An alternative approach to the random response of bilinear hysteretic systems     

Koichiro Asano  Wilfred D. Iwan 《地震工程与结构动力学》1984,12(2):229-236

An analytical representation of the bilinear hysteretic characteristic is presented. Using this representation, the response of a single-degree-of-freedom bilinear hysteretic system subjected to non-stationary random excitation is examined by equivalent linearization. An ordinary differential equation is derived for the covariance matrix of the response. Numerical examples are presented and the accuracy of the approach is demonstrated. Extension of the approach to a wider class of hysteretic systems is discussed.  相似文献   

Cerium anomaly variations in ferromanganese nodules and crusts from the Indian Ocean     

B Nagender Nath  I Roelandts  M Sudhakar  W.L Plüger  V Balaram 《Marine Geology》1994,120(3-4):385-400

Fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the Central Indian Basin and the Western Indian Ocean. The aim was to identify the processes controlling the REE patterns of the phases hosting the REE in the manganese nodules, with an emphasis on an understanding of the Ce anomaly. This has involved separating the encrusting layers and nuclei physically as well as Fe-Mn oxides from the aluminosilicate phase chemically (using a 2 M HCl leach) prior to analysis.

The presence of nodule nuclei seems to have little influence (mostly <5% to a maximum of 30%) on the overall magnitude of the Ce anomalies in these nodules. The ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat REE patterns indicating that the aluminosilicate phase contributes very little to the Ce anomalies. Interelement relations indicate that the Ce anomalies are largely controlled by the amorphous mineral phase FeOOH.xH₂O. The relationship of Fe, Ce anomaly and δ-MnO₂ further suggests that Ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with δ-MnO₂.

The regional distribution of the Ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts.  相似文献   

Comets from antiquity to the present day     

Prof.  Iwan Williams  Dr  Stephen Lowry 《Astronomy& Geophysics》2006,47(2):2.38-2.41

Iwan Williams and Stephen Lowry report on the RAS Specialist Discussion meeting held on 9 December 2005, which considered the historical and current significance of comets.  相似文献   

Jürgen Remane     

Thierry Adatte  Iwan Stössel-Sittig 《Swiss Journal of Geoscience》2004,97(3):I-II

  相似文献   

The effective period and damping of a class of hysteretic structures     

Wilfred D. Iwan  Nathan C. Gates 《地震工程与结构动力学》1979,7(3):199-211

This paper presents the results of a numerical investigation in which the maximum response of six hysteretic systems is calculated for an ensemble of twelve earthquakes. Inelastic response spectra are constructed for a range of response ductility. An effective linear period and damping are calculated for each system and ductility by determining those parameters which minimize an RMS response spectrum error. Conclusions are presented concerning the effects of deterioration, stiffness degradation, cracking and ductility on the effective linear system parameters.  相似文献   

The deployment of strong-motion earthquake instrument arrays     

Wilfred D. Iwan 《地震工程与结构动力学》1979,7(5):413-426

The International Workshop on Strong-motion Earthquake Instrument Arrays was held during 2-5 May 1978 in Honolulu, Hawaii. The goal of the workshop was to develop a workable plan for the possible future deployment of dense strong-motion arrays with primary emphasis on ground motion studies. Topics considered by the workshop included: favourable array locations, the design of arrays for source mechanism and wave propagation studies, the design of arrays for local effects studies, array construction and operation, and implementation. This paper gives a summary of the recommendations and conclusions of the workshop.  相似文献   

The peak harmonic response of locally non-linear systems     

Richard K. Miller  Wilfred D. Iwan 《地震工程与结构动力学》1978,6(1):79-87

This paper presents an approximate analytical technique for determining the steady-state response of a class of systems with spatially localized non-linearity. A method of finding the amplitude peaks in various modes is presented. Numerical examples illustrate the nature and accuracy of the results of the approximate analysis.  相似文献   

The earthquake design and analysis of equipment isolation systems     

Wilfred D. Iwan 《地震工程与结构动力学》1978,6(6):523-534

A method is presented whereby the response spectrum may be used to predict the response of equipment mounted on an isolation system with non-linear motion limiting constraints. The results of the approximate method are compared with results obtained by direct numerical integration for a representative piece of equipment.  相似文献   

Estimating inelastic response spectra from elastic spectra     

W. D. Iwan 《地震工程与结构动力学》1980,8(4):375-388

Inelastic displacement response spectra are determined for a broad class of single-degree-of-freedom hysteretic structures. Based on these spectra, effective linear period and damping parameters are defined as a function of ductility. A simple empirical formula is derived which may be used to estimate the mid-period range inelastic response spectrum of a general hysteretic structure given the linear response spectrum of the excitation. The estimates obtained from this formula are compared with those obtained by the Newmark-Hall method, the substitute–structure method and the ATC–3 tentative procedure. It is found that the empirical formula not only gives good estimates of the average behaviour of the inelastic spectrum, but also reproduces some of the details of the spectrum.  相似文献   

Asteroid 2002NY40 as a source of meteorite-dropping bolides     

Josep M. Trigo-Rodríguez  Esko Lyytinen  Daniel C. Jones  José M. Madiedo  Alberto J. Castro-Tirado  Iwan Williams  Jordi Llorca  Stanislav Vítek  Martin Jelínek  Blanca Troughton  Francisco Gálvez 《Monthly notices of the Royal Astronomical Society》2007,382(4):1933-1939

The existence of asteroidal meteoroid streams capable of producing meteorite-dropping bolides has long being invoked, but evidence is scarce. Recent modelling of previously reported associations suggests that the time-scales to keep the orbital coherence of these streams producing meteorites are too short. We present an unequivocal association between near earth object (NEO) 2002NY40 and at least one bright fireball detected over Finland in 2006 August. Another two additional fireballs recorded from Spain and Finland seem to be related, together producing a fireball-producing stream (β Aquarids). On the basis of historical data, the 2006 finding suggests the existence of a meteoroid complex capable of producing meteorites. Taking into account present time-scales for orbital decoherence, if 2002NY40 has large meteoroids associated with it, such behaviour would be the consequence of a relatively recent asteroidal fragmentation. Supporting our claim, the heliocentric orbits of two recently discovered NEOs, 2004NL8 and 2002NY40, were found to exhibit a good similarity to each other and also to the orbits of the three bolides. The fireball spectra of the two Finish bolides showed that the chemical abundances of these objects are consistent with the main elements found in chondrites. This result is consistent with the probable Low iron, Low metal (LL) chondritic mineralogy of asteroid 2002NY40. Consequently, this asteroid may be delivering LL chondrites to the Earth. Additional fireball reports found in the literature suggest that the associated β Aquarid complex may have been delivering meteorites to the Earth during, at least, the last millennium.  相似文献