The parabolic method for numerical modelling of water waves

This report describes a recently developed numerical method, known as the parabolic method, for computing wave transformations in coastal waters. This method has potential advantages over traditional ray tracing methods and has undergone rapid development since the late nineteen-seventies. A review of technical literature during this time is contained in the report, and present stage of development and future requirements are assessed. Some results are presented from a computational model based on the parabolic method which is being developed at Bristol University and Hydraulics Research Limited

The nearshore profile model - a computational model of wave and current interaction in nearshore regions

A computational model, known as the Nearshore Profile Model, has been developed at Hydraulics Research Ltd for predicting wave and current condition in nearshore regions. This report describes the theory and computational techniques used by the model, and compares its predictions against laboratory and field data. The model uses the approximation of a straight coastline with parallel depth contours, and determines wave and current conditions at fried points along a shore normal line. The theory of wave and current motion is based on general mass, energy and momentum balance equations which are applicable both inside and outside the surf zone, and includes some new approaches to the solutions of these equations. An important features is the modelling of tidal currents as well as wave-induced currents, with full interaction between the two types of current and the waves. Because the model considers one horizontal dimension only, the computational speed is greatly increased compared with 2-DH models. The model is thus capable of processing large quantities of input wave and tidal data, making it suitable for the investigation of long-term processes on beaches and in nearshore regions. The model is designed to be used in conjunction with an appropriate sediment transport routine for problems concerned with longshore movement of sediment

Current-depth refraction of water waves - a description and verification of three numerical models

This report describes three computational models for determining wave refraction by a combination of depth variations and currents. The theoretical formulation of current-depth refraction and the numerical procedures used in the models are described. The models are tested for some simples cases involving parallel depth contours and unidirectional currents for which analytical solutions are available

Wave breaking - a review of techniques for calculating energy losses in breaking waves

Wave breaking is an important consideration in many maritime engineering design calculations. Over the past twenty years a wide variety of methods have been put forward for determining various features of breaking processes, ranging from simple empirically-determined expressions for the breaker wave height to computational models of the detailed structure of breaking waves. This report contains a literature review, concentrating on techniques for determining the wave height at breaking, and the subsequent energy losses as broken waves continue forwards. The emphasis is on methods suitable for hand calculations or inclusion in computational models of wave transformation in shallow water. Assessments of the techniques are made and recommendations given

The nearshore profile model incorporating wave spectra

A computational model for determining wave and current conditions in nearshore regions, known as the Nearshore Profile Model, has been extended to incorporate wave spectra. The theory of spectral wave transformation used by the model is described, and comparisons between the spectral and monochromatic versions of the model are presented. It is concluded that in most cases where input wave spectra are adequately known, they should be used in preference to the equivalent monochromatic wave

The Nearshore Profile Model - further model development and sensitivity tests

This report describes modifications and improvements to the Nearshore Profile Model developed at Hydraulics Research for predicting detailed nearshore wave, current and sediment transport processes. These improvements are to the representation of wave energy dissipation by bottom friction and, principally, wave breaking. An accurate representation of particular provide the most important driving forces for surf zone processes

Wave prediction in deep water and at the coastline - a review of recent techniques of predicting, analysing and modelling wave conditions

This report is a review of methods of prediction, analysis and modelling of wave conditions in deep water and at inshore locations. It is intended for coastal engineers as an outline of the methods currently available for predicting wave conditions, which emphasis on the most recent techniques. The report is in two parts. Part 1 contains a description of wave generation at sea and techniques for analysing measured wave data and predicting wave conditions from wind records. Part 2 contains a description of the shallow-water processes affecting waves as they travel from deep water to the coasts, together with a review of the computational techniques for modelling these wave transformations

The effects of wave chronology on medium and long term coastal morphology

The sequencing, or chronology, of wave events plays an important role in determining how coastlines and nearshore regions evolve over medium and long timescales (from weeks to decades). However, present-day computer models of coastal morphology treat the input wave conditions in either a deterministic (i.e. a single wave sequence) or a probabilistic manner. In neither method are the effects of the full range of possible future wave sequences, for given overall statistical values, calculated. The methodology presented here addresses this problem by multiple model runs using different re-orderings of a wave sequence. A series of tests demonstrate different aspects of wave chronology and its importance in the prediction of seabed and beach levels. The method provides a means both for understanding wave chronology effects and for predicting these effects in practical engineering problems involving medium and long timescale changes to coastal morphology

Computational modelling of waves in harbours using ray methods

This thesis is concerned with the development of a new computational model for the prediction of wind-generated waves in harbours using a new type of ray tracing technique. The thesis includes a background to the study, an exposition of the theory of the new ray tracing technique, a description of the computational techniques adopted, a new method for interpreting ray diagrams, comparisons with analytical solutions, alternative numerical models and a physical model, and finally an account of the model's use in a commercial harbour design study. Most alternative computational harbour modelling techniques are limited by computational effort.to small harbour areas and/or long wavelengths. The new model is designed for the opposite case, of large harbour areas and short waves. The main theoretical problem is the construction of a ray system to represent breakwater diffraction. The conventional method of tracing rays radially from the breakwater tip is shown to break down in an unbounded area surrounding the geometric shadow boundary. A completely new ray system is adopted in this work which involves tracing rays from the shadow boundary rather than the breakwater tip. This method is shown to make good predictions of wave heights and directions everywhere except in a very small bounded area surrounding the breakwater tip. Full numerical comparisons of the new ray method with the radial ray method and Sommerfeld's analytical solution are carried out. A computational model is then developed in which this new ray tracing technique for breakwater diffraction is combined with refraction due to arbitrarily varying depth profiles, and reflections from harbor boundaries with general plan shapes and reflection coefficients. The model also includes a new technique of interpreting ray diagrams to obtain wave heights and directions in a general manner, overcoming most of the problems associated with earlier methods. This new computational model is compared against a finite-element model for a simplified harbour layout, and then against a random-wave physical model of an actual harbour design in which the processes of wave I diffraction, refraction and reflection are combined in a general manner. Finally, the computational ray model is used in parallel with a physical model in a commercial investigation, and an assessment of the merits of the computational model as a commercial tool is made

Field measurements at the NOURTEC site, Terschelling, The Netherlands, October 1994

This report describes the work carried out during a two-week field measurement campaign on the Dutch island of Terschelling in October 1994. This report describes the frames, instruments and measurement campaign, together with the initial post-campaign analysis of the data. The report is unrestricted and contains the outcome of field measurements for subsequent use for validation of computer models. It is intended primarily for experimentalists and numerical modellers in civil engineering hydraulics