Force interaction of offshore pipelines with frozen permafrost in the coastal zone of shelf

In the coastal zone of the Arctic shelf near the coast may development sediment subaqueous permfrost surrounding. Such areas can occur freezing of sediment surrounding around offshore pipeline to transport the pumped product, even if not more negative temperatures. When freezing of the soil is cryogenic (frosty) swelling, which may lead toa change in horizontal and vertical position of the offshore pipeline with the appearance of additional longitudinal (axial) stress, affecting operational reliability of the pipeline. The proposed analytical expressions to determine the stresses in the wall of the offshor epipeline allow with sufficient for engineering calculations accuracy and with minimum time spent to evaluate the stress-strain state of the offshore pipelines at the stage of pre-project developments in freezing of subaqueous permfrost surrounding in the coastal zone of the Arctic shelf.
Materials and methods
Based on the solution of a differential equation of the bent axis of the pipeline using the methods of computer algebra using standard operators and packages environment Mathematica 5.2 was derived analytical expressions for determining the stresses in the wall of the offshore pipeline. To assess the accuracy of engineering calculations was the mathematical modeling of the system behavior of the pipeline-soil using the finite element method, as implemented in standard program Ansys Mechanical 14.0.
Results
The calculated values for determining the change of the full longitudinal and equivalent stresses in the wall of offshore pipeline depending on type of pumped-over product, the overlying soil layer and the height of the heaving soil in the frosty heaving of subaqueous permfrost in the coastal zone of the Arctic shelf are given.
Сonclusions
1. On the basis of the received analytical expressions for offshore pipelines it is carried out research stress-strain state of the offshore pipeline in the frosty heaving of subaqueous permfrost in the coastal zone of the Arctic shelf.
2. Analytic expressions are obtained with sufficient for engineering calculations accuracy and with minimum time spent can be recommended to determine the stresses in the wall of an offshore pipeline at a stage of predesign research.