Investigation on Applicability and Limitation of Cosine Similarity-Based Structural Condition Monitoring for Gageocho Offshore Structure

Abstract

The key to coping with global warming is reconstructing energy governance from carbon-based to sustainable resources. Offshore energy sources, such as offshore wind turbines, are promising alternatives. However, the abnormal climate is a potential threat to the safety of offshore structures because construction guidelines cannot embrace climate outliers. A cosine similarity-based maintenance strategy may be a possible solution for managing and mitigating these risks. However, a study reporting its application to an actual field structure has not yet been reported. Thus, as an initial study, this study investigated whether the technique is applicable or whether it has limitations in the real field using an actual example, the Gageocho Ocean Research Station. Consequently, it was found that damage can only be detected correctly if the damage states are very similar to the comparison target database. Therefore, the high accuracy of natural frequencies, including environmental effects, should be ensured. Specifically, damage scenarios must be carefully designed, and an alternative is to devise more efficient techniques that can compensate for the present procedure.

Development of a Simulation Model for Digital Twin of an Oscillating Water Column Wave Power Generator Structure with Ocean Environmental Effect

“…Thus, it is evident that the natural frequencies of the concrete wave power generator structure we studied are expected to exhibit variations four times larger than those observed in the actual jacket-type offshore structure. Furthermore, in a study conducted by Kim et al [5], it was found that the impact of joint damage on the natural frequencies of the ORS was significantly smaller compared to the measured variation range of 1.23% on site reported by Yi et al [10], and it was pointed out that this influence may be an obstacle to assuring the accuracy of damage detection. Consequently, it can be inferred that, for box-type concrete structures like the one studied here, the environmental effects are required to be embodied much more precisely.…”

“…By achieving accurate model updating, they found that the strength of the concrete filled in the legs is highly likely to be much less than the design target, and emphasized the importance of considering the mass effect. Meanwhile, Kim et al [5] investigated the suitability of a similarity-based structural health monitoring method for this offshore structure. They identified the variation of natural frequency induced by nonstructural effects, such as changes in oceanic environmental conditions, as a major challenge in monitoring structural integrity.…”

“…According to those references, the radius of section, r, and the distance to its center from the boundary, H, are major factors of the boundary effect. At first, the added mass coefficient C a close to a wall is determined by Equations ( 4) and (5). Here, H < r means the cylinder is not able to move to the wall but able to be parallel to the wall whereas H > r means the cylinder can move in both directions.…”

“…As a result, the method contributed to improved usability in the field. In the second study [5], Kim et al found that how precisely the simulation model represents the dynamic properties of a real As the last part of the digital twin, the first study was performed by Kim et al [4] to develop a fast and effective technique and procedure based on cosine similarity with sensor data to enhance real-time structural health monitoring for offshore structures. The proposed method introduces the rate of changes in measured natural frequencies as a main parameter.…”

“…As a result, the method contributed to improved usability in the field. In the second study [5], Kim et al found that how precisely the simulation model represents the dynamic properties of a real structure is very important in applying the proposed method to the structure. They came to the conclusion that the accuracy of the simulation model should comprise external factors, such as the ocean environments on site, in the structural model itself, which affect the change of the dynamic properties of the structure, ensuring the high accuracy of the proposed technique.…”