An artificial viscosity augmented physics-informed neural network for incompressible flow

Physics-informed neural networks(PINNs)are proved methods that are effective in solving some strongly nonlinear partial differential equations(PDEs),e.g.,Navier-Stokes equations,with a small amount of boundary or interior data.However,the feasibility of applying PINNs to the flow at moderate or high Reynolds numbers has rarely been reported.The present paper proposes an artificial viscosity(AV)-based PINN for solving the forward and inverse flow problems.Specifically,the AV used in PINNs is inspired by the entropy viscosity method developed in conventional computational fluid dynamics(CFD)to stabilize the simulation of flow at high Reynolds numbers.The newly developed PINN is used to solve the forward problem of the two-dimensional steady cavity flow at Re=1000 and the inverse problem derived from two-dimensional film boiling.The results show that the AV augmented PINN can solve both problems with good accuracy and substantially reduce the inference errors in the forward problem.

Effects of variable viscosity and temperature modulation on linear Rayleigh-Bénard convection in Newtonian dielectric liquid

The linear Rayleigh-Bénard electro-convective stability of the Newtonian dielectric liquid is determined theoretically subject to the temperature modulation with time.A perturbation method is used to compute the critical Rayleigh number and the wave number.The critical Rayleigh number is calculated as a function of the frequency of modulation,the temperature-dependent variable viscosity,the electric field dependent variable viscosity,the Prandtl number,and the electric Rayleigh number.The effects of all three cases of modulations are established to delay or advance the onset of the convection process.In addition,how the effect of variable viscosity controls the onset of convection is studied.

Effects of Variable Viscosity on Hydromagnetic Boundary Layer along a Continuously Moving Vertical Plate in the Presence of Radiation and Chemical Reaction

The flow and heat transfer of an incompressible viscous electrically conducting fluid over a continuously moving vertical infinite plate with uniform suction and heat flux in porous medium, taking account of the effects of the variable viscosity, has been considered. The solutions are obtained for velocity, temperature, concentration and skin friction. It is found that the velocity increases as the viscosity of air or porous parameter increases whereas velocity decreases when Schmidt number increases. The skin friction coefficient is computed and discussed for various values of the parameters.

Effect of Thermal Convection on Viscosity Measurement in Vibrational Viscometer

This paper describes the experimental study of viscosity measurement error in the vibrational type viscometer, which measures viscous damping of the oscillating circular plate in a fluid in continuously increasing temperatures. The experiments are carried out to measure non-uniformity of the temperature field in the test cup of the vibrational viscometer in continuously increasing temperatures, while changing the viscosity of the target fluids. Experimental outcomes show that non-uniformity of the temperature grows in the cup and results in viscosity measurement error, when the viscosity of the fluid increases. In order to understand this phenomenon, velocity measurement by particle image velocimetry is conducted in the test cup for fluids of varying viscosity. The results indicate that mixing is enhanced in the low-viscosity fluid by the occurrence of unsteady thermal convection, while weaker convection appears in the high-viscosity fluid.

热历史对乍得原油析蜡特性及黏温性质的影响

在测试乍得原油物性的基础上,深入研究热处理温度和降温速率对析蜡特性及黏温性质影响。以乍得A、C两种原油为研究对象,测试了其蜡含量、倾点、族组分和正构烷烃碳数分布,发现乍得原油属于高含蜡原油;采用差示扫描量热法(DSC)考察了其析蜡特性,结果表明:较高的处理温度、较大的降温速率会导致析蜡点后移,更高的处理温度能够在一定程度上降低原油在降温过程中的累积析蜡量;通过测定两种原油在不同温度热处理以及不同降温速率条件下的黏度—温度关系发现,较高的处理温度、较大的降温速率能够使原油黏温特性改善;使用偏光显微镜观察发现,在降温过程中蜡晶结构逐渐致密。热历史对原油的影响为乍得原油加热输送及降凝改性输送提供了理论基础。

Solvation number, thermochemical parameter, and viscosity study of sweeteners in aqueous and non-aqueous media through ultrasonic measurements

Ultrasonic velocity measurements are used to elucidate various aspects of solvation chemistry,including solute–solute and solute–solvent interactions.Herein,an attempt is made to study a behavior of two sweeteners,D-fructose and D-sorbitol,in aqueous and non-aqueous media was attempted.D-fructose is a simple sugar found in many foods and can be consumed by diabetics and people suffering from hypoglycemia.D-Sorbitol is a sugar substitute used in diet foods,sugar-free chewing gum,mints,cough syrups,mouthwash,toothpaste etc.,D-sorbitol is an excellent humectant and texturizing agent that is also used in other products such as pharmaceuticals and cosmetics.The interactions between the solute and solvent molecules are explained in terms of the solvation numbers of both aqueous and non-aqueous solutions of D-fructose and D-sorbitol.The viscosity study correlates the viscosity of the solution with solvation;here,density,ultrasonic velocity,and viscosity of aqueous and non-aqueous solutions at various concentrations are measured at different temperatures ranging from 35 to 55℃.These parameters provide sufficient information on the interaction between molecules that may aid chemists in analyzing the mechanisms of the behavior of D-fructose and D-sorbitol in water and the water–ethanol medium through which they are consumed.The Fourier transforms infrared spectra of pure solvent,salt,and their solutions were recorded and analyzed for confirmation.

Coalescence dynamics of two droplets of different viscosities in T-junction microchannel with a funnel-typed expansion chamber

The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).

基于VOF方法的超临界二氧化碳——水两相流动孔隙尺度数值模拟

二氧化碳(CO_(2))捕集与封存技术有利于减少CO_(2)的排放量,近年来针对CO_(2)地质封存形成了从纳米尺度到油气藏尺度的大量研究成果,大多数研究只针对单一维度多孔介质中流动行为开展研究,且物理实验方法受许多不确定性因素影响,十分耗费时间和成本。为了从微观角度深入理解CO_(2)地质封存过程中的渗流行为,提高CO_(2)地质埋存量,基于追踪两相界面动态变化的VOF(Volume of Fluid)方法,分别建立了2D和3D模型,开展了超临界CO_(2)-水两相流动数值模拟研究,对比了不同润湿性、毛细管数、黏度比条件下的CO_(2)团簇分布特征、CO_(2)饱和度变化规律,揭示了孔隙尺度CO_(2)埋存的内在机理。研究结果表明:①随着岩石对CO_(2)润湿性增加,CO_(2)波及范围扩大,同时CO_(2)团簇的卡断频率减少,CO_(2)埋存量增加;②随着毛细管数的增加,驱替模式由毛细指进转变为稳定驱替,CO_(2)埋存量增加;③随着注入超临界CO_(2)黏度逐渐接近水的黏度,两相流体之间的流动阻力降低,促进了“润滑效应”,CO_(2)相的渗流能力提高,CO_(2)埋存量增加;④润湿性、毛细管数、黏度比在不同维度多孔介质模型中对CO_(2)饱和度的影响程度不同。结论认为,基于VOF方法的CO_(2)-水两相渗流模拟研究在孔隙尺度上揭示了CO_(2)地质封存过程中的渗流机理,对CCUS技术的发展有指导意义,也为更大尺度的CO_(2)地质封存研究提供了理论指导和技术支撑。

精梳工艺对涤粘混纺纱质量的影响

为评价精梳工艺在涤粘混纺纱加工过程中的应用效果,分别采用普梳涤粘混纺工艺与精梳涤粘混纺工艺纺制了混纺比为65/35、50/50、35/65的涤粘混纺纱,测试了两种混纺工艺的纤维条与纱线质量。试验结果表明:与普梳涤粘一并条相比,精梳涤粘条的条干CV值略微降低,棉结、杂质粒数以及16.5 mm以下短绒率大幅减小,纤维上四分位长度微量增长;与普梳涤粘纱相比,精梳涤粘纱的条干CV值与3 mm毛羽数明显降低,棉结、粗节、细节大幅减少,断裂强力有所增加;随着粘胶含量的增加,涤粘混纺纤维条与纱线质量呈现恶化的趋势。认为:精梳工艺能显著提高涤粘混纺纤维条与纱线质量。

液滴撞击柔性疏水表面完全反弹的实验研究

采用高速摄影与图像识别技术,研究了不同黏性液滴撞击不同弹性模量的柔性疏水材料(PDMS)表面后的完全反弹过程,获得了液滴黏性和柔性疏水材料弹性模量对液滴发生完全反弹的韦伯数区间和反弹恢复系数的影响规律。结果表明:由于液滴黏性对液滴铺展过程的速度影响及其所导致的黏性能量耗散差异,当液滴黏性增大时,液滴撞击PDMS表面后发生完全反弹的最大/最小韦伯数均增大、反弹恢复系数减小;随着PDMS弹性模量的降低,液滴撞击PDMS表面后发生完全反弹的最大韦伯数增大、最小韦伯数减小,PDMS弹性模量对反弹恢复系数无明显影响。

用台架试验研究CK-4 柴油机油的性能变化

《柴油机油换油指标》:GB/T 7607—2010标准中规定了CH-4及以下规格的柴油机油的换油指标,但对新一代CK-4规格的柴油机油却没有明确的换油指标。用GB/T 7607—2010标准规定的换油指标来指导CK-4柴油机油换油需要探讨。用“国VI”排放柴油发动机台架试验对CK-4柴油机油(CK-410W-40柴油机油)在试验过程中的100℃运动黏度,酸值,碱值,pH值及磨损铁元素含量等进行了监测,对CK-4柴油机油在试验过程中的性能变化进行研究。在发动机台架试验中,当试验进行到相当于80 Mm的行驶里程时,CK-4柴油机油虽然达到了GB/T 7607—2010标准中CH-4柴油机油的换油限值,但摩擦副仍处于正常的磨损状态,润滑性能较好。i-pH值能够更好地反映CK-4柴油机油中清净剂的消耗程度,体现了柴油机油的酸中和能力,可指导油品更换。(图5表2参考文献6)

消光制品用PVC树脂黏数测试方法的探索

分别采用母液法、滤液法和乙醇萃取法测试了消光制品用PVC树脂的黏数,并对乙醇萃取法进行了改进,确定了消光制品用聚氯乙烯树脂黏数的测试方法。

液体粘滞系数测定实验仪创新设计与实现

利用霍尔测速器改造落球法测液体粘滞系数传统实验装置,可实现升球法与落球法随意切换测液体粘滞系数,可测量透明液体与不透明液体粘滞系数,这是传统粘度系数测量实验装置无可比拟的。该实验装置不仅有效克服了传统粘度系数测量实验存在的诸多问题,提高实验测量精确度,拓宽了实验测量范围,而且有助于实践创新人才的培养,加快新工科建设。

大黏度船用燃料油的开发与试生产

某石化公司结合低硫船燃国际市场现状及未来船舶产业发展需求,在成功生产RMG380低硫船用燃料油的基础上,继续开发大黏度的RMG500和RMG700低硫船用燃料油产品。研究表明,酸值相对较低的低硫稠油渣油更适宜作为大黏度低硫船燃的调和重组分,以RMG380为基础原料调和大黏度低硫船燃完全可行。实验室配方优化后,RMG500和RMG700低硫船燃的重组分调和比例较RMG380增加2%~5%(质量分数),调和试制出的低硫船燃产品酸值、残炭等指标略有上升,各项指标满足国家强制执行标准GB 17411—2015《船用燃料油》的技术要求。经该石化公司财务部门估算,大黏度低硫船用燃料油的生产成本与RMG380相比降低了10~21元/t。该石化公司应用实验室技术调和方案,在工业装置上成功试产出了RMG500低硫船用燃料油产品2万余吨,产品使用性能通过某船舶燃料有限责任公司的认证,市场应用前景看好。

湍流大涡数值模拟进展

本文简要陈述湍流大涡数值模拟的原理、优点,着重讨论湍流大涡数值模拟方法的关键问题及其可能解决的途径,包括脉动的过滤、亚格子模型、近壁模型和标量湍流的大涡数值模拟中的特殊问题。文章强调大涡数值模拟中亚格子应力的本质是可解尺度湍流和不可解尺度湍流动量间的输运,并以作者最近提出的新型亚格子模型说明发展亚格子模型的正确途径。文章最后提出湍流大涡数值模拟近期需要迫切解决的问题和其他具有挑战性的方向。

加速度对自然超空泡特性影响的数值仿真研究

利用商业CFD软件对小空泡数下的自然超空泡形态和减阻效果进行了数值仿真研究,通过对软件自定义函数的研究,将边界条件中的来流速度改写为时间的函数并嵌入到软件中,得到了非定常情况下加速度对自然超空泡形态和减阻效果的影响规律。当加速度为正值时,在空泡数相同的条件下空泡的厚度和长度都要比定常条件下的值偏小,而加速度为负值时则刚好相反。模型的粘性阻力系数与加速度没有直接的联系,它主要与超空泡的形态和模型壁面上的含汽率有关。最后将加速度为-100m/s2时的仿真结果与实验结果进行了比较,误差最大不超过35%。

三羟甲基丙烷油酸酯基础油热氧化规律研究

采用恒温箱氧化法,将三羟甲基丙烷油酸酯(TMPTO)基础油分别在不同温度下(95、135、175、250℃)进行连续氧化,测试不同氧化时间下TMPTO的运动黏度和总酸值,获得其热氧化行为与氧化温度和氧化时间的定量关系;运用红外光谱法和差示扫描量热法对TMPTO不同氧化时间下的热氧化产物和性能进行分析,探讨其热氧化规律。结果表明:在一定温度下,随着热氧化时间的延长,TMPTO基础油运动黏度的对数和总酸值呈线性增加关系,热氧化温度越高,线性斜率越大;随着温度的升高,氧化时间的增加,TMPTO基础油的氧化诱导温度降低;FTIR分析表明TMPTO基础油在氧化过程中产生了氢过氧化物以及醇类产物。

微波辐照对发芽小麦理化特性影响的初步研究

在实验室条件下研究了微波辐照对不同品种、不同发芽时间的小麦样品其理化特性的影响。结果表明,随发芽时间延长,小麦及小麦粉的降落数值减小,表征小麦粉糊化及黏度特性的指标(面糊峰值黏度、峰值温度、崩解值、回生值)降低,面团的耐搅拌特性弱化,稳定时间缩短。微波辐照改善发芽小麦品质的作用非常明显,尤其对发芽时间短的小麦样品,可以显著增加其降落数值和峰值黏度,增强面团的搅拌稳定性。研究结果初步证实了微波辐照改善发芽小麦品质的可行性。

玉米秸秆多羟基醇液化研究

研究了玉米秸秆在多羟基醇中的液化反应,结果表明液化剂用量、反应温度、反应时间以及催化剂用量等条件对玉米秸秆液化反应有较大的影响。以聚乙二醇和甘油的混合物为液化剂,在温度为160℃、时间为30 m in、液化剂用量为玉米秸秆质量的4.5倍、浓硫酸用量为液化剂用量的3.25%时,液化率可达到90%,所得到的玉米秸秆液化产物羟值为380 mg/g,黏度为353 mPa.s。同时通过红外光谱分析了玉米秸秆液化的有关机理。

天然气混合气体粘度和雷诺数计算研究

为了探讨天然气混合气体粘度和雷诺数的计算方法,依据具体工程实例,给出了已知组分和平均流量天然气混合气体动力粘度、运动粘度和雷诺数的计算实例。并对粘度计算误差和雷诺数计算中体积流量的取值方法可行性进行了分析。同时给出了用C++Builder程序实现的人机界面。程序运行表明,这套方法的计算结果满足该系统对天然气流动状态及计量误差分析的要求。