Oscillatory Dynamics of a Spherical Solid in a Liquid in an Axisymmetric Variable Cross Section Channel

The dynamics of a solid spherical body in an oscillating liquid flow in a vertical axisymmetric channel of variable cross section is experimentally studied.It is shown that the oscillating liquid leads to the generation of intense averaged flows in each of the channel segments.The intensity and direction of these flows depend on the dimensionless oscillating frequency.In the region of studied frequencies,the dynamics of the considered body is examined when the primary vortices emerging in the flow occupy the whole region in each segment.For a fixed frequency,an increase in the oscillation amplitude leads to a phase-inclusion holding effect,i.e.,the body occupies a quasi-stationary position in one of the cells of the vertical channel,while oscillating around its average position.It is also shown that the oscillating motion of a liquid column generates an averaged force acting on the body,the magnitude of which depends on the properties of the body and its position in the channel.The quasi-stationary position is determined by the relative density and size of the body,as well as the dimensionless frequency.The behavior of the body as a function of the amplitude and frequency of fluid oscillation and relative size is discussed in detail.Such findings may be used in the future to control the position of a phase inclusion and/or to strengthen mass transfer effects in a channel of variable cross section by means of fluid oscillations.

The Optimal Cross-section Design of the “Trapezoid-V” Shaped Drainage Canal of Viscous Debris Flow

Debris flow drainage canal is one of the most widely used engineering measures to prevent and manage debris flow hazards.The shape and the sizes of the cross-section are important parameters when design debris flow drainage canal.Therefore,how to design the appropriate shape and sizes of the cross-section so that the drainage canal can have the optimal drainage capacity is very important and few researched at home and abroad.This study was conducted to analyze the hydraulic condition of a Trapezoid-V shaped drainage canal and optimize its cross-section.By assuming characteristic sizes of the cross-section,the paper deduced the configuration parameter of the cross-section of a Trapezoid-V shaped debris flow drainage canal.By theory analysis,it indicates that the optimal configuration parameter is only related to the side slope coefficient and the bottom transverse slope coefficient.For this study,the Heishui Gully,a first-order tributary of the lower Jinsha River,was used as an example to design the optimal cross-section of the drainage canal of debris flow.

Elastic scattering and total reaction cross sections of^(6)Li examined via a microscopic continuum discretized coupled-channels model

We present a systematic study of 6Li elastic scattering and total reaction cross sections at incident energies around the Coulomb barrier within the continuum discretized coupled-channels(CDCC)framework,where 6Li is treated in anα+d two-body model.Collisions with 27Al,64Zn,138Ba,and 208Pa are analyzed.The microscopic optical potentials(MOP)based on Skyrme nucleon-nucleon interaction forαand d are adopted in CDCC calculations and satisfactory agreement with the experimental data is obtained without any adjustment on MOPs.For comparison,αand d global phenomenological optical potentials(GOP)are also used in CDCC analysis and a reduction of no less than 50%on the surface imaginary part of deuteron GOP is required for describing the data.In all cases,the 6Li breakup effect is significant and provides repulsive correction to the folding model potential.The reduction on the surface imaginary part of GOP of deuteron reveals a strong suppression of the reaction probability of deuteron as a component of 6Li when compared with that of a free deuteron.Further investigation is performed by considering the d breakup process equivalently within the dynamic polarization potential approach,and the results show that d behaves in a manner similar to a tightly bound nucleus in 6Li induced reactions.

Calculations of state-selective differential cross sections for charge transfer in collisions between O^(3+) and H_2

The non-dissociative charge-transfer processes in collisions between O^3＋ and H2 are investigated by using the quantum-mechanical molecular-orbital coupled-channel （QMOCC） method. The adiabatic potentials and radial coupling matrix elements utilized in the QMOCC calculations are obtained with the spin-coupled valence-bond approach. Electronic and vibrational state-selective differential cross sections are presented for projectile energies of 0.1, 1.0 and 10.0eV/u in the H2 orientation angles of 45° and 89°. The electronic and the vibrational state-selective differential cross sections show similar behaviours： they decrease as the scattering angle increases, and beyond a specific angle the oscillating structures appear. Moreover, it is also found that the vibrational state-selective differential cross sections are strongly orientation-dependent, which provides a possibility to determine the orientations of molecule H2 by identifying the vibrational state-selective differential scattering processes.

3003Al-H14薄壁微小通道扁管波形冲压成形尺寸对截面变形的作用规律

薄壁微小通道波形扁管是建设新能源汽车锂电池组恒温系统的绝佳材料,成形尺寸是影响其冲压成形截面变形的关键因素。建立了实验验证的3003Al-H14微小通道薄壁扁管的波形冲压-回弹有限元模型。基于所建模型,研究了截面高度、管坯壁厚、内外面相对弯曲半径缩放系数等成形尺寸,对截面变形率和平均截面变形率的作用规律。研究发现:①横截面上边缘孔的截面变形率通常较大,其余孔的截面变形率相对较小且大小一致;纵截面上孔的截面变形率呈现波峰波谷高、中间段低的分布特点。②扁管的截面变形率随着截面高度增大而增大,当截面高度超过4 mm时,扁管内的筋显著弯折,横截面塌陷严重。③扁管的平均截面变形率随着壁厚增大呈指数函数下降;当壁厚等于0.1 mm时,所有截面都畸变严重,而当壁厚超过0.3 mm时,最大截面畸变率下降至24.71%。④内外面相对弯曲半径的缩放系数越大,则内外面的实际弯曲程度越小,平均截面变形率也越小。研究成果对薄壁微小通道波形扁管的精确成形具有科学意义和工程价值。

持续冲刷期内黄河下游河床演变特点分析

基于2006年10月至2018年11月黄河下游12个典型断面观测数据,通过分析断面主槽平滩形态特征参数变化率及深泓线和主槽中心线的摆动强度,探讨了持续冲刷期内下游河床的调整变化过程及特点。结果表明:黄河下游断面形态调整表现出既有横向展宽又有冲深下切或淤高态势;河床平面摆动促进了断面主槽形态调整,河相系数变化率与深泓线和主槽中心线摆动强度均成正相关关系;来水来沙条件是主槽形态改变的主要驱动力,且可引起局部河段深泓线摆动强度增大。通过调整小浪底水库的运行模式及布设控导工程可进一步塑造并维持稳定的黄河下游中水河槽。

爆炸冲击波在变截面通道中传播规律数值研究

为研究在变截面通道内爆炸冲击波的传播规律,利用LS-DYNA软件对变截面通道内部TNT爆炸进行数值模拟,在LS-DYNA中分析了不同截面变化中冲击波传播云图以及不同测点处超压时程曲线,研究了截面大小变化率和截面长度变化率对爆炸冲击波在变截面通道内传播的影响。结果表明:截面由小变大时,随着截面面积增大,消波率先迅速减小后略微增大再减小,整体上截面面积越大,消波效果越好;截面由大变小时,爆炸冲击波在刚进入截面缩小段,一部分直接以平面波的形式进入缩小段,一部分与截面变化处壁面发生碰撞反射,反射使得该部分爆炸冲击波超压变大并向反方向传播,当小截面缩小至原来一半时,出口处测得爆炸冲击波相当于原来2倍药量在直通道中爆炸的冲击波;同时得到了冲击波超压峰值在不同工况下沿变截面直通道内传播的拟合方程,可为研究新型消波系统提供理论依据。

溃坝洪水演进一维水动力模型

中国是受洪水灾害影响最严重的国家之一。洪水数值模型可准确地反映洪水的演进与致灾过程。本研究针对天然河道洪水过程存在的尺度大、水流流态复杂、河道断面形式多变以及计算建模困难等问题,提出一套基于Godunov格式的有限体积法离散圣维南方程组的一维水动力模型,并采用求解复杂断面水力要素之间关系的方法,提高了一维水动力模型求解的精度与效率,精确地反映了复杂断面河道的水流运动特性。将模型模拟得到的数值解与算例中的解析解或实测数据进行对比,结果表明:(1)构建的一维水动力模型模拟结果与理想算例解析解及实验实测数据吻合程度均较高,所有算例的E NS均大于0.5,说明模型具有良好的稳定性和适应性;(2)将模型应用至金沙江白格堰塞湖溃坝洪水算例中,模拟得到的流量峰值及整体洪水过程均与实测过程吻合较好,在叶巴滩和苏洼龙两个测点处E NS分别为0.633和0.812,证明了模型在实际应用中的适用性与可靠性。结果表明,开发的一维水动力模型对溃坝洪水等水流流态复杂、突发性强的洪水过程具有良好的模拟效果。本研究可为河道及溃坝洪水风险的初步、快速评估等工作提供有效的模拟支撑。

低频脉冲磁场慢性暴露对健康成年股四头肌收缩力及形态的影响

背景:目前已有关于低频脉冲磁场对骨骼肌结构形态影响研究发现了骨骼肌质量变化,但对接受慢性暴露后的形态变化未见相关研究。目的:观察低频脉冲磁场慢性暴露对腿部股四头肌最大自主收缩力与形态指标的影响,为使用该技术作为肌肉功能改善策略提供组织形态变化的参考依据。方法:招募普通健康受试者70名,随机分为接受磁场刺激的试验组与进行假治疗的对照组,每组35名,试验时长共计4周,试验组受试者每隔48 h进行1次15 min的低频脉冲磁刺激干预,对照组进行假治疗,干预间隔与时长与试验组一致,干预4周后观察不同组别受试者股四头肌最大自主收缩力值变化,利用B型超声影像作为评估手段,观察肌肉厚度、肌肉横截面积及羽状角指标的变化。结果与结论:①经过4周的低频脉冲磁场慢性暴露,68名受试者完成试验,试验组受试者股四头肌最大自主收缩力测试值显著增长(P=0.000),提升幅度显著高于对照组(P=0.008);②试验组受试者的肌肉形态3项指标均显著高于试验前测(P=0.000),而对照组肌肉厚度指标呈显著性下降(P=0.020),羽状角无显著性变化,横截面积显著性提升(P=0.000);③组间对比发现,试验组关于肌肉形态的肌肉厚度(P=0.012)、羽状角(P=0.003)及横截面积(P=0.049)3项指标均显著高于对照组;④上述数据证实,健康成年受试者经过4周的低频脉冲磁场慢性暴露,股四头肌的最大自主收缩力显著提升,同时观察到试验组的肌肉厚度、横截面积及羽状角3项肌肉形态指标的显著增长,对使用该技术作为肌肉改善的运动替代与医疗策略提供了肌组织形态改善的支持依据。

乌鲁木齐国际儿童医院门诊大厅结构设计

乌鲁木齐国际儿童医院由门诊医技楼、病房楼等部分组成,总建筑面积为240000m^(2)。主要介绍了门诊医技楼主体结构设计、入口雨棚设计、大厅屋盖、分叉柱、倒梯形截面设计等多个施工技术问题。通过结构选型对比分析,主体结构采用减震框架结构,雨棚和大厅屋盖均采用单层网壳结构,经济合理的同时保证了建筑效果。通过传力路径分析和有限元计算,对网壳结构进行了单体模型和总装模型的对比研究,重点分析了结构的变形问题,对整体网壳进行了几何非线性和材料非线性的整体稳定性分析,对倒梯形截面采用截面替换的方式进行了补充分析,对支座等关键部位进行有限元分析以满足受力和稳定性的要求。

缓粘结预应力技术在杭州西站项目中的应用分析

以浙江省杭州市西站工程项目为例,分析了大型公共建筑工程中,缓粘结预应力筋遇到长期预留施工通道的处理方案,并从缓粘结预应力深化图纸设计和工程实施的角度出发,重点介绍了梁中预应力筋遇型钢骨后钢绞线穿设问题、预应力筋张拉端排布问题等深化过程中关键问题的处理原则和解决方案,为大型公共建筑工程中缓粘结预应力的深化设计和工程施工提供参考。

三维激光扫描与BIM技术在泵闸流道变截面偏差检测中的应用

异形混凝土流道变截面是水利泵闸工程施工控制的重难点,为克服变截面施工质量偏差人工检测手段控制难度大、精度低等问题,有必要探索三维激光扫描技术在该部位质量检测方面的实际应用效果。总结三维激光扫描与BIM相结合的技术流程,分析三维激光扫描的技术理论方法,以新川沙泵闸工程为应用案例,通过高精度非接触式扫描技术获得异形流道的点云数据,收集三维空间坐标信息生成点云模型,与施工图纸建立的BIM模型进行对比分析。结果表明:施工质量偏差分析精确到毫米级,±20 mm以内的偏差占87.21%,点云模型站间误差最大为9.8mm,表明该方法用于泵闸工程异形混凝土流道质量偏差检测是可行的。本研究可为其他泵闸工程质量控制的精度可视化提供指导和借鉴意义。

Numerical simulation of turbulent flow in helically coiled open-channels with compound cross-sections

Turbulence structure in a helically coiled open channel flow is numerically simulated using three different turbulence models--the Launder and Ying model, the Naot and Rodi model, and the nonlinear k-ε Model (SY model). Simulation results were compared with observation of (i) turbulent flows in alternating point-bar type channel bends with rectangular sections, and (ii) straight open channel flows with compound cross-sections. Based on calculations of the impact of various channel curvatures on turbulence characteristics, accuracy of the three turbulence models was analyzed with observed data as a qualitative reference. It has been found out that the Launder and Ying model and the nonlinear k-ε Model are able to predict the same general trend as measured data, and the simulation of the effect of the centrifugal force on the formation of secondary currents produces a correct pattern.

Optimization of structural parameters for elliptical cross-section spiral equal-channel extrusion dies based on grey theory

The elliptical cross-section spiral equal-channel extrusion （ECSEE） process is simulated by using Deform-3D finite element software. The ratio m of major-axis to minor-axis length for ellipse-cross-section, the torsion angle u, the round-ellipse cross-section transitional channel L1, the elliptical rotation cross-section transitional channel L2 and the ellipse-round cross-section transitional channel L3 are destined for the extrusion process parameters. The average effective strain eave on cross-section of blank, the deformation uniformity coefficient a and the value of maximum damage dmax are chosen to be the optimize indexes, and the virtual orthogonal experiment of L16 （45） is designed. The correlation degree of the process factors affecting eave, a and dmax is analyzed by the numerical simulation results using the weights and grey association model. The process parameters are optimized by introducing the grey situation decision theory and the ECSEE optimal combination of process parameters is obtained： u of 120 , m of 1.55, L1 of 7 mm, L2 of 10 mm, and L3 of 10 mm. Simulation and experimental results show that the material can be refined with the optimized structural parameters of die. Therefore, the optimization results are satisfactory.

Numerical investigation on detonation cell evolution in a channel with area-changing cross section

The two-dimensional cellular detonation propagating in a channel with area-changing cross section was numerically simulated with the dispersion-controlled dissipative scheme and a detailed chemical reaction model. Effects of the flow ex-pansion and compression on the cellular detonation cell were investigated to illus-trate the mechanism of the transverse wave development and the cellular detona-tion cell evolution. By examining gas composition variations behind the leading shock,the chemical reaction rate,the reaction zone length,and thermodynamic parameters,two kinds of the abnormal detonation waves were identified. To explore their development mechanism,chemical reactions,reflected shocks and rarefac-tion waves were discussed,which interact with each other and affect the cellular detonation in different ways.

不同截面抗滑桩的土拱效应对比研究

土拱效应是桩土作用理论研究的重要依据,但由于对不同截面形式抗滑桩的土拱效应作用机理研究较少,在抗滑桩设计中大多采用传统截面形式,考虑到传统矩形抗滑桩在形成土拱效应方面的不足,提出梯形截面优化抗滑桩截面形式。基于材料力学理论,利用轴向受压杆件的斜截面应力计算模型推导出梯形桩桩侧土拱拱脚受压区应力状态,并结合摩尔—库伦强度准则得出梯形桩桩侧极限承载力,通过算例对比分析梯形与矩形桩桩侧土拱极限承载力,结合数值模拟分析验证理论与计算结果。研究结果表明:梯形截面桩桩侧极限承载力相较于矩形截面有较为明显的提升,最大约为矩形桩的2.5倍;相同条件下梯形截面桩桩间土位移与剪应变增量更小,应力集中现象更明显,梯形截面桩对土拱效应的形成与发展更有利。

长江三峡水库坝下游荆江段断面形态冲刷调整成因分析

长江三峡水库建成后,下游河段将发生长时间累积性的冲刷。由于边界条件的不同,不同河型河槽断面形态的冲刷调整特点存在差异。本文基于2003—2018年长江三峡水库坝下游荆江段实测河道断面形态资料,选取典型顺直河型、弯曲河型和分汊河型的典型断面,计算断面宽、平均水深和宽深比等断面形态特征参数,分析不同河型断面形态冲刷调整的异同,并探讨其成因。主要发现:1)不同河型的断面形态调整存在一致性和差异性。不同河型的平滩河槽断面总体向窄深化方向发展;顺直河型、分汊河型的枯水河槽断面宽深比总体减小,断面亦向窄深化方向发展;而弯曲河型的枯水河槽断面宽深比以增大居多,即断面总体宽浅化。2)平滩河槽和枯水河槽断面宽深比调整差异主要受水流动力轴线摆动范围控制。顺直河型、分汊河型水流动力轴线摆动范围覆盖平滩河槽与枯水河槽,即冲刷集中于平滩河槽和枯水河槽,两者均呈现窄深化特征;弯曲河型水流动力轴线摆动范围位于平滩河槽内,却超出枯水河槽,汛期摆到凸岸边滩上并冲刷凸岸边滩,枯水河槽显著展宽,凹岸深槽淤积,断面向宽浅化方向发展,且初期凸岸边滩宽度越大,宽深比变化率越大。3)蓄水后水流动力横向摆动范围缩小且水流冲刷动力集中,宽浅河段受水流冲刷下切的影响更显著,加上宽浅河段的河床组成相对较细,抗冲性弱,导致蓄水前宽深比越大的断面,蓄水后宽深比变化幅度也越大。

梯形截面战斗部预制破片爆炸飞散数值模拟

研究梯形截面杀伤战斗部预制破片飞散特性规律,为梯形截面杀伤战斗部的设计提供参考。运用ANSYS/LS-DYNA软件建立了5种不同形状梯形截面杀伤战斗部模型,并进行了爆炸驱动预制破片的数值模拟,得到了破片分布规律、梯形面上破片飞散速度、不同起爆点破片的飞散特性。结果表明:4个梯形面上的破片形成了4个破片束,下面破片飞散角最大,可达105°,梯形斜面上的破片飞散方向相对于斜面法向朝梯形下方偏转,最大偏转34.5°。θ为60°之前,梯形面上的破片平均速度随着θ的增大提高了8.6%,梯形下面破片平均速度大于梯形上面。θ过大会降低梯形下面和斜面上破片平均速度。梯形斜面上最大速度破片位于斜面上部。梯形对称轴上不同位置的起爆点对梯形面上破片周向飞散角和斜面破片偏转角影响不大,但是可以提高对侧方向破片飞散速度,下面破片增幅达3.7%。θ为45°、起爆点设置在梯形上面可使下面破片获得最大的杀伤威力。

PEMFC多级横向流道交错流场参数研究

流场结构是质子交换膜燃料电池(PEMFC)的重要组成部分,采用合适的流场结构能显著提高PEMFC的工作效率。设计了一种新型流场结构,将新型流场流道级数以及横截面积作为研究重点,利用三维软件COMSOL Multiphysics对新型流场进行了数值模拟和比较分析。结果表明,随着横向流道级数和进出口面积比的不断增加,电池输出性能均呈现出先增大后减小的变化趋势,采用三级横向流道能使新型流场结构有最高的输出性能,均匀递减型流道可以有效提升电池的输出功率。

带梯形截面导磁环的全通道有效车用磁流变减振器设计

车用磁流变减振器(MRD)往往结构尺寸较小,且传统的车用MRD阻尼通道有效工作长度较短,输出阻尼力小,导致其工程应用受到限制。针对这一问题,提出一种带梯形截面导磁环的新型全通道有效MRD以增大阻尼通道有效工作长度,减缓磁饱和,并基于磁流变液流变特性和流体动力学理论给出了具体的结构与磁路设计计算方法,将5种不同结构的MRD进行有限元仿真对比。通过阻尼特性测试试验,分析其阻尼特性并与普通MRD、带弯曲磁路全通道有效MRD进行对比,应用线性二次高斯(LQG)控制器进行减振性能分析。研究结果表明:新型全通道有效MRD能够显著提高阻尼通道有效工作长度,达到阻尼通道全长的99%以上;新型全通道有效MRD能改善小尺寸MRD易发生磁饱和的问题;在相同电流激励与尺寸约束下阻尼通道的磁场强度分布更均匀,平均磁场强度更大,具有更大的输出阻尼力;新型全通道有效MRD在结构尺寸小的同时具有更大的输出阻尼力;新型全通道有效MRD相对于普通MRD具有更好的减振性能,能够进一步降低车辆的簧上质量加速度与轮胎动变形21.51%和1.43%。该研究能有效扩宽小尺寸MRD的实际应用范围,具有一定的工程应用价值。