J. De Rouck

Wave energy on the Belgian Continental Shelf

The inexhaustible wave energy resource is at the basis of the increasing research on wave energy exploitation. Till now the resource is studied in detail for regions with a high wave energy density. As the problems to guarantee the survivability of wave energy converters (WECs) in a severe and energetic wave climate are not solved yet, the possibilities of wave power conversion in a less aggressive wave climate should be investigated. This paper describes the wave climate and correspondent wave power resource in a rather sheltered area i.e., the Belgian Continental Shelf (southern part of the North Sea). The available wave power is studied on six buoy locations. Furthermore characteristic sea states and design conditions are derived for the most suitable locations for wave energy production. The available wave power is compared with other sites in the North Sea. Near shore (< 30 km off the coast) less than 10 kW/m is available.

Numerical Simulation Of Wave Overtopping Over A Smooth Impermeable Sea Dike

The main objective of the paper is to compare the results of numerical simulations of the wave overtopping over a smooth impermeable sea dike. Four different numerical models have been used. One model, ODIFLOCS, is a one-dimensional model based on the non-linear shallow water equations. The three other models, VOFbreak, SKYLLA and 2DHYDROTUR, are two-dimensional models based on the Navier-Stokes equations and the Volume-Of-Fluid (VOF) method for treating the free surface configuration. Physical model data of the sea dike, including measurements of layer thickness, discharge, cumulative overtopping volume and average overtopping rate, have been used as validation reference data. The numerical results from the four models are presented and compared with particular attention to the average overtopping rates. Recommendations are given for further improvements of the numerical simulation.

QUALITY AND DURABILITY OF CONCRETE ARMOUR UNITS

The Labrador Sea Extreme Waves Experiment (LEWEX), is an international basic research programme concerned with full-scale measurements, analysis, modelling and simulation in test basins of 3-dimensional seas. The research is carried out in order to assess the significance of 3-dimensional sea states in engineering applications. The first phase of the programme full scale wave measurements in the North Atlantic Ocean was performed at a site and time that had a high probability of encountering severe sea states. The present publication shows examples of measured bi-modal directional sea spectra obtained with the WAVESCAN buoy and directional sea spectra measured with an airborne Synthetic Aperture Radar (SAR). Directional spectra of gravity waves are obtained with the SAR both in open waters and below an ice cover. Further work is needed in order to verify SAR-measurements with in-situ observations. In-situ measured directional spectra are also compared with hindcast spectra from the 3G-WAM model. Hindcast significant wave heights were found to be lower than the in-situ measurements.The littoral drift model developed at DHI and ISVA, see Deigaard et al. (1986b) has been extended to include the effects of the irregularity of the waves, of a coastal current and a wind acting on the surf zone. Further, a mathematical model to simulate the near-shore current pattern along a barred coast with rip channels has been developed. The influence on the littoral drift of the irregularity of waves, wind, coastal current, and rip channels is discussed. It is concluded that irregularity of waves and presence of rip channels must be considered while coastal current and wind action are of minor importance.At present, the Prodhoe Bay oil field in Alaska contributes a substantial amount of the domestic oil production of the United States. Oil is also expected to be present on the continental shelf of Alaska, and it is estimated that approximatedly 28 percent of the total U. S. reserve is located beneath the shallow ice covered seas of the Alaskan continental shelf. To expolre and to exploit these oil rich resources, engineers are confronted with hostile oceanographic conditions such as high tides, waves, strong currents and sea ice. The same area is also rich in fishery resources. Being one of the most productive fishing grounds in the nothern Pacific, the potential ecological impact due to an oil spill is of a major concern. This paper describes the methologies used for the development of a modeling system for the oil risk analysis. The system is designed with generality in mind so it can be used for other coastal areas. The development of three dimensional models used in the modeling system described here have been published in the earlier International Coastal Engineering Conferences (Liu and Leendertse, 1982, 1984, 1986) and a report published recently by RAND (Liu and Leendertse, 1987). In the oil-spill risk analysis, these three dimensional hydrodynamic models are coupled to a two-dimensional stochastic weather model and an oil weathering model.The two projects (LUBIATOWO 79 and LUBIATOWO 86) were aimed at study pore pressure behaviour in natural sand bed in the coastal zone of the Baltic sea under the action of storm waves. During both projects, the wave induced pore pressures at the various levels in the sea bed were measured. The collected data were used to verify the applicability of the various theoretical approaches. In the conclusion, the range of the application of the particular analytical method is given.The rapid recession of the shingle bank of Hurst Beach (up to 3.5m/yr) makes it an excellent natural laboratory for the study of the factors which influence the stability of shingle beaches. Studies have included: the significance of long period, high energy, swell waves the classification and quantification of overwash processes run-up and seepage characteristics the effect of settlement of the underlying strata and the implications for practices in shingle nourishment. The studies have revealed the distinctive character of shingle beaches as compared with the more fully researched sand beaches. More detailed research on shingle beaches is justified particularly in relation to (i) the run-up characteristics including its interaction with swash cusps and (ii) the influence of the subsidiary sand fraction on the beach characteristics.Environmental assessment, engineering studies and designs were completed for a new 26.5 m3/s seawater intake system in the Persian Gulf. The original intake facility consisted of a curved, 60m breakwater with one end attached to the shoreline, a settling basin immediately adjacent to the shoreline and dredged to a maximum depth of approximately 5m, and a pumphouse structure located on shore such that the seaward wall formed one side of the settling basin. The facility located on an island in the Gulf, which served multiple seawater uses, had experienced both structural and operational problems, the latter consisting principally of excessive ingestion of sediment and seaweed. These factors plus the requirement for additional demands for seawater beyond plant capacity caused the owner to initiate a study of alternative intake systems, produce a design for the most effective solution and construct the new intake system.A two-dimensional wave prediction model suitable for use on personal computers is described. The model requires the twodimensional time-dependent wind field as input. Output consists of wave height, wave period, and wave direction estimates at all grid points on a computational grid representing an enclosed or semi-closed basin. Model predictions compare favorably with observations from a wave research tower in Lake Erie. A formula is provided to estimate how long a model simulation would take on a personal computer given the surface area of the computational domain, the grid size, and the computer clock speed.Cullera Bay is a neritic ecosystem placed on the Spanish Mediterranean Littoral largely influenced by the Jucar River, that brings about lower salinities than surrounding waters, and broad variations of its values. An extensive research, with 9 samplings throughout the year, was carried out, measuring both physical and chemical parameters, and the planktonic communities. The trophic status of the ecosystem, the spatial and temporal variations of the nutrients and the planktonic communities were studied, evaluating the influence of the river loads and the littoral dynamics. Some essential basis to allow a suitable emplacement of waste waters disposals along the Valencian littoral are set up in order to minimize the gradual eutrophication of this coast.In the last two years a whole of studies was realized in order to determine precise solutions to the regeneration of Villajoyosas beach, in the Spanish mediterranean coast. Investigations were carried out to the surrounding coastal areas based in field investigations and laboratory analyses of the beaches materials.

Numerical simulation of landslide-induced water wave kinematics by LVOF

By implementing our design of the mass-force coupling scheme for slamming([6,7]), we present some results for case studies related to landslide-induced tsunami modelling in a numerical wave tank, based on our highly efficient Navier-Stokes solver([4,5]), named LVOF. LVOF is constructed by a novel VOF finite volume approach that incorporates surface tension, coupled with a dynamic subgrid-scale (SGS) turbulence model. Theoretically, our mass-force coupling model represents the coupling of a moving rigid body on the flow. More importantly, landslides are treated as a fluid, leading to the resulting discrete equations are resolved over the entire domain. Test cases concern aerial and submerged landslides in 2D and 3D, respectively. By comparison, our design of the model is of high efficiency according to the contributions from the mass-force term, raising in the Navier-Stokes equations. On the other hand, our results can also provide valuable base for the analysis of near-field characteristics of landslide generated impulsive waves, by LVOF.

Numerical simulation of water wave impacts using a Navier-Stokes solver

The calculated results for the violent impact of water waves onto rigid stationary coastal structures are presented in this paper. The simulation is performed in a numerical wave flume using our recently developed in-house Navier-Stokes solver([4]) named LVOF. It is a VOF finite volume approach that incorporates the surface tension effects, coupled with a dynamic subgrid-scale (SGS) turbulence model. Test cases concern a combination of wave propagation, shoaling, reflection, diffraction, breaking and overtopping after impact. Additionally, the effects of a current on wave-structure interactions are investigated, including the study of the influence of viscosity on the wave boundary layer under breakwater and the 3D effects. Our results demonstrate that our solver can describe most of the significant features of motions induced by regular and irregular waves. In particular, the shape of the free surface agrees well with measurements under grid refinementscaptured and even during lengthy computations.

STATIC AND DYNAMIC LOADING TESTS ON THE HARO ARMOUR UNIT

Tanah Lot Temple is situated in Tabanan Regency - Bali, on the coast of the Indonesian Ocean. Due to continuous wave attack, wind force, and weathering of the rock bank where the Temple stands, abrasion has occured which is more and more threatening the existence of the Temple. Considering that Tanah Lot Temple is a sacred place for the Hindu Balinese people and a place of high cultural value, and also an important tourism, steps to save the Temple are imperative. The Central as well as the Regional Authorities, and also the Bali nese community are very much interested in the effort to keep the Temple intact. Measures have been undertaken to protect both the seaside and land-side banks of the Temple rock bank. This paper only discusses counter measures of the sea —side bank of the Temple.

THE USE OF SAND IN BREAKWATER DESIGN

This report will update the coastal zone practitioner on the National Flood Insurance Program (NFIP) as it affects the implementation of manmade changes along the coastline. It is our intent to place in proper perspective this fast-changing and often difficult to interpret national program. Readers will achieve an overall understanding of the NFIP on the coast, and will be in a position to apply the programs requirements in their efforts. We will begin with a history of the application of the NFIP to the coastal zone. The history of the problems encountered will lead into current regulations, methodologies, and the changes the Federal Emergency Management Agency plans for the future.The spatial variability of the nearshore wave field is examined in terms of the coherence functions found between five closely spaced wave gages moored off the North Carolina coast in 17 meters depth. Coherence was found to rapidly decrease as the separation distance increased, particularly in the along-crest direction. This effect is expressed as nondimensional coherence contours which can be used to provide an estimate of the wave coherence expected between two spatial positions.Prediction of depositional patterns in estuaries is one of the primary concerns to coastal engineers planning major hydraulic works. For a well-mixed estuary where suspended load is the dominant transport mode, we propose to use the divergence of the distribution of the net suspended load to predict the depositional patterns. The method is applied to Hangzhou Bay, and the results agree well qualitatively with measured results while quantitatively they are also of the right order of magnitude.