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Progress in contact mechanics of a type of functional gradient materials

Peijian Chen, Shaohua Chen

2014, 44(1) doi: 10.6052/1000-0992-13-097

Abstract(2122)

PDF(1212)

Abstract:
In regard to a type of materials with gradient varying Young's modulus in the depth direction, considering the effects of interfacial friction, fretting and adhesion, the influences of finite scale of materials, the varying gradient law, thickness of gradient coating, thermo-friction of interface and the shape of punch on the surface contact features are summarized. The performance of resistance to wear of the gradient material surface is mainly analyzed according to the interfacial contact stresses in different contact models. Unsolved problems and prospects of future study on contact mechanics of functional gradient materials are suggested finally.

Recent progress and challenges in fundamental combustion research

Yiguang JU

2014, 44(1) doi: 10.6052/1000-0992-14-011

Abstract(3599)

PDF(3129)

Abstract:
More than 80% of world energy is converted by combustion. Development of efficient next generation advanced engines by using alternative fuels and operating at extreme conditions is one of the most important solutions to increase energy sustainability. To realize the advanced engine design, the challenges in combustion research are therefore to advance fundamental understanding of combustion chemistry and dynamics from molecule scales to engine scales and to develop quantitatively predictive tools and innovative combustion technologies. This review will present the recent progresses and technical challenges in fundamental combustion research in seven areas including advanced engine concepts using low temperature fuel chemistry, new combustion phenomena in extreme conditions, alternative and surrogate fuels, multi-scale modeling, high pressure combustion kinetics, experimental methods and advanced combustion diagnostics Firstly, new engine concepts such as the Homogeneous Charge Compression Ignition (HCCI), Reactivity Controlled Compression Ignition (RCCI), and pressure gain combustion will be introduced. The impact of low temperature combustion chemistry of fuels on combustion in advanced engines will be demonstrated. This is followed by the discussions of the needs of fundamental combustion research for new engine technologies. Secondly, combustion phenomena and flame regimes involving new combustion concepts such as fuel and thermal stratifications, plasma assisted combustion, and cool flames at extreme conditions will be analyzed. Thirdly, alternative fuels and methodologies to formulate surrogate fuel mixtures to model the target combustion properties of real fuels will be presented. A new concept of radical index and transport weighted enthalpy will be introduced to rank the fuel reactivity and to assess the impact of molecular structure on combustion properties The success and limitations of the current surrogate fuel models will be discussed by using jet fuels and biodiesels as examples. Fourthly, the difficulty of modeling large kinetic mechanism of real fuel will be discussed The multi-time scale (MTS) method and the correlated dynamic adaptive chemistry (CO-DAC) method for kinetic model reduction and computationally efficient modeling will be compared and analyzed. Fifthly, the progress and challenges of high pressure combustion kinetics for hydrogen and larger hydrocarbons will be discussed. The important pressuredependent reaction pathways and key intermediate species at high pressure will be analyzed. Fundamental experimental methods for combustion and their uncertainties in acquiring combustion properties for the validation of kinetic mechanism will be discussed. Finally, recent progress in diagnostics of HO₂, H₂O₂, RO₂, ketohydroperoxide, and other key intermediate species for high pressure kinetic mechanism development will be summarized. Conclusions and opportunities of future combustion research will be made.

Natural convection in a differentially heated cavity

Feng XU, Huimin CUI

2014, 44(1) doi: 10.6052/1000-0992-14-003

Abstract(2436)

PDF(2635)

Abstract:
The study of natural convection in a differentially heated cavity is of practical significance in nature and industry. It is of scientific value to review the studies of natural convection flows, their flow properties, dynamical mechanisms, dimensional controlling parameter dependencies and heat transfer driven by the horizontal temperature gradient in the cavity. As shown by previous studies, the development of natural convection suddenly enforced by the horizontal temperature gradient between the sidewalls of the cavity includes an initial stage, a transitional stage and a steady or a quasi-steady stage. The transient flows in the different stages are determined by the Rayleigh number, the Prandtl number and the aspect ratio. The flow in the steady or quasi-steady stage could be a steady laminar, a periodic or a turbulent flow. In addition, the studies of instability and turbulence of natural convection in the cavity are reviewed, and the prospects for the study of natural convection in the cavity are presented.

Research advances in thermo-electro-chemo-mechanical coupling problem for intelligent soft materials

Qingsheng Yang, Wei Wei, Lianhua Ma

2014, 44(1) doi: 10.6052/1000-0992-13-091

Abstract(2722)

PDF(2499)

Abstract:
This paper presents an overview of research on multi-field coupled mechanics for typical intelligent soft materials, including polymer gels, hydrogels biological soft tissues and so on. Attention is paid to the foundamental theory and research methods of thermo-electro-chemo-mechanical coupling behavior for such materials. The typical progresses on this issue in research groups over the world are reviewed. Based on phenomenological thermodynamics theory and Hamilton principle, a general theory framework on thermo-electro-chemo-mechanical coupling problem is established. The finite element formulation and one-dimesional analytical solution of the chemo-mechanical coupled systems are obtained. Several numerical examples are used to illustrate the multi-field coulped behavior of hydrogels and articular cartilages. Finally, the research topics and trends in future on the multi-field coupling for intelligent soft materials are discussed.

Advances in the control of wakes behind an in-line oscillating cylinder

Chuanping Shao, Yejun Chen, Sai Wang, Guangsu Qin

2014, 44(1) doi: 10.6052/1000-0992-14-041

Abstract(1856)

PDF(1222)

Abstract:
The methods of base blowing, splitter-plate and small strip-element are used to suppress vortex shedding from a circular cylinder oscillating in line with an on-coming uniform stream. The non-lock-on mode and three lock-on modes of vortex shedding are found in the test ranges of Reynolds number and cylinder oscillation frequency. Wind tunnel experiment results show that, the base blowing is effective for all the modes of vortex suppression, the strip element is effective for the non-lock-on and two lock-on modes, and splitter plate for only the non-lock-on and one lock-on modes. The effective zones for every method are found out at different flow and oscillation conditions, the reductions of mean drag and fluctuating lift are investigated, and the control mechanism is discussed.

Thermal properties and characterization techniques of graphene

Shulin Bai, Yunhong Zhao

2014, 44(1) doi: 10.6052/1000-0992-14-030

Abstract(2964)

PDF(1340)

Abstract:
Graphene has attracted the attention of scientific world immediately since its discovery in 2004, and raises a research wave of carbon allotrope after the finding of carbon nanotubes. A series of research works were carried out from graphene fabrication and characterization, even to possible application. From the appearance of graphene, main works were concentrated on its electric properties, especially on the supercapacitor. Comparatively, the study on its thermal properties is seldom. However, due to its extremely high thermal conductivity and negative coefficient of thermal expansion, as well as value of engineering application, the research work on its thermal properties is becoming one of hot points. In this paper, an overall review is completed on the achievements in the world about thermal properties of graphene such as thermal conductivity and coefficient of thermal expansion. It concerns single layer, multilayer graphene and graphene foam, and presents the results obtained by experiments, theories and numerical simulations. Based on the review, it finally
reveals the existing problems and proposes the possible solutions for future development.

Experimental study on the interfacial instability induced by shock waves

Xisheng LUO, Zhigang ZHAI, Ting SI, Jiming YANG

2014, 44(1) doi: 10.6052/1000-0992-14-028

Abstract(2052)

PDF(2254)

Abstract:
Interfacial instability, especially the Richtmyer-Meshkov (RM) instability, is
a significant topic in fluid mechanics because of its academic implication and engineering
applications. Much attention has been paid to RM instability since it was proposed. Great
progresses have been made through experimental, numerical and theoretical investigations.
Currently, it is an important tool for the study of RM instability to perform the experiment
of a shock wave interacting with a fluid interface in the shock tube. The generation of a
shock wave, the formation of an initial interface and the diagnostic of the flow field are the
three elements that must be considered in the experimental study of RM instability. This
review article surveys the advances in experimental investigations of RM instability, and
proposes the following issues for future study: (1) evolution of the RM instability induced
by cylindrical converging shock waves; (2) developments of the polygonal interface and the
initial perturbation with large amplitudes accelerated by shock waves; (3) the effect of the
three space dimensions on the RM instability; and (4) the formation and mixing mechanism
of the compressible turbulence.

Mapping Earth's gravity in space: Review and future perspective

Ziren LUO, Min ZHONG, Xing BIAN, Peng DONG, Yuhui DONG, Wei GAO, Hongyin LI, Yuqiong LI, Heshan LIU, Jiangjun RAN, Mingxue SHAO, Wenlin TANG, Peng XU, Ran YANG, Gang JIN

2014, 44(1) doi: 10.6052/1000-0992-14-047

Abstract(2833)

PDF(906)

Abstract:
The distribution of earth’s gravity field not only changes along with the altitude, latitude, crustal composition and mantle depth, but also varies together with the continental drift, glacier evolution, ocean current, underground water changing and phenomena of ice and snow. Therefore, the scientific data of earth’s gravity field is essential to many research fields, such as the geological hazard monitoring, geodetic survey, glaciology, hydrologic circle, solid earth physics and national defense. The measurement, recovery and application of gravity of earth were greatly promoted by the development of gravity satellite missions, for example the GRACE (Gravity Recovery And Climate Experiment) mission. In order to improve the temporal and spatial resolution of satellite gravity data, China, USA and European countries were considering launching upgraded gravity satellite missions, namely the GRACE-follow-on mission. The basic idea is to employ the laser interferometer
measurement system to replace the GRACE’s microwave ranging system. In addition, the drag-free technics is introduced to eliminate the disturbance of non-inertial
forces posed upon laser measurement system. A brief history of the development of gravity satellite missions and the earth gravity recovery techniques were reviewed here. The measurement methodology, key technologies and expected results of next generation GRACE mission were also slightly touched upon.

Mechanical behaviors and deformation mechanisms of novel nano-structured metals

ShaoxingQu, Haofei Zhou

2014, 44(1) doi: 10.6052/1000-0992-14-046

Abstract(2563)

PDF(2174)

Abstract:
Nano-structured metals and their alloys possess superior mechanical properties.
The defects inside or on the surfaces of the nano-structured metals, including grain
boundaries, dislocations, twin boundaries, voids, cracks, the second phases, etc., can influence
the materials strength and toughness significantly through their nucleation, evolution
and interactions. This review article surveys the advances in microstructure characterization
and mechanical testing, as well as computations and simulations on strengthening and
toughening mechanisms of several novel nano-structured metals. It is also proposed that the
comprehensive investigation is necessary on nano-structured metals to obtain the specific
mechanical behaviors and primary deformation mechanisms at atomic scales.

Review of aerodynamics/kinetics/flight-control coupling methods in virtual flight simulations

Laiping ZHANG, Rong MA, Xinhua CHANG, Zhong ZHAO, Xin HE

2014, 44(1) doi: 10.6052/1000-0992-14-027

Abstract(1895)

PDF(1084)

Abstract:
With the rapid development of computer science and computational fluid dynamics (CFD), the fully unsteady simulations of complex geometries, coupled with the
solution of flight dynamics equation and flight control rules, have become possible. The CFD-based virtual flight simulation (VFS) would be helpful for engineers and designers to analyze and evaluate the nonlinear, flight dynamic behavior and the stability and control performance of the aircraft both early in the design phase and throughout sustainment. In this paper, we review the progresses of the aerodynamics/kinetics/flight-control coupling methods in VFS (Virtual Flight Simulation). The key scientific and technical issues in VFS are discussed, with an emphasis on the coupling strategies of aerodynamics/kinetics/flightcontrol.
The authors’ work in this field is introduced, together with some preliminary applications. Finally, we discuss several grand challenges in VFS, as well as future research trends. We believe that along with the presence of exascale computing, the CFD-based VFS will lead to a revolutionary change on the design of new generation flight vehicles in the near future.

Regulation of the chemomechanical behaviors of self-oscillating gels and the related application

Pengfei WANG, Xinghong ZHAO, Min LIN, Tianjian LU, Feng XU

2014, 44(1) doi: 10.6052/1000-0992-14-032

Abstract(1761)

PDF(1826)

Abstract:
Self-oscillating gels are a novel branch of functional soft materials that exhibit periodic deformation driven by certain oscillating chemical reaction. They are capable of generating rhythmic swelling-shrinking behaviors without any external stimuli and continuously converting chemical energy into mechanical energy. Therefore, self-oscillating gels have great potential application in the field of engineering and biomedicine. Chemomechanically coupling behaviors of self-oscillating gels involve a series of complicated nonlinear processes and are not only significantly affected by mechanical factors (i.e., mechanical boundary conditions, external force) and the chemical factors (i.e., concentration of reactants, type of catalyst), but also controlled by other physical factors including geometric shape of gels, light intensity, temperature, etc. So far, a number of groundbreaking researches on the application of self-oscillating gels have been well investigated in the aspects of signal delivery system, self-assembly system, mass transportation, micro actuators and novel sensors. Based on the broad investigation of related literatures and years of our researches, this paper systematically reviewed the regulation of the chemomechanical behaviors of self-oscillating gels and their latest application, which may contribute to the further study of self-oscillating gels.

Isolation of circulating tumor cells under hydrodynamic loading using microfluidic technology

Cong ZHAO, Yi-Kuen LEE, Rui XU, Chun LIANG, Dayu LIU, Wei MA, Wibool PIYAWATTANAMETHA, Yitshak ZOHAR

2014, 44(1)

Abstract(1721)

PDF(1456)

Abstract:

Cancer is a leading cause of mortality worldwide causing human deaths. Circulating tumor cells (CTCs) are cells that have detached from a primary tumorand circulate in the bloodstream; they may constitute seeds for subsequent growth of additional tumors (metastasis) in different tissues. The detection of CTCs may have important prognostic and therapeutic implications but, because their number is very small, these cells are not easily detected. Circulating tumor cells are found in the order of 10–100 CTCs per mL of whole blood in patients with metastatic disease. Isolation of tumor cells circulating in the blood stream, by immobilizing them on surfaces functionalized with bio-active coating within microfluidic devices, presents an interdisciplinary challenge requiring expertise in different research areas: cell biology, surface chemistry, fluid mechanics and microsystem technology. We first review the fundamental of cell biology of CTCs and summarize the key microfluidic techniques for isolation of CTCs via cell-ligand interactions, magnetic interactions, filtration; detection and enumeration of CTCs; in vivo CTCs imaging.

2014 Vol. 44, No. 1

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