In recent years, it is required energy resources have diversified into renewable energy to realize sustainable society. &nbsp;In the ocean, offshore wind is one of renewable energy resources and has attract attention.&nbsp; If an offshore wind power generator is installed, it is required to observe continuously wind condition at hub height of wind turbine on the installed sea area for one year to estimate the capacity of power generation.&nbsp; In our research group, as a wind observation device for shallow water area with low installation cost and environment impacts, Doppler Lidar on a floating platform is investigated.&nbsp; However, floating platforms cause motion by waves, winds and currents, and it affects the accuracy of measurement, therefore the characteristics and reducing method of its motion are continuously investigated.&nbsp; As one of previous results, a spar-buoy with ring-fin motion stabilizer for shallow water area is proposed, and its motion performance has been confirmed by its 1/21.23 scale model is tested at the towing tank of Osaka Prefecture University and its 1/2.5 scale model is also tested at Sagami-bay for three months1)2).&nbsp; Meanwhile it has been also realized that when mooring lines are applied to floating platform at shallow water area, it is important to avoid the occurrence of snap load and to estimate abrasion amount caused by buoy’s motion in rough weather.&nbsp;The purpose of this study is to propose an optimal design method of the spar-buoy with ring-fin motion stabilizer with for shallow sea and its mooring system, in order to avoid the occurrence of snap load.&nbsp; The mechanism of occurrence of snap load is investigated by model tests, and design parameters for avoiding the occurrence of snap load are investigated. &nbsp;From the observation of model’s motion, it has been realized that the snap load is caused by stopping the buoy’s horizontal motion, which relaxes the mooring line, by tension of mooring line.&nbsp; Moreover, it has been confirmed that the horizontal motion is caused by that the horizontal forces acting on the center pipe and float of the buoy relating the acceleration of water particles3).In this paper, the effects of changing of design parameters of the buoy (: mass, buoyancy, diameter of super-buoy, size of stabilizer, length of mooring line) to avoid or reduce snap load are investigated by using a numerical simulation (OrcaFlex ver.11.0b), and the abrasion amount is estimated by using Takeuchi’s method.&nbsp; From the results, It is confirmed that changing the buoy’s motion mode by shortening mooring line is effective in order to avoiding the occurrence of snap load, and its reduces the abrasion amount of the mooring line.&nbsp;1)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Toru Katayama, Kazuki Hashimoto, Hiroshi Asou, Shigenori Komori：Development of a motion stabilizer for a Shallow Sea Area Spar Buoy in Wind, Tidal Current and Waves, Journal of Ocean and Wind Energy, The International Society of Offshore and Polar Engineers, Vol. 2, No. 3, pp. 182–192, 2015.2)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Toru Katayama and Yusuke Yamamoto: Motion Characteristics of a Spar-Buoy with Ring-Fin Motion Stabilizer, Proceedings of the 13th International Conference on the Stability of Ships and Ocean Vehicles (STAB 2018), pp.454-461, 2018.3)&nbsp;&nbsp;&nbsp; Toru Katayama, Taishi Morimoto, Yusuke Yamamoto, Hirotada Hashimoto, Masahiro Goto: Study on Mooring Line for a Spar-Buoy with Ring-fin Motion Stabilizer for Shallow Sea -Occurrence of Snap Load and Its Mechanism-, Annual Autumn Meeting of JASNAOE 2019 Proceedings, No.29, 2019, pp.157-162．

Effects of Design Parameter on Occurrence of Snap Load and Wear of Mooring Line for Spar-Buoy With Ring-Fin Motion Stabilizer for Shallow Sea

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.