地震作用下桥墩动水压力及Morison方程适用性试验研究EI北大核心CSCD

深水桥梁的抗震分析需要考虑地震作用下动水压力的影响。目前,广泛采用的Morison方程由波浪力的计算公式演化而来,用于计算地震动水压力尚缺乏验证;同时,对于地震作用下桥墩动水压力的变化规律缺乏试验研究。该文设计一套水下振动台试验系统,以不同尺寸的桥墩试件为研究对象,采用正弦波为输入激励,通过不同工况的振动台试验,研究桥墩加速度和地震动水压力的分布规律及其随激励幅值、激励频率、截面直径和水深的变化规律;将动水压力的试验结果与Morison方程的计算结果进行对比,以验证地震作用下Morison方程的适用性。结果表明:地震作用下桥墩加速度和动水压力应考虑激励幅值、激励频率、截面直径和水深的影响,Morison方程不适用于计算地震作用下桥墩动水压力,应通过大量的水下振动台试验加以修正。     

地震和波浪联合作用下斜拉桥随机动力分析方法

分别采用Morison方程、辐射波浪理论和绕射波浪理论求解桩基、承台所受动水压力和波浪力,考虑行波效应、空间相干效应和局部场地效应,基于虚拟激励法,建立了多维多点地震和波浪联合作用下斜拉桥随机动力分析方法。采用蒙特卡罗法计算了考虑、不考虑荷载非线性时的结构响应,通过比较计算结果验证了所建立方法的适用性;分析动水压力和波浪力对斜拉桥随机地震响应均方根的影响,研究了斜拉桥随机响应功率谱密度分布趋势和变化规律。结果表明:该方法可以考虑荷载随机性,计算多维多点地震和波浪联合作用下斜拉桥响应;动水压力刚性附加质量是导致斜拉桥水下结构纵向内力增大的原因;动水压力和波浪力对桥塔水下结构地震响应的影响随场地条件改变,地震输入能量分布在高频域时,动水压力和波浪力对桥塔水下结构影响更大。     

基于物理机制的随机地震动场中供水管网抗震功能反应分析

城市供水管网是生命线工程的重要组成部分,由于受到工程场地地震动随机性的影响,其系统结构响应和服务功能也应呈现显著的随机性。传统的埋地管线地震反应分析既不能考虑管网拓扑结构的影响,也难以反映随机地震动的作用,同时,管线的结构响应未能落实到系统的功能性评价之上。为了解决上述三个难题,该文在工程场地地震动随机场物理模型的基础之上,通过引入埋地管网地震反应分析模型,结合概率密度演化方法,实现了具有非线性特性的埋地管网的随机地震反应分析;进而,结合管网流体的瞬变流分析理论,实现了城市供水管网的动态抗震功能反应分析,为供水管网的抗震功能可靠度研究奠定了基础。     

行波效应对深水连续刚构桥地震响应的影响

跨海或库区的大跨度桥梁在地震作用下不仅需要考虑水体与桥墩的动力相互作用,同时由于各桥墩间跨度较大应考虑地震输入的行波效应。该文采用辐射波浪理论求解桥墩地震动水压力,建立了考虑地震动输入空间效应的深水桥梁地震响应分析方法,并考虑行波效应对深水连续刚构桥进行地震响应分析。研究表明:动水压力增大了桥梁结构的地震响应,其影响程度随着输入地震波和墩梁约束条件的不同而有所差异;考虑行波效应时地震动水压力对桥梁结构动力响应的影响较一致激励而言有所差别,同时地震动水压力对桥梁地震响应的影响随着视波速的不同而变化。由此得出结论,为合理评价地震动水压力对深水长大桥梁动力响应的影响应考虑地震动输入的行波效应。     

考虑流体效应的船-桥碰撞数值模拟法研究

有别于传统的不考虑流体对被撞桥墩影响的船-桥碰撞问题,该文在动水压力计算的基础上,建立了考虑流体效应的船-桥碰撞的附加质量计算模型,并与流构耦合计算模型以及不考虑流体影响的计算模型在能量转换、碰撞力、船艏撞深、桥墩位移、应力、截面内力以及计算效率等方面的结果进行了比较分析。结果表明:流体对船艏碰撞力影响较小,但能降低船舶的损毁程度;流构耦合计算模型中的墩顶水平位移响应要略小于附加质量模型和不考虑流体影响时的计算结果;不同计算模型所得桥墩有效应力基本相同且具有相同的分布规律;船-桥碰撞附加质量模型在计及流体与结构相互作用的同时,具有较高的精度和计算效率。     

确定桩承高层结构有效地震动输入的一种改进模型

本文在文献（２）基础上，采用改进的层状半空间动力Ｇｒｅｅｎ函数，并利用自由场地震动三分量反算入射波振幅的技术，提出了一种确定桩承高层结构有效地震动输入的实用计算模型，这一模型考虑了地震波传播及地基土－群桩－上部结构的动力相互作用，由该模型求得的结果可作为上部结构的地震反应分析的输入激励。     

不同场地条件下某新型核电厂房的地震响应试验研究

土-结构相互作用是准确模拟核电厂结构、附着系统和组件地震响应的重要因素。使用振动台多功能叠层剪切土箱模拟土体边界条件,对某新型核电厂房进行1:25缩尺模型地震模拟振动台试验。试验选取10组水平加速度地震动记录,按照运行安全地震动(OBE)0.15g、极限安全地震动(SSE)0.30g和超设计基准地震动(ULE)0.75g作为输入,研究不同地震动强度引起的场地土非线性反应,以及对楼层加速度响应的影响规律;该模型土-结构相互作用振动台试验表明,尽管在基岩场地上,场地仍然对结构的地震效应造成明显的放大作用,在OBE、SSE和ULE工况下,场地动力效应放大倍数分别为3.13、2.1和1.19,由于土体逐渐进入了非线性状态,这种放大作用随着输入地震动强度的增强而变小。因此,建议对基岩场地的条件进行界定,并建议在任何条件下均需要考虑土-结构相互作用的影响,特别是在对核电厂设备、管道抗震设计和地震裕度评估时,不考虑土-结构相互作用将造成评估结果偏小。     

地震动空间相关性对地下连续管线的影响

地下管线地震反应通常用波动理论求解,输入的地震动在空间上是完全相关的。台阵记录分析结果已证实,地震时地面上各点的地震动是部分相关的。地震地面运动的这种性质对地下连续管线的影响还不十分清楚。利用随机振动理论中的虚拟激励法计算了均匀介质中地下连续管线纵向和横向地震响应,给出了局部效应、相干效应对地下连续管线的影响。分析结果表明,忽略地面运动的部分相关性会给出不安全的结果,不同的部分相干模型对地下连续管线的影响不同。因此,实际计算时应考虑地震动的部分相关性,慎重选取部分相干模型。     

考虑水底柔性反射边界的深水桥墩地震动水压力分析

在深水桥墩地震动水压力分析中一般假定水底为完全反射边界,而忽略水底柔性介质对动水压力波的吸收作用。该文考虑水底柔性反射边界,基于辐射波浪理论,建立了深水桥墩地震动水压力的计算公式,深入分析了水底柔性反射边界对动水压力的影响。研究表明:水底柔性反射边界会在特定的荷载激励频率范围内对深水桥墩动水压力产生影响,且动水压力随水底反射系数的减小而减小,深水桥墩地震动水压力分析可以忽略水底柔性边界的影响。从而为长大桥梁地震灾变过程精细化模拟提供了理论依据。     

场地均质性对浅埋地铁车站地下结构地震易损性的影响

场地条件是影响地下结构地震响应的关键因素之一,该文旨在研究场地均质性对于地铁车站地下结构地震易损性的影响。以两层两跨地铁车站为研究对象,基于ABAQUS/Standard软件平台建立了考虑土-结构相互作用的二维有限元分析模型。模型考虑了循环动力荷载作用下土体的非线性与钢筋混凝土的弹塑性力学行为。采用增量动力分析方法分别计算了结构在层层场地条件下与均质场地条件下结构的地震响应,并以层间位移角为损伤指标与地面峰值加速度为地震动强度指标绘制了地铁车站结构的地震易损性曲线。结果表明,层层场地条件下结构的响应均值要显著高于均质场地,但两者标准差一致。在地震动作用下,结构处于层层场地下的破坏概率要明显高于均质场地,这主要归因于层层场地中毗邻结构的土体产生了较大的剪切变形。上述结论可为地下结构基于性能的抗震设计提供科学参考。     

Analytical Model for Pipe Wall Friction of Pseudo-Homogenous Sand Slurries

In pseudo-homogenous pipeline flow of sand-water mixtures the measured hydraulic resistance is higher than for the flow of water, but is less than for a liquid having the same density as the mixture but a viscosity equal to that of water. A new analytical model is devised for pipe wall friction in which there is a watery viscous sublayer along the pipe wall. It is assumed that the presence of solids does not affect the viscous properties of the mixture, and that grain-stresses are negligible. A satisfying result is obtained in a particle range of 0.1 to 2 mm median grain diameter and volumetric concentrations up to about 30%. It is found that the model describes a lower bound for hydraulic resistance. The theoretical concept can be used as a basis for further developments into the heterogeneous regime, where additional physical processes come into play.     

PREDICTION OF VERTICAL LIQUID SOLID PIPE FLOW USING MEASURED CONCENTRATION DISTRIBUTION

The performance of a standard (k-L) turbulence model for predicting slurry pipeline pressure gradients is examined using experimental measurements of velocity and solids concentration distribution for upward vertical flows. Assuming the solids concentration rises abruptly from a value of zero at the pipe wall over a distance corresponding to one half a particle diameter, satisfactory predictions were obtained for sand particles of median diameter up to about 800 um in a 25.8 mm vertical pipeline. No damping of fluid turbulence or additional stresses due to particle-particle interactions were included in the computational model. Velocity distributions are found to be flatter than those of turbulent single-phase flows, because of the variation of mixture properties in the vicinity of the pipe wall.     

PREDICTION OF VERTICAL LIQUID SOLID PIPE FLOW USING MEASURED CONCENTRATION DISTRIBUTION

ABSTRACT

The performance of a standard (k-L) turbulence model for predicting slurry pipeline pressure gradients is examined using experimental measurements of velocity and solids concentration distribution for upward vertical flows. Assuming the solids concentration rises abruptly from a value of zero at the pipe wall over a distance corresponding to one half a particle diameter, satisfactory predictions were obtained for sand particles of median diameter up to about 800 um in a 25.8 mm vertical pipeline. No damping of fluid turbulence or additional stresses due to particle-particle interactions were included in the computational model. Velocity distributions are found to be flatter than those of turbulent single-phase flows, because of the variation of mixture properties in the vicinity of the pipe wall.     

液氧煤油火箭发动机排放预冷数值仿真

针对预冷过程中输送系统和发动机流道内沸腾传热和两相流动过程,建立一维二流体模型。以某液氧煤油发动机为原型,对不同气枕压力、排放管径和空中排放时间条件下排放预冷过程进行仿真,分析进出口温度以及流量特性的变化情况,结果表明增大排放管径和排放压力均可以增强预冷效果,而空中排放预冷时达到同样预冷效果所需的推进剂量则与管径大小无关,并且预冷效果受到地面状态的影响。     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

ABSTRACT

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-? turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

Thermal elasto-plastic computation model for a buried oil pipeline in frozen ground

The 813-mm-diameter China-Russia Crude Oil Pipeline enters northeastern China at Lianyin, Mo'he County, Heilongjiang Province and crosses 441 km of warm discontinuous, sporadic and isolated patches of permafrost and 512 km of seasonally frozen ground before reaching Daqing, China. It is inevitable that the buried pipeline is subject to frost heave and/or thaw settlement when it passes through regions of permafrost and seasonally frozen ground with available moisture. Therefore, stress and deformation analyses of the pipe subject to frost action or thaw settlement are important for the safety, long-term stability and economic feasibility of the buried oil pipeline system. Based on the (empirical) frost heave and/or thaw settlement coefficients, a simple thermal elasto-plastic finite element computation model is put forward for analyzing the stress and strain state of the pipe. The influences of soil temperatures on the soil deformation were considered, but those of the soil deformation on the soil temperatures were ignored in the modelling. Finally, two examples of the application of the computation model are presented, in which the stress and deformation of a pipe exposed to frost heave or thaw settlement is calculated. The results of the frost action computation show that the effective stress on the pipe increases linearly with the frost heave deformation. The largest pipe deformations and stresses may occur when crossing frost mounds due to differential frost heaving. The stress and deformation smooth out from the frost mound. The results of thaw settlement computation show that the pipe stress changes greatly near the interface of thaw settlement zone and no thaw settlement zone, and the thaw settlement has small effect on the stability of oil-pipeline. The computation results show that the oil pipeline design in the permafrost regions should pay more attention on frost heave hazard than thaw settlement hazard.     

Discharge of condensed sulfur dioxide: A field test study of the source behaviour with different release geometries

The physical factors determining the mass flow rate, early dilution and the tendency to form ground deposits were studied by discharging condensed sulfur dioxide from a pressure vessel through a hole and a pipe, respectively. The results indicate that ground deposits do not easily arise and that the liquid phase evaporates very quickly. In the pipe releases, the mass flow rate was strongly dependent on the thermodynamic state in the vessel. Even a moderate excess pressure (compared to the saturation pressure) in the vessel increased the mass flow rate markedly. A theoretical model for two-phase release through ducts which agrees well with the pipe tests is also presented. In the aperture releases two-phase phenomena did not affect the mass flow rate and thus the Bernoulli formula for incompressible outflow was valid. Substantial extra air entrainment occurred near the exhaust opening because of the radial momentum produced by a vigorous flash.     

The urban unsteady and non pressure rain pipe flow routing by the dynamical wave method

The dynamical-wave method routing model of the unsteady and non-pressure rain pipe flow was be established by conservation of mass, momentum and energy in the city unsteady and non-pressure rain pipe flow, and it was resoled by applying the four concealing style differences and the pursue method. Results by experiment checking computations and comparative analysis state that this routing model can reflect flood peak propagate in pipeline attenuate and backwater etc. influence, has the higher calculation precision, possess vast sphere of application, and can adapts to performing the city rain pipe flow routing in t the distinct situation of the different incline degrees and enter runoff . This routing model supplies the scientific foundation to the Town rainfall piping design or checking, administration, and so on.     

Stress State of Bent Buried Pipelines

The authors consider edge effects in buried pipelines that occur in the region of joining of a straight buried pipe and a bent insert (factory bend, elbow, or an elastically bent segment). The action of those effects results in the appearance of additional bending moments, which are proportional to the difference between the axial force in an infinite straight pipeline and that in a closed-end pipe, and depend on the geometrical parameters of the pipeline and physical-mechanical characteristics of the soil. Specific examples of analysis of elastic interaction of a pipeline with the soil for pipe bends with various radii of the bend arc are offered. It is shown that additional bending stresses may exceed appreciably the stresses from the axial force, and therefore, they should be taken into account when designing and building pipelines. The solution for an elastically bent segment has been obtained and analyzed.