Nonlinear dynamics of an elastic cable during laying operations in rough sea

A numerical approach for predicting motion and tension of extensible marine cables during laying operations in a rough sea is presented here. The solution methodology consists of dividing the cable into straight elements, which must satisfy an equilibrium equation and compatibility relations. The system of nonlinear differential equations is solved by the Runge–Kutta method, taking the effect of regular and/or irregular waves into account explicitly.

Illustrative applications of the method are given for a typical cable laying ship. The results are presented as rms values of the cable dynamic tension and corresponding dynamic factor for two different types of cable and several values of cable stiffness. The effect of axial deformation on the maximum tension at the shipboard pulley location is highlighted.     

船舶受冲击力作用时的水动力试验研究

根据冲量相似的要求进行船舶在冲击作用下的模型试验，并将模型试验结果与理论计算及实际试验进行了对比和分析。     

渤海赤潮藻类生态动力学模型的非线性动力学研究

基于渤海典型赤潮藻类——中肋骨条藻 ,考虑浮游动物的捕食、光照及营养物质的作用 ,建立了渤海湾的浮游动物—藻类—营养物质三者的动力学模型。运用现代非线性动力学理论着重分析了模型的稳定性及分岔行为。研究了多个参数对藻类生长的影响 ,发现某些参数对藻类的生长影响不大 ,而某些参数则会致使藻类模型出现分岔乃至混沌行为 ,并给出了这些参数的阀值 ,这与赤潮的形成 (爆发性增殖 )密切相关 ;并根据渤海湾的赤潮数据进行了有效的数值模拟 ,所得结果对于研究赤潮的形成机理有一定的参考价值     

海洋平台浮托安装中横荡护舷限位和缓冲性能分析

浮托安装法,是相对于传统吊装法的一种新型海洋平台安装方法,具有起重能力大、作业周期短、安装费用低、适用范围广、操作安全方便等优点,解决了海上大型平台组块的安装问题。为了研究横荡护舷对浮托安装的影响,首先对海洋平台浮托安装中的护舷装置进行了介绍,然后针对某工程实例应用AQWA软件进行了数值模拟,并进行了模型验证。从时域方面对就位状态下的浮托模型进行了耦合动力分析,研究了横荡护舷参数对驳船运动和撞击力的影响规律。研究表明,横荡护舷可以有效地减小驳船运动和撞击力,其限位和缓冲作用与护舷尺寸及护舷刚度均有关。研究结果可为实际浮托安装工程提供重要的参考。     

Model tests on installation and extraction of suction caissons in dense sand

A series of model tests were performed on steel- and Perspex-made suction caissons in saturated dense marine sand to explore installation and extraction behaviors. The extractions of the caisson were conducted by applying monotonic loading or by pumping water into the caisson. Responses of suction caissons to pullout rates, aspect ratios, and extraction manners were examined. Test results show that a cone-shaped subsidence region occurs around the suction caisson during the suction-assisted installation. The pullout bearing capacity of the suction caisson in sand is dominated by the loading rate and the loading manner. For the suction caisson subjected to monotonic loading, the maximum bearing capacity is reached at the pullout rate of about 20.0?mm/s. The mobilized vertical displacement corresponding to the pullout capacity increases with increasing the pullout rate. The passive suction beneath the suction caisson lid reaches the maximum value when the pullout bearing capacity is mobilized. In addition, during the suction caisson extracted by pumping water into the caisson, the maximum pore water pressure in the caisson is obtained under the displacement of approximately 0.04 times the caisson diameter. The absolute values of the maximum pore water pressures for the suction caissons approximately equal those of the maximum vertical resistances at the monotonic pullout rate of 5 mm/s. When the vertical displacements of the suction caissons with the aspect ratio of 1.0 and 2.0 reach 0.92 and 1.77 times the caisson diameter, respectively, the seepage failure occurs around the caissons. Using a scaling method, the test results can be used to predict the time length required for the prototype suction caisson to be extracted from the seabed.     

潜器在冲击载荷下的运动和控制研究

潜器在水下发射火箭时会产生复杂的运动变化,对其研究很有实际意义。参照格特勒运动方程,建立潜器运动的非线性数学模型。导入实验模型的参数,对其六自由度基本运动进行了仿真,并与水池实验结果相比较,验证了仿真模型的有效性。导入发射火箭时潜器受到的完整载荷,计算分析了不同航速下潜器的运动响应和运动控制。结果表明,发射载荷对潜器运动将产生较长时间的显著影响,包括速度损失、升沉运动和纵倾角振荡。航速越小,运动变化越大,恢复所需时间越长,控制越困难。     

大连港集装箱码头后方堆场荷载统计分析和概率模型

为了解我国北方港口集装箱码头集装箱堆场荷载的情况,选择大连港集装箱码头进行集装箱荷载调查和统计分析。采用不平稳随机场模型,建立集装箱堆场的局部荷载模型和整体荷载模型,确定集装箱荷载的统计参数。研究表明:大连港集装箱码头50 a设计基准期的局部荷载最大值服从极值I型分布,平均值、标准差和变异系数分别为86 040.76 kg、24 199.05 kg和0.281 3;50 a设计基准期的整体荷载最大值也服从极值I型分布,平均值、标准差和变异系数分别为1 726.8 kg/m2、185.13 kg/m2和0.107 2。就重型集装箱而言,现行港口荷载规范规定的集装箱箱角荷载偏低,用于整体计算的荷载较高。     

Investigation of three-dimensional active earth pressure and load transfer according to aspect ratio

ABSTRACT

Although there is a noticeable difference between two-dimensional and three-dimensional earth pressures, most researchers have suggested various earth pressure theories under the two-dimensional condition. Only a few studies have been conducted on the three-dimensional load transfer to the adjacent ground, whereas most studies in literature on the three-dimensional active earth pressure have been conducted by focusing on the stability of active wall. For accurate prediction of the three-dimensional active earth pressure, it is required to study not only the three-dimensional earth pressure distribution but also the three-dimensional load transfer to the adjacent ground. In this paper, size and distribution of the three-dimensional active earth pressure as well as the load transfer according to aspect ratio of retaining wall are investigated through a series of model tests. As a results, the three-dimensional active earth pressure distribution showed the highest value at the wall height of 0.5–0.55h when the aspect ratio of equal to 1.2 or higher. The load transfer showed higher values in vertical direction than horizontal direction. The load transfer distribution can be evaluated by applying the size and effect range of the loads transferred to the adjacent soil of the retaining wall.     

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.     

A view on capsizing under direct and parametric wave excitation

The behavior of a ship that is simultaneously heaving, swaying and rolling in waves is examined by using an early developed model by Thompson et al. [Thompson, J. M. T., Rainey, R. C. T. and Soliman, M. S. (1992) Mechanics of ship capsize under direct and parametric wave excitation. Philosophical Transactions of the Royal Society London A 338, 471-490]. A second-order nonlinear differential equation has been used as a mathematical model which is analyzed by using numerical methods to obtain geometrical phase space techniques of nonlinear dynamics. Bifurcation diagrams and Poincaré maps are two of the geometrical techniques used in this study. The result of the calculation is given to allow the naval architect to make a self comparison.     

海冰动力过程的改进离散元模型及在渤海的应用

海冰的断裂、重叠和堆积等离散分布特性广泛地存在于极区和副极区的不同海域,并对海冰的生消、运移过程有着重要影响。针对海冰在不同尺度下的离散分布特点,发展海冰动力过程的离散元方法有助于完善海冰数值模式,提高海冰数值模拟的计算精度。为此,本文针对海冰生消运移过程中的非连续分布和形变特性,发展了适用于海冰动力过程的改进离散元模型(MDEM)。不同于传统离散元方法,该模型将海冰离散为具有一定厚度、尺寸和密集度的圆盘单元。海冰单元设为诸多浮冰块的集合体,其在运移和相互接触碰撞过程中,依照质量守恒发生单元尺寸、密集度和厚度的相应变化。基于海冰离散性和流变性的特点,该模型采用黏弹性接触本构模型计算单元间的作用力,并依据Mohr-Coulomb准则计算海冰法向作用下的塑性变形及切向摩擦力。为验证该模型的可靠性,本文对海冰在规则水域内的运移和堆积过程进行了分析,离散元计算结果与解析值相一致;此外,对旋转风场下海冰漂移规律的模拟进一步验证了本文方法的精确性。在此基础上,对渤海辽东湾的海冰动力过程进行了48h数值分析,计算结果与卫星遥感资料和油气作业区的海冰现场监测数据吻合良好。在下一步工作中将考虑海冰离散元模拟中的热力因素影响,发展具有冻结、断裂效应的海冰离散元模型,更精确地模拟海冰动力-热力耦合作用下的生消和运移过程。     

陀螺效应作用下水下航行体动力学模型

当安装于水下航行体上的旋转装置质量或转动惯量达到一定程度时,其对水下航行体运动与操纵的影响是不可忽略的。针对安装于水下航行体上的旋转装置,分析了水下航行体运动时装置的陀螺效应。得出了旋转装置陀螺力的明确数学方程。不失方法的一般性,假设旋转装置只在运动坐标系的X轴方向有旋转角速度,推导了在考虑陀螺效应作用的情况下水下航行体的六自由度模型方程;以此为基础,建立了水下航行体的仿真模型并对水下航行体的水下运动特性进行了仿真,分析了旋转装置的质量、角速度对水下航行体运动特性的影响规律,从而为研究在考虑陀螺效应情况下的水下航行体操纵奠定了基础。     

Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches

Tension Leg Platform (TLP) is one of the concepts which shows promising results during initial studies to carry floating wind turbines. One of the concerns regarding tension leg platform wind turbines (TLPWTs) is the high natural frequencies of the structure that may be excited by nonlinear waves loads. Since Computational Fluid Dynamics (CFD) models are capable of capturing nonlinear wave loads, they can lead to better insight about this concern. In the current study, a CFD model based on immersed boundary method, in combination with a two-body structural model of TLPWT is developed to study wave induced responses of TLPWT in deep water. The results are compared with the results of a potential flow theory-finite element software, SIMO-RIFLEX (SR). First, the CFD based model is described and the potential flow theory based model is briefly introduced. Then, a grid sensitivity study is performed and free decay tests are simulated to determine the natural frequencies of different motion modes of the TLPWT. The responses of the TLPWT to regular waves are studied, and the effects of wave height are investigated. For the studied wave heights which vary from small to medium amplitude (wave height over wavelength less than 0.071), the results predicted by the CFD based model are generally in good agreement with the potential flow theory based model. The only considerable difference is the TLPWT mean surge motion which is predicted higher by the CFD model, possibly because of considering the nonlinear effects of the waves loads and applying these loads at the TLPWT instantaneous position in the CFD model. This difference does not considerably affect the important TLPWT design driving parameters such as tendons forces and tower base moment, since it only affects the mean dynamic position of TLPWT. In the current study, the incoming wave frequency is set such that third-harmonic wave frequency coincides with the first tower bending mode frequency. However, for the studied wave conditions a significant excitation of tower natural frequency is not observed. The high stiffness of tendons which results in linear pitch motion of TLPWT hull (less than 0.02 degrees) and tower (less than 0.25 degrees) can explain the limited excitement of the tower first bending mode. The good agreement between CFD and potential flow theory based results for small and medium amplitude waves gives confidence to the proposed CFD based model to be further used for hydrodynamic analysis of floating wind turbines in extreme ocean conditions.     

丰水期珠江口黏性泥沙输运的三维数值模拟

珠江口的黏性泥沙输运对区域海洋工程和河口海洋环境有着重要的影响。本文利用SELFE模型,针对珠江河口海域建立了一个采用非结构三角形网格的三维斜压水动力模型,可耦合模拟海流、潮流及风海流水动力环境,并在此基础上开发了包括底床模块的黏性泥沙输运模型。模拟结果与实测值验证较好,再现了丰水期珠江河口的泥沙输运特征以及最大浑浊带的变化和分布特点。研究表明,丰水期珠江口悬沙质量浓度西侧大于东侧,泥沙主要来自河口上游。河口浅滩上会形成最大浑浊带,最大质量浓度可达0.5 g/L。珠江口最大浑浊带的形成主要受潮动力、重力环流及泥沙再悬浮和沉积过程影响,其中泥沙再悬浮和沉积过程对中滩的最大浑浊带影响显著,而重力环流作用对西滩的最大浑浊带影响显著。     

茅家港滩面沉积物粒度变化及其与水动力的关系

根据野外观测的原始资料，绘出粒度的分布图和不同位置的剖面图，客观地分析了茅家港滩面沉积物粒度空间分布、季节变化、粒度变化与水动力的关系，研究发现：随着离岸向海距离的增加，中值粒径逐渐变小，粒径逐渐变粗。突堤内的中值粒径比突堤外的细。冬季的中值粒径比夏季的粗。随着离岸距离的增加，水动力逐渐增强，导致滩面沉积物的粒径逐渐变粗；突堤内的水动力比突堤外的水动力弱，致使突堤内滩面沉积物的中值粒径比坝外的细：冬季的水动力比夏季的水动力强，致使冬季滩面沉积物中值粒径比夏季粗。     

潮优型河口动力对水深变化的响应机制研究——以葡萄牙Guadiana河口为例*

强人类活动(如航道疏浚)和自然气候变化(如海平面上升)对近岸河口环境不同影响的辨识是目前河口海岸学研究的热点和难点问题。在地形概化和动力简化条件下, 解析模型能够快速辨识强人类活动和自然气候变化对河口环境的影响, 它是探讨河口动力过程对外界干扰的响应机制的重要工具。本文基于前人对葡萄牙Guadiana河口不同分潮之间非线性相互作用的研究, 采用一维水动力解析模型探讨河口不同分潮潮波传播过程对水深变化(模拟航道疏浚和河道淤积过程)的响应机制。研究结果表明: 平均水深$\overline{h}$的变化影响无量纲河口地形参数γ和摩擦参数χ, 进一步影响河口动力参数包括潮波振幅参数ζ、流速振幅参数μ、波速参数λ、潮波振幅增大/衰减率参数δ以及流速与水位之间的相位差?等; 平均水深变化对河口中下游段(x=0~60km)的潮汐动力影响较大, 而对河口上游段(x=60~78km)影响较弱; 主要半日分潮(M₂、S₂、N₂)对水深变化的响应略大于全日分潮(K₁、O₁); 航道疏浚幅度小于2m时, 对河口潮汐动力格局影响不大, 而当疏浚幅度大于2m时, 将对河口潮汐动力格局及水环境(如盐水入侵等)产生较大影响; 河道淤积将导致潮汐动力减弱, 流速振幅、潮波振幅及传播速度减小, 流速和水位之间的相位差也减小。     

西湖凹陷中南部油气成藏动力学特征及成藏机理

西湖凹陷以始新世末的玉泉运动和中新世末的龙井运动形成的不整合面为界,将盆地的发展演化分为裂陷、坳陷和区域沉降三个阶段。在盆地演化的不同阶段,不同构造带的沉降速率存在差异,烃源岩的热成熟演化史也不一致。生、排烃史模拟表明：平湖组烃源岩的生烃强度最高,花港组烃源岩的生烃强度相对较小;中央背斜带及其两侧深凹部位烃源岩的生烃强度大于保斜坡带;主要应用Basin Mod盆地模拟软件系统,通过对流体势、温压系统、异常压力的分析,探讨西湖凹陷中南部油气运聚成藏的机理。     

厦门和东山外来物种沙筛贝的种群动态和结构

１９９０年首次在中国大陆沿岸厦门马銮湾和东山八尺门海堤西侧,发 现外来物种沙筛贝（Ｍｙｔｉｌｏｐｓｉｓ ｓａｌｌｅｉ）。通过挂放试板和定点取样,研究其种群动态和 结构,包括水平分布、垂直分布和季节分布,以及壳长的组成。     

浮式生产储油系统内孤立波载荷特性实验

将置于大尺度密度分层水槽上下层流体中的两块垂直板反方向平推,以基于MCC理论解的内孤立波诱导上下层流体中的层平均水平速度作为其运动速度,发展了一种振幅可控的双推板内孤立波实验室造波方法,并对内孤立波作用下浮式生产储油系统(FPSO)的载荷特性开展了系列实验。结果表明,无因次内孤立波水平力和力矩幅值均与先导内孤立子无因次振幅之间呈线性关系,其斜率与上下层流体深度比有关;在各种上下层流体深度比下,无因次内孤立波垂向力幅值与先导内孤立子振幅之间近似呈幂函数关系。