bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Reformer/Burner Thermal Integration on the Efficiency and Dynamic Response of an Onboard Fuel Processor in an Indirect Methanol Fuel Cell Vehicle
Authors: Ramaswamy Sitaram , Sundaresan Meena , Moore Robert M.
Published: November 2021

Using a fuel other than pure hydrogen in a fuel cell vehicle (FCV) employing a proton exchange membrane (PEM) fuel cell stack typically requires an on-board fuel processor to provide hydrogen-rich fuel to the stack. On board fuel processors that generate hydrogen from on-board liquid methanol (and other Hydrocarbons) have been proposed as possible alternative sources of hydrogen needed by the fuel cell. This paper focuses on a methanol fueled fuel processor that using steam reformation process to generate hydrogen. The reformation process involves a steam reformer and a catalytic burner (which provides the necessary energy for the endothermic steam reforming reactions to occur). This paper focuses on the importance of reformer/burner thermal integration and its impact on the dynamic response of the fuel processor. The model uses MATLAB/Simulink software and the simulation provides results for both dynamic response and energy efficiency.
Experimental Investigation of Convective Melting of Granular Packed Bed Under Microgravity
Authors: Jiang J. , Hao Y. , Tao Y.-X.
Published: November 2021

To improve the understanding of convective melting of packed solid particles in a fluid, an experimental investigation is conducted to study the melting characteristics of a packed bed by unmasking the buoyancy forces due to the density difference between the melt and solid particles. A close-loop apparatus, named the particle-melting-in-flow (PMF) module, is designed to allow a steady state liquid flow under a specified temperature. The module is on board NASA’s KC-135 reduced gravity aircraft for the experiments. In the test module, water is used as the fluid, and ice particles are fed to the test section at the beginning of the test. As the liquid flows though the bed, the solid grains melt. A perforate plate, through which liquid can flow while the ice particles are retained, bounds the downstream of the packed bed. From the digital video images the local packed bed thickness is measured under control flow rate, and the melting rate is determined. The temperature distribution along the horizontal direction and vertical direction is measured using 19 thermocouples. An infrared camera is mounted to record the local temperature variation between liquid and solid. The melting rates are presented as a function of upstream flow velocity, temperature and initial average particle size of the packed bed. It is found that the melting rate is influenced mainly by the ratio of the Reynolds number (Re, based on the initial particle diameter) to the square of the Froud number (Fr), and me Stefan number (Ste). In general, the dimensionless melting rate decreases as Re/Fr2 increases and increases as Ste increases. With the absence of gravity, i.e., Froud number approaches infinity, a maximum melting rate can be achieved for otherwise the same test conditions. The increase in the melting rate with the increase in Stephan number also becomes more pronounced under the zero gravity condition.
Development of an Analytical Model: Tank Pressure Control Experiment
Authors: Albayyari Jihad M. , Subramanya Karteek K.
Published: November 2021

The “Reduced-Fill Tank Pressure Control Experiment (TPCE/RF)” is a space experiment developed to meet the need for a critical aspect of cryogenic fluid management technology: “control of storage tank pressures in the absence of gravity by forced-convection mixing”. The experiment used Freon-113, at near saturation conditions and a constant 40% fill level, to simulate the fluid dynamics and thermodynamics of cryogenic fluids in space applications. The objectives of TPCE/RF were: Characterize the fluid dynamics of an axial jet-induced mixing in low gravity. Evaluate the validity of empirical mixing models, and provide data for use in developing and validating computational fluid dynamics model of mixing processes.

TPCE/RF accomplished all of its objectives in flight on the Space Shuttle flight in May 1996. The flow patterns observed generally agreed with a prior correlation derived from drop tower tests. Several existing mixing correlations were found to provide reasonable performance predictions. Low-energy mixing jets, dissipating on the order of 1% of the kinetic energy of previous mixer designs, were found to be effective and reliable at reducing thermal non-uniformities, promoting heat and mass active mixing, whether continuous or periodic, offers increased reliability and predictability in space cryogenic systems and can be accomplished with no significant boiloff penalty caused by kinetic energy dissipation.
MEMS as In-Vivo Sensors and Actuators: Challenges and Opportunities
Authors: Mahajan Roop L.
Published: November 2021

MicroElectroMechanical Systems (MEMS) is a developing field which promises to open up new fields of applications in such diverse areas as medical systems, wireless communications and space explorations. They are particularly attractive to the medical community for their consistent reproducibility, high levels of accuracy and reliability, and exceptional stability. This is achieved through silicon micro-fabrication techniques conducive to high volume manufacturing at a low cost.
Effects of Showerhead Cooling on Turbine Vane Suction Side Film Cooling Effectiveness
Authors: Ethridge Marcia I. , Cutbirth J. Michael , Bogard David G.
Published: November 2021

The process of film cooling is known to severely disturb the boundary layer around a turbine airfoil. Since most film-cooled airfoils have more than one injection station, the flow field approaching a row of film cooling holes could be altered by the presence of an upstream cooling station. To investigate this possibility, an experimental investigation was conducted on the suction side of a scaled-up turbine vane. Adiabatic effectiveness measurements were made downstream of a single row of cooling holes both with and without the upstream showerhead holes operating. A range of suction side blowing ratios, 0.3 ≤ M ≤ 1.3, were investigated with large-scale mainstream turbulence intensities of Tu∞ = 0.5% and Tu∞ = 21%. The effects of the showerhead coolant were evaluated at an engine-typical showerhead blowing ratio of Msh = 1.6, with three of the six rows of cooling holes in the showerhead directed towards the suction side of the airfoil. Experiments were conducted with a coolant-to-mainstream density ratio of DR = 1.6. An infrared camera was used to obtain spatially-resolved surface temperature measurements, which were corrected for conduction effects and converted to adiabatic effectiveness. The results showed that showerhead coolant had a strong impact on suction side adiabatic effectiveness levels under low mainstream turbulence. Although effectiveness levels increased with the showerhead operating, the suction side coolant jets increased dispersion of the showerhead coolant. Under high mainstream turbulence conditions, there was very little interaction between the showerhead coolant and the suction side coolant jets. Adiabatic effectiveness levels were considerably lower than those for the low turbulence case, which was partially due to increased dispersion of the showerhead coolant upstream of the suction side holes. The superposition model over-predicted adiabatic effectiveness levels under low mainstream turbulence conditions, but was very effective in predicting the combined performance of the showerhead and the suction side cooling holes under high mainstream turbulence conditions.
Implementation Issues in Artificial Neural Network Based Thermal Analysis
Authors: Yang K. T.
Published: November 2021

It is now known the generally it can be demonstrated that artificial neural network (ANN), particularly the fully-connected feedforward configuration with backward propagation error-correction routine, can be a rather effective and accurate tool to correlate performance data of thermal devices such as heat exchangers (Sen and Yang, 2000; Kalogirou, 1999). Good examples are the recent demonstrations for the compact fin-tube heat exchangers (Diaz et al., 1999a; Yang et al., 2000; Pacheco-Vega et al., 1999) including those with complex geometries and also two-phase evaporators (Pacheco-Vega et al., 2000) as well as the dynamic modeling of such heat exchangers and their adaptive control (Diaz et al., 1999b; Diaz et al., 2000). Unfortunately, despite such successes, there are still implementation issues of the ANN analysis which lead to uncertainties in its applications and the achieved results. The present paper discusses such issues and the current practices in dealing with them. Those that will be discussed include the number of hidden layers, the number of nodes in each hidden layer, the range within which the input-output data are normalized, the initial assignment of weights and biases, the selection of training data sets, and the training rate. As will be shown, the specific choices are by no means trivial, and yet are rather important in achieving good ANN results in any given application. Since there are no general sound theoretical basis for such choices at the present time, past experience and numerical experimentation are often the best guides. However, many of these choices and issues relating to them involve optimization. As a result. Some of the existing optimization algorithms may prove to be useful and highly desirable in this regard. The current on-going research to provide some rational basis in these issues will also be discussed. Finally, it will also be mentioned that successfully implemented ANNs have many additional uses in practice. Examples include parameter sensitivity analysis, training, design of new experiments, and clustering of data sets.
Laser Processing of Silica Aerogels Using Ultrashort Pulses
Authors: Sun J. , Longtin J. P. , Norris P. M.
Published: November 2021

Silica aerogels are unique nanostructured materials that possess many distinctive qualities, including extremely low densities and thermal conductivities, very high surface-area-to-volume ratios, and large strength-to-weight ratios. Aerogels, however, are very brittle, and are not readily shaped using traditional machining operations. Ultrafast laser processing may provide an alternative for precision shaping and machining of these materials. This paper discusses investigations of ultrafast laser machining of aerogels for material removal and micromachining. The advantages of ultrafast laser processing include a minimal thermal penetration region and low processing temperatures, precision removal of material, and good-quality feature definition. In this work, an amplified femtosecond Ti:sapphire laser system is used to investigate the breakdown threshold, material removal rate, and specific issues associated with laser processing of aerogels, as well as recommendations for further investigations for these unique materials.
Thermal Transport During Seeding and Shouldering in the Czochralski Crystal Growth
Authors: Saha A. K. , Zhang H. , Prasad V.
Published: November 2021

Czochralski (Cz) growth during seeding and shouldering of silicon single crystal has been studied. During seeding, the diameter increases from a small value to the desired value of the fully-grown crystal. The convection in the melt, conduction in the crystal and radiation from the melt surface and crystal, surface tension at the free surface of the melt and crystal rotation have been considered to investigate the effect of seeding on thermal transport. The rotational Reynolds number, the radiation from the crystal and Marangoni number are varied to investigate their effect on the interface shape. A few selected cases have been studied using a cylindrical crystal to understand the effect of geometry on the heat transfer rate and subsequently on the interface shape. The governing equations are solved using the curvilinear finite volume discretization scheme and the grids are redistributed using the multizone adaptive grid generation after each iteration. The movement of free surface is taken care by employing suitable equations for energy and stress balance. Results show the dependency of both the radiation from the crystal and rotation of the crystal on the interface shape.
Electrohydrodynamic Induction Pumping of a Stratified Liquid/Vapor Medium in the Presence of Heat Transfer
Authors: Brand K. , Seyed-Yagoobi J.
Published: November 2021

The effect of heat transfer on the performance of the EHD induction pumping of a liquid/vapor stratified medium is theoretically investigated. The analytical domain considered is represented by a two-dimensional developing plane channel flow of a liquid separated from a vapor by a horizontal interface in a channel bound from below and above by two infinite rigid boundaries. The electrodes generating the electric traveling wave are placed at the bottom of the liquid film. The liquid temperature is assumed constant at the interface of liquid/vapor media while the liquid is cooled or heated at the lower boundary. The dimensionless numerical results are obtained for three different dimensionless wall heat fluxes representing no heat transfer, cooling, and heating at the lower boundary. The controlling parameters include: vapor height, liquid height, voltage, wavelength, and frequency. For the selected operating conditions, the performance of the pump increases with increasing wall heat flux.
Mass Transfer Process of Gaseous Carbon Dioxide Into Water Jet Through Orifice Mixing System
Authors: Zheng Y. H. , Amano R. S.
Published: November 2021

This paper summarizes the mass transfer modeling that can simulate the process of gaseous carbon dioxide dissolution into water in an orifice mixing system. In order to establish the operating characteristics of the orifice mixing system, ordinary tap water and pure carbon dioxide were used as the liquid-gas system. Using the model, computations were performed for an orifice mixing system to better understand the mass transfer process of gaseous carbon dioxide into water through both the elbow tube and the junction Venturi-tube. All computed results show different performance of the carbon dioxide dissolution rates for the given inlet water and carbon dioxide conditions of the four different designs of the junction type Venturi-tubes and an orifice mixing system. After examining the computed results it was found that the mass transfer efficiency of gaseous carbon dioxide into the water stream through the orifice mixing system was superior to that through the junction Venturi-tubes.
Simulation of Micro-Scale Jet Impingement Heat Transfer
Authors: Boeschoten Paul A. , Pence Deborah V. , Liburdy James A.
Published: November 2021

The heat transfer performance of a micro-scale, axisymmetric, confined jet impinging on a flat surface at high Mach numbers (0.2 to 0.6) and low Reynolds numbers (419 to 1310) was computationally studied. The flow is characterized by Knudsen numbers, based on the jet radius, large enough (0.0013) to warrant slip-flow boundary conditions at the impinging surface. The effects of Mach number, compressibility, and slip-flow on heat transfer results are presented, along with the local Nusselt number distributions, and velocity and temperature fields near the impingement surface. Results for uniform wall heat flux show that the wall temperature decreases with increasing Mach number, with a local minimum at r/D = 0.7. The slip velocity also increases with Mach number with peak values also near r/D = 0.7. The resulting Nusselt number increases with increasing Mach number, and a local maximum in the Nusselt number is observed at r/D = 0.6, not at the centerline. In general, compressibility improves heat transfer due to increased fluid density near the impinging surface. Also, inclusion of slip-velocity increases the rate of heat transfer. However, the accompanying temperature-jump condition at the wall is found to reduce the local heat transfer rate. The net effect of the slip-flow boundary conditions applied in this study was an overall reduction in heat transfer.
Numerical Analysis of Buoyancy-Induced Flow and Heat Transfer in an Enclosure With Vents
Authors: Calmidi V. V. , Sathe S. B.
Published: November 2021

This paper reports a numerical study of buoyancy-induced flow and heat transfer in an enclosure with vents. The geometry closely resembles a “set-top-box” application frequently encountered in electronics cooling applications. The heat generating module is modeled as a planar heat source placed on a conducting printed circuit board (PCB). Full 3D and simplified 2D conjugate heat transfer models accounting for conduction and radiation in the solids and conduction and convection in the fluid were used Experiments performed to validate the 3D model have shown excellent comparisons with numerical results. A parametric study involving vent size, power dissipation, number of high conductivity power planes in the PCB has been performed with both the 3D and the 2D models. Although the quantitative results obtained from both types of analyses are similar only under certain conditions, qualitatively, the 2D analysis can be used to obtain useful insights into the complex overall transport mechanisms.
Large Eddy Simulation of Naturally Induced Fire Whirls in a Vertical Square Channel With Corner Gaps
Authors: Farouk B. , McGrattan K. B. , Rehm R. G.
Published: November 2021

Naturally occurring fire whirls are rare but highly destructive phenomena. These are mostly generated by the interaction between a buoyant fire plume and its surroundings. The whirling motion generated can enhance the plume length and sustain burning. In this paper, we report the results of a numerical investigation of whirling fires generated in vertical square channels with symmetric corner gaps. The numerical investigations of swirling fire plumes are used to analyze how the corner gaps alters the plume dynamics and combustion. An approximate (low Mach number) form of the Navier-Stokes equations is solved to calculate the mixing and transport of combustion products. Large scale eddies are directly simulated and sub-grid scale motion is represented with a Smagorinsky model. The current approach is based on a fixed heat release rate, regardless of the strength of the whirl generated by the corner slots. The effect of corner slot widths and their configuration on the swirling motion are studied systematically for a given channel geometry and fixed fuel-loss rate.
Monte Carlo Simulation for Radiometric Temperature Measurement in Rapid Thermal Processing
Authors: Zhou Y. H. , Shen Y. J. , Zhang Z. M. , Tsai B. K. , DeWitt D. P.
Published: November 2021

This work employs a Monte Carlo method to study the radiative process in a rapid thermal processing (RTP) furnace. A “true” effective emissivity, accounting for the directional optical properties, is defined and predicted in order to determine the wafer temperature from the measured spectral radiance temperature using light-pipe radiation thermometry. The true effective emissivity is the same as the hemispherical effective emissivity for diffuse wafers, in which case the Monte Carlo model gives the same results as the net-radiation method. Deviations exist between the hemispherical effective emissivity and the true effective emissivity for specular wafers because the effective emissivity is directional dependent. This research will help reduce the uncertainty in the temperature measurement for RTP furnaces to meet the future requirements for integrated circuit manufacturing.
Large Eddy Simulation of Rotating Channel Flows With and Without Heat Transfer
Authors: Meng Ning , Pletcher Richard H.
Published: November 2021

Large eddy simulation of rotating channel flow with and without heat transfer is reported. The rotation axis is parallel to the spanwise direction of the parallel plate channel. An implicit finite-volume scheme was used to solve the preconditioned time-dependent filtered Navier-Stokes equations using a dynamic subgrid-scale model to account for the subgrid-scale effects. Comparisons are made with available results in the literature for isothermal rotating flows. The combined effects of rotation and heat transfer on the structure of turbulence channel flow is discussed.
Viscosity Effects on the Propagation of Acoustic Transients
Authors: Gaunaurd G. C. , Everstine G. C.
Published: November 2021

The propagation of an impulsive excitation applied at the origin of a lossy viscous medium is studied by operational techniques as the excitation advances through the medium. The solution of the governing partial differential equation (PDE) for such transient propagation problems has been elusive. Such solution is found and quantitatively examined here using a one-dimensional model in space and time. As expected, as the transient advances through space, its amplitude decreases, and its width broadens. Such is the damping effect of viscosity that one would anticipate from elementary considerations in related disciplines such as electrodynamics. Such is also the smoothing-out effect of dispersion. We also obtain an approximate solution of the present boundary-initial value problem based on the method of steepest descents. This approximation agrees with the first term of the complete analytic solution given here. The pertinent dispersion relation associated with the governing parabolic PDE is shown to impose a restrictive condition on the allowable values of the propagation speed and the kinematic viscosity coefficient, thus assuring that propagation with attenuation does take place. Various numerical results illustrate and quantitatively describe the propagation of the transient pulse in several nondimensional graphs.
Implementation of Local, High-Order Accurate Boundary Conditions for Time-Dependent Acoustic Scattering
Authors: Thompson Lonny L. , He Dantong , Huan Runnong
Published: November 2021

A sequence of high-order accurate radiation boundary conditions involving local differential operators of auxiliary functions on a circular boundary are implemented in a spectral finite element method with mixed time integration. The semi-discrete finite element equations are integrated explicitly in time while the auxiliary functions on the circular boundary are integrated using a semi-implicit time-integration method. An efficient algorithm results which avoids the need to update either the solutions for the field variable or the boundary functions at intermediate time steps. Using this mixed time integration approach, a very natural and efficient implementation of the high-order accurate, local boundary conditions is obtained without altering the local/sparse character of the finite element equations. Numerical studies of time-dependent scattering from an elliptic object demonstrate the rapid convergence and accuracy of the implementation.
Possibilities for a Silicon Model of the Cochlea
Authors: Steele Charles R. , Fitzgerald Alissa , Kenny Thomas , Lim Kian-Meng , Puria Sunil
Published: November 2021

The purpose of this study is to resolve questions regarding the fundamental physical behavior of the cochlea of the inner ear. We seek a convergence of measurement and computation on physical models that capture essential features. Since there are unique features in the performance of the cochlea, the physical models could lead to device development. A much longer-term goal is a device for the assistance of hearing impaired individuals. The cochlea can be modeled as a tube of fluid divided by a partition, a portion of which is elastic and called the basilar membrane (BM). In preliminary work, the cochlear partition is constructed on a silicon wafer using current capabilities for micro-machining. The silicon nitride partition is inserted into a chamber of Plexiglas which is filled with solute and has a “stapes” for acoustic input and a “round window”. The silicon BM has the correct length, but is wider and isotropic. The measurements, supported by calculations, show that the deviation from the actual structure has a detrimental effect on the sharpness of the spatial distribution of the response for a fixed input frequency. Possibilities for improved models and for an active non-linear model with distributed sensors and actuators are discussed.
Photoacoustic Leak Testing
Authors: Yönak Serdar H. , Dowling David R.
Published: November 2021

Leak testing is a critical manufacturing quality control process. Unintended leaks in pressurized or evacuated containers may be detrimental to consumers, manufacturers, and/or the environment. This paper describes a leak detection and localization technique based on photoacoustic sounds produced by scanning a carbon dioxide laser over leaks emitting a photoactive tracer gas, sulfur hexaflouride. Photoacoustic signals are recorded in a bandwidth from 3 up to 110 kHz by multiple microphones. From these recorded signals, the presence or absence of a leak may be deduced by comparison with background noise levels. When a leak is present, its location is determined from a simple model of the acoustic environment and matched field processing (MFP). Current results show that a gas leak of 1 cm3 per day can be detected and localized to within ±1 mm in a few seconds using four microphones placed 0.41 m from the leak location and an incoherent average of the MFP ambiguity surfaces at twelve signal frequencies.
The Features of Flow in a Parallel-Walled Radial Vaneless Diffuser
Authors: Abidogun K. B. , Ahmed S. A.
Published: November 2021

Detailed experimental investigation of flow features in a parallel-walled radial vaneless diffuser of a centrifugal blower was carried out. Maximum flow rate through the blower, at a constant impeller speed of 1500 rpm, was maintained throughout the experiment to ensure that no self-exited flow oscillation occurs in the diffuser. The symmetrical flowfield in the diffuser was measured along a radial path using an X-wire probe. The radial and tangential velocity distributions and their statistics, as well as flow angle distribution, are reported. The results presented in this paper agree well with earlier work on this subject. For instance, the flow angle at half the diffuser width, which is the position at which critical flow angle (measured from the radial direction) have been generally reported to be about 78°, did not exceed 65° from the diffuser inlet to its outlet along the measurement path. The result also showed that the flow exiting the impeller is skewed as revealed by the triple velocity product correlations. This data is a useful tool for vaneless diffuser calculation model developers as there are very limited data that paralleled the current one as expounded in the text of this paper.
Effect of Foam Core Density and Facesheet Thickness on the Low Velocity Impact Response of Foam Core Sandwich Composites
Authors: Motuku M. , Rodgers R. M. , Jeelani S. , Vaidya U. K.
Published: November 2021

The effect of foam core density and facesheet thickness on the low velocity impact response and damage evolution in homogeneous foam core sandwich composites was studied. The failure characteristics, initiation and evolution of damage as well as the effect of impact energy were investigated. A Dynatup 8210 Impact Test Machine was utilized to conduct the low-velocity impact tests. Characterization of the impact response was performed by comparing the impact load histories, impact plots and failure characteristics. Fractography analysis was conducted through the use of scanning electron microscopy (SEM) and optical microscopy. Three types of foam cores with different densities, namely Airlite B12.5, Rohacell IG-71R63 and Airex R63.5 foam cores, were used to study the effect of core density. Considering four groups of facesheets made of different layers of cross-ply carbon prepregs performed the effect of facesheet thickness.

For all the facesheet thicknesses (0.011-0.894-cm thick) and impact energy (11-40 J) range considered in this study, the maximum load (Pm), deflection-at-maximum load (δm) and time-to-maximum load (tm) exhibited strong influence or dependence on the type of foam core as opposed to the facesheet thickness. The energy-to-maximum load (Em), total energy absorbed (Et) and total energy-to-impact energy (Et/Eimp) ratio became less sensitive on the foam core density (or type) with increasing facesheet thickness. A transition point from foam core to facesheet controlled impact behavior as a function of impact energy level was observed. The impact parameters varied either linearly or parabolically with impact energy depending on the impact energy level, type of foam core and facesheet thickness. Excellent repeatability of impact data was generally obtained with increase in foam core density.
Aspects of Strain Rate Effects on Some Composite Materials
Authors: Ayorinde Emmanuel O.
Published: November 2021

Effects of moderate straining speed on the material and damage characteristics of beam samples of graphite/epoxy and E-glass/epoxy composites were investigated. The basic fiber architecture utilized was unidirectional, axial layup, but data was also obtained for the 45-degree orientation. Ultrasonic and acoustic emission (AE) inspections were utilized. The acoustic emission records show matrix cracking. The ultrasonic images revealed the regions of failure. The results show that in general, strain rate notably affects material and damage properties.
Damping Properties of Vapor-Grown Carbon Fiber Composites
Authors: Finegan Ioana C. , Tibbetts Gary G. , Gibson Ronald F.
Published: November 2021

The objective of this paper is to investigate analytically and experimentally the dynamic mechanical properties of vapor grown carbon fiber (VGCF)/thermoplastic composites. The experimental results show that, as predicted, very low fiber aspect ratios may produce significant improvements in damping. Since VGCF have submicron diameters and lengths, with a fiber aspect ratio, l/d = 19, good dynamic properties are obtained by using them as reinforcement in a thermoplastic. Fiber length distributions and orientation in the injection molded samples are determined by scanning electron microscopy (SEM). An analytical model based on the elastic-viscoelastic correspondence principle is developed to predict elastic properties in short fiber composites having a preferential fiber orientation in the direction of injection. The mechanical damping and storage modulus are analyzed experimentally by using a Dynamic Mechanic Analyzer (DMA).
Acoustic Microscopy for Bone Characterization
Authors: Kundu Tribikram , Jorgensen Claus
Published: November 2021

Characterization of animal bones by acoustic microscopy is a relatively new field of research. Non-uniformity of bones requires a complete analysis of the interaction between the focused acoustic beam and the bone specimens for its characterization. The complete analysis produces the V(z) curve taking into account the lens angle and the elastic properties of the bone. V(z) oscillations may be generated by surface skimming Rayleigh waves and/or P-waves in different parts of the bone depending on the bone properties. In this paper after a short review of different applications of the acoustic microscopy technique a complete theory of the V(z) curve synthesis is briefly presented. A number of V(z) curves are analytically generated following this theory. These curves sometimes show a regular oscillatory shape as predicted by the simple ray theory. However, often the synthesized V(z) curves show irregularities. The synthesized V(z) curve for silicon has been compared with the experimental results to have a confidence on the analytical computation. Then additional numerical exercises are carried out to understand why sometimes the V(z) curve shapes are irregular, and whether the P-wave speed and/or the Rayleigh wave speed of the material can be extracted from such irregular shaped V(z) curves. After understanding the V(z) phenomenon the wave speeds at different points of a bone are experimentally measured from its V(z) curves.
Comparison of the Flame Characteristics of Circular and Elliptic Jets in a Cross-Flow
Authors: Gollahalli S. R. , Pardiwalla D.
Published: November 2021

This study was directed to understand the coupling effects of the noncircular geometry of the burner and a cross-flow on the combustion of gas jets. This paper compares the characteristics of propane jet flames from circular (diameter = 0.45 cm) and elliptic (major axis = 0.75 cm, minor axis = 0.26 cm) burners of equivalent exit area in a cross-flow. The elliptic burner was oriented with its major axis or minor axis aligned with the cross-flow. Experiments were conducted in a wind-tunnel provided with optical and probe access and capable of wind speeds up to 12.5 m/s. The burners were fabricated with metal tubes. Instrumentation included a Pt-Pt/13%Rh thermocouple, a quartz-probe gas sampling system, chemiluminescent and non-dispersive infrared analyzers, a video-recorder, and a computer data acquisition system. The measurements consisted of the upper and lower limits of jet velocity for a stable flame, flame configuration, and visible length. Flame structure data including temperature profiles and concentration profiles of CO2, O2, CO, and NO were obtained in a two-zone flame configuration where a planar recirculation exists in the wake of the burner tube followed by an axisymmetric tail. Emission indices of CO and NO were estimated from the composition data. Results indicate that the upper and lower limits of the fuel jet velocity increase with the cross-flow velocity for all burners, and the rate of increase is highest for the elliptic burner with its minor axis aligned with the cross-flow. That burner configuration also produces the longest flame. The emission indices show that the CO production is lower and NO production is higher for elliptic burners than for circular burners in cross-flow. Also, aligning the minor axis of the elliptic burner with the cross-stream is superior in terms of flame stability and emissions of NO and CO.
Simulation of Methanol Combustion in the NIST Reference Spray Combustor
Authors: Crocker D. Scott , Giridharan M. G. , Widmann John F. , Presser Cary
Published: November 2021

This paper describes the simulation of a methanol spray flame in the NIST reference spray combustion facility, which was predicted using a state-of-the-art, unstructured-mesh CFD code. The code solves the gas-phase equations in an Eulerian frame using the finite-volume approach while the droplet equations are solved in a Lagrangian frame. This paper focuses on the sensitivity of the predicted flame structure to the model boundary conditions, to ensure matching of the simulation to the experimental conditions. The combustor uses a simplex pressure-jet atomizer to produce a hollow-cone spray with a cone angle of 60°. The overall equivalence ratio of the baseline operating condition is 0.29. The spray initial conditions are specified from the measurement data obtained close to the atomizer. For this case, several simulations were performed with different initial and boundary conditions. The parameters that were varied from the baseline case included the air swirl velocity, equivalence ratio, spray droplet size distribution, and a pre-exponential kinetic constant. The results indicate that the existence of a central recirculation zone is sensitive to the location and rate of heat release. The predicted flame structure appears to be in reasonable agreement with NIST flame visualization. The fuel conversion is predicted to be 100 % whereas the data indicates a conversion of 80 %. This discrepancy is attributed to the uncertainty in spray initial conditions, especially for the droplet size distribution.
Size Scale Dependence of Deformation in NiTi
Authors: Gall Ken , Dunn Martin L. , Liu Yiping , Labossiere Paul , Sehitoglu Huseyin , Chumlyakov Yuriy I.
Published: November 2021

Recent work [1-5] has suggested that a lucrative future for shape memory materials such as NiTi is in the area of micro-electro-mechanical systems (MEMS). To design MEMS and predict their behavior during service, we must have quantitative information on the mechanical properties of scaled down NiTi materials. One way of obtaining the mechanical properties of scaled down materials is with unique MEMS testing fixtures. Although this approach is favorably analogous to macroscopic testing techniques it is not always feasible owing to the difficulty of handling the microscopic samples. Many smart material actuators are deposited thin films [1-5] and separating the films from their substrate and subsequently testing them is beyond our current MEMS processing and handling tools. An alternative method to quantify the properties of microscale materials is through micro-indentation, which has been previously applied to NiTi polycrystals [6]. Although micro-indentation is simple to accomplish, interpretation and quantification of the results is not as straightforward, as will be demonstrated in this work.
Stress Induced Martensitic Transformation in Shape Memory Alloys Studied by In-Situ Neutron Diffraction Techniques
Authors: Šittner P. , Novák V. , Lukáš P. , Neov D.
Published: November 2021

Shape memory alloy (SMA) elements are being embedded in smart materials and hybrid composites as actuating and/or sensing elements responding to the stress and temperature stimuli. In order to design smart composites, in-situ experimental information about evolution of internal stresses and phase fractions in the embedded SMA elements and internal stresses in neighboring matrix during actuation cycles would be of interest. Such experimental data have to be obtained nondestructively from the microscopic particles or fibres deep in the bulk specimens exposed to stress and/or thermal variations. In-situ neutron diffraction experimental techniques fulfill in principle these requirements. However, reliable evaluation of internal stresses from neutron diffraction experiments in the smart SMA composites can be made only after the lattice plane responses of monolithic SMAs in thermomechanical cyclic loads are fully understood. In this paper, the results of the in-situ investigations of stress induced martensitic transformation (SIMT) in tensile tests carried out on monolithic CuAlZnMn SMA polycrystal are reported, and the observed lattice plane responses are interpreted using a selfconsistent model of SMA polycrystal.
Power Consumption for Active Acoustic Control of Launch Vehicle Payload Fairings
Authors: Griffin Steven F. , Lane Steven A. , Leo Donald J.
Published: November 2021

Vibroacoustics during space vehicle launch has been blamed for as many as 60% of first day satellite failures. At the Air Force Research Laboratory in Albuquerque NM USA, modeling and analysis was performed to determine the feasibility of monolithic piezoceramic actuators and active acoustic control to reduce noise transmission during launch of the OSP launch vehicle with a hypothetical composite fairing. Voltage, power and energy were studied as a function of transmission reduction. The conclusion reached for the case explored in depth was that off-the-shelf monolithic piezoceramic actuators did not have sufficient control authority to reduce noise transmission at realistic sound levels.
Mechanical Characterization and Design of Shape Memory Alloy Composites for Functionally Graded Adaptive Structures
Authors: Bruck Hugh A. , Moore Charles L.
Published: November 2021

Shape Memory Alloys (SMAs) are being embedded in smart structures for sensing and actuation. The resulting structure is a composite material that possesses a heterogeneous architecture, requiring a system-based approach to optimize its design. In order to develop this approach, it is necessary to determine appropriate thermomechanical models for designing heterogeneous smart structures. In this investigation, the constitutive and actuation behavior of SMA wire-reinforced epoxy composites are charaacterized. A structural model is then verified for predicting the actuation behavior of functionally graded adaptive structures fabricated from SMA composites.
MR Fluid Sponge Materials and Devices
Authors: Carlson J. David , Chrzan Michael J.
Published: November 2021

Stable, high-strength, magnetorheological (MR) fluids and devices such as rotary brakes and linear vibration dampers that enable the benefits of controllable fluid technology are now commercially available. Recently, a new way of using MR fluids in which the fluid is contained in an absorbent matrix has been developed. Such MR fluid sponge devices enable the benefits of controllable MR fluids to be realized in cost sensitive applications. Most of the high-cost components normally associated with a fluid filled device can be eliminated with this approach. Low-cost, controllable MR fluid sponge dampers are particularly appropriate for moderate-force vibration control problems where a high degree of control authority is desired such as a new generation of high-performance, home washing machines now being developed.
Estimation of Soil Resistance Using a Strain Gauge Array
Authors: Adamchuk Viacheslav I. , Morgan Mark T. , Sumali Hartono
Published: November 2021

A vertical smooth blade with an array of strain gauges was designed to continuously measure mechanical resistance of soil at multiple depths. As the blade (tapered cantilevered beam) cuts through the soil, strain gauges detect deformation caused by varying soil resistance. Recorded strain data was used to estimate resistance pressure at different depths that cause the same deformation of the blade with known geometry and material properties. Verification of the analytical solution was performed in the laboratory by applying varying combinations of static loads, and numerically by finite element modeling. Field tests involved on-the-go measurement of integrated resistance pressures that were compared to cone penetrometer readings obtained from corresponding spots within the field.
Distributed Piezotransducers for Damage Detection
Authors: Kawiecki Grzegorz
Published: November 2021

The purpose of this paper is to show the feasibility of applying neural networks and arrays of piezotransducers for condition monitoring of basic structural components. It is shown that simple neural networks can be used to interpret damage-related anomalies in signals transferred between elements of a piezotransducer array. These relatively low frequency signals in the 0 Hz–1 kHz range carry enough information to determine damage location and size with a reasonable accuracy. The feasibility of a neural network-based expert system for signal processing is shown using a simple closed-form model of a thin, homogeneous vibrating plate. A new type of a rosette piezotransducer is presented. This type of a piezotransducer can generate and sense complex strain fields containing more damage-related information.
Dielectric Response of Adaptive Piezoelectric Sensoriactuators
Authors: Vipperman Jeffrey S. , Li Deyu
Published: November 2021

This paper closely examines the nature of the dielectric response of piezoceramics that are used as Adaptive Piezoelectric Sensoriactuators (APSAs). Firstly, it is demonstrated that he APSA possesses real time structural health monitoring abilities, based on the capacitance measurement of the piezoceramic. Secondly, nonideal behavior including lossy, hysteretic, and field dependence is measured in the piezoceramics and a method mitigating some of this response in the Adaptive Piezoelectric Sensoriactuator is proposed.
Nonlinear Coupled Transverse and Axial Vibration of a Compliant Structure: Free and Forced
Authors: Han Seon M. , Benaroya Haym
Published: November 2021

A compliant tower in the ocean environment is modeled as a beam undergoing coupled transverse and axial motion. The beam is supported by a torsional spring and has a point mass at the other end. It is assumed that the strains are small but the rotation is moderate compared to the strain so that the equations of motion for the axial and transverse motion are nonlinearly coupled. The nonlinear coupled equations of motion are derived here using Hamilton’s principle. The forced responses due to random waves are observed here. The responses are obtained numerically using the finite difference approach.
Non-Standard Reduction of Noisy Structural Systems: Shallow Arches
Authors: Vedula Lalit , Sri Namachchivaya N.
Published: November 2021

The dynamics of a shallow arch subjected to small random external and parametric excitation is invegistated in this work. We develop rigorous methods to replace, in some limiting regime, the original higher dimensional system of equations by a simpler, constructive and rational approximation – a low-dimensional model of the dynamical system. To this end, we study the equations as a random perturbation of a two-dimensional Hamiltonian system. We achieve the model-reduction through stochastic averaging and the reduced Markov process takes its values on a graph with certain glueing conditions at the vertex of the graph. Examination of the reduced Markov process on the graph yields many important results such as mean exit time, stationary probability density function.
Stability of High-Speed Milling
Authors: Insperger Tamás , Stépán Gábor
Published: November 2021

The stability charts of high-speed milling are constructed. Non-conventional unstable regions and vibration frequencies are identified. These are related to flip bifurcation, i.e. period doubling vibrations occur apart of the conventional self-excited vibrations typical for turning or low-speed milling with multiple active teeth. A new stability criterion is proposed and applied for the delayed parametric excitation model of milling.
Optimization of Gearshifting in Automatic Transmissions
Authors: Haj-Fraj Ali , Pfeiffer Friedrich
Published: November 2021

A method for the optimization of gear shift operations in automatic transmissions is proposed in this paper. Based on a mechanical model of the power train the control parameters for the clutch pressure as well as those for the load-reduction are optimized in order to improve the performance of the automatic transmission with respect to passengers comfort and gear shift duration. Scalar criteria, which are capable of describing these effects are formulated. The nonlinear optimization problem is solved with a sequential quadratic programming algorithm. The results show a significant improvement in terms of the optimization criteria.
On the Coupled Flap-Lag Bending Vibration of Propeller Blades: An Exact Dynamic Finite Element Formulation
Authors: Hashemi S. M. , Richard M. J.
Published: November 2021

An exact Dynamic Finite Element (DFE) approach for the coupled Flap-Lag vibration of blades is presented. DFE can be considered as a combination of the Finite Element Method (FEM) and the Dynamic Stiffness Matrix (DSM) formulations. The weighted residual method is used and the weighting and shape functions are chosen referring to the appropriate closed form solution of the non-coupled member equations. Based on the DFE approach, the natural frequencies for a scaled propeller blade are calculated and they are compared to the experimental data and other existing results.
Hydroadhesive Gripping by Using the Peltier Effect
Authors: Seliger Günther , Stephan Jörg , Lange Stephan
Published: November 2021

The automated handling of non-rigid sheet material, especially wovens, has to meet the requirements of damage free gripping independently of the material behavior. In this paper, a survey of different physical principles for grippers is given. Hydroadhesive gripping with frozen water as active medium has been selected as the most promising approach. Based on this principle, a novel hydroadhesive gripper prototype has been developed. The gripping process has been mathematically and numerically modeled and validated by experimental results. The analytical method enables to calculate the process parameters like gripping time, Peltier-Module geometry as well as holding forces in designing for implementation.