Molecular dynamics simulation of the flow mechanism of shear-thinning fluids in a microchannel

Shear-thinning fluids have been widely used in microfluidic systems,but their internal flow mechanism is still unclear.Therefore,in this paper,molecular dynamics simulations are used to study the laminar flow of shear-thinning fluid in a microchannel.We validated the feasibility of our simulation method by evaluating the mean square displacement and Reynolds number of the solution layers.The results show that the change rule of the fluid system's velocity profile and interaction energy can reflect the shear-thinning characteristics of the fluids.The velocity profile resembles a top-hat shape,intensifying as the fluid's power law index decreases.The interaction energy between the wall and the fluid decreases gradually with increasing velocity,and a high concentration of non-Newtonian fluid reaches a plateau sooner.Moreover,the velocity profile of the fluid is related to the molecule number density distribution and their values are inversely proportional.By analyzing the radial distribution function,we found that the hydrogen bonds between solute and water molecules weaken with the increase in velocity.This observation offers an explanation for the shear-thinning phenomenon of the non-Newtonian flow from a micro perspective.

Investigation of Projectile Impact Behaviors of Graphene Aerogel Using Molecular Dynamics Simulations

Graphene aerogel(GA),as a novel solid material,has shown great potential in engineering applications due to its unique mechanical properties.In this study,the mechanical performance of GA under high-velocity projectile impacts is thoroughly investigated using full-atomic molecular dynamics(MD)simulations.The study results show that the porous structure and density are key factors determining the mechanical response of GA under impact loading.Specifically,the impact-induced penetration of the projectile leads to the collapse of the pore structure,causing stretching and subsequent rupture of covalent bonds in graphene sheets.Moreover,the effects of temperature on the mechanical performance of GA have been proven to be minimal,thereby highlighting the mechanical stability of GA over a wide range of temperatures.Finally,the energy absorption density(EAD)and energy absorption efficiency(EAE)metrics are adopted to assess the energy absorption capacity of GA during projectile penetration.The research findings of this work demonstrate the significant potential of GA for energy absorption applications.

Temperature-Induced Unfolding Pathway of Staphylococcal Enterotoxin B:Insights from Circular Dichroism and Molecular Dynamics Simulation

In this study,circular dichroism(CD)and molecular dynamics(MD)simulation were used to investigate the thermal unfolding pathway of staphylococcal enterotoxin B(SEB)at temperatures of 298–371 and 298–500 K,and the relationship between the experimental and simulation results were explored.Our computational findings on the secondary structure of SEB showed that at room temperature,the CD spectroscopic results were highly consistent with the MD results.Moreover,under heating conditions,the changing trends of helix,sheet and random coil obtained by CD spectral fitting were highly consistent with those obtained by MD.In order to gain a deeper understanding of the thermal stability mechanism of SEB,the MD trajectories were analyzed in terms of root mean square deviation(RMSD),secondary structure assignment(SSA),radius of gyration(R_(g)),free energy surfaces(FES),solvent-accessible surface area(SASA),hydrogen bonds and salt bridges.The results showed that at low heating temperature,domain Ⅰ without loops(omitting the mobile loop region)mainly relied on hydrophobic interaction to maintain its thermal stability,whereas the thermal stability of domain Ⅱ was mainly controlled by salt bridges and hydrogen bonds.Under high heating temperature conditions,the hydrophobic interactions in domain Ⅰ without loops were destroyed and the secondary structure was almost completely lost,while domain Ⅱ could still rely on salt bridges as molecular staples to barely maintain the stability of the secondary structure.These results help us to understand the thermodynamic and kinetic mechanisms that maintain the thermal stability of SEB at the molecular level,and provide a direction for establishing safer and more effective food sterilization processes.

Study of the Relationship Between New Ionic Interaction Parameters and Salt Solubility in Electrolyte Solutions Based on Molecular Dynamics Simulation

Studying the relationship between ionic interactions and salt solubility in seawater has implications for seawater desalination and mineral extraction.In this paper,a new method of expressing ion-to-ion interaction is proposed by using molecular dynamics simulation,and the relationship between ion-to-ion interaction and salt solubility in a simulated seawater water-salt system is investigated.By analyzing the variation of distance and contact time between ions in an electrolyte solution,from both spatial and temporal perspectives,new parameters were proposed to describe the interaction between ions:interaction distance(ID),and interaction time ratio(ITR).The best correlation between characteristic time ratio and solubility was found for a molar ratio of salt-to-water of 10:100 with a correlation coefficient of 0.96.For the same salt,a positive correlation was found between CTR and the molar ratio of salt and water.For type 1-1,type 2-1,type 1-2,and type 2-2 salts,the correlation coefficients between CTR and solubility were 0.93,0.96,0.92,and 0.98 for a salt-to-water molar ratio of 10:100,respectively.The solubility of multiple salts was predicted by simulations and compared with experimental values,yielding an average relative deviation of 12.4%.The new ion-interaction parameters offer significant advantages in describing strongly correlated and strongly hydrated electrolyte solutions.

Molecular Dynamics Simulation of Shock Response of CL-20 Co-crystals Containing Void Defects

To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.

Molecular dynamics simulation study of nitrogen vacancy color centers prepared by carbon ion implantation into diamond

Nitrogen vacancy(NV)color centers in diamond have useful applications in quantum sensing andfluorescent marking.They can be gen-erated experimentally by ion implantation,femtosecond lasers,and chemical vapor deposition.However,there is a lack of studies of the yield of NV color centers at the atomic scale.In the molecular dynamics simulations described in this paper,NV color centers are pre-pared by ion implantation in diamond with pre-doped nitrogen and subsequent annealing.The differences between the yields of NV color centers produced by implantation of carbon(C)and nitrogen(N)ions,respectively,are investigated.It is found that C-ion implantation gives a greater yield of NV color centers and superior location accuracy.The effects of different pre-doping concentrations(400–1500 ppm)and implantation energies(1.0–3.0 keV)on the NV color center yield are analyzed,and it is shown that a pre-doping concentra-tion of 1000 ppm with 2 keV C-ion implantation can produce a 13%yield of NV color centers after 1600 K annealing for 7.4 ns.Finally,a brief comparison of the NV color center identification methods is presented,and it is found that the error rate of an analysis utiliz-ing the identify diamond structure coordination analysis method is reduced by about 7%compared with conventional identification+methods.

Molecular Dynamics Numerical Simulation of Adsorption Characteristics and Exploitation Limits in Shale Oil Microscopic Pore Spaces

Microscopic pore structure in continental shale oil reservoirs is characterized by small pore throats and complex micro-structures.The adsorption behavior of hydrocarbons on the pore walls exhibits unique physical and chemical properties.Therefore,studying the adsorption morphology of hydrocarbon components in nanometer-sized pores and clarifying the exploitation limits of shale oil at the microscopic level are of great practical significance for the efficient development of continental shale oil.In this study,molecular dynamics simulations were employed to investigate the adsorption characteristics of various single-component shale oils in inorganic quartz fissures,and the influence of pore size and shale oil hydrocarbon composition on the adsorption properties in the pores was analyzed.The results show that different molecules have different adsorption capacities in shale oil pores,with lighter hydrocarbon components(C6H14)exhibiting stronger adsorption abilities.For the same adsorbed molecule,the adsorption amount linearly increases with the increase in pore diameter,but larger pores contribute more to shale oil adsorption.In shale pores,the thickness of the adsorption layer formed by shale oil molecules ranges from 0.4 to 0.5 nm,which is similar to the width of alkane molecules.Shale oil in the adsorbed state that is difficult to be exploited is mainly concentrated in the first adsorption layer.Among them,the volume fraction of adsorbed shale oil in 6 nm shale pores is 40.8%,while the volume fraction of shale oil that is difficult to be exploited is 16.2%.

Exploring the molecular mechanism of action of curcumin for the treatment of diabetic retinopathy,using network pharmacology,molecular docking,and molecular dynamics simulation

Background:Based on network pharmacology and molecular docking,the present study investigated the mechanism of curcumin(CUR)in diabetic retinopathy treatment.Methods:Based on the DisGeNET,Swiss TargetPrediction,GeneCards,Online Mendelian Inheritance in Man,Gene Expression Omnibus,and Comparative Toxicogenomics Database,the intersection core targets of CUR and diabetic retinopathy were identified.The intersection target was imported into the STRING database to obtain the protein-protein interaction map.According to the Database for Annotation,Visualization and Integrated Discovery database,the intersected targets were enriched in Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes pathways.Then Cytoscape 3.9.1 is used to make the drug-target-disease-pathway network.The mechanism of CUR and diabetic retinopathy was further verified by molecular docking and molecular dynamics simulation.Results:There were 203 intersecting targets of CUR and diabetic retinopathy identified.1320 GO entries were enriched for GO functions,which were primarily involved in the composition of cells such as identical protein binding,protein binding,enzyme binding,etc.It was found that 175 pathways were enriched using Kyoto Encyclopedia of Genes and Genomes pathway enrichment methods,which were mainly included in the lipid and atherosclerosis,AGE-RAGE signaling pathway in diabetic complications,pathways in cancer,etc.In the molecular docking analysis,CUR was found to have a good ability to bind to the core targets of albumin,IL-1B,and IL-6.The binding of albumin to CUR was further verified by molecular dynamics simulation.Conclusion:As a result of this study,CUR may exert a role in the treatment of diabetic retinopathy through multi-target and multi-pathway regulation,which indicates a possible direction of future research.

基于CFD与风洞试验的边主梁涡振气动措施

为能够快捷且经济地完成开口类钝体桥梁断面涡振制振气动措施的选型,以一座边主梁叠合梁斜拉桥为背景,采用“CFD(computation fluid dynamics)数值模拟选型+风洞试验验证”的思路对其涡振制振气动措施选型进行研究.该桥原设计主梁断面在常遇风速下存在显著涡激振动,为完成气动措施的初步选型,采用CFD数值计算对原设计断面的流场进行模拟,通过研究原设计断面的旋涡脱落状态确定主要旋涡抑制对象,进而有针对性地模拟了3种气动措施(下中央稳定板、导流板与风嘴)对主要脱落旋涡的抑制作用,通过将各断面旋涡脱落状态与三分力系数进行对比分析,得到各断面涡振性能的相对优劣关系,并最终选取风嘴与下中央稳定板结合而成的组合气动措施进行风洞验证试验.试验结果表明:该组合气动措施能够有效抑制梁体在各风攻角下的涡激振动,且在+5°风攻角下,通过风洞试验得到的导流板、下中央稳定板、风嘴组合气动3种措施对原设计断面涡振振幅的减小作用依此递增,分别为2.7%、27.7%与87.4%,制振能力高低关系与数值模拟结果相一致;本次数值模拟结果符合预期要求,未来可针对不同类型桥梁断面进一步扩展数值模拟与风洞试验结果对比的数据集,以期更为准确、快捷地完成气动措施的选型.

基于CFD的LNG储罐瞬时大风环境数值模拟研究

为分析不同大风风速下储罐迎风侧和背风侧压力分布情况和风场特点,采用k-ε湍流模型,建立液化天然气(LNG)储罐区瞬时大风环境模型。利用计算流体动力学(CFD)软件Fluent对LNG储罐风环境进行模拟,利用软件分析模块生成储罐压力云图和风速矢量图。研究结果表明:LNG储罐在迎风侧承受压力高于背风侧,压力呈现对称分布;储罐前端与两侧易产生气体漩涡,但总体速度曲线较为规律,无混乱复杂的速度曲线。研究结果可为LNG场站抗灾韧性增强、极端大风天气应急疏散路径规划等多方面提供理论参考,对LNG储罐区安全建设具有重要指导意义。

变容积密集烤房的CFD分析与试验研究

为保障密集烤房装烟密度,降低烘烤的能源消耗,研发一套适用于密集烤房的变容积系统。在完成变容积装置的设计后,基于CFD方法模拟分析装置与烟叶的不同距离对烤房内部气体分布均匀性的影响。通过烘烤试验获取实际烘烤数据,对模拟值加以验证。试验结果表明:当隔板与烟叶距离为0 cm时,流速不均匀系数Kv为0.40,温度不均匀系数Kt为0.41,距离为10 cm时,Kv=0.41,Kt=0.43;距离为20 cm时,Kv=0.42,Kt=0.49。装烟区9个测量点的温度模拟值与实测值基本吻合,误差在6%以内。变容积烤房在装烟量为一半时,相比常规烤房的燃料消耗可节约13.4%。研究结果表明:当隔板与烟叶距离为0 cm时烤房内部的气体分布最均匀;CFD模型与数值模拟结果具有可靠性;变容积装置具有较好的保温效果,可保证装烟密度,降低烤烟能耗。

基于CFD的机械随动调节高度控制阀数值仿真

机械随动调节高度控制阀是列车悬挂控制装置的核心部件,其性能的好坏直接影响系统能否稳定工作。在设计过程中,采用CFD对其进行仿真计算,通过对其流场特性的分析,可以验证其流量特性是否满足系统需求。针对机械随动调节高度控制阀内部气体流动特性,建立了机械随动调节高度控制阀流场仿真模型,利用Fluent分析了机械随动调节高度控制阀阀口在不同开度下的流场特性,研究结果为机械随动调节高度控制阀流量性能指标试验提供理论支撑。

基于CFD的惰性密封箱室内气溶胶运动规律的数值模拟研究

目前,最有前景的快堆乏燃料后处理方法是干法后处理技术,利用该技术操作物料时,整个工艺过程必然会伴随有放射性气溶胶的产生,为了有效的安全性评估、安全性分析、事故溯源等,需要掌握气溶胶颗粒在惰性密封箱室内的运动规律。本文利用CFD技术对惰性密封箱体内气溶胶颗粒进行运动规律的分析与研究。结果表明:绝大多数颗粒沿着流场方向运动,在出口壁面有部分颗粒残留;壁面粗糙度数值为0.4μm,可以有效地降低颗粒在壁面的沉降。本文的研究结果为惰性密封的手套箱及热室的设计提供相关的理论依据及数据支撑。

基于CFD的辐射冷顶板与风扇耦合系统性能优化

吸音板用来解决辐射式天花板供冷系统的噪声问题,但其阻碍了辐射换热。本文提出通过风扇的调风作用来优化辐射冷顶板与风扇耦合系统,基于CFD模拟讨论了耦合系统的室内气流分布、热舒适及换热系数变化,研究了吸音板安装方式、风扇转速和风扇转向对辐射天花板性能的影响。结果表明:风扇的加入增大了顶板的对流换热系数和总换热系数;随着风扇转速的增大,室内的空气温度和人体热舒适性评价指标(PMV)降低;风扇向上吹风的效果优于向下吹风,吸音板竖直安装优于水平安装。

基于CFD流场模拟的大型卧式反应釜结构研究

近年来,加压浸出湿法冶金工程在向更大规模的发展道路受到了配套装备大型化带来的技术制约。为了适应加压浸出工艺关键核心设备-卧式反应釜的规模大型化发展,更好地保证该设备在使用过程中的可靠性与高效性。本文采用CFD流体模拟软件,针对某项目使用的300立卧式反应釜,研究其在不同长径比下的流场分布情况以及搅拌器功率消耗大小与长径比的关系。研究表明适当增加长径比有利于改善水平方向的流场特性,减小长径比有利于改善垂直方向的流场特性,减小长径比有利于搅拌功率的降低。当长径比取1.08或1.13,能够有效提高卧式反应釜内的反应效率,降低成本和系统能耗。

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

深部煤层地下煤气化原位点火的CFD模拟

地下煤气化(Underground Coal Gasification,UCG)作为一种新型采煤技术受到了广泛的关注,但UCG的实验成本较高,在开展UCG实验之前应当对煤层的演变机理进行深入的探究。计算流体力学(Calculated Fluid Dynamics,CFD)可以凭借计算机强大的计算能力,以较为低廉的成本模拟UCG的生产过程。采用Ansys公司开发的CFD软件Fluent模拟了1000 K烟气加热下深部煤层的原位加热着火过程,重点分析了温度、氧气摩尔分数和孔隙度的变化。结果表明,泵入500 s的1000 K烟气不足以点燃煤层,1000 s的烟气加热时间足以点燃煤层,该结果在时间上与劳伦斯实验室的点火时间相当。在煤层内表面,高温主要集中在靠近入口0~0.6 m内的煤层。着火前的最高温度低于加热烟气入口温度1000 K,而着火后的最高温度超过1000 K,最高温度约1250 K。O_(2)在高温区几乎全部消耗,而在其他温度较低的区域,到达煤层内表面的氧气摩尔分数不到2%。高温区孔隙度迅速增长,在1000 s时部分煤层孔隙度可达0.9左右。在煤层内部,煤层越厚,温度上升越低。在1000 s和2000 s时,7 cm线上煤层的最高温度仅为500 K左右,远低于相同加热时间下煤层内表面的最高温度。在2000 s的点火过程中,渗入7 cm和14 cm煤层中的氧气较少,内部煤层孔隙度均在0.4以下。较低的孔隙度是由较低的温度和较低的氧气摩尔分数共同造成的。对温度、氧气摩尔分数和孔隙度的模拟可为如何促进煤层内部的反应提供参考。

调谐液柱阻尼器-结构系统风致振动响应的CFD/CSD耦合分析方法

针对调谐液柱阻尼器(tuned liquid column damper, TLCD)难以建立其精确的非线性理论分析模型,且其力学性能试验成本高和耗时长等问题,首先采用计算流体动力学(CFD)数值模拟方法,对TLCD系统的力学性能和动力特征进行仿真模拟,在此基础上进一步提出了基于计算流体动力学/计算结构动力学(CFD/CSD)耦合分析方法,求解带TLCD系统的高层建筑结构的风致动力响应。通过开展某一TLCD系统在特定底部激励下的力学性能和动力特性试验,得到其内液体晃荡的自由液面波高和晃动力时程,验证了CFD数值模拟方法可以准确地分析TLCD水箱内液体的非线性晃动特征。随后对风工程领域广泛采用的76层建筑结构振动控制Benchmark模型,假设其顶部设置TLCD系统时主体结构在三种风速重现期(10、50和100年)风速对应的横风向动力风荷载激励下的风致控制效率,采用提出的CFD/CSD耦合分析方法,进行了数值仿真模拟分析。耦合分析结果表明,TLCD系统对Benchmark模型的风致加速度、速度和位移响应均有一定的控制效果,对加速度响应的控制效果要优于对位移响应的控制效果。该研究方法可为复杂TLCD系统对高层建筑的风振控制分析提供有效的参考。

基于CFD技术对冬季兔舍热环境模拟评估

本研究基于计算流体力学(CFD)模拟技术对兔舍热环境(风速和温湿度)进行三维稳定状态的模拟分析,旨在评估密闭兔舍冬季热环境质量。结果表明:密闭兔舍环境的调控采用低效率排风系统,中间区域存在气流流动死角,风速分布不均,不符合兔舍最适宜的风速范围;温度从西侧的进风口到东侧的出风口呈上升趋势,分布范围为15.56~22.40℃,符合兔舍最适宜温度范围;相对湿度的分布变化与温度则呈相反趋势,分布范围为54.39%~81.78%,略超出兔舍最适宜相对湿度范围。温度和相对湿度的实测值与模拟值的相对误差范围均低于5%,说明运用该模型评估环境因子是可行的。本研究为优化商品兔舍冬季环境的调控方案提供了参考依据。

CFD-DEM方法研究下降管结构对颗粒流动的影响

为了明确不同下降管结构内陶瓷球和生物质颗粒的流动规律,对比研究了方形和圆形下降管对颗粒轴向速度、颗粒碰撞率和生物质停留时间的影响,同时考察了管径对颗粒轴向速度和生物质停留时间的影响。搭建了CFD-DEM耦合框架,并利用粒子图像测速技术对模拟进行了速度验证。试验结果表明,模拟结果与试验结果吻合良好;混合颗粒在圆管中的时均轴向速度高于方管,圆管中陶瓷球的最大轴向速度比方管高10%左右;不同管径大小下降管中的颗粒轴向速度差异主要体现在下降管的转弯处,管径60、70和80 mm下降管转弯处的陶瓷球速度依次损失了37%、40%、45%左右,生物质的速度依次损失了49%、52%、54%左右;方管中生物质与壁面的接触碰撞频率更高,圆管中生物质与陶瓷球的接触碰撞频率更高,两种管中分别约为23%和39%的生物质颗粒与陶瓷球接触;陶瓷球的加入后方管和圆管中的生物质停留时间分布离散程度分别增加了10%和17%。研究结果为下降管热解装置中的颗粒流动状态分析及结构设计和优化提供了依据。