力学进展

Exploration and outlook of plasma-actuated gas dynamics

LI Yinghong, WU Yun, LIANG Hua, ZHU Yifei, ZHANG Haideng, GUO Shanguang

2022, 52(1): 1-32. doi: 10.6052/1000-0992-21-044

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Plasma-actuated gas dynamics is an inter-discipline that concerns both the force and flow characteristics of an object submerged in flow, and the internal flow characteristics under the interaction of plasma actuation and flow, thus standing in the frontier of aerodynamics, gas dynamics, and plasma dynamics. Plasma actuation is a controllable disturbance imposed on the flow by either the collective motion of charged particles under electro-magnetic force or the pressure, temperature, and property variation produced by gas discharge. Affected by the local unsteady plasma actuation, the status of gaseous flow will change remarkably, which leads to a potential improvement of the aerodynamic performance. There have been tremendous investigations on surface dielectric barrier discharge plasma actuation, plasma synthetic jet actuation, as well as their interactions with boundary layer flow, separate flow, and shock-dominated flow. A systematic review of these investigations leads to the conclusion that there exists a strong coupling effect between plasma actuation and the modulated flow, and plasma shock control is a key to improving the control authority. Future researches should be directed towards the development of highly efficient plasma actuation, excitation, and leverage of flow instabilities, revealing coupling mechanism, and improvement of control effect.

Review of the measurement methods for elastic moduli and internal friction of solids

XIE Mingyu, LI Faxin

2022, 52(1): 33-52. doi: 10.6052/1000-0992-21-013

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Elastic moduli and internal frictions are fundamental properties of solid materials. The accuracy and convenience of the measurements these properties are of great significance to industrial production and scientific research. This paper reviews the measurement methods of elastic moduli and internal frictions of solid materials in the past 100 years. These methods can be divided into four categories: quasi-static method, low frequency method, resonance method, and wave propagation method. Firstly, the measurement principle of each type method is introduced and evaluated. Then the resonance methods, including free-free beam method, impulse excitation technique, resonant ultrasound spectrum and piezoelectric ultrasonic composite oscillator technique (PUCOT) are presented and discussed in detail. After that, a new method called modified piezoelectric ultrasonic composite oscillator technique (M-PUCOT), proposed by the authors, are introduced. This new method is based on the principle of electro-mechanical impedance, and can measure the Young’s modulus/shear modulus and the related internal frictions simultaneously, accurately, and quickly. Finally, the significance and prospective of this new method are discussed.

Characteristics of thermobaric explosives and their advances

HU Hongwei, SONG Pu, DENG Guoqiang, XIAO Chuan

2022, 52(1): 53-78. doi: 10.6052/1000-0992-21-021

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The detonation of thermobaric explosives involves ignition, detonation, propagation and reflection of shock wave, multi-phase turbulence, and multi-mode chemical reaction. It is a coupling process of multi-scale, multi-material, multi-factor, and multi-physical field. A deep understanding of the detonation mechanism of thermobaric explosion and effective control and utilization of the explosion are critical to the innovation and development of thermobaric weapons. It can guide the design, development and applications of high-power thermobaric explosives and weapons. Firstly, this paper describes the origin of thermobaric explosives and the basic principle of thermobaric explosion, and discusses the concept and connotation of thermobaric explosives. Secondly, the characteristics of thermobaric explosives from the aspects of explosive kinds, energy release characteristics, energy composition, blast reaction mechanism, blast effect enhancement mechanism and killing mechanism are elaborated. And then the evaluation method of explosion power of thermobaric explosives in confined space and the state of art of thermobaric explosives were summarized. Finally, we give some relevant suggestions that wcould provide guidance for the design of high power thermobaric explosive, the development of thermobaric bombs and damage assessment.

On the exit behaviors of non-Gaussian stochastic dynamical systems based on large deviation theory

LI Yang, ZHAO Feng, LIU Xianbin

2022, 52(1): 79-116. doi: 10.6052/1000-0992-21-033

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This paper introduces the basic ideas of large deviation theory and its applications in the study of exit problems of non-Gaussian stochastic dynamical systems. According to different types of non-Gaussian noise, the main research methods and recent progresses of exit problems are reviewed for stochastic hybrid systems, stochastic dynamical systems with exponentially light jump fluctuations, and stochastic systems with $\alpha $-stable Lévy noises. For the stochastic hybrid systems, the quasi-steady-state diffusion approximation which is approximated by stochastic differential equations, the WKB approximation for computing quasi-potential and optimal exit paths, the research on detailed balance conditions, and progresses in exit problems of the simplified version of stochastic hybrid systems (i.e. birth-and-death processes) are introduced. For the stochastic dynamical systems driven by the exponential light jump processes, the establishment of the functional extremum problems of large deviation principle and moderate deviation principle, the definition of the quasi-potential concept and the estimation of the mean exit time are discussed. For stochastic systems with stable Lévy noises, the theoretical and numerical methods for calculating the mean exit time and exit probability, and Onsager-Machlup theory, machine learning method, maximum likelihood method and data-driven method for computing the optimal exit paths are illustrated. Finally, some open problems related to the exit phenomena of non-Gaussian stochastic dynamical systems are given.

Mechancial properties of amorphous alloys: In the framework of the microstructure heterogeneity

QIAO Jichao, ZHANG Langting, TONG Yu, LYU Guojian, HAO Qi, TAO Kai

2022, 52(1): 117-152. doi: 10.6052/1000-0992-21-038

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The intrinsic structural heterogeneities of amorphous alloys are closely related to the thermodynamics and dynamical behavior, such as relaxation/crystallization, glass transition phenomenon and plastic deformation. However, the structural information is submerged into the meta-stable disordered long-range structure, which made it very difficult to explore the structural heterogeneities of amorphous alloys. Specificlly, the correlation between the microstructural heterogeneity and mechanical properties of amorphous alloys is one of important scientific issues. The current paper reviews the structural heterogeneity of dynamics into the amorphous alloys from the time-scale point of view and inspected the relaxation of structure with various spatial scales. From the perspective of experimental results, theoretical analysis and numerical simulations, the correlation between heterogeneous structure and the dynamic relaxations, deformation mechanisms, mechanical properties and dynamic characteristics were discussed. Finally, we discuss the further development of structural heterogeneity of amorphous alloys.

Nanofabrication through forming: Techniques and mechanics

WU Bozhao, LU Cai, LIU Ze

2022, 52(1): 153-179. doi: 10.6052/1000-0992-21-041

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Exploiting the plastic deformability of materials to manufacture components is widely applied in automobile, aerospace, consumer electronics, medical equipment, and other fields. With the development trend of device miniaturization, nanofabrication techniques plays a central role in the manufacturing industry. In recent years, extensive research and remarkable progress have been made in developing micro-/nanoforming techniques, and in-depth understanding of the underlying deformation behavior. This paper will review the latest research progress of micro-/nanoforming techniques, focusing on the deformation mechanism and size effect in the micro-/nanoforming of different material classes such as polymers, amorphous alloys/bulk metallic glass, and crystalline metals. Finally, the technical challenges and key mechanical problems of micro-/nanoforming of crystalline metals are prospected.

Study on the evolution of non-modal disturbances in hypersonic boundary layer based on HLNS approach

SUN Peicheng, ZHAO Lei, DONG Ming

2022, 52(1): 180-195. doi: 10.6052/1000-0992-22-003

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Laminar-turbulent transition in hypersonic boundary layers is of fundamental importance in the design of aerospace vehicles. Subcritical transition, occurring upstream of the linear instability region, appears frequently in conventional wind-tunnel experiments. The subcritical transition is usually triggered by the evolution of non-modal disturbances and their subsequent secondary instability. In order to reveal the inherent mechanisms governing the impact of abrupt changes on hypersonic subcritical transition, a numerical framework describing the evolution of non-modal disturbances based on the harmonic linearized Navier-Stokes (HLNS) equation and its adjoint system is developed. The advantage of this framework is that the elliptic nature of the original system is retained, leading to the ability to deal with the rapid distortion of the non-modal disturbances (streaks) in the vicinity of the local abrupt changes. For a hypersonic blunt-plate boundary layer with an oncoming Mach number 5.96 and an angle of attack $ - 4^\circ $, the impact of the cavities with different depths on streak amplitude is studied. Numerical solutions indicate that streaks are enhanced by the cavities, which agrees with the experimental observations in quantity. Moreover, the enhancement effect peaks at a particular cavity depth.

Passively driven three-dimensional microfliers inspired by wind-dispersed seeds

SONG Jizhou

2022, 52(1): 196-200. doi: 10.6052/1000-0992-21-055

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By mimicking wind-dispersed seeds, researchers have developed a class of passively driven microfliers, which can reduce the flight power consumption and achieve a long-time flight.

2022, 52(1): 201-215.

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2022, 52(1): 216-219.

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2022 Vol. 52, No. 1

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