Resistance Characteristics and Form Factor Evaluation for Geosim Models

Abstract

Model test in towing tank is very important procedure for hull form design and powering performance prediction of a full scale ship before she is built. Also the model-ship correlation and extrapolation method based on the model test results are significant factors for the accurate powering performance predictions. For the extrapolation of resistance, it is assumed that the frictional or viscous resistance is equal or proportional to that of the flat plate with same Reynolds number and the residuary resistance is equal to model and full scale ship. However, the enhancement of the extrapolation method is always explored to improve the model-ship correlation. As a part of this effort, a series of geosim test is planned in MOERI. The KVLCC, KCS, and KLNG were selected as the typical commercial vessels. Four differently scaled model-ships for each hull form were manufactured and resistance tests were performed. CFD computations were also performed for the corresponding geosims by WAVIS 2.2. Resistance characteristics and form factor are analyzed based on the ITTC 1957 model-ship correlation line and ATTC friction line to investigate the scale effect on the form factor. Considerable scale effects are found in resistance characteristics and consequently in the form factor for differently scaled geosim models. Importance of the friction line for the form factor evaluation and dependency of the form factor on Reynolds nums are significant factors for the accurate powering performance predictions. For the extrapolation of resistance, it is assumed that the frictional or viscous resistance is equal or proportional to that of the flat plate with same Reynolds number and the residuary resistance is equal to model and full scale ship. However, the enhancement of the extrapolation method is always explored to improve the model-ship correlation. As a part of this effort, a series of geosim test is planned in MOERI. The KVLCC, KCS, and KLNG were selected as the typical commercial vessels. Four differently scaled model-ships for each hull form were manufactured and resistance tests were performed. CFD computations were also performed for the corresponding geosims by WAVIS 2.2. Resistance characteristics and form factor are analyzed based on the ITTC 1957 model-ship correlation line and ATTC friction line to investigate the scale effect on the form factor. Considerable scale effects are found in resistance characteristics and consequently in the form factor for differently scaled geosim models. Importance of the friction line for the form factor evaluation and dependency of the form factor on Reynolds num