The Current Status of CFD in ITTC 2: Maneuvering &Seakeeping 2: Maneuvering &Seakeeping Frederick Stern Frederick Stern IIHR ‐ Hydroscience&Engineering The University of Iowa Iowa City, IA 52242 USA 1
Table of contents 1 1. CFD based maneuvering methods in SIMMAN 2008 CFD based maneuvering methods in SIMMAN 2008 1.1 Overview 1.1 Overview 1.2 Verification and Validation (V&V) 1.3 Forces and moment coefficients 1.4 Maneuvering derivatives 1.5 PIV comparisons p 1.6 Trajectories 2. Latest application of CFD to seakeeping 3. Computational towing tank approach 2
CFD based maneuvering prediction method CFD based maneuvering prediction method No Simulation System Based Maneuvering Simulation CFD Based Maneuvering Simulation Database Method Model testing Computational methods Trajectory/Hydrodynamic Derivatives Full ‐ scale Trials Captive Model Tests Inviscid RANS Free Model Tests methods methods System Mathematical model Identification Maneuvering Derivatives, Hydrodynamic Coefficients Equation of motion Ship Ship Trajectories specification Derived maneuvering parameters (advance, transfer, overshoots etc.) C it Criteria i Maneuverability: Acceptable or not 3
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.1 Overview 4 4
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.2 Verification and Validation: 5415, IIHR, CFDShip ‐ Iowa Static drift (Fr=0.28, β =10°) Verification V ifi ti U I (% S 1 ) | ε g21 /S 1 | × 100 R g p g C g Convergence U g (% S 1 ) Without X' T 0.26 2.82 ‐ 0.70 ‐ ‐ OC 2.02 walls Y' T 0.015 0.19 ‐ 3.01 ‐ ‐ OD ‐ r= √ 2 N' T 0.020 0.97 ‐ 1.06 ‐ ‐ OD ‐ Fine ‐ medium ‐ coarse: 19M ‐ 6.9M ‐ 2.4M Validation | E | (% D ) U V (% D ) U D (%D) U SN (%D) Without Without X' T X' 7 68 7.68 4 20 4.20 3.6 3 6 2 17 2.17 walls Y' T 13.44 ‐ 5.4 ‐ r= √ 2 N' T 0.98 ‐ 2.6 ‐ ‐ Slowly damped oscillation 4 ship ‐ lengths for transient 8 ship ‐ lengths for statistical convergence ‐ Difficult to achieve monotonic convergence in Y' T and N' T ‐ X' T is not validated. 5
Pure yaw (Fr=0.28, r'=0.3) Verification: Fourier Series decomposed quantities %S 1 U I (%) ( ) | | ε k 21 | (%) | ( ) R k p k C k Convergence U k (%) ( ) X' 0 0.51 6.16 0.85 0.46 0.18 MC 92.43 X' 2 10.26 18.73 ‐ 0.39 ‐ ‐ OC 24.21 Grid Y' 1 0.32 7.61 2.52 ‐ ‐ MD ‐ (r= √ 2) Y' 3 29.36 17.16 ‐ 1.93 ‐ ‐ OD ‐ N' 1 0.16 1.17 ‐ 5.04 ‐ ‐ OD ‐ 1 N' 3 8.74 71.57 25.32 ‐ ‐ MD ‐ X' 0 0.49 1.76 0.18 2.50 1.55 MC 2.77 X 2 X' 2 0.95 0 95 31 96 31.96 0 62 0.62 0 69 0.69 0.20 0 20 MC MC 135 04 135.04 Time ‐ step Y' 1 0.21 8.64 0.49 1.04 0.35 MC 18.73 (r=2) Y' 3 5.63 10.47 1.71 ‐ ‐ MD ‐ N 1 N' 0 14 0.14 3 96 3.96 0.47 0 47 1 09 1.09 0 37 0.37 MC MC 7 96 7.96 N' 3 5.69 0.92 0.04 4.80 8.97 MC ‐ With walls, 5.5M ‐ 1.58M ‐ 0.56M ‐ Time ‐ step convergence easier to achieve than grid convergence ‐ Need marching FS analysis for more accurate U I estimation 6
Verification: Time ‐ averaged quantities U G (%D) U T (%D) U SN (%D) G T SN 1) X' T 5.50 2.60 6.08 2) Y' T 1.00 6.89 7.00 N' 2) 2) N T 0.20 0 20 7.74 7 74 7 74 7.74 Grid: Without walls, 4.5M ‐ 1.59M ‐ 0.56M, r= √ 2 Time step: r=2 Validation: Time ‐ averaged quantities |E|(%D) U V (%D) U D (%D) U SN (%D) U G (%D) U T (%D) X' 1) ) X T 18 41 18.41 8 94 8.94 6 56 6.56 6.08 6 08 5 50 5.50 2 60 2.60 2) Y' T 10.21 23.45 22.38 7.00 1.00 6.89 2) N' T 2.70 7.90 1.57 7.74 0.20 7.74 1) %D 2) % D d 1) %D, 2) % D dynamic range of Y T ’ or N T ' i f Y ’ N ' ‐ Friction tends to monotonically converge over 1 PMM period than pressure with lower U SN . ‐ Y' T and N' T are validated. Need to check U D in Y' T . 7
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.3 Forces and moment coefficients: KVLCC1 (Fr=0.142) Pure sway ( β corr =4.9°) Pure yaw (r'=0.3) y ( ) Pure sway Pure sway ‐ Over ‐ prediction in X' ‐ Good prediction in Y' and N' and N Pure yaw ‐ Large phase and amplitude difference li d diff in X' ‐ Minor phase lead in Y' compared to EFD ‐ Good prediction in N' 8
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.3 Forces and moment coefficients: KCS (Fr=0.202) Pure sway ( β Pure sway ( β corr 8 ) =8°) Pure yaw (r'=0.4) Pure yaw (r 0.4) Pure sway ‐ Over ‐ prediction in X' Over prediction in X ‐ Good prediction in Y' and N' Pure yaw ‐ High frequency oscillation High frequency oscillation for X' in CFD and Y' in EFD ‐ Minor phase lead in N' compared to EFD compared to EFD 9
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.3 Forces and moment coefficients: 5415, static drift (Fr=0.28, β =10°), IIHR, CFDShip ‐ Iowa Convection scheme/Turbulence 1) Coefficient Coefficient D D FD2 ‐ BKW TVD2S ‐ ARS FD4h ‐ BKW ‐ 0.0195 ‐ 0.02094 ‐ 0.02025 ‐ 0.02074 X' ‐ 7.4% ‐ 3.8% ‐ 6.4% E (%D) E (%D) ‐ 0.05795 ‐ 0.06576 ‐ 0.06408 ‐ 0.06566 Y' ‐ TVD2S ‐ ARS provides the ‐ 13.5% ‐ 10.6% ‐ 13.3% E (%D) best results � consistent 0 02845 0.02845 0 02875 0.02875 0 0285 0.0285 0.02872 0 02872 N' to KVLCC2 application ‐ 1.05% ‐ 0.17% ‐ 0.95% E (%D) ‐ DES only improves X'. ‐ Movie: URANS vs DES URANS, FD2 ‐ BKW 2) DES, FD4h ‐ BKW 2) Coefficient Coefficient D D URANS, FD2 BKW DES, FD4h BKW • Overall ‐ 0.0195 ‐ 0.0210 ‐ 0.02032 X' • Leeward bow ‐ 7.7% ‐ 4.21% E (%D) • Stern ‐ 0.05795 0 05795 ‐ 0.06574 0 06574 ‐ 0.0665 0 0665 Y' ‐ 13.4% ‐ 13.2% E (%D) 0.02845 0.02873 0.0291 N' ‐ 0.98% ‐ 2.28% E (%D) # of grid points: 1) 2.4M, 2) 19M 10
St ti d ift (TVD2S ARS 2 4M Static drift (TVD2S ‐ ARS, 2.4M grid points) id i t ) ‐ Forces and moment coefficients follow the EFD trend. F d ffi i f ll h EFD d ‐ Significant increase in |E| at β≥ 12° 11
turb. vs. laminar beta Coef. D TVD2S ‐ ARS Laminar X ʹ ‐ 0.0166 ‐ 0.01566 ‐ 0.00845 0 deg E (%D) 5.7% 49.1% X ʹ X ‐ 0.0195 0.0195 ‐ 0.02025 0.02025 ‐ 0.0125 0.0125 E (%D) ‐ 3.8% 35.9% Y ʹ ‐ 0.05795 ‐ 0.06408 ‐ 0.06419 ‐ Laminar solution 10 deg 10 deg E (%D) E (%D) ‐ 10.6% 10 6% ‐ 10.8% 10 8% gives better results N ʹ 0.02845 0.0285 0.0300 at larger drift E (%D) ( ) ‐ 0.17% ‐ 5.4% angles angles X ʹ ‐ 0.0287 ‐ 0.0366 ‐ 0.0246 � Expect the E (%D) ‐ 27.5% 14.3% contribution of 20 deg Y ʹ Y ʹ ‐ 0.1529 0 1529 ‐ 0.1902 0 1902 ‐ 0.1550 0 1550 transition E (%D) ‐ 24.4% ‐ 1.4% turbulence model N ʹ 0.0594 0.0690 0.0607 E (%D) ‐ 16.2% ‐ 2.2% # of grid points=2.4M, Fr=0.28 12
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.3 Forces and moment coefficients: 5415 (Fr=0.28) Pure yaw (r'=0.3) y ( ) Pure sway ( β corr =10°) y ( β corr ) Pure sway Pure sway ‐ Oscillation in X' apparent in CFD ‐ Good prediction in Y' Good prediction in Y and N': consistent to KVLCC/KCS Pure yaw Pure yaw ‐ Under ‐ prediction in X' in CFD ‐ Minor phase lag in Y' ‐ Minor phase lag in Y compared to EFD 13
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.4 Maneuvering derivatives: KVLCC2 KVLCC2, shallow water (Southampton, CFX), Fr=0.064 ‐ Shallow water effect makes estimation of h ll ff k f linear derivative less accurate. ‐ Linear derivatives are well ‐ predicted, except Linear derivatives are well predicted, except Y β ' by PARANNASOS. KVLCC2M, deep water (Toxopesu 2008, PARANASSOS), Fr=0.0, ref. JMST , p ( p , ), , 14 14
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.4 Maneuvering derivatives: 5415 (Fr=0.28), IIHR, CFDShip ‐ Iowa ‐ Linear derivatives predicted well within 10%D error. ‐ Non ‐ linear and acceleration Non linear and acceleration dependent derivatives need more accuracy. 15
1 CFD based maneuvering methods in SIMMAN2008 1. CFD based maneuvering methods in SIMMAN2008 1.5 PIV comparisons: 5415 pure sway (Fr=0.28) 16
1. CFD based maneuvering methods in SIMMAN2008 1 CFD based maneuvering methods in SIMMAN2008 1.5 PIV comparisons: 5415 pure yaw (Fr=0.28), IIHR, CFDShip ‐ Iowa X=0.135: X=0.535: X=0.935: ‐ U U ‐ U ‐ U ‐ U ‐ U ‐ V ‐ V ‐ V ‐ W ‐ W ‐ W ‐ω x ‐ω x ‐ω x ‐ TKE ‐ TKE ‐ TKE ‐ Overall trends are well ‐ predicted between CFD and EFD. ‐ Apparent momentum/TKE defect at vortex core in certain phases and cross A t t /TKE d f t t t i t i h d planes compared to the EFD data � Possible reasons are: grid resolution, momentum and turbulence convection scheme, isotropic turbulence model 17
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