海岛局部风场特性的风洞试验和数值模拟研究

针对海岛局部风效应突出的问题,采用边界层风洞试验与数值模拟相结合的方法,对3种坡度的理想化海岛地形的风剖面进行了数值拟合,定义了差异系数来描述风剖面变化,利用数值模拟研究了差异系数和最大加速比在迎风侧的分布,重点探讨了海岛坡度和高度对最大加速比和差异系数的影响;基于风洞数据,对迎风侧和背风侧顺风向、横风向和竖向湍流强度和阵风因子分布进行了研究。结果表明：数值模拟与风洞试验结果较接近,风剖面指数在迎风侧较小;靠近坡顶的加速效应尤为明显,其最大加速比为0.4～1.0;坡腰处的差异系数较小,随着岛脊线角度的增加,差异系数为0的位置有向坡脚靠近的趋势;坡度增大到25°、0°岛脊线上最大加速比和差异系数均较大;迎风侧的三向湍流强度分布较规律,而背风侧的三向湍流强度分布较杂乱,尤其是在距海岛表面100 m高度范围内;阵风因子和湍流强度的变化趋势具有较高的一致性。     

Analysis of formation pressure test results in the Mount Elbert methane hydrate reservoir through numerical simulation

Targeting the methane hydrate (MH) bearing units C and D at the Mount Elbert prospect on the Alaska North Slope, four MDT (Modular Dynamic Formation Tester) tests were conducted in February 2007. The C2 MDT test was selected for history matching simulation in the MH Simulator Code Comparison Study. Through history matching simulation, the physical and chemical properties of the unit C were adjusted, which suggested the most likely reservoir properties of this unit. Based on these properties thus tuned, the numerical models replicating “Mount Elbert C2 zone like reservoir”, “PBU L-Pad like reservoir” and “PBU L-Pad down dip like reservoir” were constructed. The long term production performances of wells in these reservoirs were then forecasted assuming the MH dissociation and production by the methods of depressurization, combination of depressurization and wellbore heating, and hot water huff and puff. The predicted cumulative gas production ranges from 2.16 × 10⁶ m³/well to 8.22 × 10⁸ m³/well depending mainly on the initial temperature of the reservoir and on the production method.This paper describes the details of modeling and history matching simulation. This paper also presents the results of the examinations on the effects of reservoir properties on MH dissociation and production performances under the application of the depressurization and thermal methods.     

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.     

水东湾潮流特征分析及三维数值模拟

基于水东湾海域利用现状及水环境综合整治工作的迫切需要,对其海洋水文要素开展野外调查,以清晰理解其潮流特征,并据此进行潮流三维数值模拟.调查结果显示,水东湾观测期间的实测潮差在2.6~2.9 m之间,平均潮差约2.8 m,湾口潮差最大,湾顶海域潮差最小,涨潮历时略长于落潮,属不正规半日潮;各观测站位的最大流速相差较大,最高值出现在湾口深槽,为134 cm/s,最低值出现在湾顶浅海海域,为31 cm/s,最大流速水平分布基本上呈现为从湾口向湾顶递减态势.模拟结果显示,水东湾内潮流基本沿潮汐通道呈往复流动,涨潮流向介于280°~300°之间,流速在0.28~1.36 m/s范围内变化;落潮流向介于128°~180°之间,流速在0.56~1.44 m/s范围内变化,流矢受地形限制显著.     

Spar平台环境载荷风洞测试及载荷分析

介绍某桁架式Spar平台风洞环境载荷测试及分析,为国内首次在风洞中开展的Spar平台风、流载荷模型试验。通过在风洞中模拟真实海洋环境,考虑倾角变化对平台载荷的影响,测试Spar平台水上部分风载和水下部分的流载,给出最大风倾覆力矩风向角,确定平台最容易发生危险的关键风向。试验结果表明:水上部分风阻随纵倾角的增大而增大;风倾覆力矩随倾角增大先增大后减小,在纵倾角10°时达到最大值;水下部分只在流向角-15°～15°范围内,流阻随倾斜角度增大而减小,但最大阻力发生在倾斜角为15°时。试验结果可以为Spar平台设计以及性能预报提供参考。     

海底孔压对波浪响应试验研究及数值模拟

孔隙水压力在海底土尤其在砂性海床中扮演着一个非常重要的角色.波浪的周期性加载作用,在砂土及粉土中产生超静孔隙水压力,其幅值大小是海床发生液化破坏的控制因素.在海上工程的历次调查中发现孔压引起许多液化破坏现象,如粉土海床的塌陷、凹坑、坡度较大处的粉砂流及构筑物基础周围的过量冲刷造成石油管架下沉等等,因此研究海床中孔压对波浪的响应具有重要的理论意义和实践意义.     

张力腿平台涡激运动模型试验与数值分析

为揭示张力腿平台涡激运动响应规律,采用数值模拟与模型试验相结合的方法研究了全水深系泊张力腿平台涡激运动响应。根据张力腿平台主尺度参数,按照几何相似制作了水池试验模型,在满足运动相似和动力相似的条件下开展了均匀流、剖面流模型试验,并将模型试验结果与数值模拟结果进行了对比,验证了数值模拟与模型试验结果的一致性。分析结果表明在均匀流作用下张力腿平台涡激运动的锁定区间在5.5<U_r<8.5,来流角对涡激运动影响较大。剖面流作用下平台涡激运动规律与均匀流作用基本一致,但剖面流造流引起的能量分散,使平台在XY平面的运动轨迹变得不规律,系泊系统提供的回复力对涡激运动幅值有抑制作用,来流角和流速对张力腿或立管模态影响明显。论文得到结论对于张力腿平台的工程设计有一定借鉴意义。     

Experimental and numerical investigations on hydrodynamic and aerodynamic characteristics of the tunnel of planing trimaran

The planing trimaran possesses distinctive hybrid hydrodynamic and aerodynamic performance due to the presence of tunnel. The research described in this paper was carried out based on the observation of wave characteristics of a planing trimaran model in towing tests, in which the resistance drops as soon as the wave surface separates from tunnel roof. In order to gain a deeper insight into the relationship between wave flow and forces in tunnel region, a comprehensive series of viscous CFD simulations considering free-surface and 2-DOF motion of the hull (heave and pitch) have been performed for the tested model at the volume based Froude numbers ranging from 3.16 to 5.87. The calculated results were validated by comparison with experimental data and showed good agreement. Numerical results of wave contours, longitudinal wave cuts and lifting force distributions at the calculated speeds were presented for the analysis of ventilation process in tunnel region and the corresponding variation of tunnel forces. It is found that, for the speeds higher than Froude number of 4.52, the aerodynamic forces provide major tunnel lift and mainly act on the straight section of the tunnel. And, therefore, numerical simulations of two modified models have also been performed for the analysis of influence of straight section length on the hydrodynamic and aerodynamic performance of planing trimaran.     

Laboratory experiment and numerical simulation on authigenic mineral formation induced by seabed methane seeps

In natural gas hydrate marine settings, cold seepage of methane fluid is a widely observed phenomenon, where authigenic minerals serve as an indication of potential gas hydrate-bearing reservoirs at depth. In this study, based on the data from the site HD196 near Dongsha Island, northern continental slope of South China Sea, laboratory experiments and numerical simulation studies were conducted to investigate the biogeochemical processes of authigenic mineral formation induced by methane seepage. The bioreactor experimental results show that in response to methane flux, pH increased to 8.5 after 20 days of reaction, and Eh declined rapidly first and then remained unchanged at about 100 mV. The decrease in SO₄²⁻, HS⁻ and HCO₃⁻ concentrations indicated the occurrence of anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR). The depletion of Fe²⁺ implied the formation of iron-bearing minerals, e.g., iron sulfides. Carbonate minerals were also identified in the experimental phase of this study. Most iron sulfides existed as massive pieces, and in some cases as spherical or rod-shape pieces. The calcium carbonates were observed as blocky pieces. Numerical simulations were also performed to reproduce the biogeochemical reactions that occurred in the reactor experiments. Based on experimental data, kinetic parameters associated with the observed reactions were calibrated. The model simulated results are general consistent with those obtained by the experiments conducted in this study. The combination of simulation and experimental studies provided a powerful tool to investigate the biogeochemical processes in the methane leakage environment at different temporal and spatial scales. This study gave a new perspective to understand the formation of cold seep authigenic minerals in marine sediments, and was significant for future investigations on the effects of hydrate decomposition.     

A three-dimensional wake impingement model and applications on tandem oscillating foils

Potential flow based vortex numerical methods have been widely used in aerodynamics and hydrodynamics. In these methods, vortices shed from lifting bodies are traced by using vortex filaments or dipole panels. When the wake elements encounter a downstream body, such as a rudder behind a propeller or a stator behind a rotor, a treatment is necessary to divert the wake elements to pass by the body. This treatment is vital to make wake simulations realistic and to satisfy the non-penetration condition during wake body interaction. It also helps to avoid pure numerical disturbances such as when a vortex filament or an edge of a dipole panel passes through the collection point of a body element; this is a singularity for induced velocity and it will introduce a large numerical disturbance. This necessary treatment for three-dimensional problems with geometrical complexity has not been found to date. In this study, a wake impingement model was developed to divert wake elements to slip over the body surface, model the vortex/body interaction, and predict forces on fluctuating components. The model was also tested on configurations of oscillating foils in tandem with an existing panel method code. Simulation results with the wake impingement model are shown to be in closer agreement with limited published experimental data than those without the model. With the established wake impingement model, force fluctuations on the after body due to the wake vortex impingement were investigated based on a series of simulations. The series varied several parameters including distance between two foils, oscillating frequency, span, rear foil pitch angle, swap angle and vertical position.     

基于非线性模型的畸形波模拟及其时频能量谱研究

采用VOF(volume offluid)方法实现了畸形波的数值模拟.将数值结果与线性理论(方程(5))计算结果进行了对比,发现数值模拟结果更能够反映非线性特征.使用小波分析方法研究了畸形波的时频能量谱,发现形成畸形波的过程中存在很强的波浪非线性相互作用,使得波浪的能量向高频端转化.变水深地形可以加强波浪的非线性相互作用.使得转化到高频端的能量更多,产生畸形程度更大的畸形波.     

Heat flow analysis of an FPSO topside model with wind effect taken into account: A wind-tunnel test and CFD simulation

The aim of this paper is to study the feasibility of a computational fluid dynamics (CFD) method to examine the effect of wind on the thermal-diffusion characteristics of floating production storage and offloading (FSPO) topside models subject to fire. It is motivated by the need to identify the fire loads on FPSO topsides, taking into account the effects of wind speed and direction as well as the effects of geometry of the FPSO topsides. The results of a wind-tunnel test and CFD simulation undertaken for these purposes on a 1/14-scale FPSO topside model of a VLCC class FPSO unit are reported here. In the wind-tunnel test, the locations of the heat source of the fire are varied, as are the speed and direction of the wind, and the temperature distribution is measured. CFD simulations, using the ANSYS CFX (2009) program, were performed on the test model, with the results compared with the experimental results. It is concluded that wind has a significant effect on the thermal-diffusion characteristics of the test model and that the CFD simulations are in good agreement with the experimental results. The insights developed in this study will be very useful for the fire engineering of FPSO topsides.     

低空急流对0212号台风"北冕"后部暴雨影响的分析和数值试验

本文首先用实测资料分析了0212号台风"北冕"造成福建大暴雨过程的环流形势和物理量场特征,指出低空偏南风急流的北抬和加强为远离风暴中心的福建东南沿海大暴雨提供了有利的水汽和动力条件.然后用中尺度模式(MM5)模拟分析了低空偏南风急流强度变化对本次暴雨过程的影响,结果表明低空急流强度变化对福建东南部的暴雨落区及强度有很大影响.     

Analysis and optimization design of submarine tunnels crossing fault fracture zones based on numerical simulation

Abstract

Fault fracture zones have always been a key problem in the construction of submarine tunnels. To efficiently summarize the safety impact of different construction schemes on a submarine tunnel crossing a fault fracture, a theoretical model using numerical simulation has been established via the benching tunnelling construction method, three-step method, Center Diaphragm method (CD method), both sides heading method, Cross Diaphragm method (CRD method) and two kinds of supporting methods: pre-grouting and shotcreting. Numerical simulation studies on the excavation and support of submarine tunnels crossing fault fracture zones have been carried out. The research indicates: the fracture zone is the main area where sedimentation instability occurs; the CRD method has the lowest horizontal convergence under the support of the diaphragm; increasing the grouting strength is more effective in controlling the deformation of the surrounding rock than increasing the range of the pre-grouting and the thickness of the shotcrete in the initial support is increased, and its resulting effect is obvious. To optimize the construction scheme, we compared the settlement, horizontal convergence and surrounding rock stress of the tunnel according to the simulation results of different excavation support methods, which could provide theoretical guidance for better on-site construction techniques.     

深水锚泊定位半潜式钻井平台性能数值与试验研究

近年来,深水半潜平台已成为海洋工程领域研究的热点。分别通过模型试验和数值模拟的方法,对不同水深和浪向条件下作业的深水半潜平台的运动以及系泊系统的受力进行全面分析。在此基础上,进一步研究平台在深水作业时的运动和动力特性,以及水深和环境海况的变化对平台运动和系泊系统受力的影响规律。同时,对比完整系泊系统的情况,对一根系泊缆破断的极端状态下平台的特性开展研究,获得运动和系泊系统受力的变化规律。对比发现试验和数值的结果能较好地相互吻合,且均能满足相应的安全度要求,保证平台实际作业时的可靠性,为深水半潜平台设计中的安全极限计算提供一定的依据。     

Research on truncation method of FPSO and offloading system in model test

The model test method of the FPSO and offloading system is investigated by using the development mode of “FPSO + CALM + TANKER” working in a 1700-m depth of offshore West Africa. An equivalent design based on static and dynamic similarity criteria for oil offloading line (OOL) is discussed, and a type of creative method for the equivalent design of OOL in a model test is proposed. Based on the static similarity criterion, the truncated design of the FPSO mooring system in water depth and horizontal directions is carried out. After that, a relevant static optimization is conducted. Meanwhile, to avoid interference between the FPSO mooring system and CALM mooring system, a horizontal equivalent design for the CALM mooring system is provided. On this basis, the model test scheme is conducted. Time domain coupled analyses for the whole system before and after truncation are later performed. After comparison, it is observed that the calculated results of the truncated system are basically consistent with those of the prototype system, and the design of the model test scheme is demonstrated to be robust and reliable.     

基于Boussinesq波浪模型的港池波浪数值模拟与泊稳分析

基于Boussinesq方程的MIKE21-BW模型,建立等水深、双突堤式的波浪数值港池,采用不同的波浪入射方向和双突堤口门宽度,分别对波浪经双突堤后的绕射情况进行模拟.根据《港口与航道水文规范》中的计算参数和突堤绕射系数结果,对BW模型进行率定和验证,结果表明二者吻合度较好,可以较好地描述港池的泊稳状况.在此基础上,...     

Internal characteristics and numerical analysis of plunging breaker on a slope

Many investigations about the direct measurements of velocities to clarify the internal mechanism of the breaker have been carried out as a result of recent progress in the measuring techniques.This research attempts to clarify the breaking wave transformation system on a slope by an experiment and numerical analysis. In an experiment, the velocities in the surf zone were measured directly using an electromagnetic current meter, and the space distribution characteristic of the vorticity ω = (∂u/∂y − ∂u/∂x) and the skewness γ = (∂u/∂y + ∂u/∂x) were examined. Also, occurrence situations of the vortices at the time of water mass inrush were measured by video tape recorder (VTR) image processing. However, because the breaker is a violent phenomenon that is entrained with plentiful bubbles, the extent to which we can clarify breaker transformation in experiments is limited. Numerical simulations are substituted for experiments as a method to clarify breaker transformation.In numerical analysis, finite amplitude wave analysis based on the potential theory (non-viscous fluid) is possible before wave breaking; however, the analysis must take into account the viscous fluid after breaking. So, we use the Reynolds equations to develop a numerical simulation system of the breaker transformation on a sloping bottom. The numerical energy dissipation model of the breaker was compared to the experimental results, and a modified Simplified Marker and Cell (SMAC) method is presented. The internal characteristics of the breaker transformation are described using application examples.     

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.     

向阳圩海塘围堰堤坝沉降特性原位实测及稳定性分析

以上海市向阳圩海塘围堰主堤为工程背景，在大量原位实测的基础上通过对各测试结果的统计分析研究了软土海滩围堰堤坝及地基沉降位移特性。结果表明：围堰堤坝及地基沉降具有显著的时效特性，沉降与时间的相关关系可用负指数时效特性曲线拟合；各测点位移值随时间具有明显突变变化，整个沉降时域可分为快速沉降时域区及缓慢沉降时域区。同时，在充分考察了沉降速率随时间变化特性的前提下提出了用该参量预测堤坝稳定时间及最终沉降位移的建议。