微穿孔板共振吸声结构在飞机喷流噪音控制上的应用研究

分析了飞机的喷流噪声产生机理,讨论了喷流噪声的控制技术.并将穿孔板共振吸声结构降噪技术应用到飞机的推进系统中,用以降低喷流噪声,并对其实际降噪效果进行了比较分析.     

磁流变减振器滞环特性试验及建模方法

由于磁流变减振器数学模型滞环特性描述通常不能兼顾简洁、精确,而限制其实际工程应用,因此,设计用于数学模型,参数辨识和验证的几组不同的连续变化的激励振幅、频率和电流强度,并应用实物磁流变减振器进行动态特性测试。根据测试结果分析无电流输入以及激励位移、速度和电流强度变化时,磁流变减振器的弹性、阻尼、电流饱和等基本特征的动态非线性特性。依据试验分析结合非线性粘塑性模型和简单非线性Bingham模型,提出应用神经网络理论中神经元S型传递函数,实现减振器活塞运动方向发生变化时力―速度特性模型中阻尼力的平滑过渡;同时借鉴非线性滞环双粘性模型以活塞加速度方向的变化,判断压缩屈服和拉伸屈服两个不同过程的方法,建立描述磁流变减振器滞环特性的数学模型。进一步分析所建模型中可控阻尼力部分各个参数的物理意义。通过试验数据对S型滞环特性数学模型进行参数辨识,并重点分析速度―力特性曲线所形成滞环的斜率及宽度相关参数的可控特性,最后以试验数据验证S型滞环模型的正确性。     

基于ANSYS的光纤连接器端面抛光仿真研究

主要利用ANSYS软件对光纤连接器抛光时端面接触压强分布的仿真分析,又与实际情况进行比较,证明分析是正确的,从而为光纤连接器端面抛光的优化分析提供了充分的理论依据。     

不同预燃室结构对甲烷湍流射流点火燃烧的影响

基于光学定容燃烧弹试验平台,通过高速纹影摄像系统在相同甲烷燃料初始温度、压力及混合气浓度下,定量分析了不同结构预燃室湍流射流点火(turbulent jet ignition,TJI)的燃烧特性,包括火焰传播速度、火焰面积、火焰形态及燃烧压力等参数。研究结果表明,预燃室孔径越小,相同时间内火焰传播得越远,火焰传播速度和火焰面积增长速度越快,燃烧压力峰值越高。随着预燃室孔径减小,着火机理会由射流中带有火焰的火焰点火转变为火焰过孔时熄灭的喷射点火。喷射点火着火时刻延迟,初始火焰速度减慢,但燃烧压力峰值受影响不大。多级加速预燃室压力升高率与压力峰值与单孔预燃室相比变化不大。虽然火焰出口时速度较慢,但是火焰出口时刻提前且速度衰减较弱,因此多级加速预燃室火焰速度在短时间内超过单孔预燃室,并且压力和火焰面积也更早达到最大值。     

Jet cup attrition testing

Jet cup attrition testing is a common method for evaluating particle attrition in fixed fluidized beds and circulating fluidized beds. An attrition index, calculated from jet cup data, is used to compare with one or more reference materials. However, this method is far from perfect despite its popularity. Results obtained at Particulate Solid Research, Inc. (PSRI) in different-sized jet cups and a 29-cm (11.5-in.) diameter fluidized bed test unit did not provide the same ranking of catalyst with respect to particle attrition. To obtain a better understanding of attrition in a jet cup, both computational fluid dynamics (CFD) and cold flow studies were performed with a 2.5-cm (1-in.) diameter Davison-type jet cup and PSRI's cylindrical 7.6-cm (3-in.) diameter jet cup. Results showed that a significant amount of material in the Davison and PSRI jet cup remained stagnant. Based on these results and additional CFD modeling, PSRI designed a new jet cup, where most of the material was hydrodynamically active. The new jet cup showed a 25% increase in attrition compared to PSRI's cylindrical jet cup under similar conditions and run times. Results were also compared to cyclone attrition data for several materials at PSRI. The new jet cup provided data that correlated with attrition results from the 29-cm (11.5-in.) diameter fluidized bed unit.     

Electrochemical polishing of monocrystalline silicon with specific crystallographic planes

In this study, an electrolytic polishing experimental system was developed to obtain a uniform, flat-surfaced monocrystalline silicon with specific crystallographic planes. Several key factors reflecting specific electrolytic polishing on monocrystalline silicon with specific crystallographic planes were summarized. These factors, including electrolyte, conduction mode, Schottky barrier, semiconductor body resistance, and unidirectional conductivity, were analyzed comprehensively through energy spectrum analysis, theoretical modeling, and potential simulation. The effects of electrolytic polishing process were obtained, and corresponding solutions were proposed. Finally, the electrolytic polishing experiment for monocrystalline silicon with specific crystallographic planes was conducted. A uniform, flat-surfaced monocrystalline silicon with no metamorphic layer was then obtained. The flatness error of the center area was less than 0.201 µm. Furthermore, the crystallographic planes of monocrystalline silicon wafers showed no change.     

Efficient calculation of the radiation heat flux surrounding a jet fire

The major objective of the paper is to address the main weakness of the reverse Monte-Carlo method applied to jet fire simulation; its slow convergence rate. This is done by replacing the use of a pseudo-random number generator for calculating ray orientations with a ray direction specification based on Sobol sequences. Sobol sequences produce sequences of points on the unit hemisphere that are not independent of each other in that new points in the sequence avoid previous points generated. This has the property that a more uniform pattern of rays on the unit hemisphere is produced, giving a ray convergence rate for the incident heat flux that is asymptotically equivalent to O(N_Ray⁻¹). The use of Sobol sequences to accelerate convergence of the Monte-Carlo method has been applied in mathematical physics and financial modelling but the results presented here are the first study of quasi-Monte-Carlo methods applied to the incident heat flux integral. The use of Sobol sequences to generate ray directions means that the Central Limit Theorem no longer holds. In its place, it has been demonstrated that it is possible to construct a Gaussian variable from the incident intensity distributions calculated using Sobol sequences. This means it is possible to calculate confidence limits for a prediction of incident heat flux and the confidence limits contract with ray number at a rate of O(N_Ray⁻¹ ln(N_Ray)).     

Experimental and CFD study on the effect of jet position on reactant dispersion performance

This paper reports the effect of jet position on the acid dispersion in a neutralization process. Experiments were carried out in a continuous stirred reactor and the effect of jet nozzle position on non-reactive dye dispersion at seven layouts was studied. Consequently, the neutralization reaction mixing was carried out at the best and worst positions. The results reveal that the ways that flow pushes the acid inside the tank are quite different and the neutralization performance can significantly be affected by the jet position. The Computational Fluid Dynamics (CFD) modeling was carried out in order to analyze the experimental observations.     

The production and anatomy of a tungsten powder jet

A tungsten powder jet is a potential candidate technology for a particle production target in a future high power (i.e. Multi-MW) particle accelerator based facility, such as a so-called conventional neutrino Super Beam, a proposed Neutrino Factory, or a future neutron source. To test the viability of producing a suitable powder jet a few simple experiments were performed using standard pneumatic conveying equipment and the encouraging results are presented.     

Influence of the transverse magnetic field intensity upon the electric resistance of the magnetorheological elastomer containing graphite microparticles

The magnetoresistor achieved and presented in this paper is based on magnetorheological elastomer (MRE) with graphite microparticles. It is shown that the resistance R of the magnetoresistor decreases with an increase of the strength H of the transverse magnetic field and of the compression force F, respectively The sum θ of the principal deformations as well as the compresibility module K is determined and the results obtained are discussed.