Experimental investigation on vortex-induced force of a Steel Catenary Riser under in-plane vessel motion

A method to identify vortex-induced forces and coefficients from measured strains of a Steel Catenary Riser (SCR) undergoing vessel motion-induced Vortex-induced Vibration (VIV) is proposed. Euler–Bernoulli beam vibration equations with time-varying tension is adopted to describe the out-of-plane VIV responses. Vortex-induced forces are reconstructed via inverse analysis method, and the Forgetting Factor Least Squares (FF-LS) method is employed to identify time-varying vortex-induced force coefficients, including excitation coefficients and added mass coefficients. The method is verified via a finite element analysis procedure in commercial software Orcaflex. The time-varying excitation coefficients and added mass coefficients of an SCR undergoing vessel motion-induced VIV are investigated. Results show that vessel motion-induced VIV is excited at the middle or lower part of the SCR and in the acceleration period of in-plane velocity, where most of the excitation coefficients are positive, while during the deceleration period, the excitation coefficients becomes too small to excite VIVs. Parameter γ [1] has strong correlation with excitation coefficients. In addition, time-varying tensions contribute significantly to the variations of added mass coefficients under the condition that the ratio of dynamic top tension to pretension exceeds the range of 0.7–1.3. Moreover, chaotic behaviors are observed in vortex-induced force coefficients and are more evident with the increase of vessel motion velocity. This behavior may attribute to the randomness existing in in-plane velocity and its coupling with out-of-plane vibrations.     

机车用铸钢轮心表面缺陷和辐板焊修的探讨

分析TB/T1400—2005《机车用铸钢轮心技术条件》,总结出一些新造机车铸钢轮心表面允许和不允许存在的缺陷。介绍某机车整体车轮崩裂事故,分析发生事故的原因。认为铁道部铁运〔2007〕128号文《铁路机车车轮管理办法》的部分规定存在不合理性,叙述对技术文件的理解和认识。     

Structural Behavior of Continuous Prestressed Steel Fiber Reinforced High Strength Concrete Beam

The flexural behaviors of continuous fully and partially prestressed steel fiber reinforced high strength concrete beams are studied by experiment and nonlinear finite element analysis. Three levels of partial prestress ratio (PPR) are considered, and three pairs of two-span continuous beams with box sections varying in size are designed. The major parameters involved in the study include the PPR and the fiber location. It is concluded that the prestressed high strength concrete beam exhibits satisfactory ductility; the influences of steel fiber on the crack behaviors for partially prestressed beams are not as obvious as those for fully prestressed ones; steel fibers can improve the structural stiffness after cracking for fully prestressed high strength concrete beams; the moment redistribution from mid-span to intermediate support in the first stage should be mainly considered in practical design.     

Riser-soil interaction model effects on the dynamic behavior of a steel catenary riser

A mathematical model employed to analyze the global dynamics of a Steel Catenary Riser (SCR) taking into account the interaction with the seafloor and the effect of the soil reaction forces is established. The choice of soil model plays an important role for the dynamic behavior of SCRs. The riser has been modeled using flexible beam with large curvature and elastic foundation beam to describe the riser-soil interaction by means of realistic nonlinear load-deflection (P–y) curves. The study is made to improve an existing finite element numerical code for dynamic analysis of mooring lines and risers, known as CABLE 3D, which is based on a slender rod assumption. Effects of nonlinear seabed model on the dynamic behavior of SCRs under vessel cyclic perturbation have further been investigated and discussed using a realistic P–y curve to simulate soil deformation and resistance forces. The interaction model depends on several factors, such as soil strength, penetration depth and riser characteristics. The dynamic responses of the riser Touchdown Point (TDP) excited by vessel periodic heave motion are studied and the results are compared with those from the linear spring model. SCR has been perturbed by 10 regular sinusoidal cycles and the responses calculated by improved code show a number of features such as suction force mobilization, gradual increasing penetration depth, and gradual reduction of soil resistance at maximum penetration. The riser behavior at the touchdown zone (TDZ) depends on the riser top motion amplitude, nonlinear soil stiffness and suction force. The impact of the riser-soil interaction model on the dynamic behavior in the TDZ has been thoroughly studied in this paper.     

钢板桩在朝阳珠江斜拉桥主塔承台施工中的应用

介绍了朝阳珠江斜拉桥主塔承台施工采用钢板桩的原因、施工方法及取得的良好效果。     

大跨度斜拉桥钢箱梁非对称安装技术

介绍了辽宁滨海公路辽河特大桥斜拉桥钢箱梁非对称悬臂安装技术,通过对本桥方案箱梁非对称悬臂安装方案—边跨钢梁高支架上直接滑移就位连接、主跨钢梁逐段悬臂安装的方案可行性研究与实施,为同类型桥梁施工提供了很好的借鉴作用。     

桥梁水中施工平台钢管桩动力特性分析

介绍了平台钢管桩动力特性的求解方法。由于洪水期水流与钢管桩产生涡激振动,故首先需要分析钢管桩自身的动力特性也就是确定钢管桩的固有频率。动力特性求解就是模态求解,在详细讨论了模态求解的原理和方法的基础上,对大桥平台钢管桩进行了模态求解分析,并讨论了不同物理参数对结构的固有频率的影响。结果表明,钢管桩的固有频率与其自身长度、桩外径以及管壁厚度成反比。     

异质桥面铺装层的永久变形及不同材料抗车辙性能研究

常用的浇注式与环氧沥青混凝土两类钢桥面铺装材料在高温抗变形方面具有明显的性能差异。利用有限元软件hbquas对浇注与环氧两类铺装材料组成的三类铺装结构进行了在60℃时的铺装永久变形仿真模拟,其中铺装材料的高温蠕变特性采用时间硬化模型进行描述。仿真结果显示：在相同厚度的三类铺装结构中,“下层3cm注式＋上层3cm环氧”抗车辙变形能力最好,“下层3．5cm注式＋上层2．5cm环氧”次之,“下层3cm环氧＋上层3cm注式”最弱。研究表明,环氧沥青混凝土对减小铺装永久变形具有很大贡献,而舍浇注式沥青混凝土的铺装结构具有较大永久变形。研究结果为钢桥面铺装结构与材料的高温变形设计提供理论支撑。     

Hilbert-Huang变换在声振信号检测钢管混凝土脱空中的应用

提出了基于Hilbert-Huang变换的钢管混凝土脱空检测方法,通过对瞬态冲击下脱空钢管的声振信号进行分析,提取出了瞬时幅值特征样本,采用改进的K均值聚类法对特征样本进行二类模式识别,从而对钢管混凝土的脱空进行判定,试验研究表明本方法的可行性。     

赣高速公路水泥混凝土路面施工新技术

在粤赣高速公路水泥混凝土路面施工建设中,采用多项新技术,成功解决了填挖交界局部差异沉降、板底冲刷破坏、热水泥在高温天气下对施工质量的影响、传力杆自动插入对施工平整度的影响等施工难题。同时介绍了分离式双钢混凝土桥面铺装、隧道路面“零位摊铺”的施工特点。