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