Interaction Of Incident Wave Research Articles

Energy Transfer Efficiency Based Nonlinear Ultrasonic Testing Technique for Debonding Defects of Aluminum Alloy Foam Sandwich Panels

In order to improve the accuracy of detection results of debonding defects of aluminum alloy thin plate, the nonlinear ultrasonic technology is used to detect the simulated defect samples, aiming at problems such as near surface blind region caused by the interaction of incident wave, reflected wave and even second harmonic wave in a short time due to the small thickness of thin plates. An integral method based on energy transfer efficiency is proposed to calculate the nonlinear ultrasonic coefficient to characterize the debonding defects of thin plates. A series of simulated debonding defects of different sizes were made using aluminum alloy plates with four thicknesses of 1 mm, 2 mm, 3 mm and 10 mm. By comparing the traditional nonlinear coefficient with the integral nonlinear coefficient proposed in this paper, it is verified that both methods can quantitatively characterize the size of debonding defects. The nonlinear ultrasonic testing technology based on energy transfer efficiency has higher testing accuracy for thin plates.

Analytical and Rothe time-discretization method for a Boussinesq-type system over an uneven bottom

We study analytically and numerically a 2D version of a Boussinesq-type model considered by M. Chen (2003) to describe water wave propagation on the surface of a channel with an irregular moving topography. Following a semidiscrete horizontal line method (Rothe’s method) implemented with FEniCS, we first discretize the temporal variable by using a finite-difference second-order Crank-Nicholson-type scheme, and then, at each time step, the spatial variables are discretized with an efficient Galerkin/Finite Element Method (FEM) using triangular-finite elements based on 2D piecewise-linear Lagrange interpolation. The numerical experiments presented are in accordance with the previous theoretical and experimental studies and show that the so-called Bragg resonant reflection emerges when surface waves modelled by the Boussinesq formulation studied interact with periodically varying bottoms. We also present some experiments to examine the interaction of incident waves with variable topographies such as the shoaling of a solitary wave on a slope and the generation of surface waves by moving topography.

Study on Tunable Magnetized Plasma Frequency Selective Surface Using JEC-FDTD Method

The tunability of traditional frequency selective surfaces (FSSs) is inconvenient using metal material patch as periodic element, utilizing genetic algorithms to model FSS layers obtaining desired filtering electromagnetic waves effect. However, plasma tube is used as an element of the frequency selection surfaces substituting traditional metal patch in this article. A 3-D finite-difference time-domain (FDTD) formulation for dispersive media called the JE convolution (JEC) method is derived using the convolution relationship between the current density $J$ and the electric field $E$ to simulate the interaction of incident wave and magnetized plasma FSS. Numerical experimental results show that the electron number density of magnetized plasma has a significant effect on the resonance frequency, which can be modulated to the desired filtering by varying the density in the magnetized plasma elements. Whereas the magnetized plasma FSSs behave exactly like a perfect electric conductor (PEC) increasing the electron number density to a certain degree. Thus, modulation based on the ionized electron number density of the magnetized plasma can be designed into a tunable plasma FSS. Both the collision model and the noncollision model of the magnetized plasma are proposed to research electromagnetic transmission characteristics of FSS. It shows that the collision frequency only affects the reflectivity while has no effect on the resonance frequency in the following numerical experiments. In addition, magnetization intensity of the plasma FSS is also taken into consideration. The users obtaining the desired resonance frequency and transmission characteristics of plasma FSS by simply tuning the plasma’s electron number density, collision frequency, and magnetization intensity. So the magnetized plasma FSS can not only improve the electromagnetic shielding effect but also facilitate the modulation and rapid response to achieve the desired filtering effect. What is more, the magnetized plasma FSS can be turned off to achieve transparency, which greatly expands the universality of magnetized plasma FSS.

Tunability Study of Plasma Frequency Selective Surface Based on FDTD

This paper is focused on using plasma as element of a frequency selective surface (FSS). FSSs have been used for filtering electromagnetic waves for many years. Conventional FSSs use metal patch pattern as periodic element. This paper takes the plasma tube as a substitution for metal patch. The 3-D finite-difference time-domain method with periodic boundary condition is utilized to simulate the interaction of incident wave and plasma FSS. Numerical calculation results in that electron number density of plasma can dominate the resonance frequency obviously. The resonance frequency increases as the increasing of electron number density of plasma to the limit of that of perfectly electric conductor. Thus, the FSS can be designed to be tunable by changing the ionized electron number density. Both of the noncollision and collisional plasma model are introduced to study the FSS characteristics. The numerical calculation results show that the collision frequency only influences the reflectivity while has no effect on the resonant frequency. The resonant frequency and transmitted power ratio can be tuned by assigning the plasma’s electron number density and collision frequency. Thus, plasma elements offer the possibility of improved shielding effect along with reconfigurability. Plasma FSS can also be made transparent by tuning the plasma off which makes the use of FSS more versatile.

Slope unit-based approach for assessing regional seismic landslide displacement for deep and shallow failure

Grid-based approach is typically adopted to estimate the Newmark-type displacement for regional seismic landslide hazard assessment. However, the approach is limited to the assumption of infinite slope and rigid block movement, which may be different from the actual behavior of slope under seismic loading. In this study, a slope unit-based approach is proposed to quickly estimate earthquake-induced displacements for finite slopes in regional scale. Hence, regional seismic landslide hazard can be assessed by the estimated displacements. The approach is advantageous as it considers slope geometry, determines the failure mode automatically, and considers the interaction of incident wave and slope. The implementation of the approach is demonstrated by considering two areas that experience severe landslides during the Chi-Chi and Northridge earthquakes. Results show that the prediction rate of the proposed method is up to 73% compared with the landslide inventory given the estimated displacements.

The three-level ripples induced by femtosecond laser on a 6H-SiC single crystal and the formation mechanism

In this paper, a line-scanning irradiation of 6H-SiC single crystal by a femtosecond laser focus was implemented for laser fluence of 2.2 J/cm2 at different scanning velocities from 1000 down to 100 μm/s. The morphology of the obtained ablation lines characterized by a scanning electron microscope shows that there progressively appear three-level ripples with average period of about 222, 600 nm and that between them. Possible formation mechanisms for these three-level ripples were analyzed by numerical simulation employing finite-difference time-domain method (FDTD). Analysis shows that as Obara proposed, the interference of incident wave with the wave scattered by scratches possibly left by fine polishing is the most possible reason for inducing 222 nm-period and 600 nm-period ripples. Main discussions were focused on the orientation characteristics of ripples. Both isolated scratches and crossed scratches with different orientation angles were considered for evaluating their role in field redistribution. The detailed simulations indicate that for scratches oriented 90° with respect to laser polarization generate a pair of strongest ripple-like optical field enhancement compared to scratches with other orientation angles. It is these advantages of 90°-oriented scratch in field enhancement that make the final ripple perpendicular to laser polarization most competitive and finally left on the surface. This complements the physical picture of Obara et al. in terms of their negligence in addressing the orientation characteristics of ripples. Further FDTD simulation of the interaction of incident wave with as-formed 600 nm-period ripples shows that the optical field enhancement located between any two adjacent 600 nm-period ripples is the driving force for splitting 600 nm-period ripples into the third ripples with period between 222 and 600 nm.

Floating pontoon-membrane breakwater in the oblique seas

Obliquely incident wave interaction with a floating rigid pontoon breakwater, consisting of triple vertical-porous-membrane structures, was investigated within the context of two-dimensional linear wave-flexible body interaction theory and Darcy’s Law The tensions in the triple membranes are achieved by hanging a heavy clump weight from the lower ends. The floating pontoon and flexible structures with clump weight are partially restrained by linear symmetric mo orings, placed both fore and aft. The dynamic behavior of the breakwater was described through an appropriate Green function, and the fluid domains are incorporated into the boundary in tegral equation. The accuracy and convergence of the developed numerical code were checked using the energy convergence formula for a limited case. The numerical results were further verified through comparisons with the experimental data. It is found that the wave reflection and transmission properties of the structures are primarily dependent upon the membrane length, which is taking a major fraction of the water column. It is also found that they are affected by the magnitude of the tension on the membrane due to the clump weight, proper mooring types and stiffness, and the permeability on the membrane that is dissipating the wave energy.

Hydrodynamic analysis of wave interactions with a moored floating breakwater using the element-free Galerkin method

This paper deals with a numerical investigation of incident wave interactions with a moored pontoon-type floating breakwater. The element-free Galerkin method, in which only nodal data are required to analyze the problem, is employed to solve the diffraction and radiation boundary value problems addressed by the modified Helmholtz equation. The numerical model includes the hydrodynamic and mooring analyses, and it is validated by previous numerical and experimental results. Using the numerical model, we are able to assess the hydrodynamic performance of a moored pontoon-type floating breakwater in regular waves. Numerical results are presented to show the effects of wave conditions and mooring system configuration. This paper also presents the simple forms of stiffness coefficients of a slack mooring line. The influence of mooring line condition on the performance of a floating breakwater is highlighted. Key words: moored floating breakwater, element-free Galerkin method, mooring line condition.

Effects of mean wave drift force on mooring tension and performance of a moored floating breakwater

This paper is a numerical investigation of incident wave interactions with a moored, pontoon-type floating breakwater. We employ a boundary element method to solve the diffraction and radiation boundary value problems describing the situation of a moored floating breakwater in waves. The numerical model includes the hydrodynamic and mooring analyses, verified by the previous numerical and experimental results. Using the numerical model, we are able to assess the hydrodynamic performance of a moored single and dual pontoon floating breakwaters in regular waves. In particular, the effects of the mean wave drift force on the mooring system and wave attenuation characteristics are examined. The numerical results show that mooring tensions are significantly influenced by the mean wave drift force. However, the effect of the drift force on the performance of the floating breakwater in regular waves is not as significant.

Numerical Simulation of 3D Breaking Wave Motions about an Offshore Structure under a Severe Sea Condition

Numerical simulation of the 3D breaking motion on a semisubmersible containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity waves was carried out. The TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of the marker-density method the 3D breaking motion is approximately implemented in the framework of rectangular grid system. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with a certain degree of quantitative and qualitative accuracy.

Diffraction Waves About an Advancing Wedge Model in Deep Water

The diffraction of regular waves by advancing wedge models is studied both experimentally and numerically. The nonlinear features of diffracted waves are visualized by wave pattern pictures and the formation is analyzed by the grid-projection method. The experimental observation indicates that the diffracted waves have a number of nonlinear characteristics similar to shock waves due to the interaction of incident waves with the advancing obstacle in the flow-field caused by the advancing motion. Bow waves of both oblique type and normal detached type are observed at remarkably lower Froude numbers than in the case of a ship in steady advance motion. Their occurrence systematically depends on the Froude number and the wedge angle. The numerical simulation of this phenomenon by a finite-difference method shows approximate agreement with the experimental results.

A Case Study of Wave–Current–Bathymetry Interactions at the Columbia River Entrance

Abstract A unique set of field observations has documented intense wave–current–bathymetry interactions in a tidal inlet, providing a severe test of existing wave theory. Hourly wave spectral estimates were acquired over ten complete tidal cycles at locations offshore of, and on, the Columbia River Bar. This site has long been recognized as an extreme hazard to navigation due to the interaction of incident waves with a strong tidal jet typified by ebb currents in excess of 2 m s−1. During the five-day observational period, offshore significant wave height ranged from 1 to 5 m; in contrast, the Bar wave height oscillated at tidal periods, sometimes doubling during a single six-hour flood-to-ebb cycle. In one case, the Bar wave height was 7.0 m with an offshore wave height of 2.9 m. A one-dimensional model, based on linear wave action–density conservation and incorporating shoaling, refraction and radiation stress, fits the data remarkably well; 85% of the observed variance in Bar swell height and 57% of th...

On the Calculation of Wave Exciting Forces on Ship Translating in Head Sea Waves

The diffraction problem appeared in the ship-wave interaction problem is treated by making use of the slender body theory under the short wave assumption. A solution which is valid in the bow near field as well as in the midship near field is derived and it turns out to be able to descrive the 3-D effect of the interaction of incident waves with a ship hull. This solution is thougth to be the extention of Faltinsen's3) in the meaning that it is valid at the vicinity of bow and also the extention of Maruo's4) in the meaning that it can treat not only zero forward speed case but also forward speed case.The wave load distribution calculated by the present method shows strong x-dependance, which can easily be attributed to the cumulative effect of the slowly varying source density function which is a representation of the effect of the interaction between incident waves and ship hull.By use of Green's theorem, the wave load can be calculated by the asymptotic behavior of the solution for the generalized radiation problem in which the 2-D Helmholtz equation is the governing field equation.Some heuristic numerical results are presented for a ship with circular cross section.

WAVE TRANSMISSION THROUGH. TRAPEZOIDAL BREAKWATERS

Previous publications resulting from this study dealt with, certain aspects of the interaction of normally incident waves with a porous structure. Madsen and White (1976a), hereafter referred to as (I), developed a semi-empirical procedure for the prediction of reflection coefficients of rough impermeable slopes. Madsen (1974) with, discussion by Kondo (1975) and Closure by Madsen (1976), collectively referred to as(ll)hereafter, developed an explicit solution for the transmission and reflection coefficients of homogeneous rectangular crib-style breakwaters. When viewing the interaction of incident waves with, a trapezoidal, multilayered breakwater as a problem of energy dissipation, the problem treated in (II) may he regarded as an idealized analysis accounting for the internal dissipation of energy within the structure, whereas (I) may be regarded as an idealized analysis of the energy dissipation on the seaward face of the breakwater, i.e., the external energy dissipation. The present paper presents a synthesis of the results obtained in (I) and (II) into an approximate procedure for the prediction of wave reflection from and transmission through trapezoidal, multilayered breakwaters. The present paper presents only the major points of the approximate procedure. Thus, extensive references to (I) and (II) are made and only the determination of the hydraulically equivalent breakwater is presented in some detail. For a presentation of the entire development of this model for the reflection and transmission characteristics of trapezoidal, multilayered breakwaters the reader is referred to Madsen and White (1975) or Madsen and White (1976b) where detailed numerical examples of the use of the procedure may also be found.