bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Haptic Rendering for Virtual Bone Surgery
Authors: Chi Xiaoyi , Leu Ming C. , Ochoa Jorge A.
Published: April 2008

Bone surgery simulation enhanced by virtual reality technology is an effective means of training and educating novice surgeons to practice common bone surgery procedures such as drilling, cutting, etc. Haptic rendering is an essential part of the development of a bone surgical simulation system. Visual displays augmented by haptic feedback provide more realistic virtual environments, thus allowing the trainee to get a realistic feel of the real-world surgery process. This paper presents our research on the development of a bone surgery simulation system, especially on the development of the haptic rendering. Our objective is to provide a high level of realism of haptic rendering, thus making the virtual surgery procedures as intuitive and interactive as the real-world surgery procedures. In order to achieve the real-time performance of the simulation system, a Divide-and-Conquer method has been introduced in the geometric modeling to manipulate the large dataset required by the surgery simulation system. A force model based on the volumetric representation of the bone geometry has been developed. Also a running time delay technique has been developed to address the vibration problem in the haptic display. The PHANToMTM desktop manipulator is used as an input device to locate the position and orientation of a virtual drill. It is also used as an output device to provide the user with haptic sensation during the drilling operation.
Determining the Set of Active Constraints When a Rigid Body Compliantly Interacts With Multiple Frictional Contacts
Authors: Huang Shuguang , Schimmels Joseph M.
Published: April 2008

In this paper, the motion of an elastically suspended rigid body unilaterally constrained by frictional contact at multiple locations is studied. In this problem, each individual contact may or may not constrain the body’s motion. The set of actual active constraints is determined by: 1) the commanded motion of the body’s compliant support, 2) the coefficient of friction at each contact point, 3) the number and geometry of all potentially constraining surfaces, and 4) the elastic properties of the support. Here, the investigated problem is restricted to quasistatic motion and the interaction is characterized by Coulomb friction. We show that, for a passive compliant system, if the coefficient of friction at each contact is upper bounded, the set of active constraints is unique. A procedure to determine both the set of active constraints and the motion of the constrained body is provided.
Numerical Modeling of the Turbulent Supersonic Flow Over a Backward Facing Step
Authors: Ponyavin Valery , Chen Yitung , Pepper Darrell W. , Hsieh Hsuan-Tsung
Published: April 2008

The flow over a backward facing step is a classic problem in applied aerodynamics. Among many other applications, backward facing steps are often used for ignition and stabilization of the flame in a scramjet engine. In this study, the steady two-dimensional viscous supersonic turbulent flow over a backward facing step was calculated using FLUENT. The one-equation Spalart and Allmaras turbulence model was employed for the turbulent flow simulation. The free stream Mach number was 2. The simulated flow field is in good qualitative agreement with flow visualizations, pressure and temperature measurements and theoretical predictions. The boundary layer ahead of the step turns through the right angle over the corner. Then a separation occurs below the corner on the step wall. The numerical results indicate that the separation point is positioned on the step face, below the corner. The overexpansion at the corner is balanced by a lip-shock. This phenomenon was observed in experimental measurements, in flow visualizations and is also obtained in the present numerical calculation.
Aviation Assembly Automation: A Case Study in MET/Industry Alliance
Authors: Anderson John , Bullen George
Published: April 2008

There is a revolution underway in military aircraft assembly. This has been spurred by a combination of customer demands for faster and less expensive solutions, competition in the global aircraft market, and the opportunity to capitalize on technologies that have been developed for other industry segments. In addition, the workforce in military aviation in the US is aging and there is a need to train and educate a new workforce. This paper describes the formation of a unique consortium and the resultant strategic alliance(s) that are formed involving aircraft manufacturers, their equipment suppliers, and education. At the forefront of the educational efforts is Mechanical Engineering Technology. MET is in a unique position to assist in the test, evaluation, modification and technology assessments for their strategic industry and supplier partners. At the same time students are familiarized with the specific processes that the technology addresses and the problems of industry that the technology is targeted to resolve. The involvement of universities in industry research facilitates the familiarization of students with the unique and current problems faced by industry so that graduates enter the work force ready to assimilate into the value stream with minimum training and instruction. The development of a collaborative project between Northrop Grumman Corporation, M. Torres, SA, and the MET Department of Purdue University is discussed. The goal of this project is to develop a lower cost method of fixturing aircraft parts during assembly, with an integrated metrology system. Particular emphasis is placed on overcoming and aligning the scheduling, cultural and business obstacles in bringing together a Spanish machine builder, an American aircraft manufacturer and an academic department to address all aspects of the problem.
The Contribution of Elastin, Collagen, and Smooth Muscle Cells to Residual Strains in Large Elastic Arteries
Authors: Wang Jingli , Pruitt Lisa
Published: April 2008

The contribution of elastin, collagen, and smooth muscle cells to residual strain in porcine aortas were evaluated by assessing several parameters: opening angle, neutral axis, and residual strain. Elastase or collagenase was used to remove elastin or collagen. Smooth muscle cells were activated using Ca2+/KCl solutions or deactivated using KCN solutions. Several statistically significant trends (P<0.05) were obtained. As elastin was removed, the opening angle increased. As collagen was removed, the opening angle decreased. In addition, the activation of smooth muscle cells reduced the opening angle. Smooth muscle cell activation and collagenase digestion resulted in: 1) a decrease in residual strain and strain gradient, 2) the neutral axis shifting toward the adventitia side of the vessel wall.
Feasibility Study of a MEMS Viscous Rotary Engine Power System (VREPS)
Authors: Cauley Thomas H. , Rosario-Rosario Jose D. , Pisano Albert P.
Published: April 2008

In this paper is presented an analytic, theoretical and numerical study of the Viscous Rotary Engine Power System (VREPS). In addition, a proposed process flow for the fabrication of the VREPS using DRIE of silicon is described. The design premise of the VREPS is to derive mechanical power from the surface viscous shearing forces developed by a pressure driven flow present between a rotating disk or annulus and a stationary housing. The resulting motion of the rotating disk or annulus is converted into electrical power by using an external permanent magnet, embedded nickel-iron magnetic circuits, and an external switched magnetic pole electric generator similar to the design proposed by M. Senesky for the UC Berkeley micro-Wankel Engine [1]. This paper will examine the power output, isentropic efficiency, and operating characteristics of the disk and annular viscous turbines using the lubrication approximation and the Creeping Flow Equations (Stokes Flow). The viscous turbine is optimized for maximum isentropic efficiency using MATLAB numerical optimization routines. Finally, a unique triple-wafer micro-fabrication process for VREPS is presented. The proposed design consists of a 250 μm thick, 3.4 mm OD / 2.4 mm ID annular rotor with embedded magnetic poles and four 10 μm driving channels on each side of the rotor. Electrical power is generated with a switched magnetic pole generator, external permanent magnet, and integrated magnetic circuits. Calculations with water predict an output power of 825 mW at an isentropic efficiency of 25% using a pressure drop of 5 MPa cross the device.
Turbulent Fluid Interfaces and Mixing Efficiency: Dynamics, Optimization, and Regularization
Authors: Aguirre Roberto C. , Catrakis Haris J.
Published: April 2008

In many fluid engineering devices, improved design and performance require knowledge of the dynamics of turbulent fluid interfaces. Depending on the device, and the application, the performance may be more sensitive to the large scales or the small scales of the interfaces. We distinguish between cases depending on whether the surface area of, or the volume enclosed by, the interfaces is practically more relevant. For turbulent interfaces, the surface area is dominated by the small scales whereas the volume enclosed is dominated by the large scales. We examine the interfacial dynamics in separated flows and we demonstrate the differences in the area-volume behavior in the context of mixing. Resolution effects on the interfacial behavior reveal that the mixing efficiency is strongly dominated by the large-scale interfacial properties. This has broad implications, at least for fluid-mixing devices, for the development of flow-prediction and flow-control techniques.
Optimum Design of Inductors Used for Wireless Power Transmission Micro-Module
Authors: Chang Chao-Liang , Jow Uei-Ming , Huang Chao-Ta , Liu Hsiang-Chi , Jeng Jr-Yuan , Hsu Yung-Yu , Yao Chih-Min , Lee Ming-Hsiao , Tzeng Kung-Yu , Shih Yu-Ching
Published: April 2008

The micro-inductor is a key component in wireless power transmission micro modules. In this paper, an optimum design for the micro-inductor was studied and related MEMS fabrication techniques were also developed. Commercial electromagnetic property analysis software, ANSOFT, was used to screen the main design factors of the micro-inductor. It was found that the high inductance and high quality factors of the micro-inductor implied high power transmission efficiency for the micro-module’s wireless power transmission. The electrical performance of the micro-inductor was affected by the thermal stress and thermal strain induced in the operational environment of the wireless power transmission micro-module. In order to investigate the reliability of the micro-inductor, commercial stress analysis software, ANSYS, was used to calculate thermal stress and thermal strain. The deformed model of the micro-inductor was then imported into ANSOFT in order to calculate its electrical properties. Glass substrate Pyrex 7740 was used to reduce the substrate loss of the magnetic flux of the micro-inductor. The surface micromachining technique, a kind of MEMS processing, was chosen to fabricate the micro-inductor; the coil of the micro-inductor was electroplated with copper to reduce the series resistance. The minimum line width and line space of the coil were 20 μm and 20 μm respectively. Polyimide (PI) was used for supporting the structure of micro-inductors. The maximum shear stress was 74.09MPa and the maximum warpage was 2.197 μm at a thermal loading of 125°C. For the simulated data, the most suitable areas for 31-turn and 48-turn coils were at an area ratio of 1.27 and 2, respectively. The electrical properties of the inductors changed slightly under thermal loading.
Advanced Microchannel Heat Exchangers: Structural Analysis
Authors: Kuang G. , Balachandran B. , Ohadi Michael , Zhao Yuan
Published: April 2008

Since conventional refrigerants have considerable ozone depleting and global warming effects (CFC/HCFC; HFC), Carbon Dioxide (CO2) is being investigated as an alternative refrigerant in vapor compression systems. Due to favorable thermo-physical properties, CO2 when utilized in microchannel heat exchangers (HXs), can result in heat exchangers that have a low weight, a high compaction, and a high heat transfer coefficient. However, CO2 vapor compression systems need to be used in transcritical and supercritical regions, where the pressures range up to 10 MPa (1,400 Psi). Combination of the high pressure requirement, the low stiffness of the microchannel tubes, and the design requirements of compact size and low weight, one will need to carry out a mechanical design and pay attention to system vibratory characteristics such as natural frequencies. To this end, in the present study, a finite-element method (FEM)-based analysis of tube-fin heat exchangers has been carried out to determine guidelines for HX design. This analysis includes fin approximation and solid modeling. Two methods were used to approximate the fins. A dynamic analysis of a full scale HX was also carried out by using a sub-structuring methodology. Predictions from numerical simulations are found to be in good agreement with the results of experimental modal analysis. The present work can serve as a guide for structural design of heat exchangers for a variety of applications.
Simulation of the Tribological Contacts in an Axial Piston Machine
Authors: Deeken Michael
Published: April 2008

A research project at the Institute for Fluid Power Drives and Controls (IFAS) sponsored a simulation tool, which was developed to analyze the tribological contacts in an axial piston machine. This paper describes the comparison between simulation and measurement results. The research project defined several objectives. These included extending the program for the tribological contacts, such as slipper/swash plate and cylinder block/valve plate pairings. Furthermore, the results of the simulations were to be verified by means of measurements conducted on the test rig and these were to be performed on a standard unit, if possible. The values to compare simulation and measurement must first be defined in order to meet these objectives.
Synchronization in Dual Delay Line SAW Sensors
Authors: Seo Duck-Bong , Feng Z. C.
Published: April 2008

Surface acoustic wave (SAW) sensors are self-excited oscillators. Self-excitation is a consequence of the finite amount of delay in the circuit. The oscillation frequency is affected by the wave propagation speed which further depends on surface adsorption. Therefore, measurement on the surface adsorption is done by measuring the frequency change of the self-excited oscillation. In dual delay line oscillators the difference between the surface physical conditions is reflected through the difference in oscillation frequencies. Delay differential equations are used to model the sensor. Bifurcation analysis of the averaged equations indicates the presence of synchronization. The occurrence of synchronization is further demonstrated through numerical simulations. Synchronization makes the frequency measurement irrelevant. We propose phase measurement as an alternative in the presence of strong coupling between the two oscillators.
Structural and Mechanical Characteristics of Healing Myocardial Scar Tissue
Authors: Gundiah Namrata , Chang Debby , Zhang Peng , Ratcliffe Mark , Pruitt Lisa
Published: April 2008

An anteroapical transmural myocardial infarction was created in Dorset sheep and resulting scar tissues were excised two (Group A, n=5, 10.6 ± 1.2 weeks) and eight months (Group B, n=6, 36.8 ± 1.4 weeks) post infarction [1]. Samples were oriented in longitudinal and circumferential directions in a biaxial stretcher, preconditioned and tested in displacement control at room temperature in BDM solution. Stress-strain plots were obtained for samples. Histology was performed by cryo-sectioning specimens into 8 μm slices and staining using Hematoxylin & Eosin. Stress-strain analyses show that circumsferential direction was stiffer than longitudinal for Group A. Group B samples show a reverse trend and are stiffer than Group A. Stained sections show more collagen in the endocardial surface for Group B samples while Group A samples have added collagen in the epicardial side. A high density of fat cells was seen in Group B samples that may affect stiffness trends.
Heterogeneous, Variable Wall-Thickness Modeling of a Ruptured Abdominal Aortic Aneurysm
Authors: Raghavan Madhavan , Kratzberg Jarin , da Silva Erasmo Sima˜o
Published: April 2008

Pressure-induced mechanical stress in ruptured abdominal aortic aneurysms (AAA) was investigated using a finite element model with measured variations in wall thickness and material properties. We harvested an 8-cm ruptured AAA from a cadaver and recorded its geometry on bi-plane photographs and three-dimensionally reconstructed. The wall thickness was measured at over 100 sites on the aneurysm surface using digital calipers. Regional mechanical property variation (failure strengths and hyperelastic material parameters) was determined using data from uniaxial extension tests of 19 test strips cut from various regions of the AAA surface. The measured data for wall thickness and mechanical properties were transferred to the 3D AAA surface model and nonlinearly interpolated on the surface to obtain the point-to-point regional distribution for thickness and material parameters. Modeling the AAA as a thick shell, finite element stress analysis was performed. The peak stress was found to be exactly at the rupture site and was substantially higher than population averages. The measured low wall thickness at the rupture site appeared to play a major role in elevating stresses indicating that localized thin wall may be an important risk factor for AAA rupture.
The Effect of Proteolytic Enzymatic Treatment on Plastic Deformation of Porcine Aortic Tissue
Authors: Kratzberg Jarin , Walker Patricia , Rikkers Elizabeth , Raghavan Madhavan
Published: April 2008

We investigated the feasibility of developing an in vitro abdominal aortic aneurysm model by mechanically stretching passive porcine aortic tissue after enzymatic degradation of its structural proteins. Individual arterial rings, taken from the thoracic and abdominal porcine aorta were exposed to specific concentrations of collagenase (to degrade collagen) and/or elastase (to degrade elastin). The specimens were then cut into flat strips and subjected to uniaxial incremental creep tests of increasing load amplitude. The plastic strain (strain at zero load) after each creep load cycle was recorded until specimen failure. The maximum plastic strain due to enzymatic degradation and mechanical loading in elastase treated specimens (mean+SD = 45.1±14.7%; p<0.001) was significantly higher than in untreated controls (19.4±7.61%). However, the plastic strain in collagenase treated specimens (18.4±10.3%; p = 0.79) was not significantly different from the controls. Because AAA is associated with a plastic deformation of 200–400%, the results suggest that it is not feasible to develop an in vitro AAA model by enzymatic degradation and biomechanical stretching of passive porcine aorta. Consequently, these findings suggest that aneurysm growth is unlikely to be solely the result of pressure induced passive stretch of a weakened aorta.
Ferrofluid Transport Analysis for Micro- and Mesoscale Applications
Authors: Ganguly Ranjan , Gaind Amit P. , Puri Ishwar K.
Published: April 2008

Magnetically induced accumulation and dispersion of ferrofluid in a forced flow of nonmagnetic fluid is studied experimentally and numerically to characterize the ferrofluid transport. The analysis would directly benefit several microscale and mesoscale applications like magnetic drug targeting and ferrofluid lithography. Experimental observation reveals existence of a ferrofluid core near the dipole, where the field gradient is high, and a washaway region. Numerical simulations show the ferrofluid mass flux in a similar configuration. Also, selective deposition of ferrofluid on a substrate wall exposed to a forced flow of nonmagnetic fluid is demonstrated numerically.
Calculation of Optimal Trajectories for the Upper Limb
Authors: Rodriguez Carlos F. , Botero Juan C. , Pamanes J. Alfonso
Published: April 2008

A novel technique for prediction of optimal movements of the human upper limb is presented in this work. The method is adapted from robotics and uses a model of the upper limb as a manipulator of seven degrees of freedom, in order to describe its kinematics. The redundancy of the model can be exploited in order to find optimal trajectories for the upper limb, using the manipulability ratio as the performance criterion. The accepted assumptions of straight line movement of the hand and a bell-shaped velocity profile for the limb segments are used. The trajectories predicted by this technique are compared with experimental results of actual movements. The presented method is an alternative to statistical methods for computation of optimal trajectories for several experimental scenarios: clinical studies, ergonomics or sports. In this sense, the proposed technique is an effort to obtain optimal upper limb trajectories in a fully objective way.
Preliminary Design and Simulation of a Pneumatic, Stored-Energy, Hybrid Orthosis for Gait Restoration
Authors: Durfee William K. , Rivard Adam
Published: April 2008

Loss of mobility due to lower limb paralysis is a common result of thoracic level spinal cord injury (SCI). Functional electrical stimulation (FES) can restore primitive gait in the vicinity of a wheelchair by using electrical stimulation to generate muscle contractions. A new concept for FES-assisted gait is presented that combines electrical stimulation with an orthosis that contains a fluid power system to store and transfer energy during the gait cycle. The Energy Storage Orthosis (ESO) can be driven through a complete gait cycle using only stimulation of the quadriceps muscles. The conceptual design of the ESO was completed and implemented in a dynamic simulation model and in a benchtop prototype for engineering measurements. No studies were conducted with human subjects. The results demonstrate the potential of the ESO concept and the validity of the simulation model as a means for designing the system.
Vibration Analysis of Composite Wings Undergoing Material and Geometrical Couplings: A Dynamic Finite Element Formulation
Authors: Hashemi Seyed M. , Borneman Stephen
Published: April 2008

The differential equations governing Geometric-Materially coupled torsion-flexural vibrations of laminated composite wings are first reviewed. Based on the finite element methodology (FEM), Euler-Bernoulli and St-Venant beam theories, the Dynamic Trigonometric Shape Functions (DTSFs) for the beam’s uncoupled displacements are thereafter derived. Exploiting the Principle of Virtual Work (PVW) and interpolating the variables based on the DTSF, the Dynamic Finite Element (DFE) formulations for uniform beams’ coupled vibrations are first developed. The variable geometrical and mechanical parameters are then incorporated in the formulation. The applicability of the DFE method is then demonstrated by two illustrative examples where a Wittrick-Williams root counting technique is used to find the systems’ natural frequencies. The proposed DFE approach can also be advantageously extended to incorporate more complexities, further coupling as well as other geometrical and mechanical parameters in the formulation.
Development of an Innovative Defrosting System for Commercial Chiller Evaporators Through Piezoelectric Elements Application
Authors: Barelli Linda , Bidini Gianni , Moraglia Simona
Published: April 2008

The present study relates to the design of an innovative defrosting system for commercial chiller evaporators. This system is based on piezoelectric plates connected to the evaporator fins and driven at ultrasonic frequencies by a suitable electronic circuit. The operational frequency of piezoelectric elements is chosen to be close to the first harmonics of the fin resonance frequency in the ultrasonic range. The electronic driving system supplies the electric voltage required at the operational frequency starting from the PVM 0–5V signal output of a microcontroller. Moreover, the measurement of the absorbed current is acquired by the microcontroller as feedback to tune the operational frequency at the variation of the fin mass due to frost deposit and detachment. Experimental results show that the approach inhibits the frost deposit during chiller operation, increasing the period between two consecutive defrosting phases which currently is typically no greater than 6 hours. This is an important result considering that while defrosting the chiller must be shut off, depending on the defrosting methods applied, with negative effects on the goods being preserved. The system was developed in collaboration of ISA S.p.A and patented [1].
Floor Vibration Control Using Three-Degree-of-Freedom Tuned Mass Dampers
Authors: Al-Hulwah Khalid I. , Kashani Reza
Published: April 2008

The use of high-strength material in buildings has resulted in the use of less building materials and, consequently, a high level of flexibility in buildings, making them vibration prone. For example, high-strength concrete has lowered the thickness of concrete slabs used in the floors of steel/concrete buildings, such as office buildings and shopping centers, resulting in excessive floor vibration stemming from heavy traffic and normal human activity. Although not dangerous, such vibration is highly annoying to the occupants of the building. The authors have been working on the use of three-degree-of-freedom (3-DOF) tuned mass dampers (TMD) to abate floor vibration. Such TMDs can provide improved effectiveness over a traditional one-degree-of-freedom TMD and yet possess all of the attractive features of a traditional TMD; namely, simplicity and low cost. As in a 1-DOF TMD, this device will be installed on a concrete floor slab, at an optimally designed/chosen location.
Nondestructive Quantification of Operational Damage and Surface Treatments for Improved Turbine Engine Maintenance and Surveillance Requirements
Authors: Akers Douglas W. , Rideout Curtis A.
Published: April 2008

Despite advances made in metallic/intermetallic alloys and surface treatments to increase performance and decrease component weight in turbine engine components, standard inspection technologies are limited in their ability to nondestructively characterize operational damage buildup and the effect of surface treatments on component performance. Key areas where nondestructive characterization is required include the ability to quantify surface and subsurface residual strain in operational components, and cold work and surface treatments that are used to improve component life. The inability of current NDI techniques to nondestructively quantify surface and bulk residual stress in turbine engine components, especially single crystal and complex geometry components, leads to overly conservative engineering designs, maintenance procedures, and operational life estimates. Photon Induced Positron Annihilation and related portable technologies have been successfully utilized to quantify surface residual stresses and structural subsurface strain in turbine engine components subjected to high stress/high temperature environments.
Finite Element Formulation for Static Shape Control of a Thin Euler-Bernoulli Beam Using Piezoelectric Actuators
Authors: Ruggiero Eric J. , Singler John , Burns John A. , Inman Daniel J.
Published: April 2008

The main component of future space satellites will be an ultra-large, ultra-low mass aperture for high bandwidth communication or high quality imaging from on-orbit. Such an aperture will require an extremely high surface precision tolerance in order to be effective, especially for imaging purposes. Such tight surface precision tolerances dictate the use of an active control scheme to enable tight control of the shape of the aperture. Further, by integrating an active control scheme during the fabrication process, the aperture will become multi-functional and enable many scientific endeavors. One possible method for analyzing ultra-flexible space structures is through the use of the finite element method. Although many commercial packages are available, careful design of a tailored finite element solver can reveal important information about the system, such as where sensors should be placed on the structure. As an illustrative example, this work formulates the weak form of the equation of motion governing the dynamics of a cantilevered, Euler-Bernoulli beam. In particular, static shape control will be implemented on such a beam using a mathematically formulated LQR controller.
Use-Conditions-Based Board Level Shock Test Development for Handheld Components
Authors: Sahasrabudhe Shubhada , Pandey Vinayak , Phillips Betty , Lee Kang Joon , Mercado Lei
Published: April 2008

For handheld electronic applications such as cell phones and Personal Digital Assistants (PDAs), drop/impact could result in considerable flexure of the printed circuit board (PCB) mounted inside the cell phone housing. The mechanical stresses may cause electrical failure of the components, with typical failure mechanisms of board trace cracking, solder joint fatigue, and solder pad cracking. A standardized test needs to be developed to assess reliability of handheld components subjected to impacts. The test should facilitate high volume testing, maximize margin for safety factors, and capture the failure mechanisms in the field environment. To develop the reliability test using use conditions based reliability methodology, comprehensive characterization of the mechanical field stresses during end use conditions is particularly essential. This paper discusses complete cell phone drop characterization along with the shock test developed to test the components subjected to such drops. Novel fixtures have been designed to simulate free fall of the cell phone in specific orientations. After the complete characterization of cell phone use conditions, board level shock test has been selected to assess component reliability. Test repeatability, number of components on the test board, and layout of the components are some of the factors considered during the board level shock test development. Several parameters like screw and washer designs, torque have been studied to yield excellent test repeatability. Nonlinear Dynamic Finite Element Simulation has been performed to provide more insight into the interaction of the bending modes and its impact on the solder joint failures. This paper demonstrates the process of understanding use conditions, developing reliability tests, validating test results and driving industry standards.
Predicting Dynamic Stress in Centrifugal Compressors
Authors: Hill D. Lee
Published: April 2008

The best analytical process to resolve the dynamic stress in rotating machinery has not yet been established. This is largely due to the different classes of the fluid induced vibration that exist today. This reported effort establishes a sound methodology of resolve fluid induced stresses that occur at resonant frequencies. The proposed process incorporates the use of transient sliding mesh computational fluid dynamics and forced frequency response finite element analysis. Details of the new process are provided along with any perceived limitations. There are 2 detailed case studies that are provided. The results obtained are validated with experimental impeller strain gauge data that was obtained during a full-load hydrocarbon test program. These case studies also provide good insight into the role volutes play on the dynamic stress of impellers.
Tool Path Generation for Machining Shrouded Turbine Blisk
Authors: Wu Xiang , Zhao Wansheng , Du R.
Published: April 2008

Shrouded turbine blisk is an important component for liquid-propellant rocket engine, airplane engine and some other high-power turbine machines. It is made from high-temperature alloy (e.g., nickel-base alloy and titanium alloy) and hence, is difficult to machine. In addition, its geometrical shape is complicated involving many semi-enclosed, twisted, free-form surfaces. In order to ensure the best performance, its dimension accuracy is very demanding. For the moment, an effective way to manufacture shrouded turbine blisk is Electrical Discharge Machining (EDM) using form tools (form electrodes). However, owing to its complicated geometry, existing commercial CAM systems cannot generate the interference-free tool path for it. In this paper, a new tool path generation method is presented. The new method is base on the quadratic programming and CNC multi-axis simultaneous control. It generates tool path in two steps. First, a feasible zone is generated by coarse search, which gives an elementary path for form tool feed. Then, within the feasible zone the actual NC tool path is found by fine search through CNC multi-axis simultaneous control simulation. In practice, a form tool follows the interference-free tool path moving into the twisted passages of blisk for machining, while the blisk is turning by a CNC turntable. The new method is validated experimentally. Compared to the existing methods, it can obtain high machining efficiency and high machining accuracy. Experimental results indicate that the new method is accurate. This new method can also be applied to many other machining applications involving complicated geometrical shape.
Thermal Control Utilizing an Electrohydrodynamic Conduction Pump in a Two-Phase Loop With High Heat Flux Source
Authors: Jeong Seong-il , Didion Jeffrey
Published: April 2008

The electric field applied in dielectric fluids causes an imbalance in the dissociation-recombination reaction generating free space charges. The generated charges are redistributed by the applied electric field resulting in the heterocharge layers in the vicinity of the electrodes. Proper design of the electrodes generates net axial flow motion pumping the fluid. The electrohydrodynamic (EHD) conduction pump is a new device that pumps dielectric fluids utilizing heterocharge layers formed by imposition of electrostatic fields. This paper evaluates the experimental performance of a two-phase breadboard thermal control loop consisting of an EHD conduction pump, condenser, pre-heater, high heat flux evaporator (HE), transport lines, and reservoir (accumulator). The generated pressure head and the maximum applicable heat flux are experimental determined at various applied voltages and sink temperatures. Recovery from dryout condition by increasing the applied voltage to the pump is also demonstrated.
Simultaneous Optimization of Removal Rate and Part Accuracy in High-Speed Milling
Authors: Kurdi Mohammad H. , Schmitz Tony L. , Haftka Raphael T. , Mann Brian P.
Published: April 2008

High-speed milling provides an efficient method for accurate discrete part fabrication. However, successful implementation requires the selection of appropriate operating parameters. Balancing the multiple process requirements, including high material removal rate, maximum part accuracy, sufficient tool life, chatter avoidance, and adequate surface finish, to arrive at an optimum solution is difficult without the aid of an optimization framework. In this paper an initial effort is made to apply analytical tools to the selection of optimum cutting parameters (spindle speed and depth of cut are considered at this stage). Two objectives are addressed simultaneously, maximum removal rate and minimum surface location error. The Time Finite Element Analysis method is used in the optimization algorithm. Sensitivity of the surface location error to small changes in spindle speed near tooth passing frequencies that are integer fractions of the system’s natural frequency corresponding to the most flexible mode is calculated. Results of the optimization algorithm are verified by experiment.
The Role of Cutter Eccentricity on Surface Finish and Milling Forces
Authors: Schmitz Tony L. , Couey Jeremiah , Marsh Eric , Tummond Michael F.
Published: April 2008

In this paper, the role of milling cutter eccentricity, commonly referred to as runout, is explored to determine its effects on surface topography and milling forces. This work is motivated by the observation that commercially-available cutter bodies often exhibit variation in the teeth/insert radial locations as a result of manufacturing issues. Consequently, the chip load on individual cutting teeth varies periodically, which can lead to premature failure of the cutting edges. Additionally, this chip load variation increases the roughness of machined surfaces. This research isolates the effect of runout on cutting forces and the machined surface finish in a series of experiments completed on a precision milling machine with 0.1 μm positioning repeatability and 0.02 μm spindle error motion. The runout is varied in a controlled fashion and results compared between experiment and a comprehensive time-domain simulation.
Thermal Stress Analysis of Concrete Arch Dams Due to Environmental Action
Authors: Sheibany Farrokh , Ghaemian Mohsen
Published: April 2008

A three-dimensional finite element analysis was carried out to determine the annual variation of temperature and thermal stresses of a concrete arch dam. Appropriate heat transfer boundary conditions in the dam body were used for air and reservoir temperature as well as solar radiation variations. Karaj arch dam in Iran was used as a case study. The rate of convergence of the numerical solution is examined. Results of the finite element analysis show that probable cracks occur in a very narrow region of the downstream face. Thermal loads have the most significant effects for causing downstream cracks in comparison with self-weigh and hydrostatic loads. The cracked areas of downstream face conform to the regions that have the highest temperature in downstream face. It can be associated to the solar radiation, which shows two-dimensional analysis of an arch dam cannot yields accurate results and three-dimensional analysis is necessary.
Prediction of the Temperature in a Long Horizontal Fin Rod Cooled by Natural Convection and Radiation
Authors: Mueller Donald W. , Abu-Mulaweh Hosni I.
Published: April 2008

The objective of this fundamental study is to numerically predict the temperature along a fin cooled by natural convection and radiation and to compare with measurements. The physical situation considered is a horizontal fin with a cylindrical cross-section. One end of the fin is maintained at a constant elevated temperature, and the fin is sufficiently long so that heat loss from the tip is negligible. Heat is transferred by conduction along the fin and dissipated from the surface via natural convection and radiation. The effect of natural convection is described with a published correlation for a horizontal cylinder, and a simple model is used for the radiative heat transfer. A finite difference formulation that allows for variable fluid property effects is used to determine the temperature distribution along the fin. A comparison is made to experimental results, and the agreement between the model and experiment is very good. Results show that the heat loss due to radiation is typically 15%–20% of the total.
Adaptive Control of MEMS Mirrors for Beam Steering
Authors: Arancibia Ne´stor O. Pe´rez , Gibson Steve , Tsao Tsu-Chin
Published: April 2008

This paper presents the design and experimental implementation of an adaptive inverse control system for a two axis MEMS tilting mirror used for optical beam steering. The theoretical issues and practical design considerations involved in this task are discussed in detail. The first topic addressed is the system identification of input-output and state-space models of the MEMS mirror. Consistency among the following two system identification methods is verified: identification of a parameterized transfer function and identification of a state-space model by a subspace method. Next, a stabilizing feedback controller and an adaptive inverse control scheme based on an adaptive inverse QR recursive least-squares filter are developed. Finally, the experimental implementation of the control loops is described and the performance of the beam steering system is analyzed.
Evaluation of the Temperature Oscillation Technique to Calculate Thermal Conductivity of Water and Systematic Measurement of the Thermal Conductivity of Aluminum Oxide – Water Nanofluid
Authors: Bhattacharya P. , Nara S. , Vijayan P. , Tang T. , Lai W. , Phelan P. E. , Prasher R. S. , Song D. W. , Wang J.
Published: April 2008

A nanofluid is a fluid containing suspended solid particles, with sizes of the order of nanometers. The nanofluids are better conductors of heat than the base fluid itself. Therefore it is of interest to measure the effective thermal conductivity of such a nanofluid. We use temperature oscillation technique to measure the thermal conductivity of the nanofluid. However, first we evaluate the temperature oscillation technique as a tool to measure thermal conductivity of water. Then we validate our experimental setup by measuring the thermal conductivity of the aluminum oxide-water nanofluid and comparing our results with previously published work. Finally, we do a systematic series of measurements of the thermal conductivities of aluminum oxide-water nanofluids at various temperatures and explain the reasons behind the dependence of the enhancement in thermal conductivity of the nanofluid on temperature.
Generic Performance Characterizations of Distributed Energy CHP Systems
Authors: Hudson C. R. , Petrov A. Y.
Published: April 2008

This paper describes work underway to quantify the amount and quality of thermal resource that is potentially available from a given amount of electrical distributed generation with combined heat and power (CHP) capability. The method of analysis has been to generically characterize the operating parameters of the various components involved in a CHP system (e.g., prime mover, exhaust heat exchanger, absorption chiller) and to determine expected steady-state conditions based upon thermodynamic behavior of the system. The goal is to develop a means to quickly estimate the amount of thermal energy available (e.g., MJ/hr) and quality of the thermal stream (e.g., temperature) based upon a minimum number of required inputs regarding the CHP system elements. From this effort, CHP system configurations can be evaluated for their potential use in a given application. Thus far, gas turbines, ranging from 30 kW to 14 MW of electric output, have been evaluated as the prime mover. The model has been benchmarked using operations data from a 30-kW CHP system at the CHP Integration Laboratory at Oak Ridge National Laboratory (ORNL). The comparison to actual system operations and the on-going research activities in this area will also be discussed in the paper.
Smooth Tool-Axis Variation in 5-Axis Surface Machining
Authors: Lee Chen-Han
Published: April 2008

In 5-axis surface machining, there are common problems of jagged tool paths if the Tool-axis orientation depends on local surface properties, such as the surface normal. These problems occur even if the geometry is properly built and appears to have good (G1) continuity properties. This paper analyzes the cause of the problems — the higher degree discontinuity of the geometry — and provides the general mathematical description of the symptoms (jagged tool paths). We also present a set of practical remedies to cope with the higher degree discontinuity and produce smooth 5-axis tool paths.
CFD Simulation and Experimental Validation of Solidification of Metal Matrix Composites (MMC) in the Presence of Cooled Fibers
Authors: Amano R. S. , Xie J. , Lee E. K. , Rohatgi P. K.
Published: April 2008

A new experimental configuration for the casting of metal matrix composites (MMCs) using Al-4.5 wt pct Cu have been used to obtain finer microstructures around the fiber reinforcement. The new configuration allows the fibers to be extended out the mold and cooled by a heat sink. By doing so, the solidification can be made more rapid, and more primary alpha-aluminum phase can be formed on the surface of the fibers. It is believed that this can lead to improvement in the properties of the composite. CFD simulation of the solidification of Al-4.5 wt pct Cu in the casting process has been carried out by using commercial CFD code. Parametric studies on the effects of different processing parameters on solidification time have been simulated using the CFD code. These parameters include, but are not limited to, the pouring temperature of the liquid melt, sink temperature, fiber length extended out of the mold, the mold initial temperature, fiber conductivity, applied pressure, and fiber bundle diameter. Selected simulation results are compared with the available experimental data obtained from the UWM Center for Composites.
Effects of Independently Rolling Wheels on Flange Climb Derailment
Authors: Wilson Nicholas , Shu Xinggao , Kramp Ken
Published: April 2008

The effects of independently rolling wheels (IRW) on flange climb derailment have been investigated through simulations using Transportation Technology Center, Inc. (TTCI)’s *NUCARSTM dynamic modeling software. Simulations of single wheelsets and hypothetcal light rail vehicles equipped with IRWs show that flange angle and flange length parameters play an important role in preventing derailments. That role is especially critical for independent rolling wheels due to their lack of self-steering capability. The speed contour concept was proposed for engineers to adopt the flange angle and flange length in a logical way for wheel profile design in new vehicles and wheel profile maintenance. It is also shown that the sensitivity of IRW to flange climb is also very dependent on particular vehicle designs.
The Modeling of Air-Cooled Absorption Chiller Integration in CHP System
Authors: Liao Xiaohong , Garland Patricia , Radermacher Reinhard
Published: April 2008

Absorption chillers are well suited for the use of exhaust heat from prime movers, and they improve the heat utilization of Cooling, Heating, and Power (CHP) systems. An air-cooled absorption chiller eliminates the cooling tower and brings considerable advantages as compared to water-cooled chillers. However, the expensive capital cost and crystallization of LiBr (Lithium Bromide) solution in certain operation conditions restrict the commercialization of air-cooled LiBr absorption machines. This paper discusses the feasibility of air-cooled absorption in CHP systems, where the control strategies based on the application can avoid the occurrence of crystallization. By using the fundamental thermodynamic principle, steady-state thermodynamic modeling and simulation have been done in Engineer Equation Solver (EES) to predict the operation of air-cooled absorption chiller integration in CHP systems with special consideration of the crystallization limits. The data of field operation acquired from a CHP system at UMD are used for validation.