Velocity Effects on Conical Structure Ice Loads

Abstract

Existing design codes and most methods for ice load calculation for conical structures do not take velocity effects into account. They were developed as an upper bound estimate for the load from slow moving ice which fails in bending against the cone. Velocity effects can be ignored when the structure is designed for an area with slow ice movement, for example, the nearshore Beaufort Sea. Sakhalin structures will be exposed to ice moving at velocities up to about 1.5 m/sec. Model tests show that quasi-static methods may underestimate the ice load on a steep cone when the interaction velocity is that high. The present paper summarizes results of published model tests with conical structures that show a velocity effect. An empirical correction factor to the Ralston method is developed to account for the increase in cone load with ice velocity. The paper also discusses velocity effects on ice failure length and possible transition from bending failure to an alternative failure mode when the ice velocity is high.

Research on short-term dynamic ice cases for dynamic analysis of ice-resistant jacket platform in the Bohai Gulf

“…Herein, it is necessary to note that we assume the ice velocity and the ice thickness are statistically independent to assess the occurrence probability of ice cases P ik by Eq. (9). This assumption has inherent limitations and indicates that it is better to study the correlation between the ice velocity and the ice thickness, especially the joint probability distribution function of the ice velocity and the ice thickness in the Bohai Gulf.…”

“…(8) rationally and efficiently for the various short-term dynamic ice cases defined by Eqs. (1), (5), (6) and (9). In this paper, the pseudo-excitation method (PEM) [32] is used to calculate the PSD of the acceleration efficiently.…”

“…Refs. [3][4][5][6][7][8][9][10][11]). The main reason for the reduction in the ice force is that a well-designed cone can change the ice failure mode from crushing to bending.…”

Experimental study on mitigation of ice-induced vibration for offshore platforms with a tuned mass damper

“…4). Several researchers have demonstrated the effectiveness of cones to reduce ice force [16][17][18][19]. However, Yue and Bi [20] found that vibration is still large after cones installation on the legs of platforms and the ice force appears to be of periodic character.…”

Finite Element Analysis of Ice-Cone Interaction

“…In recent years, some new ice resistant structures adopt the conical shape at ice acting level to reduce ice force [1][2]. Compared with cylinder leg, conical structures have the following advantages [3]: firstly, because ice sheet fails in bending mode when acting on cones, and the bending strength of ice is much lower than its compressive strength, as a result, the magnitude of bending ice force is usually much smaller than the crushing ice force on cylinder structure; on the other hand, the characteristic period of dynamic ice force on conical structure is normally higher than the eigen period of structure, which make the structure not vulnerable to ice induced vibrations. Accordingly, in order to study the performance of conical ice resistant structure, research on the subject of ice-cone interaction is necessary.…”