Predicting added resistances of a ship in actual seas is essential to optimize the hull form, to predict speed losses, to analyze speed sea trial results, to estimate the sea margin, and to find the optimum seaway route for eco-operation. This paper employs an experimental method to investigate the added resistance for KVLCC2 advancing forward in three sea states of long crested irregular head waves. The model tests have been conducted at Pusan National University's towing tank. The model is free to surge condition. ITTC wave spectrum is used to generate long crested irregular waves of sea state 4, 5 and 6. Data of five repeated experiments are combined to make a sufficient number of encounter wave. These results are compared with those using the indirect method which uses the linear superposition of energy spectra of wave and response functions in regular waves


Predicting added resistances of a ship in waves (RAW) is essential to optimize the hull form and predict speed losses, to analyze speed sea trial results, to estimate the sea margin, and to find the optimum seaway route for eco-operation.

Many studies have been performed since the 1970s to analyze the characteristics of RAW using numerical and experimental methods. RAW has shown dependency on ship motions, bow relative motions, ship speeds, wavelength, height, and heading angles, and hull form and bow shapes. Since RAW has a second order nature and is based on the mean of wave forces, its value is modest compared to the amplitude of the excitation force (Faltinsen, 1990). RAW shows strong nonlinear behaviors (Gerritsma and Beukelman, 1972; Journee, 1976; Lee et al., 2013; Shen and Wan, 2013), and the influence of surge motion on RAW may be negligible. However, the prediction of surge motion is still of importance as the motions are impacted by surge, heave and pitch coupling (Joncquez et al., 2008). The bow relative motion has correlations with RAW in a manner that the peak of the RAW is near the maximum bow relative motion (Blok, 1983; Grigoropoulos and Loukakisa., 2000; Shen and Wan, 2013). Shen and Wan (2013) showed that the maximum RAW occurs right before the ship sinks to the lowest position and the trim angle reaches the negative maximum value; whereas the minimum RAW occurs at the moment when the ship approaches even keel conditions. It may be prescribed that the transient RAW largely depends on the motions of ship - RAW increases with the ship speed (Zeraatgar and Abed, 2006). RAW is mainly caused by wave radiation via the ship motion and bow reflection of incident waves on the ship hull (Hirota et al., 2005). RAW in short waves is an important factor especially for a large ship's performance, because the significant frequency of a sea wave spectrum coincides with this range. Ship motion in short waves is near negligible and RAW in this range is primarily due to wave reflections. With increase of wave steepness, the non-linear behaviors become more notable. This may be due to the effect of green water on deck and water impacting on the deck of the ship (Gerritsma and Beukel-man, 1972; Journee, 1976). The phase differences of the ship motions for various wave steepness are small (Castiglione et al., 2011; Shen and Wan, 2013). RAW is often larger in head waves than that in beam waves (Zeraatgar and Abed, 2006). The blunt bow shape generally provides larger RAW (Blok, 1983; Naito et al., 1996; Orihara and Miyata, 2003). Many model tests have been carried out to measure the added resistance of KVLCC2 in head waves with various model scales and test conditions since Gothenburg 2010 CFD workshop (Hwang et al., 2013; Sadat-Hosseini et al., 2013; Kim et al., 2017; Lee et al., 2017).

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