			Home About us Contact

Factor Q (factor + q)

Distribution by Scientific Domains

Engineering	75%

Selected Abstracts

AVO investigations of shallow marine sediments

GEOPHYSICAL PROSPECTING, Issue 2 2001
M. Riedel
Amplitude-variation-with-offset (AVO) analysis is based on the Zoeppritz equations, which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence. High-frequency (up to 700 Hz) AVO studies, presented here, have been used to determine the physical properties of sediments in a shallow marine environment (20 m water depth). The properties that can be constrained are P- and S-wave velocities, bulk density and acoustic attenuation. The use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections. In the past, marine sediments have been modelled as elastic materials. However, viscoelastic models which include absorption are more realistic. At angles of incidence greater than 40°, AVO functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence. The influence of S-wave velocity on the reflection coefficient is small (especially for low S-wave velocities encountered at the sea-floor). Thus, it is difficult to extract the S-wave parameter from AVO trends. On the other hand, P-wave velocity and density show a considerably stronger effect. Attenuation (described by the quality factor Q) influences the reflection coefficient but could not be determined uniquely from the AVO functions. In order to measure the reflection coefficient in a seismogram, the amplitudes of the direct wave and the sea-floor reflection in a common-midpoint (CMP) gather are determined and corrected for spherical divergence as well as source and streamer directivity. At CMP locations showing the different AVO characteristics of a mud and a boulder clay, the sediment physical properties are determined by using a sequential-quadratic-programming (SQP) inversion technique. The inverted sediment physical properties for the mud are: P-wave velocity ,=1450±25 m/s, S-wave velocity ,=90±35 m/s, density ,=1220±45 kg/m3, quality factor for P-wave QP=15±200, quality factor for S-wave QS=10±30. The inverted sediment physical properties for the boulder clay are: ,=1620±45 m/s,,=360±200 m/s,,=1380±85 kg/m3,QP=790±660,QS=25±10. [source]

Scalable distributed-capacitance model for silicon on-chip spiral inductors

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2006
Fengyi Huang
Abstract We present physics-based modeling for silicon on-chip spiral inductors, taking into account the coupling capacitance between metal spirals. The coupling capacitance Cp is calculated using a distributed-capacitance model based on finite-element analysis. As demonstrated for a series of inductors with the number of turns ranging from 2.5 to 6.5 fabricated in a 0.18-,m CMOS technology, the current model provides simulation results for the quality factor Q, the S -parameter, and the self-resonance frequency fSR that are in good agreement with the measurements without any fitting parameters. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1423,1427, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21642 [source]

Seismic design of RC structures: A critical assessment in the framework of multi-objective optimization

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2007
Nikos D. Lagaros
Abstract The assessment of seismic design codes has been the subject of intensive research work in an effort to reveal weak points that originated from the limitations in predicting with acceptable precision the response of the structures under moderate or severe earthquakes. The objective of this work is to evaluate the European seismic design code, i.e. the Eurocode 8 (EC8), when used for the design of 3D reinforced concrete buildings, versus a performance-based design (PBD) procedure, in the framework of a multi-objective optimization concept. The initial construction cost and the maximum interstorey drift for the 10/50 hazard level are the two objectives considered for the formulation of the multi-objective optimization problem. The solution of such optimization problems is represented by the Pareto front curve which is the geometric locus of all Pareto optimum solutions. Limit-state fragility curves for selected designs, taken from the Pareto front curves of the EC8 and PBD formulations, are developed for assessing the two seismic design procedures. Through this comparison it was found that a linear analysis in conjunction with the behaviour factor q of EC8 cannot capture the nonlinear behaviour of an RC structure. Consequently the corrected EC8 Pareto front curve, using the nonlinear static procedure, differs significantly with regard to the corresponding Pareto front obtained according to EC8. Furthermore, similar designs, with respect to the initial construction cost, obtained through the EC8 and PBD formulations were found to exhibit different maximum interstorey drift and limit-state fragility curves. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Seismic performance and new design procedure for chevron-braced frames

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2006
Edoardo M. Marino
Abstract The paper is concerned with the seismic design of steel-braced frames in which the braces are configured in a chevron pattern. According to EuroCode 8 (EC8), the behaviour factor q, which allows for the trade-off between the strength and ductility, is set at 2.5 for chevron-braced frames, while 6.5 is assigned for most ductile steel moment-resisting frames. Strength deterioration in post-buckling regime varies with the brace's slenderness, but EC8 adopts a unique q value irrespective of the brace slenderness. The study focuses on reevaluation of the q value adequate for the seismic design of chevron-braced frames. The present EC8 method for the calculation of brace strength supplies significantly different elastic stiffnesses and actual strengths for different values of brace slenderness. A new method to estimate the strength of a chevron brace pair is proposed, in which the yield strength (for the brace in tension) and the post-buckling strength (for the brace in compression) are considered. The new method ensures an identical elastic stiffness and a similar strength regardless of the brace slenderness. The advantage of the proposed method over the conventional EC8 method is demonstrated for the capacity of the proposed method to control the maximum inter-storey drift. The q values adequate for the chevron-braced frames are examined in reference to the maximum inter-storey drifts sustained by most ductile moment-resisting frames. When the proposed method is employed for strength calculation, the q value of 3.5 is found to be reasonable. It is notable that the proposed method does not require larger cross-sections for the braces compared to the cross-sections required for the present EC8 method. Copyright © 2005 John Wiley & Sons, Ltd. [source]