Citation: Sathyanarayana, A.H.; Suvarna, P.S.; Umesh, P.; Shirlal, K.G.; Bihs, H.; Kamath, A. Numerical Modelling of an Innovative Conical Pile Head Breakwater. Water 2022, 14, 4087. https://doi.org/10.3390/ w14244087 Academic Editors: Trilochan Sahoo, Swaroop Nandan Bora and Santanu Koley Received: 15 November 2022 Accepted: 9 December 2022 Published: 14 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Numerical Modelling of an Innovative Conical Pile Head Breakwater Arunakumar Hunasanahally Sathyanarayana 1 , Praveen S. Suvarna 2 , Pruthviraj Umesh 1 , Kiran G. Shirlal 1 , Hans Bihs 3 and Arun Kamath 3, * 1 Department of Water Resources and Ocean Engineering, NITK Surathkal, Mangaluru 575025, Karnataka, India 2 Department of Civil Engineering, PACE, Mangaluru 575018, Karnataka, India 3 Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway * Correspondence: arun.kamath@ntnu.no Abstract: When moderate wave activity at the shoreline is acceptable, pile breakwaters can serve as an alternative to conventional breakwaters. Increasing the size of the pile breakwater in the vicinity of the free surface increases the hydraulic efficiency, as most of the wave energy is concentrated around the free surface. Therefore, a conical pile head breakwater (CPHB) is proposed in the present study by gradually widening the diameter of the piles towards the free surface. Using the open-source computational fluid dynamics (CFD) model REEF3D, the transmission, reflection, and dissipation characteristics of the CPHB with monochromatic and irregular waves are examined. The investigation is carried out for both perforated and non-perforated CPHBs using monochromatic waves, and the numerical results are validated using experimental data. Further, optimally configured non-perforated and perforated CPHBs are investigated numerically by subjecting them to irregular waves using the Scott–Wiegel spectrum. The wave attenuation characteristics of the CPHBs are found to be better with irregular waves compared to monochromatic waves. With irregular waves, the minimum transmission coefficients for non-perforated and perforated CPHBs are 0.36 and 0.34, respectively. Overall, the CPHB appears to be a potential solution for coastal protection. Keywords: conical pile head breakwater; perforated pile head; numerical modelling; wave transmission; wave reflection; energy dissipation 1. Introduction Constructing breakwaters to provide partial or complete protection from waves is the key concept in coastal engineering for a variety of purposes, including coastal in- frastructure protection, erosion management, and beach realignment. For some coastal facilities, such as fishing harbours, recreational harbours, oil jetties, and marinas, partial wave attenuation is sufficient. A certain extent of wave activity is desirable in coastal protection work to facilitate some sediment motion to maintain the dynamic equilibrium of beaches. Traditional breakwaters such as rubble mound and caisson breakwaters may not be an economical solution in these cases due to the massiveness of the structure. In such cases, the pile breakwater is an alternative that is capable of sheltering the coastal area to a reasonable extent. Pile breakwaters are non-gravity structures composed of single or several rows of prismatic circular piles that are equally spaced. Pile breakwaters maintain the water quality of the sheltered area with minimal interference to sediment movement and do not hamper the aesthetics of the beach [1]. The attenuation of wave energy is mainly due to the obstruction, turbulence, vortex shedding and reflection around the structure during the wave–structure interaction. The wave–structure interaction occurs while the projected area of piles obstructs a major portion of the wave propagation. The small gap between Water 2022, 14, 4087. https://doi.org/10.3390/w14244087 https://www.mdpi.com/journal/water