Journal Article•
Mathematical Analysis of Random Noise-Conclusion
About: This article is published in Bell System Technical Journal.The article was published on 1945-01-01 and is currently open access. It has received 807 citations till now.
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01 Jan 2019
TL;DR: In this article, a review of the studies on wind actions and effects on structures carried out between the late nineteenth and the mid-twentieth centuries is presented, with a focus on the development associated with the evolution and failure of suspension bridges, as well as with the new issue about the behaviour of towers and skyscrapers in the wind.
Abstract: This chapter deals with the studies on wind actions and effects on structures carried out between the late nineteenth and the mid-twentieth centuries. It starts speaking of the developments associated with the evolution and failure of suspension bridges, as well as with the new issue about the behaviour of towers and skyscrapers in the wind. It then passes to examine the renewed culture spanning the whole range of structures that came to maturity in this period; it gained ground through state of the arts and textbooks representing milestones of a discipline that is herein organised along four conceptually sequential topics: design wind speed, building aerodynamics, dynamic response to turbulent wind and aeroelastic phenomena. The presentation of the design wind speed addresses the mean and peak profiles, the time–space structure of turbulence and their probability of occurrence. Building aerodynamics is illustrated with special regard to the growing use and potential of wind tunnel facilities. The dynamic response to the turbulent wind is examined with reference to the transition from deterministic to random dynamics. Aeroelastic phenomena are discussed mainly with regard to vortex shedding, galloping and flutter.
22 citations
TL;DR: Mic microwave measurements for the density and spatial correlation of current critical points in an open billiard system and new and previous predictions of the random-wave model (RWM) are presented and an asymptotic expression for the vortex-saddle and saddle-s saddle correlation functions based on the RWM is derived.
Abstract: We present microwave measurements for the density and spatial correlation of current critical points in an open billiard system and compare them with new and previous predictions of the random-wave model (RWM). In particular, due to an improvement of the experimental setup, we determine experimentally the spatial correlation of saddle points of the current field. An asymptotic expression for the vortex-saddle and saddle-saddle correlation functions based on the RWM is derived, with experiment and theory agreeing well. We also derive an expression for the density of saddle points in the presence of a straight boundary with general mixed boundary conditions in the RWM and compare with experimental measurements of the vortex and saddle density in the vicinity of a straight wall satisfying Dirichlet conditions.
21 citations
TL;DR: In this article, the intensity scintillation index on a two-way (radar) path, in terms of the one-way index and the correlation between scintillations produced on the uplink and downlink, was developed.
Abstract: We develop an expression herein for the intensity scintillation index on a two-way (radar) path, in terms of the one-way index and the correlation between scintillations produced on the uplink and downlink. The expression is appropriate for monostatic (fully correlated) and bistatic (totally or partially uncorrelated, or anticorrelated) paths whose links are statistically similar and obey Nakagami m statistics. A companion expression for the mean apparent radar cross section (RCS) in the presence of scintillation describes enhancement on monostatic paths and energy-conserving depletion of mean apparent RCS on small-angle bistatic paths. The companion expression, which does not depend upon Nakagami m statistics nor require statistical similarity, is consistent with more detailed calculations by previous authors. Special cases of both expressions are consistent with recent monostatic measurements.
21 citations
TL;DR: In this article, the authors investigated the effects of different PDFs of "arrival times" on the far-field source spectrum of the specific barrier model, where the seismic moment is distributed in a deterministic manner on a rectangular fault plane on the basis of moment and area constraints.
Abstract: The specific barrier model (SBM) is a particular case of a composite earthquake source model where the seismic moment is distributed in a deterministic manner on a rectangular fault plane on the basis of moment and area constraints. It is assumed that the fault surface is composed of an aggregate of subevents of equal diameter, the ‘barrier interval’. Furthermore, the subevents are assumed to rupture randomly and statistically independent of one another as the rupture front sweeps the fault plane. In the formulation of the far-field source spectrum of the SBM the ‘arrival time’ of the seismic radiation emitted by each subevent is specified via a probability density function (PDF). In the SBM the subevents are assumed to be of equal sizes (an assumption relaxed in a companion paper, referred to as Part I) and the PDF of ‘arrival times’ is assumed to be uniform. In this study we investigate the effects of different PDFs of ‘arrival times’ on the far-field source spectrum of the SBM. Different PDFs of ‘arrival times’ affect the source spectra primarily at the intermediate frequency range (between the first and second corner frequencies). Such effects become more pronounced as the earthquake magnitude increases. The far-field spectrum of seismic energy observed/recorded at a site depends on the location of the site relative to the causative fault plane, the location of rupture initiation (hypocenter) and the onset times of the rupturing subevents. All the above factors are effectively taken into account by the ‘isochrons’, which vary with source-site geometry. We investigate the selection of the appropriate PDF of seismic energy arrival times at a given site by computing isochrons for a grid of stations surrounding the earthquake fault, represented by the SBM. We show that only for stations located in a direction normal to the fault plane is the assumption of uniform PDF of ‘arrival times’ valid. At other sites non-uniform PDFs of ‘arrival times’ are observed. We identify and categorize the prevalent types of PDFs by directivity (forward vs. backward vs. neutral) and source-site distance (near-fault vs. far-field), show examples in which we group the stations accordingly. We investigate the effects of the different PDF-groups on the SBM source spectrum. Selection of the appropriate PDF for a given source-site configuration when simulating strong ground motions using the SBM in the context of the stochastic method is expected to yield more self-consistent, and physically realistic simulations.
21 citations
TL;DR: In this paper, the authors investigated the response of a jacket supporting a 5MW OWT in intermediate water depths of 70m, under the influence of hydrodynamic and aerodynamic loading.
21 citations