Yongshou Liu

Acoustic nanowave absorption through clustered carbon nanotubes conveying fluid

Absorption of acoustic nanowave in specific frequency region is important for the design of acoustic filter. This paper puts forward a meta material model made up of fluid-conveying carbon nanotubes (CNT), which can absorb acoustic nanowave in a given frequency range by adjusting the lengths and fluid velocities of themselves. Absorption coefficients are calculated out through the combination of the finite element method with the theoretical model, which are 0.4~0.55 relating to different fluid velocities for the crossing-distributed model. Comparisons are made between the crossed model and the aligned one, which prove that the CNT forest with crossed distribution is more effective in acoustic wave absorption.

Free vibration analysis of fluid-conveying carbon nanotube via wave method

The wave method is introduced to vibration analysis of the fluid-conveying carbon nanotube. The constitutive relation of carbon nanotube on micro-scale is founded using the nonlocal elastic theory. The governing equation on micro-scale is obtained. And the first five orders of the natural frequency of the carbon nanotube conveying fluid with various speeds are calculated through the wave method. Besides, the critical flow velocity when the carbon nanotube loses stability is obtained. Meanwhile, a contrast is made between the result obtained through the wave method and that in previous researches.

Dynamic behaviors of multi-span viscoelastic functionally graded material pipe conveying fluid

In this paper, the dynamic behaviors of a multi-span viscoelastic functionally graded material pipe conveying fluid are investigated by dynamic stiffness method. The material properties of the functionally graded material pipe are considered as graded distribution along the thickness direction according to a power-law. Several numerical examples are performed to study the effects of volume fraction exponent, fluid velocity, internal pressure, and internal damping on the stability and frequency response of the fluid-conveying functionally graded material pipe. It’s found that the viscoelastic functionally graded material pipe exhibits some special dynamic behaviors and it could increase the stability significantly when compared with the aluminum and steel pipes. The numerical results also demonstrate that by the introduction of the functionally graded material, the stiffness of the piping system could be modulated easily by designing the volume fraction function. Therefore, if the dominant frequency contents of the external loads are known, a preferable design of the functionally graded material pipe to reduce the vibration is possible.

System reliability analysis through active learning Kriging model with truncated candidate region

System reliability analysis (SRA) with multiple failure modes is researched in this paper. Active learning Kriging (ALK) model which only finely approximates the performance function in the narrow region close to the limit state has shown great potential and several strategies based on ALK model have been proposed. The key of SRA based on ALK model is to identify the components with little contribution to system failure and avoid approximating them. However, we figure out that the existing strategies fail to fulfill this task if large numerical difference exists among the values of component performance functions. Therefore, a brand-new theory on identifying the unimportant component(s) is proposed. Based on this theory, the method based on ALK model with a truncated candidate region (TCR) is proposed and it is termed as ALK-TCR. ALK-TCR is capable to recognize and avoid approximating the unimportant component(s), even if large numerical difference arises among the components. Its high performance is demonstrated by three complicated examples.

Parametric Sensitivity Analysis for Importance Measure on Failure Probability and Its Efficient Kriging Solution

The moment-independent importance measure (IM) on the failure probability is important in system reliability engineering, and it is always influenced by the distribution parameters of inputs. For the purpose of identifying the influential distribution parameters, the parametric sensitivity of IM on the failure probability based on local and global sensitivity analysis technology is proposed. Then the definitions of the parametric sensitivities of IM on the failure probability are given, and their computational formulae are derived. The parametric sensitivity finds out how the IM can be changed by varying the distribution parameters, which provides an important reference to improve or modify the reliability properties. When the sensitivity indicator is larger, the basic distribution parameter becomes more important to the IM. Meanwhile, for the issue that the computational effort of the IM and its parametric sensitivity is usually too expensive, an active learning Kriging (ALK) solution is established in this study. Two numerical examples and two engineering examples are examined to demonstrate the significance of the proposed parametric sensitivity index, as well as the efficiency and precision of the calculation method.

The dynamic reliability analysis of pipe conveying fluid based on a refined response surface method

The dynamic reliability of the pipe conveying fluid was analyzed by a refined response surface method (RSM) in this study. In the refined RSM, a new response surface expression was proposed based on functional variables with the physical characteristics of basic random variables. The sampling points were located on Gauss Hermite integration points along the coordinate axes of standard normal random variables. The response surface was constituted via an iterative strategy, in which the information of the sampling points could be utilized richly. On the other hand, Hamilton’s principle for open systems was applied to formulate the motion equations of the pipe conveying non-uniform axial fluid. The proposed RSM was used to analyze the dynamic reliability and sensitivity of the pipe conveying non-uniform axial fluid. As shown in the numerical results, the refined response surface method leads to the better approximation of the nonlinear limit state function, higher precision and better stability of the failure probability estimation, especially for the dynamic reliability analysis of the pipe conveying fluid.

Topology Optimized Vibration Control of a Fluid–Conveying Carbon Nanotube with Non-Uniform Magnetic Field

This paper presents an approach to control the fluid-induced vibration of the carbon nanotubes (CNTs) embedded in viscoelastic medium with topology non-uniform magnetic field. Non-local continuum theory and homogenization equivalence are employed to conclude small-scale effects of the carbon nanotube (CNT) and the nanofluid, respectively. Simply supported, fixed–fixed and fixed–pinned fluid–conveying carbon nanotubes (FCCNTs) with sliding and no-sliding ends are chosen as samples to illustrate the control effect of the magnetic field, and the optimal magnetic field distributions are obtained through genetic algorithm (GA). Dynamic characteristics (the eigen-frequencies and the critical velocities) of different FCCNT models are calculated through differential quadrature (DQ) method. The control effects of the magnetic field can be validated through examining the stiffness enhancement of the Ampere’s force. Results present that the eigen-frequencies and critical velocities of different FCCNTs are all raised by 3–13% through the given magnetic fields. Contrasts between different models illustrate that the dynamic stiffness of simply supported FCCNT with no-sliding ends is enhanced mostly by the magnetic field.

A Hybrid Method for Transverse Vibration of Multi-Span Functionally Graded Material Pipes Conveying Fluid with Various Volume Fraction Laws

Both functionally graded materials (FGMs) and fluid-conveying pipes have wide applications in engineering communities. In this paper, the transverse vibration and stability of multi-span viscoelast...

Dynamic reliability of aircraft hydraulic pipelines under random pressure pulsation and vibration

Purpose – Pressure pulsations and vibration working condition lead to dynamic troubles in hydraulic devices. It is highly desirable to be able to estimate the durability at the design stage so that appropriate maintenance period can be determined for safety and reliability. The purpose of this paper is to propose a quantitative evaluation method for pulsation and vibration based on reliability.Design/methodology/approach – Pressure pulsations are approximately treaded as a stationary random process. The principle of transform function and fluid network chain rules are used to disassemble the hydraulic power unit into the series‐system. Mean square deviation of dynamic stress under the pumping source white noise exciting was calculated based on frequency responses. Statistical regularity of displacement and stress responses of pipelines under external random vibration are obtained by the spectrum analysis. Both the first‐passage failure criterion and fatigue damage accumulation failure criterion are adopte...

Effect of Thinckness on Residual Stress Fields of Cold Expansion Hole

In this paper, four axisymmetrical finite element models have been established to study effect of thinckness on residual stress fields of cold expansion hole, experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. The experiment results also show that cold expansion processing can decrease surface roughness of holes and improve surface quality. The FEM results show, at the top(bottom) surface, the volue of the radial residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical. The volue and the regularities of distribution of the circumferential residual stress vary with the plate’s thickness. At the mid-thickness surface, the volue and the regularities of distribution of radial residual stress vary with the plate’s thickness. The volue of the circumferential residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical.