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Long-Range Nonlinear Propagation in an Ocean Waveguide

Long-Range Nonlinear Propagation in an Ocean Waveguide. Kaëlig C ASTOR (1) Peter G ERSTOFT (1) Philippe R OUX (1) W. A. K UPERMAN (1) B. E. M C D ONALD (2). (1) Scripps Institution of Oceanography, La Jolla, CA 92093 USA (2) US Naval Research Laboratory, Washington DC 20375 USA.

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Long-Range Nonlinear Propagation in an Ocean Waveguide

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  1. Long-Range Nonlinear Propagationin an Ocean Waveguide Kaëlig CASTOR (1) Peter GERSTOFT (1) Philippe ROUX (1) W. A. KUPERMAN (1) B. E. MCDONALD (2) (1)Scripps Institution of Oceanography, La Jolla, CA 92093 USA (2)US Naval Research Laboratory, Washington DC 20375 USA Sponsored by Defense Threat Reduction Agency Contract No. DTRA01-00-C-0084

  2. 2 propagation codes used : • Nonlinear code (NPE, [McDonald & Kuperman, (1987)])shock propagation in an ocean waveguide • Linear Normal Mode code (KRAKEN, [Porter, (1991)]) modal structure of long-range nonlinear propagation paths. Outline OBJECTIVE : characterisation of underwater nuclear explosions (Comprehensive Nuclear-Test-Ban Treaty).

  3. NPE moving frame c0 time incremental step t =  x / c0 of the moving frame to get a time waveform at a fixed location Nonlinear Progressive wave Equation (NPE) NPE algorithm [B. E. McDonald, W. A. Kuperman, J. Acoust. Soc. Am.81, 1406-1417, (1987)] Diffraction Step : Crank-Nicholson scheme Refraction + Nonlinear steepening Step : Second order upwind flux corrected transport scheme [B. E. McDonald, J. Comp. Phys. 56, 448-460, (1984)] Refraction included. Important for ocean waveguide.

  4. Nonlinear steepening Multivalued waveform no physical sense Shock dissipation Shock wave formation Shock formation time Nonlinear Steepening and Shock Dissipation

  5. Nonlinear effects - harmonic generation - parametric interaction - shock dissipation - more uniform modal distribution - self-refraction

  6. Shallow water Pekeris waveguide 200 m 1500 m/s 0.5 dB/, 1800 kg/m3, 1550 m/s Narrowband source in Shallow Water Source characteristics : 50Hz narrowband (five-cycle sine wave) depth : 100 m level : Mach number = 3.5 10-3. Linear Nonlinear PLEASE, LOAD FIRST BOTH MOVIES : 1 - LINEAR & 2 - NONLINEAR THEN CLIC ON BOTH FRAMES TO WATCH THEM SIMULTANEOUSLY IN THE PRESENTATION - Nonlinear steepening - Shock dissipation energy distribution on each mode more homogeneous Nonlinear propagation peculiarities :

  7. Ratio Nonlinear/Linear 5 km range 20 km range Modal Amplitude vs Frequency in Shallow Water Linear Nonlinear 0 km range

  8. deep-water waveguide Munk sound speed profile 5km sediments Narrowband source in Deep Water Source characteristics : 10Hz narrowband (five-cycle sine wave), depth : 1 km level : Mach number = 3.5 10-3 Linear Nonlinear PLEASE, LOAD FIRST BOTH MOVIES : 1 - LINEAR& 2 - NONLINEAR THEN CLIC ON BOTH FRAMES TO WATCH THEM SIMULTANEOUSLY IN THE PRESENTATION smaller shock dissipation due to the spherical spreading Deep water NL propagation peculiarities :

  9. Source Depth=2.5 km Source Depth=4.5 km Modal Amplitude vs Frequency in Deep Water for different Source Depths Source Depth=1 km at 100 km range Linear Nonlinear Nonlinear Linear

  10. Redistribution of the energy during the propagation - frequency distribution parametric and harmonic - modal distribution more relative energy for high order modes In shallow water, lower geometrical spreading higher amplitudes, stronger nonlinear effects Conclusion How can we identify at long ranges a nonlinear acoustic propagation path ? What is the main difference between shallow and deep water ?

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