Dr. Paul Palo U. S. Naval Facilities Engineering Service ... · u Goal = required column height for semi design u Accurate modeling of instantaneous free surface and [nonstationary]

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MOBILE OFFSHORE BASEHYDROMECHANICS

Dr. Paul PaloU. S. Naval Facilities Engineering Service Center

Centre for Ships and Ocean StructuresNorwegian University of Science and Technology

29 October 2004

Outline

l Overview: SeaBasing and MOB

l Overview: ONR MOB S&T Program

l MOB Hydromechanics S&Tu Science & Technology (S&T) Evaluation Process

u Hydromechanics S&T and Products

u Supporting S&T Activities

l Summary

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Overview of SeaBasing and MOB

• SeaBase Function: provide completelogistics support for ground personnel

– Transit to site in reasonable time

– Receive supplies from CONUS

– Store, prepare, stage supplies

– Transport supplies to shore

SeaBasing and MOBSample Mission Requirements

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SeaBasing and MOB SeaBase Requirements #1 of 3

Single Module Transit

u Scenariou Full cargo &

u Deballasted on pontoons

u Fastest Transit Timeu Maximum Speed versus

• Sea State

• Incident Wave Direction


On-site operations

u Positioned 20-50 miles off coast

u Large Vessel Unloading through Sea State __

u Small Vessel Loading through Sea State __

u Survive Extreme Events through Sea State __

u Accommodate __-number of VTOL aircraft

u Stationkeeping (Dynamic Positioning)

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On-site operations: optional?

u CTOL Aircraft Operations

This greatly complicates the engineering:

�Multiple Module Platform• Connect through Sea State __

• Provide acceptable dynamics through Sea State __

• Optional Disconnect through Sea State __

SeaBasing and MOBFamily of SeaBase Concepts

“MOB”Platforms

Navy-favored

“SeaBase” Platform

based on MPF(F)

& V-22 Osprey

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SeaBasing and MOBRange of MOB Platform Configurations

Two ModulesSingle Module

Hinged Platform

Bridged Platform

Dyn. Pos. Platform

Semi-submersible

VLCC

CVN

M O B

300m (DB102)

455m (Seawise Giant)

320m (Nimitz)

Semisubmersible Module300-600m length130-160m beam

35m draft

SeaBasing and MOBMOB Module and Platform Sizes

Platform Configuration300-1500m length

1 to 5 modulesRigid/Hinged/Bridged/DP Connectivity

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MOB S&T Program

ONR MOB S&T ProgramONR Program Overview

♦♦ Program ObjectivesProgram Objectives•• Establish Feasibility and Cost of MOB(s)Establish Feasibility and Cost of MOB(s)

♦♦ FundingFunding•• $36M$36M•• FY96-00FY96-00

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ONR MOB S&T ProgramNFESC Program Overview

♦♦ Program ObjectivesProgram Objectives•• Establish feasibility and costEstablish feasibility and cost

•• Define a consistent design methodologyDefine a consistent design methodology•• Reduce technology gapsReduce technology gaps

•• Advance industry capability to Advance industry capability to DoDDoD req’tsreq’ts•• Make Make DoDDoD a “smart buyer” a “smart buyer”

•• 53-organization Project Team53-organization Project Team•• 26 commercial firms (domestic and int’l)26 commercial firms (domestic and int’l)•• 16 academic institutions16 academic institutions•• 11 government agencies11 government agencies

Identify MissionRequirements

Define EngineeringDesign Requirements

State-of-the-ArtCapabilities

Prioritize Science &Technology Tasks

Prioritize Science &Technology Tasks

• Still undefined as of 2004!

• Representative missions defined

Candidate PlatformCharacteristics

• Nonquantified missions èèèè unknown length

• Hierarchy of platforms based on length & connection scheme

ONR MOB S&T Program S&T Evaluation Process

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ONR MOB S&T ProgramUnprecedented Design Challenges

l Semisubmersible module size

l Multiple module platformu Connectivityu Length/configuration

l Open ocean dynamicsu Motions (Aircraft operations, vessel motions)u Wavefield (Stresses, Cargo transfer, Air gap)u Failure Modes (1st torquing mode)

�� MOB exceeded state of practiceMOB exceeded state of practice - No consensus methodology to design, down-select, build, and operate a MOB.

�� MOB as anMOB as an ““Innovative StructureInnovative Structure”” - An Innovative Structure -- “is usually the first of its kind;

few, if any, design standards directly apply and there islittle operational experience to relate to the design reviewprocess.” (National Research Council, 1991)

“Technical evaluation of such structures must be basedon fundamental engineering principles, requiring

specialists in the relevant disciplines.”

ONR MOB S&T Program MOB Uniqueness

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ONR MOB S&T ProgramRoadmap = Classification Guide

Requirements

Demands

Capacity

Analysis/DesignAssessment

3. Classification Requirements

2. Requirements & Procedures

1. General

11. Dynamic Positioning

13. Maintenance

14. Environmental Compliance

6. Materials

4. Environment 5. Loads

7. Structural Resistance

8. Engineering Analysis

9. Structural Design

10. Stability

12 . Fabrication

MOB Hydromechanics S&T

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MOB HydromechanicsScience & Technology Categories

1. Operational Dynamics

2. Survival Dynamics

3. Transit Dynamics

4. Validation Tests and Analysis

5. Exercise Models

6. Met/Ocean Specification

MOB HydromechanicsS&T Balance

MOB ClassificationGuideline

Advance & Exercise

Models

ValidationData Metocean

Specification

$4.3M$3.7M

$1.9M

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MOB HydromechanicsScience & Technology Issues

1. Operational Dynamics Models1.1 Platform dynamics1.2 Connection/Disconnection1.3 Fatigue structural loads1.4 Stationkeeping

For Each Issue -

u Identify key requirements

u Assess State-of-the-art

u Highlight advancement and product

MOB Hydromechanics 1.1 Platform Dynamics

Example Calculationsu Motions of one module

u Transitu Operations

u Motions of connected platformu Column and pontoon shape optimizationu Dynamics of berthed vessels

Key Model Requirementsu Inviscid, linear & stationary acceptableu Hydrodynamic coupling; mean drift forceu Highly efficient numerical solveru Hydroelasticity [rigid and/or elastic bodies]

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State-of-the-Art Summary (Frequency Domain)

u HOBEM (high-order, single, rigid body)

u AQWA (rigid, multiple bodies, no coupling)

� MORA (rigid, multiple bodies; adjacent coupling only)

u HYDRAN (hydroelastic, rigid, hydrodynamic coupling; computationally intensive)

� WAMIT (hydroelastic, hydrodynamic coupling; computationally intensive)

� HIPAN (single, rigid body; higher-order; computationally efficient)


MOB Frequency Domain S&T:

1.1.1 Advance WAMIT & HIPAN modelsu Refer to N. Newman presentation

1.1.2 Develop alternative dynamic model

1.1.3 Develop simplified preliminary design tool

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1.1.1 Advance WAMIT & HIPAN models

Objective: provide fully-coupled hydroelastic final design model(s)

Performer: MIT, AeroHydro

Product:u 2 associated deliverables (Fast-WAMIT & HIPAN)u HIPAN: high-order potentials on patches &

panels using b-spline body geometry descriptionè WAMIT: pre-computed FFT solver (up to 3 orders

of magnitude computational increase) makesthis the only model capable of full MOB study


1.1.2 Develop alternative dynamic model

Objective: provide numerically efficient preliminary design modelPerformer: OSA Inc. (Chakrabarti)

Product:u diffraction theory model (fully-coupled, rigid-

body)u two-stage analysis: (1) potentials for isolated

individual modules; (2) superpositionè avoids large panel problem entirely; allows

for efficient parametric configuration studies

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1.1.3 Develop simplified preliminary design tool

Objective: provide numerically efficient preliminary design model

Performer: Off Coast Inc. (Ertekin & Riggs)

Product:u based on a simplified (uncoupled, rigid body)

version of the HYDRAN diffraction theorymodel

u menu- & library-based interactive preprocessoru Rayleigh damping for [equiv] viscous dragè deliberately simplified to allow for efficient

parametric configuration studies

Key Model Requirements:u Inviscid, linear & stationary acceptableu Multiple modules with varying mean positions and

arbitrary approach pathu Impact and/or elastic loads desirable

State-of-the-Art Summary (Time Domain)u LAMP (described next)u CFD viscous models: not sufficiently mature

MOB Time Domain S&T:1.2.1 Advance LAMP model1.2.2 Develop simplified connection model (MORA)

MOB Hydromechanics 1.2 Connection/Disconnection

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MOB Hydromechanics 1.2 Connection /Disconnection

1.2.1 Advance LAMP model

Objective: advance accuracy of this nonlinear model

Performer: SAIC (Annapolis).

Product:u “fully-nonlinear” time domain model (rigid-

body; large waves and responses; multiplebodies with nonstationary mean positions)

u computationally-intensive modelè advanced free surface condition from incident

to instantaneousè Encountered fundamental air gap deficiency

(see S&T topic 2.1)

1.2.2 Develop simplified connection model

Objective: develop “piecewise stationary” preliminary analysis model for wave motions

Performer: C. J. Garrison and Assoc

Product:u efficient preliminary analysis tool (via MORA)u three stage solution: (1) determine frequency

domain behavior for two bodies at finite numberof fixed mean positions along approach path; (2)convert to time domain “retardation functions”;(3) interpolate for continuous dynamics

èavoids intensive time domain solution

MOB Hydromechanics 1.2 Connection /Disconnection

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MOB Hydromechanics 1.3 Fatigue structural loads

Key Model Requirementsu Inviscid, linear & stationary acceptableu Interface pressure distribution from arbitrary hydro panel

into arbitrary structural element surface meshes

State-of-the-Art Summary (Time Domain)u None (SAS; restricted to identical meshes)

MOB Time Domain S&T1.3.1 Universal loads generator

MOB Hydromechanics 1.3 Fatigue structural loads

1.3.1 Universal loads generator

Objective: Develop a universal pressure loadsgenerator post-processor

Performers: MIT, Aerohydro Inc, McDermott

Product:u b-spline representation for body geometry

and potentialsu convert Fast-HIPAN pressures into local

pressures for locally nonlinear responsesè allows for optimum hydro and structural

discretizations (maximum accuracy)

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StructuralABAQUSStructural

ABAQUSHydrodynamic

MIT / HIPANAeroHydro/HIP2FEA

DefineGeometry

MOB-HyLoads

Wind & Current Loads

Time history wave loads

Analysis Procedures

Mean Drift Forces

Sp

ectru

m

frequencyω1 ω2 ω3 ω4 ω5 ω6 ω7 ω8 ω9 ω10 ω11 ω12

Spre

adin

g Fu

nctio

n (G

)

Heading Angleθ1 θ2 θ3 θ4 θ5 θ6 θ7 θ8 θ9 θ10 θ11 θ12

DefineSea State

MOB Hydromechanics 1.3 Fatigue: universal loads generator

MOB Hydromechanics 1.4 Stationkeeping

Key Model Requirementsu Current and wind loads on semisubmersibles, including

viscous wakes, wave, and free surface effectsu Desirable: multi-body capability for connect simulations

and shielding effects

State-of-the-Art Summary (Time Domain)u CFD (not sufficiently mature)

MOB S&T None. (1) Hydro CFD not pursued because there are no

apparent short-term opportunities to advance modeling offree surface and high Reynolds Number flows. (2) WindCFD for aircraft landing/takeoff environment not pursuedas not critical to feasibility objective.

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2. Survival Dynamics

2.1 Extreme Motionsu Air gapu Wave impactu Run-up on columns

2.2 Extreme structural loads

MOB Hydromechanics 2.1 Extreme Motions

Key Model Requirementsu Goal = required column height for semi designu Accurate modeling of instantaneous free surface and

[nonstationary] wetted surface of bodyu Single (disconnected) rigid body; uncertain if inviscid

models are necssary

State-of-the-Art Summary (Time Domain)u LAMP model (simplified to incident free surface)

MOB S&T2.1.1 Apply LAMP model (see previous Task 1.2.1 & next

visual)2.1.2 Advance AEGIR model

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MOB Hydromechanics 2.1 Extreme Motions

2.1.2 Advance AEGIR model

Objective: advance development of this nonlinear time domain model

Performer: MIT

Product:u “fully-nonlinear” time domain model (rigid-body;

large waves and responses; inviscid;nonstationary mean positions)

u highly flexible formulation; includes run-upu Incomplete development at end of MOB program

MOB Hydromechanics 2.2 Extreme Structural Loads

Key Model Requirementsu Accurate pressures induced on [nonstationary] wetted

surface of bodyu Multiple bodies, elasticity (if connected in extreme events)u Viscosity preferrable

State-of-the-Art Summary (Time Domain)u Morison Equation, based on long wavelengths in typical

extreme seas and MOB characteristic dimensions ofcolumns and pontoons. Inviscid models (e.g., LAMP) donot include viscous damping and have been shown toyield misleading results. Uncertainties with: coefficients,shielding, and wave crest kinematics.

MOB S&T None.

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3. Transit Dynamics Models

3.1 Platform dynamics (stability, accelerations)

3.2 Nonlinear Stability

3.3 Dynamics while in damaged condition

MOB Hydromechanics 3.1 Transit Dynamics Models

Key Model Requirementsu Accurate modeling of instantaneous wave pressures and

buoyancy on [nonstationary] wetted surface of body aspontoons intermittently submerge and waves overtop

u Single, rigid body models acceptable; importance ofviscosity unknown

State-of-the-Art Summary (Time Domain)u No industry experience similar to MOB transit. LAMP

allows for changing wetted surface, but does not modeldynamics of waves above the pontoons.

MOB S&T3.1 Apply LAMP model (see previous Task 1.2.1)

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MOB Hydromechanics 3.2 Nonlinear Stability Model

2.1.2 Evaluate Stability during transit

Objective: investigate single, deballasted module dynamics (with pontoon immersion)

Performer: Univ of New Orleans

Product:u Estimation of orbits, attractors, etc to nonlinear

buoyancy and “representative” viscous dampingu Not a solved topic!u Continued development of the “Reverse MI/SO”

system identification technique @ UNO (see Task4.4)

MOB Hydromechanics 3.2 Damage Dynamics Models

Key Model Requirementsu Assess stability and motions for large heel and trim static

conditions [due to explosive detonations]

u Accurate modeling of instantaneous free surface and[nonstationary] wetted surface of body. Internal voids?

u Single, rigid body models acceptable; importance ofviscosity unknown

State-of-the-Art Summary (Time Domain)u No specific criteria yet developed. LAMP allows for

changing wetted surface.

MOB S&T3.2 Apply LAMP model (see previous Task 1.2.1)

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4. Validation Tests and Analysis

4.1 Hydroelastic Tests

4.2 Limited Hydroelastic Validations

4.3 Transit Dynamics Tests and Analysis

4.4 Air gap Tests

MOB Hydromechanics 4.1 Hydroelastic Tests

Key Data Requirementsu Accurate structural knowledge of platform responseu Accurate knowledge of spatial wavefield

State-of-the-Art Summary (Time Domain)u Limited; typically very small scale and for mats

MOB S&T4.1 Conduct hydroelastic tests of generic, connected MOB semisubmersibles

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4.1 Conduct Tests at NSWC-CD

Objective: provide a hierarchy of data for 1, 2, and 5module elastic MOB platforms with connectors

Performer: Naval Surface Warfare Center, Carderock Detachment (MASK facility)Product:

è guided by 2-day workshop of government,academia, and industry, and real-time QA

u Four 6m fully-elastic modulesu Multi-axis spring connectors

� Limited. Exhausted funding before dataanalysis. See next topic.


6m Elastic Module

Connector

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27.5m Elastic Platform Model

MOB Hydromechanics 4.2 Limited Hydroelastic Validations

Objective: conduct preliminary validations usingsubsets of NSWC-CD data

Test Performer: McDermott Technologies; OSA;University of Hawaii; University of Maine

Products:u limited evaluations for 1 and 2 module

configurationsu Opportunity??

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MOB Hydromechanics 4.3 Transit Dynamics Tests and Analysis

Key Data Requirementsu Rigid body motions of a semisubmersible at transit draft

(minimal freeboard up on the pontoons)u Nonlinear buoyancy (pontoons versus column

waterplane) results in complicated dynamics best treatedwith nonlinear phase plane techniques

State-of-the-Art Summary (Time Domain)u None; unique problem to MOB

MOB S&T4.4 Conduct transit dynamics tests

MOB Hydromechanics 4.4 Transit Dynamics Tests and Analysis

Objective: examine transit dynamics

Test Performer: U. S. Naval Academy (Annapolis)

Data Analysis: University of New Orleans

Products:u 4m model length; same as NSWC moduleu direct use of data for validation of LAMP, etc.u indirect use of data to qualify and quantify

equations of motion using “Reverse MI/SO”nonlinear systems identification technique (perNFESC).

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MOB Hydromechanics 4.4 Transit Dynamics Tests

4m Rigid Module

MOB Hydromechanics 4.5 Air Gap Tests

Key Data Requirementsu Rigid body motions and wavefield for a semisubmersible

at survival draft

State-of-the-Art Summary (Time Domain)u Proprietary (e.g., LAMP)u Industry divided as to the accuracy of state-of-the-art

modeling

MOB S&T4.5 Conduct air gap tests

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MOB Hydromechanics 4.5 Air Gap Tests

Objective: provide data for subject conditions

Test Performer: U. S. Naval Academy (Annapolis)

Pre-test Simulations: SAIC (Annapolis)

Products:u same model as for transit dynamics testsu 3 response channels; 13 wave channels

(sensors on model and fixed)u ultimately intended for validation of LAMP and

other model predictions.


5. Exercise Models

5.1 Benchmark Comparison of Existing Diffraction Models

5.2 Benchmark LAMP Exercise

5.3 Berthed Vessel Simulations

5.4 Industry Experience with Seakeeping Models

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MOB Hydromechanics 5.1 Benchmark Comparison of Diffraction

Models

Objective: benchmark existing models for MOB applications

Test Performer: Bechtel

Products:u parametric assessment of small amplitude,

linear diffraction theory modelsu HOBEM, AQWA, MORA, WAMIT, HIPAN and

HYDRAN exercised for single semisubmersiblesand connected platforms

èquantitatively established general guidance onhow to properly apply diffraction theory modelsfor VLFS semi seakeeping studies

MOB Hydromechanics 5.2 Benchmark LAMP Exercise

Objective: investigate numerical use of LAMP

Test Performer: Naval Facilities Engineering Service Center (Port Hueneme CA)

Products:u investigate discretization of: body, free surface,

and matching surface for transit conditionsu preliminary guidance on LAMP relative

accuracy versus number of panels

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MOB Hydromechanics 5.3 Berthed Vessel Simulations

Objective: examine dynamics of vessels in the confused wavefield associated with large MOB semisubmersibles

Test Performer: McDermott Engineering (Houston)

Products:u preliminary assessment of dynamic motions

during cargo handling operationsu quantify errors if incident waves only are

[incorrectly] used as excitation

MOB Hydromechanics 5.4 Industry Experience with Seakeeping

Models

Objective: indirect assessment of industry capability to correctly apply seakeeping models

Test Performers: McDermott Engineering (Houston) Kvaerner Bechtel AkerProducts:

u valuable insight regarding transition of newmodels and extrapolation of old models to MOB

èconsensus opinion: their original expectationsthat MOB was a direct extension of state-of-the-art was too simplistic

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6. Metocean Specification at O(km) Scales

6.1 Metocean Specification6.2 Wave Spatial Coherence: Data Analysis6.3 Wave Spatial Coherence: Modeling

Critical for accurate motion and stress estimatesu Low order modal responses will be excited only if

waves are long-crested and narrowbanded.

MOB Hydromechanics 6.1 Metocean Specification

Key Requirementsu Knowledge of wind/wave/current phenomena at MOB O(2

km) scale; internal waves and solitons includedu Necessary for elastic responses and cell/environmental

contour design methods in MOB Classification Guide

State-of-the-Art Summary of Wave Fieldsu None.

MOB S&T6.1 Develop general engineering-oriented specification6.2 Numerically investigate wave properties from existing data sets6.3 Advance physics-based models into “3+1” dimensions

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MOB Hydromechanics 6.1 Met/Ocean Specification

Objective: compile engineering-oriented guidance forwind/wave/current excitation of MOB

Performers: Bechtel (numerous subcontractors)

Products:u Extensive MOB Environmental Specificationu 2 Extensive MOB Climatological Databases

� 23 sites, 20 years @ 6 hrs� Pacific storms, 1 km mesh, 1 hr intervals

uExcellent general guidance for marine structures6 Missing critical wave coherence information

MOB Hydromechanics 6.2 Wave Spatial Coherence: Data Analysis

Objective: provide “quick-look” guidance regarding open ocean wave crest lengths

Performers: JHU/APL; ERIM; WHOI/UMiami; UWyoming/NASAProducts:

u Guided by ONR Workshop, Aug 1997u numerically investigate wave properties from

existing SAR, SRA, wave gauge data setsu Unresolved question: “what is a ‘wave’?”èFirst-ever measurements of the wavefield in a

Hurricane

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North Panel Northeast Panel East Panel

Allpanels:

~6x1 km

WAVES IN HURRICANE BONNIEWAVES IN HURRICANE BONNIEScanning Radar Altimeter (NASA)Scanning Radar Altimeter (NASA)

MET/OCEAN DESCRIPTORSMET/OCEAN DESCRIPTORS

MOB Hydromechanics 6.3 Wave Spatial Coherence: Modeling

Objective: advance numerical modeling of evolving 3D wavefields

Performers: MIT; UHawaii; UTorinoProducts:

u Guided by ONR Workshop, Aug 1997u MIT and Hawaii models balance physics and

computational burdenu Torino model addresses fundamental physics of

rogue waves

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Dr. Paul Palo U. S. Naval Facilities Engineering Service ... · u Goal = required column height for semi design u Accurate modeling of instantaneous free surface and [nonstationary]

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