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Results
Wave Forces Acting On Triangular Roughness of Washboard-Like Sea Bottom
Tomita, Takashi (Nagoya University) | Kim, June-Q (Nagoya University) | Iwata, Koichiro (Nagoya University) | Matsudaira, Ryuzo (Chubu Electric Power Co., Ltd.) | Miyaike, Yoshihito (Chubu Electric Power Co., Ltd.)
ABSTRACT Wave forces acting on the triangular roughness elements are experimentally investigated in 2-dlmenslonal wave flume. The roughness elements are modeis of ridges of the unconsolidated washboard-like rocky sea bottom surface comprized of an alternatlon of geosynclinais strata. Horizontal wave forces acting on the elements are manly composed of drag and inertia forces. The drag force is the prominent force component. Vortices separated from the roughness elements cause the drag forces. They are influenced by the shape of roughness elements and the distribution distance between adjacent roughness elements. Vertical forces are consisted of the drag, inertia and lift forces and hydrostatic pressure variation-caused forces, which are complicatedly mixed. INTRODUCTION With increasing demand of mull-purposes utilization of nearshore sea area in recent years, the construction slate of offshore structures for control of sea environment are expanding to many places, the bottom surface conditions of which are sandy bottom, sandy and silty bottom, rocky bottom, etc. In the intermediate water depth. A washboard-like rocky sea bottom surface is found where an al iteration of geosynclinals strata, like a flysch, exists prominently under the sea. Ridges of the bottom suffer not only a skin friction but a drag force and an inertia force by wave action of strong wind waves. A prediction of the rocky sea bottom change and discussions on stability of the rocky sea bed need information's on the wave forces acting on the ridges of the bottom surface. In particular, the wave force is very important and key factor when the rocky bottom is comprised of unconsolidated materials. The forces acting on pipelines (Shankar et al.,1988, Tsuchiya and Yamaguchi, 1974) and spheres (Iwata and Mizutani, 1989) near and on the sea bottom are investigated in detail, however, the geometrical scale of the ridges are smaller than those of the pipelines and spheres.
Wave Kinematics of Nonlinear Crossing Waves
Kang, Yoon-Koo (Nagoya University) | Tomita, Takashi (Nagoya University) | Kurata, Katsuhiko (Toyo Construction Co. Ltd) | Iwata, Koichiro (Nagoya University)
ABSTRACT In this study, a theoretical solution of the nonlinear interaction of two free wave trains crossing infinite water depth has been expanded to the 3rd-order, employing the perturbation method. The water surface elevation and particle velocities have been Investigated. Laboratory experiments were also carried out to examine the validity of the proposed theory. The proposed theory is shown to evaluate well the experimental results The skewness of the water surface elevation and particle velocities of the crossing waves are fairly affected by each wavelength of two wave trams and the crossing angle. INTRODUCTION The sea waves in nature are generally complex in form and random, and they are composed of many component waves with different heights, periods and wave directions, which are mutually interacted. The strong interaction of nonlinear waves, however, gives rise to new hydraulic characters which are difficult to be expected in the linear interaction. The freak waves have been pointed out to occur under this nonlinear interaction. Therefore, it is important to investigate the nonlinear interaction of waves such as the incident and reflected waves, the wind waves themselves, and the swell and wind waves. In recent years much interest has been paid to the nonlinear interaction of waves with the increasing utilization of coastal and ocean region; The nonlinear interaction solution of the crossing incident and reflected waves with the same wave periods in front of rigid wall has been expanded to the 3rd-order, over a few decades, by Fuchs(1952} and Hsu, et. al.(1979). Tick(1959) first dealt with the interaction of multiple component waves, and he discussed the nonlinear spectrum of deep water waves. Hamada(1965) and Hwung and Tsai(1982) theoretically investigated the secondary interaction of two component waves in finite water depth. Phillips(1960) and Longuet-Higgins(1962} discussed the nonlinear interactions of two free waves with different wave periods in deep water depth and found that the resonant interaction occur in the 3rd-order term.
Wave Forces Acting On Armor Unit of a Submerged Wide-Crown Breakwater
Rufin, Teofilo Monge (Nagoya University) | Mizutani, Norimi (Nagoya University) | Totsuka, Natsuko (Nagoya University) | Kurata, Katsuhiko (Toyo Const. Ltd) | Iwata, Koichiro (Nagoya University)
ABSTRACT The pertinent characteristics of wave forces acting on different shapes of lubble stones of a submerged wide-crown breakwater and the applicability of Morison equation were analyzed experimentally in tills paper. In general, the variations of the maximum wave forces with distance from the leading crown-edge are similar to that of the water particle velocities. Regardless of stone shape, the maximum wave force IS located near the crown-edge of the structure Thus, the vicinity around the leading crown-edge was confirmed to be the most critical location of the submerged Wide-crown breakwater. Moreover, Monson equation was revealed to be applicable in the estimation of the horizontal wave force In non-embedded condition when × / L ≤ 0.2. INTRODUCTION In a recent study conducted, remarkable number of beaches are rapidly disappearing due to beach erosion. And because of these findings, the installation of submerged breakwater in the prevention of beach erosion and other related coastal disasters is notably increasing Submerged breakwater IS one type of coastal structure that can compensate the dements on some coastal amenities brought by other types of breakwaters. This structure assists in the maintenance of aesthetic ocean view and in the preservation of environmental quality of sheltered water. In the design of submerged breakwater, the knowledge on the stability of the armor unit is of prime importance. The critical stable weight of the armor unit depends largely on the acting wave forces. A thorough knowledge of the mechanism and fundamental characteristics of the wave forces acting on armor unit is of considerable engineering importance due to its practical application m the design and construction of coastal structures. Just recently, a stability model for spherical armor unit is proposed (Mizutarn et al, 1992, Rufin et al, 1993) by considering the acting wave forces.
Wave Forces Acting On Multiple Cylindrical Structures With Large Diameter
Mizutani, Norimi (Nagoya University) | Kim, Changje (Nagoya University) | Iwata, Koichiro (Nagoya University) | Matsudaira, Ryozo (Chubu Electric Power Co., Ltd.) | Miyaike, Yoshihito (Chubu Electric Power Co., Ltd.) | Yu, Hongsun (Korea Maritime University)
ABSTRACT This paper aims to investigate the wave forces acting on multiple circular cylinders with large diameter. The laboratory experiments were carried out to measure the wave forces exerting on the two large cylinders and three large cylinders. Two types of cylinders were prepared for present experiments. One permits the wave overtopping and the other does not allow the wave overtopping. Numerical calculations were also performed using the vertical line wave source Green's function to discuss the fundamental characteristics of wave forces on cylinders. Experimental results were discussed in relation to the numerical results. Though the numerical calculation is based on the linear wave theory, it is shown that the present method can evaluate well the wave forces on the cylinders when the wave overtopping was not permitted. The wave overtopping is revealed to reduce the wave forces on large cylinders. INTRODUCTION Cylindrical structure is one of the widely-used offshore and coastal structures such as the gravity type platform. The wave force on a single large circular cylinder has been discussed by many researchers (e.g. MacCamy and Fuchs, 1954). On the other hand, the accumulated knowledge about the wave force on the multiple large cylinders have not been enough compared with that of the single cylinder. Some theoretical approaches also have been conducted on this problem (e.g. Isaacson, 1978); however, an experimental investigation about it seems not to be sufficient. This paper is to discuss the wave forces, mainly acting on two and three cylinders. The size of cylinders is large so that the wave diffraction plays an important role on the wave field around them. First, the laboratory experiments were carried out to measure the wave forces acting on cylinders. Then. the numerical calculations were performed using the vertical line wave source Green's function (Isaacson. 1978, Nakamura and Oku, 1985).