On tuned mass dampers for reducing the seismic response of structures     

Julio C. Miranda 《地震工程与结构动力学》2005,34(7):847-865

This paper presents an energy‐based theoretical model for a two degree‐of‐freedom mechanical system. After a general formulation in Appendix A, the model is specialized to study tuned mass dampers as a means to substantially increase modal damping in order to induce a consequential decrease of the seismic response of the structures thus provided. Although approximate since it neglects coupling due to damping, it is shown that the model yields a first‐order approximation to the exact frequencies, providing values of optimum damping that closely match exact results proposed by others. In view of this, it is proposed that the model be applied through an iterative numerical procedure that identifies the pertinent optimum parameters. It is also shown that for certain particular benchmark cases the model provides closed‐form equations for the parameters defining the dynamic states related to these special conditions. Despite its approximate nature the model presented in this paper is rational, and due to its explicit consideration of energy balance and overall simplicity, it provides a convenient platform for the study of tuned mass dampers, as well as for other methods of structural passive control. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Evaluation of combination rules for maximum response calculation in multicomponent seismic analysis     

Oscar A. Lpez  Anil K. Chopra  Julio J. Hernndez 《地震工程与结构动力学》2001,30(9):1379-1398

The existing rules for combining peak response to individual components of ground motion are evaluated. The response values r_e to two horizontal components of ground motion estimated by four multicomponent combination rules—SRSS‐, 30%‐, 40%‐ and simplified‐SRSS‐rules—are compared with the critical response, r_cr, obtained by the CQC3‐rule, which takes into account the direction of the principal ground components with respect to the structural axes and provides the largest response over all possible seismic incident angles. The following results are obtained in the first part of the paper and are valid for any elastic structure and any earthquake design response spectrum: For realistic values of the ratio γ of the design spectra for the two principal components of ground motion the SRSS‐rule estimate lies between 0.79r_cr and 1.00r_cr, the Simplified‐SRSS‐rule estimate lies between 1.00r_cr and 1.26r_cr, the 40%‐rule estimate lies between 0.99r_cr and 1.25r_cr, and the 30%‐rule estimate lies between 0.92r_cr and 1.16r_cr. None of the multicomponent combination rules account for the increase in response of systems if the vibration periods of the two modes that contribute most to the response to the x‐ and y‐components of ground motion are close to each other. Evaluated in the second part of the paper is the accuracy of the multicomponent combination rules in estimating the response of a range of one‐storey systems with (a) symmetrical plan and (b) unsymmetrical plan, and of two multistorey buildings. The SRSS‐rule underestimates the response by up to 16% and the other three rules overestimate it by up to 18%. Although these errors appear to be smaller than the many approximations inherent in structural design, they can be eliminated with very little additional computation by using an explicit formula for the critical response based on the CQC3 rule. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Leaf cellulose δD and δO trends with elevation differ in direction among co-occurring, semiarid plant species     

Valery J Terwilliger  Julio L BetancourtSteven W Leavitt  Peter K Van de water 《Geochimica et cosmochimica acta》2002,66(22):3887-3900

The potential to reconstruct paleoclimate from analyses of stable isotopes in fossil leaf cellulose could be enhanced by adequate calibration. This potential is likely to be particularly great in mid-latitude deserts, where a rich store of fossil leaves is available from rodent middens. Trends in δD and δ¹⁸O of leaf cellulose were examined for three species growing across climatic gradients caused by elevation and slope aspect in southeastern Utah, USA. The species differed in morphology (Pinus edulis vs. Yucca glauca), photosynthetic pathway (C₃Y. glauca vs. CAM Yucca baccata) or both (P. edulis vs. Y. baccata). The δD_LCN (leaf cellulose nitrate) and δ¹⁸O_LC (leaf cellulose) values of P. edulis decreased with elevation. Stem water δD values either increased (in spring) or did not change with elevation (in summer). Needle water δD values usually decreased with elevation and differed greatly with leaf age. These results suggest that δ cellulose values of P. edulis record the effects of climate on the isotopic composition of leaf water but not climate effects on meteoric water. In contrast to P. edulis, δD_LCN values of Y. glauca increased with elevation. The δ¹⁸O_LC values of Y. glauca also increased with elevation but less significantly and only on south-facing slopes. The δ cellulose values in both P. edulis and Y. glauca were most significantly related to changes in temperature, although temperature and precipitation were negatively correlated in the study area. Where all three species co-occurred, their δD_LCN values differed but their δ¹⁸O_LC values were the same. The disparity in δD_LCN between Y. baccata and the other species corresponds to differences in biochemical fractionations associated with photosynthetic pathway. Biochemical fractionations may also contribute to differences between the two C₃ species. Knowledge of factors affecting responses of individual plant species to environment may be required to infer climate from δD_LCN and δ¹⁸O_LC.  相似文献   

Multiphase flow dynamics during CO2 disposal into saline aquifers   总被引：2，自引：0，他引：2  

Karsten Pruess  Julio García 《Environmental Geology》2002,42(2-3):282-295

  相似文献   

Neoproterozoic zirconium-depleted boninite and tholeiitic series rocks from Adola, southern Ethiopia   总被引：1，自引：0，他引：1  

Begashaw Wolde  Zemene Asres  Zerihun Desta  Julio J. Gonzalez 《Precambrian Research》1996,80(3-4)

In Adola, southern Ethiopia, mafic and ultramafic igneous rocks occur in narrow, 4–10 km wide, north-south-trending belts bounded by high-grade gneisses and migmatites. The mafic/ultramafic rocks are complexly deformed and metamorphosed in greenschist to lower amphibolite facies and are thought to be tectonically dismembered parts of an ophiolite complex. Preliminary geochemical and geochronological data highlight that the high-grade rocks in southern Ethiopia and northern Kenya include a significant portion of juvenile rocks that were accreted at the same time as ophiolitic rocks at 885-765 Ma. This is also the time of widespread oceanic magmatism and closure in the Arabian-Nubian Shield to the north.The Adola mafic rocks were previously described as island arc tholeiites and mid-ocean ridge basalts (MORB). New chemical analyses on the Megado belt rocks reveal the presence of boninites and related dacites interspersed with tholeiitic rocks. The Adola boninites are similar to the Cambrian boninites in western Tasmania in having relatively low Zr/Sm (≤32). Boninites with similarly low ratios have not been reported from elsewhere.The Adola tholeiites have high Ti/Zr (150–300). Mixing between tholeiite and boninite magmas may have resulted in elevated Ti/Zr (80–126) in some Adola boninites. Otherwise, Ti/Zr in the latter is low (20–40). Low Ti/Zr is characteristic of Tertiary boninites in the west Pacific. The fact that both Ti/Eu and Zr/Sm increase from the Adola and Tasmania type to the Tertiary boninites at constant Ti/Zr suggests that Ti might be an element that is also metasomatically added to the source of boninites and raises doubts about the role of amphibole in boninite petrogenesis.  相似文献   

End-states of short-period comets and their role in maintaining the zodiacal dust cloud     

Julio A. Fernández 《Earth, Moon, and Planets》1988,41(2):155-161

Physical lifetimes and end-states of short-period comets are analysed in connection with the problem of the maintainance of the zodiacal dust cloud. In particular, the problem of the comet-asteroid relationship is addressed. Recent studies of the physical properties of Apollo-Amor asteroids and short-period comets (e.g., Hartmann et al., 1987) show significant differences between them, suggesting that they are distinct classes of objects. A few percent of the active SP comets might become asteroidal-like bodies in comet-type orbits due to the buildup of dust mantles. The remainder probably disintegrate as they consume their volatile content so their debris can only be observed as fireballs when they meet the Earth. Unobservable faint SP comets — i.e., comets so small (m 10¹⁴ g) that quickly disintegrate before being detected, might be a complementary source of dust material. They might be completely sublimated even at rather large heliocentric distances (r - 3 AU). Yet the released dust grains can reach the vicinity of the Sun by Poynting-Robertson drag. The mass associated with unobservable SP comets with perihelion distances q 3 AU might be comparable to that computed for the sample of observed SP co-mets with q 1.5 AU. It is concluded that SP comets (from the large to the unobservable small ones) may supply an average of several tons/sec of meteoric matter to the zodiacal dust cloud.  相似文献   

Pelagic petroleum pollution off the south-west coast of Puerto Rico     

Jorge E. Corredor  Julio Morell  Astrid Méndez 《Marine pollution bulletin》1983,14(5):166-168

Petroleum pollution in the form of floating tar balls and dissolved or dispersed hydrocarbons has been monitored off the south-west coast of Puerto Rico on a weekly basis since November 1980. Tar ball abundance estimates agree well with previously published data for the area. Dissolved/dispersed hydrocarbon concentrations are close to, but below, those found in the Mediterranean Sea and considerably lower than those for more polluted areas. Tar ball abundance is closely related to the intensity of southerly winds. Dissolved/dispersed hydrocarbon concentrations are highest during the fall and coincident with the highest surface water temperatures.  相似文献   

Packrat middens from Canyon de Chelly,northeastern Arizona: Paleoecological and archaeological implications     

Julio L. Betancourt  Owen K. Davis 《Quaternary Research》1984,21(1):56-64

In western North America, pollen data from highland lakes are often used to reconstruct vegetation on the adjacent lowlands. Plant macrofossils and pollen from packrat middens now provide a means to evaluate such reconstructions. On the basis of pollen diagrams from the Chuska Mountains, H. E. Wright, Jr., A. M. Bent, B. S. Hansen, and L. J. Maher, Jr., ((1973), Geological Society of America Bulletin, 84, 1155–1180) arrived at conservative estimates for late Pleistocene depression of highland conifers. In their interpretation, a proposed slight depression of 500 m for lower tree line precluded expansion of Pinus ponderosa into elevations now in desertscrub. Instead, it was suggested that pinyon pine and Artemisia occupied the lowland plateaus. Packrat midden records on either side of the Chuskas fail to verify this model. Early Holocene middens from Chaco Canyon, New Mexico, and a terminal Pleistocene midden from Canyon de Chelly, Arizona, show that blue spruce, limber pine, Douglas fir, dwarf juniper, and Rocky Mountain juniper expanded at least down to 1770 m elevation Neither Colorado pinyon nor ponderosa pine was found as macrofossils in the middens. Artemisia pollen percentages are high in the terminal Pleistocene midden, as they are in the Chuska Mountain pollen sequence, suggesting regional dominance by sagebrush steppe. Of 38 taxa identified, only 3 are shared by middens dated 11,900 and 3120 yr B.P. from Canyon de Chelly, indicating a nearly complete turnover in the flora between the late Pleistocene and late Holocene. Although corn was previously thought to have been introduced to the Colorado plateaus after 2200 yr B.P., the midden dated 3120 yr B.P. contains pollen of corn and other indicators of incipient agriculture.  相似文献   

Model for the Processing and Estimation of Dual Frequency Echo Sounder Observations in Detailed Bathymetries   总被引：1，自引：0，他引：1  

Raúl Pereda García  Felipe Piña García  Julio Manuel De Luis Ruiz  Raúl Husillos Rodríguez 《Marine Geodesy》2016,39(3-4):305-320

The dataset acquired by an echo sounder generally comprises outliers and erroneous measurements which must be automatically processed. The main aim of this research is the development and validation of an algorithm which permits detecting outliers, estimating their real value from data acquired with a multifrequency echo sounder, and verifying the measure according to the desired accuracy. The process considers the nature of the seabed and improves the density and number of lectures without globally compromising the precision, but enhancing it in areas with anomalous measurements. Twenty-nine percent of this type of measurements, which would have been otherwise rejected, have been estimated.  相似文献   

Hazard zoning for volcanic ballistic impacts at El Chichón Volcano (Mexico)     

Miguel A. Alatorre-Ibargüengoitia  Horacio Morales-Iglesias  Silvia G. Ramos-Hernández  Juan Jon-Selvas  Julio M. Jiménez-Aguilar 《Natural Hazards》2016,81(3):1733-1744

  相似文献