Ship icing and stability.

摘要

The objective of this research is to investigate the effect of spray icing on a ship's static and dynamic stability. To do this, a three-dimensional ship icing model has been developed for the stern trawler MT Zandberg. A grid cell mesh is superimposed on the surface of the Zandberg so that the ice load distribution as well as the total ice load can be calculated. The numerical icing model consists of two sub-programs. The first is a spraying model which is based on data from scale-model spraying experiments. This spraying model calculates the local spray flux to each grid cell. Spraying model studies suggest that the total amount of spray generated during a ship/wave collision depends on the ship speed (V{dollar}rmsb{lcub}s{rcub}{dollar}) and significant wave height (H{dollar}sb{lcub}1/3{rcub}{dollar}) according to V{dollar}rmsb{lcub}s{rcub}sp3Hsp7sb{lcub}1/3{rcub}.{dollar} The wind acts to re-distribute this spray mass. The second sub-program has three modules: a spray thermodynamics module, a brine film dynamics module, and an icing module. These work together to calculate the ice growth rate on each grid cell.; The icing model predictions depend in a significant way on all the atmospheric and oceanographic parameters included in the model except for air pressure. The disappearance of the side trawler "Blue Mist II" is used as a case study to demonstrate the performance of the icing model. The model evaluation suggests that using a heat transfer coefficient double that for a surface yields results which are more consistent with observations. Using such values for the deck and wheelhouse, the model's predictions agree reasonably well with both the NOAA and Soviet icing data.; Using the "Blue Mist II" scenario, the effect of icing on the ship's static and dynamic stability is also studied. Of the three wind directions considered (0{dollar}spcirc{dollar}, 15{dollar}spcirc{dollar}, 45{dollar}spcirc{dollar}), it is found that the ice load with a wind direction of 15{dollar}spcirc{dollar} has the most dramatic effect on the static and dynamic stability. The asymmetrical ice distribution in this case causes the ship to trim and list significantly and become statically unstable within 10 hours. A ship dynamics analysis indicates that the asymmetrical ice distribution induces a large roll motion which causes the ship to capsize with three hours of spray ice loading. Based on this new method for combined ship icing and stability analysis, some suggestions on navigation safety are presented.