Scientific Research Communications

Numerical Modeling of Flow Pattern at a Right-angled River Bend Using CCHE2D Model

Animesh Das — 2023-01-31

In this study, the unsteady pattern of the meander bend in the Gomati River flow is analyzed using CCHE2D. Different Manning's roughness factors and turbulent simulations were used to validate the CCHE2D model. For two different flow rates, simulation results were compared with data collected in the field. The results show that for both minimum and maximum discharges, smaller Manning's roughness factor are preferred to higher Manning's roughness factor . Similarly, the measured and reflected magnitudes are changed in hydraulic parameters such shear stress, velocity, flow depth, and Froude number. The results of the numerical model showed that the presence of centrifugal force and helical cells strongly impacts variation in flow structure in the river bend. In the cross sections of a meander bend, the gradient of the water surface latitude is altered by helical flow and the depth averaged velocities. The linear and direct relationship between velocity and shear stress is presented across the whole study reach, as indicated by the R-square and linear correlation coefficient (r) components. The results of the model show that the flow field within the river bend can be accurately simulated by the computational model.

Monitoring and Modelling of Sediment Flushing : A Review

Gregor Petkovsek — 2023-01-30

With ever decreasing potential for suitable new dam sites, sustainable use of existing water reservoirs is of paramount importance. In absence of appropriate measures, reservoir storage is continually reduced due to sedimentation. One option to remove sediment deposits is hydraulic flushing. During the flushing operation, bottom outlets are open and water and sediment released. Whether flushing successfully removes sediment depends on a number of factors, such as bottom outlets capacity, reservoir shape and water availability. Modelling is often used to assess viability of flushing for sediment management in the reservoir, as well as to design the operations and optimize their scheduling. One-dimensional numerical models are preferred for long term simulations, assessments on of a large number of scenarios, and optimization studies. Two- and three-dimensional numerical models and physical models can be used, each on their own or in combination as hybrid models, to understand local scouring near the gates and other details of operation. Monitoring of flushing operations can help improving their efficiency while at the same time limit downstream impacts. General monitoring of the reservoir and its catchment can help understanding the sedimentation problem and thus facilitate preparation of efficient sediment management strategies. Live monitoring of sediment concentrations is possible with modern equipment though not without challenges, and reservoir survey can be performed faster. Earth observation techniques are also an attractive option, allowing to monitor large areas and areas of difficult access, as well as to provide historical information going back several decades. This paper reviews monitoring and modelling approaches published in the literature, as well as presents some previously unpublished analyses.

A Comparison of The Performances of Conventional and Low Salinity Water Alternating Gas Injection for Displacement of Oil

Emmanuel Bucyanayandi — 2023-01-30

This study focuses on identifying the crucial physical and chemical factors, such as gravity, initial oil phase, injection depth, vertical to horizontal permeability contrast, and salinity of injected water for improving oil recovery factor during water alternating gas (WAG) injection. The conventional WAG injection attracts interest from oil and gas industry and hence, has become one of the most reliable enhanced oil recoveries (EOR) techniques. During WAG injection, due to gravity effect, water subsides below oil layer while gas overflow above the oil layer. In fact, water sweeps bottom zones of the reservoir and gas sweeps the attic oil at the upper zones of the reservoir.

Although the conventional WAG does improve oil recovery factor, there still remains a substantial amount of oil in reservoir pores due to rock-fluid and fluid-fluid interfacial tensions (IFT) that leads to the capillary forces impeding the microscopic displacement efficiency. The low salinity waterflooding (LSWF) was therefore proposed to break the IFT between rock clay and fluids, and further increase oil recovery factor. Recent researches revealed that LSWF alters oil-wet reservoir to water-wet behavior. This wettability alteration is believed to be the main mechanism of LSWF to improve oil recovery. Other mechanisms of LSWF include multi-ion exchange (MIE) between rock clay minerals and injected salt water, pH increase, and fines migration. In this study, the CMG GEM simulator was used to simulate conventional WAG injection and LSWAG injection. The simulation results showed that there is an increase of oil recovery factor of about 6% for WAG injection with low salinity water of 1027ppm to sea water of 51,346 ppm. The simulations have also showed that the physical factors namely, gravity, initial oil phase, injection depth, vertical to horizontal permeability contrast are influential on the displacement efficiency and must be studied thoroughly in the design of LSWAG operations besides the salinity and chemical composition of the injection water.

A Novel Wastewater Load Allocation Approach for River Basins Using Simulation-Optimization Models

Derya Sadak — 2023-01-30

In this study, a new wastewater load allocation approach using a linked simulation-optimization model is proposed to determine the receiving body-based discharge limits by considering the discharge standards used by the European Union Water Framework Directive. By using the proposed approach, wastewater loads of point sources can be determined in such a way that the parameters exceeding the water quality targets (WQT) in receiving water bodies meet the relevant WQT. The simulation part is used to determine pollutant concentrations throughout the river system using the AQUATOX water quality simulation model. However, since AQUATOX is an independent simulation model and its source code is not publicly available, it is not possible to execute it with the optimization model for the generated load combinations. Therefore, a concentration-response matrix (CRM) is developed as a surrogate water simulation model by using the outputs of the AQUATOX model. After this process, the developed CRM is integrated into an optimization model where the heuristic differential evolution (DE) optimization approach is used. The performance of the proposed simulation-optimization approach is evaluated on a sub-watershed of the Kucuk Menderes River Basin by considering different waste load allocation scenarios for the CBOD₅water quality parameter. The results showed that the proposed simulation-optimization approach can effectively allocate the wastewater loads among different point sources by considering the WQT values of the CBOD₅parameter.

Lucas Polynomial Solution of the Single Degree of Freedom System

Nurcan BAYKUS SAVASANERIL — 2023-01-31

Free vibration of a single degree of freedom system is a fundamental topic in mechanical vibrations. The present study introduces a novel and simple numerical method for the solution of this system in terms of Lucas polynomials in the matrix form. Particular and general solutions of the differential equation can be determined by this method. The method is illustrated by a numerical application and the results obtained are compared with those of the exact solution.