分层流体中拖曳球体尾流及辐射内波试验研究

在大型分层流水池中采用 PIV 方法对跃变分层流体中小球尾流场进行了测量,获得了不同拖曳速度工况下跃层处的尾流及内波流场,对体效应稳态内波和尾流效应非稳态内波的特征有了形象直观的了解,获得了内波流场速度大小随内傅氏数的变化规律。     

Reliability analysis of ovalized deep-water pipelines with corrosion defects

The accurate assessment of the remaining strength of corroded pipes is a subject that has been increasingly investigated over the past decades. This is because of the risk of significant social, economic, and environmental effects that may be caused by an accident. The finite element method has been successfully used to predict the collapse pressure considering external load. It was also used in this study. The literature primarily focused on the corroded pipes subjected to internal pressure. In this study, the out-of-roundness (ovalization) of the pipe was considered to evaluate the collapse pressure. Uncertainties should be incorporated into a computational model to assess the reliability of corroded pipes. Three methods for evaluation of the probability of failure were used: the first-order reliability method (FORM), traditional Monte Carlo (MC), and a new proposed methodology that combines MC results with the kernel density estimation method (MCkde). The probability of failure of ovalized corroded pipes subject to external pressure was computed. The results exhibited a good agreement between FORM and MCkde method. The statistical importance of each random variable was observed and the results were compared with those from intact ovalized pipes. The computation cost of the MC method with numerical simulation limits its use to the application under study. Solutions using the FORM and MCkde methods exhibited good agreement with those of the full MC method. However, the computational effort of the latter was independent of the stochastic dimension, and it was a derivative-free method. As expected, in general, the solutions based on empirical methods were conservative.     

Flexural buckling of circular concrete-filled stainless steel tubular columns

Concrete-filled steel tubular (CFST) columns are currently used in offshore structures and oil and gas drilling platforms, from which the external steel tubes become at risk due to the aggressive ocean climate and/or sea water. Therefore, the CFST columns in corrosive environment lose their excellent mechanical performances and safety as the thicknesses of steel tubes decrease due to corrosion. This has recently led to the introduction of the concrete-filled stainless steel tubular (CFSST) columns, which benefit from the stainless steel as a superior metallic corrosion resistant material. Accordingly, CFSST short columns have recently attracted the scientific community. However, circular CFSST slender columns have received very little attention. Currently, this paper provides a nonlinear finite element (FE) inelastic analysis for the axially-loaded circular CFSST slender columns to substitute the lack in their behaviour; especially when the relative cheap lean duplex stainless steel material (EN 1.4162) is utilised. The FE models are firstly validated by using the available test results in literature. This validation stage is, then, followed by a parametric analysis to explore the fundamental behaviour of such columns considering the most important factors. The paper divides the slender columns into intermediate length and long columns based on the type of the overall buckling that takes place, and then the behavioural differences between both types are clearly addressed. The obtained FE axial strengths are additionally compared with those predicted by the European (EC4) and American (AISC) specifications. Based on these comparisons, a formula, based on Eurocode 4, is suggested for the routine compressive design practice of these columns, which is found to fit well with the axial strengths of current slender columns which utilise the lean duplex stainless steel material.     

Rigid finite element method in applications to dynamic optimization of motion of a riser in reentry

Overloading of a riser, with possible subsequent damage, can be caused when the bottom end of the suspended riser encounters an obstacle during its relocation realized in reentry. Such collisions can be avoided by appropriate horizontal and vertical displacements of the riser, which can be realized by planning the motion of the base or use of Heave Compensation Systems − HCS. Simulation tasks concerned with this problem can be solved by use of numerically effective models of a riser's dynamics and optimization methods. The model of dynamics of a riser presented in this paper and formulated by means of the rigid finite element method (RFEM) is validated against experimental measurements and calculation results presented by other researchers. Due to its very good numerical effectiveness, the model is then applied to the solution of two optimization problems. The first optimization task consists in choosing the horizontal displacements of the upper end of the riser so that the bottom end of the riser is positioned as closely as possible to the final position with reduced vibrations at the end of the base motion. In the second task the upper end of the riser is moved vertically in such a way that the bottom end of the riser stays at a safe distance from an obstacle during riser relocation. The results of optimization simulations for a number of cases are presented and discussed.     

SV波入射下衬砌尺寸对引水隧道动力响应的影响

采用波函数的Fourier-Bessel级数展开方法,得到了SV波入射时,大型引水隧道平面地震响应的解析解,并对建立的场地模型进行数值计算.计算结果表明：SV波入射时,引水隧道衬砌的径向动应力随隧道内径的增大而增大,径向动应力的最大值与隧道内径呈线性关系,SV波入射引起的引水隧道衬砌的切向动应力随隧道内径的增大而增大.当入射角小于临界角时,切向动应力受隧道内径变化的影响很大.此外,引水隧道衬砌的径向动应力随衬砌厚度的增大而增大,切向动应力则随衬砌厚度的增大而减小.     

铁山湾海域风浪数值模拟研究

随着北部湾的快速发展,铁山湾海域将规划建设数百个泊位．基于SWAN建立了该海域风浪数学模型,选取铁山湾海域影响较大的5个风向,研究不同风要素组合作用下的波浪特征,计算得到了建港方案实施前、后的波浪场分布．研究结果表明：S-SSW风向对该海域的风浪影响最大,SE-SSE和SW-WSW风向次之,E-ESE和W-WNW风向的影响相对较小．建港方案实施后,工程区的波浪强度整体小于工程前的;人工岛起到了很好的掩护作用．     

基于CFD方法的舰船顶浪运动响应幅值算子计算

基于计算流体力学(CFD)方法,给出了舰船在波浪中运动的数值模拟方法,采用边界造波法生成了精确的三维规则波浪,实现了DTMB 5512船模在2种不同波高规则波中顶浪运动时的垂荡及纵摇耦合运动数值模拟,求取了垂荡及纵摇运动的响应幅值算子,通过船模水池实验数据及势流理论方法验证了数值模拟方法的精确性.     

探地雷达检测混凝土含水率试验研究

混凝土含水率对混凝土材料和结构性能有很大影响,但其无损检测技术不能满足实际需要.雷达电磁波的传播速度主要由材料介电常数决定,而影响混凝土材料介电常数主要是其含水率.本文对探地雷达检测混凝土含水率技术进行研究,采用干燥法得到混凝土试块含水率,利用探地雷达测得雷达波在混凝土板中的波速,得到了探地雷达波速和混凝土含水率的关系,发现探地雷达波速和混凝土含水率具有良好的线性关系.     

爆破地震波对桥梁结构安全的影响

桥梁工程作为重要的交通运输基础设施,其安全性尤为突出,研究爆破地震波对桥梁的安全的影响具有重要的经济效益和社会效益。