T. I. Eldho

Groundwater remediation optimization using a point collocation method and particle swarm optimization

Groundwater contamination is a major problem in many parts of the world. Remediation of contaminated groundwater is a tedious, time consuming and expensive process. Pump and treat (PAT) is one of the commonly used techniques for groundwater remediation. Simulation-optimization (S/O) models are very useful in appropriate design of an effective PAT remediation system. Simulation models can be employed to predict the spatial and temporal variation of contaminant plumes. Optimization models, on the other hand, can be used to minimize the cost of pumping or recharge. Generally, grid or mesh based models using Finite Difference Methods (FDM) or Finite Element Methods (FEM) are used for groundwater flow and transport simulation. Recently, Meshfree (MFree) based numerical models have been developed due to the difficulty of meshing and remeshing in these methods. The MFree Point Collocation Method (PCM) is a simple MFree method to simulate coupled groundwater flow and contaminant transport. It saves time for pre-processing such as meshing or remeshing. Evolutionary algorithm based techniques such as for particle swarm optimization (PSO) and genetic algorithms (GA) have been found to be very effective for groundwater optimization problems. In this paper, a simulation model using MFree PCM for unconfined groundwater flow and transport and a PSO based optimization model are developed. These models are coupled to get an effective S/O model for the groundwater remediation design using PAT. The S/O model is applied to the remediation design of an unconfined field aquifer polluted by Total Dissolved Solids (TDS) by using pump and treat and flushing. The model provides an effective remediation design of pumping rate for the selected wells and costs of remediation.

Performance Study of Modified Savonius Water Turbine with Two Deflector Plates

Savonius rotor is a vertical axis rotor with simple in design and easy to fabricate at lower cost. The rotation of the rotor is due to the drag difference between the advancing blade and returning blade. Net driving force can be increased by reducing the reverse force on the returning blade or increasing the positive force on the advancing blade. Former can be realized by providing a flow obstacle to the returning blade and latter can be realized by concentrating the flow towards the advancing blade. The objective of the present work is to identify the optimal position of the deflector plate (on advancing blade side) placed upstream to the flow which would result in increase in power generated by the rotor. Tests are conducted to identify the optimum position of the deflector plate on the advancing blade side in the presence of a deflector plate on the returning blade side at its optimum position. Results suggest that two deflector plates placed at their optimal positions upstream to the flow increase the coefficient of power to 0.35. This is significantly higher than the coefficient of power of 0.14 observed for the rotor without deflector plates.

An enhanced technique in construction of the discrete drainage network from low-resolution spatial database

A digital elevation model (DEM) of a watershed can be used to acquire various parameters such as basin-wide information about overland flow direction, flow accumulation and area contributing flow to any point. The resolution and quality of a DEM are important to achieve a significant level of accuracy in derived parameters. Inadequate elevation information exacerbated by applied interpolation methods, reduce DEM accuracy, resulting in pits and flat areas and makes flow tracing a difficult task. These types of problems are more prominent in cases of residual undulating terrains. In the present paper, an attempt has been made to review and suggest an improved method for the generation of a DEM from raster contour data. Further, a criteria-based region growing method (CBRGM) is presented for the extraction of discrete drainage network (cell size: 20x20m) of the watershed. Here, the flat area removal algorithm, with a variable increment, is used to generate the DEM. This induces a gradual slope even in the case of a large contour interval (20m) extended over larger area, as is commonly available from a topographic map at a scale of 1:50,000. Further, in order to capture topographic information in flow tracing, the CBRGM is followed. The rasterised stream network from the same topographic sheet is used as ancillary data to make the concentrated flow lines to follow the channel. The methodology has been tested over Gandheshwari subwatershed under the lower part of Chhotanagpur Plateau in Eastern India. The DEM generated using this method gives a better representation of the terrain, which shows good agreement with the terrain information delineated by using the contour and channel information available in the topographic sheet. The drainage network derived shows additional extra-concentrated flow lines, many of which match the drainage network obtained from satellite imagery (cell size: 23.5x23.5m). The algorithm thus shows superiority over other available methods for the extraction of drainage networks.

Study on the Interaction between Two Hydrokinetic Savonius Turbines

Savonius turbine is simple in design and easy to fabricate at a lower cost. The drag is the basic driving force for Savonius turbine. Savonius turbines are mainly used for the small-scale electricity generation in remote areas. In real life, multiple Savonius turbines are to be arranged to form a farm to scale up the electricity generation. So, it is important to study the interaction among them to avoid the power loss due to negative interaction between turbines. The purpose of this investigation is to examine closely the effect of interaction between two Savonius turbines arranged in line. Experimental investigations are carried out to study the mutual interaction between turbines with water as the working medium at a Reynolds number of 1.2×105 based on the diameter of the turbine. Influence of separation gap between the two Savonius turbines is studied by varying the separation gap ratio (𝑋/𝑅) from 3 to 8. As the separation gap ratio increases from 3 to 8, becomes lesser the mutual interaction between the turbines. Results conclude that two turbines placed at a separation gap ratio of 8 performed independently without affecting the performance of each other.

Solution of stokes flow using an iterative DRBEM based on compactly-supported, positive-definite radial basis function☆

Abstract This paper describes an iterative dual reciprocity boundary element method (DRBEM) based on the compactly-supported, positive definite radial basis function for the solution of Stokes flow problems. The method involves the solution of Laplace equations for vorticity, and Poisson equations for velocity with the solenoidal components of vorticity as right-hand sides. These equations are solved using iterative BEM and DRBEM. For the DRBEM, the compactly supported, positive definite radial basis function is used to approximate the body force term to convert it to boundary integrals. A relaxation method is devised such that the resulting algebraic equations are solved without the need of assembling a matrix. Hence, large systems of equations such as the fine discretization needed for Stokes flow problems can be handled easily. The results of Stokes flow in a square cavity and a circular cavity are presented and compared with other numerical model results. The iterative DRBEM solution is found to be satisfactory.

Solution of the advection-diffusion equation using the Eulerian-Lagrangian boundary element method

Abstract In this paper, an Eulerian–Lagrangian boundary element method (ELBEM) is proposed by the combination of the Eulerian–Lagrangian method and boundary element method for the solution of advection–diffusion problems. Based on the concept of Eulerian–Lagrangian method (ELM), the formulation of ELBEM and its associated fundamental solution is obtained for the advection–diffusion equation. Combining ELM and BEM makes it easier to handle the variable velocity field. The ELBEM model performs well for both advection-dominated and diffusion-dominated flow fields. To verify the feasibility and accuracy of the ELBEM, the model is applied to different case studies of advection–diffusion problems and the analytical solutions are compared. Fairly accurate results are obtained in all the case studies for the entire range of Peclet numbers, from very small to infinite with less oscillations, numerical dispersion and diffusion problems.

Groundwater flow simulation in unconfined aquifers using meshless local Petrov-Galerkin method

Abstract The complex behaviour of the aquifer system is generally studied by solving a set of governing equations using either analytical or numerical methods. Numerical techniques like finite difference method (FDM) and finite element method (FEM) are generally being used to solve such problems, as analytical solutions can be obtained only for simple cases. The Meshless methods are the recently developed numerical technique which can be alternatively used for solving the groundwater problem. A variety of Meshless methods are under intense research for the development of solution for many engineering problems. As no meshing, it can save substantial cost and time on pre-processing, unlike mesh based methods, which require meshing and re-meshing. In this paper, the Galerkin equivalent of Meshless Local Petrov–Galerkin (MLPG) method with Exponential/Gaussian Radial basis function (EXP–RBF) is used for the first time for solving the unconfined groundwater problem. Computer models in MATLAB have been developed in 2D for the solution of unconfined aquifer problems. The developed models are verified with available analytical and numerical solutions. The results are found to be satisfactory. The present study shows that the MLPG based method can be used in the effective simulation of groundwater flow problems.

Performance evaluation of modified versions of SCS curve number method for two watersheds of Maharashtra, India

One of the popular methods for computing the depth of surface runoff for a given rainfall event is the Soil Conservation Service Curve Number (SCS-CN) method. Research conducted on the applicability of the SCS-CN method suggested a need for improvement. Consequently, several modifications of the method have been suggested and reported in literature. The important modified versions of the method include Mishra and Singh (MS) model, Michel et al. model, Sahu et al. model and SME model. These modified models have been reported to perform better than the original method for U.S. watersheds. In the present study, these modified models are applied to two Indian watersheds in Maharashtra and are compared with each other for their performance. The results indicated that the SME and the Sahu et al. model perform equally well compared to each other, and the duo perform consistently better than the original SCS-type method and the others for both the Amba and Kalu watersheds. Further, the performance of the MS model is found to be better than the Michel et al. model.

Simulation of Radial Collector Well in Shallow Alluvial Riverbed Aquifer Using Analytic Element Method

To withdraw large quantities of groundwater from the alluvial aquifers for various uses near riverbeds, radial collector (RC) wells are often preferable to the installation of several small diameter tube wells. In regions where rivers are not perennial or have low flow conditions during most part of the year, the RC wells are placed in the riverbed to obtain uninterrupted supply of naturally filtered groundwater through highly permeable saturated riverbed aquifers. Due to the complexities of flow, no exact analytical solution exists to provide steady state discharge drawdown relationship for RC well. Numerical model construction using finite difference or finite element method is quite cumbersome because of the radial orientation of laterals. To overcome these difficulties, in this study a steady state simulation model based on analytic element method (AEM) is developed to simulate the discharge-drawdown relation for RC well in an unconfined riverbed aquifer. In the model, line-sink elements are used to r...

A combined BEM–FEM model for the velocity–vorticity formulation of the Navier–Stokes equations in three dimensions

Abstract This paper describes a combined boundary element and finite element model for the solution of velocity–vorticity formulation of the Navier–Stokes equations in three dimensions. In the velocity–vorticity formulation of the Navier–Stokes equations, the Poisson type velocity equations are solved using the boundary element method (BEM) and the vorticity transport equations are solved using the finite element method (FEM) and both are combined to form an iterative scheme. The vorticity boundary conditions for the solution of vorticity transport equations are exactly obtained directly from the BEM solution of the velocity Poisson equations. Here the results of medium Reynolds number of up to 1000, in a typical cubic cavity flow are presented and compared with other numerical models. The combined BEM–FEM model are generally in fairly close agreement with the results of other numerical models, even for a coarse mesh.