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621.
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
622.
623.
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
624.
625.
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
626.
627.
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
628.
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
629.
GPS measurements were collected within the framework of the VLNDEF (Victoria Land Network for DEFormation control) project, which was started in 1999 with the aim of detecting crustal deformation in Northern Victoria Land (Antarctica). The network was established in 1999 and is composed of one permanent station (TNB1), which has been observing since 1998, and 28 periodically surveyed control points. Three complete campaigns and some partial surveying of the network have been carried out to date.Data processing and analysis have been performed using an undifferenced approach for the network position within the ITRF. A double-differences-based strategy has been applied for movement detection. The data processing and analysis of results have been carried out for all available data, both periodically acquired and long time series.GPS measurements collected between December 1999 and February 2006 indicate a mean “absolute” motion of the region of ve = 11.3 mm/yr and vn = − 11.1 mm/yr and rock uplift rates of vu = 2.8 mm/yr. These values are consistent with Antarctic plate motion and the general postglacial rebound models of the region. The relative motions within VLNDEF are small and only few points show velocities greater than the confidence levels. 相似文献
630.
Masoud Moghaddasi Gregory A. MacRae J. G. Chase Misko Cubrinovski Stefano Pampanin 《地震工程与结构动力学》2015,44(11):1805-1821
This paper introduces a simple method to consider the effects of inertial soil–structure interaction (SSI) on the seismic demands of a yielding single‐degree‐of‐freedom structure. This involves idealizing the yielding soil–structure system as an effective substitute oscillator having a modified period, damping ratio, and ductility. A parametric study is conducted to obtain the ratio between the displacement ductility demand of a flexible‐base system and that of the corresponding fixed‐base system. It is shown that while additional foundation damping can reduce the overall response, the effects of SSI may also increase the ductility demand of some structures, mostly being ductile and having large structural aspect ratio, up to 15%. Finally, a design procedure is provided for incorporation of the SSI effects on structural response. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献