Model Tests on a Spar in Level Ice and Ice Ridge Conditions

Abstract

1:30 and 1:50 model-scale ice tests of an ice-resistant Spar design were carried out to determine the loads on the Spar in level ice and ice ridges. Due to limitations in the depth of the ice test facility, the hull draft and mooring system were truncated. The 1:30 scale model was towed through the ice on a fixed and compliant dynamometer. The stiffness characteristics of the compliant dynamometer matched the horizontal stiffness of the full-scale mooring system. The purpose of these tests was to compare the mooring and ice loads measured in fixed and compliant conditions. The 1:50 scale model was truncated by 70 m. Its mooring system was modeled using a four-line system designed to give the same global restoring forces as the full-scale mooring system. The model was fitted with vertical plates on the exterior of the hull to compensate for loss of added mass and added moment of inertia. A limited number of tests were carried out at the two model scales in the same ice conditions to investigate scaling effects. The mooring and ice loads measured in the fixed and compliant conditions were found to be similar, indicating that loads estimated, assuming the structure is fixed, provide good estimates. Good agreement between the two models was also found for the tests carried out in the same ice conditions, suggesting that the scaling effects may be negligible.

Offshore Wind Turbine-Ice Interactions

“…12 Monopile wind turbine with ice-breaking cone (Shi et al 2016) Offshore Wind Turbine-Ice Interactions, Fig. 13 Comparison of the shear force in the fore-aft direction at MSL under various load conditions (Shi et al 2016) Murray et al (2009) did model tests on scales of 1:30 and 1:50 to predict the ice loads of an iceresistant spar design. Nord et al (2015) identified the force induced by level ice on a generic bottomfixed offshore structure using a joint input-state algorithm to describe experimental ice-induced vibrations.…”

Influence of pitch motion on level ice actions

“…In recent years, several model test campaigns have been conducted on various moored structures exposed to drifting ice, and the observed motions of these structures have been discussed (e.g., Aksnes, 2010a;Bruun et al, 2009;Dalane et al, 2008Dalane et al, , 2009Ettema and Nixon, 2005;Murray et al, 2009). Both model test campaigns and full-scale measurements have frequently studied the mooring line forces (e.g., Comfort et al, 1999;Jensen et al, 2008;Løset et al, 1998;Toyama and Yashima, 1985;Wright, 1999), but the excitation forces created by the ice features are seldom recorded, as they are difficult to measure.…”

“…Both model test campaigns and full-scale measurements have frequently studied the mooring line forces (e.g., Comfort et al, 1999;Jensen et al, 2008;Løset et al, 1998;Toyama and Yashima, 1985;Wright, 1999), but the excitation forces created by the ice features are seldom recorded, as they are difficult to measure. When ice excitation forces are given, they have generally been based on back-calculated forces via equations of dynamic equilibrium (Dalane et al, 2008;Karulin et al, 2004;Lundamo et al, 2008;Murray et al, 2009). Back calculations can be an efficient means of extracting ice actions from an experiment when all dynamic parameters in the calculation are known.…”

A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

“…Several investigations have been carried out to estimate the ice load on cylindrical or large steep structures in model tests, full scale measurements, and numerical simulations. Murray et al (2009) performed experiments with scales of 1:30 and 1:50 to measure the forces on a spar that was designed to resist ice action [20]. Jefferies et al (2011) carried out a series of model tests to measure ice loads and the response of the Molipaq platform with nearly vertical sides [21].…”