![]() ![]() However, a mesh that would cover the volume of water that would affect the animals is far too large to be tractable, so a geometric acoustics approach must be used. It’s possible to resolve the noise field around a single turbine using a finite element mesh. Modeling the cumulative noise from an array of tidal turbines presents a simulation challenge due to the size difference of the turbines where noise is generated (tens of meters) and the volume of water over which the noise impacts marine species (kilometers). Underwater sound pressure spectral density measured 200 m from an Andritz Hydro Hammerfest tidal turbine. The vibration in the drivetrain travel through the turbine structure to the blades, nacelle walls, and support structures, where they interact with the surrounding water and radiate away as tonal noise (Figure 3).įigure 3. A second source of vibration is produced from cogging forces in the generator, which are caused by interactions between the magnets and coils as they pass each other, these vibrations are around 500 Hz to 2 kHz. Typically, gearboxes have three step-up stages - the low-speed stage, intermediate stage, and high-speed stage - which produce tonal vibrations ranging between 10–30 Hz, 80–150 Hz, and 200–1000 Hz, respectively. Commonly, the highest levels of tonal noise are produced by the meshing of teeth in the gearbox. Mechanical noise from tidal turbines is a result of vibrations from their gearboxes and generators. A tidal turbine waiting dockside for deployment at the MeyGen project. The energy is then exported by underwater cables to the onshore grid.įigure 2. The rotation speed of the rotor uses a step-up gearbox to convert electrical energy with a generator. Tidal turbines have similar layouts to horizontal-axis wind turbines, with a rotor consisting of three blades connected via a hub and a drive shaft (Figure 2). Harbor seals are the main focus of this research because the population that inhabits the area near the MeyGen project site has significantly declined over the past few decades therefore, the MeyGen project is taking particular care not to adversely affect them. The models were then used to generate spatial and temporal three-dimensional noise maps, which have been compared by SAMS to their data on the movement and behavior of harbor seals and porpoises for a better understanding of how marine mammals interact with these clean-energy-producing devices. Recent underwater noise measurements of the MeyGen project, collected by the Scottish Association of Marine Science (SAMS), provide an opportunity to validate these models. Xi has previously used the COMSOL Multiphysics ® software to estimate the likely noise level generated by tidal turbines before they were deployed into the ocean and subjected marine life to their presence. Image licensed under CC BY-SA 4.0, via Wikimedia Commons. ![]() A harbor seal, one of the marine species impacted by tidal turbine designs. There is a “Goldilocks” noise level of operational noise that turbines produce it’s desirable that the level be loud enough to warn marine species of the presence of the turbine to allow them to avoid collision, while being not so loud to cause them injury.įigure 1. In the case of tidal turbines, environmental impacts may include the risk of injury to marine species, such as collision with a turbine’s moving parts or high levels of operational noise. While curbing greenhouse gas emissions is important to the wellbeing of the earth, it must be done in a manner that does not have other detrimental environmental impacts. Recently, an array of tidal turbines has been deployed at this project site, where tides flowing between the Atlantic Ocean and North Sea are funneled into a high-energy stream between mainland Scotland and the Island of Stroma.Ī Goldilocks Approach to Tidal Turbine Design This process is the foundation of the MeyGen project, a massive renewable energy project that is planned to be the world’s largest tidal energy plant. Tidal energy can be harnessed by deploying tidal turbines into tidal streams. ![]() A viable, renewable energy source are ocean tides, which, unlike solar and wind resources, are not weather dependent, making them predictable. Guest blogger Brett Marmo, technical director of Xi Engineering, discusses using acoustics simulation to analyze the impact of tidal turbines on harbor seals.Ĭreating clean energy alternatives for energy sources that generate greenhouse gas is crucial if we are to avoid excessive global heating and the rising climate crisis. ![]()
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