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41.
A probabilistic damage identification approach for structures with uncertainties under unknown input 总被引:1,自引:0,他引:1
Kun ZhangHui Li Zhongdong DuanS.S. Law 《Mechanical Systems and Signal Processing》2011,25(4):1126-1145
To avoid the false positives of damages in the deterministic identification method induced by uncertainties in measurement noise, a probabilistic method is proposed to identify damages of the structures with uncertainties under unknown input. The proposed probabilistic method is developed from a deterministic simultaneous identification method of structural physical parameters and input based on dynamic response sensitivity. The deterministic simultaneous identification method is first derived. The effect of uncertainties caused by measurement noise on the identified parameters is then investigated. The statistical parameters of the identified structural parameters are calculated. The damage index is derived from the statistical parameters of the physical parameters of intact and damaged structure. The probability of identified damage, defined as the probability of identified structural stiffness smaller than that of intact structure, is further derived using the probability method. A twelve-story building and a nine-bay three-dimensional frame structure are, respectively, analyzed numerically and experimentally using the proposed method. The research results indicate that the probabilistic simultaneous identification method for damage and input can decrease the false positives of damages in contrast with the deterministic method under intensive measurement noise, and it can also achieve an accurate identification for structural unknown input. 相似文献
42.
Covaci A Gerecke AC Law RJ Voorspoels S Kohler M Heeb NV Leslie H Allchin CR De Boer J 《Environmental science & technology》2006,40(12):3679-3688
Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentrations were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shiftfrom the high percentage of the gamma-HBCD stereoisomer in the technical products to a dominance of the alpha-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects. 相似文献
43.
Chien Hwa Chong Chung Lim Law Michael Cloke Luqman Chuah Abdullah Wan Ramli Wan Daud 《Drying Technology》2013,31(10):1286-1293
Sun drying of chempedak (Artocarpus integer) was carried out on different sample sizes to investigate the effects on product quality. Fick's second law model was used to determine the effective diffusivities of sun–dried chempedak slabs based on the drying rate versus moisture content plots. In addition, texture degradation and total color changes were investigated. The texture and color changes of dried chempedak were relatively significant (p < 0.05) compared to fresh chempedak. There was an increase in dried fruit hardness and chewiness but a decrease in springiness and cohesiveness during drying. 相似文献
44.
Haisheng Di Xin He Peng Zhang Zhi Wang Margaret S. Wooldridge Chung K. Law Cuiping Wang Shijin Shuai Jianxin Wang 《Combustion and Flame》2014
Experimental and numerical studies have been performed on the thermal and chemical effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane. Experiments were conducted using a recently developed rapid compression machine in the temperature range of 600–850 K. Three buffer gases were studied including nitrogen (N2), argon (Ar), and a mixture of Ar and carbon dioxide (CO2) at a mole ratio of 65.1%/34.9%. Iso-octane was studied at 20 bar, ? = 1, and a dilution level of buffer gas to O2 of 3.76:1 (mole ratio). n-Heptane was studied at 9 bar, ? = 1, and a dilution level of buffer gas to O2 of 5.63:1 (mole ratio). For experiments where two-stage ignition was observed, the buffer gas composition had no impact on the first-stage ignition time but, as expected, it caused differences in the total heat release, pressure and temperature rise after the first-stage ignition. As a consequence, significant differences were observed for the total ignition delay time as a function of the buffer gas composition, with up to 40% and 42.5% faster total ignition time for iso-octane and n-heptane, respectively, by using Ar instead of N2. The chemical effects of the buffer gas composition were studied experimentally by comparing the results of the N2 and Ar/CO2 (65.1%/34.9%) mixtures, recognizing that while the Ar/CO2 mixture has the same heat capacity as N2, its predicted combined third-body collision efficiency is about 76% higher than N2. The experimental results showed negligible chemical effects on the first-stage and total ignition delay times. Numerical simulations were carried out over a wider range of temperatures for pure N2, Ar, and CO2 as buffer gases. Results showed that thermal effects are very pronounced and dominated at the negative temperature coefficient and two-stage ignition conditions, which is consistent with the experimental results and previous studies in the literature. However, the simulation results also showed at temperatures higher than 850 K, the chemical effects of CO2 became more important than the thermal effects. 相似文献
45.
1 INTRODUCTIONTheγ TiAlbasedintermetallicalloyshavere centlyreceivedmoreandmoreattentionbecauseoftheirpotentialasadvancedhigh temperaturestruc turalmaterials.MicrostructurehasbeenfoundtohaveaconsiderableeffectonmechanicalpropertiesofTiAlalloys,whiledupl… 相似文献
46.
The study and use of some types of syntbetic lubricants can be traced back 50 years.1 Within the past twenty years, rapid advances in technology have resulted in syntbetic lubricants that can operate satisfactorily over temperature extremes well beyond the capabilities of conventional petroleum-based oils. Current emphasis is on the ability of some types of synthetic lubricants to allow more efficient system operation, with concomitant energy savings and extended equipment and oil life. Several definitions have been proposed for synthetic lubricants. In this paper, the authors define a synthetic lubricant as a product which consists of base fluids manufactured by chemical synthesis and containing necessary performance additives. Thus the base fluids are tailored, through specific chemical reactions, to meet predetermined physical and chemical quality targets. In this paper, discussion will be limited to (a) a review of the types of chemicals which have been studied for use in synthetic lubricants and (b) selected application data which dramatise some of the advantages gained through use of the synthetic lubricant. 相似文献
47.
An experimental study, supported by computation, was conducted on the coupling of NTC-chemistry and transport in the low-temperature ignition and the associated steady burning in nonpremixed DME/air counterflow. In particular, the presence of low-temperature chemical reactivity was detected nonintrusively by using a photomultiplier tube combined with a filter to capture the chemiluminescence of HCHO, which is a characteristic intermediate species formed in low-temperature chemistry. Furthermore, the ignition temperature was determined through high-sensitivity infrared imaging with proper discrimination of the background signal. Experimental results show that the transport-coupled low-temperature, NTC chemical reactivity is enhanced with smaller strain rate, higher air boundary temperature, and is insensitive to the fuel concentration. These findings agree well with those obtained from computation using detailed chemistry, leading to further identification of the controlling chemistry. 相似文献
48.
49.
Mohamed M Ghanem Lori A Battelli Brandon F Law Vincent Castranova Michael L Kashon Joginder Nath Ann F Hubbs 《Particle and fibre toxicology》2009,6(1):21-12
Background
Many polycyclic aromatic hydrocarbons (PAHs) can cause DNA adducts and initiate carcinogenesis. Mixed exposures to coal dust (CD) and PAHs are common in occupational settings. In the CD and PAH-exposed lung, CD increases apoptosis and causes alveolar type II (AT-II) cell hyperplasia but reduces CYP1A1 induction. Inflammation, but not apoptosis, appears etiologically associated with reduced CYP1A1 induction in this mixed exposure model. Many AT-II cells in the CD-exposed lungs have no detectable CYP1A1 induction after PAH exposure. Although AT-II cells are a small subfraction of lung cells, they are believed to be a potential progenitor cell for some lung cancers. Because CYP1A1 is induced via ligand-mediated nuclear translocation of the aryl hydrocarbon receptor (AhR), we investigated the effect of CD on PAH-induced nuclear translocation of AhR in AT-II cells isolated from in vivo-exposed rats. Rats received CD or vehicle (saline) by intratracheal (IT) instillation. Three days before sacrifice, half of the rats in each group started daily intraperitoneal injections of the PAH, β-naphthoflavone (BNF). 相似文献50.
Law S. Edward Marchant John A. Bailey Adrian G. 《Industry Applications, IEEE Transactions on》1985,(3):685-693
Fluorescent tracer studies experimentally quantified the spatial distribution of droplet mass transfer and charge transfer characterizing three modes of electrostatic pesticide spraying onto barley-weed-soil target arrays. Droplet charging in the 1.5-4.5 mC/kg range provided significant deposition increases on all plant surfaces while beneficially reducing residues on underlying soil. With the intense space-charge spray clouds utilized (e.g., 10 μC/m3 ), externally applied driving fields as great as 37 kV/m provided no significant deposition increases but instead exacerbated gaseous charge exchange between the spray cloud and the target via undesirable leaf-tip coronas. Nonuniformity characterized deposition of both uncharged and charged sprays throughout the target array, with no improvement provided by spray-entrainment air velocities as great as 2 m/s. Results will guide prototype design by establishing the relative importance of the space charge, the applied field, and the aerodynamic force components for selectively targeting specific sites within living-plant arrays. 相似文献