Experimental validation of a model for prediction of dynamic ice-structure interaction

Abstract

Vertically sided offshore structures subjected to level ice are designed to withstand the effects of ice-induced vibrations. Such structures are, for example, offshore wind turbines on monopile foundations, multi-legged oil-and gas platforms or lighthouses. For the prediction of dynamic interaction between ice and structures, several phenomenological models exist. The main challenge with these models is the limited amount of data available for validation, which makes it difficult to determine their applicability. In this study, an attempt is made to validate one of the existing models. First, the parameters which define the ice in the model were derived from new model-scale experiments with a rigid rectangular structure. The model was subsequently applied to simulate the interaction between ice and two compliant rectangular structures with different structural properties. Finally, model-scale experiments were conducted for the two compliant structures. Results of the experiments and model were compared to assess the capability of the model to predict dynamic ice-structure interaction. Results show that the adopted approach allows for a definition of the input parameters of the model and accurate prediction of frequency lock-in and continuous brittle crushing for compliant structures. Intermittent crushing was not observed in the model-scale experiments due to the model-scale ice bending significantly during low ice speeds. As a consequence, the model could not be validated for this regime of interaction. The approach followed-and challenges encountered during its application-are discussed.

On a simple oscillator problem describing ice-induced vibrations of an offshore structure

“…Curve 1 corresponds to the displacements calculated by the model proposed in this paper, Curve 2 is built up by using the displacement values found in the model from [26], and Curve 3 is based on experimental data as given in [26]. The amplitudes of displacements as obtained in this paper are close to the displacements found in [26] and are in a good agreement with the experimental data. In Figure 7b, Curve 1 describes displacements obtained with the help of the model proposed in this paper for the continuous brittle crushing at 0.13 ms −1 ; Curve 2 describes displacements for the same regimes, but obtained by using the model proposed in [26], and Curve 3 describes experimental data from [26].The curves presented in Fig.…”

“…Because of that, we take δ 0 = 3 × 10 9 Pa s and β = 0.75 × 10 9 Pa s in our calculations. Figure 7a compares the oscillator displacement in the lock-in regime with the results obtained in [26] for a 0.023 ms −1 speed. Curve 1 corresponds to the displacements calculated by the model proposed in this paper, Curve 2 is built up by using the displacement values found in the model from [26], and Curve 3 is based on experimental data as given in [26].…”

“…Figure 7a compares the oscillator displacement in the lock-in regime with the results obtained in [26] for a 0.023 ms −1 speed. Curve 1 corresponds to the displacements calculated by the model proposed in this paper, Curve 2 is built up by using the displacement values found in the model from [26], and Curve 3 is based on experimental data as given in [26]. The amplitudes of displacements as obtained in this paper are close to the displacements found in [26] and are in a good agreement with the experimental data.…”

“…In Sect. 3, it has been shown that the solution q(t) of (97) can be approximated by q 0 = A(τ ) sin( t + φ(τ )), where A(τ ) and φ(τ ) have to satisfy (25) and (26), respectively. From Sect.…”

“…Note that if β δ 0 , then this last resonance is much stronger than the resonances between the oscillator and the external load (ice crushing). For the phase φ, one has (see also (26)):…”