半永久磁気による自差とその修正について(日本航海学会第20回講演会)

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タイトル別名
  • Deviation and Correction caused by Semi-permanent Magnetism of the Ship
  • 半永久磁気による自差とその修正について
  • ハンエイキュウ ジキ ニ ヨル ジサ ト ソノ シュウセイ ニ ツイテ

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抄録

For a short period after ship-building, the deviation of the magnetic compass varies by the attenuation of the ship's permanent magnetism or semi-permanent magnetism of the ship. Generally it has been considered that the deviations have decreased monotonously until they have arrived at the steady values. But when the ships were built by block systems, it happened that although the deviation were very small imediately after the ship building they increased for a period and then decreased. The change rate of deviation caused by semi-permanent magnetism can be calculated by considering that the permanent magnetism of each block decreases according to the attenuation function e^<-βt>, where t is the time from the ship-building, and β the attenuation constant. Several calculated results are shown in the figures, from which we can see that when the effect of each block to the magnetic compass has the same direction the change rate of deviation is monotone, in the other hand when it has the opposite direction the deviation first increase and then decrease as described above. In the former we correct the deviation by a kind of steel having the attenuation constant approximately equal to the average of each block, but in the latter we must use two kinds of steel having the different attenuation constants.

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