Energy-consistent integration method and its application to hybrid testing     

Bin Wu  Tianlin Pan  Haowen Yang  Jinzhe Xie  Billie F. Spencer Jr 《地震工程与结构动力学》2020,49(5):415-433

The time-integration algorithm is an indispensable element to determine response of the boundary of the numerical as well as physical parts in a hybrid test. Instability of the time-integration algorithm may directly lead to failure of the test, so stability of an integration algorithm is particularly important for hybrid testing. The explicit algorithms are very popular in hybrid testing, because iteration is not needed. Many unconditionally stable explicit-algorithms have been proposed for hybrid testing. However, the stability analysis approaches used in all these methods are valid only for linear systems. In this paper, a uniform formulation for energy-consistent time integrations, which are unconditionally stable, is proposed for nonlinear systems. The solvability and accuracy are analyzed for typical energy-consistent algorithms. Some numerical examples and the results of a hybrid test are provided to validate the effectiveness of energy-consistent algorithms.  相似文献   

Dynamic analysis of track nonlinear energy sinks subjected to simple and stochastice excitations     

Jingjing Wang  Bin Wang  Nicholas E. Wierschem  Billie F. Spencer Jr 《地震工程与结构动力学》2020,49(9):863-883

Track nonlinear energy sinks (track NESs) have been shown to be an effective and applicable strategy to mitigate structural response in recent years. However, previous studies on track NESs has mainly focused on demonstrating the benefits of track NESs through numerical simulations and experiments, with relatively little attention paid to the analytical understanding of the unique dynamics of track NESs. This study analyzes the responses of a track NES when subjected to impulsive and harmonic excitations by the harmonic balance method. Special attention is given to the cause and effect of the peaking behavior that is a prominent characteristic of the track NES's restoring force–displacement relationship. Analytical results reveal that the special energy–frequency characteristics of track NESs can be, at times, utilized to enhance the energy robustness that is absent in the conventional cubic NESs. Based on the analytical response expression, an equivalent linearization method (ELM) for the track NESs is developed for stochastic analysis. This ELM is numerically validated on the systems with strong nonlinearities. Stochastic optimization built on the ELM is performed to obtain design parameters of the track NES that can lead to minimum response variances of the primary structure. In particular, the proposed optimization procedure can be applied to seismic optimum design in which the seismic excitations are modeled as filtered white-noise ground motions. The analytical techniques provided in this study lay the groundwork for the practical implementation of track NESs as a robust and effective control strategy for engineering structures.  相似文献   

Marine and estuarine shallow water science and management: The interrelationship among habitats and their management     

Francis J. Reill  Ralph J. Spagnolo  Edward Ambrogio 《Estuaries and Coasts》1999,22(3):731-734

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Analytic investigation of climate stability on Titan: sensitivity to volatile inventory     

Ralph D. Lorenz  Christopher P. McKay  Jonathan I. Lunine 《Planetary and Space Science》1999,47(12):1503-1515

We develop a semiempirical grey radiative model to quantify Titan’s surface temperature as a function of pressure and composition of a nitrogen-methane-hydrogen atmosphere, solar flux and atmospheric haze. We then use this model, together with non-ideal gas-liquid equilibrium theory to investigate the behavior of the coupled surface-atmosphere system on Titan. We find that a volatile-rich Titan is unstable with respect to a runaway greenhouse—small increases in solar luminosity from the present value can lead to massive increases in surface temperature. If methane has been photolyzed throughout Titan’s history, then this runaway can only be avoided if the photolytic ethane is removed from the surface-atmosphere system.  相似文献   

Map Use by Adults with Visual Impairments     

Mark Blades  Simon Ungar  Christopher Spencer 《The Professional geographer》1999,51(4):539-553

In this paper we summarize five experiments that were designed to investigate how tactile maps contribute to the cognitive maps of people with visual impairments. In two experiments we demonstrated that tactile maps can contribute to peoples' ability to learn a route through an unfamiliar area. From the results of two further studies, we argue that compared to people with sight, people with visual impairments have greater difficulty encoding information from a map. We considered this directly in a fifth experiment by investigating how people with visual impairments search and learn a map. We found that they used less efficient strategies than people with sight. We conclude that tactile maps are an important source of geographical information when people need to learn about new environments, but we also point out that to benefit most from tactile maps people need to encode the map information as effectively as possible. As people with visual impairments do not always use the most appropriate encoding strategies we suggest that tactile map users might benefit from greater experience and training in map encoding strategies.  相似文献   

Thermoluminescence screening of non‐diagnostic sherds from stream sediments to obtain a preliminary alluvial chronology: An example from Cyprus     

Katleen Deckers  David C.W. Sanderson  Joel Q. Spencer 《Geoarchaeology》2005,20(1):67-77

In this paper, simple thermoluminescence (TL) dating procedures utilizing non‐diagnostic sherds from fluvial deposits are described. This approach may provide preliminary insights into the chronology of fluvial sequences in areas where transported ceramics are common, but alluvial chronologies are not well developed. Our method deviates from conventional TL‐ dating methods in that simple screening measurements are made from small, heavily abraded sherds, and dose rates are estimated rather than being measured from each sample. This results in rapid and inexpensive laboratory measurements, which can be used to support field surveys. The limitations in precision and accuracy relative to quantitative luminescence procedures are discussed. It is argued that the results can be used to estimate an approximate maximum age of alluvial deposition events. The approach is illustrated with results from a geoarchaeological survey in Cyprus. © 2005 Wiley Periodicals, Inc.  相似文献   

Astrometric radio source catalogs     

K. J. Johnston  J. H. Spencer  G. H. Kaplan  W. J. Klepczynski  D. D. McCarthy 《Celestial Mechanics and Dynamical Astronomy》1980,22(2):143-151

A review of the accuracy of radio interferometric positions of extragalactic sources is given. A mean catalog of radio positions is presented. With the accuracy currently attainable, radio observations can contribute significantly to the determination of astronomical constants.  相似文献   

Travel-time inversion for simultaneous earthquake location and velocity structure determination in laterally varying media   总被引：13，自引：0，他引：13  

Carl Spencer  David Gubbins 《Geophysical Journal International》1980,63(1):95-116

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Titan's surface before Cassini     

Ralph D. Lorenz  Jonathan I. Lunine 《Planetary and Space Science》2005,53(5):557-576

We review current understanding of Titan's surface, synthesizing a paradigm from Earth-based radar observations and near-infrared surface maps, together with reanalysis of Voyager data and results from published theoretical models. Based on these we suggest that Titan has a varied landscape with a variety of tectonic and erosive features indicative of geologic activity, and an impact crater population reflective of the dense atmosphere.  相似文献   

Numerical calculations of the longevity of impact oases on Titan     

David P. O'Brien  Ralph D. Lorenz  Jonathan I. Lunine 《Icarus》2005,173(1):243-253

A promising setting for the formation of interesting prebiotic molecules on Titan is the transient liquid water environment formed by a comet impact, as originally suggested by Thompson and Sagan (1992, in: Symposium on Titan, ESA SP, vol. 338, p. 167). The impact melt (water or a water-ammonia mixture) generated in such an event can react with the abundant photochemical hydrocarbons and nitriles deposited on the surface of Titan to form more complex molecules such as purines and amino acids. We use a finite-difference thermal conduction code to calculate how long it takes for realistic liquid deposits in crater floors to freeze in the Titan environment. Our results suggest that 15 km diameter craters can sustain liquid water or water-ammonia environments for ∼¹⁰²-10³ yr and 150 km craters can sustain them for ∼¹⁰³-10⁴ yr. We discuss the implications of these timescales for organic chemistry on Titan.  相似文献