Now showing 1 - 10 of 11
  • Placeholder Image
    Publication
    On the Recommendations for Reducing CPU Time of Multigrid Preconditioned Gauss–Seidel Method
    (01-01-2021)
    Faruqi, Abdul Hannan
    ;
    Siddique, M. Hamid
    ;
    ;
    Anwer, Syed Fahad
    Gauss–Seidel method is one of the simplest available iterative methods for solving systems of linearized equations. It can effectively reduce high-frequency errors but performs poorly with errors of low frequency. Multigrid (MG) utilizes this quality of the point-wise methods by successively coarsening the grid, so that the lowest frequency errors appear as high frequency and can be easily reduced. In this work, optimization study was performed to lower the CPU time of the Multigrid method. We have considered several parameters, such as the number of grid levels used, the number of inner iterations (iterations at each intermediate grid), the overall coarsening and interpolation cycle (V and W), and the number of these cycles in each iteration. A surrogate model is used to predict optimum value for these parameters. In this chapter, MG is used with a Gauss–Seidel solver for a 2D conduction problem with Dirichlet boundary condition on a 256 × 256 structured grid. The results suggest that a W cycle is more efficient than a V cycle and should be executed to the penultimate grid level during both restriction (coarsening) and prolongation.
  • Placeholder Image
    Publication
    Optimal design of a marine current turbine using CFD and FEA
    (01-01-2019)
    Karthikeyan, Thandayutham
    ;
    Mishra, Lava Kush
    ;
    Ocean currents that are produced due to motion of tides can be utilized in power extraction by using suitable turbines. The turbine should be structurally and hydrodynamically strong. In this paper, a 0.8 m horizontal axis marine current turbine (MCT) with three blades is analyzed. A 3D CAD model of a turbine is optimized using CFD and FEA tools. The performance of the turbine is based on the coefficient of power; however, the turbine should resist the loads acting on it. The fatigue load damages the turbine which is mainly due to wave loads and it must be evaluated to avoid the cost of replacing a new turbine. Only a turbine with high power coefficient and good material strength will result in a favorable design. The parameters like pitch angles, number of blades, and turbine material are modified to study the performance and structural stability of the turbine. The detailed CFD study including boundary conditions and methodology has contributed to get an insight of the flow physics. The best suitable pitch angle and number of rotor blades for the turbine are analyzed and discussed. The optimized turbine has two rotor blades with a pitch angle of 19.5° and has achieved a significant 25% increase in CP. Later, different materials are chosen to identify the variation in stress and tip deflection of the turbine blades. This will direct toward a safe design of the turbine blades.
  • Placeholder Image
    Publication
    Combined Casing Groove and Blade Tip Treatment for Wave Energy Harvesting Turbine
    (01-01-2021)
    Madhan Kumar, P.
    ;
    Halder, Paresh
    ;
    The Wells turbine is a self-rectifying air turbine, used in oscillating water column (OWC) to harvest wave energy. It produces unidirectional torque as the flow oscillates inside the OWC chamber. It has inherent disadvantage of narrow operating range due to stall at high airflow rate. Whereas, a wider operating range is essential to improve the turbine power output. A casing groove modifies the tip leakage flow pattern and improves the operating range. In addition, a radiused tip can alter the tip leakage flow and delay the stall. To enhance the performance further, this paper investigates the combined effect of tip groove and radiused tip (CG&RT) design modification. The flow was simulated by solving steady, incompressible Reynolds averaged Navier–Stokes equations in Ansys CFX 15.0. As expected, the CG&RT blade enhanced the relative operating range and the turbine power output by 44.4% and 23.8%, respectively.
  • Placeholder Image
    Publication
    Optimization of Gap-to-Chord Ratio of Wells Turbine with Guide Vanes for Wave Energy Conversion
    (01-01-2021)
    Varghese, F. A.
    ;
    Wells turbine (WT) used for harnessing wave energy has narrow operating range and poor starting characteristics. To enhance its starting and running characteristics, guide vanes (GV) are installed upstream and downstream of the rotor. This paper studies the effect of the gap-to-chord (G/ lr) ratio of the WT GV on the turbine performance numerically. The work incorporates validation of the numerical simulations with experimental results and application of optimization techniques to find the optimal G/ lr ratio. A range for G/ lr ratio is suitably selected for the analysis and metamodel based on Kriging algorithm is developed. Following this, the optimization algorithm of screening is utilized to find the optimal conditions to achieve the objective function.
  • Placeholder Image
    Publication
    Analyzing Different Methods to Increase the Natural Period of a Compact Wave Energy Converter
    (01-01-2021)
    Vijayasankar, Vishnu
    ;
    In this article, we present the numerical analysis performed on a compact mechanical-based direct drive wave energy converter (WEC), in order to improve its performance on longer wave periods. For this work, the numerical modeling of the point absorber is done with the help of an open-source code written in MATLAB, WEC-Sim and the hydrodynamic parameters of the WEC are determined using the BEM code AQWA. From the past experience, it is a known fact that the range of frequencies for which a point absorber can perform satisfactorily is less if they are small-sized. In this work, we make an effort to increase the operational bandwidth of a point absorber and to match the natural period of the system with the period of sea waves, without increasing its size (diameter). During the process, the variation in different hydrodynamic coefficients and performance parameters, triggered by the proposed design alteration is studied. In the end, it has been concluded that the proposed modification was able to improve the operational bandwidth of the device and the resonant frequency of the system was reduced, as expected.
  • Placeholder Image
    Publication
    Preface
    (01-01-2019) ; ;
    Saha, Nilanjan
    ;
  • Placeholder Image
    Publication
    Surrogate-based optimization of a biplane wells turbine
    (01-01-2019)
    Das, Tapas K.
    ;
    Oscillating Water Column (OWC) is one of the most popular wave energy converters being used for the last two decades. The pneumatic energy from water waves inside the air chamber of OWC is converted into mechanical energy with the help of Wells turbine. Biplane Wells turbine has inherent advantage over the monoplane turbine in terms of starting characteristics and operating range. The main parameters affecting the performance of biplane Wells turbine are the gap between the planes and the offset angle between blades in two planes. Surrogate-based optimization represents the optimization methodologies that use surrogate modelling techniques to find out maxima or minima. Surrogate modelling techniques are very useful for design analysis that uses computationally expensive codes such as Computational Fluid Dynamics (CFD). In the present work, flow over a biplane Wells turbine is simulated using CFD and optimized using surrogate approach. Radial Basis Neural Network (RBNN) method is used to create the surrogate. Blade thickness and the offset angle defining the circumferential position of blades in two planes are considered as the two variables and the objective function is taken as efficiency of the turbine rotor. The comparison of performance between the reference blade and the optimized blade is presented in this article.
  • Placeholder Image
    Publication
    Control-oriented wave to wire model of oscillating water column
    (01-01-2019)
    Suchithra, R.
    ;
    The interest in wave energy converters (WECs) is increasing, the study of grid connection of WEC along with the control system has become inevitable. WEC such as an oscillating water column (OWC) device involves conversions in various physical domains, thus a model describing the conversions at each stage and coupling between them should be accurate yet simple enough to reduce the computation time involved. The already existing models do not include all the components of wave to wire conversion. This paper presents a wave to wire model for control system studies. The model reduction technique is used to create a dynamically equivalent model for any large systems have more interconnecting stages. The dynamics involved in conversion stages are hydrodynamic and aerodynamic coupling at the capture chamber, aerodynamic and thermodynamic coupling inside the capture chamber, aerodynamic and rotor dynamic coupling in air turbine; and rotor dynamics and generator dynamics in the turbine generator coupling. Thus, a wave to wire model is represented to capture all the dynamics involved. It is observed that the model retains its fundamental physics, improves the computation time and reduces the number of unknowns to describe the state-space of OWC system. The accuracy and efficiency of the model is investigated through various static and dynamic analyses and found acceptable for OWC-WEC control system studies.
  • Placeholder Image
    Publication
    Hysteresis behavior for wave energy conversion device under alternative axial flow conditions
    (01-01-2019)
    Halder, Paresh
    ;
    Das, Tapas K.
    ;
    ;
    Mohamed, Mohaned H.
    Wells turbine is an axial flow air turbine extensively used in the oscillating water column (OWC) of ocean energy harvesting device. The turbine has low aerodynamic efficiency at higher flow rate and poor starting characteristics. In this paper, the characteristics of the hysteresis behavior of a Wells turbine for a wave energy conversion device under alternative axial flow conditions are reported. The numerical work is carried out by solving the three-dimensional unsteady Reynolds Average Navier–Stokes equations (URANS) with two-equation eddy viscosity model. It is noticed that the unsteady numerical results are associated with two hysteresis loop. In the clockwise hysteresis loop, larger flow separation can be noticed on the blade suction side due to stronger vortex while flow separation decreases due to weaker vortex during counterclockwise hysteresis loop. Also, the effect of the blade sweep and blade profile thickness on the hysteresis behavior of the wave energy conversion device are reported.
  • Placeholder Image
    Publication
    Design and Optimization of Bio-inspired Fluidic Diode for Wave Energy Harvesting System
    (01-01-2023)
    Hithaish, Doddamani
    ;
    Two coupled turbines are used to harness wave energy using a pair of fluidic diodes (FDs). A better FD should have a higher diodicity defined as the ratio of pressure drop in reverse to forward flow direction. The reverse flow occurs when the wave pushes air out of the system, and one diode-linked turbine gets power, while the forward flow gives power to the other diode-linked turbine. In this article, an FD is proposed and studied numerically by solving three-dimensional Reynolds Navier–Stokes equations. The FD shape is optimized using a surrogate-based optimization technique. The result shows that the optimized diodicity is increased by 185% because the reduction in the throat diameter of the model facilitated a higher resistance to the reverse direction.