Characterization of Marine Mammal Biomechanics to Evaluate Tidal Turbine Collision Impact

Abstract

Tidal energy has an immense potential for creating renewable energy from the ocean's moving tides and is under investigation worldwide. In this emerging field, potential environmental consequences of installing tidal turbines must be evaluated. Marine mammals often use tidal channels for feeding or traveling and may collide with the spinning blades. In the United States, tidal turbines must comply with the Marine Mammal Protection Act and not threaten or harass marine mammals, thus this risk must be evaluated. Since tidal turbines move relatively slowly, this injury may be non-fatal and sustained to soft tissue. The extent and severity of a turbine strike can be modeled numerically to understand this potential injury before installing tidal turbines. Though some finite element models have been developed for this purpose, improved material models are necessary to more accurately model this interaction. Marine mammals' outer layers are composed of a thin epidermal and dermal layer, skin, then blubber, a thicker subcutaneous fat layer. Uniaxial tensile testing of the skin and blubber layers across a series of marine mammals was conducted to determine four material properties: elastic modulus, tensile strength, strain to failure, and yield strength. The skin and blubber compressive elastic modulus were tested using spherical indentation, bulk modulus using volumetric compression, and shear modulus with a rotational test. The results of these tests were analyzed using a principal component analysis to understand the relationship among the material quantities and differences between species. The material properties are used to represent the soft tissue of each species in a material constitutive model which is validated by comparison with a variety of material tests. Ultimately, a finite element analysis of an impact between a tidal turbine and marine mammal can be created, showing the regions of tissue impacted by a tidal turbine strike. With those models, regulators can evaluate the safety for these protected marine mammals. This result is useful in permitting new tidal turbines, allowing effective management of the ocean's resources.