海岸裂流的浮子示踪法实验测量

研究模型实验中采用浮子示踪法测量沙坝海岸裂流的方法,讨论了该方法的具体技术实现和测量结果的精度。实验中裂流由波浪在垂直岸线的直墙上的反射所形成的两列交叉的波浪生成。通过处理CCD图像的浮子轨迹得到了流场的详细速度分布,如旋涡分布等,显示了该方法优于流速仪定点测量的一些特点。与ADV流速仪测量结果的对比表明,由浮子轨迹得到的表层平均流速具有可靠的精度,特别是也可以应用于波浪破碎产生的裂流这样复杂流场的测量。     

Three-dimensional unstructured modelling of wave-induced circulation over a plane and irregular beach

Nearshore currents have a complicated circulation structure over a beach due to the mutual interaction between waves and currents. To investigate the wave-induced circulation over a beach, a three-dimensional unstructured model accounting for the combined actions of waves and currents is established. The wave distribution over the beach is computed by a wave model and the depth-dependent wave radiation stresses with the surface roller are employed in the hydrodynamic model. The present model takes the mixing coefficients and the bottom shear stress under waves and currents into account. To evaluate the three-dimensional unstructured model, the laboratory experiments over a plane and irregular beach are used to test the performance of the model. The undertow over a plane beach is well reproduced and the vertical variability is captured. The performance of the model over an irregular beach is well displayed in the reproduction of pairs of counter-rotating primary circulations at the embayment troughs. Meanwhile, the secondary circulations are observed in the swash zone. The model captures the circulation systems over a beach and the circulation structures of the wave-induced currents are well exhibited.     

粗糙床面振荡紊流边界层运动的三维格子玻尔兹曼模拟

该文采用格子玻尔兹曼(LB)方法建立了紧密排列颗粒粗糙床面振荡紊流边界层模拟的三维数学模型。收集粗糙床面波浪水槽实验结果,对水槽实验条件下的振荡流边界层进行模拟,模拟得到的平均流速、紊动特性、等效粗糙高度、摩阻系数和边界层厚度等与实验结果进行了全面对比,并对三维涡旋结构进行了分析。结果表明,所建立的LB数学模型可以合理模拟粗糙床面振荡流边界层流动,能够反映三维涡旋特性,可进一步应用于粗糙床面振荡流紊动特性以及床面粗糙参数的研究。     

高进水塔地震波斜波入射有限元分析

在水工结构抗震动力分析中,反应谱和时程分析都是基于地震波垂直入射来考虑地震荷载的影响,而实际地震波的传播方向往往是斜波入射。斜入射地震波会引起地面运动的非一致变化,从而对结构产生很大的影响。基于波动理论和黏弹性人工边界波动输入方法,采用有限元模拟地震波斜波入射,并比较在45°斜波入射情况下进水塔与基岩接触的上游建基面、塔背回填混凝土与塔身接触位置等关键部位的顺水流向和竖向加速度、位移、应力时程曲线,结果表明,采用黏弹性人工边界等效荷载方法可以实现地震波斜入射的输入,计算结果与理论分析结果一致。     

Rip currents near coastal structures in Lake Michigan: Characterization and assessment for warnings

Rip currents near coastal structures commonly occur in Lake Michigan in the Great Lakes region of the United States. Lack of timely warning due to undocumented characteristics of rip currents and no assessment tool can contribute to tragic drownings incidents. In this paper, we characterized rip current occurrences near breakwater structures and developed an assessment tool for providing timely rip current warnings to beachgoers at the study site, City of Port Washington, WI. Characteristics of rip currents near the structure were observed from field measurements or visual images. Deflection rip currents had speeds of ～ 0.2 m/s and lasted for several hours. The rip current occurrences were associated with environmental proxies. It was found that rip currents can occur even when the water appears calm near the structure. A Structure Rip Checklist and Assessment Matrix (SRiCAM) with a four-tiered risk was developed and validated using observations. Furthermore, the SRiCAM was integrated into cyberinfrastructure with a data contingency plan to provide real-time warnings to the public. The applicability of the SRiCAM to other locations across Lake Michigan was further tested and results are promising. Overall, the SRiCAM has the potential to be widely extended to foster recreational water safety and resilience to rip current hazards in the Great Lakes.     

An experimental study of impact loading on deck of shore-connecting jetties exposed to oblique waves and current

The impact pressure from waves is an important issue to be considered in the design of coastal structures. In this paper, the waves acting on the deck of a shore-connecting jetty on a slope exposed to oblique waves and in the presence of current are examined based on laboratory experiments. The impact pressures are measured on a 1：50 scale model of a jetty head with down-standing beams and berthing members. The relations of the impact pressure with the incident wave angle and the current velocity are examined. It is shown that the impact pressure is sensitive to the wave angle and the current velocity. A computational model for the impact load on the deck of shore-connecting jetties exposed to oblique waves and current is developed.     

3-D simulation of transient flow patterns in a corridor-shaped air-cushion surge chamber based on computational fluid dynamics

The 3-D characteristics of the water-air flow patterns in a corridor-shaped air-cushion surge chamber during hydraulic transients need to be considered in the shape optimization. To verify the reliability of the water-air two-phase model, namely, the volume of fluid model, the process of charging water into a closed air chamber is successfully simulated. Using the model, the 3-D flow characteristics under the load rejection and acceptance conditions within the air-cushion surge chamber of a specific hydropower station are studied. The free surface waves, the flow patterns, and the pressure changes during the surge wave process are analyzed in detail. The longitudinal flow of water in the long corridor-shaped surge chamber is similar to the open channel flow with respect to the wave propagation, reflection and superposition characteristics. The lumped parameters of the 3-D numerical simulation agree with the results of a 1-D calculation of hydraulic transients in the whole water conveying system, which validates the 3-D method. The 3-D flow structures obtained can be applied to the shape optimization of the chamber.     

非一致地震动输入下高面板坝地震反应特性

为研究地震波非一致输入对三维高面板坝动力反应的影响,采用波场分离的思路将人工动力边界处的总波场分解为无局部场地效应影响的自由场和局部场地效应引起的散射场,借助黏弹性边界建立地震波在自由场作用下地震动非一致输入,实现考虑地基辐射阻尼和地震波行波效应的地震动输入。对我国西南地区某高面板坝进行非一致地震动反应分析,研究P波和SV波作用下坝体结构的动力反应规律。结果表明:当P波非一致输入时,随着入射角度的增加,竖向加速度和动位移极值逐渐减小,水平向加速度和动位移极值逐渐增大;SV波非一致输入时,地震动反应规律与P波入射时相反。入射角度对地震波的行波效应以及坝顶加速度反应谱幅值等都有较显著的影响。     

基于SWASH模型的近岸波浪传播变形数值模拟

SWASH模型是一种新型的非静压时域波浪模拟。为了探讨SWASH模型对于解决近岸波浪传播变形问题的适用性,在对其控制方程、边界条件、数值解法等进行介绍的基础上,采用该模型分别模拟了正向规则波、斜向规则波和斜向不规则波入射条件下L形防波堤附近水域的波浪场和波生流场,并与物理试验结果进行对比。结果表明,SWASH模型较好地复演了波浪在近岸区域所发生的浅水变形、折射、破碎,以及堤前反射、堤内绕射等物理现象,波高沿断面的定量分布与试验结果吻合良好,同时较好地模拟了不同波况下防波堤附近水域的波生流场,说明该模型适用于复杂岸线和地形条件下波浪传播变形的数值模拟。     

TWO DIMENSIONAL SIMULATION OF WIND-DRIVEN CIRCULATION IN RESERVOIR

1 .　INTRODUCTIONThethree physicalcausesaffectingreservoirflowandsedimentationarewind ,solarradiationandriverinflow .Themostimportantcauseformixinganddispersionofmassandenergyiswind ,whichatmoderatespeedcanbreakupthermalstratificationanddensityflow .Thusnumericalsimulationofwinddrivencirculationisessentialinprovidinginformationonmasstransportconditioninreservoirandindeterminingthelocation ,wherethewatercanbesafelyabstracted .Italsohaspracticalapplicationinmonitoringreservoir .Thisisveryim…     

Numerical simulation and comparison of potential flow and viscous fluid models in near trapping of narrow gaps

Numerical simulation results of fluid oscillation in narrow gaps subjected to incident water waves are presented in this paper. Both viscous fluid model and potential flow model with artificial viscous damping are employed to investigate wave motions in a single narrow gap separated by twin bodies and double narrow gaps formed by three identical bodies. Variation of wave heights in the narrow gaps with incident wave frequency is compared with experimental data available in literatures. The numerical results demonstrate that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well. However the conventional potential flow model (without introducing the artificial viscous damping) significantly over-predicts the wave height in narrow gaps around the resonant frequency. The potential flow model with artificial damping predicts resonant wave heights well with a properly tuned (or calibrated) damping coefficient. The horizontal wave force on the individual body is also examined in this work. It is found that a properly calibrated damping coefficient is also very important for estimating the horizontal wave forces on the structures. A damping coefficient of 0.4 in the potential flow model is found to result in satisfactory predictions of wave heights in the narrow gaps and the horizontal hydrodynamic force for the cases considered in this work.

     

平面SV波斜入射下重力坝动力响应分析

为了研究地震动斜入射情况对重力坝的影响,在考虑无限地基辐射阻尼效应的前提下,基于隐式有限元结合应力型黏弹性人工边界的方法,通过大型有限元软件ANSYS APDL实现地震波等效荷载的转换,并从无限地基中截取三维地基验证了地震波等效输入的正确性,建立了重力坝-库水-地基-黏弹性人工边界的有限元动力分析模型,重点研究了平面SV波斜入射对重力坝坝体地震反应的影响。结果表明:随着平面SV波斜入射角度的增大,坝体关键部位的竖直向位移呈现出逐渐增加的趋势,顺河向位移呈现出逐渐降低的趋势,其中坝顶竖直向位移最大增加幅度达到52%,最大降低幅度达到34.9%;坝体关键部位的应力对平面SV波入射角度的改变敏感程度不太一致,其中坝踵处第一主应力呈现出逐渐降低的趋势,入射角度为30°时第一主应力最小值达到2.045 27 MPa,坝趾处的第三主应力呈现出逐渐增加的趋势,入射角度为30°时第三主应力最大值达到8.228 54 MPa,在同类工程设计中应重点关注。     

波浪潮流共同作用下长兴岛海区二维悬沙输运数值模拟研究

根据近岸地区波浪、潮流与泥沙运动的规律,把波浪运动概化为在潮周期中具有时均意义的波浪流分布场,将波浪辐射应力以及波流底部剪切应力耦合到潮流运动方程和悬沙输运方程中,建立了非结构网格下近岸波浪和潮流共同作用下的二维悬沙输运数值模型。时间离散采用欧拉向前格式,空间离散采用有限体积法的显式格式。将模型应用于矩形海湾实验和大连长兴岛附近海区悬沙冲淤过程的实际算例。结果表明:波浪对潮位影响很小,但是对近岸流速有较为明显的影响;波流共同作用对近岸泥沙浓度影响比单纯考虑潮流作用可提高40%～100%的幅度。     

地震波斜入射下混凝土重力坝的塑性损伤响应分析

我国西南强震区建设有大量混凝土坝,复杂地形条件下地震波入射角度对混凝土坝动力响应影响较大,然而,目前相关研究以线弹性模型为主,在合理考虑坝体的真实破坏状态方面存在局限性。本文以Koyna混凝土重力坝为研究对象,建立三维非线性有限元分析模型,采用了基于黏弹性边界的地震波动输入方法,结合塑性损伤模型分别分析了地震P波和SV波斜入射下坝体的动力响应,并提出地震破坏评价模型对震后坝体损伤进行评估。研究表明,地震波入射角度及波型对坝体动力响应影响较大,P波入射下位移应力和损伤在60°时达到最大,SV波入射下在0°时达到最大,证明了考虑地震波入射角的必要性;采用塑性损伤本构结合损伤评价指标合理地反映了坝体破坏程度,并针对薄弱地区提出抗震设计改进。因此,在同类型工程的安全评价中应该综合考虑地震波斜入射和筑坝材料的非线性特征。     

近岸波浪及沿岸流数值模拟研究

利用抛物型缓坡方程计算波浪场,并以波浪辐射应力为近岸动力因素,建立深度平均的二维近岸流的控制方程。运用该近岸流方程,对美国Santa Barbara Leadbetter海岸波浪斜向入射所产生的波浪场及波浪破碎所形成的沿岸流进了数值模拟,其中抛物型缓坡模型采用Crank-Nicolson格式进行数值离散,近岸流方程采用ADI差分格式离散。与现场实测资料的对比表明,无论考虑或不考虑波浪非线性因子,模拟结果与实测结果均吻合良好。     

REFLECTION OF OBLIQUE INCIDENT WAVES BY PERFORATED CAISSONS WITH TRAVERSE WALL

The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to expand velocity potentials in each domain. A phase relation is introduced for wave oscillation in each caisson, and the structure geometry is considered in constructing the models of reflection waves. The reflected waves with the present analysis include all of the waves traveling in different directions when incident wave period is short. Numerical examinations show that velocities at the inner and outer sides of the front walls of caissons are close to each other, and reflection coefficients satisfy the energy conservation relation very well when porous effect parameter is infinite. Numerical results show that the reflection coefficients of oblique incident waves are smaller for shorter caissons at low frequency, and decrease with the increase of wave incident angle.     

基于抛物型缓坡方程模拟近岸波流场

波浪向近岸传播的过程中由波浪破碎等效应所形成的近岸波流场是近岸缓坡区域重要的环境动力因素之一。本文基于近岸波浪传播的缓坡模型对近岸波浪场及近岸波浪斜向入射破碎后所产生的沿岸波流场进行了数值模拟。考虑到波浪向近岸传播中局部复杂区域波向不易确定，计算时直接从波浪辐射应力定义出发，采用抛物型缓坡方程所给出的辐射应力公式来计算波浪产生的辐射应力，在此基础上耦合近岸波流场数学模型对近岸波浪破碎形成的波流场进行了数值模拟研究，结果表明本文的数值模型是有效的。     

二维溃坝洪水波的演进绕流和反射的数值模拟

本文采用改进的时空守恒元和解元方法(简称CE／SE法)构造了求解二维浅水方程的数值格式,建立了模拟大坝瞬间全溃和局部溃所致的洪水演进、绕流和反射过程的数学模型。应用此数学模型对局部溃坝的洪水的演进、绕流和反射的情况进行了模拟。算例结果表明CE／SE法精度高、稳定性好,很好的展示了溃坝波的运动特性,是一种研究溃坝洪水波较高精度的数值方法。     

非淹没双直立圆柱系统波浪爬升的数值模拟

波浪爬升是近海构筑物和海洋平台结构设计中的重要参数。全面掌握波浪的爬升特性有利于结构的安全保证和优化。采用有限元方法建立了求解Berkhoff缓坡方程的数值模型，并计算了非淹没单个直立圆柱周围的波高分布，计算结果与解析解吻合很好。以非淹没双直立圆柱为研究对象，探讨了圆柱间距对波浪爬升的影响。结果表明:上游圆柱周围的波高分布曲线波动较大，但最大相对波高和最小相对波高的发生位置基本与单个圆柱的情况相同；当圆柱间距为1/4波长的奇数倍时，最小相对波高明显减小，圆柱肩部出现第二峰值；而当圆柱间距为1/4波长的偶数倍时，最小相对波高则明显增加，圆柱肩部出现第二谷值。下游圆柱周围的波高分布曲线与单个圆柱的情况相似，但波高相对较小。     

Surf-zone dynamics derived from basin-scale experiments

Surf-zone hydrodynamics forced by oblique wave shoaling and breaking on beach slopes were investigated. The results showed that in wave-basin experiments with incident angles in the range of 15°–30°, wave breaking was initiated at a breaker coefficient of around 0.67, which was significantly less than that predicted from empirical relations based on normally incident waves for a given beach slope and deep-water wave steepness. The measurements also showed that subsequent saturated breaking occurred at a breaker coefficient of around 0.47 that was independent of beach slope in the range of 1:10 to 1:100. This result is likely applicable to both oblique and normally incident waves. It is shown that the measured wave heights and longshore velocity profiles in wave-basin studies can be reasonably well predicted by theory with proper adjustments to the process parameters. Best-match formulations were identified for quantifying bottom friction, eddy viscosity, and energy loss due to surface rollers.