CFD ANALYSIS OF THE PERFORMANCE OF A FAST CATAMARAN WITH ROUGH SEA

Transcription

1 STAR EUROPEAN CONFERENCE 2011 Amsterdam, March CFD ANALYSIS OF THE PERFORMANCE OF A FAST CATAMARAN WITH ROUGH SEA G. Lombardi, M. Maganzi Dept. of Aerospace Engineering of Pisa Italy

2 The Problem A new vessel was under development in cooperation with italian defence industry Requirements: Very high speed High stability platform Maximum performance up to Sea State 3 Large surface for Load allocation A catamaran configuration was chosen The development of the project requires a deep analysis of the performance and stability characteristics of the hull STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 2

3 The CONFIGURATION Cruise Speed: 45 Kts (24.3 m/s) Max. Speed: 80 Kts (43.2 m/s) Length: m Width: 4.25 m Static Draft: 0.60 m Max. Displacement: 9.7 Tons Surface propellers STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 3

4 THE APPROACH In a previous paper G. Lombardi, M. Maganzi, A. MarioV FREE MOTION SIMULATION OF A SAILING YACHT IN UP WIND CONDITION WITH ROUGH SEA, STAR EUROPEAN CONFERENCE 2010 was highlighted that STAR CCM+ has the capability to evaluate the moton of the complete boat with rough sea IT WAS DECIDED TO VERIFY THE POSSIBILITY TO USE THE SAME APPROACH TO EVALUATE THE PERFORMANCE AND THE STABILITY CHARACTERISTICS OF THE NEW CONFIGURATION STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 4

5 THE APPROACH The use of computational fluid-dynamics techniques would be a key-point in the analysis to optimise the platform and the system performances, generating inputs for the detailed design : Speed Attitude Stability characteristics Power requirements Weight effects Loads... STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 5

6 SOFTWARE CAD GEOMETRY CATIA V5 R19 Surface GRID ANSA Volume GRID and CFD STAR CCM+ v STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 6

7 HARDWARE Full time available: Linux cluster: 16 SUN Fire X4100. Each server: 2 AMD Opteron 285 (Dual Core) processors and 4GB RAM each (64 processes) For this activity we use also the National Facility for Nuclear Physics managed by the INFN-Pisa. It is a 512 cores cluster based on the AMD 8356 processors. We use it thanks to the scientific collaboration we have from many years with the INFN-Pisa, using the time left free by the physics activity. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 7

8 SURFACE GRID Base size for hull 4.5 cm Base size for deckhouse 9.0 cm Base size for domain external surfaces 1.5 m Total surface elements Skewness<0.5. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 8

9 VOLUME GRID ComputaTonal domain: Lenght 60 m Width 25 m air height 5 m water height 20 m Trimmed volume grid with prism layers around the hull Grid refinement at the free surface in order to have a corrected representaton of the wave profile. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 9

10 Refinement Box: Free Surface Refinement Flat Sea: ± 0.5 m around the free surface Rough Sea (0.5 m wave height): ± 1.0 m around the free surface In all the cases further refinements in local zones Total volume elements 510,000 (coarse grid) 4,100,000 (refined grid) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 10

11 PHYSICAL MODEL 3D unsteady k ε standard turbulence model Wave model (VOF Waves) 6 degrees of freedom rigid body moton (6 DOF MoAon) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 11

12 WAVE MODEL (VOF Waves) Volume of Fluid Waves Model, with two phases (MulAphase Mixture). The sea wave dynamics is represented by the 5 order Stokes theory. The following characteristcs are assigned: Wave height, H Wave Length, L Sea depth, d DirecTon and velociy of the sea Tde, c E H c E d STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 12

13 6 DOF MoAon set up Total mass C.G. position Inertial Moments ARE ASSIGNED The applied power is kept constant The thrust is evaluated as a function of the speed and it is applied in the direction of the propeller axle Propulsion efficiency = 0.92 Time step: s Iterations per step 10 Starting Speed: 5 m/s STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 13

14 SensiTvity to grid resoluton Flat sea STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 14

15 SensiTvity to grid resoluton Flat sea STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 15

16 SensiTvity to grid resoluton Flat sea STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 16

17 SensiTvity to grid resoluton Flat sea THE BEHAVIOUR IS SIMILAR FOR ALL THE CHARACTERISTICS OF THE MOTION From the QUANTITATIVE point of view, moving from the coarse to the refined grid, occur that: The maximum speed is slightly higher ( + 4 % ) The dominant frequency is very close ( % ) The mean trim angle is very close (from 2.38 to 2.5 deg) Computational time for 100 seconds of simulation: Coarse Grid 5 hours Refined Grid 16 hours ( 6 hours with 256 processes) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 17

18 RESULTS A large amount of data is obtained by the evaluaton Performance Boat moton Stability characteristcs InformaTon are available on: Hydrodynamics behaviour of the hull Aerodynamics behaviour of the upper deck Loads CorrelaTon between different data for a beker understanding of the different effects... STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 18

19 Max. Boat Speed, Flat sea (1900 HP) 7 sec 22 sec Regime (oscillating) No oscillations Oscill. transient STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 19

20 Boat MoTon, Flat sea (1900 HP) Sea level STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 20

21 Drag and acceleratons, Flat sea (1900 HP) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 21

22 Dynamic Behaviour (regime condition) Fourier transforms of the time histories A dominant frequency at 0.80 Hz is evident. The motion is practically harmonic. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 22

23 The MoTon (CFD SimulaTon) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 23

24 The MoTon (real view) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 24

25 StaTsTcal values (1900 HP, regime conditon) Mean St. Dev. Min. Max. Speed (m/s) Vert. Displ. (m) Trim Angle (deg) Drag (N) Long. Acc. (g) Vert. Acc. (g) Correlation Analysis LONG. and VERT. ACCELERATIONS are in phase ( Corr. Coeff. = 0.97 ) SPEED and VERT. DISPL. Have a 90 phase angle ( Corr. Coeff. = ) TRIM ANGLE and VERT. DISPL. are not in phase ( Corr. Coeff. = ) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 25

26 Max. Speed vs. Power? The increase in speed is higher than the increase in power STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 26

27 ExplainaTon: Drag vs Speed 7 s 22 s dz 0.5 m dz 0.4 m dz 0.2 m mean value The hull escapes from the water Sea level Drag reduction Speed increasing (delayed by inertial and apparent mass forces) Opposite behaviour STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 27

28 The shut off characteristcs The time and space to arrest boat is particularly important. This phase is simulated setting zero thrust at time = 75 sec. 10 s: speed 13.7 space 280 m 20 s: speed 2.7 space 330 m Clearly, these data are conservative, because the thrust reverse is not considered. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 28

29 The effect of the weight Weight reduced by 20%, same power Time to regime significantly reduced Reduced weight Max speed increases from 40 to 41 m/s The Fourier spectra show that the dominant frequency remains exactly the same Dynamics characteristics are unchanged (Note: inertial moments are NOT varied) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 29

30 The effect of the InerTal Moments Also Inertial Moments reduced by 20% The behaviour appears very similar Red. Inert. Mom. Max speed slightly decreases from 41 to 40.7 m/s The Fourier spectra show that: The frequency of the motion increases (from 0.80 to 0.88 Hz) The amplitude of oscillations decreases (St. Dev. from 0.30 to 0.26) STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 30

31 ROUGH SEA set up With the rough sea, the resolution of the coarse grid appears not sufficient to represent the wave shape. Wave directon 0 from the hull simmetry plane Sea depth Sea Tide 0 WAVE SET-UP 100 m Wave height 0.5 m Wave lenght 20 m STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 31

32 ROUGH SEA Wave height 0.5 m STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 32

33 Wave ROUGH SEA Wave height 0.5 m ( Power 2000 HP) Reduced Oscillation Amplitude Increased Frequency 0.60 = Sea level No Wave Boat remains more time in air (Mean value from 0.52 to 0.59 m) Mean value similar STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 33

34 Wave ROUGH SEA Wave height 0.5 m (Power 2000 HP) No Wave Max speed is higher (boat is sustained in air by waves) No Wave Reduced Oscil. Ampl. Increased Frequency Wave The motion keeps harmonic with rough sea But frequency increases from 0.8 to 2.7 Hz its energy is significantly reduced

35 CONCLUSIONS (1 of 2) The moton of a catamaran hull is evaluated taking into account its inertal characteristcs Rough sea is considered The case was sevng in STAR CCM+ without problems All results are congruent with the real behaviour of this type of boat The moton of the hull is harmonic with flat sea With rough sea (opposite to the boat moton) the maximum speed increases and the moton remains harmonic, with a significant increase of frequency. The correlaton analysis between forces and moton characteristcs gives important informaton to understand flow behaviour STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 35

36 CONCLUSIONS (2 of 2) THE ABILITY OF STAR CCM+ TO ANALYSE THE DYNAMIC BEHAVIOUR OF A CATAMARAN HULL IS HIGHLIGHTED POTENTIALITIES OF THE PROPOSED APPROACH ARE RELEVANT IN PARTICULAR, IT IS POSSIBLE: to evaluate performances to analyse stability characteristcs to have an accurate evaluaton of the loads, in order to size and optmise the structural scheme STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 36

37 ACKNOWLEDGEMENTS Thanks are due to A. Ciampa and E. Mazzoni (INFN of Pisa) to make the computng system very efficient and easy to use, resultng from their research actvites on computng networks, applied to our cluster. STAR EUROPEAN CONFERENCE 2011 G. Lombardi, M. Maganzi 37

38 THANK YOU