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In order to disclose the essential relationship between the beach processes and wave characteristics, two dimensional model tests are often performed for beach profile changes due to incident breaking waves normal to the beach. In applying the results of such experiments to the prototype of beaches, the scale effects of waves and sediments on the beach processes with equilibrium beach profiles should necessarily be considered. In this paper, as an approach to solve this problem in two dimensional beach studies, the effects of wave height and sediment size on the shore line movement and equilibrium beach profiles are discussed based on the results of experiments made by the authors and other experiments with smaller and larger scales by some researchers. It has been found that the ratio of wave height to sediment diameter is a very significant factor in this problem. In addition, the changes m a character of breaking waves during the time period of wave action from the beach having an initial constant slope to that with an equilibrium profile are presented.

The applicability of a k-e turbulence model for low-Reynolds numbers to oscillatory boundary layers is examined. Through several numerical computations, characteristics of the mean velocity and tur...

Two-dimensional laboratory experiments were performed to investigate the sediment transport due to waves on a smooth fixed sloping beach. Polystyrene particles and glass balls were used as tracers ...

This paper was presented at the general meeting for establishment of the society as an invited memorial lecture. The paper involves a review of multiphase flow appearing in civil engineering field.First of all, the phenomena of multiphase flow in civil engineering are classified in Table 1, and especially features of mudflow in mountains and extremely high concentration flow in Yellow River are introduced as peculiar phenomena of one directional two-phase flows with water and sediment. Secondly sediment transport on the beach and beach deformation by waves are discussed as a typical two-phase flow problem in coastal engineering, and in addition, a pneumatic breakwater using air bubble curtain flow is introduced as an application of two-phase flow with air and water.

In order to clarify the non-linear effect of the width between two adjacent orthogonals on the wave height change due to refraction, the equations of transformation for finite amplitude waves inclu...

At the Edogawa moterboat racing stadium located at a tidal river channel in Tokyo, moterboat races have sometimes become difficult to open by wind waves during spring gales. A pneumatic breakwater has been planned to be adopted to protect the racing field from the wind waves because it has an advantage of no interruption of common boat navigations through the river channel. However, the breakwater performance of wave damping in the water field where the tidal current exists in addition to the river current is not clear yet.The present study shows the results of the field test and discusses the applicability of the pneumatic breakwater to tidal rivers. It is found from the data analysis that the pneumatic breakwater in the field with the tidal current maintains almost same performance of wave damping as that without the current.

In order to clarify the water particle velocity field of breaking waves on beaches, experiments were carried out for three kinds of beach slopes (1/10, 1/20 and 1/30). Neutrally buoyant particles were used as tracers to measure the velocities with a 16 mm high speed cinecamera. Since photographs of the wave profile near breaking were also taken in the same films, the change of the wave profile near breaking was also examined. It was found that vertical distributions of horizontal water particle velocities at the crest and trough phases of breaking waves on beaches cannot be explained by the finite amplitude wave theories for uniform depth. Then, they were discussed in comparison with the breaker types. As a result, it was shown that the dimensionless vertical distribution of horizontal water particle velocity at the crest phase of breaking waves is determined by the combination of the beach slope and the deep-water wave steepness.

This paper has examined the change of wave grouping of storm waves during wave growth and decay by analyzing the field wave data observed off Gobo Coast in Wakayama Prefecture and at Lake Biwa in Shiga Prefecture (Japan) with some parameters to describe the magnitude of wave groups. For the mean lengths of runs and total runs of wave heights, the comparison of the observed results with the theoretical ones by Kimura (1980) has been done. Besides, the effect of shallow water on wave grouping has been discussed.The main results are as follows: (1) To describe the magnitude of wave groups, at least two parameters are needed; one is the magnitude of the sequence of high waves in a time series, and the other is the magnitude of the variation of wave energy or wave height around the mean value. (2) Concerning the wave data observed at Gobo, wave grouping was pronounced in the main stage of storms where three parameters of the correlation coefficient of successive wave heights, the mean length of runs an...

Numerical analysis of turbulent bottom boundary layers has been performed by applying the finite element method.At first, in order to check the validity of the numerical procedure, calculations for...

The phenomenon of wave refraction due to current is an important factor in the longshore current generation and the wave transformation in the vicinities of narrow strait and river mouth. The existing numerical models of wave refraction due to current are all for regular waves. A numerical model is proposed for the computation of the change of the directional spectral density of irregular waves due to current‐depth refraction. The wave action equation is applied as the basic equation, in which the wave direction is introduced as the fourth independent variable. Several sample computations show that this model can explain the change of the directional spectra due to current. It is found that the significant wave height changes more rapidly than that of the corresponding regular waves having the same wave height, period and direction as those of the irregular waves. The change of a mean wave direction of the irregular waves is different from that of the corresponding regular waves.

This paper discusses wave grouping of wind waves observed at Lake Biwa from the physical viewpoint of wave modulational instability. Amplitude modulation periods obtained from the smoothed instantaneous wave energy history (SIWEH) of the observed data proposed by Funke and Mansard are compared with the values predicted by the modulational instability theory using the Zakharov equation for a finite constant water depth derived by Stiassnie and Shemer. The modulation period normalized by the typical wave period corresponds to the length of total run. It is shown that the amplitude modulation periods of the observed data agree satisfactorily with the predicted values. Thus, it is concluded that the modulational instability is a hydrodynamical cause of grouping of high waves.

In this paper, a theory of the roll-wave trains in laminar water flow on a steep slope surface is developed by Dressler's method as the further research of the thin sheet flow.The analysis proves that if the discharge, the bed slope and the kinematic viscosity of water are given, then the solution is obtained uniquely and both wave and flow characteristics of the roll-wave trains can be determined.The experimental results obtained by the wave profile recorder are compared with above described theoretical ones, and the validity of this theory is recognized in good agreement.

The critical tractive force for gravels on a granular bed in turbulent stream is an interesting and fundamental problem connected with the critical tractive force for mixed sand and gravel, the sieving action of flowing water and the effect of rubble on river bed protection from scouring. In 1953, experiments on the incipient motion of discrete particles resting on a stream bed of fixed granular roughness were carried out by A. T. Ippen and R. P. Verma using four samples of plastic and glass spheres, and an empirical entrainment function was produced. But nothing about the mechanism and its analysis of incipient motion of discrete particles was touched.In this paper, theoretical cnosiderations on the incipient motion of spheres on a fixed granular bed are made by means of the same treatment as in the previous paper and other modified treatment. From these considerations, it is shown that the dimensionless critical tractive forces are expressed as a function of the roughness Reynolds Number with respect to granular bed and the ratio of diameters of sphere and bed material, and that this function results in good agreement with the experimental data. Moreover, based upon the results obtainedd by the theoretical considerations described above, the critical tractive force for mixed sand and gravel is discussed.

In studying the mechanism of water erosion of land-surfaces by rain water flow, it is necessary to evaluate experimentally the relations between the factors related to the phenomena of soil detachment from land-surfaces and transportation of detached soil. In this paper, erosion of land-surfaces consisting of sand or sandy soil by stream flow is treated. For this approach, hourly variations of the rate of detachment of soil, the discharge of surface flow and grain diameters of transported soil, and rates of sediment transportation by rain water flow are measured. The experimental results are discussed comparing with those obtained by some authorities. Moreover, a dimensionless expression on the rates of detachment of soil is proposed.

SYNOPSISIn designing seawalls and seadikes, it is very important to estimate the quantity of wave overtopping or the height of wave run-up. In this paper, the effects of wave height and sea water level on wave overtopping and wave run-up are discussed based on existing experimental results. It is shown in the discussion that the maximum values of the wave run-up height and the quantity of wave overtopping do not always appear at the maximum wave height or the highest of sea water level.

In forecasting ocean waves in shallow water, the value of the bottom friction factor must be known for the calculation of wave energy loss due to bottom friction.In this paper the attenuation data ...

SYNOPSISOne of the most important problems in coastal engineering is the estimation of the transformation of waves as they approach the shore through shallow water. This report is based on the results of the wave observation off the Akita coast. From the corresponding values of the significant wave heights at two stations, the loss of wave energy due to bottom friction is investigated quantitatively and the bottom friction factor of this coast is estimated. The estimated values of the bottom friction factor are 0.033∼0.090 and the mean is 0.057.

In this paper, as the Ist. report of the studies on the thin sheet flow, the experimental results obtained by the wooden experimental flume, rectangular section of 40cm width and 19cm depth, with smooth surface are described.By this detailed experiment, the process of change of velocity distribution in transition from laminar flow to turbulent flow and the relation between Chezy constant, coefficient of frictional resistance and Reynolds' number are made clear, and the transition region is also determined. Moreover, the mean velocity formula in case of gentle slope is obtained.

As a breaking limit of progressive waves, many conditions have been proposed. One of them is that the water particle velocity at the wave crest is equal to the wave celerity.To examine this condition experimentally, the wave profile and the horizontal water particle velocity at the water surface near the crest of breaking waves were measured. These waves progress and break on a very gentle slope beach (1/200), which may be regarded as horizontal bottom.Experimental results of the wave profile and the horizontal water particle velocity at the water surface near the crest of breaking waves are presented and compared with theoretical values, and the breaking condition of progressive waves is examined experimentally.

SynopsisSandy beaches are defensive zones created by nature, protecting the land against aggressive oceanic forces. They are very flexible and their configulations are varying daily, seasonally and annually, depending on many factors, such as wave characteristics, beach materials, shore structures and the others. The investigation of beach erosion is one of the most important and difficult subjects in coastal engineering.In this paper, a method for investigating the mechanism of beach erosion is presented, concerning the investigation practice of beach erosion along the north coast of the Akashi Strait, and the author's opinion of the following three subjects to be investigated is described:(a) Distribution of sand drift along the coast,(b) Distribution of sand drift along the beach profile, and(c) General characteristics of sand drift, suCh-as the type of sediment transport, the direction of drift and the others.

Is is very difficult for engineers to deal with the cnoidal wave theory for practical application, since this theory contains the Jacobian elliptic functions, their modulus k, and the complete elliptic integrals of the first and second kinds, K and E respectively. This paper firstly proposes formulae for various wave characteristics of new waves named "hyperbolic waves", which are derived from the cnoidal wave theory under the condition that k = 1 and E = 1 but K is not infinite and are a function of T/g/h and H/h, so that cnoidal waves can be approximately expressed as hyperbolic waves by primary functions only, in which T is the wave period, h the water depth and H the wave height. Secondly, as an application of the hyperbolic wave theory, the present paper deals with wave shoaling, that is, changes in the wave height, the wave crest height above still water level, and the wave velocity, when the waves proceed into shallow water from deep water.

Characteristics of mean velocity and turbulence properties in oscillatory bottom boundary layers are investigated with low- Reynolds number turbulence model. Since this model is capable to describe the flow field close to the bottom, special attentions are paid on the characteristics of the viscous sublayer. Several interesting results, which coincide with or differ from existing knowledge on steady bottom boundary layers, are presented in paticular on the mean velocity profile, turbulent viscosity coefficient and growth of the viscous sublayer.

This paper discusses wave grouping of wind waves from the physical viewpoint of wave modulational instability. Amplitude modulation periods obtained from the smoothed instantaneous wave energy history (SIWEH) of the observed data are compared with the predicted values by the modulational instability theory using the Zakharov equation for a finite constant water depth derived by Stiassnie and Shemer(1984). The modulation period normalized by the typical wave period corresponds to the length of total run. It is shown that the amplitude modulation periods of the observed data agree satisfactorily with the predicted values. Thus we conclude that the modulational instability is a hydrodynamical cause of grouping of high waves.