The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
권호 표지
DOI QR코드

DOI QR Code

Measurements of Ultrasound Attenuation Coefficient at Various Suspended Sediment Concentrations

부유물 농도 변화에 따른 초음파 신호의 감쇠계수 측정

  • 이찬길 (한양대학교 해양융합과학과 해양음향연구실) ;
  • 최지웅 (한양대학교 해양융합과학과 해양음향연구실)
  • Received : 2013.08.21
  • Accepted : 2013.09.26
  • Published : 2014.01.31
Download PDF
⟨ Previous Next ⟩

Abstract

Coastal water including estuaries has distinctive environmental characteristics where sediments are transported and deposited by flowing river water, providing an environment in which fluid mud layers can be formed. Acoustic method is mostly used to detect or monitor the fluid mud layer. However, since sound propagating in this layer suffers severe attenuation, it is important to estimate the accurate attenuation coefficient for various concentrations of fluid mud layer for the successful use of the acoustic method. In this paper, measurement results of attenuation coefficient for 3.5, 5, and 7.5 MHz ultrasounds were presented. The measurements were made in a small-size water tank in which suspended sediment samples with various sediment concentrations were formed using kaolinite powder. The results were compared to the model predictions obtained by attenuation coefficient model in which the mean grain size (called as Mass-median-diameter, D50) was used as input parameter. There were reasonable agreements between measured attenuation coefficients and model outputs predicted using the particle range of D50 ${\pm}20%$. The comparison results imply that although the suspended sediments consist of various-sized particles, sound attenuation might be greatly influenced by amount of particle with a size which has a larger attenuation than that of any particle in the suspended sediments for the frequency used.

하구와 연안은 육지와의 근접성으로 인해 강이나 하천 등에 의한 퇴적물 공급이 외해에 비해 활발하게 이루어지는 지역으로서 때로는 고농도의 부유퇴적물이 조성되기도 한다. 부유퇴적물은 외부 작용으로부터 쉽게 환경이 변하는 특성을 가지기 때문에 부유물층 탐지 및 연구를 위해 주로 음향 장비를 이용하지만 고농도 부유물 환경에서는 음파감쇠가 심하고, 이로 인해 음파의 이동 거리가 크게 감소한다. 따라서 부유물 환경에 대한 연구를 하기 위해서는 부유물 환경 특성과 주파수 변화에 따른 감쇠계수 특성을 파악하는 것이 매우 중요하다. 본 논문에서는 간이수조 내에서 고령토 가루를 이용하여 다양한 농도의 부유물을 조성한 후, 초음파 대역 (3.5, 5, 7.5 MHz)에 대한 감쇠계수를 측정하였으며, 감쇠계수 모델과 비교하였다. 감쇠계수 모델의 입력인자인 부유물의 평균입자 크기를 다양하게 변화시키며 실측값과 비교한 결과 평균 입자크기 (D50)을 기준으로 약 ${\pm}20%$ 범위 내에서 비교적 일치하였다. 이러한 오차 발생 원인은 부유물은 다양한 크기의 입자들로 구성되어 있으며, 음파 감쇠는 특정주파수에 우세한 영향을 미치는 크기의 입자분포에 영향을 받기 때문으로 판단된다.

Keywords

References

  1. G. C. Kineke, R. W. Sternberg, J. H. Trowbridge, and W. R. Geyer, "Fluid-mud processes on the Amazon continental shelf," Cont. Shelf Res. 16, 667-696 (1996). https://doi.org/10.1016/0278-4343(95)00050-X
  2. S. D. Richards, A. D. Heathershaw, and P. D. Thorne, "The effect of suspended particulate matter on sound attenuation in seawater," J. Acoust. Soc. Am. 100, 1447-1450 (1996). https://doi.org/10.1121/1.415991
  3. S. D. Richards, T. G. Leighton, and N, R, Brown, "Viscoinertial absorption in dilute suspensions of irregular particles," Proc. R. Soc. Lond. A 459, 2153-2167 (2003). https://doi.org/10.1098/rspa.2003.1126
  4. C. Lee and J. W. Choi, "5-MHz volume backscattering strength measurements from suspended sediment concentrations" (in Korean), J. Acoust. Soc. Kr. 32, 14-26 (2013). https://doi.org/10.7776/ASK.2013.32.1.014
  5. H. K. Ha, W. -Y. Hsu, J. P. -Y. Maa, Y. Y. Shao, and C. W. Holland, "Using ADV backscatter strength for measuring suspended cohesive sediment concentration," Cont. Shelf Res. 29, 1310-1316 (2009). https://doi.org/10.1016/j.csr.2009.03.001
  6. G. P. Holdaway, P. D. Thorne, D. Flatt, S. E. Jones, and D. Prandle, "Comparison between ADCP and transmissometer measurements of suspended sediment concentration," Cont. Shelf Res. 19, 421-441 (1999). https://doi.org/10.1016/S0278-4343(98)00097-1
  7. H. K. Ha, J. P.-Y. Maa, K. Park, and Y. H. Kim, "Estimation of high-resolution sediment concentration profiles in bottom boundary layer using pulse-coherent acoustic Doppler current profilers," Mar. Geol. 279, 199-209 (2011). https://doi.org/10.1016/j.margeo.2010.11.002
  8. D. M. Admiraal and M. H. Garcia, "Laboratory measurement of suspended sediment concentration using an Acoustic Concentration Profiler (ACP)," Experiments in Fluid, 28, 116-127 (2000). https://doi.org/10.1007/s003480050016
  9. D. Perkey, T. Pratt, N. Ganesh, "Comparison of SSC measurements with acoustic backscatter data : West bay sediment diversion, Mississippi river," 2nd Joint Federal Interagency Conference, Las Vegas (2010).
  10. H. Chanson, M. Takeuchi, and M. Trevethan, "Using turbidity and acoustic backscatter intensity as surrogate measures of suspended sediment concentration in a small subtropical estuary," J. Environ. Manage. 88, 1406-1416 (2008). https://doi.org/10.1016/j.jenvman.2007.07.009
  11. D. M. Hanes, "On the possibility of single-frequency acoustic measurement of sand and clay concentrations in uniform suspension," Cont. Shelf Res. 46, 64-66 (2012). https://doi.org/10.1016/j.csr.2011.10.008
  12. G. He, Y. Mao, and W. Ni, "A new fractal modification of ultrasonic attenuation model for measuring particle size in mineral slurries," Int. J. Miner. Process. 82, 119-125 (2007). https://doi.org/10.1016/j.minpro.2006.09.005
  13. J. Sessarego, and R. Guillermin, "High-frequency sound-speed, attenuation, and reflection measurements using watersaturated glass beads of different sizes," IEEE J. Ocean. Eng. 37(3), 507-515 (2012). https://doi.org/10.1109/JOE.2012.2194410
  14. M. Su, M. Xue, X. Cai, Z. Shang, and F. Xu, "Particle size characterization by ultrasonic attenuation spectra," Particuology, 6, 276-281 (2008). https://doi.org/10.1016/j.partic.2008.02.001
  15. J. Krautkr amer and H. Krautkr amer, Ultrasonic Testing of Materials, 4th edn (Springer, New York, 1990).
  16. P. D. Thorne, and R. Meral, "Formulations for the scattering properties of suspended sandy sediments for use in the application of acoustic to sediment transport processes," Cont. Shelf Res. 28, 309-317 (2008). https://doi.org/10.1016/j.csr.2007.08.002