Razvan Rusovici

A Coupled Field Finite Element Modeling Procedure for Design of a Synthetic-Jet Actuators

The development and validation of a modeling procedure used for design of piezoceramic-driven, SJAs, which is based on ANSYSTM FE software, is described. This approach holds the advantage over others in that it fully couples the complex physical interactions among the structure of the actuator, the working fluid, and the driving piezoelectric actuation. The procedure employed was two FEMs: one used a fully coupled acoustic-structural-piezoelectric, while the other used a fully coupled fluid-structure-piezoelectric field formulation. The acoustic-structural-piezoelectric model was useful in that it was used to predict quickly the acoustic and structural resonant frequencies of the actuator device for rapid design. While the fluid-structural-piezoelectric model was more computationally expensive than the acoustic-structural-piezoelectric model, it was superior in that it provided insight into transient synthetic-jet output velocity time and spatial dependence, displacement, and structural stress time histories. This procedure allows investigation of actuator design and of fluid dynamics of synthetic-jets. The models’ predictions were compared to experimental data obtained for a sample actuator configuration and good agreement was found. Both FEMs were defined for an axisymmetric, single-diaphragm piezoelectric actuator, but the procedure may be extended to other actuator geometries.

A finite element parametric study of clavicle fixation plates.

A finite element simulation on a fracture fixated clavicle was performed to study the effects of different fracture fixation parameters on the callus region. Specifically, parameters such as plate material, thickness, plate/bone gap, screw length, and locking vs. non-locking screws were explored. Plate thickness and locking vs. non-locking screws were found to be influential to construct stiffness where plate/bone gap and number of screws were not as sensitive.

Finite Element Modeling, Validation and Parametric Investigations of A Retinal Reattachment Stent

A new retinal reattachment surgical procedure is based on a stent that is deployed to press the retina back in place. An eye-stent finite element model studied the strain induced by the stent on retina. Finite element model simulations were performed for several stent geometric configurations (number of loops, wire diameter, and intraocular pressure). The finite element model was validated against experiment. Parametric studies demonstrated that stents could be successfully designed so that the maximum strain would be below permanent damage strain threshold of 2%.

Experimental Modal Analysis Study of a Standing Soldier and Rifle System

The response of the human body to shock and vibration has been a subject of interest to many researchers in the aerospace and automotive industry. In a new study, an experimental modal analysis of a rifle-armed, standing soldier in a standard firing position was performed. The purpose of the study was to determine the modes of vibration of the soldier-weapon system in order to gain an understanding of its response during the firing event. The weapon firing accuracy, especially during closely-repeated semi-automatic or fully-automatic fire, as well as the energy transmitted to the body of the soldier depend not only on the weapon itself but also on the soldier body’s dynamic characteristics. Rapid weapon fire does not allow a soldier to consciously control muscles needed to bring back the weapon to its original position, so the weapon location after each fire is influenced more by the dynamic characteristics of the human-rifle system. The experimental modal analyses were performed using multi-averaged, impact-force and electrodynamic shaker force excitation (mainly sine sweeps) and roving triaxial acceleration response at various locations on the body. It was observed that testing of human subjects poses significant difficulties since an increasing number of measurement averages could lead to muscle fatigue and ensuing tremors that could negatively influence coherence. The soldier stance during the tests could also change due to the unconscious need to adjust to a more comfortable body position. The positioning of the accelerometers was difficult since attachment could be made to skin only. While there was in general large variability in soldier size, mass and body strength, the study allowed the identification of some lower modes of interest which appeared to have the same mode shape, albeit at different frequencies, for all the various individuals tested. The signals were acquired with a National Instruments hardware and processed using ModalView software. For an average size soldier the first mode occurred at approximately 2 Hz. The first mode shape exhibited combined bending (backward) and twisting characteristics which are generally seen in a “up and to the right” motion of a right-shoulder held weapon during firing. More modes in the 0–20 Hz range were identified.

Design of Retinal Stent using Finite Element Analysis

The motivation for the herein presented research stems from a new retinal reattachment procedure, which consists of carefully pressing the detached retina tissue into place via a shape memory alloy (SMA) and self-expanding stent. The initial study described in this article focused on modeling the mechanical interaction among stent and neighboring human eyeball tissues: retina, choroid and sclera. The study was performed via finite element analysis (FEA). The tissues were modeled with either hyperelastic or linear elastic material models in order to predict strain distributions on retina and the rest of the eye tissues due to stent placement. The FEA model included the following eyeball tissue: retina, choroid, sclera, cornea, zonular fibres, lens, and ciliary muscle. The simulations, shown for a sample stent configuration, have shown that the strain distribution developed due to stent placement was below levels which would induce permanent retina damage at the stent location. The simulations have shown that, by assuming that the retina was subjected to physiological internal ocular pressure (16.5 mmHg) in parallel to stent pressure (2200 Pa), the retinal strain reached a maximum of 2.67% , which was below a permanent damage strain threshold of 3.3%.

FINITE ELEMENT MODELING OF HUMAN CLAVICLE UNDER DYNAMIC LOADING

Clavicle fractures are common injuries that may from dynamic events such as falls or blunt-body trauma. Methods of repair may be non-operative, or surgical. Surgical repair is accomplished via fixation plates or intramedullary rods. The research investigated the use, and prediction accuracy, of advanced material models within a finite element framework to predict dynamic stresses and strains within the clavicle body which would be subjected to a dynamic load. The material models used were considered to be viscoelastic and orthotropic. The proposed finite element models were successfully verified against experimental results available in literature. The models were then used to predict the timevarying stresses and strains within the clavicle as a result of arbitrarily-chosen, short-impact dynamic loading. A comparison of predictions, corresponding to each material model, was performed.

Design of Retinal Stent Using Finite Element Analysis

The retina is a light-sensitive tissue layer that lines the inside of the eye and relays visual information directly to the brain via the optic nerve. Retinal detachment occurs when the retina is lifted or pulled from its physiological location. This condition can result in partial or total vision loss. Retinal detachmentis a leading cause of permanent vision loss.Copyright

Smart actuation of inlet guide vanes for small turbine engine

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 UAVs 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 compressors operating envelope [4]. Turbine jet- engines which employ variable IGV were developed by Rolls Royce (Trent DR-900) and General Electric (J79).

DESIGN OF A PIEZOCERAMIC-DRIVEN SYNTHETIC-JET ACTUATOR FOR AERODYNAMIC PERFORMANCE IMPROVEMENT

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.

Investigations on the development of a mixed displacement-pressure formulation for an anelastic displacement-field finite element

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 Poisssons 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.