The 5 th TSME International Conference on Mechanical Engineering 17-19 th December 2014, The Empress, Chiang Mai CST024 Wave Forces on Large Cylindrical Structure using CFD Simulation Chanatha Netrasiri 1,a , Somchai Chucheepsakul 1,b and Duangrudee Kositgittiwong 1,c 1 Department of Civil Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 126 Pracha Uthit Rd., Bang Mod, Thung Khru, Bangkok 10140,Thailand a chanatha.net@gmail.com, b somchai.chu@kmutt.ac.th, c duangrudee.kos@kmutt.ac.th Abstract In this paper, a simulation using the commercial computational fluid dynamic software is performed to investigation of wave propagation and wave forces on a large cylindrical structure. The regular waves were generated according to the linear wave theory based on the three-dimensional unsteady Navier- Stokes equations. The free surface was described by using the method of Volume of Fluid (VOF). A wave absorbing method was employed by the porous media model at the downstream to prevent the wave reflection. The simulation models demonstrated the results of inertia force caused by the wave on fixed cylinder. The total horizontal forces acting on the cylinder obtained by using CFD were compared with the results from the Morison equation and the diffraction theory, and they are found to be in close agreement. It also can be concluded that the CFD can be used to predict the wave forces on large cylindrical structures with the limitation of   ⁄ less than 0.7. Keywords: wave force, porous media, Morison equation, the diffraction theory 1. Introduction The large cylindrical structures are commonly employed in many coastal and offshore engineering applications, to name a few, caisson concrete structures and spar offshore platforms. These structures are sustained under severe environmental loadings. Furthermore, the interaction between wave and structure is a complex phenomenon. Therefore, it is essential for design engineers to have good understanding on wave-structure interaction behavior. In the analysis of wave forces on large cylindrical structures, it requires an accurate mathematical model in order to have a good prediction of wave force. Wave disturbing force is an important component of the stability of structure. There are many research studies on numerical simulation using commercial software to examine the hydrodynamic loading acting on the offshore structures, especially with the slender bodies. For example, Teixeira [1] discussed the acting of waves on a vertical pile with a square section using the commercial software, FLUENT [ 2011 ]. The represent problems associated with the interaction among wave and three-dimensional structures, and a user defined function (UDF) is introduced to maintain the elevation of wave along the wave tank. Repalle [2] described the boundary treatments device in FLUENT. It is shown that the out flow boundary condition should be set to allow the continuity through the boundary with a minimum of reflection. Iftelhar [3] had conducted the simulation model on slender