A new typeofdissipaterofreflected waves from vertical walls was proposed. The sectionofthis dissipater is very simple, which comprises a vertical barrier on the front and a vertical wall on the back. Performance of this dissipater was examined experimentally and theoretically for both regular and irregular waves. The dissipation mechanism of reflected waves is to enhance the vortex flow under the front curtain wall by the piston-mode wave resonance in the water chamber. Major advantage of this new dissipater is to be able to decrease the breadth of the water chamber, say 1/10 of a wave length. Therefore, it is possible to dissipate much longer waves by the new dissipater having the same size as the conventional perforated type. Another advantage may be easy berthing of ships to the dissipater because of a flat front wall without any holes and slits.
Applicability of liner and second order solutions of wave field inside and outside a rectangular harbour is investigated. The matching conditions are used without any simplification. The normal derivatives of the forced waves have unreasonable characteristics along the boundaries.This comes from the Gibbs phenomenon in the linear solution. But the linear waves calculated on the lines through the matching points have good agreements with the results with boundary element method concerned with the harbour resonances.
Breakwater caissons with armor blocks are builted at so many places. It is very simple structure that it has armor blocks in front of caisson. It needs a lot of blocks where it built deep sea, because armor blocks setted by gentle slope.Then it needs high-cost. Setback parapet breakwater caisson with cylindical piler is one of this type caisson, but top of armor block is lower and parapet was setted back from caisson face. The parapet is pressed by impuct breaking wave pressure becouse it is not covered by armor blocks. Then cylindical pilers gain wave force for parapet. This paper reports typical wave pressure distribution of this type caisson in case of instability.
This paper presents wave transmission and reflection characteristics of a vertically slitted permeable breakwater filled with used automobile tires. A numerical model using the boundary element method is developed. Resistance coefficients for both the region filled with used tires and the slitted walls are determined through matching wave transmission and reflection coefficients obtained from hydraulic experiments with those from numerical computation. The numerical results agree reasonably well with the experimental ones.
The Submerged Breakwater has been used in compensation for detached Breakwater. Occasionally the bottom of Submerged Breakwater was partially scoured. In this paper, the characteristics of bottom pressure behind the Submerged Breakwater was investigated experimentally. The main conclusions were that the range of bottom pressure was 0.6times of wave height, and at wave trough the base pressure was nearly hydrostatic pressure.
In order to reduce secondary effects caused by high reflection waves from conventional curtain-walled breakwaters, a double-walled breakwater consisting of a permeable and impermeable walls was newly proposed. Inclined plate array with the same draft as a rear wall was used as the front wall. Effect of the inclination angle of the plate array on the wave transmission and reflection coefficients as well as energy dissipation ratios was extensively examined. It was confirmed that the front wall comprised of the plate array with downward inclination angle is more effective than the one with upward inclination angle.
The purpose of this study is to clarify the time-related fluctuation of wave overtopping discharge on seawalls by random wave using many experimental results until now. Seawall shape with the object in this study are upright seawall, upright seawall with set back parapet, perforated upright seawall and gentle slope-type seawall. To begin with, representative wave overtopping discharge by the definition equal to the representative wave height was obtained for these seawalls. Next, the shape parameter as the weibull distribution applied appearance probability distribution of wave overtopping discharge of individual wave was required. In addition, the relationship between this shape parameter and the relative water depth, wave steepness, relative crest height, wind velocity, etc.are discussed for the case of each seawall.
This study is to investigate, experimentally and numerically, wave-induced flow inside and around a porous structure. Laboratory experiments were conducted to visualize the wave-induced flow field. Numerical simulations were also performed for quantitative investigation of the flow and its governing quantities. The calculated wave height distribution is confirmed in good agreement with experimental result. Flow passing through the permeable structure is also confirmed in both experiments and computations. Moreover, it is found that the flow near the corner can play an important role on overall flow field inside and around the structure.
This study investigates the characteristics of the vortex and the velocity field around a submerged breakwater utilizing flow visualization by PIV technique. From experimental observation, it is found that the Triple type breaking causes energy higher rate dissipation than the Plunging breaking. In addition, the steady vortex is generated at seaward edge of the submerged breakwater in case of the Triple type breaking. That is, the structural vortex on the crown strongly depends on the breaker type.
This study focuses on the shock wave pressures on a wave dissipating caisson with semi-circular hollow projections in front of the wall, both theoretically and experimentally. Through a series of experiments in shallow and deep sea wave conditions, the model of the nonporous semi-circular wall reduces the shock pressure by 20-30% compared with the ordinary caisson of vertical wall and porous type reduces more. Especially in shallow sea wave conditions, the least shock pressure are obtained when the opening ratio is 30%, the value of the shock pressure is approximately 45% of the same on the vertical wall. A theoretical model of the shock pressure proposed for the porous semi-circular wall is verified through the experiments.
Twin-Tower Pier was designed as a new type of pier for a bridge which is constructed at deep sea site. The feature of the Twin-Tower Pier is two slender towers that are enable to reduce the volume of the concrete, resulting the reduction of the construction cost. Tidal current forces acting on the Twin-Tower Pier had been measured by the hydraulic model test in previous paper because the shape of the pier is more complicated than the shape of a conventional pier which is usually a column type. This paper describes the numerical simulation which is modeled to predict the tidal current force on the Twin-Tower Pier without using hydraulic model tests. The tidal current forces predicted by the numerical simulation are compared with those measured by the hydraulic model test. The comparison between them shows good agreement with the error level of less than 10%.
In order to make clear the feature of vortex shedding which is generated from the edge of oil boom's skirt by waves, velocity vector and vorticity fields around the skirt have been measured by using PIV. For the first step to develop a new oil boom which is possible to useunder strong weather in waves, the oil boom has been simulated by fixed thin plate in present experiments. In thetypical case that the draft of thin plate is6.5cm which is 1.5 times comparing with the draft of D type oil boom, itwas found that there was a difference of vortex formation between the front region and the back one separated with the plate. Especially, in the range of high frequent incident wave, the vortex shedding which is formed in the front region approaches to water surface.
With rapid progress of computer technology, direct wave simulation techniques based on CFD (Computational Fluid Dynamics) have been applied to practical problems in coastal and/or port and harbor engineering. A numerical wave flume, which is considered one of the representative direct simulation techniques, has been expected to substitute for hydraulic model tests. In this paper, we consider characteristics of wave transformation on a reef, as one of the applications of the numerical wave flume to coastal structures. By observing its numerical results and comparing them with the experimental results previously obtained, we discuss its applicability to wave transformation on a reef.
The horizontal plate has usually been used for coastal and ocean structures, such as an upper slab of pier and a buffer structure around a bridge pier. And there have been also a lot of research on the use of horizontal plate for submerged breakwater against beach erosion and artificial sea bed for the fish-raising industry. Much effort has so far been devoted to the research of wave fields around a horizontal plate, especially about the impact force to pier and the wave deformation around submerged horizontal plate in terms of the design for the structure. However, the flow pattern around horizontal plate in a wave field has not been explicated. The current study has attempted to numerically analyze some of the wave fields around a horizontal plate. Based on the results of this study, this paper discusses the characteristics of the evolution process of fluid motion and eddy motion around a horizontal plate.
A new wave barrier named ‘L-Type Curtain Wall Wave Barrier’ is developed and its function is studied using a numerical wave flume. The wave barrier comprises a curtain wall and a horizontal flat plate to reflect incident wave effectively; the transmission coefficient of the new wave barrier even with its relatively small width B and small submerged depth d is very low compared with a curtain wall or with a horizontal plate. The calculations were made using the numerical wave flume which is under development by a special research group including the authors. The calculation with its animation can clearly show the mechanism of wave reflection and wave energy dissipation.
The purpose of this study is to numerically investigate the wave control effect of two trains of submerged breakwaters located a certain distance apart and the non-linear interaction between the breakwaters and random waves. The numerical method is the so-called boundary integral method in which Green's Identity Formula is used for the expression of the velocity potential of wave motion. The reflection coefficients are calculated for several cases of the two trains of submerged breakwaters, and for a single submerged breakwater which has the same width as the width added up the two train of the submerged breakwaters as well. The power spectra of the water surface oscillations behind the submerged breakwaters are further calculated for each case. By comparing the reflection coefficients and the power spectra of the water surface oscillations, it is found that two trains of submerged breakwaters is more effective on wave control than a single submerged breakwater.
The results of the spectral analysis for field wave data indicate that a lot of wave spectra show multi-peaked forms. The multi-peaked spectral waves affect the tranquility in a harbor, the construction plan of marine structures and the motion of a moored ship. However, the characteristics of multi-peaked spectral waves have not been well known. The present paper investigates the occurrence characteristics of directional random waves with multi-peaks through the statistical analysis of directional spectra. The directional spectra are computed from field wave data observed off Omaezaki for one year. The appearance probability of multi-peaked spectra occupies more than 30% on yearly average and the correlation analysis shows that the correlation is high between the significant wave heights of short and long wave groups which are components of multi-peaked spectral waves.
Stability of concrete armor units with tight interlocking on the rubble mound was examined experimentally for both regular and irregular waves. Especially, focusing on the reflected waves from the sloped mound, stability of the concrete units against waves is discussed, such as the reflection coefficient from the sloped mound and the relation between the displacement of the unit and spatial variations of partial standing wave height on the slope. By using the damping wave theory, wave height distributions and wave forces on the concrete unit about the sloped mound were also examined theoretically. It was pointed out that location of the node and anti-node of standing waves on the sloped mound is closely related to the displacement of the armor unit, especially for regularly placed units.
This paper shows the new machine to generate compressed air automatically by water waves. First, the new hydraulic turbine is devised which is rotating toward only one way by wave forces going and returning with using two one-way ratchet gears. This turbine can work as well as a common water turbine for one way current. Then, a new compressor cylinder is shown having the new crank mechanism converting a rotating motion into a reciprocating motion through a connecting rod moving straightly by employing the hypo-cycloid technique. With installing this compressor cylinder to the devised turbine, compressed air can be generated by water waves. Finally the laboratory experiments have been done to examine how the compressed air can be generated and injected into water automatically by using this mechanical system. From the experimental results, we expect that this mechanism can be applied in fields to generate compressed air for abstraction of natural wave energy and air bubble curtain in sea water for improvements of coastal environment.
The concept of the excavated channel at Shimokita arm is considered to increase the tidal exchange between the innerpart of the Mutsu Bay and the open sea.The change of flow velocity is calculated by FEM under two conditions with and without the excavated channel.In additions, the utilizing the excavated chamel as seaway gives the possibility of the reduction of carbon dioxide emission and energy consumption due to shortcut of seaway route.And, the possibility of reduction of goods movement cost is also investigated in the paper.
To understand the environments of water quality, sediments and ecology in a coastal sea area, the characteristics of coastal currents must be clarified, In this study, we analyzed observation data of flow velocity and wind velocity in Tomakomai Coast including the area of Mukawa River mouth. Along Tomakomai Coast, a strong south-west or south-east wind often cased eastward or westward currents parallel to the shoreline in winter. Flow velocity in offshore of Siraoi Coast was strong and more than 30cm/s at a depth of 50m. In both summer and winter wind occurred currents parallel to the shoreline.In summer, fiow fluctuations with the period of about one day were occured by sea and land wind.
There are currently offshore oil and natural gas drilling projects being carried out in the Sea of Okhotsk near the northern part of Sakhalin. Following a small-scale oil spill that occurred soon after oil production started due to a detached hose on the oil deserving tanker, there has been an increased awareness of the risk of a major oil spill affecting the coastal areas of Hokkaido on both the Japan Sea and Okhotsk Sea sides. The recovery of spilled oil in the sea is greatly affected by weather conditions, sea condition and the viscosity of the oil. Authors have developed a new efficient method for the recovery of spilled oil, and basic experiments were carried out in this study to test the effectiveness of this method.
There are currently several offshore oil and natural gas drilling projects being carried out in the Sea of Okhotsk. Therefore there has been increased the possibility of the ocean pollution of the coastal areas of Hokkaido on both the Japan Sea and Okhotsk Sea sides. Oil spilled from the oil tanker Nakhodka was recovered using buckets lowered from grab dredgers and self-propelled grab barges. This method of oil recovery was effective, but one problem was the large volume of sea water collected in buckets together with the oil. To resolve this problem, the authors developed a new type bucket with many holes in the bottom. The principle of the recovery method is to utilize difference in viscosity. This paper reports the recovery method for spilled oil by using newly developed buckets.
To find the characteristics of coastal sea surface temperature (CSST) variations in the Kuroshio/Oyashio frontal region, the calculation of the heat flux and the interpretation of satellite data are performed. The CSST and meteorological data from January through December 1995 are used to estimate the net surface heat flux and heat content for the Sendai Bay. The largest heat gain (+56 Wm-2) occurs in the Matsukawaura, where strong Kuroshio/Oyashio interaction produces anomalous CSSTs and wind is more moderate than other regions over most of the year. The lowest heat gain (+35 Wm-2) occurs around the Tashiro Island, where the temperature difference between air and sea surface is lower and wind is stronger. The heat loss is larger during winter. From the AVHRR and SeaWiFS data, the offshore condition between the bay and Eno Island is differentiated by Ojika Peninsula, with varying dominant current. It is shown that the temporal behaviors of SSTs are closely connected with the air-sea heatflux and offshore condition.
Offshore wind has potential to generate electric power at lower prices than other renewable energy. However it is said offshore wind generation is more costly than onshore. Therefore we verified power curves for time varying wind velocities offshore and on land, taking into consideration the difference of mean wind speed ratio, vertical distributions of wind velocity, and wind spectra of the offshore and land respectively. As a result we found that while the power curve for the land is worse than that for the offshore, they are inferior to the theoretical power curve as a steady velocity. Then we estimated power generation yields and costs for land and offshore wind farms by using the actual data i.e. the annual occurrence of mean wind velocities measured at the Port of Akita and Akita Regional Meteorological Observatory. Thus the annual energy yields depends on the ratio of mean velocity offshore to on land and the offshore is more competitive from 1.1 to 1.9 than the land. Furthermore, condition of being feasible is that the mean velocity offshore is twenty percent larger than on land. The paper also describes dynamic structural analytical results against wind and wave loadings as vibration characteristics of wind turbine system consists of blade; turbine, tower and sub sea base structure which become important to design the offshore wind farm.
This paper shows Fundamental experimental study on Deep seawater outfall. The result showed that condition of plume mixing, Deep seawater outfall is related to internal-Froude-number (Fr). Deep seawater has three characters. The characteristic of Deep seawater is higher purity, cold and nutrient-rich. Coastal environment is recovered isoyake by utilizing nutrient-rich or cold Deep seawater. A new technology essential for the control Deep seawater outfall.
Damage caused by ice floes drifting down from the Sea of Okhotsk has a severe economic impact on communities located along the coast of Hokkaido, particularly those located on the Okhotsk Sea side. The force closure of many harbors and fishing ports along the coast of Hokkaido during the winter also has a severe economic impact. However, the total economic losses in Hokkaido due to damage and closure of ports caused by ice floes has not been clarified yet. The aim of this study was therefore to clarify, through questionnaires and interviews, the totaleconomic losses incurred due to damage and closure of ports in Hokkaido during the passage of ice floes.
The plane pressure panel sensor has the capability of measuring manypressures inside a small area, and has recently been applied to evaluation of icepressure inice/structure interaction. However, it is not clear how the sensor responds to various test conditions. The purpose of this paper is to examinethe characteristics of the plane pressure panel sensor under various test conditions through loading tests, and evaluate its applicability to ice strength measurements.
Field indentation tests using medium-scale model structures have been conducted since the winter of 1996. In the winter 1998 tests, two-dimensional pressure sensing panels were first installed on the face of the indentor. These panels clearly showed actual contact area, ice pressure distribution and movement of ice force location on the indentor surface during interaction. Ice flaking failure associated with a thin line-like contact area was observed from 3-D plots of pressure data in tests with an indentor velocity of 3.0mm/s. In the winter 1999 tests, a spring system (spring constant 15KN/mm) was first installed in the model structure to simulate a vibrating structure. These tests showed structure stiffness difference causes different manner of ice failure.
In cold region, the design load for offshore structures is often given by first-year ice ridges, it isimportant to obt ain knowledge about ice ridge, especially consolidated parts, in designing offshore structures. However, the physical properties and strength of sea ice ridge appear to be much more complex than those of undeformed ice or level ice. We performed a preliminary series of tests (unconfined compression tests) in the laboratory to investigate the strength and the physical properties of the consolidated part. In order to construct an ice ridge, cubic ice blocks of varies size (a) were place in the ice tank filled with salt water that had greater salinity than that of the ice blocks. After they were refrozen, using varies size core drill (d), we collected core test samples of varies sizes and various d/a ratio, due to combination (a) and (d). and then weexamined its physical properties and its strength characteristics in considerations with the size effects.
Development of oil and natural gas deposits off Sakhalin's northern coast in the Sea of Okhotsk is currently under way. An accident involving a spill of crude oil or other effluents during the current development of the oil and natural gas deposits off the eastern coast of northern Sakhalin could be expected to affect the environment and economy of the Hokkaido's Okhotsk and Pacific coast. This paper describes a recovery method for spilled oil under a pack ice field established through a systematic experiment.
Many rivers flowing through the cold region are ice-covered in winter. At these rivers, the phenomenon that a group of ice foes accumulates in the river section, during the process of ice-cover and break-up, occurs. And this phenomenon called ice jam. The ice jam makes the decrease of section product of the river, and cause a flood. Moreover, when ice jam is made at the front of the river structures, it acts the ice force and produces localized scour of river bottom and causes collapse of structures. This phenomenon is indispensable condition for the design of river structures constructed at cold region. When the ice floes arrive at floating obstacle, the ice floes will either submerge under the obstacle or remain at the edge of the obstacle. The submerged ice floes form the ice jam. This paper reports the study on the stability of ice floes at the edge of the obstacle that have important meaning in the process of ice jamming.
Ice scouring is a phenomenon which occurs when moves in contact with seabed. It has been reported tohave caused damage to communication cables and water intake pipelines. Therefore, it will be veryi mportant to estimate rational maximum scour depth due to complicate behavior of ice, and will also bevery important to evaluate forces acting on sea bed and stress that is transmitted via the seabed andd eformation of soil. We have developed the rational experimental device system as compared to previous device system. Under the renewal conditions, we conducted a lot of test series, and werevealed relationships between iceforces and beha vior of ice, variations of its behavior due to varies condition (attack angle, travellingvelocity). And we also revealed the probability distribution of some random variable under the same experimental condition.
Model tests were carried out at an ice tank to study the dynamic responses of an off-shore structure interacting with an ice sheet. A specially designed apparatus was used to simulate dynamic characteristics of the structure. Tests were made for a wide range of interaction speed of 4 to 500mm/s. Three modes of structural responses were observed depending on the interaction speed; they are quasi static responses, steady-state vibrations and small response. Discussion is made on the speed and acceleration of the structure under the steady-state vibrations and the transition between the steady-state vibrations and small response.
Model testing at an ice tank is an indispensable tool for the design of offshore structures or ships to be used in ice. Model ice is used to represent sea ice at model scale. Mechanical properties of model ice should be properly scaled down from those of sea ice so that results of model testing in ice are of significance. This paper discusses mechanical properties of model ice based on data obtained at the ice tank of Ship Research Institute.
Field indentation tests to measure ice load have been conducted at Notoro lake in Hokkaido, using an indentation test apparatus. Test data and observations on failure of an ice sheet (first-year ice) have been accumulated. The failure of the ice sheet is discussed based on the observation of the contact surface between indentor and ice sheet. The simplified model for flaking failure is proposed under the assumpution that the failure continues at constant shear strength of the ice. The model roughly matched the flaking failure of the ice sheet in the field test. Cleavage cracking criterion and bending failure were also discussed in relation to fracture toughness and Euler's equation.
An experiment is conducted to clarify the mechanism of damage of gentle-slope sea dike constructed near the shoreline. Damage proceeds in the order, vanishing of sands on the slope, damage of foundation works, piping of backfilling stones, subsidence of armor units. The gentle-slope sea dike was the most easy to receive damage when it was founded in shoreline. It was considered to be one reason to cut the embedded depth of foundation works in shoreline by half of offshore side. The scouring depth in front of foundation works was the largest when the sea dike was founded in offshore side. Though the precise solution to the effect of slope on scouring depth could not be obtained, the maximum value of it predominated in case of 1/3 slope.
Large floatings tructures are expected to be among alternatives for ocean space utilization in deeper coastal area. It has been reported that elastic response is dominant over rigid motions due to their large dimensions with comparatively small bending rigidities. The elastic response must be decreased in order for the enhancement of the rate of operation and the applicability to severer sea area.L-shape attachment structure which is attached to the weather side of the floating structures is especially investigated for this purpose here. First, the attachment structure is experimentally shown to be effective from the viewpoint of vertical response. Numerical calculations are also conducted by use of rigorous numerical method proposed by a part of the present authors. It is shown that the numerical results have a good accordance with the experimental results. In order to clarify the response reduction mechanism, numerical studies are carried out.
As became clear in the Hansin/Awaji earthquake of Jan.17, 1995, the access from the sea to the areas struck by disasters may be an effective alternative way for emergency and first aids. Therefore we proposed the design concept or a permanent floating emergency facility through the quayor wharf of areas suffered from the natural disastfer such as earthquakes at the symposium of Civil Engineering in the Ocean last year. It was a kind of floating structure such as a Quick Installation Platform (QIP) or a self-elevating platform for Shimizu port in Miho bay where a tsunami up to 4 meters is expected as a result of the likely Tokai earthquake. In order to confirm our concept from a viewpointof safety such as deck wetness, stability of the structure against tsunami forces, we conducted a 1/38 scale model testin both (usual) semi-floating and (unusual) lifted condition. In consequence, it turned out that the facility couldn't stand or the tsunami up to 3 meter in the semi-floating condition; therefore it is necessary to elevate the deck to afvoid tsunami forces. To do this, the deck must be elevated duringarrival time to the facility from the epicenter.
Tsunami is brought about an earthquake in the bottom of the sea. Tsunami's wave height becomes higher in shallower sea. Under that condition, Tsunami is considered as shallow water long period wave. Wave load from Tsunami has much influenced to the motions and mooring tensions of a floating structure in offshore area. For this reason, wave load from Tsunami is essential to planning protection against calamities. Since, an estimation method on Tsunami wave exciting forces in the stage of basic design of floating structure has been presented in this study. Summaries of this study are shown as follows; 1) A concept of solitary wave corresponding to Tsunami has been proposed. Tsunami wave exciting forces can be calculated with lessor labor. 2) The effects of Tsunami wave loads have been made clear comparing two kinds of calculation results. The former is calculation results with Tsunami, the latter is calculation results with wind waves.
This research is concerned with the characteristics of wind velocity on through the measurement of wind velocity of nearby sea surfacec ontinuously by using a multichannel anemomaster. The main conclusion from this study is as follows; t he coefficient of friction calculated by assuming Karman constant as 0.4 ranges between 0.01 and 0.07. Furthermore, there is linear relation between roughness parameter and the coefficient of friction.Wind velocity fluctuation spectra showed that it differs depending upon the height from sea level. A strong eddy occurs at the back of a floating body when the wind velocity measured used in numerical modelling the response of the floating body, which implies that this fact must be taken into account in wind load estimation.
We proposed small sized wave energy converter system named Heave & Pitch Buoy Wave energy converter system (HPB) using two rotary vane pumps to applying for 5-10kw class, which will be adapted to set at T=4-6sec, 4.5m sea depth for personal use and energy-supply for developing project of deep sea water. It has been developing by demand of economical market study of Center of Business Creation of OTARU Univ. of Commerce. In this paper, we examined the characteristics of this HPB to use 1/15 scale model subjected wave channel by using parameters: T, pump torque, wave height. This HPB system has 2 rotary vane pumps for getting Heave and pitch energy individually. In these experimental parameters, we observed that energy efficiency of HPB system was about 63% maximum.
In open sea region with severe wave attacks, a breakwater covered with wave-dissipating blocks have been widely used. However, the application of this breakwater at greater depths implies the increase of construction costs because it requires a large quantity of wave-dissipating concrete blocks. Therefore, the authors developed a new type of breakwater. This breakwaterconsists of wave absorbing caisson and sloping top caisson. In this paper, through the sliding experiment of this new type breakwater using a 1/60 model, we prove the stability and define the hydraulic characteristics of this breakwater.
A Flaring Shaped Seawall (FSS) can make reduce crest height rather than conventional seawall in rough sea. However, the FSS has not been sufficiently made a study of application for road seawall in the neighborhood of shoreline.In order to clarifyt he hydraulic characteristics of the FSS as road seawall in that sea, two-dimensional wave experimentsw ere carried out, and wave run-uph eight, overtopping rate, pressured istribution and others were measured.It is confirmed that the characteristics of the FSS are more superiort o the verticalw all, and that are almost similar to the vertical wall protected with block mounds. So it is found that the FSS is suited to road seawall without wave-dissipating blocks.
Wave forces on a curtain-walled breakwater of gravity-type were dealt with experimentally and theoretically. Using the two different super structures such as a rectangular body and a thin wall, characteristics of wave forces on these super structures and submerged mound structures were examined extensively. The thin-wall super structure is adopted as a simplified model of a curtain-walled breakwater. Stability test of the breakwater against waves was also carried out. From the comparison between the two results regarding wave forces and breakwater displacements, major factors relating to the stability of the breakwater were clarified.
This paper describes the development process for tension legs type Submerged Floating tunnels (SFT) in shallow water. SFT is a completely new type of tunnels, unlike anything ever seen before. SFTs have attacked attentions as a new access to solve the problems not adequately dealt with by conventional structures. But, there are still many unknown factors, as no such structures. Therefore, Hokkaido University, Hokkaido Development Bureau and the Society Submerged Floating Tunnel Technology Research have studied on SFT technology, such as, design methods, tunnel structure, mooring systems, foundations, its construction in this several years. So, we are able to develop the design and construction methods for tension legs type Submerged Floating tunnels in shallow water.
A model experiment is conducted to investigate water-exchange performance of newly-developed breakwater with vertical slits. It is confirmed that a large amount of water can be introduced to the backside area of the breakwater. Variation of submergence area of the slits due to tide change has no significant effect on the waterexchange performance of the breakwater, which is advantageous for the breakwater to be used in the large-tidechanging inland sea. Also conducted is a model experiment for a vertically water-mixing wharf, which shows more than the amount of surface water obtained in the breakwater experiment is introduced to the bottom layer in front of the wharf.
Deterioration of water quality becomes severe problems in some harbors because the circulation of water in the enclosed region by breakwaters is weakened and exchange of water becomes inactive there. Submerged breakwaters and floating breakwaters have an advantage over the impermeable breakwaters in that they can more easily exchange water. However, they are not effective to maintain harbor tranquility. We have already shown that breakwaters with slope-type channel and step-type channel effectively reduce transmitted wave height when compared with a straight-type channel. In this study, the flow rate through the breakwater with channel is examined by experiments and numerical model to investigate the effect of channel in tidal current. It is found that the flow rate can be estimated from the non-linear Darcy's law where the difference between the water surface levels in and outside of the harbor plays an important role.
The beach profile will be influenced by the on-offshore movement of the longshore bar. The rate of littoral drift and the hight of longshore bar was surveyed by the field observation. It became clear in this paper that distances from a longshore bar to a shoreline and a bed equilibrium point were given by water depths of them.
Observation of an internal waves was carried out by a baymouth of the Ishikari bay. In order to ask for the internal wave height of the Ishikari bay and the Shakotan peninsula circumference ocean space, the Coriolis tank was used and Hydraulic model test was carried out. Consequently, the internal waves of a reverse phase angle was observed the almost same period as tide waves in the 40m of the maximum wave height. Moreover, internal wave energy concentrates and the ocean space of 80m or more of wave height accepted to the Ishikari bay and the Iwanai bay. By this investigation, possibility of upwelling utilization using internal wave energy was verified.