مطالعه آزمایشگاهی تاثیر امواج درونی بر روی انتشار امواج صوتی

نویسندگان

1 دانشجوی پژوهشگاه ملی اقیانوس شناسی و علوم جوی

2 مدیر گروه موسسه ژئو فیزیک دانشگاه تهران

3 هیات علمی پژوهشگاه ملی اقیانوس شناسی و علوم جوی

4 مدیر گروه فیزیک دریا دانشگاه بابلسر

چکیده

برای محاسبه‌ی فشار اکوستیکی در دریا با استفاده از روش‌های معمول، دانستن نحوه‌ی توزیع میدان چگالی و به تبع آن نحوه‌ی تغییرات سرعت صوت در محیط بسیار مهم است. عوامل محیطی بسیاری بر توزیع میدان چگالی در دریا تاثیرگذارند که بسته به شرایط محیطی و جغرافیایی شدت و ضعف هر یک از آن‌ها متفاوت می‌باشد. یکی از این عوامل امواج درونیاست که ساختار آنباعث تغییرات زمانی مکانی میدان چگالی و به تبع اثر گذاری روی نحوی انتشار امواج صوتی در اقیانوس می شود.هدف از این مطالعه بررسی آزمایشگاهی تاثیر امواج درونی ناشی از نوسان یک استوانه در یک کانال چینه بندیشده، بر روی انتشار امواج صوتی می-باشد. در این مطالعه ابتدا با استفاده از روش‌های معمول امواج درونی در محیط تشکیل داده شد و با استفاده از فرستنده و گیرنده صوتی تاثیر امواج درونی بر روی انتشار امواج صوتی بررسی شد. همچنین علاوه بر نتایج عملی شبیه سازی با یک نرم افزار انتشار صوتی صورت گرفت که نتایج آن مطابقت خوبی با نتایج آزمایشگاهی داشت. نتایج آزمایشگاهی نشان داد که امواج درونی در حالاتی باعث جمع‌شدگی و پراکندگی پرتوهای امواج صوتی می شود و در حالاتی قدرت سیگنال صوتی تا 54 درصد را کاهش دهد. در محیطهای دریایی نیز به دلیل وجود این امواج تغییرات سیگنال صوتی می تواند رخ دهد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

A laboratory study of the effect of internal waves on acoustic propagation

نویسنده [English]

  • Hamed Deldar 1
1
2
3
4
چکیده [English]

For calculating the acoustic pressure due to sound propagation at sea using usual methods (pressure variations signals), knowing the density distribution and consequently, changes the speed of sound in the environment is very important. Many environmental factors affect the distribution of the density at sea, depending on environmental conditions and geographical location and the weaknesses of each of them are different. One of them is internal waves which usually cause temporal and spatial changes and consequently affect the acoustic wave propagation in the ocean. Internal waves can be generated by tidal currents over sea floor sloping that is very common in the stratified oceans. Results of study in the some researches showed that internal waves can effected on sound waves in two ways: 1-Internal waves can be decrease sound level up to 25 dB due to sound mode coupling in an exact frequency. 2- Internal waves can fuscous and defocus sound waves because of sound speed fluctuation.
The purpose of this study is a laboratory investigation of internal waves caused by fluctuation of a cylinder in a stratified glass channel with 3 meters long, 0.5 meter width and 1 meter height, on the sound waves propagation. In this study, using the double bucket and filling box method for generating stratification that stratification can be measured by one pair of salinity and temperature meters fixed on a rail moved up and down. Using the usual methods of setting up internal waves and using acoustical transducers in 53 KHz frequency, internal wave's effects on the propagation of sound waves, were investigated. In this study with usual optical method (Synthetic Schlieren) internal waves generated in the tank can be detected. In this method Internal wave generated in the glass tank change optical index of water layers and cased deviation of Straight lines designed on the back of tank. Laboratory results showed that sound waves can be focused and defocused due to the normal modes of internal waves. Some 9 experiments were done mainly in cases withvertical linear density stratified fluid. As the modal structure of internal waves in the water tank change due to the waves, constant density surfaces change slopes, hence changing the sound ray's paths and the amount of signals reaching the receivers. Similar results of numerical simulation also show similar behavior in the strength of the acoustic signal. Numerical simulation modeled by AcTUP v2.2L software that use KERAKENC method based on normal mode method. The acoustic signal can be weakened up to 54 per cent depending on the degree of sound ray divergence. We can conclusion that in the laboratory tank in this study internal waves effects on sound waves by focusing and defocusing and not by mode coupling.
Similar behaviors can be expected in the open ocean as the existence of internal waves is ubiquitous. For this goal dimensionless numbers should be use. Bowen (1993) showed that for simulating a sound waves interaction with a phenomenon in laboratory scale we can use ka = k'a'. With this formula we can compare laboratory results with real results on oceans.

کلیدواژه‌ها [English]

  • Internal waves
  • propagation of sound waves
  • focusing and defocusing of sound waves
Aguilar, D., Sutherland, B.R. and Muraki, D.J., 2006, Laboratory generation of internal waves from sinusoidal topography, Deep Sea Research Part II: Topical Studies in Oceanography, 53(1), 96-115.
Baines, W. D. and Turner, J. S., 1969, Turbulent buoyant convention from a source in a confined region, J. Fliud Mech., 37, 51-80.
Bowen, S. G., 1993. Forward scattering of a pulsed continuous wave signal through laminar and turbulent thermal plumes.MASSACHUSETTS INST OF TECH CAMBRIDGE.
Dalziel, S.B., Hughes, G.O. and Sutherland, B.R., 2000, Whole-field density measurements by ‘synthetic schlieren’, Experiments in Fluids, 28(4), 322-335.
Dohan, K. and Sutherland, B., 2005, Numerical and laboratory generation of internal waves from turbulence, Dynamics of atmospheres and oceans, 40(1), 43-56.
Gostiaux, L. and Dauxois,T., 2007, Laboratory experiments on the generation of internal tidal beams over steep slopes,  Physics of Fluids (1994-present),19(2), 028102.
Griffiths, R. W. and Bidokhti,A. A., 2008, Interleaving intrusions produced by internal waves: a laboratory experiment, Journal of Fluid Mechanics, 602, 219-239.
Katsnel’son, B. and Pereselkov,S.,2004, Space-frequency dependence of the Horizontal structure of a sound field in the presence of intense internal waves, Acoustical Physics,50(2), 169-176.
Katsnel’son, B. and Pereselkov, S., 2000, Low-frequency horizontal acoustic refraction caused by internal wave solitons in a shallow sea, Acoustical Physics, 46(6), 684.
Katsnel’son, B. G.,Pereselkov, S.A., Petnikov, V.G., Sabinin, K.D., and Serebryanyi, A.N., 2001, Acoustic effects caused by high-intensity internal waves in a shelf zone,  Acoustical Physics,47(4), 424-429.
Lynch, J. F., Lin, Y.T., Duda, T. F. and Newhall, A. E., 2010, Acoustic ducting, reflection, refraction, and dispersion by curved nonlinear internal waves in shallow water, Oceanic Engineering, IEEE Journal of , 35(1), 12-27.
Mathur, M. and Peacock,T., 2009, Internal wave beam propagation in non-uniform stratifications, Journal of Fluid Mechanics, 639, 133-152.
Morgunov, Y. N., Polovinka, Y. A. and Strobykin, D.S., 2008, an experimental study of the effect of tide on acoustic field formed along a stationary track in the shelf zone of the Sea of Japan, Acoustical Physics, 54(4), 506-507.
Munk, W.,Zetler, B., Clark, J., Glll, S., Porter, D., Spiesberger, J. and Spindel, R., 1981, Tidal effects on long‐range sound transmission, Journal of Geophysical Research: Oceans (1978–2012), 86(C7), 6399-6410.
Preisig, J. C. and Duda,T. F.,1997, Coupled acoustic mode propagation through continental-shelf internal solitary waves, Oceanic Engineering, IEEE Journal of ,22(2), 256-269.
Pond, S. and Pickards, G. L., 1983, Introductory Dynamical Oceanography, Butterworth and Heineman Ltd., 328 pp.
Reeder, D. B., Duda, T.F. and Ma, B., 2008, Short-range acoustic propagation variability on a shelf area with strong  nonlinear internal waves, OCEANS 2008-MTS/IEEE Kobe Techno-Ocean, IEEE.
Roberts,J., 1975, Internal gravity waves in the ocean, AlaskaUniv College Inst Of Marine Science.
Ross, T. and Lavery,A., 2009, Laboratory observations of double-diffusive convection using high-frequency broadband acoustics, Experiments in Fluids, 46(2), 355-364.
Rubenstein, D., 1999, Observation of cnoidal internal waves and their effect on pagation in shallow water, IEEE J. Ocean Eng., 24(3), 346-357.
Rutenko, A., 2005, The effect of internal waves on the sound propagation in the shelf zone of the sea of Japan in different seasons, Acoustical Physics, 51(4), 449-456.
Scotti, A. and Pineda,J., 2004, Observation of very large and steep internal waves of elevation near the Massachusetts coast, Geophysical research letters, 31(22).
Sutherland, B. and Linden,P., 2002, Internal  wave excitation by a vertically oscillating elliptical cylinder, Physics of Fluids (1994-present), 14(2), 721-731.
Thorpe, S. A., 2005, The turbulent ocean, Cambridge University Press,pp 230.
Turgut, A., Orr, M. and Pasewark, B., 2007, Acoustic monitoring of the tide height and slope-water intrusion at the New Jersey Shelf in winter conditions, The Journal of the Acoustical Society of America, 121(5), 2534-2541.
Warn-Varnas, A.C., Chin-Bing, S.A., King, D.B., Hallock, Z. and Hawkins, J.A, 2003, Ocean-acoustic solitary wave studies and predictions, Surveys in Geophysics, 24(1), 39-79.
Zhou, J. X., Zhang, X.Z. and Rogers, P. H., 1991, resonant interaction of sound wave with internal solitons in the coastal zone, The Journal of the Acoustical Society of America, 90(4), 2042-2054.