Now showing 1 - 10 of 11
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    Development of a reduced order wave to wire model of an OWC wave energy converter for control system analysis
    (15-01-2019)
    Suchithra, R.
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    Ezhilsabareesh, K.
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    Wave energy converters (WECs) face difficulties such as low operating range, low power output and, fluctuating power. A seamless synchronization among WEC components is required to get a better performance. For control system studies, the model should capture all the necessary dynamics involved in each conversion stages, however the interlinked complexity in each subsystem increases the computation time. This article presents a reduced order wave-to-wire (WTW) model of an oscillating water column (OWC) based WEC. The approach involves modeling of hydrodynamic and aerodynamic coupling of 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. The result shows that the model retains its fundamental dynamics and reduces the number of unknowns to describe the state space. The model indicates the correlation of each variable represented in the state space. The model predicted power output for different sea state. It also shows that the accuracy and the efficiency of the model are acceptable for OWC-WEC control system studies. The present model can be used as a time domain tool to design an effective control system for OWC device for different sea states, and the overall device performance can be improved significantly.
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    Publication
    Control-oriented wave to wire model of oscillating water column
    (01-01-2019)
    Suchithra, R.
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    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.
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    Performance Analysis of an Air Turbine for Ocean Energy Extraction Using CFD Technique
    (01-06-2019)
    Thandayutham, Karthikeyan
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    Salam, A.
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    Baruah, D.
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    Dudhgaonkar, P. V.
    The oscillating water column, which has a pneumatic section, can convert wave energy to air pressure, and thus, it rotates the turbine. The system has an inherent weakness of having low efficiency. Typically, the small Wells or axial turbines without any modifications have an efficiency of less than 40% under good sea wave condition which is a drawback and considered as less efficient to extract energy from the oceans. In this paper, the performance of the turbine is studied and analyzed by a computational fluid dynamics technique. ANSYS commercial code is used to discretize the mass, momentum, energy equations, and the turbine efficiency was evaluated. Different guide vane angles and turbine diameters were considered for the simulations. The modified turbines are simulated to operate in various rotational speeds which are similar to an actual working of oscillating water column. This helps to find a suitable operational range for the proposed turbine for energy extraction. It was found that the bigger turbines are expected to produce relatively higher efficiencies at lower speeds and lower pressures.
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    A pareto optimal front of fluidic diode for a wave energy harnessing device
    (15-09-2022)
    Hithaish, Doddamani
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    Siddique, M. Hamid
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    A twin-turbine or turbine duo (TUD) is constructed from a pair of unidirectional turbines. Flow reversal hampers the performance of these units. A Fluidic diode (FD) that offers a variable resistance to the flow can be used with TUD to prevent flow reversal, and its performance is governed by diodicity. With the increase in diodicity, flow blockage improves, but the resistance across the turbines increases too. As these turbines operate under a smaller pressure drop, the FD used with them should have higher diodicity with lesser fluid resistance across them. This study presents a multi-objective shape optimization of an FD to maximize diodicity and minimize pressure drop. The shape optimization is performed by simultaneously varying six design parameters. The performance of FD was evaluated by solving the 3D Reynolds Averaged Navier-Stokes equations. The popular evolutionary search algorithm (NSGA-II) with an artificial neural network produced a set of non-dominated optimal solutions (Pareto optimal set). Compared to the base model, the optimal design set shows improved diodicity from 17.2 to 21.57% and pressure drop from −2.535% to 78.67%, respectively. Further, the flow analyses of optimal designs show that the nozzle angle and the toroidal cup radius affect more than the other variables.
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    Performance enhancement of an impulse turbine for OWC using grouped grey wolf optimizer based controller
    (15-10-2019)
    Ezhilsabareesh, K.
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    Suchithra, R.
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    This work deals with unsteady analysis and control of a bi-directional impulse turbine equipped in oscillating water column (OWC) wave energy converter (WEC). The Unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved to get the turbine characteristics and the maximum efficiency tracking for different axial velocities. The grouped grey wolf optimization (GGWO) algorithm finds the optimal gains of proportional-integral-derivative (PID) controllers of a permanent magnet synchronous generator (PMSG), such that a maximum efficiency tracking can be achieved. The URANS analysis show that the best efficiency point (BEP) occurs at a flow coefficient of 1.25. The GGWO based controller increases efficiency by 61.5% and 4% compared to the uncontrolled and conventionally controlled case, respectively and limits the peak-to-average power ratio by 38.6% compared to the uncontrolled case.
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    Surrogate based optimization of a Bi-Directional impulse turbine for OWC-WEC: Effect of guide vane lean and stagger angle for pseudo-sinusoidal wave conditions
    (15-04-2021)
    Ezhilsabareesh, K.
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    Suchithra, R.
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    Thandayutham, Karthikeyan
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    An oscillating water column (OWC) wave energy device can use a bidirectional flow impulse turbine for energy extraction. The airflow velocity profiles during inhalation and exhalation of the OWC are asymmetric, and the flowrate at exhalation is higher. Hence, this article presents an optimized turbine to work for asymmetrical airflow conditions. The rotor blade setting angle (γ) was made asymmetric with a non-zero setting angle, and the guide vane shape was optimized. The unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved to get the objective function values for the Latin hypercube sampling (LHS) generated design space. A pseudo-sinusoidal velocity profile replicating the flow inside the OWC device was used for the transient simulations. A weighted average surrogate model generated the initial population for a hybrid genetic algorithm to produce optimum designs. The effect of turbine induced damping and starting characteristics were analyzed under irregular flow conditions obtained from the Pierson–Moskowitz wave spectrum. The optimized turbine resulted in better starting and running characteristics. Also, the mean efficiency of the optimized turbine was increased relatively by 9.5%.
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    Optimization based higher order sliding mode controller for efficiency improvement of a wave energy converter
    (15-11-2019)
    Suchithra, R.
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    Ezhilsabareesh, K.
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    This paper deals with the efficiency maximization of a wave energy converter (WEC). The WEC is an oscillating water column (OWC) device and drives a permanent magnet synchronous generator (PMSG) through a bidirectional flow impulse-turbine. The converter faces challenges such as large peak-to-average power ratio, low overall efficiency, and inefficient energy absorption for regular and irregular sea states. In this context, a higher order sliding mode controller (HOSMC) was proposed, and its gains were optimized to control through the best efficiency point tracking (BEPT) of the turbine. The flow through the turbine-passage was simulated by the computational fluid dynamics (CFD) technique, and the BEPT characteristics were obtained. An adaptive inertia-weight particle-swarm algorithm and a grouped grey-wolf algorithm were used for optimization. The Optimized HOSMC reduced chattering, minimized the reaching time and improved the mean efficiency by about 67% compared to the uncontrolled cases. In addition, the relative improvement of the mean efficiency was at least 4.8% compared to conventional controllers. The controller reduced the peak-to-average power ratio of at least 35.6% relative to the uncontrolled case of the turbine under different sea states.
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    Design and Optimization of Bio-inspired Fluidic Diode for Wave Energy Harvesting System
    (01-01-2023)
    Hithaish, Doddamani
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    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.
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    Dynamic performance of a fluidic diode subjected to periodic flow
    (15-01-2023)
    Doddamani, Hithaish
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    This paper presents the dynamic behavior of a fluidic diode (FD) subjected to periodic flow (oscillatory flow). This study captures the transient performance of the FD, which a steady-state flow analysis cannot predict, helping in better prediction of the performance and in designing an efficient model for the real sea flow profile. The FD offers variable resistance to the flow depending on its geometrical shape. Its performance is given by diodicity, which is a ratio of pressure drop in reverse to forward flow. It is used with the turbine to improve flow rectification. The numerical model is solved for three-dimensional unsteady Reynolds-Averaged Navier Stokes equations using ANSYS Fluent 16.1. The article presents the FD's detailed transient flow behavior and performance with the turbine. The FD operating in oscillatory flow performed better than in a steady flow because of the dynamic nature of the fluid. The analytical study shows that the performance of FD with turbine performed better at lower flow-coefficient.
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    Design Optimization of a Fluidic Diode for a Wave Energy Converter via Artificial Intelligence-Based Technique
    (01-09-2023)
    Hithaish, Doddamani
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    Das, Tapas K.
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    Takao, Manabu
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    A pair of turbines can harness power from a wave energy Converter. Their performance is poor than individual turbines due to flow reversal. A fluidic diode (FD) which offers variable resistance to the flow, can be used to prevent flow reversal and improve the performance of these units. Its performance is given by diodicity (ratio of reverse to forward flow pressure drop). A higher diodicity enables it to prevent flow reversal better and improve the turbine unit’s overall efficiency. In this work, the geometrical shape of the FD is optimized to obtain higher diodicity. Six geometrical variables of the FD are varied to obtain sample points using the sampling technique, which is numerically investigated by solving steady-state Reynolds averaged Navier–Stokes (RANS) equations. These numerical results were fed into a neural network code that produced an optimal FD design. The optimum model showed a 36.5% improvement in diodicity at 0.35 m3/s. The fluid flowing through the optimized model experience higher resistance in the reverse direction because of the increased vortex strength than the base model. Among all the design variable considered, nozzle angle is a highly sensitive parameter in the optimization process. The optimum FD model enhanced the overall efficiency of the turbine unit by 13.3.