2022 Vol. 43, No. 1

Solid Mechanics
Research Progresses of Wavelet Methods and Their Applications in Mechanics
LIU Xiaojing, ZHOU Youhe, WANG Jizeng
2022, 43(1): 1-13. doi: 10.21656/1000-0887.420388
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Abstract:

The wavelet theory shows very unique time-frequency localization and multi-resolution analysis ability in signal processing and function approximation. The wavelet basis function has excellent mathematical properties such as orthogonality, compactness, low-pass filtering and interpolation, which endows the wavelet analysis theory with great application potential in the fields of computational mathematics and computational mechanics, and creates new opportunities for breakthrough development in these fields. Since the 1990s, a large number of studies have proved that the numerical method based on the wavelet theory has very obvious advantages in solving differential equations, but at the same time, have exposed some limitations of numerical calculation application caused by the wavelet basis function itself and its unique approximation method. In order to promote the innovative application of the wavelet theory in the fields of computational mathematics and mechanics and provide researchers with a new research perspective, the development background of the wavelet analysis and the research history of methods based on the wavelet theory were reviewed, and the numerical method problems were emphasized and the research progresses made in recent years discussed. The conclusions and comments may provide a meaningful reference for the further development and improvement of quantitative mathematical solution methods based on the wavelet theory and applications in mechanics as well as solutions of a wide range of engineering problems.

Active Control on Band Gap Properties and Interface Transmission of Elastic Waves in Piezoelectric Metamaterial Beams
SUN Wenjing, WANG Yize
2022, 43(1): 14-25. doi: 10.21656/1000-0887.420125
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Abstract:

The active control on band gap properties of elastic wave metamaterial beams was studied by means of the negative capacitance circuits attached to piezoelectric sheets periodically. External circuits were used to change the material constants of the connected piezoelectric materials, which could tune the equivalent parameters of the structure and control the band gap characteristics. Through controlling the unit cell, the generation and disappearance of band gaps can be observed with the active control system. Then, an elastic wave metamaterial beam with the interface was constructed to discuss the effects of the active control system on the interface transmission.

Structure-Preserving Layout Optimization of Precision Devices in Spacecraft
JIANG Ruisong, XU Mengbo, ZHANG Fan, HU Weipeng, DENG Zichen
2022, 43(1): 26-33. doi: 10.21656/1000-0887.420095
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Abstract:

The stability and the accuracy of the precision devices installed in spacecraft depend on the local vibration characteristics of the spacecraft. In return, the local vibration characteristics of the spacecraft are influenced by the layout of the precision devices, which implies that, a rational layout of the precision devices in the spacecraft is the precondition for the stable and efficient work of the precision devices. The dynamic model for a flexible panel bearing several precision devices was presented and the structure-preserving method was developed to investigate the local vibration characteristics of the panel. In view of the sizes of the precision devices and the heat dissipation clearances between the precision devices, the layout optimization for the precision devices was performed to minimize the weighted values of the out-of-plane vibration accelerations of the precision devices. The optimization results show that, benefiting from the excellent structure-preserving properties of the numerical method employed during the vibration analysis, the weighted values of the out-of-plane vibration accelerations of the precision devices decrease by about 88.05% through the layout optimization, which provides a useful guide for the layout scheme of the precision devices in the spacecraft and improves the stability of the precision devices.

Nonlinear Numerical Simulation of Finite Elements Based on Fiber Beam Elements With Shear Effects for Structures
LI Jiayu, CHEN Mengcheng, WANG Kaixin
2022, 43(1): 34-48. doi: 10.21656/1000-0887.420032
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Abstract:

The classical fiber beam model based on the Euler-Bernoulli beam theory ignores the influence of shear deformation on the section. To get a more accurate beam element model, based on the fiber beam element with shear effects and the Timoshenko beam theory, the stiffness matrix of the fiber beam element was deduced, and the dual effects of geometric nonlinearity and material nonlinearity were considered at the same time, combined with the elastoplastic incremental theory. Then, the nonlinear finite element analysis theory for the structure under the complex stress state of compression, bending and shear was established. Finally, a program was coded on MATLAB to conduct finite element numerical simulation of the typical compression-bending-shear members of reinforced concrete and rectangular concrete-filled steel tube, and the nonlinear full-process load-displacement curves were obtained. The analysis of the numerical examples show that, the established nonlinear finite element analysis theory is universal, feasible and correct.

Fluid Mechanics
壁面结构对三维可压缩气泡群影响的数值模拟研究
WANG Jincheng, GUAN Hui, WEI Zhijun, WU Chuijie
2022, 43(1): 49-62. doi: 10.21656/1000-0887.420041
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Abstract:

基于流体体积(VOF)法追踪自由液面,研究了壁面结构对三维可压缩气泡群流动的影响。通过在待测壁面上设置不同形状的壁面结构(长方体、椭球体和圆锥体)并改变它们各自的几何参数(位置和长度),来研究壁面结构对壁面附近的气泡群流动的影响,该影响表现为气泡群对壁面的空间平均压力。研究发现,壁面结构对气泡群的拓扑结构的影响会造成壁面压力的变化,其中长方体壁面结构降低壁面平均压力的效果最好,且通过适当调整该结构的位置和长度,能使壁面的压力脉动现象消失。

Study on Droplets Impacting on Orifice Plates With Different Wettabilities Based on the Lattice Boltzmann Method
LIANG Jia, GAO Ming, CHEN Lu, WANG Dongmin, WANG Zhiyun, ZHANG Lixin
2022, 43(1): 63-76. doi: 10.21656/1000-0887.420076
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Abstract:

Based on the lattice Boltzmann method, the numerical simulation of droplet impacting on orifice plates with different wettabilities was carried out. The effects of the Weber number (We), the wettability of the orifice surface and the orifice size on different states of droplets passing through orifice plates during impacts were studied. The numerical simulation results show that, different phenomena will occur in the processes of droplets impacting on the orifice plates. If the orifice plate is hydrophilic, the droplet will not detach from the orifice plate surface, but adhere to the lower surface of the orifice plate for a relatively low We number, and then the droplet will rise for a certain distance in the orifice channel under the action of capillarity, forming the liquid plugging phenomenon. For relatively high We numbers, droplets will pass through the orifice plates and rupture will occur. If the orifice plate is hydrophobic, the droplet will not pass through the orifice plate and migrate to the lower surface for a relatively low We number, and will finally stabilize in the orifice channel. For higher We numbers, droplets will pass through the orifice plates, and then break up, leaving droplet remains on the surfaces of the orifice plates. For various orifice sizes, the droplet will be more difficult to pass through the plate for a smaller orifice size or a lager orifice plate thickness.