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621.
A new, passive, vibroprotective device of the rolling‐pendulum tuned mass damper type is presented that, relying on a proper three‐dimensional guiding surface, can simultaneously control the response of the supporting structure in two mutually orthogonal horizontal directions. Unlike existing examples of ball vibration absorbers, mounted on spherical recesses and effective for axial‐symmetrical structures, the new device is bidirectionally tuneable, by virtue of the optimum shape of the rolling cavity, to both fundamental structural modes, even when the corresponding natural frequencies are different, in such a case recurring to an innovative non‐axial‐symmetrical rolling guide. Based on Appell's non‐holonomic mechanics, a non‐linear dynamic model is first derived for the bidirectional absorber mounted on a 1‐storey 3‐degrees‐of‐freedom linear structure translating under the effect of both imparted base motion and applied dynamic forces. A laboratory‐scaled prototype of the device is then tested to experimentally demonstrate the bidirectional tuning capability and to validate the mathematical model. The design procedure and the seismic performance of the absorber are finally exemplified through numerical simulation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
622.
Nonlinearity and complexity in gravel bed dynamics 总被引:1,自引:1,他引:0
Arvind Singh Stefano Lanzoni Efi Foufoula-Georgiou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(7):967-975
The dynamics of river bed evolution are known to be notoriously complex affected by near-bed turbulence, the collective motion
of clusters of particles of different sizes, and the formation of bedforms and other large-scale features. In this paper,
we present the results of a study aiming to quantify the inherent nonlinearity and complexity in gravel bed dynamics. The
data analyzed are bed elevation fluctuations collected via submersible sonar transducers at 0.1 Hz frequency in two different
settings of low and high discharge in a controlled laboratory experiment. We employed surrogate series analysis and the transportation
distance metric in the phase-space to test for nonlinearity and the finite size Lyapunov exponent (FSLE) methodology to test
for complexity. Our analysis documents linearity and underlying dynamics similar to that of deterministic diffusion for bed
elevations at low discharge conditions. These dynamics transit to a pronounced nonlinearity and more complexity for high discharge,
akin to that of a multiplicative cascading process used to characterize fully developed turbulence. Knowing the degree of
nonlinearity and complexity in the temporal dynamics of bed elevation fluctuations can provide insight into model formulation
and also into the feedbacks between near-bed turbulence, sediment transport and bedform development. 相似文献
623.
R. Mladek J. Barckicke P. Binder P. Bougeault N. Brzovic C. Frei J. F. Geleyn J. Hoffman W. Ott T. Paccagnella P. Patruno P. Pottier A. Rossa 《Meteorology and Atmospheric Physics》2000,72(2-4):111-129
Summary The precipitation forecasts of four operational numerical weather prediction models over the Alpine region are evaluated
and intercompared for two periods of interest to the Mesoscale Alpine Programme (MAP). The new analysis of Alpine rainfall
of Frei and Scha?r (1998) is used to validate the models. It is found that the models have a tendency to overestimate the
total precipitation and the frequency of intense rain events over high orography. The skill scores show good consistency between
models, except for the ability to forecast light rain or heavy rain events. The partition between convective and stratiform
rainfall is rather variable between the models.
Received March 15, 1999/Revised July 12, 1999 相似文献
624.
625.
The paper presents the main characteristics of an innovative platform which has been conceived and designed to extend the
operational capabilities of current unmanned surface vehicles in terms of platform stability in waves and of powering requirement
at a relatively high speed. The main idea which rules the project is the realization of a small autonomous surface unit (about
6 m in length) capable of undertaking several tasks in the marine environment even with moderate rough sea conditions. The
designed vessel has the ability to locate, recover, and launch other members of the autonomous fleet (like AUVs or other underwater
devices) and at the same time could carry out a surveillance service of the surrounding areas. To manage these tasks, the
vehicle is designed to provide a fairly good autonomy which is needed to face intermediate-range missions (100 nautical miles).
The choice of a small waterplane area twin hull (SWATH) form has been motivated by its excellent properties of seakeeping
qualities, combined with a non-conventional low resistance underwater hull shape, currently under patenting process, which
is able to reduce to a minimum the resistance of the vessel especially at higher speeds. To obtain the most efficient profile
of the underwater bodies, a systematic optimization with an automatic procedure based on a parametric definition of the geometry,
a state-of-the-art computational fluid dynamics (CFD) flow solver, and a differential evolution global minimization algorithm
have been created and used. As expected, all the final CFD computations on the best design have demonstrated the superior
efficiency of the developed unconventional SWATH technology with respect to different alternatives of current hull typologies. 相似文献
626.
627.
The authors thank the discusser for the additional information,which is provided related to the historical interventions of the church through the centuries.This information was known to the authors,however they decided not to include it in the paper because of lack of space.Additional details regarding the retrofit interventions of the church can also be found in the MCEER report regarding the L'Aquila earthquake (Cimellaro et al.,2010). 相似文献
628.
629.
Research studies on the damped cable system (DCS) for seismic protection of frame structures are presented in this paper and the accompanying one. This technology includes prestressed steel cables linked to pressurized fluid viscous spring‐dampers fixed to the foundation at their lower ends, and to the top floor, or one of the upper floors, at their upper ends. The cables have sliding contacts with the floor slabs, to which they are joined by steel deviators. The general characteristics of the system, as well as of the constituting spring‐dampers and cables, are initially discussed. The results of a laboratory testing campaign developed on a DCS prototype are examined, and transferred into the formulation of the finite element model of the system, conceived to be easily generated by commercial structural analysis programs. A second dynamic experimental investigation follows, concerning a pilot installation of the system on a full‐scale mock‐up building. The benefits of the protective technology are evaluated in terms of maximum displacements and accelerations, as well as of equivalent viscous damping coefficient and MDOF transmissibility ratio. Further sections of the study, including a preliminary sizing criterion of DCS, additional numerical enquiries aimed at optimizing its geometrical layout, and the application to a real case study building, are offered in the companion paper. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
630.
Fabio Canova Cristiano Tolomei Stefano Salvi Giovanni Toscani Silvio Seno 《地球表面变化过程与地形》2012,37(3):273-286
The paper presents the results of a multi‐temporal, differential interferometric synthetic aperture radar (DInSAR) analysis aiming to identify active surface deformation phenomena in south‐eastern Sicily. The study area has been chosen because of its strong seismicity, high concentration of industrial and agricultural activities, and high density of people living in the coastal area. Furthermore, the morphology, lithology and climatic features of this sector of the Hyblean foreland are suitable for an interferometric analysis, providing a high coherence over the area. The Small BAseline Subset (SBAS) multitemporal DInSAR technique was used to calculate mean ground velocity maps and displacement time series from a large data set of European Remote Sensing Satellites (ERS 1–2) images spanning the time period 1992–2000. The reliability of the DInSAR results was tested calculating the EastSAR and UpSAR values over two permanent global positioning system (GPS) stations in the area, and comparing them with the EastGPS and UpGPS values. The residuals between GPS and DInSAR velocities were 1 and 0.6 mm/yr for the Up and East components, respectively. Four main subsiding areas, previously undetected, have been identified, corresponding with the towns of Augusta, Siracusa, Priolo, and Villasmundo. The observed deformation phenomena are located within coastal structural basins, filled with Pleistocene and Holocence deposits, except the Villasmundo land subsidence, which is located on the Hyblean plateau. The measured deformation rates reach values up to ?18 mm/yr in Augusta, –6 mm/yr in Siracusa, –5 mm/yr in Villasmundo and ?4.5 mm/yr in Priolo. The examination of velocity profiles, time series, and geological data allows us to relate all the detected deformation patterns primarily to groundwater over‐exploitation. A multi‐dimensional interpolation with kriging was performed to obtain a field subsidence map. A first‐order elastic deformation model was used to simulate the peculiar features of the Villasmundo subsidence. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献