مطالعه‌ی آزمایشگاهی تاثیر نصب اسپویلر و پیگیبک‌لاین در لوله‌های موازی مستغرق قرارگرفته در بستر فرسایشی تحت جریان یک‌طرفه

استفاده از اسپویلر و پیگیبک‌لاین بر روی لوله، تاثیر بسزایی در کاهش عمق آبشستگی دارد. از این‌رو، در پژوهش حاضر تاثیر موقعیت قرارگیری اسپویلر و پیگیبک‌لاین و هندسه‌ی آن‌ها و همچنین فاصله‌ی بین لوله‌های مستغرق موازی بر عمق آبشستگی زیر لوله‌ها به‌صورت آزمایشگاهی بررسی شده و ﻧﺘﺎﯾﺞ ﻧﺸﺎن داده است که تغییرات گودال آّبشستگی، تابعی از: فاصله‌ی قرارگیری لوله‌ها، زاویه‌ی قرارگیری اسپویلر یا پیگیبک‌لاین، و همچنین موقعیت آن‌ها بر روی لوله‌ است. در حالی که شکل مقطع پس از نصب، تاثیر قابل‌توجهی در گودال آبشستگی ندارد. بیشترین مقادیر آبشستگی در زیر هر دو لوله با افزایش فاصله‌ی لوله‌ها از یکدیگر و قرارگیری اسپویلر و پیگیبک‌لاین در زوایای 180 و 135 درجه رخ داده است. این موضوع در حالی است که با کاهش فاصله‌ی لوله‌ها از هم، کمترین مقادیر آبشستگی در زوایای 90 و 270 درجه اتفاق افتاده است، که می‌تواند به‌عنوان سازه‌ی حفاظتی بررسی شود.

Experimental investigation of the impact of the spoiler and piggyback line on scour holes of the parallel pipe lines under the erodible bed

The bed formations of submarine pipelines models were measured to investigate the effect of design parameters such as the distance between two submarine pipelines and also the effect of adjusted rectangular spoiler due to different angles of adjustment. To investigate the hydraulic parameters, three experimental models of parallel pipelines with three distances were made through the hydraulic laboratory. By considering the threshold velocity, the bed profiles were measured experimentally by employing the point gauge apparatus due to changing the angle of considered spoilers. Results indicate that increasing the distance between two submarine pipelines is the reason why that the downstream scour hole was formed independently from the upstream scour hole, which was developed under the upstream pipelines. Also, due to different angles of spoilers, the scour hole of spoiler with angle 90o formed the same as the witness model (with no spoiler), showing that angle 90o has no marginal effect on scour hole formation process. However, the angle of 180o adjusted on two submarine pipelines made the maximum scour hole under the upstream and downstream pipelines. It is assumed that the spoiler 180o affects the downstream flow of the pipelines and by creating the region with low pressure behind the pipelines, the scour holes were plunged to the bed and the depth of the scour holes increased significantly. Also, the investigation of spoiler position on the two pipe lines illustrates that by adjusting the spoiler on the downstream pipelines, the downstream pipe was buried under the sediment. These conditions were observed by angles of 135o, 180o, and 225o. It is assumed that increasing the distance between two submarine pipelines diminishes the rate of selfburial conditions. It appears that by increasing the distance between two pipelines, the effect of the upstream pipeline was omitted because the downstream and upstream pipelines were scoured as two single pipes; thus, the upstream pipelines did not affect the downstream pipelines.