Coupling a Fluidic Flexible Matrix Composite (F2MC) to an air-pressurized fluid port produces a fundamentally new class of tunable vibration isolator. This device provides significant vibration reduction at an isolation frequency that can be tuned over a broad frequency range. The material properties and geometry of the F2MC element, as well as the port inertance, determine the isolation frequency. A unique feature of this device is that the port inertance depends on pressure so the isolation frequency can be adjusted by changing the air pressure. For constant port inertance, the isolation frequency is largely independent of the isolated mass so the device is robust to changes in load. A nonlinear model is developed to predict isolator length and port inertance. The model is linearized and the frequency response calculated. Experiments agree with theory, demonstrating a tunable isolation range from 9 Hz to 36 Hz and minimum transmitted force reductions of 90% at the isolation frequency.

This paper presents a novel Tuned Vibration Absorber (TVA) using Fluidic Flexible Matrix Composites (F2MC). Fiber reinforcement of the F2MC tube kinematically links the internal volume with axial strain. Coupling of a fluid-filled F2MC tube through a fluid port to a pressurized air accumulator can suppress primary mass forced vibration at the tuned absorber frequency. 3-D elasticity model for the tube and a lumped fluid mass develops a 4th-order model of an F2MC-mass system. The model provides a closed form isolation frequency that depends mainly on the port inertance, orifice flow coefficient, and the tube parameters. A small amount of viscous damping in the orifice increases the isolation bandwidth. With a fully closed orifice, the zero disappears and the system has a single resonant peak. Variations in the primary mass do not change the isolation frequency, making the F2MC TVA robust to mass variations. Experimental results validate the theoretical predictions in showing a tunable isolation frequency that is insensitive to primary mass variations, and a 94% reduction in forced vibration response relative to the closed-valve case.

Replacing rigid pitch links on rotorcraft with coupled fluidic devices has the potential to reduce the aerodynamic blade loads transmitted from the blade root to the swashplate. An analytical model of two coupled fluidic isolators is derived and experimentally validated for even and odd harmonic pitch link loads. The system consists of two elastomeric pumpers with fluid chambers that are coupled by an inertia track. This passive fluidic device can be tuned to reduce the transmitted force at a particular odd harmonic of the rotor speed by tailoring the fluid inertance in the inertia track. Benchtop experimental results agree with theory, demonstrating a reduction in odd harmonic pitch link loads of up to 90% compared to the system without fluid. The coupled fluidic isolators also significantly reduce transmitted loads relative to a rigid pitch link over a wide frequency range. Simulation of a UH-60 Blackhawk retrofit example shows potential for targeted odd harmonic excitation loads reduction up to 94% for multiple frequencies without affecting the even harmonic excitation response.

This paper investigates passive and semi-active vibration control using fluidic flexible matrix composites (F2MC). F2MC tubes filled with fluid and connected to an accumulator through a fixed orifice can provide damping forces in response to axial strain. If the orifice is actively controlled, the stiffness of F2MC tubes can be dynamically switched from soft to stiff by opening and closing an on/off valve. Fiber reinforcement of the F2MC tube kinematically relates the internal volume to axial strain. With an open valve, the fluid in the tube is free to move in or out of the tube, so the stiffness is low. With a closed valve, however, the high bulk modulus fluid resists volume change and produces high axial stiffness. The equations of motion of an F2MC-mass system are derived using a 3D elasticity model and the energy method. The stability of the unforced dynamic system is proven using a Lyapunov approach. A reduced-order model for operation with either a fully open or fully closed valve motivates the development of a zero vibration (ZV) controller that suppresses vibration in finite time. Coupling of a fluid-filled F2MC tube to a pressurized accumulator through a fixed orifice is shown to provide significant passive damping. The open-valve orifice size is optimized for optimal passive, skyhook, and ZV controllers by minimizing the integral time absolute error cost function. Simulation results show that the optimal open valve orifice provides a damping ratio of 0.35 compared with no damping in closed-valve case. The optimal ZV controller outperforms optimal passive and skyhook controllers by 32.9% and 34.2% for impulse and 34.7% and 60% for step response, respectively. Theoretical results are confirmed by experiments that demonstrate the improved damping provided by optimal passive control F2MC and fast transient response provided by semi-active ZV control.

Tuned vibration absorbers have been shown to reduce the forced vibration response at a specific frequency for many applications. This paper presents a novel absorber using fluidic flexible matrix composites (F2MC). Fiber reinforcement of the F2MC tube kinematically links the internal volume with axial strain so that fluid flows in and out of an axially vibrating tube. Coupling of an F2MC tube through a fluid port to a pressurized air accumulator produces a novel absorber that can suppress vibration at the tuned absorber frequency. A 3-D elasticity model for the tube and a lumped model for the fluid mass produce a fourth-order F2MC-mass model. The analytical closed-form isolation frequency is derived and shown to depend primarily on the port inertance, orifice flow coefficient, and the tube parameters. Viscous damping in the orifice can be adjusted to reduce the resonant peak and broaden the isolation bandwidth. With a fully closed orifice, the zero disappears and the system has a single resonant peak. For a constant port inertance, variations in the primary mass do not change the isolation frequency, making the F2MC absorber robust to mass variations. Experimental results validate the theoretical predictions by demonstrating a tunable isolation frequency that is insensitive to primary mass variation as well as a 94% reduction in forced vibration response relative to the closed-valve case at the isolation frequency.