随机载荷作用下平台结构疲劳寿命预测

海洋等工程结构物在服役过程中的受载历程是一个随机过程。研究裂纹在谱载荷作用下的扩展规律对可靠预报平台等结构物的疲劳寿命具有十分重要的意义。提出了一个由应力比和裂纹尖端约束及塑性区尺寸为主要参数计算裂纹张开比,来考查载荷相互作用下疲劳裂纹扩展寿命的计算模型。用该模型对几种谱载荷作用下疲劳实验结果进行了预测,将预测结果与不考虑裂纹闭合的线性损伤模型及疲劳计算程序FASTRAN的预测结果进行了比较,表明本模型能较好地预测谱载荷作用下的疲劳裂纹扩展。     

关于裂纹柱壳韧性断裂的研究

本文基于实验结果,利用壳单元有限元方法,对周向壁穿裂纹圆柱壳在不同初始裂纹长度条件下的弯曲韧性断裂进行了模拟,计算了裂纹尖端张开位移（ＣＴＯＤ）的裂纹起裂临界值以及裂纹连续扩展条件下裂纹尖端张开角度（ＣＴＯＡ）Ｒ曲线,考察了这些断裂参数作为材料特性的适用性。     

强流脉冲电子束辐照诱发金属纯镍中的空位簇缺陷

利用强流脉冲电子束(high-current pulsed electron beam,HCPEB)技术对多晶纯Ni进行了辐照处理,采用透射电子显微镜详细分析了辐照诱发的缺陷结构.HCPEB辐照后,纯镍表层积聚了幅值极大的残余应力,沿{111}晶面形成了稠密的位错墙及孪晶结构,另外还形成了大量的包括位错圈、堆垛层错四面体(SFT)及孔洞在内的空位簇缺陷.SFT缺陷的数量远高于其他空位簇缺陷,其周围区域位错密度很低.孔洞缺陷主要出现在SFT密集区域.HCPEB瞬间的加热和冷却诱发的幅值极大的应力和极高的应变     

海洋玻纤增强热塑性柔性管的理论与数值分析

近年来海洋复合柔性管道逐渐在海洋工程中崭露头角。相对于钢管,复合柔性管凭借其弯曲性能好、重量轻、抗腐蚀能力强等一系列优异的性能在油气开采领域不断受到青睐。本文研究对象为一种三层粘结型玻璃纤维增强的热塑性复合柔性管,该类型管道包含外保护层(高密度聚乙烯HDPE)、中间复合材料增强层以及内衬层(高密度聚乙烯HDPE)。研究内容主要基于三维弹性理论和复合材料层合板理论,建立了玻纤增强热塑性复合柔性管的理论计算模型,推导了复合柔性管在轴对称载荷作用下的平衡微分方程,主要分析了管体在内压载荷作用下的应力与变形规律,并将理论计算结果与ABAQUS数值模拟结果进行比较分析,结论表明理论计算与数值仿真结果具有较好的一致性。最后基于该理论模型,研究了内衬层(外保护层)与增强层相对厚度对柔性管应力和变形的影响规律,结果表明管道的增强层为主要承载构件,在增强层纤维方向的应力远大于其他方向的应力,随着增强层从内向外扩展,纤维方向的应力逐渐减小,且内衬层(外保护层)厚度对管道整体的力学性能几乎没有影响。     

中子嬗变掺杂前后Ge纳米晶的结构和性质

采用第一性原理计算模拟Ge纳米晶在中子嬗变掺杂(NTD)后受空位、O和As杂质的影响.结果表明,退火方法引入的O并不能消除纳米晶中的辐照致空位缺陷的影响,而NTD 产生的As掺杂能补偿这些空位缺陷并消除禁带中产生的杂质能级,从而改善半导体掺杂性能.计算还发现,由于较高的电负性,纳米晶中O对Ge原子较强的吸附作用阻止了空位的形成,导致与缺陷相关的非辐射发光中心的浓度减小,发光效率提高,因此中子辐照掺杂前的高温退火处理是非常有必要的.计算较好地解释了已报道的实验结果.     

海洋结构薄板承载性能的裂纹群体效应

大型海洋结构长期服役中构件裂纹不可避免,结构承载性能必然随之弱化。针对含非均匀分布裂纹的薄板,以有限元方法对小变形状态下其极限承载能力进行计算,得到裂纹数量、长度、分布等因素对薄板屈曲临界应力的影响规律。发现裂纹不仅改变截面的有效承载面积,同时改变局部结构的变形状态,多种因素共同作用使板的承载性能非单调变化,即多裂纹对板承载性能的影响具有一定的"群体"效应。     

管节点与船舶甲板结构中疲劳裂纹扩展方向的研究

线性断裂力学中研究裂纹的扩展通常用应力强度因子的断裂准则，但是对复合型裂纹，应力强度因子理论就发生了困难。本文用光弹性方法求得裂纹前缘的应力强度因子，然后用应变能密度因子理论研究了船舶大开口舱口角隅处疲劳裂纹和Ｔ型管节点热点处表面裂纹的扩展规律和方向，得到较好的结果     

剪切作用下Cu(100)扭转晶界塑性行为研究

本文采用分子动力学方法研究了在剪切载荷作用下,Cu(100)扭转晶界对Cu柱屈服强度的影响.模拟结果发现,在加载过程中,低角度扭转晶界形成的位错网发生位错形核与扩展,位错之间的塞积作用提高了Cu柱的屈服强度;对于高角度扭转晶界,晶界发生滑动降低了Cu柱的屈服强度.同时发现,随着扭转角度的增加,Cu柱的屈服强度先增大,当扭转角度大于临界角度时,Cu柱的屈服应力逐渐减小.这表明剪切载荷作用下,两种不同的机理主导Cu柱的屈服,对于小于临界角度的扭转晶界,Cu柱的屈服由晶界位错形核和扩展机理主导,对于大于临界角度     

黄河水下三角洲沉积物输运及海底冲淤研究

根据黄河水下三角洲的特点,建立了一个垂直平均二维沉积物输运数学模型,结合潮流和沉积物资料,模拟研究了沉积物输运机制和海底冲淤演变过程。模拟结果表明,垂直河口射流的潮流决定了本区沉积物净输运的总体格局,风应力对悬浮泥沙和推移质泥沙运动也起到重要作用。潮流底应力和活动层厚度分布表明,黄河口门和埕岛油田附近海域是潮流底应力和活动层厚度高值区,为沉积物活跃区,海底稳定性弱,易于侵蚀再搬运。冲淤计算表明,埕岛油田附近海域为冲刷中心区;现在河口水下三角洲在断流时为冲刷区,正常行河时则转为淤积区。     

涠洲岛附近海域溢油数值模拟

采用潮流控制方程和湍封闭方程构建完整的三维浅海潮波定解方程组,建立涠洲岛附近海域的三维潮流数值模型来计算涠洲岛附近海域的潮流和潮位变化情况,采用大海域计算得出的调和常数值作为开边界的输入值,从潮位验证、潮流验证和流场的变化规律等多方面情况看,计算结果与实际监测符合良好,具有较高的精确度,模拟计算结果较真实地反映了涠洲岛附近海域的潮位变化和潮流运动状况.在潮流模拟验证正确的情况下,建立溢油预测模型,采用欧拉-拉格朗日追踪方法,进行油膜中心轨迹的预测,并预测了油膜漂移的扩展面积、扫海面积和残留量随时间的变化值.     

Ice Induced Low Temperature Fatigue Crack Propagation in Offshore Structural Steel A131

To investigate the low temperature fatigue crack propagation behavior of offshore structuralsteel A131 under random ice loading,three ice failure modes that are commonly present in the Bohai Gulfare simulated according to the vibration stress responses induced by real ice loading.The test data are pro-cessed by a universal software FCPUSL developed on the basis of the theory of fatigue crack propagationand statistics.The fundamental parameter controlling the fatigue crack propagation induced by randomice loading is determined to be the amplitude root mean square stress intensity factor K_(arm).The test resultsare presented on the crack propagation diagram where the crack growth rate da/dN is described as thefunction of K_(arm).It is evident that the ice failure modes have great influence on the fatigue crack propaga-tion behavior of the steel in ice-induced vibration.However,some of the experimental phenomena and testresults are hard to be physically explained at present.The work in this paper is an init     

Fatigue Crack Propagation in Steel A131 Under Ice Loading of Crushing,Bending and Buckling

Three types of ice loading, which are most commonly present when ice acts on structures, are chosen and simulated for use of fatigue crack propagation tests on offshore structural steel A131. The three types of ice categorized in accordance with the failure modes when acting on structures called crushing ice, bending ice, and buckling ice, respectively. This paper presents an experimental investigation on the fatigue crack propagation behavior of widely used high strength steel A131 for offshore jackets in the loading environment of ice crushing, bending, and buckling. The test results of fatigue crack propagation in steel A131 under these simulated ice loading at temperature 292K. are presented and analyzed in detail in this paper. The amplitude root mean square stress intensity factor is optimized to be the fundamental parameter of fatigue crack propagation for all types of ice loading histories. The results are also compared with constant amplitude fatigue crack propagation conclusions as in wave loa     

Cover deformation above steep, basement normal faults: Insights from 2D discrete element modeling

A discrete element model is used to investigate progressive cover deformation above a steep (70°), basement normal fault. The cover materials are homogenous with frictional material behavior. In the model shown here both normal and reverse faults in the cover accommodate displacement on the underlying basement fault. The earliest faults are curved, reverse faults which propagate upwards from the basement fault tip into the proto hanging wall. These are replaced, progressively towards the footwall, by subvertical to steep normal faults and finally by a normal fault which dips at an angle predicted by Mohr-Coulomb theory. Thus, most early, secondary structures are located in the hanging-wall of the final, through-going, fault. This structural evolution produces an asymmetric, triangular zone of deformation above the basement fault tip which superficially resembles that associated with trishear; however, its progressive development is quite different. Results also emphasize that the occurrence of reverse faults in extensional settings is not diagnostic of inversion.     

天然气水合物开采区内海床不均匀沉降对管道力学性能的影响

海底管道是天然气水合物大规模开采和集输的关键装备。天然气水合物的开采过程会扰动沉积层的结构，改变沉积层的强度和力学特性，诱发海床发生不均匀沉降，并对水合物开采区内海底管道的力学特性产生影响，如引起管道发生大变形、悬跨、屈曲、断裂等。基于ABAQUS有限元软件，建立天然气水合物开采区内“海床-管道”耦合作用模型，模拟了天然气水合物开采过程中海床沉降变形及其对管道应力、应变、弯矩、悬跨等力学行为的影响。研究结果表明，在天然气水合物开采过程中，海床的不均匀沉降将引起管道发生显著位移并发生弯曲，管道的应力、应变随着变形的增大而增大。当海床沉降量达到某一程度时，管道将脱离海床，产生悬跨，并引发涡激振动风险。     

Scenarios of local tsunamis in the China Seas by Boussinesq model

The Okinawa Trench in the East China Sea and the Manila Trench in the South China Sea are considered to be the regions with high risk of potential tsunamis induced by submarine earthquakes. Tsunami waves will impact the southeast coast of China if tsunamis occur in these areas. In this paper, the horizontal two-dimensional Boussinesq model is used to simulate tsunami generation, propagation, and runnp in a domain with complex geometrical boundaries. The temporary varying bottom boundary condition is adopted to describe the initial tsunami waves motivated by the submarine faults. The Indian Ocean tsunami is simulated by the numerical model as a validation case. The time series of water elevation and runup on the beach are compared with the measured data from field survey. The agreements indicate that the Boussinesq model can be used to simulate tsunamis and predict the waveform and runup. Then, the hypothetical tsunamis in the Okinawa Trench and the Manila Trench are simulated by the numerical model. The arrival time and maximum wave height near coastal cities are predicted by the model. It turns out that the leading depression N-wave occurs when the tsunami propagates in the continental shelf from the Okinawa Trench. The scenarios of the tsunami in the Manila Trench demonstrate significant effects on the coastal area around the South China Sea.     

氢对奥氏体不锈钢在酸性氯离子溶液中SCC作用初探

关于奧氏体不锈钢在氯化物溶液中的应力腐蚀开裂(SCC),有人认为受阳极溶解控制,有人认为受氢脆控制。Jani等(1991)通过透射电子显微技术研究了奥氏体不锈钢在沸腾MgCl2溶液中的SCC,结果表明,氢能进入金属诱发马氏体相变,使不锈钢发生脆性断裂,提出了奥氏体不锈钢SCC的氢脆机理。乔利杰等(1987,1988)对304,321,310不锈钢在沸腾MgCl2溶液中的SCC的研究表明,在SCC过程中氢确实能进入金属,但其浓度不足以引发氢脆,发生SCC的门槛应力强度因子KISCC低于发生氢脆时的应力强度因子KIHC,虽然氢在SCC过程中不起控制作用,但却能加速不锈钢的阳极溶解过程,应力和氢对不锈钢的阳极溶解过程存在协同效应。奥氏体不锈钢在酸性氯离子溶液中发生SCC时,氢的产生是必然的,因而有必要研究氢在SCC过程中所起的作用。同时我们注意到Jani等(1991)所做的研究是在断裂后的试样断口上进行的,他们得出的实验结果是否能反映裂尖的情况,马氏体相变是否是在裂尖前沿首先发生等问题,我们认为是值得进一步深入探讨的。只有对裂尖和已经形成的裂纹表面同时进行观察研究,才能反映真实的SCC过程。本文通过氢对不锈钢阳极溶解的影响,透射电镜观察,X射线衍射等实验初步探讨了氢对奥氏体不锈钢于酸性氯离子溶液中SCC的作用,以便为应力腐蚀开裂机理研究提供证据。     

Geometry and evolution of fold-thrust structures at the boundaries between frictional and ductile detachments

Fold-thrust belts formed above a ductile detachment typically contain detachment folds, whereas those formed above frictional detachments contain fault-related fold complexes, such as imbricate thrust systems. Analog models, using silica sand to represent sediments and silicone gel to represent salt were conducted to study the fold geometry, fold-fault relations, and sequential development of structures formed in each setting and at the boundaries between the two settings. The results showed a relatively thinner wedge above a ductile detachment, so that the deformation front propagated farther forward than that above a frictional detachment. The thrust front connects across the two settings with a significant change in position and a resulting change in orientation. The geometry of the deformation front is strongly controlled by that of the detachment boundary, so that an oblique detachment boundary results in an oblique thrust front in the transition zone. Modifications in the taper geometry also result from the presence of a frictional belt behind a ductile belt, the width of the ductile detachment which limits the location of the deformation front, and the lateral propagation of thrust faults between the two regimes. The experimental models can be used to explain observed geometries in natural examples of fold-thrust belts marked by transitions between frictional and ductile detachments.     

Fatigue Test of Homemade Z Direction Steel Welded T Tubular Joints

This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.     

Volume change during sediment diagenesis and the development of growth faults

The stress system induced the weight of a sediment and the pore fluid it contains, termed the passive stress system, is capable of deforming the sediment. This volumetric deformation is examined with respect to the evolution of porosity and permeability during burial. The effect of this self deformation on the shape of growth faults and normal faults in extensional terrains is considered.