CFD based form factor determination method

Kadir Burak Korkmaz,Sofia Werner,Nobuaki Sakamoto,Patrick Queutey,Ganbo Deng,Gao Yuling,Dong Guoxiang,Kevin Maki,Haixuan Ye,Ayhan Akinturk,Tanvir Sayeed,Takanori Hino,Feng Zhao,Tahsin Tezdogan,Yigit Kemal Demirel,Rickard Bensow

doi:10.1016/j.oceaneng.2020.108451

Abstract

The 1978 ITTC Power Prediction method is used to predict the propulsive power of ships through towing tank testing. The form factor approach and its determination in this method have been questioned. This paper investigates the possibility to improve the power predictions by introducing Combined CFD/EFD Method where the experimental determination of form factor is replaced by double body RANS computations applied for open cases KVLCC2 and KCS, including first-time published towing tank tests of KVLCC2 at ballast condition including an experimental uncertainty analysis specifically derived for the form factor. Computations from nine organisations and seven CFD codes are compared to the experiments. The form factor predictions for both hulls in design loading condition compared well with the experimental results in general. For the KVLCC2 ballast condition, majority of the form factors were under-predicted while staying within the experimental uncertainty. Speed dependency is observed with the application of ITTC57 line but it is reduced with the Katsui line and nearly eliminated by numerical friction lines. Comparison of the full-scale viscous resistance predictions obtained by the extrapolations from model scale and direct full-scale computations show that the Combined CFD/EFD Method show significantly less scatter and may thus be a preferred approach.

Highlights

Performance prediction of a ship is one of the most important tasks during the design phase
Statistics of CF and CPV The simulations in model scale comprise computations from seven different codes and six different turbulence models with wall functions and wall resolved approaches. These computations include the Computational Fluid Dynamics (CFD) setups according to the best practice guidelines (BPG) or standard settings and setups that deviated from recommended guidelines since one of the aim of this study is to identify the methods that are not well suited for the form factor determination
This paper presents an investigation on CFD based form factor

Summary

Introduction

Performance prediction of a ship is one of the most important tasks during the design phase. According to the majority of commercial tendencies presented by shipyards and ship owners, towing tank tests are still considered as the last step of the performance prediction. Towing tank testing has remained as the only practice for more than a century with high accuracy to predict the performance of a ship in deep and calm water since William Froude introduced the extrapolation procedures in the 1870s. Ten institutions known to have access to sea trials for different types of ships evaluated each method by starting from their model test results to calculate the shaft power and propeller rate of revolution (ITTC, 1978). The 1978 ITTC Performance Prediction Method emerged as a result of comparing approximately one thousand sea trials to model test predictions and it is still in effect after going through several revisions

Objectives

Methods

Results

Conclusion