Intelligent technology-based control of motion and vibration using MR dampers

Due to their intrinsically nonlinear characteristics, development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task. In this study, two control strategies are proposed for protecting buildings against dynamic hazards, such as severe earthquakes and strong winds, using one of the most promising semiactive control devices, the magnetorheological (MR) damper. The first control strategy is implemented by introducing an inverse neural network (NN) model of the MR damper. These NN models provide direct estimation of the voltage that is required to produce a target control force calculated from some optimal control algorithms. The major objective of this research is to provide an effective means for implementation of the MR damper with existing control algorithms. The second control strategy involves the design of a fuzzy controller and an adaptation law. The control objective is to minimize the difference between some desirable responses and the response of the combined system by adaptively adjusting the MR damper. The use of the adaptation law eliminates the need to acquire characteristics of the combined system in advance. Because the control strategy based on the combination of the fuzzy controller and the adaptation law doesn’t require a prior knowledge of the combined building-damper system, this approach provides a robust control strategy that can be used to protect nonlinear or uncertain structures subjected to random loads. Supported by: Hong Kong Research Grant Council Competitive Earmarked Research Grant HKUST 6218 / 99E and by the National Science Foundation under grant CMS 99-00234.     

Sedimentary response of Pagham Harbour, southern England to barrier breaching in AD 1910

This paper examines the evolution of Pagham Harbour, southern England following storm-induced breaching of a protective barrier in AD 1910. Stratigraphic studies of sediments collected from intertidal areas show the presence of a distinct stratigraphic horizon in the northeast of Pagham Harbour at ca. 0 to +1.0 m ordnance datum (OD). Radiometric data indicate that this horizon is a ‘reclamation surface’ formed after land claim in AD 1846. Following marine flooding in AD 1910, sediment has accreted relatively rapidly (at a broadly constant rate of between 4 and 8 mm a⁻¹), wave and/or tidal energy have decreased and extensive marshes have developed. An asymptotic reduction in sediment accretion rate through time, as predicted in various theoretical models of salt marsh accretion, is not observed. Over the entire Pagham Harbour area, the period between AD 1948 and AD 1986 has seen an average marsh loss of 0.0087 km² a⁻¹, which is relatively small in comparison with other more exposed sites in the local area. Historically breached sites such as Pagham Harbour are common around European coasts, and these provide important natural laboratories within which the medium-term (decadal to centennial) coastal response to barrier breaching, and to managed-realignment coastal protection schemes, can be assessed.     

大震下被动与智能隔震结构动力可靠度的对比

对被动及智能隔震结构在“大震”条件下的动力可靠度进行探讨。将被动及智能隔震体系均取作弹塑性模型,并用退化Bouc-W en滞变模型描述上部结构的恢复力,用非退化Bouc-W en模型描述隔震层的恢复力。采用虚拟激励法计算结构的随机响应,根据我国抗震规范中“大震不倒”的设防目标,采用各层最大层间位移峰值响应和累积滞变耗能构造双参数的随机疲劳累积损伤指数,作为功能状态指标。假定各层失效相关,用串联系统计算体系动力可靠度。通过数值算例,对比了被动隔震、智能隔震与非隔震体系的条件失效概率,从动力可靠度角度显示了智能隔震体系的减震优势。     

Application of clan member signal method in structural damage detection

It is well known that in most cases, a reference is necessary for structural health diagnosis, and it is very difficult to obtain such a reference for a given structure. In this paper, a clan member signal method (CMSM) is proposed for use in structures consisting of groups (or clans) that have the same geometry, i.e., the same cross section and length, and identical boundary conditions. It is expected that signals measured on any undamaged member in a clan after an event could be used as a reference for any other members in the clan. To verify the applicability of the proposed method, a steel truss model is tested and the results show that the CMSM is very effective in detecting local damage in structures composed of identical slender members.     

The agricultural revolution as environmental catastrophe: Implications for health and lifestyle in the Holocene

One of the most fundamental developments in the history of our species—and one having among the most profound impacts on landscapes and the people occupying them—was the domestication of plants and animals. In addition to altering landscapes around the globe from the terminal Pleistocene and early Holocene, the shift from foraging to farming resulted in negative and multiple consequences for human health. Study of human skeletal remains from archaeological contexts shows that the introduction of grains and other cultigens and the increase in their dietary focus resulted in a decline in health and alterations in activity and lifestyle. Although agriculture provided the economic basis for the rise of states and development of civilizations, the change in diet and acquisition of food resulted in a decline in quality of life for most human populations in the last 10,000 years.     

An Inconvenient Truth: blurring the lines between science and science fiction

Al Gore’s movie An Inconvenient Truth gives a variety of unusually biased interpretations of the state of climate science and global warming theory. These cover a wide range of natural events and processes which could potentially be impacted by global warming, but which the movie misrepresents as clear examples of the human influence on climate. A few examples include the mixing up of cause and effect in his graphical portrayal of temperature and carbon dioxide variations over hundreds of thousands of years; the repeated depiction of ice calving from glaciers as a sign of global warming; the implication that Hurricane Katrina was the fault of humans; and the particularly extreme view that the Greenland ice sheet will melt, flooding coastal cities worldwide. Ultimately, all of these are related to the widespread perception that scientists have uniquely tied global warming to anthropogenic greenhouse gas emissions. The real inconvenient truth is that science has no idea how much of recent warming is natural versus the result of human activities.     

Sulfur volcanism on Io

In February 2003, March 2003 and January 2004 Pele plume transmission spectra were obtained during Jupiter transit with Hubble's Space Telescope Imaging Spectrograph (STIS), using the 0.1″ wide slit and the G230LB grating. The STIS spectra covered the 2100-3100 Å wavelength regions and extended spatially along Io's limb encompassing the region directly above and northward of the vent of the Pele volcano. The S₂ and SO₂ absorption signatures evident in these data indicate that the gas signature at Pele was temporally variable, and that an S₂ absorption signature was present ∼12° from the Pele vent near 6±5 S and 264±15 W, suggesting the presence of another S₂ bearing plume on Io. Contemporaneous with the spectral data, UV and visible-wavelength images of the plume were obtained in reflected sunlight with the Advanced Camera for Surveys (ACS) prior to Jupiter transit. The dust scattering recorded in these data provide an additional qualitative measure of plume activity on Io, indicating that the degree of dust scattering over Pele varied as a function of the date of observation, and that there were several other dust bearing plumes active during the observations. We present constraints on the composition and variability of the gas abundances of the Pele plume as well as the plumes detected by ACS and recorded within the STIS data, as a function of time.