This paper presents an application of a Rankine panel method in seeking for optimum trim, which corresponds to the lowest resistance for the definite specified displacement and the given specified forward speed. A 3100TEU container ship is taken as an object ship. A wooden ship model with scale ratio 1:50 is manufactured., and a series of towing tests to the ship model was performed. By use of the measured towing drag, the numerical method is validated. Then a systematical investigation on the object ship at three different main displacements with various forward speeds was carried out. It is found that at different loading conditions and forward speeds, tendency and the value of the optimum trim are quite different. It should be searched case by case. Though value of optimum trim does not mean large, reduction of drag could be quite remarkable. Therefore, seeking optimum trim is meaningful and becomes necessary. Numerical wave patterns, contours and many other results are given and discussed.
With the adoption of IMO EEDI and EEOI regulations, energy saving design has become more active. Among them, trim adaptation is considered to be a simple mean able to reduce ship resistance quite a bit. Trim of a ship can be adapted by adjusting cargo arrangement or ballast water distribution. After investigation on transom stern vessels with bulbous bows in different draughts and speeds, Bertram, Höppner and Fach (2010) found out that the lowest resistance indeed corresponds to some trim. In order to improve the accuracy in seeking the best trim, Wang, Lu and Wang (2010) developed a more elaborate program for ship hull optimization by taking sinkage and trim into account and the nonlinear wave making resistance was numerically solved, where DTMB 5414 transom-stern ship model was investigated as an example.
Though linear wave-making theory has been well developed, for large hull ships nonlinearity of the free surface condition emerges. Jensen, Soding, and Mi (1990) applied Rankine method to the prediction of steady wave resistance. Tarafder and Suzuki (2008) modified the Rankine panel method to calculate the wave-making resistance to attack the nonlinearity. Gao Zhiliang (2008) developed a high-order Rankine panel method based on Non-Uniform Rational B-Spline to solve the three-dimensional radiation and diffraction problems. Zhang Baoji (2009) combined the Rankine source method with the nonlinear programming to obtain a hull form with the minimum wave-making resistance, where S60 hull form was selected as the original hull. Chen Jingpu (2010) predicted the wave-induced ship motions in regular head waves using Rankine source method in time domain. He and Kashiwagi (2012) developed a higher-order boundary element method. Lv, Wu, Sun and Tu (2013) presented a potential-based panel method to optimize the trim. Söding (2014) predicted added resistance in head waves for a Wigley hull by employing a Rankine panel method and an extended Reynolds-Averaged Navier- Stokes (RANS) solver.
