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Collaborating Authors
Results
New Design Criteria of Coastal Engineering For Disaster Prevention
Dong, Sheng (College of Engineering, Ocean University of China) | Wei, Yong (Department of Ocean and Resource Engineering, University of Hawaii at Manoa) | Li, Feng (College of Engineering, Ocean University of China) | Liu, Defu (College of Engineering, Ocean University of China)
ABSTRACT Compared with traditional one-dimensional extreme value statistical method, the new design criteria are put forward based on joint probability theory for structural design. The proposed procedure considers the combined effect of storm surge, large waves and winds impacting on coastal structures. Because it is difficult to solve the joint probability of non-Gaussian correlated multivariate distribution, Importance Sampling Procedure (ISP) is utilized to solve this problem. Results show that ISP is a simulating technique with advantages of advance, high efficiency and fast convergence. The design criteria are also given out for engineering construction in coastal zone of Qingdao. INTRODUCTION The coastal cities are mostly regional economic development centers in China. Frequently typhoon attacking and associated surge flooding cause heavy loss of lives and properties in these areas. The determination of the coastal engineering design criteria against natural disaster plays an important role in the sustainable development of coastal cities. For instance, Qingdao, a coastal city of east China, was severely flooded along the coastline in 1992 when typhoon-induced storm surge coincided with high tides and large waves. 26 lives were taken away and the properties damages were reported to be over 80 million dollars during this tragedy. In a general way, traditional design criteria for most coastal structures, which assume to be acted on by one single load, are established based on one-dimensional extreme value analysis. However, more rigorous approach is in need to take into consideration of the joint impacts from waves, tides and winds during a storm event. The loads induced by extreme storms are critical in the design of coastal disaster-prevention structures. The load arises from a combination of waves, tidal levels and wind, though waves are generally the dominant factor. This topic has attracted many researchers' attention (Wen, 1991; Forristall et al, 1991; Tromans, 1995).
ABSTRACT Despite wave set up onshore low crested breakwaters may reveal quite important for the functional design of these structures, the experimental studies on this topic are up to now extremely limited, especially under random wave attacks. This contribution discusses results of large scale model tests the Authors conducted at the Grosser WellenKanal (GWK) of Hannover, Germany on an idealized 2D model of low crested/submerged breakwater. Analysis showed the importance of momentum release of breaking waves for submerged breakwaters and of the mass balance for low crested ones. INTRODUCTION Detached low crested/submerged breakwaters are shore parallel barriers built in a way that waves, breaking on the top or front face, considerably reduce their momentum in the leeward zone. At the same time, a large amount of water is "pumped" over and through the breakwater. This net "inflow" must be compensated by an equal "outflow" which, in an open 3D situation, will take place by a combination of longshore and transverse currents. Both reduction of wave thrust and "pumping" drive a difference in the mean water level between seaward and shoreward sides of structure, usually called "setup" or "piling-up". The linkage between set-up and characters of mean circulation in the protected areas makes it relevant for engineering purposes. Recent experience of practicing engineers, in fact, indicate that strong currents may be generated behind the breakwaters which can result in more beach erosion instead of less. Nevertheless, little researches have been up to now conducted on this topic, the main of which are those by Diskin et al. (1970) and Loveless et al. (1998). On contrary more attention has been addressed in studying the similar problem of set-up on coral reefs (see Gourlay, 1996 for an overview). However most of researches have been performed using regular waves.
ABSTRACT Within the EU-funded project DELOS, 3D tests were performed in the 12.5 m x 9.7 m wave basin at Aalborg University, DK, with the aim of analysing waves and currents around low-crested structures. The paper shows some experimental results on velocity fields in a symmetrical layout, composed by two detached breakwaters with a gap in between. An original scheme for evaluating overtopping processes with varying structure submergence and wave attacks is presented and discussed in comparison with experimental mass balance. INTRODUCTION Low Crested Structures (LCS) are nowadays among the most common beach defence structure. Their functionality has been investigated in the past 20–30 years through analytical, numerical and experimental studies. The first documented investigation of the effects of these structure on water piling-up in the lee side was done by Diskin et al. (1970). Loveless (1997) performed an experimental study of wave transmission, wave set-up, structural stability, overtopping discharge and flow over and within the structure, through flume model tests of LCS. Kobayashi et al. (1989) and Losada et al. (1998) performed numerical studies on wave transmission and return flow. Overtopping discharge has also been investigated by Loveless et al. (1998) and Drei et al. (1999). Tirindelli et al. (2001) studied wave setup and wave transmission on a physical model of an existing structure built in Adriatic Sea (Italy). Ruol & Faedo (2002) performed an experimental study on wave transmission and overtopping discharge at emergent and zero freeboard LCS under breaking wave conditions. Within the framework of DELOS Project (DELOS EVK-CT-2000–00041), a series of 3D basin tests have been performed in summer 2002 on small scale models of LCS. This paper describes a study of current flows around LCS through the analysis of a new set of data derived from these 3D basin tests.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (1.00)
ABSTRACT Breaking wave judgment with the vertical water pressure gradient IS discussed. The judgment of wave breaking of the progressive waves and the standing waves is carried out. Using the amount of energy loss due to hydraulic jump from the viewpoint of analysis, the wave energy loss due to wave breaking of the progressive waves and the standing waves was proved. The quast-bore model is defined in time & main. The simulation results are validated in the breaking wave experiment in a long wave tank. INTRODUCTION The Boussinesq model is widely employed to estimate non-linear wave transformation in shallow water. Reproduction of breaking wave phenomenon is done in the Boussinesq equation model with same approximation because the model obeys kinematics-boundary conditions for the continuous water surface. On the other hand, the wave and current deformation in the vicinity of the wave break point is more important in practical usage than breaking wave mechanism at a local point. In early studies, several breaking wave models have been developed. Such models judge the existence of wave breaking by the deformed wave profiles in shallow water and evaluate the energy loss caused by wave breaking m wave height calculation results, However, in the judgment of wave breaking existence, the former breaking wave models required the following complicated parameters like wave velocity, wave direction, relative bottom slope in the wave direction, and some uncertain experimental coefficients. The specified parameters are not suitable to define the wave breaking observed in real seas. In this study, the breaking wave model that is independent from bottom slope and the wave direction is proposed. It is applicable to simple judgment of the occurrence of wave breaking, The wave energy loss due to wave breaking is estimated with high accuracy in the new model.
ABSTRACT In this paper, we propose the modified mild-slope equation that is able to treat with waves scattering against a vertical barrier, ignoring the local effects. This equation includes a scattering term in terms of the reflection coefficient of a single barrier. As well as the numerical results, we present two theoretical solutions to demonstrate the performance of the proposed mild-slope equation for two scattering problems; the first one is for the scattering problem due to widely spaced multiple barriers, and the second one is for the resonant problem due to a single barrier constructed at a rectangular harbor. Good agreement between theoretical and numerical solutions is found in both problems. INTRODUCTION The breakwater of surface-piercing type has been developed mainly for application within bays or estuaries that are semi-protected from the direct impact of large waves. Most of bays have soft foundation which is too weak to bear the weight of gravity type breakwater. Thus the surface-piercing breakwater is taken into account as an alternative tool to reduce wave heights in the bay to an acceptable level. Differently from the ordinary breakwater of gravity type, the surface breakwater reduces the transmitted waves mainly due to the reflection of incident waves from the barrier body. Traditional breakwaters, seawalls and jetties reflect or direct wave energy in destructive ways or concentrate it in local hot spots so that the concentrated energy leads to the destruction of marine facilities. Among a number of breakwaters, the vertical barriers with gaps are recently favored from the point of view of marine environment since they do not in general partition the natural sea. Free exchange of water mass through the structures is possible so that the water in the sheltered region can be kept circulating and therefore prevent stagnation and pollution.
Study On The Layout Of Floating Breakwater Units
Nakamura, Takayuki (Department of Civil and Environmental Engineering, Ehime University) | Mizutani, Norimi (Department of Geotechnical and Environmental Engineering, Nagoya University) | Hur, Dong Soo (Department of Civil Engineering, Nagoya University) | Kim, Do Sam (Division of Civil and Environmental System Engineering, Korea Maritime University)
ABSTRACT This paper proposes the new layout of the floating breakwater units to reduce the transmitted waves more efficiently. In the proposed layout, the centerline of each floating unit is obliquely arranged to the centerline of the floating breakwater. The dynamic responses of a floating breakwater unit to waves have been investigated by conducting the two-dimensional and three-dimensional laboratory experiments. Wave height distributions had also been measured in both experiments. Numerical analysis has been carried out for both two- and threedimensional interaction between wave and floating breakwaters. The floating breakwater arranged by the newly proposed method had been confirmed to reduce the transmitted waves behind the breakwater more than the conventional one. INTRODUCTION The opportunity for construction of the floating breakwater is increasing, particularly in inland seas like Setonaikai, Japan. The floating breakwater consists of some floating units. The arrangement of the units is usually straight, and the longitudinal axis of the unit coincides with that of the floating breakwater. The breakwater units are set to their given locations by mooring lines. In this case, the mooring lines of the adjacent units may touch each other if the lines extend to the outer side of the unit, so called open-type mooring, which may lead to the breaking of the mooring line. Adopting a different method in stretching the mooring lines of the adjacent units may be effective in preventing such a problem. However, the dynamic behavior of the units may vary and difficulty in evaluating the overall effectiveness of the floating breakwater arises. Generally, the wave transmission evaluated by the three dimensional experiment becomes large compared with that evaluated by the two-dimensional experiment because of the wave diffraction and propagation through the gap between adjacent units.
- Asia > Japan (0.34)
- North America > United States (0.28)
Simulation of Wave Transformation In Vertical Permeable Structure
Karim, Mohammed Fazlul (Department of Civil & Environmental Engineering, Saitama University) | Tanimoto, Katsutoshi (Department of Civil & Environmental Engineering, Saitama University) | Hieu, Phung Dang (Department of Civil & Environmental Engineering, Saitama University)
ABSTRACT Wave motion in porous structures and hydraulic performances of vertical permeable walls are investigated. A numerical hydrodynamic model for 2-D wave field is developed to simulate the wave transformation inside and outside the structure. Governing equations of porous flow are solved using SMAC algorithm for the time evolution of the velocity and pressure field. A two-phase model is incorporated to treat the prime variables at the air water interface. Experimental studies are done to calibrate the numerical model. The drag and inertia coefficients in the governing equations are calibrated for a typical porous material. The model is applied to assess the effect of structure width and porosity on the hydraulic performances for a vertical permeable structure. It is observed that there exist optimum values of width and porosity that can maximize hydraulic performances. INTRODUCTION Many coastal structures constructed for the purpose of harbor securing and shore protection are porous. These structures are designed mainly to provide protection by reflection and/or dissipation of wave energy. For many years, rubble-mound type porous structures are extensively used. However, vertical permeable structures are seldom used due to limited information on the hydraulic performances. In general, a wave train through porous structure, irrespective of its regular or random nature, is reflected, transmitted and dissipated. All these processes induce significant changes in the wave properties such as height, energy and force inside the porous structure. All these changes depend on the structural parameters (width, material size, porosity) and incident wave conditions. Therefore, it is essential to investigate the influences of all these parameters on functional variables such as wave damping, reflection, dissipation and transmission. Due to the complexities of both porous flow and non-linear wave behavior, the problems related to it are extremely difficult to solve and are being investigated for many years.
- Asia > Japan (0.29)
- North America > United States (0.28)
- Research Report > New Finding (0.66)
- Research Report > Experimental Study (0.48)
ABSTRACT Different problems concerning the transformations of waves on coral reefs during storms are presented. A numerical model based on the VOF method is introduced and its applicability to the problem of wave transformations on coral reefs is discussed. The model is used to simulate the wave breaking and attenuation on different reef profiles. Good agreement for wave attenuation on a coral reef is found between the model and experimental results obtained by other authors. The model is used to treat the case of infragravity wave generation on reefs due to incidence of wave groups. The results are encouraging and show that the development of VOF type models is a very important tool to analyze the hydrodynamics of coral reefs. INTRODUCTION Coral reef are confined roughly to the tropical regions of the Pacific, Indian and Atlantic Oceans. In Japan, due to the presence of the Kuroshio Current, which brings warm water to the southern islands, coral reefs can be found up to around 30oN latitude. These southern islands of Japan are affected seasonally by tropical storms (typhoons). At the island of Okinoerabu, an existing coastal protection situated by the shore on a coral reef experiences heavy overtopping during typhoon season. At another location on the same reef, anomalous sea level during storm conditions disturbs the operation of a thermal power plant by exposing a cooling water intake to the air. Yet at another place in the same reef, damage to 55 ton concrete armor blocks, in front of the breakwater of a fishery port, have been the source of concern for coastal defense managers from the prefectural government. These examples of damages, caused by high amplitude wave interaction with the coral reef during storms, show the difficulties for proper estimation of the wave parameters for these conditions.
- North America > United States (0.93)
- Asia > Japan (0.69)
Wave Forecast At Harbor Entrance to Support Entering Ships Under Rough Weather
Shinji, Mizui (Department of Maritime Technology Hiroshima National College of Maritime Technology) | Kubo, Masayoshi (Research Institute for Marine Cargo Transportation Kobe Univ. of Mercantile Marine) | Sass, Kenji (Department of Maritime Technology Hiroshima National College of Maritime Technology) | Nagase, Satom (System Design Department Mitsui Engineering Shipbuilding Co., Ltd)
ABSTRACT It is known that the ship's entering is limited at Japanese coastal harbors under severe wave conditions. This limit condition becomes difficult to maintain the on-schedule service and safety of the maritime transportation. In this paper, authors review the method of wave forecast at the turning point of the ship near harbor entrance. In other words, we study to establish a supporting system for ships to enter the harbors so that the fishermen can pass the dangerous point of operation under rough weather conditions at small wave grouping. 1. INTRODUCTION It is known that the ship's entering is limited at the Japanese coastal harbors under severe wave conditions (Kubo, et al., 1993). This limit is critical for the on-schedule service and safety of the maritime transportation (Kubo, et al., 1994). According to the studies based on the actual measurement and questionnaires, they reveal that the most dangerous point of ship operation would be the turning point where rolling, yawing and broaching can happen at the same time (Kubo, et al., 1995). In this paper, the authors review the method of wave forecast at the turning point. In other words, the authors study to establish a supporting system for ships to enter harbors so that fishermen can pass the dangerous point of operation under rough weather conditions at small wave groupings. This paper proposes the wave forecast that aims at helping the fishermen decide whether the ship's entry is possible or not and when is the best timing for entry under rough weather conditions. 2. WAVE DATA IN USE 2-1 Observed wave data (Sea of Japan data) The wave data are those observed during the experiment of 27 days from December 20, 1999 to January 15, 2000 at Kasumi-nishi Fishing Harbor in Hyogo Prefecture.
ABSTRACT The aim of this study is to investigate the capacity of the breakwater with channel to exchange water in longshore current generated by obliquely incident waves and to propose numerical model for predicting the capacity. We examined the performance of the breakwater with channel of the model harbor in a three-dimensional wave basin by generating the longshore currents under the incidence of regular and irregular waves. The applicability of the proposed numerical model was also examined using experimental results. It is found that the time required to exchange whole water in the harbor of the regular wave test can be estimated from the water volume in the harbor, the representative longshore current velocity induced by regular wave, and the opening ratio of the channel in the breakwater. The capacity of the breakwater with channel to exchange water induced by irregular wave can also be estimated by using the significant wave height for evaluating the velocity of longshore current. INTRODUCTION Deterioration of water quality becomes severe problems in some harbors because the circulation of water in the enclosed region by breakwaters is weakened and exchange of water becomes inactive there. We focused on the function of breakwaters with channel to exchange water in harbors, because submerged breakwaters and floating breakwaters are not effective to maintain harbor tranquility in spite of their merit for exchanging water. We have already shown that breakwaters with slope-type channel and step-type channel effectively reduce transmitted wave height when compared with a straight-type channel (Morita and Deguchi, 1999), and the flow rate through the breakwater with channel can be estimated by applying the non-linear Darcy''s law. We also investigated the capacity of the breakwater with channel in the model harbor to exchange water in uniform flow (Morita and Deguchi, 2001).
- Asia > Japan (0.30)
- North America > United States (0.28)