Investigation of torsional vibration using weak FSI capabilities

To evaluate the condition of the oil in an engine or other lubricant, the fluid's viscosity is one of the most important indicators. In many cases, direct sampling is not an option, and process-integrated sensors are often required. This chapter discusses resonant sensors, which allow for process integration and the measurement of the viscosity of a fluid without sampling. A key aspect of this measurement method is the interaction of the sensor with the fluid. We discuss different modeling methods to describe the fluid–structure interaction of the resonant sensor with the surrounding fluid using a weak coupling. The benefit of weak coupling is that it allows for different approaches when modeling the fluid and structural domains. Within the structural domain, the resonator is described either by a single degree of freedom, multiple degrees of freedom, or as a continuous resonator. The fluid interaction with the resonator is described by two parameters within the structural domain, one for mass loading and the other for damping. These parameters are derived from the flow field surrounding the resonator. We discuss how to derive these parameters and how to compute the flow field. Methods for solving the flow field around simple geometries, such as a flat plate or a cylinder, are discussed. For more complex structures, a numerical approach is presented. In the final section, we describe a method of coupling different structural models and analytical fluid models to describe the fluid–structure interaction of a torsional resonator