Numerical investigation of oscillations induced by submerged sliding masses within a harbor of constant slope

Oscillations within a rectangular harbor of constant slope induced by submerged sliding masses are investigated numerically based on Boussinesq-type equations and results are used to reveal the characteristics of the generated oscillations. The numerical result of each transverse eigenfrequency is very close to the theoretical prediction and the spatial structure of each mode of the oscillations may also be well captured by the existing analytical solutions based on shallow water equations. The investigation shows that relatively small-scale sliding masses whose width is small compared with the harbor width may induce obvious transverse oscillations. The predominant transverse components are those with small mode numbers when the solid slides start moving from the backwall. In comparing the oscillations induced by the slides of constant velocity and those accelerated by gravity force with bottom friction, it is observed that the movements accelerated by gravity force may facilitate the development of very low transverse oscillation modes while those with constant velocity may also be in favor of the higher ones. The augmentation of the sliding velocity along the constant slope may shift the amplitudes of the oscillation components to smaller values, which corresponds to the physical understandings of the waves generated by underwater sliding masses or landslides. While the sliding masses may not act on an isolated point of the bottom but follow a certain trajectory along the harbor, the transverse oscillations induced by them are sensitive to their position of departure in both the cross-harbor direction and the offshore direction. Longitudinal oscillations may be induced by relatively large sliding masses of harbor width on a constant slope within the harbor. Although the longitudinal oscillations may not reach a steady state without forcing terms at the entrance of the harbor, some patterns of several low-mode ones occur and wavelet spectra are used to analyze their evolutions and comparisons are made with theoretical predictions. It is revealed that the longitudinal oscillations are also sensitive to the moving velocity and initial location of the sliding masses.     

Study on Influences of Fringing Reef on Harbor Oscillations Triggered by N-Waves

Influences of topographic variations of the offshore fringing reef on the harbor oscillations excited by incident Nwaves with different amplitudes and waveform types are studied for the first time. Both the propagation of the Nwaves over the reef and the subsequently-induced harbor oscillations are simulated by a Boussinesq-type numerical model, FUNWAVE-TVD. The present study concentrates on revealing the influences of the plane reef-face slope,the reef-face profile shape and the lagoon width on the maximum runup, the wave energy distribution and the total wave energy within the harbor. It shows that both the wave energy distribution uniformity and the total wave energy gradually increase with decreasing reef-face slope. The profile shape of the reef face suffering leading-elevation Nwaves(LEN waves) has a negligible impact on the wave energy distribution uniformity, while for leading-depression N-waves(LDN waves), the latter gradually decreases with the mean water depth over the reef face. The total wave energy always first increases and then decreases with the mean water depth over the reef face. In general, the total wave energy first sharply decreases and then slightly increases with the lagoon width, regardless of the reef-face width and the incident waveform type. The maximum runup subjected to the LEN waves decreases monotonously with the lagoon width. However, for the LDN waves, its changing trend with the lagoon width relies on the incident wave amplitude.     

An analytic investigation of oscillations within a harbor of constant slope

Longitudinal and transverse oscillations within a harbor of constant slope are analyzed. Based on the linear shallow water approximation, longitudinal oscillations are described with Bessel equations. Ignoring friction, oscillations are forced using the period of the incident perpendicular wave field by the method of matched asymptotics. The analytic results show that the varying depth shifts the resonant wave numbers to lower values than those for the same geometric harbor with constant depth. Furthermore, we extend the shallow water equations to a linear, weakly dispersive, Boussinesq-type equation by modifying the offshore velocity component, and then use it to investigate possible existing transverse oscillations in the harbor of constant slope. These oscillations are types of standing edge waves. Their character is quite sensitive to the boundary condition at the backwall of the harbor.     

Harbor resonance induced by subaerial landslide-generated impact waves

Past studies of harbor resonance have mainly been restricted to the quasi-steady oscillations induced by steady wave conditions. This paper investigates the response of a rectangular harbor to subaerial landslide-generated impact waves based on physical models, in order to compare the oscillations induced by steady and transient waves. In response to steady incident waves, oscillations within the harbor need to experience a long process to obtain their maximum value before the input energy and the losses are balanced. Landslide-generated impact waves usually include components with solitary wave characteristics and also components with dispersive wave characteristics. Each component travels with a different celerity. Usually, solitary wave components propagate faster, and arrive in the harbor first. Oscillations attain their maximum status as soon as these components arrive. The subsequently arriving components with dispersive characteristics do not enhance the resonance oscillations. So the waves with solitary characteristics are considered to play an important role in harbor resonance. Numerical experiments, using the FUNWAVE model, were conducted in order to further verify these conclusions.     

Resonance Induced by Edge Waves in Hua-Lien Harbor

This article first reviews previous numerical studies on the resonance problem of Hua-Lien Harbor. All the research leads to the conclusion that resonance can be stimulated by 2-D infragravity waves. However, a literature survey suggests that outside the harbor these plane infragravity waves are too small to excite violent water-body movement inside. On the other hand, 3-D infragravity waves trapped along the coastline, also known as edge waves, are more likely to exist outside the harbor and their effect needs to be thoroughly discussed. Based on previous measurements, the response of Hua-Lien Harbor is best simulated using edge waves of 160 and 140 second periods and their resonance mechanisms are analyzed. The former case has a longitudinal resonant mode and hence the amplitude in the inner harbor is large. The latter case has a transverse mode in the outer basin and hence only berths in the outer basin are influenced. These features are both consistent with field measurement. Therefore, it is very likely that edge waves are responsible for the resonance of Hua-Lien Harbor. Finally, based on observation after the construction of the present offshore breakwaters, a theory is proposed to explain the trapping of incident edge waves, and a measure to further reduce the resonance is discussed.     

宁波港北仑港区深水资源及港口建设

宁波北仑地区海域水文泥沙条件为：深水贴岸、港域受控于落潮流且掩护条件好、近岸水体含沙量高;港口建设中,码头走向应与主流向一致,码头与岸应以透空栈桥相连接。     

大、小洋山建港总体规划中的水流泥沙问题

水流、泥沙一直是建港中关键问题之一。从现场水文泥沙条件分析和数学模型计算等方面,分析比选了洋山港规划方案,提出了洋山港总体规划以单通道方案为宜,不但能简化现场的复杂的水流,选择合适的口门宽度还能维持深槽水流、水深条件,经计算分析提出了西口门宽度为3．5km的规划方案较好,此外还从平衡水深的角度对单通道方案的维持水深进行了计算。     

Numerical investigation of oscillations within a harbor of constant slope induced by seafloor movements

A numerical model, which can simulate wave generation and propagation is developed to simulate oscillations induced by seafloor movements inside a harbor of constant slope, and once verified and then validated through comparison with experimental results, the numerical results are used to examine the analytic solutions presented in Wang et al. (Wang, G., Dong, G., Perlin, M., Ma, X., Ma, Y., 2011. An analytic investigation of oscillations within a harbor of constant slope. Ocean Engineering 38, 479–486). Small-scale seafloor movement usually induces small longitudinal oscillations, but evident larger transverse oscillations. These transverse oscillations are sensitive to the location of the moveable seafloor. The numerical result of each transverse eigen frequency compares well with the theoretical solution; in addition the spatial structure of each mode is also well-captured by the theory. Furthermore, evident/larger longitudinal oscillations induced by large-scale seafloor movements are simulated, and the numerical resonant frequencies agree favorably with the analytical solutions. These longitudinal oscillations are sensitive to the horizontal location of the moveable seafloor.     

厦门高集海堤开口改造工程潮流泥沙物理模型试验研究

通过潮汐水流和悬沙淤积物理模型试验,研究厦门高集海堤开口改造工程潮流泥沙问题,研究表明,高集海堤开口后,东、西海域两股水流的汇流区和分流区在高集海堤附近,东海域涨潮流速有所增大,落潮流速有所减小,西海域则相反;随着开口宽度增大,流速变幅增大,开口大于800 m后流速变幅趋缓;海堤开口后净输水方向为自东海域向西海域,有利于厦门湾内水体与外海的交换;高集海堤开口对东渡港区泥沙淤积影响不大.综合分析认为高集海堤开口宽度800～1 000 m较为合适,开口800 m时大潮条件下1d的净输水量约0.91×108m3,东渡北港区港池年平均回淤强度增大0.18 m/a左右,航道淤强增大0.05 m/a左右.     

On a translating and transversely oscillating cylinder. Part 1—The effect of the strouhal number on the hydrodynamic forces and the near-wake structure

The problem of unsteady, laminar flow past a circular cylinder which starts translating and oscillating impulsively from rest in a viscous fluid is numerically investigated at a Reynolds number of R = 10³. The flow is incompressible and two-dimensional, and the cylinder oscillations are harmonic. The transverse oscillations are only allowed when the maximum oscillatory-to-translational velocity ratio is 0.5. The investigation is based on an implicit finite difference scheme for integrating the unsteady Navier-Stokes equations together with the mass-conservation equation in their vorticity stream function formulation. A non-inertial coordinate transformation is used so that the grid mesh remains fixed relative to the accelerating cylinder. Present calculations are performed within the range of sufficiently large oscillation amplitude to induce separation. The time variation of the in-line and transverse force coefficients are presented. The study also focuses on the laminar asymmetric flow structure in the near-wake region. In this flow regime, it is found that there is alternate shedding of vortices from either side of the cylinder over an oscillation cycle (as predicted experimentally); this is the classical mode of vortex shedding leading to formation of the Kármán street.     

Interaction of ocean waves with floating and submerged horizontal flexible structures in three-dimensions

A three-dimensional general mathematical hydroelastic model dealing with the problem of wave interaction with a floating and a submerged flexible structure is developed based on small amplitude wave theory and linear structural response. The horizontal floating and submerged flexible structures are modelled with a thin plate theory. The linearized long wave equations based on shallow water approximations are derived and results are compared. Three-dimensional Green’s functions are derived using fundamental source potentials in water of finite and infinite depths. The expansion formulae associated with orthogonal mode-coupling relations are derived based on the application of Fourier transform in finite and infinite depths in case of finite width in three-dimensions. The usefulness of the expansion formula is demonstrated by analysing a physical problem of surface gravity wave interaction with a moored finite floating elastic plate in the presence of a finite submerged flexible membrane in three-dimensions. The numerical accuracy of the method is demonstrated by computing the complex values of reflected wave amplitudes for different modes of oscillation and mooring stiffness. Further, the effect of compressive force and modes of oscillations on a free oscillation hydroelastic waves in a closed channel of finite width and length for floating and submerged elastic plate system is analysed.     

涌浪作用下港内波况试验研究

基于秘鲁钱凯港的防波堤三维整体模型试验结果,研究了涌浪绕射、透射联合作用对港内波况的影响.分析了不同波向、不同谱峰周期的入射波条件下港内不同功能区的波况分布规律,并对比分析了具有不同周期的入射波对港内不同区域波高的影响,兼顾分析了波向的影响.结果表明,在涌浪作用下,受透射、绕射影响,不同入射波条件下港内比波高分布规律相...     

黄骅港地区潮滩过程与港口选址

对黄骅地区潮滩过程的基本特征进行了讨论,结果表明,该区潮滩发育主要受黄河泥沙的控制,黄河从本区或其附近入海期间是潮滩迅速淤涨期,当黄河远离本区时,潮滩便开始退缩进入调整期。目前本区潮滩过程的主要物质是潮滩本身的沉积物。漳卫新河的来沙是本区的主要物源。本潮滩的潮下带宽达9km以上,破波带外界在约4．0m水深处,港址选在泥沙活跃的破波带内是值得商榷的。建议港口建设应尽量避开破波带．     

Influence of offshore topography on the amplification of infragravity oscillations within a harbor

The main purpose of this article is to systematically investigate the influence of offshore fringing reef topography on the infragravity-period harbor oscillations. The infragravity (IG) period oscillations inside an elongated harbor induced by normally-incident bichromatic wave groups are simulated using a fully nonlinear Boussinesq model, FUNWAVE 2.0. Based on an IG wave decomposition method, effects of plane reef-face slopes, reef-face profile shapes and the existence of reef ridge on bound and free IG waves and their relative components inside the harbor are comprehensively studied. For the given harbor and reef ridge, the range of the reef-face slopes and the various profile shapes studied in this paper, results show that the amplitude of the free IG waves inside the harbor increases with the increasing of the reef-face slope; while the bound IG waves inside the harbor seem insensitive to it. The effects of the profile shapes on the IG period waves inside the harbor are closely related to the width of the reef face. The existence of the reef ridge can relieve the bound IG waves to some extent when the incident short wave amplitudes are relatively large, while its effects on the free IG waves are negligible.     

港口功能评价方法研究及应用

根据港口评价的过程和特点,引入层次分析、模糊综合评判等研究方法,进而提出了修正AHP-模糊综合评判方法,并以此为理论基础建立港口评价模型。该方法在一定程度上减小了主观因素对评价的影响并使港口评价定量化。工程的应用结果证明,该评价方法是可行的。     

Effects of depth discontinuity on harbor oscillations

The effects of water depth discontinuity near the harbor mouth on harbor oscillations are examined. Linear long-wave equations are used as the basis of the present study. For simplicity, only the normal incident waves are considered. Assuming that the harbor mouth is small in comparison with wavelength, the method of matched asymptotic expansion is employed to obtain the ocean impedance and the harbor responses. It is found that the incident waves can be trapped over the depth discontinuity which causes large oscillations near the harbor mouth. The radiation damping also decreases because of the appearance of the depth discontinuity, which leads to large amplifications at the lowest mode.     

澳门内港水域低氧区空间分布及形成机制研究

澳门内港及附近水域(包括内港、筷子基北湾和南湾)历来是澳门海域富营养化最严重的区域, 水质恶化常引发大规模鱼类死亡。本文利用近10年的澳门水质监测统计数据, 采用三维水动力—水质模型模拟了澳门内港溶解氧的分布特征和水文动力过程。研究结果表明, 内港区低氧现象为澳门海域潮、径流物理及生化过程综合作用的结果。内港没有明显的外海往复流和水体层化现象, 其整体的弱动力和筷子基水域的半封闭造成污染物滞留作用, 是形成低氧区的关键物理机制。筷子基水体自身生化耗氧是导致内港低氧的驱动要素, 底泥耗氧进一步加剧了内港的低氧程度。     

日照港西部海域海底地形与表层沉积特征

利用单波束测深仪和蚌式取样器进行了日照石臼港扩建码头西侧约50km~2海域1:2 000~1:10 000的水深地形测绘和底质分析工作。调查结果表明,日照港西部海域可分4个水深区,其地形和沉积特征如下:1)航道区,浅水航道区等深线平行于码头岸线,水深11m,经过疏浚已形成向南倾斜的四级阶梯地形,疏浚中心处水深24m。航道区底质以分选中等的砾砂为主;2)港池区,水深6 m,等深线与港池岸线平行,水深向南渐增,海底地形平坦,坡降比3‰。底质以分选较好的粉砂和砂质粉砂为主,近岸有少量分选较差的泥质砂质砾;3)涛雒-付疃河口区,水下三角洲地形明显,5m以浅等深线呈弧形向东南方向凸出,坡降比最大可达14.2‰,底质类型为分选极好的砂和粉砂质砂;4)浅海区,海底地形平坦,平均坡降比1.9‰,6~10m等深线呈NE-SW向平行向外海增大,近南扩码头端向东偏转,底质类型为分选好的砂质粉砂和粉砂,并呈平行于海岸线向深水区呈粗-细-粗的带状分布。底质类型分布与水深条件基本吻合,但深水区出现的底质粗化现象,分析认为可能与南扩码头的挑流作用有关,海底沉积物呈向南运移趋势。     

连云港港口海域污染物总量控制研究

通过对连云港港口海域水质现状监测评价,发现了该海域的污染状况和主要污染物。在对污染源调查分析基础上,利用建立的港口海域潮流数值模型、浓度模型,计算了港口海域各个排污口CODCr的总量控制目标,并提出港口海域不同时期污染物控制规划,对解决港口海域的环境污染问题有很强的针对性和可操作性。