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Computational Fluid Mechanics And Heat Transfer

With the rapid developments in numerical methods for fluid mechanics,computational modeling has become an attractive tool for studying flow/sediment transport and associated pollutant fate processes in such different environments as rivers,lakes,and coastal areas,over the past three decades,a large number of computational hydrodynamic/sediment transport models have been developedThe article traces the devel-opmental stages of current representative(1D,2D,and 3D)models and describes their main features,strengths,and limitations,and is intended as a first guide to readers interested in immersing themselves in modeling and at the same time sets the stage for discussing current limitations and future needsThe article provided model formulation,the spatial and temporal characteristics,the coupling/linkage of the hydrodynamic and sediment components,the model capabilities to handle unsteady flows,bed load and suspended load,sediment exchange processes,type of sediment(cohesive versus cohesion-less),and multi-fractional sediment transportSome examples of the different model applications are summarized,the reader can use these case studies as a reference guide for model setup,calibration,and verificationThe authors also attempt to provide an insight for model users about model choice,problem and way to improve model input and calibrationThe article discussed model limitations such as simulating complex turbulent flows,sediment entrainment,multi-fractional transport rates,the treatment of the dispersion and diffusion coefficients,soil contributions from the bank or the hill slopes and floodplains,coupling between flow and sediment processes,and highlighted the future research needs for improving available hydrodynamic/sediment transport modelsAt last,the two-phase flow approach to formulate models of sediment-flow interaction and other cross-cutting issues are discussed and reviewed

Sediment transport modeling review―current and future developments

Surface runoff is a critical input in watershed management. Runoff is a driving force for soil erosion which causes sedimentation of reservoirs located at downstream of watersheds. The present study aimed to model surface runoff using the Soil and Water Assessment Tools (SWAT) model in Ketar watershed, Ethiopia. Ketar river crosses mountainous steep slope areas. High surface runoff from the Ketar watershed flows to Lake Ziway. The Ketar watershed was delineated into 35 sub-basins and 147 Hydraulic Response Units (HRUs). In this work, surface runoff was simulated using 36 years (1980–2015) meteorological data as input. The model was calibrated and validated for streamflow using sequential uncertainty fitting-2 (SUFI_2) of the SWAT Calibration and Uncertainty Programs (SWAT_CUP). The model calibrated using 12-year measured streamflow data (1988–1997) and validated using 7-year streamflow data (1998–2004). The coefficient of determination (R2) and Nash–Sutcliffe (NSE) were used to measure the performance of the model. R2 and NSE were 0.82 and 0.7 during calibration and 0.78 and 0.71 during validation, respectively. The results show that there was an excellent relation between monthly observed and simulated streamflow during both calibration and validation. Simulated average monthly surface runoff of the watershed was 112.82 mm per month. The southwest part of the watershed, which was characterized by highest annual surface runoff, covers 27% of the total area.

Surface runoff modeling in Ketar watershed, Ethiopia

The highlands of Ethiopia are highly threatened by soil erosion. Surface runoff is essential input to manage the watershed. Runoff causes soil erosion which makes sedimentation of reservoirs. The study aimed to simulate surface runoff using the Soil and Water Assessment Tools (SWAT) model in Dabus watershed, Ethiopia. The Dabus River is one of the major tributaries of the Blue Nile River which starts from southeastern highland and flows toward north. Since the topography of the watershed is mountainous steep slope areas, surface runoff is high. The Dabus watershed was delineated into 33 sub-basins and 82 hydraulic response units (HRUs). In this study, surface runoff was simulated using 30 years (1987–2016) meteorological data as an input. The model was calibrated and validated for stream flow using sequential uncertainty ftting-2 (SUFI_2) of the SWAT Calibration and Uncertainty Programs (SWAT_CUP). The model was calibrated using 9-year measured streamflow data (1994–2003) and validated using 8-year streamflow data (2004–2011). The coefficient of determination (R2) and Nash–Sutclife (NSE) were used to measure the performance of the model. R2 and NSE were 0.82 and 0.70 during calibration and 0.78 and 0.71 during validation, respectively. The results show that there was very good relation between monthly observed and simulated streamflow during both calibration and validation. Simulated average annual surface runoff of the watershed was 690.84 mm. The southeast part of the watershed was characterized by the highest annual surface runoff. Thus, this study shows that SWAT hydrological model can be used to model Dabus watershed for better assessment and simulation of the hydrological responses. The study recommends more researches which incorporate the land use change of the watershed in the model.

Surface runoff modeling using SWAT analysis in Dabus watershed, Ethiopia

Controlling erosion and deposition zones that are usually forming at rivers confluences are important for improving river hydraulic efficiency. The flow in rivers confluences is highly complex, due to rapid changes associated with the river flow dynamics, sediment transport, and morphology. A two-dimensional (2D) numerical model was used to simulate the confluence between Kurau and Ara rivers, Perak, Malaysia. The numerical model has been calibrated and validated by using field data. The model was used to investigate the effectiveness of different shapes and sizes of 30o obstacles/vanes in controlling erosion and deposition zones at the confluence of Kurau and Ara rivers. The simulation results show that the best performance of 30o obstacles/vanes was found when a single obstacle/vane was introduced in the flow.

/pdf/assessment-of-vanes-effectiveness-in-controlling-erosion-and-3wcmx6pim9.pdf

Hydar Lafta Ali

Papers

Assessment of Vanes Effectiveness in Controlling Erosion and Deposition Zones at a River Confluence using a 2D model