Showing 6 results for Dispersion
M. Mousaei Sanjerehei, M. Bassiri,
Volume 11, Issue 40 (7-2007)
Abstract
Selection of efficient indices is very important for detecting and measuring random, uniform and clumped distribution patterns of plants in different plant communities. To compare and evaluate indices of dispersion patterns of plants, three stands were selected in Nodushan, Yazd. A (50m*100m) area was selected within each stand for sampling. Sampling was randomly systematicly conducted. Measurements and counts were made at 50 points and (1 and 2m2) quadrats which were randomly selected along four 100m transects within each sampling area. Indices of dispersion using quadrate studied in this survey include: Standardized index of Morisita, Morisita's index, Green's index, Dispersion (variance/mean ratio) index , Lloyd's index of patchiness and distance indices of dispersion including Pielou, Hopkines, T square, Eberhardt , Hines, Johnson and Zimer and Holgate indices. Results showed that T square and Holgate indices were more powerful than the other indices for detecting intensity of small-scale and tightly clumped pattern of shrubs because the two indices could distinguish between single individuals and the individuals on the edges of dense and small clumps. Johnson and Zimer index and Standardized index of Morisita (in shrublands with plant cover greater than 5%) were more efficient than the other indices for determining spatial pattern of these small clumps and single individuals. Among studied indices of dispersion, Green's index had the highest precision and with the exception of this index, distance indices were more precise than the quadrate indices.
E Marouf Pour, H Moazed, H.a Kashkouli, H Moahamad Vali Samani,
Volume 12, Issue 46 (1-2009)
Abstract
Tracer experiments are very important in the studies related to aquifer contamination for determination of dispersion coefficient. In this study, the effect of sampling method on the dispersion coefficients of two simulated sandy aquifers was examined. The physical model was made from Plexiglas material with inner length, width and height of 72, 10 and 120 cm, respectively. A solution containing 9 g/l sodium chloride (Ec = 14 ds/m) was used as the non - reactive (conservative) contaminant. Homogeneous sands with coarse and medium particle sizes were used as media for the simulated aquifers. The experiments were carried out in the aquifers with various thicknesses from 20 to 100 cm with 10 cm thickness increment. Point and mixed samples were taken through all experiments. The results of the study showed that (1) for both simulated aquifers, the dispersion coefficient values obtained by point sampling method were close to the values obtained by other researchers from laboratory experiments (2) In all the experiments, the dispersion coefficient values obtained by mixed sampling method were higher than those obtained by the point sampling method (3) with increasing the aquifer thickness, the dispersion coefficient values obtained from the mixed samples varied but did not have a uniform trend which could be due to the unavoidable experimental errors and (4) there was no difference between the breakthrough and pore volume curves of various aquifer thicknesses obtained from point and mixed samples. Overall, based on the results obtained from this research, in studies related to aquifer contamination, it is recommended to take point samples instead of mixed samples to obtain more precise results.
S. Baghbanpour* and S. M. Kashefipour, ,
Volume 16, Issue 61 (10-2012)
Abstract
Rivers as a main sources of supplying water for urban areas, agriculture and industry, are very important. This point reveals the necessity of the control, improvement and solving the problems of rivers, especially all problems relating to water quality. In this study, transport of the suspended sediment is numerically modeled. The Saint-Venant hydrodynamic equations and also advection-dispersion equation (ADE) are applied for modelling flow and suspended sediment transport. It is necessary to choose appropriate empirical and/or semi-empirical equation to accurately estimate the equilibrium suspended sediment discharge, as well as the appropriate equation describing longitudinal dispersion coefficient. In this research, 5 and 6 equations were applied in the ADE for estimating equilibrium suspended sediment discharge and longitudinal dispersion coefficient, respectively. 30 combinations of these equations were made and the final model was run for each of them separately. Comparison of the predicted suspended sediment concentrations and the corresponding measured values at the survey site, Abdelkhan Station, for the calibration and verification periods showed that the combination of the Van Rijn's equilibrium suspended sediment equation and the Fischer's longitudinal dispersion equation performed very well. The maximum percentages of errors in estimation of suspended sediment concentrations were 19.56% and 26.3% for the calibration and verification periods, respectively.
A. Mirhashemi, M. Shayannejad,
Volume 23, Issue 1 (6-2019)
Abstract
Urban and industrial wastewaters are considered as the most contaminant of surface water. Entrance of these pollutants to the river reduces the concentration of dissolved oxygen and aquatic life will be threatened. So, one of the main qualitative characteristics of water resources management is the concentration of dissolved oxygen. The base of the developed model in this investigation is the convection- diffusion equation in soil. Terms of production and decay of dissolved oxygen were added to this equation. The final equation was discretized using the finite difference method with the implicit scheme. With applying the initial and boundary conditions, the equation set was solved by the Thomas algorithm. The calculations were done by programming in the MATLAB software. For the calibration and validation of the model, data obtained from two reaches of Zayanderoud River, including steel melt and Mobarakeh Steel factories, were used. The temporal and spatial variations of the dissolved oxygen were plotted and compared with the real data and the results of the MSP and CSP models. The results showed that the concentration of the dissolved oxygen could be well predicted through solving convection-diffusion equation with introducing two terms for the decay and production of oxygen. The comparison between the results of the model and two other models showed that the model led to better results in comparison to the MSP and CSP models.
S. Mirhashemi, M. Shayannejad,
Volume 23, Issue 3 (12-2019)
Abstract
Nowadays, environmental pollutions especially water pollution is increasingly developing. One of the problems of entering the pollutants to rivers is reduction in the concentration of river dissolved oxygen. In order to manage the water resources, amount of dissolved oxygen should be predicted. This study presents a novel equation for simulating the concentration of river dissolved oxygen by adding the oxygen production and consumption in the river factors to equation for transmission-diffusion of minerals in the soil. The resultant equation was separated in finite differential method and by using implicit pattern. Calculations were done by encodings in MATLAB software. In order to calibrate and confirm the dissolved oxygen model, data derived from Zayanderood River around Zob-Ahan factory of Isfahan and Mobarakeh Steel Complex was used. By using some data, coefficients of model were determined. Analyzing the sensitivity of model coefficients showed that aeration constant (Kr) had the most effect on predicting the model. Since depends on hydraulic parameters of river, sensitivity of depth and pace of river was studied and finally depth of river was introduced as the most sensitive variable.
F. Ansari Samani, S. H. Tabatabaei, F. Abbasi, E. Alaei,
Volume 23, Issue 3 (12-2019)
Abstract
Simulation of water and salt transfer in soil is very effective in managing optimal water and fertilizer use in the field. In this study, the HYDRUS-1D model was used to simulate the transfer of water and bromide in a laboratory column of soil with clay loam texture. Soil hydraulic parameters (including air entry point) α, (saturated hydraulic conductivity) ks, (residual moisture content) θr (saturation moisture content) θs, (pore and particle joint parameter) l (parameter of moisture curve shape) n through measurement and using Retc software was obtained Solubility transfer parameters including difiusion coefficient and actual velocity were estimated using soil hydraulic parameters and bromide concentration data by reverse modeling method. According to the target coefficients, the sensitivity analysis of the physical model was performed .The results showed that the correlation coefficient of observation and simulation bromide concentration in optimal mode was 0.84%. accordingly, the diffusion coefficient was estimated to be 4.9 cm. based on the results of the sensitivity analysis, the saturation hydraulic conductivity had the greatest effect on the variation of this parameter, so that the amount sensitivity coefficient of this parameter was 2.64 The RMSE coefficient with a value of 0.04 was the lowest and ME coefficient with the value of -0.0001 had the most parameter variations.
