a method of applying linear seakeeping panel … · spectral fatigue analysis ... (abs, 2010)...

A Method of Applying Linear Sea-keeping Panel Pressure to full ship Structural ModelsCOMPIT 2012 – Liège, 16-18 April 2012/1

MAESTRO-Waveby DRS-DS, USA

NDAR, France

A METHOD OF APPLYINGLINEAR SEAKEEPING PANEL PRESSURE

TOFULL SHIP STRUCTURAL MODELS

Ming Ma - DRS Defence Solutions, USAChengbi Zhao - SCUT, ChinaNick Danese - NDAR, France



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Introduction

State of the art review

The MAESTRO / MAESTRO-Wave integrated approach

MAESTRO-WAVE Comparison

Extreme Load Analysis / Design Wave

Spectral Fatigue Analysis

Conclusion



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M.A.E.STR.O. (Dr. Hughes, DRS-DS) FE everywhere FE as a design tool 1980 : adequacy parameters, limit state analysis 1996 : graphical interactive topological modelling 2000 : added mass, DNV HSLC equivalency factors 2004 : sparse solver 2008 : COM-MAESTRO 2011 : MAESTRO - NAPA Steel one click 2012 : MAESTRO - Seakeeping one click Extreme Load Analysis / Design Wave Spectral Fatigue Analysis 16 April 2012 : MAESTRO 10 with MAESTRO-Wave released

Introduction.



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Balanced ModelUnbalanced Model

FE analysis of floating structures requires hydro-s/d balancing.

Significance of equilibrium for finite element analysis.

Unbalanced

Balanced

Draft

3.96m 4.07m

Trim -0.382 Deg

0.437 Deg

Weight Distribution Buoyancy Distribution

VBM VBM

3-node deflection shape 2-node deflection shape



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Panel based hydrodynamic analysis is computational intensive, coarser meshes Customarily, two different mesh models are maintained: Hydrodynamic (coarser)

and Structural (finer)

In some cases, the hydrodynamic analysis may not use a surface model at all, still need to get panel pressures for FE (MAESTRO-Wave does).

Hydrodynamic mesh Structural mesh

Hull form

Hydrostatics

HydrodynamicsStructures

…

Design Spiral

Transfer hydrodynamic loads to a FE model.



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Load mapping methods.

Direct pressure mapping PROS: Intuitive, easy for third party development CONS: unbalanced structural model, “inertia relief” corrective approach

(ABS, 2010) modifies accelerations, potentially unrealistic.

Source strength mapping (BV, 2008) PROS: structural model is balanced by definition CONS: may be difficult for third party users (no access to source strengths

and mapping facilities)

HYDRODYNAMIC MESH STRUCTURAL MESH



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Hydrostatic restoring forces

Equations of motion:

Hydrostatic restoring matrix:Using pressure integration

Inconsistency

Hydrostatic restoring force matrix.



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Panel pressure correction methods.

For each panel, the elemental Forces and Moments are:

By the original hydrostatic restoring matrix:

By the pressure integration:

BV’s proposed approach: adding a gravity term to all FE elements in the complete ship model

MAESTRO’s approach: adding correction nodal forces using Quadratic Programming to wet nodes only

Quadratic Programming



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MAESTRO integrated approach.

One mesh used for both FE and hydrodynamics

One Graphical User Interface FE model supplies weights, CGs, etc. Embedded linear frequency domain 3D panel

hydrodynamic analysis• The hydrodynamic model is generated from the

FE wet panels and nodes• Source strengths mapped to FE mesh =

hydrodynamic equilibrium by default• Nodal force adjustment uses Quadratic

Programming (heave, pitch), not inertia Fully integrated structural analysis

• Extreme Load Analysis / Design Wave• Spectral Fatigue Analysis

Failure mode evaluation (structural adequacy, limit states), the heart of first principles FE

9



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Hydrodynamic comparisons.

S175



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Hydrodynamic comparisons, cont'd.



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An integrated solution:NAPASteelFE exportMAESTRO-WaveELA/SFA Failure mode evaluation

Structural Model FEA Model

Hydrodynamic Model VBM RAOs of all sections



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Design Waves.

• If the static load case is balanced andif the hydrodynamic loads are balanced, thenthe combined load case is balanced, by definition.

• Then, the FE response analysis can be run directly.

• Wet elements automatically receive hydrostatic loads, while Dry elements do not

• MAESTRO will balance the static load case.

• MAESTRO-Wave will balance the corresponding hydrodynamic load cases using panel pressures on the FE mesh and quadratic programming for heave and pitch correction.



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Extreme DesignCase #4 with 180deg Shift

Extreme Design WaveCase #4 with 180deg Shift

Extreme DesignCase #4

Extreme Design WaveCase #4

Design Waves: dynamic, s/p static, combined.

Extreme DesignCase #1

Extreme DesignCase #1 with 180deg Shift



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ELA - Extreme Load Analysis calculation procedure.

Full Ship Structural Model

Short/Long Term Extreme Loads

Hull GirderUltimateStrength

Local Structural Failures

ELAStrength Assessment

Cached Unit Wave Load Database

(Accelerations, Panel Pressure)

Hull Girder Global Loads RAO Wave Spectrum

Hull Girder Global LoadsResponse Spectrum

Extreme Load for Each Sea State

Operational Conditions

)()(, 0 VPPTHPTTn s

zi

Equivalent Extreme Regular Wave

StaticLoadUnitWaveScaleDLyyScale

dlp

)(

max

Long/Short TermEnvironment

12 Headings30 Frequencies

5 Speeds

MAESTRO FE model



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SFA – Spectral Fatigue Analysis calculation procedure.

Cached Unit Wave Stress Response

Database

S-N Curves Miner’s Rule

12 Headings30 Frequencies

5 Speeds

esAllSeaStat

i

miii

n

nn

m

p

fppmKTD

k

10

1

2/ 12

2

1

10

100

1000

1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Number of Cycles

Stre

ss R

ange

(N/m

m2)

BCD

FF2

E

G

W

Stress Range PDF

Full Ship Structural Model

Cached Frequency Domain Stress RAO Database

Coarse Mesh Full Ship Fatigue

Damage Screening

Fine Mesh Selected Area Fatigue

Damage Assessment

Element Stress RAO Wave SpectrumMAESTRO FE model

Element Stress Response Spectrum

Operational Conditions (speed, heading)

Long TermEnvironment



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SFA – Coarse mesh full model fatigue screening.



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Obtain wet FE mesh from MAESTROExport it to hydrodynamic code using MAESTRO-WaveFrom the discretized boundary integral equations obtain the panel source strength

of each potentialMap the source strengths of each panel to the FE meshCompute hydrodynamic added mass, damping and restoring coefficients by

integrating the wet panels (FE panels ≡ hydro panels)Construct the equations of motion, obtain the motion RAOsCompute the panel pressures on the FE mesh and the corrective restoring

nodal forcesLoad the FE model by applying panel pressures (unbalanced model) MAESTRO-Wave balances the FE model by applying corrective forces

using quadratic programming

What was that all about ?



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MAESTRO-Wave : integrates FE and seakeeping

Full model, supports any shape

Purpose-dense mesh (very coarse to very fine)

Runs ELA and SFA at once

Fast, use in every day design work (mesh density speed)

Neutral format interface file (.wet)

Interfaces / integrates with any seakeeping code

One-stop ship-shop

Conclusion.



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THANK YOU

a method of applying linear seakeeping panel … · spectral fatigue analysis ... (abs, 2010)...

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