ANALOG COMPUTER SOLUTION TO THE DYNAMICALLY DEVELOPED FORCES AT THE BOW OF AN ICEBREAKER

The Academy Scholars Project was undertaken to produce a workable analog computer solution to the dynamically developed forces created at the bow of an icebreaker ramming a virtually unyielding ice mass. The mathematical model describing these forces which will break the ice was taken from free body diagrams developed by CDR R.M. White, USCG, in his Doctoral thesis in Naval Engineering. The project required transferring this mathematical model to a reliable simulation of the actual system on the analog computer. The analog computer simulation provides the naval architect with a cheaper and faster method of designing certain parameters which affect the force produced in icebreaking without his having to employ full scale or model testing. Through operation of the analog program with respresentative runs on the WINDCLASS, GLACIER, LENIN, ST. LAURENT icebreakers along with the M-6 and M-13 experimental icebreakers designs the following ship parameters were observed to affect the force available to break the ice: length, beam, displacement, bollard thrust, initial velocity upon impact, the angle of the bow measured from the waterline, and the angle of the bow normal to the bow plating. In the analog simulation, the ship was observed initially to crush and penetrate the ice and then to slide up on the ice, approaching a state of static equilibrium when a downward force is exerted on the ice. The center of gravity was observed to rise and move toward the ice, while the ship rotated about the center of gravity with the bow rising. Upon impact, velocities in the vertical and rotational directions increased sharply, while the forward velocity decreased slightly. As the ship continued up on the ice all velocities tended to decrease toward zero. Force at the bow was seen to rise to a sharp peak upon initially crushing the ice. When the bow began to slide up on the ice, the force dropped significantly and increased until static equilibrium was reached. These data were correlated with the full scale tests. In the full scale tests, the ship was observed to crush the ice locally to accommodate the bow, and then to slide up on the ice coming to a stop in the forward direction. There was a rise in the ship and rotation with the bow rising. Strain gauges placed on bulkheads in the bow showed a stress that had to be produced by some external force peaking shortly after impact, dropping and then fluctuating without approaching the initial peak. At this point a workable analog computer program exists with which icebreaking forces may be observed in their relationship to time; the associated distances, velocities, and accelerations can also be graphed. velocities, and accelerations can also be graphed.