The effect of bathymetry interaction with waves and sea currents on the loading and thrust of a tidal turbine

This paper reports work undertaken to advance analytical methods used to evaluate the influence of bathymetry on wave- current interactions with tidal turbines. The model takes in to account the wave transformation due to a sudden depth change in the sea level. The functions developed provide solutions for wave transformation by changes in bathymetry to find how this change effects the torque and thrust exerted over a tidal turbine. Costal site data for the west coast of the US, from the US DoE, has been used to access the robustness of these analytical methods. The high resolution data sets used have monitored wave, sea and climatic conditions over a period of 8 years

Towing tank and flume testing of passively adaptive composite tidal turbine blades

Composite tidal turbine blades with bend-twist (BT) coupled layups allow the blade to self-adapt to local site conditions by passively twisting. Passive feathering has the potential to increase annual energy production and shed thrust loads and power under extreme tidal flows. Decreased hydrodynamic thrust and power during extreme conditions means that the turbine support structure, generator, and other components can be sized more appropriately, resulting in a higher utilization factor and increased cost effectiveness

Towing tank testing of passively adaptive composite tidal turbine blades and comparison to design tool

Passively adaptive bend-twist (BT) tidal turbine blades made of non-homogeneous composite materials have the potential to reduce the structural loads on turbines so that smaller more cost effective components can be used. Using BT blades can also moderate the demands on the turbine generator above design conditions. This paper presents experimental towing tank test results for an 828 mm diameter turbine with composite BT blades compared to a turbine with geometrically equivalent rigid aluminum blades. The BT blades were constructed of a graphite-epoxy unidirectional composite material with ply angles of 26.8° to induce BT coupling, and an epoxy foam core. For steady flow conditions the BT blades were found to have up to 11% lower thrust loads compared to rigid blades, with the load reductions varying as a function of flow speed and rotational speed. A coupled finite element model-blade element momentum theory design tool was developed to iterate between the structural (deformation and stresses) and hydrodynamic (power and thrust loads) responses of these adaptive composite blades. When compared to the experimental test results, the design tool predictions were within at least 8% of the experimental results for tip-speed ratios greater than 2.5

Resource assessment of the marine current developed in the Cozumel Channel

Renewable energy based systems are expected to contribute on the reduction of greenhouse gases and carbon emission, while satisfying global energy demands. In Mexico, the Cozumel Channel located in the Caribbean Sea has been identified as a potential energy source in the region. Preliminary studies have shown that the ocean current is characterized by almost uniform and unidirectional flow velocities of up to 2.0 m/s within its mid-section with water depths > 500 m. Nevertheless, a detailed resource assessment in shallow waters of the Cozumel Channel is required to address sites potentially suitable for the installation of marine energy converters. Field measurements were taken during September 23rd-29th, 2018 to describe the spatial variation of the marine current velocities at various points along the east-side of the Cozumel Channel, at water depths less than 50 m. Flow velocities higher than 1.0 m/s were identified on the northern east of the Cozumel Channel, at a distance >600 m from the shoreline and over the continental shelf with water depths <50 m. Both energy and power intensity exceedance curves were developed from depth averaged velocities from ADCP measurements. Potential sites were identified where an array of marine energy converters could be installed preventing the devastation of the rich ecosphere renown in the region

Flume testing of passively adaptive composite tidal turbine blades under combined wave and current loading

The tidal energy industry is progressing rapidly, but there are still barriers to overcome to realise the commercial potential of this sector. Large magnitude and highly variable loads caused by waves acting on the turbine are of particular concern. Composite blades within-built bend-twist elastic response may reduce these peak loads, by passively feathering with increasing thrust. This could decrease capital costs by lowering the design loads,and improve robustness through the mitigation of pitch mechanisms. In this study,the previous research is extended to examine the performance of bend-twist blades incombined wave-current flow, which will frequently be encountered in the field. A scaled 3 bladed turbine was tested in the flume at IFREMER with bend-twist composite blades and equivalent rigid blades, sequentially under current and co-directional wave-current cases. In agreement with previous research, when the turbine was operating in current alone at higher tip speed ratios the bend-twist blades reduced the mean thrust and power compared to the rigid blades. Under the specific wave-current condition tested the average loads were similar on both blade sets. Nevertheless, the bend-twist blades substantially reduced the magnitudes of the average thrust and torque fluctuations per wave cycle,by up to 10% and 14% respectively

Erratum to: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition) (Autophagy, 12, 1, 1-222, 10.1080/15548627.2015.1100356

non present