A novel efficient energy absorber with free inversion of a metal foam-filled circular tube

In this paper, a novel efficient energy absorber with free inversion of a metal foam-filled circular tube(MFFCT) is designed, and the axial compressive behavior of the MFFCT under free inversion is studied analytically and numerically. The theoretical analysis reveals that the energy is mainly dissipated through the radial bending of the metal circular tube, the circumferential expansion of the metal circular tube, and the metal filled-foam compression. The principle of energy conservation is used to derive the theoretical formula for the minimum compressive force of the MFFCT over free inversion under axial loading. Furthermore, the free inversion deformation characteristics of the MFFCT are analyzed numerically. The theoretical steady values are found to be in good agreement with the results of the finite element(FE) analysis. The effects of the average diameter of the metal tube, the wall thickness of the metal tube, and the filled-foam strength on the free inversion deformation of the MFFCT are considered. It is observed that in the steady deformation stage, the load-carrying and energy-absorbing capacities of the MFFCT increase with the increase in the average diameter of the metal tube, the wall thickness of the metal tube, or the filled-foam strength. The specific energy absorption(SEA) of free inversion of the MFFCT is significantly higher than that of the metal tube alone.

Experimental investigation on flow characteristics in circular tube inserted with rotor-assembled strand using PIV

Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube inserted with rotor-assembled strand was conducted and the flow characteristics on transverse section and longitudinal section were analyzed.The results showed that swirling flow was produced in the tube inserted with rotors and it was particularly strong within the swing diameter of the rotor on the section that contains the rotor;the average turbulence intensity and the radial velocity were improved notably; the velocity vectors on the longitudinal section remained along the direction of a straight line; both the swirling flow and average turbulence intensity were higher for the rotor with three blades than for the rotor with two blades except that the radial velocity was approximate, but they were all reduced by enlarging the lead of the rotor.Characterization of the flow patterns in a circular tube contributes to understanding the heat transfer efficiency and scale inhibition performance of the rotor-assembled strand and provides guidance for its application.

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.

Heat transfer characteristics of nanofluid through circular tube

Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.

Numerical Perspective of Second-Harmonic Generation of Circumferential Guided Wave Propagation in a Circular Tube

The effect of second-harmonic generation （SHG） by primary （fundamental） circumferential guided wave （CGW） propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.

Natural dynamic characteristics of a circular cylindrical Timoshenko tube made of three-directional functionally graded material

The natural dynamic characteristics of a circular cylindrical tube made of three-directional(3 D)functional graded material(FGM)based on the Timoshenko beam theory are investigated.Hamilton’s principle is utilized to derive the novel motion equations of the tube,considering the interactions among the longitudinal,transverse,and rotation deformations.By dint of the differential quadrature method(DQM),the governing equations are discretized to conduct the analysis of natural dynamic characteristics.The Ritz method,in conjunction with the finite element method(FEM),is introduced to verify the present results.It is found that the asymmetric modes in the tube are controlled by the 3 D FGM,which exhibit more complicated shapes compared with the unidirectional(1 D)and bi-directional(2 D)FGM cases.Numerical examples illustrate the effects of the axial,radial,and circumferential FGM indexes as well as the supported edges on the natural dynamic characteristics in detail.It is notable that the obtained results are beneficial for accurate design of smart structures composed from multi-directional FGM.

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

Nosing process of empty and foam-filled circular metal tubes on semispherical die by theoretical and experimental investigations

Nosing process of circular metal tubes in empty and polyurethane foam-filled conditions on a semispherical rigid die was analyzed by theoretical and experimental methods.A new theoretical model of plastic deformation of circular metal tubes was demonstrated during the nosing process on a rigid semispherical die.Based on the analytical model,some theoretical relations were calculated to estimate instantaneous forming load and dissipated energy of empty and foam-filled circular metal tubes versus axial displacement.Some circular brazen and aluminum tubes were prepared and shaped into semispherical nosed nozzles to verify the present theory.Comparison of theoretical predictions and the corresponding experimental measurements reveals that predicted load?displacement and dissipated energy?displacement diagrams by theoretical formulas have a good correlation with the corresponding experimental curves and it proves verity of the theory.Also,the present theory shows that dissipated energy and axial load of empty tubes depend on material type,wall thickness and diameter of the tubes and they are independent of tube initial length.Furthermore,the experimental results show that the presence of polyethylene Teflon-constraints increases ultimate axial displacement of the forming process.

Numerical Simulation and Optimization of Perforated Tube Trolley in Circular Cooler

Three symmetrically perforated tubes were arranged in the circular cooler trolley as auxiliary cooling inlet to improve the cooling performance of the sintered body during the production process. Fluent 15.0 has been used to simulate the process;the study shows that the perforated tube structure trolley has changed the temperature field within the sintering area, thereby improving the sintering area of the cooling effect and uniformity, also greatly reducing the cooling time. Compared with the traditional trolley, the best structure of the porous tube trolley has reduced 41% cooling time and increased 50% waste heat recovery.

Local Tensile Strength of Connection Between H-Steel Beam Flange and Concrete-Filled Circular Column Tube with Through Diaphragm

This paper focused on investigating local tensile strength of connection between steel beam flange and concrete-filled circular column tube with through diaphragm. Three specimens were designed and tested to failure, and the structure behavior was studied by experiment and FEM analysis. On the basis of the results obtained, an estimation for local plastic and ultimate strengths of the connections using yield line theory was attempted, which results in a good prediction.

Experimental Observation of Cumulative Second-Harmonic Generation of Circumferential Guided Wave Propagation in a Circular Tube

The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.

Response features of nonlinear circumferential guided wave on early damage in inner layer of a composite circular tube

A theoretical model to analyze the nonlinear circumferential guided wave(CGW) propagation in a composite circular tube(CCT) is established. The response features of nonlinear CGWs to early damage [denoted by variations in third-order elastic constants(TOECs)] in an inner layer of CCT are investigated. On the basis of the modal expansion approach, the second-harmonic field of primary CGW propagation can be assumed to be a linear sum of a series of double-frequency CGW(DFCGW) modes. The quantitative relationship of DFCGW mode versus the relative changes in the inner layer TOECs is then investigated. It is found that the changes in the inner layer TOECs of CCT will obviously affect the driving source of DFCGW mode and its modal expansion coefficient, which is intrinsically able to influence the efficiency of cumulative second-harmonic generation(SHG) by primary CGW propagation. Theoretical analyses and numerical simulations demonstrate that the second harmonic of primary CGW is monotonic and very sensitive to the changes in the inner layer TOECs of CCT, while the linear properties of primary CGW propagation almost remain unchanged. Our results provide a potential application for accurately characterizing the level of early damage in the inner layer of CCT through the efficiency of cumulative SHG by primary CGW propagation.

HYBRID PERTURBATION-GALERKIN SOLUTION OF THE FLOW IN A CIRCULAR CROSS-SECTION TUBE WITH CONSTRICTION

Using hybrid perturbatin_Galerkin technique,a crcular cross_section tube model with sinusoidal wall is studied.This technique can remove the limitation of small parameters for perturbation and the difficulty of selecting good coordinate functions about Galerkin technique.The effects caused by the boundary conditions and the Reynolds number on the flow were discussed.The position of the separate and reattachment points was obtained.The tendency of the variation about the shear stress on the wall and friction factor along the axis direction were also analyzed.The results at a small parameter have good agreements with the perturbation ones.

The Influence of Notch Depth on the Response of Local Sharp-Notched Circular Tubes under Cyclic Bending

In this paper, the mechanical behavior and buckling failure of SUS304 stainless steel tubes with different local sharp-notched depths subjected to cyclic bending were experimentally investigated. It can be seen that the experimental moment-curvature relationship exhibits cyclic hardening and becomes a steady loop after a few cycles. However, the experimental ovalization-curvature relationship exhibits an increasing and ratcheting manner with the number of the bending cycles. In addition, higher notch depth of a tube leads to a more severe unsymmetrical trend of the ovalization-curvature relationship. It has been observed that the notch depth has almost no influence on the moment-curvature relationship. But, it has a strong influence on the ovalization-curvature relationship. Finally, the theoretical model proposed by Kyriakides and Shaw [1] was used in this study for simulating the controlled curvature-number of cycles to produce buckling relationship. Through comparison with the experimental data, the theoretical model can properly simulate the experimental

Characterization of inner layer thickness change of a composite circular tube using nonlinear circumferential guided wave:A feasibility study

The feasibility of using the nonlinear effect of primary circumferential guided wave(CGW)propagation for characterizing the change of inner layer thickness of a composite circular tube(CCT)has been investigated.An appropriate mode pair of the fundamental and double-frequency CGWs(DFCGWs)has been selected to enable the second harmonics of primary wave mode in the given CCT to accumulate along the circumferential direction.When changes in the inner layer thickness(described as the equivalent inner layer thickness)take place,the corresponding nonlinear CGW measurements are conducted.It is found that there is a direct correlation between change of equivalent inner layer thickness of the CCT and the relative acoustic nonlinearity parameter(Δβ)measured with CGWs propagating through one full circumference,and that the effect of second-harmonic generation(SHG)is very sensitive to change in the inner layer thickness.The experimental result obtained demonstrates the feasibility for quantitatively assessing the change of equivalent inner layer thickness in CCTs using the effect of SHG by primary CGW propagation.

Effects of Microstructure on Quasi⁃Static Transverse Loading Behavior of 3D Circular Braided Composite Tubes

The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained to analyze the effects of braiding parameters including the braiding angle, the wall thickness, and the diameter on the transverse loading of 3D circular braided composite tubes. Breaking loads, moduli and strengths had also been used to describe the transverse loading behaviors. The failure morphologies were shown to reveal damage mechanisms. From the results, the increase in braiding angle, wall thickness and diameter increases the ability of anti-deformation and breaking load of braided tubes. The breaking load of specimen with a braiding angle of 45° is about 1.68 times that of specimen with a braiding angle of 15°. The breaking load of specimen with 4 layers of yarns is about 2.15 times that of specimen with 2 layers of yarns. The breaking load of the tube with a diameter of 25.5 mm is about 2.39 times that of the tube with a diameter of 20.5 mm.

圆钢管型钢再生混凝土组合柱滞回性能非线性有限元分析

基于圆钢管型钢再生混凝土组合柱低周反复荷载试验研究,采用OpenSees软件对该组合柱进行了滞回性能数值分析,获取了组合柱的滞回曲线及抗震性能指标,并与试验结果进行了比较,验证了组合柱数值模型的合理性。在此基础上,对组合柱的滞回性能开展了参数影响分析。结果表明:再生骨料取代率从0增大到100%,组合柱的峰值荷载下降了7.78%,延性略有降低;提高再生混凝土强度、型钢强度及圆钢管强度,对于提升组合柱的承载力及刚度是有利的,但却使组合柱的脆性增大;随着轴压比的增大,组合柱的承载力呈现先上升后下降的趋势,而延性逐渐变差;型钢配钢率从5.54%增至9.99%,组合柱的峰值荷载提高了24.34%,但对于改善组合柱的延性不明显;增大钢管壁厚对组合柱的承载力和延性均是有利的。

内置工字型CFRP型材高强圆钢管高强混凝土轴压短柱组合效应分析

目的 研究内置工字型CFRP型材的高强圆钢管高强混凝土短柱在轴心压力作用下三种材料的组合效应。方法 采用有限元分析软件ABAQUS对其进行数值模拟,通过相关试验验证模型的准确性,并对典型构件的破坏形态、受力全过程曲线进行分析,揭示构件各组成部分之间的相互作用和工作机理,评估CFRP配置率、钢材屈服强度、混凝土抗压强度、约束效应系数对组合效应的影响。结果 在高强圆钢管高强混凝土柱中内置CFRP型材,对构件的延性及安全裕度有显著提高,并改善了高强圆钢管对高强混凝土的约束,提高了构件的组合效应。结论 CFRP配置率控制在5.9%~8.4%,约束效应系数在1.2~1.4,钢材屈服强度不大于770 MPa时,构件中三种材料组合效应最佳。

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。

玄武岩纤维增强复合材料拉挤圆管抗弯性能研究

为使玄武岩纤维增强复合材料(Basalt Fiber Reinforced Polymer,BFRP)拉挤圆管在桥梁工程中得到更广泛地应用,对其抗弯性能进行试验及有限元分析。对2根长度为750 mm的BFRP拉挤圆管进行三点抗弯试验;采用LS-DYNA有限元软件对试验过程进行模拟,验证有限元模拟的正确性;在保持BFRP拉挤圆管总厚度不变的条件下,研究内、外层双向纤维布的铺设厚度和角度对抗弯性能的影响。结果表明:试件从加载至破坏分为线弹性阶段、下降阶段和残余阶段,试件破坏后残余强度较大且卸载后迅速回弹恢复几何形状;有限元模拟试件的荷载~滑移曲线、失效现象和试验结果吻合较好,有限元模拟正确;布置适量厚度的内、外层双向纤维布可以提高试件的抗弯承载力;将内、外层双向纤维布铺设方向由90°变为45°后,抗弯承载力进一步提高,随着外层45°纤维布厚度增加,破坏时的挠度下降。建议制作BFRP拉挤圆管时,布置适量厚度的双向纤维布,角度以45°为宜。