· · · Repository Hydraulic Engineering Reports

Over the past two or three years, Texas A &: M University has been operating facilities offshore of Panama City, Florida, to observe and collect environmental oceanographic data in the Gulf of Mexico. Waves are measured using Hytech resistance type wave staffs. The data is recorded more or less continuously in digital form on magnetic tape. The recording stations are located approximately 150 yards, 1. 7 nautical miles and 11 nautical miles offshore in water depths of about 8, 60 and 100 feet, respectively. NESCO, in the course of a current research project on the modification of wave spectra on the continental shelf, has been utilizing this wave data system. A series of computer programs has been developed to analyze the wave data. Results of probability densities and spectral analyses of simultaneous station data obtained during Hurricane Dora are presented. Comparison of directly measured statistics and spectral statistics are made.

The aim of this workshop was to take advantage of the recent freedom available to scientists in the Soviet Union (now Commonwealth of Independent States) to travel to the West in order to develop both contacts and an awareness of current research between research workers from East and West, most of whom have formerly had little contact. We consider this aim was achieved and are grateful for the substantial financial support from the European Office of the U.S. Office of Naval Research and the European Research Office of the U.S. Army. In addition we thank the home institutions or other fund providers which supported the travel costs of participants and the subsistence of western participants. The support of Bristol University's Department of Mathematics in holding the meeting is greatly appreciated.

Volume I of this report presents the results of a research program to evaluate and develop water wave theories for engineering application. A second volume of this report presents wave tables developed for preliminary design in offshore problems. Volume I describes: (1) an evaluation of the degree to which various available wave theories satisfy the nonlinear water wave mathematical formulation and (2) a comparison of water particle velocities measured in the laboratory with those predicted by a number of available wave theories. The results of these studies indicated that the Stream function wave theory provided generally better agreement with both the mathematical formulation and the laboratory data. Volume I also includes a number of examples illustrating the application of the wave tables (described below) to offshore design problems. Based on the evaluation phase described above, a set of wave tables was developed and is presented as Volume II. The tables consist of dimensionless quantities which describe the kinematic and dynamic fields of a two dimensional progressive water wave. In addition, quantities are included which are directly applicable to frequently required design calculations and also parameters which should be of interest to the researcher and scientist

A method is presented for the evaluation of an orthogonal coordinate system of particular use in the study of the diffraction of long gravity waves near islands of irregular shape. The problem involves a conformal mapping of the island onto a coordinate plane in which the island contour is a unit circle. The mapping relation is evaluated by an iterative procedure which is reminiscent of a method introduced by Theodorsen, but has the advantage that it is applicable to an island contour in which the island contour relation r(9) , in polar coordinates, is multivalued for a given range of 9. This generality is achieved by employing a parametric representation of the island contour in which the arc length on the island contour enters as the parameter. Application is made for two specific cases, Wake Island and Kauai.

Retrieval of ocean surface data, in particular wave spectral data, both from space based and ground based instrumentation has reached a level, both in terms o f amount and quality, where a further assessment of societal benefit becomes important. There are engineering and industrial application sectors known to be in need for such data, both in planning, design, and in operations and real-time applications such as in monitoring and forecasting. At the COST conference «Provision and Engineering/Operational Applications of Ocean Wave Data», remote sensing and wave scientists met with potential users of such data within different sectors of ocean and coastal activities. These users were represented by academic and operational experts within naval architecture, offshore explorations and production, port and harbour management and operation and coastal engineering. The majority of presentations are included in these proceedings. It is believed that the conference has provided a broader and more pragmatic view on the future requirement for ocean wave data, as retrieved both from space and ground based instrumentation. The followup of the conference, accordingly, will be the development of joint project proposals in order to provide future ocean data products more adapted to the user requirements. A «Conference Whitepaper» was prepared immediately after the conference and is attached in the Annex at the end of these proceedings.

International conference January 26-30, 1998.

This report presents a theory for ocean wave transmission past breakwaters by overtopping, based on an evaluation of the energy content of the overtopping water. While several coefficients are subject to further investigation, the data shows that the general form of the equations developed is correct. Comparison with large-scale model tests reinforces this belief, and comparison of an intermediate theoretical result predicting the volume of overtopping water with published data again shows reasonable agreement. An envelope curve for the transmission coefficient, based on all available data, gives a simple tool for preliminary design estimates of the transmission coefficient.

Explosion waves were simulated by plunging a parabolic surface of revolution in and out of an indoor t est basin 3 feet deep by 92 feet square. These impulsively-generated Water waves are found to be dispersive as evident from the following properties : The period and the celerity of the individual waves increase with travel time, and the amplitude of each wave group decreases. It is shown that the eventual shoaling in approaching the coast limits the dispersion process, and that the waves eventually amplify like other gravity waves. The run-up on the beach is a function of the wave steepness (H/L) at the beginning of the slope and the steepness of the slope itself. The run-up of any one wave is also affected by the preceding and following waves in the group. Experimental results on dispersive wave attenuation in water of constant depth are in fairly close agreement with theory. The results on amplification due to shoaling indicate that a modification of Green's Law is necessary for describing these waves.

preprints of all full papers of the workshop of wave hindcasting and forecasting, Monterey, California

Lecture notes, University of California, refraction, braking

The correct generation of a second order wave field in a laboratory wave tank is of importance in several experimental investigations, particularly those of nonlinear evolutions and sediment transport. In the present work, which was carried out under the MLTP (medium long-term planning) of DELFT HYDRAULICS for improving experimental techniques, expressions are found for the motion of a waveboard to generate a correct second order wave field. These expressions are valid for both regular and irregular waves. Two important features of the procedure adopted here are that the computing time for the motion of the waveboard is signifcantly smaller compared to a method based on the frequency domain and that the accuracy of the physical representation increases with decreasing spectral width. The assumption of a narrow band spectrum is sufficient for realistic sea states described by spectral shapes of JONSWAP and Pierson-Moskowitz types. Results of some experimental investigations into the performance of the software based on the wave generation theory are also included in the report. Although the overall agreement between the theory and the experiment is good, some discrepancies are apparent from the limited analysis carried out so far, all of which cannot be attributed to the wave generation theory. Further analysis (and possibly a set of new experiments) is required in order to resolve aH the discrepancies.

The major part of the research on berm breakwaters has concentrated on the berm reshaping of a trunk section exposed to head-on waves. Recent research included aspects related to individual stone movements under perpendicular wave attack (eg Tomasicchio et al). For a berm breakwater trunk section consisting of berm stones smaller than a certain size, the stones will continue to move in the wave direction (longshore transport) when the breakwater is exposed to oblique waves. Only a little research has been made to study the effect of oblique waves on the reshaping and longshore transport of berm breakwaters (eg Burcharth and Frigaard, and Van der Meer and Veldman). A series of comprehensive model tests and subsequent analyses were carried out with the aim to study the influence of wave obliquity on the reshaping process, on the initiation of longshore transport, and on the longshore transport rate. The model set-up and test programme are described in Juhl et al.

Table for wave computations.

Het doel van het onderzoek is om te komen tot een inventarisatie van literatuur met betrekking tot snelheidvelden in golven. Aan de hand van deze inventarisatie kan in een later stadium inzicht worden verkregen in de toepasbaarheid van bestaande golftheorieen of worden overgegaan tot de opzet van een beschrijvend model van het snelheidsveld onder een golf, wanneer deze de kust nadert.

The engineer required to calculate theoretical wave characteristics such as wave profiles and wave forces and moments on piling, is confronted with a problem which includes (1) selecting one of a number of available theories and (2) calculating the required information which, for some of the theories, is a relatively complicated procedure. This paper presents criteria for assessing the validity of various wave theories; these criteria are then applied to test the validity of several theories for two wave conditions and, it is found that for these conditions, the Stream function numerical wave theory is the most valid of those tested. The Stream function theory is developed into graphs of dimensionless crest displacement, and total maximum wave forces and moments on a vertical piling.

Momentum flux considerations are used to formulate a differential equation governing the growth, with distance, of the mean longshore current velocity in the surf-zone on a plane, impermeable beach due to monochromatic waves. The equation is solved for the flow situation downstream of a surf-zone barrier and is shown to compare favorably with laboratory measurements. The asymptotic (uniform flow) form of the relation is also shown to be in good agreement with the field and laboratory data of other investigators. Conclusions are reached governing the size of laboratory models necessary to represent conditions of fully developed longshore currents.

The suspension of sediment particles by turbulent eddy diffusion in a non- uniform flow region was studied, using the convective-diffusion equation as a mathematical model. A simplified form of the equation for which mixing characteristics and flow velocities 'vere assumed uniform was found to accurately describe the sediment concentration profiles which had been measured in a 24-foot long flume. The experiments also showed that turbulent mixing was more uniform than predicted by existing theories, and that it depended on the geometric characteristics of the mobile, wavy bed. Although diffusivities in the non- uniform region tended towards uniformity with downstream distance the vertical diffusive transport rate was related to depth as a power law function. An expression with analytic support was derived for the diffusion coefficients as functions of sediment and hydraulic variables.

Design, construction and calibration of wave overtopping simulator