科研之友
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摘要
Numerical implementation of the Neumann-Michell (NM) theory of ship waves is considered. A practical solution procedure based on four main elements is reported. (i) We use an iterative solution procedure in which the initial approximation given by the Hogner slender-ship approximation is improved iteratively via the correction to the wave component defined by the NM theory. (ii) This iterative solution procedure is implemented within the framework of a low-order panel approach that assumes piecewise linear variations of the hull geometry, the flow potential, and the flow velocity within the flat triangular panels that approximate the ship hull surface. (iii) Physically unrealistic or inconsequential short gravity waves are removed, using parabolic extrapolation within a thin layer in the vicinity of the free surface with physics-based relations for the variation of the related extrapolation height. (iv) We use numerical smoothing of the flow velocity, determined in the NM theory as the derivatives of the flow potential along two orthogonal unit vectors tangent to the hull surface. Filtering of short waves and numerical smoothing of the flow velocity are found to be critical elements of the solution procedure. For validation purposes, illustrative applications are reported for eight ship hulls that correspond to a relatively broad range of displacement ships and Froude numbers. These applications show that the practical numerical implementation of the NM theory considered here yields robust predictions that are realistic and in good overall agreement with experimental measurements. In particular, a highly simplified approach, based on the sum of the friction drag given by the ITTC friction formula and the wave drag predicted by the NM theory, is found to predict the total drag within about 10% of experimental measurements. We also note several extensions of this highly simplified approach that may be expected to significantly improve accuracy.
- 出版日期2013-12
