Mechanism of the Large Surface Deformation Caused by Rayleigh-Taylor Instability at Large Atwood Number

Studying the dynamical behaviors of the liquid spike formed by Rayleigh-Taylor instability is important to understand the mechanisms of liquid atomization process. In this paper, based on the information on the velocity and pressure fields obtained by the coupled-level-set and volume-of- fluid (CLSVOF) method, we describe how a freed spike can be formed from a liquid layer under falling at a large Atwood number. At the initial stage when the surface deformation is small, the amplitude of the surface deformation increases exponentially. Nonlinear effect becomes dominant when the amplitude of the surface deformation is comparable with the surface wavelength (~0.1λ). The maximum pressure point, which results from the impinging flow at the spike base, is essential to generate a liquid spike. The spike region above the maximum pressure point is dynamically free from the bulk liquid layer below that point. As the descending of the maximum pressure point, the liquid elements enter the freed region and elongate the liquid spike to a finger-like shape.

Chip Formation Mechanism of Inconel 718: A Review of Models and Approaches

Inconel 718,a nickel,chrome and iron alloy,has special advantages,such as high-temperature strength,thermal resistance and corrosion resistance,which facilitate wide usage in the aerospace industry,especially in the hot sections of gas turbine engines.However,machining this alloy is correlated closely with the material’s inherent properties such as excellent combination of strength,hardness and toughness,low thermal conductivity and the tendency to adhere to cutting tools.This nickel alloy also contains inclusions of hard abrasive carbide particles that lead to work-hardening of the workpiece material and thus abrasive wear of the cutting tool.That is,the machining of Inconel 718 is always influenced by high mechanical and thermal loads.This article reviews the chip formation mechanism of Inconel 718.One of the main characteristics in machining of Inconel 718 is that it will produce serrated or segmented chips in a wide range of cutting speeds and feeds.Existing studies show that the chip serration or segmentation by shear localization affects the machined surface integrity,and also contributes to the chip’s evacuation and the automation of machining operations.Thus,research conclusion indicates that the serrated or segmented chip phenomenon is desirable in reducing the level of cutting force,and detailed analysis of models and approaches to understand the chip formation mechanism of Inconel 718 is vital for machining this alloy effectively and efficiently.Therefore,this article presents some summaries on the models and approaches on the chip formation in machining of Inconel 718.

Single planet formation regime in the high-ionization environment:Possible origin of hot Jupiters and super-Earths

We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 〈 10^（-7.4）M_☉yr^（-1）, only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes（tandem planet formation regime and dispersed planet formation regime）, in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.

Mechanics of formation and rupture of human aneurysm

The mechanical response of the human arterial wall under the combined loading of inflation, axial extension, and torsion is examined within the framework of the large deformation hyper-elastic theory. The probability of the aneurysm formation is explained with the instability theory of structure, and the probability of its rupture is explained with the strength theory of material. Taking account of the residual stress and the smooth muscle activities, a two layer thick-walled circular cylindrical tube model with fiber-reinforced composite-based incompressible anisotropic hyper-elastic materials is employed to model the mechanical behavior of the arterial wall. The deformation curves and the stress distributions of the arterial wall are given under normal and abnormal conditions. The results of the deformation and the structure instability analysis show that the model can describe the uniform inflation deformation of the arterial wall under normal conditions, as well as formation and growth of an aneurysm under abnormal conditions such as the decreased stiffness of the elastic and collagen fibers. From the analysis of the stresses and the material strength, the rupture of an aneurysm may also be described by this model if the wall stress is larger than its strength.

The origin of high eccentricity planets:The dispersed planet formation regime for weakly magnetized disks

In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability（MRI）.We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites.In the present paper,we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk.We calculated two cases of BZ 3.4 × 10^-3 G and BZ = 3.4 × 10^-5 G at 100 AU as well as the canonical case of BZ = 3.4 × 10^-4 G.We found that tandem planet formation holds up well in the case of the strong magnetic field（BZ 3.4 × 10^-3 G）.On the other hand,in the case of a weak magnetic field（BZ= 3.4 × 10^-5 G） at 100 AU,a new regime of planetary growth is realized：the planets grow independently at different places in the dispersed area of the MRl-suppressed region of r-8-30 AU at a lower accretion rate of M 〈 10^-7.4M⊙yr^-1.We call this the ＂dispersed planet formation＂ regime.This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions.

Tandem planet formation for solar system-like planetary systems

We present a new united theory of planet formation,which includes magneto-rotational instability（MRl） and porous aggregation of solid particles in a consistent way.We show that the ＂tandem planet formation＂ regime is likely to result in solar system-like planetary systems.In the tandem planet formation regime,planetesimals form at two distinct sites：the outer and inner edges of the MRl suppressed region.The former is likely to be the source of the outer gas giants,and the latter is the source for the inner volatile-free rocky planets.Our study spans disks with a various range of accretion rates,and we find that tandem planet formation can occur for M = 10^7.3- 10^-6.9Myr^-1.The rocky planets form between 0.4-2 AU,while the icy planets form between 6-30 All;no planets form in 2-6 AU region for any accretion rate.This is consistent with the gap in the solid component distribution in the solar system,which has only a relatively small Mars and a very small amount of material in the main asteroid belt from 2-6 AU.The tandem regime is consistent with the idea that the Earth was initially formed as a completely volatile-free planet.Water and other volatile elements came later through the accretion of icy material by occasional inward scattering from the outer regions.Reactions between reductive minerals,such as schreibersite（Fe-jP）,and water are essential to supply energy and nutrients for primitive life on Earth.

Comparison of Formation Mechanism Between Helium and Argon Atmospheric Pressure Plasma Jets

To compare the formation mechanisms of He and Ar atmospheric pressure plasma jets(APPJs),an intensified charge-coupled device(ICCD)are utilized to observe the dynamic process of APPJ.The experimental results show that,He APPJ is first ignited,which is independent of the dielectric barrier discharge(DBD)between the two wrapped electrodes when the high voltage placed at the downstream.The intensity and APPJ length under positive discharge pulses are bigger than that under negative discharge pulses due to the space charge effect.The He APPJ is formed by the DBD development when the high-voltage electrode placed at the upstream side of tube.However,the plasma plume in Ar APPJ is formed by the propagation of DBD whatever the high-voltage electrode is arranged on upstream or downstream side of ground electrode.The difference in formation mechanism between He and Ar APPJs is mainly caused by the gas properties.Moreover,during the discharges,Ar tends to lead to thermal instability and electron Maxwellian instability.

Spatial pattern formation of a ratio-dependent predator-prey model

This paper presents a theoretical analysis of evolutionary process that involves organisms distribution and their interaction of spatially distributed population with diffusion in a Holling-III ratio-dependent predator-prey model, the sufficient conditions for diffusion-driven instability with Neumann boundary conditions are obtained. Furthermore, it presents novel numerical evidence of time evolution of patterns controlled by diffusion in the model, and finds that the model dynamics exhibits complex pattern replication, and the pattern formation depends on the choice of the initial conditions. The ideas in this paper may provide a better understanding of the pattern formation in ecosystems.

泾河油田页岩油储层井壁失稳机理研究

针对鄂尔多斯盆地南部泾河油田延长组长7段页岩地层井壁失稳技术难题,开展了页岩矿物组分、微观结构及理化性能测试分析以揭示井壁失稳机理。结果表明,长7段页岩地层层理、裂缝发育,属于弱水敏硬脆性页岩,地层层理结构造成岩石弱结构面被破坏,黏土水化引起岩石结构强度降低,钻具机械扰动导致井壁失稳;同时,建立了页岩地层三压力剖面,理想钻井液密度为1.13 g/cm^(3),对于泾河油田页岩油“安全、高效、经济”钻探具有借鉴意义。

巴东组泥岩大断面隧道开挖面大变形滑塌失稳机制与防治措施研究

隧道穿越富水软弱地层时易发生开挖面滑塌失稳破坏,为此,本文以郑万高铁巴东隧道为工程依托、以巴东组紫红泥岩为研究对象,开展系列室内试验,揭示泥岩遇水软化的力学特征。综合考虑围岩节理发育及施工扰动等因素的影响,基于Hoek-Brown强度准则将室内试验获取的完整岩体的强度参数转化为现场岩体参数,并采用两相单质点流固耦合物质点法(MPM)对隧道开挖面滑塌失稳大变形全过程进行模拟,并结合现场评价超前帷幕注浆预加固措施的有效性。研究结果表明:开挖面滑塌失稳过程可大致分为开挖面隆起变形、开挖面局部失稳及滑塌体加速运动、滑塌体稳定这3个主要阶段。随着开挖面前方滑塌体的加速运动,围岩的渗流场发生明显的变化,渗水形态呈“漏斗状”,水流向开挖面“缺口”汇集;滑塌体稳定后呈锥体状堆积,滑塌体坡脚与开挖面的距离约25 m,与现场滑塌体最终形态较吻合。采取超前帷幕注浆预加固措施后围岩稳定性较好,确保了隧道施工安全顺利推进。流固耦合物质点法可动态再现地下水渗流作用下软弱地层隧道滑塌失稳破坏全过程,可为类似工程研究提供参考。

破碎地层井壁坍塌压力及井周失稳区域研究

地层裂缝发育状况对井壁坍塌压力及井周失稳区域的分布方位和深度存在一定影响,但常规井壁稳定分析方法将地层视为各向同性介质,未考虑到破碎地层的裂缝特征。为研究破碎地层井壁坍塌压力及井周失稳区域变化规律,文中结合修正的MC强度准则和三向应力作用下的裂缝面强度准则,建立了破碎地层井壁坍塌压力和井周失稳区域预测模型,研究了裂缝数量及井眼轨迹对井壁稳定的影响。研究发现:三向应力作用下,破碎地层井壁坍塌深度主要受裂缝倾角的控制,与裂缝倾向无关,而井壁的坍塌方位与裂缝倾角无关,仅随裂缝倾向的变化而改变;井壁坍塌主要受某条特殊产状裂缝的控制,可通过调整井眼轴向与该裂缝面的相对夹角,达到减轻或控制井壁失稳程度的目的。

富水粉细砂隧道失稳破坏特征分析及增稳固结技术研究

桃树坪隧道穿越富水粉细砂地层,施工过程中极易出现大变形、涌水涌砂和坍塌等一系列破坏特征。通过对隧道失稳破坏的分析,总结了隧道在富水粉细砂条件下失稳破坏的特征,分析了破坏特征发生的机制,认为隧道的破坏主要由围岩岩性和地下水造成;由隧道破坏机理提出了增稳固结措施,通过超前降水、超前小导管注高分子化学浆对掌子面前方砂层进行预先固结,提高钢架整体刚度,通过对扰动砂层进行灌浆和回填等措施进行固结,围岩的自承能力得到提高。从处理后围岩的情况、涌水量和监测情况分析发现,增稳固结技术能从根本上提高围岩的自承能力,抑制发生失稳破坏,为隧道在富水粉细砂地层中的施工提供借鉴。

云南省永仁县民族小学滑坡形成机理及失稳分析

文中以云南省永仁县民族小学滑坡为例,通过现场调查以及山地工程等方法,查明了该区域地质环境内滑坡地质灾害的变形特征以及形成机理。研究表明,H1滑坡在自然工况下处于欠稳定状态,暴雨工况各计算剖面处于不稳定状态,地震工况各计算剖面均处于不稳定状态,因此可以得出,滑坡灾害主要受区内地形条件和地表水影响,故有效抑制水害影响和改善地形条件可提高滑坡灾害防治效果。

苏里格气田多层理泥岩井壁坍塌机理分析

井壁失稳是制约苏里格气田泥岩地层低成本钻进长井段水平井的首要技术难题。在评价泥岩矿物组分、层理发育及力学特性的基础上,综合理论分析、实验评价以及数值仿真模拟等手段,研究了多层理泥岩在流体作用下的力学行为及破坏失稳特征。由于苏里格气田山西组泥岩层理和微裂缝的存在,岩石在钻井液侵入后将会发生强度劣化。泥岩弱面的导流能力远高于岩石基质,钻井液沿弱面渗透到地层中,会直接导致泥岩结构面强度的下降,易发生井壁坍塌。对苏里格气田实钻过程中的泥岩地层坍塌压力进行了计算,将井斜角、方位角和钻井液浸泡时间分别代入岩石力学参数劣化模型,给出了目的层段安全钻井液密度,对实现苏里格气田多层理泥岩井壁稳定和安全钻井具有重要的指导意义。

Instability Mechanisms of Supported Liquid Membrane for Phenol Transport

The instability mechanisms of the supported liquid membrane using Celgard 2500 membranes as support and tributyl phosphate dissolved in kerosene as carrier for phenol transport was studied by ele.etroehemical impedance spectroscopy. Emulsion formation is demonstrated to be one of the main causes for the instability of supported liquid membrane in the present system. The emulsion-facilitated conditions, such as higher membrane liquid concentration, faster stirring speed, lower salt concentration and higher HLB value, would accelerate the degradation of supported liquid membrane. Other mechanisms including solubility and osmotic pressure work together to increase the membrane liauid loss.

Turing Instability and Pattern Induced by Cross-Diffusion for a Nonlinear Reaction-Diffusion System of Turbulence-Shear Flow Interaction

The Turing instability and the phenomena of pattern formation for a nonlinear reaction-diffusion(RD) system of turbulence-shear flowinteraction are investigated.By the linear stability analysis,the essential conditions for Turing instability are obtained.It indicates that the emergence of cross-diffusion terms leads to the destabilizing mechanism.Then the amplitude equations and the asymptotic solutions of the model closed to the onset of instability are derived by using the weakly nonlinear analysis.

深层硬脆性泥页岩井壁稳定力学化学耦合研究进展与思考

深层及超深层油气资源正逐步成为我国重点勘探开发的关键领域,但钻井过程中深层硬脆性泥页岩地层井壁失稳问题频发,严重制约着深层及超深层油气资源高效开发。力学化学耦合作用下的深层硬脆性泥页岩井壁稳定问题,是一个涉及微观、细观及宏观跨尺度演化的复杂问题。阐述了力学化学耦合作用下硬脆性泥页岩井壁失稳的基本原理,并分别从微观、细观和宏观尺度,总结了硬脆性泥页岩与入井流体间的作用机理、细观结构损伤演化的定量表征、泥页岩水化宏观力学劣化效应及井壁稳定性定量分析方面的研究进展,从考虑化学效应的断裂力学角度,提出了探索硬脆性泥页岩井壁稳定性问题的新思路。

微生物无固相钻井液体系构建及其固壁作用机理研究

钻探过程中,常遇到破碎性地层,容易发生井壁失稳而诱发井下复杂事故。增强破碎块之间的胶结力,提升井壁围岩力学强度,是解决该类地层井壁失稳的有效途径之一,微生物诱导碳酸钙沉淀(MICP)技术为实现这一途径提供了很好的借鉴。为此,通过实验研究,分析了巴氏芽孢杆菌在无固相钻井液体系中的生长情况,得到适合巴氏芽孢杆菌生长的无固相钻井液,由此构建微生物无固相钻井液体系。利用岩心浸泡实验和扫描电镜(SEM)分析方法,探讨了微生物无固相钻井液体系的固壁效果及其作用机理。结果表明:巴氏芽孢杆菌在由植物胶、聚丙烯酰胺(PAM)、羧甲基纤维素钠(CMC)组成且含有培养基的无固相钻井液中的生长情况最好,经过24 h的生长,600 nm波长处的吸光值(OD600)达到1.54。故确定微生物无固相钻井液体系的配方为:0.1%植物胶+0.1%PAM+0.1%CMC+巴氏芽孢杆菌(OD600=0.8)+0.25%氯化钠+1%尿素+0.75%酪蛋白胨+0.25%大豆蛋白胨。在微生物无固相钻井液体系中添加钙源,可以获得更好的固壁效果,固结后试样的抗压强度达到0.183 MPa。该体系的固壁机理是微生物在松散颗粒间诱导生成碳酸钙晶体,填充于孔隙中,增强了松散颗粒间的胶结力,使原本松散的碎石土形成整体,从而发挥固壁作用。

海底不稳定性研究进展及展望

海底不稳定性及次生海底地质灾害广泛存在于海洋之中,对海岸港口设施、海洋钻井平台、海底管道光缆等海底基础建设颇具威胁。但目前对海底不稳定性的成因机制与主控因素仍知之甚少,为加深对海底不稳定性的认识,本文回顾了海底不稳定性研究进展,梳理了海底不稳定性及次生海底地质灾害的主要类别、全球分布情况和地球物理识别特征,归纳了目前海底不稳定性研究的定量分析方法,进一步分析了其成因机制、控制因素及工程地质灾害风险,探讨了海底陆坡失稳演化过程试验模拟技术的适用范畴与技术瓶颈。最后,从海底不稳定性的致灾机理研究、多源数据智能分析和海底失稳立体监测3个维度提出了未来海底不稳定性研究的发展方向与对策建议,以期为海底不稳定性的模拟、预测和预警等工作提供指导性建议。

中江区块沙溪庙组井壁失稳机理及烷基糖苷防塌钻井液

针对川西中江区块沙溪庙组井壁失稳技术难题,分析了沙溪庙组泥岩的矿物组成、微观结构及理化性能,揭示了沙溪庙组井壁失稳机理。沙溪庙组属于典型的硬脆性泥岩,黏土矿物含量高,水化作用强,其中伊利石含量最高,微纳米尺度裂隙发育,钻井液滤液侵入后,伊利石、伊蒙混层等分布不均匀,比亲水量大,水化膜斥力大,裂缝不断扩展,易发生井壁坍塌。结合“多元协同”井壁稳定理论,优选了烷基糖苷类抑制剂、微纳米封堵剂等,构建了适用于沙溪庙组的烷基糖苷高性能防塌钻井液体系。通过室内实验可知,该体系流变性良好,API滤失量小于3 mL,高温高压滤失量不大于8 mL,岩样滚动回收率为98.87%,膨胀率小于3%,抑制性优良,对微裂缝和孔隙封堵能力强。现场应用表明,烷基糖苷高性能防塌钻井液能有效抑制沙溪庙组地层坍塌,机械钻速高,无井下复杂事故发生,为保证中江区块沙溪庙组“安全、高效、经济”钻井施工提供了技术支撑。