The quadratic B-spline curve fitting for the shape of log cross sections

This paper describes a new method for simulation of the cross section shape of log. The self-developed MQK3102 log shape recognizing machine was used to acquire the finite discrete sampling points on the cross section of log and those points were fitted with the quadratic B-spline parametric curve. This method can clearly stimulate the real shape of the log cross section and is characterized by limited sampling points and high speed computing. The computed result of the previous curve does not affect the next one, which may avoid the graphic distortion caused by the accumulative error. The method can be used to simulate the whole body shape of log approximately by sampling the cross sections along the length direction of log, thus providing a reference model for optimum saw cutting of log.

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.

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.

Conceptual design of a Cs2LiLaBr6 scintillator‑based neutron total cross section spectrometer on the back‑n beam line at CSNS

To reduce the experimental uncertainty in the 235 U resonance energy region and improve the detection efficiency for neutron total cross section measurements compared with those obtained with the neutron total cross section spectrometer(NTOX), a dedicated lithium-containing scintillation detector has been developed on the Back-n beam line at the China Spallation Neutron Source. The Fast Scintillator-based Neutron Total Cross Section(FAST) spectrometer has been designed based on a Cs2Li La Br6(CLLB) scintillator considering the γ-ray flash and neutron environment on the Back-n beam line. The response of the CLLB scintillator to neutrons and γ-rays was evaluated with different 6Li/7 Li abundance ratios using Geant4. The neutron-γdiscrimination performance of the CLLB has been simulated considering different scintillation parameters, physical designs,and light readout modes. A cubic 6Li-enriched( > 90%) CLLB scintillator, which has a thickness of 4-9 mm and side length of no less than 50 mm to cover the Φ 50 mm neutron beam at the spectrometer position, has been proposed coupling to a side readout SiPM array to construct the FAST spectrometer. The developed simulation techniques for neutron-γ discrimination performance could provide technical support for other neutron-induced reaction measurements on the Back-n beam line.

Analysis of the mass of behind-armor debris generated by RHA subjected to normal penetration of variable cross-section EFP

Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.

Study of LHCD in HL-2A Non-Circular Cross Section Tokamak

Using the Grad-Shafranov equation, the magnetic configuration is obtained. With this configuration, Brambilla＇s ray tracing theory has been used to study the propagation of LH waves. The qualitative study of the feasibility of LHCD in the non-circular cross section tokamak HL-2A is made. The optimized current drive method is discussed.

Study of LHCD in Non-Circle Cross Section HL-2A Tokamak

In the review paper of N. J. Fish[1], the topics concerning the basic theory of lower hybrid wave heating and current drive are presented. Brambilla＇s spectrum determines the injecting wave resonance regime and its power distribution. The theories and experiments have demonstrated that the LH waves interact efficiently with the high energy electrons in the tail of their distribution in velocity space. LHCD has been used in many devices such as JET, JT-60U, and ASDEX,

Fast-electron-impact ionization process by 3p of hydrogen-like ions in Debye plasmas

The plasma screening of fast-electron-impact-ionization by excited state（3p） of Hydrogen-like ions was investigated in the first Born approximation with a plasma screening length δ varying from 1000a0 to 10a0. The generalized oscillator strength densities showed dramatic changes： some accessional minima occurred along with a remarkable enhancement in certain continuum-energy domains. The double-differential cross sections exhibit not only the same structures as the Bethe surface for moderate and large momentum transfers, but also a broadened enhancement for small momentum transfers.The single-differential cross sections exhibit a near-zero-energy-enhancement and prodigious multiple-shape resonances,depending on the continuum energy and the plasma screening length. These features are analogous to those of the photoionization cross section. These findings, for both types of cross section, can be explained by processes associated with continuum electrons, as long as the potential has a short-range character.

局部外形参数对高速飞行器的RCS影响

为了降低高速飞行器的雷达散射截面(radar cross section,RCS),采用多层快速多极子算法和物理光学法研究局部外形参数对飞行器雷达散射特性的影响。在此基础上,提出一种变半径弧形的边缘钝化形式,以提高飞行器仰视对抗能力。所提出的变半径弧形钝化外形具有良好的RCS减缩能力,与传统圆弧钝化外形相比,在前向重点角域内,RCS对数均值降低了22.88%;随着仰角的增大,变半径弧形钝化形式还具备全向RCS减缩能力,在全向角域内RCS对数均值降低了13.37%。最后,研究所提出的变半径弧形钝化方式在不同雷达波频段下的RCS特性,结果表明这种钝化方式对于频率较高时仰视对抗能力更好。

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。

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。

橡胶粗细集料含量对FRP约束橡胶混凝土应力-应变关系的影响

为研究橡胶粗细集料体积分数对纤维增强复合材料(fiber reinforced polymer, FRP)约束橡胶混凝土应力-应变关系的影响,提出了橡胶粗细集料体积替换率的概念,并通过收集已发表文献的110组应力-应变关系试验曲线,分析了橡胶粗细集料体积替换率对FRP约束不同截面橡胶混凝土柱应力-应变关系关键参数的影响,基于分析结果建立了FRP约束橡胶混凝土的应力-应变关系模型和抗压强度模型,两个模型中均考虑了橡胶粗细集料体积替换率和橡胶混凝土截面形状的影响.模型评估结果表明:随着橡胶粗细集料体积替换率、FRP约束应力比和截面倒角半径比的增加,FRP约束橡胶混凝土的抗压强度均呈增大的趋势;建立的抗压强度模型可准确预测橡胶颗粒取代部分细集料或粗细集料的FRP约束橡胶混凝土抗压强度,平均误差仅为1.03;建立的应力-应变关系模型能够较好预测FRP约束橡胶混凝土的应力-应变关系曲线变化.

异形多腔钢管混凝土分叉短柱抗震性能试验及数值计算

针对某超高层巨型框架结构中异形截面多腔钢管混凝土(concrete-filled steel tube, CFT)分叉柱,为研究截面加强构造对分叉短柱抗震性能的影响,进行了4个试件在竖向轴压力及水平往复两次的低周反复荷载下的抗震性能试验研究,试件上部为五边形四腔体钢管混凝土双柱肢,下部为八边形十三腔体钢管混凝土单柱肢,以此形成分叉柱;研究的截面构造包括四种:基本构造,钢管钢板整体加厚构造,距中和轴较远的钢管角部钢板内表面贴焊等肢角钢的局部钢板加厚构造,距中和轴较远的钢管腔体内置圆钢管构造。基于试验结果及截面构造特点,进行了数值计算。试验及数值计算结果表明:异形截面多腔钢管混凝土分叉短柱的破坏主要发生在上柱根部分叉截面处,表现为距离中性轴较远处的钢板撕裂以及局部焊缝开裂引起的整块钢板撕裂;内置圆钢管的加强构造承载力提高7.6%、变形能力提高14.4%,综合耗能能力最强,局部钢板加强构造承载力提高9.2%、变形能力下降18.7%,钢管钢板整体加厚构造承载力略有提高、但变形能力下降较多;提出的异形多腔钢管混凝土柱简化建模方法计算效率较高,精度满足工程设计要求。

可转位浅孔钻螺旋容屑槽结构优化及实验研究

钻头排屑性能直接影响切削性能,为了解决可转位浅孔钻在切削过程中出现的缠屑和振动问题,进而避免由此引发的加工异常和孔壁质量差的情况,采用了理论分析和仿真模拟相结合的方法,深入研究了螺旋容屑槽横截面形状结构和螺旋角结构对钻体刚性的影响,并通过实验验证了所设计钻体具有良好的刚性和排屑性能。仿真模拟结果分析表明,在芯径一致时钻体受到的最大应力为761 MPa、应变为0.003367,钻体头部横向位移量为0.3971 mm、转动变化量为0.006500 rad;变螺旋角在20°-16°时,钻体受到的最大应力为695 MPa、应变为0.002688,钻体头部横向位移量为0.3641 mm、转动变化量为0.006140 rad,此时钻体刚性和排屑性能达到良好的平衡;分析表明,螺旋角越大、叶宽差值越大,则芯径越小,钻体刚性越差;所设计的钻体在实验工况下未发生缠屑情况,表现出更好的排屑性能,并有较高的孔径一致性和良好的孔壁质量。

基于复合修形技术的低雷达散射截面微带天线

设计了一款基于复合修形技术的低雷达散射截面(Radar Cross Section,RCS)微带天线。通过在辐射贴片和金属底板同时采用修形技术,减少天线金属部分的面积,实现天线RCS减缩并且维持天线辐射特性。基于复合修形技术的微带天线相比传统未修形的微带天线在1~4 GHz频带内实现天线RCS减缩,最大RCS减缩量为20 dB。对设计的低RCS天线进行加工并测试,测试结果验证了仿真分析的正确性。

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。

V形截面管充液压制圆角充填行为研究

基于力学分析,利用有限元模拟和充液压制成形实验研究了V形截面管圆角成形所需内压。在不同内压下对成形管材壁厚的变化进行了充液压制实验研究。并通过理论计算选择合适的实验参数,成形出符合要求的扭力梁结构件。结果表明:圆角半径越小,成形所需内压越大;V形截面管内圆角半径随着内压的增加而减小,外圆角半径随着内压的增加而增大;V形截面管壁厚增厚主要发生在上侧圆角区,减薄主要发生下圆角区,并且最大减薄发生在下圆角中心区。

一种基于扼流结构的基站天线碗状振子异频去耦方法

针对双频嵌入式布局的基站天线中存在高频振子辐射性能受低频振子严重干扰的问题,提出一种基于扼流结构的基站天线碗状振子异频去耦方法。设计了含去耦结构的基站天线,在低频振子臂上加载微带形式的扼流结构,通过分析扼流结构的等效电路、在高频天线工作频段的感应电流及单站雷达散射截面(Radar Cross-Section,RCS),调整扼流结构的性能参数,有效降低低频振子对高频振子的影响。通过设计具有去耦功能的双频双极化基站天线阵列,验证所提方法的可行性。结果表明,低频振子具有良好的阻抗匹配特性,所提方法能有效减弱高频振子受低频振子影响导致的交叉极化恶化问题,且能够稳定方向图波束宽度。

重卡桥壳轴向环向补料液压胀形内压加载路径的确定

轴向环向补料液压胀形变形过程复杂,合理的加载路径确定困难,成形时易发生失稳起皱及胀裂。通过变形分析,揭示了轴向环向补料液压胀形两个阶段各典型位置发生变形所需内压的变化规律,确定了线性增压—恒压—线性降压的加载路径,推导出各阶段的内压计算公式,给出了上控制模平面高度与最大扩径量的关系。针对某载荷10 t重卡桥壳,通过有限元模拟及工程试验验证了加载路径的正确性,揭示出加载路径线性降压段的降压系数、上控制模高度系数对管坯成形质量的影响,确定了二者的合理范围,消除了失稳起皱及开裂的隐患。