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1.
An approach by which the scour depth and scour width below a fixed pipeline and scour depth around a circular vertical pile in random waves can be derived is presented. Here, the scour depth formulas by Sumer and Fredsøe [ASCE J. Waterw., Port, Coastal Ocean Eng. 116 (1990) 307] for pipelines and Sumer et al. [ASCE J. Waterw., Port, Coastal Ocean Eng. 114 (1992) 599] for vertical piles as well as the scour width formula by Sumer and Fredsøe [The Mechanics of Scour in the Marine Environment, World Scientific, Singapore, 2002] for pipelines combined with describing the waves as a stationary Gaussian narrow-band random process are used to derive the cumulative distribution functions of the scour depths and width. Comparisons are made between the present approach and random wave scour data. Tentative approaches to related random wave scour cases are also suggested. 相似文献
2.
《Coastal Engineering》2004,51(10):1051-1065
An approach by which the scour depth and protection layer width around the head of vertical-wall breakwaters, the scour and deposition depths as well as the protection layer widths at the round head of rubble-mound breakwaters in random waves can be derived is presented. Here the formulas for scour depth by Sumer and Fredsøe (1997) for vertical-wall breakwaters for regular waves and Fredsøe and Sumer (1997) for rubble-mound breakwaters for irregular waves are used. They are combined with describing the waves as a stationary Gaussian narrow-band random process to derive the scour and deposition depths as well as protection layer widths in random waves. Comparisons are made between the present approach and the Fredsøe and Sumer (1997) random wave scour data for rubble-mound breakwaters. 相似文献
3.
Onset of scour below pipelines and self-burial 总被引：1，自引：0，他引：1
This paper summarizes the results of an experimental study on the onset of scour below and self-burial of pipelines in currents/waves. Pressure was measured on the surface of a slightly buried pipe at two points, one at the upstream side and the other at the downstream side of the pipe, both in the sand bed. The latter enabled the pressure gradient (which drives a seepage flow underneath the pipe) to be calculated. The results indicated that the excessive seepage flow and the resulting piping are the major factor to cause the onset of scour below the pipeline. The onset of scour occurred always locally (but not along the length of the pipeline as a two-dimensional process). The critical condition corresponding to the onset of scour was determined both in the case of currents and in the case of waves. Once the scour breaks out, it will propagate along the length of the pipeline, scour holes being interrupted with stretches of soil (span shoulders) supporting the pipeline. As the span shoulder gets shorter and shorter, more and more weight of the pipeline is exerted on the soil. In this process, a critical point is reached where the bearing capacity of the soil is exceeded (general shear failure). At this point, the pipe begins to sink at the span shoulder (self-burial). It was found that the self-burial depth is governed mainly by the Keulegan–Carpenter number. The time scale of the self-burial process, on the other hand, is governed by the Keulegan–Carpenter number and the Shields parameter. Diagrams are given for the self-burial depth and the time scale of the self-burial process. 相似文献
4.
This paper provides a practical stochastic method by which the maximum equilibrium scour depth around a vertical pile exposed to long-crested (2D) and short-crested (3D) nonlinear random waves plus a current can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the empirical formulas for the scour depth by Sumer and Fredsøe (2002). Comparisons are made between the present approach and the Sumer and Fredsøe (2001) data for 2D random waves plus current. An example calculation is provided. 相似文献
5.
This paper provides an approach by which the scour depth below pipelines in shoaling conditions beneath non-breaking and breaking random waves can be derived. Here the scour depth formula in shoaling conditions for regular non-breaking and breaking waves with normal incidence to the pipeline presented by Cevik and Yüksel [Cevik, E. and Yüksel, Y., (1999). Scour under submarine pipelines in waves in shoaling conditions. ASCE J. Waterw., Port, Coast. Ocean Eng., 125 (1), 9–19.] combined with the wave height distribution including shoaling and breaking waves presented by Mendez et al. [Mendez, F.J., Losada, I.J. and Medina, R., (2004). Transformation model of wave height distribution on planar beaches. Coast. Eng. 50 (3), 97–115.] are used. Moreover, the approach is based on describing the wave motion as a stationary Gaussian narrow-band random process. An example of calculation is also presented. 相似文献
6.
This paper provides a stochastic method by which the random wave-induced scour depth at the trunk section of vertical-wall and rubble-mound breakwaters can be derived. Here the formulas for regular wave-induced scour depth provided by Xie [Xie, S.L., 1981. Scouring patterns in front of vertical breakwaters and their influence on the stability of the foundations of the breakwaters. Report. Department of Civil Engineering, Delft University of Technology, Delft, The Netherlands, September, 61 pp.] for vertical-wall breakwater and Sumer and Fredsøe [Sumer, B.M., Fredsøe, J., 2000. Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coast. Eng. 40, 59–87] for rubble-mound breakwater are used. These formulas are combined with describing the waves as a stationary Gaussian narrow-band random process to derive the random wave-induced scour depth. Comparisons are made between the present method and the Sumer and Fredsøe [Sumer, B.M., Fredsøe, J., 2000. Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coast. Eng. 40, 59–87.] random wave scour data for rubble-mound breakwater, as well as the Hughes and Fowler [Hughes, S.A., Fowler, J.A., 1991. Wave-induced scour predictions at vertical walls. ASCE Proc. Conf. Coastal Sediments vol. 91, 1886–1899] random wave scour data and formula for vertical-wall breakwater. A tentative approach to random wave-induced scour at a vertical impermeable submerged breakwater is also suggested. 相似文献
7.
AbstractThe scour phenomena around vertical piles in oceans and under waves may influence the structure stability. Therefore, accurately predicting the scour depth is an important task in the design of piles. Empirical approaches often do not provide the required accuracy compared with data mining methods for modeling such complex processes. The main objective of this study is to develop three data-driven methods, locally weighted linear regression (LWLR), support vector machine (SVR), and multivariate linear regression (MLR) to predict the scour depth around vertical piles due to waves in a sand bed. It is the first effort to develop the LWLR to predict scour depth around vertical piles. The models simulate the scour depth mainly based on Shields parameter, pile Reynolds number, grain Reynolds number, Keulegan–Carpenter number, and sediment number. 111 laboratory datasets, derived from several experimental studies, were used for the modeling. The results indicated that the LWLR provided highly accurate predictions of the scour depths around piles (R?=?0.939 and RMSE = 0.075). Overall, this study demonstrated that the LWLR can be used as a valuable tool to predict the wave-induced scour around piles. 相似文献
8.
This paper provides a stochastic method by which the two-dimensional onshore scour characteristics along the base of submerged breakwaters exposed to normally incident random waves on both sloping and horizontal sandy seabed can be derived. Here the formulas for the regular wave-induced scour characteristics provided by Young and Testik (2009) are used. These formulas are combined with describing the waves as a stationary Gaussian narrow-band random process to derive the random wave-induced onshore scour characteristics; the maximum scour depth, the scour length, and the distance of the maximum scour depth location from the onshore breakwater face. An example of calculation is also provided. 相似文献
9.
This paper provides an approach by which the burial and scour of short cylinders under combined second order random waves and currents can be derived. Here the formulas for burial and scour for regular waves plus currents presented by Catano-Lopera and Garcia [Catano-Lopera, Y.A. and Garcia, M.H. (2006). Burial of short cylinders induced by scour under combined waves and currents. ASCE J. Waterway, Port, Coastal and Ocean Eng. 132(6), 439–449., Catano-Lopera, Y.A. and Garcia, M.H. (2007). Geometry of scour hole around, and the influence of the angle of attack on the burial of finite cylinders under combined flows. Ocean Eng. 34(5, 6), 856–869.] are used together with Stokes second order wave theory by assuming the basic harmonic wave motion to be a stationary Gaussian narrow-band random process. An example of calculation is also presented. 相似文献
10.
为了验证新型伞式吸力锚基础的防冲刷效果,本文利用Flow-3D软件建立三维海床-吸力锚-波浪相互作用模型,基于JONSWAP随机波浪谱,结合某海域风区资料模拟随机波,对随机波浪作用下伞式吸力锚基础(USAF)局部冲刷演变进行分析,试验土体为非黏性土.首先探讨了随机波浪作用下基础周围流场变化规律和冲刷演变模式,其次分析了... 相似文献
11.
Dag Myrhaug Muk Chen Ong Henrik Føien Cecilie Gjengedal Bernt J. Leira 《Ocean Engineering》2009,36(8):605-616
This paper provides a method by which the scour depth below pipelines and around single vertical piles for combined random waves plus current including effects of second-order wave asymmetry can be derived. Here the empirical formulas proposed by Sumer and Fredsøe [1996. Scour below pipelines in combined waves and current. In: Proceedings of the 15th OMAE Conference, Florence, Italy. Vol. 5, ASME, New York, pp. 595–602] for pipelines, and by Sumer and Fredsøe [2002. The mechanics of scour in the marine environment. World Scientific, Singapore] for vertical piles are used together with Stokes second-order wave theory by assuming the basic harmonic wave motion to be a stationary Gaussian narrow-band random process. Comparisons are made with the Sumer and Fredsøe [1996. Scour below pipelines in combined waves and current. In: Proceedings of the 15th OMAE Conference, Florence, Italy. Vol. 5, ASME, New York, pp. 595–602; 2001. Scour around pile in combined waves and current. Journal of Hydraulic Engineering, 127(5), 403–411] data for linear random waves plus current. An example of calculation is also presented. 相似文献
12.
The flow-structure interaction in an ocean environment, for a pile placed in an erodible bed where currents and waves are of prime concern, changes the bed elevation due to scour in the vicinity of the obstruction. There are certain difficulties in predicting the scour depth, as the particulate movement of sediments due to scour is time-dependent. Considering the complexity of the problem, an instrumentation system has been developed for measuring scour depth with time. This paper outlines the experimental laboratory techniques used to measure scour around pile foundations in silty-clay sediments. Detailed laboratory testing on model piles having a diameter of 50-110 mm was carried out in a wave flume having a length of 30 m and a width of 2.0 m. The motivation of these studies is to obtain observational experience of scour rate in silty-clay soil. Scour depths were monitored continuously for different combinations of wave characteristics and current velocities, and scour-time history is measured. Based on the measurements, a relationship for the scour depth in terms of duration of flow, soil properties, model characteristics, and fluid parameters is presented. 相似文献
13.
Understanding the sediment transport and the resulting scour around coastal structures such as pile breakwaters under local extreme wave conditions is important for the foundation safety of various coastal structures. This study reports a wave-flume experiment investigating the scour induced by solitary waves at a pile breakwater, which consists of a row of closely spaced large piles. A wave blacking gate with a simple operation procedure in the experiment was designed to eliminate possible multiple reflections of the solitary wave inside the flume. An underwater laser scanner and a point probe were used in combination to provide high-resolution data of the bed profile around the pile breakwater. Effects of incident wave height and local water depth on the maximum scour depth, the maximum deposition height and the total scour and deposition volumes were examined. An existing empirical formula describing the evolution of the scour at a single pile in current or waves was extended to describe the scour at the pile breakwater under the action of multiple solitary waves, and new empirical coefficients were obtained by fitting the formula to the new experimental data to estimate the equilibrium scour depth. It appears that the maximum scour depth and the total scour volume are two reliable quantities for validation of numerical models developed for the scour around pile breakwaters under highly nonlinear wave conditions. 相似文献
14.
1 .IntroductionWiththedevelopmentofexploitationofmarineresources ,theconstructionofoffshorestructuresdevelopsrapidly ,suchasmarineoilplatforms ,deep waterbreakwaters ,marinebridges ,largehar bors,etc .Thesestructureswillchangesurroundingwaveandcurrentconditionsandleadtolocalscourofseabed ,resultinginstructuraldamage .Therefore ,localscouraroundmarinestructuresaswellastheirprotectionhasdrawnmuchattentionfromrelativeengineeringfields .Manyscholarshaveconduct edtheoreticalanalysisandexperimentals… 相似文献
15.
Five generalized physical models of drfferent distortion ratios were bruit according to DOU Guo-ren‘s similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given. 相似文献
16.
Scour of the Seabed Under A Pipeline in Oscillating Flow 总被引：3，自引：0，他引：3
The scour of the seabed under a pipeline is studied experimentally in this paper. Tests are carried out in a U-shaped oscillatory water tunnel with a box imbedded in the bottom of the test section. By use of the standard sand, clay and plastic grain as the seabed material, the influence of the bed material on the scour is studied. The relationship between the critical initial gap-to-diameter ratio above which no scour occurs and the parameters of the oscillating flow is obtained. The self-burial phenomenon, which occurs for the pipeline not fixed to two sidewalls of the test section, is not observed for the fixed pipeline. The effect of the pipe on sand wave formation is discussed. The maximum equilibrium scour depths for different initial gap-to-diameter ratios, different Kc numbers and different bed sands are also given in this paper. 相似文献
17.
Local scour below a vibrating pipeline under steady current is investigated by a finite element numerical model. The flow, sediment transport and pipeline response are coupled in the numerical model. The numerical results of scour depths and pipeline vibration amplitudes are compared with measured data available in literature. Good agreement is obtained. It is found that pipeline vibrations cause increases of scour depth below the pipeline. The scour pit underneath a two-degree-of-freedom vibrating pipeline is deeper than that under a pipeline vibrating only in the transverse flow direction. The effects of water depth are also investigated. The present numerical result shows that water depth has weak effect on the scour depth. However it does affect the time scale of the scour. The shallower the water depth is, the less time it requires to reaches the equilibrium state of scour. It is found that the vibration forces vortices to be shed from the bottom side of the pipeline. Then vortex shedding around a vibrating pipeline is closer to the seabed than vortex shedding around a fixed pipeline. This contributes to the increase of the scour depth. 相似文献
18.
采用当地海床的天然粉沙进行试验床面的设计,对海底管道在实际海床受到的极限波浪和最大水流作用进行试验,在管道上方铺设混凝土联锁排,对联锁排块体稳定性和其对管道防护的有效性进行研究。通过物理模型试验,研究了在极限波浪和最大水流作用下,管道在粉沙床面最大冲刷深度。通过不同水深中波流条件下研究了混凝土联锁排防护效果及其周围床面的冲刷变化,观测了联锁排的稳定性。试验结果表明:按半经验半理论简化公式得出的联锁排厚度能满足稳定性的要求,比水利部规范计算的联锁排厚度偏大的公式更加适合应用,试验期间混凝土联锁排的排面稳定,能有效保护管道,在该防护下管道没有冲刷,只在联锁排上下游与床面接触的来流段和尾端有冲刷,但该冲刷深度不影响联锁排整体的稳定性。 相似文献
19.
20.
The results of a laboratory experimental program aimed at better understanding the scour around and burial of heavy cylindrical objects under oscillating flow on a sandy bed are described. This study was motivated by its application to the dynamics of isolated cobbles/mines on a sandy floor under nonlinear progressive waves, such as that occur in shallow coastal waters beyond the wave-breaking region. In the experiments, nonlinear progressive waves were generated in a long wave tank of rectangular cross-section with a bottom slope. Model mines (short cylinders) were placed on the sandy bottom and the temporal evolution of the bed profile and the velocity field in the near field of the object were observed. Experiments were conducted at relatively high Reynolds numbers for a range of flow conditions, which can be characterized by the Keulegan–Carpenter number and Shields parameter. Depending on the values of these parameters, four different scour regimes around the cylinder including periodical burial of cylinder under migrating sand ripples were observed; they were classified as: (i) no scour/burial, (ii) initial scour, (iii) expanded scour, and (iv) periodic burial cases. A scour regime diagram was developed and the demarcation criteria between different regimes were deduced. Semi-empirical formulae that permit estimation of the scour depth with time, the equilibrium maximum scour depth and length, and conditions necessary for the burial of the cylinder as a function of main external parameters are also proposed. 相似文献