Inertial effects on the transport of an anisotropic particle in surface gravity waves

We study the transportation and rotational dynamics of a finite-sized spheroidal particle in a linear monochromatic surface gravity wave to better understand the transport dynamics of microplastics in oceanic flows. A spheroidal particle, modeled as an anisotropic tracer, attains preferential alignment in a linear wavy flow. We analyze the drift of a finite-size anisotropic particle and find that the horizontal drift of such particles can either increase or decrease depending on the initial orientation and the ratio of the size of the particle to the wavelength of the background wave field. Next, we derive the finite-size modification to the preferred alignment of the spheroidal particle with the flow propagation direction of the wave. In most scenarios, particles in the ocean can have a wide range of densities and are classified into positively and negatively buoyant particles. Negatively buoyant particles settle in a wavy flow with complex trajectories. We study the effect of the orientation and size of such particles on settling and show that the aspect ratio of the particle could alter the trajectory in the wave propagation direction. We also obtain a non-zero vertical Stokes drift. Finally, we consider the effects of fluid and particle inertia in our coupled evolution equations and study the drift and the orientation of an anisotropic particle in a wavy flow field. We demonstrate that considering such an effect could provide a complete picture of the transport and dynamics of microplastics in the upper part of the ocean that can be described more accurately.