computational mechanics and signatures - …onlinepubs.trb.org/onlinepubs/nec/093009couchman.pdfnavy...
Post on 17-Mar-2018
217 Views
Preview:
TRANSCRIPT
Computational Mechanics and Signatures
Presented to the National AcademySept. 30, 2009
Luise CouchmanCode 331
Office of Naval Research
6.1 Computational MechanicsCode 331, Ship Systems & Engineering DivisionCode 331, Ship Systems & Engineering Division
34AX Couchman
Program Objective/Goal:Develop fundamental advances in the state of the art of physics-based modeling of mechanical structures. Via experiments and simulations obtain improved understanding of the linear and nonlinear mechanical behavior of complex structures. Apply the enhanced understanding to develop approaches for predicting the behavior. Develop physics- based models and evaluate their predictive capability against measurement. Develop methods for increasing the speed of input model generation.
Rationale:• Requirement for much more efficient, accurate modeling
of highly complex structures• Currently months-long input model generation times
S&T Products/Deliverables:• Advanced techniques for structural modeling
• Advanced techniques for speeding input model generation
Major Accomplishments:• XFEM, Extended Finite Element Method (Ted
Belytschko, Northwestern U) Fields Medal• Isogeometric Analysis (Thomas R. Hughes, Stanford/U.
Texas)• LOGOS Fast Linear Equation Solver (Robert Adams, U.
Kentucky)• Ghost Fluid Stabilized Method (Charbel Farhat,
Stanford)• FETI Substructuring Method for Shells (Charbel Farhat,
U. Colorado/Stanford)• DEM Finite Element Approach (Charbel Farhat, U.
Colorado/Stanford)
Description of work in FRC: Improve the accuracy and efficiency of the modeling of the linear and nonlinear mechanical behavior of complex structures
Primary S&T Focus Area /Sub Area: Survivability and Self-Defense
Secondary S&T Focus Area(s) /Sub Area(s): Affordability, Maintainability, and Reliability
Customers: Navy Shipbuilders, Navy Ship Acquisition Programs, NAVSEA Warrant Holders and their SME’s
Current Focus:• Fundamental Computational Mechanics• Residual Strength of Structures in Fire• Air Blast• Rapid Input Model Generation
Interelement crack method
XFEM
Results for Kalthoff Experiment
ExperimentElement Deletion
Displacement field is decomposed into continuous and discontinuous parts
Level sets are used to describe the topology of the discontinuity (crack)
cont disc enrich
continuous discontinuous
enrichment
, , , ,
, ,
, , ,
I I J JI J
K KK
t t t t
N t N H t t t
N t t t
u X u X u X u X
X u X X X q
X X X r
ε
XFEMT. Belytschko
Northwestern U.
New Method for Treating Fluid Structure Interaction and Two-phase Flows: GFSMP - FSI
Log
(rela
tive
erro
r)
‐12 ‐10 ‐8 ‐6 ‐4 ‐2 0‐14
‐12
‐10
‐8
‐6
‐4
‐2
0
Log (t)
2.01
Previous GFSM – FSI New Stanford GFSMP - FSI
Structure surface mesh (S)
Fluid mesh with ghost domain (F)
Real nodes Ghost nodes
fluid sidestructure
side
FSI
Theoretical justification or analysis -
NONE
Extensive numerical experiments -
only 1st-order accuracy exhibited in all cases
Stanford Analysis-
At the fluid-structure interface
GFSM is unconditionally inconsistent at the FSI!
This reduces its accuracy elsewhere from 2nd-orderto 1st-order
c2tcut
= ( )ux
+ O(t) + O(x)4x2
• Fundamentally new approach to structural modeling
• Based on technologies (e.g., NURBS) from computational geometry used in:
– Design (CAD) – Animation– Graphic art– Visualization
• Includes standard FEA as a special case, but offers other possibilities:
– Integration of design and analysis– Superior approximation properties– More robust analysis– Precise and efficient geometric
modeling
N
nnn xPaxu
1)()(
Isogeometric
Analysis: A New Finite Element Method
Thomas J. R. Hughes
University of Texas at Austin
NURBS Have Better Approximation Properties
Lagrange polynomials
p=7p=5p=3
NURBS
p=7p=5p=3
NURBS Give Lower Frequency Errors:
Comparison of FEM and NURBS Frequency
Errors for Vibration of a Finite Elastic Rod with Fixed
Ends
FEM
NURBS
h
h / n / N
Acoustic branch
Optical branch
Variation Diminishing Property
Fire on Naval Composite Structures (BA1, NICOP, SBIRs)Vision:• Understanding of heat conduction, charring, buckling, and residual strength of composites under simultaneous heat and load• Models to predict failure timesCritical Scientific IssueThe failure of composites during a fire involves a wide range of physical and chemical effects which are still poorly understood, and thus cannot be predicted when applying them in a design.Approach:
Via testing and analysis determine the significant physical effects and develop the ability to model them
Debonding
Microcracking
Multi-layerLaminate
Fire-protection
Burning
Outgassing
Bal
sa c
ore
Load
Load
Bur
ner
0 500 1000 1500 20000
50
100
150
200
250
Edg
ewis
e C
ompr
essi
ve S
treng
th (M
Pa)
Exposure Time (s)
Skin Failure
Buckling Failure
Sam
ple
Modeling of Blast Failure of FRP Composite Ship Structures:
UCSD
• Objective:–develop an understanding and predictive capability for
the failure of naval composites under blast.• Approach:
–Via small and large-scale testing develop the understanding and material parameters required to develop a predictive model
–DDG1000 is providing the Quarter-Scale Deckhouse to UCSD for sample extraction
–DDG1000 is sending funding to conduct tests on the quarter-scale deckhouse specimens
Nose Geometry
Elastomer Foam
Computational SignaturesCode 331, Ship Systems & Engineering DivisionCode 331, Ship Systems & Engineering Division
34AR Couchman
Technical Approach:Develop fundamental advances in the state of the art of signature modeling
Recent Breakthroughs• Sub-grid Modeling was developed under this
program• Energy Finite Element Analysis (EFEA) developed
under this program is replacing the conventional Statistical Energy Analysis (SEA)
S&T Products/Deliverables:• Ability to analyze whole-ship models• Rapid transition between disciplines, eg. acoustic,
magnetic, radar• Rapid turn-around of predictions
Description of work in FRC: Develop improved understanding and predictive capabilities for ship and submarine acoustic and electromagnetic signatures. Develop algorithms and methods that will enable the development of improved design, analysis, and prediction tools.
Primary S&T Focus Area /Sub Area: Survivability and Self-Defense
Secondary S&T Focus Area(s) /Sub Area(s): Affordability, Maintainability, and Reliability
Program Objective/Goal:• Increased reliability and efficiency of signatures
prediction• Early integration of signatures effects into the design• Multi-disciplinary optimization of the early concept
design over signatures, structures, and hydrodynamics• Rapid re-evaluation of effects of design changes on
signatures• Decreased need for re-design due to failure to meet
signature requirements
S&T Technical Challenges/Issues:• More accurate and efficient modeling of acoustic and
EM signatures of highly complex platforms and systems
• Greatly decreased input model generation times
Energy Finite Element MethodVlahopoulos, Univ. of Michigan
Validation
6
4
2
5
3
1
7
Finite Element Analysis• Take pressure or displacement as the
unknown quantity• Approximate the unknown as a sum over a
basis set• Find an approximate solution to the
differential equation by a variational approach
Energy Finite Element Analysis• Take energy as the unknown quantity
EFEA Model
n
n xcxu )()(
Displacement continuous across a joint
Energy density discontinuous across a joint
uuu )(2
022 pk
Energy Finite Element Analysis on CVN78 (Collaboration of U. Mich. with Northrop Grumman Newport News)
• CVN 78 is the first CVN to have radiated noise goals
• Meeting those goals within the Program’s cost and weight limits requires detailed knowledge of the hull’s noise transmission properties
– Very little test data exists from previous CVN’s– Data from other surface combatants does not apply due to large
differences in plate thickness
• Existing noise prediction tools were not suited to the extremely large size of the CVN
• Developed under ONR sponsorship, the Energy Finite Element Analysis method meets the program’s needs
– Geometry taken directly from existing hull structural models →
No new geometry creation required
– Coarse computational mesh means smaller models than conventional FEA approaches → Faster run times
– EFEA code operates on a PC in Windows environment → No special hardware / software required
– Substructuring feature allows tradeoff between model size, run times, and available PC memory
– Previous code validation ensures confidence and reduces risk
Conventiona l FEA
Energy Finite Element Model
A Technology Transition SuccessA Technology Transition Success
Implosion: Integrated BA1-FNC Program Multidisciplinary University Research Initiative:Develop improved methods for modeling both
the failure of the structure and the resulting two-phase flow.
In addition, due to the complexity and multidisciplinary nature of the physics, significant effort is required in order to produce highly efficient numerical methods to evaluate the physical model.
FNC EPE-FY08-06:• Develop validated, user-friendly tools
enabling the designer to predict the implosion of payloads of all sizes, implosion effects, and mitigation techniques:
1)
a payload design tool, and 2)
a physics-based model for complex analyses.
• Develop the relevant materials data base• Validate against small and large scale data
Other BA1 Base Programs Leveraged:• Computational Mechanics base program
(Couchman)• Solid Mechanics base program (Barsoum)• National Naval Responsibility in Naval
Engineering (Cooper)
NAVSEA Small Business Program (SBIR):Conduct large-scale at-sea implosion tests
Background:
NAVSEA 05P and NAVSEA 05U approached ONR to request assistance on the issue of implosion.
Inability to predict accurately enough the magnitude of shock waves produced by the implosion of underwater structures is resulting in extremely conservative designs, and in some cases obviating the approval of desired systems and functions. Thkl;atlakehtlaksetjl;askjtlkasetjBA1/BA2 Base Program Dedicated to Implosion:
develop an improved understanding of the process of implosion, including the precise mode of failure, the mechanism of production of the shock wave, the importance of fluid jets through fractures in the structure, the onset and rate of structural collapse, cavitation, and the two-phase fluid dynamics of the shock wave.
Aluminum
6.1 Program Tank Tests NAVSEA SBIR: Large-scale At-sea Tests
Description: Develop the capability to design and qualify external payloads for implosion avoidance and platform survivability. Current inability to predict implosion effects requires severe conservatism in payload design, limiting payload capability and impacting cost and schedule.
FNC Product: Payload Implosion and Platform Damage AvoidanceCode 331, Ship Systems & Engineering DivisionCode 331, Ship Systems & Engineering Division
3DA2 Couchman
Program Objective/Goal:The affordable introduction of new underwater vehicles capabilities using external payloads requires the development of design tools for modeling payload implosion and its effects on the platform. This would remove the most significant obstacle to the Navy’s goal of affordably enhancing warfighting capability using external payloads, without restricting operating depth or payload capability.
S&T Technical Challenges/Issues:• Inadequate ability to predict the implosion
pressure pulse• Difficulty of conducting validation experiments• Unavailability of material-parameters data
Technical Approach:• Develop a physics-based tool to model the
implosion pressure pulse and platform damage• Validate via small and large-scale tests• Develop the relevant materials data base• Develop a rapid design tool based on the
experiments and physics-based model results.
S&T Products/Deliverables:Validated, user-friendly tools enabling the designer to predict the implosion of payloads of all sizes, the magnitude of the implosion pressure pulse, and the efficacy of mitigation techniques:
1) a payload design tool for conventional geometries, and
2) a physics-based model for complex analyses
Task E’Test Series
Plan Task A – Weidlinger United KingdomAt-Sea Testing
Task BFabrication
Task C – UT AustinMaterial Characterization
Task D – Stanford/NorthwesternPhysics-Based Model Development
Task E - WeidlingerDesign/Assessment Tool Development
Task D – Navy LabsPre-test Calculations
Task D – Navy LabsCode Validation Against At-Sea Data
FY08 FY09 FY10 FY11 FY12
Task FPressure Tank Testing
Time (msec)
Pre
ssur
e (p
si)
TASK D – PHYSICS BASED COMPUTATIONAL MODEL DEVELOPMENT
100
150
200
250
300
350
400
0.0004 0.0009 0.0014 0.0019 0.0024 0.0029 0.0034
Experimental
AERO-F/XFEM(coarse mesh inside)
top related