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51.
52.
本文提出根据白光散斑图像数据模拟刚体位移复位的相关性恢复方法,以解决物体大变位情况下的变形测量问题 相似文献
53.
A. N. Kudryavtsev S. G. Mironov T. V. Poplavskaya I. S. Tsyryul’nikov 《Journal of Applied Mechanics and Technical Physics》2006,47(5):617-627
The evolution of disturbances in a hypersonic viscous shock layer on a flat plate excited by slow-mode acoustic waves is considered
numerically and experimentally. The parameters measured in the experiments performed with a free-stream Mach number M
∞ = 21 and Reynolds number Re
L = 1.44 · 105 are the transverse profiles of the mean density and Mach number, the spectra of density fluctuations, and growth rates of
natural disturbances. Direct numerical simulation of propagation of disturbances is performed by solving the Navier-Stokes
equations with a high-order shock-capturing scheme. The numerical and experimental data characterizing the mean flow field,
intensity of density fluctuations, and their growth rates are found to be in good agreement. Possible mechanisms of disturbance
generation and evolution in the shock layer at hypersonic velocities are discussed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 3–15, September–October, 2006. 相似文献
54.
55.
利用主元分析法对数字图像相关技术所测结构变形信息进行数据压缩,并进一步用于力学模型未知参量的反求计算。首先,为降低数字图像相关技术所测庞大数据的应用成本,提出利用主元分析法对结构表面变形场数据进行压缩,实现在保留结构表面变形信息主要特征的前提下显著降低数据量的目的;其次,针对压缩后的数据建立了基于最小二乘法的力学模型参量反求模型,并利用高斯牛顿法进行求解;最后,以具体算例从计算精度、收敛速度和抗噪性等方面验证了数据压缩对模型参量反求的效果。研究结果表明,所提方法在显著降低使用数据量的前提下,能够有效提高力学模型参量反求计算的收敛速度,特别是对于包含多个模型参数的反求问题,具有较高的精度和较好的稳定性。 相似文献
56.
This paper reports an experimental investigation of open channel turbulent flow over hemispherical ribs. A row of ribs consists of hemispheres closely placed to one another in the spanwise direction and cover the entire span of the channel. The pitch-to-height ratio is varied to achieve the so-called d-type, intermediate and k-type roughness. The Reynolds numbers based on water depth, h, and momentum thickness, θ, of the approach flow are respectively, Reh = 28,100 and Reθ = 1800. A particle image velocimetry is used to obtain detailed velocity measurements in and above the cavity. Streamlines, mean velocity and time-averaged turbulent statistics are used to study the effects of pitch-to-height ratio on the flow characteristics and also to document similarities and differences between the present work and prior studies over two-dimensional transverse rods. It was observed that interaction between the outer flow and the shear layers generated by ribs is strongest for k-type and least for d-type ribs. The results also show that hemispherical ribs are less effective in augmenting flow resistance compared to two-dimensional transverse ribs. The levels of the Reynolds stresses and budget terms increase with increasing pitch-to-height ratio inside the roughness sublayer. 相似文献
57.
L. Cavaleri 《International Journal of Non》2006,41(9):1068-1083
A dynamic identification technique in the time domain for time invariant systems under random external forces is presented. This technique is based on the use of the class of restricted potential models (RPM), which are characterized by a non-linear stiffness and a special form of damping, that is a product of the input power spectral density (PSD) matrix and the velocity gradient of a non-linear function of the total mechanical energy. By applying stochastic differential calculus and by specific analytical manipulations, some algebraic equations, depending on the response statistics and on the mechanic parameters that characterize RPM, are obtained. These equations can be used for the dynamic identification of the above mechanic parameters once the response statistics of the system to be identified are evaluated. The proposed technique allows one to identify single-degree-of-freedom or multi-degrees-of-freedom systems in the case of unmeasurable input. Further, the probabilistic characteristics of the external forces can be completely estimated in terms of PSD matrix. 相似文献
58.
在高速水洞中运用人工通气方法进行了航行体模型超空泡形态特性的系列实验研究.获得了不同通气流量、不同空化数和不同弗鲁德数下的空泡形态,建立了以弗鲁德数为参数的空泡几何特征参数与空化数的对应关系、空化数与通气流量系数之间的对应关系.验证了空化数是决定空泡尺度的主要无因次参数,通过改变通气流量可以有效地调控空化数,进而达到控制空泡形态的目的.文中同时给出了通气流量系数的实验曲线拟合公式,并与国外的相关实验和公式进行了比较,两者基本一致.所得结论对进一步的水下超高速航行体空泡形态控制技术研究具有参考价值. 相似文献
59.
以舰船船体结构、惯性导航系统、被试导航设备以及天文经纬仪为物理对象,提出了一套利用光学系统原理和计算机图像处理技术对联合基座进行水平变形测量的方法,解决了各设备因安装位置的不同所造成的安装基座间产生的水平变形量问题。 相似文献
60.
A. N. Golovanov 《Journal of Applied Mechanics and Technical Physics》2006,47(5):637-642
A gas-dynamic flow in an axisymmetric convective jet is studied experimentally. It is demonstrated that the jet flow with
Grashof numbers Gr = (0.4–2.0) · 106 is self-similar. Acoustic oscillations directed perpendicular to the axis of symmetry transform the profiles of the gas-flow
parameters; two temperature maximums located outside the axis can appear. The results obtained indicate that flow instability
is generated in high-gradient regions.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 27–33, September–October, 2006. 相似文献