Tuning of centrifugal pendulum vibration absorbers operating in a fluid

The subject of linear and nonlinear tuning of centrifugal pendulum vibration absorbers operating in a fluid is addressed. These absorbers are used to reduced engine order torsional vibrations in rotating machinery, and they are often housed in a rotating enclosure filled with a fluid, an important example of which is the automotive torque converter. The pressure field in the rotating fluid generates an effective buoyancy on the pendulum mass, thereby affecting its oscillation frequency. This effect is well known for simple pendulums operating in a static fluid under gravity and is herein generalized to the case of a finite-sized centrifugal pendulum operating in a rotating fluid. A sample shape for the pendulum absorber is considered in detail, showing how the expected results from a simple, small-volume absorber are generalized to account for more realistic geometries. The main results are expressed in terms of kinematic parameters for the path of the pendulum that allow one to tune the small- and large-amplitude dynamics of the absorber. The tuning depends on the ratio of the fluid density to the absorber material density and a pair of dimensionless parameters that account for the absorber shape. It is also shown that tuning that ignores the fluid can lead to ineffective, even adverse, operation of the pendulum absorber.