力学进展

Progresses and challenges of high Reynolds number wall-bounded turbulence

ZHENG Xiaojing, WANG Guohua

2020, 50(1) doi: 10.6052/1000-0992-19-009

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High Reynolds number wall-bounded turbulence (HRNWT) has been a hotspot and difficult issue in the field of turbulence research in recent years. The understanding of flow phenomena, laws of physics and mechanisms are insufficient and studies on HRNWT are restricted by various deficiencies of research techniques. There is still a long way to go to establish a thorough theoretical framework for HRNWT. Based on the introductions of the leading research techniques, this paper summarizes and reviews the research progresses in statistical characteristics of the HRNWT and very large scale motions (VLSMs) including their morphologies, originations, influences on the turbulent flows, as well as the interactions between turbulence and moving particles in the HRNWT. The contributions of the author's research team on these issues, especially the turbulence-particle interactions are combined. Finally, we highlight the prospects of direction, trends and remaining challenges of further researches.

Progress in multi-wave structure and stability of oblique detonations

TENG Honghui, JIANG Zonglin

2020, 50(1) doi: 10.6052/1000-0992-19-011

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Oblique detonation is an important direction in gaseous detonation physics and has great potential in the application of new-concept aeronautic and astronautic propulsion. As the fast combustion induced by shock, the oblique detonation wave could be simplified into a discontinuity with energy input. However, in oblique detonation flow, there concern several complicated fluid phenomena, such as shock wave and turbulence, which are coupled with the heat release and result in complicated flow and combustion mechanisms. A theoretical investigation is hard to be performed due to the characteristics of multi-scale and nonlinearity. Meanwhile, experimental investigation encounters the difficulties from measuring the flow fields of high temperature, high pressure, and high velocity. In the last two decades, the main progress of oblique detonation is achieved by numerical investigation through comprehensive simulation and analysis. First of all, the multi-wave structure of the initiation region and surface stability are introduced in the ideal inflow conditions. Then, derived from the application in engines, the effects of inflow inhomogeneity and interaction with expansion waves are studied and analyzed. Finally, some suggestions on future work are proposed and discussed.

Research progress of field measurements and inversion methods of ice loads on ship structure during ice navigation

WANG Jianwei, DUAN Qinglin, JI Shunying

2020, 50(1) doi: 10.6052/1000-0992-20-007

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The ice load is an important environmental factor affecting the navigation safety of polar ships. The field monitoring of ship structure is a reliable approach to obtain the ice load. In view of the complexity of the ship-ice interaction, it is currently difficult to measure the ice load directly. Generally, the ice load is inverted indirectly through the measured data of the local or global response of ship structure, such as structural strains and six-degrees-of-freedom motion parameters. Firstly, according to the action scope of the ice load, the monitoring methods of the ice load on ship structure are divided into two categories in this paper, i.e., those for local ice loads and those for global ice loads. The information such as the date, the area, and the measurement scheme of ice load field measurements for 18 polar ships is systematically summarized and analyzed. Then, five ice load inversion methods for ship structure such as Influence Coefficient Matrix Method, Support Vector Machine Method, Green's Function Method, Motion Parameter Method, and Work-energy Relationship Method are comprehensively introduced from the aspects of fundamental principles, application scope, strengths and weaknesses, application status, and development prospects. The field measurement results of the Arctic shuttle tanker, MV Timofey Guzhenko, and the icebreaking research vessel, IBRV Araon, are emphatically analyzed. On this basis, the related research progress of the local ice pressure, the peak ice force, the probability distribution of ice loads, and the ice-induced vibration acceleration are discussed in depth. Finally, the problems existing in the ice load field monitoring for ship structure are dissected from three aspects, including measurement technology, inversion methods, and ice load characteristics. Moreover, the corresponding research directions are discussed. The review of field measurements and inversion methods of ice loads on ship structure in this paper can provide scientific reference for subsequent research and engineering applications, so as to better promote the development of ice-resistant structure design and ice navigation technology of polar ships in our country.

The biomechanics of injury and prevention

WANG Lizhen, FAN Yubo

2020, 50(1) doi: 10.6052/1000-0992-19-020

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The biomechanics of injury and prevention is an important branch of modern biomechanics and a multi-disciplinary subject that is applied to the analysis of the mechanism of biological tissue or organ damage and its prevention. The goal of it is to prevent the human body from damage or minimize injury for tissue or organ when subjected to loads. It covers the study of the response of tissue subjected load, the mechanism and the tolerance of injury, and the methods and effective devices to reduce injury. Higher loads have high lethality due to its short-term action and explosiveness. Therefore, the ability to anti-injury under overload has been a severe constraint for the development of aircraft, the improvement of automobile performance and the enhancement of athletes' competitive ability. In particular, the emergence of the modern faster and more flexible fighter, the life-saving of supersonic ejection and the protective of maneuver flight of high load and load has presented new challenges for the subject of injury and prevention biomechanics but also provided enormous opportunities for the development of it. In recent years, the impact injury involved in aerospace, traffic accidents, sports and falls of the elder has presented the features of high incidence and low protection efficiency. However, it is difficult to obtain the actual data due to the damage caused by experiments to humans. Meanwhile, since the biological tissue has the characteristics of nonlinearity, viscoelasticity, regeneration and reconstruction, it involves how to describe the constitutive relations of biological tissue or organs, and the correlation between the anatomical features and its mechanical properties accurately. It also involves how to establish the mechanism and tolerance of tissue injury at multi-scales, the methods and the principle to design protective devices. The present paper focuses on the summarization of the major research contents and its methods to the biomechanics of injury and prevention. The types, mechanisms (including the response of the biomechanics and mechanobiology), tolerance, and the protective method of injury under complex loading for the human body are summarized, and the primary advancement and the possible tendency of development in these fields are introduced. The study on the biomechanics of injury and prevention is of great significance to protect and improve human safety under complex load. It could guide the establishment of standards and evaluation methods of musculoskeletal injuries involved in aerospace, transportation, and sports. This research is vital to guide the optimization design of protective devices and has great potential to the development and application of bionic engineering materials and protective devices.

The empirical potential of two-dimensional nanomaterials and their heterostructures

Tan Yawen, Jiang Jinwu

2020, 50(1) doi: 10.6052/1000-0992-19-010

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The atomic interaction is a fundamental ingredient in the research of two-dimensional (2D) nanomaterials that have been widely investigated for decades. The atomic interaction can be described by empirical models, which are of both high accuracy and efficiency owing to their physics-inspired functional forms. We outline some typical empirical potential models for the 2D material and its heterostructures, including the vertical van der Waals heterostructure and the lateral heterostructure. The present survey shall offer some help in choosing potential models for the simulation of these 2D-material-based systems. We also discuss some prospects and current challenges at the end of the article.

System design and mechanical modeling of soft smart robots

YIN Shunyu, XU Yi, CEN Nuo, JIN Piaopiao, LI Tiefeng

2020, 50(1) doi: 10.6052/1000-0992-19-017

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The conventional machines and mechanical structures are usually composed of rigid parts such as motors, gears, and hinges. Possessing the advantages of sufficient power and high precision, those rigid robots still have challenges in low noise and high adaptability. Inspired by the soft structure and high environmental adaptability of natural organisms, the design, and manufacture of soft robots have been widely studied in the field of robotics. Soft smart materials can produce responses under various external stimulation. With the advantages of excellent flexibility, good biocompatibility, and easy manufacturing, soft smart materials can be widely used in the design and fabrication of bionic soft robots. Several types of soft smart materials and structures with the actuating function have been extensively studied recently, including the pneumatic soft muscle, shape memory alloy/polymer, ion-exchange polymer, dielectric high-elastic body, and responsive hydrogel. In this paper, various types of soft smart robots with different actuating methods are introduced, and the system design and mechanical modeling of soft smart robots are summarized and discussed.

Review of controlling flow separation over airfoils with periodic excitation

LIU Zhiyong, LUO Zhenbing, YUAN Xianxu, TU Guohua

2020, 50(1) doi: 10.6052/1000-0992-19-019

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Active flow control is one of the most promising techniques that are employed in aeronautics and astronautics engineering in the 21st century. It will be a new degree of freedom of design for future air vehicles. Using this technique to control flow separation over airfoils is very meaningful for both fundamental research and applied research. Since periodic excitation is an efficient and convenient control method, it is significant to review the investigations on controlling flow separation over airfoils with periodic excitation. An evaluating parameter is introduced firstly, which is followed by some discussions about excitation frequency, intensity, location, and Reynolds number. Three aspects which are extracted from publications and should receive appropriate attention are presented. One is the evaluation criterion of efficiency, which can guide the design of forcing devices and operation modes. Another is the acoustic-dominated mode, which is observed in the high-frequency forcing cases. This mode may exacerbate flow separation. The third one is a phenomenon of drag anomaly that, in certain conditions, form drag is larger than total drag with excitation. At last, some recommendations for future research are made. This review is helpful for applications of flow separation control with periodic excitation.

Research progress of aero-optical effect

SUN Xiwan, LIU Wei

2020, 50(1) doi: 10.6052/1000-0992-19-003

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Optical imaging detection is an important research direction in the precision guide field. The quality of observation would be profoundly deteriorated due to the aberration, jitter, and change in optical path length when light propagates through the density-varying flowfield, videlicet, aero-optical effect. Investigation on such a field possesses both considerable engineering and academic values. On the one hand, based on the physical understanding concerning the impact of flow structures on light propagation, the methods for effective reduction of the aero-optical phenomenon have attracted widespread attention. On the other hand, optical interrogation has shown considerable potential in flowfield inspection since the light beam inevitably records the signature of flow structures. In the current study, recent advances of aero-optical effects have been reviewed in an interdisciplinary perspective of aerodynamics and optical engineering. The commonly-used evaluation parameters are introduced in the first place, followed by various theoretical, experimental, and numerical methods summarized in sequence. Whereafter, we put an eye on the research progress from three aspects, namely the impact of aero-optical effects on image aberration, the methods for reduction of aero-optical effect, and the flow structure examination via novel aero-optical detection method. An additional discussion focuses on the difficulty in numerical validation attempts for aero-optical problems. Prospects based on the development stages of aero-optical effects are proposed in the end.

Application of finite element method in ultrasonic guided waves testing technique

CHEN Honglei, LIU Zenghua, LI Ziming, WU Bin, HE Cunfu

2020, 50(1) doi: 10.6052/1000-0992-18-019

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Ultrasonic guided waves have the ability of long-distance nondestructive testing for defects in waveguide structures, and have been one of the hotspots in the field of nondestructive testing for many years. Finite element method (FEM) has the ability to calculate various complex dynamics problems and has become an important tool in the research of ultrasonic guided wave testing technique. Considering the hot issues in the research, a brief review of the relevant FEM is proposed. The development of FEM and its application in the excitation and reception of guided waves under multi-physical coupled field mechanism, the propagation characteristics of guided waves in linear elasticity and viscoelastic structures and nonlinear ultrasonic guided waves are introduced. Finally, the research emphasis and development direction of the relevant FEM in the future is prospected based on the research trend of ultrasonic guided wave testing technique.

The researches on the stochastic dynamics based on the large deviation theory

ZHU Jinjie, CHEN Zhen, KONG Chen, LIU Xianbin

2020, 50(1) doi: 10.6052/1000-0992-18-021

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This paper introduces the basic ideas and concepts of large deviation theory and its application in the study of exit problems. Three critical indicators of exit problems are reviewed: mean first passage time, exit location distribution and most probable escape path. Among them, the characterization of the most probable escape path is a structural conundrum. For the mean first passage time, its relationship with quasi-potential is introduced, and it is applied to analyze the time matching mechanism in stochastic resonance and self-induced stochastic resonance. For the exit location distribution, the relevant algorithms to accelerate the Monte Carlo numerical simulation are discussed, and the probability evolution method is specially clarified with some interesting examples. For the study of the most probable escape path, several calculation methods are discussed, and the singularity of the topological structure and its dynamical implications of the Lagrangian manifold formed by the auxiliary Hamilton system trajectories are analyzed. Furthermore, the corrected action method under the condition of finite noise intensity is given. Finally, the prospect of some open problems for the application and development of large deviation theory is discussed.

Big Data in mechanical research: Potentials, applications and challenges

YANG Qiang, MENG Songhe, ZHONG Zheng, XIE Weihua, GUO Zaoyang, JIN Hua, ZHANG Xinghong

2020, 50(1) doi: 10.6052/1000-0992-19-002

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Big Data has developed rapidly and made remarkable achievements. The unique thinking and methodology of Big Data provide a new paradigm for scientific research. High spatial-temporal resolution and multiple-parameter synchronous observation methods are offering opportunities for Big Data driven mechanics. Applications of Big Data or machine intelligence methods in mechanical researches have grown rapidly. This review is focused on the impact of Big Data method and its way of thinking on mechanical research and the corresponding challenges. First, the connotation and research situation of Big Data in three aspects, i.e. Big Data itself, Big Data science and Big Data technologies are discussed, and Big Data development plans of governments and organizations are summarized. Comparative analysis of the mechanical methodology and the Big Data methodology were carried out, with focuses on paradigm differences in utilization of data. Instead of partial differential equations used by mechanics, data driven models are used for mathematical descriptions of the underlying physical problem in the Big Data paradigm. The latter shows advantages in simulations and predictions of complex systems. Latest researches in material performance prediction, constitutive modeling, turbulence modeling, structural health monitoring, and experimental mechanics using Big Data, as well as Big Data driven new paradigm of modeling and simulation including Dynamic Data Driven Application System and Digital Twin are reviewed. Three kinds of Big Data driven mechanical researches are summarized, i.e. data driven improvement of existing methods, data mining for hidden and intrinsic physical laws, and data based new methodologies and theories for mechanics. A mechanics-centric approach employing both the prior knowledge of mechanics and advantages of Big Data methodology is recommended for a vision of breakthroughs along with new subject directions in mechanics.

Mechanical thoughts and applications in cognitive neuroscience

WANG Rubin, WANG Yihong, XU Xuying, PAN Xiaochuan

2020, 50(1) doi: 10.6052/1000-0992-20-008

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This review article systematically summarizes the neural energy theory and methods proposed by our team in the field of brain science, and the internal relationship between mechanics and neural energy theory. This paper introduces how to construct an equivalent W-Z neuron model with the H-H model using the idea of analytic dynamics. Based on this, a large-scale neural model with neural energy as the core and a theoretical framework of global neural coding are proposed in the field of neuroscience. The unique functions and advantages of this novel neuron model are confirmed in the aspects of information processing, including visual perception, brain intelligence exploration, prediction of new working mechanisms of neurons and explanation of experimental phenomena challenging to explain in neuroscience. Because plasticity is the core of cognitive neuroscience and intelligent behavior, through the classical mechanical analysis of protein molecular machines, it is further clarified that the plasticity and neurodevelopment of neurons are not only biochemical reaction processes but also the role and contribution of mechanics are indispensable and important factors. It shows that the research thought of mechanics science in neuroscience and life science and its profound influence on internal logic. These studies will promote the integration of experimental neuroscience and theoretical neuroscience in the future, abandon the shortcomings in the research methods of reductionism and holism in the field of neuroscience, and integrate their respective advantages effectively. It is extremely important to promote the penetration of theories and methods of mechanical science.

2020 Vol. 50, No. 1

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