Modelling of dynamic behavior of sub-marine pipelines subject to wave motion

Marine outfall systems are composed of submarine pipeline transmitting wastewater, diffusers and pumping system. Diffusers generally replaced at the end of pipeline have the multiports at certain intervals and diameters to discharge wastewater by dilution. They can be also built as laid freely on sea bottom, suspended at the artificial weights and buried under the sea bottom.At first stage of design, internal flow of wastewater and energy level arising with pumping must be calculated as its energy will be consumed at end of diffuser. The volume of water to be discharged from multiports has been increasing with gradually and wastewater progress toward its end with decreasing volume after passing each channel. Internal constant velocity corresponding to the decreasing volume of water causes varying gradually and incrementally cross section of pipe. The fundamental flow parameters such as internal pressure, velocity and energy at any point of diffuser can be calculated. External pressure induced by wave motion should be considered while getting these parameters. Wave pressures and flow parameters are differentiated by wave teories. Here the linear wave theory is considered. The external reaction forces result from reducing cross section of pipe and reacting water jet to be discharged by using impuls and momentum equations. Such forces, varying with time, on diffuser cause being dynamic effects. In this situation, vibration of diffuser together with the dynamic analysis should be studied. This analysis can be performed by the Single and Multi-Degree of Freedom system (the SDOF and MDOF system).In this study, diffuser, having cross sections varying gradually and incrementally, due to wave motion is analyzed by using the SDOF system. Dynamic analysis for diffuser alternatives relating on sharp-edged and multiple ports designed by burying in soil and resting freely on sea bottom, their vibrations and displacement equation varying with location and time for any point on diffuser are computed. The dynamic solution of the problem are performed both Single-Degree of Freedom System by analytically and Time History Analysis with SAP2000 software by numerically.Key words; Wastewater Diffusers, Wastewater Discharges, SDOF System in Submarine Pipelines, Wave-Diffuser-Soil Interaction.