Development of a measurement method for abrasion irrigation channel using underwater ultrasonic wave

Abstract

Japan has many concrete irrigation channels with total length of about 400,000 km. Most of these channels are now too old for continued use. It would be too costly to reconstruct these channels. The concrete surfaces of the channels have been abraded by the flow of water and sand. The roughness of the concrete surface causes a decline in the water flow function. Over the years, considerable attention has been paid to the measurement of the arithmetic mean roughness. However, a method that can measure roughness underwater has not yet been developed. The purpose is to develop a sensor able to measure roughness underwater. We propose a method using underwater ultrasonic waves. We used 200 kHz frequency sensor. We measured the reflected waves and analyzed the peak to peak. We examined four experiments. The propagation loss became larger as the distance was reduced. The theoretical value and the measured value showed good agreement. The dispersion of measured values stabilized within 0.5% using a 10-point moving average. The measurement range was considered and found to be 300 mm. Its application to measure roughness was considered by testing the relationship between the measured value and the arithmetic mean roughness as measured by another method. The measured value decreased as the arithmetic mean roughness increased. The determination coefficient R² at a distance of 500 mm was 0.91. The R² at a distance of 1000 mm was 0.79. The results of these experiments show that the underwater ultrasonic wave sensor is an effective tool for underwater.