Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
TELFER’S GEOSIM METHOD REVISITED BY CFD (DOI No: 10.3940/rina.ijme.2019.a4.563)
C Delen and S Bal, Department of Naval Architecture and Marine Engineering, Istanbul Technical University, Turkey SUMMARY
In this study, Telfer’s GEOSIM method for the computation of ship resistance at full scale has been applied by CFD (Computational Fluid Dynamics) approach. For this purpose, the KCS (KRISO Container Ship) hull has been investigated numerically with k-ε turbulence model for three different scales and full scale analyses by URANS (Unsteady Reynolds Averaged Navier-Stokes) method. Full scale ship resistance has been predicted using the numerical results computed at different model scales by Telfer’s GEOSIM method. The numerical results at three scales have also been extrapolated separately to that at full scale by ITTC 1978 performance prediction method. An experimental study has also been carried out at a model scale for validation. The results byTelfer’sGEOSIM method have been calculated almost in full compliance with those of CFD approach. While the difference between the results of CFD and those of ITTC extrapolation method is about 5% at full scale, the difference between the results of CFD and those of Telfer’s GEOSIM method has been found to be less than 1% at full scale. In addition, this method has been applied to estimate the nominal wake coefficient at full scale from model scales. A very good correlation has also been found for nominal wake coefficient.
NOMENCLATURE B
CA
CAA CR CB CF
CFD CT eext ea
EFD Fr
FVM g
GCI
KCS LBP
LCB LWL N/A Ni p
R r
Re RT S
SIMPLE Breadth (m)
Correction allowance Air resistance coefficient
Residual resistance coefficient Block coefficient
Frictional resistance coefficient Computational Fluid Dynamics Total resistance coefficient Extrapolated relative error Approximate relative error Experimental Fluid Dynamics Froude number
Finite Volume Method
Acceleration of gravity (m s-2) Grid Convergence Index
GEOSIM Geometrically similar ITTC k
International Towing Tank Conference Form factor
KRISO container ship
Length between perpendiculars (m) Longitudinal Center of Buoyancy (m) Length on waterline (m) Not available
Total mesh number of ith grid Apparent order of method Converged condition Refinement factor Reynolds number Hull resistance (N)
Wetted surface area (m2)
Semi-Implicit Method for Pressure- Linked Equations
Subscript-M Model scale Subscript-S Full scale T
UD
UGCI UV
Draught (m)
Uncertainty value in experiments. Uncertainty value in simulation. Validation Uncertainty
URANS V
V&V wn ∇
ΔCF Δt ʎ τ
ϕi 1.
Unsteady Reynolds Averaged Navier- Stokes
Service speed (ms-1)
Verification and validation Nominal wake fraction Displacement volume (m3) Roughness allowance Time step (s) Scale ratio
Density of fluid (kg m-3) Sinkage (m) Trim (º)
Kinematic viscosity (m2 s-1 ) Solution of key parameter of ith grid INTRODUCTION
One of the main issues in the design of a marine vessel is the correct estimation of power required at the desired velocity. Overestimation of power would cause an increase in production and operational costs as well as in emissions from ship. On the other hand, underestimation of power would cause not to satisfy the operational criteria of the vessels. For this purpose, the vessel resistance and power at a desired speed should be determined precisely.
Telfer’s GEOSIM method is one of the significant methods to estimate the ship resistance and power at full scale by using model tests. Total resistance is predicted without theoretical decomposition of resistance (Bertram, 2011). This method, unlike other conventional methods, provides an extrapolating technique to full scale by using only total resistance values at model scales (Molland et al., 2011). The main purpose in original Telfer’s GEOSIM method is to determine a relationship between the total resistance of the ship and the Reynolds number by carrying out model tests with geometrically similar (GEOSIM) models at corresponding Froude numbers (Telfer, 1927). However, carrying out model experiments with a series of model family is both time consuming and
©2019: The Royal Institution of Naval Architects A-467
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