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Measured Frequencies (measured + frequency)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

Empirical estimate of fundamental frequencies and damping for Italian buildings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2009
Maria Rosaria Gallipoli
Abstract The aim of this work is to estimate the fundamental translational frequencies and relative damping of a large number of existing buildings, performing ambient vibration measurements. The first part of the work is devoted to the comparison of the results obtained with microtremor measurements with those obtained from earthquake recordings using four different techniques: horizontal-to-vertical spectral ratio, standard spectral ratio, non-parametric damping analysis (NonPaDAn) and half bandwidth method. We recorded local earthquakes on a five floors reinforced concrete building with a pair of accelerometers located on the ground and on top floor, and then collected microtremors at the same location of the accelerometers. The agreement between the results obtained with microtremors and earthquakes has encouraged extending ambient noise measurements to a large number of buildings. We analysed the data with the above-mentioned methods to obtain the two main translational frequencies in orthogonal directions and their relative damping for 80 buildings in the urban areas of Potenza and Senigallia (Italy). The frequencies determined with different techniques are in good agreement. We do not have the same satisfactory results for the estimates of damping: the NonPaDAn provides estimates that are less dispersed and grouped around values that appear to be more realistic. Finally, we have compared the measured frequencies with other experimental results and theoretical models. Our results confirm, as reported by previous authors, that the theoretical period,height relationships overestimate the experimental data. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Crack identification of a planar frame structure based on a synthetic artificial intelligence technique

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2003
Mun-Bo Shim
Abstract It has been established that a crack has an important effect on the dynamic behaviour of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a planar frame structure, a method is presented in this paper which uses a synthetic artificial intelligence technique, i.e. adaptive-network-based fuzzy inference system (ANFIS) solved via a hybrid learning algorithm (the backpropagation gradient descent and the least-squares method) and continuous evolutionary algorithms (CEAs) solving single objective optimization problems with a continuous function and continuous search space efficiently are unified. With ANFIS and CEAs it is possible to formulate the inverse problem. ANFIS is used to obtain the input (the location and depth of a crack),output (the structural eigenfrequencies) relation of the structural system. CEAs are used to identify the crack location and depth by minimizing the difference from the measured frequencies. We have tried this idea on 2D beam structures and the results are promising. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Processing Conditions and Aging Effect on the Morphology of PZT Electrospun Nanofibers, and Dielectric Properties of the Resulting 3,3 PZT/Polymer Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
Ebru Mensur Alkoy
Lead zirconate titanate (PZT) nanofibers are obtained by electrospinning a sol,gel based solution and polyvinyl pyrrolidone (PVP) polymer, and by subsequent sintering of the electrospun precursor fibers. The average diameter of the precursor PZT/PVP green fibers has increased with the aging of the precursor solution along with an increase in the viscosity. Bead-free uniform green PZT/PVP fibers were collected at about an ,230 nm average fiber diameter using a 28 wt% PVP ratio solution with a viscosity of 290 mPa. Shrinkage of 40% was recorded on the fiber diameter after sintering. The X-ray diffraction pattern of the annealed PZT fibers exhibits no preferred orientation and a perovskite phase. Preparation of 3,3 nanocomposites by the infusion of polyvinylester into the nanofiber mat facilitates successful handling of the fragile mats and enables measurements of the dielectric properties. The dielectric constant of the PZT/polyvinylester nanocomposite of about 10% fiber volume fraction was found to be fairly stable and vary from 72 to 62 within the measurement range. The dielectric loss of the composite is below 0.08 at low frequencies and reaches a stable value of 0.04 for most of the measured frequencies. [source]

Theoretical study of the electronic structure and the totally symmetric vibrations of selected CoMoCat carbon nanotubes

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008
Kürti
Abstract In situ Raman spectroelectrochemical studies of CoMo-Cat single-walled carbon nanotubes enriched in (6,5) tubes have been carried out recently. We performed calculations on the density functional level using local density approximation for the electronic and vibrational properties of the most abundant tubes in these samples. The following chiral semiconducting tubes were investigated: (6,4), (7,3), (6,5), (9,1), (8,3) and (7,5). The calculated and the measured frequencies of the RBM and G, modes agree within several wave numbers. The calculated E11, E22 transition energies -after 30% and 20% upscaling, respectively- are comparable with the experimental values. The quenching of the RBM band with p- and n-doping can be interpreted within the rigid band approximation. The validity of the rigid band approximation was shown by calculating the density of states for neutral and charged tubes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]