bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotating Stall Acoustic Signature in a Low-Speed Centrifugal Compressor: Part 1—Vaneless Diffuser
Authors: Lawless P. B. , Fleeter S.
Published: May 2009

An experimental study is performed to identify spatially coherent pressure waves, which would serve as precursors to the development of an instability in the Purdue Low-Speed Centrifugal Research Compressor when configured with a vaneless diffuser. To achieve this, sensitive electret microphones were uniformly distributed around the circumference in the inlet and diffuser sections of the compressor. Fourier analysis of simultaneously sampled data from these microphone arrays was employed to identify the development of dominant spatial modes in the pressure field in the compressor. The transition to stall was observed to be a gradual process, with the growth of the pressure waves into those corresponding to a large-scale stall condition occurring over a time span of 26 impeller revolutions. The excitation of the pressure waves, as indicated by spatial Fourier analysis, occurred 14 impeller revolutions before small changes were evident in the microphone signals, and 26 revolutions before the stall condition could be considered fully developed.
Mean Streamline Aerodynamic Performance Analysis of Centrifugal Compressors
Authors: Aungier R. H.
Published: May 2009

Aerodynamic Performance prediction models for centrifugal compressor impellers are presented. In combination with similar procedures for stationary components, previously published in the open literature, a comprehensive mean streamline performance analysis for centrifugal compressor stages is provided. The accuracy and versatility of the overall analysis is demonstrated for several centrifugal compressor stages of various types, including comparison with intrastage component performance data. Detailed validation of the analysis against experimental data has been accomplished for over a hundred stages, including stage flow coefficients from 0.009 to 0.15 and pressure ratios up to about 3.5. Its application to turbocharger stages includes pressure ratios up to 4.2, but with test uncertainty much greater than for the data used in the detailed validation studies.
Heat Transfer Measurements on Turbine Airfoils Using the Naphthalene Sublimation Technique
Authors: Ha¨ring M. , Bo¨lcs A. , Harasgama S. P. , Richter J.
Published: May 2009

Results of heat transfer measurements on a typical turbine blade and a vane in a linear cascade have been obtained using the naphthalene sublimation technique. The tests on the vane were performed at the nominal flow angle, whereas for the turbine blade an off-design angle was chosen to study the influence of a separation bubble on the heat transfer. The exit Mach number was varied from M2 = 0.2 to 0.4 and the exit Reynolds number ranged from Re2 = 300,000 to 700,000. Comparisons with numerical codes have been conducted. The measurements were performed in a linear test facility containing five airfoils. Two tailboards and two bypass vanes allowed us to achieve a good periodicity of the flow. The aerodynamic flow conditions were measured using pressure taps and Laser-Two-Focus (L2F) anemometry. About 40 static pressure taps gave a precise Mach number distribution over the suction and the pressure side of the airfoil. L2F measurements were used to determine the downstream flow angles. The heat transfer coefficient was measured using the naphthalene sublimation technique. This method is based on the heat and mass transfer analogy for incompressible flow. A 0.5 mm thin naphthalene layer was applied to the middle airfoil and exposed to the flow for about 45 minutes. The sublimation was then measured in over 500 points on the airfoil, which allowed a high resolution of the heat transfer coefficient. Due to its high resolution, the sublimation technique shows the presence of and the precise location of the laminar-to-turbulent transition point and the separation bubble. The measurements on the vane were compared with two separate two-dimensional boundary layer programs, which were TEXSTAN (Texas University) and TEN (Sussex University). The programs incorporate the k–epsilon turbulence model with several different formulations. The laminar–turbulent transition was predicted quite well with TEN, which slightly damps out the production of turbulent kinetic energy in order to ensure a smooth transition zone. In the case of the blade, the naphthalene sublimation technique was able to predict the size and the location of the separation bubble as well as the reattachment with a very high precision.
Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib Turbulator
Authors: Panigrahi P. K. , Acharya S.
Published: May 2009

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large-scale structures, and that the dynamics of the large-scale structures, associated with sweep, ejection, and inward and outward interactions, all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important, accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.
Stall Inception and the Prospects for Active Control in Four High-Speed Compressors
Authors: Day I. J. , Breuer T. , Escuret J. , Cherrett M. , Wilson A.
Published: May 2009

As part of a European collaborative project, four high-speed compressors were tested to investigate the generic features of stall inception in aero-engine type compressors. Tests were run over the full speed range to identify the design and operating parameters that influence the stalling process. A study of data analysis techniques was also conducted in the hope of establishing early warning of stall. The work presented here is intended to relate the physical happenings in the compressor to the signals that would be received by an active stall control system. The measurements show a surprising range of stall-related disturbances and suggest that spike-type stall inception is a feature of low-speed operation while modal activity is clearest in the midspeed range. High-frequency disturbances were detected at both ends of the speed range and nonrotating stall, a new phenomenon, was detected in three out of the four compressors. The variety of the stalling patterns, and the ineffectiveness of the stall warning procedures, suggests that the ultimate goal of a flightworthy active control system remains some way off.
The Computation of Adjacent Blade-Row Effects in a 1.5-Stage Axial Flow Turbine
Authors: Emunds R. , Jennions I. K. , Bohn D. , Gier J.
Published: May 2009

This paper deals with the numerical simulation of flow through a 1.5-stage axial flow turbine. The three-row configuration has been experimentally investigated at the University of Aachen where measurements behind the first vane, the first stage, and the full configuration were taken. These measurements allow single blade row computations, to the measured boundary conditions taken from complete engine experiments, or full multistage simulations. The results are openly available inside the framework of ERCOFTAC 1996. There are two separate but interrelated parts to the paper. First, two significantly different Navier–Stokes codes are used to predict the flow around the first vane and the first rotor, both running in isolation. This is used to engender confidence in the code that is subsequently used to model the multiple blade-row tests; the other code is currently only suitable for a single blade row. Second, the 1.5-stage results are compared to the experimental data and promote discussion of surrounding blade row effects on multistage solutions.
Sliding Mode Control for a Membrane Mirror Strip Actuated Using Multiple Smart Actuators
Authors: Renno Jamil M. , Reddy C. Konda , Inman Daniel J. , Ruggiero Eric J.
Published: May 2009

The sliding mode technique is used to control the deformation of a membrane mirror strip. A membrane mirror strip is augmented with two macro fiber composite (MFC) bimorphs. The first bimorph is actuated in bending whereas the second is actuated in tension. Membrane strips are usually tensioned uniformly. However, the presence of the tension bimorphs induces a local tension at its location. The membrane strip is modeled as an Euler-Bernoulli beam under tensile load, whereas the MFCs are modeled as monolithic piezoceramics. To cast the system into a finite dimensional state space form, the finite elements method (FEM) is used. The control action is switched when the membrane strip approaches its original undeformed shape. Simulation results demonstrate the effectiveness of the proposed control law.
Experimental and Computational Study of Vaporization of Volatile Organic Compounds
Authors: Amano Ryo S. , Lucci Jose Martinez , Guntur Krishna S.
Published: May 2009

Heated Soil Vapor Extraction (HSVE) is a technology that has been used successfully to clean up subsurface soils at sites containing chlorinated solvents and petroleum hydrocarbons. The costs have been extremely high due to the large amount of energy required to volatilize high molecular weight polycyclic aromatic hydrocarbon (PAH) compounds present in the soil matrix. One remediation contractor states that hydrocarbons are oxidized in situ by achieving temperatures in the >1000 F range near the heaters [1]. A critical question is whether the volatile portion of manufactured gas plant (MGP) hydrocarbons (VOCs) can be stripped out at lower temperatures such that the remaining contaminants will be unavailable for transport or subsequent dissolution into the groundwater. Soil remediation by heated soil vapor extraction system is a relatively new technology developed at the University of Wisconsin-Milwaukee [2]. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. The process developed at UWM, consists of a heater/boiler that pump and circulates hot oil through a pipeline that is enclosed in a larger-diameter pipe. This extraction pipe is vertically installed within the contaminated soil up to a certain depth and is welded at the bottom and capped at the top. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. Our previous studies had removed higher boiling compounds such as naphthalene, etc., to non-detectable level. Thus, the current technology is very promising for removing most of the chemicals compounds; and can also remove these high boiling compounds from the saturated zone. Gas chromatography (GC) is utilized in monitoring the relative concentration changes over the extraction period. Gas chromatography-mass spectrometry (GCMS) assists in the identification and separation of extracted components. The experimental research is currently being conducted at the University of Wisconsin-Milwaukee. The objectives of this study are to identify contaminants and time required to remove them through HSVE treatment and provide data for computation fluid dynamics CFD analysis.
Measurement of Wave Propagation Characteristics of Flexible Hoses
Authors: Johnston D. Nigel , Way Tim M. , Cone Kerry M.
Published: May 2009

A method for measuring the impedance matrix and the dynamic properties of liquid-filled flexible hose is described in this paper. Dynamic hose properties are presented for a wide range of hose types. Nylon-reinforced hoses are shown to have considerably lower bulk moduli and stiffnesses than steel-reinforced hoses. The dynamic bulk moduli and stiffnesses are shown to be significantly and consistently higher than the static values. These results may be used to give an estimate of representative properties for a hose, based on its maximum pressure rating and its type of reinforcement.
Dynamic Analysis of Handling Compliant Sheet-Metal Blanks
Authors: Liao Gene Y.
Published: May 2009

Automating material handling of flexible sheet-metal blanks in stamping process requires attention due to its significant impact on product quality and productivity. This paper investigated the capability of a fully dynamic and nonlinear finite element technique in developing virtual material handling process of compliant sheet-metal blanks subject to time varying movability conditions. The technique used explicit time integration to avoid the formulation of stiffness matrix by a direct integration of the equations of motion. The influence of holding end-effector layout scheme and movability conditions on the final part quality was investigated.
Experimental Study of Binary Drop Collisions for Drops of Greatly Unequal Size
Authors: Post S. L. , Hales A. M.
Published: May 2009

The collisions and coalescence of liquid drops is important in many spraying applications. Those sprays with high injection velocities tend to generate a very turbulent flow field, which induces relative velocities between the spray drops leading to collisions. If those collisions result in frequent coalescence, this will increase the mean drop size of the spray and reduce the overall vaporization rate, and generally result in poorer spray performance. Multi-dimensional spray simulation codes are commonly used in computational simulations of spray. These codes have sub-models for the drop collision rate and coalescence efficiency. The model that is most commonly used for the coalescence efficiency was developed more than thirty years ago, and was validated with binary drop collision experiments for water drops of comparable size to each other. This model is used in simulations with many different spray liquids, and in sprays that have a wide drop size distributions. The experimental results presented here show that the commonly used model is not valid for collisions between drops whose sizes differ by an order of magnitude.
Friction Stir Welding of Aluminum 7136-T76511 Extrusions for Aerospace Applications
Authors: Hamilton Carter , Dymek Stanisław , Blicharski Marek
Published: May 2009

This research program evaluates the residual properties of 7136-T76511 aluminum extrusions joined through friction stir welding (FSW). AA 7136 is a new aluminum alloy developed by Universal Alloy Corporation for high strength aerospace applications that also demand good corrosion resistance, such as those on the Boeing 787 or the Airbus A380. Mechanical and corrosion testing were performed on the baseline material and on panels friction stir welded at 175, 225, 250, 300, 350 and 400 RPM (all other welding parameters were held constant). Mechanical test results demonstrate that the highest joint efficiency, 74%, is achieved at 350 RPM, but for each weld condition, the elongation of the welded material is significantly reduced, 50 – 75%, from the baseline value. Fracture of the tensile specimens consistently occurred on the retreating side of the weld along the interface between the heat affected zone (HAZ) and the thermo-mechanically affected zone (TMAZ), independent of the rotational speed. Examination of fracture surfaces through SEM revealed microvoid nucleation and coalescence around secondary phase particles in the microstructure, as well as numerous stepped or laminar facets characteristic to both the baseline and welded conditions. Exfoliation corrosion testing revealed a performance gradient across the weld with the weld nugget rating the poorest at EC and the heat affected zone rating the best at EA. Qualitative assessment of corrosion resistance is supported by mass loss calculations between the baseline and welded conditions.
Multilayer Wick Structure of Loop Heat Pipe
Authors: Cai Qingjun , Chen Chung-Lung , Asfia Julie F.
Published: May 2009

Loop heat pipe (LHP) is known as a two-phase heat transfer device that utilizes the evaporation and condensation of an operating fluid to transfer heat. At the LHP low operating temperatures, heat leakage induced by saturated temperature differences between the evaporator and compensation chamber is more serious than at high operating temperatures, due to inherent thermophysical properties of the operating liquid. The serious heat leakage at the low operating temperature not only causes high liquid subcooling requirement but also leads to high total temperature difference and degraded heat transfer performance. In this paper, research efforts are placed on reducing the heat leakage by introducing a multilayer wick structure into the LHP. Based on the previous research results of LHP non-metallic wick structures, the multilayer wick LHP combines advantages of both metallic and non-metallic wick structures, retains good heat conduction from the evaporator case to the liquid/vapor interface and inhibits the reverse heat transfer from the interface to compensation chamber. By demonstrating the concept on a methanol LHP, experimental results exhibit a significant enhancement in reducing heat leakage and the total heat transfer resistance.
A Study on Laser Engineered Net Shaping Prototyping Technology
Authors: Xu Z. , Amano R. S. , Lucci J. M. , Marek Steven Gerard , Rohatgi Pradeep , Zheng Baolong
Published: May 2009

The objectives of this work are to study Laser Engineered Net Shaping (LENS™) produced materials and identify the microstructures. Numerical method was used to examine the influence of materials’ type and LENS™ process parameters on the forming of the specific microstructures from thermodynamics and fluid dynamics point of view. Samples of 316L stainless steel were examined, microstructures of samples were used to estimate the corresponding cooling rate, and the cooling rate was compared with the results of three different level of simplified models.
An Interactive Lung Model for Pressure Oscillation Assessment
Authors: Reddy Prasika I. , Al-Jumaily Ahmed M.
Published: May 2009

Exploratory clinical studies use ovine neonates to study the efficacy of new respiratory support treatments for human neonates with respiratory distress syndrome. A mathematical model of the ovine neonatal respiratory system is developed to understand the mechanisms of respiratory improvement noticed in clinical trials. Simulating the ovine lung as a five-lobe branched system, the model aims to simulate the behaviour of the individual lobes, pleural compartment, chest wall and the branching structure of the first few bifurcations of airways. Results from the model are correlated with published data from ovine neonates.
Development of Particulate Unit Operations and Morphology Property Relations of Particulate Products
Authors: Takao Yasumasa , Asai Tsuyoshi , Shimada Yasuhiro , Shuzenji Kiyotaka , Tachibana Takeshi
Published: May 2009

Some particulate unit operations (apparatus engineering) are developed to control the particle morphology. The innovative aspect of this operation is the correspondence between the necessary material properties and their apparatus optimization. Spherical powders of aluminum oxynitride and aluminum nitride are directly prepared by flame synthesis (in spite of the fact that oxygen serves as an indispensable reactant). Non-oxide powders are commonly non-spherical with a size below the submicrometer scale. The major limiting factors in their synthesis are free energy, reaction temperature, and reaction rate. The innovative aspect of this flame synthesis technology assisted by DC arc plasma concerns the reducing gas composition beyond 1500 K. A chemical equilibrium calculation indicates that the plasma heating compensates the lack of reaction temperature under a low oxygen condition. This burner realizes a high-speed reaction with the help of reactive species in the arcs. We also report the multilayer-coated cosmetic powders with regard to material application, and the powder bed shear force evaluation equipment with regard to apparatus optimization.
High Resolution Detection and Configuration of Bacteria Using Microscale Pores
Authors: Mulero Rafael , Moraga Alejandro , Kim Min Jun
Published: May 2009

A novel method for detecting and configuring bacteria using a micro-scale pore is presented. The method distinguishes between different species of bacteria by measuring the ionic current blockage (resistive pulse) as bacteria electrophoretically translocate the micro-pore. Both wild-type flagellated (HCB 33) and non-flagellated Escherichia coli (HCB 5), and Polystyrene microbeads were used in this study to demonstrate the efficacy of this method. High resolution electrical signal readout enabled discrimination of the orientation of both non-flagellated and peritrichously flagellated bacteria as they move through the solid-state pore.
Advanced Exergoeconomic Evaluation and Its Application to Compression Refrigeration Machines
Authors: Tsatsaronis George , Morosuk Tatiana
Published: May 2009

Splitting the exergy destruction within each component of an energy conversion system into endogenous/exogenous and unavoidable/avoidable parts enhances an exergy analysis and improves the quality of the conclusions obtained from the analysis. The potential for improving each system component is identified and priorities, according to which the design of components should be modified, are established. We call this detailed exergy analysis advanced exergy analysis. For improving the cost effectiveness of an energy conversion system, splitting the investment cost into endogenous/exogenous and unavoidable/avoidable parts is also helpful. The designer should focus on the avoidable thermodynamic inefficiencies (exergy destruction), their costs and the avoidable investment costs. The paper discusses the calculation of these costs in general and the resulting advanced exergoeconomic evaluation that is based on the avoidable endogenous and the avoidable exogenous values for exergy destruction, cost of exergy destruction and investment cost. An application of this methodology to a compression refrigeration machine is presented.
A New Extension of Particle Swarm Optimization and Its Application in Electronic Heat Sink Design
Authors: Alrasheed M. R. , de Silva C. W. , Gadala M. S.
Published: May 2009

Particle Swarm optimization (PSO) is a robust stochastic evolutionary computation technique which is based on the movement and intelligence of swarms. In this paper the PSO algorithm is modified to improve its performance in a class of design applications in heat transfer. The developed approach includes a new term called a chaotic acceleration factor (Ca) into the algorithm, which enhances its convergence rate and its accuracy. The modified PSO is empirically tested with well-known benchmark functions. Next it is applied in plate-fin design with the objective of dissipating the maximum heat generation from an electronic component by minimizing the entropy generation rate to obtain the highest heat transfer efficiency.
A Model for the Two-Phase Flow Through a Dual-Scale Porous Medium in Liquid Composite Molding
Authors: Yamaleev N. K. , Mohan R. V.
Published: May 2009

The macroscopic flow during processing of composite structures by liquid composite molding is accompanied by the microscopic flow through individual fiber bundles. This concurrent microscopic flow occurs at length and time scales different than those of the macroscopic flow and influences the macroscopic flow behavior, impacting the void formation during composite manufacturing. A reduced-order model developed by the authors of this paper in [Proc. 2005 ASME Conf., IMECE2005-82436] for modeling the microscopic impregnation of individual fiber bundles is currently used to simulate the transient dynamics of the 1-D two-phase flow though a dual-scale porous medium during resin transfer molding (RTM). As has been show in our previous work [Inter. J. of Multiphase Flow, Vol. 32, pp. 1219–1233, 2006] the vapor-liquid phase transition and multidimensional effects of the gas entrapped inside fiber tows can play a significant role in the advancement of the macroscopic resin front and the formation of voids, thus indicating the need to account for these phenomena in the simulation of liquid composite molding processes. These effects are quantified by introducing a nonzero sink term into the right hand side of the mass conservation equation for the dual-scale porous medium, which couples the microscopic two-phase flow inside fiber bundles with the macro-flow through the perform. Two numerical methods, one of which is based on the moving coordinate system associated with the macroscopic resin front and the other one based on the fill factor technique on a fixed Eulerian coordinate system, are used to solve the resin flow through the preform. The comparative analysis of the fill factor and moving front methods as well as the results demonstrating the effect of phase transition and impregnation of individual fiber bundles on macroscopic flow parameters during RTM are presented.
Design Optimization of Power Plants by Considering Multiple Partial Load Operation Points
Authors: Ju¨des Marc , Tsatsaronis George
Published: May 2009

The design optimization of complex energy conversion systems requires the consideration of typical operation conditions. Due to the complex optimization task, conventional optimization methods normally take into account only one operation point that is, in the majority of cases, the full load case. To guarantee good operation at partial loads additional operation conditions have to be taken into account during the optimization procedure. The optimization task described in this article considers altogether four different operation points of a cogeneration plant. Modelling requirements, such as the equations that describe the partial load behavior of single components, are described as well as the problems that occur, when nonlinear and nonconvex equations are used. For the solution of the resulting non-convex mixed-integer nonlinear programming (MINLP) problem, the solver LaGO is used, which requires that the optimization problem is formulated in GAMS. The results of the conventional optimization approach are compared to the results of the new method. It is shown, that without consideration of different operation points, a flexible operation of the plant may be impossible.
On Thermomechanical Durability Analysis Combined With Computational Fluid Dynamics Thermal Analysis
Authors: Johansson Jonas , Leisner Peter , Lee JungChuan , Twigg David W. , Rassaian Mostafa
Published: May 2009

Results are presented on durability analysis of an electronic module subjected to thermal and power cycles, and vibration. A hierarchical analysis process for analyzing the durability of the module is described. The initial step is a transient thermal analysis of the unit in which the module is located. The three operating modes of the unit are modeled and analyzed using a commercially available computational fluid dynamics (CFD) tool. The tool generates a time history of the temperature at all points within the unit and module. The second step comprises exporting temperatures from the transient temperature analysis to a durability prediction tool. The temperatures calculated by the global analysis are mapped to the printed wiring assembly (PWA) mounted within the box, yielding the temperature distribution of the PWA as functions of time. The durability tool utilizes a modified Coffin Manson formula together with the transient temperature profile to estimate the durability of each lead and solder joint included in the module. Thermomechanical fatigue level of leads and solder joints within the unit are reported as a cumulative damage index (CDI). The CDI is the ratio of the number of cycles required for the test item to endure under a life time to the number of cycles the item is predicted to sustain before failure. Durability analysis of solder joint due to vibration is performed separately. The environment is specified according to the location where the unit is mounted. CDI due to vibration is added to form an overall CDI based on Miner’s rule.
Infrared Radiative Properties of Submicron Metallic Slit Arrays
Authors: Chen Y.-B. , Lee B. J. , Zhang Z. M.
Published: May 2009

Submicron metallic slit arrays with different geometry were designed and fabricated on silicon substrates. Their infrared radiative properties (transmittance, reflectance, and absorptance) were investigated both experimentally and theoretically. The normal transmittance of three fabricated Au slit arrays was measured at wavelengths between 2 and 15 μm using a Fourier-transform infrared spectrometer. The experiment results were compared with the values calculated from the rigorous coupled-wave analysis. The applicability of the effective medium theory for modeling radiative properties was also examined. The agreement between the measurement and modeling results demonstrates the feasibility of quantitative tuning of the radiative properties by employing periodic micro/nanostructures.
Numerical Implementation of Nonlinear Piezoelectric Models in Commercially Available Tools
Authors: Qidwai M. A. Siddiq , DeGiorgi V. G. , Wimmer S. A.
Published: May 2009

Commercially available finite element programs currently provide only linear piezoelectric models for device analysis, precluding their use in understanding domain-switching based failure mechanisms, and thus, limiting their usefulness in predicting accurate life cycle estimates for devices. This work is an initial attempt to bridge this gap by slightly modifying and implementing an existing macromechanical theoretical framework, which represents a broader class of nonlinear model development, in commercial software. The rate-independent evolution equations of remanent variables in the original model are replaced by their rate-dependent form which better imitates physical reality and facilitate quick implementation. Decoupled ferroelectric and ferroelastic versions of the model have been successfully realized and tested. Ongoing work is focused on incorporating the fully coupled model, which will then be used to simulate switching near cracks in PMN-PT single crystal material.
Post-Buckling of Functionally Graded Cylindrical Shells
Authors: Gunes Recep , Apalak M. Kemal , Tasdemir H. Abdullah
Published: May 2009

In this study, the post-buckling analysis of functionally graded cylindrical shells was carried out using the non-linear finite element method. The longitudinal shell edges were hinged under a central transverse concentrated load. The shells were composed of ceramic (Al2O3) and metal (Ni) phases and the mechanical properties at the region between the metal and ceramic layers vary continuously through the shell thickness according to a power-law distribution of the volume fractions of the constituents. The arc-length method was implemented. The effects of material composition and layer number as well as various shell thicknesses on the post-buckling response of the functionally graded cylindrical shells were investigated. The functionally graded shells exhibit both snap-through and snap-back post buckling behaviours. The layer number through the shell thickness has a minor effect on the post-buckling behaviour whereas the compositional gradient exponent varies from 0.1 to 10.0 the snap-through behaviour becomes more obvious whilst both the snap-through and snap-back behaviours appear for a thinner shell.
Fluorescence and Fiber-Optics Based Real-Time Thickness Sensor for Dynamic Liquid Films
Authors: Ng T. W. , Narain A.
Published: May 2009

To overcome the limitations/disadvantages of many known liquid film thickness sensing devices (viz. conductivity probes, reflectance based fiber-optics probes, capacitance probes, etc.), a new liquid film thickness sensor that utilizes fluorescence phenomena and fiber-optic technology has been developed and reported here. Measurements from this sensor are expected to facilitate better understanding of liquid film dynamics in various adiabatic, evaporating, and condensing film flows. The sensor accurately measures the instantaneous thickness of a dynamically changing liquid film in such a way that the probe does not perturb the flow dynamics in the proximity of the probe’s tip. This is achieved by having the probe’s exposed surface embedded flush with the surface over which the liquid film flows, and by making arrangements for processing the signals associated with the emission and collection of light (in distinctly different wavelength windows) at the probe’s flush surface. Instantaneous film thickness in the range of 0.5 to 3.0 mm can accurately (with a resolution that is within +/− 0.09 mm over 0.5 to 1.5 mm range and within +/− 0.18 mm over 1.5 to 3.0 mm range) be measured by the sensor described in this paper. Although this paper only demonstrates the sensor’s ability for dynamic film thickness measurements carried out for a doped liquid called FC-72 (perfluorohexane or C6F14 from 3M Corporation), the approach and development/calibration procedure described here can be extended, under similar circumstances, to some other liquid films as well.
Temperature-Controlled Stop Bands for Elastic Bloch-Floquet Waves in Periodic Thermo-Elastic Structures
Authors: Jones I. S. , Movchan A. B.
Published: May 2009

An important feature of phononic band gap structures is the presence of stop bands in the dispersion diagrams. Waves of frequencies within the stop bands do not propagate through the structure. It is possible to design structures, possessing such stop bands, by incorporating appropriately designed resonators within the elementary cell of the (periodic) structure [1]. In particular, this enables one to design a filter for waves of a sufficiently large wavelength using structures whose elementary cells are relatively small in size. The applications may range from acoustic filters to filters of elastic waves in earthquake resistant structures. A possible mechanism is discussed to control the stiffness of resonators, using variable temperature, and hence to alter the position of the stop band in the dispersion diagram. A thermally inhomogeneous resonator is chosen to include elements which buckle under the thermal load combined with mechanical constraints imposed by the surrounding structure. The spectral characteristics of the modified structure are thus changed and this is reflected in the dispersion diagrams.
A Preliminary Safety Analysis of an Ultracapacitor Power Subsystem for a Prototype Alternative Fuel Vehicle
Authors: Quinn A. , Hill N. , Sherman B. , Etherton J. , Wayne S.
Published: May 2009

In today’s rapidly changing world, the need for safe, more fuel-efficient and environmental friendly vehicles is in high demand. Private and public sector proponents of alternative fuel vehicles have joined forces to create a university-based competition, Challenge-X, to safely increase fuel economy as well as reduce emissions. The safe performance of vehicle testing, maintenance and rescue tasks are integral to the competition. At West Virginia University, a mechanical engineering team is developing a vehicle powered by a 1.9-L direct injection turbodiesel engine using bio-diesel fuel. Energy storage in the vehicle is via 750 kJ ultracapacitors which power two 13 kW AC induction wheel hub motors. A system safety analysis performed by a WVU industrial engineering team focuses on the ultracapacitor portion of the system. Designsafe© software is used to systematically identify tasks, hazards, risks, and risk reduction measures. An emergency rescue plan and a procedure for emergency rescue for vehicles with this design is described. The emergency safety plan identifies ‘no cut’ areas or areas of the car that would be very dangerous to cut due to the high voltage. The risk reduction plan includes procedures for performing maintenance on the electrical system, including the ultracapacitor system.
Numerical and Microfluidic-Based Cell-Sorting Devices
Authors: Taylor Jay K. , Ren Carolyn L. , Stubley G. D.
Published: May 2009

The development of Lab-on-a-Chip devices with integrated bio-analysis functions requires a complex network of microfluidic transport and processes. Many of these functions call for the isolation or separation of specific bio-particles or cells. The design of a miniaturized cell-sorting device for handheld operation must follow the strict parameters associated with Lab-on-a-Chip technology. The limitations include applied voltage, high efficiency of cell-separation, repeatability, size, flow control, and cost, among others. Currently used designs have achieved successful levels of cell-isolation. However, further improvements in the microfluidic chip design are important for incorporation into larger systems. This study evaluates specific design modifications that contribute to the reduction of required applied potential aiming for developing portable devices, improved operation reliability by minimizing induced pressure disturbance when electrokinetic pumping is employed and incorporating online filters to reduce channel blockage, and improved flow control by incorporating directing streams achieving dynamic sorting and counting. The chip designs fabricated in glass and polymeric materials include asymmetric channel widths for sample focusing, nonuniform channel depth for minimizing induced pressure disturbance, directing streams to assist particle flow control, and online filters for reducing channel blockage. Fluorescence-based visualization of electrokinetic focusing, flow field phenomena, and dynamic cell-sorting demonstrate the advantages of the chip design. Numerical simulations in COMSOL are validated by the experimental data and used to investigate the effects of channel geometry and fluid properties on the flow field.
Virtual Five-Axis Flank Milling of Jet Engine Impellers: Part 2 — Feed Rate Optimization of Five-Axis Flank Milling
Authors: Ferry W. , Altintas Y.
Published: May 2009

This paper presents optimization schemes for the five-axis flank milling of jet engine impellers based on the mechanics model explained in Part I. The process is optimized by varying the feed automatically as the tool-workpiece engagements, i.e. the process, varies along the tool path. The feed is adjusted by limiting feed-dependent peak outputs to a set of user-defined constraints. These outputs are tool shank bending stress, tool deflection, maximum chip load (to avoid edge chipping) and the torque limit of the machine. The linear and angular feeds of the machine are optimized by two different methods — a multi-constraint based virtual adaptive control of the process and a non-linear root finding algorithm. The five-axis milling process is simulated in a virtual environment, and the resulting process outputs are stored at each position along the tool path. The process is recursively fitted to a first order process with a time varying gain and a fixed time constant, and a simple Proportional Integral controller is adaptively tuned to operate the machine at threshold levels by manipulating the feedrate. As an alternative to virtual adaptive process control, the feedrate is optimized by a non-linear root-finding algorithm. The optimum feed is solved for iteratively, respecting tool stress, tool deflection, torque and chip load constraints, using a non-linear root finding algorithm. Both methods are shown to produce almost identical optimized feed rate profiles for the roughing tool path discussed in Part I of the paper. The new feed rate profiles are shown to considerably reduce the cycle time of the impeller while avoiding process faults that may damage the part or the machine.
Optimized Mapping of Pressure in Lubricated Point Contacts Based on Measured Film Thickness
Authors: Polisˇcˇuk Radek , Vaverka Michal , Vrbka Martin , Krˇupka Ivan , Hartl Martin
Published: May 2009

The surface topography plays significant role in lifetime of highly loaded machine parts with lubricated contacts. Many elements like gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions, where the lubricant film behavior closely implies the main practical performance parameters such as friction wear, contact fatigue and scuffing. For prediction of wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are often required. The usual theoretical approach based on numerical solution of physical-mathematical models built around the Reynolds equation can be extremely time consuming, especially when lubricant films are very thin, and contact load and required resolution very high. This study presents a further refined approach to our previously published experimental method, based on on inverse elasticity theory and fast convolution transformation between the lubricant film thickness map and the pressure distribution within the point contact. The experimental film thickness maps of EHD lubricated contacts with smooth and dented surfaces were processed using colorimetric interferometry and validated using numerical solution, in order to calibrate numerical parameters and to find limits of the new approach.
Assembly Systems Coordinated by Revenue-Sharing Contracts in a Fuzzy Environment
Authors: Wang Junyan , Zhang Yuhua
Published: May 2009

From an industry and organization point of view, this paper considers the assembly systems with one assembler and multi-manufacturer under a revenue-sharing contract in a fuzzy environment which will contribute new insights to the engineering management. Market demand and assembler’s assemble capacity are characterized as fuzzy variables, respectively. Game theory is used to analyze the behavior of the members in the assembly systems. Both non-cooperative game and cooperative game models between the assembler and manufacturers are constructed. The coalition optimal solution of cooperative game model is obtained. The property of the contract is proved. Finally, the two kinds of settings are compared. The conclusion proposed is convenient to refer by the decision maker in engineering management.
Heavy Truck Hub and Wheel-Off Accidents: A Mechanical Analysis
Authors: Ferrone Christopher W.
Published: May 2009

Hub retention is the foundation of wheel retention. The hub attaches securely to the spindle or axle tube. The brake drum, brake rotor, wheel and tire all mount to the hub. If the hub comes off of the spindle or axle tube, the driver and other motorists are faced with a potentially dangerous situation. This paper will analyze the phenomenon of hub loss and subsequent wheel-off accidents by using the analysis of several of the author’s most recent investigations. The analyses will describe the mechanics of the system, how it functions, its failure modes, preventative measures and an alternative design which can mitigate this phenomenon from occurring. Specifically, this paper is focused on the phenomenon related to the rotational dynamics of wheels on the left side of the vehicle unwinding the spindle nut(s)—allowing for the loss of the entire wheel end assembly.
Geometric Modeling of Cutter/Workpiece Engagements in 3-Axis Milling Using Polyhedral Models
Authors: Aras Eyyup , Yip-Hoi Derek
Published: May 2009

Modeling the milling process requires cutter/workpiece engagement (CWE) geometry in order to predict cutting forces. The calculation of these engagements is challenging due to the complicated and changing intersection geometry that occurs between the cutter and the in-process workpiece. This geometry defines the instantaneous intersection boundary between the cutting tool and the in-process workpiece at each location along a tool path. This paper presents components of a robust and efficient geometric modeling methodology for finding CWEs generated during 3-axis machining of surfaces using a range of different types of cutting tool geometries. A mapping technique has been developed that transforms a polyhedral model of the removal volume from Euclidean space to a parametric space defined by location along the tool path, engagement angle and the depth-of-cut. As a result, intersection operations are reduced to first order plane-plane intersections. This approach reduces the complexity of the cutter/workpiece intersections and also eliminates robustness problems found in standard polyhedral modeling and improves accuracy over the Z-buffer technique. The CWEs extracted from this method are used as input to a force prediction model that determines the cutting forces experienced during the milling operation. The reported method has been implemented and tested using a combination of commercial applications. This paper highlights ongoing collaborative research into developing a Virtual Machining System.
In-Situ Measurements of Water Transfer Due to Different Mechanisms in a PEM Fuel Cell
Authors: Husar Attila , Higier Andrew , Liu Hongtan
Published: May 2009

Water management is of critical importance in a proton exchange membrane (PEM) fuel cell. Yet there are very limited studies of water transfer through the membrane and no data are available for water transfer due to individual mechanisms through the membrane electrode assembly (MEA) in an operational fuel cell. Thus it is the objective of this study to measure water transfer through the MEA due to different mechanisms through the membrane electrode assembly (MEA) of an operational PEM fuel cell. The three different mechanisms of water transfer, i.e., electro-osmotic drag, diffusion and hydraulic permeation were isolated by specially imposed boundary conditions. Therefore water transfer through the MEA due to each mechanism could be measured separately. In this study, all the data were collected in an actual assembled operational fuel cell, and some of the data were collected while the fuel cell was generating power. The measured results showed that water transfer due to hydraulic permeation, i.e. the pressure difference between the anode and cathode is at least an order of magnitude lower than those due to other two mechanisms. The data for water transfers due to electro-osmosis and diffusion through the MEA are in good agreement with some of the data and model predications in the literature for the membrane. The methodology used in this study is simple and can be easily adopted for in-situ water transfer measurement due to different mechanisms in actual PEM fuel cells without any cell modifications.