| ATTRIBUTE | VALUE |
|---|
| type | A |
| database id | 7338 |
| title | A fractal approach for characterizing microroughness in gravel streams |
| authors | Tsakiris A. G., Papanicolaou A. N. Thanos |
| pages | 29 — 43 |
| full text link | http://www.ibwpan.gda.pl/storage/app/media/ahem/ahem55str029.pdf |
| keywords | cluster, microforms, shape, fractal, cell-counting |
| affiliations | - University of Iowa, Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, Iowa City, IA 52242-1585, USA, e-mail: apapanic@engineering.uiowa.edu
|
| abstracts | Discrete cluster microforms, or simply clusters, in gravel streams result from organization of particles found in the surface layer of the gravel bed into disconnected patches. Clusters are the outcome of feedback interaction between flow, sediment and stream planform geometry. The complexity of this interaction results in several different cluster shapes, i.e. line, rhomboid and triangular. The objective of this research is to provide a quantitative characterization of cluster shape. To achieve this, we employed a novel method based on fractal theory and used for the shape description of clusters. Our novel method utilized the cell-counting method for the estimation of the areal fractal dimension, DA for two major datasets, namely fabricated clusters with well-defined shapes, and clusters developed in the laboratory. The principal finding of this research is that the proposed method successfully characterized cluster shape in quantitative terms. Specifically, it was shown that the new approach could identify clusters of different shapes 84% of the time, under different arrangements. This finding is of great importance for bed pattern recognition studies of stream reaches with superimposed roughness elements such as clusters. The findings of the current work could also assist numerical modellers in the development of more representative models of flows over roughness features such as clusters and in the interpretation of results from such models. |
| attributes | [reviewed] [scientific] |
| language | en |
| ATTRIBUTE | VALUE |
|---|
| type | A |
| database id | 7337 |
| title | Shear stress statistics in a compound channel flow |
| authors | Czernuszenko W., Rowiński P. M. |
| pages | 3 — 27 |
| full text link | http://www.ibwpan.gda.pl/storage/app/media/ahem/ahem55str003.pdf |
| keywords | open channel, turbulence, measurements, Reynolds stresses, coherent structures |
| affiliations | - Institute of Geophysics, Polish Academy of Sciences, Księcia Janusza 64, 01-452 Warszawa, Poland, e-mail: wczer@igf.edu.pl
|
| abstracts | The results of comprehensive measurements of three-dimensional turbulent velocities carried out in a laboratory compound channel are presented. Tests were performed in a two-stage channel with a smooth main channel bed consisting of concrete and rough floodplains and sloping banks. Instantaneous velocities were measured with the use of a three-component acoustic Doppler velocimeter. The main aim of the study is the recognition of structure of Reynolds stresses in turbulent open channel flows. Particular attention has been paid to bursting events such as ejections and sweeps. The bursting phenomenon occurs originally near the buffer layer and then shows a coherent or organized flow structure during its convection process.
The probability density distributions of the turbulent velocities were measured at different distances from the bed in the main channel and also above the inclined walls. In the main channel, the lateral turbulent velocity is seen to follow the normal Gaussian distribution more closely than the remaining two components. Above the inclined walls, all distributions turned out to have greater skewness. The probability density distributions of correlations between velocity fluctuations were also calculated. These distributions have long tails and sharp peaks and fit the theoretical distributions very well. The structure of instantaneous Reynolds stresses was analyzed by a quadrant technique with an arbitrarily chosen threshold level. It has been shown that the largest contribution to turbulent stresses comes from the second quadrant (ejection) and the fourth quadrant (sweep). The basic temporal characteristics for quadrant events, like the average and maximum time for a zero hole size, have been determined in the study. Calculations of maximum duration times for all events reveal that times are greater for even quadrants than for odd quadrants. |
| attributes | [reviewed] [scientific] |
| language | en |
| ATTRIBUTE | VALUE |
|---|
| type | A |
| database id | 7163 |
| title | 3D and 2D formulations of incremental stress-strain relations for granular soils |
| authors | Sawicki A. |
| pages | 45 — 53 |
| full text link | http://www.ibwpan.gda.pl/storage/app/media/ahem/ahem55str045.pdf |
| keywords | granular soils, pre-failure deformations, instability, anisotropy, constitutive equations |
| affiliations | - Institute of Hydro-Engineering PAS, ul. Kościerska 7, 80-328 Gdańsk-Oliwa, Poland, e-mail: as@ibwpan.gda.pl
|
| tasks | 4 T07A 028 39 |
| abstracts | 3D formulation of incremental relations, describing pre-failure deformations of granular soils, is presented. The starting point are respective equations formulated previously for the axi-symmetrical configuration, as that in the tri-axial apparatus. These relations, proposed for particular configuration, are generalized in the form of tensor equations for the strain increments. Similarly, the loading/unloading criterion and the instability line have been generalized for 3D conditions. A kind of cross-isotropy of granular soil is taken into account. Then, the incremental stress-strain relations for the plane strain state are re-derived from general equations, as such conditions are most often used for simulations of practically important problems. The procedure proposed in this paper is practically oriented, as the soil parameters can be determined just from the tri-axial tests. |
| attributes | [reviewed] [scientific] |
| language | en |
| points | 4 |