To ensure successful ship operations it is important to be able to predict, reliably and efficiently, ship performance in a seaway. For ship design evaluation, for weather routing, for prediction of sea margin and for logistics planning it is important to be able to predict the attainable speed and power consumption in a given sea state, and for that purpose, the total resistance in waves is a key parameter.
This study investigates estimation of the ship total resistance in deep water through utilization of different theoretical models based on potential fluid flow theory with partial inclusion of viscous effects. The complexity of the models and therefore their difficulty in practical application from the perspective of the theoretical studies is varied. This is done in order to investigate and exemplify the level of accuracy of the different theoretical methods concerning both qualitative and quantitative distribution of the calm water wave resistance and the added resistance in regular waves in deep water. The estimation of the total resistance in a seaway is carried out through utilization of the simplified ITTC [2] approach according to Skejic and Jullumstrø [7]. The method is based on the linear superposition of the calm water resistance and the added resistance in regular waves in deep water.
With respect to the prediction of the calm water resistance, the current work applies ordinary and modified Michell wave theory including the viscosity parameter and also three dimensional boundary element method (3D BEM) (see Skejic [5]). The differences between the applied methods are discussed and their applicability as seen from the perspective of accuracy and common engineering practice are given.
The estimation of the added resistance is carried out by several theories capable to cover the whole range of wavelengths of interest for a displacement ship operating at the forward speeds corresponding to moderate Froude numbers in preselected regular wave conditions realistically resembling the harsh sea state situations. In the short wavelength range (length below about 0.45 times ship length), where the added resistance in waves is mainly due to the wave reflection and where the ship motions are insignificant, the added resistance is predicted according to Faltinsen et al. [20], modified Fujii and Takahashi [23], Kuroda et al. [24] and Liu et al. [27] theoretical models. The last three models were investigated in particular details by considering the influence of the variation of the different parameters that formulate the mentioned models. When it comes to longer wavelengths, where the added resistance in waves is largely due to significant ship motions, Salvesen [10] and Maruo [8, 9] theoretical methods are used. Guidance concerning the practical applicability of the mentioned theories is given by taking into account the influence of the surge motion mode upon estimation of the added resistance in waves. In addition, a short discussion concerning the propulsive performances of a displacement type of the vessels in a seaway is included.
To exemplify and compare the studied theoretical calculation methods, two modern and distinctively different ship hull forms, i.e. the KRISO MOERI Container Ship KCS with the block coefficient CB = 0.6505 and KRISO MOERI Tanker KVLCC2 with the block coefficient CB = 0.8098 have been studied. The obtained calculation results were compared with published experimental and theoretical results and found to be in good agreement. Finally, recommendations concerning the practical applicability of the above-mentioned theories are given and discussed.
On Total Resistance of Ships in a Seaway
Lecture Notes in Civil Engineering
Practical Design of Ships and Other Floating Structures ; 2019 ; Yokohama, Japan September 22, 2019 - September 26, 2019
2020-10-06
23 pages
Article/Chapter (Book)
Electronic Resource
English
On Total Resistance of Ships in a Seaway
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