Research on a Rapid Calculation Method for External Unsteady Temperature Field of Long-Distance Buried Pipelines

Summary During the transportation process of long-distance buried pipelines, the medium inside the pipeline and the semi-infinite soil space outside form a 3D unsteady heat transfer system. When simulating dynamic operational processes, the pipeline is modeled as a 1D system, thereby rendering the calculation of the external 3D unsteady soil temperature field the primary computational effort in overall simulations. Traditional analytical methods are unable to characterize the complex problem of 3D unsteady temperature fields, while numerical calculation methods have the problem of slow calculation speed. In this paper, we propose a rapid calculation method for unsteady temperature fields. Using the superposition principle and the Duhamel principle, the boundary conditions are decomposed to obtain the auxiliary problem. A proxy solution is constructed to represent the auxiliary problem, and the unsteady temperature field is rapidly solved by superimposing the proxy solution with the original boundary conditions. Compared with numerical methods, the new method improves the calculation speed of the global temperature field outside a single pipeline by 21 times. For the critical temperature field near the pipeline, which directly affects the overall heat transfer coefficient, the calculation speed is improved by 120 times, with a maximum temperature error of no more than 0.15°C across the entire domain and period. The method also applies to more complex scenarios, such as parallel double pipelines. This approach provides an accurate and efficient solution for calculating the external unsteady temperature field of long-distance buried pipelines, offering significant engineering application value.