轻微弯曲输流管道的非线性强迫振动特性

为了掌握轻微弯曲输流管道在外激励下的非线性振动特性,基于哈密顿原理建立了轻微弯曲输流管道的非线性振动方程,并使用伽辽金截断法将振动方程离散为非线性常微分方程组。利用增量谐波平衡法求解系统的非线性动力学响应,并使用Floquet理论研究系统响应的稳定性和分岔行为。研究结果表明,轻微弯曲输流管道在一些参数下同时具有软弹簧特性和硬弹簧特性。分析系统参数对响应的影响表明,随着管道弯曲程度增加,系统的响应特性由硬弹簧特性转变为软弹簧特性。可见,管道的初始弯曲是影响输流管道系统振动特性的重要因素,因此在输流管道的设计中必须考虑管道弯曲构型的影响。

基于多角度弯曲高压输流管道流固耦合分析

弯曲高压输流管道在工程实践中应用广泛,为分析其输流特性,通过构建动力学模型,应用SolidWorks软件建立定圆角多弯曲角度管道有限元模型,ANSYS的Workbench平台搭建Fluent模块和瞬态结构模块进行流固耦合,创建数据传输进行模态分析,进而研究高压流体流入管道后在弯道处对管壁的冲击力大小、应力、应变的数值变化。结果表明,不同角度输流管道对管壁的影响不同,从而为工程实践合理规避管道压力的危害提供理论参考。

渠底超高法和弯曲导流板法在凤凰水库溢洪道的应用

综合利用了渠底超高法和弯曲导流板法对凤凰水库弯段陡槽的设计,较好地解决了大底坡急流弯道流态的控制问题,可有效地消减冲击波、减小横向水面差、改善弯道水流流态,消能效果明显。实例表明,该设计方法是一种十分有效的工程措施。

让自来水弯曲流下

把水龙头拧开一点,水会缓缓地垂直流下。如果拿一枝圆珠笔或一把塑料梳子,在羊毛衫或毛料布上用力摩擦使它带电。

纳米石墨烯改性沥青流变性能研究

在国内外研究现状的基础上,通过布氏粘度、动态剪切流变试验(DSR)和低温弯曲梁流变试验(BBR)研究了纳米石墨烯改性沥青的流变性能,试验结果表明:石墨烯能够明显增加沥青的粘度,改善沥青的高温抗永久变形能力,但对低温性能会产生不利影响。

钢圆筒结构渗流分析方法研究

钢圆筒结构在国内外港口、跨海桥梁等工程中应用,但对钢圆筒结构渗流分析的方法依然不多.钢圆筒结构渗流分为缝隙渗流与接头渗漏,为解决钢圆筒结构缝隙渗流中局部流线弯曲引起的水头损失增加的计算,引入附加阻力概念,将增加的水头损失用弱透水层进行等效,即可在平面应变条件下进行计算;接头渗漏区域引入附加阻力概念进行等效计算,发现缝隙尺寸的大小对弱透水层渗透系数的影响不大,当缝隙尺寸增大400倍时,等效渗透系数仅增加1.6倍,渗流计算中可认为接头缝隙不透水.采用该等效方法利用水平面二维有限元程序对港珠澳大桥西人工岛钢圆筒结构进行渗流分析,通过与三维数值计算进行对比,计算结果相近.

采用波动法研究有限板振动功率流

对有限尺寸十字型多板耦合结构建立波动法耦合运动模型,通过弯曲波和面内波波幅系数矩阵的组合与离散,得到板在线连接处的耦合运动方程的一般形式,对比波动法的半解析结果与有限元数值结果,验证自编波动法MATLAB程序的收敛性和准确性。探讨板连接角和激励角等参数对弯曲波功率流和面内波功率流的影响。频率较低阶段,弯曲波功率流明显大于面内波功率流,面内振动功率流可以忽略,随着频率的增加,面内波功率流增大,可能与弯曲波数量级一致。在全频域范围内,激励板的弯曲振动功率流均随激励角度的增大而增大,而接受板面内波功率流是连接处的波形转化和直接激励力的相反作用的结果。板连接角在90°附近时,接受板功率流较大,振动衰减明显。

摆线推进器任意方向角的水动力计算方法研究

本文提供了一个能够在任意方向角状态下计算摆线推进器水动力性能的方法。该方法是以朱典明和谷口中所用方法为基础,用“弯曲流管”代替“单向流管”,将摆线推进器抽象为斜向作用盘,在斜向作用盘的作用下,产生斜向诱导速度,使水流方向发生改变。通过这样一个模型建立水动力方程,并在相互垂直的两个方向应用动量定理,得到诱导速度计算公式,然后,通过数值迭代求解,计算出摆线推进器在任意方向角状态下的水动力特性。应用本文方法对NSRDC摆线推进器在进速系数J>0,方向角β=-90°^+90°范围内进行了计算,其计算结果与实验结果吻合比较好。

基于温度应力的温拌沥青胶结料低温力学性能

为准确评估Sasobit温拌产品对沥青胶结料低温力学性能的影响,同时考虑温拌沥青胶结料在降温过程中所产生的累积和松弛作用,基于小梁弯曲流变(BBR)试验计算获得了温拌沥青胶结料的温度应力,运用Huet模型进行参数拟合并采用统计学方法对温拌产品的影响效果作了进一步分析.结果表明:2%及以上Sasobit温拌产品的加入使得沥青材质变硬,致使温拌沥青胶结料出现更高的低温PG分级、更大的温度应力和更高的临界开裂温度;Huet模型的参数分析和统计学方法分析进一步证实了此硬化影响的存在.

The Correlation between Density and Low-Temperature Creep Property of Asphalt

The density of asphalt was measured with the pycnometer and densitometer. Creep properties of the asphalt were investigated with the bending beam rheometer at temperatures ranging from 0 ~C to -36 ~C. The asphalt density data used to correlate with the creep properties were calculated from the regression equation of density and temperature. The asphalt sample used to determine the creep property was aged by the standard RTFOT test and the PAV test. The test results showed that the asphalt density had a linear relationship with temperature changes. The logarithm of the creep stiffness and the slope of the logarithm of the stiffness at 60 seconds all demonstrated a linear relationship with the density, and the regression coefficient of these data was around 0.99. The creep stiffness and the slope of the creep stiffness can be calculated from the asphalt density at the same temperature.

Influence of deflection angles on flow behaviours in openchannel bends

The deflection angle of a river bend plays an important role on behaviours of the flow within it, and a clear understanding of the angle's influence is significant in both theoretical study and engineering application. This paper presents a systematic numerical investigation on effects of deflection angles(30°, 60°, 90°, 120°, 150°, and 180°) on flow phenomena and their evolution in open-channel bends using a Re-Normalization Group(RNG) κ-ε model and a volume of fluid(VOF) method. The numerical results indicate that the deflection angle is a key factor for flows in bends. It is shown that the maximum transverse slope of water surface occurs at the middle cross section of a bend, and it increases with the deflection angle. Besides a major vortex, or, the primary circulation cell near the channel bottom, a secondary vortex, or, an outer bank cell, may also appear above the former and near the outer bank when the deflection angle is sufficiently large, and it will gradually migrate towards the inner bank and evolve into an inner bank cell. The strength of the secondary circulations increases with the deflection angle. The simulation demonstrates that there is alow-stress zone on the bed near the outer bank and a high-stress zone on the bed near the inner bank, and both of them increase in size with the deflection angle. The maximum of shear stress on the inner bank increases nonlinearly with the angle, and its maximums on the outer bank and on the bed take place when the deflection angle becomes 120°.

Stress Analysis of Top Tensioned Riser Under Random Waves and Vessel Motions

The bending stresses of top tensioned riser(TTR) under combined excitations of currents,random waves and vessel motions are presented in this paper,and the effect of the internal flowing fluid on the riser stresses is also considered.The computation programs which are used to solve the differential equations in the time domain are compiled and the principal factors of concern including the angular movements at the upper and lower ends of the riser,lateral displacements and bending stresses are presented.Then the effects of current velocity,random wave,top tension,vessel mean offset,low frequency motion and internal flow velocity on the bending stresses of the riser are analyzed in detail.

Experimental study on pressure fluctuation characteristics of slug flow in horizontal curved tubes

In order to study the pressure characteristics of slug flow in horizontal curved tubes,two kinds of curved tubes with central angle 45° and 90° respectively are studied,of which are with 0. 5m circumference and 26 mm inner diameter are used. When the superficial liquid velocity or the superficial gas velocity is constant,the pressure fluctuations and the probability distribution of the average velocity of slug flow are clear for all of the five experimental conditions. The results of experiment show that the pressure characteristics of slug flow in curved tubes have periodic fluctuations. With the rise of central angle,the period of pressure fluctuation is more obvious. The system pressure of the slug flow increases with the increasing of superficial liquid/gas velocity. Meanwhile,the probability distribution of pressure signal shows regularity,such as unimodal,bimodal or multimodal.

Effects of bubbly flow on bending moment acting on the shaft of a gas sparged vessel stirred by a Rushton turbine

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine,as one of the results of fluid and structure interactions in stirred vessels,was measured using a moment sensor equipped with digital telemetry.An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment,which indicates the elasticity nature of shaft material against bending deformation,follows the Weibull distribution.The trends of amplitude mean,standard deviation and peak deviation characteristics manifest an "S" shape versus gas flow.The "S" trend of the relative mean bending moment over gas flow rate,depending on the flow regime in gas-liquid stirred vessels,resulted from the competition among the nonuniformity of bubbly flow around the impeller,the formation of gas cavities behind the blades,and the gas direct impact on the impeller when gas is introduced.A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident.The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.

Effects of Moisture on Rheological Properties of PAV Aged Asphalt Binders

For the most coastal areas where the air is very humid,study on the effect of humidity on the performance of asphalt has its practical significance.However,limited research has been done to investigate the effect of humidity on rheological properties of asphalt.In this study,asphalt binders were aged in the pressure aging vessel(PAV)under different conditions of moisture and aging time.Then Dynamic Shear Rheometer(DSR)and Bending Beam Rheometer(BBR)measurements were conducted to obtain the parameters relating to the complex modulus,phase angle,failure temperature,and creep stiffness.It was found that the low temperature performance decreased as evidenced by the results of the creep stiffness.While there were no significant differences among conditioned binders based on complex modulus G*and phase angleδ,it was found that theδvalue increased when the humidity increased from 0% to 80% ,and then theδvalue decreased when the humidity increased to 100% .In addition,the results of the failure temperature indicated that the humidity of 80% would be a critical point for the high temperature performance of the asphalt binders.

CFD study of turbulent jet impingement on curved surface

The heat transfer and flow characteristics of air jet impingement on a curved surface are investigated with computational fluid dynamics(CFD)approach.The first applied model is a one-equation SGS model for large eddy simulation(LES)and the second one is the SST-SAS hybrid RANS-LES.These models are utilized to study the flow physics in impinging process on a curved surface for different jet-to-surface(h/B)distances at two Reynolds numbers namely,2960 and 4740 based on the jet exit velocity(U_e)and the hydraulic diameter(2B).The predictions are compared with the experimental data in the literature and also the results from RANS k-εmodel.Comparisons show that both models can produce relatively good results.However,one-equation model(OEM)produced more accurate results especially at impingement region at lower jet-to-surface distances.In terms of heat transfer,the OEM also predicted better at different jet-to-surface spacings.It is also observed that both models show similar performance at higher h/B ratios.

Effects of stator bending on pressure field and loss of transonic turbine stage

To study effects of the upstream flow field changing on the downstream flow field of transonic turbine, different three-dimensional bowed blades, which are the stator blades of transonic turbine stage, were designed in this paper. And then numerical calculations were carried out. The effects on downstream flow field were studied and analyzed in detail. Results show that, at the middle of stator blades, although the increasing Maeh number causes the increase of shock-wave strength and friction, the middle flow field of downstream rotors is improved obviously. It is an important change in transonic condition. This causes the loss of the rotor＇ s middle part decreased greatly. Correspondingly, efficiency of the whole transonic stage can be increased.

Combined effects of local curvature and elasticity of an isothermal wall for jet impingement cooling under magnetic field effects

The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.

Characteristics of gas explosion flow fields in complex pipelines

The explosion flow field in five straight pipes with different diameters and one bending pipe selected from a domestic coal mine are studied by the method of numerical simulation. And the results show that,both in the straight and bending pipes, the pressure wave and velocity wave are accelerated by the rising of reaction rate. As the explosion progressed, with the temperature reaching approximately 3000 K, only one pressure wave and one reaction rate wave were observed, while several velocity waves were found.The larger diameter presented the highest relative pressure as well as the largest velocity increase and subsequent decrease inside the tube. The bent pipes caused both turbulence and kinetic energy to increase, resulting in the acceleration of the reaction rate. The burning time was 7.4% shorter than the burning time observed for the straight pipe. Based on these results, designing one explosion resistance device, and in the practical engineering applications, it was to be proved to meet the security requirements fully.

长江城陵矶——湖口河段历史演变

长江自城陵矶至湖口全长480多公里,地跨湖南、湖北、江西三省。它与荆江一起同属长江中游河段,但在河流形态上却迥然不同:荆江特别是下荆江属蜿蜒性河型;城陵矶至湖口段则属于分汊性河型。这种河型上的差异,是由它们所处地段的地质地貌条件不同决定的。它们在历史时期的演变模式也有重大区别。(形势图)