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1.
Yovanni A. Cataño-Lopera 《Ocean Engineering》2011,38(10):1256-1268
The scour and burial of conical frustums placed on a sandy bed under waves alone (WA) and combined flows (CF) conditions was investigated. The observations indicate that equilibrium burial depth is smaller than burial of other objects such as short cylinders laying on a sand bed under equivalent hydrodynamic conditions. Truncated cone offers less resistance to the flow field due to its more round shape when compared to a horizontally placed short cylinder characterized by sharp edges. A smaller disruption to the flow field translates to less turbulent intensity and to smaller sediment transport capacity of the flow around the object and less burial. The equilibrium burial depth shows a significantly weaker dependency on the Shields parameter than on the Keulegan-Carpenter number, contrary to the case of finite short cylinders. A new empirical predictor based on the relative strength of the wave to the wave plus current velocity, the Keulegan-Carpenter number, and the Shields parameter is proposed for estimating the equilibrium burial of truncated cones under combined flows. Both the Keulegan-Carpenter number and the Shields parameter determine the width of the scour hole around the cone. The former however, is the most dominant parameter influencing the length of the scour hole. 相似文献
2.
《Oceanic Engineering, IEEE Journal of》2007,32(1):91-102
Burial of instrumented mine-like cylinders as a result of wave-induced scour was measured during experiments conducted in shallow water (15-16 m) with fine-sand (133-mum) and coarse-sand (566-mum) sediments off Indian rocks beach (IRB), FL. scour pits developed around the instrumented cylinders in the fine-sand site when significant waveheights exceeded 2 m, causing the cylinders to pitch, then roll into the developing scour pits, often changing heading to align parallel with the wave crest. Final cylinder burial was nearly 40 cm (about 70%-80% mine diameter) relative to the sediment-water interface, but only 20%-50% relative to surface area covered. The difference was caused by the lack of complete infilling of scour pits. Little development of scour pits and burial was noted on the coarse-sand site and the cylinders buried to only 20%-40% of the cylinder diameter below the sediment surface. Burial results, although variable, are in general agreement with the wave-induced scour model developed by Trembanis et al. (2007) for the fine sand, but not for the coarse sand where measured burial was much less than predicted. 相似文献
3.
针对水下桩墩的局部冲刷问题,提出一种适用范围广、防冲促淤效果显著的防护措施。该防护措施把一种相对密度略大于水、几何特征特殊的中性网格结构完全覆盖在冲刷坑或可能出现冲刷坑的床面上,以减弱冲刷坑内水动力,促进泥沙落淤,达到减轻局部冲刷的目的。通过数值模拟和水槽试验探讨了中性网格结构对圆桩周围冲刷坑内水动力及床面形态的影响,并研究了网孔尺寸对防冲促淤效果的影响规律。结果表明：该中性网格结构能显著减小局部冲刷坑内的流速,有效抑制局部冲刷,且对桩前来流来沙的影响微弱。孔径比7.7的网格防护结构可以使无黏性沙床上圆桩的局部冲刷深度减少92%,已存在的冲刷坑则可被修复73%。这些研究成果为桩墩局部冲刷防护提供一种新的思路。 相似文献
4.
桥墩基础冲刷是桥梁毁坏的重要因素,是桥梁基础设计的关键指标之一。目前国内外对于桥墩基础在复杂动力条件下冲刷深度的研究常采用物理模型试验方法,利用正态系列模型方法,在波流水槽中研究了水流、潮流和波流共同作用下青州航道桥索塔基础周围流态变化和局部冲刷特征。研究结果表明,桥墩最大冲刷深度和冲淤范围与水流流速、桥墩轴线与水流夹角和波浪等因素有关;在潮流最大流速和恒定流流速一致情况下,桥墩局部冲刷深度达到平衡后,将会达到与恒定流基本一致的最大冲深;波流共同作用下的最大冲刷深度比恒定流增加10%左右。设计桥墩形状在100年一遇水流和波浪共同作用下桥墩基础局部最大冲刷深度为13.7 m。 相似文献
5.
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
6.
An approximate, semi-analytical technique is developed to calculate the wave-induced loads and added-mass and radiation damping coefficients for idealized ocean structures consisting of arrays of large-diameter, truncated, vertical circular cylinders. The approach involves replacing the complete wave field scattered/radiated by one cylinder in the vicinity of another cylinder by a plane wave together with a non-planar correction term and so is essentially a large-spacing approximation. Numerical results are presented which illustrate the accuracy of the approximate approach and provide estimates of the hydrodynamic characteristics of several practical array configurations. 相似文献
7.
Manish Pandey P. K. Sharma Z. Ahmad Umesh Kumar Singh Nilav Karna 《Marine Georesources & Geotechnology》2018,36(6):663-676
The experimental results of time average velocity components measured around circular pier models during transient scour stage using acoustic Doppler velocimeter are shown for flow pattern and turbulence characteristics. Totally, four experiments were performed under clear water scour conditions in a model of gravel bed stream. Four circular pier models of diameter 6.6, 8.4, 11.5, and 13.5?cm were used for this study. Detailed controlled measurements on velocity components, and turbulence intensities near the pier and in scour hole at 0° and 180° plane are shown. Flow structure around a pier model in the presence of a scoured region was compared with the flow structure similarly noticed around all pier model runs by utilizing the observations taken at 0° and 180° plane from flow axis. Size of the primary vortex at 0° plane with largest diameter pier model in place (R4 run) is found to be maximum and was approximately 61% larger than that for smallest diameter pier model in place (R1 run). The time-averaged velocity components of turbulence intensities plots at 0° and 180° planes are also presented around each pier. 相似文献
8.
《Coastal Engineering》2001,44(2):153-190
This paper summarizes the results of the European Union Marine Science and Technology (EU MAST) III project “Scour Around Coastal Structures” (SCARCOST). The summary is presented under three headings: (1) Introduction; (2) Flow and scour processes with the subheadings: flow and scour processes around vertical cylinders; flow and scour processes at detached breakwaters; flow and scour processes at submerged breakwaters; and the effect of turbulence on sediment transport; and (3) Sediment behaviour close to the structure with the subheadings: field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; non-linear soil modelling with respect to wave-induced pore pressures and gradients; wave-induced pressures on the bottom for non-linear coastal waves, including also wave kinematics; development of a numerical model (linear soil modelling) to calculate wave-induced pore pressures—the effect of liquefaction on sediment transport; penetration of blocks in non-consolidated fine soil; and cyclic stiffness of loose sand.The paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design. 相似文献
9.
Vibration of two elastically mounted cylinders in an oscillatory flow at a Keulegan-Carpenter number of 10 is simulated numerically. The two cylinders are rigidly connected with each other and are allowed to vibrate in the cross-flow direction only. The aim of this paper is to identify the effects of the orientation of the cylinders and the gap between the cylinders on the vibration. The two-dimensional Reynolds-Averaged Navier-Stokes equations are solved to predict the flow and the cylinder vibration is predicted using the equation of motion. When the two cylinders are in a tandem arrangement, a combined single pair flow regime and attached pair flow regime are observed as reduced velocity exceeds 10 and this combined regime and the single pair regime occurs intermittently. Periodic vibration is found when the two cylinders are in a staggered arrangement with a 45° flow attack angle. When the two cylinders are in a side-by-side arrangement, a new single vortex regime is observed. This single vortex remains attached to the cylinder surface and rotates around the cylinder. The intermittent switch between this single vortex regime and the single pair regime are observed. 相似文献
10.
An array of large concentric porous cylinder arrays is mounted in shallow water exposed to cnoidal waves. The interactions between waves and cylinders are studied theoretically using an eigenfunction expansion approach. Semi-analytical solutions of hydrodynamic loads and wave run-up on each cylinder are obtained using first approximation to cnoidal waves. The square array configuration of four-legged identical concentric porous cylinder is investigated in present study. Numerical results reveal the variation of dimensionless wave force and wave run-up on individual cylinder with angle of incidence, porosity parameter, spacing between outer and inner cylinders, spacing between concentric porous cylinders and wave parameter. Different mechanism of wave force is found under different range of scattering parameter. 相似文献
11.
This paper presents the results of an experimental investigation on the near-bed flow patterns, the bed shear stress amplification and scour around the head of a vertical-wall breakwater, using regular waves. The Keulegan-Carpenter number (KC), based on the diameter of the breakwater head, is found to be the major parameter that governs the flow and the equilibrium scour depth. Basic flow structures are identified as function of KC. The scour depth is found to increase with increasing the Keulegan-Carpenter number. The necessary extent of the conventional stone protection is studied. An empirical formula is worked out for the width of the protection layer as function of KC. Also, the effects of head shape, the angle of attack and the presence of a co-directional current are investigated. The results indicate that the scour depth is increased considerably in the presence of a current. Likewise, the scour depth is increased when the head shape is changed from a round shape to a sharp-edged one. It is found that the angle of attack is also an influencing factor as regards the scour depth. 相似文献
12.
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
13.
基于局部冲刷研究的大型圆柱周围波浪特性分析 总被引：2，自引：0，他引：2
波浪环境下,大型圆柱的存在改变了周围原有波浪条件,直接导致局部冲刷。利用MacCamy和Fuchs的绕射理论对相对柱径较大(0.15相似文献
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16.
A finite-volume method (FVM) using a multi-block grid technique has been applied to investigate the hydrodynamic coefficients and to categorize the two-dimensional flow pattern around a pair of adjacent cylinders (known here after as double cylinders). Matching grids were used at the interface between blocks (cylinders), and the boundary conditions are imposed around the periphery to exchange physical values across the interface. To validate the developed numerical method, a case with laminar viscous flow around a single cylinder was carried out, the results showed good agreement compared to previously published data. Hydrodynamic coefficients, Strouhal number, and stagnation point change were thoroughly investigated as a function of the separation between the two cylinders. It is found that the changes of hydrodynamic coefficients due to variations in separation are well characterized by the five different vortex flow patterns, which can also be used to explain the flow and vortex pattern around the double cylinders. 相似文献
17.
H. Omara G. M. Abdeelaal K. Nadaoka A. Tawfik 《Marine Georesources & Geotechnology》2020,38(2):133-143
AbstractBecause scour is one of the main reasons for bridge failure, this study focuses on accurately predicting the maximum scour depth around different vertical and inclined piers. Scouring is an issue of concern in the bridge design process, as most existing equations for predicting local scour near bridge piers suffer from over- or underprediction issues, resulting in higher foundation costs or bridge failure and inaccurate predictions of the scour around piers. The dimensionless maximum scour depths (ys/D) of vertical and inclined piers were investigated for seven pier shapes with different L/D ratios and four inclination angles (θ) under shallow flow conditions. The inclined pier configuration reduced the ys/D of the piers. The maximum ys/D was observed for a rectangular pier with an L/D of 4.5 in both vertical and inclined configurations (θ of 10, 15 and 21°, respectively). The ys/D was significantly decreased by increasing the angle of the pier from 10 to 30°. The ys/D of the inclined rectangular piers decreased as θ decreased from 30 to 10° and the L/D ratio increased from 1 to 4.5. The best ys/D results were obtained for inclined rectangular piers at a θ value of 30° and an L/D ratio of 7.5 compared to other shapes and inclination angles. New equations were developed to predict the local scour depth for circular, square and rectangular bridge piers. The equations yielded excellent results for predicting the maximum clear water scour depth around vertical and inclined piers with inclination angles of 10, 15, 21 and 30°, respectively. 相似文献
18.
The interaction of a solitary wave with an array of surface-piercing vertical circular cylinders is investigated numerically. The wave motion is modeled by a set of generalized Boussinesq equations. The governing equations are discretized using a finite element method. The numerical model is validated against the experimental data of solitary wave reflection from a vertical wall and solitary wave scattering by a vertical circular cylinder respectively. The predicted wave surface elevation and the wave forces on the cylinder agree well with the experimental data. The numerical model is then employed to study solitary wave scattering by arrays of two circular cylinders and four circular cylinders respectively. The effect of wave direction on the wave forces and the wave runup on the cylinders is quantified. 相似文献
19.
AbstractSediment has a severe effect on bridge stability, and time-domain reflectometry (TDR) is a suitable method for assessing scour depth. This paper presents a fundamental study to demonstrate the suitability of a circular TDR system to enhance the resolution when monitoring scour depth with consideration of detailed local changes over a wide area around piers. A total of 32 electrodes are vertically installed on a cylinder pier around the circumference at ～7.36?mm intervals. Scour depth is investigated through small-scale laboratory experiments, where a measured waveform reflects the artificially constructed scour depth with high resolution (≈5?mm). Different scour types including circular, mushroom, elliptical, and irregular shapes are developed to verify the application of circular TDR, and shapes are predicted through the detailed local distribution. The influences of the reflected waveform according to water level change, temperature variation, and salinity effect are investigated as additional considerations, and the relative deviation of scour depth is analyzed. This study demonstrates that the proposed circular TDR system achieves better resolution than existing single TDR systems and may provide a better alternative technique for monitoring scour depth. 相似文献
20.
Local scour around a bridge pier is an important pm‘mneter for the design of a bridge. Compared with the local scour in a mono-directional current, the local scour in a tidal current has its unique characteristics. In this paper, several aspects of local scour around bridge piers in tidal current, including the scour development process, the plane form of a scour hole and the maximum scour depth, are studied through movable bed flume experiments. 相似文献