Abstract: The wear performances of three types of ceramics (ZrO2, Al2O3, Si3N4)/1Cr18Ni9Ti stainless steel rubbing pairs were analyzed under 0% (pure water), 10%, 30%, 50%, 70% and 90% hydrogen peroxide (H2O2) solution. The results showed that, under different concentrations of H2O2 solution, the worn surface roughness of the 1Cr18Ni9Ti stainless steel was bigger than that under pure water when the counterpart was ZrO2 ceramic ball, while the worn surface roughness of the 1Cr18Ni9Ti stainless steel was smaller than that under pure water when the counterpart was Al2O3 ceramic ball. For the ZrO2, Al2O3, Si3N4 ceramics ball, the average worn surface roughness of Al2O3 ceramic ball was the smallest, and the average worn surface roughness of Si3N4 ceramic ball was the biggest. When the concentration of H2O2 solution was 10%, the metal particles from the ZrO2/1Cr18Ni9Ti and Al2O3/1Cr18Ni9Ti stainless steel rubbing pairs had the features with large size and bright surface. The surfaces of the metal particles were oxidized clearly when the concentrations of H2O2 solution were 70% and 90%.
Abstract: For hypersonic compressible turbulence, the correlations with respect to the density fluctuation must not be neglected. A Reynolds averaged K-ε model is proposed in the present paper to include these correlations, together with the Reynolds averaged Navier-Stokes equations to describe the mean flowfield. The K-equation is obtained from Reynolds averaged single-point second moment equations which are deduced from the instantaneous compressible Navier-Stokes equations. Under certain hypotheses and scales estimation of the compressible terms, the K-equation is simplified. The correlation terms of the fluctuation field appearing in the resulting K-equation, together with a conventional form of the ε-equation, are thus correlated with the variables in the average field. The new modeling coefficients of closure terms are optimized by computing the hypersonic turbulent flat-plate measured by Coleman and Stollery [J. Fliud Mech., Vol. 56 (1972), p. 741]. The proposed model is then applied to simulate hypersonic turbulent flows over a wedge compression corner angle of 34 degree. The predicting results compare favorably with the experimental results. Also, comparisons are made with other turbulence models. Additionally, an entropy modification function of Harten-Yee’s TVD scheme is introduced to reduce artificial diffusion near boundary layers and provide the required artificial diffusion to capture the shockwaves simultaneously.
Abstract: Experiment of unsteady pressure measurement on the surface of wing with 75° sweep delta wing has been carried out in a wind tunnel in order to investigate unsteady characteristics of breakdown vortices over delta wing after the leading edge vortices were breakdown. The result of experiment shows that alter of RMS pressure fluctuations and fluid state of leading edge vortices on the top surface of delta wing are correlative. At the angle region with vortex breakdown, RMS of pressure fluctuations are very huge, similarly buffeting strength of delta wing are large. With increasing angle of attack, alter of buffeting strength is in accordance with RMS pressure fluctuations. Analysis of the pressure signal shows the spiral wave of the breakdown vortex flow over the wing is the primary part of whole RMS pressure fluctuations. Delta wing produces buffeting because of the spiral wave.
Abstract: The aerodynamic performances of a high speed train will significant change under the action of the crosswind. Large eddy simulation (LES) was made to solve the flow around a simplified CRH2 high speed train with 250km/h and 350km/h under the influence of a crosswind with 28.4m/s base on the finite volume method and dynamic layering mesh method and three dimensional incompressible Navier-Stokes equations. Wind tunnel experimental method of static train with relative flowing air and dynamic mesh method of moving train were compared. The results of numerical simulation show that the flow field around train is completely different between Wind tunnel experiment and factual running. Many vortices will be produced on the leeside of the train with alternately vehicle bottom and back under the influence of a crosswind. The flow field around train is similar with different vehicle speed.
Abstract: This paper points out the problems in software engineering course teaching, and then proposes that by adjusting the curriculum system and using the "project-driven" model teaching could the problem be solved. Besides, this paper completes the course evaluation system, and introduces the evaluation system. And there have achieved remarkable results in the actual process of teaching.
Abstract: The building-integrated dual-function solar collector has two independent operating modes: passive space heating mode in cold days, and solar water heating mode during hot days such as the summer. The novel system avoids summer overheating in hot climate and water-freezing in cold climate, meanwhile remains low operating cost as a passive solar heating system. In this study, the energy performance of the novel system in passive space heating mode was studied by experiment and numerical simulation. The experimental and numerical results show that the system performed a high ability in utilizing solar energy for building when working in passive space heating mode and the value of the transient operating efficiency generally kept as a constant.
Abstract: It's well recognized that the PKM is one of the essential factors to an individual's development and success in the era of knowledge-oriented economy. Based on the introducing and analysis of some features and functions of both Blog and PKM,this paper argues that Blog not only improve intercommunication but also support and facilitate PKM. Furthermore,some effective approaches to supporting the PKM with Blog are explored,and some problems and suggestions are put forwarded in this paper too.
Abstract: In this paper, the vibration and power flow characteristics of stiffened plate and cylindrical shell structures are investigated by using finite element method. The power flow formulas of basic shell structural elements are given at first. Then a simply supported plate and stiffened plate’s input power flow characteristics and power flow vectors are investigated. The effects of stiffeners in plates are discussed. For a simply supported cylindrical shell, the influence of the structural damping, viscous damper and stiffeners on the cylindrical shell’s input power flow characteristics and propagated power flow characteristics are discussed in detail. The power flow vectors are visualized to reveal the distribution of energy in the shell structures. Some useful conclusions are drown and helpful for the vibration control of plate and shell structures.
Abstract: PC/PLA composite material introduces the degradability of PLA to PC with great performance, but their compatibility and impact resistance are poor. Aiming at this deficiency, ABS is used to modify PC/PLA. This paper established the ternary compound system of PC/PLA/ABS by melt blending and studied the impact of adding ABS and compatibilizer ABS-g-MAH on the composite’s morphology, thermal properties, rheology and mechanical properties. The results showed that: ABS bettered the brittle fracture of PC/PLA and improved the impact strength of composite with the optimum proportion of 30% of PC/PLA mass. In addition, ABS-g-MAH effectively improved the compatibility of the composites as well as mechanical properties of materials. With the increase of ABS, the crystallization ability of PLA in the composite improved and the thermal stability of the system deteriorated slightly, the melt shear viscosity of composite also decreased.
Abstract: In order to solve the higher cost of system maintenance and higher risk bringing by MSP430 MCU and DSP site commissioning by using emulator, the Ethernet-based telephone communication system management software was designed based on the hardware platform of VOIP telephone communication system, which realize the remote management, maintenance, and the DSP and MSP430 MCU software online update for the network telephone communication system. The management software developed in Visual C # platform, using a Socket to the network communications. This management software has been put into use, which shows the advantages’ of good stability, simple operation and work efficiency, etc.