基于FLUENT的换热设备中并联管组均流模型设计

基于流体动力学基本原理和FLUENT软件,以并联管组的支管直径为设计参数,利用敏感性分析法确定敏感参数。通过多元线性拟合得出流量分布不均匀系数与敏感参数的二元三次关系式,计算得出当流量分布不均匀系数在敏感参数取值范围内取最小值时的支管直径大小。利用FLUENT对同尺寸并联管组的流量分布不均匀系数进行验证计算。计算结果表明:优化后的流量分布不均匀系数比优化前降低了68.2%,提高了并联管组的流量分布均匀性,为今后并联管组的工程设计提供了一种方法。     

Testing and Modeling of a New Moment Connection of Concrete-Filled FRP Tubes to Footings under Monotonic and Cyclic Loadings

This study explores a new moment connection of concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) to concrete footing. The tube is tightly fitted and adhesively bonded to a short reinforced concrete stub protruding from the footing, which facilitates concrete filling of the tube without the need for shoring. To establish the critical stub length (Xcr), specimens with heavily steel-reinforced stubs varying in length from 0.5D to 2.0D, where D = diameter of the CFFT, were fabricated and tested in flexure by using a cantilever setup. The Xcr required to achieve flexural failure of the CFFT was 1.05D. Additional specimens with a sufficient stub length of 1.5D were then fabricated to examine the effect on strength and ductility of the steel reinforcement ratio (ρs) in the stub. The optimal ρs of the stub required for the CFFT to reach flexural failure was 3.2%. Finally, the effect of low-cycle reversed bending fatigue was studied with and without an axial compression load. Remarkable ductility associated with the formation of a plastic hinge was observed at ρs of 2%. An analytical model capable of predicting (1)?moment capacity of the connection, (2)?whether failure is governed by flexure or bond, and (3)?Xcr was developed and validated. It was then used in a parametric study to explore the effects of CFFT mechanical and geometric properties on Xcr.     

Collapse of pressurized elastoplastic tubular members under lateral loads

The present work examines the collapse of tubular members subjected to lateral (transverse) quasi-static loading in the presence of uniform pressure. In particular, it investigates pressure effects on the ultimate lateral load of tubes and on their energy absorption capacity. External pressure is mainly considered, whereas internal pressure effects are also discussed. Tubes are modeled with shell finite elements, accounting for geometric and material nonlinearities. Relatively thick steel and aluminum tubes (D/t50), which exhibit significant inelastic deformations, are considered. Two-dimensional cases are examined first, where lateral loading is imposed by either two rigid plates or by two opposite radial loads. Three-dimensional cases are also analyzed, where the load is applied either through a pair of opposite wedge-shaped indenters or a single spherical indenter. The results are presented in terms of load–deflection curves for different levels of pressure, and indicate that the presence of pressure has significant effects on tube response. Deformed shapes of tubes are depicted and discussed, and comparison with test data from non-pressurized pipes is conducted. Finally, simplified analytical models are presented for two-dimensional and three-dimensional load configurations, which yield closed-form expressions, compare fairly well with the finite element results and illustrate some important features of tube response in an elegant manner.     

平面弯管的计算机辅助设计与绘图

探讨以AutoCAD为图形支撑软件,以C语言为编程语言,通过.DXF文件,将C语言程序的计算结果与AutoCAD的 图形显示连接起来,在AutoCAD系统下显示和输出图样,实现了平面弯管的计算机辅助设计与绘图。     

换热器传热管固有振动的罚单元有限元计算方法

罚单元的有限元法可以有效地处理换热器中传热管与折流板之间的约束联结。本文提出了在局部斜坐标系下建立管（梁）与板在联结点处的约束方程，并通过引入伪节点应变和应力，推导了罚单元的单元刚度阵，通过推导证明了采用罚单元的方法，约束方程可以得到近似满足。本文提出的方程扩大了罚单元对复杂联结情况的描述，也避免了在整体坐标下建立约束方程的复杂性。通过对一个多圈螺旋式传热管固有振动的计算，证明了本方法的有效性。     

Section slenderness limits of very high strength circular steel tubes in bending

This paper investigates the bending behavior of very high strength (VHS) circular steel tubes. The tested VHS tube has a normal yield stress of 1350 MPa and an ultimate strength of 1500 MPa. A total of 12 specimens, with the normal diameter ranging from 31.8 to 75 mm and the tube thickness between 1.6 and 2.0 mm, were tested. Large bending deflection was achieved for VHS tubes with the diameter to thickness ratio up to 24. Full plastic moment was reached for tubes with the section slenderness of 197 or less. New plastic slenderness limits of 117 and 153 were proposed based on the beam plastic rotation capacity of 4 and 3. A yield slenderness limit of 264 was proposed for VHS tubes.     

Fatigue Life Assessment and Static Testing of Structural GFRP Tubes Based on Coupon Tests

Fiber-reinforced polymer (FRP) hollow tubes are used in structural applications, such as utility poles and pipelines. Concrete-filled FRP tubes (CFFTs) are also used as piles and bridge piers. Applications such as poles and marine piles are typically governed by cyclic bending. In this paper, the fatigue behavior of glass-FRP filament-wound tubes is studied using coupons cut from the tubes. Several coupon configurations were first examined in 24 tension and five compression monotonic loading tests. Fatigue tests were then conducted on 81 coupons to examine several parameters; namely, loading frequency as well as maximum-to-ultimate (σmax/σult) and minimum-to-maximum (σmin/σmax) stress ratios, including tension tension and tension compression, to simulate reversed bending. The study demonstrated the sensitivity of test results and failure mode to coupon configuration. The presence of compression loads reduced fatigue life, while increasing load frequency increased fatigue life. Stiffness degradation behavior was also established. To achieve at least one million cycles, it is recommended to limit (σmax/σult) to 0.25. Models were used to simulate stiffness degradation and fatigue life curve of the tube. Fatigue life predictions of large CFFT beams showed good correlation with experimental results.     

Concrete-Filled Square and Rectangular FRP Tubes under Axial Compression

This paper presents results of an experimental study on the behavior of square and rectangular concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) under concentric compression. FRP tubes were designed as column confinement reinforcement and were manufactured using unidirectional carbon fiber sheets with fibers oriented in the hoop direction. The effects of the thickness and corner radius of the tube, sectional aspect ratio, and concrete strength on the axial behavior of CFFTs were investigated experimentally. Test results indicate that FRP confinement leads to substantial improvement in the ductility of both square and rectangular columns. Confinement provided by the FRP tube may also improve the axial load-carrying capacity of the square and rectangular columns if the confinement effectiveness of the FRP tube is sufficiently high. The results also indicate that the confinement effectiveness of FRP tubes is higher in square columns than in rectangular columns, and in both sections the effectiveness of confinement increases with the corner radius. Furthermore, for a given confinement level, improvement observed on the axial behavior of concrete due to confinement decreases with increasing concrete strength.     

带包覆层铁磁性管道腐蚀脉冲涡流检测技术

应用脉冲涡流检测技术,对带包覆层的铁磁性管道腐蚀进行了检测。对不同厚度的包覆层、不同面积和深度的腐蚀缺陷进行了试验,分析检测灵敏度的变化。试验结果表明,对于较大面积的腐蚀缺陷,即使包覆层较厚,在合适的检测参数下,脉冲涡流也具有很好的检测能力。     

超声引导经阴道穿刺治疗输卵管积水

目的探讨超声引导经阴道穿刺治疗输卵管积水的临床效果。方法对61例输卵管积水患者行超声引导经阴道穿刺抽液及无水乙醇凝固治疗,随访3～12个月。结果61例患者中58例成功完成了液体抽吸及无水乙醇凝固治疗。术后3个月随访53例,其中治愈47例（88．7％）,好转2例（3．8％）,无效4例（7．5％）,总有效率为92．5％。术后12个月随访41例,其中治愈36例（87．8％）,好转2例（4．9％）,无效3例（7．3％）,总有效率为92．7％。所有囊内液细胞学检测均未发现癌细胞。结论超声引导经阴道穿刺治疗输卵管积水技术操作简单、疗效可靠。