Frequently Asked Questions (FAQ) and Common Errors

  1. “Invalid Particle” error stops the simulation

    This error can appear when running actuator-based turbine simulations coupled to OpenFAST. AMR-Wind uses particles to keep track of actuator points, and the positions of these points are determined by the turbine model. If the velocity field in AMR-Wind becomes huge or unrealistic (e.g., not a number), then the turbine model can return bad particle positions that do not fit into the AMR-Wind domain. If this error stops your simulation, check the velocity field leading up to the error to determine if something went wrong there. If the velocity field is faulty, reevaluate your problem setup.

  2. The simulation will not start and the code outputs many lines from the input file

    This happens when a required input file argument is missing. Because AMReX outputs this error from every process, and the error message lists all of the lines found in the input file, it can be a lot of text to sort through for bigger cases. Search for the string “ParmParse” within the output text to locate the expected input argument that is missing from the input file so that it can be added.

  3. There are many different source terms related to buoyancy or gravity. What do they do and when should they be used?

    The basic buoyancy term often included in ICNS.source_terms is BoussinesqBuoyancy. This source term calculates buoyancy based on the difference between the local temperature and a reference temperature, which can be a field or a uniform constant, based on the physics setup of the simulation. The resulting buoyancy term is proportional to the thermal expansion coefficient (\(\beta\)).

    When an ABL simulation that has BoussinesqBuoyancy as a source term has a pressure_outflow boundary condition, the source term ABLMeanBoussinesq should also be added. This source term helps offset the pressure field using a mean temperature profile to be compatible with the pressure boundary conditions. If this source term is omitted, nonphysical behavior can appear as the flow nears the pressure outflow boundary, especially where thermal stratification occurs.

    When the MultiPhase physics module is active, the GravityForcing source term should be used. This source term calculates the force of gravity based on the local density. Because temperature variations do not cause significant density variations in water, this source term is essential for capturing the effect of gravity in a multiphase flow. Adding the input line ICNS.use_perturb_pressure = true formulates GravityForcing as a perturbation from a reference density field. This makes the source term compatible with pressure_outflow conditions as well as other perturbational buoyancy terms. For example, a multiphase ABL case would need BoussinesqBuoyancy activated to include the buoyancy effects of temperature in the air, would potentially also need ABLMeanBoussinesq activated if a pressure outflow is being used, and would also need GravityForcing to capture gravity effect on the water with perturbational pressure turned on.