Numerical simulation of small section rectangular tube in parallel welding

The welding temperature field and deformation of parallel arrangement small-section rectangular tubes is calculated by using a non-contact model. After comparing the computed results with the experimentally measured results, it shows that there exist big errors when applying this model to the numerical simulation of small-section rectangular tube＇ s welding temperature field and deformation. Based on a simple analysis of the errors, a contact model is presented. The heat transfer and stress analysis between small-section rectangular tubes and clamping fixture are simulated by using direct constraints method, and then the laws of the temperature distribution, which coincide with experiment, are obtained. A further numerical analysis of the stress and deformation are made, it shows that a ＂T＂ shaped stress-field is formed in the vicinity of the weld. As the stress-field departs from the centroid of tubes＇, this leads to the small rectangular tubes not only have a longitudinal deflection, but also have a transverse bending and deformation.

Cross-sectional distortion behaviors of thin-walled rectangular tube in rotary-draw bending process

The cross-sectional distortion usually appears during rotary-draw bending process of thin-walled rectangular tube with small bending radius.To study the cross-sectional distortion of the tube,a three-dimensional finite-element model of the process was developed based on ABAQUS/Explicit code and its reliability was validated by experiment.Then,the cross-sectional distortion behaviors of the tube were investigated.The results show that a zone of larger circumferential stress appears on the tube when bending angle reaches 30°.And in the larger circumferential stress zone,the sagging phenomenon is produced obviously.The maximum cross-sectional distortion is located in the larger circumferential stress zone and the angle between the plane of maximum cross-sectional distortion and the bending reference plane is about 50°.The position of the maximum cross-sectional distortion keeps almost unchanged with the variation of the clearances between dies and tube.

Cross-sectional deformation behavior of double-ridged rectangular tube with fillers in different stages of H-typed bending

The bent double-ridged rectangular tube(DRRT)with high forming quality is helpful to improve the microwave transmission accuracy.For reducing the cross-sectional deformation in the H-typed bending process,in addition to using rigid mandrel to support the inside of tube,ridge groove fillers are also added to restrict the deformation of ridge grooves.Because of the change of stress and strain state of bent tube in bending,rigid mandrel retracting and specially twicespringback stages,and the springback of fillers,the cross-sectional deformation of tube in each stage may be different.Therefore,based on the ABAQUS platform,the finite element models(FEM)for H-typed bending,mandrel retracting and twice-springback stages of H96 DRRT with fillers were established and validated.It is found that,for the height and width deformation of tube and spacing deformation of ridge grooves,retraction of mandrel can make the distribution of these deformations more uniform along the bending direction.The first springback can reduce these deformations significantly,which should be emphasized.But the second springback only increases them by less amount,which can be ignored.The smaller height deformation of ridge groove and filler can be neglected.

Cross-sectional deformation of H96 brass double-ridged rectangular tube in rotary draw bending process with different yield criteria

Different yield criterion has great difference in predicting the deformation of tube with different material.In order to improve the prediction accuracy of the cross-sectional deformation of the double-ridged rectangular tube(DRRT)during rotary draw bending(RDB)process,Mises isotropic yield criterion,Hill’48 and Barlat/Lian anisotropic yield criteria commonly used in practical engineering are introduced to simulate RDB of DRRT.The inverse method combining uniaxial tensile test of whole tube and response surface methodology was proposed to identify the parameters of Hill’48 and Barlat/Lian yield criteria of small-sized H96 brass extrusion DRRT as well.Then based on ABAQUS/Explicit platform,the FE models of RDB process of DRRT considering Mises,Hill’48 and Barlat/Lian yield criteria were built.The results show that:The variation trend of cross-sectional deformation ratio is same when using different yield criteria.The cross-sectional deformation ratio by using Mises yield criterion is close to that by using Hill’48 yield criterion.However,there is a quite difference between by using Barlat/Lian yield criterion and by using Mises or Hill’48 yield criteria.The prediction values of cross-sectional height deformation by using three yield criteria all underestimate the experiment ones,and the prediction values of cross-sectional width deformation overestimate the experiment ones.By comparing the simulation results of cross-sectional deformation of the DRRT with different yield criteria and experiment ones,Barlat/Lian yield criterion is found to be suitable for describing the RDB process of DRRT.

Thermal cracking characteristics of n-decane in the rectangular and circular tubes

To investigate the effect of regenerative cooling channel geometry on pyrolysis of endothermic hydrocarbon fuel,a series of supercritical pyrolysis experiments of n-decane in the rectangular and circular tubes were conducted.Moreover,sensitivity analysis of production of propylene and methane as well as CFD simulation were also done.The results showed that gas yield and conversion in the circular tube with an inner diameter of 2 mm had a similar tendency with the one of 1.5 mm in inner diameter.The conversion in the circular tube was much less than that in the rectangular tube at the same outlet temperature.The heat sink of the rectangular tube at the same outlet temperature was larger than that of circular tubes,but the temperature at the corner of the rectangular tube was relatively high.According to the experimental data of the test tubes,a correlation between the conversion and the temperature in the rectangular and circular tubes at the same outlet temperature was fitted,providing a reference for the design of regenerative cooling channels.

Experimental study of the pinned double rectangular tube assembled buckling-restrained brace

目的:通过双矩管装配式防屈曲支撑的滞回试验研究,探讨防屈曲支撑可能存在的破坏模式及各设计参数对支撑耗能性能的影响,验证支撑端部构造细节的合理性,提出支撑设计建议。创新点:1.试验研究铰接双矩管装配式防屈曲支撑的滞回性能;2.获得4种支撑破坏模式。方法:通过对7根铰接双矩管装配式防屈曲支撑的滞回性能试验,研究支撑外围盖板厚度、内核加强翼板高度和外围槽钢翼缘高度等参数对防屈曲支撑破坏机理及耗能性能的影响。结论:1.外围盖板厚度太薄,支撑易发生端部折曲破坏;2.端部转动受限制的支撑,其滞回性能优于纯铰接防屈曲支撑,但支撑连接节点处的附加弯矩不容忽视;3.支撑均表现出优良的屈曲耗能性能,验证了试验试件端部构造细节的合理性。

Ductility and Ultimate Capacity of Concrete-Filled Lattice Rectangular Steel Tube Columns

A kind of concrete-filled lattice rectangular steel tube(CFLRST)column was put forward.The numerical simulation was modeled to analyze the mechanical characteristic of CFLRST column.By comparing the load-deformation curves from the test results,the rationality and reliability of the finite element model has been confirmed,moreover,the change of the section stiffness and stress in the forcing process and the ultimate bearing capacity of the column were analyzed.Based on the model,the comparison of ultimate bearing capacity and ductility between CFLRST column and reinforced concrete(RC)column were also analyzed.The results of the finite element analysis show that the loading process of CFLRST column consists of elastic stage,yield stage and failure stage.The failure modes are mainly strength failure and failure of elastoplastic instability.CFLRST column has higher bearing capacities in comparison with reinforced concrete columns with the same steel ratio.In addition,the stiffness degeneration of CFLRST column is slower than RC column and CFLRST column has good ductility.

An Experimental Study of Condensation Heat Transfer in Sub-Millimeter Rectangular Tubes

The characteristics of local heat transfer and pressure drops were experimentally investigated using condensing R134a two-phase flow, in single rectangular tubes, with hydraulic diameter of 0.494, 0.658, and 0.972 mm. New experimental techniques were used to measure the in-tube condensation heat transfer coefficient especially for the low heat and mass flows. Tests were performed for a mass flux of 100, 200, 400, and 600 kg/m2s, a heat flux of 5 to 20 kW/m2, and a saturation temperature of 40℃. In this study, effect of heat flux, mass flux, vapor qualities, and hydraulic diameter on flow condensation were investigated and the experimental local condensation heat transfer coefficients and frictional pressure drop are shown. The experimental data of condensation Nusselt number are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large inner diameter round tubes.

An Open Rectangular Waveguide Grating for Millimeter-Wave Traveling-Wave Tubes

Millimeter-wave traveling-wave tube （TWT） prevails nowadays as the amplifier for radar, communication and electronic countermeasures. The rectangular waveguide grating is a promising all-metal interaction circuit for the millimeter-wave TWT with advantages of high power capacity, fine heat dissipation, scalability to smaller dimen- sions for shorter wavelengths, compact structure and robust performance. Compared with the traditional closed structure, the open rectangular waveguide grating （ORWG） has wider bandwidth, lower cut-off frequency, and higher machining precision for higher working frequencies due to the open transverse. It is a potential structure that can work in the millimeter wave and even Terahertz band. The rf characteristics including dispersion and interaction impedance are investigated by both theoretic calculation and software simulation. The influences of the structure parameters are also discussed and compared, and the theoretical results agree well with the simula- tion results. Based on the study, the ORWG will favor the design of a broadband and high-power millimeter-wave TWT.

Experimental investigation of enhanced heat transfer for fined circular tube heat exchanger with rectangular fins

Presents a set of data for flow and heat transfer of finned-tube bundle under the condition of high air flow velocity. Air flow and heat transfer over a 4×4 (columns×rows) finned-tube heat exchanger with rectangular fins was investigated experimentally in a wind tunnel with constant wall temperatures condition. The air flow velocity based on the minimum flow cross-section area over flow channel ranged from 13.8 to 50.2 m/s, the heat transfer rate ranged from 21.8 to 47.1 kW, and the air temperatures increase ranged from 10.9 to 19.8 ℃. The present results were compared with results calculated from correlations proposed by CSPE. For air flow velocity less than 25 m/s, these two results of heat transfer agreed well with each other, whereas for larger velocity, our test data disagreed with the CSPE correlauions. For the friction factor, present data are much higher than the predicted results in the whole range. Finally, correlations for friction factors and heat transfer coefficients are proposed based on the experimental results.

基于回归分析法的矩形槽圆管吸能特性研究

为了研究矩形槽圆管吸能特性规律,提出了一种基于回归分析法的结构参数与吸能特性关系的拟合方法。针对轴向冲击下的圆管动态响应,首先,建立了6005A-T6材料的Cowper-Symonds本构模型,并验证了仿真模型的准确性;其次,设计了正交试验,建立了吸能特性与结构参数之间的计算模型;然后,利用多元线性与非线性回归分析方法对计算模型参数求解,并对比了两种拟合结果,得到了峰值力和吸能量的经验公式;接着,对比经验公式与有限元数值计算值表明,经验公式在研究范围内具有较高准确性,误差在8%以内;最后,引入吸能性能指标并使用遗传算法对圆管进行了结构优化,优化结果表明,在研究范围内当直径和槽端距最小、壁厚和槽宽最大、槽深最浅时,矩形槽圆管的吸能性能最优。

矩形管下气相螺旋爆轰的结构及传播方式

为探索极限条件下矩形管道截面长宽比对于螺旋爆轰传播的影响,采用基于五阶WENO有限差分格式和两步总包反应模型的Euler方程,对三维气相螺旋爆轰波在矩形截面管道中的结构及其传播方式进行了数值研究。通过模拟不同管道截面尺寸下爆轰波的三波线运动轨迹、流场分布及高压印记结构,揭示了截面几何尺寸对气相临界爆轰波稳定传播的影响规律。结果表明:螺旋爆轰能在一定范围的小管道截面尺寸内通过横、竖两条三波线及其相互作用形成的斜三波线的运动来维持传播;随着管道截面尺寸长宽比的增加,螺旋爆轰在壁面上形成的高压印记逐渐由倾斜的条带结构变成局部点状分布结构,波阵面上的斜三波线的轨迹也由方管中沿着单一方向的圆周运动逐渐发展为具有转向机制的复杂运动轨迹;当长宽比进一步增加时,三维螺旋爆轰存在向二维结构的单头爆轰结构退化的趋势。

超临界甲烷在矩形通道内传热特性研究

为探究重力对单侧受热情况下矩形再生冷却通道换热性能的影响,采用RNGk-ε湍流模型对超临界压力下甲烷在矩形弯曲管内流动和传热性能进行研究。考察了4种受热情况下重力对内壁面温度、传热系数和热流密度等参数的影响,并引入综合换热评价因子(PEC)着重分析了重力对强化换热能力的作用。结果表明,在直管段重力的存在使管道内形成二次流动,流体间掺混加剧,管道传热性能提升,但在部分弯管段重力使传热性能略微降低;θ=90°时,4种加热工况下传热系数均出现峰值,从无量纲数的分布得知,通道传热能力达到最优,且无重力管道更为显著;通过对比PEC因子,发现重力使再生冷却管道整体换热性能增强,上壁面受热时更为明显。

矩形钢管混凝土束风机塔筒风振特性研究

随着风电资源优势区开发逐渐饱和,风电开发的重心开始向风资源条件相对恶劣的低风速地区转移,分布式、大功率、高塔筒和长叶片已经成为风电行业发展趋势。基于此提出了一种新型的矩形钢管混凝土束风机塔筒,该塔筒由矩形钢管混凝土束拼接而成,具有强度高、刚度大和耗能能力强的优点。为研究该塔筒结构的风振响应特性,选用Kaimal脉动风速功率谱,采用谐波合成法模拟风荷载时程曲线,对其进行了动力时程分析,并计算了风振系数及等效静力风荷载。结果表明:该新型塔筒在额定风速下位移塔顶位移最大值为911.84 mm,对应的水平位移角为1/154,符合规范要求。塔筒各构件的强度较好,且具有较大的安全富余度。基于位移等效的阵风荷载因子法计算得到的风振系数值较低;在惯性风荷载法计算得到的等效静力风荷载作用下,结构位移、基底剪力与结构随机振动分析得到的基本一致。

应用于方矩管生产的扁方吹杆压管机的设计研究

为了解决方矩管在实际生产过程中出现顶吹杆生产效率低、安全系数低的问题,基于生产实际设计了一款扁方吹杆压管机,设计的扁方吹杆压管机由底座、安装板、压管机构等组成,通过对设计的设备进行应用研究,发现扁方吹杆压管机能够有效解决方矩管在生产过程中的吹杆问题,同时提升了方矩管的生产效率,减少了设备的磨损损耗。

学位帽造型铝方通百叶施工技术

大型体育场馆外立面采用铝方通百叶比较少见,采用学位帽造型的铝方通百叶更是罕见。本文结合某项目现场实际施工情况,阐述了施工过程中遇到的难点,为类似工程施工积累了经验。

内置异形箍筋矩形钢管混凝土柱的轴压力学性能

钢管混凝土作为一种发展前景广阔的结构形式,具有较好的承载力和塑性变形能力。矩形钢管混凝土柱作为其中常见的一种形式,在实际工程中的应用较为广泛。该研究基于矩形钢管混凝土在实际应用中存在的长短边约束不一致和对核心混凝土约束不足两个问题,探究一种新型的矩形钢管混凝土构件,即内置异形箍筋矩形钢管混凝土柱。为此,对11根内置异形箍筋矩形钢管混凝土柱、2根内置跑道形箍筋的矩形钢管混凝土柱、2根普通矩形钢管混凝土柱开展了轴压力学性能试验,重点分析了并束距、钢管壁厚、混凝土强度等级、箍筋间距、箍筋直径、内置用钢量等重要参数对内置异形箍筋矩形钢管混凝土柱的轴压承载力和延性的影响规律。结果表明:在总用钢量不变的情况下,将矩形钢管的壁厚减薄,并加工成异形箍筋内置于核心混凝土中,能够有效地提高试件的轴压承载力和延性;内置异形箍筋矩形钢管混凝土柱的轴压过程可以分为4个阶段——弹性阶段、弹塑性阶段、塑性强化段、下降段;相比于普通矩形钢管混凝土柱,内置异形箍筋矩形钢管混凝土柱有更为饱满的塑性强化段。在试验和参数分析结果的基础上,采用已有的约束混凝土本构模型,推导得到内置异形箍筋矩形钢管混凝土柱的轴压承载力计算公式。该研究可为实际工程应用提供科学依据和数据参考。

新建市政隧道下穿多线运营铁路施工地表沉降研究——以郑州火车站操场街隧道工程为例

新建隧道近距离下穿运营铁路施工安全风险高,易导致上方运营铁路路基、轨道变形,影响列车行车安全。为降低施工风险,减少对运营铁路的影响,以郑州火车站操场街隧道工程为研究背景,基于有限元数值模拟,分析矩形顶管法和管幕暗挖法施工引起的运营铁路路基沉降变化。并对矩形顶管法和管幕暗挖法进行施工工艺、施工进度、沉降控制等多方面的综合比选,给出新建隧道下穿既有运营铁路安全施工方案。研究表明,运营铁路与新建隧道正交时,隧道正上方铁轨沉降最大,隧道中心点两侧铁轨沉降呈对称分布;矩形顶管法施工铁轨累计沉降值最大为5.6 mm,管幕暗挖法施工铁轨累计沉降值最大为4.04 mm,管幕暗挖法对运营铁路铁轨沉降的影响小于矩形顶管法。

E波段矩形环对角双杆行波管的研究

高功率、宽频带是当前科研人员研究行波管的主流方向,中国工信部最新规定E波段的频率范围在71-76 GHz/81-86 GHz。虽然传统的环圈慢波结构有更高的互作用阻抗,但是当其达到E波段及以上由于其结构特点在现实中难以加工,所以难以实现工作在E波段,为了提升输出功率,本文设计了E波段矩形环对角双杆慢波结构行波管的研究,对其进行注波互作用模拟仿真和计算,带状电子注采用19.1 kV的电压,电流为0.14 A的条件下,行波管可获得最大400 W的瞬时输出功率,增益为46.02 dB、电子效率15%。

Simulation Analysis of Torsion Beam Hydroforming Based on the Fluid-Solid Coupling Method

Hydroformed parts are widely used in industrial automotive parts because of their higher stiffness and fatigue strength and reduced weight relative to their corresponding cast and welded parts.This paper reports a hydraulicforming experimental platform for rectangular tube fittings that was constructed to conduct an experiment on the hydraulic forming of rectangular tube fittings.A finite element model was established on the basis of the fluid–solid coupling method and simulation analysis.The correctness of the simulation analysis and the feasibility of the fluid–solid coupling method for hydraulic forming simulation analysis were verified by comparing the experimental results with the simulation results.On the basis of the simulation analysis of the hydraulic process of the torsion beam using the fluid–solid coupling method,a sliding mold suitable for the hydroforming of torsion beams was designed for its structural characteristics.The effects of fluid characteristics,shaping pressure,axial feed rate,and friction coefficient on the wall thicknesses of torsions beams during formation were investigated.Fluid movement speed was related to tube deformation.Shaping pressure had a significant effect on rounded corners and straight edges.The axial feed speed was increased,and the uneven distribution of wall thicknesses was effectively improved.Although the friction coefficient had a nonsignificant effect on the wall thickness of the ladder-shaped region,it had a significant influence on a large deformation of wall thickness in the V-shaped area.In this paper,a method of fluid-solid coupling simulation analysis and sliding die is proposed to study the high pressure forming law in torsion beam.