Electromechanical Coupling and Signal Distribution of a Circular Cylindrical Shell Coupled With Segmented Sensors

The direct piezoelectric effect has long been recognized as an effective electromechanical coupling effect applied to designs of various transducers. Conventional sensor design usually follows three design principles: 1) the tension/compression design, 2) the bending or flexible design and 3) the shear design. These are mostly point-type transducers monitoring responses of discrete locations and, thus, they are not suitable to dynamic spatial monitoring of large-scale distributed structures, such as shells and plates. Accordingly, distributed designs and configurations, such as the segmentation and shaping techniques, have been proposed and evaluated in the last two decades. This study is to evaluate electromechanical coupling and signal generations of a coupled piezoelectric/elastic circular shell structure. A generic open-circuit signal equation of electromechanical coupling and signal generation is presented first, followed by a simplification to signal generation of a circular cylindrical shell case. The total signal generation and its contributing components are analyzed in the modal domain. Spatially distributed modal signals of various shell modes are calculated and the spatial signal distribution illustrates distinct modal characteristics resulting from microscopic modal strain behaviors. Thus, the optimal sensor location(s) for specific shell modes can be identified from the modal signal distribution plots.

Simulation of Phonon Transmission at Semiconductor Interfaces Using an Atomistic Green’s Function Method

An atomistic Green’s function method is applied to study phonon transport across interfaces between two semi-infinite semiconductors. We investigate the dependence of phonon transmission function on interface atomic configuration, roughness layer thickness and phonon frequency. The transmission function is obtained for a number of interface configurations, including Si/Ge/Si confined structures and a single Si/Ge interface. An interface with a regularly-patterned roughness is investigated to illustrate how the rough interface influences phonon transmission. The results show that the cutoff frequency and the local density of states are modified due to the rough interface. The transmission function is found to strongly dependent on the presence of atomic-scale roughness.

An Experimental Evaluation of Shock Wave Strength and Peak Pressure in a Conventional Shock Tube and a Free-Piston Compressor

The aim of this work is to provide a comparative experimental study on the performance of the conventional shock tube and a free-piston compressor. Experimental measurements of shock strength, peak pressure and surface temperature change of air-air as a driver/driven gas are then presented and compared with another set of experimental measurements using gas combination of He-air. The results provide very good estimates for the above mentioned parameters obtained after diaphragm rupture and also provide significant information on the role of the free piston in the facility operation conditions over the full length of the facility.

A Kinematic/Kinetic Hybrid Airplane Simulator Model

A kinematics-based flight model, for normal flight regimes, currently uses precise flight data to achieve a high level of aircraft realism. However, it was desired to further increase the model’s accuracy, without a substantial increase in program complexity, by determining the vertical velocity and vertical acceleration using EUROCONTROL’s Base of Aircraft DAta (BADA) model [1]. BADA is a well-known aircraft performance database model maintained and developed by EUROCONTROL Experimental Centre in France. The hybrid model uses the BADA algorithm to determine the vertical velocity and gives original results for determining the vertical acceleration. The approximate accuracy of these vertical parameters was checked by comparing them with preexisting test distributions [2] and an in-house flight simulator application. The hybrid model uses kinematic algorithms for all other functions and parameters. To obtain specific results, C code was written to access text data from BADA’s collection of approximately one hundred airplanes. Accessing this database causes an increase in overall program execution time that was deemed acceptable due to the infrequency of changing plane types. Also, by examining many airplane trajectories obtained from different BADA airplanes, we determined that the model is accurate enough to uniquely represent many different types of aircraft.

Thermal Management Using Composite Structures

The continuing increase in integrated circuits (IC) power levels and microelectronics packaging densities has resulted in a need of materials with higher thermal conductivities and new thermal management solution designs. A base plate design that uses integrated metalized dielectric including Aluminum nitride or polycrystalline diamond (PCD) joined to a diamond/Al composite heat spreader with fins or foam attached by a single step casting is proposed. A numerical study of the design parameters is presented and analyzed. The new material and integrated bonding design can be further improved by changing the materials to a diamond/Copper base plate with polycrystalline diamond dielectric and graphitic foams for convective transport.

A Heat Plate Leading Edge for Hypersonic Vehicles

The intense thermal flux at the leading edges of hypersonic vehicles (traveling at Mach 5 and greater) requires creative thermal management strategies to prevent damage to leading edge components. Carbon fiber composites and/or ablative coatings have been widely utilized to mitigate the effects of the impinging heat flux. This paper focuses on an alternative, metallic leading edge heat pipe concept which combines efficient structural load support and thermal management. The passive concept is based on high thermal conductance heat pipes which redistribute the high heat flux at the leading edge stagnation point through the evaporation, vapor flow, and condensation of a working fluid to a location far from the heat source. Structural efficiency is provided by a sandwich construction using an open-cell core that also allows for vapor flow. A low temperature proof-of-concept copper–water system has been investigated by experimentation. Measuring of the axial temperature profile indicates effective spreading of thermal energy, a lowering of the maximum temperature and reduced overall thermal gradient compared to a non-heat pipe leading edge. A simple transient analytical model based on lumped thermal capacitance theory is compared with the experimental results. The low-temperature prototype shows potential for higher temperature metallic leading edges that can withstand the hypersonic thermo-mechanical environment.

A Numerical Study of Geometrical Effects on the Strouhal Number of a Circular Cylinder

In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α = 0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d = 0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α = 0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was increased from zero to 90°, the percentage reduction in Strouhal number decreased; however, as the blade angle was further increased from 90° to 150°, the percentage reduction in Strouhal number increased. Although the modifications studied here decrease the vortex shedding frequency they make the vortices shed from the cylinder farther and stronger hence increasing the magnitude of the fluctuating forces.

Spatial Electrostrictive Modal Actuation of Conical Shells

Horns, nozzles and load carrying structures of rockets, e.g., inter-stage joint, satellite-rocket joint, solid rocket motor case, etc., are usually made of circular conical shell sections. This study is to investigate distributed electrostrictive actuation and to evaluate spatially distributed microscopic control actions of distributed electrostrictive actuator segments bonded on conical shell surfaces. Mathematical model and open-loop control equations of a generic conical shell are defined first, followed by simplification to a free-free truncated conical shell section with segmented electrostrictive actuators. Natural mode shape functions are defined based on the Donnell-Mushtati-Vlasov approximation; independent modal control equation is derived by the modal expansion. Distributed control actions induced by the electrostrictive actuator segments are evaluated in the modal domain and the total control effect can be divided into four microscopic control actions: the longitudinal/circumferential membrane and bending control actions. Detailed parametric analyses of two mode groups indicate that 1) magnitudes of control actions comply with the quadratic increase with respect to control voltages and 2) the circumferential membrane control action is the most dominating component in the total shell control effect. Also, the spatially distributed modal actuation plots can be used to locate the most effective locations and/or regions of electrostrictive actuators placed on the shell surface.

Simulator Validation Results and Proposed Reporting Format From Flight Testing a Software Model of a Complex, High-Performance Airplane

Computer simulations are often used in aviation studies. These simulation tools may require complex, high-fidelity aircraft models. Since many of the flight models used are third-party developed products, independent validation is desired prior to implementation. Due to the variety of processes used by the different industries and organizations that make use of flight models, the proprietary nature of some desired data, the relative availability of data-rich pilot manuals, and their standardized, rigorous nature, formal processes based in experimental and certification flight test are proposed for objectively and consistently validating these models and their associated aircraft types. The results of application of these detailed flight test techniques is then reported using a blade element theory-based flight model with a complex, high-performance aircraft model. Finally, a concise data analysis and reporting format is proposed and demonstrated using this same aircraft model.

Sensitivity Analyses for Viscoelastic Strength of Materials and Corresponding Continuum Mechanics Formulations

Comparison analyses are conducted for straight and curved viscoelastic beams based on Euler-Bernoulli strength of materials prescriptions and on rigorous formulations in terms of 3-D field equations. The concepts of elastic straight and curved beam analyses are well established. In the present paper, these geometric principles are extended to linear viscoelastic materials. The beams are considered subjected to un-symmetric bending as well as to thermal expansions. The distinct conditions leading to shear center and neutral axis motions in time, previously observed in straight beams are investigated. The applicability of the elastic-viscoelastic correspondence principle (analogy) in terms of integral transforms is demonstrated by application to several simulations. Comparison studies are based on pure bending loading configurations as these offer the least distinct geometric deformation patterns.