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1.
E. V. Ermanyuk 《Experiments in fluids》2002,32(2):242-251
This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly
stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating
in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional
similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by
vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids
having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients
is based on Fourier analysis of the time-history of damped oscillation tests.
Received: 25 September 2000 / Accepted: 6 July 2001 Published online: 29 November 2001 相似文献
2.
3.
Due to the Meissner effect, a permanent magnet is levitated, when released above a high temperature superconductor. When there is an inhomogeneous temperature field around the magnet, the magnet might start to oscillate with increasing amplitude until it remains in a continuous rotation. A mathematical model for the described effect is presented which couples heat transfer and electromagnetic forces with the equation of motion, yielding to a multiphysics task. In a detailed analysis it is found, that the torque which drives the rotation of the magnet, is explicitly given in terms of Bessel functions and the Fourier coefficients of order zero and one of the temperature field of the surrounding air. 相似文献
4.
Using the multipoles method, we formulate the problems of radiation (both heave and sway) of water waves by a submerged sphere
in deep as well as in uniform finite depth water with an ice-cover, with the ice-cover being modelled as an elastic plate
of very small thickness. In each case this leads to an infinite system of linear equations which are solved numerically by
standard techniques. The added-mass and damping coefficients for a heaving and swaying sphere are obtained and depicted graphically
against the wave number for various values of the radius of the submerged sphere and flexural rigidity of the ice-cover to
show the effect of the presence of ice-cover on these quantities. When the flexural rigidity is taken to be zero, the numerical
results for the added-mass and damping coefficient for water with a free surface are recovered. 相似文献
5.
The Crank–Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one-dimensional system with an initial singularity, subdivision of the first time interval into a number of equal subintervals (the Pearson method) works rather well, and so does division with exponentially increasing subintervals, where however an optimum expansion parameter must be found. This method can be computationally more expensive with some systems. The simple device of starting with one backward implicit (BI, or Laasonen) step does damp the oscillations, but not always sufficiently. For electrochemical microdisk simulations which are two-dimensional in space and using CN, the use of a first BI step is much more effective and is recommended. Division into subintervals is also effective, and again, both the Pearson method and exponentially increasing subintervals methods are effective here. Exponentially increasing subintervals are often considerably more expensive computationally. Expanding intervals over the whole simulation period, although capable of satisfactory results, for most systems will require more cpu time compared with subdivision of the first interval only. 相似文献
6.
The measurement of radial directional natural frequency and damping ratio in a vehicle tire has been studied. Natural frequencies and damping ratios in the radial direction of various tires, from passenger car tires to truck bus tires, are reported. The radial direction modal parameters of tires subjected to different levels of inflation pressure, have been determined by using a frequency response function method. To obtain the theoretical natural frequency and mode shape, the plane vibration of a tire has been modeled as though it were that of a circular beam. By using the Tielking method that is based on Hamilton’s principle, theoretical results have been determined by considering the rotational velocity, tangential and radial stiffness, radial directional velocity and tension force which is due to tire inflation pressure. The results show that experimental conditions can be considered as the parameters that shift the natural frequency and damping ratio. 相似文献
7.
HUANG HouBing MA XingQiao YUE Tao XIAO ZhiHua SHI SanQiang & CHEN LongQing 《中国科学:物理学 力学 天文学(英文版)》2011,(7)
The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ... 相似文献
8.
低温环境起动性能是表征车辆动力性能的一项重要指标。对液力机械传动车辆而言,由于综合传动装置自身技术特点,改善车辆起动性能除应当考虑发动机自身起动阻力外,还应当考虑综合传动装置的起动阻力。在系统分析综合传动装置技术特点和功率流向的基础上,总结了发动机起动过程的主要特征,提出采用稳态试验与动态试验相结合的台架试验方法进行综合传动装置起动扭矩测试。以某高速履带车辆为研究对象,进行了综合传动装置起动扭矩测试。试验结果表明,传动油温的变化和各类油泵的功率消耗是决定综合传动装置起动扭矩大小的关键因素,为改进车辆总体设计和提高车辆起动性能提供了依据。 相似文献
9.
The aim of this work is to evaluate the dynamic properties of nonwoven flax, hemp, kenaf and glass fibre-reinforced polypropylene (PP) composites. Also, the influence of some parameters, such as the type of reinforcement, the fibre/matrix weight ratio, the fibre orientation and the porosity content, on the damping behaviour of these nonwoven composites is investigated. To this end, a free flexural vibrations analysis was conducted to experimentally identify their natural frequencies and their associated loss factors. The obtained results show that the nonwoven composites reinforced by natural fibres present higher loss factors compared with those of the glass-PP composite. These interesting damping properties make these nonwoven composites very attractive for automotive applications where the dissipation of vibrations is highly requested. 相似文献
10.
滑带土动力学性质试验研究 总被引:3,自引:0,他引:3
为了研究地震高烈度区老滑坡的复活变形原因,本文对滑坡滑带土的动力学特性进行了系列研究。本次试验采用扰动土样,制样基本物理指标按滑带土的现场测试指标确定,在不固结不排水条件下,运用MTS810Teststar程控液压伺服土动三轴仪对单个样品逐级放大动应力的分级试验方法进行。侧向压力 (围压 )分别采用 100kPa、20 0kPa、300kPa三级,通过施加轴向振动荷载 (力 )模拟地震作用,振动波形为正弦波,频率为 1Hz,振幅随试样性质确定。研究结果表明,滑带土在动荷载作用下的动力学性质与其静荷载作用下的力学性质有着较大的差异,主要表现在滑带土的动应力与动应变关系的非线性、滞后性及变形积累特点,动弹性模量与动强度的显著降低以及动阻尼比的显著增大特性。这揭示了动力作用下的滑坡复活原因之一,同时为滑坡稳定性评价和动力作用下的变形机制模拟分析提供了基础资料,也为分析滑带土动力本构模型提供了基本内容。 相似文献