力学进展

Mechanical frontiers in shale-gas development

Yuewu LIU, Dapeng GAO, Qi LI, Yizhao WAN, Wenjie DUAN, Xiaguang ZENG, Mingyao LI, Yewang SU, Yongbo FAN, Shihai LI, Xiaobing LU, Dong ZHOU, Weimin CHEN, Yiqin FU, Chunhui JIANG, Shaoji HOU, Lisheng PAN, Xiaolin WEI, Zhiming HU, Xianggang DUAN, Shusheng GAO, Rui SHEN, Jin CHANG, Xiaoyan LI, Zhanli LIU, Yujie WEI, Zhemin ZHENG

2019, 49(1) doi: 10.6052/1000-0992-17-020

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Abstract:
The development ofshale gas involves two critical processes including fracturing andtransportation. To realize reticular fractures in the shale layerof multi-phase under more than 2000 m subjected to complexgeo-stress and to collect the free and adsorbed gases encapsulatedin the layer, we face many key mechanical challenges to beaddressed. There are several cut-on-edge research topicsassociated with shale gas development: the huge span in structuralsize and fracture eveents from nanoscale to even severalkilometers, free and adsorbed gas transporting at temperal scalesfrom microseconds to the life-long mining of a shale-gas well, thefluid-solid interaction at different time and length scales, andthe in-situ monitoring on internal damage states duringfracturing. In view of the achievements in shale-gas explorationand the mechanical research frontiers for subsequent development,we give a comprehensive review on the basic characteristics anddevelopment techniques of shale-gas reservoirs. We cover in thisreview six aspects of the latest research progress, the mechanicalproperties of shales and their characterization, shale gasreservoir experimental techniques, shale gas micro-flow mechanismand fluid-solid coupling characteristics, numerical simulation ofhydraulic fracturing process, micro-seismic monitoring technologyof hydraulic fracturing process and high-efficiency andenvironmentally friendly waterless fracturing technology.Combining with the engineering practice of shale-gas reservoirdevelopment, the key issues of mechanics are presented, to providea theoretical basis for the practitioners engaged in thedevelopment and research of shale-gas field. We suspect that theprogress summarized here may help guide general research inmechanics, especially in geotechnical mechanics.

A brief review of the homotopy analysis method

LIAO Shijun, LIU Zeng

2019, 49(1) doi: 10.6052/1000-0992-18-005

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In this paper, a brief review of the current advances of the homotopy analysis method (HAM) in theory and applications is given. The HAM is an analytic approximation method for highly nonlinear problems. Traditionally, perturbation methods were widely used. However, perturbation methods are strongly dependent upon the existence of small physical parameters (called perturbation quantity), and besides perturbation approximations often become divergent as perturbation quantity enlarges. However, unlike perturbation methods, the HAM has nothing to do with the existence of small/large physical parameters, since it is based on the homotopy, a basic concept in topology. Especially, the HAM provides a convenient way to guarantee the convergence of solution series. In addition, the HAM provides great freedom to choose the base-functions and the equation-type of high-order equations so that good approximations can be obtained more efficiently. As illustrated in this paper, the HAM has been used to solve some challenging nonlinear problems in nonlinear mechanics, quantum mechanics, applied mathematics, finance and so on.

Dynamics problems of micro/nano channel resonators for detection and characterization

YAN Han, ZHANG Wenming

2019, 49(1) doi: 10.6052/1000-0992-18-006

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Micro/nano-channel mechanical resonators have ultra-high resonance frequency, quality factor, and sensitivity in liquid environment. Hence they are usually used for high-precision detection and characterization in liquid environments. These resonators have broad application prospects in the fields of biology, medicine, and chemical industry. The detection and characterization functions of micro/nano-channel mechanical are highly dependent on their dynamic characteristics. Such devices are coupled systems composed of multiple components, including resonant structure, internal fluid, detected object, external excitation and so on. As a result, the involved dynamic problems are much complicated, and they have become a hotspot and bottleneck in the research of resonant devices. In this paper, the research progress of micro/ nano-channel mechanical resonators is reviewed. The dynamic design principles for high-precision detection and characterization are summarized. The dynamic characteristics, including stability, frequency response characteristics, energy dissipation, frequency fluctuations and so on, are discussed in detail. The physical mechanism of different dynamics and its influence on the performance of the resonator are expounded. It can provide theoretical reference and technical support for deep understanding of the dynamic design problem of micro/nano-channel mechanical resonators and improve the dynamic performance of the devices. And it is of great significance for the design, manufacture, and application of ultra-high frequency and ultra-high sensitivity devices.

Review on long-rod penetration at hypervelocity

JIAO Wenjun, CHEN Xiaowei

2019, 49(1) doi: 10.6052/1000-0992-17-021

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Made by high-density metals, long-rod penetrators have excellent performances on penetration and perforation when launched at hypervelocities around 1.5$\sim $3.0km/s. Due to their important background in the military application, long-rod penetration at hypervelocity has become an active research focus. The present paper reviews research advance up-to-date on long-rod penetration at hypervelocity. Firstly, basic concepts, research methods, and theoretical models are introduced. Secondly, highlighted issues which are focused in past studies and their applications, including rod and target materials, nose shape, $L/D$ effect and segmented rods, ceramic targets and interface defeat, as well as non-ideal long-rod penetration, etc. Finally, some future research proposals are suggested.

Interface defeat of ceramic armor

TAN Mengting, ZHANG Xianfeng, BAO Kuo, WU Yang, WU Xue

2019, 49(1) doi: 10.6052/1000-0992-17-015

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Interface Defeat, which can effectively defeat the long-rod projectile (LRP), is a specific phenomenon of ceramic armor. Studies on this area have been conducted for the last three decades both at home and abroad proving that delaying dwell time or increasing interface defeat/penetration transition velocity can defeat projectile and enhance the ballistic performance of ceramic armor. Related researches on the experimental techniques, theoretical models and numerical simulations of interface defeat are introduced, including the study of interface defeat at the micro and macro scale, a method for the design of the ceramic composite armor, etc. According to the insufficient work of interface defeat, some suggestions are proposed in this paper.

Research progresses and prospects of unsteady hydrodynamics characteristics for cavitation

JI Bin, CHENG Huaiyu, HUANG Biao, LUO Xianwu, PENG Xiaoxing, LONG Xinping

2019, 49(1) doi: 10.6052/1000-0992-17-012

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Cavitation is an important kind of complex multiphase flow with strong three-dimensional characteristic and high unsteadiness, which frequently occurred in a wide range of fluid machinery, marine propulsor, and hydraulic engineering and can generate the destructive behavior. Cavitation has been one of the most difficult and key problems in the area of hydrodynamics for quite a long time. In this paper, the research progress of unsteady hydrodynamics characteristics for cavitation is reviewed from the viewpoints of experimental and numerical investigations, respectively. And the existing problems in the cavitation research are also discussed. For the experimental study, the progress of the cavitation mechanism tunnel, measurement technology for cavitating flow and simultaneous sampling technique are introduced. For the numerical investigations, some of the most popular cavitation models and turbulence models are introduced by categorization, and the applications of large eddy simulation (LES) approach and validation & verification in cavitation simulations are discussed in detail. Then, mainly based on attached cavity but also other kinds of cavitation, such as cavitation cloud, cavitation erosion, and vortex cavitation, several basic but important problems are discussed. Problems discussed herein includes the evolution of attached cavity, the three dimensional structures of cavitation, the shedding mechanism of attached cavity, the unsteadiness mechanism of cavitation and its connection with the pressure fluctuations, the interaction between cavitation and vortex, the fluid-structure interaction in the cavitating flow around a flexible hydrofoil, influence of cavitation on the wake flow, and so on. Finally, prospects of the direction and trends of cavitation hydrodynamics research are discussed.

Time discretization methods in the computation of unsteady flow

ZHANG Weiwei, GONG Yiming, LIU Yilang

2019, 49(1) doi: 10.6052/1000-0992-17-018

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For the numerical computation of unsteady flow, the computational accuracy and efficiency would have a significant difference with different time discretization methods. This paper based on the summarize of the development situation of time discretization methods at present, briefly introduces the time discretization methods developed in recent years like the nonlinear frequency domain method, harmonic balance method, time spectral method, time spectral element method, time finite difference method and so on. Based on the difference between discrete versions, the time discretization methods can be divided into four types: time domain marching method, frequency domain harmonic method, time domain collocation method and hybrid method. This paper briefly introduces the mathematical thought and study progress of each discretization method, and selective compare the accuracy, efficiency, and scope of application of each time discretization method in the computation of unsteady flow. Then we systematically summarize the characteristic of each time discretization method and advise how to choose appropriate time discretization methods in different unsteady flow problems. Finally, briefly introduce the application of current time discretization methods in the projects and discuss the development directions of the time discretization method in the future.

Analytical dynamics of continuous medium and its application

LIANG Lifu, GUO Qingyong, SONG Haiyan

2019, 49(1) doi: 10.6052/1000-0992-17-019

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First, the studying progress of domestic and foreign scholars on analytical dynamics of continuum is reviewed. This paper mainly studies the problem of applying the Lagrange equation to the continuum dynamics. By using Lagrange-Hamilton system, Lagrange equations and their applications are investigated for non-conservative nonlinear elastic dynamics, incompressible viscous fluid dynamics, viscoelastic dynamics, thermal elastic dynamics, rigid-elastic coupling dynamics and rigid-liquid coupling dynamics. The establishment of finite element calculation model by using Lagrange equation was analyzed. Finally, the prospects of applying the Lagrange equation to problems of the continuum dynamics are discussed.

Recent progress on finite element model updating: From linearity to nonlinearity

Hao ZHANG, Dongsheng LI, Hongnan LI

2019, 49(1) doi: 10.6052/1000-0992-18-004

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Finite element (FE) analysis is extensively applied in practical engineering. However, FE model usually differs much from actual engineering structures due to modeling errors caused by meshing scales, boundary conditions, and material properties. Therefore an FE model has to be modified or updated by test data to make the FE model as close as possible to the real structure so that the updated model can be convincingly used for structural simulation, dynamic analysis, health monitoring or other engineering applications. Over the years, although FE model updating has been applied to many engineering applications successfully, the development of modern technology has put forward higher requirements on updated models, not only higher accuracy level but also higher confidence level. However, current methods are mostly confined to the linear structure hypothesis, which disagrees with the actual situations in many cases. Based on the background, this paper comprehensively reviews traditional FE model updating techniques with civil engineering structure as an example. Furthermore, influential model updating methods and their progress are surveyed and critically commented including recent progress of FE model validation. Especially, the evolution from linear to nonlinear FE model updating technology and essential research findings are summarized, then attractive perspectives are forecasted, and several promising issues are sketched out.

Review of peridynamics for multi-physics coupling modeling

GU Xin, ZHANG Qing, MADENCI Erdogan

2019, 49(1) doi: 10.6052/1000-0992-18-007

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Generally, peridynamics is a theory focusing on the evolution of a physical system, which is based on the assumption that each material point interacts with the other material points within a certain domain through non-contact or nonlocal interactions. It provides a unified mathematical framework for analyzing problems involving the evolving discontinuities and nonlocality. After a brief introduction of the peridynamic solid models and the urgent requirements on multi-physics models and corresponding commercial software, which have the capability of dealing with the evolving discontinuities, we made a systematic review on peridynamic nonlocal diffusion and peridynamic multi-physics coupled modeling. It can be found that the existing multi-physics coupled modeling studies mostly concentrated on the problems in the electronic components, electronic packaging and geotechnical engineering fields, including the un-coupled, partial coupled and fully coupled models about thermo-mechanics, hygro-thermo-mechanics, thermo-oxidative, thermo-mechanics-oxidative, mechanics-electronics, thermo-electronics, thermo-mechanics-electronics, fluid-solid interaction model for porous medium. Finally, several potential problems in the theoretical model, numerical algorithm and engineering application of peridynamic diffusion modeling and multi-physics coupled modeling are suggested.

Mechanics 2006--2015: Situation and prospect

BAI Kunchao, ZHAN Shige, ZHANG Panfeng, TAN Zongying, MENG Qingguo

2019, 49(1) doi: 10.6052/1000-0992-18-016

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Based on strategy report for 2016--2020 of the department of mathematics and physics of NSFC and the series of research reports on the development of the disciplines-mechanics 2016--2015: China and World, the authors introduce funding of the National Natural Science Foundation in the discipline of mechanics in brief. The article analyzes the development of the discipline of mechanics through studying the number of papers, the number of citations and top 1% papers, the citation rate of papers, the frequency of citations, the impact of citations on papers, the output rate of top 1% high citation papers, international cooperation and autonomy research from 2006 to 2015, and puts forward opinions and advices on the future development of mechanics in last.

2019 Vol. 49, No. 1

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