Author(s)

O. T. Gudmestad, T. M. Jonassen, C.-T. Stansberg & A. N. Papusha

Abstract

The phenomenon of sudden unexpected high frequency large amplitude displacements of offshore structures has not been well understood since it was first identified in wave tank testing about two decades ago. The accelerations associated with the ringing displacements increased the loading by approximately 40%, to the despair of the designers. We have decided to revisit the phenomena and have used system identification theory to identify mathematical models that could give such \“burst” type responses. In the case of negative damping these effects appear. The model has been termed the β-damping term. By comparing predictions of the model with tank test data, we have found good correlations. Furthermore, the comparison has also revealed new insight into the use of the previously used models for the prediction of ringing response. Keywords: structural vibration, ringing, burst type response, negative damping, FNV method. 1 Introduction The problem of ringing response (sudden unexpected high frequency large amplitude displacements) of offshore structures has gained much interest since this type of response was first identified in the wave tank while testing the Draugen concrete mono tower for Northern North Sea wave conditions. Further data from offshore has confirmed that ringing response also exists in the natural

Keywords

structural vibration, ringing, burst type response, negative damping, FNV method.