The Fluid-Structure Interaction, Fixed Geometry multiphysics coupling could be added in versions earlier than 5.4. It has been superseded by an augmented version of the Fluid-Structure Interaction multiphysics coupling. The node will still be present and functional in models originally created in previous versions. It is however recommended that you update to the new way of modeling fixed geometry problems, as the Fluid-Structure Interaction, Fixed Geometry node may not be supported in the future.