Torsional Characteristics of Single Walled Carbon Nanotube with Water Interactions by Using Molecular Dynamics Simulation

The torsional characteristics of single walled carbon nanotube(SWCNT) with water interactions are studied in this work using molecular dynamics simulation method. The torsional properties of carbon nanotubes(CNTs) in a hydrodynamic environment such as water are critical for its key role in determining the lifetime and stability of CNT based nano-fluidic devices. The effect of chirality, defects and the density of water encapsulation is studied by subjecting the SWCNT to torsion. The findings show that the torsional strength of SWCNT decreases due to interaction of water molecules and presence of defects in the SWCNT. Additionally,for the case of water molecules encapsulated inside SWCNT, the torsional response depends on the density of packing of water molecules. Our findings and conclusions obtained from this paper is expected to further compliment the potential applications of CNTs as promising candidates for applications in nano-biological and nano-fluidic devices.

CFD Analysis of Ship-to-Ship Hydrodynamic Interaction

A numerical study of ship-to-ship interaction forces is performed using a commercial CFD code,and the results are compared with experimental data and with the results of a panel method analysis.Two ship models have been used in the interaction forces analysis:a tug and a tanker,advancing parallel to each other with different lateral distances and two different values of the fluid depth.Computations are carried out with four different flow models:inviscid and viscous flow with the free surface modeled as a rigid wall and inviscid and viscous flow with the deformable free surface.A fair agreement was obtained with available experimental data and results obtained by panel method.The influence of viscosity in the computations is found to be comparatively weak,while the wavemaking effects may be important,at small magnitude of the horizontal clearance.

Molecular dynamics simulations of CH4 diffusion in kaolinite: influence of water content

Understanding the interaction of CH4 with kaolinite is significant for researchers in the fields of coalbed CH4 and shale gas.The diffusion behaviors of CH4 in kaolinite with water contents ranging from 0 to 5 wt% have been analyzed by molecular dynamics simulations.The results of the simulations indicate that CH4 molecules can jump between adjacent holes in the kaolinite matrix.CH4 diffusion coefficient was very low (3.28 × 10-9 m2/s) and increased linearly with the increasing of water content.As the water content decreased,the value of radial distribution function first peak between CH4 and oxygen was larger,meaning that with lower water content,the interaction energy between CH4 and oxygen in kaolinite is stronger.The interaction between CH4 and water is linearly positively correlated with water content,in contrast,the interaction energy between kaolinite and water as well as between kaolinite and CH4 decreased linearly with increasing water content.On the other hand,the diffusion of CH4 molecules adsorbed on the surfaces also can be accelerated by the fast diffusion of water molecules in the middle micropore of the kaolinite.

DYNAMIC RESPONSE ANALYSIS OF PLATFORM-CYLINDERGROUP FOUNDATION DUE TO IMPACT BY WATER WAVE FLOW

This paper deals. with the problem of dynamic response of platform-cylinder group foumdation. Dynamic interaction of cylinder group foudation-water-soil is taken into account and the analysis of dynamic response to excitation of water wave force is given by analytic method ..The numerical examples are presented and the influence of systent’s parameters on the dynamic behaviour is discussed.

Effect of hydrophobicity on the water flow in carbon nanotube-A molecular dynamics study

This work focuses on the study of the effect of hydrophobicity on the water flow in carbon nanotubes(CNTs)using a molecular dynamics(MD)approach for a wide range of potential applications such as water purification and high efficiency of nanofluid energy absorption systems(NEAS).The hydrophobicity between liquid water and surface of CNTs was characterized by interaction-energy-coefficient(IEC)—a parameter describing the energy interaction strength between water molecules and carbon atoms.It is shown that the static contact angles between water and carbon surface decrease from 155° to 44°when the values of IEC increase from 0.042 kJ/mol to 2.196 kJ/mol.In addition,the pressure drops in CNT became independent of IEC when the IEC value was higher than 1.192 kJ/mol for a given flow rate.It was found that the hydrophobicity of CNT surface has a significant impact on the pressure drop of water flow in the CNTs and MD method provides a quantitative evaluation of the impact.

Mechanical characteristic variation of ballastless track in highspeed railway:effect of train–track interaction and environment loads

Due to the fact that ballastless tracks in highspeed railways are not only subjected to repeated train–track dynamic interaction loads,but also suffer from complex environmental loads,the fundamental understanding of mechanical performance of ballastless tracks under sophisticated service conditions is an increasingly demanding and challenging issue in high-speed railway networks.This work aims to reveal the effect of train–track interaction and environment loads on the mechanical characteristic variation of ballastless tracks in high-speed railways,particularly focusing on the typical interface damage evolution between track layers.To this end,a finite element model of a double-block ballastless track involving the cohesive zone model for the track interface is first established to analyze the mechanical properties of the track interface under the loading–unloading processes of the negative temperature gradient load(TGL)followed by the same cycle of the positive TGL.Subsequently,the effect of wheel–rail longitudinal interactions on the nonlinear dynamic characteristics of the track interface is investigated by using a vehicle-slab track vertical-longitudinal coupled dynamics model.Finally,the influence of dynamic water pressure induced by vehicle dynamic load on the mechanical characteristics and damage evolution of the track interface is elucidated using a fluid–solid coupling method.Results show that the loading history of the positive and negative TGLs has a great impact on the nonlinear development and distribution of the track interface stress and damage;the interface damage could be induced by the wheel–rail longitudinal vibrations at a high vehicle running speed owing to the dynamic amplification effect caused by short wave irregularities;the vehicle dynamic load could produce considerable water pressure that presents nonlinear spatial–temporal characteristics at the track interface,which would lead to the interface failure under a certain condition due to the coupled dynamic effect of vehicle load and water pressure.

Soil pressure and pore pressure for seismic design of tunnels revisited: considering water-saturated, poroelastic half-space

This paper describes a systematic study on the fundamental features of seismic soil pressure on underground tunnels, in terms of its magnitude and distribution, and further identifi es the dominant factors that signifi cantly infl uence the seismic soil pressure. A tunnel embedded in water-saturated poroelastic half-space is considered, with a large variety of model and excitation parameters. The primary features of both the total soil pressure and the pore pressure are investigated. Taking a circular tunnel as an example, the results are presented using a fi nite element-indirect boundary element(FE-IBE) method, which can account for dynamic soil-tunnel interaction and solid frame-pore water coupling. The effects of tunnel stiffness, tunnel buried depth and input motions on the seismic soil pressure and pore pressure are also examined. It is shown that the most crucial factors that dominate the magnitude and distribution of the soil pressure are the tunnel stiffness and dynamic soil-tunnel interaction. Moreover, the solid frame-pore water coupling has a prominent infl uence on the magnitude of the pore pressure. The fi ndings are benefi cial to obtain insight into the seismic soil pressure on underground tunnels, thus facilitating more accurate estimation of the seismic soil pressure.

Seismic Response Analysis of Portal Water Injection Sheet Pile

To further the study on the newly developed portal water injection sheet pile under static loads, in this paper, by adopting the nonlinear calculation module of FEM software ANSYS, a model for the interaction between the soil and the sheet piles is set up, and the seismic response analysis for this type of space-retaining structure is performed. The effects of the embedded depth and the distance between the front pile and the back pile on the dynamic characteristics of the portal water injection sheet pile are studied.

泥岩卸荷损伤-水次序作用下的劣化规律研究

工程开挖建设导致软岩形成卸荷损伤,其在水-岩作用下的劣化特征与卸荷损伤程度密切相关。以巴东地区红层泥岩为研究对象,设计进行了泥岩卸荷损伤模拟试验,随后对卸荷损伤泥岩试样进行水-岩作用试验,结果显示:卸荷损伤导致泥岩局部矿物颗粒形态破坏、微裂缝发育,在后续水-岩作用下颗粒间胶结程度持续弱化,孔隙、裂缝进一步扩展。宏细观参数随水-岩作用时间的增长,其中质量m呈现先上升后骤然下降再趋于稳定的趋势,纵波波速P呈现先减少后上升的趋势,体积应变εv呈现逐渐增大的趋势,分形维数K呈逐渐增长的趋势;且各参数的增长速率均随卸荷损伤程度D的增大呈幂函数增加,当D≥0.49时,各参数的增长速率急剧增大;确定以质量、纵波波速、体积应变和分形维数作为与水反应系统的变量,并运用非线性动力学理论建立了水-岩作用下的泥岩劣化模型,并验证了模型的合理性。研究结果表明所建模型能表征卸荷损伤泥岩在水-岩作用下的宏细观特征参数变化趋势提供一定理论参考。

基于氡同位素示踪的洞庭湖区枯水期湖水与地下水交互作用研究

洞庭湖区水系发达,水文地质条件复杂,人类活动强烈,地表水和地下水的水力联系变化频繁,其研究的难度以及由此造成的研究不足影响了对湖区地下水赋存和运动规律的深入认识。本文以洞庭湖整体为研究对象,采用水位动态分析和氡(222 Rn)同位素示踪法,定性和定量研究枯水期洞庭湖区地表水与地下水的交互作用关系与交互通量。枯水期洞庭湖区水位和氡浓度空间分布特征指示研究区内地下水向湖水排泄,尤以东洞庭湖最为显著。氡箱模型计算结果显示枯水期地下水排泄222 Rn通量为455.09 Bq/(m^(2)·d),占总输入222 Rn通量的60.07%,地下水排泄总量为0.29×10^(8)m^(3)/d,平均排泄速率为56.27 mm/d,地下水排泄对湖水的贡献率为7.04%。敏感性分析表明:风速、地下水和湖水222 Rn浓度以及湖面面积等参数较为敏感,合理布置取样点并提高敏感参数测量准确度能提高模型计算结果的可靠度。氡同位素示踪法物理意义明确、操作过程简便,是研究复杂区域地下水补、径、排特征的有效方法。研究成果一定程度上提供了洞庭湖区水量均衡的更多认识,可为洞庭湖区地下水资源评价和管理提供参考。

喷水推进器进水流道格栅流固耦合特性研究

为了研究格栅部件对喷水推进船舶效率的影响,本文拟采用流固耦合的数值计算方法系统地对格栅表面受力及其强度特性进行计算,结合有限元方法和流固耦合理论,以STARCCM+和ABAQUS软件为工具,根据目前已知的格栅剖面设计方法,对目前格栅的剖面形式进行改进,形成新型对称剖面形式的格栅。基于上述计算流体力学与流固耦合计算方法对其进行周围流场、结构静力强度、结构动力强度进行计算与分析。结果表明:对称形式的格栅剖面对于降低格栅的变形与应力水平有一定的帮助,采用新型对称形式的剖面结构使格栅总体变形模式发生了变化,但是最大变形位置与最大应力出现在格栅的位置未发生明显变化,新型对称剖面形式格栅具有比较好的静强度与动强度特性,各栅条均匀承受流体载荷。

喷水式超声检测的声−流耦合模型

为研究超声波在射流水柱中的传播特性,提出了喷水式超声检测的声−流耦合建模方法。使用计算流体动力学方法得到喷水探头内部流场的湍动能、速度和压力,并通过弱形式偏微分方程将其映射到声学网格作为声场分析的边界条件,用线性纳维−斯托克斯方程求解湍动能、流速等引起的声学变化,建立了喷水式超声检测的声−流耦合模型。仿真计算了不同流速时工件内部的声压分布,进水口流速的变化不会改变工件中声压的分布规律,但空间声压幅值随着流速的增大而减小。仿真计算了不同流速时的平底孔回波,回波幅值随着流速的增大而减小,通过与实验结果对比,验证了本文方法的准确性。

基于分子动力学模拟的木材细胞壁与水分相互作用研究进展

木材是一种典型的天然高分子材料,在分子尺度上解读水分对木材微纳结构的影响,是木材中水分研究的重难点。文中概述了分子动力学模拟的一般过程,重点介绍了近年来分子动力学模拟在木材-水分的研究领域中,对细胞壁化学组分纤维素、半纤维素、木质素与水分相互作用以及细胞壁各组分之间的界面与水分相互作用等方面的最新研究进展,最后提出了相关的现存问题,并就未来的发展方向进行展望,以期为深入揭示木材与水分的相互作用提供参考。

低温输送管道稠油的黏附机理

为从微观角度揭示高含水稠油低温输送黏附机理,以分子动力学模拟为主要方法,从稠油/水/管壁体系的界面特性、扩散性能、组分与特征结构分布以及胶质沥青质协同作用等角度出发,研究了该体系的黏附作用机理。结果表明,体系的界面特性显著影响稠油黏附作用,且与沥青质含量之间存在正相关关系,同时体系中的范德华引力相互作用是影响稠油黏附的主要作用之一。结果发现沥青质和胶质分子主要分布在油水界面和油/管壁界面附近,而正庚烷和甲苯分子分布在油滴的疏水内部,这是由于胶质沥青质分子存在强极性所导致的。沥青质分子中含有O原子的官能团优先分布在油水界面,通过与水分子结成氢键防止水分子向管壁运动并与烃类混合物分子产生竞争黏附;含有N原子和S原子的官能团在油滴和管壁之间的黏附作用中出现优先接触黏附的现象,对稠油黏附层起到“衔接与桥梁”的作用;C_(5)长侧链会抑制胶质和沥青质分子向油水和油/壁界面的运移,削弱稠油的黏附强度。在胶质沥青质协同作用中,沥青质含量超过8wt%时,胶质分子的增溶效应被抑制,体系中逐渐形成沥青质多聚体,促进稠油黏附现象的发生,危害集输管道安全平稳运行。可见高含水稠油低温输送黏附机理是由低温下的范德华引力为主导,胶质沥青质等极性大分子的杂原子官能团优先与管壁接触黏附现象为桥梁,沥青质聚集效应和胶质增溶效应为协同作用的复杂相互作用机理。

基于分子动力学模拟的α-SiO_(2)纳米颗粒油-水界面吸附行为研究

纳米颗粒相界面吸附与自组装被广泛应用于石油采收、泡沫浮选、药物输送及新型功能材料等研究领域。然而,由于溶剂化力、静电斥力等多种相互作用所导致的吸附势垒,纳米颗粒自发吸附至界面的过程受到阻碍。基于分子动力学方法研究了α-SiO_(2)纳米颗粒相界面吸附动力学特征,深入分析了水化层结构及离子浓度对颗粒吸附行为的影响。首先,通过修饰表面基团获取了不同亲疏水性α-SiO_(2)纳米颗粒的吸附特征:纳米颗粒自发扩散至亚界面后会经历弛豫吸附至界面、快速吸附以及在界面区域经历一段弛豫后达到动态平衡三个过程。随后,从径向分布函数、角度分布、氢键密度分布等对纳米颗粒水化层结构以及氢键结构和进行了量化和比较,通过水化层内水分子驻留自相关函数以及氢键寿命分析了水化层结构及氢键结构的动力学特性。结果表明:水化层结构依赖于所作用颗粒的表面特性,与亲水表面相比,水分子在疏水表面具有明显的择优取向和更强的流动性;表面-水间氢键相互作用和水化层内特殊氢键结构是影响颗粒吸附的重要原因;不同离子效应可以通过共同作用干扰氢键结构以促进纳米颗粒相界面吸附。本研究为理解纳米颗粒相界面吸附动力学特性以及吸附壁垒形成机制提供参考,对于纳米颗粒相界面可控吸附在石油采收、新型功能材料等应用领域具有指导意义。

松辽盆地十屋断陷流体-岩石相互作用

根据松辽盆地十屋断陷199个水化学分析测试数据,探讨该区地层水化学特征所反映的成岩作用过程,以揭示水化学特征的分布以及演化过程,示踪流体-岩石相互作用过程.水化学的空间分布特征受流体动力场控制:大气降水沿盆地的边缘及断层复杂的中央隆起带下渗,导致该地区盐度降低(小于4.5g/L),向盆地中心盐度逐渐增加到7～10g/L;垂向明显分为3个带:自由交替带(0～1250m深度)为NaHCO3型流体,交替阻滞带(1250～1650m深度)为Na2SO4型流体,交替停滞带(深于1650m)为CaCl2型流体.水化学的时间演化过程受流体-岩石相互作用的控制:地层水中Cl-与HCO3-和Na++K+与Ca2+的关系表明,地层水早期为富含HCO3-的低盐度流体,含钠矿物与碳酸盐矿物的溶解导致了流体中各种离子及盐度的增高,随后的钠长石化作用导致流体中富集Ca2+而Na+亏损,形成CaCl2型流体.十屋断陷水化学特征所反映的流体-岩石相互作用过程得到了其它地质观察的佐证.

松辽盆地地层水化学特征及其流体—岩石相互作用探讨

地层水化学的空间分布特征研究是追踪流体运移及油气运移、聚集的重要手段之一。通过对松辽盆地水化学测试数据的分析,阐明了该盆地水化学特征的空间分布规律及其所反映的流体-岩石相互作用过程,指出水化学的时间演化特征受流体-岩石相互作用的控制。再通过研究水化学中C l--HCO3-和N a+-K+-Ca2+的关系进一步阐明了该盆地地层水早期为富含HCO3-的低盐度流体,含钠矿物(N aC l)与碳酸盐矿物的溶解作用导致了流体中各种离子及流体盐度的增高,随后的钠长石化作用导致流体中Ca2+的富集与N a+的亏损,形成了CaC l2型流体。最后指出松辽盆地水化学特征所反映的流体-岩石相互作用过程得到了其它地质观察的证明,认为地层水化学可以示踪流体-岩石相互作用过程,有广泛的用途。

水热耦合作用下尿素转化为铵态氮的动力学模型

在4种温度、5种土壤含水量共20种处理的室内控制条件下,研究了土壤含水量、温度及其耦合作用与尿素转化为铵态氮的关系,探讨水热耦合作用下尿素转化为铵态氮的动力学过程,以及旱地农田尿素利用率。研究结果看出,在本试验条件下,提高土壤温度和土壤含水量均可以促进尿素向铵态氮的转化,且在尿素转化为铵态氮的过程中,土壤温度和土壤含水量存在着交互效应。同时建立了土壤中尿素转化中铵态氮含量变化的动力学模型(Y=a+bt+c／t),模型分析表明,土壤温度和水分对a值存在负交互效应,而对b、c值却存在正交互效应。此外,通过对试验各温区比温值的分析,发现施用尿素后铵态氮产生的最敏感温区及最敏感湿度,并针对施肥方法提出了一些建议。

基于CEL算法的水陆两栖飞机水上降落动力特性分析

水陆两栖飞机水上降落属于复杂的流固耦合问题,文中建立了某水陆两栖飞机机头的入水流固耦合模型,采用耦合的欧拉-拉格朗日(CEL)算法分析了机头入水瞬时的结构动力响应,对比了不同入水角度和不同垂直速度下机头的应力、冲击力及质心速度变化.结果表明:机头入水初期船底冲击力即出现峰值,之后随着机头抬高,船底冲击力将再次出现峰值;入水过程中机头骨架受力变化明显;随着入水角度的减小,机头应力也减小;入水速度减小,机头应力和船底冲击力都随之减小.

安徽月山矿田夕卡岩型矿床形成的水岩作用

文章分析了安徽月山矿田夕卡岩型矿床形成过程中水岩作用的类型和特征。估算和讨论了水岩作用过程中的质量_体积变化和动力学问题。结论认为 :水岩作用对流体成矿系统中夕卡岩和蚀变矿化作用的发生、发展 ,成矿流体的形成 ,成矿物质的富集 ,矿床定位等具有重要意义 ;水岩作用的水岩比值 (W/R)小于 0 .1;