Dynamic response and optimal design of structures with large mass ratio TMD     

Maurizio De Angelis  Salvatore Perno  Anna Reggio 《地震工程与结构动力学》2012,41(1):41-60

This paper investigates the dynamic behavior and the seismic effectiveness of a non‐conventional Tuned Mass Damper (TMD) with large mass ratio. Compared with conventional TMD, the device mass is increased up to be comparable with the mass of the structure to be protected, aiming at a better control performance. In order to avoid the introduction of an excessive additional weight, masses already present on the structure are converted into tuned masses, retaining structural or architectural functions beyond the mere control function. A reduced order model is introduced for design purposes and the optimal design of a large mass ratio TMD for seismic applications is then formulated. The design method is specifically developed to implement High‐Damping Rubber Bearings (HDRB) to connect the device mass to the main structure, taking advantage of combining stiffness and noticeable damping characteristics. Ground acceleration is modeled as a Gaussian random process with white noise power spectral density. A numerical searching technique is used to obtain the optimal design parameter, the frequency ratio alpha, which minimizes the root‐mean‐square displacement response of the main structure. The study finally comprises shaking table tests on a 1:5 scale model under a wide selection of accelerograms, both artificial and natural, to assess the seismic effectiveness of the proposed large mass ratio TMD. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Evaluation of remotely‐sensed DEMs and modification based on plausibility rules and initial sediment budgets of an artificially‐created catchment     

Anna Schneider  Horst H. Gerke  Thomas Maurer  Stefan Seifert  Rossen Nenov  Reinhard F. Hüttl 《地球表面变化过程与地形》2012,37(7):708-725

To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely‐sensed DEMs for an improved quantification of initial sediment mass changes in an artificially‐created catchment. DEMs were constructed from photogrammetry‐based, airborne (ALS) and ground‐based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three‐dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region‐by‐region for rill, interrill and alluvial areas, based on logical and hydro‐geomorphological principles. Additional DEMs were constructed by combining multi‐source, modified data. Models were evaluated by comparison with d‐GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry‐based DEMs were suited to quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited to rill areas, while ALS DEMs performed best in vegetation‐covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry‐ and TLS‐based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro‐geomorphic surface structures can be better represented by applying region‐specific modifications. Photogrammetry‐based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro‐geomorphic evolution. Results of the critical comparative evaluation of remotely‐sensed elevation data can help to better interpret DEM‐based quantifications of earth‐surface processes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Effects of pollen leaching and microbial degradation on organic carbon and nutrient availability in lake water     

Stefan?R?sel  Anna?Rych?a  Christian?Wurzbacher  Hans-Peter?GrossartEmail author 《Aquatic Sciences - Research Across Boundaries》2012,74(1):87-99

Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus and total dissolved nitrogen (up to 0.04 and 1.5 mg L⁻¹, respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for ≥80, ≥40, ≥50% for organic C, N and P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of temperate lakes. This requires further attention in aquatic ecology.  相似文献   

Changes in vertical distribution and aggregative behaviour in response to population density for larval sea urchins (Strongylocentrotus droebachiensis) and sea stars (Asterias rubens)     

Amy Roy  Anna Metaxas  Rémi M. Daigle 《Marine Ecology》2012,33(2):194-204

We examined the effects of the presence of larval conspecifics on larval vertical distribution of four‐arm and six‐arm plutei of Strongylocentrotus droebachiensis and bipinnaria of Asterias rubens, in laboratory experiments, by manipulating population density. Larvae were introduced to experimental columns (10 × 10 × 30 cm) at one of two or three population densities (S. droebachiensis: 0.1 and 10 larvae·ml^?1; A. rubens: 0.1, 1 and 10 larvae·ml^?1). Subsequent changes in vertical distribution were determined from images of the larvae in the columns illuminated by a 532‐nm laser and captured by a high‐resolution camera. Larvae of both species were found higher in the water column in the high than in the low and intermediate population densities. The relationship between vertical swimming velocity and nearest neighbour distance (NND) was measured for four‐arm plutei of S. droebachiensis, and used to determine a range in distances among individuals that may affect potential interactions. The variation in swimming velocity decreased with increasing proximity below a threshold distance among individuals of 10 mm, which was greater than the estimated distance in the high population density. We suggest that the increased larval aggregation near the water surface under high population density is the result of a behavioural response to conspecifics.  相似文献   

Genetic variability of the blue and red shrimp Aristeus antennatus in the Western Mediterranean Sea inferred by DNA microsatellite loci     

Rita Cannas  Flavio Sacco  Maria Cristina Follesa  Andrea Sabatini  Marco Arculeo  Sabrina Lo Brutto  Teresa Maggio  Anna Maria Deiana  Angelo Cau 《Marine Ecology》2012,33(3):350-363

Genetic variation at eight microsatellite loci was studied in nine populations of the blue and red shrimp Aristeus antennatus to investigate whether distinct stocks are present in the Western Mediterranean Sea. A high level of gene flow and no evidence of genetic partitioning were discovered. No significant variation was found (F_ST = 0.00673, P-value = 0.067) even when shrimps from exploited and those from deep-water unexploited grounds were compared. No evidence of reduction or expansion of population size in the recent past was found, as indicated by the bottleneck and interlocus g-tests. Our results are consistent with previous studies using mitochondrial gene methods and allozymes, indicating that, for this species, extensive pelagic larval dispersal and adult migration are probably responsible for the genetic homogeneity observed. In particular, due to a different bathymetric distribution of males and females, reported to be associated with different water masses and hence with possible differential dispersal capacity between sexes, the hypothesis of sex-biased dispersal was tested. Mean values of corrected assignment indices and mean relatedness values were higher for males, suggesting that females are the more widely dispersing sex. Molecular assessment of A. antennatus from the Western Mediterranean provides data of biological and evolutionary interest for the successful management of such a highly valuable fishery resource.  相似文献   

Detection of field significant long-term monotonic trends in spring yields     

Ondrej Ledvinka  Anna Lamacova 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(5):1463-1484

Trend analysis is a frequently used tool in hydrology and climatology for the identification of long-term changes. However, studies are usually only oriented on local trends. This paper rather focuses on the spatial application of trend analysis in groundwater data. For this purpose, a modification of the Mann-Kendall test was developed, based on the trend-free pre-whitening approach. This method was successfully tested on 157 series of yields from headwater springs collected in Czechia during the 1971–2007 period. The analysis was done separately for year, each season and each month. Field significant trends in spring yields were identified in hydrogeological regions. The results showed that the field significant trends are outnumbered when cross-correlation is not taken into account. In the case of annual series, 4 of 18 hydrogeological regions investigated showed a significant decreasing trend after corrections for cross-correlation, compared to 12 regions with field significant trend when not considering cross-correlation.  相似文献   

Wave climate of the Hellenic Seas obtained from a wave hindcast for the period 1960–2001     

Anna Zacharioudaki  Gerasimos Korres  Leonidas Perivoliotis 《Ocean Dynamics》2015,65(6):795-816

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Detection of the Long Period Long Duration (LPLD) Events in Time-and Frequency-Domain     

Anna Kwietniak 《Acta Geophysica》2015,63(1):201-213

Long Period Long Duration (LPLD) signals are unusual seismic events that can be observed during hydraulic fracturing. These events are very similar in appearance to tectonic tremors sequences, which were first observed in subduction zones. Their nature is not well known. LPLD might be related to the productivity of the reservoir. Different methods of the LPLD events’ detection recorded during hydraulic fracturing are presented. The author applied two methods for LPLD detection–Butterworth filtering and Continuous Wavelet Transform (CWT). Additionally, a new approach to LPLD events detection–instantaneous seismic attributes–was used, common in a classical seismic interpretation but not in microseismic monitoring.  相似文献   

Overwintering of terrestrial Arctic arthropods: the fauna of Svalbard now and in the future     

María Luisa Ávila-Jiménez  Stephen J. Coulson  Torstein Solhøy  & Anna Sjöblom 《Polar research》2010,29(1):127-137

There are over 500 species of arthropods recorded from Svalbard. These animals overwinter either within the soil or on the ground surface, and have to tolerate an environment where the ground is frozen for over 9 months each year. Three cold-tolerance strategies have been described from Svalbard invertebrates: freeze avoidance, freeze tolerance and desiccation. Once in a cold-tolerant state the animals can be extremely cold tolerant in terms of both minimum exposure temperature and period of exposure. How the overwintering capabilities of these animals will be affected by climate changes during the next 100 years, as predicted by climate models, is not yet known. Four principle factors with an impact on overwintering of the terrestrial arthropod fauna are outlined here: (1) warmer winter temperatures, with an increased frequency of extreme events such as freeze–thaw cycles and surface icing; (2) changes in snow fall and snow lie; (3) pollutant load; and (4) dispersal of invertebrates to Svalbard. Finally, areas where further research is required are highlighted: including the development of controlled multi-season field experiments; effect of freeze–thaw cycles; changes in thickness and distribution of snow lie, with the subsequent effects on duration of the summer period; chill susceptibility of soil arthropods; assessing potential colonizing species and the likelihood of these species becoming established; assessing the effect of gene flow from surrounding populations; interactions between pollution and cold tolerance; anoxia stress; and the genetics of cold tolerance.  相似文献   

Uncertainties in probability of occurrence of strong earthquakes for fault sources in the Central Apennines,Italy   总被引：1，自引：1，他引：0  

Aybige Akinci  David Perkins  Anna Maria Lombardi  Roberto Basili 《Journal of Seismology》2010,14(1):95-117

Using the characteristic earthquake model, we calculate the probability of occurrence of earthquakes M _w > 5.5 for individual fault sources in the Central Apennines for the 30-year period (2007–2037). We show the effect of time-dependent and time-independent occurrence (Brownian passage time (BPT) and Poisson) models together with uncertain slip rates and uncertain maximum magnitudes and, hence, uncertain recurrence times. In order to reduce the large prior geological slip rate uncertainty distribution for most faults, we obtain a posterior slip rate uncertainty distribution using a likelihood function obtained from regional historical seismicity. We assess the uncertainty of maximum magnitude by assuming that the uncertainty in fault width and length are described by a normal distribution with standard deviation equal to ±20% of the mean values. We then estimate the uncertainties of the 30-year probability of occurrence of a characteristic event using a Monte Carlo procedure. Uncertainty on each parameter is represented by the 16th and the 84th percentiles of simulated values. These percentiles bound the range that has a 68% probability of including the real value of the parameter. We do these both for the Poisson case and for the BPT case by varying the aperiodicity parameter (α value) using the values 0.3, 0.5, and 0.7. The Bayesian posterior slip rate uncertainties typically differ by a factor of about 2 from the 16th to the 84th percentile. Occurrence probabilities for the next 30 years at the 84th percentile typically range from 1% to 2% for faults where the Poisson model dominates and from 2% to 21% where one of the BPT models dominates. The uncertainty in occurrence probability under the time-dependent hypothesis is very large, when measured by the ratio of the 84th to the 16th percentile, frequently being as much as two orders of magnitude. On the other hand, when measured by standard deviation, these standard deviations range from 2% to 6% for those faults whose elapsed time since previous event is large, but always 2% or less for faults with relatively recent previous occurrence, because the probability of occurrence is always small.  相似文献