Unmanned Aerial Vehicles (UAVs) have gained popularity over the past few years to become an indispensable part
of aerial missions that include reconnaissance, surveillance, and communication [1]. As a result, advancements in
small jet-engine performance are needed to increase the performance (range, payload and efficiency) of the UAV.
These jet engines designed especially for UAV's are characterized by thrust force on the order of 100N and due to
their size and weight limitations, may lack advanced flow control devices such as IGV [2]. The goal of the current
study was to present a conceptual design of an IGV smart-material based actuation mechanism that would be simple,
compact and lightweight.
The compressor section of an engine increases the pressure and conditions the flow before the air enters the
combustion chamber [3]. The airflow entering the compressor is often turbulent due to the high angle of incidence
between engine inlet and free-stream velocity, or existing atmospheric turbulence. Actuated IGV are used to help
control the relative angle of incidence of the flow that enters the engine compressor, thereby preventing flow
separation, compressor stall and thus extending the compressor's operating envelope [4]. Turbine jet- engines which
employ variable IGV were developed by Rolls Royce (Trent DR-900) and General Electric (J79).
The interest in synthetic-jet actuators is elicited by their employment in fluid-control applications, including boundary-layer
control, combustion control etc. These actuators are zero net-mass-flux devices, and generally consist of a
diaphragm mounted to enclose a volume of fluid in a cavity. The diaphragm bends sinusoidally, and fluid is periodically
absorbed into and ejected from the cavity through an orifice. The outflow entrains the fluid around it and establishes a
mean jet flow at some distance from the source. Piezoceramic materials have been employed to drive the actuator
diaphragm, especially when actuation frequencies are in excess of a few hundreds of hertz. The piezoceramic is glued
directly to a silicon diaphragm. In combustion systems, improved turbulent mixing of air and fuel proper can
significantly improve efficiency and reduce pollution. In boundary-layer separation control applications, synthetic-jets
are used to improve aerodynamic performance by delaying separation and stall over the airfoil. The current work
describes the modeling and design process of a piezoceramic-driven synthetic-jet actuator intended, amongst other
applications, to improve the aerodynamic characteristics of a specific airfoil. A separate study consisting of numerical
analyses performed with the aid of computational fluid dynamics (CFD) have been run to define the necessary
performance parameters for the synthetic-jet actuator. The synthetic-jet actuator design task was achieved by running
fluid-structure numerical analyses for various design parameters.
Space and weapon delivery systems contain guidance components and payload that need to be protected from the extremely harsh acoustic excitation present during launch operations. The above example represents just one application where high-damping viscoelastic materials are used in the design of shock and vibration isolation components. The shock transients generally encountered are characterized by a broad frequency spectrum. Widely available finite element codes do not offer the proper tools to model the frequency- dependent mechanical properties of viscoelastic materials over the frequency domain of interest. An added difficulty is the large Poissson's ratio exhibited by some of these materials, which indicates that previously developed displacement-based finite element formulations should be complemented with mixed pressure-displacement finite element formulations. A pure displacement-based finite element generally predicts the displacements well, if the mesh used is fine enough, but the same thing may not be said about the values of the predicted stresses. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency-dependence of material properties within a time-domain finite element framework and using a mixed displacement-pressure finite element formulation. Finite elements based on this new formulation are developed.
Synthetic-jet actuators have been intensely studied recently. The interest in these devices is elicited by their usefulness in fluid-control applications, including boundary-layer control, combustion control etc. A synthetic-jet actuator is a zero-net-mass-flux device, and is comprised of a diaphragm mounted to enclose a volume of fluid in a cavity. The diaphragm bends sinusoidally, and fluid is periodically absorbed into and ejected from the cavity through an orifice. The outflow entrains the fluid around it and establishes a mean jet flow at a distance from the source. Piezoceramic materials have been used to drive the vibrating diaphragm, where the piezoceramic is glued directly to a silicon diaphragm. In combustion systems, improved turbulent mixing of air and fuel proper can significantly improve efficiency and reduce pollution. In boundary-layer separation control applications, synthetic-jets are used to improve aerodynamic performance by delaying separation and stall over the airfoil. The current work describes the modeling and design of a single-crystal piezoceramic-driven synthetic-jet actuator, and demonstrates that the efficiency of the actuator increases when single-crystals piezoceramic materials are used instead of the more conventional polycrystalline piezoceramics.
Space systems comprise sensitive electronics and delicate mechanical instruments that need to be protected against harsh vibration and shock loads encountered during launch or landing. High damping viscoelastic materials are often used in the design of geometrically complex, shock and vibration isolation components. Since shock transients are characterized by a broad frequency spectrum, and since viscoelastic materials are characterized by frequency-dependent mechanical properties, it is necessary to properly model this behavior over the frequency domain of interest. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency-dependence of material properties within a time-domain finite element framework. A solid, four-node tetrahedron, ADF-based finite element is developed for single and multiple ADF. This particular element is then validated and used for the general purpose of investigating damping in given structures that employ viscoelastic materials. The new three-dimensional finite element may also be used to investigate the potential phase dependence of the Poisson's ratio for such materials. The model predictions are compared against theory.
The development of a new class of devices for the suppression of structural vibration becomes possible by exploiting the unique properties of single crystal piezoceramics. These vibration absorbers will be compact, robust, and demand minimal power for operation. They will be characterized by frequency agility, which means that the absorber tuning parameters can adapt rapidly to controller command and tuning can be accomplished over a wide frequency range. Identified applications include control of turbomachinery vibration, flexible space structures, jitter control in optical systems, and vibration isolation in machinery mounts. The current state of the art adaptive vibration absorber tuning range is fundamentally limited by the electromechanical coupling of presently available polycrystalline piezoceramic materials. The narrow tuning range characteristic of current vibration absorbers severely limits the implementation of the solid-state absorber concept. This work presents efforts related to the design of vibration absorbers that use the single-crystal piezoceramic large electromechanical coupling to achieve greatly enhanced tuning over a wide frequency range. Absorber electromechanical coupling-coefficients greater than 50% were obtained. Design issues specifically related to the use of single crystals in vibration absorbers were identified and addressed. Several device configurations were analyzed and tested. Good agreement was observed between analytical and experimental results.
KEYWORDS: Wave propagation, Finite element methods, Motion models, Matrices, Neon, 3D modeling, Signal attenuation, Thermodynamics, Particles, Data modeling
Sensitive mechanical or electrical components often require protection from the potentially damaging effects of vibration and shock loading. High-damping viscoelastic materials are usually used in the design of impact-absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material parameters over the frequency range of interest. The Anelastic Displacement Fields (ADF) method is used to incorporate frequency-dependence within a finite element formulation. This method considers the effect of material anelasticity on the displacement field, as opposed to directly modeling physical damping mechanisms. ADF-based, plane-stress, and plane-strain finite elements are developed in order to facilitate the modeling of complex viscoelastic structures. The governing equations and assumptions underlying the various finite element developments are presented. In this paper, corresponding finite element models are used to model shock propagation and absorption through viscoelastic beams. The model predictions are validated against wave propagation theory, which shows that ADF-based finite element models are capable of capturing wave propagation phenomena, such as geometric dispersion, and viscoelastic attenuation and dispersion of longitudinal waves in beams. The behavior of mechanical filters in realistic shock conditions is also investigated. ADF three-dimensional finite element models could thus be successfully employed to design mechanical filters, or compare the benefits of using one viscoelastic material over another for a given shock-mitigating task.
The primary purpose of this paper is to present a conceptual design for an adaptive materials driven actuator, to be used for rotorcraft retreating blade stall control. The displacement of a single induced strain actuator is hydraulically amplified and the resulting output displacement is used to actuate a split-flap. Such an actuator is designed to produce high displacements through high amplification factors. The actuator design procedure is presented for a sample case. The required actuator force, displacement and amplification are computed. The effects of the flap deployment on the performance of the helicopter are not presented.
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