The distribution function of extreme wave heights is characterized with a new parameterγ50 defined as the ratio of 50-year wave height to 10-year wave height. The threshold criterion for permissible sliding distance is set such that the probability of total sliding distance over 0.3 m during the lifetime is less than 0.10. The Monte Carlo simulations are made for search of optimal design of caisson breakwaters. An extreme distribution with a large γ50 value demands a large caisson width in the location where the water depth is greater than about 2.5 times the equivalent deepwater wave height. In shallow waters, however, the effect of the distribution disappears because of the dominance of random breaking process. The optimal return period of design wave is 4 to 5 times the service lifetime in the offshore zone, but it becomes shorter than the lifetime in shallow waters.
In this paper, we investigated the severe sea condition around the Kyusyu-Yamaguchi area caused by the typhoon 9918 by using the wave hindcasting method. At the beginning of the investigation, the wind field was simulated by using the typhoon model (Myers' model) with appropriate parameters. Especially, the wind field on the Sea of Suou surrounded by the lands was carefully examined with the measured wind data, and was corrected in consideration of the influence of the lands. Based on the simulated wind field data, we simulated the sea conditions by using the third generation wave hindcasting model, WAM. As a results of the simulations, some characteristics of the sea conditions caused by the typhoon was clarified. In addition, we also simulated the sea conditions by using the first generation wave hindcasting model, MRI. This paper discussed the accuracy and applicability of the WAM and MRI models based on the observed records such as wave heights and periods as well as the directional wave spectra.
The coastal area around Hiroshima Bay suffered from the wide inundation due to storm surge and severe wind waves generated by Typhoon 9918. It is of great importance to investigate the causes of the inundation for the mitigation of storm surge disaster. The resent paper has made numerical simulations of the storm surge and windgenerated waves in Hiroshima Bay to check their reproducibility. Though the computation through Myer's typhoonmodel overestimated wind speed comparing with the observed one, the storm surge numerically simulated by the wind speed well agreed with the observed one under the consideration of the unusual rise of sea level at that time. The wind waves predicted by WAM model were much less than the observed waves. Therefore, the computed wave heights are revised to agree with the observation. The estimated area of inundation due to storm surge and waves quite well agree with the inundation survey area.
We have upgraded from the 1st generation wave model to the 2nd generation wave model, and the 3rd one (in the Jurisdiction Waves Prediction Upgrade Investigation). In addition, we have also upgraded from the shallow water significant wave method to the shallow water TOHOKU-II model for inner bays like Suo-nada and Ariakesea. In this time, the 3rd generation wave prediction model is applied to the upgrade of the waves prediction technique in the inner bays, and various problems on the shallow water region in the inner bays are examined. It is necessary to consider the tidal change for the waves prediction by the model on the shallow water region in inner bays.
Waves generated by ship navigation become a subject of discussion from the viewpoints of various utilization and ecological environment preservation in a coast. In the present paper, the method of numerical simulation for ship waves was applied to open sea with a constant water depth and a coast with straight, parallel depth contours in order to investigate characteristics of propagation and transformation of ship waves. The ship length is 76m, the breadth is 11.5m, and the draft is 2.5m. The ship sails on a straight course of 12m deep with a constant speed. The ship speed is changed to cover so that the range of Froude number at the sailing depth is from 0.6 to 1.2. Transformations due to shoaling and refraction occur when the ship waves propagate on the sloping coast. The ship waves are greatly influenced by the depth Froude number. When the ship speed is near-critical at the sailing depth, the maximum wave height exceeds 1.5m at the water depth of 1m.
A filed observation on waves and long-period waves were conducted at the nearshore area of Naoetsu port during winter. Water surface elevations and water velocities were measured at 9 points inside and outside the Naoetsu port. The spectral properties of long-period waves were investigated. Comparing between observed long-period and bound waves calculated from primary wave spectra, it is confirmed that the long-period wave comporment in the nearshore area is mostly free wave.
Numerical simulation method by applying wave ray theory was developed to predict wave field on the complex seabed topography. The distribution of wave height and wave direction around the shoal of spherical surface was predicted. The results were compared with the predicted distributions by parabolic model. Both results agreed considerably well.
The Boundary element method (BEM) implemented by the Green's integral equation is used to solve wave field governed by the Laplace or Helmholts equation. When the boundary is divided into small segments and the integral on each segment is performed by a numerical method, the boundary integral equation is approximated by a liner algebraic equation. Locating the singular point on each segment, a simultaneous equation is obtained and can be solved by use of standard matrix method. Usually a simple trapezoidal rule is used on the numerical integration on the segments, and it has suitable accuracy at least in the linear analysis. But when the method is extended to nonlinear analysis, much higher accuracy is needed in the integral of multiplication of the linear potential and its derivatives in the forcing terms of surface condition. In the present paper, we investigate the accuracy of boundary integral with the Legendre-Gauss quadrature.
This paper investigates the applicability of a few methods to evaluate wave forcesacting on a tower of wind power station installed on a composite breakwater. One method adopted here is toestimate that as the drag force, useing both velocity and elevation of overtopping waves calculated by Sugawara et.al.(1992). A comparison of wave forces by this method with physical model shows that the accuracy depends on the relative position between the tower and the horizontal surface hit by overtopping waves. It can indicate suitablepositions for installing a tower. Furthermore, Goda's experimental formula is applied for a test as well as a numerical wavetank model with VOF function.
The construction of the wind farms in Japan has been planed nearshore such as oncaissons of a harbor. However several offshore wind farms have already been constructed in European countries.Since oscillations of the offshore wind turbine have potential of fatigue damage to the wind turbine structures, itis necessary to appropriately select from various sub sea base structures such as a mono-pile, a caisson and a jacket, corresponding to the soil condition of the foundations, water depth and environmental condition so on. Here weconducted the time domain structural analyses for a blades-nacelle-tower-foundation system subjected to fluctuatingwind and wave loadings in order to examine the effect of the sub sea foundation to the vibration characteristics ofthe system. The foundation structures having the three (high, medium, low) level of flexural rigidity were analyzed. Asfor wind force calculations, two kinds of offshore wind spectra were used, while wave forces were obtained through Morison equation with the associated area and volume of a sub sea base structure. The paper describes theresults of dynamic analyses for the structural system in the operational and extreme conditions along with the naturalperiods of the structural system.
A Flaring Shaped Seawall (FSS) can drastically reduce a crest height and waveovertopping quantity incomparison with a conventional upright one. In this study, systematic hydraulicexperiments by irregular waves were carried out using a two-dimensional flume. As a result, a diagram to estimatethe crest height and overtopping rate of the FSS was made, and it is found that the overtopping rate and reflectioncoefficient of the FSS are almost similar to those of an upright seawall covered with wave-dissipating blocks. Furthermore pressures by regular waves were compared with ones by irregular waves, and a wave force formula for the FSS in an extreme shallow sea was investigated.
The purpose of this study was to clarify the characteristics of reflected wavesabout the new type structure for wave control (under water strutted structure system with fin memberson the front pipe piles array). The parameters of hydraulic model test about fin members were setting angle inplane, setting range in water depth, opening ratio of the front pipe piles array with fin members, etc. The main results of this study are that the characteristics of reflected waves aresimilar to slit wall caisson, the rational setting angle of fin members in plane is 90 degrees to thedirection of incident waves, and the rational setting range of fin members is 60 percent sea water depth, etc.
Recently, it has increased the case to be constructed the breakwaters where thewater depth is deeperand the wave height is greater. The authors developed a new type of breakwater.This breakwater consists of wave absorbing caisson and sloping top caisson. Through the model experiments, the wave force formula, the reflection coefficient, and the wave overtopping quantity weredefined. However, it was not defined the relation between the crown height and the transmission coefficient ofthis breakwater. When the crown height of the breakwater is higher it can be tranquil. Otherwise, thebreakwater width must be extended because of the wave force increased. Then, it is important to define therelation between the crown height of the breakwater and the transmitted wave height and find theappropriately crown height of the breakwater. In this paper, the authors carried out the experiments for several types ofbreakwaters by using irregular waves, and defined the formula for the transmission coefficient and the crown height of the breakwater to be required.
Floating breakwaters have been adopted in the comparatively deep sea area with a mild wave climate, such as inland seas. In that area, aquacultural facilities, such as fish ponds, oyster farming facilities and so on, are usually installed. The development of highly dissipative floating breakwaters has been devoted in that sea area for reducing reflected waves from newly constructed breakwaters and sea walls, which are usually adopted for protecting the newly reclaimed land from wave actions. In this study, a new type of floating breakwater intending to reduce both the reflected and transmitted waves was proposed. There are two major dissipation mechanisms presumed in this model. One is the wave slamming loss of the horizontally installed circular cylinders near the water surface in the breakwater. The other is the enhancement of vortex flows around the lower end of side curtain walls arranged with some spacing. Here, the piston mode wave resonance between the two side curtain walls is used for the enhancement. By the use of various sections of the breakwater, especially changing side curtain wall configurations, performance of each breakwater model has been extensively examined.
This paper is concerned with a numerical model of nearshore currents using one-equation turbulent model. In this study, a quasi-two dimensional model was proposed and applied to the vertical circulation in the surf zone. The present model was calibrated and verified by comparing with laboratory tests. First, the relationships among the vertical distribution of the turbulent length scale, eddy viscosity coefficient and undertow was investigated by comparing with the data measured in the small wave tank. Secondly, the present model was applied to undertow velocity measured in the large scale wave tank. Finally, the applicability of the present model was discussed
Abrasion of sand particles due to littoral drift was studied experimentally by large scale oscillatory flow apparatus. Abrasion of sand of 1.5mm in median diameter generates fine-grained sand with a wide range (2μm-1000μm) diameter. Fine-grained sand accumulates below the layer of sheet-flow sediment motion. The characteristics of vertical distribution of grain size are studied.
The diffusion of negatively buoyant jets issued horizontally was investigated experimentally focusing on the behavior in the impinging zone. The profiles of temperature were measured clearly and the shape of them that progress on the floor horizontally are Gaussian. The jet issued from the height of water surface dilutes much more than that from the height in the water. Dilution of velocity and temperature along the path of jet are presented as well as the thickness.
River transportation on Ishikari river has been proposed. But there are many technical problems to establish a system of river transportation such as seasonal fluctuation in water level, maintenance of a channel, bank erosion, accumulation of sand, effect on the fishing industry, problem of freezing, problems concerning loading, unloading and mooring facilities and so on. In this study the authors clarified salt diffusion caused by obstacles in two stratified flows
In the Nahotokha oil spill, which occurred in the Japan Sea in the winter of 1997, recovery operations using buckets hauled up by crane barges and grab dredgers showed good results. It was thought that this method would be more useful than other oil recovery methods for the recovery of high viscosity oil because crane barges and grab dredgers can operate even in rough sea, and crane buckets have proven to be effective for the recovery of oil of high viscosity. However, one drawback of this method is that a huge volume of water is collected together with the oil. A large storage pit and an efficient method for treating the polluted water are therefore needed. Thus, for effective utilization of the bucket recovery method, a method for separating oil and water and increasing the oil/water ratio is needed. Experiments were conducted in the present study to find an effective method for separating oil from seawater recovered using buckets in a low-temperature such as the Okhotsk Sea in winter.
Average depth of Lake Nakaumi is 5.4m in depth, and a lot of hollows of 10m or more in depth exist in the Yonago bay. The deepest place is 16m in depth. In Lake Nakaumi, a stable stratification with a halocline is formed by the density difference between seawater flowing in through the Sakai Channel from the Sea of Japan and freshwater from the many rivers which flow into the lake. This stable two layer structure produces a peculiar aquatic environment. The highly saline water mass below this halocline can easily become anoxic due to both weak vertical mixing between the upper and lower layer, and generate the nutrient release in the lower layer. It is well known that internal waves with a large amplitude of 2-3m and period of 24 hours are often driven by tidal and wind drift effects around Yonago Bay of Lake Nakaumi (Fujii, 1997). Then, we carry out the observation to detect the internal oscillation and flow and its effect on the vertical distribution of water properties, and found a dynamical relation between the internal oscillation and the anoxic water movement in the hollows. As a result, internal oscillation with a large amplitude of 2-3m and period of 20 hours are observed in the hollow and changed periodically. Therefore, it is though that the water of the hollow periodically creeps up towards the neighboring water regions by internal oscillation, greatly affecting the general water quality and biological environment.
Stirring-up of soft sea bed material in Osaka Bay were investigated through field observations and hydraulic experiments. Field observations were carried out at the point of 14m-deep and 15km apart from Kansai International Airport. The bed material size at the filed is 0.01mm in mean diameter. Echo Intensity data of ADCP were used to detect the stirring-up of bottom material induced by wave and current. The threshold value of current velocity for stirring-up has been estimated to be about 20-cm/s. The different properties of stirring-up between fine sand and silt were has experimentally been checked in wave oscillatory flow in t e wave channel. In less than 10cm/s flow condition, the fine sand was stirried-up easily with ripple formation. The silt needs fas er current for stirring-up because it could not move individually.
This research uses deep sea water ashore, when spraying the water on ocean again, it examines the effect exerted on the reproduction and the amount of resources of a kelp to which the high-concentration nutrient salts contained in deep sea water. And the numerical model considered the motion after water-drainage of deep sea water about the relation between water-drainage and the influence range. As a result of carrying out an early growth examination using the gametophyte of Laminaria religiosa, nitrogen conditions required for reproduction of a kelp were presumed to be 5.0 μM (The winter average nitrogen concentration of the Sea of Japan coast is 4.2μM) by the nitrogen concentration of winter. Furthermore, the year production density of a kelp became clear increasing with the increase in year average nitrogen concentration. It was quantitatively shown that draining deep sea water contributed to the reproduction and the production of a peripheral shore reef kelp bed.
Recently, the collapse of ecosystem balance caused by the dominant multiplication of single species is focused in various artificial tidal flats. In this study, it was investigated that the causes of extraordinary distribution of the chlorophyceae, especially Ulva sp. in Yatsu tidal flat, and the environmental factors composed with water quality. As the result, the ratio (CN/CP) on the concentration between NH4-N and PO4-P was estimated at the average value as 4.2 by the onsite investigation in two canals connected Yatsu tidal flat and Tokyo Bay. Otherwise, the optimum ratio for growth of Ulva sp. was detected as 4.25 by the culture experiment operated in our laboratory. It is considered for the reason to be extraordinarily distribution of Ulva sp. in Yatsu tidal flat, that the ratio in the field is similar value as the optimum value for growth of Ulva sp. The ratio control in two canals and the shift from the optimum value for growth of Ulva sp. are considered to be efficiency method for the restraint of the irregular growth/distribution of Ulva sp.
The thermal environment is one of the important factors for activities of various benthic organisms in a tidal flat. Seasonal observations of the thermal environment were carried out at the Koajiro and Ena tidal flats located on the Miura Peninsula. The measured surface temperature showed wide daily and seasonal variations. During the emersion period, the surface temperature increased to 35°C in the daytime of June and August, and decreased to 1°C in the nighttime of February. During the immersion period, the surface temperature was dominated by the seawater temperature. The accumulated heat in the surface layer diffuses the deeper layer. Hence, the thermal diffusivity is the most important parameter for describing the thermal environment in the sediment. The thermal diffusivity was estimated from an analytical solution of one-dimensional heat conductive equation. It was higher at a sandy tidal flat of Koajiro thanat a muddy tidal flat of Ena.
The artificial spawning material in which Japanese sandfish lays eggs was developed. The 1st purpose is development of the mitigation technology which complements a spawning function until natural seaweed is reproduced. The breakwater to which Japanese sandfish is laying eggs in the present at Tomakomai Higashi port will be moved in the future. The 2nd purpose is the technical development for adding the function of seaweed to a coast structure in the deep place of depth of water where natural seaweed cannot grow. The quality of the material is polypropylene of specific gravity 0.18. Therefore, it stands straight underwater by buoyancy. Although the form referred to the seaweed, the number of branches and the number of roots were made several times more than natural seaweed. Japanese sandfish laid eggs to all of the artificial spawning material installed in 2000.
In recent years, spawning of sandfish was observed in gulfweeds adhering to a breakwater in a sandy beach area of the Tomakomai East Port. This suggested that the breakwater served as a reef for sandfish to spawn on. This study focused on light and flows around a spawning ground of sandfish, for the purpose of adding a function as fish spawning grounds to breakwaters and other coastal structures. The study was based on the results offield surveys conducted in the Tomakomai East Port, where spawning on a breakwater had been observed, and in the Nemuro sea area, which is known as a natural spawning ground. As a result, it was found that gulfweeds were distributed mainly at depths where light attenuationfactors were over the approximate range of 0.05 to 0.09, although distribution depths differed between the Tomakomai East Port and the Nemuro sea area. Also, in spawning grounds of sandfish, the flow velocity at the time of adhesion of gulfweed embryos was considered to be of higher significance than that during spawning.
Wè considered that decreasing of the coastal area resources was due to concrete coastal structures that are unable to provide a sustainable habitat for living creatures. To overcome this problem, we have invented a new type of concrete which could suck and maintain plenty of water in it, and keeps the concrete surface under moisture condition. The current paper describes process of the invention as well as trial of the concrete applied to bank panel which may provides living spaces for crabs and eel.
Seaweed forests of Eisenia bicyclis Setchell and Ecklonia cava Kjellman are broadly distributed along the rocky coastal area of central Honshu Island, Japan, facing the Pacific Ocean. We aimed to clarify a process of zonation that are consisted of the two plants. We measured attaching force of holdfast of one-year old plants to the substratum in a field and fluid forces on the plants in a laboratory. Attaching forces of the holdfasts depended on a condition of substratum surface. Dominant fluid force excerted on one-year old plants was a drag force different from adult plants because of little development of stipe part. One-year old plants have attaching forces greater than the maximum fluid forces in situ estimated by the model.
Recently, the coasts which has environmental and biological effects, such as a sandy beach, tidal flat and rocky coast, have been drawing attentions in the field of coastal and environmental engineering. Accordingly, theplacement of artificial materials in an inorganic coast has been tried to enhance the worth of the coast in the environmental and biological aspects. As for artificial rocky coasts, which can be placed near a seawall or breakwater, most of them are superficial imitations of the nature. Because the micro-topography of a natural rocky coast is not taken into account in their designs, their biological effects are only a little. In this research, we investigated the micro-topography of natural rocky coasts, and tried to estimate their effects on marine organism. As a result, we clarified the effects of horizontal depressions, represented by a visor and notch.
How to prevent sucking in a large crowd of jelly fishes at intakes of sea waters is an old but still important problem for most of Japanese thermal-power stations which make use of sea waters for cooling, because they make us impossible to take waters, and will be a large amount of waste matters of which we must dispose. But, basic knowledge about jelly fish, such as their distributions and densities of a crowd, is not enough to design effective facilities that defend against jelly fish attack. We observed a crowd of jelly fish around our power plants, and got some knowledge.(a) Observed jelly fishes were crowded in the aria several hundredmeters around.(b) Most of jelly fishes were caught at lower layer that was about 8m below water surface and high salinity (32psu).(c) On and after rainy season, their size didn't change so much and frequency of appearance was getting small.
The purpose of this study is to establish the construction technique of man-made rocky coast with various marine organisms. From this viewpoint, the field observations on vertical distribution ofmarine organisms were carried out in three man-made rocky coasts at Osaka Bay and Tohban coast. As a result, the vertical distribution of marine organisms varies with the rate of seawater flow due to wave and current. And, between critical inhabiting height of marine organism and the rate of seawater flow, there is the linear relation approximately. It is suitable for the beach play in the place which faced the open sea side in the man-made rocky coast.
The interaction of surface and internal water waves with floating/submerged platforms was studied considering the nonlinear properties of the fluid motion and the flexibility of the oscillating plates. First, a set of nonlinear governing equations for the interaction between a multi-layer fluid system and floating/submerged elastic thin plates was obtained. In each fluid layer, the Lagrangian was integrated vertically taking the nonlinear boundary conditions on the interfaces into account. Then the variational principle was applied to yield a set of time-dependent, horizontally two-dimensional, fully nonlinear equations. Secondly, using this model, several numerical computations were carried out for the surface/internalong waves and the oscillations of horizontally very large platforms. The resonated pressure beneath the plate floating on the sea surface in the two-layer system was compared with that in the one-layer case. The surface/internal waves generated by the trembling of the floating/submerged elastic plates were also simulated.
An articulated buoyant tower developed more than fifteen years ago for offshore oil and gas development has often been used for marine communication tower in Japan. Owing to a set of universal joints at bottom and abuoyant tank attached to intermediate part of the tower, the tower rotates small against rough waves; however it isaffected to the tidal changes, thus the height of a navigation light on the top of the tower from sea surface varies. So we designed the new buoyant tower having a slide beneath the joints, which permits amount of vertical movementso as to keep the height almost constant. Therefore we conducted the time domain analysis for the pitching and heaving motion of the vertical movable tower to the waves, currents and winds. In this study, we intended to make clear the both effect of the nonlinear drag damping which caused by the relative velocity between tower and water particle and the natural periods to the response. The paper describes the nonlinear effects of the damping caused by the wave and current to the response characteristics for the towers installed at the three kinds of water depth, along with the changes of the natural period in accordance with the draft and inclination of the tower.
In case of submerged floating structures moored by inclined tension legs, unpredictable slack and snap are occasionally observed in experiment under severe wave condition. The authors assume that the nonlinearity in restoring force is caused by the self-deformation of tension leg, usually called catenary curve, decided by the balance of self-weight and buoyancy of leg. In this paper, the non-linearity in restoring force is investigated first with varying the self-weight and buoyancy as well as the inclination angle of tension leg. The effects brought by the non-linearity in restoring force on the dynamic characteristics of SFT is discussed and the dynamic response of SFT due to wave is compared with those assuming its linearity. As a conclusion, how the non-linearity affects on the dynamic response of SFT is reported as well as some important findings.
While floating structures have many advantages such as environment-friendly, their rolling vibration caused by waves makes people indisposed and stevedoring inefficient. It is necessary to improve working efficiency on them by reducing their vibration to spread floating structures. We have developed vibration reduction systems. This paper shows validity of those systems by numerical analysis and experiments, and design methods of them.
Field verification of the holding power of mooring anchors was conducted on a seabed composed of soft mud located in Tokyo Bay, Japan. The observed holding power of the anchors was compared with the estimates based on the current design. The holding power depends strongly on the properties of the seabed deposit, the type of anchor and the duration of service. The coefficient of holding power, which is defined as the ratio of the maximum holding power to the submerged weight of the anchor, was introduced to examine the effects of the loading rate and angle of the mooring wire of the anchors. Because of the action of the overturning moment, the effect of a loading rate was negligible for concrete block anchors with a loading angle of 45 degree or less. The coefficient of holding power was 0.6 or less for the above case. The holding power for suction anchors increased with the suction inside anchor. There was a weak correlation between the holding power and the loading rate for soft mud.
This paper discusses the characteristics of wave fields around the Double Barriers Floating Breakwater (DBFB) which is proposed as a new floating breakwater against wind waves or ship waves in a marina. The DBFB has a rectangular body and double vertical plates to make energy dissipation with vortex flow around the tip of plates. The current study has been attempted to analyze experimentally and numerically some of the wave fields around the DBFB. It is found that the DFBF is much more effective as a breakwater than the simple rectangular floating breakwater by hydraulic model tests. Moreover it is found that the vertical motion of the DBFB is smaller than the simple rectangular floating breakwater. The numerical analysis is performed, based on two dimensional linear potential theory and an energy loss model by the vertical motion of the DBFB. The numerical results have good agreement with hydraulic model test.
The water quality deterioration such as harbors might become a problem by demanding the public opinion of the environmental problem. There is a seawater exchange breakwater as one of the countermeasures. However, the seawater exchange function decreases in the point where the tidal condition. In this study, the seawater exchangable breakwater of the floating rubber body type was developed, and the characteristic was understood by the model experiment. As a result, it was found that it was a structural type with an excellent performance.
A midwater artificial floating reef is set in the middle layer of the depth from 500m to 1500m. The fish reef has a cylindrical shape. Its diameter and height are 2m and 7m respectively. The upper part of the mooring line is made of the wire rope with a diameter of 32mm. The lower part of the mooring line is made of the polyester rope with a diameter of 42mm. This fish reef rarely is carried away to the sea surface by the snapping of the mooring line. As this measure, the fish reef has the alarm sending device and sonar reflecter. However it is generally difficult to recognize to floating fish reef after sunset and the sound of engine hinder the warning sound. Further, the safety devices are not always normality operated by an attached organism. So, we have to consider the possibility of that the fishing boat has a collision with the floating reef. In this study, we investigate the collision force between the fishing boat and the floating reef on sea surface by the hydraulic model experiment.
Artificial reefs and submerged breakwaters have been constructed for protecting coast from erosion and replaced detached breakwaters. The construction causes topographical change around them, such as local scour and sedimentation. This study shows the result of opinionaire on the change and gives the analysis on the scour. The result shows that the scour relates with the width of structure spacing.
In harbours facing to the open sea, long breakwaters tend to be built to decrease wave heights. Also, it is cleared that the influence of moored ship motions has to be considered. On the other hand, ship motions at harbour entrances due to waves are one of the most serious problems in ship handling. However, ship motions near harbour entrances are not discussed and observed so much. Therefore, it is necessary to research on ship motions offshore and near harbour entrance. In this study, we observe ship motions during the navigation, entering to and departing from harbours. Ship motions are measured by the new type of measurement equipment consisted of GPS, optical fiber gyro and gyro compass. Observed data at the departure from the harbour shows that the rapid growth of ship motions can be recognized as the important factor, which causes the difficulty of ship handling near the harbour entrance. So, it is verified that harbours should be constructed and operated based on the numerical influence of ship motions due to waves near harbour entrances and offshore.
During the period of the rubble mound seawall construction there is no armor stones or concrete armor units to protect the structure against wave forces. Therefore, if the recession occurs during the construction period, it should be considered that the completion would be delayed. In this paper, wave basin test has been conducted in multidirectional random waves to investigate deformations of rubble mound seawall with pier head during construction. And a substitute plan that is able to shorten the construction period about three month is proposed.
Numerical simulation was enforced for the purpose of precision inspection of large-scale underwater structures installation system. Observation values by compound measurement system that used GPS and SONAR areadjusted by observation equations with constraints. Numerical simulation used observation values formed by BoxMuler method, and enforced comparison with adjustment results by the above-mentioned method. SONAR system cannot ignore sound speed changes that originate in water temperature changes in the real sea. Using the theory value of sound speed distribution that was supposed to typical water temperature day change, the precision of revision method was inspected. As a result, satisfactory performance for vertical distribution and day change of sound speed was confirmed.
A method has been developed for pouring hardened bottom mud into water. This method can be used for largescale projects at rates up to 1, 000m3/hr without polluting the seawater at the site. When it was first used for hardening and placing work in actual ocean water, 160, 000m3 was deposited in a short time at an average rateof 700m3/hr. Here, an outline and explanation of the advantages of this method are presented. Next, it was proposed that this method be used as earth cover material to cover polluted sea bottoms, taking advantage of the fact that the hardened material can be poured without polluting the ocean. To verify that this use would be effective, elution testing of nutrient salts and the like from the hardened soft clay wasperformed. The results confirmed that it could be used effectively as earth cover material restricting the elution of nutrient salts from undredged material.
Some methods regarding stress calculation etc. of a caisson have to be updated because they follow the former conventional ones. In this study, improvement of the structural design method to a caisson was examined on the following two points. (1) Reduction in the span length of wall and slab. (2) Effect of filling sand in a caisson chamber on bending moment induced in a wall. As a result, essential data to rationalize of structural design methods were obtained. The main findings were summarized as follows: (1) The span length of wall and slab could be reduced, because fixed supporting points existed in the haunch region. (2) Due to resistance of filling sand, bending moment of a side wall became smaller than that without filling sand when loads were applied to the wall. Moreover, diagonal pull-off tests were carried out on hooks for suspension of a caisson. The equation of design shear capacity of concrete around the hooks for suspension was reviewed, and a modified equation was proposed based on the test results.
The Performance-Based Design can be used as a method of rationally determining thesection of a breakwater. We have already proposed the designing method of the breakwater for two failure modes of sliding and settlement as well as its safety evaluation method. In this paper, the above methods are applied to a half-submerged sloping top caisson breakwater and the stability against wave action is studied, considering the applicability of safety indexes and the difference of the structural type. As a result, it is shown that there is the difference between each section designed by the amount of expected deformation, function loss probability, and life-cycle cost, for a half-submerged sloping top caisson breakwater. This result is different from that for a vertical caisson breakwater. Also, it is found that it is important to control the function loss probability, which is here defined as the occurrence probability of the breakwater's fatal damage.
A calculation method for static mechanical behavior of double wall type structure has not been established. In this paper, A numerical calculation method by stiffness matrix method is proposed to predict static mechanical behavior of double wall type structure. This proposed method applies theoretical equations that were obtained by Ohbori et al considering both the interaction between walls and filling material above ground and lateral resistance of walls under ground. Then, this method was considering elasto-plastic. behavior of filling sand and ground. The calculated results by this proposed method coincide well with the behavior of model structures in The paper of Ohbori et al. Furthermore, to apply this proposed method for design calculation and to evaluate the behavior of new type double wall structures, several double wall type structure models were calculated.
This paper is concerned with modeling for simplified analyses of Submerged Floating Tunnel (S. F. T.). The simple model that we proposed is a beam on elastic foundation. It is known that this modeling of S. F. T. as a beam on elastic foundation is applicable only to a limited range of support stiffness, spacing and flexural rigidity of the tunnel from the aspect of structural mechanics. If this modeling gives satisfactory solution for global behaviors of the structure, it is very effective for designers to assume structural dimensions and evaluate the basic characteristics quickly. In this paper we investigate the applicability of this modeling in applying the structural conditions and dimensions of really assumed S. F. T. to the condition of equivalence between S. F. T. and beams on elastic foundation. Furthermore, we consider the effects of boundary condition when this beam model on elastic foundation can be applied.
Through the rapid progress of computer technology, direct wave simulation techniques using CFD (Computational Fluid Dynamics) have been applied to practical problems in coastal, port and harbor engineering. A numerical wave flume, which is one of the representative direct simulation techniques, has been expected to substitute for hydraulic model tests. In this paper, wave transformation of bore on a reef, sand spit and lagoon is computed by the numerical wave flume. The applicability of numerical wave flume is examined through comparisons of numerical results with experimental ones.
The Multigrid method (MG) was applied to the 2D and 3D simulations for water waves on various topographies, and the efficiency in terms of computation speed was discussed in this paper. Purpose of this paper is to remove the limitation of computational costs for numerical investigations by introducing MG and to evaluate the availability of this numerical method for practical estimations in the actual wave field. The computational time and number of iteration that MG requires is quantitatively compared with the conventional Gauss-Seidel method (GS). It is found that the MG makes the computational time to save 90-95% for the two-dimensional simulation and 65-80 % for the three-dimensional simulation. Further improvement of the scheme is also discussed in this paper.