力学进展

Sloshing

O. M. FALTINSEN

2017, 47(1): 1-24. doi: 10.6052/1000-0992-16-017

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Resonant liquid motions in various engineering fields are exemplified. Sloshing in ship tanks associated with violent flow are discussed in detail. A nonlinear analytically based multimodal method that facilitates investigations of wave regimes, multi-branched solutions and physical stability is described. The importance of 3D flow with, for instance, swirling and chaos in nearly square-base tanks as well as in vertical cylindrical and spherical tanks is emphasized. Sloshing-induced slamming involves a broad variety of inflow conditions that depend on the liquid depth-to-tank length ratio. The many physical phenomena involving fluid mechanic and thermodynamic parameters as well as hydroelasticity effecting slamming load effects and associated scaling from model to full scale for prismatic liquefied natural gas (LNG) tanks are discussed.

Review on fluid-solid coupling and dynamic response of vortex-induced vibration of slender ocean cylinders

CHEN W M, FU Yiqin, GUO Shuangxi, JIANG Chunhui

2017, 47(1): 25-91. doi: 10.6052/1000-0992-16-005

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The recent development on the mechanism and response analysis of vortex-induced vibration (VIV) of flexible cylinders, particularly the slendr risers in deep water, are presented. The main characters of VIV, such as self-excited, self-limited and span coherence and fluid-solid coupling, along with principle influence factors are presented, and different prediction approaches (incluing empirical and numerical methods) and experiments are reviewed. Then we are trying to give our perspectives on some challenging issues, e.g., multi-mode and wide-band VIV, dynamic interaction between top-end motion and submarine riser, VIV suppression, CF and IL motion and large scale experiment at high Reynolds number, of slender riser's VIV so that the future researches on VIV would be focued on those areas.

Review on underwater sound absorption materials and mechanisms

WANG Yuren, MIAO Xuhong, JIANG Heng, CHEN Meng, LIU Yu, XU Wenshuai, MENG Dan

2017, 47(1): 92-121. doi: 10.6052/1000-0992-16-008

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As China accelerates the implementation of the marine power strategy, the demand for advanced underwater sound-absorbing materials has become increasingly urgent. Unlike air absorption, the high hydrostatic pressure and complex marine environment impose more stringent requirements regarding underwater sound-absorbing materials. The essence of the sound absorption problem is how to efficiently transform elastic energy into heat or other forms of energy. This paper reviews the traditional underwater sound absorbing materials based on both the intramolecular friction and the energy dissipation mechanisms. The main problem of traditional underwater sound-absorbing material is attributable to its poor sound absorption performance under low frequency and high hydrostatic pressure. On the one hand, this is because the underwater sound-absorbing material is of limited thickness. Besides, due to the limitation of the mass density law, it cannot effectively absorb the low-frequency sound waves from the water. On the other hand, elastic material, such as polymer, becomes "hard" under high hydrostatic pressure, thus the conversion efficiency of acoustic elastic energy is greatly reduced. With the development of local resonance theory and the concept of metamaterials, a series of new underwater sound absorbing materials have been produced, which provide new ways to solve the problems encountered in developing underwater sound absorbing materials. The local resonance theory states that a small-scale structure can control the spread of long sound waves. Therefore, it can solve the problem of sound absorption at low-frequencies. This paper focuses on the theory of local resonance, the development of new sonar wood and phonon glass, and other novel underwater sound absorbing materials. Based on the local resonance theory, the phonon glass material can improve the compression performance by introducing the porous metal skeleton structure, and solve the problem of poor sound absorption performance under high hydrostatic pressure. At the end of this paper, the future development of underwater sound-absorbing materials is explored.

Creep crack-tip constraint effect in high temperature structures

WANG Guozhen, XUAN Fuzhen, TU Shandong

2017, 47(1): 122-149. doi: 10.6052/1000-0992-16-019

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Accurate prediction and assessment of creep crack growth life are key problems for structural integrity assessment, life design, and service maintenance of high temperature components. The life assessment method based on a single-parameter C^* in creep fracture mechanics cannot effectively incorporate crack-tip constraint effect, thus the assessment result is either over-conservative or non-conservative. At present, theoretical framework and technical methodology for creep life assessment of high temperature structures have not been established, and there is yet no high temperature structure integrity assessment codes incorporating the creep constraint effect. This paper reviews our recent research work on the constraint effect in high temperature creep fracture. It includes:effect and mechanism of the crack-tip constraint on creep crack growth behavior of materials; the creep crack-tip field, and definition and influencing factors of a constraint parameter R; proposition of a load-independent creep constraint parameter R^* and its applications; the creep constraint parameter R^* solutions and creep life assessments incorporating the creep constraint effect for surface cracks in pressurized pipes; correlation of the creep crack-tip constraint between test specimens and axially cracked pipelines; study on a unified characterization parameter A_c of in-plane and out-of-plane creep constraints based on crack-tip equivalent creep strain; establishment of constraint-dependent creep crack growth rates of materials; numerical prediction of creep crack growth rate and its constraint effect in a wide range of C^*; effect and mechanism of the material constraint on creep crack growth behavior in welded joints. The research work may lay foundation of theory and technology for establishing the life assessment methodology of creep crack growth incorporating the crack-tip constraint effect for high temperature structures. We also present prospects for future explorations.

Cell mapping methods-beyond global analysis of nonlinear dynamic systems

Jian-Qiao SUN, Fu-Rui XIONG

2017, 47(1): 150-177. doi: 10.6052/1000-0992-16-027

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The cell mapping methods created by Hsu in 1980s have been popular choices for the researchers in nonlinear science communities. There have been new applications and new algorithm developments of the cell mapping methods. This paper presents a discussion of the literature of some control applications and recent algorithm developments of the cell mapping methods. In particular, we present studies of multi-objective optimization problems with the cell mapping methods, multi-objective optimal control designs, and zeros finding of nonlinear algebraic equations. The problems solved with the cell mapping methods are now in moderately high dimensional space with the help of parallel computing.

Flow focusing and jet instability

SI Ting, LI Guangbin, YIN Xiezhen

2017, 47(1): 178-226. doi: 10.6052/1000-0992-16-026

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Flow focusing is an effective method to form thin jets. It can be characterized by the formation of a steady cone-jet configuration in the core of a focusing high-speed fluid stream, as the focused fluid is continuously supplied through a capillary needle. The jet issued from the vertex of the cone passes through an orifice, and eventually breaks up into monodisperse droplets due to flow instability. First proposed in 1998, the flow focusing principle has been adopted to develop a series of capillary flow techniques such as single flow focusing, electro-flow focusing, co-flow focusing and microfluidic flow focusing. These techniques are steady, controllable and gentle in producing monodisperse droplets, particles and capsules down to micrometer scale and below. Therefore they have great significance in science, technology and engineering applications. In flow focusing, the formation of the stable cone is the prerequisite condition to form the stable jet; the process parameters influence the perturbations deposited on the jet interface; and the growth of perturbations results in the breakup of the jet. This is a complex problem in fluid mechanics due to its multi-scale, multi-interface and multi-coupling characteristics. Jet instability analysis is the most useful tool for exploring the mechanisms of jet breakup. In this paper, we review the progress of flow focusing with different geometrical structures during recent two decades, and summarize the key mechanics problems of flow focusing including process control, flow modes, scaling laws and instability analyses. The methods and achievements in the study of jet instability are also briefly described. Finally, some future research topics and opportunities for applications are provided.

Nanofluidic energy absorption system: A review

CAO Guoxing

2017, 47(1): 227-262. doi: 10.6052/1000-0992-16-029

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The energy absorption system designed on the basis of nanofluidic behavior (also called nanofluidic energy absorption system, NEAS) will have a higher energy ab-sorption density than the conventional energy absorption materials, and can be repeatedly used. Thus it shows great advantages over the conventional energy absorption materials, especially for applications with a limited volume. In this paper, we reviewed the state-of-the-art of the energy absorption behavior of NEAS from both experimental investigations and numerical studies:the experimental work mainly includes quasi-static compression and dynamic compression tests; the computational simulations are mainly based on molecular dynamics simulations developed from the empirical potentials. Using quasi-static compres-sion, we can measure the load-displacement relationship of NEAS, determine the critical infiltration pressure, understand the loading-unloading-reloading behavior of NEAS (closely related to the repeated energy absorption performance of NEAS), and estimate the energy absorption density from the area below the load-displacement curve. By use of the dynamic compression tests, the NEAS performance of the protection against the impact load can be measured, which can be represented by decreasing the impact pulse magnitude and expand-ing the pulse width. The computational studies can clearly show the micro-level response of NEAS to the external load, based on which we can fully understand the energy absorption mechanism and the main controlling parameters of energy absorption density. The present study can help researchers understand the latest research progress of NEAS, and provide an important guideline for the design and optimization of NEAS.

The mesoscopic structures of dense granular materials

SUN Q C., Xiaoxing LIU, Guohua ZHANG, Chuanqi LIU, Feng JIN

2017, 47(1): 263-308. doi: 10.6052/1000-0992-16-021

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A dense granular material (GM) is composed of dense random packing of solid particles and posses disorder structures which has been a long-standing mystery. On the one hand, GMs are amorphous materials with no long-range structural order; on the other hand, both topological and mechanical short range order are pronounced in these materials, due to their high granular packing density. The unique internal structure of GMs underlies their unique mechanical ad physical properties, which render GMs are useful for various applications in more and more engineering and industries in recent years, such as rock-filled dams, granular type debris flows, and the pebble-bed High Temperature Reactor. However, fundamental knowledge on the structural aspect of GMs remains seriously lacking. For example, how the granular mesoscopic structures are formed on the short-to-medium range, how the structure differs in different GMs and changes with granular composition, external loadings, and processing history and methods, and more importantly, how the structure influences the properties of GMS, are still well answered questions. Granular materials are currently the most actively studied materials. In this paper, we review the tremendous efforts over the past decades devoted to unraveling the particle-level structure of GMs and the structural origin of their unique mechanical behaviors, including the simplified inter-particle contact models and the structure measurement techniques and analysis methods. The failure of granular materials play a vital role in transition from solid-to fluid-like states. The related jamming transition, the concepts of"soft spots"and the micro-displacement measurement techniques are then analyzed. Outstanding questions in this research area will be outlined. Suggestions are proposed as well. The studies on the fundamental problems of granular materials should employ the cutting edge studies of the condensed physics and mathematics to establish new concepts. Because of extensive uses in engineering and industries, the fundamental studies are suggested to closely connect with engineering and industries by focusing on the core technologies, which would greatly prompt the development of this research area.

Advance from biomechanics to mechanobiology

JIANG Z l

2017, 47(1): 309-332. doi: 10.6052/1000-0992-16-023

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In the present paper, we introduce the development of biomechanics and the contribution of Dr. Y. C. Fung, the concept and development of mechanobiology, the development of biomechanics, as well as the advance of mechanobiology in China. We reflect the current status and progress from biomechanics to mechanobiology, and further prospect the vision of biomechanics in China.

Mechanics problems in application of acoustic black hole structures

JI Hongli, HUANG Wei, QIU Jinhao, CHENG Li

2017, 47(1): 333-384. doi: 10.6052/1000-0992-16-033

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Acoustic black hole (ABH) efiect utilizes the gradient variance of the structural conflguration or material properties to diminish wave velocity in the structure. The wave velocity decreases to zero in an ideal scenario, resulting in zero reflection. The mainstream method to realize ABH efiect is to tailor the structure thickness properly, such that energy is captured in a certain area. Great advantages and potential in applications for flexural wave manipulation in thin-walled structure result from its high e-ciency, broadband characteristics and flexible implementation. We introduce basic principles of ABH efiect, recent progress of related mechanical problems, and problems to be further explored. We describe the modeling and analysis method of ABH structure, the method and progress of experimental studies, manipulation and propagation of waves in ABH structures, and related issues in engineering applications of ABH structures.

Sono-elasticity of ships and the related applications

ZOU Mingsong, WU Yousheng

2017, 47(1): 385-428. doi: 10.6052/1000-0992-16-031

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Dynamics of coupled fluid-structure interaction of ships has great demand for applications, and vast vistas in improving motion behavior and structural safety, controlling vibration and noise, and enhancing stealth capability of ships. In this paper, we summarize the status-of-the-art of theoretical and experimental developments of ship hydroelasticity and ship sono-elasticity, as well as applied techniques. We briefly describe the results obtained by the authors' research group in the three-dimensional sono-elasticity theory based on a three-dimensional hydroelasticity theory (Wu 1984), the improvements of computational techniques, and the extensions in engineering applications. Some future directions are also discussed.

Flight dynamics in the gravitational fields of irregular asteroids

LI Junfeng, ZENG Xiangyuan

2017, 47(1): 429-451. doi: 10.6052/1000-0992-16-042

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Asteroid exploration is one of the main topics of deep space exploration, and has great scientific significance. Due to the irregular gravitational field of most asteroids, dynamical behaviors of spacecraft close to them are very complicated. Affected by the central gravity, the perturbing forces from the fast spin of the irregular shapes of asteroids, the solar radiation pressure force, etc., the spacecraft easily collide with the asteroids or escape from them. In this article, an overview of the status of asteroid research and the irregular gravitational field modeling methods is given. Particularly, this article focuses on the dynamic characteristics of irregular gravitational fields, including equilibrium points, local manifolds, natural periodic orbits and body-fixed hovering flights, and tries to propose new research directions.

Applications and prospects of magnetohydrodynamics in aeronautical engineering

LI Yiwen, ZHANG Bailing, LI Yinghong, XIAO Lianghua, WANG Yutian, HE Guoqiang

2017, 47(1): 452-502. doi: 10.6052/1000-0992-16-036

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This article reviews the applications of magnetohydrodynamics in aeronauti-cal engineering, including magnetohydrodynamic (MHD) combined ramjet, MHD combined turbine engine, post combustion chamber MHD power generation, surface MHD power gen- eration, MHD acceleration wind tunnel, MHD thrust-vectoring, large-size MHD flow control, boundary layer separation flow control, boundary layer transition control, and air vehicle head heat flow control. In addition, this article discusses the key scientific and techni-cal problems in MHD applications, and analyzes the conductive fluid generation, MHD experimental equipment and experimental technology, multi-field coupling mechanism and numerical simulation methods. At last, this article reviews and envision the applications of MHD in aeronautical engineering.

Nonlinear Lamb waves in plate/shell structures

LIU Yaolu, HU Ning, DENG Mingxi, ZHAO Youxuan, LI Weibin

2017, 47(1): 503-533. doi: 10.6052/1000-0992-16-032

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In view of the fact that conventional ultrasonic detection technology is not effective for the detection of distributed fne damage and contact-type structural damage in materials, nonlinear ultrasound technology has been attracting more and more attention in recent years. Ultrasonic waves propagate in the form of Lamb wave modes in the structure of plates and shells. However, due to the dispersion and multimode characteristics of Lamb waves, the progress of theoretical and experimental research on nonlinear Lamb waves is slow. Based on the classical nonlinear theory, this paper summarizes the theoretical and experimental research progress of nonlinear Lamb waves induced by the inherent nonlinear-ity of material, and summarizes the application of the second harmonics of Lamb waves in damage evaluation of material. The current status of the research on nonlinear Lamb waves induced by contact-type structural damage is discussed based on contact acoustic nonlin-earity. At the end, this paper envisions the future research topics and trends in nonlinear Lamb waves.

Biomechanics of stem cells

Lü Dongyuan, ZHOU Lüwen, LONG Mian

2017, 47(1): 534-585. doi: 10.6052/1000-0992-16-041

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As an important branch of biomechanics, stem cell biomechanics has made great progress in mechano-biological, mechano-chemical coupling, and other related felds in recent years. It has become one of the most active felds in biomechanics and biomedical engineering, and made signifcant impacts on the areas of stem cell biology, tissue repair, regenerative medicine, and so on. Stem cells have unique mechanical properties, which can sense, transmit, transduce and respond to changes in physiological and mechanical microen-vironment, thus regulating the function of stem cell growth and differentiation, showing a typical mechano-biological coupling characteristics. This paper reviews the mechanical properties of stem cells and cell mechanics models, the effects of in vivo mechanical mi-croenvironment on stem cell growth and differentiation, and the responses of stem cells to external mechanical stimuli.

2017 Vol. 47, No. 1

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