Experimental Study On Measuring Method Of Sediment Transport Rate Based On Acoustic Principle

The research on the regularity of gravel bed-load movement is of great significance to predict the riverbed evolution,reservoir erosion and siltation,and also to execute waterway regulation and maintenance.Drawbacks of existing methods to observe the natural gravel bed-load movement can be described as difficulty in capturing the dynamic process and obtaining the spatial and temporal distribution of the flow.Those measurement methods are intrusive and restrict the key mechanisms of the gravel movement.Therefore,the development of effective and real-time measurement procedures is essential and urgent in gravel transport research.To date,acoustic method have been widely used to monitor gravel transport at home and abroad.Encouraging preliminary results have been obtained using this method.A few of its main advantages,are that the underwater acoustic signal beneficiates from low attenuation,quick transmission,and long-term continuous sampling.Consequently,further research is called for on the application of this methodology in gravel observation.Here,the underwater multi-target tracking technology,water surface audio frequency method and the Gravel Pressure and Voice Synchronous observation system(GPVS)which are all based on underwater acoustical principle.Those methods have been analyzed with theoretical analysis combined with laboratory test and field measurement.Are presented here the main conclusions of this study.1)A tracking algorithm based on underwater multi-target tracking theory for the location is introduced,simultaneously,itself rationality is confirmed in theory.Nevertheless,the system has several shortcomings that make it unattractive for use in tracking gravel transport,namely high measurement costs,low time resolution,and difficulty in recovering since the transmitters are buried.2)Inhere,an identification technology for gravel bed-load transport by underwater audio recorder is proposed.Only when the total first third order coefficient of energy eigenvector can be brought up to 0.8?1,meanwhile the peak frequency ranges from 1400 to 4000Hz,and the pitch frequency is in the range of 2000?3800Hz,the audio signals can be considered as the gravel transport sound.This method allows for a fast extraction of gravel movement sound from long term complex and noisy audio signals.Compared to the conventional prototype monitoring method,it has a number of advantages:it is reusable,easily set up,interference-free,and can be used for extended periods of time for continuous observation.However,due to the fact that the equipment is far from the river bed and close to the water surface of the water,the signal to noise ratio is very low and the sound of gravel movement is easily masked by the noise of the boat engine during the measurement,resulting in difficulties in the analysis of the raw data,and reduced accuracy of the results.3)The GPVS integrates audio observation system and pressure monitoring system.When the discharge of gravel bed-load is small,the audio system plays a dominant role while the pressure system is ineffective because of low accuracy.In contrast,when the discharge is large enough to cover the device,the audio system fails but pressure system is in charge of all monitoring.Compared to the underwater multi-target tracking method and the water surface audio frequency method,GPVS overcomes the problem of not only environmental noise interference but also the problem of gravel burial,also it can be re-used and at low cost.GPVS achieves the real-time monitoring of the dynamic process of the gravel bed-load transport through transmitting the data synchronously in wired transmission mode.