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Penn State Center for Acoustics and Vibration (CAV)
Structural Vibration and Acoustics GroupPresented as part of the 2017 CAV Spring workshop
Stephen Hambric, Group Leader
April 2017
Ben BeckRobert CampbellJames ChatterleyStephen ConlonCarl CotnerTyler DareJohn Fahnline
Sabih HayekKevin KoudelaKyle MyersDan RussellMicah ShepherdAlok SinhaAndrew Wixom
2/33April 2017
CAVToday’s topics
• Accelerated Composite Fatigue Testing• Chet Kupchella, MS 2017, and Drs. Rob Campbell, Kevin
Koudela, and Steve Hambric
• Transient Structural-Acoustics• Dr. John Fahnline
• Hybrid Method for Predicting Heavy Fluid Loading of Structures• Dr. Micah Shepherd
• Uncertainty in Structural Acoustic Systems• Dr. Andrew Wixom
• Noise and Vibration Emerging Methods 2018 (NOVEM)
3/33April 2017
CAVOther Student Projects• Student posters:
– Bolted Joint Dynamics• Trevor Jerome, PhD student, and Drs. Micah Shepherd and Steve
Hambric, advisors– Large Chiller Vibration and Sound
• Steve Wells, PhD student, and Drs. Steve Hambric and Tim Brungart, advisors
• Just starting out:– Small Reciprocating Compressor Noise and Vibration
– John Cunsolo, MS student, and Drs. Tim Brungart and Steve Hambric– Adaptive Acoustic Metamaterials
• Aaron Stearns, PhD, Dr. Ben Beck, advisor– Acoustics of Golf Putter – Ball Impact
• Arjun Shankar, MS, Dr. Dan Russell, advisor– Optimization of Acoustic Black Hole Designs
• Cameron McCormick, PhD, Dr. Micah Shepherd, advisor
4/33April 2017
CAVOther Student Projects• Graduated!!!
– Axtell, Wesley, Acoustics, Force reconstruction using force gauges and modal analysis
– Kerrian, Peter, Acoustics, Acoustic and vibrational analysis of golf club drivers
– Feurtado, Phil, Acoustics, Quiet Structure Design using Acoustic Black Holes
– Ken Aycock, Biomedical Engineering, Fluid-Structure Interaction Modeling of Blood Clot Migration and Entrapment in the Inferior Vena Cava
5/33April 2017
CAV
Accelerated Composite High Cycle Fatigue Testing
Principal Investigator: Chet Kupchella, MS AcousticsDr. Rob Campbell, Kevin Koudela, and Steve Hambric,
Advisors
Sponsor:
6/33April 2017
CAVMotivation – Fatigue Failure of Fiber-Reinforced Polymer Composites
FibersGlass or carbon
MatrixPolymer resin
7/33April 2017
CAVFailure Mechanisms
I. Matrix cracking until crack
saturation (wear-in)
II. Isolated fiber separation
III. Delamination and fiber failure
Naderi 2012
8/33April 2017
CAVHigh Cycle Fatigue Life Projection
Strauch 2008
R = -1: Fully Reversed is most limiting
9/33April 2017
CAVAccelerated Testing
• Traditional fatigue testing is performed on expensive (usually Instron) machines at low frequencies– Takes a long time to accumulate 10M (or more) cycles
• Use resonant beam apparatus to test at higher frequencies – Obtain S-N data more quickly– Or, run to higher cycle counts– Lower cost
10/33April 2017
CAVResonant Beam with Bonded Composite Sample
Composite sample experiences fully-reversed cyclic loading
End masses adjust apparatus resonance frequency
11/33April 2017
CAVShaker Testing
“tip” accel
Strain Gage and Thermocouple
12/33April 2017
CAVTrack Resonance Frequency Shifting Throughout Testing
22 H
z55
Hz
30 H
z11
0 H
z
13/33April 2017
CAVTemperature Correction• Specimens heat up at higher frequencies
14/33April 2017
CAVResonance Frequency Reductions over Time
Initial Data
TemperatureCorrection
Applied
= , + −More frequency
reduction at lower frequencies
15/33April 2017
CAVResidual Strength vs. Residual Modulus – 10M Cycles
• Infer residual elastic modulus from resonance frequency shifting
• Measure residual strength on Instron machine
Good correlation
However, in general less damage with higher frequency loading
16/33April 2017
CAVConclusions so far
• Higher frequency testing does not induce the same damage as lower frequency testing for the same number of cycles
• Open questions:– Is there any benefit to higher frequency testing?
• Need more tests at equivalent ‘wall clock’ times– Example: 110 Hz for 5x more cycles than 22 Hz testing
– Do composites accumulate damage differently at higher frequencies?
• If so, fatigue testing may be necessary at different frequencies
17/33April 2017
CAV
Transient Structural-Acoustic Computations
Principal Investigators: John Fahnline and Robert Campbell
Sponsor:
18/33April 2017
CAV• Background:
– Stable transient boundary element formulations have been developed using Burton-Miller formulations
• Objective: – Develop a stable transient equivalent
source formulation• Technical Approach:
– Tripole sources are used to create a hybrid source with cardioid directivity
– The sound radiates primarily in the outward direction
Transient Equivalent Sources
= 0, 01 ⁄ , 0
Reflection from back wall
Simple Sources
z
ra
Piston in a Cylindrical Baffle
Tripole Sources
z = a, r = 0z = a, r = a / 2z = a, r = az = a, r = 2 a
19/33April 2017
CAV• Objective:
– Develop a time-stepping formulation for structural-acoustic problems
• Technical Approach: – The transient ES solution gives an
equation relating pressure and volume velocity
– This is converted to a sparse acoustic coupling matrix relating nodal pressures and velocities for the current time step
– Convolution summations account for sound radiated in the past and are computed in parallel
Transient FE/ES Computations
Drive
Ribbed Cylinder
20/33April 2017
CAVAdvantages/Disadvantages• Advantages:
– The computations are efficient because a wide frequency band can be analyzed with a single transient analysis
– For large practical problems, the time step size can be chosen so that the matrix solution times for the uncoupled and coupled problems are the same (the acoustic analysis is “free”)
– The coupled FE/ES formulation can be adapted to nonlinear vibration problems
• Disadvantages:– The time-stepping procedure adds a small amount of algorithmic damping
due to the finite difference approximations– Time-domain modeling of material damping is more difficult than in the
frequency domain
J. B. Fahnline, ”Solving transient acoustic boundary value problems with equivalent sources using a lumped parameter approach,” The Journal of the Acoustical Society of America, 140(6), 4115–4129 (2016).
J. B. Fahnline and M. R. Shepherd, “Transient finite element / equivalent sources using direct coupling and treating the acoustic coupling matrix as sparse,” Submitted to The Journal of the Acoustical Society of America,March 2017.
Refs:
21/33April 2017
CAV
Hybrid Method for Predicting Heavy Fluid Loading of Structures
Principal Investigators: Dr. Micah Shepherd, Dr. John Fahnline, Dr. Tyler Dare, Dr. Rob Campbell, Dr. Steve Hambric
Shepherd, et. al., “A hybrid approach for simulating fluid loading effects on structures using experimental modal analysis and the boundary element
method,” J. Acoust. Soc. Am., 138 (5), 3073-3080, Nov 2015
22/33April 2017
CAVHybrid Method for Inferring Fluid Loading
(1) Estimate the in-vacuonatural frequencies and
mode shapes using in air experimental modal
analysis (EMA)
(2) Apply fluid loading numerically using boundary
element (BE) method based on EMA grid
L
v f s
11 m m
ω =ω +
Measuring the natural frequencies and damping loss factors of structures in
heavy fluids can be difficult and expensive
23/33April 2017
CAVOverview of Procedure
[ ] 2 2 2 T 1i −μ μ μ μ = − ω + A fξ ω η ω + Φ Φ φ
T TΠ = Φ ΦRe{ A }ξ ξu = Φξ
6 cLf
= =λ
2
2 2 2
fMd i
αμαμ
α μ μ μ
Φ=
ω − ω + η ω Mμ
μ
Φ
( ) ( ) ( ) ( )0H000 ωωω=ω VSUH
24/33April 2017
CAVNi-Al-Brz (NAB) Plate Experiment
1 7/8” thick NAB plate, 13x31 grid of excitation
points (1” spacing)
Suspended with 100 lbtest fishing line – in air
and in water
Hit points connected to form boundary elements which behave as dipoles with
equivalent source amplitude determined by the nodal velocities
25/33April 2017
CAVComparison of Mode shapes, Velocity and OTO Loss Factors
Measured in airMeasured in water
BE-based radiation loss factors can be removed from total loss factors to
estimate in-vacuo structural damping Estimated material loss factor
Coincidence estimate: 6.2 kHz
26/33April 2017
CAV
Uncertainty in Structural Acoustic Systems Application of Generalized Polynomial Chaos
Presenter: Andrew Wixom
Collaborators: Micah Shepherd, Sheri Martinelli, Robert Campbell, Stephen Hambric
Sponsor: ARL/Penn State
27/33April 2017
CAV
• Pinned beam with an uncertain spring
• How does the uncertainty affect the response of the beam?– Natural frequencies?– Mode shapes?– Modal response?– Full system response?
An example problem
0.3 L0.6 L
L
Applied Force
Spring, with uncertainspring constant. The distribution (PDF) of the spring constant is assumed to be known.
28/33April 2017
CAV
• Building on the work of K. Sepahvand et al., and text by D. Xiu
• Expansion by orthonormal polynomials= ( )( ) =• Stochastic Collocation to evaluate coefficients
– “Black box” calculation: sample at quadrature points to evaluate integrals= =
Generalized Polynomial Chaos
29/33April 2017
CAVNatural Frequency PDFsCompared to Monte Carlo Simulation
PDFs of First Three Natural FrequenciesSpring PDF
0 100 200 3000
0.01
0.02
0.03
0.04
0.05
0 100 200 3000
2
4
6 10-3
0 100 200 3000
0.002
0.004
0.006
0.008
0.01
Normal
Uniform
Log-Normal
Blue Bars are approximate PDFs from Monte Carlo simulationOrange Curves are PDFs calculated by gPC expansion
30/33April 2017
CAVMode Shape, Modal Response, and System Response
0.22 0.24 0.26 0.280
2
4
6
8
Uniform Spring Distribution, Mode 1
31/33April 2017
CAVMode Shape, Modal Response, and System Response
0.4 0.45 0.5 0.550
0.5
1
Uniform Spring Distribution, Mode 2
This mode may have a node at forcing location!
32/33April 2017
CAVSummary
• Generalized Polynomial Chaos can be used to characterize the propagation of uncertainty throughout a structural-acoustic system– Possible quantities of interest include: natural frequencies, mode
shapes, and various responses
• Moving forward– Uncertainty in boundary conditions– Stochastic forcing functions (e.g. turbulent boundary layer)– Alternatives to stochastic collocation for modal quantities
Want more? Come see our ASA talk in Boston!
33/33April 2017
CAVNoise and Vibration Emerging Methods (NOVEM) 2018
• Co-organized by CAV International Liaisons and other friends
– A. Berry, Sherbrooke– L. Cheng, HK Poly– S. De Rosa, University Federico– O. Guasch, La Salle– S. Hambric, PSU– J-G Ih, KAIST– B. Mace, Auckland (formerly ISVR)– G. Pavic, INSA
• Topics:– Structural Vibration– Vibro-Acoustics– Flow-Induced Noise and Vibration– Noise and Vibration Control
• Abstracts due 15 Oct 2017