共查询到20条相似文献，搜索用时 15 毫秒
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Rubble mound breakwaters usually consist of armour, filter and core layers. The units used in the armour layer are natural rock or concrete. Although natural rock is usually preferred, it is not always possible to apply it. There are some advantages to using concrete units: they have a high stability coefficient under wave attack, and they are easily produced at work sites. Tetrapod and cube blocks are widely used in breakwaters as armour units.Rubble mound breakwaters are subjected not only to wave activity but also other types of environmental loading, such as earthquakes. Although rubble-mound breakwaters are most likely the most common type of breakwaters, they have received little attention regarding their response to seismic activity. The objective of this study is to present the dynamic response of a breakwater armoured by tetrapods placed by two different placement methods and armoured by cubes during seismic loadings experimentally and numerically. A shaking tank was developed for the experimental study. The breakwater models sit on a rigid bed, and the model scale is 1/50. A one-dimensional shaking tank was used to understand simple responses of the rubble mound breakwaters under seismic loads. The tank allows only one degree of freedom. A raining crane system was developed to achieve the same packing density and porosity for the core material. The shape of the model breakwater before and after the tests was measured using a profiler and was recorded by computer. However, crest lowering and the level of damage on slopes were determined from profiler records. The dynamic responses of the model breakwaters were also investigated using an image processing technique. For numerical simulation, software using finite element method was used.The results obtained from the experiment and numerical model may help designers build breakwaters armoured by artificial units. 相似文献
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Ocean waves can be destructive as steeper waves due to their high energy eroding the sandy beaches. During storm surge or high tide, the water level rises and if large waves occur, they will break closer to the beach, releasing enormous amount of energy resulting in strong currents. This causes heavy loss of beach material due to large-scale erosion. If these waves are made to break prematurely and away from the beach, they can be attenuated so as to reduce beach erosion. The reef, which is a homogeneous pile of armour units without a core, breaks the steeper ocean waves, dissipates a major portion of their energy and transmits attenuated waves. This paper experimentally investigates the armour stone stability of the submerged reef and the influence of its varying distance from shore and crest width on ocean wave transmission. 相似文献
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Stability formulae for armour layers of rubble mound breakwaters are usually being applied assuming perpendicular wave attack. Often the effects of oblique waves are neglected. This is however a conservative assumption since the stability of armour slopes generally increases for oblique waves. New wave basin tests have been performed to assess the effects of oblique waves on the stability of rock slopes and the stability of cube armoured rubble mound breakwaters. The physical model tests were focussed on wave directions between perpendicular (0°) and parallel (90°). The test programme included tests with long-crested waves and tests with short-crested waves. The results show that for rock slopes the influence of oblique waves is larger for long-crested waves. Based on the test results a design guideline is provided to account for effects of oblique waves on the stability of rock slopes, armour layers with a double layer of cubes, and armour layers with a single layer of cubes. 相似文献
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Sun Jingshi Zhu Yiming
Research Professor Tianjin Research Institute of Water Transport Engineering Tianjin
Associate Professor Dalian Aquatic Product Institute Dalian 《中国海洋工程》1995,(1)
Through hydraulic model experiment and site investigation, this paper has derived a calculation formula of dry-laid stone armour layer thickness of rubble mound breakwaters for fishery harbours. The influences of the friction force between stone blocks and the variations of wave length or period and water depth are considered in the formula. The calculated results of several existing structures are in good agreement with field data. This formula is more practical than those ever published both at home and abroad, and has been adoptted by the technical standards of aquatic projects published by the Ministry of Agriculture of China. It is applicable for the calculation of dry-laid stone armour layer of breakwater for small- or medium-size harbours. 相似文献
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《Coastal Engineering》2006,53(4):381-394
The aim of the paper is to describe hydraulic stability of rock-armoured low-crested structures on the basis of new experimental tests and prototype observations.Rock armour stability results from earlier model tests under non-depth-limited long-crested head-on waves are reviewed.Results from new 2-D and 3-D model tests, carried out at Aalborg University, are presented. The tests were performed on detached low-crested breakwaters exposed to short-crested head-on and oblique waves, including depth-limited conditions. A formula that corresponds to initiation of hydraulic damage and allows determining armour stone size in shallow water conditions is given together with a rule of thumb for the required stone size in depth-limited design waves.Rock toe stability is discussed on the basis of prototype experience, hard bottom 2-D tests in depth-limited waves and an existing hydraulic stability formula. Toe damage predicted by the formula is in agreement with experimental results. In field sites, damage at the toe induced by scour or by sinking is observed and the volume of the berm is often insufficient to avoid regressive erosion of the armour layer.Stone sinking and settlement in selected sites, for which detailed information is available, are presented and discussed. 相似文献
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The short communication presents application of the conventional Van der Meer stability formula for low-crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms. The method is verified (Burcharth, 2008) by comparison with the reshaping of a large Norwegian breakwater exposed to the North Sea waves. As a motivation for applying the Van der Meer formula a discussion of design parameters related to berm breakwater stability formulae is given. Comparisons of front erosion predicted by the use of the Van der Meer formula with model test results including tests presented in Sigurdarson and Van der Meer (2011) are discussed. A proposal is presented for performance of new model tests with the purpose of developing more accurate formulae for the prediction of front slope erosion as a function of front slope, relative berm height, relative berm width, method of armour stone placement, and hydraulic parameters. The formulae should cover the structure range from statically stable berm breakwaters to conventional double layer armoured breakwaters. 相似文献
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The commonly used formulae like Hudson's [(1959), Laboratory investigations of rubblemound breakwaters. WES report, Vicksburg], Iribarren's or Vander meer's [(1988), Rockslopes and gravel beaches under wave attack. Ph.D. thesis, Delft University of Technology, The Netherlands], do not give us the design cross section of a rubblemound breakwater for varying core porosity values. The paper presents the results of the experimental study carried out to compute the effects of core porosity on the stability and run-up characteristics of rubblemound breakwaters. Regular waves were made to attack the structure, with different core porosity values in a normal direction. The porosity of the armour and the secondary layers was neglected. It was observed that as core porosity increased the stability also increased considerably within the limits of the experimental data values. This may be due to large inflow and energy dissipation within the core of the structure. The run-up on the rubblemound slope was found to decrease with the increase in the porosity for the same reason. 相似文献
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The geometrical properties of the armor layer of rubble mound breakwaters were investigated by observations made on two cases. The first case is a laboratory-scaled model of natural rock, designed with a composite slope. The second is a breakwater in the sea, constructed with a uniform slope of tetrapods. In both cases the cross-section underwent changes, resulting in an apparently stable profile of composite slope. This implied that for stability the optimal armour layer should be of composite slope. The general nature of this profile was implied by the geometrical similarity between the two cases which were basically so different. 相似文献
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The application of directional waves in design processes has clearly received much interest during recent years. Thus, in model testing with moored ships and offshore structures, significant deviations have been revealed between results obtained in traditional uni-directional wave trains and those obtained in directional wave fields. Whether the same tendency is valid in connection with the design of rubble mound breakwaters is studied in the present project. A breakwater with a front slope of 1:2 is tested at the scale 1:40. The weight and diameter of the stones in the core, filter and armour layers were carefully selected, and the sources of scatter in repeated tests were minimized. Furthermore, the incident wave energy was accurately adjusted to keep the same level in both uni-directional and directional waves. For the actual rubble-mound breakwater unambiguous results were obtained. When uni-directional waves were applied, the damage increased by 30–50% relative to the directional wave situation. 相似文献
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《Coastal Engineering》1987,11(3):219-239
New practical design formulae have been developed which describe the stability of rubble mound revetments and breakwaters under random wave attack. The formulae are based upon a series of model tests. More than two hundred and fifty tests have been performed in order to ensure that all the relevant variables could be varied systematically. As a result of the present series of investigations the main shortcomings in Hudson-type formulae have been solved. Stability formulae are given which include the influence of wave period, number of waves, armour grading, spectrum shape, groupiness of waves and the permeability of the core. A clearly defined damage level parameter is introduced in the formulae. 相似文献
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Based on recent experiments carried out in wave basin on breakwaters with armour layer of rocks and cubes, this paper examines the dependence of the reflection coefficient on wave directional spreading and obliquity. Results suggest that long-crested and short-crested waves give similar reflection. The reflection coefficient is markedly dependent on the wave angle of incidence. The performance of formulae available in the literature is checked against the new dataset and a significant improvement is proposed by including the wave obliquity factor that appears in the traditional expression for the overtopping discharge. 相似文献
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This paper discusses some previous, and presents some new experimental results on wave transmission oversubmerged breakwaters. The objective of this study is to evaluate wave transmission coefficient and develop two-dimensional (2D) model as an improvement to the existing wave transmission coefficient models. Factors which affect wave transmission over submerged breakwaters are discussed through series of laboratory experiments. Basic recommendations for evaluation and design of submerged rubble-monud breakwaters are presented.From the test results, calculation formula of wave transmission coefficient is proposed. 相似文献
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《Coastal Engineering》2006,53(5-6):395-417
This paper is the second part of the work presented by Garcia et al. [Garcia, N., Lara, J.L., Losada, I.J., 2004. 2-D numerical analysis of near-field flow at low-crested breakwaters. Coastal Engineering 51 (10), 991–1020]. In the mentioned paper, flow conditions at low-crested rubble-mound breakwaters under regular wave attack were examined, using a combination of measured data of free surface, bottom pressure and fluid velocities from small-scale experiments and numerical results provided by a VOF-type model (COBRAS) based on the Reynolds-Averaged Navier–Stokes (RANS) equations. This paper demonstrates the capability of the COBRAS model to reproduce irregular wave interaction with submerged permeable breakwaters. Data provided by the numerical model are compared to experimental data of laboratory tests, and the main processes of wave–structure interaction are examined using both experimental and numerical results. The numerical model validation is carried out in two steps. First, the procedure of irregular wave generation is verified to work properly, comparing experimental and numerical data of different cases of irregular wave trains propagating over a flat bottom. Next, the validation of the numerical model for wave interaction with submerged rubble-mound breakwaters is performed through the simulation of small-scale laboratory tests on different incident wave spectra. Results show that the numerical model adequately reproduces the main aspects of the interaction of random waves with submerged porous breakwaters, especially the spectral energy decay at the structure and the spectrum broadening past the structure. The simulations give good results in terms of height envelopes, mean level, spectral shape, root-mean-square height for both free surface displacement and dynamic pressure inside the breakwater. Moreover, large-scale simulations have been conducted, on both regular and irregular incident wave conditions. The overall pattern of the wave interaction with a large-scale submerged breakwater is adequately reproduced by the numerical model. The processes of wave reflection, shoaling and breaking are correctly captured. The good results achieved at a near prototype scale are promising regarding the use of the numerical model for design purposes. 相似文献
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The semi-empirical formulae by Pedersen (1996) for wave loads on vertical front faces of stiff crown walls are based on model tests with deep and intermediate water wave conditions. A new series of model tests performed at the same test facility as used by Pedersen has revealed that the formulae by Pedersen overpredict the loads in shallow water wave conditions. This paper presents a modification/expansion of the formulae to cover loads in both deep and shallow water wave conditions. The modification is based on a series of 162 physical model tests on typical rubble mound breakwaters with crown wall superstructures. The implementation of shallow water wave conditions in the formulae is done by modifying the term for wave run-up to be dependent on the incident wave height distribution. Moreover, the adjusted formulae provide more accurate estimates of the wave loads on free walls without front armour protection. Pressure transducers with very high eigen-frequencies were used in the present model tests as opposed to the transducers applied by Pedersen which in some cases seem to have been affected by dynamic amplifications. 相似文献
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基于开源程序REEF3D,通过建立高精度二维数值波浪水槽,系统研究了聚焦波浪在浅堤上传播变形的规律,着重分析了聚焦波浪通过浅堤的水动力过程及能量变化规律,讨论了不同波浪要素对聚焦波浪传播特性的影响。除此之外,还考虑了双浅堤布置对聚焦波浪传播变形的影响。研究结果表明:极端波浪通过浅堤时,堤顶水深越小,波浪主频能量衰减越显著。在给定堤顶水深条件下,聚焦点与浅堤的相对位置对聚焦波浪能量的衰减影响较小。在双浅堤布置条件下,随着浅堤间距的增加,上下游浅堤的相互影响逐渐减弱,高频段的波浪能量也随之减小。 相似文献
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A parametric experimental study is conducted to compare the reflection and transmission characteristics of submerged hemi-cylindrical and rectangular rigid and water-filled flexible breakwater models. The results show that, for the rigid breakwaters, rectangular models are more effective than hemi-cylindrical ones in terms of reduction of transmitted waves. As for the flexible breakwaters, the hemi-cylindrical models may give better wave reflection than rectangular ones. However, the energy loss induced by the rectangular breakwaters is much larger and more significant to result in an overall better efficiency in terms of reduction in wave transmission. The effects of internal pressure show that the lowest pressurized flexible models considered in this work are the most effective in the reduction of the transmitted wave height. Higher wave reflection, lower wave transmission and higher energy loss are obtained consistently at the lower submergence depth ratio. 相似文献
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Tetrapod, one of the well-known artificial concrete units, is frequently used as an armor unit on breakwaters. Two layers of tetrapod units are normmaly placed on the breakwaters with different placement methods. In this study, the stability of tetrapod units with two different regularly placement methods are investigated experimentally in irregular waves. Stability coefficients of tetrapod units for both placement methods are obtained. The important characteristic wave parameters of irregular waves causing the same damage ratio as those of the regular waves are also determined. It reveals that the average of one-tenth highest wave heights within the wave train (H1/10) causes the similar damage as regular waves. 相似文献