共查询到20条相似文献,搜索用时 27 毫秒
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面波产生的地震动转动分量的试验验证 总被引:1,自引:0,他引:1
迄今为止,地面运动转动分量主要是通过弹性波动理论方法间接由平动分量获得,但并未得到证实。首次运用面波试验验证了这种求取转动分量的方法的合理性。重锤击落地面,在半无限空间弹性介质的地表附近,可产生面波(瑞利波和乐夫波),合理布置拾振器位置,测得产生面波的时程,利用两点差原理可以测得地面近似转动分量;将实测转动分量和用理论方法求得的转动分量的时程曲线以及傅立叶谱进行对比,由两种方法得到的转动分量加速度时程在振动持续时间内的开始阶段、强震阶段和衰减阶段基本一致;Fourier谱峰值、峰值点个数、峰值出现的位置以及谱曲线的形状走向是接近的。 相似文献
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Matt Harrington Michael Lin Kerstin N. Nordstrom Wolfgang Losert 《Granular Matter》2014,16(2):185-191
Many recent advances in the study of granular media have stemmed from the improved capability to image and track individual grains in two and three dimensions. While two-dimensional systems readily yield both translational and rotational motion, a challenge in three-dimensional experiments is the tracking of rotational motion of isotropic particles. We propose an extension of the refractive index matched scanning technique as a method of measuring individual particle rotation. Initial measurements indicate that shear-driven rotational motion may stem from gear-like motion within the shear zone. 相似文献
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《International Journal of Engineering Science》1986,24(11):1717-1730
Stresses developed in a rapid simple shear flow of disks are quantified. Collisional momentum transfer is considered to be the dominant stress generating mechanism. The disks are inelastic and frictional. The restitution coefficient and the coefficient of friction together determine the transfer of momentum and dissipation of energy during a collision. The frictional coefficient generates and maintains a rotational motion of disks. The total fluctuation motion of disks consists of two translational modes and one rotational mode. The rotational mode is found to depend on both the restitution and the friction coefficient. Equipartition of energy among all modes of motion is absent. The mean rotation depends only on the mean flow gradient. The analysis assumes fluctuation modes all have constant magnitudes. Comparison with a computer simulated disk flow shows good agreement. This implies that the distribution of velocity magnitude may not be crucial to the quantification of stresses. 相似文献
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Uniform rotational motion compensation for inverse synthetic aperture radar with non-cooperative targets 总被引:1,自引:0,他引:1
In the current scenario of high-range resolution radars, the rotational motion of the target usually generates migration through resolution cells (MTRC) in the inverse synthetic aperture radar (ISAR) images. A technique to correct the MTRC in the case of uniform rotation rate is proposed. An estimation of the rotation vector of the non-cooperative targets is not required. The approach compensates the rotational motion in two steps: the slant-range rotation compensation (SRRC) and the cross-range rotation compensation (CRRC). CRRC is based on an extension of phase difference (PD) and on a robust method to delete outliers. The technique is verified both with simulated and live data from a millimetre-wave linear frequency-modulated continuous wave radar. A comparison with a minimum entropy-based technique is also made. 相似文献
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《International Journal of Engineering Science》2005,43(11-12):953-976
The first part of this paper investigates the motion of a solid spherical particle in an incompressible axisymmetric micropolar Stokes flow. A linear slip, Basset-type, boundary condition has been used. Expressions for the drag force and terminal velocity has been obtained in terms of the parameter characterizing the slip friction. In the second part, we consider the flow of an incompressible axisymmetrical steady semi-infinite micropolar fluid arising from the motion of a sphere bisected by a free surface bounding a semi-infinite micropolar fluid. Two cases are considered for the motion of the sphere: perpendicular translation to the free surface and rotation about a diameter which is also perpendicular to the free surface. The speed of the translational motion and the angular speed for the rotational motion of the sphere are assumed to be small so that the nonlinear terms in the equations of motion can be neglected under the usual Stokesian approximation. Also a linear slip, Basset-type, has been used. The analytical expressions for velocity and microrotation components are determined in terms of modified Bessel functions of second kind and Legendre polynomials. The drag for the translation case and the couple for the rotational motion on the submerged half sphere are calculated and expressed in terms of nondimensional coefficients whose variation is studied numerically. The variations of the drag and couple coefficients with respect to the micropolarity parameter and slip parameter are tabulated and displayed graphically. 相似文献
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Wang X Xin H Leonard JN Chen G Chwang AT Jiang Q 《Journal of nanoscience and nanotechnology》2007,7(4-5):1512-1517
The authors have studied, using molecular dynamic (MD) simulations, the oscillatory characteristics of a 2C60/CNT oscillator system, in which two C60 fullerenes oscillate inside a single walled carbon nanotube (CNT) in two basic modes, i.e., the symmetric and non-symmetric motions. In the symmetric mode, with each oscillation the two fullerenes move symmetrically from the CNT ends towards the CNT center where they bounce off each other and head back towards the ends. In the non-symmetric mode, the two fullerenes move back and forth inside the CNT crossing the center point of the CNT together with each oscillation. The simulations show that the non-symmetric oscillation mode is stable for the prescribed initial (maximum) velocities up to 300 m/s, while the symmetric oscillation mode however, experiences dynamic instabilities for a prescribed initial (maximum) velocity larger than 250 m/s. The instability takes place as a result of the transfer of energy from the translational to the rotational motion of the fullerenes. This characteristic differentiates 2C60/CNT oscillators from double-walled CNT oscillators. The rotation is primarily caused by the inter-colliding of the two fullerenes, which subjects the fullerenes to large van der Waals repelling forces. These repelling forces are not necessarily aligned perfectly along the CNT axis nor precisely pointing towards the mass centers of the fullerenes. These misalignments cause the fullerenes to rock around the CNT's axis, while their offsets from the mass centers cause the fullerenes to rotate. The rocking motion, being severely confined by the CNT, does not gain much energy itself, but instead, channels energy from translational to rotational motion. The energy channeling is found to be reversed in some very short time intervals, but the rotational motion always gains energies from the translational motion over a time interval that is long enough at the MD time scale. This feature, contrary to our experiences in the macroscopic world, appears to be unique for such nanoscopic mechanical systems. 相似文献
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本文建立了自立式微波通讯塔在复合地震动作用下的振动方程,给出了计算弹性结构反应统计量的有关公式。应用给出的地震动转动分量的随机模型及修正的Kanai-Tajimi 平动模型,对山西某地的微波通讯塔进行了平稳随机反应分析,得到了一些对实际工程有意义的结果。最后对某些问题进行了讨论。 相似文献
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Katsuhiko Satoh 《Thin solid films》2008,517(4):1411-1416
Molecular dynamics simulation was performed at constant temperature and pressure to investigate the effect of pressure on molecular dynamics for disc-shaped molecules. The generic Gay-Berne model, GB(0.345, 5.0, 1, 3), was used to study the phase transition behaviour, and translational and rotational dynamics, under two different reduced pressures P?, 10.0 and 20.0. Obvious shifts were detected in the transition temperatures. Both systems have the same phase sequence with different pressures: isotropic, discotic nematic and columnar phases. Translational motion is characterised by the parallel and perpendicular components of diffusion coefficients, with respect to the director in the orientational ordered phase. With regard to rotational dynamics, the correlation time of the first-rank orientational time autocorrelation function, which corresponds to end-over-end rotational motion of a molecule, has been investigated. A clear jump in the temperature dependence of the correlation time has been found at the isotropic-nematic phase transition point. The retardation factor g|| as a function of the reduced temperature T?/TNI? shows an apparent pressure effect on the rotational dynamics. 相似文献
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《Zeolites》1989,9(4):312-317
The translational and rotational motions of methane adsorbed at different loadings in NaZSM-5 have been studied by quasi-elastic neutron scattering at two temperatures: 200 and 250 K. The translational motion does not simply follow Fick's law, but a jump diffusion model with a Gaussian distribution of jump lengths satisfactorily simulates the experimental results. The diffusion coefficient that is obtained for long-range translational motion does not vary much on the loading in the range that was studied: it is of ⋍ 2.7 × 10−5 cm2 s−1 at 200 K and ⋍ 5.5 × 10−5 cm2 s−1 at 250 K. Good agreement is found between the neutron and n.m.r. results for this motion, but large discrepancies are observed with the macroscopic measurements. The rotational motion is well described by an isotropic rotational diffusion model, and this motion is found to be much slower in the zeolite than in physisorbed layers or in bulk solid methane. 相似文献
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Yan Gu Wei Sun Gufeng Wang Michael T. Zimmermann Robert L. Jernigan Ning Fang 《Small (Weinheim an der Bergstrasse, Germany)》2013,9(5):785-792
A full understanding of cell mechanics requires knowledge of both translational and rotational dynamics. The single particle orientation and rotational tracking (SPORT) technique is combined here with correlation analysis to identify the fundamental rotational modes: in‐plane rotation and out‐of‐plane tilting, as well as other more complex rotational patterns, from the vast image data captured at a temporal resolution of 5 ms for single gold nanorod probes in live cell imaging experiments. The unique capabilities of visualizing and understanding rotational motions of functional nanoparticles on live cell membranes allow correlation of the rotational and translational dynamics in unprecedented detail and provide new insights into complex membrane processes. Particles with functionalized surfaces, which interact with the membrane in fundamentally different ways, can exhibit distinct rotational modes and are, for the first time, directly visualized, and these show the early events for membrane approach and attachment. 相似文献
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Warner JH Ito Y Zaka M Ge L Akachi T Okimoto H Porfyrakis K Watt AA Shinohara H Briggs GA 《Nano letters》2008,8(8):2328-2335
The rotation of fullerene chains in SWNT peapods is studied using low-voltage high resolution transmission electron microscopy. Anisotropic fullerene chain structures (i.e., C300) are formed in situ in carbon nanopeapods via electron beam induced coalescence of individual fullerenes (i.e., C60). A low electron accelerating voltage of 80 kV is used to prevent damage to the SWNT. The large asymmetric C300 fullerene structure exhibits translational motion inside the SWNT and unique corkscrew like rotation motion. Another asymmetric fullerene chain containing mixed fullerene species is prepared by fusing smaller C60 fullerenes to a larger Sc@C82 fullerene, and this also exhibits corkscrew rotational motion. Chains of Sc3C2@C80 in SWNT peapods adopt a zigzag packing structure, and the entire zigzag chain rotates inside the SWNT to induce structural modifications to the SWNT diameter and cross-sectional shape of the SWNT. The expansion and contraction of the diameter of the SWNT is measured as 17%, demonstrating nanoactuation behavior in carbon nanopeapods. 相似文献
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It has been shown that in the context of a linear theory for a floating body with six degrees of freedom each of the 6× 6 added-mass and damping matrices contains three distinct Cartesian second-order tensors in regard to translational, rotational and interaction between translational and rotational oscillations. As a result of this, a new technique based on the transformation law of second-order tensors is introduced for motion analysis of offshore platforms which can be used as an alternative to the common methods in offshore engineering. 相似文献
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When molecules of a low density diatomic gas strike a solid surface both translational energy and the internal energy modes of rotation and vibration will contribute the energy exchange that occurs. Theoretical studies indicate that accomodation coefficient for rotational energy should be less than that for translational energy, and this is confirmed by experimental results. The experimental apparatus described in this paper uses the electron bream fluorescence detector to measure simultaneously both rotational and translational energy accommodation coefficients of room temperature nitrogen reflecting from a solid surface. A bakeable ultra high vacuum system was built to provide a clean vacuum environment for control of the solid surface properties. In addition to being the only known direct measurement of rotational accomodation coefficient the system offers an advantage over some previous methods of translational accommodation measurement in that there are few restrictions on solid surface temperature or composition. 相似文献