深水缓波形脐带缆结构响应及参数敏感性分析

对某采用缓波形布局的深水脐带缆进行静态分析,得到了脐带缆的整体结构响应,包括脐带缆初始线形、有效张力和弯曲曲率的分布特性。同时对脐带缆缓波形布局下的总体布局参数进行了参数敏感性分析,得到了浮子段长度、浮力因子、浮子段起始位置及顶部悬挂角对脐带缆结构响应的影响。这些研究结果可以为深水脐带缆的缓波形布局设计提供参考。     

基于最敏感设计参数的斜拉索有限元动力模型修正

基于较完善的斜拉索有限元模型,分析讨论了斜拉索张力、抗拉刚度、抗弯刚度以及线密度等不同设计参数对长索和短索计算频率的相对灵敏度,确定了最敏感设计参数.在此基础上,根据优化理论,对洞庭湖大桥拉索进行基于最敏感设计参数的动力模型修正,修正后的模型的动力特性更加趋近于实测值.修正后的斜拉索有限元模型可以作为拉索张力评估的基准.     

通过附加浮筒改良的张力腿平台多体耦合运动响应

为了改善张力腿平台在极端海洋环境下的运动响应,提出了在张力腿上附加浮筒的新形改良方式,建立了附加浮筒后张力腿平台多体耦合运动分析模型,并给出了在时域下对该模型迭代求解的方法。考虑不同的附加浮筒尺寸和就位水深,应用绕射和辐射波浪理论和流体动力学分析软件AQWA12.0,数值模拟了平台上体及附加浮筒的水动力参数,分析了在风、浪、流分别作用和联合作用下平台上体、多个附加浮筒以及张力腿之间的多体耦合运动响应。结果表明：张力腿平台的纵荡和垂荡响应主要由风和流引起,纵摇主要由波浪引起;附加浮筒能明显减小张力腿平台各方向的总的和低频慢漂部分的运动响应,作用效果将受到附加浮筒尺寸和就位水深的影响,而平台波频部分的运动响应没有明显改变。     

深海脐带缆总体响应特性比较研究

在给出悬链线和缓波形理论公式的基础上,对某一深海脐带缆进行悬链线布局和缓波形布局两种不同布局形式的选型设计研究,计算得到脐带缆在两种布局下的静态和动态响应,及其有效张力和弯曲曲率的分布特性。结果显示有效张力的最大值都发生在悬链线布局和缓波形布局的顶部悬挂点,而弯曲曲率的最大值发生在悬链线布局的触地点和缓波形布局的上升段末端;缓波形布局在减小有效张力的同时还减小顶部浮体和波浪运动对脐带缆的动态干扰。     

错位转换高层建筑结构竖向地震作用下的抗震性能研究

关于错位转换高层建筑结构在竖向地震作用下的动力特性和受力特性的研究目前还鲜有文献,本文采用Sap2000V9有限元程序对一实际带错位转换高层结构竖向动力特性和动力反应进行了分析研究。研究了竖向振型数对上、下部转换梁内力和主要竖向受力构件轴力的影响;用反应谱法和时程分析法计算了竖向加速度、竖向层间位移及竖向动应变,分析了上部、下部转换梁梁端点及梁托柱点所在位置节点动力反应随楼层变化情况,并将转换梁端点的反应和梁托柱的反应进行了对比分析研究。还计算了上、下部转换层梁托柱、承托墙肢、框支剪力墙、框支柱等的轴力,并将其与重力荷载代表值下轴力比值进行了对比研究。研究分析表明,竖向基本振型对构件内力起主要作用,竖向第5阶以上振型对转换梁和各竖向主要构件轴力影响很小;梁托柱点竖向位移、竖向加速度远大于其梁端点的反应;上、下部转换梁端点处竖向构件竖向应变在转换层上一层发生突变;同时会使两错位转换层之间楼层竖向构件竖向应变局部增大;楼层越高,其相应竖向构件的反应谱法与重力荷载代表值、时程均值与重力荷载代表值内力比值就越大;竖向地震作用下承托墙肢顶部一层和框支剪力墙底部三层轴力会发生突变。     

基于多元Copula函数的桥梁体系地震易损性分析方法研究

为了考虑桥墩、支座等构件地震需求之间相关性,引入多元Copula函数对构件地震需求之间的相关结构进行描述,提出了桥梁体系易损性分析的新方法。基于增量动力分析结果建立了单个构件的易损性,采用核光滑方法对各构件的边缘分布函数进行估计;基于离差平方和最小准则和最小距离法对多元Copula函数进行了参数估计及优选;结合单个构件的易损性及多元Copula函数,建立了桥梁体系的易损性曲线,分析了构件地震需求之间相关性对桥梁体系易损性的影响。结果表明:桥墩、支座等构件地震需求之间的相关性对桥梁体系易损性影响显著;基于离差平方和最小准则构造的多元Copula函数,能够准确描述构件地震需求之间的相关结构,有效降低桥梁体系易损性分析的难度。     

预应力CFRP布加固损伤RC梁的动力特性研究

从理论上推导了预张力与损伤RC梁固有频率之间的定量关系。同时进行了预应力CFRP布加固RC梁的动力特性试验,测定不同预张力条件下,完好梁与损伤梁的一阶频率值。而后利用ANSYS软件建立钢筋混凝土完好梁的有限元模型,根据损伤梁的动力测试结果,运用优化分析的方法得到损伤梁混凝土刚度折减系数;利用一阶频率的试验值对公式进行线性拟合,得到频率影响因素及损伤梁频率计算公式。最后将加固损伤梁一阶频率的理论值与试验值进行比较,发现在低预应力作用下,理论计算结果基本能反映出试验值随预张力变化的趋势,试验值与理论值吻合较好。     

海洋细长结构参数激励不稳定区的确定方法

分别采用变形参数法,改进的变形参数法及傅立叶分析法确定海洋细长结构参数振动Hill方程的不稳定区,比较三种方法的优缺点,并给出了前三阶不稳定区图像,为张力腿、立管等海洋细长柔性结构的设计提供参考。     

连续梁桥横向抗震挡块简化分析方法研究

地震作用下,经过合理设计的挡块对桥梁上部结构具有很好的限位作用。《公路桥梁抗震设计细则》仅在构造措施中要求设置挡块,但未明确其具体设计方法。为简化挡块设计过程,提高计算效率,对连续梁桥计算模型的简化方法进行研究,并通过简化模型的动力特性与有限元模型对比,验证了其简化的合理性;对简化分析中需考虑的参与振型进行了研究,结果表明,规则桥梁仅需考虑横向平动振型就可基本满足工程精度要求;相较于美国规范和日本规范的计算方法,简化方法基本介于两者之间说明了计算结果的可靠性,且由于考虑了结构自身动力特性的影响,计算的挡块地震力随着墩高的增大而减小,计算结果更为合理。     

近爆作用下钢筋混凝土板动态破坏的数值模拟研究

当爆炸在结构构件表面发生时,产生的冲击波将会对结构构件造成损伤和破坏,而准确预测潜在的爆炸对结构构件造成的损伤是进行重要建筑物和防护结构抗爆设计的基础。为研究近爆作用下钢筋混凝土板的抗爆性能,采用AUTODYN软件建立了混凝土和钢筋的三维分离式实体模型,数值模型考虑了应变率对钢筋和混凝土材料动力本构特性的影响以及炸药-空气-结构之间的流固耦合相互作用,分析了不同炸药量作用下钢筋混凝土板的损伤机理和破坏特征,合理展现了钢筋混凝土板从混凝土开裂、碎片形成、部分钢筋屈服断裂到板局部震塌的动态演变过程。随着炸药量的增大,钢筋混凝土板的破坏模式逐渐由整体弯曲破坏转变为局部的冲切破坏     

深海立管涡激共振疲劳寿命简化计算方法

针对深海顶端张紧式立管固有的特点,采用解析与经验公式相结合的方法建立了海洋立管涡激振动下疲劳寿命的简化预报模型,该模型能充分计及轴向张力对振型的变化以及对疲劳寿命的影响,通过实例计算指出了深海立管涡激振动诱发疲劳破坏的危险区域,并讨论了流速对疲劳寿命的影响。该模型形式简洁、计算量少,适合对深海立管等细长挠性受拉构件的疲劳寿命进行初步校核计算。     

Tailoring the particle swarm optimization algorithm for?the?design of offshore oil production risers

In offshore oil production activities, risers are employed to connect the wellheads at the sea-bottom to a floating platform at the sea surface. The design of risers is a very important issue for the petroleum industry; many aspects are involved in the design of such structures, related to safety and cost savings, thus requiring the use of optimization tools. In this context, this work presents studies on the application of the Particle Swarm Optimization method (PSO) to the design of steel catenary risers in a lazy-wave configuration. The PSO method has shown good efficiency for some applications, but its performance is dependent on the values selected for the parameters of the algorithm. Therefore, this work describes some variants of the method, and presents results of several experiments performed to analyze the behavior of its parameters, trying to improve the performance of the method and tailor it for the application to the design of riser systems. The resulting method and its best set of parameters can then be taken as the default values in an implementation of the PSO method in the in-house OtimRiser computational tool, oriented to the design of risers, and also incorporating other optimization methods based on evolutionary concepts.     

Modelling top venting vessels undergoing level swell.

The storage and processing of fluids in a two-phase state at pressure requires the consequences of a failure of the vessel wall or a pipe break due to corrosion or third party interference, be considered as part of a safety analysis. The present paper describes a mathematical model for predicting outflow rates from top venting high-pressure vessels undergoing level swell. A key aspect of the models development is there are no free parameters that require adjustment to predict the correct outflow from a top venting vessel. The mathematical model is validated by comparing predicted flow parameters such as vessel pressure and mass flow rate with measurements and existing mathematical models. The new model agrees more closely with the experimental measurements than previous approaches over the range of experimental conditions considered.     

Fractional factorial analysis to the configuration of simulated annealing applied to the multi-objective optimization of master production scheduling problems

Searching for the global optimal solution in a Master Production Scheduling problem usually demands an effort most industries are not willing to pay. Therefore, the use of meta-heuristics that generates good solutions in reasonable computer time becomes an attractive alternative. However, such strategies are usually complex to implement and configuring their parameters is not a trivial task because of the number of usually conflicting objectives involved. The use of statistical methods that facilitate the set-up of the heuristic's parameters becomes therefore necessary. Knowing which parameters are more important, that is, the ones that really affect the solution quality, and those that are irrelevant, is very important for chosen technique performance. This work presents how fractional factorial analysis can be applied to the configuration of simulated annealing used for optimization of Master Production Scheduling problems. Two scheduling scenarios illustrate the use of the proposed method.     

Compressional behaviour of carbon fibres

Spectroscopic-mechanical studies have been conducted on a range of carbon fibres by bonding single filaments on the top surface of a cantilever beam. Such a loading configuration allows the acquisition of the Raman spectrum of carbon fibres and the derivation of the Raman frequency strain dependence in tension and compression. Strain hardening phenomena in tension and strain softening phenomena in compression were closely observed. The differences in the slopes of the Raman frequency versus applied strain curves in tension and compression respectively, have been used to obtain good estimates of the compression moduli. A method of converting the fibre Raman frequency versus strain data into stress-strain curves in both tension and compression, is demonstrated. Values of fibre stress and fibre modulus at failure in compression compare exceptionally well with corresponding estimates deduced from full composite data. The mode of failure in compression has been found to depend upon the carbon fibre structure. It is demonstrated that certain modifications in the manufacturing technology of PAN-based fibres can lead to fibres which show resistance to catastrophic compressive failure without significant losses in the fibre compressive modulus.     

Analysis and design of modified Wollaston prisms

An exact analysis of the working parameters of a modified Wollaston prism is presented. Parameters include the output splitting angle, the retardation, and the location of the plane of the interference fringes (plane of apparent splitting). Results are presented for the entire range of optical axis inclinations and wedge angles. Approximate expressions from the literature are evaluated. An angle of incidence that causes the plane of the interference fringes to be perpendicular to the axis of the optical system is found for each configuration analyzed. This is then applied to the design of modified Wollaston prisms for Nomarski differential interference contrast microscopy.     

Strain-analysis of neck formation and propagation in glassy polymers

The mechanism of the phenomenon of initiation and propagation of neck in polycarbonate of Bisphenol A tension specimens, which present a well-defined yield point, is analysed. A detailed analysis of the strain field in the whole specimen at definite loading steps before and during the neck initiation and propagation is undertaken by the mechanical interference (moiré) method. It was found that a strongly non-uniform strain field presenting localized maxima predominates in the neck. The three-dimensional character of this field is revealed and analysed. It was established that, as the neck propagates, the strain distribution in the necked region becomes more and more uniform, while the neck fronts tend to become normal to the boundaries of the specimen. The whole phenomenon of the initiation and evolution of the neck in polycarbonate is compared with the analogous phenomenon in metals and the similarities and differences between them are discussed and analysed.     

Local and global instabilities in nanosize rectangular prismatic gold specimens

We use molecular mechanics simulations with the tight-binding potential to study local and global instabilities in initially defect-free nanosize rectangular prismatic specimens of gold deformed in tension/compression and simple tension/compression. Whereas in simple tension/compression atoms on end faces are constrained to move axially but are free to move laterally and the cross-sectional dimensions of end faces can change, in tension/compression all three components of displacements of atoms on end faces are prescribed and the cross-section of an end face does not change. The three criteria used to delineate local instabilities in a specimen are: (i) a component of second-order spatial partial derivatives of the displacement field has large value relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the potential energy of an atom is negative, (iii) a relatively high value of the common neighborhood parameter. A specimen becomes globally unstable when its potential energy decreases noticeably with a small increase in its deformations. It is found that the three criteria for local instability are met essentially simultaneously at the same atomic position. Deformations of interior points of a specimen are different when it is deformed in simple tension/compression from those in tension/compression. It is found that the initial unloaded configuration (or the reference configuration) of the minimum potential energy has significant in-plane stresses on the bounding surfaces and non-zero normal stresses at interior points. This initial stress distribution satisfies Cauchy’s equilibrium equations for a continuum. In deformations of a nanobar studied here, the yield stress defined as the average axial stress when the average axial stress vs. the average axial strain curve exhibits a sharp discontinuity depends upon the specimen size. It is shown possibly for the first time that deformations of the specimen are reversible if it is unloaded prior to yielding but have a permanent strain if unloaded after it has yielded. Because of residual stresses in the reference configuration, the average axial stress at yield in compression is nearly one-half of that in tension. The slope of the average axial stress vs. the average axial strain curve during unloading after it has yielded is the same as that during initial loading up to the yield point.