Improvement and application of wall function boundary condition for high-speed compressible flows

In order to develop a wall function boundary condition for high-speed flows so as to reduce the grid-dependence of the simula- tion for the skin friction and heat flux, a research was performed to improve the compressible wall function boundary condition proposed by Nichols. Values of parameters in the velocity law-of-the-wall were revised according to numerical experiments and the expression of temperature law-of-the-wall was modified based on theoretical analysis and numerical simulation. Be- sides, the formula of the heat conduction term in near-wall region was derived so that the coupling between the wall function boundary condition and CFD code was realized more accurately. Whereafter, the application study of the modified wall func- tion was carried out. The numerical case of supersonic turbulent boundary layer on a flat plate illustrated that the modified wall function produces reasonable results of skin friction and heat flux, and profiles of velocity, temperature and turbulent eddy viscosity for coarse grids with the initial wall spacing of y＋〈400, and that the modifications to the original wall function can obviously improve the simulation precision. As for the application of separation flows, it was found from the numerical cases of supersonic cavity flow and hypersonic axisymmetric compression comer that the compressible velocity law-of-the-wall originally established based on the fully-developed attached turbulent boundary layer approximately holds in the near-wall re- gion inside the separation flows, which ensures that reliable skin friction and heat flux can be given by the wall function inside the separation flows, while for the region near separation and reattachment points, the wall function gives results with a rela- tively large error, because the velocity law-of-the-wall used in the wall function takes on obvious deviation from the real ve- locity profiles near the separation and reattachment points.

Density Functional Theory Study of MoO_3 Molecule Encapsulated inside Single-walled Carbon Nanotubes

The binding energies, geometric structures and electronic properties of molybde- num trioxide （MOO3） molecule encapsulated inside （8, 0）, （9, 0）, （10, 0） and （14, 0） single-walled carbon nanotubes （SWNTs） have been investigated using density functional theory （DFT） method. Due to curvature effect, the calculated binding energy values are different, the variation of which indicated that the stability of MoO3/SWNT systems increases with increasing the radius of SWNTs. At the same time, owing to the presence of MoO3 molecule, the band gap of MoO3/SWNTs systems decreases. The analysis of density of states （DOS） reveals hybridization between C-2p and Mo-4d and between C-2p and O-2p orbitals near the Fermi level, which results in electron transfer from SWNTs to MoO3 molecule. The present computations suggest that electronic properties of SWNTs can be modified by doping MoO3 molecule.

Thermo-magnetic analysis of thick-walled spherical pressure vessels made of functionally graded materials

This study presents an analytical solution of thermal and mechanical displacements, strains, and stresses for a thick-walled rotating spherical pressure vessel made of functionally graded materials (FGMs). The pressure vessel is subject to axisymmetric mechanical and thermal loadings within a uniform magnetic field. The material properties of the FGM are considered as the power-law distribution along the thickness. Navier’s equation, which is a second-order ordinary differential equation, is derived from the mechanical equilibrium equation with the consideration of the thermal stresses and the Lorentz force resulting from the magnetic field. The distributions of the displacement, strains, and stresses are determined by the exact solution to Navier’s equation. Numerical results clarify the influence of the thermal loading, magnetic field, non-homogeneity constant, internal pressure, and angular velocity on the magneto-thermo-elastic response of the functionally graded spherical vessel. It is observed that these parameters have remarkable effects on the distributions of radial displacement, radial and circumferential strains, and radial and circumferential stresses.

THE ANALYSIS OF THIN WALLED COMPOSITE LAMINATED HELICOPTER ROTOR WITH HIERARCHICAL WARPING FUNCTIONS AND FINITE ELEMENT METHOD

In the present paper, a series of hierarchical warping functions is developed to analyze the static and dynamic problems of thin walled composite laminated helicopter rotors composed of several layers with single closed cell. This method is the development and extension of the traditional constrained warping theory of thin walled metallic beams, which had been proved very successful since 1940s. The warping distribution along the perimeter of each layer is expanded into a series of successively corrective warping functions with the traditional warping function caused by free torsion or free beading as the first term, and is assumed to be piecewise linear along the thickness direction of layers. The governing equations are derived based upon the variational principle of minimum potential energy for static analysis and Rayleigh Quotient for free vibration analysis. Then the hierarchical finite element method. is introduced to form a,. numerical algorithm. Both static and natural vibration problems of sample box beams axe analyzed with the present method to show the main mechanical behavior of the thin walled composite laminated helicopter rotor.

Revisiting the elastic solution for an inner-pressured functionally graded thick-walled tube within a uniform magnetic field

In this paper, the mechanical responses of a thick-walled functionally graded hollow cylinder subject to a uniform magnetic field and inner-pressurized loads are studied. Rather than directly assume the material constants as some specific function forms displayed in pre-studies, we firstly give the volume fractions of different constituents of the functionally graded material(FGM) cylinder and then determine the expressions of the material constants. With the use of the Voigt method, the corresponding analytical solutions of displacements in the radial direction, the strain and stress components, and the perturbation magnetic field vector are derived. In the numerical part, the effects of the volume fraction on the displacement, strain and stress components, and the magnetic perturbation field vector are investigated. Moreover, by some appropriate choices of the material constants, we find that the obtained results in this paper can reduce to some special cases given in the previous studies.

PROBABILITY DISTRIBUTION FUNCTION OF NEAR-WALL TURBULENT VELOCITY FLUCTUATIONS

By large eddy simulation （LES）, turbulent databases of channel flows at different Reynolds numbers were established. Then, the probability distribution functions of the streamwise and wall-normal velocity fluctuations were obtained and compared with the corresponding normal distributions. By hypothesis test, the deviation from the normal distribution was analyzed quantitatively. The skewness and flatness factors were also calculated. And the variations of these two factors in the viscous sublayer, buffer layer and log-law layer were discussed. Still illustrated were the relations between the probability distribution functions and the burst events-sweep of high-speed fluids and ejection of low-speed fluidsIin the viscous sub-layer, buffer layer and loglaw layer. Finally the variations of the probability distribution functions with Reynolds number were examined.

EFFECT OF WALL FUNC TION IN NUMERICAL STUDY ON TURBULENT IMPINGING JET

A low Reynolds number k-ε model is used in the numeri cal study on a circular semi-confined turbulent impinging jet . The result is c ompared with that of the standard k-ε model and a refined k-ε mode l, which re-consi-dered the fluctuating pressure diffusion term in the dissipa tion rate equation (ε-equation) through modeling. It shows that the low Re ynolds number k-ε model and the standard k-ε model yield very poor performance, while the predicting ability of the refined k-ε model is mu ch improved , especially for the turbulent kinetic energy k. So it can be co ncluded that the poor performance of the standard k-ε model is owing to t he incorrect considering the effect of the fluctuating pressure diffusion term r ather than the use of the wall function near the wall just as presumed in the re ference.

Suitability of the Composite Made of Multi Wall Carbon Nanotubes-Polyvinylpyrrolidone for Culturing Invertebrate <i>Helix aspersa</i>Neurons

Carbon nanotubes have been used as scaffolds for tissue engineering. However, the identification of these nanomaterials disperses in biological solutions and their direct interaction with nerve cells is still controversial. The aim of this work is to characterize the topographic and ultra-structural distribution of the composite made of multi wall carbon nanotubes-polyvinylpyrrolidone (MWCNTs-PVP) deposited on the Helix aspersa neurons and over glass coverslip. Scanning Electron Microscopy (SEM) and Confocal Microscopy (CM) studies were done to analyze the properties of such MWCNTs-PVP composite. The cerebral ganglion of Helix aspersa was treated and incubated with MWCNTs-PVP, fixing it in paraformaldehyde at 4% and was observed with SEM and CM. Although the nanotubes were not labeled or stained with fluorescent compounds, the MWCNTs-PVP deposited on glass and on nerve cells, was observed by the confocal microscope in the reflection mode. In SEM studies, it was observed that MWCNTs-PVP was attached to the surface on neurons. Moreover, in CM studies, it was possible to observe that MWCNTs-PVP was attached to the neuronal membrane, crossing the cell membrane and getting into the cytoplasm. These results support the hypothesis that carbon nanotubes interact with the neuronal cell membrane and can be useful for neuronal tissue engineering. In addition, these results open new alternatives for toxicological studies, in order to elucidate the cytotoxicity of MWCNTs-PVP composite in neurons and other excitable cells.

New perspective in statistical modeling of wall-bounded turbulence

Despite dedicated effort for many decades,statistical description of highly technologically important wall turbulence remains a great challenge.Current models are unfortunately incomplete,or empirical,or qualitative.After a review of the existing theories of wall turbulence,we present a new framework,called the structure ensemble dynamics （SED）,which aims at integrating the turbulence dynamics into a quantitative description of the mean flow.The SED theory naturally evolves from a statistical physics understanding of non-equilibrium open systems,such as fluid turbulence, for which mean quantities are intimately coupled with the fluctuation dynamics.Starting from the ensemble-averaged Navier-Stokes（EANS） equations,the theory postulates the existence of a finite number of statistical states yielding a multi-layer picture for wall turbulence.Then,it uses order functions（ratios of terms in the mean momentum as well as energy equations） to characterize the states and transitions between states.Application of the SED analysis to an incompressible channel flow and a compressible turbulent boundary layer shows that the order functions successfully reveal the multi-layer structure for wall-bounded turbulence, which arises as a quantitative extension of the traditional view in terms of sub-layer,buffer layer,log layer and wake. Furthermore,an idea of using a set of hyperbolic functions for modeling transitions between layers is proposed for a quantitative model of order functions across the entire flow domain.We conclude that the SED provides a theoretical framework for expressing the yet-unknown effects of fluctuation structures on the mean quantities,and offers new methods to analyze experimental and simulation data.Combined with asymptotic analysis,it also offers a way to evaluate convergence of simulations.The SED approach successfully describes the dynamics at both momentum and energy levels, in contrast with all prevalent approaches describing the mean velocity profile only.Moreover,the SED theoretical framework is general,independent of the flow system to study, while the actual functional form of the order functions may vary from flow to flow.We assert that as the knowledge of order functions is accumulated and as more flows are analyzed, new principles（such as hierarchy,symmetry,group invariance,etc.） governing the role of turbulent structures in the mean flow properties will be clarified and a viable theory of turbulence might emerge.

Purified oxygenand nitrogen-modified multi-walled carbon nanotubes as metal-free catalysts for selective olefin hydrogenation

Oxygen and nitrogen-functionalized carbon nanotubes （OCNTs and NCNTs） were applied as metal-free catalysts in selective olefin hydro- genation. A series of NCNTs was synthesized by NH3 post-treatment of OCNTs. Temperature-programmed desorption, N2 physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygen- and nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 ℃ led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis.

Experimental Evaluation of Thermal Conductivity and Other Thermophysical Properties of Nanofluids Based on Functionalized (-OH) Mwcnt Nanoparticles Dispersed in Distilled Water

A possible way to increase thermal conductivity of working fluids, while keeping pressure drop at acceptable levels, is through nanofluids. Nanofluids are nano-sized particles dispersed in conventional working fluids. A great number of materials have potential to be used in nanoparticles production and then in nanofluids;one of them is Multi-Walled Carbon Nano Tubes (MWCNT). They have thermal conductivity around 3000 W/mK while other materials used as nanoparticles like CuO have thermal conductivity of 76.5 W/mK. Due to this fact, MWCNT nanoparticles have potential to be used in nanofluids production, aiming to increase heat transfer rate in energy systems. In this context, the main goal of this paper is to evaluate from the synthesis to the experimental measurement of thermal conductivity of nanofluid samples based on functionalized (-OH) MWCNT nanoparticles. They will be analyzed nanoparticles with different functionalization degrees (4% wt, 6% wt, and 9% wt). In addition, it will be quantified other thermophysical properties (dynamic viscosity, specific heat and specific mass) of the synthetized nanofluids. So, the present work can contribute with experimental data that will help researches in the study and development of MWCNT nanofluids. According to the results, the maximum increment obtained in thermal conductivity was 10.65% in relation to the base fluid (water).

腹腔镜腹壁切口疝修复术中腹壁功能重建

腹壁切口疝的治疗已从单纯的修补(repair)、加强(reinforcement)向重建(reconstruction)、重塑(restora⁃tion)和再生(regeneration)进展。腹壁切口疝有肌前、肌后、腹膜前、腹腔内等修补层次,均可通过开放或腹腔镜手术来完成。腹腔镜手术主要包括腹腔内补片修补术(IPOM)和微创非腹腔内补片修补术(MINIM)。无论哪种技术,既要遵循腹壁功能重建的原则,又要结合自身的微创特性,才能充分体现其临床价值。腹腔镜腹壁切口疝术中腹壁功能重建的核心可归纳为恢复腹壁解剖结构(Anatomy),保护腹壁生物力学(Biomechanics),维持腹壁顺应性(Compliance),提供机体整体动态活力(Dynamics)。

深厚覆盖层上土石坝防渗墙损伤开裂精细化分析及防渗功能评价

混凝土防渗墙是覆盖层上土石坝坝基的关键防渗结构,由于防渗墙与覆盖层的刚度和尺度差异巨大,通常的数值分析方法难以保证精度,且现有基于强度的安全评价方法,无法适应防渗墙作为防渗结构而非承载结构的功能评价要求。本文提出了比例边界元-有限元耦合跨尺度离散、塑性损伤模型和内聚力模型分离描述压损伤和受拉开裂、破损后防渗功能目标评价的精细化分析方法,实现了深厚覆盖层上土石坝防渗墙的性态演化评价。研究结果表明:超深覆盖层上悬挂式防渗墙在两岸底部因近似垂直于岸坡的高压应力发生压损伤,类“外伸梁”的面内弯曲变形使靠近防渗墙两岸的顶部和底部区域产生坝轴向高拉应力导致槽段间出现竖向裂缝;在防渗墙两岸的上游侧局部设置辅助防渗措施,可有效降低防渗墙破损后的渗流量。本文方法揭示了混凝土防渗墙的损伤开裂模式,定位了防渗墙薄弱区域,评价了防渗墙损伤开裂对防渗功能的影响,量化防渗措施效果,实现了防渗墙从传统承载能力评价到功能性态评价的跨越,可为深厚覆盖层上土石坝防渗墙的安全评价和设计优化提供理论和技术支持。

Spectroscopic Investigation of Modified Single Wall Carbon Nanotube (SWCNT)

We have investigated the effects of chemical treatment on Single Wall Carbon Nanotube (SWCNT) before and after being modified with HNO3/H2SO4 by Raman, FTIR and UV-Vis-NIR spectroscopy. The results show successful carboxylation of the CNT sidewalls as observed from FTIR and UV-Vis-NIR spectroscopy. This successful functionalization is achieved in 6-8 hrs of refluxing. We also report changes in the first and second order Raman spectra of SWNTs functionalized with oxygenated groups. During the experiment, we observe some important Raman features: Radial breathing mode (RBM), Tangential mode (G-band), and Disordered mode (D-band);which are affected due to the chemical oxidation of carbon nanotubes. We found that the ratio of D- to the G-band intensity (Id/Ig), increase after functionalization and the RBM mode in acid treated SWCNTs is almost disappeared.

Structural,curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube

This paper systematically studies the rolling effects of the （n, n） single-wall carbon nanotubes （SWCNT） with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs.

Mechanical performance and negative pressure instability for venous walls

Mechanical properties, such as the deformation and stress distributions for venous walls under the combined load of transmural pressure and axial stretch, are examined within the framework of nonlinear elasticity with one kind of hyper-elastic strain energy functions. The negative pressure instability problem of the venous wall is explained through energy comparison. First, the deformation equation of the venous wall under the combined loads is obtained with a thin-walled circular cylindrical tube. The deformation curves and the stress distributions for the venous wall are given under the normal transmural pressure, and the regulations are discussed. Then, the deformation curves of the venous wall under the negative transmural pressure or the internal pressure less than the external pressure are given. Finally, the negative pressure instability problem is discussed through energy comparison.

Properties and Structural Studies of Multi-Wall Carbon Nanotubes-Phosphate Ester Hybrids

Long chain phosphate esters bearing at least one or two aryl groups have been synthesized and used for the preparation of stable multi-walled carbon nanotube (MWCNT) hybrids. The non-covalent interaction ester/MWCNT has been investigated by several techniques (SEM, UV-vis, 31P-NMR, RAMAN). The used phosphate ester derivatives demonstrated the ability to produce an excellent dispersion of MWCNT in CHCl3. The obtained dispersions showed a great stability from one to at least three weeks in the range of concentration considered. Thermal analysis showed an increase in the decomposition temperature for the hybrids with respect to pristine MWCNT.

Analysis of dynamic stress intensity factors of thick-walled cylinder under internal impulsive pressure

Dynamic stress intensity factors are evaluated for thick-walled cylinder with a radial edge crack under internal impulsive pressure. Firstly, the equation for stress intensity factors under static uniform pressure is used as the reference case, and then the weight function for a thick-walled cylinder containing a radial edge crack can be worked out. Secondly, the dynamic stresses in uncracked thick-walled cylinders are solved under internal impulsive pressure by using mode shape function method. The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary condi- tions, and the history and distribution of dynamic stresses in thick-walled cylinders are derived in terms of Fourier-Bessel series. Finally, the dynamic stress intensity factor equations for thick-walled cylinder containing a radial edge crack sub- jected to internal impulsive pressure are given by dynamic weight function method. The finite element method is utilized to verify the results of numerical examples, showing the validity and feasibility of the proposed method.

Isolation and characterization of a novel wall-associated kinase gene TaWAK5 in wheat(Triticum aestivum)

Wall-associated kinases(WAKs) play an important role in plant defense and development.Considerable progress has been made in understanding WAK genes in Arabidopsis thaliana.However, much less is known about these genes in common wheat. Here, we isolated a novel wheat WAK gene TaWAK5 from sharp eyespot disease-resistant wheat line CI12633,based on a differentially-expressed sequence identified by microarray analysis. The transcript abundance of TaWAK5 was rapidly increased following inoculation with the pathogen Rhizoctonia cerealis. TaWAK5 in resistant wheat lines was induced to higher levels than in susceptible lines at 7 days post inoculation with R. cerealis. The expression of TaWAK5 was also induced by treatments with exogenous salicylic acid, abscisic acid, and methyl jasmonate. The deduced TaWAK5 protein contained a signal peptide, two epidermal growth factor(EGF)-like repeats, a transmembrane domain, and a serine/threonine protein kinase catalytic domain. Subcellular localization analyses in onion epidermal cells indicated that the TaWAK5 protein was localized to the plasma membrane. Virus-induced gene silencing of TaWAK5 in CI12633 plants showed that the silencing of TaWAK5 did not obviously impair wheat resistance to R. cerealis, suggesting that TaWAK5 may be not the major gene in wheat defense response to R. cerealis, or that it is functionally redundant with other genes. This study paves the way for further research into WAK functions in wheat stress physiology.

建筑幕墙装饰装修工程施工探讨

在当前建筑工程及技术水平高度发展的背景下,大众对各种建筑的功能性、装饰性与实用性的需求有所增高。这一点在建筑幕墙装饰装修工程中体现得十分明显。对此,通过探讨建筑幕墙工程施工中影响工程质量、工程效率的关键因素,总结能够用于建筑幕墙装饰装修工程的关键技术,提高工程建设效果的有效方法。