Overview of BV R&D activities in Marine Hydrodynamics

Transcription

1 Overview of BV R&D activities in Marine Hydrodynamics Special attention to hydro-structure interactions Šime Malenica Bureau Veritas Marine & Offshore Division Research Department Harbin, 29th of June 2012

2 Content Introduction Numerical models Hydrodynamics Coupled hydrodynamic mooring & risers dynamics Hydro-structure interactions Design methodologies Conclusions 2

3 INTRODUCTION

4 Behavior at Sea Similar issues for ships & offshore 4

5 Available methods and associated difficulties Model tests Expensive Limited number of cases Problems of similitude (hydroelasticity, viscosity,.) Numerical models Numerical modeling difficulties Lack of full validation CPU time Full scale measurements Limited number of operating conditions Difficulties related to the measurement of the sea states Overall difficulty Choice of the representative design conditions!! 5

6 HYDRODYNAMICS

7 Available numerical methods Potential flow methods CFD Common practice is to use potential flow methods either in frequency or time domain Up to now, CFD used on a case by case basis only essentially for some local problems which are clearly non-potential (impacts, overtopping, VIV, propulsion ) 7

8 Potential flow theory Fully non linear boundary value problem (BVP) for velocity potential HYDROSTAR 8

9 Some particular features of Hydrostar

10 Side by side operations and moonpool dynamics 10

11 Side by side operations and moonpool dynamics Modified boundary conditions Free surface Body Modified Boundary Integral Equations 11

12 Side by side operations and moonpool dynamics 12

13 Wave current interactions Important for free surface sur-elevation and Wave Drift Damping evaluation Interaction of steady and unsteady potentials at the free surface Potential decomposition Solution involves the integral over the free surface (rapidly converging) 13

14 Second order drift forces for multibody Farfield formulation for multibody not possible Direct integration not accurate Midfield formulation proposed! 14

15 Second order springig of TLP High frequency response 2 nd order Hydrostar module 15

16 Mixed panel stick seakeeping model Mixed panel stick model 3D BEM method for important parts of the structure Morison model for beam parts 16

17 Hydrostar recent applicatios TLP 17

18 Hydrostar recent applicatios Floating wind mill 18

19 GLOBAL PERFORMANCE

20 Global performance numerical tools Hydrodynamic behavior of the floater Coupling with mooring lines & risers behavior Weak coupling Full coupling Numerical model highly dependent on the type of unit Response driven by the excitation and by the floater natural periods Opera 20

21 Example of the different time scales TLP tendons T T 0 T m T m + T LF T m + T LF + T WF T m + T LF + T WF + T HF T = T m + T LF + T WF + T HF t T 0 T m T LF T WF T HF Static (pretension) Mean (second order mean) Low frequency (second order difference frequency) Wave frequency (linear first order wave frequency) High frequency (second order sum frequency) 21

22 HYDRO STRUCTURE INTERACTIONS

23 Different aspects of the hydrodynamic loadings and structural responses Global Local Linear Weakly nonlinear Nonlinear Frequency domain (periodic) Time domain (impulsive) Static - Quasi static Hydroelastic Regular waves Irregular waves 23

24 LINEAR QUASI STATIC STRUCTURAL RESPONSE IN FREQUENCY DOMAIN

25 Global quasi-static linear ship response to harmonic wave excitation Floating body considered as a rigid body with 6 degrees of freedom HYDRODYNAMICS Linear potential flow model Frequency domain STRUCTURE Quasi static structural response after pressure transfer Hydrodynamic and structural calculations can be performed separately!! 25

26 Main hydro-structure issue for quasi static responses PRESSURE TRANSFER!! 26

27 PRESSURE TRANSFER Most of the methods use different interpolation schemes between the two meshes Inaccurate Not robust Recalculation of the pressure at structural nodes seems to be better choice Possible thanks to the source method Extremely robust and accurate Easy to implement 27

28 Recalculation of motions! Integration of pressure over the structural FE mesh! New motion equation which ensures the full balance of FE model 28

29 About boundary conditions 29

30 Quasi static linear structural response GLOBAL LOCAL 30

31 WEAKLY NONLINEAR QUASI STATIC STRUCTURAL RESPONSE IN TIME DOMAIN

32 Froude-Krylov approximation 32

33 LINEAR HYDROELASTIC RESPONSE IN FREQUENCY DOMAIN

34 Linear hydroelastic model Frequency domain Time domain 34

35 Mapping procedure 35

36 Springing - Typical response 36

37 Hydroelastic analysis of wind mill installation vessel 37

38 Hydroelastic analysis of wind mill installation vessel 38

39 NONLINEAR HYDROELASTIC TRANSIENT RESPONSE IN TIME DOMAIN

40 Transient hydroelastic response 40

41 SOME RECENT DEVELOPMENTS

42 Hydroelastic response of liquid cargo ships Semi analytical solution and validation of numerical model General numerical solution by HOMER 42

43 Hydroelastic response of large LNG vessels 43

44 DESIGN METHODOLOGIES

45 Exceedence per hour Overall procedure Operating conditions Deterministic models Short term & long term responses Extreme Fatigue 1000 Hs 100 Linear Non linear Whipping 10 Postprocessing Wave bending moment (GN.m) Tp 45

46 Metocean data - Example Waves Winds Currents 46

47 Some recent applications

48 Circular FPSO 48

49 TLP 49

50 THANKS FOR YOUR ATTENTION 50