复合材料纵横加筋圆柱壳自由振动分析

使用能量法分析了两端简支复合材料纵横加筋圆柱壳的自由振动特性,从Love's理论出发,分别计算壳体面板和纵横加筋结构的应变能和动能,然后代入Lagrange方程得到频率方程.通过比较,文中的计算方法所得到的结果与文献比较吻合.采用平均法计算的结果比采用离散方法计算的结果偏小.最后还研究了壳体和加筋结构参数以及静水压力的变化对圆柱壳自由振动频率的影响.文中利用平均法来处理加筋结构,简化理论推导并减少了计算.     

Finite element study on circular armour wire lateral buckling in umbilicals

The present paper addresses the circular armour wire lateral buckling in umbilicals. An asymmetric non-linear finite element model is developed to analyze a single armour wire subjected to combined constant axial compression and uniform cyclic curvatures. A parametric case study is performed for an armour wire from a nine-hose umbilical cable, where the armour wire pitch number, applied axial compressive load and minimum and maximum curvatures in the applied cyclic bending are varied. The armour wire end shortenings, transverse sliding in cyclic bending, the buckling shapes and equilibrium paths after numerous bending cycles, the critical buckling loads, the stress states at the onset of lateral buckling, and the required number of bending cycles that triggers lateral buckling are obtained and extensively discussed. The critical buckling loads given by the FE model have been compared with an existing analytical formulation, indicating that the analytical model is reliable for small cyclic curvatures. Moreover, an empirical model is proposed for the required number of bending cycles to trigger the lateral buckling and good correlation with the FE results has been observed.     

弹性地基梁弯矩系数的影响因素

针对文克尔地基上的两种不同断面(矩形和倒梯形)的弹性地基梁,分析了地基反力系数、外加荷载、混凝土强度等级以及梁的长高比、宽高比等因素对弯矩系数的影响规律。结果表明:弯矩系数随着地基反力系数的增加而减小,随着混凝土强度等级的增加而增加,随着梁长高比的增加而减小,随着外加荷载和梁的宽高比的增加不变;同等条件下,倒梯形断面形式的地基梁在受力方面优于矩形断面形式梁。     

合拢弯矩作用下复合材料曲梁突变屈曲的研究

研究了复合材料曲梁在受到合拢弯矩作用下发生的屈曲情况,并给出一种理论解析方法来分析这种很可能发生在复合材料弯曲结构中的脱层耦合屈曲问题.该方法是基于曲梁大变形理论及断裂力学而提出来的.文中并用该解析方法分析了一个特定的常见的情况,在该题例中脱层发生在非常靠近内表面处并且突变屈曲就发生在该薄脱层.在文中也对脱层裂纹的弧角对极限载荷的影响进行了研究.     

面内流固冲击载荷下初缺陷矩形薄板的动力屈曲

取样条函数作为挠度试函数,运用加权残值法求得初缺陷矩形薄板动力屈曲的控制方程,采用四阶Runge-Kutta法求解该控制方程,并用Fortran语言编制了相应的计算程序。构造的B样条函数能适应板侧边上的任意弹性转动约束,讨论了初始几何缺陷、冲击载荷持续时间和弹性约束的影响。     

静水压力下具有轴对称初始缺陷圆柱壳承载能力研究

文章针对含有轴对称初始缺陷和局部轴对称凹陷的圆柱壳在静水压力下的稳定承载能力问题进行了研究。通过一种数值计算方法,给出了初始缺陷幅值、壳体半径与厚度比、壳体长度、局部凹陷长度及位置对静水压力下圆柱壳屈曲临界压力的影响。并针对不同缺陷幅值对圆柱壳的刚度进行折减,给出了初始缺陷幅值与刚度折减系数的关系。研究结果表明,对于轴对称初始缺陷对圆柱壳稳定承载能力的影响,本质上是降低圆柱壳轴向弯曲刚度和轴向的薄膜刚度从而造成圆柱壳稳定承载能力的下降,因此针对轴对称初始缺陷可以增加纵筋提高其弯曲刚度,增加稳定承载能力。     

An expeditious algebraic formulation to the buckling critical load of risers under dynamic compression

Dynamic compression of risers can play an important role in the structural stability of submerged pipes in catenary-like configuration. In this paper, the analytical formulation for the buckling critical load, developed in the early 2000's, is revisited and extended to cover a wider range of practical cases. A purely algebraic expression for the critical load is provided, eliminating the original formulation requirement related to solving transcendental equations, for both free and anchored risers. The analytic formulations and respective algebraic approximations are compared with numerical simulations, presenting a fairly good agreement. A discussion on the differences and similarities of each formulation ends this paper, highlighting their range of validity. Also, from the comparison, the analytical formulation developed in this work was more suitable for precise and fast determination of the critical buckling load for both riser types, rigid and flexible, and for most typical operating conditions. The proposed algebraic expressions were highly accurate and may substitute the previous analytical formulations for critical load prediction.     

高速船复合材料层合板非线性动力失稳分析

对高速船复合材料层合板在轴向线性增长载荷作用下的非线性动力失稳进行了研究。基于极的大挠度基本假设,导出四边简支矩形层合板的非线性动力方程及变形及协调方程;用级数展开把非线性偏微分方程组化为易于求解的Kronecker内积形式的二阶常微分方程组,并由四阶Runge-kutta法数值求解,讨论了加载速率对复合材料层合板动力失稳的影响。由于本文在方程求解中采用了Kronecker内积,故提高了解的精度及效率。     

特征载荷下海工管状结构屈曲临界载荷分析

圆柱形管状结构在海洋工程领域中应用较多,在进行结构设计时,需重点关注其侧向受载时的屈曲强度问题。通过理论分析和数值模拟,对比研究径向线性载荷变化下圆柱壳的屈曲行为,以经典的Donnell壳体理论为基础,得到圆柱壳的屈曲控制方程,并通过本征值分析方法得到结构屈曲的临界条件。采用有限元软件ABAQUS对线性变化径压下圆柱壳的屈曲进行数值仿真。分析得出径厚比是径向线性分布载荷下圆柱壳屈曲临界载荷的主要影响因素,三角形径压下屈曲临界载荷值约为均布径压下屈曲临界载荷值的2倍。     

剪切流对水平轴潮流能水轮机水动力性能影响

为了研究剪切流下潮流能水平轴水轮机水动力载荷特性,本文基于CFD方法,建立剪切流模型,计算了剪切流下水平轴水轮机的水动力载荷,并分析得出剪切率对水动力载荷的影响规律。结果表明：剪切流情况下,水动力载荷系数时历曲线发生明显波动,除弯矩系数的波动频率和叶轮旋转频率一致外,其他系数的波动频率均是叶轮旋转频率的2倍,且剪切率越大,水动力载荷系数的波动幅值就越大;随着速比增大,弯矩系数的波动幅值逐渐增加,而侧向力系数波动幅值先增加再减小,在最优速比左右达到最大值。研究成果可为潮流能水平轴水轮机的结构设计和性能优化提供依据。     

实肋板式耐压液舱结构计算方法研究

应用弹性力学经典理论和求解环肋柱壳的传统方法,将耐压液舱结构的几种结构形式综合成统一的力学模型,进行整体求解,获得各应力解析表达式;提出了液舱区耐压船体壳板极限承载能力及波舱壳板失稳压力的计算方法。力学模型清晰合理,求解简便,计算结果符合实际,可应用于工程设计。     

Effect of pitting corrosion on local strength of hold frames of bulk carriers (2nd Report)—Lateral-distortional buckling and local face buckling

Pitting corrosion is typical corrosion observed on coated hold frames of bulk carriers which exclusively carry coal and iron ore. In order to secure the safety of these types of bulk carriers, it is important to understand the effect of pitting corrosion on local strength of hold frames.

In order to investigate this effect, a series of 4- and 3-point bend tests on structural models which consist of web, shell and face plates has been carried out. Artificial pitting was created on the web plate to simulate pitting. In the 4-point bend tests, two equal concentrated loads have been applied vertically at the one-third points of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, lateral-distortional buckling occurred before reaching the ultimate strength and local buckling of the face plate was observed after reaching the ultimate strength. The effect of web plate pitting on the lateral-distortional buckling strength was found to be small but the ultimate strength decreases with increase in the degree of pitting intensity. In the 3-point bend tests, concentrated load has been applied vertically at the center of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, local face buckling occurred just after reaching the ultimate strength. The ultimate strength is found to be decreasing with increase in the degree of pitting intensity.

A series of non-linear FE analyses has been performed to simulate the deformation behavior observed in the tests. It has been revealed that even in the case of randomly distributed pitting corrosion the ultimate strength of the structural models was almost the same as that of the structural models with uniform corrosion corresponding to the average thickness loss.     

Dynamic impedances and load carrying mechanism for skirted foundations

Dynamic impedances of foundations include dynamic stiffness and damping which have important effect on the internal forces in the structure. In some cases, such as offshore wind turbines, the influence of the foundation impedances on the system's natural frequency and overall damping could potentially have a significant effect on the fatigue life of the structure. The vertical, horizontal and rocking impedances of a skirted foundation (also termed bucket foundation in offshore wind industry) embedded in a fully saturated poroelastic seabed are addressed in this paper. The vertical impedance is most relevant for jacket foundations supported on three or four bucket foundations, while horizontal and rocking impedances are applicable for mono-bucket foundations. The dynamic vibration problems are solved semi-analytically with the help of dual integral equations and Green's functions. Numerical results for dynamic impedances are obtained; damping ratio are also obtained to show the importance of radiation damping for bucket foundations, even at very small excitation frequencies. The influence of length-to-radius ratio, Poisson's ratio, permeability of soil, excitation frequency and thickness-to-radius ratio on the impedances are also studied. Besides, the dynamic load sharing among the top plate, bucket shaft and bucket tip is obtained for vertical load, horizontal load and moment to shed light on the carrying mechanism of bucket foundation at dynamic working loads. It is found that for a rigid bucket foundation, even when the length-to-radius ratio is small (e.g. l/a = 1.0), most of the loads are carried by the shaft, while the top plate and tip of the bucket take only a small portion of the loads. The results of this study will be helpful for understanding the load-carrying mechanism of offshore bucket foundations for normal operation conditions.     

带止屈器的复合材料圆柱壳结构屈曲分析及优化

针对海洋工程上的复合材料圆柱壳结构,基于有限元软件ABAQUS,利用Python语言编程实现参数化建模、屈曲分析以及在后处理中提取屈曲因子。研究复合材料圆柱壳结构在单独受到轴向压力、侧向压力以及两种压力组合作用下止屈器的位置对屈曲极限强度的影响,并利用遗传算法多参数优化的方法对止屈器的位置进行优化,最终找到最优解。研究结果可以为复合材料圆柱壳结构抵抗屈曲失效的优化设计提供参考。     

Analytical study on controlled lateral thermal buckling of antisymmetric mode for subsea pipelines triggered by sleepers

Subsea pipelines exposed to high temperature and high pressure (HTHP) conditions is susceptible to lateral buckling. In order to control lateral buckling, engineered buckle initiators, such as sleepers, are introduced to initiate planned lateral buckles along the pipeline at specific locations in order to ensure that the stress in each lateral buckle remains acceptable. In this study, taking the interaction of adjacent buckles into account, analytical solutions of antisymmetric lateral buckling mode triggered by sleepers are derived. With the proposed formulations, the method to obtain the accurate locations of lateral displacement amplitude and maxima of bending stress is presented and discussed. And a detailed comparison between symmetric and antisymmetric mode of lateral buckling triggered by single sleeper is presented. Moreover, the influence of the sleeper spacing on controlled lateral buckling behaviour with the consideration of axial interaction between adjacent buckles is conducted. Finally, a detailed analysis about the influence of the sleeper height, lateral frictional coefficient and submerged weight of the pipeline on the controlled post-buckling behaviour is presented. Our results show that, for smaller sleeper friction or smaller sleeper height, the symmetric mode is more likely to happen, while the antisymmetric mode is prone to occur for larger sleeper friction and larger sleeper height. One effective method to reduce displacement amplitude and maximum stress is to decrease the sleeper spacing. The minimum critical temperature difference decreases with increasing sleeper height and increases with increasing lateral friction coefficient or submerged weight of the pipeline. And an alternative way to reduce the maximum stress is to reduce the lateral friction coefficient or submerged weight of the pipeline even though the displacement amplitude increases.     

Progressive collapse analysis of ship hull girders subjected to extreme cyclic bending

This paper introduces a novel analytical method to predict the buckling collapse behaviour of a ship hull girder subjected to several cycles of extreme load. This follows the general principles of the established simplified progressive collapse method with an extended capability to re-formulate the load-shortening curve of structural components to account for cyclic degradation. The method provides a framework for assessing residual hull girder strength following a complex series of unusually extreme load events where the wave induced bending moment rises close to, or even surpasses, the monotonic ultimate strength. These load events may be sequential, such as might be caused by a series of storm waves, or they may occur as a collection of discrete events occurring over a longer period. The extreme cyclic bending amplifies the distortion and residual stress initially induced by fabrication in the flanges of the girder, which results in a deterioration of the residual ultimate strength. Validation is firstly completed through a comparison with previously published experimental work and secondly via comparison with numerical simulation on four ship-type box girders using the nonlinear finite element method.     

Stress concentration factors at welds in pipelines and tanks subjected to internal pressure and axial force

In this paper, analytical expressions for stress concentration factors in pipes subjected to internal pressure and axial force are derived for a number of design cases based on classical shell theory. The effect of fabrication tolerances in simple butt welds is assessed. Analyses based on classical mechanics are compared with results from axisymmetric finite element analyses for verification of the presented methodology. Stress concentration factors are presented for circumferential butt welds in pipes welded together from pipes with different thicknesses, welds at buckling arrestors, welds at flanged connections in pipelines, and welds at ring stiffeners on the inside and the outside of the pipes. It also includes stress concentration factors at end closures in pipes for gas storage. Larger pipes are fabricated from plates with a longitudinal weld. This fabrication process introduces out-of-roundness in the pipes. The actual out-of-roundness is a function of internal pressure. An analytical expression for the bending stress in the pipe wall due to this out-of-roundness is presented. The derived stress concentration factors can be used together with a hot spot stress S–N curve for calculation of fatigue damage.     

恒定荷载对海工高性能混凝土抗氯离子渗透性能的影响

通常混凝土构件均处于受力状态,而对自由状态的混凝土试件开展耐久性研究很难真实地反映出混凝土构件的耐久性状况。本研究采用施加恒定压荷载和弯曲荷载的方式,研究荷载对混凝土抗氯离子渗透性能的影响。结果表明:混凝土试件纯受弯段的氯离子浓度随弯曲应力水平的提高而增大,且混凝土内的氯离子渗透深度随应力水平的增加而增大。试件距暴露面相同深度处的氯离子浓度随着压应力水平的提高先减少后增大。混凝土试件的氯离子扩散系数随压应力水平提高而先减少后增大,压应力水平较低时可提高混凝土的抗氯离子渗透性能。对于典型的海洋工程高性能混凝土配合比,混凝土试件的弯曲应力与其恒定荷载影响因子之间呈近似指数函数关系,在混凝土结构耐久性设计中应考虑弯曲荷载对氯离子扩散系数的影响。     

基于滑轮试验台的钢丝绳弯曲疲劳试验研究

钢丝绳的使用寿命是钢丝绳行业内重点关注和研究的核心问题。而在钢丝绳-滑轮系统中,钢丝绳失效的主要型式是弯曲疲劳损伤。本文针对钢丝绳的简单弯曲、角度弯曲和反向弯曲等三种典型弯曲类型特点,专门设计了五滑轮弯曲疲劳试验台。通过调整钢丝绳工作行程和试验载荷,旨在研究钢丝绳在简单弯曲、角度弯曲和反向弯曲中的疲劳寿命。提出了反向弯曲相对简单弯曲的折算方法和折算系数,得出钢丝绳简单弯曲的总寿命次数与载荷的相关函数,为钢丝绳在特定条件下的使用寿命预测提供了试验数据支撑和计算方法。     

基于多种失效模式SPS复合钢板替换船用钢板的优化设计

在SPS复合钢板的设计中获取不同的失效模式。以减重为目标,应用序列二次规划法对SPS复合钢板进行等效船用钢板的优化设计,同时对SPS复合钢板进行多目标优化,应用层次分析法定各目标的权重。在这两种优化方法的基础上,对船用钢板与SPS复合钢板进行了屈曲、弯曲对比数值分析,同时将结果与理论计算结果对比分析。结果表明,SPS复合钢板重量能够减轻37%以上,刚度增加两倍多,但厚度增加70%。