Coastal Engineering Problems Research Articles

Inclusion of additional energy dissipation due to plunging breakers in parametric type wave models

One of the most critical issues in coastal engineering problems is to accurately predict the wave height profile across the surfzone. Parametric wave models are broadly used in modelling the wave energy dissipation in this regard. Three parametric wave models based on the bore energy dissipation model were evaluated against new field measurements under various conditions from mild to stormy. The results indicate that a discrepancy between models and data occurred near the break point for cases where the wave breaking was of the plunging type but after the breakpoint the wave height decay rates compared well. In order to improve this model shortcoming, comprehensive new laboratory tests were conducted to quantify the additional energy dissipation due to plunging breakers. Based on the data, new empirical equations were derived and incorporated into the most recent bore dissipation parametric wave model. The inclusion of the extra energy dissipation due to plunging breakers results in significant improvement in the prediction of the wave height profile.

Application of a stochastic differential equation to the prediction of shoreline evolution

Shoreline evolution due to longshore sediment transport is one of the most important problems in coastal engineering and management. This paper describes a method to predict the probability distributions of long-term shoreline positions in which the evolution process is based on the standard one-line model recast into a stochastic differential equation. The time-dependent and spatially varying probability density function of the shoreline position leads to a Fokker–Planck equation model. The behaviour of the model is evaluated by applying it to two simple shoreline configurations: a single long jetty perpendicular to a straight shoreline and a rectangular beach nourishment case. The sensitivity of the model predictions to variations in the wave climate parameters is shown. The results indicate that the proposed model is robust and computationally efficient compared with the conventional Monte Carlo simulations.

Smoothed Particle Hydrodynamics for coastal engineering problems

Smoothed Particle Hydrodynamics is a numerical method to solve problems of computational fluid dynamics. The method has been proven to be suitable to reproduce free-surface phenomena such as breaking waves, fluid–structure interaction and no-linear behaviour of the fluid are studied. DualSPHysics is a SPH code that enables the simulations of several million particles in a reasonable computational time, making possible the study of real engineering problems. The code is validated with analytical and experimental data showing reliability, accuracy and efficiency. Finally, the capabilities of DualSPHysics to reproduce wave–structure interaction are shown where wave heights and forces exerted onto objects of the coast are numerically computed. The case of study mimics a realistic promenade including the urban furniture and with dimensions and geometries close to the real ones.

Assessing the hydrodynamic boundary conditions for risk analyses in coastal areas: a multivariate statistical approach based on Copula functions

Abstract. This paper presents an advanced approach to statistically analyse storm surge events. In former studies the highest water level during a storm surge event usually was the only parameter that was used for the statistical assessment. This is not always sufficient, especially when statistically analysing storm surge scenarios for event-based risk analyses. Here, Archimedean Copula functions are applied and allow for the consideration of further important parameters in addition to the highest storm surge water levels. First, a bivariate model is presented and used to estimate exceedance probabilities of storm surges (for two tide gauges in the German Bight) by jointly analysing the important storm surge parameters "highest turning point" and "intensity". Second, another dimension is added and a trivariate fully nested Archimedean Copula model is applied to additionally incorporate the significant wave height as an important wave parameter. With the presented methodology, reliable and realistic exceedance probabilities are derived and can be considered (among others) for integrated flood risk analyses contributing to improve the overall results. It is highlighted that the concept of Copulas represents a promising alternative for facing multivariate problems in coastal engineering.

Optimal dynamics of soft shapes in shallow waters

A sandy sea bottom is seen as a structure with low stiffness which adapts to the motion of water in a shallow domain described by the Saint Venant equations. The coupling is based on the minimization of water wave energy with minimal sand transport. The approach is shown being similar to the use of an original Exner equation for the bottom with non local flux expressions. Also, examples of the applications of the framework to inverse problems in coastal engineering are shown.

Implementation of a discontinuous Galerkin morphological model on two-dimensional unstructured meshes

The shallow water equations are used to model large-scale surface flow in the ocean, coastal rivers, estuaries, salt marshes, bays, and channels. They can describe tidal flows as well as storm surges associated with extreme storm events, such as hurricanes. The resulting currents can transport bed load and suspended sediment and result in morphological changes to the seabed. Modeling these processes requires tightly coupling a bed morphology equation to the shallow water equations. Discontinuous Galerkin finite element methods are a natural choice for modeling this coupled system, given the need to solve these problems on unstructured computational meshes, as well as the desire to implement hp-adaptivity for capturing the dynamic features of the solution. However, because of the presence of non-conservative products in the momentum equations, the standard DG method cannot be applied in a straightforward manner. To rectify this situation, we summarize and follow an extended approach described by Rhebergen et al., which uses theoretical results due to Dal Maso et al. appearing in earlier work. In this paper, we focus on aspects of the implementation of the morphological model for bed evolution within the Advanced Circulation (ADCIRC) modeling framework, as well as the verification of the RKDG method in both h (mesh spacing) and p (polynomial order). This morphological model is applied to a number of coastal engineering problems, and numerical results are presented, with attention paid to the effects of h- and p-refinement in these applications. In particular, it is observed that for sediment transport, piecewise constant (i.e., finite volume) approximations of the bed are very over-diffusive and lead to poor sediment solutions.

Coupled FEMDEM/Fluids for coastal engineers with special reference to armour stability and breakage

Sea-level rise and increased storminess present huge challenges to coastal engineers worldwide. The seaward slope of many breakwaters and shoreline defence structures consists of thousands of interlocking units of concrete or rock making up a massive granular defence against wave attack. The units are placed freely to form an armour layer which is intended to both dissipate wave energy and remain structurally stable. Design guidance on the mass and shape of these units is based on empirical equations derived from Froude scale physical model tests. The two main failure modes for concrete armour layers are displacement (hydraulic instability) and breakage (structural instability) which are strongly coupled. Breakage mechanisms cannot all be faithfully reproduced under scaled physical models. Fundamental understanding of the forces governing such wave-structure interaction remains poor and unit breakages continue to baffle the designers of concrete armour units. This paper illustrates a range of DEM and FEMDEM methods being developed to model the granular solid skeleton of freely packed brittle units. Such discrete element methods are increasingly being used by engineers for solids modelling. They are especially powerful when coupled with a CFD model which can resolve ocean wave dynamics. The aim is to describe a framework for coupled modelling technologies applicable to coastal engineering problems. Preliminary simulation test cases, still at proof of concept stage, but based on a wealth of validation studies are presented. Thus, we report a snap-shot of progress towards a future where designers combine multi-physics numerical technology with knowledge from scaled physical models for a better understanding of wave energy turbulence, block movement, and internal stresses within armour units.

Incompressible SPH simulation of water entry of a free‐falling object

AbstractIn this paper an incompressible smoothed particle hydrodynamics (Incom‐SPH) model is used to simulate the interactions between the free surface flow and a moving object. Incom‐SPH method is a two‐step semi‐implicit hydrodynamic formulation of the SPH algorithm and is capable of accurately treating the free surface deformations and impact forces during the solid–fluid interactions. For a free‐falling object, its motion is tracked by an additional Lagrangian algorithm based on Newton's law to couple with the Incom‐SPH program. The developed model is employed to investigate the water entry of a free‐falling wedge. The accuracy of the computations is validated by the good agreement in predicting the relevant hydrokinematic and hydrodynamic parameters. Finally, a numerical test is performed to study the influence of spatial resolution on the water entry features. The Incom‐SPH modeling coupled with the solid–fluid interaction algorithm could provide a promising computational tool to predict the slamming problems in coastal and offshore engineering. Copyright © 2008 John Wiley & Sons, Ltd.

Overview on the applications of random wave concept in coastal engineering

When "coastal engineering" was recognized as a new discipline in 1950, the significant wave concept was the basic tool in dealing with wave actions on beach and structures. Description of sea waves as the random process with spectral and statistical analysis was gradually introduced in various engineering problems in coastal engineering through the 1970s and 1980s. Nowadays the random wave concept plays the central role in engineering manuals for maritime structure designs. The present paper overviews the historical development of random wave concept and its applications in coastal engineering.

Shape optimization of geotextile tubes for sandy beach protection

AbstractThis paper describes how to tackle new challenging coastal engineering problems related to beach erosion with a shape optimization approach. The method modifies the shape of the sea bottom in order to reduce beach erosion effects. Global optimization is shown to be necessary as the related functionals have several local minima. We describe the physical model used, the proposed protection devices against beach erosion and real case applications. Copyright © 2007 John Wiley & Sons, Ltd.

CFD Analysis on Current Flow Past Two Large Rectangular Cylinders in Tandem

The motivation of this work came from the design and construction of a new suspension bridge in the Tacoma Narrows next to an existing bridge. The new bridge like the old one was designed to be supported on two large concrete piers at its two ends. The new caissons were in close proximity to the piers of the existing bridge. The two caissons were built floating in place so that the draft of the caissons continually increased as the construction progressed. In order to determine the forces due to the current flow around the piers CFD analysis was made for a large number of cases. The Reynolds number of the flow around the piers was on the order of 108 (100 million). The commercial software AcuSolve was employed to solve for the flow field around the pier/caisson assembly and the current forces were derived numerically. Most of the CFD runs were made in full scale. However, a few runs were also made in a model scale. This allowed a comparison of the results between the full and model scale so that any scale effect could be studied. This paper makes detailed analysis of the fluid flow past the piers, their interaction and shadowing effects. The effect of the variation in the current flow direction is also investigated. Critical analysis of the variation of the drag and lift coefficients with Reynolds number, spacing parameters, and Strouhal number are made in this paper. The time varying inline, transverse lift and vertical forces are also studied. In view of the analysis results the feasibility and accuracy of the CFD results for such high Reynolds number are examined. The results herein have obvious applications not only in coastal engineering problems, but in several offshore applications as well.

A boundary integral equation formulation for the Helmholtz equation in a locally perturbed half-plane

In this paper we study the application of boundary integral equation methods to the solution of the Helmholtz equation in a locally perturbed half-plane with Robin or impedance boundary conditions. This problem models outdoor noise propagation from a cutting onto a surrounding flat plane, and also the harbour resonance problem in coastal engineering. We employ Green's theorem to derive a system of three coupled integral equations. The three unknowns are the pressure on the boundary of the disturbance and the pressure and its normal derivative on the interface with the upper half-space. We prove that the integral equation formulation has a unique solution at all wavenumbers by proving equivalence of the boundary value problem and the integral equation formulation and proving uniqueness of solution for the boundary value problem.

Recent Developments in the Geomorphic Investigation of Engineered Tidal Inlets

In recent years, numerous technological advances have made field studies and laboratory analyses of tidal inlets more time efficient while also substantially improved data quality. Mapping channel bathymetry was once a labor-intensive task that was accomplished by measuring water depths along a detailed network of channel profiles. Now aircraft-operated LIight Detection and Ranging (LIDAR) can accurately map the bathymetry of most tidal inlets in a few hours' time. If greater detail of the channel bottom is required, then a multibeam acoustic system is utilized, although this technique is deployed from a boat and is less time efficient. The topographic version of LIDAR enables the construction of inlet shoreline maps and determination of volumes associated with shoreline gains and losses. In another advancement, side scan sonar mosaics now provide a picture of the bottom indicating different sediment types, bedrock outcrops, and bedform distributions. These surveys have also become essential for identifying scour holes next to rock jetties and assessing the susceptibility of these structures to collapse. The accretionary history and/or migrational trend of a tidal inlet can be determined from ground-penetrating radar transects on land and from shallow seismic surveys in water. These records provide a representation of the layers of sediment left behind as the inlet shifted positions. The hydraulic regime of a tidal inlet can be much more accurately determined using the Acoustic Doppler Current Profiler (ADCP). This instrument produces velocity profiles for an entire inlet cross section and provides almost instantaneous discharges for small and moderately sized inlets. In a slightly different mode, ADCP technology has been used for directional wave measurements. Finally, significant upgrades in the manipulation of information, including Geographic Information System (GIS) and image analysis methods, have greatly facilitated the analyses and interpretation of the field data. These advancements have provided scientists with more effective means of gathering data, testing numerical models, and finding solutions to coastal engineering problems.

DAM-BREAK FLOW OVER A UNIFORMLY SLOPING BOTTOM

A solution is derived for dam-break flow over a uniformly sloping bottom, under the assumption that each receding characteristic line of flow is parabolic. The hydraulic resistance of the bottom is not considered in the derivation. The validity and characteristics of the solution are examined through comparisons with Matsutomi's approximate solution under the same flow conditions, and with Ritter's and Peregrine et al.'s solutions. The solution is expected to be useful in examining or solving practical problems in hydraulic or coastal engineering, and any result obtained from it can be easily compared with experimental data.

Review of Coastal Processes with Engineering Applications by Robert G. Dean and Robert A. Dalrymple

Being a specialist in wave dynamics, I was a little bit surprised to find the names of Professors Dean and Dalrymple as the authors of the new book Coastal Processes with Engineering Applications. Professor Dean as the great developer of the stream function theory and the nonlinear spectral interactions, and Professor Dalrymple as the highly elaborated wave transformation analyst; they are the joint authors of the famous textbook Water Wave Mechanics for Engineers and Scientists. However, my small bewilderment turned out to be a reflection of my ignorance of their innumerable contributions to the study of coastal processes, as I learned by reading this book. The present review is a report of my learning of coastal processes with this book rather than a critical review by a peer in the field of littoral transport and beach morphology. Professor Dean is the promoter of the equilibrium beach profile concept, which refers to a mean equilibrium defined by averaging beach profiles over a long period. The equilibrium beach profile concept was initially conceived and proposed by Bruun in 1954 and 1962, but Professor Dean expanded the concept by correlating the proportionality parameter with the mean sediment diameter and demonstrated its usefulness with many applications. The equilibrium profile concept is now serving as the indispensable tool of American coastal engineers in analysis, planning, and design of shoreline protection projects. Part III of the Coastal Engineering Manual ~draft! by the U.S. Army Corps of Engineers attests the power of the equilibrium profile concept. Coastal Processes with Engineering Applications comprises four parts. Part I, ‘‘Introduction to Coastal Processes,’’ has three chapters and provides the reader with access to various examples of coastal engineering problems, description of sediment characteristics, and several shoreline planforms such as spits, tombolos, barrier islands, etc. that evolve in the long-term coastal processes. This part is quite readable even for nontechnical people and may serve as a means of communications with them. Part II, ‘‘Hydrodynamics of the Coastal Zone,’’ is made up of two chapters: one on tides and storm surges and another on waves and wave-induced hydrodynamics. This part is a summary of the subject listed above, but a detailed review is given on the lowfrequency motions at the shoreline. Swash zone dynamics is also discussed in detail over six pages, starting from the balance of forces acting on elemental swash particle. Part III, ‘‘Coastal Responses,’’ is the core of this book, covering 210 pages with five chapters. The first chapter in Part III introduces the techniques of field measurements and analysis. The next chapter elaborates the concept of equilibrium beach profiles over 48 pages. Anyone unfamiliar with this concept can gain a good idea of this concept and its applications by studying this chapter. The third chapter discusses the longshore and cross-shore

Manipulation of numerical coastal flow and water quality models

Nowadays, numerical flow and water quality models are widely applied to solve coastal engineering problems. The outcomes of the algorithmic execution often deviate from those anticipated, particularly when the model is set up initially. This necessitates the modeler to perform the manipulation procedure, which comprises feed back and modification. As such, it is desirable that expert system technology be integrated into the modeling system to furnish assistance for the novice user who lacks the requisite knowledge to establish the model and assess the results. In this paper, a prototype expert system on manipulation of numerical coastal flow and water quality models is developed and implemented by employing an expert system shell, Visual Rule Studio, as an Active Designer under Microsoft Visual Basic environment. Through the successful development of this prototype system, it is shown that the expert system technology can be coupled into numerical modeling for mimicking the manipulation process. It assists the user to formulate a suitable strategy for striking a balance between accuracy and effectiveness and to tune the model to accomplish satisfactory modeling of real phenomena. It is able to bridge the existing gap between numerical modelers and practitioners in this field.

Application of a Biological Tool for Estimating Current Annual Rates of Erosion and Deposition in Modern Coastal Environments: A Case Study in the Bay of Bengal Coast

The marine polychaete Diopatra cuprea (Bosc) produces tubes that protrude above the sediment surface. To the part above the sediment surface the worm attaches foreign particles. A sharp boundary separates the parts above and below the sediment surface. With subsequent erosion, part of the tube without attached particles becomes exposed and this exposed part indicates the amount of erosion. With subsequent sedimentation, the tubes are enlarged upward and the sharp boundary is found below the sediment surface indicating the amount of subsequent sedimentation. This mode of construction of tubes during an average life span of two years renders tubes as simple but excellent natural tools for precise and easy measurement of the latest annual rates of erosion and deposition in coastal areas, data that are essential for the solving of coastal engineering and geoenvironmental problems. Comparison of this tool with expensive long-term coastal profiling data in four areas in the Bay of Bengal coast indicates its correctness and high applicational value. This revised model can be applied to modern coastal environments only for calculating latest annual rates of both erosion and deposition as correctly as latest physical techniques. Being based on the similar organosedimentary principle, it distinctively contrasts with the earlier model of Myers which provides information on the amount of sediment accumulation only without any time connotation and, it may generate erroneous results if applied to the geologic past unless some limitations evolved in the processes of dewatering, compaction, lithification and diagenesis are removed.

VISION AND PROBREMS FOR REFLECTION OF EFFECTS OF LONG-PERIOD WAVES INTO DESIGN OF COASTAL FACILITIES

The long-period waves have been researched in recent years because of its importance in the various problems of coastal engineering, such as long-period oscillation, long-period motions of moored vessels, sediment transport, wave-overtopping and stability of coastal structures. Importance of long period waves have been well recognized, however, its reflection of effects of the long-period waves into design of coastal facilities is not sufficient.In this paper, we review previous researches on the long period waves and consider the problems in the reflection of effects of long-period waves into design of coastal facilities.

Numerical results of the joint probability of heights and periods of sea waves

The short-term joint probability of wave heights and periods is of major importance in many coastal and offshore engineering problems. The existing results cover sufficiently only the limiting case of narrow band spectra, a gross approximation to real life data. This paper presents numerical evaluation of the joint probability based on the theoretical framework discussed in a companion paper. The obtained results are valid mainly for wide band spectra and compare well with the available data. The improved behaviour of the present model over past theories is demonstrated, especially in the range of high spectral width parameter.

First record of the introduced fouling tubewormFicopomatus enigmaticus(Polychaeta: Serpulidae) in Hawke Bay, New Zealand

Abstract The brackish-water serpulid polychaete Ficopomatus enigmaticus (Fauvel) is recorded from Hawke Bay, New Zealand (c. 39°30′S, 176°52′E), where it had established a colony causing fouling problems at a flood protection pumping station. Hitherto this introduced species had been known only from northernmost New Zealand <37°S). The species produces dense aggregations of calcareous tubes, and if it spreads further in New Zealand it could cause additional fouling and coastal engineering problems.