Nonlinear dynamics of imperfectly-supported pipes conveying fluid

In this paper, the nonlinear dynamics of a pipe imperfectly supported at the upstream end and free at the other and conveying fluid is investigated. The imperfect support is modelled via cubic translational and rotational springs. The equation of motion is obtained via Hamilton’s principle for an open system, and the Galerkin method is used for discretizing the resulting partial differential equation. The dynamics of a system with either strong rotational or strong translational stiffness is examined in details. Numerical results show that similarly to a cantilevered pipe, the system undergoes a supercritical Hopf bifurcation leading to period-1 limit cycle oscillations. The Hopf bifurcation may, however, occur at a much lower flow velocity compared to the perfect system. At higher flow velocities, quasi-periodic and chaotic-like motions may be observed. The amplitude of transverse displacement is generally much higher than that for a cantilevered pipe, mainly due to large-amplitude rigid-body motion. In addition, effects of the mass ratio, internal dissipation, hardening- or softening-type nonlinearity, as well as concentrated- or distributed-type nonlinearity on the dynamics of the system are examined.     

Numerical approach for generic three-phase flow based on cut-cell and ghost fluid methods

In this paper, we introduce numerical methods that can simulate complex multiphase flows. The finite volume method, applying Cartesian cut-cell is used in the computational domain, containing fluid and solid, to conserve mass and momentum. With this method, flows in and around any geometry can be simulated without complex and time consuming meshing. For the fluid region, which involves liquid and gas, the ghost fluid method is employed to handle the stiffness of the interface discontinuity problem. The interaction between each phase is treated simply by wall function models or jump conditions of pressure, velocity and shear stress at the interface. The sharp interface method “coupled level set (LS) and volume of fluid (VOF)” is used to represent the interface between the two fluid phases. This approach will combine some advantages of both interface tracking/capturing methods, such as the excellent mass conservation from the VOF method and good accuracy of interface normal computation from the LS function. The first coupled LS and VOF will be generated to reconstruct the interface between solid and the other materials. The second will represent the interface between liquid and gas.     

DISCUSSION ON THE APPLICATION OF NUMERICAL EXPERIMENT IN EXPERIMENTAL TEACHING OF FLUID MECHANICS

为强化学生对流体力学课程理论知识及实验教学环节的掌握,本文针对传统实验教学过程中受限于硬件设施、模型等问题,将数值模拟技术与流体力学实验教学相结合。以伯努利实验为例,应用数值模拟软件进行物理建模、网格划分、变参数数值模拟等实验内容,通过压力云图、流线等模拟结果对能量转换特性进行了分析,增强了学生对流体力学理论知识及相关参数的物理意义、变化特征等的理解,使学生在实验中产生强烈的“参与感”,有效地提高了教学水平和教学质量。     

有水平流时双流体混合物对流的时空演变

在水平流动作用下混合流体(比如水和酒精)的Rayleigh-Benard对流,由于外部强制力和内在行波传播的耦合,构成了研究开流系统中斑图选择和非线性耗散波的理想模型系统,本文介绍对该系统初步的研究成果.首先简述了线性稳定性分析以及水平流对行波非线性分岔特性的影响,然后主要给出我们对这一系统在有限空间非周期边界条件下一维行波对流的研究成果,包括存在的时空形态及其特性对Rayleigh数和槽道长度的依赖关系,最后给出了进一步工作的展望.      

TiB2增强Al2O3陶瓷刀具高速干切削摩擦磨损性能

采用TiB2增强Al2O3陶瓷刀具对淬硬钢进行高速干切削试验,利用切削高温作用下的摩擦化学反应,在刀具表面原位生成具有润滑作用的反应膜,从而实现Al2O3/TiB2陶瓷刀具的自润滑.结果表明:低速干切削时,Al2O3/TiB2陶瓷刀具的磨损机制主要表现为粘着磨损和磨料磨损;而在高速干切削时,刀具的磨损机制主要表现为氧化磨损,刀具表面经由氧化反应生成具有润滑作用的反应膜而起到固体润滑作用,从而使刀具的耐磨性能提高,随着TiB2含量和切削速度的增加,反应膜的减摩抗磨作用增强;而在切削区通入氮气时,由于刀具表面氧化膜形成受阻,刀具的抗磨能力有所降低.     

聚晶立方氮化硼刀具切削高锰钢的磨损机制

在半精加工试验条件(切削深度ap=0．5mm，进给量f=0．3mm／r，干切)下研究了聚晶立方氮化硼刀具切削奥氏体高锰钢时的磨损机制，用WDH-Ⅱ型光电温度计测量了切削温度，用工具显微镜测量后刀面磨损量，进而考察了切削时间和切削速度对后刀面磨损量的影响，采用S-250MK型扫描电子显微镜观察刀具前、后刀面的磨损形貌和组成变化．结果表明：当切削温度为400～750℃时，聚晶立方氮化硼刀具同高锰钢中的γ相及其析出相(Fe，Mn)3C之间产生严重的机械磨损；当切削温度超过800℃时，聚晶立方氮化硼刀具同高锰钢单一γ相之间产生扩散磨损；聚晶立方氮化硼刀具适合于高速切削.     

Regulation of Cytokines and Dihydrotestosterone Production in Human Hair Follicle Papilla Cells by Supercritical Extraction-Residues Extract of Ulmus davidiana

This study was conducted to examine the anti-hair loss mechanism of the supercritical fluid extraction-residues extract of Ulmus davidiana by the regulation of cytokine production and hormone function in human dermal follicle papilla cells (HDFPCs). To investigate the modulatory effects on H₂O₂-induced cytokines, we measured transforming growth factor-beta and insulin-like growth factor 1 secreted from HDFPCs. To investigate the regulatory effects of supercritical extraction-residues extract of Ulmus davidiana on dihydrotestosterone hormone production, cells were co-incubated with high concentrations of testosterone. The supercritical extraction-residues extract of Ulmus davidiana significantly inhibited the secretion of transforming growth factor-beta but rescued insulin-like growth factor 1 in a dose-dependent manner. The supercritical extraction-residues extract of Ulmus davidiana markedly reduced dihydrotestosterone production. These results suggest that the supercritical fluid extract residues of Ulmus davidiana and their functional molecules are candidates for preventing human hair loss.     

Experimental study of heat transfer characteristics in oscillating fluid flow in tube

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger under different frequencies, tidal displacement, and heat fluxes is carried out. The effect of different parameters on experimental effective thermal conductivity and convective heat transfer coefficient in cooling region is studied using correlations given by different researchers. A correlation for experimental effective thermal conductivity in terms of S²√ω is derived based on experimental data. This correlation is useful for predicting the optimum value of S²√ω before onset of turbulence.