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2024, Volume 54,  Issue 3

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Review
Wavelet-based numerical methods and their applications in computational mechanics
YANG Bing, WANG Jizeng, LIU Xiaojing, ZHOU Youhe, FENG Yonggu
2024, 54(3): 427-476. doi: 10.6052/1000-0992-24-009
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Abstract:
Mechanics research advances towards interdisciplinary research, cross-scale correlations, and extreme environmental impacts. Strong nonlinearity, strong discontinuity, significant multi-physics coupling, multiscale, and complex geometries have become common characteristics in solving various mechanics problems quantitatively. Long-term quantitative research indicates that one of the core ingredients for solving such problems effectively lies in constructing numerical methods that can accurately identify, locate, capture, and separate different scale characteristics especially small-scale local characteristics, under multiscale and nonlinearity circumstances. These numerical methods should also possess the capacity to isolate and decouple the large-scale lower-order approximation from the small-scale higher-order truncation error effectively. The intrinsic multiresolution analysis and time-frequency localization characteristics of wavelet theory, as well as the various selectivity of basis functions, align precisely with the demands of this mathematical feature. Therefore, they can provide fundamental theory and diverse approaches for developing efficient quantitative methods to address various complex mechanics problems. Based on this fact, this paper provides a comprehensive discussion of wavelet theory, focusing on the theoretical framework of biorthogonal multi-resolution analysis and the construction method of frequently used wavelet bases. Furthermore, wavelet approximation of the function defined on a finite domain is presented in detail. The fundamental principles, development, merits, and shortcomings of different wavelet-based numerical methods are systematically elucidated. Several novel wavelet-based methods with outstanding performance developed recently are elaborated especially, and their applications in solving typical mechanics problems are reviewed. Meanwhile, the present paper also points out challenges encountered by the existing wavelet-based numerical methods when addressing complex and strongly nonlinear mechanics problems. This may provide valuable references for the development of wavelet-based numerical methods and their applications in complex mechanics and engineering problems, and introduce new perspectives and methods for solving these problems efficiently, accurately, and universally.
Modeling of joint structure interface friction mechanics: A review
SHEN Minmin, YANG Xiaodong
2024, 54(3): 477-521. doi: 10.6052/1000-0992-24-008
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Abstract:
Joints, as fundamental components of industrial machinery, are pivotal for extensive research and optimization in the realm of equipment manufacturing. Currently, due to the nonlinearity, complexity, and uncertainty of joint interfaces, the behavior mechanism of cross-scale and multi-physical field complex mechanics is unclear, making it difficult to accurately predict the dynamic characteristics of joint structures and monitor their dynamic service performance. This has become a bottleneck that restricts the breakthrough in precision structural dynamics analysis, high-fidelity simulation, design, optimization, and control. However, joint structures are widely used, and engineering and technical personnel have further demand for the mechanism and multifunctionality of joint structures. This article mainly reviews the analytical modeling, finite element modeling, and experimental systems of joint structure interface friction mechanics, and proposes the development trend of new joint structure design. Firstly, based on the requirements of the joint's working environment, engineering problems, and the lack of effective strength and stiffness prediction theory, this paper reviews the load types of bolted connection structures and the application of precise joint equivalent models. Secondly, several mainstream theoretical models of friction joint structures were summarized, including a constitutive model that analyzes the multi-scale physical behavior and laws of the joint interface at the micro/nano scale, a phenomenological model that derives macroscopic dynamic responses using system identification theory and methods, and a phenomenological constitutive friction model that integrates the microscopic contact mechanism of the constitutive model with the macroscopic perspective of system identification. Then, reviewing the simulation method based on the finite element and experimental methods of joint structures, which include direct finite element modeling, indirect equivalent finite element modeling, experimental benchmark systems, and anisotropic excitation joint structure experimental platforms. Finally, a new joint design concept addressing the multifunctional requirements of joint structures in the equipment field is proposed. This concept involves “transmitting static and suppressing dynamic” joint components as well as lightweight biomimetic joint components.
Research progress of biomimetic design and preparation of functional surfaces for droplet transport
LIU Ming, CHEN Shaohua
2024, 54(3): 522-562. doi: 10.6052/1000-0992-24-015
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Abstract:
Functional surfaces for droplet transport has important applications in green energy, medical technology, new materials and other fields, such as fog collection, drug targeted therapy, etc. The surfaces of natural creatures with specific functions of directional transport and fixed-point transfer of droplets provide excellent examples for design and preparation of functional surfaces for droplet transport, a large number of novel and flexible bionic research achievements have been arisen. Firstly, the typical surfaces of natural creatures with self-driven functions of droplet transport are summarized and the basic theories of wettability on solid surface are elaborated; then, the biomimetic research progress of functional surfaces for droplet transport based on different self-driven mechanism is reviewed, the mechanism and influencing factors of droplet transport on different functional surfaces are compared and analyzed; furthermore, the current research of the functional surface for directional transport or fixed-point transfer of droplet under the action of external field such as magnetic field, electric field, temperature field and etc. are elaborated and analyzed; finally, the applications and future directions of such biomimetic functional surfaces are summarized and prospected.
Progress in assessing hazards of asteroid impact on earth
DANG Leining, BAI Zhiyong, SHI Yilei, HUANG Jie
2024, 54(3): 563-605. doi: 10.6052/1000-0992-23-047
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Abstract:
Asteroid impact on earth poses a potential threat to humanity. Over the past 20 years, planetary defense has become a hot research area internationally, and it is also a crucial security requirement for our country. Assessing the hazards of asteroid impact on earth is a significant research topic within planetary defense. It is noted that asteroid impacts on earth exhibit characteristics of low probability, high hazard and randomness. These hazards include overpressure, thermal radiation, earthquake, tsunami, and global effects. Hazard assessment is applied in three scenarios: defense decision-making, defense implementation, and ground civil defense. The input and output of hazard assessment, the progress of numerical simulation and engineering computation in hazard assessment in terms of model, method and software, as well as the research status of the five types of hazards, are summarized. Furthermore the advancement of hypervelocity issues of earth impact by asteroid is presented. Finally, the current research limitations are identified, and prospects for future work are provided.
The multiscale digital core of shale and its application
JI Lili, LIN Mian, JIANG Wenbin, CAO Gaohui
2024, 54(3): 606-628. doi: 10.6052/1000-0992-24-006
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Abstract:
Reconstructing digital core that can fully characterize the multiscale pore (fracture) and matrix structure of the rock is one of the most advancing front issue in the field of unconventional oil and gas research, and is also an important foundation for shale oil and gas exploration and development. This article comprehensively analyzes the research progress in characterizing organic pore clusters, multiscale pore (fracture) structures, and representative element volumes (REV) of shale. Based on the analysis of the structural characteristics of marine shale in the Sichuan Basin, a new method for fully characterizing its multiscsal pore (fracture) structure has been proposed. On this basis, the digital cores are applied to the impact of multiscale pore (fracture) structures on acoustic properties and the gas content evaluation, and provides new technical methods for shale reservoir evaluation and sweet spots prediction.

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