Stationary waves measured in sand transport pipes

Dredge pipeline systems are an essential part of operations. Pipeline systems consists of straight pipes and diverse components which may influence transport conditions more than only locally. For efficient dredging operations it is important to reliably predict hydraulic losses in hydrotransport. Local flow may deviate from the uniform equilibrium conditions covered by available models for hydrotransport. The datasets upon which these models are calibrated could also be biased by data of flows which were actually not in uniform equilibrium. It is the objective to explore the extent of such conditions in hydraulic transport. This paper concerns the first results of experimental research into the influence of pipe diameter on transients in hydraulic transport of sand. Results of laboratory experiments on the flow of concentrated sand-water-mixtures downstream of 180 degree bends are described. A novelty is the measurement and analysis of the extent of waves in a 80 m long straight section of 300 mm diameter pipe situated in the CCCC National Engineering Research Center of Dredging Technology and Equipment (NECRD) laboratory in Shanghai. To quantify the extent of transient processes, the full length of this straight section of pipe is equipped with an extensive array of pressure sensors. The occurrence of stationary harmonic waves after a disturbance is confirmed for larger pipelines than utilized in previous research in Delft and Prague. Measured longitudinal pressure profiles reveal stationary standing waves in the heterogeneous transport regime. This indicates that the velocities and cross-sectional area occupied by bed and suspension vary over distance. These waves are the strongest in the sliding bed regime close to the deposit limit velocity. This is exactly in the operating range of dredge pipelines. Typical wave lengths are of the order of 40 to 60 pipe diameters. The impression is that a broad grain size distribution may reduce the severity of wave formation. This needs to be investigated further in addition to extending the sand concentration range and a variation of median grain size.