XLVII. The drifting force on a ship among waves
XLVII. The drifting force on a ship among waves
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DOI：
10.1080/14786444208521213
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发表时间：
1942-06
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影响因子：
--
通讯作者：
T. Havelock
中科院分区：
文献类型：
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作者：
T. Havelock
1. 当一艘船在波浪中前进时，它所经历的平均稳定阻力大于在平静水中以相同速度行驶时的平均稳定阻力。毫无疑问，产生这一结果有几个因素；例如，一种可以描述为由于海浪被船表面反射或散射而产生的波浪压力（Kreitner，1939）。在完整的理论中当然必须考虑到这一点，但对其的研究涉及流体动力学方程中的二阶项，并且该问题的令人满意的解决方案将是困难的。我最近（1940）给出的某些计算似乎表明，这个原因不太可能解释观测结果的一小部分。实验表明，当船舶迎浪周期接近船舶振荡自然周期时，效果最为显着；无论是直接还是间接，这种现象显然与船舶的起伏和纵摇运动有关。在已经引用的论文（1940）中，有人提出，本身纯粹是周期性的一阶效应之间的相互作用很可能通过相位差产生稳定的附加阻力。本说明的目的是提供一些初步的计算，以放大和说明这一建议。为此，我们求助于近似理论，该理论忽略了船表面对波浪运动的干扰作用。在适当的情况下，我们也许会将反射波的必要补充视为小修正，例如，对于一艘又长又窄的船（1937）。这一假设是 W. Froude 在其关于船舶在波浪中横摇的研究中提出的理论的基础，在这种情况下，假设波长比船舶的波束大。克里洛夫在他对船舶在波浪中的起伏和纵摇的著名分析中也明确使用了它。后一项工作仅涉及船舶的振荡，而不是现在正在考虑的额外运动阻力。确实，该问题至少在某种形式上涉及二阶项，并且对这些项的任何部分单独检查都不能令人满意；以下计算
1. WHEN a ship is advancing through a train of waves it experiences an average steady resistance greater than that at the same speed in smooth water. There are no doubt several factors operative in producing this result; one, for instance, may be described as wave pressure due to the reflexion or scattering of the ocean waves by the surface of the ship (Kreitner, 1939). This must certainly be taken into account in a complete theory, but investigation of it involves second-order terms in the hydrodynamical equations and a satisfactory solution of the problem would be difficult. Certain calculations which I have given recently (1940) seem to show that this cause is not likely to account for more than a small fraction of the observed results. Experiment shows that the effect is most prominent when the period of encounter of the ship with the waves is near the natural periods of the ship's oscillations; whether directly or indirectly, the phenomenon is clearly associated with the heaving and pitching motions of the ship. In the paper already quoted (1940) it was suggested that it may well be that interactions between first-order effects which in themselves are purely periodic may, through phase differences, give rise to steady additional resistances. The object of the present note is to give some tentative'calculations amplifying and illustrating this suggestion. For this purpose we fall back on the approximate theory which neglects the disturbing effect of the ship's surface upon the wave motion. In suitable cases we may perhaps regard the necessary additions for the reflected waves to be small corrections, as, for instance, for a long narrow ship (1937). This assumption was the basis of the theory developed by W. Froude in his work on the rolling of a ship among waves, in which case the wavelength is assumed large compared with the beam of the ship. It was also used explicitly by Kriloff in his well-known analysis of the heaving and pitching of a ship among waves. This latter work dealt only with the oscillations of the ship, and not with the extra resistance to motion which is now under consideration. It is true that the problem involves, in some form at least, second-order terms, and any partial separate examination of such terms is unsatisfactory; the following calculations