Journal of Hydraulic Structures
Volume:6 Issue: 1, Winter 2020

Numerous researches have been investigated on the mass transfer phenomena and hydrodynamics for the fluid in the vicinity of the membrane surface by the mathematical modelling and simulation. Due to complexities involved in solving transport phenomena within membranes, the application of CFD simulation study for determining the concentration polarization (CP) profile in the membrane channel is limited. In this study, a 2D CFD modelling and simulation of CP phenomena in nanofiltration of an aqueous solution of MgSO47H2O in a vertical spacer-filled flat sheet membrane module was presented. A response surface methodology (RSM) statistical analysis has been designed in order to fully capture effects of variations of the feed liquid flow and the transmembrane pressure (TMP) on the permeate flux and concentration. It was also shown that increasing TMP or the liquid flow rate led to enhancing the permeate flux while increasing the feed concentration decreased it. The simulated results were validated and compared with the available experimental data, showing a satisfactory agreement. Eventually, the mass transfer coefficient derived from CFD simulations and calculated from Sherwood empirical relationships were compared which showed 10% and 33% difference in lower and higher liquid flow rates, respectively.

The statistical tests such as T-test and Kruskall-Wallis test were used to study and analyze the difference between the quantitative parameters before and after constructing dams and the effect of different factors on water quality. The results of statistical tests showed that the values of the investigated water quality parameters (except EC value) before constructing (pre) dams were significantly different from the values after constructing dams in reservoir downstream stations. Sulfate (SO2-4) concentration in downstream stations of Marun Dam (Behbahan and Cham Nezam) reduced by 30 and 23 percent, respectively, and Cl- concentration increased 21 and 12 percent, respectively. Similarly, the difference between the values before and after constructing Jarreh dam at Mashin station was a 106% reduction in the concentration of sulfate ion (SO2-4) and a 78% increase in the concentration of chlorine ion (Cl-). The reason for this increase is probably due to the effect of river flows on the Formation and the relationship between the reservoir and the Formations where water has a long residence time and then reduced due to the exposure to the Geological Formations as well as the existence of agricultural activities downstream and before quality monitoring stations could be another reason for this claim. In addition, in the reservoir system, the concentration of soluble salt may be diluted by runoff from winter snowmelt and spring rains. Therefore, it can be concluded that water quality characteristics of Marun and Roudzard rivers in the studied basin has been affected by the constructed reservoir dams.

The main goal of this study is investigating the effect of air flow above the free surface on the behavior of gravity current. Lock-release gravity current has been simulated in a channel, by using VOF method, for modeling free surface at the interface of gas and liquid phases. Eulerian approach is used to consider the presence of particles in the flow. The results of simulation with free surface assumption are in a well agreement with the previous experimental results. It is observed that the flows containing particles with larger diameter experience higher deposition rate, due to their higher terminal velocities which are 0.000129m/s, 0.000359m/s and 0.000808m/s for the particles with 12μm, 20μm and 30μm diameters respectively. Increasing the size of particles diameter leads to decrease in the driving force, the front position of flow containing particles with 30μm diameter is 11% less than that of flow containing particles with 12μm diameter, thereby the flow velocity decays quickly. The results show that the presence of particles leads to a reduction in the value of entrainment rate. It is concluded that the velocity of air-phase affects the shape of flow and instabilities. By considering three different values of 0.1m/s, 0.12m/s and 0.18m/s for the air-phase velocity, it is observed that the amount of run-out length, in the case where the air velocity is 0.18m/s, is nearly 3% more than that in other cases at the end of channel, moreover it leads to an increase in the value of entrainment rate.

Natural rivers have several bends along the path that are not generally uniform and some are convergent. Installing the bridge piers in river convergent bends may result in complicated flow and erosion patterns around the bridge piers. Most of previous studies on the flow and the scour pattern around piers were carried out in straight channels and fixed-width bends. Studying the local scouring around pier located at a converging bend, experimentally and numerically, has brought novelty to this paper. In this research, a physical hydraulic model with a 90° convergent bend and central radius of 170 cm was built. A cylindrical pier with a diameter of 60 mm was installed in positions of 0, 30, 45, 60, and 75 degrees and local scour were studied under clear-water conditions. The SSIIM-2 numerical model was also used to simulate the scour pattern and the results were compared with experimental results. The results showed that, increasing the convergence and changing the pier position in a bend leads to an increment in the continuity between the flow lines and secondary currents, respectively, so that the maximum depth and volume of the scour hole occurred in the second half of the bend at an angle of 75 degrees. The comparison between experimental and numerical data shows that SSIIM-2 model can efficiently simulate the scour pattern in a 90° convergent bend. Furthermore, in all cases by increasing the Froude number, maximum depth and volume of the scour hole were increased.

The water crisis in different countries of the world has made the earth undergo tremendous changes compared to the past years. Therefore, it is very necessary to have intelligent systems that can help managers make correct and optimal decisions in various possible conditions. In recent years, the biggest challenge faced by water resource managers in the Karun Basin in Iran has been the decline in the quality of surface waters in the downstream areas of the basin. In this research, a surrogate-based model has been developed for predicting and controlling the quantity and quality of water in different parts of the basin. As a decision support system, this model can evaluate the quantity of water at different points in the basin and also predict its quality in various probable conditions. This model will also be used to extract optimal operating policies with the aim of satisfying quality constraints in different conditions. The model can help decision makers in the optimal management of the system and also greatly reduce the losses caused by quality issues in possible future situations.

Groundwater aquifers are one of the most significant freshwater resources in the world. Hence, the monitoring of these resources is particularly important for available water resources planning. Piezometric wells have traditionally been used to monitor groundwater. This approach is costly and pointwise, which is not feasible for places with steep topography and mountainous areas. Nowadays, remote sensing techniques are widely used in various fields of engineering as appropriate alternatives to traditional methods. In water resources management, the Gravity Recovery and Climate Experiment (GRACE) satellites can monitor groundwater changes with acceptable accuracies. This paper applied the GRACE satellite data for a 40-month period to assess the variation of the groundwater level in Khuzestan province. The Global Land Data Assimilation System (GLDAS) model was used to counteract the soil moisture effect in final results. The observed data from piezometric wells were pre-processed to detect outliers using the Mahalanobis algorithm in Khuzestan province. At last, the outputs of GRACE were compared with these processed observed data. Despite the relatively small size of the area in question, the results indicated the efficiency of GRACE data (RMSE = 0.8, NRMSE = 0.2) for monitoring the groundwater level changes.