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41.
A tuned liquid damper (TLD), which consists of rigid tanks partially filled by liquid, is a type of passive control device relying upon liquid sloshing forces or moments to change the dynamical properties and to dissipate vibrational energy of a structure. An analytical non-linear model is proposed for a TLD using rectangular tanks filled with shallow liquid under pitching vibration, utilizing a shallow water wave theory. The model includes the linear damping of the sloshing liquid, which is an important parameter in the study of a TLD as it affects the efficiency of the TLD. Shaking table experiments were conducted for verification; good agreement between the analytical simulations and the experimental results was observed in a small excitation amplitude range. The simulations of TLD-structure interaction by using the proposed model show that the TLD can efficiently suppress resonant pitching vibration of a structure. It is also found that the effectiveness of a TLD for suppressing the pitching vibration depends not only on the mass of liquid in the TLD but also on the configuration of the liquid as well as upon the position where the TLD is located. If the configuration of the liquid, i.e. the liquid depth and the TLD tank size, is designed suitably, the TLD can have a large suppressing moment and can be very effective even with a small mass of liquid. 相似文献
42.
Yusuke Seto Daisuke Hamane Takaya Nagai Kiyoshi Fujino 《Physics and Chemistry of Minerals》2008,35(4):223-229
We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K,
corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition
process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm.
With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO2 + perovskite via reactions with SiO2. Magnesite is not the only host phase for subducted carbon—solid CO2 also carries carbon in the lower mantle. Furthermore, CO2 itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for
diamond formation in the lower mantle. 相似文献
43.
This paper conducts elaborate analyses to evaluate the effectiveness of pounding countermeasures and the serviceability of elevated bridges subject to severe ground motions using detailed 3‐dimensional non‐linear modeling of an entire bridge structure system. A three‐span elevated steel bridge is selected for a case study. The peak and residual magnitude of gaps between girders and the maximum shear deformations of bearings are computed and used in the serviceability evaluation. The results show that under proper configurations the mitigation devices work effectively in reducing pounding actions in both the longitudinal and rotational directions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
44.
Past severe earthquakes indicate that pounding may cause considerable damage or even lead to collapse of colliding structures. The aim of this paper is to present an analysis of pounding between superstructure segments of an isolated elevated bridge induced by the propagating seismic wave. High-damping rubber bearings (HDRBs), used as isolation devices, are modelled by proposed non-linear formulation and the significance of the bearings model for pounding is indicated. The results of the study show that pounding leads to the increase or decrease of the forces acting on piers, depending on the gap size between superstructure segments. © 1998 John Wiley & Sons, Ltd. 相似文献
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Tomohiro Ohuchi Shun-ichiro Karato Kiyoshi Fujino 《Contributions to Mineralogy and Petrology》2011,161(6):961-975
Creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric
conditions [P (pressure) = 1.3 GPa and T (temperature) = 973–1,373 K]. For the A-orientation (shear direction [001] on (100) plane), the samples have transformed
completely to clinoenstatite and much of the deformation occurred after transformation. In contrast, for the B-orientation
(shear direction [001] on (010) plane), samples remained orthoenstatite and deformation occurred through dislocation motion
in orthoenstatite. The strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all
experimental conditions. Flow of the B-orientation samples is described by a power-law, and the pre-exponential constant,
the apparent activation energy, and the stress exponent are determined to be A = 10−9.5 s−1·MPa−4.2, Q = 114 kJ/mol and n = 4.2. However, for the A-orientation, the results cannot be fit by a single flow law and we obtained the following: A = 108.9 s−1·MPa−3.0, Q = 459 kJ/mol and n = 3.0 at high temperatures (≥1,173 K), and A = 10−27.4 s−1·MPa−14.3, Q = 296 kJ/mol and n = 14.3 at low temperatures (<1,173 K). The stress exponent for the low-temperature regime is high, suggesting that deformation
involves some processes where the activation energy decreases with stress such as the Peierls mechanism. Our study shows that
orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that
orthopyroxene may reduce the strength of the lithosphere, although the extent to which orthopyroxene weakens the lithosphere
depends on its orientation and connectivity. 相似文献
48.
Multiple Tuned Mass Dampers (MTMD) consist of a large number of small oscillators with natural frequencies distributed around the natural frequency of a controlled mode of the structure. In the present paper, the modal characteristics and efficiency of the MTMD are studied analytically. Perturbation solutions for the modal properties of the MTMD–structure system are obtained and the modal characteristics are discussed. An explicit formula to estimate the effectiveness of the MTMD subjected to harmonic forces is also derived. It is shown that the MTMD is efficient when at least one of the oscillators is strongly coupled with the structure in any mode. Based on this observation, a critical bandwidth of the natural frequencies of the MTMD to make the system multiply tuned is derived in a simple form, and furthermore a robustness criterion for the frequency tuning under a given bandwidth is proposed. It is shown that, when properly designed, the MTMD can be much more stable (robust) than a conventional single TMD while maintaining more or less the same efficiency. Numerical studies verify the accuracy of the perturbation solutions and the proposed formulas. 相似文献
49.
Active control of slightly sagged cables using the axial motion at the cable support is studied experimentally and analytically. Non-linear modal equations of a cable are presented, and two control schemes are identified, i.e. active stiffness control and active sag-induced force control. In this study, emphasis is placed on the active sag-induced force control. Additional damping is analytically expressed when a velocity feedback control is used. Although the active sag-induced force control can be applicable only for in-plane symmetric modes, it is shown that it is very efficient for the first mode. An experiment is conducted using a scaled cable model of 2 m length. First, it is shown by the experiment that the analytical model can predict well the non-linear cable motion. Next, sag-induced force control is examined using free vibration and harmonic excitations. The results agree well with the analytical predictions and confirm that additional damping can be obtained efficiently from the axial support motion. 相似文献
50.
In high-grade (granulite facies) quartzofeldspathic rocks the progressive development of a fabric records contrasting deformation
behaviour of quartz and feldspar. Feldspar has undergone deformation mainly by recrystallization-accommodated dislocation
creep and produced smaller recrystallized grains progressively in the course of deformation. Quartz has not deformed solely
by dislocation creep but also by a diffusion-controlled mechanism. Dislocation climb is important in the dislocation creep
of quartz. In contrast to feldspar, quartz grains have not recrystallized into smaller grains at any stage of deformation.
Rather, they have transformed initially to short monocrystalline ribbons and ultimately to long polycrystalline ribbons. This
textural change of quartz is a continuous process and has taken place in the course of bulk textural change of the rocks during
the deformation. 相似文献