Underwater Acoustics and Instrumentation Technical Group. CAV Workshop

Transcription

1 Underwater Acoustics and Instrumentation Technical Group CAV Workshop 3 May 2016 Amanda D. Hanford, Ph.D. Head, Marine & Physical Acoustics Department, Applied Research Laboratory ald227@arl.psu.edu 1

2 Research Areas/Core Competencies Ocean Acoustics Seafloor characterization Water column characterization Acoustic modeling and simulation Underwater threat neutralization Weapon Countermeasures Ocean array experiments Radiated/self noise Physical Acoustics Atmospheric infrasonic monitoring arrays Thermoacoustics Acoustic metamaterials 2

3 The Five Octave Research Array (FORA) ONR-FORA data acquisition system 277m length 490 acoustic channel Has completed 15 successful sea-trials since its shakedown cruise in Currently participating in the 2017 Seabed Characterization Experiment (SCEX17) at Woods Hole Oceanographic Institute understanding the impact that low-soundspeed seabeds have on acoustic propagation and acoustic inversion of seabed properties The FORA system has been used in many different areas of acoustics and oceanographic research Geoacoustic inversion Long-range propagation Target characterization Continuous and pulsed-active sonar comparison Signal coherences studies biologic surveys Nordic Seas Fish-abundance Survey, Norway,

4 Acoustic Clutter Statistics Normalized Return Level [db] clutt er research target array location Acoustic clutter is a term use to describe acoustic backscatter returns which appear similar to target returns These returns cause false alarms for traditional sonar systems and can be challenging for even experienced sonar operators to distinguish from targets in a timely manner This work involves analyzing the statistics of acoustic clutter returns to characterize these events and link them to the environment (i.e. fish schools and other biologics, geoacoustics, and surface dynamics) Statistical analyses include mono- and bi-static backscattered acoustic intensity distributions as well as temporal and spatial pulse correlation dynamics Acoustic and environmental modeling includes range-dependent normal mode propagation model used to help understand the impact of environmental parameters in the shallowwater littoral sonar environment 4

5 Propagation and Reverberation Modeling based on energy flux ideas (energy conserving) improved physics (ducts and range dependence) & improved efficiency Benchmark Current Fleet model Energy Flux w/focus captures main (large-scale) interference structure, (operationally, the most important features to predict) Objective: Acoustic focusing by seabed scattering. Solve the eikonal equation of high frequency acoustics on a fixed grid. 5

6 Bottom Backscattering Database ARL-PSU has developed a prototype bottom scattering database ( khz) for shallow water. Gives more than 12 db improvement for active sonar systems in shallow water area of operational interest. Bottom scattering often dominates reverberation from active sonar Deficiency: current Fleet Bottom Scattering Pred. capability: (< 10 khz): has NO frequency dependence and NO location dependence BBS = log(sinθ sinφ) 6

7 Acoustic Scattering of Rock Outcrops Scattering from rocks cause false alarms in almost every active sonar system (weapons, MCM, ASW) Physics-based predictive models are nonexistent, and field measurements are sparse Olson, Lyons and Sæbø, Measurements of highfrequency acoustic scattering from glaciallyeroded rock outcrops J. Acoust. Soc Am.,

8 Synthetic Aperture Sonar y (m) Seafloor relief models x (m) Relief (m) Simulated SAS imagery examine relationships of environmental properties of sediment, water column or rock to coherence in time, space, and frequency via analysis of experimental SAS data develop and compare predictive models of the relationship between environmental parameters and coherence as a function of frequency, repeat-pass time, etc. develop simulation capabilities based on predictive models capable of generating realistic 8 training datasets for ATR 8

9 Automatic Target Recognition Example SAS Image Michelson Contrast color notionally indicates expected ATR performance develop MCM imagery Performance Estimation tool for in situ assessment of ATR effectiveness 9

10 Acoustic Metamaterials 10

11 Metamaterial Unit Cells Metamaterial Definition: artificial structure that responds to applied fields and acts like a continuous material with desired properties Same complex reflection and transmission = equivalent for waves Internal structure generally needs to be subwavelength for homogenization to be independent of sample size 11 11

12 Motivation Realizable Unit Cells Additive Manufacturing Zhu et. al. (2014) Jour. App. Phys. 116(16), Zhu et. al (2015) Jour. Phys. D. 48(30) Xiong et. al. *2015) Int. Jour. of Mod. Phys. B 29(27)

13 Metal Foam Samples Commercially Available Aluminum Foam Cymat: 1 Sample ERG Aerospace: 3 Samples Density= 3-12 % PPI= 10, 20, 40 Young s Modulus = 103 MPa

14 Powder Bed Fusion Additive Manufacturing Direct Metal Laser Sintering

15 Additive Manufactured Parts Fully Dense and Lattices Partially Sintered Powder 15 15

16 Additive Manufactured Lattices 0.5 in 16 16

17 Experimental Set -Up 17 17

18 Second Experiment Fixed Mass Loaded Cantilever Beam Assumes Beam of Negligible Mass (m b <<m) 18 18

19 Summary of Results Beam Mass [g] Mass [g] Frequency [Hz] Young s Modulus % of Fully Stiff Density [kg/m^3] Lattice Gpa Cymat Foam GPa ERG PPI MPa ERG PPI MPa ERG PPI MPa

20 Static anisotropic solid inclusion math x h l If h l, then the propagation in the x and y direction will be different. y Uniform in the z direction

21 Static anisotropic solid inclusion 2.4 Effective density and bulk modulus as a function of aspect ratio x x y y A density and bulk modulus less than that of the background fluid cannot be obtained with a single material solid rigid inclusion Similarly, only a modest anisotropic factor (ρ x /ρ y ) is attainable

22 Dynamic anisotropic solid inclusion k m k Consider the mass rigid with compliant mounts Or cantilever spring mount 22 22

23 Dynamic anisotropic solid inclusion results x y x y Much larger changes in anisotropy attainable with changing stiffness Bulk modulus below that of the background 4/22/2017 ASA Honolulu - Fall 2016 fluid 23 23

24 Optimized dynamic anisotropic solid inclusion results Static τ τ Dynamic Stiff spring Soft spring Frequency: 5000 Hz 10-3 Static τ = 2.22 Dynamic τ =

25 Comparison with desired values x y Static τ = 2.22 Dynamic τ = 2.14 Desired values - Dynamic Realized values - Dynamic Realized values - Static Desired values - Static x y

26 Results in a ground cloak Ideal Static Dynamic No cloak 4/22/2017 ASA Honolulu - Fall

27 Periodic arrays of piezoelectric transducers creates an active metamaterial Z Electrical shunts or control schemes can significantly alter the mechanical and acoustic wave propagation behavior. 27

28 Actively induced band gaps correspond to large reduction in vibration amplitude [9] 28

29 A negative capacitance shunt within a metamaterial unit cell predicts high loss Z in R S 1 iωc n Choice of R s Change frequency 29

30 Negative capacitance shunted metamaterial induces large control of vibration Large magnitude of attenuation Frequency response confirmed experimentally 30

31 Metamaterial honeycomb panel T. Yu, G. Lesieutre, AIAA Journal,

32 Metamaterial sandwich panel 32 32