Szemcsés anyagok sztatikus és dinamikai szerkezete = Static and dynamical structure of granular materials

Számítógépes szimulációkkal vizsgáltuk a mágneses szemcsék lavináinak tulajdonságait. A rendszert a mágneses és a gravitációs kölcsönhatás erősségének f hányadosa jellemzi. A rézsűszög és a felületi durvaság lineárisan változik f-fel. Hasonlóan a kohézív rendszerekhez, a lavinadinamika szempontjából két tartomány figyelhető meg. Tanulmányoztuk a nyírási sávok kialakulását három dimenzióban, triaxiális elrendezésben. Kidolgoztuk a nyírási sávok numerikus azonosításának technikáját. Szimmetriasértő sávokat találtunk, amennyiben a külső kényszer ezeket nem akadályozta meg. A kísérletekkel egyezésben elmozdulási keményedést azonosítottunk. A sávon belül kritikus sűrűség áll be, amelynek végtelen súrlódáshoz tartozó határértéke csak a szemcsék alakjától függ. Általánosítottuk korábbi, nyírási sávokra vonatkozó elméletünket. Az új modell a kísérletekkel kiváló egyezésben írja le a módosított Couette?cellás kísérleteket. Megjósoltuk és szimulációval igazoltuk, hogy különböző súrlódású közegek határán a fénytöréshez hasonló nyírási sáv refrakció következik be. Vizsgáltuk, hogy torlódott állapotú rendszer perturbációjának hatását. Hatványfüggvény-szerű lecsengést találtunk az elmozdulási térben, ahol az exponens a súrlódás nem triviális függvénye, hasonlóan az elmozdulást kiváltó kritikus erő nagyságához és a behatolási mélységhez. Ezt a nem-monoton kapcsolatot összefüggésbe hoztuk a korábban, a sztatikus erőhálózatokban talált fluktuációk súrlódás-függésével. | Using computer simulations we studied the properties of avalanches of magnetic grains. The system is characterized by the ratio f of the magnetic and gravitational interaction. The angle of repose and the surface roughness vary linearly with f. Similarly to cohesive systems, we could distinguish two regimes from the point of view of the avalanche dynamics. We investigated the formation of shear bands in three dimensional axisymmetric arrangement. We constructed the techniques of identifying the sear bands. We found symmetry breaking bands whenever the external constraints did not hinder them. In agreement with experiments we found strain hardening. Within the band a critical density developed, which, in the infinite friction limit, had a value depending only on the shape of the grains. We generalized our earlier theory of the shear bands. The new model describes the experiments in the modified Couette-cell excellently. We predicted and proved by simulations that on the boundary of two media with different frictions refraction of shear bands takes place, similarly to the refraction of light. We investigated the effects of perturbations of the jammed state. We found power law decay in the displacement field where the exponent is a non-trivial function of the friction, similarly to the critical force and the penetration depth. These non-monotonic dependences were related to the friction-dependence of fluctuations in the force network found earlier static packings

Modelling of the annual mean maximum urban heat island with the application of 2 and 3D surface parameters

The primary aim of this study was to reveal quantitatively what effect urban structure has on the development, magnitude and spatial distribution of the annual mean maximum urban heat island using a selected representative sample area in Szeged, Hungary. In order to quantify what effect urban structure has on the development of the mean urban heat island a relatively new surface parameter (weighted volumetric compactness) was used that characterises the volume, structure and thermodynamical role of buildings. This new parameter was used in conjucntion with other established surface parameters. How the new parameter and other surface parameters can pinpoint the magnitude and structure of the heat island was investigated. The compactness of approximately 11 000 buildings in onethird of the town was determined by geoinformatical analysis. A stepwise multiple linear regression model was used to determine to what extent each parameter adds to the annual mean urban heat island intensity. According to the results presented here, the connection between compactness and the annual mean (‘all weather’) heat island intensity is stronger than with the sky view factor. Using this modelequation, the absolute deviations of the generated heat island (calculated for an independent 1 yr period) remained under 0.5°C throughout almost the entire investigated area of Szeged. The structure of the estimated heat island with its characteristic features showed clear similarities to the real conditions

Urban temperature excess as a function of urban parameters in Szeged : Part 2: Statistical model equations

This study examines the quantitative influence of urban surface factors on the surface air temperature field of the medium-sized city of Szeged, Hungary, using of mobile measurements under different weather conditions between March 1999 and February 2000. Tasks include the determination of statistical model equations in the studied periods, distinguishing heating and non-heating seasons within the one-year period. Multiple correlation and regression analyses are used to examine the effects of urban surface parameters (land-use characteristics and distance from the city centre determined in a grid network) on the urban heat island (UHI) in its peak development during the diurnal cycle. The results indicate that strong relationships exist between urban thermal excess and distance, as well as built-up ratio, but the role of water surface is negligible in this case

The main result of the nearly 30-year-old urban climatological research in Szeged, Hungary

Összefoglalás - A dolgozat egy közepes méretű magyar városban. Szegeden folyó városklímakutatás legfontosabb eredményeit tekinti át, amely közel 30 éves múltra vezethető vissza. Az áttekintés az 1967 és 1995 közötti korszakot elemzi és ismertet minden olyan fellelhető munkát (cikket, disszertációt és kéziratot), amely Szeged városklímájával foglalkozik. A sokéves dokumentáció azért is értékes, mert általa a vidéki városaink közül itt nyerhetjük a legrészletesebb, legátfogóbb képet egy nagyobb város klímamódosító hatásairól. Summary - This paper describes the most important results of urban climatological investigations, which goes back to the 1960s, in a medium-sized Hungarian town. Szeged. The overview analyses the period between 1967 and 1995 and it contains every retraceable work (papers, theses and manuscripts) which dealt with the urban climate of Szeged. So many years of documentation is also valuable as it gives the most detailed and most extensive picture among the Hungarian country towns of the climate modification effects of a bigger town

Urban heat island studies in Szeged, Hungary - an overview based on papers published over the past forty years, 1980-2020

The overview summarizes briefly the contents and results of the papers published in journals dealing with urban heat island investigations in Szeged, Hungary between 1980 and 2020. The thermal data they used came from urban station networks, mobile measurements, local-scale simulations as well as aerial and satellite images

Intra-urban relationship between surface geometry and urban heat island: review and new approach

This paper provides a comprehensive review of the intra-urban sky view factor (SVF)–temperature relationship. A new approach to reveal the real connection between SVF and air temperature in an entire city is presented. The results found in the literature are rather contradictory, possibly due the fact that previous investigations were limited to the central or specific parts (e.g. inner city, urban canyons) of cities and used few sites and measurements. Comparisons were often based on element pairs measured at selected sites. In some cases areal means were also discussed, but always in connection with one of the variables examined. For comparison, the present study in Szeged, SE Hungary, utilizes a large number of areal means of SVF and air temperature. The values are related to almost a whole city and based on numerous measurements. The results show a strong relationship in the intra-urban variations of these variables, i.e. urban surface geometry is a significant determining factor of the air temperature distribution inside a city if the selected scale is appropriate. Therefore, investigation of a sufficient number of appropriate-sized areas covering the largest part of a city or the entire city is needed to draw well-established conclusions