Propagation In Urban Areas Research Articles

Flash flood flow experiment in a simplified urban district

This paper describes the experiments carried out on the flooding of an urban district model for the purposes of mathematical model testing and validation. A model urban district made up of concrete blocks has been placed in an instrumented physical model of a short reach of the Alpine Toce River to simulate the flooding of a populated area. Water depth history at certain locations has been recorded for several configurations of the model city, the surrounding terrain and the intensity of the flooding conditions. The urban district appears to the flood as an obstruction leading to the formation of a strong hydraulic jump in front of the buildings. When the flood wave enters the city a complex flow pattern is established made up of oblique waves and reflections. The measurements can be readily used for validation of mathematical models of flood propagation in urban areas.

Numerical solution to a two-dimensional hypersingular integral equation and sound propagation in urban areas

A mathematical model of sound propagation from a noise source in urban areas is constructed. The exterior Neumann problem for the scalar Helmholtz equation is reduced to a system of hypersingular integral equations. A numerical method for solving the system of integral equations is described. The convergence of the quadrature formulas underlying the numerical method is estimated. Numerical results are presented for particular applications.

Mitigation of urban flooding: A simplified approach for distributed stormwater management practices selection and planning

The urbanization process and the hydraulic insufficiency of drainage systems are two of the most common causes of urban flooding. In some technical regulations, distributed stormwater management practices (DSMPs) are regarded as a solution for urban flooding problems. They can prevent the formation of runoff, dispose of it locally, or dampen its peak before it reaches the drainage system. Due to their diffuse localization and the wide number of available solutions, the evaluation of their efficiency in terms of flood reduction is very difficult. The methodology proposed in the present paper relies on the concept that the mitigation effects of DSMPs can be expressed as a function of the changes of the hydrological parameters of a catchment. Once the relation between a DSMP and the equivalent hydrological parameter is established, the efficiency of DSMPs can be evaluated using mathematical models simulating the runoff formation and propagation in urban areas and applying methodologies similar to parameter sensitivity analysis and model uncertainty propagation. Studying the effect of parameter variation on model output, it is possible to analyse quickly several different stormwater management solutions and to identify the best distribution of measures in order to achieve a defined mitigation task. The simplified procedure has been compared with a more detailed approach obtained by fully integrate DSMPs in the drainage system hydrodynamic model. The procedure has been applied to the real case study of Mondello catchment in Palermo (Italy), and the analysis of the results allows the identification of some guidelines for the mitigation plan preparation.

Ray propagation in a random lattice: a maximum entropy, anomalous diffusion Process

The typical model for diffusion in disordered systems is that of a random walk that proceeds in discrete steps over a random lattice, where not all the nearest sites can be reached at each step. We study the related problem of ray propagation in percolating lattices, and observe that it follows an anomalous diffusion process, whose appropriate metric is the "Manhattan" distance defined by the lattice geometry. The proposed solution is the one that exhibits the maximum Shannon's entropy, among all propagation processes with appropriate moment constraints imposed by the geometry of the lattice. Ray propagation in percolating lattices has been recently proposed as a model for urban area propagation of radio waves. We discuss implications of our results in this scenario.

Sound field modeling in a street canyon with partially diffusely reflecting boundaries by the transport theory

The transport theory, applied to the concept of sound particles, seems to be well adapted to predict the sound propagation in urban areas, including most complex effects, like diffuse scattering by building facades, atmospheric attenuation, scattering by urban objects in streets, etc. In this paper, the transport theory is then applied to the sound field modeling in an empty street canyon with partially diffusely building facades. In this case, the temporal and spatial distribution of sound energy in a street is the solution of a transport equation, with mixed specular-diffuse boundary conditions. Using an asymptotic approach, the transport equation may be reduced to a diffusion equation for the sound energy, where the diffusion coefficient depends only on the building facades properties. Comparisons with experiments show that the diffusion model gives consistent results with experimental data, both for the sound attenuation level and the reverberation time.

Mobile communication systems

From the Publisher: Presents the fundamental aspects of mobile communications systems. Covers the radio communications channel, its wide-band and narrow-band characterization, and its utilization in mobile and cellular communications systems. Both analogue and digital systems are considered, with emphasis on the latter. Discusses the propagation of signals (including propagation in urban areas), the interference created by the terrain, digital techniques associated with two-way, speech-based communication systems, the TACS cellular system, and digital techniques for high capacity cellular systems. Illustrated.

Identification of propagation path from low antenna height base station in urban area

AbstractThe delay spread characteristics in low antenna height propagation in urban areas are difficult to accurately estimate by statistical methods that are highly dependent on the location. To understand how the road system affects the propagation characteristics, the propagation mechanism was analyzed. In practice, the identification of the propagation paths has been attempted by measuring the direction of arrived waves and the delay propagation time (propagation path length) at line‐of‐sight and non‐line‐of‐sight locations. The results clearly showed that many arrived waves are propagated by geometric optical reflections by the walls of buildings, diffractions at the corners of intersections, and their combinations. Furthermore, the calculated results and measurements were compared based on geometric optical methods and wedge diffraction theory to demonstrate the usefulness of geometric optical computational methods. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 41–51, 2001

A scale model experiment for the study of sound propagation in urban areas

A 1:50 scale model experiment for the study of sound propagation in streets is developed. Special interest is focused on the realization of the scale model in order to reproduce fundamental physical phenomena in streets such as multiple reflections and diffuse-scattering by façade irregularities. Acoustic measurements in the model are achieved using a spark discharge sound source with high level, very good reproducibility and broad band spectra. Digital processing of the measured signals in the scale model are especially developed, first to compensate the excess of atmospheric attenuation in the scale model in relation to the atmospheric attenuation in the full scale model, then, to extend the sound decay of the impulse responses beyond the noise level. The sound attenuation and the reverberation measured in the scale model are compared with real measurements in a street. The validity range of the model experiment is then discussed.

OPTIMIZATION OF TRANSPORTATION NETWORKS DURING URBAN FLOODING1

ABSTRACT: In this paper a numerical model for flood propagation in urban areas is proposed. It has been applied to evaluate flooding hydraulic characteristics in terms of potential flood elevations, depths, and inundated areas. Furthermore, the algorithm efficiency and the consequent reduced computation time allow the use of the hydraulic model as a part of a more complex system for civil protection actions, planning, and management. During flood events, the transportation network plays a main role both in rescuing people when they are more vulnerable and in moving people and materials from and toward affected areas. The reduced efficiency of this transportation network is evaluated based on a least‐flood‐risk path‐finding algorithm. The results of a case study concerning the northern part of the city of Rome, show that the numerical model for unsteady flow in open channel networks achieves the proposed aims. It has proven to be able to describe the flood hydraulic characteristics and to be suitable for real‐time flood emergency management in urban areas.

An object oriented approach to lattice gas modeling

We present a parallel library which can be used for any lattice gas (LG) application. A highly reusable implementation, as well as a general parallelization scheme, based on a graph partitioning technique are developed. We show that the performance we obtain with our approach compares favorably with the plain, classical implementation of LG models on regular domains and can be even better for irregular domains. We propose a theoretical expression for the execution time and we validate our analysis in the case of a specific application, namely wave propagation in urban areas.

A new MF and HF ground-wave model for urban areas

Following discussions (Luo Lichun 1997) on the propagation and regularities of HF ground waves in urban areas in China, and processing the HF experimental data obtained from 1993 through 1997 and MF data obtained in 1995 and 1997 in Beijing, a new model for MF and HF ground-wave propagation in urban areas is proposed in this paper. The key novelty in the proposed model is the inclusion of three building-complex parameters, r/sub b/, r/sub s/ and r/sub e/, and a new height-gain factor, G/sub h/. A qualitative derivation of these is offered. The method of selecting these building parameters is discussed. Some HF and MF ground-wave propagation losses, which occur under different conditions of the operating frequencies, heights, and locations of the transmitting antennas, are calculated by means of the new model and, for contrast, by means of some earlier models. The new model can be used to calculate either the coarse prediction of ground-wave loss, or to calculate fine predictions, even for a point site. The accuracy of the calculation using the new model is superior to that of the earlier models.

Sound propagation in urban areas: a periodic disposition of buildings.

A numerical simulation of background noise propagation is performed for a network of hexagonal buildings. The obtained results suggest that the prediction of background noise in urban spaces is possible by means of a modified diffusion equation using two parameters: the diffusion coefficient that expresses the spreading out of noise resulting from diffuse scattering and multiple reflections by buildings, and an attenuation term accounting for the wall absorption, atmospheric attenuation, and absorption by the open top. The dependence of the diffusion coefficient with geometrical shapes and the diffusive nature of the buildings are investigated in the case of a periodic disposition of hexagonal buildings.

Slow fading cross-correlation against azimuth separationof base stations

A model is proposed to describe the cross-correlation of slow fading signals received from non-colocated base stations. The model summarises the results obtained from a bootstrap analysis of 900 MHz urban area propagation measurements.

Average field attenuation in the nonregular impedance street waveguide

The propagation of electromagnetic (EM) waves in a city with a regularly planned building as a model of a straight street with buildings lining its sides is investigated. The street is considered as a planar two-dimensional (2-D) multislit waveguide with Poisson distributed screens (building walls) and slits (gaps between buildings). The electrical properties of the buildings' walls are taken into account by introducing the electrical impedance as a function of their surface permittivity and conductivity. The average field from the vertical electric dipole placed inside the street lower than rooftop level in the conditions of line-of-sight is investigated using Green's function formalism and real boundary conditions on the building walls. Evaluations show that the total field inside the waveguide can be presented as a superposition of a continuous spectral propagation component, which does not exist in the ideal unbroken waveguide, and a discrete spectral component, which describes the exponential attenuation of reflected and diffracted waves at distances of up to 23 km depending on the width of street. The presented model and evaluated formulas are in a good agreement with experimental data of ultrahigh-frequency (UHF)/L-band wave propagation in urban areas with a crossing-street plan.

An empirical path loss model for HF/VHF propagation in urban areas

A number of models have been proposed in the literature to predict the propagation path loss in built‐up areas (urban and suburban) at VHF and UHF. However, none of these models is applicable at frequencies below 80 MHz. Other models proposed for application at frequencies between 20 and 10,000 MHz are only accurate when propagation is over rural irregular terrain. This paper describes the development of a path loss model applicable to frequencies between 3 and 450 MHz and propagation in urban and suburban areas. The model has been developed from path loss measurements at 3.195, 4.44, 16.08, 26.63, 49.8, and 446 MHz, where little reported data is available. In addition, previously reported VHF and UHF data have also been used to complement these measurements in the development of the model. The measurements indicate that even at frequencies as low as 3 MHz the electromagnetic field in an urban area will exhibit random spatial variations caused by multipath interference. Thus the received signal is best described in terms of mean and median signal levels. The model describes the frequency and range dependence of the median path loss and should be useful in predicting the performance of point‐to‐point and mobile HF/VHF communications links located in built‐up areas and employing low‐elevation antennas.

Cordless telephone system and its propagation characteristics

The cordless telephone system is designed to replace the indoor portion of a subscriber line with a radio so that a telephone set can be carried about freely and used anywhere within a limited service area. Therefore, it can be considered to be a partial realization of a portable telephone system. A description of the cordless telephone system using the 250-MHz and 400-MHz bands, which is scheduled to be put into commercial service is presented. The propagation characteristics, such as indoor propagation and urban area propagation for short distances, which are important for the system are also presented. Finally, the ultrasmall zone (minicellular zone) composition, which is newly employed in the system, is described.

Nomogram for estimating noise propagation in urban areas

A nomogram, generated numerically, is presented for estimating sound levels generated by point noise sources in urban street complexes. The nomogram accounts for street width, distance of the receiver from the source, reflection coefficient of the building walls, and includes cases where the receiver is across one or more street intersections or is around a street corner from the source. The effect of ground reflection is included. Subject Classification: 50.80; 20.20; 28.40.

Sound propagation in urban areas

An investigation of the propagation of sound from identifiable sources in urban areas has recently been concluded. As a result of this study, sound-level estimation procedures have been developed for typical configurations including: propagation through intersections, both single and multiple; propagation around corners, also both single and multiple; and propagation into side streets. These procedures apply to near-ground-level noise sources which are identifiable above background level and can be approximated by either a point or line source. Methods were developed for assessing the modification of the basic estimation procedures due to diffraction, ground interference effects, and sound-level nonuniformity across street sections near intersections. Additional modification of the basic estimation procedures accounting for building surface irregularities has been determined and can be used in sound-level prediction. Levels predicted by the estimation procedures have been compared with both field and model data. [Work supported by U. S. Department of Transportation and National Science Foundation.]

Numerical model of sound propagation in urban areas

A numerical technique has been developed for estimating the outdoor sound levels due to transportation noise sources moving through urban areas. A Monte Carlo method is used to account for the effects of reflection and scattering at building facades on the sound propagation. Inputs to the model are the geometry of the area, fitted to a rectangular grid, the source location and sound power level, and the absorption and scattering coefficients of the building facades. The user can then request the sound pressure level at any location in the area. This research has two objectives. The first is to develop a useful tool to assist in transportation planning in urban areas. The second is to further our basic understanding of multipath sound propagation in complex urban areas as part of a general program of noise propagation research at MIT.

Sound propagation near ground level in the vicinity of street intersections

An investigation is in progress of the propagation of sound from ground level noise sources in complex urban areas. The first problem to be considered was sound propagation into side streets due to point or traffic flow line sources in a perpendicular arterial street. Experimentally, this topic was approached with a series of field and model studies employing calibrated noise sources. Model experiments included measurements of sound level distribution near an intersection, the delay of sound level down the side street, and a simulation of the field experiments. From this data base, prediction laws were formulated and judged. In the further investigations of sound propagation in urban areas, propagation through and around multiple intersections is considered. [Work supported by the U.S. Department of Transportation.]