Hidehiro Katsui

INCEPTION OF SAND MOTION AROUND A LARGE OBSTACLE

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.

NON-REFLECTED MULTI DIRECTIONAL WAVE MAKER THEORY AND EXPERIMENTS OF VERIFICATION

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Bottom Shear Stress in Coexistent Field of Superimposed Waves and Current and Scouring Around a Large-Scale Circular Cylinder

ABSTRACTIn predicting a bottom change around an offshore structure, bottom shear stress must be properly estimated. The method for estimating the bottom shear under a wave or wave-current field has been already established in the two-dimensional system, where a water particle moves reciprocally along a straight line. Around a large-scale structure, however, diffracted waves superimpose on incident waves and water particles move along elliptical orbits, which may cause differences in the bottom shear. This paper deals with the bottom shear stresses in a wave-current coexistent system using a linear turbulence theory. An improved theory on the bottom shear is applied to the numerical simulation of bathymetric change, and its validity is examined through comparisons with experimental observation of sand movement.

ASYMMETRIC BOUNDARY LAYER FLOW ABOVE SAND RIPPLES UNDER PROGRESSIVE WAVES

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

A Simulation of Deformation of Rubble Structures based on the Stochastic and Dynamic Theory

In order to construct an economical and reasonable structure, design methods, which can take economical efficiency into consideration, is necessary. The performance based design that specifies the performance of a structure is one of the economical design methods. An economical design would be established by allowing deformation of a structure within limits which satisfy the performance demanded. Therefore, the deformation of a structure should be estimated quantitatively. A probability which the deformation occurs should be evaluated also. Conventionally, this is done by hydraulic model tests. The model tests, however, have scale effects, and they might be expensive. Accordingly, the development of the numerical computational method for the deformation is useful for the performance based design. One of the coastal and maritime structures with the higher applicability for the performance based design night be a rubble mound structures, such as a sloping breakwater, an artificial lead, or a rubble submerged breakwater. Two prediction methods of deformation for rubble mound structures were developed in this study. One is a deterministic method, and the other is a stochastic method. A deterministic method is consisted of fluid analysis and distinct element analysis. The stochastic method is an approximately method which expanded the deterministic method based on the reliability theory. The methodology and the applicability of two methods are investigated in this study.

NEW LAUNCHING ERECTION METHOD FOR SUBMARGED TUNNELE

A new construction method for a submerged tunnel has been developed. The new method is an application of the launching erection method for a bridge construction technique. Caissons that is an element of a tunnel are constructed at the tunnel entrance, and then they are pushed into the sea. Thus the method does not need huge construction space and navigation restriction. The technical subject of the new method is reduction of launching force. We developed the machine ‘HYDRO SLIDER’ to cut off the friction force. We carried out small and large scale experiments to investigate the problems in practical use of HYDRO SLIDER. The experiments show that HYDRO SLIDER makes possible to reduce the friction force. We also carried out experiments to investigate the wave forces and the fluid forces caused by a cruising a ship. The results show that the wave forces are larger than the fluid forces caused by ship. Finally, the motion of the caissons caused by waves are simulated numerically, and it was found that the motions are negligibly small.