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Research progress of fatigue crack propagation method based on finite element technology
SU Yukun, MA Tao, ZHAO Xiaoxin, ZHANG Guangliang, ZHU Jialei, ZHANG Peng
 doi: 10.6052/1000-0992-23-049
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Abstract:
Fatigue cracks are one of the important factors causing fracture and failure of engineering structures. At present, the commercial software for fatigue crack propagation finite element simulation includes ANSYS, ABAQUS, FRANC3D, ZENCRACK, etc., which provide strong support for the study of fatigue crack propagation process. The current finite element simulation methods for fatigue crack propagation are reviewed in this paper. The definition of fatigue crack and the necessity of studying fatigue crack propagation behavior are clarified. Three finite element methods for simulating fatigue crack propagation are introduced: Extended Finite Element Method(XFEM), Cohesive Zone Model (CZM) and Virtual Crack Closure Technique (VCCT). The basic theories and core ideas of the three methods were summarized, and the application as well as development of the three methods were classified and summarized. Finally, the three finite element methods are analyzed, the advantages and limitations of each method are pointed out, and suggestions are given for the future improvement of the finite element simulation technology for fatigue crack propagation.
Research on structure topology optimization design empowered by deep learning method
CHEN Xiaoqian, ZHANG Zeyu, LI Yu, YAO Wen, ZHOU Weien
 doi: 10.6052/1000-0992-23-052
Abstract(546) HTML(218) PDF(194)
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This article comprehensively discusses the relevant research progress in the field of structural topology optimization and the cross-integration development of deep learning technology in recent years. Focusing on the core methods and key modules of structural topology optimization design, two major types of empowerment methods are systematically sorted out from the perspective of deep learning empowerment. The study points out that the global surrogate model construction method for structural optimization design based on deep learning technology, as a direct mapping structural design method, has been widely studied because of its simple and typical design ideas. However, the global surrogate model has limitations in computation and generalization. The limitations and deficiencies in performance are also particularly obvious. The structural optimization design method with local sub-link acceleration and replacement integrated with deep learning technology is a more flexible and diverse form of local empowerment, with good universality and unique advantages. The article looks forward to the future development of intelligently empowered structural optimization. Further research work would focus on the organic combination of deep learning and structural design, as well as the co-driven design paradigm of data and knowledge.
Research progress of process and structures optimization for 3D printed continuous fiber-reinforced polymers
YE Hongling, DONG Yongjia, MAO Pengqi, XIAO Yang, XIE Jialin
 doi: 10.6052/1000-0992-23-048
Abstract(279) HTML(69) PDF(90)
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Continuous fiber-reinforced polymers (CFRP) has been broadly applied in the aerospace engineering due to its excellent specific strength, specific stiffness, designability and lightweight feature. The development of 3D printing has changed the manufacturing process of CFRP structures, which makes the free form of complex structures possible and provides more design space for advanced structural materials. In order to give full play to the performance advantages of CFRP and the flexibility of 3D printing process, and achieve innovative structural design and performance improvement, researchers explored the solutions of design and manufacturing integration for 3D printing CFRP from the aspects of material performance and structural design, respectively. In this paper, the development of properties analysis, process improvement and structure optimization of CFRP is reviewed systematically. Various multi-scale optimization methods of CFRP are summarized and illustrated, the development trend of real-time, functional and intelligent structural design method of advanced materials in the future is discussed and prospected.
Review on dynamics and control of space structure in the process of on-orbit assembly
WU Zhigang, JIANG Jianping, WU Shunan, LI Qingjun, WANG Xing, TAN Shujun, DENG Zichen
 doi: 10.6052/1000-0992-23-041
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On-orbit assembly is a crucial means to construct large and ultra-large space structures such as space stations, large satellite antennas, large-aperture space telescopes, and space solar power stations. However, complicated dynamics and control problems, such as the configuration increasement, parameter variations, orbit-attitude-structure coupled effects, and contact problems, will be encountered during the process of on-orbit assembly and bring challenges to accomplishing the assembly task accurately, efficiently, and safely. The development status of dynamic modelling methods of large space structures, special dynamic phenomena of ultra-large space structures, and dynamic modelling studies of space structures during on-orbit assembly process were reviewed. Then, the control methods of the on-orbit operation stage, the assembly sequence planning methods, and the control methods for the on-orbit assembly process were introduced. In addition, the key techniques of gravity unloading, scale model design and testing, nonlinearity and uncertainty quantification techniques with ground tests in the assembly process were summarized. Finally, to address the increasing configuration and discontinuously varying parameters of the ultra-large space structures during on-orbit assembly process, a few suggestions were put forward to deal with the dynamic and control problems.
Review
Fundamental principles and research progress of non-Hermitian mechanical systems
GENG Linlin, YUAN Jinbo, CHENG Wen, HU Gengkai, ZHOU Xiaoming
2024, 54(1): 1-60.   doi: 10.6052/1000-0992-23-034
Abstract(776) HTML(212) PDF(369)
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Non-Hermitian theory, originated from quantum mechanics, is a theoretical framework for investigating the dynamics of open systems. New phenomena can be revealed with this theory, including exceptional point, chiral mode switching, and topological skin effect, which provide novel concepts for unusual wave and vibration control. This review will provide a comprehensive introduction to basic concepts of non-Hermitian theory in terms of classical mechanical systems, clarify the relationship between classical and non-Hermitian systems, and summarize the cutting-edge research progress in this field. Exceptional points and parity-time symmetry in non-Hermitian systems are firstly introduced. Then, the perturbation theory near exceptional points and its application to enhanced sensitivity are presented. Subsequently, the eigenvalue topological structure near exceptional points and eigenmode evolution in the process of dynamical encircling of exceptional points are discussed. Finally, the topological phase property of non-Hermitian mechanical systems is introduced.
Review and prospect on the efficient synthetic jet
LU Yiran, WANG Jinjun
2024, 54(1): 61-85.   doi: 10.6052/1000-0992-23-038
Abstract(386) HTML(139) PDF(92)
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As a significant active flow control method, the synthetic jet has been considered to be promising and of great potential in applications. Due to its superior control performance, synthetic jets have wide application in improving aerodynamic characteristics of aircrafts, suppressing vibration and noise, cooling electronic devices and etc. In recent years, a large number of synthetic jet models with higher accuracy have been proposed and the underlying mechanism of the efficient entrainment has been explored more vividly. The optimization of the synthetic jet actuator and further improving its controlling efficiency has attracted more and more attention. The optimization of the actuator and its application are summarized from three aspects respectively, i.e., the actuator structure, the geometric parameters and the actuating signal. Moreover, the possible issues for future investigation have been suggested.
Research progresses and prospects of vortex cavitation dynamics
CHENG Huaiyu, JI Bin, LONG Xinping, PENG Xiaoxing
2024, 54(1): 86-137.   doi: 10.6052/1000-0992-23-045
Abstract(638) HTML(107) PDF(167)
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Vortex cavitation, a cavitation phenomenon that occurs at the vortex center on propeller blades, often appears first on propeller prototypes. Once it occurs, it will seriously affect the acoustic stealth performance of naval vessels (the noise can increase by more than 10 dB), which limits the further increase in the critical speed of naval vessels to a great extent. Therefore, it has long been one of the key and challenging topics in the field of cavitation hydrodynamics. In this paper, the characteristics of vortex cavitating flow compared with other forms of cavitating flow are briefly introduced first, with tip vortex cavitation as the main research object. The evolution behaviors and flow mechanisms of vortex cavitation inception and development are then expounded. At the same time, the influential factors of vortex cavitation inception and development and their mechanisms are discussed in depth from the perspective of cavitation elements. In addition, the relevant research progress on several key issues, including scale effect and flow control in vortex cavitating flow, is reviewed. The internal causes of vortex cavitation scale effect and the controlling methods and ideas for vortex cavitating flow are systematically sorted. Finally, aimed at the key and tricky problems in the current research field of vortex cavitation, the experimental measurement and numerical simulation technologies used in the future research on vortex cavitating flow are summarized and outlooked.
Recent progress of experimental fluid mechanics for EUV sources
DENG Weiwei, ZHAI Tianqi, GAO Lihao, XU Chenghao, ZHAO Xinyan, LIU Yanchu
2024, 54(1): 138-172.   doi: 10.6052/1000-0992-23-044
Abstract(575) HTML(116) PDF(212)
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The extreme ultraviolet (EUV) source is the enabling component of the EUV lithography. The commercialized EUV source is based on laser produced plasma from tin droplet target. EUV source is essentially a fluid-state light source, which involves rich and complex fundamental fluid mechanics problems with four characteristic time scales ranging from picoseconds to milliseconds. This review surveys the research progress of experimental fluid dynamics for EUV sources. First, the fundamental and technical aspects of the generation and control of jet, droplet and liquid film targets are introduced. Second, the dynamic response of the three types of targets to pulsed lasers were summarized, with an emphasis on droplet targets. Finally, in order to improve the stability, brightness and life the EUV sources, three key research topics in experimental fluid mechanics worthy of attention are proposed: (i) the precise generation and manipulation of fine tin droplet targes with long spacing at high frequencies; (ii) the quantitative physical picture of the expansion and radiation of the laser produced plasma, and (iii) the deformation and fragmentation mechanism of droplet targets and suppression, collection and cleaning technologies for debris.
Mesoscopic modeling of complex multiphase fluids: Dissipative particle dynamics (DPD) method and its applications
PAN Dingyi, HU Guohui, CHEN Shuo, PHAN-THIEN Nhan
2024, 54(1): 173-201.   doi: 10.6052/1000-0992-23-033
Abstract(393) HTML(30) PDF(104)
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Complex multiphase fluids, such as suspension, emulsion and foam, which contain large number of particles, droplets and bubbles, respectively, with characteristic scale ranges from nanometer to micron. For these kinds of dispersed materials, either individually or in clusters, complex kinematic behavior is exhibited under the imposed flow, affecting the bulk rheological properties of these multiphase fluids. Investigations of these complex fluids by using mesoscopic numerical methods are among the most effective and economic approaches. In particular, dissipative particle dynamics (DPD) is a typical mesoscopic numerical method. Due to its particle-based nature, it is especially suitable for the modeling and investigating of these types of complex fluids. In this review, we thoroughly introduce the applications of DPD methods in the modeling of suspension, emulsion and bubbles as well as the corresponding developments in DPD methods. Meanwhile, we also discuss relevant shortcomings and certain aspects that require further improvement. Finally, we provide a conclusion and outlook for DPD methods.
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2024, 54(1): 202-212.  
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