2005 Fiscal Year Final Research Report Summary
Study on the acoustical measurements of surficial marine sediments using acoustical reflection
| Project/Area Number |
16560703
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Naval and maritime engineering
|
|---|
| Research Institution | TOKAI UNIVERSITY |
|---|
Principal Investigator |
KIMURA Masao TOKAI UNIVERSITY, SCHOOL OF MARINE SCIENCE AND TECHNOLOGY, PROFESSOR, 海洋学部, 教授 (10119670)
|
|---|
| Project Period (FY) |
2004 – 2005
|
| Keywords | acoustical reflection / seabed / transition layer / acoustical measurement / porosity / Biot-Stoll model / reflection coefficient / longitudinal wave velocity |
|---|
| Research Abstract |
1.Theoretical analyses
The frequency characteristics of the reflection coefficients form the transition layer of surficial marine sediments were calculated using OASES (Biot-Stoll model). In this calculation, the transition layer was divided into 200 layers which was good approximation to the continuous layer. From the calculated results, it was seen that the cut-off frequency and the slope of the reflection coefficients to the frequency varies with the variation of the depth dependence of the porosity.
2.Tank experiments
Silt sampled at the Shimizu harbor was used as a sediment model. This model was set in the bottom of the cylindrical tank. The wideband piezoelectric transducer with the resonant frequency of 500 kHz was used. The Fourier transforms of the reflected signal form the water-sediment model interface and that from the water-air interface. Using these transformed results, the frequency characteristics of the reflection coefficients were obtained. It was seen that the measured results of the frequency characteristics of the reflection coefficients was almost agrees with the calculated results.
3.In situ experiments
First, the design and fabrication of the system for the in situ acoustic reflection measurements were performed. In situ experiments were performed in the Shimizu harbor. The measuring system was taken down from a small ship and set on the sea bottom. The wideband piezoelectric transducer with the resonant frequency of 100 kHz was used. The porosity was measured for each 1-cm-long sample from the top of the sediment, after taking sample using GS-type core sampler. It was seen that the measured results of the frequency characteristics of the reflection coefficients was almost consistent with the calculated results.
From the above-mentioned results, it was indicated that the estimation of the porosity profile with the depth using the measured results of the frequency characteristics of the reflection coefficients are possible.
|
