Download presentation

Presentation is loading. Please wait.

Published byMatteo Cowell Modified over 3 years ago

1
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 Sponsored by Defense Threat Reduction Agency Contract No. DTRA01-00-C-0084

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

3
Nonlinear Progressive wave Equation (NPE) NPE algorithm Refraction + Nonlinear steepening Step : Second order upwind flux corrected transport scheme [B. E. McDonald, J. Comp. Phys. 56, 448-460, (1984)] Diffraction Step : Crank-Nicholson scheme c0c0 NPE moving frame time incremental step t = x / c 0 of the moving frame to get a time waveform at a fixed location Refraction included. Important for ocean waveguide. [B. E. McDonald, W. A. Kuperman, J. Acoust. Soc. Am. 81, 1406-1417, (1987)]

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

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

6
Narrowband source in Shallow Water Linear - Nonlinear steepening - Shock dissipation energy distribution on each mode more homogeneous Nonlinear propagation peculiarities : 200 m 0.5 dB/, 1800 kg/m 3, 1550 m/s Shallow water Pekeris waveguide 1500 m/s Source characteristics : 50Hz narrowband (five-cycle sine wave) depth : 100 m level : Mach number = 3.5 10 -3. Nonlinear PLEASE, LOAD FIRST BOTH MOVIES : 1 - LINEAR & 2 - NONLINEAR1 - LINEAR2 - NONLINEAR THEN CLIC ON BOTH FRAMES TO WATCH THEM SIMULTANEOUSLY IN THE PRESENTATION

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

8
Narrowband source in Deep Water LinearNonlinear deep-water waveguide Munk sound speed profile sediments 5km Source characteristics : 10Hz narrowband (five-cycle sine wave), depth : 1 km level : Mach number = 3.5 10 -3 smaller shock dissipation due to the spherical spreading Deep water NL propagation peculiarities : PLEASE, LOAD FIRST BOTH MOVIES : 1 - LINEAR & 2 - NONLINEAR1 - LINEAR 2 - NONLINEAR THEN CLIC ON BOTH FRAMES TO WATCH THEM SIMULTANEOUSLY IN THE PRESENTATION

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

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

Similar presentations

Presentation is loading. Please wait....

OK

Processes altering seismic amplitudes

Processes altering seismic amplitudes

© 2018 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on self discipline for students Ppt on html tags with examples Ppt on machine translation tools Ppt on corruption in hindi language Ppt on nitrogen cycle and nitrogen fixation cycle Ppt on water scarcity articles Ppt on google driverless car Sell your house quickly by appt only Ppt on acids bases and salts for class 10 Ppt on public health nutrition