Overview of BV R&D activities in Marine Hydrodynamics · Overview of BV R&D activities in Marine...

© - Copyright Bureau Veritas

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 OS_R&D_2015 © - Copyright Bureau Veritas

Content

►Introduction

►Numerical models

Hydrodynamics

Coupled hydrodynamic – mooring & risers dynamics

Hydro-structure interactions

►Design methodologies

►Conclusions


INTRODUCTION


Behavior at Sea – Similar issues for ships & offshore


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 !!


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…)


Potential flow theory

Fully non linear boundary value problem (BVP) for velocity potential

HYDROSTAR


Some particular features of Hydrostar


Side by side operations and moonpool dynamics



► Modified boundary conditions

Free surface

Body

Modified Boundary Integral Equations


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)


Second order drift forces for multibody

► Farfield formulation for multibody not possible

► Direct integration not accurate

► Midfield formulation proposed!


Second order springig of TLP

► High frequency response

► 2nd order Hydrostar module


Mixed panel stick seakeeping model

► Mixed panel – stick model

3D BEM method for important parts of the structure

Morison model for beam parts


Hydrostar recent applicatios

TLP


Hydrostar recent applicatios

Floating wind mill


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


Example of the different time scales

TLP tendons

𝑻𝟎 Static (pretension) 𝑻𝒎 Mean (second order mean) 𝑻𝑳𝑭 Low frequency (second order difference frequency) 𝑻𝑾𝑭 Wave frequency (linear first order wave frequency) 𝑻𝑯𝑭 High frequency (second order sum frequency)

𝑻𝟎

𝑡

𝑻𝒎

𝑻𝒎 + 𝑻𝑳𝑭

𝑻𝒎 + 𝑻𝑳𝑭 + 𝑻𝑾𝑭

𝑻𝒎 + 𝑻𝑳𝑭 + 𝑻𝑾𝑭 + 𝑻𝑯𝑭

𝑇

𝑻 = 𝑻𝒎 + 𝑻𝑳𝑭 + 𝑻𝑾𝑭 + 𝑻𝑯𝑭


HYDRO STRUCTURE INTERACTIONS


Global – Local

Linear – Weakly nonlinear – Nonlinear

Frequency domain (periodic) – Time domain (impulsive)

Static - Quasi static – Hydroelastic

Regular waves – Irregular waves

Different aspects of the hydrodynamic loadings

and structural responses


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!!


Main hydro-structure issue for quasi static responses

PRESSURE TRANSFER !!


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


Recalculation of motions!

► Integration of pressure over the structural FE mesh!

► New motion equation which ensures the full balance of FE model


About boundary conditions


Quasi static linear structural response

GLOBAL

LOCAL


WEAKLY NONLINEAR QUASI STATIC

STRUCTURAL RESPONSE IN TIME DOMAIN


Froude-Krylov approximation


LINEAR HYDROELASTIC

RESPONSE IN FREQUENCY DOMAIN


Linear hydroelastic model

Frequency domain

Time domain


Mapping procedure


Springing - Typical response


Hydroelastic analysis of wind mill installation vessel


NONLINEAR HYDROELASTIC TRANSIENT

RESPONSE IN TIME DOMAIN


Transient hydroelastic response


SOME RECENT DEVELOPMENTS


Hydroelastic response of liquid cargo ships

Semi analytical solution and validation of numerical model

General numerical solution by HOMER


Hydroelastic response of large LNG vessels


DESIGN METHODOLOGIES


Overall procedure

0.1

1

10

100

1000

Wave bending moment (GN.m)

Exceed

en

ce p

er

ho

ur

Linear

Non linear

Whipping

Short term & long term responses

Extreme

Fatigue

-80

-60

-40

-20

0

20

40

60

80

-150 -100 -50 0 50 100 150

12 3 4

567

8 910

1112

13 14 15 16 1718

19 20

2122

23 24 2526

27 2829 30

31 32 33 34 3536 37

3839

4041 42 43

44 45 46 47 48 49 50 51 52 53

5455 56 57 58

59

60 61 62 63

6465

6667 68

69 70 71

72 7374 75 76 77 78 79 80

81 8283

8485

86 87 88 89 90 91 92 93

94 95 96 97 98 99 100 101102

103104

Hs

Tp

Operating conditions

Deterministic models

Postprocessing


Metocean data - Example

Waves

Winds

Currents


Some recent applications


Circular FPSO


TLP


THANKS FOR YOUR ATTENTION

Overview of BV R&D activities in Marine Hydrodynamics · Overview of BV R&D activities in Marine...

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