COUPLED 2025

Efficient Techniques For Barely Coupled Multiphysics

  • Lohner, Rainald (George Mason University)
  • Cebral, Juan (George Mason University)
  • Antil, Harbir (George Mason University)
  • Schoeps, Sebastian (TU Darmstadt)

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Over the last five decades computational mechanics has matured rapidly. In each of the core disciplines - fluid dynamics, structural dynamics, combustion, heat transfer, acoustics, electromagnetics, mass transfer, control, etc.- robust and efficient numerical techniques have been developed, and a large code base of academic, open source and commercial codes is available. The acquisition of many of these commercial codes by the leading CAD-vendors attests to the desire to streamline the typical computational mechanics workflow (CAD, definition of boundary conditions, loads and physical parameters, solution, mesh adaptation, post-processing) by integrating all parts into a single application. Many coupled problems exhibit large disparity of timescales. Examples include evaporative cooling (where the flowfield may be established in seconds while the temperature field requires minutes, see Figure below), sedimentation of rivers and estuaries (where the flowfield is established in seconds while the filling up of a channel takes weeks), deposition of cholesterol in arteries (where the flowfield is established after two heartbeats while the deposition can take years), the wear of semi-autogenous grinding (SAG) mills (where the movement of steel balls and mineral-rich rocks and mud is established in minutes while the wear of the liners can take hours), and many others. We denote this class of problems as `barely coupled'. In each of these cases a coupling is clearly present. However, due to physics and nonlinear effects one can not simply run with a fully coupled time discretization using very large timesteps. This would lead to incorrect results. It then becomes very costly to run in a strictly time-accurate manner. The recourse advocated here is to run each problem to a quasi steady-state, and to couple the different disciplines in a loose manner. This approach also offers the possibility of coupling different software packages (in-house, open source or commercial) in an easy manner. The final paper will describe this approach in detail, and give options and measures as to when a switch from one code/field to another is needed.