Hydrokinetic Devices Research Articles

Effects of moisture absorption on damage progression and strength of unidirectional and cross-ply fiberglass–epoxy composites

Abstract. Fiber-reinforced-polymer composites (FRPs) possess superior mechanical properties and formability, making them a desirable material for construction of large optimized mechanical structures, such as aircraft, wind turbines, and marine hydrokinetic (MHK) devices. However, exposure to harsh marine environments can result in moisture absorption into the microstructure of the FRPs comprising these structures and often degrading mechanical properties. Specifically, laminate static and fatigue strengths are often significantly reduced, which must be considered in design of FRP structures in marine environments. A study of fiberglass epoxy unidirectional and cross-ply laminates was conducted to investigate hygrothermal effects on the mechanical behavior of a common material system used in wind applications. Several laminates were aged in 50 ∘C distilled water until maximum saturation was reached. Unconditioned control and the saturated samples were tested in quasi-static tension with the accompaniment of acoustic emission (AE) monitoring. Cross-ply laminates experienced a 54 % reduction in strength due to moisture absorption, while unidirectional laminate strengths were reduced by 40 %. Stress–strain curves and AE activity of the samples were analyzed to identify changes in damage progression due to aging.

Modeling underwater noise propagation from marine hydrokinetic power devices through a time-domain, velocity-pressure solution.

Marine hydrokinetic (MHK) devices generate electricity from the motion of tidal and ocean currents, as well as ocean waves, to provide an additional source of renewable energy available to the United States. These devices are a source of anthropogenic noise in the marine ecosystem and must meet regulatory guidelines that mandate a maximum amount of noise that may be generated. In the absence of measured levels from in situ deployments, a model for predicting the propagation of sound from an array of MHK sources in a real environment is essential. A set of coupled, linearized velocity-pressure equations in the time-domain are derived and presented in this paper, which are an alternative solution to the Helmholtz and wave equation methods traditionally employed. Discretizing these equations on a three-dimensional (3D), finite-difference grid ultimately permits a finite number of complex sources and spatially varying sound speeds, bathymetry, and bed composition. The solution to this system of equations has been parallelized in an acoustic-wave propagation package developed at Sandia National Labs, called Paracousti. This work presents the broadband sound pressure levels from a single source in two-dimensional (2D) ideal and Pekeris wave-guides and in a 3D domain with a sloping boundary. The paper concludes with demonstration of Paracousti for an array of MHK sources in a simple wave-guide.

An experimental study of a flow-accelerating hydrokinetic device

Tidal energy researchers and developers use experimental testing of scaled devices as a method of evaluating device performance. Much of the focus to date has been on horizontal axis turbines. This study is focused on a novel vertical axis turbine which incorporates variable-pitch blades and a flow accelerator. The research involves laboratory testing of scale model devices in a recirculating flume. Computational fluid dynamic modelling is used to reproduce the measured flow data to investigate disparities in experimental data. The results show that the device is capable of achieving localised flow acceleration of up to a factor of 2 above the freestream velocity and achieved a mechanical power efficiency of 40%.

Impact Damage Prediction for Wave Energy Converters

Marine and hydrokinetic energy is of growing interest across the globe because it has the potential to provide a large source of renewable energy from the world’s oceans and rivers. These marine and hydrokinetic devices, such as wave energy converters, must operate remotely in all weather conditions, including severe storms. Thus, these devices can suffer from structural damage affecting their performance and lifespan. Therefore, there is interest in developing structural health monitoring systems that can identify new damage, estimate its severity, and then make a decision to provide crews with a maintenance or control recommendation. In this study, we investigate using the electromechanical impedance response of piezoelectric transducers to actively monitor the structural health of composite materials similar to those used in several marine and hydrokinetic devices. Recurring impact damage experiments were completed on five plates using a test drop stand, consisting of five consecutive impacts at the same location for each plate. Classification and regression methods were evaluated in an attempt to predict impact damage on a new plate. Machine learning algorithms were used on data collected over a frequency range of 10 kHz to 100 kHz for two types of piezoelectric transducers.

Assessment of hydrokinetic resources of small and medium-size rivers: the Lithuanian case

The aim of the study is to assess hydrokinetic energy resources of small and medium-size rivers in Lithuania. The estimation of technical resources was carried out for river segments, where for average longterm runoff the flow velocity exceeded 0.4 m/s, and the average depth was more than 0.5 m. The results of hydrological studies were used to calculate the average flow rate and the relationship between flow velocity and river depth. The width and depth of the river channel was estimated in accordance with physical and geographical factors. Part of the favourable for use sites of rivers located within protected areas cannot be used for energy production because of the priority of environmental protection. Navigation, recreation and other factors also limit the use of streams for energy production. In addition, in winter due to ice phenomena, hydrokinetic devices in small and medium rivers should be protected from mechanical obstacles. Moreover, Lithuania is a flat country and available hydrokinetic resources of such plain rivers are very small. Their estimated capacity comprises 13.6 MW, and they can generate 79.4 GWh of electric energy per year.

Multi-scale temporal patterns in fish presence in a high-velocity tidal channel.

The natural variation of fish presence in high-velocity tidal channels is not well understood. A better understanding of fish use of these areas would aid in predicting fish interactions with marine hydrokinetic (MHK) devices, the effects of which are uncertain but of high concern. To characterize the patterns in fish presence at a tidal energy site in Cobscook Bay, Maine, we examined two years of hydroacoustic data continuously collected at the proposed depth of an MHK turbine with a bottom-mounted, side-looking echosounder. The maximum number of fish counted per hour ranged from hundreds in the early spring to over 1,000 in the fall. Counts varied greatly with tidal and diel cycles in a seasonally changing relationship, likely linked to the seasonally changing fish community of the bay. In the winter and spring, higher hourly counts were generally confined to ebb tides and low slack tides near sunrise and sunset. In summer and fall of each year, the highest fish counts shifted to night and occurred during ebb, low slack, and flood tides. Fish counts were not linked to current speed, and did not decrease as current speed increased, contrary to observations at other tidal power sites. As fish counts may be proportional to the encounter rate of fish with an MHK turbine at the same depth, highly variable counts indicate that the risk to fish is similarly variable. The links between fish presence and environmental cycles at this site will likely be present at other locations with similar environmental forcing, making these observations useful in predicting potential fish interactions at tidal energy sites worldwide.

An uncertainty analysis of propagated sound from an array of marine hydrokinetic devices

Marine hydrokinetic (MHK) devices provide an alternate energy source from tidal, current, and wave motion; however, these devices introduce anthropogenic noise in the marine ecosystem and must meet regulatory guidelines. Paracousti is a 3D finite-difference, time-domain solution to the governing velocity-pressure equations and is used to predict the propagation of sound from an array of MHK sources in any environment. This solution allows for multiple sources, each with unique sound profiles, and for spatially varying sound speeds, bathymetry, and soil composition. However, fluctuations in the hydrodynamic field will introduce operational uncertainties for the sound profiles of the MHK devices, which may not be captured through idealized sound profiles. Preliminary results for a single device in a Pekeris waveguide indicate differences in broadband sound pressure levels of 25 and 60 dB re 1μPa for peak amplitudes and frequencies of 1-20 m, 150 Hz and 1 m, 50-300 Hz, respectively. A Monte Carlo approach is presented for an array of sources to further characterize the range of uncertainties associated with variations in source amplitude and frequency. It is demonstrated that the idealized, deterministic solution, vastly underestimates the compounding uncertainty on the final sound field.

Investigation of error of propagated sound due to bathymetric interpolation

Paracoustic is a parallelized acoustic-wave propagation package developed by Sandia National Laboratories to model marine hydrokinetic (MHK) devices in complex environments. It solves a linearized set of the velocity-pressure partial differential equations using the finite-difference method and allows for 3D variations in medium densities, sound speeds, and bathymetry. In-situ measurements of these quantities, or the solution resolution from hydrodynamic models, are sometimes resolved at a coarser spacing than is required to accurately predict the propagated sound levels within Paracousti. This will therefore require interpolation of these quantities onto a refined grid, introducing model errors. The size of the refined grid is determined by the maximum frequency of an MHK source profile and the underwater sound speed. A single point source in a two-layer waveguide with realistic bathymetry is used to compare the model error between three interpolation schemes: nearest-neighbor, linear, and cubic. Preliminary results indicate that there are significant differences in model error due to the particular interpolation scheme used.

Dynamic model and experimental validation for the control of emersion manoeuvers of devices for marine currents harnessing

Finding solutions for fully automated performing emersion and immersion manoeuvers of submerged hydrokinetic devices with which to harness renewable energies requires the study of simple and reliable dynamic models. This paper presents a simple dynamic model for an approximately cylindrical body when it performs open loop emersion motions. It includes free surface motion with a single degree of freedom.The proposed method allows a dynamic model to be obtained that can be used to both evaluate the dynamics of a submerged/semi-submerged body and design control systems for closed loop depth control purposes. This model is fully parameterized and requires a minimal computational effort. It is based on the computation of a hydrodynamic and a hydrostatic effect, namely: i) the added mass of the body in motion and ii) the buoyancy force. A simple new interpolated method is developed to compute the variation of the added mass when the body is partially submerged and the device velocities with regard to fluid are not constant. The inherent instability of any submerged compressible body is proved by using Lyapunov/Chetaev functions.The appropriateness of the proposed model has been validated by comparing simulation results with real-time experimental-laboratory prototype measured signals, resulting in excellent agreement.

Stochasticism in noise generated by an array of marine hydrokinetic devices

Marine hydrokinetic (MHK) devices generate electricity from the motion of tidal and ocean currents and ocean waves and provide another source of renewable energy. Additionally, MHK devices are also a new source of anthropogenic noise in the marine ecosystem and must meet regulatory guidelines that mandate a maximum amount of noise that may be generated. In the absence of measured levels from in-situ deployments, a model for predicting the propagation of sound from an array of MHK sources in a real environment needs to be established. A 3D finite-difference, time-domain solution to the governing velocity-pressure equations is used, which permits a finite number of complex sources and spatially varying sound speeds, bathymetry, and bed composition. However, deterministic solutions to these types of problems cannot capture uncertainties in the source profiles that may result from operational changes. This work presents the broadband sound pressure levels from an array of MHK sources as the amplitude and frequency from each source are allowed to vary. This Monte Carlo approach demonstrates that the idealized, deterministic solution, vastly underestimates the compounding uncertainty on the final sound field and that these small variations in the source profile cannot be ignored.

Technical and financial valuation of hydrokinetic power in the discharge channels of large hydropower plants in Colombia: A case study

This work presents an assessment of the potential use of hydrokinetic turbines in the discharge channels of large hydroelectric power plants in Colombia. The assessment is performed at a pre-feasibility stage in order to evaluate the technical and financial potential of using hydrokinetic devices as a way to exploit kinetic energy in such channels. As a case study, two large hydropower plants were selected, one operated by a Francis turbine and the other operated by a Pelton turbine. The analysis assessed the hydraulic characteristics of the channels and the corresponding discharge flows. A prefeasibility financial analysis in an environment of uncertainty was also carried out using Monte Carlo simulation. The results show that the technology is not currently feasible for the Colombian market conditions, but the situation should be monitored in order to identify the right time for its optimal use in the future. The proposed methodology can be applied to research the feasibility of hydrokinetic energy for other kinds of applications.

Estimating the probability of fish encountering a marine hydrokinetic device

Strong tidal currents in eastern Maine, USA, make that region attractive for tidal power development. Little is known about the effects of marine hydrokinetic (MHK) devices on fish, yet many fish species use tidal currents for movements. We used empirical data from stationary and mobile hydroacoustic surveys to examine the probability that fish would be at the depth of an MHK device and may therefore encounter it. The probability was estimated using three components: 1) probability of fish being at device-depth when the device was absent; 2) probability of fish behavior changing to avoid the device in the far-field; and 3) probability of fish being at device-depth in the near-field when the device was present. There were differences in probabilities of fish encountering the MHK device based on month, diel condition and tidal stage. The maximum probability of fish encountering the whole device was 0.432 (95% CI: [0.305, 0.553]), and the probability of fish encountering only device foils was 0.058 (95% CI: [0.043, 0.073]). Mobile hydroacoustics indicated that fish likely avoided the device with horizontal movement beginning 140 m away. We estimated the encounter probability for one device, but results can be applied to arrays, which may have bay-wide implications.

Cross flow water turbines: HARVEST technology

This paper describes all the main features of the hydrokinetic devices developed during the HARVEST program. Such devices, which eliminate the well-known weaknesses of Darrieus turbines, are composed of two counter-rotating twin columns of cross flow water turbines (CFWT) built in a support structure with a twin towers shape. Among other advantages, it is shown that the twin towers geometry facilitates the optimal design of arrays of HARVEST Power Systems. In particular simple 2D models can be used in a first approach to predict power extraction of single-row arrays. Blade Element Momentum–Reynolds-Averaged Navier-Stokes Simulations (BEM-RANS) models are currently developed to yield a fast and accurate prediction of the power output produced by a row of many power systems. Relevant momentum source terms describing the rotor effects, which are required by this simplified modelling, are defined beforehand from a set of high-fidelity Unsteady Averaged Navier-Stokes Simulations (URANS) simulations for an isolated HARVEST Power System.

Fast power output prediction for a single row of ducted cross-flow water turbines using a BEM-RANS approach

A numerical model is proposed to efficiently compute the power produced by a row of Vertical Axis Water Turbines (VAWTs) deployed in parallel for various water flow conditions. As the computational cost of the unsteady Reynolds Averaged Navier Stokes (URANS) approach is high, a coupled Blade Element Momentum (BEM)/Reynolds Averaged Navier–Stokes (RANS) approach is developed, restricted to a 2D approximation. The HARVEST hydrokinetic devices considered in this study are made of twin contra-rotating VAWTs of ducted H -Darrieus type rotors. Momentum source terms are derived for such rotors from URANS simulations taking into account the presence of fairings and also incorporating the optimal tip speed ratio (TSR), thanks to a procedure based on local flow conditions upstream of the rotor path and on the mass flow through each rotor.

Characterizing the Juvenile Fish Community in Turbid Alaskan Rivers to Assess Potential Interactions with Hydrokinetic Devices

AbstractInstallation of hydrokinetic power‐generating devices is currently being considered for the Yukon and Tanana rivers, two large and glacially turbid rivers in Alaska. We sampled downstream‐migrating fish along the margins of both rivers, a middle island in the Yukon River, and mid‐channel in the Tanana River in order to assess the temporal and spatial patterns of movement by resident and anadromous fishes and hence the potential for fish interactions with hydrokinetic devices. Results suggest that (1) river margins in the Yukon and Tanana rivers are primarily utilized by resident freshwater species, (2) the mid‐channel is utilized by Pacific salmon Oncorhynchus spp. smolts, and (3) only Chum Salmon O. keta smolts utilize both river margin and mid‐channel areas. Some species exhibited distinct peaks and trends in downstream migration timing, including Longnose Suckers Catostomus catostomus, whitefishes (Coregoninae), Arctic Grayling Thymallus arcticus, Lake Chub Couesius plumbeus, Chinook Salmon O. tshawytscha, Coho Salmon O. kisutch, and Chum Salmon. Due to their downstream migration behavior, Pacific salmon smolts out‐migrating in May–July will have the greatest potential for interactions with hydrokinetic devices installed in mid‐channel surface waters of the Yukon and Tanana rivers.

Effects of Using Channelling Devices to Increase Efficiency of Hydrokinetic Devices

Abstract In the rivers of Latvia and of many other countries the flow velocity in the places that are most suitable for installation of hydrokinetic devices is 0.4 to 0.9 m/s. In a stream or a river the hydrokinetic devices can reach full efficiency starting from about twice higher flow velocities. It is advisable to at least double this velocity thus increasing the efficiency and power output of the hydrokinetic devices installed in such places. Since Latvia has abundance of slow rivers and almost none are fast, research in this field is of high importance. Diversified technical methods are known that allow increasing substantially the efficiency of hydrokinetic devices. These methods include the use of diffusers, concentrators, different types of other channelling devices and means of flow control. Desirable effects are achieved through changing the cross-section and/or direction of a flow, its pressure, minimizing the turbulence, etc. This work substantiates the use of such devices for increasing the efficiency of hydrokinetic devices. A method is proposed for evaluation of the effects on power output gained owing to the use of channelling devices. Results show that the efficiency of hydrokinetic devices can be increased by at least 110%.

Impact of sediments on wear performance of critical sliding components of hydrokinetic devices

The work discussed here is a continuation of the study presented in [1], in which a customized test apparatus was presented that was capable of conducting tribological related experiments on sliding components commonly used in hydrokinetic devices such as bearings, drive shaft and seals. The wear on critical sliding components introduces unnecessary clearances which can significantly reduce the performance and reliability of hydrokinetic devices. In the previous study [1], four types of bearings, namely Vesconite, CIP, Feroform T814, and Poly Crystalline Diamond (PCD) coated bearings were tested for 60 h in clean water. The data showed that PCD bearings outperformed polymer based bearings in terms of wear and frictional resistance. In the present study, the same set of bearings were tested for 60 h in fresh sedimented water. The experimental data revealed that PCD bearings had higher wear resistance as compared to its polymer based counterparts. In addition to wear on bearing surface, a significant amount of wear on the drive shaft was observed. These results reveal that (in addition to high wear resistant polymer bearings) a surface hardened shaft may increase the longevity of bearing-shaft assembly in sedimented water.

Model Scaling of Ocean Hydrokinetic Renewable Energy Systems

Numerical simulations are performed to validate a nondimensional dynamic scaling procedure that can be applied to subsurface and deeply moored systems, such as hydrokinetic ocean renewable energy devices. The prototype systems are moored in water 400 m deep and include: subsurface spherical buoys moored in a shear current and excited by waves; a subsurface ocean current turbine excited by waves; and a deeply submerged spherical buoy in a shear current excited by strong current fluctuations. The corresponding model systems, which are scaled based on relative water depths of 10 and 40 m, are also studied. For each case examined, the response of the model system closely matches the scaled response of the corresponding full-sized prototype system. The results suggest that laboratory-scale experimentation of complete ocean current renewable energy systems moored in a current is possible.

Evaluation of the Power Generation Capacity of Hydrokinetic Generator Device Using Computational Analysis and Hydrodynamic Similitude

This paper presents a similitude and computational analysis of the performance of a scaled-down model of a paddle wheel style hydrokinetic generator device used for generating power from the flow of a river. The paddle wheel dimensions used in this work are one-thirtieth scale of the full-size paddle wheel. The reason for simulating the scaled-down model was to prepare for the testing of a scaled-down physical prototype. Computational Fluid Dynamics using ANSYS Fluent 14.0 software was used for the computational analysis. The scaled-down dimensions were used in the simulations to predict the power that can be generated from the scaled size model of the paddle wheel, having carried out similitude analysis between the scaled down size and its full-size. The dimensionless parameters employed in achieving similitude are the Strouhal number, power coefficient, and pressure coefficient. The power estimation of the full-size was predicted from the scaled size of the paddle wheel based on the similitude analysis.

Characterizing the mean flow field in rivers for resource and environmental impact assessments of hydrokinetic energy generation sites

The use of hydrokinetic technology in rivers for energy generation is an area of active research with potential applications in urban and rural settings. Negating the need for a physical barrier to the flow, in-stream hydrokinetic devices are viewed as having less environmental impact than conventional hydropower. The introduction of any device that alters the flow field, however, has the potential to affect both the river morphology and the ecosystem it supports. Characterizing the pre-installation flow conditions and monitoring changes following device installation are necessary to evaluate the ecological costs associated with this developing technology. This study presents techniques for quantifying the mean flow field throughout a study reach using an acoustic Doppler current profiler. Employing two survey procedures that provide flexibility in terms of the resolution and extent of measurements, quantities ranging from bulk flow features, such as discharge, to mean three-dimensional velocity profiles can be obtained. Results of the different survey procedures are demonstrated using data collected on the lower Roanoke River, USA. Recommendations are given to aid in the design of field data collection to best match the stage of the project. These measurements contribute to resource assessment at the site scale, designing turbines and planning installation, and environmental impact studies.