Structural design and Stability of a 6,000 ton Capacity Floating Dock as per DNVGL Rules AKHIL KARTHIKA AJITH 7 th EMship cycle: September 2016 − February 2018 Master Thesis Development Of Flap Rudder Systems For Large Container Vessels Supervisor: Dr. Nikolai Kornev, University of Rostock , Rostock, Germany I nternship tutor: Mr. Steve Leonard, I BMV Maritime I nntionsgesellschaft , Rostock, Germany Reviewer: Mr. Jean-Baptiste Souppez, Southampton Solent university , UK La spezia, February 2018 Kodathoor Midhun , 7 th EMship cycle: 2016 − 2018 Defence of Master Thesis, Szczecin, January 2018
Why Flap Rudd dder For Containership p Opera ration? • Higher safety and higher side force compared to conventional rudders • Better maneuvering ability • Compared to conventional rudder lesser rudder area required to provide same side force • Improved course keeping with reduced rudder angle. • Reduced tug assistance for small feeder vessels EMSHIP 2016-18 2
Obje jectives o of t the Study • Feedback from large containership owners regarding the low maneuvering problem in shallow water • Previous CFD analyses indicates that flow separation starts from the flap rather than the leading edge • Existing linkage mechanism means relatively aggressive flap operation at small rudder angles • Initial project aim to develop new flap actuation ratios EMSHIP 2016-18 3
Bec Becker Flap Rudder r CFD An Analysis • Two dimensional analysis 1. New flap ratios find out by changing the value of a/b ratios. 2. a/b values from 1.5 to 1.7 incremented by 0.05 3. Flow analysis conducted at slow speed (8 knot) and cruise speed (23 knot) conditions. 4. Wake values are derived from the model test result at 14.5 m draft (V A ). EMSHIP 2016-18 4
Details of 2D CFD Pl Plan • Flow analysis conducted at +0.7R & -0.7R of the rudder horizontal section • Domain size fixed based on chord length of rudder • 50000 to 80000 cells used (polyhedral) • Base size fixed at 0.9m with 1.05 times surface growth • Prism layer count fixed at 7 with steady case & full scale rudder • 5 to 10 minutes for meshing & analysis using 383 processor server EMSHIP 2016-18 5
Results ts o of Two Dimensional Analysis Lift vs Flap Ratios (uppeside -port-slow speed, +0.7R) 7.00 x 10000 6.00 5.00 Lift Force (N) 4.00 Lift Force 3.00 Lift Force Lift Force 2.00 Lift Force 1.00 Lift Force 0.00 0 5 10 15 20 25 30 Rudder Angle (Deg) EMSHIP 2016-18 6
Flow Separation at 12° for Existing ng Flap R Rud udder EMSHIP 2016-18 7
Result o of Two Dimensional CFD D Stud udy • Analysis result recommend that Flap Ratios D (a/b=1.7) has reduced aggressiveness in flap operation • Stall angle delayed 6 to 8 degree for each case of Ratio D • Further increase of a/b ratio not possible due to space limitations caused by trunk/stock dimensions • Flow separation appears to start from the forward part of flap / end point of suction side of rudder EMSHIP 2016-18 8
Three Dimensional An Analysis • Flow analysis done with the ship hull and virtual propeller. • Wake calculated independently, file as table in STAR-CCM+. • Comparison of existing ratios and optimum ratios • Impact of water depth in rudder side force. • Hull force in different water depth. EMSHIP 2016-18 9
Details of T Three Dimensional CFD Pl Plan • Base size fixed 30.3 m • 1/3 of the ship hull considered for the analysis • Analysis done at full scale • Steady-state • 5 to 6 million cells used per case • k-omega SST turbulence model used • 383 processors • Run time – about 2 hours per case EMSHIP 2016-18 10
Details of Three Dimensional CFD Pl Plan EMSHIP 2016-18 11
Result t of T Three Dimensional Analysis Rudder Lift vs Rudder Angle 6.00E+00 Millions 4.00E+00 LIFT FORCE (N) 2.00E+00 0.00E+00 Ratio D,shallow depth -40 -30 -20 -10 0 10 20 30 40 -2.00E+00 Port Starboard exisiting ratios ,shallow depth -4.00E+00 -6.00E+00 -8.00E+00 Rudder Angle (Deg) EMSHIP 2016-18 12
Result t of T Three Dimensional Analysis • Result from the 3D analysis are diffrent from the 2D analysis • From the flow analysis realized that flow seperation start from the leading edge • Rudder Bulb appear to triger flow seperation EMSHIP 2016-18 13
Result t Of T Three Dimensional Analysis Rudder Lift vs Rudder Angle 6.00E+00 Millions 4.00E+00 LIFT FORCE (N) 2.00E+00 0.00E+00 Ratio D,slow speed -40 -30 -20 -10 0 10 20 30 40 exisiting ratios ,slow speed -2.00E+00 Starboard Port without bulb -slow speed -4.00E+00 -6.00E+00 -8.00E+00 Rudder Angle EMSHIP 2016-18 14
Shear S r Stress D Distri ribution A At 18° Rudder An r Angle Rudder with normal condition Rudder with the absence of bulb EMSHIP 2016-18 15
Leading Edge Flow S Separation & Rudder r Bulb Inter eraction on • Present flow analysis for the twisted flap rudder with bulb shows that flow separation starts from the leading edge of intersection of bulb and rudder geometry. • Bulb is present to reduce fuel consumption – elimination of propeller hub vortex. • Bulb optimized for power-saving. Investigate effect of removing bulb EMSHIP 2016-18 16
Symmetrical rudder without bulb Symmetrical rudder with bulb Twisted Rudder with horizontal Twisted rudder with blended LE transition plate EMSHIP 2016-18 17
Ne New Ge Geom ometries es Vs Existing T g Twisted ed Flap Rudder er Rudder vs performance 1.20E+00 Millions 9.00E-01 6.00E-01 symmetric rudder Lift Force (N) 3.00E-01 symmeric rudder without bulb 0.00E+00 blended Leading Edge -40 -30 -20 -10 0 10 20 30 40 twisted rudder with transition plate -3.00E-01 Port Starboard exisiting rudder -6.00E-01 -9.00E-01 -1.20E+00 Rudder Angle (Deg) EMSHIP 2016-18 18
Shea ear F Force C ce Comparison on -Existing & & Symmetrical Rudder G r Geometry (Rudde dder a and F d Flap r p rotate 2 25° towards ds port s side) e) Existing rudder with new ratio D Symmetric rudder with new ratio D EMSHIP 2016-18 19
Impac act o of Ship Hu Hull a at Di Different W Water De Depths (8 k knot ots) ) • In this section we compare the ship hull forces and moments with approximate rudder turning moment • Ship hull force & turning moment are calculated with different turning radii to ship length ratio (R/L) and drift angle β EMSHIP 2016-18 20
Rudder er S Side F e Force I e In Differ erent W t Water er D Depths EMSHIP 2016-18 21
Hu Hull M Moment &R &Rud udder M r Moment –Suez C Canal al & & De Deep De Depth Hull Moment 1000 800 Hull Moment in million (N.m) 600 shallow depth R/L=100 shallow depth R/L=10 400 shallow depth R/L=5 Deep water R/L=100 Deep water R/L=10 200 Deep water R/L=5 0 0 2 4 6 8 10 12 -200 Drift Angle (Deg) EMSHIP 2016-18 22
Hu Hull M Moment &R &Rud udder M r Moment –Suez C Canal al & & De Deep De Depth Hull Moment & Rudder Moment comparison 1000 800 Hull Moment in million (N.m) shallow depth R/L=100 600 shallow depth R/L=10 shallow depth R/L=5 400 Deep water R/L=100 Deep water R/L=10 200 Deep water R/L=5 Flap rudder -Max. rudder moment 0 0 2 4 6 8 10 12 -200 Drift Angle (Deg) EMSHIP 2016-18 23
Ho How t to Overcome the E Existing Problem o of Hi High Hull F Hu Force & & Turning M Moment • Hull forces dominate in shallow water condition compared to deep water. Solutions Benefits Penalties Increasing operation difficulties Increasing the side force rudder Area production cost Improving the flow Improving the Unlikely to provide characteristics, Increasing rudder section sufficient improvement the side force Twin-screw Increasing the side force in gain in side force vs propulsion large magnitude production expense? EM SHIP 2016-18 24
Conclusions • 2D& 3D analysis results are different • Flap ratio D has better performance • Rudder bulb appears to start the flow separation at leading edge • Numerical analysis of flow around rudder recommend that symmetrical rudder without bulb have improved flow separation & side forces than existing one • Large container ships in shallow water – hull forces dominate. • Vessel operated in shallow water require a specific recommendation of maneuvering operation EMSHIP 2016-18 25
Future W e Works & Recom ommen endation ons • Transient analysis with explicit propeller (rotating mesh) • Full 3D restrictions (include banking) • Bulb details • Model tests Thank you EMSHIP 2016-18 26
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