Auroral Beads as a Signature of Substorm Onset

AbstractA geometric wedge model of the near‐Earth nightside plasma sheet is used to derive a wave equation for low‐frequency shear flow‐interchange waves which transmit sheared zonal flows along magnetic flux tubes toward the ionosphere. Discrepancies with the wave equation result used in Kalmoni et al. (2015, https://doi.org/10.1002/2015JA021470) for shear flow‐ballooning instability are discussed. The shear flow‐interchange instability appears to be responsible for substorm onset. The wedge wave equation is used to compute rough expressions for dispersion relations and local growth rates in the midnight region of the nightside magnetotail where the instability develops, forming the auroral beads characteristic of geomagnetic substorm onset. Stability analysis for the shear flow‐interchange modes demonstrates that nonlinear analysis is necessary for quantitatively accurate results and determines the spatial scale on which the instability varies.

Overview of localised flexural waves in wedges of power-law profile and comments on their relationship with the acoustic black hole effect

In the present paper, the relationship between localised flexural waves in wedges of power-law profile and flexural wave reflection from acoustic black holes is examined. The geometrical acoustics theory of localised flexural waves in wedges of power-law profile is briefly discussed. It is noted that, for wedge profiles with power-law exponents equal or larger than two, the velocities of all localised modes take zero values, unless there is a wedge truncation. It is demonstrated that this effect of zero velocities of localised flexural waves in ideal wedges is closely related to the phenomenon of zero reflection of flexural waves from ideally sharp one-dimensional acoustic black holes. A possible influence of localised wedge modes on flexural wave reflection from one-dimensional acoustic black holes having rough edges is discussed. With regard to two-dimensional acoustic black holes, the role of localised flexural waves propagating along wedge edges that are curved in their middle plane is considered. Such waves can propagate along edges of inner holes in two-dimensional acoustic black holes formed by circular indentations in plates of constant thickness. A possible impact of such localised waves on the processes of scattering of flexural waves by edge imperfections of inner holes in two-dimensional acoustic black holes is discussed, including their influence on the efficiency of two-dimensional acoustic black holes as vibration dampers.

Nonlinear effects of micro-cracks on acoustic surface and wedge waves

Micro-cracks give rise to non-analytic behavior of the stress-strain relation. For the case of a homogeneous spatial distribution of aligned flat micro-cracks, the influence of this property of the stress-strain relation on harmonic generation is analyzed for Rayleigh waves and for acoustic wedge waves with the help of a simple micromechanical model adopted from the literature. For the efficiencies of harmonic generation of these guided waves, explicit expressions are derived in terms of the corresponding linear wave fields. The initial growth rates of the second harmonic, i.e., the acoustic nonlinearity parameter, has been evaluated numerically for steel as matrix material. The growth rate of the second harmonic of Rayleigh waves has also been determined for microcrack distributions with random orientation, using a model expression for the strain energy in terms of strain invariants known in a geophysical context.

Nonlinear Elastic Waves in a Solid Isotropic Wedge with Defects

The paper presents experimental data for linear and nonlinear elastic waves in an acute-angled wedge made of D16 isotropic polycrystalline alloy with defects. The localization of waves at the edge of the wedge has been studied using laser vibrometry. The velocities of wedge waves have been measured by a pulse method in the frequency range 0.25–1.50 MHz. Measurements have not revealed any dispersion. The second harmonic of the wedge waves has been found. The dependences of the velocity and amplitude of the second harmonic on the amplitude of the first harmonic have been studied. It is noted that nonlinear effects observed in wedge waves may be explained in terms of the Murnaghan classical five-constant theory of elasticity. They are attributed to a defect-induced structural nonlinearity present in the wedge.

Study on Liquid Level Sensing based on Wedge Waves Propagation

Study on Liquid Level Sensing based on Wedge Waves Propagation

Measuring Liquid-Level Utilizing Wedge Wave.

A new technique for measuring liquid-level utilizing wedge wave is presented and demonstrated through FEM simulation and a corresponding experiment. The velocities of wedge waves in the air and the water, and the sensitivities for the measurement, are compared with the simulation and the results obtained in the experiments. Combining the simulation and the measurement theory, it is verified that the foundation framework for the methods is available. The liquid-level sensing is carried out using the aluminum waveguide with a 30° wedge in the water. The liquid-level is proportional to the traveling time of the mode 1 wedge wave. The standard deviations and the uncertainties of the measurement are 0.65 mm and 0.21 mm using interface echo, and 0.39 mm and 0.12 mm utilized by end echo, which are smaller than the industry standard of 1.5 mm. The measurement resolutions are 7.68 μm using the interface echo, which is the smallest among all the guided acoustic wave-based liquid-level sensing.

Design of wedge structure with non-dispersive wedge wave propagation.

This paper focuses on designing a structure using a laser ultrasound technique, wherein wedge waves can propagate without dispersion. First, the impact of curvature radius and truncations on the wedge waves are investigated using finite element method, and the dispersion curves are obtained using a two-dimensional Fourier transformation method. Subsequently, the propagation of non-dispersive wedge waves is realized via a special wedge shape, which was designed with a unique relationship between the curvature radius and truncation, and its correctness is validated using numerical simulation. Finally, experiments are performed to detect the wedge waves, wherein a pulsed laser is coupled with optical fiber excitation, and the waves are detected using an optical vibrometer.

Intersection Waves

AbstractIntersections in a fracture network control the connectivity of the flow paths through rock. The long near‐linear geometric nature of fractures makes them difficult to identify and characterize. We present a new type of elastic wave, an intersection wave, which travels along an intersection and is sensitive to the coupling between two orthogonal fractures that define the intersection. Group theory for C2v and C4v point groups predicts sets of propagating elastic waves confined to the fracture intersection. Along with the use of the wave equation and displacement discontinuity boundary conditions, the dispersion relationships for intersection waves are predicted. Experimental ultrasonic measurements on a nonwelded linear intersection between two orthogonal, synthetic fractures in aluminum confirm the existence of multiple modes that travel between the speed of wedge waves (sub‐Rayleigh waves) when the intersection is completely, and bulk shear waves, when the intersection is closed, as predicted by theory. Between these two limits, the intersection behaves as a nonwelded contact and yields these new intersection waves that are dispersive and sensitive to the coupling along the intersection. Intersection waves provide the foundation for new geophysical approaches for characterizing the hydraulic connectivity of fracture networks.

Characterization of wedge waves propagating along wedge tips with defects

Wedge waves are guided acoustic waves propagating along the tip of a wedge with the energy tightly confined near the wedge. Anti-symmetric flexural (ASF) modes are wedge waves with their particle motion anti-symmetric with the apex mid-plane. This study investigates the behaviors of ASF modes propagation along wedge tips with perfect and imperfect rectangular defects. Numerical finite element simulations and experimental measurements using a laser ultrasound technique are employed to explore the behaviors of ASF modes interacting with defects. Complex reflections and transmissions involved with direct reflections and transmissions as well as the newly discovered mode conversions will be explored and quantified in numerical as well as experimental ways.

The Application of GA-BP Neural Network on Parameter Inversion of Wedge

An inversion model based on neural network combined with genetic algorithm was established to obtain the material parameters of an unknown wedge. Firstly, a back propagation (BP) neural network was introduced and the genetic algorithm was implied to optimize the initial weights and thresholds of the BP neural network. Wedge wave dispersion curves with different angles, density and young’s modulus were obtained by simulation. Then the phase velocity of first-order mode in the anti-symmetrical flexural mode was chosen as the inputs of our inversion model, the corresponding parameters were taken as the outputs. The first-order mode data measured from samples were used to test the validity. It is found that the inversion models can inverse angle, density and young’s modulus simultaneously. Compared with the single BP neural network, it has the advantages of fast convergence speed and high precision.

Numerical Simulation on the Generation and Propagation of Wedge Waves

Numerical Simulation on the Generation and Propagation of Wedge Waves