Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Design and Analysis for Mooring Line of Wave observation Buoy System
Wei Tao, Shuqing Wang
Shandong Provincial Key Laboratory of Ocean Engineering, Ocean University of China.
Qingdao, Shandong Province, China

cylindrical buoy, spherical buoy, and ship-shaped buoy according to theshape of its substructure. Among them the disc-shaped buoy is widely
deployed in global sea areas because of its large effective space, superiorstability, and pleasant wave following performance. Typically, thesubstructure diameter of the disc-shaped buoy is as large as 12~15 m andas small as 1~3 m.
In general, the wave observation buoy is anchored to the seabed throughone mooring line. The buoy motions excited by wind, wave, and current
are limited to a certain range through the mooring line. Nevertheless,there is a key consideration that the heaving motion of the buoy isrequired to be compliant to provide pleasant wave flowing performance.
There are three main mooring configurations for the wave observation
buoy: chain-catenary mooring, semi-taut mooring, and inverse-catenary
mooring (Hamilton, 2016). The determination of the mooring
configuration much depends on the water depth and the budget cost.
Among them the cost of the chain-catenary mooring configuration is thelowest, but this kind of mooring configuration is only suitable to shallow
water where the water depth is less than 50 m. With the increase of water
depth, the self-weight of the chain-catenary mooring increases sharply,
as well as its manufacturing and installation costs (Yu, Zhang, Yang, Xin,and Gao, 2020). The mooring line, as one of the most critical components
in the buoy system, often fractures and loses effectiveness under theaction of the marine environmental load. Therefore, it is crucial toaccurately estimate the mooring tension of the wave observation buoywith the marine environmental load excitation. At present, quasi-static
analysis and dynamic analysis are two frequently used methods to predictthe responses of the mooring system (API RP 2SK, 2005). Kim, Sung,Hong, and Jung (2010) derive nonlinear equilibrium equation forcatenary structure with its elastic deformation considered, and compare
the sag and tension of the non-elastic catenary structure with those ofelastic catenary structure based on the established numerical model. Kim,Sung, Kim, ang Hong (2013) respectively use the linear spring method
and the nonlinear finite element method to investigate the dynamic
coupled behavior of floating structure and mooring system in time
domain, and take weathervane ship and semi-submersible structure as
two example to validate the difference of these two numerical methods.
Chang, Xu, Li, Tang, and Zhang (2009) chose a linear strain tension toequivalent the mooring stiffness, and investigated the nonlinear dynamic

ABSTRACTThe wave observation buoy system is widely used in wave measurement
for exploiting marine oil and gas resources, in which the mooring line is
one of the most critical components. At present, the design and analysis
for the mooring line mainly relies on quasi-static analysis with a large
dynamic magnification factor based on the engineering experience
instead of dynamic analysis, resulting in high computational efficiency
but inaccurate dynamic response prediction. Therefore, it is ofsignificance to validate the deviation between quasi-static analysis anddynamic analysis for ensuring sufficient design safety. This paper carries
out a series of quasi-static analysis and dynamic analysis for the mooringline of a disc-shaped wave observation buoy in regular waves. Throughcomparing the maximum mooring tension in the two analysis methods,
it is found out that the dynamic magnification factor is related to thewater depth, chain diameter, mooring length, and wave conditions.
Eventually, the recommended value of dynamic magnification factor
under different occasions is obtained to provide guidelines forengineering designers.

KEY WORDS: Wave observation buoy; mooring line; quasi-staticanalysis; dynamic analysis; dynamic magnification factor.

INTRODUCTION
The prerequisite of developing and utilizing the tremendous ocean
resources is to accurately grasp the atmospheric and oceanographic data,such as the wind velocity, current profile, wave characteristics of sea
areas. These hydrometeorological data is of great significance tomaritime activities. At present, one of the most reliable, effective, andimportant means in marine observation is based on the ocean data buoywith various measuring sensors in its substructure. Take measuring wave
height and period as an example, the wave observation buoy, one kind ofocean data buoy, can provide long-term, high-precision, and real-timewave parameters through the satellite correspondence in various
complex marine environments. With the rapid development in last eightyyears, the ocean data buoy can be divided into disc-shaped buoy,874