Fluid–structure–acoustic Interaction, Algorithms and Implementations Using the Finite Element Method

An advanced Finite Element Method is presented which is being applied to simulate fluid flow interacting with a soft structure. Furthermore, the generated sound from fluid flow and structural mechanics is also taken into account. To get a correct model for the acoustic source terms resulting from the fluid flow Lighthill’s analogy is applied, while structural mechanics is coupled to acoustics via the common interface. As a result we have a coupling between fluid flow, structural mechanics and acoustics. While we assume the acoustics has no back reaction neither on the fluid nor on the structure, fluid and structure influence each other in a strong sense. Therefore, additionally to the non–linearity arising from the Navier–Stokes equations the strong coupling yield a further non–linearity, which needs to be tackled. Different kind of iterative algorithm can be applied to solve the problem, like the relaxation according to Aitken. A further challenge is the mesh deformation which occurs due to the movement of the structure. We apply an Arbitrary Lagrangian Eulerian (ALE) approach. Dealing with all three physical fields, their interactions and the above mentioned difficulties is very costly concerning computational time and therefore we limit ourselves to 2d simulations. The resulting algorithms are implemented in the research code CFS++ and find its application in simulating the human phonation process, a prefect example since all mentioned physical fields and their interactions are present. Due to airflow through the trachea, generated by compression of the lungs, the vocal folds, positioned inside the larynx, start to vibrate. The vibration in turn causes the airflow to pulsate, which generates the main frequency of the human voice, the so called phonation.