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
Content Introduction Numerical models Hydrodynamics Coupled hydrodynamic mooring & risers dynamics Hydro-structure interactions Design methodologies Conclusions 2
INTRODUCTION
Behavior at Sea Similar issues for ships & offshore 4
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
HYDRODYNAMICS
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
Potential flow theory Fully non linear boundary value problem (BVP) for velocity potential HYDROSTAR 8
Some particular features of Hydrostar
Side by side operations and moonpool dynamics 10
Side by side operations and moonpool dynamics Modified boundary conditions Free surface Body Modified Boundary Integral Equations 11
Side by side operations and moonpool dynamics 12
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
Second order drift forces for multibody Farfield formulation for multibody not possible Direct integration not accurate Midfield formulation proposed! 14
Second order springig of TLP High frequency response 2 nd order Hydrostar module 15
Mixed panel stick seakeeping model Mixed panel stick model 3D BEM method for important parts of the structure Morison model for beam parts 16
Hydrostar recent applicatios TLP 17
Hydrostar recent applicatios Floating wind mill 18
GLOBAL PERFORMANCE
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
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
HYDRO STRUCTURE INTERACTIONS
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
LINEAR QUASI STATIC STRUCTURAL RESPONSE IN FREQUENCY DOMAIN
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
Main hydro-structure issue for quasi static responses PRESSURE TRANSFER!! 26
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
Recalculation of motions! Integration of pressure over the structural FE mesh! New motion equation which ensures the full balance of FE model 28
About boundary conditions 29
Quasi static linear structural response GLOBAL LOCAL 30
WEAKLY NONLINEAR QUASI STATIC STRUCTURAL RESPONSE IN TIME DOMAIN
Froude-Krylov approximation 32
LINEAR HYDROELASTIC RESPONSE IN FREQUENCY DOMAIN
Linear hydroelastic model Frequency domain Time domain 34
Mapping procedure 35
Springing - Typical response 36
Hydroelastic analysis of wind mill installation vessel 37
Hydroelastic analysis of wind mill installation vessel 38
NONLINEAR HYDROELASTIC TRANSIENT RESPONSE IN TIME DOMAIN
Transient hydroelastic response 40
SOME RECENT DEVELOPMENTS
Hydroelastic response of liquid cargo ships Semi analytical solution and validation of numerical model General numerical solution by HOMER 42
Hydroelastic response of large LNG vessels 43
DESIGN METHODOLOGIES
Exceedence per hour Overall procedure 38 39 80 1 2 3 4 60 5 6 8 9 11 10 7 12 20 13 14 15 16 17 19 18 40 26 21 23 24 25 27 2829 30 22 31 32 33 34 35 41 42 43 20 44 45 46 47 55 0 54 Operating conditions 64 36 37 40 50 48 49 51 52 53 62 56 57 58 60 61 63 59 66 69 70 71 65 67 68 72 73-20 74 75 76 77 78 79 80 81 82 84 83 85 86 87 88 89 90 91 92 93-40 102 94 95 96 97 98 99 100 101 104 103-60 -80-150 -100-50 0 50 100 150 Deterministic models Short term & long term responses Extreme Fatigue 1000 Hs 100 Linear Non linear Whipping 10 Postprocessing 1 0.1 Wave bending moment (GN.m) Tp 45
Metocean data - Example Waves Winds Currents 46
Some recent applications
Circular FPSO 48
TLP 49
THANKS FOR YOUR ATTENTION 50