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.

Reliability analysis of circular concrete-filled steel tube with material and geometrical nonlinearity

Most of the previous research on concrete-filled steel tube is restricted to a deterministic approach. To gain clear insight into the random properties of circular concrete-filled steel tube, reliability analysis is carried out in the present study. To obtain the Structural nonlinear response and ultimate resistance capacity, material and geometrical nonlinear analysis of circular concrete-filled steel tube is performed with a three-dimensional degenerated beam ele- ment. Then we investigate the reliability of concrete-filled steel tube using the first-order reliability method combined with nonlinear finite element analysis. The influences of such parameters as material strength, slenderness, initial geo- metrical imperfection, etc. on the reliability of circular concrete-filled steel tube column are studied. It can be con- cluded that inevitable random fluctuation of those parameters has significant influence on structural reliability, and that stochastic or reliability methods can provide a more rational and subjective evaluation on the safety of CFT structures than a deterministic approach.

Simulation and Experimental Analysis of Vortex Tube Using Steel Material

Experimental and computational fluid dynamics (CFD) are investigated through the vortex tube system. The benefit of vortex tube is a counter flow type tube, which has further designed and fabricated for investigation. The whole set up is consisting of a simple device that can separate a single stream of compressed air into two streams;one is at high temperature and the other is lower temperature following an inlet gas stream. The advantages of this tube are their compactness, safety, and low equipment cost mainly used in cooling and heating applications. This study addressed three-dimensional flows;the domain is using computational fluid dynamics (CFD) method and experimental approach to optimize the direction of RHVT. Through the CFD analysis, the best cold end diameter (dc), number of nozzles, and the best parameters for obtaining the highest hot gas temperature and lowest cold gas temperature were obtained and verified by experimental procedures.

The Packaging Materials with Carbon Nanotube/Polymer Composites

A polymer-based carbon nano-tubes (CNTs) composite with high electromagnetic (EM) wave shielding effectiveness (SE) and with high mechanical property is developed for packaging of electronic modulus or devices.The liquid crystal polymers (LCP) and melamine formaldehydes (MF) polymer are used to study the orientation effect of CNTs in various polymeric matrix.The influences of orientation,aspect ratio,and mass fraction of CNTs upon the shielding effectiveness (SE) of CNTs-composites are investigated.The higher the orientation,aspect ratio,and weight percentages of nano-materials are, the higher the SE of the carbon composites.The highest SE for the CNTs/LCP nano composite obtained is more than 62 dB. This results may lead to the developing for CPU IC chip packaging.

Experimental and numerical study of the blast wave decrease using sandwich panel by granular materials core

Among the intrinsic properties of some materials,e.g.,foams,porous materials,and granular materials,are their ability to mitigate shock waves.This paper investigated shock wave mitigation by a sandwich panel with a granular core.Numerical simulations and experimental tests were performed using Autodyn hydro-code software and a shock tube,respectively.The smoothed particle hydrodynamics(SPH)method was used to model granular materials.Sawdust and pumice,whose properties were determined by several compression tests,were used as granular materials in the sandwich panel core.These granular materials possess many mechanisms,including compacting(e.g.,sawdust)and crushing(e.g.,pumice)that mitigate shock/blast wave.The results indicated the ineffectiveness of using a core with low thickness,yet it was demonstrated to be effective with high thickness.Low-thickness pumice yielded better results for wave mitigation.The use of these materials with a core with appropriate core reduces up to 88%of the shock wave.The results of the experiments and numerical simulations were compared,suggesting a good agreement between the two.This indicates the accuracy of simulation and the ability of the SPH method to modeling granular material under shock loading.The effects of grain size and the coefficient of friction between grains have also been investigated using simulation,implying that increasing the grain size and coefficient of friction between grains both reduce overpressure.

Calculation and Analysis of Acoustic Characteristics of Straight-Through Perforated Pipe Muffler Based on Multilayer Sound Absorbing Material

Using the multi-physical field simulation software COMSOL,the acoustic characteristics of the multilayer sound absorbing material straight-through perforated pipe muffler are studied by the finite element method.The results show that the finite element calculation of the multilayer sound absorbing material straight-through the perforated pipe muffler agrees well with the experimental measurement results.The reliability of the finite element method for studying the acoustic performance of the straight-through perforated pipe muffler with multilayer sound absorbing materials is shown.Furthermore,the influence of some structural parameters of porous sound absorbing material and micro-perforated plate on the acoustic performance of the multilayer sound absorbing material straight-through perforated pipe muffler is analyzed.The muffler based on multilayer sound absorbing material is different from the traditional muffler.After applying the multilayer sound absorbing material to the straight-through perforated pipe muffler,the transmission loss value greatly increases,which provides new ideas and directions for future research on the muffler.

Attenuation Effect of Expansion Configuration and Acoustic Material on Propagation of Blast Waves in a Duct

With recent increase of cars, the noise problem has been caused by the exhaust sounds released from exhaust pipes, which consist of weak and pulsed shock waves called blast waves. To diminish the noise, a silencer is set up in front of the exhaust pipe. In the present study, reflectors were installed in the high-pressure section of the shock tube to generate blast waves, and three types of expansion region were investigated, combined with acoustic material of glass wool. The pressure decay was evaluated by transmission factor and reflection factor for the incident blast wave, together with pressure histories and high-speed Schlieren photography. As results, it was confirmed that the acoustic material greatly contributed to blast-wave attenuation: the one stage expansion model with glass wool recorded the highest decay of the peak over pressure for transmission, and other models with glass wool showed the second highest. The acoustic material also contributed to decay of reflected shock waves propagating toward an upstream duct.

Carbon Nano Material Synthesis from Polyethylene by Chemical Vapour Deposition

Three different types of Polyethylene family, High Density Polyethylene, (HDPE), Low Density polyethylene (LDPE) and Linear Low Density polyethylene (LLDPE) polymers having different molecular weight and density;were pyrolyzed in the temperature range of 550°C - 1050°C under H2, N2 and Ar gases. Taguchi Optimization technique was applied to find out the best operating conditions to get maximum yield of carbon nano material (CNM). For Taguchi op- timization, experimental set up was done in two different temperature ranges i.e. 550°C - 750°C and 850°C - 1050°C. CNMs synthesized were characterized by SEM, TEM, Micro Raman and XRD analysis. HDPE was found to yield maximum CNM. Its pyrolysis at 750°C under hydrogen atmosphere for 2h gave carbon nano beads and some carbon nano tubes. Whereas under same conditions at 1050°C more multi wall carbon nano tubes (MWCNT) were produced, with some carbon nano beads. XRD data confirmed the graphitic nature of carbon-nanotube. The intensities of G-band and D-band of Raman spectra suggested that CNM has more defect sites and spectra were similar for CNM obtained in both the temperature ranges. The TGA analysis of CNM obtained at 550°C - 750°C, indicated that they are not amor- phous carbon and CNM obtained at 850°C - 1050°C decomposed at 624°C - 668°C;suggesting that CNT synthesized at this temperature range were more crystalline than what was obtained at the 550°C - 750°C.

Eddy Current Test for Detection of Foreign Material using Rotating Probe

There are several elements that affect on the integrity of steam generator tubes. One of the elements is loose parts located on outside of the tubes. It causes erosion which is possible to lead fatal defect like crack on the outside surface of the tubes. In this study, artificial loose parts on Inconel 690 tube are demonstrated and eddy current testing data of the region is acquired using rotating probe. Ferromagnetic and nonmagnetic foreign materials were used to demonstrate artificial loose parts. Eddy current channel of 100 KHz frequency shows definite signals of those foreign materials but stainless steel was not clearly detected. This result can be explained based on the electrical conductivity of the materials and it can be confirmed with lissajous window and C-scan. In addition, no indication was detected when the distance of the gap between the foreign materials and the tube is increased to more than 3 mm under this test condition. Based on these experimental inspections, we were able to find suitable methods for analyzing the signals obtained under various conditions that could occur when conducting steam generator eddy current test in NPP.

Numerical analysis on phase change material melting process of a conical spiral tube energy storage tank

Spiral tube heat exchangers have been widely used in phase change energy storage due to the compact structure and large heat transfer area.Therefore,this study numerically analyzes the effects of spiral tube diameter,number of rotations,and unsteady heat source on the melting process in conical spiral tube energy storage tanks using Fluent software.The results indicate that when the tube diameter is increased from 8 to 11 mm and the number of rotations is increased from 5 to 8,the melting time is extended by 15.74%and 17.83%,respectively.The energy storage capacity increases by 0.64%and 1.83%,respectively.The average energy storage rate decreases by 13.05%and 13.58%,respectively.Furthermore,the sinusoidal wave heat source with small heat source periods has little effect on the melting process,while large heat source periods can significantly accelerate the melting.And the influence of amplitudes on the thermal storage performance under large heat source periods is more obvious.When the heat source period is increased from 2 to 160 min and the amplitude is increased from 5 to 20 K,the melting time is reduced by 24.50%and 17.20%,respectively.The total energy storage capacity decreases by 6.36%and increases by 1.62%,respectively.The average energy storage rate increases by 24.03%and 22.74%,respectively.The study provides guidance for the performance optimization of spiral tube phase change systems.

Revisiting the elastic solution for an inner-pressured functionally graded thick-walled tube within a uniform magnetic field

In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subject to a uniform magnetic field and inner-pressurized loads are studied. Rather than directly assume the material constants as some specific function forms displayed in pre-studies, we firstly give the volume fractions of different constituents of the functionally graded material(FGM) cylinder and then determine the expressions of the material constants. With the use of the Voigt method, the corresponding analytical solutions of displacements in the radial direction, the strain and stress components, and the perturbation magnetic field vector are derived. In the numerical part, the effects of the volume fraction on the displacement, strain and stress components, and the magnetic perturbation field vector are investigated. Moreover, by some appropriate choices of the material constants, we find that the obtained results in this paper can reduce to some special cases given in the previous studies.

Analysis of High-temperature Boiler Tube Failure for T91 &T22

The tube failures took place frequently in the superheater of 2x600MW units in a power plant. According to the condition of tube failures, the mechanical property and microstructure on running and failed tubes were tested and evaluated. The chemical composition and structure phase of inner oxide scale and deposit inside of the tubes were examined.The fractured surfaces of failed tube samples were observed. And the material examination was performed for original tube steels SA213-T91 and SA213-T22. The results show that raw materials of SA213-T91 and SA213-T22 tube in superheater are qualified. Besides, the characteristics of the SA213-T91 and SA213-T22 tube failure are typical short-term overheated rupture. The rupture temperature is located between two phase Ac1 ～ Ac3 of the two steels. It is recognized that putting SA213-T22 tubes in operation under the condition of long-term over heating causes the rupture of SA213-T91 and SA213-T22.

Optimal design of functionally graded Pm PV/CNT nanocomposite cylindrical tube for purpose of torque transmission

Carbon nanotube(CNT)/polymer nanocomposites have vast application in industry because of their light mass and high strength. In this work, a cylindrical tube which is made up of functionally graded(FG) PmP V/CNT nanocomposite, is optimally designed for the purpose of torque transmission. The main confining parameters of a rotating shaft in torque transmission process are mass of the shaft, critical speed of rotation and critical buckling torque. It is required to solve a multi-objective optimization problem(MOP) to consider these three targets simultaneously in the process of design. The three-objective optimization problem for this case is defined and solved using a hybrid method of FEM and modified non-dominated sorting genetic algorithm(NSGA-II), by coupling two softwares, MATLAB and ABAQUS. Optimization process provides a set of non-dominated optimal design vectors. Then, two methods, nearest to ideal point(NIP) and technique for ordering preferences by similarity to ideal solution(TOPSIS), are employed to choose trade-off optimum design vectors. Optimum parameters that are obtained from this work are compared with the results of previous studies for similar cylindrical tubes made from composite or a hybrid of aluminum and composite that more than 20% improvement is observed in all of the objective functions.

Development of non-shrinkable ceramic composites for use in high-power microwave tubes

Al_2O_3–CaO–SiC-based ceramic composites with four different compositions were sintered at 1700℃ for 3 h in an air furnace. The phase analysis, microstructural characterization, and elemental composition determination of the developed composites were performed by X-ray diffraction(XRD), field-emission scanning electron microscopy(FESEM), and energy-dispersive X-ray(EDAX) analysis, respectively. The shrinkage, thermal properties, and electrical resistivity of the composites were also studied. The experimental results showed the effects of adding silicon carbide and calcia to alumina on the thermal, electrical, and shrinkage properties of the resultant composites. Among the four investigated ceramic composites, the one composed of 99 wt% alumina, 0.5 wt% CaO, and 0.5 wt% SiC exhibited the best characteristics for use as a potting material in a dispenser cathode of a microwave tube. The material exhibited slight expansion instead of shrinkage during drying or firing. Other properties of the composite powder, such as its thermal properties and electrical resistivity, were comparable to those of a commercial alumina powder.

Linear and nonlinear torsional free vibration of functionally graded micro/nano-tubes based on modified couple stress theory

The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory contains one material length scale parameter, which can capture the small scale effect. The FGMT model accounts for the through-radius power-law variation of a two-constituent material. Hamilton＇s principle is used to develop the non-classical nonlinear governing equation. To study the effect of the boundary conditions, two types of end conditions, i.e., fixed-fixed and fixed-free, are considered. The derived boundary value governing equation is of the fourthorder, and is solved by the homotopy analysis method （HAM）. This method is based on the Taylor series with an embedded parameter and is capable of providing very good approximations by means of only a few terms, if the initial guess and the auxiliary linear operator are properly selected. The analytical expressions are developed for the linear and nonlinear natural frequencies, which can be conveniently used to investigate the effects of the dimensionless length scale parameter, the material gradient index, and the vibration amplitude on the natural frequencies of FGMTs.

二维管束状多孔炭材料的制备及在超级电容器中的应用

生物质是优异电极材料的重要来源,植物基生物质在制备多孔炭材料方面具有独特的结构优势。本文以面条菜为原料,KOH为活化剂,探讨了不同比例的KOH溶液对炭材料微观形貌的影响,制备出一系列具有二维管束状的炭材料,通过扫描电镜、X射线衍射和拉曼光谱等物理手段对炭材料的结构进行了深入分析。结果表明当碱碳比为3:1时,炭材料SCLC-3含有微孔-介孔等丰富的孔隙结构,为电解液离子在炭材料中的传输和存储提供了有利条件,在电流密度为1A·g^(-1)时SCLC-3比电容高达290F·g^(-1),经过5000次充放电循环测试电容保留率高达98%,表明炭材料具有良好的循环寿命。将其制作成固态电极材料进行不同角度的弯折,结果显示其电化学性能几乎没有发生变化,呈现出较好的抗弯折性能。

水声材料声振特性的驻波管测量方法

提出了一种基于驻波管的测量方法,以获得水声材料在静水压条件下的声学和振动特性参数。设计了带有气压补偿功能的低频发射换能器,作为驻波管的声源,通过水柱将换能器的平面活塞振动耦合到水面下的被测样品。在被测样品背衬上安装加速度计,测量样品背面振速;同时在管壁中嵌入一对水听器,测量水柱声压。导出样品声波入射面的振速和声压,进而计算出样品前表面和背衬面之间的振速传递系数(去耦系数)、样品的输入阻抗和声压反射系数。建立低频驻波管测试系统,声管尺寸为内径300 mm、外径600 mm、高3 m,工作频率范围100~1000 Hz,利用水层样品和多层穿孔橡胶样品开展了实验研究。实验结果显示,测量数据与仿真计算数据吻合较好,验证了测量方法的有效性。

油气田注入井况中管材氧腐蚀的研究进展

油气田注入井况中管材腐蚀问题突出,造成油气行业严重的资源浪费及安全隐患,而氧腐蚀已成为导致管材穿孔失效的主要原因之一。综述了近年来油气田注入环境中管材氧腐蚀的研究进展,重点关注了注入井况、注入参数(如工艺条件、温度、含氧量、流速等)对金属材料氧腐蚀的影响,探讨了氧腐蚀的机理及防护方法,并分析了目前研究中存在的不足。结合油气田工程需求,对未来该领域的研究工作提出了建议。

轴力作用下焊接方管Π型节点的极限承载力分析

目前规范中还未规定Π型构造形式的方管节点承载力计算公式。该文在经过试验验证有限元分析准确性的基础上,基于两种方管不同区域的材料本构关系模型,利用Abaqus软件对85组在轴力作用下的节点进行了数值模拟,得到了方管Π型节点在轴力作用下的极限承载力。随后,通过参数化分析和多元回归,得出影响Π型节点极限承载力的因素以及修正的承载力计算公式。结果表明,支管-主管宽度比β对节点极限承载力和初始刚度影响较大,增大支管宽度,能够显著提高节点的极限承载力,支管上施加的荷载由主管上表面的抗弯、抗剪作用和主管侧壁共同承担,节点的破坏模式也取决于β;主管宽厚比2γ越大,意味着主管上翼缘和支管连接区域变得更加细长,降低了主管上翼缘的抗弯刚度,节点承载力和初始刚度因此降低;支管-主管高宽比η和支管间距g对节点极限承载力有一定影响,增大支管截面的高度和支管间隙,即增大了沿主管纵向方向的支管、主管相交区域,使得支管在主管翼缘更宽的区域传递荷载,节点的塑性区域更大,材料利用更充分,因此提高了节点的承载能力;支管-主管厚度比τ对节点极限承载力和初始刚度影响不大,支管的壁厚增加,提高了支管的承载力,但节点最终破坏是主管上翼缘达到屈服破坏而并非支管破坏,因此支管厚度的变化对节点承载能力影响不明显。根据有限元模型的分析结果,通过曲线拟合提出了计算方管Π型节点极限承载力的参数方程,并对该方程的准确性进行了评价,为这类节点的进一步研究和工程应用提供了参考。

油气田酸化压裂环境下碳钢油套管材的腐蚀行为研究

为了明确某油田在酸化压裂环境下鲜酸、残酸对油套管材料腐蚀性能的影响规律及材料的适应性,采用腐蚀失重法、三维体视光学显微镜观察等方法分析了P110、C110油管材料在酸化全过程的腐蚀损伤发展趋势、点蚀敏感性和不同条件下的腐蚀形貌特征,并优化了酸化缓蚀剂。结果表明:随着鲜酸酸化温度的逐渐升高,材料腐蚀程度均呈增大趋势,当温度≥180℃时,C110的平均腐蚀速率v_(corr)=127.7 g/(m^(2)·h),P110的平均腐蚀速率v_(corr)=407.0 g/(m^(2)·h),均远高于指标要求;在模拟鲜酸温度为100℃时材料表面已出现点蚀形核现象,随着温度的升高,点蚀敏感性逐渐增大。在超高温180℃的残酸环境下,C110和P110材料均发生极严重腐蚀。酸化液组分中缓蚀剂在高温条件下明显失效,导致残酸返排环境下管材遭受严重腐蚀损伤。优化后的改性曼烯碱酸化缓蚀剂通过多层吸附膜的形成明显减缓了材料的腐蚀速率,在180℃高温鲜酸环境下缓蚀率为89.4%。