Bohai Sea oil spill model: a numerical case study

An operational Bohai Sea oil spill serving module (BSOSSM) that can provide users with trajectory and movement information of the released oil is developed for the purpose of informing mitigation of oil spill incidents in the Bohai Sea, China. BSOSSM is one of the serving modules that had been integrated in China digital ocean prototype system, a marine information platform for managing, displaying and disseminating all the data investigated by China 908 Program. The oil spill trajectory is calculated by an oil spill model (OSM), which serves as a component in BSOSSM. The impacts of wind, current, as well as Stokes drift on oil spill trajectory are studied by sensitivity experiments conducted using OSM. Simulation results indicate that wind forcing is the most important factor in controlling the oil trajectory at the sea surface in Bohai Sea, whereas current and Stokes drift play relatively less important roles. However, because the direction of waves generally follows that of the wind, Stokes drift does lead to an increase in oil drift and spreading velocity. Case studies of the Penglai 19-3 oil spill incident (June 2011) and Xingang oil spill (April 2005) demonstrate that OSM can generally reproduce the oil spreading, and is therefore capable of supporting the emergency response of future oil spills in the Bohai Sea through BSOSSM.     

长江口宝钢码头溢油事故油膜漂移扩散数值模拟

溢油事故发生后, 油膜的漂移扩散会对周围水域和环境敏感目标造成污染。研究溢油事故后油膜漂移扩散, 可为溢油事故的处理提供理论指导。本文应用河口海岸三维水动力模式ECOM-si(semi-implicit estuarine, costal and ocean model), 耦合溢油漂移扩散模块, 模拟和分析长江口宝钢码头发生溢油事故后油膜的漂移扩散, 以及对环境敏感保护目标的影响。基于长江口崇明东滩气象站实测风速风向资料, 给出影响溢油漂移的主导风和不利风向。在冬季多年平均1月径流量11700m³·s^-1、主导风、3个不利风和潮汐作用下, 数值模拟并详细给出了宝钢码头溢油事故发生后油膜的平面分布、油膜到达和离开4个水库取水口和饮用水水源保护区以及其他环境敏感保护区的时间、持续影响时间和最大油膜厚度。长江口宝钢码头溢油事故发生后, 油膜随涨落潮流作上下游来回振荡, 径流使油膜向海输运, 风使油膜朝风向方向漂移。在主导风北风5.6m³·s^-1风速下, 油膜沿长江口南岸向下游漂移扩散, 小部分进入北槽南侧。在不利风向东南风4.0m³·s^-1风速下, 油膜西北方向漂移, 聚集于南支北岸, 受径流作用沿南支和北港的中北侧向下游输运。在不利风向西北风4.8m³·s^-1风速下, 西北风减轻了溢油事故点上游和北港、崇明东滩外侧敏感目标的影响, 加重了南港和南槽的环境敏感保护目标的影响。在不利风向西南风3.2m³·s^-1风速下, 大部分油膜在北港中北侧向下游漂移扩散, 小部分油膜聚集在北槽的中北侧。西南风减轻了溢油事故点上游和下游南港、南槽环境敏感目标受到的影响, 加重了对北港和崇明东滩外侧敏感目标的影响。不同风向作用下油膜的分布和对环境敏感保护目标影响显著不同, 风在油膜漂移扩散中起着十分重要的作用。     

福宁湾海域溢油扩散影响的数值模拟研究

应用非结构化网格形式的MIKE 21水动力模型及溢油模块建立福宁湾海域海工工程施工期溢油扩散的数学模型,对在静风、全年主导风及不利风等3种不同风况条件下,一个潮周期内包括涨憩、落急、落憩、涨急等4个典型潮时分别发生100 t燃料油持续泄露30 min的事故溢油工况进行溢油扩散数值模拟.分析显示,事故溢油在福宁湾海域的扩散过程主要受潮流和风的影响.计算结果给出了事故溢油发生后24 h内的影响范围及0. 05 mg/dm3油浓度(一类或二类水质标准)溢油最快到达福宁湾内主要敏感目标的时间,为海洋环境影响评价和溢油事故应急措施的制定提供了科学依据.     

渤海海域溢油应急预测预警系统研究Ⅰ.海洋动力要素预测技术研究

采用“油粒子”模型,模拟溢油在海洋中的漂移扩散运动,将海流、波浪和风场的模拟结果作为溢油漂移计算的外强迫,来驱动溢油漂移模型,计算其漂移路径.把计算的溢油漂移结果与地理信息系统等平台相结合,建立了渤海海域应急预测预警系统.本文作为该系统研制中的一部分,主要介绍了海流数值计算模型、波浪数值计算模型、风场数值计算模型和溢油...     

Wave-induced drift of an elliptical surface film

This study investigates experimentally the drift velocity of an elliptical surface film advected by deep-water waves. Thin polyethylene sheets were used to simulate the inextensible surface film. The drift velocities were obtained by recording and analyzing a sequence of images captured using a video camera. The results show that the drift velocity increases with the longitudinal length of the polyethylene sheet until approximately 0.8 times the wavelength. Beyond that, further increment would not result in substantial increase in the drift velocity. The effect due to the normalized transverse width is found to be significant within a particular range. At large wave steepness, the drift velocity appears to be limited by the Stokes drift. A set of best-fit empirical equations based on the sigmoidal function is introduced for oil spill trajectory prediction.     

基于MIKE SA模型的厦门西港海域溢油影响的数值模拟研究

基于MIKE SA溢油模块,以燃料油为油种,建立了厦门西港海域溢油模型,模拟静风、主导风向（东北东风）和不利风向（西南风）3种风场条件下,一个潮周期内涨急、高潮、落急和低潮4个时段发生10 t溢油后油膜的漂移路径和影响范围.结果显示,发生在厦门西港海域的溢油在海面的漂移过程主要受潮流和风的影响,其中潮流起着主导作用.不同风向条件下,24 h内油膜的影响范围不同,静风条件下溢油浓度超一类（或二类,≥0.05 mg/dm3）、超三类（≥0.30 mg/dm3）和超四类（≥0.50 mg/dm3）的总影响面积分别为31.33、19.63和11.74 km2;主导风向条件下溢油浓度超一类（或二类）、超三类和超四类的总影响面积分别为99.62、69.01和8.99 km2;不利风向溢油浓度超一类（或二类）、超三类和超四类的总影响面积分别为8.38、5.05和2.10 km2.该预测结果可给出溢油事故发生后的影响范围、影响程度和影响敏感目标的时间,可为溢油事故应急决策的制定及溢油损害评估提供科学决策和支持,提升厦门海域环境风险管理应急能力建设.     

The effects of random surface waves on the steady Ekman current solutions

The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42, 134–149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313–351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313–351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971–5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift.     

Numerical modelling of boom and oil spill with SPH

The protection of coastal areas against oil pollution is often addressed with the use of floating booms. These bodies are subject to an empirical design always based on physical models. Indeed, the numerical modelling of a two-phase flow (oil and water) with complicated free surface in the vicinity of a floating body is a challenging issue. The Smoothed Particle Hydrodynamics (SPH) Lagrangian numerical method is appropriate to such simulations since it allows the modelling of complex motions and fluid–structure interactions. In this paper we first study the mechanism of oil leakage by entrainment due to combined turbulent production and buoyancy. Then, we present the main features of the SPH method in a turbulent formalism and apply this model to predict the motion of a boom and an oil spill in an open-channel and a wave flume, for three types of oil (heavy, light and emulsion). Numerical results are compared to experiments and used to depict criteria for oil leakage. It appears that oil leakage by entrainment occurs when the surface water velocity upstream the boom exceeds a critical value which was estimated around 0.5 m/s for a light oil under steady current. A more accurate criterion is derived from theoretical considerations and successfully compared to numerical experiments. In the case of wave flume, no validation from experiments could be made. However, it appears that leakage occurs from a critical wave height between 0.5 and 1.0 m, for the tested wave period of 4 s. A more extended panel of numerical tests would allow a better knowledge of the involved mechanisms and critical parameters. An extensive use of this model should extend our knowledge regarding the mechanisms of oil leakage under a boom and allow a better and easier design of booms in the near future.     

蓬莱19-3 油田事故溢油数值模拟

利用FVCOM(Finite-volume coastal ocean numerical model)数值模型和MM5风场预报模式,在对渤海海域水动力场进行数值模拟的基础上,基于"油粒子"的欧拉-拉格朗日跟踪法和随机走动原理,并考虑风对溢油油膜漂移扩散的直接作用,建立了海洋溢油油膜漂移轨迹和扩散的数值预测模型。利用建立的模型对2011年6月蓬莱19-3油田事故溢油进行了数值模拟,模拟结果与RADARSAT卫星遥感监测数据相吻合。研究结果表明:在渤海中部地区夏季事故溢油模拟预测中,风漂移因子取0.024最为合理,模型可用于渤海蓬莱19-3油田附近事故溢油轨迹和扩散的快速预报,从而为该区域的溢油事故应急响应提供科学依据。     

随机波浪下斯托克司漂移速度是否引起水面漂移物离散的研究

漂浮于自由水面的污染物的的迁移、扩散会受到天然随机海浪的影响。之前的研究（以Herterich和Hasselmann（1982）为代表）普遍认为，随机波浪作用下的斯托克司漂移速度会引起水面污染物的离散，这个离散甚至有可能跟风和海流引起的离散同一量级。本研究就随机波浪作用下的斯托克司漂移速度是否会引起水面漂移物的离散进行理论和试验探讨。从理论推导可知，随机波浪下的质量输移速度是个定常分量，因此它不会随时间变化而引起水面漂移物的离散。随后我们在实验室水槽中进行了漂移物在随机波浪（P-M谱）作用下的漂移过程的测量。试验结果也印证了随机波浪作用下的斯托克司漂移速度不会引起水面漂移物离散的结论。     

On the effects of wave drift on the dispersion of floating pollutants

The movement of floating pollutants such as oil slicks on the surface of the sea is due to a number different factors, among which wave drift is certainly significant.In principle, it has been known since Stokes' time that a floating particle is subject to the movement caused by the orbital motion of water particles and that an average drift velocity results because the trajectories are not closed. In the past, however, this effect was often either disregarded or simply included with the surface wind induced current. In recent times the difference between the two effects has been conceptually clarified, so that the average wave drift in random one-dimensional seas has been the object of research and the results are now included in most handbooks and models for oil slick forecasting.Due to the chaotic nature of the wave field, however, the drift also causes floating substances to disperse, and this phenomenon is a much more neglected area of research. Recent work by Bovolin et al. [IAHR Congress, 1997] and Sobey and Barker [J. Coast. Res. 13 (1997)] has brought the subject to attention, and computational tools can now be made to quantify the effect and to verify when and how it should be taken into consideration in oil slick accident practise.The work presented in this paper is based on random simulation of the wave induced Eulerian velocity field in a directional sea, by making use of standard offshore wave directional models and on the ensemble averaging of floating particles trajectories in order to compute the spatial dispersion.     

无人机海上溢油跟踪监测系统设计及仿真

海上环境变化多端,造成溢油的漂移和扩散会出现不可预测的情况,精确、实时地监测海上溢油是现今亟待解决的问题.无人机以其部署快、成本低、环境适应性强的优势在海上溢油监测领域得到重视,但单架无人机监测能力弱,而多架无人机监测的准确性仍需提高.为此,本文提出一种无人机群海面溢油自动导航跟踪监测的架构和方法,根据海上溢油浓度的变化进行路径规划.该方法包括建立溢油模型和设计无人机跟踪控制系统.溢油模型主要描述海上溢油时空变化的形态复杂性;控制器可控制无人机追踪和监测溢油漂移及扩散的情况.同时,将无人机跟踪控制系统与人工势场法相结合,避免无人机相撞.最后,进行数值仿真,结果表明该跟踪系统与溢油的重合率达到70％～80％,验证了该方法的可行性.未来,该系统可广泛应用于无人机群对不同环境现象和灾害的跟踪监测.     

Oil dispersal modelling: reanalysis of the Rena oil spill using open-source modelling tools

ABSTRACT

Oil spill forecast modelling is typically used immediately after a spill to predict oil dispersal and promote mobilisation of more effective response operations. The aim of this work was to map oil dispersal after the grounding of the MV Rena on Astrolabe Reef and to verify the results against observations. Model predictions were broadly consistent with observed distribution of oil contamination. However, some hot spots of oil accumulation, likely due to surf-zone and rip current circulation, were not well represented. Additionally, the model was run with 81 differing wind conditions to show that the events occurring during the grounding represented the typical likely behaviour of an oil spill on Astrolabe Reef. Oil dispersal was highly dependent on prevailing wind patterns; more accurate prediction would require better observations of local wind patterns. However, comparison of predictions with observations indicated that the GNOME model was an effective low-cost approach.     

高频表面波对定常Ekman流解的影响

基于Jenkins(1989)建立的包含Stokes漂流、风输入和波耗散影响的修正Ekman模型,采用Paskyabi等(2012)使用的推广的Donelan等(1987)中的谱和波耗散函数,并利用Paskyabi等(2012)中修正方法给出的包含高频波的风输入函数,在粘性不依赖于水深及粘性随深度线性变化的条件下,研究了包含高频毛细重力波的随机表面波对Stokes漂流和Song(2009)导出的波浪修正定常Ekman流解的影响。结果表明高频表面波使Stokes漂流在海表面剪切加强,对定常Ekamn流解的影响通常不能忽略,但对Ekman流场的角度偏转影响很小。最后,将考虑高频表面波尾谱影响所估算的定常Ekman流解与已有观测结果以及经典Ekman解进行了比对分析。     

2011年6月-8月渤海湾溢油事故长期后报数值模拟

三维业务化溢油应急预报系统不仅能提供逐时的海洋环境信息预报和溢油漂移扩散,还能对溢油事件进行后报数值模拟。2011年6月4日在渤海湾蓬莱19-3B采油平台发生溢油事件,同月17日19-3C平台也发生溢油事件。此次溢油事故造成了数千平方公里海水受污染。本文采用国家海洋环境预报中心自主研发的溢油模型对蓬莱19-3溢油事件进行长期后报数值模拟,在风流海洋环境场的驱动下,模拟了2016年6月到2016年8月,两个平台溢油的漂移扩散情况、影响范围,靠岸时间和影响岸段等。风场采用基于WRF模型模拟得到的再分析风场,并用实测风对再分析风场进行订正,流场采用基于POM模式在再分析风场驱动下得到的海流。后报结果显示,溢油主要向西北方向漂移,并最终靠岸,其扫过的海域也主要在平台的西北方向,这与观测结果一致,验证了后报的可靠性。     

Uncertainty in predictions of oil spill trajectories in open sea

A method is introduced to calculate and to account for the uncertainties in the predictions of oil spill trajectories using a classic oil spill model. The method considers the output of the oil spill model as a function of random variables, which are the input parameters, and calculates the standard deviation of the output results which gives a measure of the uncertainty of the model given the uncertainties of the input parameters.Instead of a single trajectory that is calculated by the oil spill model using the mean values of the parameters, a band of trajectories can be defined when various simulations are done taking into account the uncertainties of the input parameters. This band of trajectories defines envelopes of the trajectories that are likely to be followed by the spill given the uncertainties of the input.The method is applied to an oil spill that occurred in open sea near Madeira Islands, in the Atlantic Ocean, in December 1989. The simulations allow the understanding of how a change in the wind direction drove the spill towards the Islands.The envelope of likely trajectories that is obtained with the uncertainty modelling shows a band of trajectories that is in better agreement with the observations than the single trajectory simulated by the oil spill model, based on mean parameters.     

平潭竹屿湾水交换能力和溢油风险数值模拟

应用非结构网格有限体积海洋模型对平潭竹屿湾水交换能力和溢油扩散开展了数值模拟。水交换能力计算表明,竹屿湾大部分水域水体半交换时间小于1.0 d,平均滞留时间约3.0 d左右,水体冲洗时间为15.0 d,水交换能力较强。48 h溢油扩散计算结果表明,油粒子扫海范围及运动路径与油粒子的释放时刻及风的作用紧密相关。静风条件下,溢油运动主要受当地潮流影响,呈南-北往复运动。不利风作用下,竹屿水道的溢油可以扩散至平潭坛南湾、平潭草屿岛、塘屿岛及高山湾等海域,最远可到南日岛西北海域。     

多极化SAR溢油探测影响因素分析研究

Polarimetric synthetic aperture radar(SAR) oil spill detection parameters conformity coefficient(μ), Muller matrix parameters(|C|, B_0), the eigenvalues of simplified coherency matrix(λ_(nos)) and the influence of SAR observing parameters, ocean environment and noise level are investigated. Radarsat-2 data are used to make systematic analysis of polarimetric parameters for different incidences, wind speeds, noise levels and the ocean phenomena(oil slick and look likes). The influence of the SAR observing parameters, the ocean environment and the noise level on the typical polarimetric SAR parameter conformity coefficient has been analyzed. The results indicate that conformity coefficient cannot be simply used for oil spill detection, which represents the image signal to the noise level to some extent. When the signals are below the noise level for the oil slick and the look likes, the conformity coefficients are negative; while the signals above the noise level corresponds to positive conformity coefficients. For dark patches(low wind and biogenic slick) with the signal below the noise,polarization features such as conformity coefficient cannot separate them with oil slick. For the signal above the noise, the oil slick, the look likes(low wind and biogenic slick) and clean sea all have positive conformity coefficients, among which, the oil slick has the smallest conformity coefficient, the look likes the second, and the clean sea the largest value. For polarimetric SAR data oil spill detection, the noise plays a significant role. So the polarimetric SAR data oil spill detection should be carried out on the basis of noise consideration.     

一个新的破碎波统计模式

由运动方程和涡度方程所导得的两个首次积分估计给出了海波破碎的发生条件和破碎波的波面限制。由这两个条件所构造的新的破碎波统计模式，可导出海波的破碎面积率、破碎体积率和破碎能量损耗率的解析表达式，加之一个简单的白冠物理模型又导出了一个新的白冠覆盖率的解析表达式。     

海流作用下海底管道溢油扩散实验研究

采用物理模型试验研究了海流作用下海底输油管道溢油扩散特性。水槽中的原油从管道的泄漏点溢出，并从海底扩散到海面。采用非接触式光学测量技术，设计了图像采集与数据分析系统，研究原油泄漏机理和特性。通过该系统获得了溢油的轨迹、速度和海面上升时间。从定性和定量两个角度分析了水流和溢油量对溢油行为的影响。之后给出了特征物理量对各种因素的敏感性研究。溢油在水下主要以不同粒径的散状颗粒的形式分布。原油的上升过程可分为三个阶段：饱满、分散和聚集阶段。溢油量是影响油粒子上升时间的主要因素。在油粒子的上升过程中，原油的垂直速度主要受溢油量的影响，横向速度则更依赖于水流速度。不同水流与溢油量下，横向溢油速度的偏差远大于海面上升时间和垂直溢油速度的偏差。该研究可为溢油应急预测系统提供理论参考。