Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2015, 31 (6)   Published: 20 December 2015
Forced motion of an elastic filament through a narrow tube
L. B. Freund

A polymer filament consisting of many similar molecules linked in a one-dimensional array is very flexible. As a result, shapes with a relatively large curvature can be accommodated elastically. When loosely confined in a thermal environment, such a flexible strand may become tangled owing to its flexibility. When confined within a narrow “tube” over its full length, a flexible molecule may behave quite differently. Here, we consider the qualitative nature of deformation of an ind...

Transport mechanisms of contaminants released from fine sediment in rivers
Pengda Cheng, Hongwei Zhu, Baochang Zhong, Daozeng Wang

Contaminants released from sediment into rivers are one of the main problems to study in environmental hydrodynamics. For contaminants released into the overlying water under different hydrodynamic conditions, the mechanical mechanisms involved can be roughly divided into convective diffusion, molecular diffusion, and adsorption/desorption. Because of the obvious environmental influence of fine sediment (D90 = 0.06 mm), non-cohesive fine sediment, and cohesive fine sedimen...

Improved delayed detached-eddy simulation of massive separation around triple cylinders
Zhi-Xiang Xiao, Kun-Yu Luo

The massively separated flow past triple cylinders (TriC) in tandem arrangement is simulated using the improved delayed detached-eddy simulation (IDDES) method based on the shear stress transport (SST) model, coupled with the high order adaptive dissipation scheme. The spacing between adjacent cylinders is sub-critical (1.435D). IDDES prediction of two cylinders (TC) with the same spacing is compared to experimental data for validation, and the numerical results agree well with the a...

Experiments on self-excited oscillation in a thin-walled collapsible tube
Hai-Jun Wu, Lai-Bing Jia, Xie-Zhen Yin

Self-excited oscillation in a collapsible tube is an important phenomenon in physiology. An experimental approach on self-excited oscillation in a thin-walled collapsible tube is developed by using a high transmittance and low Young's modulus silicone rubber tube. The elastic tube is manufactured by the method of centrifugal casting in our laboratory. An optical method for recording the evolution of the cross-sectional areas at a certain position along the longitudinal direction of the tube i...

Effects of imperfect experimental conditions on stress waves in SHPB experiments
Xianqian Wu, Qiuyun Yin, Yanpeng Wei, Chenguang Huang

Experimental and numerical simulations were undertaken to estimate the effects of imperfect conditions on stress waves in split Hopkinson pressure bar (SHPB) experiments. The photonic Doppler velocimetry (PDV) measurement results show that the rise and fall times of an incident wave increases with an increasing inclination angle; also, the fluctuations of the incidentwave disappear gradually with the increase of inclination angle. The following characteristics for various defects in the SHPB ...

An experimental study on seepage behavior of sandstone material with different gas pressures
Sheng-Qi Yang, Yan-Hua Huang, Yu-Yong Jiao, Wei Zeng, Qing-Lei Yu

The seepage evolution characteristic of brittle rock materials is very significant for the stability and safety of rock engineering. In this research, a series of conventional triaxial compression and gas seepage tests were carried out on sandstone specimens with a rock mechanics servo-controlled testing system. Based on the experimental results, the relationship between permeability and deformation is firstly analyzed in detail. The results show that the permeability- axial strain curve can ...

Static response analysis of structures with interval parameters using the second-order Taylor series expansion and the DCA for QB
Qi Li, Zhiping Qiu, Xudong Zhang

In this paper, based on the second-order Taylor series expansion and the difference of convex functions algorithm for quadratic problems with box constraints (the DCA forQB), a newmethod is proposed to solve the static response problem of structures with fairly large uncertainties in interval parameters. Although current methods are effective for solving the static response problem of structures with interval parameters with small uncertainties, these methods may fail to estimate the region o...

Fracture analyses of different pre-holed concrete specimens under compression
Hadi Haeri, Alireza Khaloo, Mohammad Fatehi Marji

Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-likematerial containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement (PPC), fin...

Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression
Sheng-Qi Yang, Yan-Hua Huang, P. G. Ranjith, Yu-Yong Jiao, Jian Ji

Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code (PFC2D). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failur...

A modified model for concurrent topology optimization of structures and materials
Xingjun Gao, Haitao Ma

This paper presents a study on the concurrent topology optimization of a structure and its material microstructure. A modified optimization model is proposed by introducing microstructure orientation angles as a new type of design variable. The new model is based on the assumptions that a structure is made of a material with the same microstructure, and the material may have a different orientation within the design domain of the structure. The homogenization theory is applied to link the mat...

Receptivity of hypersonic boundary layer due to fast-slow acoustics interaction
Jun Gao, Ji-Sheng Luo, Xue-Song Wu

The objective of receptivity is to investigate the mechanisms by which external disturbances generate unstable waves. In hypersonic boundary layers, a new receptivity process is revealed, which is that fast and slow acoustics through nonlinear interaction can excite the second mode near the lower-branch of the second mode. They can generate a sum-frequency disturbance though nonlinear interaction, which can excite the second mode. This receptivity process is generated by the nonlinear interac...

Lumped parameter analytic modeling and behavioral simulation of a 3-DOF MEMS gyro-accelerometer
Payal Verma, Sandeep K. Arya, Ram Gopal

Anewanalytical model of a 3-degree-of-freedom (3-DOF) gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with each DOF of the system by vector analysis. The coupled differential equations thus established are solved analytically for their responses in both the time and frequency domains. Considering these frequency response equations, novel device design concepts are derived by forcing the sen...

Effect of partial elastic foundation on free vibration of fluid-filled functionally graded cylindrical shells
Young-Wann Kim

The free vibration characteristics of fluid-filled functionally graded cylindrical shells buried partially in elastic foundations are investigated by an analytical method. The elastic foundation of partial axial and angular dimensions is represented by the Pasternak model. The motion of the shells is represented by the first-order shear deformation theory to account for rotary inertia and transverse shear strains. The functionally graded cylindrical shells are composed of stainless steel and ...

Numerical analysis of the three-dimensional aerodynamics of a hovering rufous hummingbird (Selasphorus rufus)
Songyuan Yang, Weiping Zhang

Hummingbirds have a unique way of hovering. However, only a few published papers have gone into details of the corresponding three-dimensional vortex structures and transient aerodynamic forces. In order to deepen the understanding in these two realms, this article presents an integrated computational fluid dynamics study on the hovering aerodynamics of a rufous hummingbird. The original morphological and kinematic data came from a former researcher's experiments. We found that conical and st...

The effect of low fluoride concentrations on microdamage accumulation in mouse tibias under impact loading
Qing Luo, Nan Chen, Yan-Heng Zhou, Qi-Guo Rong

Microdamage accumulation in bone is one of the mechanisms for energy dissipation during the fracture process. Changes in the ultrastructure and composition of bone constituents due to aging or diseases could affect microdamage accumulation. Low concentration (1mM) of sodium fluoride (NaF) has been used in this study to investigate the effect of ultrastructural changes on microdamage accumulation in mouse tibias following free-fall impact loadings. Twenty-two tibias were divided randomly into ...

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