Vibrations Caused by Ship Traffic on an Ice-Covered Waterway

摘要

Vibrations have been felt on shore along the St. Marys River in Michigan during the passage of ships through ice. Vibration measurements were made on a ship, on the ice, on the shore, and on buildings along the shore. Vibration levels in 1979 were about an order of magnitude lower than levels that would cause damage to building walls. Two factors, however, could have reduced the vibration levels in 1979: a lack of ice jams and a record high snow cover which prevented the soil from freezing. Vibration levels with an ice cover are about four times those without an ice cover. Icebreaking and opening the channel can reduce vibration levels by about 50% for a ship following closely behind another ship. The dominant frequencies measured on shore were associated with propeller excitation. The dominant frequencies and magnitudes measured on the bow of a ship are an order of magnitude higher than those on the shore and are related to icebreaking by the bow. Vibration magnitudes are dependent upon the velocity of the ship, the energy expended by the ship, the cross-sectional area of the ship, weather, conditions of the ice and soil, and site-specific conditions. Further studies are needed to determine the effects of these factors and to determine the mode of energy transmission. (Author)