RESISTANCE EVALUATION OF SHIP NAVIGATION IN BRASH ICE CHANNELS WITH PHYSICALLY BASED MODELING

摘要

Finnish–Swedish ice class rules (FSICR) require estimation of a ship’s resistance in brash icernchannels for each ship to obtain certification of an ice class, and evaluation of resistance “basedrnon more exact calculations or values based on model tests might be approved.” Our group hasrndeveloped a numerical simulation method to evaluate ship resistance in brash ice channels tornprovide a more exact calculation method. This simulator uses physically based modeling. Thisrnpaper presents evaluation of channel resistance on a model scale using the simulator, andrnestimation of the resistance on a real scale using the cubic law. For the simulation, a ship is towedrnin a channel filled with small spherical and cubic ice pieces. The ship and ice pieces are modeledrnas rigid bodies; a virtual fluid force acts on each ice piece to reproduce the fluid effect around thernship. Buoyancy with static pressure is also considered. The coefficient of restitution is set tornzero and the friction coefficient between ice pieces is set to 1.35, as given from descriptions inrnthe related literature. Ship bows of two types, five channel lengths and two sizes of ice pieces arerntested.rnResults of numerical simulations show that our simulator can simulate motions of ice pieces andrncan evaluate ship resistances in brash ice channels under certain conditions. Channel resistancesrnestimated from the simulations are of the same order of magnitude as that of FSICR rule formula,rnbut twice as much as that, which suggests that the simulator overestimates channel resistance.rnEffects of size distribution and friction coefficient are discussed.