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www.sea-technology.com June 2016 / st 41 O ffshore wind power is achieving great- er prominence and is evolving very fast in the current energy market. One key factor driving the performance of offshore wind energy is the wind profle depicting wind velocity and direction at a particular location along a height above sea level. The wind profle can be measured using a lidar device using laser light instead of ra- dio waves. To achieve accuracy, the device must stay as stationary as possible. This is typically done by placing the lidar on a stable platform or a pontoon of sorts. How- ever, a much more economical solution is to mount the lidar on a foating buoy that can be relocated easily. This article proposes a design for a foat- able lidar platform that could help in ac- curately recording measurements from two differently shaped buoys. The device would be able to operate autonomously for an ex- tended period of time. Numerical Methods Numerical methods offer an inexpensive and fast alternative to test multiple situations. The models in this article use a combi- nation of mesh-based and mesh-free numerical methods, along with a kinematic simulator. Owing to its capability to model large deformations, the Smoothed Particle Hydrodynamics (SPH) method, which is a Mesh-free Particle Method (MPM), is used in this study for modeling the waves in the water domain. This technique uses particles to discretize the domain. Modeling of the buoy along with the platform is done using the mesh-based method, Finite Element Method (FEM), which is a Lagrangian method. The two methods are coupled using a contact algorithm. The result of the coupled FEM-SPH simulation will yield the movement of the holding frame of the stabilization mechanism. This is given as input to Universal Mechanism (UM) software, a commercially available kinematic and dynamic simulation software for me- chanical systems that handles the movements of mechanisms. The most important parameters to describe a wave are its wavelength, wave height and the wave period. The wave celerity is defned as the ratio of wavelength and wave period. The wave amplitude is half of wave height. Representative sea state data from the Thornton Bank wind farm off- shore Belgium, provided by 3E and GeoSea, are used to model the sea environment. Numerical Wave Tank The numerical wave tank model has: a fap-type wave generator, known as the paddle; a representative domain with a length of three wavelengths; and an SPH-symmetry plane at the side opposite to the wave genera- tor. The water in the tank is mod- eled using SPH particles with a particle mass of 8 kg, which yields 1.5 million particles for the complete water domain with a particle volume of 0.008 m 3 or a cube of side 0.2 m. Based on the sea state data provided by GeoSea, a representative sea state is modeled as: 5.594-s wave period, 224.46-cm wave height, 275.69-cm maximum wave height, and 48.27-m wavelength. The accuracy of the wave tank model has been verifed by comparing these theoretical values to the simulated values. Comparison of Two Buoys Both the 3E prototype and the PEM58 buoys are simulated with the SPH wave tank. The buoys are modeled using fnite ele- ments (FE) and are assumed to be rigid. The precise mass, center of gravity and geometry of all (sub)components have been taken into account, and the numerical submersion depth under grav- ity load has been validated. It clearly proves that the 3E proto- type buoy gives more time for the stabilization mechanism to control the lidar module. Lidar Frame Model Since the goal is to develop a stabilization mechanism to reduce the rotations of the lidar module mounted on the buoy, a gyroscope-based mechanism is utilized in this work. Gyro Gyroscope-Based Floating Lidar Design Proposal for Stable Offshore Wind Velocity Profles By Kameswara Sridhar Vepa • Wim Van Paepegem Comparison between the rotations of 3E and PEM58 buoys.