We develop an idealized experimental system for studying how a small amount of gas can cause large net (rectified) motion of an object in a vibrated liquid-filled housing when the drag on the object depends strongly on its position. Its components include a cylindrical housing, a cylindrical piston fitting closely within this housing, a spring suspension that supports the piston, a post penetrating partway through a hole through the piston (which produces the position-dependent drag), and compressible bellows at both ends of the housing (which are well characterized surrogates for gas regions). In this system, liquid can flow from the bottom to the top of the piston and vice versa through the thin annular gaps between the hole and the post (the inner gap) and between the housing and the piston (the outer gap). When the bellows are absent, the piston motion is highly damped because small piston velocities produce large liquid velocities and large pressure drops in the Poiseuille flows within these narrow gaps. However, when the bellows are present, the piston, the liquid, and the bellows execute a collective motion called the Couette mode in which almost no liquid is forced through the gaps. Since its damping is low, the Couette mode has a strong resonance. Near this frequency, the piston motion becomes large, and the nonlinearity associated with the position-dependent drag of the inner gap produces a net (rectified) force on the piston that can cause it to move downward against its spring suspension. Experiments are performed using two variants of this system. In the single-spring setup, the piston is pushed up against a stop by its lower supporting spring. In the two-spring setup, the piston is suspended between upper and lower springs. The equilibrium piston position is measured as a function of the vibration frequency and acceleration, and these results are compared to corresponding analytical results (Torczynski et al., 2017). A quantitative understanding of the nonlinear behavior of this system may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

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