bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison Study of Mahalanobis-Taguchi System and Neural Network for Multivariate Pattern Recognition
Authors: Hong Jungeui , Cudney Elizabeth A. , Taguchi Genichi , Jugulum Rajesh , Paryani Kioumars , Ragsdell Kenneth M.
Published: April 2008

The Mahalanobis-Taguchi System is a diagnosis and predictive method for analyzing patterns in multivariate cases. The goal of this study is to compare the ability of the Mahalanobis-Taguchi System and a neural network to discriminate using small data sets. We examine the discriminant ability as a function of data set size using an application area where reliable data is publicly available. The study uses the Wisconsin Breast Cancer study with nine attributes and one class.
Intelligent Approach to Floor Vibration Control
Authors: Martell Janice L. , Ebrahimpour Arya , Schoen Marco P.
Published: April 2008

Genetic Algorithms (GAs) have been used to solve a multiple of engineering problems with the civil engineering applications ranging from optimal placement of sensors and actuators on structures to pipeline layouts. GAs are especially useful in finding optimal solutions to problems that have many parameters with complex search spaces and a high level of interaction among the describing parameters. The novel experimental control approach presented in this paper uses a GA and a piezoelectric actuator to control the vibration of an aluminum cantilever beam. This set-up is based on a floor vibration problem, where the human perception of vibration dictates the sensitivities in the cost function of the GA. Lightweight floors can be excited by occupant activities such as walking, jumping and dancing. Humans are especially sensitive to vibrations in the range of 4 to 8 Hz. The occupancy of a floor system — whether the floor is used in an office, a shopping mall, or a ballroom — determines the degree to which humans are annoyed by the vibration. In this paper, the GA based control limits the peak acceleration within a predefined bandwidth. Since the cantilever beam has a higher natural frequency than a lightweight floor system a bandwidth of approximately 1.6–15.9 Hz (10–100 rad/s) is used as the frequency range to control. The control to be designed will be a genetic algorithm-robust controller. The analytical results indicate that this novel approach works well.
Leveraging the Open-Loop Stiffness of Pneumatic Actuators to Enable High-Stiffness Surface Simulation in Impedance-Type Haptic Interfaces
Authors: Shen Xiangrong , Goldfarb Michael
Published: April 2008

The stable simulation of high-stiffness surfaces remains a challenge in impedance-type haptic simulation of mechanical environments. In this paper, the authors propose an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By utilizing the open-loop component of actuator stiffness as the primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from closed-loop control of the actuator. A stability analysis is presented indicating that this approach enhances significantly the range of passivity of haptically simulated high-stiffness surfaces. Experimental results both with and without a human operator are presented that demonstrate the effectiveness of the approach.
Lessons in Teaching an Interdisciplinary Mechatronics Class
Authors: Turner Michael
Published: April 2008

It is common for engineers but rare for engineering students to be asked to work on projects with people whose expertise is in other fields. In an effort to address this shortcoming at the University of Dayton, an interdisciplinary mechatronics class was developed. This lab based course with equal numbers of electrical engineering and mechanical engineering seniors focused on designing, building and controlling electromechanical systems. This paper covers the development of the course and the challenges posed in teaching such a course. The course is centered on the concept of building an autonomous system by integrating a well designed mechanism with a well designed electrical controller. Particular emphasis is placed on the challenge of covering material which is basic and familiar to one set of students while being novel and challenging to another set of students. Additional discussion is included on encouraging cross-disciplinary communication, preventing asymmetrical workloads and stimulating innovation.
Toy Asparagus Spear Risk Analysis
Authors: Brickman Dennis B. , Power Erik D. , Hayes Wilson C.
Published: April 2008

A tragic accident occurred in a day care center when a 5 year old child fell face down with a plastic toy asparagus spear in his mouth, puncturing the soft palate and dissecting the internal carotid artery. Approaches utilized in the risk analysis include: literature review, safety standards research, accident statistics survey, biomechanical testing, and evaluation of alternative toy asparagus designs. The goal of this investigation is to make toy designers and users more aware of the puncture/impaling hazard and to identify design alternatives to prevent similar injuries from occurring.
Hybrid Control of the Berkeley Lower Extremity Exoskeleton (BLEEX)
Authors: Huang Lihua , Steger Ryan Ryan , Kazerooni H.
Published: April 2008

The first functional load-carrying and energetically autonomous exoskeleton was demonstrated at U.C. Berkeley, walking at the average speed of 0.9 m/s (2 mph) while carrying a 34 kg (75 lb) payload. The original BLEEX sensitivity amplification controller, based on positive feedback, was designed to increase the closed loop system sensitivity to its wearer’s forces and torques without any direct measurement from the wearer. The controller was successful at allowing natural and unobstructed load support for the pilot. This article presents an improved control scheme we call “mixed” control that adds robustness to changing BLEEX backpack payload. The walking gait cycle is divided into stance control and swing control phases. Position control is used for the BLEEX stance leg (including torso and backpack) and the sensitivity amplification controller is used for the swing leg. The controller is also designed to smoothly transitions between these two schemes as the pilot walks. With mixed control, the controller does not require a good model of the BLEEX torso and payload, which is difficult to obtain and subject to change as payload is added and removed. As a tradeoff, the position control used in this method requires the human to wear seven inclinometers to measure human limb and torso angles. These additional sensors require careful design to securely fasten them to the human and increase the time to don (and doff) BLEEX.
Structural Integrity of Hydrogen Storage Tanks at Pre-Stressing and Operating Pressures
Authors: Parham J. L. , Guo Y. B. , Sutton W. H.
Published: April 2008

With the fuel prices reaching record highs and ever-increasing tighter environmental policies, hydrogen-powered vehicles have great potential to substantially increase overall fuel economy, reduce vehicle emissions, and decrease dependence on foreign oil imports. While hydrogen fuel is exciting for automotive industries due to its potentials of significant technical and economic advantages, design and manufacture safe and reliable hydrogen tanks is recognized as the number one priority in hydrogen technology development and deployment. Real life testing of tank performance is extremely useful, but very time consuming, expensive, and lacks a rigorous scientific basis, which prohibits the development of a more reliable hydrogen tank. However, very few testing and simulation results can be found in public literature. This paper focused on the development of an efficient finite element analysis (FEA) tool to provide a more economical alternative for hydrogen tank analysis, though it may not be an all-out replacement for physical testing. A FEA model has been developed for the hydrogen tank with 6061-T6 aluminum liner and carbon-fiber/epoxy shell to investigate the tank integrity at pre-stresses of 45.5 MPa, 70 MPa, and 105 MPa and operating pressures of 35 MPa, 70 MPa, and 105 MPa. The residual stresses induced by different pre-stresses are at the equivalent level in the middle section but vary significantly in other tank sections. Residual stress magnitudes may saturate at a certain pre-stress level. In contrast, the residual strains in the middle section increases with pre-stress. The simulation results indicate that the optimal pre-stress level depends on the specific operating pressure to enhance tank integrity. A certain area of the neck and the top and bottom domes also experiences peak stress and strain at pre-stressing and regular operating pressures. The research findings may help manufacturing industries to build safety into manufacturing practices of hydrogen storage infrastructures.
Microstructure in the Sedimentation of Anisotropic and Deformable Particles
Authors: Saintillan David , Darve Eric , Shaqfeh Eric S. G.
Published: April 2008

We use large-scale simulations to study the microstructure and concentration fluctuations in sedimenting suspensions of anisotropic particles such as spheroids, and deformable particles such as viscous droplets in the Stokes flow regime. An efficient method based on point-particle interactions is used allowing the simulation of full-scale suspensions with both periodic and slip boundary conditions, where the latter are used to qualitatively reproduce the effects of container walls. The concentration instability occurring in such systems is adequately captured, and we show that the formation of inhomogeneities is closely linked to the large-scale fluctuations of the disturbance flow. In particular, our simulations suggest that the presence of walls is important for a wavenumber selection to be observed, as they lead to a decay of the initial large-scale recirculation that otherwise dominates the flow in periodic systems. Results for the sedimentation rates and orientation distributions are also presented, and show good agreement with published experimental results.
Design of an Engine Load Simulator
Authors: Radpukdee T. , Jirawattana P.
Published: April 2008

This paper discusses the design details of an engine load simulator. A proportional valve is used to regulate a resistant to the flow from a hydraulic pump. Due to the fact that pressure drop across an orifice is proportional to the square of the flow which is similar to an aerodynamic drag that is proportional to the velocity square. While this is true, more sophisticated control methods can be incorporated. However, the dynamic characteristics of the valve can not be included in designing a controller with an adaptive control method. As will be discussed, the valve effect can be eliminated mechanically or electronically. With the dynamic pressure compensation from the main valve to the pilot valve, the inertia effect of the spool can be reduced. On the other hand, the pressure in the pressure line can be read and compensated for the signal to the pilot valve directly. In addition, a variable structure control for a load simulator will be presented.
Improvement of Ventilation Analysis in Turbine Generator
Authors: Taniyama Yoshihiro , Kabata Yasuo , Hashidate Yoshio , Shioda Kazunori , Katayama Hitoshi
Published: April 2008

Most of large electric rotating machines, for example, the generator and the motor adopt the cooling type that the coolant gas such as hydrogen and air is circulated inside. To improve the performance of the machine and the competitiveness of the product, development of cooling technology such as efficient and effective ventilation of coolant gas becomes important. In addition, it is also important to calculate the coolant gas distribution with high accuracy. This is because it is necessary to cancel the increase in the heat density by it. In this study, a new cooling design system for the turbine generator is developed, where calculation accuracy of the coolant gas distribution is developed and calculation time is reduced. The following shows the outline of this technical approach: 1) Development of a method of the fluid network system analysis that satisfy continuous condition and pressure condition in each branch, and considers divergence loss on branch point and convergence loss on joint point by the one dimensional transient fluid analysis. 2) A pressure loss database such as divergence loss on branch point and convergence loss on joint point reflects knowledge by the elemental experiment and 3D-CFD. In this paper, a basic code of the fluid network system analysis is introduced and verified by a one-slot ventilation model with half axial length of actual stator core.
On-Line Self-Learning Neural Network Control for Articulated Pneumatic Robot Position System
Authors: Xue Yang , Jing Zhongliang
Published: April 2008

In this paper, a NNI (Neural Network Identifier) is presented to learn model for an articulated multiple DOF (Degrees of Freedom) pneumatic robot position system. It can adjust the weights and biases of NNC (Neural Network Controller) on line. This controller can effectively solve the difficult problems of single rod cylinders, which are mainly caused by asymmetric structures and different friction characteristics in two directions. On these bases an articulated four DOF pneumatic robot is designed and its work space is analyzed. Experimental results prove that, the dynamic performance of the system can be much improved. The system using NN (Neural Network) has strong self-adaptability and robustness. It obtains desired percentage overshoot and repeatability in steady-state responses.
Precision Modular Thermal Deformation Modeling
Authors: Batson Jennifer , Hashemi Ab
Published: April 2008

The thermal response test of payloads in a vacuum chamber, commonly referred to as TVAC, is one of the most widely used performance characterizations of the payload in the aerospace industry. This verification test almost always requires modeling and validation of the performance of the payload under operational and off-design mission scenarios. To obtain high-precision performance predictions, the thermal analyst must accurately model the chamber environment, including any temperature variation along the shroud. Then, the subsystems that have already been modeled and tested are integrated into a larger assembly and tested at the system level. Using a modular technique, the analyst can preserve the subsystem models and the chamber seamlessly and develop an integrated model for the test configuration. Also, since many subsystems or components are similar in configuration, but different in size, the need for models amenable to scaling without recreating the thermal boundary conditions and couplings in the model are required. This paper describes a methodology that was developed for adaptive integrated modular modeling for precision thermo-structural analysis of optics. The details of the modeling technique are explained using the thermal vacuum test chamber with two scaleable payloads. This methodology is not limited to the problem described here and is fully relevant to a wide range of applications.
Shape Parameters Measurement of Profile-Shifted Spur and Helical Gears
Authors: Lin Ah-Der , Kuang Jao-Hwa
Published: April 2008

Various measurement methods have been proposed to measure the tooth shape parameters of profile-shifted spur and helical gears. This study proposes an over-balls measurement technique based on the tooth form equations of the profile-shifted spur and helical gears. The relations between the over-ball distance and the tooth parameters, i.e. the profile-shifted factor and the pressure angle, are derived for the two gears. The effect of the ball size on the accuracy of the measurements is investigated. An algorithm is proposed to extract the profile-shifted factor and the pressure angle from the measured over-ball chordal lengths. A good agreement is found between the calculated data and the measured results. Hence, the proposed inverse measurement method provides a feasible approach for obtaining highly accurate estimates of the tooth shape parameters of profile-shifted spur and helical gears.
The Classical Nusselt Problem of Film Condensation: Direct Steady and Unsteady Computational Simulations That Yield Results on Stability and Wave Effects
Authors: Phan L. , Post S. L. , Narain A.
Published: April 2008

Accurate steady and unsteady numerical solutions of the full 2D governing equations for the Nusselt problem (film condensation of quiescent saturated vapor on a vertical wall) are presented and related to known results. The problem, solved accurately up to film Reynolds number of 60 (Reδ ≤ 60), establishes various features of the well known steady solution and reveals the interesting phenomena of stability, instability and non-linear wave effects. The wave effects are shown to arise from the intrinsic flow instabilities as well as sensitivity to ever present minuscule transverse vibrations of the condensing surface. The results also suggest ways to enhance wave fluctuations and heat transfer rates.
Using Phased Array Technology and Embedded Ultrasonic Structural Radar for Active Structural Health Monitoring and Nondestructive Evaluation
Authors: Yu Lingyu , Giurgiutiu Victor
Published: April 2008

The embedded ultrasonic structural radar (EUSR) was developed based on phased array technology. It can interrogate large structural areas from a single location using ultrasonic guided Lamb and Rayleigh waves generated by tuned piezoelectric wafer active sensors (PWAS) that are permanently attached to the structure. This paper brings together several aspects of the implementation and application of EUSR to structural damage detection: (a) improving the near field damage detection; (b) designing optimized phased-array patterns; (c) designing a mini phased array for compact structures with complicated geometries and multiple boundaries. Firstly, we deduced a generic formulation for phased array directional beamforming using the exact traveling waves formulation without the limiting parallel-rays assumption used by other investigators. This algorithm has been implemented in the EUSR LabVIEW program and its performance has been verified through simulation and experimental tests. Secondly, we studied the beamforming and lobe steering characteristics of a 1-D linear array design. The influence of several geometry parameters was discussed in order to achieve the optimal directionality, including the number of sensors in the phased array, the spacing between adjacent sensors, and the steering direction angles. Extensive simulation studies have shown that the well-behaved directional beamforming can be achieved with judicious array design. Proof-of-concept experiments for testing these results have also been set up and the preliminary results are confirming the effectiveness of our approach. Thirdly, we investigated the possibility of applying the EUSR phased array method to compact specimens and proposed the design of a mini phased array. Laboratory experiments have been carried out to prove the successful implementation of this concept. Finally, the paper ends up with discussions and conclusions regarding the beamforming, optimization and implementation of the PWAS phased arrays, as well as suggestions for further work.
An Investigation of Friction Dynamics of Mass Spring System With Base Excitation
Authors: Fawzy A. , Youness Y. K. , El-Butch A. M. A. , Ibrahim I. M.
Published: April 2008

The friction force between coupled machine members in relative motion exerts sometimes significant influence on system dynamic behavior, giving rise to undesirable self-excited oscillation. The aim of this paper is to investigate the contribution of each design parameter and operating conditions on the system dynamic performance theoretically and experimentally. The theory presents a comparative analysis between different dynamic coefficient of friction which may exist between the sliding mass which connected to two springs and a harmonic base excitation surfaces. Furthermore, results are obtained for arbitrary values of natural frequency, excitation frequency and amplitude of exciting base displacement. A test rig has been constructed to test several contacting material combinations. Results for sliding mass acceleration have been obtained for a wide range of exciting base frequencies, masses of slider and amplitudes of exciting base displacement, good agreement with theoretical results have been achieved.
On Self-Sensing Actuators for Electrohydraulic Valves: Comparisons Between Boxcar Window Observer and Kalman Filter
Authors: Yuan Qinghui , Li Perry Y.
Published: April 2008

Self-sensing refers to extracting the position information from the electromagnetic signals instead of from a physical position sensor. Self-sensing actuator has the benefit of significantly reducing hardware effort. In this paper, we investigate two types of observers: Boxcar Window Observer and Kalman Filter. The performance of both observers has been compared in simulation and experimentally.
A Nanoindentation-Based Microbridge Testing Method for Mechanical Characterization of Thin Films for MEMS Applications
Authors: Cao Zhiqiang , Zhang Tong-Yi , Zhang Xin
Published: April 2008

Plasma-enhanced chemical vapor deposited (PECVD) silane-based oxides (SiOx) have been widely used in both microelectronics and MEMS (MicroElectroMechanical Systems) to form electrical and/or mechanical components. In this paper, a novel nanoindentation-based microbridge testing method is developed to measure both the residual stresses and Young’s modulus of PECVD SiOx films on silicon wafers. Theoretically, we considered both the substrate deformation and residual stress in the thin film and derived a closed formula of deflection versus load. The formula fitted the experimental curves almost perfectly, from which the residual stresses and Young’s modulus of the film were determined. Experimentally, freestanding microbridges made of PECVD SiOx films were fabricated using the silicon undercut bulk micromachining technique. The results showed that the as-deposited PECVD SiOx films had a residual stress of −155±17 MPa and a Young’s modulus of 74.8±3.3 GPa.
Modeling of Radiative and Optical Behavior of Nanofluids Based on Multiple and Dependent Scattering Theories
Authors: Prasher Ravi S. , Phelan Patrick E.
Published: April 2008

There is a lot of interest in the research community about nanofluids due to their high thermal conductivity and potential applications as heat transfer fluids. In this paper we calculate the optical and radiative properties of nanofluids. Results indicate that the radiative properties of nanofluids can be very different from those of the base fluid, suggesting that these properties can be tailored to satisfy specific applications. Results also suggest that multiple and dependent scattering effects can be very dominant in nanofluids.
Nonlinear Vibrations of Non-Uniform Beams Including Inertia Effects
Authors: Caruntu Dumitru I. , Stroe Ion
Published: April 2008

This papers deals with nonlinear vibrations of non-uniform beams with geometrical nonlinearities such as moderately large curvatures, and inertia nonlinearities such as longitudinal and rotary inertia forces. The nonlinear fourth-order partial-differential equation describing the above nonlinear effects is presented. Using the method of multiple scales, each effect is found by reducing the nonlinear partial-differential equation of motion to two simpler linear partial-differential equations, homogeneous and nonhomogeneous. These equations along with given boundary conditions are analytically solved obtaining so-called zero-and first-order approximations of the beam’s nonlinear frequencies. Since the effect of mid-plane stretching is ignored, any boundary conditions could be considered as long as the supports are not fixed a constant distance apart. Analytical expressions showing the influence of these three nonlinearities on beam’s frequencies are presented up to some constant coefficients. These coefficients depend on the geometry of the beam. This paper can be used to study these influences on frequencies of different classes of beams. However, numerical results are presented for uniform beams. These results show that as beam slenderness increases the effect of these nonlinearities decreases. Also, they show that the most important nonlinear effect is due to moderately large curvature for slender beams.
Multiple Fault Diagnosis Method in Multi-Station Assembly Processes Using State Space Model and Orthogonal Diagonalization Analysis
Authors: Kong Zhenyu , Kumar Ramesh , Gogineni Suren , Zhou Yingqing , Lin Jijun , Huang Wenzhen , Ceglarek Dariusz
Published: April 2008

Dimensional control has a significant impact on the overall product quality and performance in large and complex multi-station assembly systems. From measurement data, the way to identify root causes for large variation of Key Product Characteristics (KPCs) is one of the most critical research topics in dimensional control. This paper proposes a new approach for multiple fault diagnosis in a multi-station assembly process by integrating multivariate statistical analysis with engineering model. Based on product/process information, by using the state space model, a set of fault patterns for multi-station assembly process are developed, which explicitly represent the relationship between the error sources and KPCs. The vectors of these patterns form an affine system. Afterwards, the Principal Component Analysis (PCA) is applied to conduct orthogonal diagonalization of the measurement data. Thus, the measurement data can be easily projected to the axes of the affine system. Whereby, the significance of each fault pattern shall be estimated accurately. Finally, a few case studies are also provided to validate the proposed methodology.
Tribo-Fatigue
Authors: Sosnovskiy Leonid A. , Senko Veniamin I.
Published: April 2008

By the end of the last century it was realized that most critical units of any machine are the ones which are called active systems, i. e. any mechanical system that operates in the conditions of contact interaction of elements (during sliding, rolling, slippage, etc.) and transmits cycle load simultaneously. In these cases complex wear-fatigue damage of materials takes place. Such systems and processes of their damage became the main object of studies in tribo-fatigue — the science that emerged on the verge of fatigue strength, tribology and the theory of reliability of mechanical systems. Practically the development of tribo-fatigue opens new ways for solving problems of improving lifetime and reliability of machines on main criteria of workability with simultaneous reduction of labour, means and material expenditure for their manufacture and operation. The basic ideas of tribo-fatigue and its interrelation with related disciplines (tribology, fatigue strength, reliability of mechanical systems) are presented in the report [1,2]. In the present work we will give a very brief report of some basic results obtained in tribo-fatigue.
Fundamental Ideas of Tribo-Fatigue and Their Study in Belarus
Authors: Senko Veniamin I. , Sosnovskiy Leonid A.
Published: April 2008

Discipline “Fundamentals of Tribo-Fatigue” is taught in Belarusian State University of Transport and State Technical University named after Sukhoi since 1996 for future mechanical engineers [1, 2]. Course of lections was delivered at the mechanics and mathematics faculty of Belarusian State University. By now a complete set of training and systematic text-books is published in Russian. Main text-book is published in English [3].
Edge Effects on the Determination of Fickian Mass Diffusivity of Polymers
Authors: Aktas Levent , Hamidi Youssef K. , Altan M. Cengiz
Published: April 2008

Models based on one-dimensional solution of Fickian diffusion equation are commonly used to characterize diffusion coefficients of polymers. These methods are known to have errors due to edge effects, which are believed to be compensated by correction factors. In order to better understand these errors and performance of various correction factors, non-dimensional solution of diffusion equation in a three-dimensional rectangular domain is used to simulate artificial mass diffusion data. The simulated data is then utilized to analyze the errors associated with commonly used methods of diffusivity determination for a variety of geometries with aspect ratios ranging from 1 to 100. The diffusivity values are shown to be highly dependent on the approach used in determining the initial slope of the percent mass gain versus root square time curve. The previously proposed correction factors failed to yield accurate diffusion coefficients and are found to have up to 70% error. A simple, yet accurate method for determination of mass diffusivity of isotropic materials based on the solution of Fickian equation in three-dimensional domain is proposed. The applicability of the method is demonstrated with experimental data and good agreement is observed.
Automatic Process Adjustment for Reducing Dimensional Variation in Discrete Part Machining Processes
Authors: Wang Hui , Huang Qiang
Published: April 2008

Traditional Statistical Process Control (SPC) has been widely employed for process monitoring in discrete part manufacturing. However, control charts do not consider any adjustment preventing the process drift from target. Furthermore, many in-line adjustment approaches, such as thermal error compensation and avoidance, are designed only for machine tool error reduction. This paper intends to fully utilize the engineering process information and to propose a control algorithm that can automatically reduce the overall process variations. Considering three types of error sources in a machining process, we propose to use fixture locators to introduce process adjustment based on our previously proposed Equivalent Fixture Error (EFE) concept. The dynamic property of EFE is investigated for feedback adjustment of both kinematic and quasi-static errors in machining processes. A Minimum-Mean-Square-Error (MMSE) controller is designed based on the dynamic EFE model. We then evaluate the performance of the controller such as stability and sensitivity. Self-updating algorithm for controller has been proposed to track the latest process information as well. Finally, we simulate this process adjustment using the data collected from a real machining process. The results show that this algorithm can effectively improve the machining accuracy and reduce the process variations.
Solidification Heat Transfer and Base Separation Analysis in the Casting of an Energetic Material in a Projectile
Authors: Sun Dawei , Annapragada S. Ravi , Garimella Suresh V. , Sing Sanjeev
Published: April 2008

This paper investigates the problem of base separation in the casting of energetic materials in a projectile. Special challenges that arise in casting high Prandtl number energetic materials in projectiles of complex geometries are addressed. A comprehensive numerical model is developed by integrating finite volume and finite element methods to analyze the thermal and flow fields as well as the residual stresses. The predictions, which are confirmed by experimental measurements, suggest that sustenance of a linear temperature profile along the projectile axis can eliminate base separation, and also reduce residual stresses in the final casting.
Hybrid Stepper Motor Backstepping Control in Micro-Step Operation
Authors: Selk Ghafari Ali , Alasty Aria
Published: April 2008

A nonlinear position controller based on backstepping control technique is proposed for a hybrid stepper motor in micro-step operation. Backstepping control approach is adapted to derive the control scheme, which is robust to parameter uncertainties and external load disturbance. Simulation results clearly show that the proposed controller can track the position reference signal successfully under parameter uncertainties and load torque disturbance rejection.
Direct Computational Simulations for Condensation Inside Tubes and Channels
Authors: Phan L. , Wang X. , Kulkarni S. , Narain A.
Published: April 2008

The paper presents accurate numerical solutions of the full 2D governing equations for steady and unsteady laminar/laminar internal condensing flows of pure vapor (R-113 and FC-72) inside a vertical tube and a channel. The film condensation is on the inside wall of a tube or one of the walls of a channel (the lower wall in case of a downward sloping channel). The new geometry in this paper is the cylindrical in-tube geometry with axisymmetric flows (vertical 1g or 0g flows). The new results encompass both the cylindrical and the earlier studied channel geometry. Exit condition specifications are again found to be important. The computations are able to predict whether or not a steady flow exists under a natural exit condition (selected from a range of choices available at the exit). If natural steady/quasi-steady flows exist — as is shown to be the case for gravity dominated or strong shear dominated condensate flows — the computations are able to predict both the natural exit condition and the associated condensate flow’s point of transition from stable to unstable behavior. Compared to gravity driven, shear driven cases (zero gravity or horizontal cases) tend to destabilize easier and generally have much larger pressure drops, much slower wave speeds, much larger role of surface tension, and much narrower flow regime boundaries within which the vapor flow can be modelled incompressible. It is found that only in gravity driven cases, be it vertical in-tube or inclined channel geometry, interfacial waves are able to cause a concurrent enhancement in heat transfer rates along with an enhancement in interfacial shear. Also it is found that this enhancement is significant if the condensing surface noise is in resonance with the intrinsic waves.
Computation of Multiphase Flows With Lattice Boltzmann Methods
Authors: Premnath Kannan N. , Nave Jean-Christophe , Banerjee Sanjoy
Published: April 2008

Lattice Boltzmann methods (LBM) have several features that make them attractive for computation of large fluid mechanics problems in complex geometries. For example, in comparison with the conventional projection methods that are widely used in computational fluid dynamics, LBM does not require solution of a pressure Poisson equation which usually accounts for ~ 80% of the computational time required per time step, and it is also local, making parallelization straightforward, and run time on distributed memory architectures linearly scalable. LBM has therefore been considered for direct simulation of multiphase flows, but its application has been limited because of instabililties that arise when the viscosities become small and/or the density mismatch between the fluids is large. Current approaches to computation of multiphase systems using LBM are reviewed, and new approaches based on multiple relaxation times and a regularization procedure which maintain stability at low viscosities are discussed and a technique using time-splitting, that alleviates the density ratio constraint, is proposed. Applications of the LBM to magnetohydrodynamic (MHD) multiphase flows will be discussed.
A Comparative Study of Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundles Using Bond Graph Approach
Authors: Malik M. Afzaal , Rashid Badar , Khushnood Shahab
Published: April 2008

Flow-induced vibration (FIV) has been a major concern in the nuclear and process industries involving steam generator and heat exchanger tube bundle design. Various techniques and models have been developed and used for the analysis of cross-flow induced vibration of tube bundles. Bond Graph approach has been applied to existing FIV excitation models, followed by a comparative study. Results have been obtained using 20-SIM software. It is expected that the current approach will give a new dimension to the FIV analysis of tube bundles.
Modeling and Material Damage Identification of a Sandwich Plate Using MDOF Modal Parameter Estimation and the Method of Virtual Forces
Authors: White Jonathan R. , Adams Douglas E. , Jata Kumar
Published: April 2008

High temperature and low density metallic materials are being considered for thermal protection systems (TPS) for future aerospace applications. In this paper, a method for damage detection, location, and quantification using one actuator with distributed vibration sensors is presented for estimating virtual forces introduced by damage in a model aluminum honeycomb (H/C) TPS panel. A simplified analytical transverse vibration model of a homogeneous flat plate is considered to verify the method, which is then applied to the model aluminum H/C sandwich panel to demonstrate the method experimentally. First, a fully populated frequency response function matrix from the healthy panel is measured using an equal number of actuators and sensors. Virtual forces due to damage are then estimated by filtering data from the damaged panel using the healthy baseline response matrix. Second, a modal dynamic model for the sandwich panel is extracted using a single degree-of-freedom modal parameter estimation algorithm (Global Least Squares). The estimated modal frequencies and residues are used to build a dynamic observer to synthesize frequency response measurements unavailable with only one actuator. Modal impact testing is used to acquire frequency response functions, which serve as inputs to the frequency and residue parameter estimation process. It is shown that the virtual force method, with or without a modal observer, can detect damage due to density changes.
Intrinsic Harmonic Distortion of Atomic Force Microscopy Cantilever Position Detection Methods
Authors: Crittenden S.
Published: April 2008

There has been recent interest in the utility and physical information content of higher harmonics in Atomic Force Microscopy: theoretically as a way to better understand the dynamical behavior of the cantilever-sample system and experimentally both as feedback signals to enhance scanning stability under liquid and as indicators of the properties of the tip-sample interaction force such as the Hamaker constant and Young’s Modulus. However, the great majority of investigations of cantilever motion have assumed the cantilever position detection system to be linear in cantilever position when in fact it is not. The output of both beam-bounce and interferometric detection systems are nonlinear and this nonlinearity leads to harmonic distortion of the output signal. Importantly, the magnitude of this distortion can easily be equal to or greater than the actual harmonic components of the cantilever motion, thus rendering attempts to use harmonic signals for feedback or as keys to the reconstruction of the tip-sample interaction force non-quantitative. We examine both beam-bounce and interferometric detection systems theoretically and experimentally, discuss the various sources of nonlinearity in each, and propose a simple technique for minimizing the harmonic distortion and extracting the real harmonic components of the cantilever motion from the distorted output signal.
Effect of Laser Preheating the Workpiece on Micro-End Milling of Metals
Authors: Jeon Yongho , Pfefferkorn Frank
Published: April 2008

Micro-end milling is a fast and direct method of creating net-shaped functional micro parts, micro molds, and prototypes. However, the materials that can be micro machined efficiently are limited by the small flexural stiffness, strength, and hardness of the tool. The small flexural stiffness and strength of micro-end mills limits the size of cut that can be taken and the productivity. The flexural stiffness and strength are a strong function of the tool diameter. It is not expected that in the near term a new material will be developed that offers a combination of hardness and yield strength that will result in a significantly improved strength for tools with diameters measured in the 10s and 100s of microns. To enable a significant increase in performance requires higher spindle speeds and increased chip loads. Laser-assisted micro-end milling has the potential to increase the chip load and productivity by reducing the yield strength at the cutting location. This study examines the effect of laser preheating on micro-end milling of 6061-T6 aluminum and 1018 steel. 300 micron-diameter, two-flute, carbide end mills are used to cut 85 micron-deep slots at a constant 40,000 rpm spindle speed. The laser power and chip load are varied, including no preheating, to show their effect on cutting forces, specific cutting energy, burr formation, surface finish, and temperature. The results are related to average material removal temperature by predictions from a heat transfer model of the workpiece undergoing laser preheating. Results indicate that chip load and productivity can be significantly increased during dry machining of 6061-T6 aluminum and 1018 steel by locally preheating the workpiece immediately ahead of the micro-end mill.
Two Phase Electrohydrodynamic Instability Micromixing
Authors: Reddy Varun , Zahn Jeffrey D.
Published: April 2008

This work characterizes two phase electrohydrodynamic (EHD) instability micromixing of two immiscible organic and aqueous fluid phases. EHD mixing of the two phase microflow is promoted by creating an unstable flow profile by electrically inducing motion of the phase boundary. The aqueous phase is assumed to be infinitely conducting due to dissolved salt ions, while the organic phase is assumed to be non-conducting. As electrodes are biased, charges accumulate at the aqueous/organic interface. At a critical voltage the interface becomes unstable so that the aqueous and organic layers will mix. This is modeled for both inviscid and viscous flows using linear stability analysis considering the interfacial kinematic and stress conditions which predicts the stability criteria with a range of unstable wavenumbers which may be excited The mixing of an unstable “sausaging” and “kink” modes are visualized using epifluorescent microscopy of the dyed organic phase. The characteristic unstable wavenumbers predicted using linear stability theory are determined from the power spectrum of the captured images and compared to the analytical model. Onset of instability is seen at 40 volts RMS at a frequency of 250 kHz. This voltage corresponds to an electric field of Eo = 8 × 105 V/m across the organic phase. The instability becomes progressively more dynamic as the field strength is increased. The system recovers after the field is removed. At low field strengths the theoretical field and fastest growth wavenumbers for mixing compares favorably with the initially applied field whereas at higher field strengths the theoretical field is much larger than the initially applied field. This is attributed to the larger level of mixing and the ability of the instability to grow beyond the linear range while the electric field increases as the mixing process occurs due to entrainment of highly conductive fluid decreasing the effective dielectric spacing.
Detection of Multiple Cracks in Beams Using Genetic Algorithms
Authors: Huo Shihong , Xue Xiaojie
Published: April 2008

The detection and identification of structural damages play a key role in the monitoring and servicing of structural safety and reliability. This paper applies the real-coded Genetic Algorithm to the crack detection problems of multi-cracked beams. The objective function of the Genetic Algorithm was minimized by comparing the changes of measured vibration data of cracked and uncracked structures with those of the analytical model before and after updating. In the analytical model, the massless spring was used to simulate the open crack in the beam. Based on the frequency changes and the mode shape changes caused by the presences of cracks, the analytical model is updated to find the crack locations and sizes. A thorough explanation on how to find the mutation rate, crossover rate, population size, and weights of the vibration data are also discussed.
Guaranteeing Lanekeeping Performance With Tire Saturation Using Computed Polynomial Lyapunov Functions
Authors: Switkes Joshua P. , Gerdes J. Christian
Published: April 2008

Lanekeeping assistance systems hold the promise to save thousands of lives every year by preventing unintended lane departure. The potential field lanekeeping assistance system assists the driver in the lanekeeping task by effectively placing the vehicle in an artificial potential well with minimum at lane center. Previous work mathematically guarantees the performance of the system in the linear region of tire forces, but no guarantees of performance or even stability exist for saturating tires. These guarantees are crucial to ensure safety when the vehicle speed is too high for a given turn or the friction coefficient of the road is low due to surface conditions. Here we explore ways to numerically find Lyapunov functions for a vehicle with lanekeeping assistance and realistic tires. First the nonlinearity is modeled as a sector bounded disturbance, and a Lyapunov function is found for all vehicle trajectories that fit this sector bounded disturbance. Next, a polynomial fit is performed on the HSRI tire model, and a Lyapunov function is found for these polynomial dynamics. Each of these approaches provide Lyapunov functions valid well into the nonlinear region.
A Study of Gyroscopic Effects on Stability of High Speed Milling
Authors: Movahhedy Mohammad R. , Mosaddegh Peiman
Published: April 2008

Dynamic stability of machine tools during operations is dependent on many parameters including the spindle speed. In high and ultra high speed machining, the gyroscopic on the spindle dynamics becomes more pronounced and can affect the borders of stability of the rotating system. In this paper, a finite element based model of spindle, tool holder and cutting tool based on Timoshenko beam theory is used to obtain the dynamic response of the system when gyroscopic terms are included. An iterative scheme is used to update the speed dependent frequency response of the system for obtaining system stability characteristics. It is shown that the gyroscopic effect reduces the critical depth of cut in high speed milling.
Effects of Catalysts Supporting Layer on Carbon Nanotubes Growth
Authors: Yung K. P. , Wei J. , Tay B. K.
Published: April 2008

Due to their extraordinary electrical, thermal and mechanical properties, carbon nanotubes have been foreseen as potential materials for electronics devices in the future. To integrate carbon nanotubes in electronic applications, carbon nanotubes would need to be grown on different metal layer. In this study, carbon nanotubes growth with Ni as catalyst on three different support layers, Cu, Al and Cr, by hot filament chemical vapor deposition (HFCVD) is reported. The nanotubes were grown using C2H2 acetylene as carbon feedstock, in a hydrogen and nitrogen atmosphere. The catalyst layers and their support layers were deposited by magnetron sputtering technique. Deposited films were annealed at 600 °C for 10 minutes before exposing to C2H2 for the growth of nanotubes at same temperature for another 10 minutes. The effects of the support layer have been investigated with reference to nanotubes formation. The morphology and microstructure of the films were measured and analyzed by scanning electron microscopy (SEM) and Raman spectrometer. It was found that reaction of the catalyst with its supporting layer has significant effects on the growth of nanotubes. For Cu or Cr as support layer, its effect on the nanotubes growth was minimal. However Al support layer prevented the growth of carbon nanotubes. The possible mechanisms for the observed results are proposed.