Download or read book Numerical Modeling of the Effects of a Free Surface on the Operating Characteristics of Marine Hydrokinetic Turbines written by Samantha Jane Adamski and published by . This book was released on 2013 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt: Marine Hydrokinetic (MHK) turbines are a growing area of research in the renewable energy field because tidal currents are a highly predictable clean energy source. The presence of a free surface may influence the flow around the turbine and in the wake, critically affecting turbine performance and environmental effects through modification of the wake physical variables. The characteristic Froude number that control these processes is still a matter of controversy, with the channel depth, the turbine's hub depth, the blade tip depth and the turbine diameter as potential candidates for a length scale. We use a Reynolds Averaged Navier Stokes (RANS) simulation with a Blade Element Theory (BET) model of the turbine and with a Volume of Fluid model, which is used to track the free surface dynamics, to understand the physics of the wake-free surface interactions. Pressure and flow rate boundary conditions for a channel's inlet, outlet and air side have been tested in an effort to determine the optimum set of simulation conditions for MHK turbines in rivers or shallow estuaries. Stability and accuracy in terms of power extraction and kinetic and potential energy budgets are considered. The goal of this research is to determine, quantitatively in non-dimensional parameter space, the limit between negligible and significant free surface effects on MHK turbine analysis.

Download or read book Computational Methods and Experimental Measurements XVIII written by G.A. Carlomagno and published by WIT Press. This book was released on 2017-09-20 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: Papers presented at the CMEM 2017 conference form this book, which includes research from scientists, researchers and specialists who perform experiments, develop computer codes and carry out measurements on prototypes. A wide variety of topics related to new experimental and computational methods are explored.

Download or read book Modeling and Optimizing Hydrokinetic Turbine Arrays Using Numerical Simulations written by Olivier Gauvin Tremblay and published by . This book was released on 2021 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to plan a river hydrokinetic turbine array deployment and to maximize its energy extraction, turbine array simulations are often carried out. However, in a context where tens of turbines are deployed, it is unthinkable to simulate the complete rotating geometry of every turbine. It is therefore necessary to use simplified models that reproduce accurately the turbines and that incorporate all the main interactions taking place in a turbine array, namely the turbine-wake interactions, the blockage effects and the interaction with the resource. The Effective Performance Turbine Model (EPTM) is a suitable tool in that sense, allowing to test and analyze a large amount of different array configurations at a low computational cost. Although the EPTM has been developed to serve as a tool for array analysis, it has only been tested up to now in a uniform flow with a low turbulence level. For this reason, the EPTM has been validated and adapted in this work to ensure a proper and reliable use in river array flow conditions. Herein, the efforts has been mainly put on a cross-flow turbine (CFT) technology. First, a numerical methodology has been developed to reproduce river flow conditions and array flow conditions, which include shear, large-scale temporal fluctuations and (modeled) turbulence. Following 3D blade-resolved turbine simulations, it is found that a turbine operating in those conditions sees a reduction of its performance, especially when the shear aspect is present. However, it turns out that the effective drag coefficient remains essentially unchanged, allowing to use the same local effective force coefficient distribution in every situation. Moreover, although the effective power coefficient appears to be lower than for a turbine in idealized flow conditions, it does not vary depending of the type of perturbation and its decrease is small under free-surface conditions. This is important for the use of the EPTM, since the simplified model is based on this assumption. Multiple comparisons between EPTM and blade-resolved turbine simulations in river/array flow conditions have confirmed that the EPTM-CFT is always able to predict accurately the performances of the turbines and to reproduce their mean wake with a high degree of reliability. Following this validation procedure, a series of turbine array simulations have been conducted using the EPTM-CFT. Assuming a turbulent flow environment, many vertical-axis turbine array configurations have been tested to study more precisely the effect of local blockage, lateral and longitudinal spacing, array staggering and direction of rotation on turbine performance. Results have shown that all aspects of blockage, local and global, must be considered simultaneously with the possibility of turbine-wake interaction, especially when the turbines generate a wake that deflects sideways down-stream. The latter aspect could play an important role in determining whether or not the array should be staggered. For a multiple-row array, this aspect also affects the relevance of the different array parameters used. Indeed, in this context, the lateral spacing becomes more meaningful than the local blockage value. To help decide on the optimal lateral and longitudinal spacing to set within an array, a new parameter has been proposed: the marginal power per turbine. As many economic variables can come into play, this parameter helps quantifying the benefit of adding rows or columns of turbines in comparison to the already installed power. Finally, it is possible, for an identified optimal turbine array, to assess its impact on the resource. Based on an actual river site, a realistic simulation of a turbine array in river has been performed using the methodology previously developed. The simulation results, compared with the results of more simplified simulations, have pointed out that an appropriate channel geometry and an accurate inflow velocity distribution are essential to obtain reliable array performances. Although it arises that taking into account the free surface has negligibly affected the array performances and the water level upstream for the case considered, it remains that the assessment of the impact on the resource is always relevant since the rise in the water level can be larger if the blockage ratio or the Froude number are higher.

Download or read book Numerical Simulation for Moored Marine Hydrokinetic Turbines written by Basil L. Hacker (Jr.) and published by . This book was released on 2013 with total page 69 pages. Available in PDF, EPUB and Kindle. Book excerpt: The research presented in this thesis utilizes Blade Element Momentum (BEM) theory with a dynamic wake model to customize the OrcaFlex numeric simulation platform in order to allow modeling of moored Ocean Current Turbines (OCTs). This work merges the advanced cable modeling tools available within OrcaFlex with well documented BEM rotor modeling approach creating a combined tool that was not previously available for predicting the performance of moored ocean current turbines. This tool allows ocean current turbine developers to predict and optimize the performance of their devices and mooring systems before deploying these systems at sea. The BEM rotor model was written in C++ to create a back-end tool that is fed continuously updated data on the OCT's orientation and velocities as the simulation is running. The custom designed code was written specifically so that it could operate within the OrcaFlex environment. An approach for numerically modeling the entire OCT system is presented, which accounts for the additional degree of freedom (rotor rotational velocity) that is not accounted for in the OrcaFlex equations of motion. The properties of the numerically modeled OCT were then set to match those of a previously numerically modeled Southeast National Marine Renewable Energy Center (SNMREC) OCT system and comparisons were made. Evaluated conditions include: uniform axial and off axis currents, as well as axial and off axis wave fields. For comparison purposes these conditions were applied to a geodetically fixed rotor, showing nearly identical results for the steady conditions but varied, in most cases still acceptable accuracy, for the wave environment. Finally, this entire moored OCT system was evaluated in a dynamic environment to help quantify the expected behavioral response of SNMREC's turbine under uniform current.

Download or read book Analytical and Numerical Modeling of Performance Characteristics of Cross flow Hydrokinetic Turbines written by Alex J. Johnston and published by . This book was released on 2011 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Flow and Fluid Structures on the Performance of Vertical River Hydrokinetic Turbines written by Amir Hossein Birjandi and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Integrated Nonlinear Wind Waves Model for Offshore Wind Turbines written by Enzo Marino and published by Firenze University Press. This book was released on 2010 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents a numerical model capable of simulating offshore wind turbines exposed to extreme loading conditions. External condition-based extreme responses are reproduced by coupling a fully nonlinear wave kinematic solver with a hydro-aero-elastic simulator. First, a two-dimensional fully nonlinear wave simulator is developed. The transient nonlinear free surface problem is formulated assuming the potential theory and a high-order boundary element method is implemented to discretize Laplace's equation. For temporal evolution a second-order Taylor series expansion is used. The code, after validation with experimental data, is successfully adopted to simulate overturning plunging breakers which give rise to dangerous impact loads when they break against wind turbine substructures. Emphasis is then placed on the random nature of the waves. Indeed, through a domain decomposition technique a global simulation framework embedding the numerical wave simulator into a more general stochastic environment is developed. The proposed model is meant as a contribution to meet the more and more pressing demand for research in the offshore wind energy sector as it permits taking into account dangerous effects on the structural response so as to increase the global structural safety level.

Download or read book Recent Advances in Mechanical Engineering written by Gaurav Manik and published by Springer Nature. This book was released on 2022-09-08 with total page 1149 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the select proceedings of 2nd International Congress on Advances in Mechanical and Systems Engineering (CAMSE 2021). It focuses on the recent advances in mechanical and systems engineering and their growing demands for increase in several design and development activities. The contents in this book cover a blend of mechanical engineering, computer-aided engineering, control engineering, and systems engineering to design and manufacture useful products. Various additional topics covered include mechanics, machines, materials science, thermo-fluids, and control with state-of-the-art computational methods to analyse, innovate, design, implement and operate complex systems which are economic, reliable, efficient and sustainable. Given the contents, this book will be useful for researchers and professionals working in the field of mechanical engineering and allied fields.

Download or read book Numerical Simulation of a Cross Flow Marine Hydrokinetic Turbine written by Taylor Jessica Hall and published by . This book was released on 2012 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the search for clean, renewable energy, the kinetic energy of water currents in oceans, rivers, and estuaries is being studied as a predictable and environmentally benign source. We investigate the flow past a cross flow hydrokinetic turbine (CFHT) in which a helical blade turns around a shaft perpendicular to the free stream under the hydrodynamic forces exerted by the flow. This type of turbine, while very different from the classical horizontal axis turbine commonly used in the wind energy field, presents advantages in the context of hydrokinetic energy harvesting, such as independence from current direction, including reversibility, stacking, and self-starting without complex pitch mechanisms. This thesis develops a numerical simulation methodology that applies the Reynolds Average Navier Stokes equations and the three-dimensional sliding mesh technique to model CFHTs. The methodology is validated against small scale experiments, available within NNMREC at the University of Washington and is used to investigate the efficiency of the energy capture and the hydrodynamic forces acting on the blades. First, we study the stationary turbine and conclude that the developed methodology accurately models the starting torque of a turbine initially in static conditions; some limitations are found, however, in predicting separated flow. The dynamic performance of the rotating turbine is predicted with reasonable accuracy using the sliding mesh technique. Excellent qualitative agreement with experimental trends is found in the results, and the actual predicted values from the simulations show good agreement with measurements. Though limitations in accurately modeling dynamic stall for the rotating turbine are confirmed, the good qualitative agreement suggests this methodology can be used to support turbine design and performance over a wide range of parameters, minimizing the number of prototypes to build and experiments to run in the pursuit of an optimized turbine. This methodology can also provide a cost-effective way of evaluating detailed full scale effects, such as mooring lines or local bottom bathymetry features, on both turbine performance and environmental assessment.

Download or read book Fractal Grid turbulence and Its Effects on a Performance of a Model of a Hydrokinetic Turbine written by Altayeb Mahfouth and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on generating real world turbulence levels in a water tunnel rotor test using fractal grids and characterizing the effect of the fractal grid generated-turbulence on the performance of hydrokinetic turbines. The research of this thesis is divided into three studies: one field study and two laboratory studies. The field study was conducted at the Canadian Hydro Kinetic Turbine Test Centre (CHTTC) on the Winnipeg River. An Acoustic Doppler Velocimeter (ADV) was used in the field study to collect flow measurements in the river. The laboratory studies were conducted at the University of Victoria (UVic) fluids research lab and the Sustainable Systems Design Lab (SSDL). In addition, the Particle Image Velocimetry (PIV) technique was used in the experiential studies to obtain quantitative information about the vector flow field along the test section, both upstream and downstream of the rotor's plane.The first study is a field study aiming to provide real flow characteristics and turbulence properties at different depths from the free-surface to boundary layer region of a fast river current by conducting a field study in the Winnipeg River using ADV. A novel technique to deploy and control an ADV from free-surface to boundary layer in a fast-current channel is introduced in this work. Flow characteristics in the river, including mean flow velocities and turbulence intensity profiles are analyzed. The obtained results indicate that the maximum mean velocity occurs below the free-surface, suggesting that the mean velocity is independent of the channel depth. From the free-surface to half depth, it was found that changes in both the mean velocity and turbulence intensity are gradual. From mid-depth to the river bed, the mean velocity drops rapidly while the turbulence intensity increases at a fast rate. The turbulent intensity varied from 9% at the free-surface to around 17.5% near the river bed. The results of this study were used in the second lab study to help designing a fractal grid for a recirculating water flume tank. The goal was to modify the turbulence intensity in the water tunnel such that the generated turbulence was similar to that in the river at a location typical of a hydrokinetic device. The properties of fractal-generated turbulence were experimentally investigated by means of 2D Particle Image Velocimetry (PIV). The streamwise turbulent intensity profiles for different grids along the channel are presented. Additionally, visualization of the average and fluctuating flow fields are also presented. The results are in good agreement with results in literature. The third and final study investigated the power coefficient of a scale hydrokinetic turbine rotor in controlled turbulent flow (7.4 % TI), as well as in the low-turbulence smooth flow (0.5% TI) typical of lab scale testing. PIV was employed for capturing the velocity field. The results show that using realistic TI levels in the water tunnel significantly decrease the turbine's power coefficient compared to smooth flow, highlighting the importance of considering this effect in future experimental campaigns.

Download or read book An Evaluation of the U S Department of Energy s Marine and Hydrokinetic Resource Assessments written by National Research Council and published by National Academies Press. This book was released on 2013-04-23 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing renewable energy development, both within the United States and abroad, has rekindled interest in the potential for marine and hydrokinetic (MHK) resources to contribute to electricity generation. These resources derive from ocean tides, waves, and currents; temperature gradients in the ocean; and free-flowing rivers and streams. One measure of the interest in the possible use of these resources for electricity generation is the increasing number of permits that have been filed with the Federal Energy Regulatory Commission (FERC). As of December 2012, FERC had issued 4 licenses and 84 preliminary permits, up from virtually zero a decade ago. However, most of these permits are for developments along the Mississippi River, and the actual benefit realized from all MHK resources is extremely small. The first U.S. commercial gridconnected project, a tidal project in Maine with a capacity of less than 1 megawatt (MW), is currently delivering a fraction of that power to the grid and is due to be fully installed in 2013. As part of its assessment of MHK resources, DOE asked the National Research Council (NRC) to provide detailed evaluations. In response, the NRC formed the Committee on Marine Hydrokinetic Energy Technology Assessment. As directed in its statement of task (SOT), the committee first developed an interim report, released in June 2011, which focused on the wave and tidal resource assessments (Appendix B). The current report contains the committee's evaluation of all five of the DOE resource categories as well as the committee's comments on the overall MHK resource assessment process. This summary focuses on the committee's overarching findings and conclusions regarding a conceptual framework for developing the resource assessments, the aggregation of results into a single number, and the consistency across and coordination between the individual resource assessments. Critiques of the individual resource assessment, further discussion of the practical MHK resource base, and overarching conclusions and recommendations are explained in An Evaluation of the U.S. Department of Energy's Marine and Hydrokinetic Resource Assessment.

Download or read book Numerical Modeling of Hydrokinetic Turbines Using Actuator Disks written by Domenico Andrés Sciolla Piñeyro and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: El desarrollo de nuevas tecnologías para aprovechar la energía de las corrientes de marea en las zonas costeras, requiere una comprensión en profundidad de las interacciones entre el flujo natural en las tres dimensiones (3D) sobre batimetrías arbitrarias y las turbinas marinas hidrocinéticas (MHK), que se podrían instalar en un sitio específico. El diseño óptimo de las granjas de turbinas y la evaluación de sus impactos ambientales requiere un enfoque en múltiples escalas para analizar los efectos, a partir de una escala local en las proximidades de los dispositivos hasta una escala mayor que comprende toda la región costera afectada. A pesar de los recientes avances en el estudio de la hidrodinámica del flujo en la presencia de conjuntos de turbinas, todavía existe la necesidad de desarrollar modelos numéricos capaces de resolver las estelas generadas por múltiples dispositivos en flujos turbulentos con altos números de Reynolds, capturando las interacciones con geometrías complejas presentes en los ambientes acuáticos reales, utilizando recursos computacionales asequibles.

Download or read book Numerical Investigation of Marine Hydrokinetic Turbines written by Amir Teymour Javaherchi Mozafari and published by . This book was released on 2014 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: A hierarchy of numerical models, Single Rotating Reference Frame (SRF) and Blade Element Model (BEM), were used for numerical investigation of horizontal axis Marine Hydrokinetic (MHK) Turbines. In the initial stage the SRF and BEM were used to simulate the performance and turbulent wake of a flume- and a full-scale MHK turbine reference model. A significant level of understanding and confidence was developed in the implementation of numerical models for simulation of a MHK turbine. This was achieved by simulation of the flume-scale turbine experiments and comparison between numerical and experimental results. Then the developed numerical methodology was applied to simulate the performance and wake of the full-scale MHK reference model (DOE Reference Model 1). In the second stage the BEM was used to simulate the experimental study of two different MHK turbine array configurations (i.e. two and three coaxial turbines). After developing a numerical methodology using the experimental comparison to simulate the flow field of a turbine array, this methodology was applied toward array optimization study of a full-scale model with the goal of proposing an optimized MHK turbine configuration with minimal computational cost and time. In the last stage the BEM was used to investigate one of the potential environmental effects of MHK turbine. A general methodological approach was developed and experimentally validated to investigate the effect of MHK turbine wake on the sedimentation process of suspended particles in a tidal channel.

Download or read book Analysis of Hydrokinetic Turbines in Open Channel Flows written by Arshiya Hoseyni Chime and published by . This book was released on 2013 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rivers and irrigation canals are good candidates to produce small-scale hydrokinetic power. Traditionally, gates are used to control water flow in such waterways by dissipating kinetic energy of the flow. This study investigates potential of replacing these gates with Horizontal Axis Hydrokinetic Turbines (HAHT). These machines are designed so that not only power can be extracted but also flow is going to be maintained at the required flow rate. This application increases renewable energy capacity and decreases energy dependency on foreign resources. In this study, theoretical and numerical approaches are used to model HAHT in open channel flows. Theoretical method uses one-dimensional control volume analysis to predict maximum power that an ideal rotor can extract from the flow as useful power and wake mixing at a given Froude number and blockage ratio. This method is then compared to three-dimensional Actuator Disc Model (ADM) developed in commercial Computational Fluid Dynamic (CFD) code ANSYS Fluent. This model uses a porous media to represent HAHT and Reynolds-Average Navier-Stokes (RANS) equations along with Volume of Fluid (VoF) model to solve for flow field and track the free surface. Same computation method is implemented with a more advanced model, Virtual Blade Model (VBM), which uses blade element theory to consider geometry of the blade and operating conditions such as angular velocity and pitching angle. This method is used to optimize the turbine geometry for maximum power and find operating limits to avoid cavitation. Previous literature mostly concentrates on performance of Horizontal Axis Tidal Turbines in channels where blockage ratio is low and consequently free-surface deflection is not a matter of interest. Even in cases where blockage was considered in order to validate flume experiments, velocity deficit of wake region was the main focus. However, this research attempts to fill the gap in literature for better understanding the power extraction of HAHT and subsequent head loss (flow control) in highly blocked flows using three methods mentioned above. In addition, this work attempts to use validated VBM to answer if one-dimensional theory and CFD ADM are capable of predicting power production of HAHTs in highly blocked and low head flows such as irrigation canals.

Download or read book Numerical Modeling of Tethers and Its Experimental Validation Under Slack Conditions with Applications to Tethered Marine Hydrokinetic Energy Systems written by Neelav Ankit and published by . This book was released on 2021 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development and Assessment of a Modeling Method for Hydrokinetic Turbines Operating in Arrays written by Sébastien Bourget and published by . This book was released on 2018 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to contribute to the development of the hydrokinetic power industry, a new line of research has been initiated recently at the Laboratoire de Mécanique des Fluides Numérique (LMFN) de l'Université Laval. It is related to the optimization of turbine farm layouts. As the numerical modeling of turbine farms has been little investigated in the past at the LMFN, the objectives of this work are to develop a numerical methodology that will allow the study of turbine farm layouts at reasonable simulation cost and to verify its reliability. Inspired from numerical models found in the available literature, an original modeling approach is developed. This modeling approach is referred-to as the Effective Performance Turbine Model, or EPTM. The EPTM reliability is assessed in terms of its capacity to predict correctly the mean performances and the wake recovery of the turbines. The results of "high-fidelity" CFD simulations, which include at high cost the complete rotor geometry, are used as a reference. Results of the performance assessment show that the EPTM approach is appropriate for the modeling of both axial-flow (horizontal-axis) turbines and cross-flow (vertical-axis) turbines operating in clean flow conditions. Indeed, the EPTM provides very good predictions of the value of the optimal angular speed at which the rotor should be rotating to operate near maximum power extraction, the magnitude of the mean forces acting on the turbine and the mean power it extracts from the flow. The EPTM also succeeds to generate the adequate nearwake flow topology of each of the reference turbine investigated. However, the steady turbulence modeling approach used in the EPTM simulations appears inadequate in some cases. Possible model improvements are discussed as a conclusion.

Download or read book Numerical Analysis of an Axial Flow Horizontal Axis Marine Hydrokinetic Turbine written by Aarshana Parekh and published by . This book was released on 2019 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tidal energy extraction using marine hydrokinetic devices has become an important area of research in the renewable energy field in recent years because of the highly predictable nature of the tides. Due to its early stage of development, many studies need yet to be done before deployment of these devices at tidal sites. It is essential to have a thorough understanding of the turbine performance and wake properties before determining the array arrangement for tidal farms. In this thesis, flow behavior in the wake of a counter-rotating dual rotor horizontal axis tidal turbine is studied by numerically solving the Reynolds Averaged Navier Stokes (RANS) Equations. The rotational effects of the turbine are modeled using the sliding mesh technique. The realizable k-epsilon model is employed to solve the closure problem. The methodology is validated against experimental data measured in open channel tests conducted at the St. Anthony Falls Laboratory of the University of Minnesota, in collaboration with Sandia National Laboratory, to investigate the turbine efficiency and the physical dynamics of the wake. The transient performance of the turbine is predicted with good accuracy using the sliding mesh model, with some level of disagreement found in predicting the velocity deficit in the flow. The limitations of accurately predicting the turbulent flow properties for the turbine are addressed and the sliding mesh technique is proven to capture effectively the different coherent structures in the wake. The qualitative agreement of the method suggests that this model can be used to explore turbine design and wake characteristics over various parameters in a cost-effective manner. This method can also provide critical parameters needed for designing efficient tidal farms.