Changes in Dynamic Characteristics of Monopile-Type Offshore Structures According to Tidal Environments and Boundary Conditions Jung, Byung-Jin; Park, Jong-Woong; Yi, Jin-Hak; Park, Jin-Soon;
Because a change in the natural frequencies of a structure indicates structural health problems, monitoring the natural frequencies crucial. Long-term measurement for the Uldolmok tidal current power plant structure has shown that its natural frequencies fluctuate with a constant cycle twice a day. In this study, lab-scale tests to investigate the causes of these natural frequency fluctuations were carried out in a circulating water channel. Three independent variables in the tests that could affect the fluctuation of the natural frequencies were the water level, current velocity, and boundary condition between the specimen and the bottom of the circulating water channel. The experimental results were verified with numerical ones using ABAQUS. It was found that the fluctuation of the natural frequencies was governed by a decrease in stiffness due to the boundary condition much more than the effect of added mass. In addition, it was found that the natural frequency would decrease with an increase in the tidal current velocity because of its nonlinearity when the boundary condition was severely deteriorated due to damage.
Natural frequency;Added mass;Monopile-type offshore structures;Tidal effects;Circulating water channel;Boundary condition;
Dassault Systemes Simulia Corp., 2010. Abaqus/CAE user's manual. Version 6.10, Rhode Island, USA. [online] Available at [Accessed 22 Jan, 2014].
DNV, 2010. Recommended Practice DNV-RP-C205 Environmental Conditions and Environmental Loads.
Hallam, M.G., Heaf, N.J., Wootton, L.R., 1977. Dynamics of Marine Structures: Methods of Calculating the Dynamic Response of Fixed Structures Subject to Wave and Current Action. 1st Edition, Ciria Underwater Engineer Group, London.
Hwang, D.H., Kim, H.S., Ahn, J.S., Lee, J.S., 2013 Study of Hydraulic Properties and Stability Evaluation using Hydraulic Experiment of POD-LOCK. Proceedings of the Korea Society for Marine Environment and Energy, 2013(5), 62.
Korea Ocean Research and Development Institute (KORDI), 2011. Development of Utilization Technique for Tide and Tidal Current Energy. Final Report Submitted to the Ministry of Land, Transport and Maritime Affairs.
Lee, S.Y., Kim, J.T., Yi, J.H., Kang, Y.K., 2009. Structural Health Mornitoring of Harbor C0aisson-type Structures using Harmony Search Method. Journal of Ocean Engineering and Technology, 23(1), 122-128.
Sedlar, D., Lozina, Z.., Vucina, D., 2011. Experimental Investigation of the Added Mass of the Cantilever Beam Partially Submerged in Water. Technical Gazette, 18(4), 589-594.
Weiner, E.O., Julyk, J.L., Rezvani, M.A., 1994. Hydrodynamically Induced Loads on Components Submerged in High-level Waste Storage Tanks. Report of US Department of Energy.
Yi, J.H., Oh, S.H., Park, J.S., Lee, K.S., Lee, S.Y., 2013a. Flow-Turbine Interaction CFD Analysis for Performance Evaluation of Vertical Axis Tidal Current Turbines(I). Journal of Ocean Engineering and Technology, 27(3), 67-72.
Yi, J.H., Park, J.S., Han, S.H., Lee, K.S., 2013b. Modal Identification of a Jacket-type Offshore Structure Using Dtnamic Tilt Responses and Investigation of Tidal Effects on Modal Properties. Engineering Structures. 49, 767-781.
Yi, J.H., Park, J.S., Park, J.S., Lee, K.S., 2012. Long-Term Measurement of Static Strains of Jacket Type Offshore Structure under Severe Tidal Current Environments. Korean Society of Civil Engineers, 32(6A), 389-398.
Yi, J.H., Yun, C.B., 2004. Comparative Study on Modal Identification Methods using Output-only Information. Structural Engineering and Mechanics, 17(3-4), 445-466.