An ER Microactuator with Built-in Pump and Valve

The paper presents a 3-DOF microactuator having a Fluid Inertia (FI) micropump and ER microvalves for in-pipe working micromachines of about 10 mm in diameter, and so on. The ER microvalve controls an Electro-Rheological Fluid (ERF) flow due to the apparent viscosity increase in the electric field. The FI micropump generates high-output-fluid power using the fluid inertia effect in an outlet pipe. First, the 3-DOF ER microactuator with built-in pump and valves was proposed, and its construction was clarified. Second, in order to pump high viscosity fluids such as ERFs, a multi-reed valve was proposed for the inlet check valve of the FI micropump. The characteristics of the newly-devised pump were clarified through simulation and experiments. Then, based on the results, a 10 mm-diameter FI micropump was successfully developed. Finally, in the first stage of this study, a 1-DOF valve-integrated ER microactuator was designed and fabricated. The validity of the actuator with the fabricated 10 mm-diameter FI micropump was experimentally confirmed.

Aeroelastic Flutter of a Rotating Disk in an Unbounded Compressible Inviscid Fluid

The aeroelastic flutter of an unbaffled flexible disk rotating in an unbounded fluid is investigated, by modeling the disk-fluid system as a rotating Kirchhoff plate coupled to irrotational flow of a compressible inviscid fluid. The fluid motions are governed by the wave equation of linear acoustics. Fluid-structure coupling is achieved between the disk and the fluid by means of the fluid loading on the disk and the velocity matching boundary conditions on the disk surface. A perturbed eigenvalue formulation is used to compute systematically the coupled system eigenvalues. A series solution is presented for the dual integral equations, arising from the mixed boundary value problem governing the fluid motions. It is found that two distinct aerodynamic effects occur — radiation damping into the surrounding fluid and added fluid inertia effect. Provided the disk has zero material damping, the radiation damping causes the flutter speed to coincide with the critical speed. This flutter instability is a degenerate bifurcation with eigenvalues crossing into the right half plane through the origin with zero speed. The added fluid inertia effect modifies the frequencies of the traveling waves but does not affect the critical speed.