Methods to Improve Accuracy of Planing Hull Resistance Prediction

Abstract

Accurate prediction of planing hull resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing provides the most accurate results, but is usually only used in cases of necessity due to time and cost, whereas empirical formulas and the CFD method do not always provide results with the expected accuracy and reliability. Therefore, this paper will present methods to improve and ensure the accuracy of planing hull resistance values predicted by Savitsky’s empirical formula based on using our modified computation procedure, and by the CFD method based on ensuring the quality of 3D hull mesh and defining the simulation parameters suitable for a study planing hull. This study has been applied to Vietnam’s large displacement high speed passenger vessel with design symbol K88 and obtained good results with the deviations between the resistance model test data and the corresponding values predicted by the Savitsky method using our modified computation procedure, and by the XFlow CFD software using our suitable inputs in calculation cases are within 65% and 63%, respectively. In planing hull design, accurate prediction of its resistance is a difficult task due to complex hydrodynamic interactions at high speeds and is often performed by three methods: model testing, empirical formulas, and computational fluid dynamics (CFD). Model testing is the most reliable approach but it is expensive and time-consuming, so it is often used in cases where it is necessary, or used to verify and validate the results predicted by others. Also, since dynamic similarity cannot be fulfilled in model tests, it is necessary to use Froude or Prohaska methods to extrapolate results from model scale to full scale, which causes certain errors. Empirical formulas or graphs are established based on the systematization of resistance data of series model tests with hull form similarities (Holtrop & Mennen 1982; Faltinsen 2006). As a result, there are many different empirical resistance formulas and graphs depending on the type of ship used in the model tests. Table 1 shows some common empirical formulas or graphs for planing hull resistance with different ranges of hull parameters that can be found in related documents, such as Kafali (1959), Nordstrom (1951), Groot (1951), Almeter (1993), etc.