Offshore structures are inevitably exposed to flow induced loads and flow-induced vibrations. The effect of these loads will affect the responses of structures, and the combined of two together on the response can lead the structures to induce different phenomena. The effect of damping is to counteract any dynamic response; however, “negative damping” increases the response amplitude. For example, the response amplitude may increase and can lead to structure instabilities, and it might cause damage in the short time. In order to achieve the best possible structural design, it is then relevant to study conditions under which structure instabilities occur. The purpose of this paper is to discuss the conditions under which offshore structures could induce “negative damping” and different structural phenomena that have been caused by “negative damping”. The discussion suggests a damping model with linear and time-varying terms, and shows theoretically that the model is negative under certain wave conditions.

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