Influences of the Helical Strake Cross-Section Shape on Vortex-Induced Vibrations Suppression for A Long Flexible Cylinder

An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ cross-section on the vortex-induced vibrations （VIV） suppression of a flexible cylinder. The square-sectioned and round-sectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow （CF） and in-line （IL） directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and round-sectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the square-sectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with square-section.

Evaluation of “J”-shaped Uterine Incision during Caesarean Section in Patients with Placenta Previa:A Retrospective Study

This study evaluated the efficacy and safety of ＂J＂-shaped uterine incision for caesarean section for patients diagnosed with placenta previa. A total of 55 consecutive cases of placenta previa treated in Union Hospital were retrospectively analyzed over a period of two years and 10 months. The subjects were divided into two groups with respect to the uterine incision. Twenty-four pregnant women with placenta previa who were indicated for caesarean section underwent the procedure using a new ＂J＂-shaped uterine incision and 31 pregnant women with placenta previa received caesarean section that used the traditional transverse incision. The two groups were compared in terms of operation time, estimated blood loss, infant expulsion time, exhaust time and postoperative recovery. Meanwhile, comparison was also made in neonatal clinical data between the two groups. Compared with the ＂J＂-shaped incision group, the traditional incision group had a lower Apgar scores （P〈0.05）. However, there existed no statistically significant differences in the overall time of operation and postoperative period of breaking wind （P〉0.05）. It is concluded that, with caesarean section for placenta previa patients, the ＂J＂-shaped uterine incision significantly decreases intraoperative blood loss and facilitates the fetal delivery.

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.

Numerical calculation on solar temperature field of a cable-stayed bridge with U-shaped section on high-speed railway

Based on transient temperature field theory of heat conduction,the solar temperature field calculation model of U-shape sectioned high-speed railway cable-stayed bridge under actions of concrete beams and ballast was established.Using parametric programming language,finite element calculation modules considering climate conditions,bridge site,structure dimension and material thermophysical properties were compiled.Six standard day cycles with the strongest yearly radiation among the bridge sites were selected for sectional solar temperature field calculation and temperature distributions under different temperature-sensitive parameters were compared.The results show that under the influence of sunshine,U-shape section of the beam shows obvious nonlinear distribution characteristics and the maximum cross-section temperature difference is more than 21 °C; the ballast significantly reduces sunshine temperature difference of the beam and temperature peak of the bottom margin lags with the increase of ballast thickness; the maximum cross-section vertical temperature gradient appears in summer while large transverse temperature difference appears in winter.

Optimization of Cross-sectional Shapes of the Bi-2223/Ag Wires before Flat Rolling

Rolling process plays an important role in the manufacture of Bi-based high temperature superconductor tapes, and the plastic flow regularities of the superconducting wires during deformation will directly affect the ultimate quality of the tapes. In order to investigate the effect of cross-sectional shapes before fiat rolling on the performance and homogeneity of the tapes, some numerical models of Bi-2223/Ag wires with different cross-sectional shapes including circular, square, elliptical and racetrack cross-sections are constructed during the rolling process. By comparing the relative density, logarithmic strain ratio and length-width ratio on the filaments, it is revealed that Bi-2223/Ag wire with special-shaped cross-section can achieve better conductivity than the round wire, in particular, the racetrack cross-sectional wire has the second best performance among four wires. Based on material processability and experimental condition, tri-pass racetrack drawing technique is employed to optimize the process and obtain racetrack cross-sectional wire. The rolling process of Bi-2223/Ag wire with racetrack cross-section causes more intensive deformation of filaments in the center of the tape and achieves the filaments with larger length-width ratio. Also, the deformation distribution of filaments verifies the numerical results. Consequently, the racetrack drawing technique can be utilized for a reference during the mechanical processing and to increase the current transmission capacities of Bi-2223/Ag tapes.

Optimal Cross-Sectional Shape of Gas/Air Ducts

In industrial plants, ships, and buildings, a large amount of gas and air ducts are applied for equipment connection, HVAC, medium transport, and exhaust, etc. These ducts can be designed in varied cross-sectional shapes, such as round or rectangle. The author reveals through geometric calculation of the duct cross-sectional shapes and engineering experiences that the round cross-section is an optimal shape in the duct system. The round duct has the shorter perimeter than the other cross-sectional shape ducts and the stronger structure in the same working condition. The material saving of the round duct due to the shorter perimeter is quantitatively determined. In the pater, it is shown that the round duct is economically attractive. The economic analysis for the material cost saving is illustrated by an example. For a long duct system, the material and material cost savings are significant. It is suggested that the round duct in the gas and air duct system should have priority as long as the field conditions are allowed. In the paper, the material cost saving is also converted to PW, AW, and FW used for LCC economic analysis.

An algorithm for 3D shape matching using spherical sectioning

3D shape searching is a problem of current interest in several different fields. Most techniques are developed for a particular domain and used to reduce a shape into a simpler shape representation. The techniques developed for a particular domain will also find application in other domains. We propose a new shape matching method. The SSRD (spherical sectioning railroad diagram) algorithm has the general shape distribution’s properties and overall features of the original model. The SSRD’s useful properties are discussed. We show the experimental results for the validity of our method.

煤矿掘进巷道断面尺寸变化对噪声传播的影响

为研究煤矿掘进巷道长空间内断面尺寸变化对噪声传播的影响,采用仿真模拟方法研究巷道内噪声传播,分析煤矿掘进巷道断面积大小、断面形状及断面面积突变率的变化对巷道内噪声传播影响。结果表明:煤矿掘进巷道内断面面积大小、断面形状及断面面积突变率均会影响巷道内噪声的传播,当噪声源功率、频率相同时,声压级衰减随巷道截面积增大而增大;对于给定的断面面积(18 m2),当断面形状不同时,声压级衰减也不同,且断面形状为拱形时会产生明显的声聚焦效应,不利于噪声衰减;当断面面积发生突变时,巷道内的声压级分布会有所变化,其中断面面积由大变小时不利于噪声的衰减,断面面积由小变大时仅影响突变后的声场,而对巷道内整体声压级影响并不明显;巷道内噪声衰减现场测试与数值模拟结果基本一致,验证了搭建的模型及模拟结果的可靠性。

冷冻剑结构对块冰机制冰性能影响的数值模拟

目的:在直冷式块冰机冰模蒸发器内部增设冷冻剑以实现快速制冰。方法:使用COMSOL模拟冷冻剑截面形状及冷冻剑倾角对制冰过程的影响。结果:随着制冰过程的持续进行,增设不同截面形状冷冻剑的冰模内部平均温度不断降低,冰模内固相体积分数也随时间而增加,但在相同时间内增设圆形截面冷冻剑的冰模内部平均温度要比三角形、矩形和菱形低0.1~0.2℃。此外,冷冻剑倾角越小制冰速率越快。结论:冷冻剑截面形状为圆形或近圆形时,制冰速率较快;且在保证便于脱冰的前提下,应尽可能减小冷冻剑倾角。

边箱式π型断面涡振性能及导流板措施参数研究

π型断面因构造简单与受力性能好,被广泛应用于桥梁建设中,但其抗风性能差,易产生涡激振动问题.本文以边箱式π型断面桥梁为研究对象,采用宽高比10∶1的π型断面刚体节段模型进行同步测振测压试验,并且通过计算流体力学方法加以对比验证,研究π型断面涡振性能与导流板抑振机理.试验结果表明:边箱式π型断面在0°、±3°风攻角下发生显著涡激振动,通过在断面两侧加设特定形式及尺寸参数的导流板措施可抑制断面竖弯及扭转涡振.其中,倒L型导流板措施气动优化效果显著,可有效消除涡振振幅,而水平导流板措施的抑振效果有限,相较于竖弯涡振,扭转涡振对于水平导流板尺寸参数更为敏感.通过对比数值模拟结果与表面气动压力分布,表明倒L型导流板措施能够优化断面气动外形,削弱断面上下表面旋涡脱落尺度和能量,同时降低断面所受的周期性气动力,从而有效抑制断面涡振.

蜗壳断面形状对大型双吸泵性能影响的数值模拟

为研究蜗壳不同断面形状对大型双吸离心泵性能的影响,在确保其他因素不变的条件下,设计3种不同的蜗壳方案进行瞬态数值模拟。结果表明:3种蜗壳断面方案在设计工况下,圆形蜗壳的效率最高为90.7%,其次是梨形蜗壳,效率为90.2%,矩形蜗壳的效率最低为88.9%,且圆形蜗壳的高效区有所扩大;在各流量工况下圆形蜗壳能量损失率均为最少,在设计工况时圆形蜗壳的能量损失率为0.3%,矩形蜗壳的能力损失率为1.1%;在大流量和设计流量下,圆形蜗壳的叶轮所受径向力均最小,梨形蜗壳次之,矩形蜗壳最大;在设计工况下,3种蜗壳方案对蜗壳上的压力脉动均呈现周期性变化,圆形蜗壳在各检测点处压力脉动的振幅幅度均为最小。

高地应力缓斜半煤岩巷道断面形状优化研究

为了优化高地应力缓斜半煤岩巷道的断面形状,以东欢坨矿3018工作面运道为工程背景展开研究。通过复变函数理论推导得出了倾斜煤层中不同断面形状的应力解析解,然后运用FLAC3D数值模拟求解了不同断面形状巷道的应力集中和塑性区情况,并以此为基础确定了巷道最优断面形状,最后结合现场工业性试验对研究结果的可靠性进行了验证。研究结果表明:高地应力作用下缓斜半煤岩巷道破坏呈现非对称形式;不管断面形状如何,巷道均在左、右两底角处呈现高应力集中,且应力集中程度矩形>梯形>直墙拱形;直墙拱形巷道稳定性最佳,梯形巷道次之,矩形稳定性最差,确定直墙拱形为最终巷道断面形状;现场巷道表面位移量监测结果表明,直墙拱形巷道更能满足现场安全生产要求。

工字形钢梁-矩形钢管柱单向螺栓节点抗弯承载力理论计算方法

针对工字形纯钢梁和钢-混凝土组合梁分别与矩形钢管柱和矩形钢管混凝土柱采用单向螺栓(也称单边拧紧螺栓)连接形成的4种节点形式,对其在弯矩作用下的受力机理及破坏模式进行分析,讨论导致节点失效的因素。总结节点在弯矩作用下的9种失效模式,包括:单向螺栓拉断、端板受弯屈服、矩形钢管柱壁翼板受拉屈服、矩形钢管柱壁翼板受压屈服、矩形钢管柱壁腹板受压屈曲、混凝土楼板局部压溃、钢筋屈服、矩形钢管柱内混凝土局部压溃、矩形钢管柱壁腹板受压屈服,进而基于破坏模式给出节点各组件承载力的计算公式。对4种节点在不同破坏模式下的正弯矩承载力和负弯矩承载力进行分析,给出节点承载力计算公式。将节点抗弯承载力的理论计算结果与试验结果进行对比,验证理论计算方法的可靠性。

大跨PK断面钢箱梁斜拉桥涡振性能及优化措施研究

红莲大桥主桥为主跨580 m的双塔斜拉桥,中跨主梁采用PK断面钢箱梁,该类主梁断面易发生涡振,需对其涡振性能及抑振措施进行研究。基于该桥有限元动力特性分析结果,制作PK断面钢箱梁1∶60缩尺比节段模型进行测振风洞试验,研究桥梁原始设计断面主梁的涡振性能,讨论增加结构阻尼比(增加至0.010和0.027)措施的涡振抑振效果,并对增设稳定板、水平导流板、部分封闭桥面栏杆等不同气动优化措施及组合对主梁涡振性能的影响进行分析。结果表明:原始设计PK断面钢箱梁的涡振振幅明显超过规范限值;增大结构阻尼比虽然可以有效抑制涡振响应,但阻尼比增加至0.027时竖弯涡振振幅仍然显著;在桥面检修栏杆上缘外挑1.6 m宽水平导流板可将涡振振幅降低到可忽略的水平;采用在检修栏杆上缘外挑1.1 m宽水平导流板、优化桥面燃气管道位置、调整防撞护栏下部封闭高度为0.42 m,或移除检修道栏杆底座、错列布置封闭检修道栏杆和防撞护栏等组合措施,虽不足以完全抑制涡振的发生,但可将涡振振幅控制至明显小于规范限值。

截面型式及槽宽比对高填明洞土压力影响分析

利用离散元软件PFC2D,考虑到土体的离散性与不均匀性,通过分析洞顶平均竖向土压力、内外土柱相对沉降差以及颗粒间接触力链的变化规律,探讨截面型式(矩形、1/4拱形、1/2拱形)及槽宽比(B/b=1.5∶1,2∶1,3∶1,4∶1)变化对高填黄土明洞土压力的影响,结合顾安全公式,分析高填明洞沉降差与土压力间的函数关系,并修正该函数,使其可以适用与不同的截面型式与槽宽比下的高填明洞。结果表明:(1)B/b确定,明洞采用矩形截面时,接触力链在洞顶分布,平均土压力更大,明洞采用拱形截面时,平均土压力更小,但拱顶存在局部应力集中现象;(2)明洞截面型式一定,随着B/b的增大,洞顶平均竖向土压力与沉降差均随之增大,当B/b较小时,边坡作用增强,外侧土柱沉降降低,对内土柱的作用力变小,从而导致明洞顶竖向土压力更小;(3)内外土柱沉降差与附加土压力呈线性相关,相对于矩形截面,拱形截面下较小的沉降差会产生相同的附加土压力,更有利于结构的稳定。

毛管压力理论与地质建模在定向井部署中的融合应用——以柴达木盆地英东油田下盘油藏为例

英东油田下盘油藏是柴达木盆地的典型长井段多油层单斜断鼻油藏。针对油藏开发矛盾,以沉积和构造控藏为出发点,将传统的单纯油水过渡带计算与储层地质模型预测的单一维度流体分布表征方法相结合,提出了毛管压力理论与地质建模相融合的定向井轨迹部署方法,有效地规避了单一因素在井位部署过程中带来的钻探风险。由于实验室毛管压力的测量环境与实际地层的不同,在计算油柱高度前,要将实验室毛管压力转换为相应的油藏毛管压力,使得计算结果更贴近真实的油藏信息。同时,直接利用平均J函数曲线建立的油柱高度模型,虽然一定程度上弥补了单一岩样表征不全的缺陷,但针对多层强非均质性油藏,需多点、多段的分析和计算,且必须结合工区沉积、构造特征及测井资料修正模型参数,才能进一步提高油气刻画精度。研究结果表明:利用毛管压力曲线可相对有效地定量评价多层砂岩油藏发育规模,在高精度三维模型建立基础上,可为井位轨迹的部署设计提供参考。该方法的应用有利于“牙刷状”油藏的后期开发方式调整及效益动用。

从肥袋足鬲看商时期北方长城地带东段地区的文化互动

肥袋足鬲是商时期在北方长城地带东段地区不同考古学文化中共有的一类器物。虽然不同地区的考古学文化中肥袋足鬲形态存在差异,但在面对商文化的扩张过程中,不同地区的肥袋足鬲消长、中断与复兴的时间却几乎相同。肥袋足鬲所体现的文化传播,反映了华北平原北缘地区与晋陕高原地区人群的交流与互动。晚商时期使用肥袋足鬲的人群往往与佩戴卷云形金耳饰的人群在空间上重合,反映了北方长城地带东段不同考古学文化之间的共性。

大断面浅埋隧道地表沉降Peck修正公式及其应用

针对经典Peck公式未考虑隧道断面形状、埋深对大断面浅埋隧道地表沉降影响的不足,考虑断面形状与隧道埋深修正系数改进Peck公式。利用白塔山隧道地表沉降实测数据对修正公式进行验证,两个监测断面预测值与实测值平均相对误差8.3%,最大相对误差18.4%。进而采用修正Peck公式对不同断面形状、不同埋深隧道开挖引起的地表沉降进行预测。结果表明:地表最大沉降与断面形状修正系数成正相关,地表最大沉降依次为矩形-1(Ⅰ)>马蹄形-1(Ⅱ)>圆形(Ⅴ)>矩形-2(Ⅲ)>马蹄形-2(Ⅳ);随着大断面浅埋隧道埋深增加,地表最大沉降减小而地表沉降槽宽度相应增大。地表沉降曲线形态由窄而深过渡到宽而浅,地表核心沉降区面积也逐渐减小。研究成果可为类似工程提供理论支持和技术参考。

试样形状对含倾斜软弱夹层复合岩体力学性质的影响

为研究试样形状对含有倾斜软弱夹层的复合岩体力学性质与破坏模式的影响,对长方体、圆柱体两种复合岩体试样进行了单轴压缩试验。研究结果表明:试样形状引起了软弱夹层破坏形态的不一致,圆柱体试样中倾向于产生斜裂纹破坏并引起复合试样侧向滑移,长方体试样倾向于产生端部的剥落与颈缩破坏;软弱夹层不同的破坏形态也导致硬岩初始压缩状态下的受压面积均存在不同形式的折减,实际受力出现不同情况的应力集中,长方体试样总体产生垂直于软弱夹层面发育的裂纹,圆柱体试样总体产生垂直于实际受压面发育的裂纹。同时,长方体试样无论是软弱夹层的弹性模量与峰值强度还是硬岩的峰值强度都明显高于圆柱体试样,但是应力分布相较圆柱体试样也明显更不均匀。

倾斜煤层回采巷道断面形状优选及支护研究

为解决香山矿倾斜煤层回采巷道变形复杂、稳定性差、支护难的问题,以香山矿二水平己一采区己_(16-17)倾斜煤层为工程研究背景,通过数值模拟比较分析巷道不同断面形状围岩变形情况,选择合适巷道断面并提出相应的支护方式,结合现场观测以验证选取巷道断面以及支护方式的有效性。结果表明:采用斜顶梯形巷道断面及锚网索支护后巷道顶板最大下沉量与支护前相比降低了19%,两帮最大位移量降低了12.7%,梯形巷道断面支护可以将巷道围岩的变形和破坏控制在较小的范围内,回采巷道变形得到有效控制。研究香山矿倾斜煤层回采巷道稳定性,可为矿井安全生产提供依据。