Simulating environmental changes due to marine hydrokinetic energy installations

Abstract

Abstract-Marine hydrokinetic (MHK) projects will extract energy from ocean currents and tides, thereby altering water velocities and currents in the site's waterway. These hydrodynamics changes can potentially affect the ecosystem, both near the MHK installation and in surrounding (i.e., far field) regions. In both marine and freshwater environments, devices will remove energy (momentum) from the system, potentially altering water quality and sediment dynamics. In estuaries, tidal ranges and residence times could change (either increasing or decreasing depending on system flow properties and where the effects are being measured). Effects will be proportional to the number and size of structures installed, with large MHK projects having the greatest potential effects and requiring the most in-depth analyses. This work implements modification to an existing flow, sediment dynamics, and water-quality code (SNL-EFDC) to qualify, quantify, and visualize the influence of MHK-device momentum/energy extraction at a representative site. New algorithms simulate changes to system fluid dynamics due to removal of momentum and reflect commensurate changes in turbulent kinetic energy and its dissipation rate. A generic model is developed to demonstrate corresponding changes to erosion, sediment dynamics, and water quality. Also, bed-slope effects on sediment erosion and bedload velocity are incorporated to better understand scour potential.

Characterising the near-wake of a cross-flow turbine

“…Contours of turbulence kinetic energy are shown in Figure 10 (1,3,6,9) times the turbine rotational frequency and the shaded grey region indicates the 95% confidence interval for a χ 2 variable with eight degrees of freedom -twice the number of frequencies over which spectral values were averaged to reduce noise. velocity unsteadiness in this area.…”

“…However, these are still not able to fully capture turbine wake dynamics. [5] A model often used to predict flow and performance in turbine arrays is the actuator disk model, which is much simpler and computationally less expensive than the actuator line model, [6][7][8] and is useful when computing power is to be focused on modelling the flow through an array rather than at turbine surfaces. As numerical models are refined, experimental data -such as that presented here -will help evaluate their effectiveness, and also enable the development of new mathematical models from keener physical insight.…”

Technological Cost-Reduction Pathways for Axial-Flow Turbines in the Marine Hydrokinetic Environment.

“…3,[16][17][18][19][20][21][22] These simulations are essential to accurately predicting the loads that will be applied to structural models. Stall and turbulence transition models are active areas of CFD research that will have large effects on the performance and loading results.…”

Simulating Collisions for Hydrokinetic Turbines

“…These energy generation devices can also be installed near population centers, thus reducing transmission costs. On the other hand, apart from the understandable economic disadvantage inherent of any emerging technology, MHK turbines will inevitably interact with and alter the surrounding ecosystem, thus giving rise to potential environmental effects such as accelerating sediment transport, distorting erosion/deposition dynamics, and interacting negatively with aquatic biota by increasing the probability of hazardous strike on the blades (James et al 2010). …”

“…Although early reviews recognized that a rich knowledge base can be transferred from these fields (Batten et al 2006), research specialized in hydrodynamics and environmental impact of MHK turbines remains limited (Kang et al 2012). Previous computational fluid dynamics (CFD) studies described the altered flow conditions that arise in the proximity to MHK turbines by modeling the device as a sink/source term of momentum and turbulence (James et al 2010, Churchfield et al 2013, Harrison et al 2010. Such an approach is advantageous in that, while being computationally affordable, it allows for the description of flow conditions over large domains, as well as for assessment of optimized placement/arrangement of multiple units "MHK turbine farms"); however, it precludes the evaluation of the most extreme and adverse hydrodynamic conditions present very close to the unit (one-turbine diameter).…”