bluuebunny/crossref_metadata_2025 huggingface dataset:
Zero Phase Wavelet Transform for Detecting Bearing Localized Defects
Authors: Li C. James
Published: April 2008

This study designed a wavelet in such a way that its Fourier transform has zero phase (hence the name zero-phase wavelet). Since the wavelet has zero phase, the resulted wavelet transform’s phase part solely depends on the phase of the signal within the passing band of the wavelet used. With its ability to localize in time and frequency domains, the magnitude part reveals local amplitude modulation and the phase part reveals local phase modulations associated with the frequency band defined by the wavelet. This study established the utility of the zero phase wavelet for bearing localized defect detection, examined the magnitude and phase of zero phase wavelet transform of bearing signals to determine if they can detect periodic structural ringings as effectively as the prevailing envelope spectrum technique and if the phase part brings any additional diagnostic information. It was found that the zero-phase wavelet transform is more effective than the envelope spectrum and the additional phase information complements the amplitude information and enhances the sensitivity for the detection.
Water Lubricated Polymer Hydrodynamic Bearing With Full and Grooved Bearing Bushing
Authors: Litwin Wojciech
Published: April 2008

The topic of this article is conducting of the measurements on water lubricated main shaft bearings. The article contains the following parts: • Introduction in which the genesis and the main idea of work are described. • Description of the test stand, the simulated working conditions, and the bearing specifications. • Presentation and description of the conducted measurements. • Comparison of hydrodynamic bearing with the typical main shaft bearing with a grooved bearing bushing working in a semi fluid friction conditions. • Conclusion.
Flow Boiling in a Microchannel Heat Sink
Authors: Liu Dong , Garimella Suresh V.
Published: April 2008

Flow boiling heat transfer in a microchannel heat sink is experimentally investigated. The microchannels considered are 275 μm wide and 636 μm deep, and the experiments are conducted at inlet water temperatures in the range of 66 to 95°C and mass fluxes of 341 to 936 kg/m2s. Convective boiling heat transfer coefficients are measured and compared to predictions from correlations proposed for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in the microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new heat transfer model is developed to correlate the data in the saturated boiling regime. Good agreement with the experimental measurements indicates that this correlation is suitable for use in the design of two-phase microchannel heat sinks.
Preparing for a Team Project in a Diverse Class of New Students
Authors: Bannerot Richard
Published: April 2008

Semester-long, team design projects are supposed to fun but can appear daunting to beginning engineering students, especially if they don’t know anyone else in the class. This paper discusses how the “daunting” aspect of early design projects has been addressed in a sophomore design course in a BSME program. The issue is addressed from three viewpoints: student diversity, project formulation, and support from the other activities in the class. A sample project is discussed in detail. A survey at the end of the semester indicted that the students enjoyed the class (averaging over 4.5 on the usual five-point Likert scale for four statements about the course), learned (averaging 4.18 supporting improved abilities related to seven ABET criterion 3 issues) and also strongly supported a series of statements about other learning issues.
Jet Impingement Heat Transfer on a Circular Cylinder by Radial Slot Jets
Authors: Zuckerman Neil , Lior Noam
Published: April 2008

To better understand and facilitate design of an impinging jet device, the heat transfer on a cylindrical target exposed to radial impinging slot jets was investigated using numerical methods. Numerical models were created to test the performance of the Shear Stress Transport (SST), Standard and Realizable k-epsilon, v2f, and Reynolds Stress Model (RSM) turbulence models versus published test data. Based on the validation study the v2f model was ultimately selected for further work. Models were then constructed to simulate a cylinder exposed to a radial array of slot jets. Parametric variations were conducted to produce information about the influence of jet speed, nozzle count, and other independent design variables upon heat transfer. Nozzle count was varied from 2 to 8, jet Reynolds number ranged from 5,000 to 80,000, and target diameter varied from 5 to 10 times the nozzle hydraulic diameter. The interaction of adjacent opposed wall jets caused a static pressure rise and resulted in flow separation on the surface of the cylindrical target. This separation and the fountain flow between the two wall jets greatly influenced the local heat transfer, causing a rise in Nu of an order of magnitude. The resulting average Nu values varied from 19 to 217 and were condensed into a correlation equation incorporating target curvature, number of nozzles, Re, and Pr.
Actuated Tweezers for Precision Microassembly
Authors: Bailar James M. , Kast Brian A. , Jones James F.
Published: April 2008

Sandia National Laboratories is exploring assembling micro, meso, and miniature scale parts into a variety of tiny devices. These devices are comprised of parts ranging from tens of microns to a few millimeters in size. In support of this activity, a rapid prototyping assembly workstation that enables an operator to assemble three-dimensional devices with a minimum of fixturing has been developed. This workstation consists of precision robotics, stages, cameras, and sensors integrated in a way that facilitates human interaction. Although many of the workstation components are commercially available, no inexpensive and durable grippers of suitably large range of motion could be found. This paper describes the design and testing of a novel micro gripper based on precision tweezers and actuated with a micro servo that has proven extremely useful for the operator directed assembly of micro scale devices.
Experimental and Computational Comparisons of Fan-Shaped Film-Cooling on a Turbine Vane Surface
Authors: Colban W. , Thole K. A. , Haendler M.
Published: April 2008

The flow exiting the combustor in a gas turbine engine is considerably hotter than the melting temperature of the turbine section components, of which the turbine nozzle guide vanes see the hottest gas temperatures. One method used to cool the vanes is to use rows of film-cooling holes to inject bleed air that is lower in temperature through an array of discrete holes onto the vane surface. The purpose of this study was to evaluate the row-by-row interaction of fan-shaped holes as compared to the performance of a single row of fan-shaped holes in the same locations. This study presents adiabatic film-cooling effectiveness measurements from a scaled-up, two-passage vane cascade. High resolution film-cooling measurements were made with an infrared (IR) camera at a number of engine representative flow conditions. Computational fluid dynamics (CFD) predictions were also made to evaluate the performance of some of the current turbulence models in predicting a complex flow such as turbine film-cooling. The RNG k-ε turbulence model gave a closer prediction of the overall level of film-effectiveness, while the v2-f turbulence model gave a more accurate representation of the flow physics seen in the experiments.
Raman Thermometry of an Electro-Thermal Microactuator
Authors: Kearney Sean P. , Phinney Leslie M. , Baker Michael S.
Published: April 2008

Experimentally measured temperature profiles along the micron-scale beam of a working thermal actuator are reported for the first time. Using a surface Raman scattering technique, temperature measurements are obtained in a noncontact fashion with submicron spatial resolution and to within an uncertainty of better than ±10 K. The experimental data are used to validate computational predictions of the actuator thermal performance with reasonable agreement between the data and predicted temperatures.
Thermal Fluid Flow Transport Phenomenon Over Vertical Slot-Perforated Flat Fins With Heat Sink in Natural Convection Environment
Authors: Torii Shuichi , Yang Wen-Jei , Iino Naoko
Published: April 2008

A theoretical study is performed to investigate unsteady thermal and fluid flow transport phenomena over vertical slot-perforated flat fins with heat sink, which are placed in a natural convection environment. Emphasis is placed on the effects of Rayleigh number and fin pitch on heat transfer performance and velocity and thermal fields. It is found from the study that (i) in the high Rayleigh number region, the alternating changes in the fluid flow take place for larger fin pitch, (ii) the alternating flow in the space area between two fins is mutually interacted by the corresponding one from the adjacent in-line plate fines, resulting in an amplification of heat transfer performance, and (iii) heat-transfer performance is intensified with an increase in the fin pitch, whose trend becomes larger in the higher Rayleigh number region considered here.
New Sealing Technology to Overcome Plant/Piping Leakages
Authors: Efremov Anatoly I.
Published: April 2008

Maintenance practice of petrochemical, petroleum refining, fossil fuel and nuclear power generation, and other process industries has demonstrated that plant/piping leakages still remain an unresolved problem, and to overcome leakage occurences in many situations it is necessary to resort to additional remedial maintenance actions including fastener retightening, plant shutdowns, equipment repair or replacement, and so on. One of the main reasons of plant/piping leakages is a low leak tightness of the bolted flanged connections (BFCs) due to operating creep of the fasteners and gaskets. New sealing technology based on “negative creep effect” of the fasteners and gaskets with cores manufactured from shape memory alloys (SMAs) is experimentally studied. The first results of the experiments with the BFCs having cores from SMAs reveal significant decrease of operating creep providing better sealing against plant/piping leakages.
Convective Transport in an Optical Fiber Coating Applicator for a Non-Newtonian Fluid
Authors: Yoo Sang-Yeoun , Jaluria Yogesh
Published: April 2008

Convective transport in an optical fiber coating applicator and die system has been simulated for a non-Newtonian fluid. Low density Polyethylene (LDPE) is employed for the numerical analysis, though ultraviolet (UV) curable acrylates are commonly used, because of lack of property information for acrylates and similar behavior of these two materials. The equations governing fluid flow and heat transfer are transformed to obtain flow in a cylindrical domain. A SIMPLE-based algorithm is used with a non-uniform grid. In contrast to the isothermal case, streamlines for the non-Newtonian fluid are found to be quite different for various fiber speeds. The temperature level in the applicator is much higher for the Newtonian case, due to the larger fluid viscosity and associated viscous dissipation. The shear near the fiber is found to be lower for the Newtonian fluid. As expected, the effects become larger with increasing fiber speed. A very high temperature rise is observed in the die, regardless of fiber speed. This study focuses on the non-Newtonian effects during the coating process, and several interesting and important features, as compared to the Newtonian case, are observed.
Tribological Synergism Between Borates and Sn(II) or Sn(IV) Compounds
Authors: Hu Jianqiang , Liu Guanglong , Xie Feng
Published: April 2008

Dibutyl tin and stannous dialkyldithiocarbamates were synthesized. A four-ball tester was used to evaluate the tribological performances of these additives plus organic borate in a mineral oil. The results indicate that the combination of an oil-soluble tin compounds such as dibutyl tin and stannous dialkyldithiocarbamates with organic borates gave better antiwear protection to base oil than either component separately. The surface examination of the rubbing zone indicated that the atomic concentration of tin produced on the boundary layers by such combinations was greater than those without borates. On the basis of the results of tribological and chemical investigation, an antiwear synergistic mechanism can be postulated in which borates with electron-deficient p orbits in boron catalyse the triboreduction of tin compounds on rubbing surfaces.
Experimental Study of Water and Air Based Permeabilities of Washed and Screened Sands
Authors: Lei Shu-Ye
Published: April 2008

The permeability of narrow screened washed sands of granularity 100–450 μm was measured experimentally using water and air to investigate the effect of slip on the gas based permeability. The experimental data show that the air based permeability of the unconsolidated particle media is not proportional to the square of the mean particle diameter and that slip significantly affects the air based permeability measurements for unconsolidated porous media. The velocity slip effect is significant even for Kn<10−3. Slip effects were not found in the water based permeability measurements with the same sand samples. All of the experimental data lay around the curve k/d=0.283φ2.67 within ± 4.1%. However, the water based permeability was not below all of the air based permeability as expected. The air based permeability eliminated slip effects was about 59 % lower than that water based one, much larger than possible measurement. The experimental results showed that the standard air viscosity value in the handbooks was not its actual, the actual air viscosity may be over twice of that in handbooks.
Control of Frost Accumulation on a Horizontal Cold Plate Using DC Electric Fields
Authors: Tudor V. , Ohadi M. M.
Published: April 2008

With the rapid advancement and expansion of affordable electronics and their applications to computer-driven process control, the prospects for electronically controllable heat transfer surfaces utilizing electric fields are very encouraging. The effects of DC electric fields on frost crystal growth with wire and flat-plate insulated electrodes were studied in this paper. Results showed that the electrode geometry played a major role in the frost control process. Up to 39% frost reduction was obtained when an insulated plate electrode was used with an applied voltage of 17kV, while in similar experiments only 22% frost reduction was obtained using a wire electrode. The plate temperature varied from −20°C to −40°C, while the air temperature was varied from 0°C to −10°C with air relative humidity ranging from 45% to 90%. Both natural and forced convection (Reynolds number = 5,000) conditions were considered in this study. The average power consumption for these experiments was 31 mW. The main findings of this study suggest that the presence of a DC electric field can greatly affect both the frost crystal growth pattern and mass accumulation on a cold plate. For the first time, the ice surface’s electrical properties and basic electrostatics were used to explain the main findings in this paper. Numerical simulation results of the electric fields utilizing a state-of-the-art commercial software were in agreement with the experimental findings from this study. The effect of charge accumulation on the dielectric coating of the electrodes is also addressed.
A Near Input-Output Linearizing Force Tracking Controller for an Electrohydraulic Actuatorn
Authors: Ayalew Beshahwired , Kulakowski Bohdan T. , Jablokow Kathryn W.
Published: April 2008

Under simple practical assumptions, the theory of feedback linearization can be applied to a physical model of an electrohydraulic rectilinear actuator. This paper presents the derivation of a near input-output (IO) linearizing force tracking controller and its experimental implementation on a fatigue testing electrohydraulic actuator. Comparisons are conducted against a linear state feedback with integral controller and a standard PID controller. It is shown that, within the limits of investigated system bandwidth and smoothness restrictions of the desired force trajectory, the near IO linearizing controller has better tracking properties. It is also noted that a sliding mode controller can be interpreted as a robust version of the near IO linearizing controller. Experiments are conducted to investigate the robustness of the controlled system to the parameters of the near IO linearizing controller.
Teaching Courses for an Engineering Student Abroad in Iraq
Authors: Sonnenmeier James R. , Wu Yi
Published: April 2008

A student soldier assigned to go overseas was able to continue his education while abroad by taking key courses in an engineering program online. Using a course management system (CMS) software package and the internet, the courses were taught online in parallel with the normal semester courses. Generally, students take a leave of absence from the university when deployed with the military. This time away from study (called a “stopout”) lengthens the time required to complete a degree program. However, sometimes it will actually preclude the completion of the program. Offering these distance learning courses was an effort to avoid that outcome. The tools included in the CMS allowed for the exchange of information and assignments in support of guided self-study. The faculty were able to control the student access to the information to maintain course integrity. The result has generally been satisfactory, however possible improvements are discussed.
Measures for Wheel Slippage and Sinkage Detection in Rough-Terrain Mobile Robots
Authors: Reina Giulio , Ojeda Lauro , Milella Annalisa , Borenstein Johann
Published: April 2008

Mobile robots are increasingly being used in high-risk, rough terrain situations, such as planetary exploration and military applications. Current control and localization algorithms are not well suited to rough terrain, since they generally do not consider the physical characteristics of the vehicle and of its environment. Poor attention has been devoted to the study of the dynamic ill-effects occurring at the wheel-terrain interface, such as slip and sinkage. These effects compromise odometry accuracy and traction performances leading to danger of entrapment with consequent mission failure. This paper describes methods for wheel slippage and sinkage detection aiming at improving vehicle mobility on highly challenging terrain. Novel measures for wheel slip detection are presented based on observing different sensor modalities implemented onboard and defining deterministic conditions for vehicle slippage. A vision-based algorithm for wheel sinkage estimation is also discussed based on edge detection strategy. Experimental results, obtained by a Mars rover-type robot operating in a rough-terrain environment, are presented. It is shown that these techniques are effective in detecting the dynamic effects due to wheel-terrain interaction and can lead to an efficient understanding of the vehicle physical behavior.
Innovative Mechanical Fastening Systems for New Materials: Today’s Situation and Future Perspectives
Authors: Friedrich C. , Hoffmann U. , Bohlender T.
Published: April 2008

The need for the best material behavior at any location within high performance component systems leads to diversified material combinations. One example is the material mixture in today’s vehicles: steel, aluminum, magnesium, plastics, fibers, glass and other solids. These combinations need new or modified fastening technologies, because traditional techniques like welding or bolting up to now are mainly focused on single material joints. Besides this, the loading level during operation of the components increases continuously, so the behavior of the involved fastening systems under operating conditions also has to be known. Fastening systems with light metals show a significant thermal induced change of clamping/preload. This paper gives an overview with some optimized exemplary fastening systems from the automotive sector which could be partly transferred to other industry branches. The paper also emphasizes that various details of designing fastening systems are decisive for reliability and stability.
Monte-Carlo Simulation of Ion Transport at the Polymer-Metal Interface
Authors: He Xingxi , Leo Donald J.
Published: April 2008

The transport of charge due to electric stimulus is the primary mechanism of actuation for a class of polymeric active materials known as ionomeric polymer transducers. Continuum-based models of ion transport have been developed for the purpose of understanding charge transport due to diffusion and migration. In this work a two dimensional ion hopping model has been built to describe ion transport in ionomeric polymer transducer (IPT) with Monte-Carlo simulation. In the simulation, cations are distributed on 50nm × 50nm × 1nm (or 50nm × 10 nm × 1nm) lattice cells of IPT while the same number of negative charges are uniformly scattered and fixed as background. In the simulation, thermally activated cations are hopping between multiwell energy structures by overcoming energy barriers around with a hopping distance of 1nm during each time step. A step voltage is applied between the electrodes of the IPT. In one single simulation step, coulomb energy, external electric potential energy and intrinsic energy of the material are calculated and added up for the energy wells around the cations. And then hopping rates in every potential hopping direction are obtained. Due to the random nature of the ion transitions, a weighting function from Monte-Carlo algorithm is added in to calculate the ion hopping time. Finally hopping time is compared, the minimum hopping time is chosen and one hopping event is completed. Both system time and ions distribution are updated before the next simulation loop. Periodic boundary conditions are applied when ions hop in the direction perpendicular to the electric field. The influence of the electrodes on both faces of IPT is presented by the method of image charges. The charge density at equilibrium state is compared with the result from a continuum-based model. The property of charge density has charge neutrality over the central part of the membrane and the charge imbalance over boundary layers close to the anode and cathode. Electric field distribution is obtained after charge distribution. After it is demonstrated that ion hopping model leads to the results qualitatively matching the property of IPT, the paper uses the model to analyze the polymer-metal interface when the electrode shape inside transducer varies.
Time-Resolved Microscale Temperature Measurements of High-Power Semiconductor Lasers
Authors: Chan Paddy K. L. , Sathe Amul D. , Pipe Kevin P. , Plant Jason J. , Juodawlkis Paul W.
Published: April 2008

Nonradiative recombination and other heat generation processes affect both the performance and lifetime characteristics of semiconductor diode lasers. This is especially true for high-power devices, where facet heating due to nonradiative recombination can lead to catastrophic optical damage (COD). Here we present for the first time temperature measurements of a semiconductor laser in which the surface temperature profile (and hence the current density profile) of the laser is measured as it evolves in time. The laser studied is a λ=1.55μm 1-cm-long InGaAsP/InP watt-class slab-coupled optical waveguide laser (SCOWL). The ridge width of the SCOWLs examined here is approximately 5 μm. Temperature measurements are taken using multiple microthermocouples with sizes less than 20μm. Surface temperature fluctuations in time are seen to be quite large, as high as 20% of the total temperature increase of the device. Time-resolved measurements allow us to see both positive correlation (in which the temperature rises at the same time across an area of the device) as well as negative correlation (in which part of the device gets hot at the same time as another part of the device gets cold). Negative correlations are likely due to facet heating processes which cause bandgap shrinkage and hence increased current flow to a facet, pulling current away from the center of the device. Time-resolved measurements of the surface temperature profile therefore show promise as a nondestructive method for characterizing the failure mechanisms of a laser, as facet damage over time is otherwise very difficult to measure before the COD runaway process destroys the device.
Effect of Machine Tool Structure Dynamic on Machine Cutting Performances
Authors: Kushnir E.
Published: April 2008

Quality of machine tool structure is defined by it static and dynamic compliance. The effect of static stiffness at part shape and machine productivity is one of the reasons that structure static stiffness is used as a main criterion in machine design. The machine dynamic stiffness or compliance directly effect roundness (for example, profile of cross section in turning), surface finish, and indirectly tool life and life of machine components. These effects are defined by structure resistance to transmit vibration in cutting zone or other points of interest in machine tool structure. Dynamic compliance defines accuracy of machining, because it stipulates how machine response to any exciting force, occurring inside and outside machine structure. Dynamic compliance limits the productivity of cutting because it defines maximum depth of cut that may be achieved at a machine in particular set up. The goal of dynamic analysis is to find parameters of the structure that have dominant effect at it dynamic compliance and improve structure based at this information. Usually dynamic analyses required more complicated methodological approach because of coupling between different modes of vibration. The methodology of dynamic analysis of machine tool is illustrated by analysis of mobile spindle module and turning center. The obtained theoretical results are compared with actual testing data.
Design and Optimization of Thermomechanical Actuator via Contour Shaping
Authors: Chen Shih-Chi , Culpepper Martin L.
Published: April 2008

In this paper we disclose how to contour the beams of micro-scale thermomechanical actuators (TMAs) in order to enhance the actuator’s thermal and mechanical performance. In this approach, we vary the cross section of the driving Joule heated beams over the length of the beam. Using this approach, (1) the stored mechanical energy and axial stiffness of beam may be modified to achieve an optimized force-displacement relationship, (2) the maximum achievable thermal strain of a driving beam may be increased by 29%, (3) actuator stroke may be increased by a factor of 3 or more, (4) identical force or displacement characteristics may be achieved with 90% reduction in power. This paper presents the theory and models used to predict the thermal and mechanical behavior of the actuator. The theory and models were used to create a deterministic link between the actuator’s design parameters and the actuator’s performance characteristics. The theory and models were combined within a design tool that shows less than 5% error from non-linear Finite Element Analysis simulations. The design tool has been used to generate plots that enable designers to (1) understand the qualitative relationships between design parameters and performance and (2) select first-pass design parameters. The theory was used to create a design tool, posted at http://psdam.mit.edu, that may be used to perform qualitative design assessment and optimization.
String Stable Control and Position Assignment for Unmanned Air Vehicles in Formation
Authors: Kaplun Michael , Simon Christopher P. , Girard Anouck R.
Published: April 2008

This paper presents a method for string stable formation control and formation position assignment for several unmanned air vehicles. The model addresses two main issues of formation control; (a) stability analysis of the interconnected system, (b) vehicle position assignment and switching. The vehicles move along a given trajectory in a specified formation shape. This allows us to decouple the formation shape problem from the motion of the group along a given path. Each vehicle maintains its position relative to an inertial waypoint, and its position relative to its neighbors. Thus, we are developing a leaderless formation control scheme. A specific leader is not desirable, because it may lead to instability of the interconnected system in the case of an error associated with the leader vehicle, and is not fault tolerant. We include an analysis of the error dynamics of the system for a V-shaped formation. This specific shape was selected as birds use it frequently and NASA has shown that this formation is energy efficient. Our system is mesh stable and spacing errors do not exacerbate downstream of the origin. When planes fly in V-formation, the front plane uses more energy and, therefore, more fuel. The trailing planes benefit from the vortex created by the wings of the plane in front of them and use less energy to maintain a cruising speed. For the purposes of maximizing fuel efficiency in an entire team of UAVs, the model uses a simple proximity algorithm to assign the vehicles’ positions and determine when and which vehicles to switch. The only physical variables that need to be observed are the positions of each plane relative to an arbitrary virtual leader position, and the velocities and fuel reserves of each plane, and a small number of other indicial variables. The fuel burnt by the front plane determines when to signal for a switch in position and the geometry of the formation in combination with the fuel levels of the remaining planes controls the decision making process. The different aspects of the model are all meant to work together and individually. Matlab simulation plots of path motion and error convergence are shown as proof of concept.
Oxygen Separation/Enrichment From Atmospheric Air Using Magnetizing Force: Air Flow in a Duct Under Magnetic Field Gradient
Authors: Asako Yutaka , Suzuki Yohei
Published: April 2008

Oxygen is paramagnetic gas and it has relatively high magnetic susceptibility. On the contrary, nitrogen is diamagnetic gas and it has relatively low and negative magnetic susceptibility. This results in counter magnetizing forces acting on these gases. The possibility of oxygen separation/enrichment from atmospheric air flow using a magnetizing force was investigated numerically. Direct Simulation Monte Carlo (DSMC) method was utilized to obtain distribution of oxygen concentration of air flow in a parallel-plate duct under a strong magnetic field gradient. The molecular movement was calculated by taking into account the magnetizing forces on the molecules. The computations were performed for a wide range of pressure and magnetic flux density gradient. The simulation results showed that there is a possibility of oxygen separation/enrichment from decompressed air under a strong magnetic field gradient.
Comparetive Performance Study of Jatropha Methyl Ester as Diesel Fuel Substitute on Di Diesel Engine With Emphasis on Vibration and Noise as Potential Engine Parameters
Authors: Sastry G. Ravi Kiran , Kumar I. N. Niranjan , Prasad S. Chandra , Rao B. V. A.
Published: April 2008

Among the biomass resources, vegetable oils are observed to be good alternative fuels for use in diesel engines and are also attractive because of renewability. However, there are fundamental problems of engine performance and exhaust emissions due to high viscosity and low volatility of the pure vegetable oil. The present work aims at evaluating the performance of Jatropha methyl ester (JME) by evaluating the combustion properties and engine vibration & noise. This generates a corroborative method to ascertain the engine combustion quality, as the vibration trend developed by the engine is synonymous with the excitation generated by combustion.
An Improved Analytical Model for Deflections of a Circular Multi-Layer Piezoelectric Actuator
Authors: Deshpande Mandar , Saggere Laxman
Published: April 2008

Models for simple closed-form analytical solutions for accurately predicting static deflections of circular thin-film piezoelectric microactuators are very useful in design and optimization of a variety of MEMS sensors and actuators utilizing piezoelectric actuators. While closed-form solutions treating actuators with simple geometries such as cantilevers and beams are available, simple analytical models treating circular bending-type actuators commonly used in MEMS applications are generally lacking. This paper presents a closed-form analytical solution for accurately estimating the deflections and the volume displacements of a circular multi-layer piezoelectric actuator under combined voltage and pressure loading. The model for the analytical solution presented in this paper, which is based on classical laminated plate theory, allows for inclusion of multiple layers and non-uniform diameters of various layers in the actuator including bonding and electrode layers, unlike other models previously reported in the literature. The analytical solution presented is validated experimentally as well as through a finite element solution and excellent experiment-model correlation within 1% variation is demonstrated. General guidelines for optimization of circular piezoelectric actuator are also discussed. The utility of the model for design optimization of a multi-layered piezoelectric actuator is demonstrated through a numerical example wherein the dimensions of a test actuator are optimized to improve the displaced volume by three-fold under combined voltage and resisting pressure loads.
Effects of Liquid Heat Dissipation on Heat Transfer Coefficient in Spray Cooling
Authors: Lei Shu-Ye , Lu Qiu-Min
Published: April 2008

The effects of the heat flux and liquid temperatures during spray cooling heat transfer were experimentally studied for non-boiling water spray cooling. The experiments show that the heat flux strongly affects the heat transfer coefficient, especially for high temperature sprays or low heat fluxes. A key effect is the heat dissipation from the liquid to the environment. The heat dissipation increases with the spray inlet temperature or the heat flux. To explain the strong dependence of the heat transfer on the heat dissipation in single phase, a spray cooling heat transfer model was suggested which includes the heat dissipation. Experimental measurements of the radial spray droplet temperature profile showed the complex nature of the heat dissipation.
Cast In-Situ Al (Mg,Mo)-Al2O3 (MoO3) Composite: Characterization and Tribological Behavior
Authors: Hamid Abdulhaqq Q. , Jain Sataish C. , Ghosh Prakriti K. , Ray Subrata
Published: April 2008

Aluminum alloy-based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO3) in molten aluminum at the processing temperature of 850 °C. During processing, displacement reaction between molten aluminum and MoO3 particles, results in formation of alumina particles in-situ also releases molybdenum into molten aluminum. A part of this molybdenum forms solid -solution with aluminum and the remaining part reacts with aluminum to form intermetallic phase Mo(Al1−xFex)12 of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in-situ, by molten aluminum and help to retain these particles inside the melt. The mechanical properties (ultimate tensile stress, yield stress, percentage elongation and hardness) of the cast in-situ composite are relatively higher than those observed either in cast commercial aluminum or in cast Al-Mo alloys. The wear and friction of the resulting cast in-situ Al(Mg, Mo)Al2O3(MoO3) composites have been investigated using a pin-on-disc wear testing machine, at different normal loads of 9.8, 14.7, 19.6, 24.5, 29.4, 34.3 and 39.2 N and a constant sliding speed of 1.05 m/s, under dry sliding conditions. The results indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar load and sliding conditions. Beyond about 30-35 N loads, there appears to be a higher rate of increase in the wear rate in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or cast Al-Mo alloy. The coefficient of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or cast Al-Mo alloy remain more or less the same. Beyond a critical normal load of about 30-35 N, the coefficient of friction decreases with increasing normal load in all the three materials.
Evaluation of Approximative Methods for Rainflow Damage of Broad-Banded Non-Gaussian Random Loads
Authors: Karlsson Magnus
Published: April 2008

Two different methods for approximating the fatigue damage of broad banded non-Gaussian random loads using the rainflow cycle count method are evaluated using loads measured on a truck. Results for Gaussian loads are summarized, and transformations for non-Gaussian loads are discussed. One of the two methods is based on the spectral moments of the process, and the results are obtained as a linear combination of an upper and lower bound. The second method is based on the assumption that the sequence of turning points of the load can be considered a Markov chain, for which results can be obtained. Measurements performed on different markets are used to study the two methods. Results are presented in terms of expected damage and amplitude spectra. Problems and possible improvements of the models are discussed.
Characterization of Mg/MgO Nanocomposites Synthesized Using Powder Metallurgy Technique
Authors: Goh C. S. , Wei J. , Gupta M.
Published: April 2008

Magnesium nanocomposites with 0.1, 0.2, 0.3 and 0.4 volume percentages of MgO were synthesized using the powder metallurgy technique. The nanocomposite billets obtained were subsequently hot extruded at a temperature of 350 °C with an extrusion ratio of 20.25:1. The extruded nanocomposites were characterized for their microstructural, physical and mechanical properties. The microstructures of the nanocomposites showed individual particles of MgO uniformly distributed in the magnesium matrix. The thermomechanical analysis results revealed that a more thermally stable magnesium nanocomposite could be obtained with a threshold amount of MgO. The tensile properties results indicated that the yield strength peaks at 0.3 vol.% of reinforcement incorporated, with an improvement of approximately 17%. An attempt is made to correlate the volume fraction of the MgO with the resultant physical and mechanical properties of the magnesium nanocomposites.
Flow Investigations in an Aero Gas Turbine Engine Afterburner
Authors: Kumar S. Suresh , Ganesan V.
Published: April 2008

This paper is concerned with the prediction of flow and flame characteristics behind complex flame stabilizer used in aero gas turbine afterburners. The numerical calculation is performed using SIMPLE algorithm with unstructured grid arrangement in which time averaged transport equation for mass, momentum, turbulence and energy are solved using finite volume method. The turbulence effects are simulated using RNG κ-ε model. Flow analysis has been carried out for the non-reacting and reacting conditions. Meshing of the flow domain is done in GAMBIT. A detailed analysis of non-reacting flow in a 60°sector afterburner from inlet to exit of the afterburner is carried out in FLUENT solver code. The various thermodynamic properties are analyzed and presented along the length of the afterburner. Three different combustion models viz. prePDF, eddy dissipation and finite rate/eddy dissipation model are used in order to predict the reacting flow. An experimental investigation of the three-dimensional confined flow fields behind a “V” shaped complex flame stabilizer in an isothermal model of an afterburner is carried out to validate the CFD code. From the present study it is concluded that the prediction procedure adopted especially for non-reacting flow can be used with confidence in the development of an afterburner at a lower cost. Since measurements were not possible under reacting conditions no attempt has been made for reacting flow validation.
Embedded Enterprise Learning: About, Through, For and From
Authors: Handscombe Robert , Rodriguez-Falcon Elena , Patterson Eann A.
Published: April 2008

Much enterprise teaching is carried out in business schools. A number of approaches are identified and their appropriateness for non-business school students reviewed. A particular focus is placed on science and engineering students and White Rose Centre for Enterprise (WRCE), formed in 1999 as part of the UK Science Enterprise Challenge initiative. Its remit was to increase enterprise learning and entrepreneurship activity, thus bringing about a ‘cultural change’. WRCE emphasizes the need to make learning ‘real’ for the student and to weave an enterprise strand through the full course of study. The findings support the argument that a combination of teaching approaches and the embedding of enterprise within a discipline subject is needed for effective learning to take place. This paper makes observations on the experiences in the White Rose Universities (Leeds, Sheffield and York). An enterprise learning framework is proposed and described in the context of international variations.
Relief Holes for Stress Mitigation in Infinite Thin Plates With Single Circular Hole Loaded Axially
Authors: Sanyal Shubhashis , Yadav Priti
Published: April 2008

The stress concentration factor in an infinite thin plate with single circular hole, loaded axially is approximately 3. The reason of this high stress is explained through stress flow lines, similar to stream lines in a ideal fluid flow around a circular obstacle. Various methods for stress mitigation have been reported in literature. In the case considered it can also be reduced by removing material from the vicinity. In the present work the removal of the material, introduction of two smaller relief holes, is proposed in such a way that the stress flow lines will follow an elliptical path and thus reducing the stress concentration effect. The size of the relief holes and center distance between the holes are formulated for minimizing the stress concentration effect. The problem is analyzed using FEA software ANSYS. The result is encouraging in a way that for a particular circular singularity the size of the relief hole and center distance is formulated for minimizing the stress concentration factor.
Advanced Automotive Engine Thermal Management: Simplified Diesel Engine Model and Experimental Validation
Authors: Simoson Christopher J. , Wagner John R.
Published: April 2008

Diesel engines fulfill diverse demands in urban and rural areas throughout the world. While the advantages of compression ignition engines are superior to other internal combustion engines in torque generation and fuel efficiency, some diesel exhaust emissions pose health and environmental problems. Emission reduction techniques generally diminish one type of tailpipe gas yet often sacrifice engine performance and may even raise other emission levels. For instance, exhaust gas recirculation can reduce NOx emissions. However, the dilution of the combustion charge with hot inert exhaust gas hinders the engine’s power characteristics. To solve this problem, an EGR cooler allows the exhaust gases to be cooled prior to mixing with intake air allowing a denser cylinder charge for combustion. The effective application of cooled EGR requires a smart thermal management system. In this paper, a real time empirical and analytical model will be introduced to estimate the diesel engine’s overall performance. The simplified model considers the engine’s combustion chemistry, as well as the thermal, emissions, and rotational dynamics. Representative numerical and experimental test results are presented and discussed to validate the model. Eventually, an on-board computer controller will use this model to regulate the EGR valve’s functionality and the smart thermal system.
Convective Heat Transfer of Laminar Single-Phase Flow in Randomly Rough Microtubes
Authors: Bahrami M. , Yovanovich M. M. , Culham J. R.
Published: April 2008

Convective heat transfer of laminar, single-phase flow in rough microtubes is studied. Wall roughness and slope are assumed to possess Gaussian, isotropic distributions. Fractal concepts are used to model the rough microtube. It is shown that due to the existence of wall roughness, both cross-sectional and inside surface areas are increased. A new concept is defined as a figure of merit for assessing thermal performance of rough microtubes. As a result of increasing roughness, an enhancement is observed in the thermal performance of microtubes. The present model can be extended to analyze other geometries such as rectangular and trapezoidal microchannels.
Forming Limit Analysis of Aluminum Tailor-Welded Blanks
Authors: Jie M. , Chow C. , Cheng C. H. , Chan L. C.
Published: April 2008

This paper presents an investigation on forming limits of tailor-welded blanks (TWBs) made of 5754-O aluminum sheets using both experimental and numerical approaches. A TWB is composed of two or more welded flat metal sheet of different thicknesses, shapes or mechanical properties. Due to the existence of weldment and the individual configurations of parent blanks, a TWB should be considered as heterogeneous in its structure. The mechanical properties of those parent metals and weld metal required for the simulation were measured individually. With the aid of the acquired data, finite element simulations for analyzing the forming process of TWBs were carried out using a general purpose finite element package, LS-DYNA. A localized necking criterion based on the vertex theory is employed to predict forming limit strains and failure locations of the aluminum TWBs. The theoretical predictions were satisfactorily validated with those obtained from the experiments.