For the problem of diffraction and radiation of water waves from an arbitrary shapcd body, John's Green function (1950) has been used by several authors. However this John's Green function seems to have a ill behavior when the problem solved numerically through discretization.In this paper we point out that this ill behavior is caused from the definition of delta function which is used by John, and propose a new Green function as a Modified Green function, and check the application of this Green function for wave field.
This paper discusses a practical way of generating progressive fluid waves in a wave tank of limited length that may readily be mounted on a centrifuge.The wave tank used was equipped with a flap-type wave generator, together with a slotted vertical partition in front of its far end. A comprehensive series of centrifugal wave tests with either water or silicone oil of scaled viscosity, showed that for a slotted area ratio of 0.3, the reflection coefficient of the partition became as low as 0.13 when the distance between the partition and the end wall was adjusted to be approximately equal to quarter the incident wave length. This finding then facilitated a range of centrifuge tests that were designed for looking at the response of fine-grained sand beds to nearly progressive waves, with viscous scaling introduced.
To prepare space for mooring of pleasure boats, various marinas or harbors are planned to be constructed. In such planning, full investigation of natural environment has to be carried out to maintain safety mooring and amenity of the marina. In this study the effect of ship generated waves on a tranquility of marina is investigated. For the evaluation of ship generated waves, a simple neumerical method is proposed where an unsteady mild slope equation is utilized. The applicability of the method is examined by model experiments and the effect of the position of fairway in marina on the harbor tranquility is investigated nuemerically.
The phisical characterristics of breaking wave are investigated in cases of permitting to occur the return current and compulsorily removing it.Breaking wave motion is complicated by variety factors and connecting them.Effective one of these factors is return current which have a large scale effect compair with other factors as viscosity, capiraly stress, and turbulent. Therefore it is very important to investigate how the return current affect to the inner velocity field at breaking.Since the fluid motion is temporally and spacially unsteady in the breaking zoon, the messurement of fluid motion should be carry out in the view of these aspects.In this paper, the inner velocity at breaking is spacially investigated by perticle image velocimeter.Especially, we could understand that the structure of fluid motion is sufferd by the return current.
A wave dissipating pile support sutructure with a permeable pile wall and wave chamber has the advantage of low wave reflection. Experiments were conducted to investigate characteristics of the reflection coefficients for structures. The results of the experiments indicate that the reflection coefficients are influenced by pile section type. A practical calculation method is derived for the prediction of refrection coefficients of the structure on the basis of Tanimoto's theory for the wave dissipating caisson.
Experiments are carried out in a wind water tunnel. In this paper, wind-waves mean the waves newly generated by wind bihind the pole type wind fence. Wind velocity and wave height behind the wind fence are observed. Three kinds of wind velocity, 7, 9, 11m/s, and four kinds of air gap density of wind fence, 75, 50, 25, 0%, are used in this experiment. The reducing effect of the pole type wind fence on wind and wind-waves is discussed.
In this paper. the characteristics of the wave control were investigate for the case of the multi-span type using the flexible sheet with many springs on both sides. Consequently. the coefficient of transmitted wave becomes sufficiently small in the case of multi-span type that of one sheet. It was found that the multi-span type had excellent effect for the wave control. Nextly, the magnitude of vortex which was generated around the flexible sheet was measured visually using the video-system. Relation between a quantity of vortex and energy loss was discussed.
Crescent-type submerged mound and delta-type reef were combined to use as a coastal structure for enjoying surf-riding. Delta-type reef has the effect of the promotion of oblique wave breaking and rip currents. By arranging a crecent-type submerged mound in front of a delta-type reef and collecting waves to the top of the reef, breaking wave height was amplified up to twice or more. Suitable waves for beginner or average surfers were generated around the reef.
A simple method is proposed to calculate an instantaneous bottom shear stress under waves and current crossing at an arbitrary angle, on the basis of the theoretical study of Tanaka and Shuto (1981). Although the exact solution derived Tanaka and Shuto is expressed in terms of the complex-valued Bessel functions, the approximate solution presented in this study is very simple with reasonable accuracy. This method can, therefore, be extensively applied to practical coastal problems such as sediment transport and wave energy attenuation under coexistence of waves and current.
Beach changes around Oyazawabana sand spit in Lake Hinuma located in the eastern part of Ibaraki Prefecture were investigated through the field observation as well as the aerial photographying of the sand spit. This sand spit composed of coarse materials protrudes into the lake, and littoral drift from east to west dominates due to wind waves generated by east winds prevailing in this area.This study summarizes the specific topographic features caused by this littoral drift around the spit.It is found that the results well correspond to the beach changes generally observed on the seashore.
On september 30, 1994 typhoon 9426 hit the Kanto Plain and strong winds blowed for a long time with severe rainfall.Due to this typhoon lake level rapidly rose in Lake Hinuma in Ibaraki Prefecture and high waves were incident to seawalls.This study summarizes beach erosion caused by wave overtopping and the damages of wooden seawall located at Oyazawabana sand spit. Furthermore future measures to enhance the stability of bank protection are proposed.
Geometrical similitude of the plane shape of a recurved sand spit of various scales found in lakeshores and on sandy beaches is investigated. It is found that the method originally proposed by Hsu-Evans as a predictive model of the plane shape of bay-shaped beaches is applicable to the general expression of of the plane shape of a recurved sand spit. The method is applied to Wadabana spit in Lake Kasumugaura, Wadanohana spit in Tokushima Prefecture, Notsukezaki compound spit in Hokkaido, Mihono-matsubara compound spit in Shizuoka Prefecture and Sandy Hook on the U.S. east coast.
Formative process of a coral sandy island was studied experimentally by using a wave tank. Topographic changes due to wave action around the model reef edge composed of sand was investigated under the changing condition of sea level and wave height. It is found that critical condition of the formation of a coral sandy island is given by Shields number. A model was developed to predict formation of the sandy beaches on a coral reef.
On the Mochiishi coast in Shimane Prefecture a headland was built as a countermeasure against beach erosion. Original beach width was narrow and the distance from the shoreline to the seawall was less than 20m. After the completion of the headland beach erosion proceeded on the surrounding beaches and wave overtoppoing above the seawall increased. This paper summarizes this situation and shows further measure to prevent from beach erosion and wave overtopping.
On the Numazu Ushibuse coast located south of Numazu City a headland was built as a measure against beach erosion and beach nourishment was carried out at the updrift side of the headland. Beach changes after the completion of the construction of this headland was observed by aerial photographying and characteristic beach changes around the headland was studied. A part of the nourished beach was largely deformed by littoral drift. A method which reduces further beach changes is proposed.
In recent years, domestic sewage and industrial waste water are having a bad influence on water Quality of the Omura Bay in Nagasaki prefecture. Therefore it is need to monitor water quality and clean up the Omura Bay. In this paper, sea water of satellite observation are classified into water of the Omura Bay and water of the Sasebo Bay by maximum likelihood method, and currents of the Omura Bay are investigated. And the result are compared with currents in a hydrogeological model of the Omura Bay.
The experimental paper on a digital camera has been published by us in the Proceedings of Civil Engineering in the Ocean, 1994. In this paper, Standard CIE chromaticity analyses are applied to the mesurement of upwelling irradiance spectra expressed as transparency and suspended solid amounts using the digital camera and satellite (LANDSAT-5/TM) data. The results of these analyses serve as a basis for discussion of several problems (high and low altitude remote sensing techniques) in the application of chromaticity to water quality prediction.
The knowledge of tidal exchange out of a stagnant bay is often required in understanding the behavior of the water quality. Hiroshima Bay which is located deep inside the Seto Inland Sea is chosen as the subject area. A variety of Lagrangean methods are tested to give the best method to reproduce the analytical results. To test the validity of this method, the results of a numerical study is compared with a float dispersion study using the hydraulic model, demonstrating effectiveness of the numerical methods.
It has been reported that the seabed in the Akashi Strait, a crucial entrance to the Osaka Bay, has risen 5 m due to a recent major tremor, a scale believed to be certain to cause a major change in the residual circulation of the Osaka Bay. The present study investigates tidal exchange phenomenon carrying out a float dispersion study using both square-shaped model bay and Osaka Bay. The result shows that either embankment or seabed swelling does affect the major circulation and hence tidal exchange of a bay
The waterfront (Coastal Region) is situated at “the third land space”, which is neither land nor the ocean that surrounds it, and is a peculiar mix of land and sea. However there is no accurate definition in a technology sense. A study of salt damage as one of the environmental problems concerning the Coastal Region has been proceeding for a long time. A field investigation on the generation of sea-salt particles in the Kitakyushu Area was conducted to obtain fundamental data for planning the development of the waterfront (Coastal Region) from a complete environmental point of view. This paper presents briefly an outline for a method of investigation, precisely explaining about the field measurements and results of analysis.
In order to properly meet the requirements for enviromental conservation which will be more accelerated in future, there has been promoted the construction of the fishing ports as harmonized with nature that is to synthesize and materialize the concept for that purpose such as the design and execution of the structure and construction method harmonized with natural environment. This research presents, as a case study, a proposal for the section of a breakwater to be harmonized with nature for Suttsu fishing port, incorporating biological study.
Tokyo port is in innermost of Tokyo Bay which is the enclosed water. Kasai seaside park is on the east location of Tokyo port. This park are enclosed with Arakawa, Edogawa and Tokyo Bay, and mainly consists of the water. On this area, the shoals of old still survive and many organisms of sea live at present. This paper aims to investigate in the relation on the change of sea bottom and the organisms. We compare the shoals with the deep bottm or intertidal zone, and will find out the merit of the shoals.
The behavior of the fish school around the aggregation devices is evaluated numerically and experimentally. Numerical model of the fish behavior is based on the Sannomiya's model and is applied to the behavior of the Goldfish. In the tank tests the movement of the fish near of the artificial aggregation devices was analyzed by video system. Results of numerical simulation are compared with experimental results. Finally the attraction and repulsion parameters of the devices found to be a very important in estimating the the fish behavior.
In Japan, the improvement works of revetment and offshore breakwater have been promoted for coastal conservation. However, recently in the coastarea, there are occurring lots of problems such as increasing of oceaniction and draining of natural resources. To cope with such problems, it is inevitably required that the coastal structures are to be improved on a multi-purpose basis and on the other hand, the related facilities are to be improved in view of environment like fishery resources. In order to meet such social requirements, this Paper introduces a recommendable cross-section of the multi-purpose artificial reef which is observed most promising as a new model facilty for coastal conservation as well as fishery function.
It is known empirically that coastal structures such as breakwaters serve as foundations of seaweed beds. In recent years, various field experiments which aim to increase the ability as seaweed beds have been conducted so that the structures may harmonize and coexist with the surrounding environment. In this study, comparative experiments were conducted in Kutsugata Port and Oniwaki Port on Rishiri Island using ordinary concrete blocks and such blocks whose surfaces had been treated with ferrous sulfate, in order to determine differences in the ability to enable seaweed to take root. A roughly equal ability was determined for the two types of block when measured two years after installation.
The field survey on the growth of marine organisms on silt curtain was conducted on the site of Tokyo Bay, District K. Blue mussel was superior in numbers among the marine organisms on silt curtain. The average unit weight of the growth or the fouling on each side of curtainis 25 .0kgf/m2. And the average submerged unit weight of that is 3 .0-5 .0kgf/m2. Those weight are almost the same as those of any locations aroud the coast in Japan. The species of marine organisms growing on silt curtain were investigated with reference to sea water pollution. The species were classified into two categories. One is the species which dominated in polluted/eutrophic water. The other is those which dominated in clear/oligotrophic water. Accumulating the field survey on the fouling, indices of marine organisms on sea water pollution would be found.
The purpose of this study is to disclose the best habitable conditions for marine organisms in man-made lagoon. From this view point, the following four test pieces of construction materials, i.e., concrete, granite, andesite and sandstone were set in the field both in man-made lagoon as well as in natural one respectively. It is found that the numbers of species of marine organisms vary with the characteristics of the materials and also concrete is recommended for the construction material of man-made lagoon.
Nowadays people enjoy a variety of sports and recreations on frozen surfaces in winter. It is important to estimate the bearing capacity of an infinite ice sheet in order to ensure their safety. In this study, (1) we show in charts and graphs the estimated bearing capacity of ice sheets obtained by the deflection of ice sheets per unit load without breaking the ice; (2) we obtain an equation to calculate the bearing capacity of ice sheets with holes and indicate the results in charts; and (3) we describe in charts the critical traveling speed of loads moving on ice sheet when the bearing capacity is at minimum.
A design method for breakwaters on steep slopes has not been established, because the wave forces have been unable to be estimated accurately. In this paper, the stability of wave dissipating blocks and wave forces acting on breakwaters on steep slopes have been investigated experimentally. The common formula is applicable in estimating wave forces acting on breakwaters covered with wave dissipating blocks, but under some conditions, a stronger than usual wave pressure acts. When the incident wave height is large relative to the water depth, the blocks at the end of the slope suffer great damage.
In Hokkaiko pack ice usually reaches the area along the coast freeze over. Ice floes intruding into Wakkanai harbor cause cancellation of ferry services to and from the islands, and in Nemuro harbor fishing boats cannot leave to go fishing. Therefore, There is a call for the development of measures to prevent intrusion of ice floes into harbor. The authors have developed sink-and-float type ice boom SFIB for the purposes. In this study the authors report on the ice forces acting on SFIB.