Effects of the slip boundary condition on dynamics and pull-in instability of carbon nanotubes conveying fluid

This paper addresses the effects of the slip boundary condition on dynamics and pull-in instability of carbon nanotubes (CNTs) containing internal fluid flow. Both the clamped–clamped and the cantilever boundary conditions are considered. The structure of CNTs is modelled using the size-dependent strain gradient theory (SGT) of continuum mechanics. It is shown that the Knudsen number (Kn) has a significant effect on the static and dynamic CNT response due to pull-in voltage loading and the existence of the instability region.     

Critical rotational speed,critical velocity of fluid flow and free vibration analysis of a spinning SWCNT conveying viscous fluid

In this article, the influences of rotational speed and velocity of viscous fluid flow on free vibration behavior of spinning single-walled carbon nanotubes (SWCNTs) are investigated using the modified couple stress theory (MCST). Taking attention to the first-order shear deformation theory, the modeled rotating SWCNT and its equations of motion are derived using Hamilton’s principle. The formulations include Coriolis, centrifugal and initial hoop tension effects due to rotation of the SWCNT. This system is conveying viscous fluid, and the related force is calculated by modified Navier–Stokes relation considering slip boundary condition and Knudsen number. The accuracy of the presented model is validated with some cases in the literatures. Novelty of this study is considering the effects of spinning, conveying viscous flow and MCST in addition to considering the various boundary conditions of the SWCNT. Generalized differential quadrature method is used to approximately discretize the model and to approximate the equations of motion. Then, influence of material length scale parameter, velocity of viscous fluid flow, angular velocity, length, length-to-radius ratio, radius-to-thickness ratio and boundary conditions on critical speed, critical velocity and natural frequency of the rotating SWCNT conveying viscous fluid flow are investigated.     

考虑内流压力时输流曲管的混沌运动及其抑制模型

考虑内部流体压力因素的影响,研究了具有非线性运动约束输流曲管的混沌运动及其抑制模型.首先,在输流曲管的运动微分方程中计入流体压力作用项,并采用微分求积法对此方程进行离散化处理.然后,通过数值迭代计算,分析了在流体压力这一参数区域内曲管的多种运动形态(包括混沌运动).研究表明,流体压力因素对曲管的动力响应有较大的影响,在实际工程中应给予充分考虑.在此基础之上,提出了一种曲管的混沌抑制模型,有效的消除了系统的混沌运动.     

Nonlocal divergence and flutter instability analysis of embedded fluid-conveying carbon nanotube under magnetic field

This paper deals with nonlocal divergence and flutter instability analysis of carbon nanotubes (CNTs) conveying fluid embedded in an elastic foundation under magnetic field. Nonlocal constitutive equations of Eringen and Euler–Bernoulli beam theory are used in the formulations. Also, the foundation is described by the Winkler and Pasternak models. The governing equation of motion and boundary conditions are derived using extended Hamilton’s variational principle. The extended Galerkin’s approach is adopted to reduce the partial differential equation governing the dynamics of the CNTs to a system of coupled ordinary differential equations. In the present study, four different boundary conditions are considered, namely the pined–pined (P–P), clamped–pined (C–P), clamped–clamped (C–C) and clamped–free (C–F). A detailed parametric study is conducted to elucidate the effects of the nonlocal effect, longitudinal magnetic field, elastic Winkler and Pasternak foundations and geometrically boundary conditions on the instability characteristic of CNTs. It was observed that the only instability type for the investigated CNT with clamped–free boundary condition (cantilever) is flutter, while CNT conveying fluid with both ends supported loses its stability by divergence first and then by flutter with increase in fluid velocity. It was also found that the magnetic field and the Winkler and Pasternak foundations increase the stiffness of the system. Therefore, flutter instability region is enlarged significantly due to the existence of springs, shear foundations and magnetic field. Also, results show that the nonlocal parameter has a prominent effect on the stability behavior of CNTs, in which increasing nonlocal parameter results in the decrease in stability region. Furthermore, it was shown that the stability behavior of CNT is strongly affected by different boundary conditions. Finally, the validity of the present analysis is confirmed by comparing the results with those obtained from the literature.     

Size-dependent vibration analysis of multi-span functionally graded material micropipes conveying fluid using a hybrid method

Microscale fluid-conveying pipes and functionally graded materials (FGMs) have many potential applications in engineering fields. In this paper, the free vibration and stability of multi-span FGM micropipes conveying fluid are investigated. The material properties of FGM micropipes are assumed to change continuously through thickness direction according to a power law. Based on modified couple stress theory, the governing equation and boundary conditions are derived by applying Hamilton’s principle. Subsequently, a hybrid method which combines reverberation-ray matrix method and wave propagation method is developed to determine the natural frequencies, and the results determined by present method are compared with those in the existing literature. Then, the effects of material length scale parameter, volume fraction exponent, location and number of supports on dynamic characteristics of multi-span FGM micropipes conveying fluid are discussed. The results show that the size effect is significant when the diameter of micropipe is comparable to the length scale parameter, and the natural frequencies determined by modified couple stress theory are larger than those obtained by classical beam theory. It is also found that natural frequencies and critical velocities increase rapidly with the increase of volume fraction exponent when it is less than 10, and the intermediate supports could improve the stability of pipes conveying fluid significantly.     

Nonlocal free dynamic analysis of periodic arrays of single-walled carbon nanotubes in the presence of longitudinal thermal and magnetic fields

This paper deals with transverse vibrations of three-dimensional vertically aligned periodic arrays of single-walled carbon nanotubes acted upon by both longitudinal magnetic and thermal fields. For this purpose, a nonlocal higher-order beam theory is employed for modeling of the nanosystem. Accounting for the intertube van der Waals forces, a discrete-based model as well as a continuous-based model is established. For various geometries of the nanosystem and under various applied thermal and magnetic fields, the results of the continuous model are successfully checked with those of the discrete model. Through a comprehensive parametric study, the effects of the nanotube’s radius, slenderness ratio, nonlocality, ensemble’s population, temperature change, and strength of magnetic field on fundamental frequencies of the nanosystem are addressed and displayed.     

Application of the Green function method to flow-thermoelastic forced vibration analysis of viscoelastic carbon nanotubes

In this paper, the Green function method (GFM) is implemented for forced vibration analysis of carbon nanotubes (CNTs) conveying fluid in thermal environment. The Eringen’s nonlocal elasticity theory is used to take into account the size effect of CNT with modeling the CNT wall–fluid flow interaction by means of slip boundary condition and Knudsen number (Kn). The derived governing differential equations are solved by GFM which demonstrated to have high precision and computational efficiency in the vibration analysis of CNTs. The validity of the present analytical solution is confirmed by comparing the results with those reported in other literature, and good agreement is observed. The analytical examinations are accomplished, while the emphasis is placed on considering the influences of nonlocal parameter, boundary conditions, temperature change, structural damping of the CNT, Knudsen number, fluid velocity and visco-Pasternak foundation on the dynamic deflection response of the fluid-conveying CNTs in detail.     

Wave propagation in double-walled carbon nanotube conveying fluid considering slip boundary condition and shell model based on nonlocal strain gradient theory

In this paper, wave propagation in fluid-conveying double-walled carbon nanotube (DWCNT) was investigated by using the nonlocal strain gradient theory. In so doing, the shear deformable shell theory was used, taking into consideration nonlocal and material length scale parameters. The effect of van der Waals force between the two intended walls and the DWCNT surroundings was modeled as Winkler foundation. The classical governing equations were derived from Hamilton’s principle. Results were validated by comparing them to the results of the references obtained through molecular dynamic method, and a remarkable consistency was found between the results. According to the findings, the effects of nonlocal and material length scale parameters, wave number, fluid velocity and stiffness of elastic foundation are more considerable in the nonlocal strain gradient theory than in classical theory.     

Parametric studies of coupled vibration of cylindrical pipes conveying fluid with the wave propagation approach

The wave propagation approach is extended to the coupled frequency analysis of finite cylindrical pipes conveying dense fluid. The downstream, upstream and mixed frequencies of the pipe are defined and discussed. The effects of fluid and shell parameters on the coupled frequencies are investigated. The difference between the coupled and uncoupled frequencies decreases with the circumferential mode n, but increases with the mode n after the number n where the fundamental frequency is obtained. The fundamental frequency can change from one circumferential mode to another circumferential mode with the h/R ratios. However for a shorter shell the fundamental frequency may keep with the same mode n in the interested h/R ratios. For different boundary conditions the transition of fundamental frequency between circumferential modes occurs at different h/R ratios. The downstream frequency increases with increasing fluid velocity, whereas the upstream frequency decreases as the fluid velocity increases. However, the mixed frequency of the pipe decreases with the increase of the fluid velocity. For a given flow velocity all the three frequencies decrease with decreasing h/R ratios. However the mixed frequency drops more with increasing fluid velocity at small h/R ratios than at large h/R ratios. Therefore negative frequencies may occur for small h/R ratios if the fluid velocity is large enough, which means that instability occurs first for thinner pipes.     

旋转Timoshenko输流管道的固有频率和稳定性分析

基于Timoshenko梁模型,本文研究了旋转输流管道在自由振动状态下的流固耦合振动特性.考虑流体压力、重力、初始轴应力作用,基于Hamilton原理和欧拉角转换,推导得到了旋转Timoshenko输流管道的偏微分方程.根据Galerkin截断法将运动方程进行离散,通过求解系统的特征方程即可得到输流管一阶复频率的实部和虚部,实部代表固有频率,虚部代表能量变化.在流速较高时,研究发现必须考虑4阶及以上Galerkin截断,才能得到稳定的结果.通过与EulerBernoulli梁模型对比,验证了本文的结果正确性.研究发现针对短粗型管道,Timoshenko梁模型更加精确.此外研究了多种参数对旋转Timoshenko输流管道固有频率和振动稳定性的影响.研究结果表明质量比、流速、剪切系数对Timoshenko输流管道流固耦合振动的稳定性影响显著,而转动惯量、重力、流体压力和初始轴应力在一定程度上也会影响管道振动的频率和稳定性.转速的出现将管道频率分为两个量值,但转速并不影响系统能量变化.     

Surface generation analysis in micro end-milling considering the influences of grain

The micro end-milling method is a universal micro manufacturing method used to fabricate micro parts and complex 3D micro structures with many materials. Although micrometer size is achieved, their surface quality is not satisfactory. In this paper, the influences of different metal phase grains are researched, and the micro end-milling process is described considering the workpiece with anisotropic properties in micro scope. In this research, the physical characteristics of different grains, specifically friction coefficient μ and elastic modulus E, are very critical to determine the processes of the chip formation and the surface generation. And the chips are often discontinuous because of the grain boundary effect. Through the micro end-milling experiment, the results of bottom surface correlate very well with the theoretical analysis.     

变流速输液管的周期和混沌振动

研究了参数激励和外激励联合作用下输流管道的非线性振动问题．只考虑管道变形的几何非线性因素,利用Hamilton原理得到单侧受简谐均布载荷作用下输液管的非线性动力学方程,对系统运动偏微分方程综合运用多尺度法和Galerkin离散方法,得到了主参数共振-1／2亚谐共振和1：2内共振情况下的平均方程．数值模拟结果表明参数激励和外激励联合作用下的悬臂输液管呈现周期运动、多倍周期运动和混沌运动的变化规律．     

Vibration analysis of suspended microchannel resonators characterized as cantilevered micropipes conveying fluid and nanoparticle

Microsystem Technologies - This paper performs a theoretical analysis of suspended microchannel resonators (SMRs) containing one single or two parallel channels, modeled here as cantilevered...     

Analysis of nonlinear vibration and instability of electrostatic functionally graded micro-actuator based on nonlocal strain gradient theory considering thickness effect

Microsystem Technologies - In this work, we develop a model of an electrostatic functionally graded (FG) micro-actuator based on the nonlocal strain gradient theory (NSGT) incorporated the...     

Small scale effect on the pull-in instability and vibration of graphene sheets

Microsystem Technologies - In this paper, the small scale effect on the pull-in instability and frequency of graphene sheets subjected to electrostatic and van der Waals forces is studied....     

Enhanced age estimation by considering the areas of non-skin and the non-uniform illumination of visible light camera sensor

Most previous research on human age estimation based on the detection of multiple feature points using the active appearance model (AAM) method. However, it is difficult to use the AAM-based methods in actual applications, because their performance is strongly affected by image backgrounds, head movements, and non-uniform facial region illumination. Furthermore, they require significant processing time. Other age estimation methods based on a detected face box area may be considered as an alternative; however, noise areas that include hair, backgrounds, and non-uniform illumination of visible light camera sensor may be inadvertently included in the face box, which reduces age estimation accuracy. Therefore, we propose a new age estimation method that is robust to these noise areas. Our proposed method is novel in following four ways. First, we propose an age estimation method using a weighted multi-level local binary pattern (wMLBP) based on a fuzzy-logic system. Second, two input values (the difference between the mean gray levels of the sub-block and the central area of the face, and the distance from the sub-block to the center of the facial region) are determined considering the noise areas of hair, background, and non-uniform illumination of visible light camera sensor. Then, the optimal weights are determined using a fuzzy-logic system with these two input values, which does not require a time-consuming training process. Third, by assigning an optimal weight to the histogram features extracted by the MLBP method in each sub-block, age estimation accuracy is enhanced. Finally, the age is estimated using a SVR method based on a combination of weighted MLBP features and Gabor wavelet features. Experimental results obtained using the public PAL and MORPH age databases demonstrate that the accuracy of our method is superior to other previous methods.     

碳纳米管修饰电极的制备及其电化学敏感性研究

介绍了一种碳纳米管修饰电极的制备工艺,并对其电化学敏感性进行测试和分析.该工艺辅助聚合物聚酰亚胺,利用机械球磨、可控刻蚀等工艺,实现了碳纳米管的均一分布,露出碳纳米管的断口和缺陷.在玻碳电极上涂覆碳纳米管/聚酰亚胺复合膜,结合扫描电子显微镜观察,得到了可控、均一、稳定的电极界面.利用循环伏安法对电极进行性能测试,讨论了...     

A new process-based cost estimation and pricing model considering the influences of indirect consumption relationships and quality factors

In a manufacturing environment containing complex consumption relationships and quality influences, the application of traditional activity-based costing (ABC) method is limited. In this paper, a new improved process-based model for cost estimation and pricing is presented. Through utilizing the input–output analysis method, the complex indirect consumption relationships (such as reciprocal relationships) of a manufacturing system are expressed. By solving these relationships, the consumption characteristics of all production activities (mainly presented by the activity rates) are extracted. Then with the consumption characteristics, the quality characteristics and usage amounts of these activities, the cost prices of products are estimated for their pricing. A case study is given based on the compressor products of a manufacturing company, and its effectiveness is shown. As the cost influences of complex consumption relationships and quality factors are fully considered, the proposed approach has a higher estimation accuracy than the traditional ABC method.