静振の減衰振動と減衰係数・線型摩擦係数の評価ついて
1979 年 40 巻 2 号 p. 102-109
詳細
1979 年 40 巻 2 号 p. 102-109
The frictional effect on the period of surface seiches in Lake Biwa has been discussed by TAKAHASHI and NAMEKAWA (1931). They concluded that the seiches of the longest period of 4 hours in Lake Biwa may be considered as a bay oscillation in the southern basin, and the difference of the period between the observed and theoretical one is due to an elongation effect of internal friction of the seiches. The same authors evaluated the linear frictional coefficient, K0 as 0.69cm/sec. However, the above estimation is not consistent with the observed darning coefficient. Such an inconsistency must be due to incorrect positioning of the bay mouth when calculating the theoretical period.
In the present paper, the authors give an estimation of the frictional effect on the period length in consideration of mouth correction, and also introduce a renewal frictional factor, estimated from field survey of diminishing seiches in the southern basin. The evaluation of the frictional factor in the present study gives K0=0.260.05 (cm/sec), which is consistent with the magnitude of the damping coefficient, γ= (2.75.9) ×10-5 (1/sec).
Finally, it is also shown that the square of damping coefficient is inversely proportional to the mean depth of the lake and the period of oscillation in various lakes of the world.
