A time-dependent wave equation is derived so as to take into account the effects of currents and rapidly-varying bottom topography, based on the variational principle governing irrotational fluid motion. The derived wave equation is reduced to the equation of Kirby (1984) if there is no rapidly-varying bottom undulations. Some numerical computations are done, by using the equation, under the condition of constant slope with a certain current field.
The Boundary Element Method (BEM) implemented by the Green's integral equation is used to solve wave field governed by the Laplace equation or the Helmholtz. When a singular function of Source type is used to induce the integral equation, the potential on the singular point is represented by the boundary integral. And when a singular function of potential is represented by the boundary integral. Usually the former type of the integral equation is used in the normal problem of BEM. But in particular problems, wave field around thin structures or thin barriers, the latter type of the integral equation is useful. However the singularity of Doublet type singular function is very strong. Therefore for the Doublet type it is difficult to obtain necessary accuracy from the numerical boundary integral. In the present paper, we investigate the accuracy of boundary integral with the trapezoidal rule and with the liner approximation for both the Source type and the Doublet type singular functions.
The wave field governed by the Helmholtz equation with a constant depth and the linearized water surface condition can be solved with Boundary Integral Method implemented by the Green's integral equation. In this method, suitable boundary conditions should be established corresponding to the types of boundaries. The present paper proposes new boundary conditions for open boundary, partial reflection boundary and incidentabsorbing boundary. These condition do not depend on the incident angle, the number of wave components and the types of waves (plane waves and cylindrical waves). Numerical results show the complete validity of these conditions.
To control the wave field, several type of structures have been proposed, submerged plate and submerged breakwater, for example. Submerged flexible sheets are another example, which are composed of textile sheets fixed in frames with elastic springs. It was reported that the later one is more effective because of the resonant interaction between the motion of sheets and waves. An analysis of wave field around this structure has been proposed by Kato et al (1993) using a potential matching method in a vertical 2-D case. But it will rise a difficulty to solve 3-D case using the same method, because of the large number of unknown valuables. In this paper, a new method of analysis is proposed in which the boundary element method with a doublet type of Green function is used and the displacement of sheet is assumed to be half of sinusoidal function. In this method, the necessary number of unknown valuable can be reduced to only one for one sheet and frame system. the numerical results show the validity of this method.
Using vorticity equation and Poisson equation for stream function for governing equation, flow structure around a circular cylinder in water waves was calculated numerically. Calculated results were expressing appropriately the behavior of vorticity, stream line and pressure field. Next, fluid force acting on the circular cylinder was calculated using the values of pressure field obtained by numerical analysis. The coefficients CD, CM of Morison equation were obtained applying the Minimum square method to in-line force with time. Consequently, it was found that when Keulegan-Carpenter number, K. C. became larger, coefficients CD, CM were different gradually compare with these of potential flow.
In spite of occur usually wave breaking, it is defficulte to make clear its a phenomenon. Especially, breaker on the Submerged Breakwater is complicates by existence return current. This research is attemped to measureed velocity field using PTV (Particle Tracking Velcimetory) and carried out to elucidate its time-varied magunitude and direction. Moreover, we measured surface elevation around the circumference submerged breakwater at the same time and calculated the mean sea level.
Three-dimensional fluid velocity field in a surf zone was experimentally investigated to obtain spatial characteristics of mean flow, such as return current, and turbulence flow caused by wave breaking. It is possible that three-dimensional organized vorticities, generated after breaking, indirectly affect to mean flow and induce three-dimensional steady flow. In two-dimensional wave flume, return current contributes three-dimensionality of fluid motion in a surf zone. The effect of return current to a front bore is also investigated by the particle image velocimetry.
The shock pressure due to breaking wave caused by specific waves, which is not estimated properly using the Goda's formula, often occurs in case that the port structure has a steep slope on the sea bed in front of itself. The interior area of Suruga Bay has steep slope sea bed ranging from 1/3 to 1/5. The hydraulic experiment has been carried out to clarify the condition under which the shock pressure due to breaking wave occurs. The effectiveness and hydraulic characteristic of the submerged break water for reducing the wave pressure was investigated by the experiment.
The experimental results of the interaction among wave, current and a submerged mound have been reported in this paper. This study is carried out for the cases where the wave is propagating in the following and the opposite direction of the current over a submerged mound of parabolic cross section. The phenomenon is investigated for varying forced currents, mound geometry and relative water depths. It is found that following current amplify the wave height over the mound but reverse current over the whole domain. Other results indicate that current of both directions affect the wave characteristics significantly over the mound.
By solving eight equations with some approximations, we have found an explicit expression describing the energy flux at the breaking point in terms of wave quantities in deep sea. This expression enables evaluation of the rational and precise mean waves which are used in the littoral drift computation. This method is applied to the Yuriage coast by utilizing observed data over six years. Good correlation between littoral drift and the energy flux is found to fix the littoral drift coefficient.
A numerical model for the hydrodynamic pressure on submarged structure during earthquakes is developed by use of two dimensional source distribution method.A green's function satisfiying boundary value problem consists of acoustic wave equation in water, water surface condition and partial reflective bottom condition is newly derived. Property of wave reflection on bottom is estimated from sound speeds and densities of water and bottom material. Comparison with analytical result for vertical wall shows good agreement. Difference of reflection ratio according to bottom materials have much influence on characteristics of hydrodynamic pressure is shown.
Installing artificial fish reefs is expected to play important roles on improvement and preservation of sea environment as well as fish cultivation. As far as its effects are concerned, fish reefs should have adequate function to gather fish. In this research, the wave generated sound from fish reef is considered to be one of the most important factor to gather fish and the sound from fish reef models was measured by conducting laboratory experiments. Spectral analysis of measured sound shows that the vortex caused by wave and structure interaction generates the sound. The frequency, however, is much higher than that of vortex formation and behavior of vortex affects the properties of generated sound.
In this paper, characteristics of the wave control for vertical permeable breakwater with a horizontal slit at under still water level were investigated experimentally. In the experiments, the motion of sea surface wave facing a vertical breakwater, reflected wave and transmitted wave were measured. Relation between water surface displacement and the slit heights were discussed. And these relationships were compared with submerged breakwater of vertical wall type. It was clearly that the slit height having a good effect on wave control of permeable breakwater was determined.
A new concept of caisson having the function of water exchange and wawe dissipation is proposed in this paper. This caisson is a kind of a permeable slit caisson with a submerged vertical plate in a water camber. By carrying out the experiment, the following results were obtained; 1) The caisson is able to generate one-way flow from outer sea into habor. Consequently, water exchange is enhanced effectively. 2) The caisson has a good wave dissipating performance comparing ordinary caissons. In this paper, the design method of the caisson is also presented.
A new type of breakwater with a step-shaped slit caisson has been developed and some very fascinating results have been found.It was found that this breakwater has low reflection in a wider range of wave fre quency compared to conventional slit-type breakwaters.A numerical analysis which combines the method of matched asymptotic expansions with a boundary element method has been applied for calculation of the reflection coefficients for these structures.However the previous studies were on the condition of non rubble mound.The present paper focuses on the reflection coefficients of the step-shaped slit caisson on the rubble mound in order to apply the step-shaped slit caisson for practical use.
Scale effect was clearly that model experiment of wave transformation was examined for permeable breakwaters with precast concrete armour unit in shallow water region. Results of model experiment were not rely on that Reynolds number, Re was less than 4×104. These were investigated with following parameter: ratio of incident wave height to block scale, HI/d', ratio of dimensionless linealized friction coefficient, f.
This paper deals with the wind changed by wind fence and the waves generated by this wind. The experiments are carried out in a wind water tunnel. The test fence is made with polypropylene wire, and is a piece of actual wind fence. The reducing effect of this wire-mat-type fence on wind and waves is discussed. The most suitable air gap density of the wire-mat for our wind fence is found.
A newly developed device, which is to be installed on the seaward side of promenade breakwaters, can be used as a warning system against wave overtopping. This system generates wave splashing and sounds before wave overtopping occurs, warning people nearby of possible danger on the promenade breakwater. The run-up height of wave splashing and characteristics of the sounds from this system are studied based on the results of hydraulic model tests. According to these tests, this system has been constructed at the Port of Mombetsu.
Submerged breakwaters armored by steel frame units are examined to establish the optimum design method of artificial reefs. The influences of the armor units configurations on the wave deformation such as wave reflections, wave transmissions and the wave-induced flow around the submerged breakwater are discussed based on the hydraulic model tests results.
The unsteady mild-slope wave equation to calculate wave deformation over a submerged breakwater is derived and some numerical calculation has been conducted with the result compared with the experimental data in order to assess the applicability of the derived equations. As a result, the breaking wave attenuation coefficientis found to be 0.015 to obtain a good reproduction for the case of wave breaking over a submerged breakwater. The numerical result gives the breaking wave profiles over a submerged breakwater in a great detail both in space and time.
The characteristic of waves and currents around a submerged breakwater is studied by a large scale three-dimensional experiment. The wave height decreases on the submerged breakwater by plunging breaker.The wave heights measured in laboratory simulation are compared with those estimated in numerical models.The comparison demonstrates the applicability of the Boussinesq model to estimate wave profiles on the submerged breakwater. The experimental formula for the wave height estimation is also proposed. The velocity of the steady current at the backward of the submerged breakwater is much larger than that at the forward. The large current may occur the serious scoring.
It has been reported that construction of a submerged breakwater results in a higher mean water level and generates offshore currents and currents toward the coast, causing erosion of the seashore. To prevent this phenomenon, development of a new-type submerged breakwater is necessary. To prepare for such development, we determined the the characteristics of currents behind the conventional submerged breakwater, and propose a method of quantitatively evaluating effects of a new-type submerged breakwater on currents, based on the results of experiments with a twodimensional hydraulic model.
SPS is a single pile dolphin which can absorb the most of berthing energy or bear mooring force through its large deflection. The pile of SPS is designed to utilize the lateral resistance of the ground beyond the elastic region. It is generally necessary to use high-tensile steel for the material of pile; however, thanks to its structural simplicity and flexibility, SPS is superior to conventional dolphins consisted of multiple piles in terms of the construction period and cost. The first SPS in Japan for the use of breasting dolphin has been constructed for an LNG vessel of 130, 000m3. This paper describes the characteristics of SPS, its design method, comparison with conventional dolphins. In addition, construction of the SPS and lateral loading experiments for the purpose of design verification are reported.
A new concept of prefabricated-piled-pier techniques is introduced into the design of an emergency container wharf in the reconstruction of the port of Kobe. Damaged caisson type quay walls are used as earth retainings and steel pipe piles are driven in front of them . Precast concrete procedures for upper concrete.works are employed to shorten construction time. A precast floor slab with uniform thickness is applied instead of an ordinary beam and floor slab. PC hollow beams are used to connect the gap between them. These concrete members are installed by a large floating crane.
A jacket structure is applied to the restoration work at Nakatottei pier in Kobe port damaged by the Hyogoken-Nambu earthquake in 1995 from the following reasons;the damaged old RC caissons can not be removed as a ferry terminal and hotel building has been built close to the pier, further, water area around the pier is not wide enough to reconstruct the RC caissons due to the area is one of the most congested water front in Kobe port. This paper presents some topics in design and construction of the jacket structure.
Wave transformation by an array of offshore breakwaters is examined in multi-directional irregular waves. Especially, concerning the ratio of an array pitch length to a representative wave length, plane wave interactions with the arrayed breakwaters are examined extensively. It is pointed out that the wave height variation behind the breakwater array changes from a long-crested pattern to a shortcrested one with increasing a pitch length of periodically arrayed breakwaters as compared to a wave length.
Floating bridges with independent column-type floating foundations have been studied in this paper. Wave response analyses of the proto-type floating bridges (Bergsoysund bridge, Norway) have been performed, and the effect of arch-action of the horizontal arch system has been examined. In the analysis, the interaction effect of the elastic deformation of the structural system with fluids are included. The analytical results have shown that the dynamic fluid-structure coupling effect of the floating foundations is essentially important, and this influences much not only on the vertical responses but also on the horizontal responses.
A few field observations of moored ship motions have been carried out. But it was impossible to measure long period horizontal motions by using a accelerometer. In this study, the observation system of three dimensional motions of moored ship using 3D traker is described. The field measurement of a small craft motions is carried out and the results are compared with those by the other equipment. The applications of the system are also discussed in the paper.
As a part of Japan's national program that calls for the construction of oil storage terminal, the Shirashima Oil Storage Terminal, located about 8km off the northern coast of Kyushu, is under construction and is scheduled for completion by August 1996. Eight 700, 000-kl-capacity oil storage barges are moored in a 60 ha basin protected by breakwaters to enable a capacity of 5, 600, 000 k1 in total. Admission of oil storage barges into the mooring basin is accomplished by opening and closing some caissons of the east breakwater. In order to operate the works safely and effectively, meteorological and oceanographical forecast is performed accurately, and an active mass damper for a suspended load on a floating crane has been developed to improve the operational efficiency as well.
In Noshiro Port, troubles for cargo handling activity occure by long period waves.In this study, the characteristics of long period ship motions due to long period Waves are examained, and countermeasures of the mooring system which consists of mooring ropes and rubber fenders are also discussed with numerical simulations. For large ship motions, it is confirmed to occur when the dominant period of long period waves agrees with the natural period of surge motion. To reduce ship motions due to long period waves, it is valid to adjust the natural period of mooring systems to avoid dominant period of long period waves.
Abuoy system which follows to the wave direction is proposed and the moving mechanism is analysed. The buoy system is composed of a T-shape skelton with a buoy at each horizontal end and a weight at the vertical end. By water channel experiments, it is concluded that, when the buoy system is relatively small compared with the wave length added, the horizontal bar of the system is arranged perpendicular to the wave direction.
First of all, ship collision accidents in Japan are collected and analyzed. Experimental results by the hydraulic model test for ship's impact force to fender systems which protected piers of bridges from ship collision are discussed. The numerical simulation model to evaluate ship motions and fender deflections by ship collision are also presented and evaluated.
Dynamics of a floating breakwater to waves is examined theoretically and experimentally. Both methods, the time domain analysis and the frequency domain analysis, are applied to estimate the dynamic response of a floating breakwater to waves. Especially, focusing on the effect of wave drift forces on the variation of restoring forces by the mooring system, the resultant dynamics and the performance of the breakwater are clarified. In addition to the above examination, effect of the damping forces on the dynamics of the floating breakwater is also studied. Key words: Wave response, Floating breakwater, Wave drift force, Damping force
The floating breakwater of dolphin type was adopted for outlying facilities of marina. This breakwater has some salient features which are small influence of river current due to floating breakwater presence, exellence regulation of sea water with incoming and outgoing tides and good visibility from marina site during low tide.le discribe the hydraulic charateristics of floating breakwater setted near river-mouth.
The Japanese Ministry of Transport has been developing a wave power extracting caisson breakwater. A test breakwater was constructed in the summer of 1989 in Sakata Port and the field experiment began in the winter of 1989. The first stage of the experiment was successfully completed in 1991. The design and construction as well as the operation of the system were demonstrated by the experiment. The field experiment was extended to investigate remaining problems, especially the way to utilize the converted power. This report describes the results of the second stage experiment, which includes a large scale water pumping test and a prototype-test to connect the wave power to commercial electric power lines.
The Japanese Ministry Of Transport has been developing a special caisson breakwater which can convert wave power into electric power. The breakwater has nearly reached the level of practical use after an eight-year field experiment in Sakata Port. It is very important to develop practical systems to exploit the converted energy, in order to promote the use of wave energy by the breakwater. In this report, case studies of several systems which fit the characteristics of water energy are described.
This paper deals with a wave power generation system with water-valve rectifer. The water-valve rectifer converts oscillating air flow into steady air flow. The rectifier doesn't have a mechanical moving element, so the system is simple and maintenance free. However, because of the characteristic form of the rectifier, the loss in the rectifier is large and it is difficult to understand the characteristics of loss. In the paper, we indicate the characteristics by changing the cross-sectional area and the number of air pipes which affects the loss of water-valve rectifier.
The dynamic response of seabed around caisson structure with suction force acting between the bottom of caisson and seabed was numerically evaluated in the frequency domain by means of caisson structure-seabed interaction analysis already proposed by authors. In this paper, caisson structure was assumed to be a rigid rectangular prism with skirt, whose base has several square compartments and the suction force was to act on each compartment. While the seabed was assumed to be a fluid-saturated poroelastic medium whose behavior is governed by Biot's theory of wave propagation. The displacement and pore water pressure of seabed around caisson structure with suction force were numerically investigated under some conditions.
The effect of specimen size on consolidation parameters in standard oedometer tests was investigated though laboratory testing. To take into consolidation the application of a small diameter sampler with two chamber hydraulic pistons in practical use, the specimen sizes used in the standard oedometer tests were a small specimen (d 30 specimen) of 3 cm in diameter and 1 cm in height and a standard size specimen (d 60 specimen) of 6 cm in diameter and 2 cm in height. The d30 and d60 specimens have similar consolidation behaviors for the undisturbed samples with Ip-values ranging from 27 to 81%. Keywords: cohesive soil, size effect, consolidation parameter, oedometer test.
In situ consolidation parameters for Iwakuni clay were investigated in terms of the volumetric strain (εv o) measuring effective overburden pressure of e-log p curve in the standard oedometer test. The prediction of settlement behavior of the test embankment at the Iwakuni replacement airport was performed on the estimated in situ consolidation parameters. The computed settlement behavior used by the in situ consolidation parameters agrees well with the settlementobservations at the test embankment.
A new small diameter sampler with two chamber hydraulic pistons (45 sampler) was developed. An outline of the 45 sampler is shown, and its applicability is also investigated through the unconfined compression tests for the holocene and the pleistocene clay deposits in Mito city in Japan. The undrained shear strength for the samples obtained from the 45 sampler are larger than that of the stationary piston sampler (75 samler) used by the Japanese Geotechnical Society.
The characteristics of local scour and embedment of Artificial Fish Reef (AFR) by wave action are investigated experimentally, and the mechanism of embedment is discussed. With selected models of AFR, the experiment was conducted in a twodimensional wave tank. The vortex patterns near the angled part of AFR are also observed by the hydrogen-bubble method. The patterns of scour, the maximum scour depth, the embeded volume and the bottom-contact area of AFR model are revealed to be controled by KC number and shape of AFR on the movable bed.
Pore water pressure and sand transport occurred by oscillatory flow with pressure change, oscillatory flow and pressure change are experimentally studied. The pressure propagations into sand beds by oscillatory flow with pressure change are better than by merely pressure change. The wave height of sand ripples generated by oscillatory flow with pressure change decreases with increase of pressure change.
Water wave interactions with porous seabeds or breakwaters are investigated theoretically and experimentally. Solutions are obtained analytically by solving the linear equation of motion with the continuity equation in the porous medium and the fluid region instead of solving Laplace equation. Theoretical results are compared with existing analytical results and experimental data to show the validity of the present theory.
The occurrence probability distributions of astronomical tidal level at 96 ports in Japan are calculated with four major tidal constituents. The distribution shapes are able to be classified into several categories mainly depending on the locations by the cluster analysis. The encounter probabilities of siliding and overturning, and expected sliding quantities of the present breakwaters for the durable years are computed in the probabilistic design theory with the estimated tidal probabilities. The encounter probabilities estimated with four major tidal constituents become smaller than those estimated with a simple cos-shaped tidal change in the shallow water area.
Long waves with periods of 1-5 minutes sometimes terminate the cargo handling and cause the break of mooring ropes in Japanese several ports. These long waves mainly consist of the setdown waves bounded in the grouping waves. Preventing such long waves from penetraing into harbors has great importance to keep the safe loading and un-loading. The present paper experimentally investigates the effects of breakwaters located at the port entrance for preventing long waves. The amplitudes of long waves can be reduced by the appropriate installation of breakwater without any amplification of harbor oscillation.
Recently, It is said that the artificial reef works are very effective for shore protection from the standpoints of durability and landscape. But, its works are very expensive and occupy large sea area. The authors proposed new shore protection work, doubly-placed submerged rubble mounds. This beach erosion control work is more economical of construction cost in comparison with artificial reef work, and useful for fishing grounds. In this paper, the authors clarified the hydraulic properties of the work.
The first semi-circular breakwaters have been erected at Miyazaki Port in Japan. This type of breakwater, having a hollow structure with a semi-circular cross section, is expected to exhibit superb characteristics in terms of sliding stability and low reflectively under a severe natural environment that includes high waves and poor soil conditions. In addition, its unique design provides excellent scenery enhancement. Field demonstration tests by erecting test breakwaters have been conducted since 1991 at Miyazaki port in an effort to verify stability, member safety and construction ease of the semi-circular breakwater in an actual sea area, as well as to establish practical design and construction methods.
The gentle slope seawalls which has 1:3 front grade with wave dissipating blocks is supposed to be constructed at the northwest part of the Ise bay. The experimental study has been carried out to clarify the characteristics of wave overtopping of the seawalls. The experiment clarified the total rates and its horizontal distribution of wave over topping, comparing to the normaltype of wave dissipating seawalls which has 1:4/3 front grade. In addition, the figures assumed the amount of wave overtopping at any height of seawalls are developed. It will be very useful to design the height of seawalls.
Field survey on wave overtopping was carried out at Fukui port during winter season in 1996. Water depth in wave dranage channel between the walls which sectioned the wave dranage channel was measured during the wave overtopping. Overtopping rate was estimated by two ways: Rate of volume change to the time and the discharge formula over surpressed weir using the water depth of overflow. The significant wave height 6.1m with its wave period 11.6s resulted in the mean overtopping rate of 10-4m3/s/m in the order of magnitude. Overtopping rate due to wave group is also estimated to be about ten times the mean overtopping rate. The mean overttoping rate are compared with estimated ones using the experimental formula by Takayama et al.(1972).