不同节点布置下二维涡激振动的无单元法参数化分析

尝试建立1种基于无单元法的涡激振动数值模拟算法,并给出适用于涡激振动分析的前处理自动布点方法.基于无单元法理论,使用动最小二乘法构造形函数,利用无单元伽辽金法,采用速度和压力分离模式,及手工布点和自动布点2种方法所得出的节点布置形式,对流场控制方程进行空间离散,模拟二维涡激振动的流场形态,并对VIV相关参数进行分析,计算不同节点布置情况下的升力系数(Cl)、曳力系数(Cd)及斯特罗哈数(St),并与物理模型实验结果进行对比.计算结果表明,无单元伽辽金法应用于立管VIV分析是可行的,且文中采用2种布点方法均能较好的模拟流场中泻涡脱落的形态,计算结果与传统方法和物理模型实验结果吻合良好.证明文中2种布点方法都能用于固定圆柱的二维VIV分析,但自动布点法能够更好地适用于复杂问题的计算及圆柱体在流场中的VIV动力响应分析.     

The effect of yaw angle on VIV suppression for an inclined flexible cylinder fitted with helical strakes

Experimental studies were carried out to investigate the response features of an inclined flexible bare cylinder as well as a straked cylinder in a towing tank, with the main purpose of further improving the understanding of the effect of yaw angle on vortex-induced vibration (VIV) suppression. Four yaw angles (a = 0°, 15°, 30°, 45°), which is defined as the angle between the cylinder axis and the plane orthogonal to the oncoming fluid flow, were tested. The cylinder model was towed along the tank to generate a uniform fluid flow. The towing velocity was in the range of 0.05–1.0 m/s with an interval of 0.05 m/s. The corresponding Reynolds number ranged from 800 to 16000. The strakes selected for the experiments had a pitch of 17.5D and a height of 0.25D, which is generally considered as the most effective configuration for VIV suppression of a flexible cylinder in water. The experimental results indicate that VIV suppression effectiveness of the inclined flexible straked cylinder is closely related to the yaw angle. The displacement amplitudes are significantly suppressed in both cross-flow (CF) and in-line (IL) directions at a = 0°. However, with increasing yaw angle, the suppression efficiencies of the CF and IL displacement amplitudes gradually decrease. In addition, the CF dominant frequencies of the straked cylinder obviously deviate from those of the bare cylinder at a = 0° and 15°. This deviation is substantially alleviated with increasing yaw angle. The IL dominant frequencies show less dependency on the yaw angle. Similar trends are also observed on the dominant modes of vibration and the mean drag coefficients.     

用AMSR数据极化比PSSM算法检测渤海海冰边缘线

利用高级微波扫描辐射计数据和冰间湖信号模拟算法探测渤海海冰,提取海冰外缘线信息。探测的海冰边缘线与Jason-1高度计海冰探测结果和ENVISAT ASAR海冰探测结果做比较,验证了该方法的有效性。     

Efficient Approximate Method of Global Reliability Analysis for Offshore Platforms in the Ice Zone

Ice load is the dominative load in the design of offshore platforms in the ice zone, and the extreme ice load is the key factor that affects the safety of platforms. The present paper studies the statistical properties of the global resistance and the extreme responses of the jacket platforms in Bahai Bay, considering the randomness of ice load, dead load, steel elastic modulus, yield strength and structural member dimensions. Then, based on the above results, an efficient approximate method of the global reliability analysis for the offshore platforms is proposed, which converts the implicit nonlinear performance function in the conventional reliability analysis to linear explicit one. Finally, numerical examples of JZ20-2 MSW, JZ20-2NW and JZ20-2 MUQ offshore jacket platforms in the Bahai Bay demonstrate the satisfying efficiency, accuracy and applicability of the proposed method.     

Prediction Model for Vortex-Induced Vibration of Circular Cylinder with Data of Forced Vibration

A model based on the data from forced vibration experiments is developed for predicting the vortex-induced vibrations (VIV) of elastically mounted circular cylinders in flow. The assumptions for free and forced vibration tests are explored briefly. Energy equilibrium is taken into account to set up the relationship between the dynamic response of self-excited oscillations and the force coefficients from forced vibration experiments. The gap between these two cases is bridged straightforwardly with careful treatment of key parameters. Given reduced mass m and material damping ratio ζ of an elastically mounted circular cylinder in flow, the response characteristics such as amplitude, frequency, lock-in range, added mass coefficient, cross-flow fluid force and the corresponding phase angle can be predicted all at once. Instances with different combination of reduced mass and material damping ratio are compared to investigate their effects on VIV. The hysteresis phenomenon can be interpreted reasonably. The predictions and the results from recent experiments carried out by Williamson's group are in rather good agreement.     

利用直方图方法处理二类水体剖面数据研究

剖面法是国际上公认的测量表观光学量的首选方法,但在二类水体的数据处理中,其关键参数漫射衰减系数的数据处理误差较大.论文就此提出利用直方图分析的方法进行数据的处理,并选用2002年的黄海试验数据进行验证,结果表明,这种方法在一定程度上减小了主观因素对数据处理的不利影响,提高了数据处理的准确度.     

燃烧氧化-非色散红外吸收法测定海水中溶解有机碳

采用燃烧氧化-非色散红外吸收法测定了海水中的溶解有机碳.结果表明,标准曲线的线性较好,精密度较高,方法检出限为0.024 mg/L;所测海水样DOC质量浓度的最高值为3.95 mg·L-1,最小值为1.47 mg·L-1;采样点距离海岸越远,DOC质量浓度越低.海水样品置于4 ℃下冷藏保存,滴加饱和HgCl2溶液的水样,其保存效果要好于不加饱和HgCl2溶液的水样,且在55 d内,其DOC质量浓度基本上没有发生变化.     

过硫酸钾氧化法测定水中总有机碳

根据《海洋监测规范》规定的总有机碳分析方法 ,利用HW 5 61 0非色散红外CO2 气体分析仪 ,设计制造成功总有机碳分析装置 ,对《海洋监测规范》的方法进行了根本的改进 ,方法成熟可靠。用该仪器和方法测定TOC ,检出限低于 0 .0 1mg/L ,重现性优于 1 % ,达到了与进口TOC分析仪相近的分析精度及再现性 ,而该TOC分析仪的制造成本仅相当于进口仪器价格的 1 / 1 0～ 1 / 5 ,值得海洋、河流、湖泊等有关监测和研究部门借鉴。     

用直接法分析超大型浮体的水弹性响应

探讨了浮舟桥型超大型浮体结构的水弹性响应分析问题。将超大型浮体结构简化成弹性平板模型,用压力分布法计算流体压力,用直接法计算流体-结构系统,给出了它们的数学计算模型。计算表明本计算方法和程序是正确的,并能保证充分的精度,进而计算了更大尺度的超大型浮体,分析了波长、波向等对响应振幅的影响。     

瞬变电磁法在工程地震安全性评价中的应用

介绍瞬变电磁法的基本原理,论述了几种在地震安全性评价工作中常用的物探方法。通过应用实例分析表明,瞬变电磁法用于地震安全性评价工作有其独特和重要的现实意义。     

主频计算法对测井曲线沉积旋回的精细分析

用主频计算法对长庆气田主力储层中下奥陶统马家沟组马五1段碳酸盐岩的自然伽玛测井曲线进行了分析，得出其主要沉积旋回周期为100、57、36和26ka，基本与米兰科维奇旋回的地球自转偏心率和地轴倾角变化周期相一致，因崦，可以认为储层的沉积旋回是地球自转偏心率和地轴倾角变化引起气候周期性变化形成的，其中又以偏心率影响最大，表明主频计算法用于测井曲线进行分辩率较高的沉积旋回分析是可行的。     

利用MAPX实现空间数据库与属性数据库的挂接

数据库是 GIS的基础 ,而空间数据库与属性数据库的挂接则是 GIS的要点。本文以渤海区域地质信息管理系统数据为例 ,阐述了基于 GIS的海洋地学管理信息系统中数据库的组织方法 ,包括空间数据库与属性数据库数据分类、分层方案 ,命名及编码规则。在此基础上 ,重点讨论了在 VisualBasic环境下运用 MAPX实现空间数据库与属性数据库的挂接方法。     

有航速浮体时域分析的混合边界元法

给出了一种联合瞬态格林函数和Rankine源进行有航速浮体时域水动力分析的混合——边界元方法。在三维混合边界元方法中,通过一个匹配面将流体域划分为内域和外域,在内域中使用Rankine源以模拟直壁或非直壁船体及线性或非线性自由面条件,在外域中使用瞬态格林函数以满足自由面条件和远方辐射条件。使用该方法计算了一个有航速潜没圆球的波浪力,和解析结果的比较证明了该方法的正确性。进一步给出了一个有航速Wigley船的水动力结果,计算结果稳定,没有外传波向内反射的现象发生。     

关于端基分析法测定壳低聚糖的相对数均分子质量问题的探讨

为使端基分析法更具合理性。文中以铁氰化钾为显色剂。以盐酸氨基葡萄糖和N-乙酰基-D-葡萄糖胺为还原糖的标准品,建立了端基分析法测定低聚糖相对数均分子质量的标准曲线。实验结果证明：通过不同浓度的标准溶液绘制的标准曲线,测得壳低聚糖的相对数均分子质量差别比较大。以凝胶色谱法测定的相对数均分子质量为对照,经分析得：以盐酸氨基葡萄糖为标准品建立的标准曲线方程和以N-乙酰基-D-葡萄糖胺为标准品建立的标准曲线方程更为合理。     

基于CEL法的埋深海底管道受坠物撞击损伤分析

海底管道一旦受到坠物撞击损伤,会造成严重的环境污染及经济损失,为保证管道在运行期间的安全性,常对其进行埋深处理。对于有埋深的海底管道,坠物的撞击会造成管道上覆土体的大变形,在数值模拟中会导致网格畸变,甚至无法收敛。耦合欧拉-拉格朗日法(CEL法)可有效处理土体大变形问题,本文基于此方法建立了坠物-管道-土体有限元模型,分析了坠物撞击速度、质量、形状、海床土体性质(弹性模量、内摩擦角、黏聚力)、埋深对海底管道塑性变形的影响。结果表明,管道的凹痕深度随坠物撞击速度和质量的增加而增加;坠物与海床土体及管道接触面积越小,管道的凹痕深度越大;管道的埋置深度及海床土体的性质对吸收坠物的撞击能量有直接关系:海床土体的强度越高、埋深越大,管道所受到的损伤程度越小。分析结果可为管道的设计与防护工作提供科学依据,且与现行规范比较,本文方法更加经济、合理。     

Numerical analysis of water exit for a sphere with constant velocity using the lattice Boltzmann method

In this paper, the three-dimensional water exit of a sphere with different vertical velocities is investigated numerically using the lattice Boltzmann method (LBM). In this method, the liquid-gas two-phase flow is simplified as a single-phase free surface flow. To capture the free surface, a mass tracking algorithm is incorporated into the LBM. The gravity as a body force is introduced in the form of calculating the equilibrium distribution with an altered velocity, while the surface tension is neglected. Besides, the employed bounce-back boundary conditions are used for a moving sphere. What’s more, the Wall-Adapting Local Eddy (WALE) viscosity model is employed to capture the turbulent structures of the flow and stabilize the simulation. The accuracy of the numerical results is demonstrated through comparisons with the previous numerical and experimental results in the literature. The results show that the spike height is significantly influenced under the Froude number (Fr) below 4.12 and slightly affected under the Fr varying from 4.12 to 8.24. After the sphere exits water totally, the evolution of the free surface waterfall can be described as two phases and becomes more intense with the Froude number increasing. The non-uniform distribution of velocity results in the breaking of the free surface after the sphere completely exits the water. Moreover, the Reynolds number greatly affects the wake dynamics and hydrodynamics acting on the sphere when it moves beneath the water surface.