Numerical Modeling Of Wave Propagation Research Articles

HEATING OF THE PARTIALLY IONIZED SOLAR CHROMOSPHERE BY WAVES IN MAGNETIC STRUCTURES

ABSTRACT In this paper, we show a “proof of concept” of the heating mechanism of the solar chromosphere due to wave dissipation caused by the effects of partial ionization. Numerical modeling of non-linear wave propagation in a magnetic flux tube, embedded in the solar atmosphere, is performed by solving a system of single-fluid quasi-MHD equations, which take into account the ambipolar term from the generalized Ohm’s law. It is shown that perturbations caused by magnetic waves can be effectively dissipated due to ambipolar diffusion. The energy input by this mechanism is continuous and shown to be more efficient than dissipation of static currents, ultimately leading to chromospheric temperature increase in magnetic structures.

Can the Rayleigh distribution be used to determine extreme wave heights in non-breaking swell conditions?

A reliable set of tools for prediction of low-exceedance design waves is of high importance when designing coastal protection structures. The significant wave parameters are typically obtained from buoys or numerical wave propagation models and design values are found by extreme analysis. Statistical wave height distributions are used to transform the significant wave height to lower exceedance wave heights. These extreme single waves will cause the highest loads and wave overtopping volumes on structures and thereby represent the design conditions. An under-prediction of the design maximum wave height causes unsafe designs, while an over-prediction causes too conservative and thus expensive designs. The wave height distribution by Longuet-Higgins (1952) (Rayleigh-distribution) for deep-water non-breaking waves is in the present paper evaluated against data from numerical tests with long period and long-crested swell waves. The numerical model is validated against data from physical model tests. Generally, it is concluded that the Rayleigh-distribution is under-predicting the low-exceedance wave heights in irregular swell waves. This is expected to be caused by wave non-linearity and thus a new modified wave height distribution is suggested, where the shape parameter in the distribution is dependent on the wave non-linearity, represented by the Ursell-number. The new proposed wave height distribution for non-linear and non-breaking waves is highly applicable for practical engineering design of both near-shore and offshore structures under influence of swell-waves.

Two-dimensional numerical modeling of flood wave propagation in an urban area due to Ürkmez dam-break, İzmir, Turkey

This study investigated flood inundation in an urban area due to a possible failure of Urkmez Dam in Izmir, Turkey. The estimation of flood hydrograph upon partial failure of the dam and routing of the flood hydrograph along the narrow valley downstream were first performed by the one-dimensional hydraulic routing model HEC-RAS. The two-dimensional hydraulic routing model FLO-2D is then used to simulate the spreading of the dam-break flood after the flood wave exits the valley. Land use and land cover digital maps were utilized to find the spatially varying roughness coefficient for the floodplain. The influence of the buildings on the flood propagation was represented in the numerical model by the area reduction factor as well as the width reduction factor. The peak flow depth, peak flow velocity and time moment of the peak flow depth maps were shown in the GIS environment. The results reveal that flow depths can reach about 3 m in the residential area. In about 40 min after the dam-break, houses in the large section of the town would be under the maximum flow depths. The two-dimensional hydrodynamic model results were tested against experimental dam-break flow data of the distorted physical model of Urkmez Dam, which is consisted of the reservoir, dam body and downstream area including Urkmez Town. The model successfully simulated experimental flow depth data measured at different measurement locations.

A phase-resolved, depth-averaged non-hydrostatic numerical model for cross-shore wave propagation

In this study, a phase-resolved and depth-averaged non-hydrostatic numerical model (SNH model) is developed. The non-incremental pressure-correction method is employed to solve the equation system in two successive steps. Firstly, an approximate Riemann solver in the framework of finite volume methods is employed to solve the hydrostatic shallow-water equations (SWE) on a collocated grid to obtain provisional solutions. Then, the intermediate solutions is updated by considering the non-hydrostatic pressure effect; a semi-staggered grid is used in this step to avoid predicting checkboard pressure field. A series of benchmark tests are used to validate the numerical model, showing that the developed model is well-balanced and describes the wetting and drying processes accurately. By employing a shock-capturing numerical scheme, the wave-breaking phenomenon is reasonably simulated without using any ad-hoc techniques. Compared with the SWE model, the wave shape can be well-preserved and the numerical predictions are much improved by using the SNH model.

A two-dimensional depth-integrated non-hydrostatic numerical model for nearshore wave propagation

In this study, we develop a shallow-water depth-integrated non-hydrostatic numerical model (SNH model) using a hybrid finite-volume and finite-difference method. Numerical discretization is performed using the non-incremental pressure-correction method on a collocated grid. We demonstrate that an extension can easily be made from an existing finite-volume method and collocated-grid based hydrostatic shallow-water equations (SWE) model to a non-hydrostatic model. A series of benchmark tests are used to validate the proposed numerical model. Our results demonstrate that the proposed model is robust and well-balanced, and it captures the wet–dry fronts accurately. A comparison between the SNH and SWE models indicates the importance of considering the wave dispersion effect in simulations when the wave amplitude to water depth ratio is large.

Quantifying wave power and wave energy converter array production potential

Global wave energy inventories show that the West Coast of Canada possesses one of the most energetic wave climates in the world, with an annual wave energy flux of 40–50kW/m at the continental shelf. With this wave climate there is an opportunity to generate significant quantities of electricity through wave energy conversion (WEC) technologies. However, detailed knowledge of both the temporal and spatial distribution of both wave climate and energy production characteristics are missing precursors to the development of this regional wave energy opportunity.To quantify the gross wave energy resource along the West Coast of Vancouver Island, and hence the feasibility of deploying WEC technologies, a detailed Simulating WAves Nearshore (SWAN) numerical wave propagation model was developed. The SWAN model encompasses 410,000km2, covers 1500km of the Western Canadian coastline and the resolution is optimised by water depth and proximity to areas of high wave energy flux. The SWAN model hindcasts wave conditions for the 10year period, at a 3h temporal resolution. Independent validation of the SWAN model indicates a 0.92 correlation coefficient for significant wave heights and 0.80 for average wave periods.To translate the gross resource data into electricity generation estimates, novel methods to reveal high priority WEC farm deployment locations were implemented. Using generic WEC performance metrics, theoretical wave farm outputs were synthesized over a decade long time scale. Regional WEC farms were shown capable to providing up to 139.92GWh of energy to the electrical grid annually. The seasonality of the WEC generated electricity correlates well with the load demand within the region.This updated understanding of the wave climate and wave power production opportunity in Western Canada provides the necessary data to electrical utilities and policy makers to assess the opportunity benefits and costs associated with future WEC industry in Canada.

Numerical modeling of vegetation-induced dissipation using an extended mild-slope equation

This paper presents an incorporation of vegetation-induced wave dissipation in a planar numerical wave propagation model based on the extended mild-slope equation (EMSE). The implementation was incorporated in a purely mathematical method in the light of current theoretical studies. To examine the performance of the phase-resolving model, a comprehensive comparison with phase-averaged SWAN is made to test and validate the implementation. Moreover, new in-situ measurements in a mangrove forest are presented aiming to test the wave energy damping by vegetation using the observed wave spectra. From our validation results it can be concluded that wave dissipation due to vegetation is equally well reproduced in this model. It is found that the wave parameters (wave height and period) and vegetation parameters (plant width, height and density) are all influencing factors. An interesting finding is that relatively high-frequency waves are more dissipated than low frequency waves, especially for larger wave heights. In this study, we found that diffraction is of great significance in wave propagation over inhomogeneously distributed vegetation. Theoretically, the phase resolving EMSE represents the physical process of diffraction better than the phase-averaged model SWAN.

A new formulation for vegetation-induced damping under combined waves and currents

Based on energy conservation a new analytical formulation for the evaluation of wave damping under the combined effect of waves and both following and opposing currents is presented. The formulation obtained for regular and random waves allows the derivation of analytical expressions for the vegetation drag coefficient as a function of wave damping parameters. These parameters are calibrated using a unique experimental set obtained in a large-scale wave basin considering the interaction of waves and currents with real vegetation representative of salt marshes, namely Spartina anglica and Puccinellia maritime. Comparisons show the quality of the analytical formulation under different hydrodynamic conditions, vegetation species and various Reynolds numbers formulated in terms of plant characteristics such as the deflected plant length accounting for the flow-induced bending of the vegetation. The new formulation can be useful to be implemented in phase averaged and phase resolving numerical models of wave propagation.

Wall stress and deformation analysis in a numerical model of pulse wave propagation.

To simulate pulse wave propagation, we set up a wave propagation model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the wave propagation model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation.

A three-dimensional refractive index model for simulation of optical wave propagation in atmospheric turbulence

Numerical modeling of optical wave propagation in atmospheric turbulence is traditionally performed with using the so-called “split”-operator method, when the influence of the propagation medium’s refractive index inhomogeneities is accounted for only within a system of infinitely narrow layers (phase screens) where phase is distorted. Commonly, under certain assumptions, such phase screens are considered as mutually statistically uncorrelated. However, in several important applications including laser target tracking, remote sensing, and atmospheric imaging, accurate optical field propagation modeling assumes upper limitations on interscreen spacing. The latter situation can be observed, for instance, in the presence of large-scale turbulent inhomogeneities or in deep turbulence conditions, where interscreen distances become comparable with turbulence outer scale and, hence, corresponding phase screens cannot be statistically uncorrelated. In this paper, we discuss correlated phase screens. The statistical characteristics of screens are calculated based on a representation of turbulent fluctuations of three-dimensional (3D) refractive index random field as a set of sequentially correlated 3D layers displaced in the wave propagation direction. The statistical characteristics of refractive index fluctuations are described in terms of the von Karman power spectrum density. In the representation of these 3D layers by corresponding phase screens, the geometrical optics approximation is used.

Finite difference elastic wave modeling with an irregular free surface using ADER scheme

In numerical modeling of seismic wave propagation in the earth, we encounter two important issues: the free surface and the topography of the surface (i.e. irregularities). In this study, we develop a 2D finite difference solver for the elastic wave equation that combines a 4th- order ADER scheme (Arbitrary high-order accuracy using DERivatives), which is widely used in aeroacoustics, with the characteristic variable method at the free surface boundary. The idea is to treat the free surface boundary explicitly by using ghost values of the solution for points beyond the free surface to impose the physical boundary condition. The method is based on the velocity-stress formulation. The ultimate goal is to develop a numerical solver for the elastic wave equation that is stable, accurate and computationally efficient. The solver treats smooth arbitrary-shaped boundaries as simple plane boundaries. The computational cost added by treating the topography is negligible compared to flat free surface because only a small number of grid points near the boundary need to be computed. In the presence of topography, using 10 grid points per shortest shear-wavelength, the solver yields accurate results. Benchmark numerical tests using several complex models that are solved by our method and other independent accurate methods show an excellent agreement, confirming the validity of the method for modeling elastic waves with an irregular free surface.

Seismic attenuation in fractured porous media: insights from a hybrid numerical and analytical model

Seismic attenuation in fluid-saturated porous rocks can occur by geometric spreading, wave scattering or the internal dissipation of energy, most likely due to the squirt-flow mechanism. In principle, the pattern of seismic attenuation recorded on an array of sensors contains information about the medium, in terms of material heterogeneity and anisotropy, as well as material properties such as porosity, crack density, and pore-fluid composition and mobility. In practice, this inverse problem is challenging. Here we provide some insights into the effects of internal dissipation by analysing synthetic data produced by a hybrid numerical and analytical model for seismic wave propagation in a fractured medium embedded within a layered geological structure. The model is made up of one anisotropic and three isotropic horizontal layers. The anisotropic layer consists of a porous, fluid-saturated material containing vertically aligned inclusions representing a set of fractures. This combination allows squirt-flow to occur between the pores in the matrix and the model fractures. Our results show that the fluid mobility and the associated relaxation time of the fluid-pressure gradient control the frequency range over which attenuation occurs. This induced attenuation increases with incidence angle and azimuth away from the fracture strike-direction. Azimuthal variations in the induced attenuation are elliptical allowing the fracture orientations to be obtained from the axes of the ellipse. These observations hold out the potential of using seismic attenuation as an additional diagnostic in the characterisation of rock formations for a variety of applications including hydrocarbon exploration and production, subsurface storage of CO2, and geothermal energy extraction.

Modelling the Impacts of Mangrove Vegetation Structure on Wave Dissipation in Ben Tre Province, Vietnam, under Different Climate Change Scenarios

Cuc, N.T.K.; Suzuki, T.; Ruyter van Steveninck, E.D. de, and Hai, H., 2015. Modelling the impacts of mangrove vegetation structure on wave dissipation in Ben Tre Province, Vietnam, under different climate change scenarios. Journal of Coastal Research, 31(2), 340–347. Coconut Creek (Florida), ISSN 0749-0208. Mangroves are widely distributed along the coastline of Vietnam, where they provide protection against sea waves caused by extreme weather. Impacts of climate change, together with population growth and economic development, are expected to exert pressure on these vulnerable systems. In this study the numerical wave-propagation model SWANVEG (Simulating Waves Nearshore–Vegetation) was used to simulate the possible impacts of climate change on the wave-dissipation capacity of different types of mangrove vegetation. Vegetation characteristics were assessed in planted plots (Rhizophora apiculata and a mix of R. mucronata, Sonneratia caseolaris, Avicennia alba, and Nypa fructicans) and in natural regenerated areas (A. alba and S. caseolaris) in Thanh Phu Natural Reserve, Mekong Delta, Vietnam; these assessments were used as model input. Different sea levels and mangrove vegetation characteristics were used to simulate the potential impacts of climate change. Planted plots with a cover of 70% reduced the height of incoming waves by 60%, compared with 40% for natural regenerated forest. Reducing the vegetation cover in planted plots from 70% to 50%, 35%, and 0% resulted in wave-height reductions of 51%, 42%, and � 4%, respectively. A sea level rise (SLR) up to 0.96 m did not change the wave-dissipation potential of R. apiculata planted in the plots. However, an assumed decline in the width of vegetation from 1.5 km to 0.5 km, e.g. as a consequence of coastal erosion, reduced the height of incoming waves 21% (no SLR) and 29% (0.96 m SLR), as compared to 60% and 59%, respectively, without erosion.

Numerical model for coastal wave propagation through mild slope zone in the presence of rigid vegetation

The study of wave propagation on coastal vegetation field is fundamental to assessing the effectiveness and limitations of vegetation in coastal protection. This paper presents a refraction–diffraction wave model for the investigation of wave propagation through a coastal mild slope zone in the presence of rigid vegetation via numerical simulation. The model is based on the implementation of a module for vegetation-induced wave energy dissipation in the parabolic mild slope equation. The model is capable of simulating both wave refraction and diffraction and economical in computation and may bridge the gap between the wave energy spectrum and the phase-resolved models for wave propagation through coastal vegetation fields. The model is validated through by comparison with experimental results. The model is subsequently applied to a simulation of a wave propagating on a plane in the presence of different patterns of rigid vegetation. The sensitivity of the wave height to the plant height, the diameter and the stem density is investigated by comparison of the numerical results for wave height attenuation that results from different patterns of rigid vegetation. The numerical results show that wave height attenuation due to rigid vegetation has a higher variability for the different rigid plant conditions and that the attenuation of the wave height due to the rigid vegetation increases alongside the plant height under water as well as the diameter and plant stem density. The results further indicate that for wave propagates through coastal rigid vegetation zones with a high plant height under water, large diameter and high stem density, the wave height along the propagating direction is decreased nonlinearly with the increase of the wave propagating distance, and nonlinearity is more obvious for the plant with a higher height under water as well as a larger diameter and higher stem density.

Three-dimensional numerical modeling of ultrasonic wave propagation in concrete and its experimental validation

To understand the characteristics of ultrasonic wave propagation in concrete more completely, we propose a time domain simulation tool based on the finite integration technique (FIT) and an image-based modeling approach. When modeling ultrasonic wave propagation in concrete, it is important to introduce three-dimensional mesoscopic and microscopic structures because ultrasonic waves in solids are transmitted by mechanical interaction between adjacent media. In this paper, wave velocity, center frequency, and attenuation of ultrasonic waves in concrete are evaluated quantitatively by comparing the waveforms obtained by FIT simulation with those obtained by experimental measurement. It was observed that these factors were in good agreement between the simulation and measurements. It was also observed that amplitude of the transmitted signal was sensitive to the allocation pattern of the aggregates. Thus, attenuation due to multiple scattering by aggregates is more dominant than the attenuation by intrinsic absorption and geometrical spreading in concrete.

Comparative Analysis of 3D Viscoelastic and Poroelastic Dynamic Boundary-Element Modelling

3D dynamic boundary-value problems of linear viscoelasticity and poroelasticity are considered. Laplace integral transform and its numerical inversion are used. Classical viscoelastic models, such as Maxwell model, KelvinVoigt model, standard linear solid model, and model with weakly singular kernel (Abel type) are considered. Boundary integral equations (BIE) method is developed to solve three-dimensional boundary-value problems. A numerical modelling of wave propagation is done by means of boundary element approach.

Numerical earthquake model of the 31 October 2013 Ruisui, Taiwan, earthquake: Source rupture process and seismic wave propagation

We build a numerical earthquake model, including numerical source and wave propagation models, to understand the rupture process and the ground motion time history of the 2013 ML 6.4 Ruisui earthquake in Taiwan. This moderately large event was located in the Longitudinal Valley, a suture zone of the Philippine Sea Plate and the Eurasia Plate. A joint source inversion analysis by using teleseismic body wave, GPS coseismic displacement and near field ground motion data was performed first. The inversion results derived from a western dipping fault plane indicate that the slip occurred in depths between 10 and 20km. The rupture propagated from south to north and two asperities were resolved. The largest one was located approximately 15km north of the epicenter with a maximum slip about 1m. A 3D seismic wave propagation simulation based on the spectral-element method was then carried out by using the inverted source model. A strong rupture directivity effect in the northern area of the Longitudinal Valley was found, which was due to the northward rupture process. Forward synthetic waveforms could explain most of the near-field ground motion data for frequencies between 0.05 and 0.2Hz. This numerical earthquake model not only helps us confirm the detailed rupture processes on the Central Range Fault but also gives contribution to regional seismic hazard mitigation for future large earthquakes.

Ultra‐wide band antenna designs and numerical system modelling for forward‐looking GPR

ABSTRACTThis paper presents ultra‐wide band (UWB) horn feeder and parabolic reflector antenna designs, which are considered highly suitable for forward‐looking vehicle‐mounted ground‐penetrating radar (GPR) systems and time‐domain numerical modelling of impulse GPR signal radiation, wave propagation and target scattering. In this context, the partial dielectric‐loaded Vivaldi shaped TEM horn (PDVA), TEM horn fed double‐ridged horn (PDTEM‐RHA) and their compact versions are investigated, designed simulated and measured. An offset parabolic reflector antenna prototype with a compact PDTEM‐RHA feeder is proposed to reach hyper‐wide band impulse radiation performances from 500 MHz up to 15 GHz for a multi‐band forward‐looking GPR operation that can provide deep subsurface detection with high‐resolution imaging, due to a big advantage of narrowed beam widths. The antenna gain and radiation pattern performances are demonstrated with measurement results.

Advanced numerical modelling of tsunami wave propagation, transformation and run-up

This paper presents a series of numerical models tests performed to assess the ability of the OpenFOAM® modelling system to represent the physics that stands behind the propagation of tsunami waves in coastal regions and in particular their transformation (by means of shoaling, refraction, reflection) over uneven bathymetries and their interaction with the shoreline (run-up, run-down, breaking). A series of tests is selected from the literature to explore the accuracy, applicability and limitations of this particular computational fluid dynamics model solving the three-dimensional Navier–Stokes equations for incompressible multiphase fluids. The range of scenarios tested includes experimental work on wave propagation over shoals, solitary wave run-up and the Monai valley tsunami physical model test recreating the Hokkaido–Nansei–Oki 1993 tsunami that struck Okushiri Island, Japan. This allowed direct comparison with experimental data from physical model tests as well as with other established two-dimensional – that is, depth integrated – and three-dimensional numerical models.

Numerical modeling of the pulse wave propagation in large blood vessels based on liquid and wall interaction

The purpose of this article is to develop a non-linear, one-dimensional model of pulse wave propagation in the arterial cardiovascular system. The model includes partial differential equations resulting from the balance of mass and momentum for the fluid-filled area and the balance equation for the area of the wall and vessels. The considered mathematical model of pulse wave propagation in the thoracic aorta section takes into account the viscous dissipation of fluid energy, realistic values of parameters describing the physicochemical properties of blood and vessel wall. Boundary and initial conditions contain the appropriate information obtained from in vivo measurements. As a result of the numerical solution of the mass and momentum balance equations for the blood and the equilibrium equation for the arterial wall area, time- dependent deformation, respective velocity profiles and blood pressure were determined.