Sand eddies induced by cyclic tilt of a retaining wall     

Chien-Hsun Chen  Dimitrios Kolymbas 《Acta Geotechnica》2016,11(2):269-280

The cyclic tilt of a retaining wall induces a peculiar motion in the backfill (sand), which exhibits closed trajectories (eddies). In this paper, the motion of the backfill has been optically traced and analyzed by means of particle image velocimetry, also known as digital image correlation. The results are of importance for cyclically loaded structures (e.g, piles for off-shore structures) and can also serve to test numerical simulations of large deformation.  相似文献   

Flooding a landscape: impact of Holocene transgression on coastal sedimentology and underwater archaeology in Kiladha Bay (Greece)     

Morgane Surdez  Julien Beck  Dimitris Sakellariou  Hendrik Vogel  Patrizia Birchler Emery  Despina Koutsoumba  Flavio S. Anselmetti 《Swiss Journal of Geoscience》2018,111(3):573-588

Franchthi Cave, bordering Kiladha Bay, in Greece, is a key archaeological site, due to its long occupation time, from?~?40,000 to?~?5000 year BP. To date, no clear evidence of Neolithic human dwellings in the cave was found, supporting the assumption that Neolithic people may have built a village where there is now Kiladha Bay. During the Neolithic period/Early Holocene, wide areas of the bay were indeed emerged above sea level. Bathymetric and seismic data identified a terrace incised by a valley in?~?1 to 2 m sediment depth. Eight sediment cores, up to 6.3-m-long, were retrieved and analysed using petrophysical, sedimentological, geochemical, and chronostratigraphic methods. The longest core extends into the exposure surface, consisting of a layer of carbonate rubble in a finer matrix, representing weathering processes. Dated organic remains place this unit at?~?8500 cal year BP. It is overlain by stiff silty mud representing an estuarine environment. This mud is capped by reduced sediments with roots marking an exposure surface. A shell-layer, dated to?~?6300 cal year BP, overlies this terrestrial sequence, reflecting the marine transgression. This layer occurs at 10.8 mbsl, 7.7 m deeper than the global sea level at that time, suggesting tectonic subsidence in the area. It is overlain by finer-grained marine carbonate-rich sediments. The top of the core shows traces of eutrophication, pebbles and marine shells, all likely a result of modern anthropogenic processes. These results are interpreted in the context of human occupation: the exposed surface contains pottery sherds, one dating to the Early to Middle Neolithic period, indicating that Neolithic people were present in this dynamic landscape interacting with a migrating coastline. Even if the artefacts are isolated, future investigations of the submerged landscape off Franchthi Cave might lead to the discovery of a Neolithic village, which eventually became buried under marine sediments.  相似文献   

Cavity expansion in cross‐anisotropic rock     

Dimitrios Kolymbas  Peter Wagner  Anastasia Blioumi 《国际地质力学数值与分析法杂志》2012,36(2):128-139

Schistous rock can be considered—in a first approximation—as cross‐anisotropic linear elastic material. The determination of the corresponding material constants on the basis of the laboratory investigation of rock samples often fails, as the extraction of appropriate cores proves to be unfeasible (the cores disintegrate if the schistosity is pronounced). In this paper a new method is presented to determine the material constants of a linear elastic cross‐anisotropic rock on the basis of cavity expansion field tests, e.g. with a radial jack. To this purpose, an analytic approximation for the deformation of a hydrostatically loaded cylindrical cavity in cross‐anisotropic rock is derived which serves to the inverse analysis of the material parameters. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The temperature structure in a stably stratified internal boundary layer over a cold sea     

Dimitrios Melas 《Boundary-Layer Meteorology》1989,48(4):361-375

Data from the Öresund experiment are used to investigate the structure of the stably stratified internal boundary layer (SIBL) which develops when warm air is advected from a heated land surface over a cooler sea. The present study is based on a theory developed by Stull (1983a, b, c). He proposed that the turbulence and the mean structure of the nocturnal boundary layer is controlled by the time-integrated value of surface heat flux and that the instantaneous heat flux is of less importance.Dimensional arguments are used to define simple, physically consistent, temperature, velocity and length scales. The dimensionless surface heat flux has a high value immediately downwind of the shoreline and it decreases rapidly in magnitude with increasing distance from the coast. Farther away, it is essentially constant. The dimensionless potential temperature change exhibits an exponential profile. It is estimated that turbulence accounts for 71% of boundary-layer cooling while clear-air radiational cooling is responsible for the remaining 29%.Finally it is found that theoretical predictions for the height of the SIBL are in a good agreement with observations.  相似文献   

Using a simple resistance law to estimate friction velocity from sodar measurements     

Dimitrios Melas 《Boundary-Layer Meteorology》1991,57(3):275-287

Sodar measurements are used to study the layer-averaged winds in the unstable Planetary Boundary Layer (PBL). The field data are from the öresund experiment which was carried out over öresund, the strait between Denmark and Sweden during the period May 15 to June 14 1984. A simple resistance law proposed by Garratt et al. (1982) is used to derive friction velocity from sodar measurements of the mean wind. This was found to be in very good agreement with observations.The author is currently doing his military service in the Greek army.  相似文献   

Incompatible deformation in rock mechanics     

Dimitrios Kolymbas 《Acta Geotechnica》2007,2(1):33-40

Compatibility, i.e., continuous displacement field, is often taken for granted but experience teaches that rock deformation is in most cases discontinuous. The relation between incompatible deformation and continuous distribution of dislocations is established since long and is recalled in this paper. Contrary to several applications of Cosserat theory to already laminated (jointed) rock, the main goal of this paper is to give an explanation for the formation of discontinuities (joints) in rock as a result of a particular type of buckling which leads the body outside of the Euclidean space of its original configuration.  相似文献   

Hydrodynamic,neotectonic and climatic control of the evolution of a barrier beach in the microtidal environment of the NE Ionian Sea (eastern Mediterranean)     

Serafim E. Poulos  George Ghionis  Efthymia Verykiou  Grigoris Roussakis  Dimitrios Sakellariou  Aikaterini Karditsa  George Alexandrakis  Stelios Petrakis  Dafni Sifnioti  Ioannis P. Panagiotopoulos  Periklis Andris  Panos Georgiou 《Geo-Marine Letters》2015,35(1):37-52

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AMRVAC and relativistic hydrodynamic simulations for gamma-ray burst afterglow phases     

Zakaria Meliani  Rony Keppens  Fabien Casse  Dimitrios Giannios 《Monthly notices of the Royal Astronomical Society》2007,376(3):1189-1200

We apply a novel adaptive mesh refinement (AMR) code, AMRVAC (Adaptive Mesh Refinement version of the Versatile Advection Code), to numerically investigate the various evolutionary phases in the interaction of a relativistic shell with its surrounding cold interstellar medium (ISM). We do this for both 1D isotropic and full 2D jet-like fireball models. This is relevant for gamma-ray bursts (GRBs), and we demonstrate that, thanks to the AMR strategy, we resolve the internal structure of the shocked shell–ISM matter, which will leave its imprint on the GRB afterglow. We determine the deceleration from an initial Lorentz factor  γ= 100  up to the almost Newtonian     phase of the flow. We present axisymmetric 2D shell evolutions, with the 2D extent characterized by their initial opening angle. In such jet-like GRB models, we discuss the differences with the 1D isotropic GRB equivalents. These are mainly due to thermally induced sideways expansions of both the shocked shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete all the surrounding medium located within its initial opening angle. Part of this ISM matter gets pushed away laterally and forms a wide bow-shock configuration with swirling flow patterns trailing the thin shell. The resulting shell deceleration is quite different from that found in isotropic GRB models. As long as the lateral shell expansion is merely due to ballistic spreading of the shell, isotropic and 2D models agree perfectly. As thermally induced expansions eventually lead to significantly higher lateral speeds, the 2D shell interacts with comparably more ISM matter and decelerates earlier than its isotropic counterpart.  相似文献   

Analysis of fault rupture propagation through uniform soil cover     

Dimitrios Loukidis  George D. Bouckovalas  Achilleas G. Papadimitriou 《Soil Dynamics and Earthquake Engineering》2009,29(11-12):1389-1404

This paper presents results from numerical simulations of the propagation of an active dip–slip fault rupture through a uniform soil layer covering the rigid bedrock. Following verification of the numerical methodology against field evidence, a parametric study is performed for loose and dense sand, for normally consolidated and overconsolidated clay, as well as for different fault dip angles (normal and reverse faults) and for different thicknesses of the soil cover. The soil is modeled as an elasto-plastic, strain-softening material that obeys the Mohr–Coulomb failure criterion. The study aims at establishing criteria for the approximate depiction of the location and the width of the zone with significant ground surface distortion, where the differential ground displacements induced by the fault rupture may threaten the integrity of man-mad structures.  相似文献   

Mean monthly air temperatures in Athens, Greece     

N. K. Sakellariou  H. D. Kambezidis  M. A. Gouvas 《Theoretical and Applied Climatology》2000,67(3-4):201-203

Summary  In this paper some statistical parameters of the mean monthly air temperatures in Athens are examined, namely trends, periodicities and cross-correlations between months. It is found that there is not any significant trend for most of the months and the periodicities don’t allow the extraction of any general conclusion. On the other hand, cross-correlation analysis shows that some correlation between the temperature in certain months exists. Received March 10, 2000  相似文献