Study On Mechanics Of Bionic Deposit-enhancement And Scour Prevention For Underwater Pipeline Protection

Underwater pipelines, widely used as marine/river transportation tools for oil and gas, are exposed to water flow which may cause scour and wreckage. Every year there are many pipes crashed caused by scouring. Therefore, it is quite necessary and very important to study the anti-scour methods for underwater pipeline protection. Based on flume tests, this paper studies characteristics of vegetation flow, explores the motion mechanics of water and sediment nearby plant-mattress which covered pipes and discusses the effectiveness of scour prevention of artificial plant-mattress for underwater pipeline protection.Experiments were designed for fixed-bed and alluvial bed, respectively. Flow structure and the changes of bed roughness under the conditions of submerged plants in a uniform open flume with fixed-bed are experimentally studied. It was measured in this experiment that the vertical flow velocity distribution with plants belonged to approximately S-type. A turning point occurred at the top of the plant layer. The vertical velocity distribution did no longer sitisfay with the original logarithmic distribution, which was complexly affected by the plants and the external environment. The presence of submerged plants increased the flow gradient, hence the bed roughness became larger to resist flow. The correlation between the non-dimensional plant density and plant characteristics roughness is analyzed according to the experimental data. A logarithm relationship between the plant drag force and the plant characteristics roughness is established.In the alluvial-bed flume, a variety of experiments were conducted for artificial plant-mattress pipe erosion protection, the bed erosion/deposition and flow characteristics were experimentally observed around the underwater pipeline with biomimetic plant mattress. This paper describes the phenomena of the pipe erosion prevention, analyzes sediment motion nearby the plant-mattress, and discusses the influence of Fr number, pipeline diameter on the erosion/deposition around the pipeline. Using Levy's formula for sediment incipient criterion, the critical velocity of sediment motion was calculated, the scour protection mechanism of plant-mattress was discussed. It is obtained from the experiments that the lay of artificial plant-mattress can effectively prevent the erosion around the underwater pipeline. The scour protection effectiveness of artificial plant-mattress may be impacted by the marine environments and mattress material property.Finally, for the application of artificial bionic plants in the underwater pipeline scour protection and sediment deposition promotion, this paper presents several ideas for designers and discusses applicable conditions and methods in engineering practice.