Simplified Wave Research Articles

Spallation mechanism of RC slabs under contact detonation

The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely. Correctly predicting the damage caused by any potential contact detonation can lead to better fortification design to withstand the blast loadings. It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls. Existing studies on this topic often employ simplified material models and 1D wave analysis, which cannot reproduce the realistic response in the spallation process. Numerical simulations are therefore carried out under different contact blast loadings in the free air using LS-DYNA. Sophisticated concrete and reinforcing bar material models are adopted, taking into account the strain rate effect on both tension and compression. The erosion technique is used to model the fracture and failure of materials under tensile stress. Full processes of the deformation and dynamic damage of reinforced concrete (RC) slabs and plain concrete slabs are thus observed realistically. It is noted that with the increase of quantity of explosive, the dimensions of damage crater increase and the slabs experience four different damage patterns, namely explosive crater, spalling, perforation, and punching. Comparison between the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent, and meanwhile attenuate the ejection velocity and decrease the size of the concrete fragments. Therefore, optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.

Soliton pulse compression through cascaded quadratic nonlinearity in difference-frequency generation

Cascaded nonlinearity based soliton pulse compression in the process of femtosecond difference frequency generation is studied theoretically. A set of simplified coupled wave equations under the conditions of large phase mismatch and matched group velocities is obtained, which reveals the physical mechanism of soliton compression in this process. Numerical simulations demonstrate that in the presence of group velocity dispersion and equivalent cross phase modulation, both the pump and the signal pulses can be compressed with a high compression ratio.

GIS Modeling of Wave Exposure at the Seabed: A Depth-attenuated Wave Exposure Model

Several studies have documented relationships between wave exposure and distribution, density, and size of marine species. Hence, this factor is at a high level in the hierarchical habitat classification system EUNIS and is one of the Water Framework Directive water typology criteria of coastal waters. Isæus (2004) has developed a continuous simplified wave model (SWM) that has been applied to several Nordic countries. Here we refine this model by introducing depth-attenuation, giving us the advantage of a model for wave exposure as it will actually work at the seabed. The values of the depth-attenuated model SWM(d) are approximately similar to the SWM model in shallow areas but noticeably lower in deep areas. The two models were compared in an analysis of the distribution of seabed substrate in the Stockholm archipelago. Using the depth-attenuated wave exposure instead of the SWM model as predictor in substrate modeling improved these models considerably.

Longshore transport estimation and inter-annual variability at a high-energy dissipative beach: St. Trojan beach, SW Oléron Island, France

This study investigates the annual and inter-annual longshore transport at a high-energy dissipative beach (St. Trojan, SW Oléron Island, France), over the period 1997–2006. This study is divided in two parts: (1) a short-term study, based on field measurements carried out during, low, moderate and high-energy swell conditions, and permitting to calibrate a wave propagation model and both empirical longshore sediment transport formulas and a hydro-sedimentary numerical model; and (2) a long-term study, combining global optimization methods using WAVEWATCH III (WW3) model outputs and wave numerical modelling to define the nearshore wave climate and then to compute the annual and inter-annual longshore transport. A good agreement between the different methods was obtained and values for the annual longshore transport ranged from about 50,000±20,000 m 3/yr to 140,000±30,000 m 3/yr. The net annual longshore transport displayed an inter-annual variability, whereas values were always 3–10 times less than those proposed in previous studies. Such differences point out the necessity of calibrating empirical transport formulas and computing accurately the nearshore wave climate. The relatively low values for the net annual longshore transport were explained by a weak contribution of the most energetic swells, which systematically approach the shore with a frontal obliquity and also generate episodes of reverse transport. The methodology itself was also discussed, pointing out the limitations of this study but also the advantages of using WW3 data and simplified wave climates.

Numerical analysis of simplified relic-birefringent gravitational waves

Some theories suggest that gravitational waves created in the early universe may be observable with future gravitational wave interferometers. As a result, identifying the characteristics of these gravitational waves and their corresponding power spectrums at different epochs has become an important area of study. The general solutions to these equations can become quite complex, making the task of obtaining analytical results a difficult one without simplifying assumptions. Using numerical techniques, a general solution to the birefringent gravitational wave equation is explored. This form of the gravitational wave equation is partly composed of a mode function that resembles the Coulomb wave equation from quantum mechanics, which has been explored computationally in the past. An attempt is then made to numerically solve these equations and the corresponding power spectrum for the present universe. Current/planned observatories such as LISA and Advanced LIGO can test these results.

On the theory of self-modulation instability in an FEL amplifier due to stimulated scattering of counterpropagating waves

We present the results of numerical simulation of the self-modulation processes in an amplifier based on the effect of stimulated scattering of two counterpropagating transverse electromagnetic waves by a relativistic electron beam (FEL amplifier). Two models of the studied system are considered. One model allows for the effects of overbunching of electrons and is based on the modified method of macroparticles. The other is a simplified wave model obtained in the approximation that the amplitude of a combination wave is small if the nonlinearity of the electron-beam processes is negligibly small. The mechanisms of self-modulation are studied. The scenarios of transition to chaos, observed with increase in the input-signal intensity and system length, are examined.

Two- and three-body descriptions of hybrid mesons

Hybrid mesons are exotic mesons in which the color field is not in its ground state. Their understanding deserves interest from a theoretical point of view, because it is intimately related to nonperturbative aspects of QCD. In this work, we analyze and compare two different descriptions of hybrid mesons, namely, a two-body $q\overline{q}$ system with an excited string, or a three-body $q\overline{q}g$ system. In particular, we show that the constituent gluon approach is equivalent to an effective excited string in the heavy hybrid sector. Instead of a numerical resolution, we use the auxiliary field technique. It allows us to find simplified analytical mass spectra and wave functions, and still leads to reliable qualitative predictions. We also investigate the light hybrid sector, and found a mass for the lightest hybrid meson which is in satisfactory agreement with lattice QCD and some effective models.

Hybrid mesons with auxiliary fields

Hybrid mesons are exotic mesons in which the color field is not in the ground state. Their understanding deserves interest from a theoretical point of view, because it is intimately related to nonperturbative aspects of QCD. Moreover, it seems that some recently detected particles, such as the π1(1600) and the Y(4260), are serious hybrid candidates. In this work, we investigate the description of such exotic hadrons by applying the auxiliary fields technique (also known as the einbein field method) to the widely used spinless Salpeter Hamiltonian with appropriate linear confinement. Instead of the usual numerical resolution, this technique allows to find simplified analytical mass spectra and wave functions of the Hamiltonian, which still lead to reliable qualitative predictions. We analyse and compare two different descriptions of hybrid mesons, namely a two-body q¯ system with an excited flux tube, or a three-body q¯g system. We also compute the masses of the 1-+ hybrids. Our results are shown to be in satisfactory agreement with lattice QCD and other effective models.

Contraction Analysis of Time-Delayed Communications and Group Cooperation

We study stability of interacting nonlinear systems with time-delayed communications, using contraction theory and a simplified wave variable design inspired by robotic teleoperation. We show that contraction is preserved through specific time-delayed feedback communications, and that this property is independent of the values of the delays. The approach is then applied to group cooperation with linear protocols, where it is shown that synchronization can be made robust to arbitrary time delays.

Three-dimensional analysis of rows of piles as passive barriers for ground vibration isolation

This paper presents a theoretical study on the ground vibration isolation efficiency by multi-rows of piles as passive barrier in a three-dimensional context. Integral equations governing Rayleigh wave scattering are derived according to the Green's solution of Lamb problem. The integral equations are solved accurately and efficiently with an iteration technique. They are used to predict the complicated Rayleigh wave field that is generated by a number of irregular scatterers embedded in an elastic half-space solid. The method is verified with a numerical solution available in the literature for a simplified Rayleigh wave scattering problem. Passive isolation effectiveness of ground vibration with two or three rows of small piles is further studied in detail. Effects of relevant parameters on the effectiveness of vibration isolation are analyzed and presented.

A simplified kinematic wave model at a merge bottleneck

A merge is a point of a highway where two or more streams of traffic flow into one. It is always easy to solve the demand–supply problem at a merge when the merge is operating under uncongested condition. However, when congestion backs up exceeding the merging point where multiple streams of traffic meet, one is typically faced with splitting downstream supply among the merging branches. Solutions of this situation are multiple and several merge queuing models have been proposed in the past. To address the drawbacks of the past models, this paper proposes a capacity-based weighted fair queuing (CBWFQ) model that is characterized by its fidelity (approximation to real situation), simplicity, and extensibility. Based on the CBWFQ merge queuing model, a simplified kinematic wave model is formulated to model traffic operation at a merge bottleneck.

On the solitary wave solutions of the CQNLS

Abstract In this paper, coexistence and simplified formulations of the solitary waves of the cubic–quintic non-linear Schrodinger equation (CQNLS) are investigated by analyzing the steady bifurcation and the energy integral of the conservative dynamical system satisfied by the wave packet. It is found that the bright solitary waves can coexist with kinks and anti-kinks in a range of the bifurcation control parameter. There exists a critical parameter value at which the dark solitary waves are distinguished from the bright solitary waves, kinks and anti-kinks. All of the simplified solitary wave solutions, kinks and anti-kinks are obtained by using our previously developed approximate method.

Continuous and Discrete Trajectory Models for Dynamic Traffic Assignment

A continuous trajectory model is presented in which transportation networks are represented as topological constructs. The general formulation enhances existing analytic dynamic traffic assignment models by incorporating continuous single-link traffic flow models in a general, coherent, and relatively intuitive manner. Specific exact formulation based on a simplified kinematic wave traffic flow model with physical queues is presented as well.

A plane wave approximation to sound transmission in parallel sheared mean flow

In a number of fluid machinery applications, a simplified plane wave analysis of the problem of sound transmission in a sheared mean flow is often sufficient for engineering purposes. Although there exists an extensive literature on 3-D solution of this problem, a simplified non-isentropic plane wave formulation is not seen. A quasi 1-D theory is presented in this paper in a general form encompassing non-uniform ducts, compressible and axially non-uniform flows. An analytical solution of these equations is presented for uniform ducts carrying an incompressible mean flow and the wave field is shown to consist of superposed forward and backward acoustic waves and a hydrodynamic wave, which occur in general as coupled waves. The propagation constants and the corresponding modal matrix that determines the degree of the coupling are analyzed with reference to applications to some standard mean flow profile shapes and compared with previous results.

Macroscopic arc performance models with capacity constraints for within-day dynamic traffic assignment

In this paper, we present a new nonstationary link-based macroscopic arc performance model with capacity constraints, derived from an approximate solution to the simplified kinematic wave theory which based on the assumption, often introduced in the algorithms solving Dynamic Traffic Assignment, that the arc inflows are piece-wise constant in time. Although the model does not require to introduce any spatial discretization, it is capable of taking implicitly into account the variability of the flow state along the arc accordingly to any concave fundamental diagram. To appreciate the effect of the approximation introduced, the model has been compared in terms of efficiency and effectiveness with three typical existing models, which have been to this end suitably modified and enhanced.

Application of group theory to plane wave expansion method for photonic crystals

A simplified plane wave expansion method (PWM) based on the group theory is introduced into the calculation of the photonic band gap, the transmission and Bragg reflection spectra. Calculated by the simplified PWM, the transmission and Bragg reflection spectra are compared with its photonic band structure. Their precise correspondence confirms the reliability of the simplified PWM. The comparison results indicate that the simplified algorithm can reduce the number of plane waves used in the equation and significantly ease the numerical burden and the requirement on computer memory space.

Visualization of Respiration in the Embodied Virtual Communication System and Its Evaluation

A proposed embodied virtual communication system provides a virtual face-to-face communication environment in which two remote talkers can share embodied interaction by observing their interaction with two types of avatars. One is VirtualActor, a human avatar that represents talker communicative motion and respiratory motion. The other is VirtualWave, an abstract avatar that expresses human behavior and respiration by simplified wave motion. By using the system for the analysis by synthesis of embodied communication, the effectiveness of the visualization of respiration in VirtualActor and VirtualWave is demonstrated by the analysis of the entrainment of interaction and the sensory evaluation in remote communication.

Wave-induced hydraulic forces on submerged aquatic plants in shallow lakes.

Hydraulic pulling forces arising from wave action are likely to limit the presence of freshwater macrophytes in shallow lakes, particularly those with soft sediments. The aim of this study was to develop and test experimentally simple models, based on linear wave theory for deep water, to predict such forces on individual shoots. Models were derived theoretically from the action of the vertical component of the orbital velocity of the waves on shoot size. Alternative shoot-size descriptors (plan-form area or dry mass) and alternative distributions of the shoot material along its length (cylinder or inverted cone) were examined. Models were tested experimentally in a flume that generated sinusoidal waves which lasted 1 s and were up to 0.2 m high. Hydraulic pulling forces were measured on plastic replicas of Elodea sp. and on six species of real plants with varying morphology (Ceratophyllum demersum, Chara intermedia, Elodea canadensis, Myriophyllum spicatum, Potamogeton natans and Potamogeton obtusifolius). Measurements on the plastic replicas confirmed predicted relationships between force and wave phase, wave height and plant submergence depth. Predicted and measured forces were linearly related over all combinations of wave height and submergence depth. Measured forces on real plants were linearly related to theoretically derived predictors of the hydraulic forces (integrals of the products of the vertical orbital velocity raised to the power 1.5 and shoot size). The general applicability of the simplified wave equations used was confirmed. Overall, dry mass and plan-form area performed similarly well as shoot-size descriptors, as did the conical or cylindrical models of shoot distribution. The utility of the modelling approach in predicting hydraulic pulling forces from relatively simple plant and environmental measurements was validated over a wide range of forces, plant sizes and species.

Applicability of Kinematic, Noninertia, and Quasi-Steady Dynamic Wave Models to Unsteady Flow Routing

Propagation of flood waves in an open channel can be mathematically approximated by the Saint-Venant equations (dynamic wave) or by their simplifications including the kinematic wave, noninertia wave, gravity wave, and quasi-steady dynamic wave models. All of these wave approximations differ not only in the physical propagation mechanism, but also in the degree of complexity involved in computation. In order to efficiently implement the approximate wave models for flood routing, their criteria of applicability should be developed. The applicability of the kinematic wave, noninertia wave, and quasi-steady dynamic wave approximations to the full dynamic wave equations for unsteady flow routing is examined by comparing the propagation characteristics of a sinusoidal perturbation to the steady gradually varying flow for different simplified wave models. Development of the applicability criteria provides a guideline for selecting an appropriate wave model for unsteady flow modeling, thus enabling an assessment of the capabilities and limitations of different simplified wave models. By using the linear stability analysis, the derived criteria can be expressed in terms of dimensionless physical parameters that represent the unsteadiness of the wave disturbance, characteristics of the downstream boundary condition (backwater effect), and the location along the channel. The developed criteria are for a specific point and time, thereby providing a more refined indication than the integrated criteria based on the testing for a hydrograph found commonly in the literature. In this study, we have justified whether the simplified wave models such as the kinematic, noninertia, or gravity wave models would be appropriate and reliable approximations to the full Saint-Venant equations with a comparable accuracy for a given flow condition. The downstream backwater effect has been taken into consideration in the developed criteria for broader engineering applications. One hypothetical example is presented for illustration.

Fundamental study of a λ/4 microwave‐band wave absorber using conductive paper

AbstractThis paper discusses a λ/4‐type wave absorber for the microwave band made with conductive paper, which is paper with a coating of conductive material. A simplified wave absorber of this type is first designed and constructed for the X band and Ku band. Using the resulting absorption characteristics, experimental formulas are derived for the relative permittivity and surface resistance. These formulas are then used to design and construct a more practical wave absorber, whose absorption characteristics are measured. Excellent absorption characteristics, better than 20 dB, are verified in the intervals from 8.2 to 10.6 GHz and from 14.1 to 17.2 GHz for wave absorption in the X band and Ku band, respectively, although there is a difference of approximately 0.4 dB between the designed matching frequency and the measured value. Design guidelines for such a microwave absorber using a conductive coating are then presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(10): 100–107, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1180