Static bay beach concept for scientists and engineers: A review

Headland-bay beach (HBB) is one of the most prominent physiographic features on the oceanic margin of many countries in the world. Under the influence of a predominant swell, its curved periphery in natural environment may reach static equilibrium and remains stable without sediment supply from updrift and/or a riverain source within its own embayment. Coastal scientists and engineers have attempted to develop mathematical expressions to quantify this ideal bay shape since the 1940s. As the scenario with depleting sediment supply has become a common reality on many parts of the world coastline in more recent time, some coastal engineers have advocated a rational approach to mimicking the static bay shape found in nature in order to mitigate beach erosion as well as for coastal management. Nowadays, many useful applications have emerged since the publication of the parabolic bay shape equation (PBSE) developed for static equilibrium planform (SEP) in late 1980s. The advance in modern computer technologies and international collaboration has further facilitated the exchange of knowledge and applications of this static bay beach concept (SBBC).     

海岸波浪多次破碎波能耗散模型

在坡度很缓(接近或小于1∶100)的海岸,波浪在向海岸传播的过程中,可能经历多次破碎,而在两次波浪破碎之间将伴随着波浪恢复(波浪恢复到不破碎状态)。在现有海岸波高计算模型中,波浪破碎是通过波能耗散来模拟的,但所采用的波能耗散模型都不能自动考虑波浪出现多次破碎的过程,特别精确模拟这一过程中出现的波浪恢复。本文提出了解决这一问题的新的波能耗散模型,模型的建立是通过在Dally模型中重新建立稳定波能、饱和波高水深比和波能耗散系数,并引入了波浪恢复的判断条件实现的。该模型的波能耗散在波浪恢复区的值很小故能描述波浪恢复区的波浪运动。与实验结果的对比表明,新模型可以适合缓坡情况波浪多次破碎的波高模拟,而且对不同坡度的平坡和沙坝海岸(1∶100～1∶10)的破碎波模拟都可以给出与实验结果符合的结果,并且可以自动识别多次波浪破碎的存在和波浪恢复的发生。     

A three-dimensional multi-level turbulence model for tidal motion

A three-dimensional multi-level turbulence model is developed to simulate tide induced circulation in coastal waters. Based on the bathymetry data, the coastal waters are divided into a number of layers. In every layer, the velocities are integrated along the layer depth. The eddy viscosity and diffusivity are computed from the Prandtl mixing length turbulence model. This multi-level model solves for the water surface elevations and currents in different water depths. Comparison of numerical results with the measured data shows good conformity.     

A numerical model of coastline deformation for sandy beach at downstream of a jetty

A reformed numerical model based on the “one-line theory” for beach deformation is presented. In this model, the change of beach slope during coastline procession is considered.A wave numerical model combined with wave refraction, diffraction and reflection is used to simulate wave climate to increase numerical accuracy.The results show that the numerical model has a good precision based on the adequate field data. The results can be applied to practical engineering.     

A coupled numerical model for simulation of wave breaking and hydraulic performances of a composite seawall

A numerical model is developed by combining a porous flow model and a two-phase flow model to simulate wave transformation in porous structure and hydraulic performances of a composite type low-crest seawall. The structure consists of a wide submerged reef, a porous terrace at the top and an impermeable rear wall. The porous flow model is based on the extended Navier-Stokes equations for wave motion in porous media and k−ε turbulence equations. The two-phase flow model combines the water domain with the air zone of finite thickness above water surface. A unique solution domain is established by satisfying kinematic boundary condition at the interface of air and water. The free surface advection of water wave is modeled by the volume of fluid method with newly developed fluid advection algorithm. Comparison of computed and measured wave properties shows reasonably good agreement. The influence of terrace width and structure porosity is investigated based on numerical results. It is concluded that there exist optimum value of terrace width and porosity that can maximize hydraulic performances. The velocity distributions inside and in front of the structure are also investigated.     

A three-dimensional numerical model of hydrodynamics and water quality in Hakata Bay

The hydrodynamics and water quality in Hakata Bay, Japan, are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three-dimensional hydrodynamics and water quality model has been developed to simulate the long-term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal areas. It is a 3-dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality, through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay.     

A new kind of nonlinear mild-slope equation for combined refraction-diffraction of multifrequency waves

This paper presents the numerical solution of a new nonlinear mild-slope equation governing waves with different frequency components propagating in a region of varying water depth. There are two new nonlinear equations. The linear part of the equations is the mild-slope equation, and one of the models has the same non-linearity as the Boussinesq equations. The new equations are directly applicable to the problems of nonlinear wave-wave interactions over variable depth. The equations are first simplified with the parabolic approximation, and then solved numerically with a finite difference method. The Crank-Nicolson method is used to discretize the models. The numerical models are applied to a set of published experimental cases, which are nonlinear combined refraction-diffraction with generation of higher harmonic waves. Comparison of the results shows that the present models generally predict the measurements better than other nonlinear numerical models which have been applied to the data set.     

基于双层Boussinesq方程的三维波浪数值模型及其验证

Liu等给出的最高导数为2的双层Boussinesq水波方程具有较好的色散性和非线性,基于该方程建立了有限差分法的三维波浪数值模型。在矩形网格上对方程进行了空间离散,采用高阶导数近似方程中的时、空项,时间积分采用混合4阶Adams-Bashforth-Moulton的预报—校正格式。模拟了深水条件下的规则波传播过程,计算波面与解析结果吻合较好,反映出数值模型能很好地刻画波面过程及波面处的速度变化;在kh=2π条件下可较为准确获得沿水深分布的水平和垂向速度,这与理论分析结果一致。最后,利用数值模型计算了规则波在三维特征地形上的传播变形,数值结果和试验数据吻合较好;高阶非线性项会对波浪数值结果产生一定的影响,当波浪非线性增强,水深减少将产生更多的高次谐波。建立的双层Boussinesq模型对强非线性波浪的演化具有较好的模拟精度。     

σ-Coordinates hydrodynamic numerical model for coastal and ocean three-dimensional circulation

A three-dimensional finite-difference hydrodynamic model has been developed using σ-coordinate for the vertical dimension. An explicit scheme for temporal integration and a staggered grid for spatial discretization have been adopted. The model has been tested against analytical or literature cases for wind and tide induced circulation. Results are in good agreement both with analytical solutions under idealised conditions and with results from the model of Shankar et al. (1996).     

细粒酒精模型冰物理力学性质评价的新指标

依据酒精细粒模型冰制冰过程中的物理本质和控制细粒酒精模型冰物理力学性质的物理本质,建立了一项适合于喷雾技术细粒模型冰性质评价综合指标.阐明了这一评价指标的物理意义,并给出这一指标与细粒酒精模型冰物理力学性质参数的关系.     

Oil migration driven by exhumation of the Canol Formation oil shale: A new conceptual model for the Norman Wells oil field,northwestern Canada

Thermal history, petroleum system, structural, and tectonic constraints are reviewed and integrated in order to derive a new conceptual model for the Norman Wells oil field, and a new play type for tectonically active foreland regions. The thermal history recorded by Devonian rocks suggests that source rocks experienced peak thermal conditions in the Triassic–Jurassic, during which time oil was likely generated. After initial oil generation and expulsion, the Canol Formation oil shale retained a certain fraction of hydrocarbons. The shallow reservoir (650–350 m) is a Devonian carbonate bank overlain by the Canol Formation and resides within a hanging wall block of the Norman Range thrust fault. Both reservoir and source rocks are naturally fractured and have produced high API non-biodegraded oil. Thrust faults in the region formed after the Paleocene, and a structural cross-section of the field shows that the source and reservoir rocks at Norman Wells have been exhumed by over 1 km since then.The key proposition of the exhumation model is that as Canol Formation rocks underwent thrust-driven exhumation, they crossed a ductile–brittle transition zone and dip-oriented fractures formed sympathetic to the thrust fault. The combination of pore overpressure and new dip-directed subvertical fractures liberated oil from the Canol Formation and allowed for up-dip oil migration. Reservoir rocks were similarly fractured and improved permeability enhanced charging and pooling of oil. GPS and seismicity data indicate that strain transfer across the northern Cordillera is a response to accretion of the Yakutat terrane along the northern Pacific margin of North America, which is also the probable driving force for foreland shortening and rock exhumation at Norman Wells.     

Process-based model for nearshore hydrodynamics, sediment transport and morphological evolution in the surf and swash zones

Hydrodynamics and sediment transport in the nearshore zone were modeled numerically taking into account turbulent unsteady flow. The flow field was computed using the Reynolds Averaged Navier–Stokes equations with a k–ε turbulence closure model, while the free surface was tracked using the Volume-Of-Fluid technique. This hydrodynamical model was supplemented with a cross-shore sediment transport formula to calculate profile changes and sediment transport in the surf and swash zones. Based on the numerical solutions, flow characteristics and the effects of breaking waves on sediment transport were studied. The main characteristic of breaking waves, i.e. the instantaneous sediment transport rate, was investigated numerically, as was the spatial distribution of time-averaged sediment transport rates for different grain sizes. The analysis included an evaluation of different values of the wave friction factor and an empirical constant characterizing the uprush and backwash. It was found that the uprush induces a larger instantaneous transport rate than the backwash, indicating that the uprush is more important for sediment transport than the backwash. The results of the present model are in reasonable agreement with other numerical and physical models of nearshore hydrodynamics. The model was found to predict well cross-shore sediment transport and thus it provides a tool for predicting beach morphology change.