Simulating the movement of bed and suspended loads in the coastal environment

A dynamic computer simulation model is implemented to simulate wave-induced transport of bed and suspended material, and the associated development of nearshore profiles. The model uses the Airy, Stokes', cnoidal and solitary wave theories to compute the height, length, celerity, steepness, breaker indices, and horizontal, veritical, mass drift and orbital velocities of random waves propagating along a flat slope. With shoreward wave propagation both bed and suspended loads are computed at discrete grid points.The FORTRAN '77 simulation program is executed for 3000 iterations, with each iteration corresponding to one twelfth of a tidal cycle. The simulated results demonstrate that sediment movement is controlled by the magnitude of the drift, orbital and horizontal wave velocity components, with wave breaking having a direct influence on the deposition of transported bed load. The shallow water regions of cnoidal and solitary waves are characterized by the presence of high concentrations of suspended material. Over the runlength of the simulation, transport of bed and suspended material cause the initialized profile state to change through a sequence of ill-defined transient states to a final morphological state. Examination of the sequence of profile states indicate weak resemblances of barred and nonbarred profile configurations.     

Particle simulation of compression waves

Our primary aim in this paper is to develop a new method for modeling waves on a digital computer. The approach will be a quasi-molecular, particle approach which lends itself readily to computer experiments. Explosive type disturbances will be simulated first which will generate compression waves. These waves then propagate by each particle's interaction locally with its immediate neighbors. Computer examples which illustrate physically correct physical phenomena related to compression wave motions will be illustrated and discussed.     

微结构固体中孤立波的动力学稳定性

描述微结构固体中波传播的一种KdV类方程作为控制方程并利用积分因子方法,对微结构固体中传播的孤立波的动力学稳定性进行了数值模拟研究。主要以高斯波、Ricker子波以及双曲正割波作为初始扰动,考察了不同小扰动下孤立波能否较长时间保持波形结构和传播速度而稳定传播问题。模拟结果表明,不同的小扰动对孤立波的影响不同,孤立波的稳定传播与扰动幅度和宽度都有关系,只有受到幅度和宽度都非常小的扰动下在微结构固体中传播的孤立波才能显现出一定程度的抗干扰性和动力学稳定性,可在微结构固体中较长时间稳定传播。     

微结构固体中孤立波的动力稳定性

描述微结构固体中波传播的一种KdV类方程作为控制方程并利用积分因子方法,对微结构固体中传播孤立波的动力学稳定性进行了数值模拟研究.主要以高斯波、Ricker子波以及双曲正割波扰动作为初始扰动,考察了不同小扰动下孤立波能否较长时间保持波形结构和传播速度而稳定传播问题.结果表明,不同的小扰动对孤立波的影响不同,孤立波的稳定...     

Long range numerical simulation of short waves as nonlinear solitary waves

A new numerical method has been developed to propagate short wave equation pulses over indefinite distances and through regions of varying index of refraction, including multiple reflections. The method, “Wave Confinement”, utilizes a newly developed nonlinear partial differential equation that propagates basis functions according to the wave equation. These basis functions are generated as stable solitary waves where the discretized equation can be solved without any numerical dissipation. The method can also be used to solve for harmonic waves in the high frequency (Eikonal) limit, including multiple arrivals. The solution involves discretizing the wave equation on a uniform Eulerian grid and adding a simple nonlinear “Confinement” term. This term does not change the amplitude (integrated through each point on the pulse surface) or the propagation velocity, or arrival time, and yet results in capturing the waves as thin surfaces that propagate as thin nonlinear solitary waves and remain 2–3 grid cells in thickness indefinitely with no numerical spreading. With the method, only a simple discretized equation is solved each time step at each grid node. The method can be contrasted to Lagrangian Ray Tracing: it is an Eulerian based method that captures the waves directly on the computational grid, where the basic objects are codimension 1 surfaces (in the fine grid limit), defined on a regular grid, rather than collections of markers. In this way, the complex logic of current ray tracing methods, which involves allocation of markers to each surface and interpolation as the markers separate, is avoided.     

Biomimetic robot lobster performs chemo-orientation in turbulence using a pair of spatially separated sensors: Progress and challenges

Lobsters are capable of tracking turbulent plumes to their sources faster than can be accomplished by estimating a spatial gradient from time-averaging the concentration signal. We have used RoboLobster, a biomimetic robot lobster to investigate biologically scaled chemotaxis algorithms using two point concentration sampling to track a statistically characterized turbulent plume. Our results identify the range of effectiveness of these algorithms and, with studies of lobster behavior, suggest effective strategies beyond this range. They suggest that a lobster’s chemo-orientation strategy entails an unidentified means of dealing with the intermittency of the concentration signal. Extensions of these algorithms likely to improve are discussed.     

基于决策树的羽流追踪机器人自主决策方法研究

针对无法获得可靠羽流流向信息不利于实现羽流追踪的问题，提出了一种基于决策树的羽流追踪移动机器人自主决策方法。该方法通过移动机器人两侧的浓度传感器采集到的浓度信息，利用追踪的行为规则建立决策树模型，获得行为决策信息，使机器人高效地追踪到羽流并精确地定位。由于浓度变化关系蕴含了羽流的流向及流速信息，从而取代了传统方法中流向及流速传感器。在扩散环境下，通过移动机器人羽流追踪实验，实现了良好的源定位效果。     

Particle modeling simulation of atmospheric dispersion using the MC-LAGPAR package

A Monte Carlo model and computer code (MC-LAGPAR) for simulating atmospheric transport and diffusion of plumes are described. The turbulent diffusion is simulated by the semi-random motion of Lagrangian particles. The particles are emitted by a point source and dispersed in a computational domain by pseudo-velocities derived from vertical profiles of meteorological variables.The MC-LAGPAR code includes the implementation of special algorithms for the simulation of a dynamic plume rise, chemical decay, deposition and resuspension effects. Furthermore, computer-graphics displays have been developed. The model, here used in its two dimensional version, is validated in the well-known case of homogeneous and stationary turbulence. In this case, we compared the concentration fields obtained by our model with those calculated by the known analytical solution. In both computations, the standard deviations of wind velocities are calculated according to the Taylor formulas.In the nonhomogeneous case, the vertical structure of turbulence is parameterized according to the scheme suggested by Hanna. As an example of the non-homogeneous case, we present numerical simulations in convective (unstable) conditions in which the influence of updraughts and downdraughts is empirically taken into account.     

Comparison of the ParTrack mud/cuttings release model with field data

The oil industry promotes the development of numerical models for prediction of impacts from their discharges to sea. A model for the simulation of the spreading and deposition of drilling mud and cuttings on the sea floor as well as the spreading of chemicals (and small-sized particles) in the water column has been developed. The simulation is based on a Lagrangian ‘particle’ approach, which means that the properties of the discharge are represented by moving ‘particles’ in the model domain. The initialization of the particles is based on the output from an Eulerian near field underwater plume model. In addition, the model applies external current fields for the horizontal advection of the particles.This paper presents a comparison between simulated and measured concentrations of barium (barite) in surface contaminated sediment in the vicinity of an oil production field. As a part of the regular surveillance of oil production sites on the Norwegian Continental Shelf, the barium content in surface sediments is measured. These data might therefore serve as an opportunity for comparing simulation results with measured depositions of barium (barite) on the sea floor.The paper explains details in the comparison made between the measured barium concentrations in the sediment and the simulated deposition on the sea floor from the drilling of three exploration wells and 18 production wells off the west coast of Norway.     

An improved algorithm for the detection of plumes caused by natural or technological hazards using AVHRR imagery

Fires caused by natural or technological disasters emit large amounts of smoke which, once formed into plumes, may affect the human health and the environment. Satellite remote sensing data provide an effective tool to achieve detection and monitoring of these plumes over large areas on a routine basis. Discrimination of plumes on satellite images is a prerequisite to study and retrieve physical, chemical and optical properties of emitted smoke. An improved algorithm for the detection of plumes caused by natural or technological hazards using AVHRR imagery is presented in this study. The method is based on a multi-temporal and multi-spectral change detection algorithm. It is performed in two main steps: a) appropriate spectral and spatial filters are applied on the images acquired before and after a fire event in visible and near-infrared ranges in order to extract the core of the plume; b) a criterion on spectral information is defined as an homogeneity measure that enables, through a modified version of the region-growing method, the spatial expansion of the detected core to include the complete area covered by the plume. Through this approach, a pixel is identified as a plume pixel if it is “close” to the core plume pixels in both spatial and spectral spaces. The algorithm was developed and calibrated using AVHRR images acquired over Spain before and during a major forest fire event on July 16, 2005. It was applied using past events of natural and technological hazards in several locations to ensure its global applicability and robustness. The algorithm produced accurate results in all cases of plumes, either in natural or in technological fire events. Three application cases are presented in this study: A major fire in an industrial installation in London (December 11, 2005), a major fire in Baghdad during the recent war in Iraq (April 1, 2003) and a forest fire in California (September 29, 2005).     

Nebulization of water/glycerol droplets generated by ZnO/Si surface acoustic wave devices

Efficient nebulization of liquid sessile droplets (water and water/glycerol mixtures) was investigated using standing waves generated using ZnO/Si surface acoustic wave (SAW) devices under different RF powers, frequencies and liquid viscosity (varied glycol concentrations in water). At such high RF powers, there are strong competitions between vertical jetting and nebulization. At lower SAW frequencies of 12.3 and 23.37 MHz, significant capillary waves and large satellite droplets were generated before nebulization could be observed. At frequencies between 23.37 and 37.2 MHz, spreading, displacement or occasionally jetting of the parent sessile droplet was frequently observed before a significant nebulization occurred. When the SAW frequencies were increased from 44.44 to 63.3 MHz, the minimum RF power to initiate droplet nebulization was found to increase significantly, and jetting of the parent droplet before nebulization became significant, although the average size of the nebulized particles and ejected satellite droplets appeared to decrease with an increase in frequency. With the increase of glycerol concentration in the test sessile droplets (or increase in liquid viscosity), nebulization became difficult due to the increased SAW damping rate inside the liquid. Acoustic heating effects were characterized to be insignificant and did not show apparent contributions to the nebulization process due to silicon substrate’s natural effect as an effective heat sink and the employment of a metallic holder beneath the ZnO/Si SAW device substrates.     

Generation of internal solitary waves in the Sulu Sea and their refraction by bottom topography studied by ERS SAR imagery and a numerical model

ERS-2 SAR images acquired over the Sulu Sea reveal that there are at least three areas where internal solitary waves are generated: (1) at the sill between Dok Kan Island and Pearl Bank; (2) at the sill between Pearl Bank and Talantam Shoal; and (3) at the sill between Talantam Shoal and Sentry Bank. It is observed that the internal solitary waves generated at different source regions merge into a single solitary wave system. When the solitary waves propagate into shallow water, the distance between the solitary waves in a wave packet decreases. Furthermore, when the water depth decreases in the direction of the soliton's crest line, the crest line is bent towards the shallow water region. These observational facts are explained by a wave refraction model which is based on the Korteweg–de Vries equation which is also valid for large amplitude internal solitary waves provided the pycnocline is sufficiently broad.     

A numerical computation of a 3-D stokes problem in the description of intestinal peristaltic waves

The mathematical aspects of a physical model of intestinal peristaltic waves involve numerical methods for calculating and simulating the solution. A finite element method is applied to Stokes' equations in R³ in order to calculate the velocity-pressure couple at each vertex of the pentahedron elements of the geometrical model domain, for viscous and non-compressible fluid. By using special computational programs, the domain may be stitched to create a grid domain in R³. The finite reference element of the grid is a pentahedron. The resultant linear system may be solved by applying Gauss' direct method to obtain velocities and pressures at each grid point. Graphical representations of velocity profiles in R³, show positive and negative zones for the output, with positions that vary from one geometrical model to another. The calculated velocity and pressure values are shown to change according to the applied vector efforts. The numerical results obtained are in good agreement with experimental data. This suggests that the finite element method is useful for solving Stokes' equations to describe intestinal peristalsis waves.     

Waves and spatially localized structures in the turbulent flows of a viscous fluid: Calculation results

A direct numerical simulation was performed of intermittent and turbulent flows of viscous incompressible fluid in an infinite circular pipe. The Navier-Stokes equations were integrated at the Reynolds numbers of 1800 ≤ Re ≤ 4000 calculated from the mean velocity and a pipe diameter of D = 2R. The numerically obtained solutions belong to the class of mean streamwise periodic solutions with a very large period λ_max = 16πR. The Fourier harmonic components of the velocity fluctuations corresponding to very low longitudinal wavenumbers are shown to be the most energetic. A detailed study was carried out of the structures of the calculated turbulent and intermittent flows. The accuracy and the very possibility of the approximation of the turbulent velocity field by the superposition of traveling and standing waves are analyzed. It is shown that the parameters of such a representation (wave amplitudes, phase velocities, and the position of the wave front) are strongly dependent on whether or not very low longitudinal wavenumbers are included in the mathematical model of the flow The numerical solutions at Re = 2200 and 2350 describe the intermittent type of the flow, for which the localized turbulent structures (turbulent puffs) propagate downstream while retaining their spatial dimensions. The space-time structure of the calculated turbulent puffs is compared with the available experimental data. The main statistical characteristics of the turbulence inside and outside the turbulent puff are calculated and the convective rate of the puffs downstream expansion is determined.     

A thermal plume in the Tay estuary detected by aerial thermography

The appearance of a small thermal plume detected on two successive overflights by an airborne infrared scanner operating in the 8-12 μm band is described. The spatial and temporal resolution achieved is discussed with reference to applying this technique to plumes from sewage outfalls and power stations.     

On a 16° N chlorophyll plume along the east coast of India

The plume rich with chlorophyll‐a concentration (>0.3 mg/l) observed on 22 March 2003 along the 16° N in the western Bay of Bengal off the Krishna–Godavari river delta was studied. Relatively high sea surface temperature (>30° C) observed in the plume area indicated their origin in the coastal waters. The bloomy plume was found spreading 400 to 500 km offshore in the form of an offshore jet extending as far as 86° E in the Bay of Bengal. An offshore flow was observed with geostrophic velocity exceeding 50 cm/s with a cyclonic eddy on its north around 17° N, 82° E and an anti‐cyclonic eddy around 14° N, 83° E to its south. The hydrographic data of the area were studied with the observations made by GTS data buoy indicated coastal upwelling. Similar plumes were also observed during the years 2004 and 2005.     

Seismic inverse problems: determining seismic wave speeds using arrival times

The speeds of propagation of seismic waves are computed by detecting the effect of the waves that propagate when a pulse of energy, in the form of a small explosion, is released near the surface of the ground. The pulse is detected and recorded by underground sensors. The times between the initiation of the pulse and the point when it reaches the various sensors are denoted the travel times. In this paper we consider two questions. Is it possible to compute the wave speed profile from accurately measured travel times? If so, how can this be done?