Flume experiments to examine hydrophone characteristics
Akira ODA, Takahisa MIZUYAMA, Michinobu NONAKA and Miwa MATSUOKA
Abstract
A hydrophone is capable of determining the number of pulses when the sediment
rate is high. This study varied the grain size, sediment rate, length of pipe,
location where the grains of sand collided, and sensitivity of the microphone,
and examined the relationships between these parameters and the number of pulses
to determine characteristics using a hydrophone. The flume experiment used a rectangular
9]m]long flume with a changeable inclination and a rectangular flume 20 m long
and 1.0 m wide, with an inclination of 1/50. L] and U]type steel pipes with circular
cross]sections were used. The outside diameter was 27.2 mm and the inside diameter
was 25.2 mm. With the U]type pipe, a microphone was positioned at both ends, and
a filter made of sponge was installed on one side. The following results were
obtained: 1) the channel that best detected the pulse differed with the grain
size; 2) when the sediment rate was high, there was a high probability that the
number of pulses decreased unless the sensitivity of the microphone was adjusted
using a filter; 3) the length over which the sediments collided influenced the
change in the number of pulses more than did the length of the steel pipe; and
4) when the sensitivity was decreased by placing a filter over the microphone,
pulses were detected even in the high sensitivity condition. Based on these characteristics
of the hydrophone, it is thought that it is possible to correspond by shortening
length over which the sand collides, and decreasing the microphone sensitivity
under the condition the pulse's large the amount of the sediment rate decreasing.