OMAE2003-37397 TESTS ON DYNAMIC ICE-STRUCTURE INTERACION

ABSTRACT This paper addresses the problem of ice induced vibration of offshore structures. Compliant structures having vertical ice walls may suffer from very severe vibrations. Several theories have been proposed to predict these vibrations. However, physical details of this phenomenon are not fully understood. Conical structures are deemed to be less sensitive to vibrations. Recent full-scale measurements made in the Bohai Bay indicate that also these structures my experience excessive vibrations caused by ice. Indentation tests were done at the ARCTEC laboratory at the Hamburg Ship Model Basin, Hamburg to clarify details of ice induced vibration. Sheets of columnar grained saline ice was used in the tests. The parameters that were varied included the structure's compliance and damping, indentation velocity and the structural geometry at the water line. The paper provides tests results that were obtained using vertical and conical model structures

Finite ice failure depth in penetration of a vertical indentor into an ice edge

This paper presents a partial analysis of data from an extensive series of laboratory indentation tests. The tests were conducted using flat indentors pushing against sheets of fresh-water ice of thickness 65 to 115 mm. The aspect ratio ranged from 0.9 to 2.6 with indentor velocities of 10 to 80 mm s−1. Details of an ice failure mode known as “crushing with flaking” are studied by making use of measured force-displacement signals and high-speed photography. With these test conditions, ice failure is associated with a production of symmetrical flakes which emanate simultaneously up and down. The failure begins in the middle level of the ice sheet as a rapid expansion of the ice. The post-peak phase of the ice failure involves loss ol the ice material over the whole contact area. The amount of ice that is extruded after the occurrence of the peak force is characterized by a finite failure depth parameter. According to present data, this failure depth is around 70% of the total depth of crushing and flaking that occur during a cycle of loading and unloading.</jats:p

Mitigation of steady-state vibrations induced by ice

Offshore structures are prone to ice-induced vibrations when they are subjected to the action of drifting level ice. These vibrations may cause liquefaction of the seabed. They may also cause fatigue problems and have adverse effects on the working conditions on an offshore structure. This paper describes first a mechanism in ice-structural interaction, which is responsible for the generation of steady-state vibrations. Second, parametric studies are carried out with a numerical model. The results show that steady-state vibrations can be prevented by using solutions which provide a sufficient amount of structural damping

Mitigation of steady-state vibrations induced by ice

Offshore structures are prone to ice-induced vibrations when they are subjected to the action of drifting level ice. These vibrations may cause liquefaction of the seabed. They may also cause fatigue problems and have adverse effects on the working conditions on an offshore structure. This paper describes first a mechanism in ice-structural interaction, which is responsible for the generation of steady-state vibrations. Second, parametric studies are carried out with a numerical model. The results show that steady-state vibrations can be prevented by using solutions which provide a sufficient amount of structural damping