Experimental and Theoretical Study of the Effect of Hull Roughness on Ship Resistance

Abstract

Hull roughness increases ship frictional resistance and, thus, results in economic and environmental penalties. Its effect has been prevalently predicted using the similarity law scaling procedure. However, this method has not yet been validated with experimental data using a model ship. This study presents an experimental investigation into the effect of roughness on ship resistance and provides a validation of the similarity law scaling, by using tank testing of a flat plate and a model ship. Both the plate and the ship were tested in smooth and rough surface conditions, respectively. For the rough surface conditions, sand grit (aluminum oxide abrasive powder) was applied on the surfaces of the flat plate and the ship model. The roughness functions of the rough surface were derived by using the results obtained from the flat plate tests. Using the roughness function and the flat plate towing test, frictional resistance was extrapolated to the length of the model ship following the similarity law scaling procedure. The total resistance of the rough ship model was first predicted using the extrapolated frictional resistance and the result of the smooth ship model, and then compared with the results from the rough ship model. The predicted total resistance coefficients for the rough ship model showed a good agreement with the measured total resistance coefficient of the rough ship model, thus proving the validity of using Granville's similarity law scaling to extrapolate the roughness effect on ship resistance. 1. Introduction Roughness of a ship's hull, which is often caused by hull fouling (Townsin 2003) and corrosion (Tezdogan & Demirel 2014), can dramatically increase the ship resistance and hence its fuel consumption and greenhouse gas emissions, as well as the cost associated with dry-docking (Schultz et al. 2011); Granville (1958; 1978). Accordingly, there have been numerous investigations into the roughness effect on ship resistance from the earliest times to the present (e.g., McEntee 1915; Hiraga 1934; Kempf 1937; Benson et al. 1938; Watanabe et al. 1969; Loeb et al. 1984; Lewkowicz & Das 1986; Lewthwaite et al. 1985; Haslbeck & Bohlander 1992; Schultz 1998; Schultz & Swain 1999; Schultz 2002; Schultz 2004; Andrewartha et al. 2010; Schultz et al. 2011; Demirel 2015; Demirel et al. 2017a; Demirel et al. 2019).

Investigating the Effect of Heterogeneous Hull Roughness on Ship Resistance Using CFD

“…where + is the roughness Reynolds number based on the peak roughness height over a 50 mm interval (i.e., = 50 = 353 µm). As shown in Figure 2, the roughness function model of Song et al [25] agrees well with the experimental roughness function [24]. [24] and the roughness function model of Song et al [25] Equation (6).…”

“…Song et al [24] evaluated the roughness function of the sand grit (60/80 grit aluminium oxide abrasive powder) from the results of flat plate towing tests. Later on, a mathematical model of the roughness function (i.e., roughness function model) was proposed by Song et al [25] to be used in CFD simulations.…”

“…Recently, Song et al [24,25] validated Granville's method and the CFD method by comparing the predictions against a ship model test with a rough surface.…”

“…In this study, CFD simulations of the Wigley hull were developed with different hull roughness conditions using the modified wall-function approach with the roughness function model of the sand-grain surface, which were determined from previous studies [24,25]. The CFD simulations of the Wigley hull model were performed with different hull conditions.…”

“…Experimental ΔU+ (Song et al[24]) ΔU+ model (Song et al[25], Equation 6) Different hull conditions of the Wigley hull simulations.…”