bluuebunny/crossref_metadata_2025 huggingface dataset:
Repetitive Control for Rejection of Periodic Multiplicative Disturbances and Adaptive Identification of the Unknown Period
Authors: Mishra Sandipan , Yamada Manabu , Tomizuka Masayoshi
Published: April 2008

Repetitive control has been used extensively for rejection of periodic disturbances, in systems that have to follow periodic trajectories. To date, most repetitive controllers have focused on rejection of additive periodic disturbances. This paper suggests the use of a repetitive control algorithm for rejection of periodic multiplicative disturbances. The first result is a simple design method of a new controller to reject the multiplicative disturbance effectively, provided that the period of the disturbance is known. This controller is based on the internal model principle and the design method consists of a simple norm condition. It is shown that this repetitive-type controller can reject the disturbance. The second result is an extension of the first one to the case that the period of the disturbance is unknown. A period estimator is added to the control system to identify the period of the multiplicative disturbance. The algorithm, consisting of an adaptive recursive least mean square method, is simple. It is shown that this adaptive controller can reject the disturbance with an uncertain period and guarantee the stability of the adaptive closed-loop system including the period estimator.
Rethinking the Design of Presentation Slides: The Importance of Writing Sentence Headlines
Authors: Alley Michael , Robertshaw Harry
Published: April 2008

Presentation slides are often used for teaching engineering classes, presenting engineering research, and explaining engineering designs. For those presentations in which the presenter desires to communicate and defend results, using a succinct sentence headline for all slides but the title slide has three advantages over relying on a phrase headline. The first is that a sentence headline not only can identify the topic, but also can state an assertion about the topic. Emphasizing the assertions in an engineering presentation is advantageous, because audiences are more inclined to believe an argument if they realize the assertions and sub-assertions. Also, for a presentation that serves as a classroom assignment, having the student write sentence headlines provides a written record for the faculty member of that student’s assertions in the presentation. A second advantage of using sentence headlines, rather than phrase headlines, is that a sentence headline can clarify much more effectively the role of the slide in the presentation. Such a clarification not only helps the audience during the presentation, but also serves the audience reviewing the slides days or weeks later. Yet a third advantage, and perhaps the most important, is that a sentence headline forces the presenter to come to grips with the main purpose of each slide. If the presenter cannot create a sentence headline that states the slide’s main purpose in the presentation, then the presenter should consider cutting that slide from the presentation. For engineering presenters who have used this design, the result has been that significantly fewer slides are presented, thus helping the presenters avoid a frenetic pace, which undermines so many engineering presentations. This paper uses several examples from the Mechanical Engineering Department at Virginia Tech to show these three advantages. The paper also analyzes why faculty and students are reluctant to use sentence headlines. Finally, the paper includes a preliminary assessment on the effectiveness of these sentence headlines in engineering presentations.
Performance Evaluation of Four Cell Flow Chambers: How Well Is Stress Controlled at a Cellular Level?
Authors: Anderson Eric J. , Sorkin Adam , Knothe Tate Melissa L.
Published: April 2008

Fluid structure interactions at the cellular level are poorly understood yet they appear to be universal across tissue types and may hold the key to unraveling mechanisms of mechanotransduction at a cellular and subcellular level. Due to practical difficulties in studying cells in situ during normal physiologic activity, cell perfusion chambers have been developed to simulate physiologic fluid flow in vitro. While this approach has obvious advantages for unraveling cell signaling pathways in mechanotransduction, little is known with regard to how well these in vitro flow profiles emulate actual physiologic flow. The purpose of this computational study was to compare the local stress imparted through fluid flow in four cell perfusion chambers. From the computational models, in each chamber, varying velocity components cause the local shear stress imparted to the cells to vary as a function of location, and in fact only a limited number of cells are exposed to target stress. Due to differences in flow regimes between the four chambers, comparison between experimental data obtained using different perfusion chambers may be inappropriate.
Probe Radius Compensation for On-Machine Measurement of Sculptured Surfaces
Authors: Srinivasan Sreeram , Kovvur Yashpal , Anand Sam
Published: April 2008

Accurate dimensional measurement of freeform surfaces is a key step in CNC machining. Usually, a CMM equipped with a touch trigger probe is employed for measurement of such surfaces. In such a precision measurement, probe radius error is a serious concern. Traditionally, probe radius compensation methods are based on using the design (CAD) surface. In specific instances, the inaccuracy of these compensation techniques could be one order magnitude higher than the repeatability of the probe. Probe radius compensation based on ideal machined surface (generated when the milling cutter accurately moves through the cutter location (CL) points) is superior in principle to the one based on design surface, since it is one level of abstraction closer to the final surface realized. On Machine Measurement (OMM), where the measurement process is accomplished on the machining center by replacing the milling cutter with the Touch Trigger Probe, affords such a possibility without resorting to computationally intensive surface localization. This paper presents the implementation and performance analysis of a proposed new probe radius compensation technique based on both the design surface data (CAD model) and machined surface data (CL points). The proposed method efficiently compensates the probe radius error of on-machine measurement data for sculptured surfaces. The model was implemented on the simulated CMM data of a bi-cubic Bezier surface machined by a ball-end mill and compared with the conventional compensation techniques. The results show that this method compensates the probe radius error better than the existing techniques and yields superior precision.
A Partially Validated Finite Element Whole-Body Human Model for Organ Level Injury Prediction
Authors: Shah Chirag S. , Lee Jong B. , Hardy Warren N. , Yang King H.
Published: April 2008

A finite element whole-body human model, which represents a 50th percentile male, was developed by integrating three detailed human component models previously developed at Wayne State University (WSU): a thorax model with detailed representation of the great vessels [1], an abdomen model [2], and a shoulder model [3]. This new model includes bony structures such as scapulae, clavicles, the vertebral column, rib cage, sternum, sacrum, and illium and soft tissue organs such as the heart, lungs, trachea, esophagus, diaphragm, kidneys, liver, spleen, and all major blood vessels including the aorta. In addition to model validations already reported at the component level, the new whole-body model was further validated against two sets of experimental data reported by Hardy [4]. In these experiments, human cadavers were loaded either by a seatbelt or by a surrogate airbag about the mid-abdomen, approximately at the level of umbilicus. It is believed that exercising a validated human model is an inexpensive and efficient way to examine potential injury mechanisms. In some cases, this can provide insight into the design of subsequent laboratory experiments.
Stochastic Characterization of Epoxies to Predict Performance Uncertainty of Photonic Packages
Authors: Radhakrishnan S. , Subbarayan G. , Nguyen L. , Mazotti W.
Published: April 2008

There is considerable uncertainty in the prediction of performance of a system mainly due to idealizations in geometry, material behavior, and loading history. Uncertainties in geometry can be predicted and controlled using tighter tolerances. However, the models currently used to describe material behavior are mostly deterministic. To predict the coupling efficiency of a photonic system to greater degree of confidence, stochastic analysis procedures are necessary. As part of this analysis, the behavior of materials must be stochastically characterized. In this paper, we present extensive experimental data on thermally and UV-cured epoxies typically used in photonic packages to enable stochastic analysis. The test data includes the viscoelastic behavior. We present analytical model to obtain the variation in the displacement of the epoxies resulting from its stochastic viscoelastic behavior. We utilize the analytical model to predict the uncertainty in the coupling efficiency of a generic photonic package.
Effects of Saturated and Degassed Solutions on Flow Through a Hydrophobic Microchannel
Authors: Tretheway Derek C. , Stone Shannon , Meinhart Carl D.
Published: April 2008

This work examines the effects of soluble gasses and absolute pressure on fluid slip in a hydrophobic microchannel. Previous experiments with hydrophobic surfaces have indicated the presence of an apparent fluid slip. Tretheway and Meinhart (Phys. of Fluids 16, 1509) proposed a mechanism responsible for the apparent fluid slip observed by Pit. et. al. (Phys. Rev. Lett., 85, 980–983), Zhu and Granick (Phys. Rev. Lett., 87, 096105), and Tretheway and Meinhart (Phys. of Fluids, 14, L9-L12). Tyrell and Attard (Phys. Rev. Lett. 87, 176104) observed the presence of nanobubbles on a hydrophobic surface. Tretheway and Meinhart (Phys. of Fluids 16, 1509) modeled these nanobubbles as a thin gas layer and solved for the velocity profile between two infinite parallel plates, which yields an apparent fluid slip consistent with the experimentally observed results. As the slip length is highly dependent on the nanobubble or gas layer thickness, varying the soluble gas concentration or absolute pressure should increase and decrease the apparent fluid slip. This work explores the proposed mechanism by measuring velocity profiles and calculating slip lengths for various saturated and degassed solutions and a range of absolute pressures.
Dynamic Modeling and Control of Hysteresis in a Shape Memory Alloy Actuator
Authors: Dutta Sushant M. , Ghorbel Fathi H. , Dabney James B.
Published: April 2008

In this paper, we develop a complete mathematical model of a shape memory alloy (SMA) wire actuated by electric power and a bias spring. The operation of the SMA actuator involves different physical phenomena, such as heat transfer, phase transformation with temperature hysteresis, stress–strain variations and electrical resistance variation accompanying the phase transformation. We model each of these phenomena in a modular fashion. A key feature of the proposed model is that one or more of its modules can be extended to fit other SMA applications. At the heart of the proposed model is a dynamic hysteresis model capable of representing minor hysteresis loops. We generate the temperature profile for the hysteresis model using lumped parameter analysis. We extend the variable sublayer model to represent actuator strain and electrical resistance. The dynamic properties of the hysteresis model are developed and are exploited in developing control system strategies. Control simulation case studies are presented.
Parallelization of the Lattice Boltzmann Method in Simulating Buoyancy-Driven Convection Heat Transfer
Authors: Niavarani-Kheirier Anoosheh , Darbandi Masoud , Schneider Gerry E.
Published: April 2008

The main objective of the current work is to utilize Lattice Boltzmann Method (LBM) for simulating buoyancy-driven flow considering the hybrid thermal lattice Boltzmann equation (HTLBE). After deriving the required formulations, they are validated against a wide range of Rayleigh numbers in buoyancy-driven square cavity problem. The performance of the method is investigated on parallel machines using Message Passing Interface (MPI) library and implementing domain decomposition technique to solve problems with large order of computations. The achieved results show that the code is highly efficient to solve large scale problems with excellent speedup.
Investigation of Strut Thickness in Coronary Stents via Finite Element Analysis
Authors: Yazdani Saami K. , Berry Joel L.
Published: April 2008

Strut thickness in coronary stents has been shown to affect their clinical performance. The purpose of this investigation was to understand how stent strut thickness influenced stress in the vessel wall. Finite element modeling was used to compare stress distribution between a thick and thin strut stent in a curved coronary artery model. Specifically, we modeled two 8 mm long Guidant MULTI-LINK VISION stents, one with strut thickness of 81 μm and the other with strut thickness of 112 μm. Results showed larger values of stress, both in the radial direction and in the circumferential direction, for the thicker stent model. As expected, these higher stress values occurred beneath the stent struts and at the edges of the stent. Stented vessel compliance measurements of both models revealed that the thick strut VISION stent is less compliant than the thin strut VISION stent. These results support the hypothesis that compliance mismatch between the stent and the host vessel contributes to excessive stress in the walls of stented vessels.
Computational Micromechanics Analysis of Ionic Polymers With Cluster Morphology
Authors: Weiland Lisa Mauck , Leo Donald J.
Published: April 2008

In recent years there has been considerable study of the potential mechanisms underlying the electro-mechanical response of ionic-polymer-metal composites (IPMCs). Most of these efforts have employed assumptions of uniform and balanced ion distribution within spherical cluster shapes, in the ionic polymer layer of the IPMC. Inspired by the results of a preliminary computational study, the present work investigates the impact of dispensing with these assumptions. A computational micromechanics model has been developed to study ion response in a single cluster of these ionomeric transducers. Assuming a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface response force, and external electric field loading. Results suggest that the classic assumptions will tend to under-predict electromechanical response and that charge imbalance has significant impact of cluster behavior.
Rethinking the Design of Presentation Slides: Creating Slides That Are Readily Comprehended
Authors: Alley Michael , Robertshaw Harry
Published: April 2008

Presentation slides, when designed well, can significantly increase the amount of information that the audience comprehends. However, when the slide has type that can not be quickly read, the audience often gives up on the slide. Moreover, when the slide does not orient well, when the slide has too much information, or when the order of information on the slide is unclear, the audience can easily become confused. Given that these mistakes can prevent the audience from comprehending the presentation’s content, presenters should strive to format slides that can be quickly read, that effectively orient, that have a reasonable amount of information, and that have a clear order of information. Unfortunately, the slide formats that many engineering presenters use do not meet these goals. Presented in this paper are recommendations for the format of presentation slides—specifically, the typography, color, and layout of presentation slides (or overheads). An assumption for these recommendations is that the purpose of the presentation is to communicate technical information efficiently to the audience. Given that assumption, the goal of a slide’s typography is to have type that can be read as quickly as possible. To obtain that goal, this paper recommends a bold sans serif typestyle such as Arial that is at least 18 points. In regard to color, the most important goal is to have colors that can be clearly distinguished from each other. To obtain that goal, this paper recommends either a dark color against a light background or a light color against a dark background. In regard to layout, the goal is to have a slide design for which the audience can quickly discern the point of the slide and then can divide attention between the presenter and the slide as the presenter discusses the slide. To obtain that goal, this paper recommends the national laboratory design of a short sentence headline supported primarily by images. Other reasons exist for choosing this national lab design. Although this paper focuses on how readily that slides following this national lab design can be comprehended, the paper does direct the reader to references that discuss two other reasons for using this national laboratory design: (1) how well the slide design helps the audience remember details, and (2) how persuasive the slide design is.
Brownian Particle Distribution in Tube Flows
Authors: Cao Jinhua , Wereley Steve
Published: April 2008

A rigid spherical particle translating at small tube Reynolds number in a shearing flow experiences lateral migration due to small inertia and wall effect. In a suspension flow of sufficiently small particles, Brownian motion is another factor. In this work, we investigate this migration phenomenon of Brownian particles in a pressure-driven flow for a range of particle volume fractions (φ) much less than 0.01. The flow velocity is varied, which results in bulk Pecle´t number (Pe) ranging over four orders of magnitude. Both the velocity and the particle distributions were measured. It has been found that when Pe is smaller than 1000, particles migrate away from the channel wall, and that the particle concentration in regions remote from the wall (more than 10 particle diameters) is nearly uniform; When Pe increases beyond 1000, particles move toward a preferred position with the migration effect becoming progressively stronger as Pe increases.
Mixing Characteristics in a Serpentine Micro-Channel
Authors: Chamarthy Pramod , Wereley Steve
Published: April 2008

Mixing characteristics in a 2D serpentine micro-channel were studied experimentally to understand the role of Dean vortices in enhancing mixing. Mixing plane deformation was visualized at Reynolds numbers ranging from 1 to 200 with the corresponding Dean numbers ranging from 1 to 205. The 2D serpentine micro-channel was found to be a poor mixer for Re<50 even though a strong presence of Dean vortices was observed. The generation of flow separated regions at sharp corners, above Re=100, was observed to cause a sharp increase in the mixing obtained. The interaction between the Dean vortices and the corner vortices was studied by imaging pathlines at varying depths near the sharp corners. The interaction produced rapid stretching and folding of the two fluids, which was determined to be the reason for the increased mixing at Re>100. This study will have a significant impact on the understanding of transport properties of flows in similar geometries.
Time Optimal Transfer Function of a Mechanism in the Presence of Dissipative Forces
Authors: Goun A. A. , Sliva O. K.
Published: April 2008

A variety of optimization problems in theoretical mechanics are related to the problem of finding the quickest operating mechanism among all possible mechanisms. Let us consider a mechanical system with one degree of freedom consisting of leading and lagging links with masses M1 and M2 respectively. Source of mechanical energy is attached to the leading link and its potential energy is known as a function of the position of the leading link. Positions of the leading - x and lagging links - y are related through the position function. Now the optimization problem can be formulated in the following way: find the position function such that the lagging link is transferred from initial to the final position in the shortest time. The analytic solution for this problem for the case when dissipative forces can be neglected was found using variational calculus method. In the case when dissipative forces can be described as viscous friction the problem can be solved using iterative methods. The differential equation that describes the stationary point of these iterations was obtained. The dependence of the optimal position function on the magnitude of friction is analyzed. In the case when dissipative forces are of the dry friction type the approach based on the variational calculus fails. We were able to find the optimal position function problem using Maximum Principle. New qualitative features of the solution arising due to dry friction are discussed. Approaches developed in this paper can be generalized for a variety of mechanisms where the operating time is critical.
Flow Around Rectangular Cylinders With Trailing Jets
Authors: Pidugu Srikanth B.
Published: April 2008

The problem of flow past bluff bodies was studied extensively in the past. The problem of drag reduction is very important in many high speed flow applications. Considerable work has been done in this subject area in case of circular cylinders. The present study attempts to investigate the feasibility of drag reduction on a rectangular cylinder by flow injection from the rear stagnation region. The physical problem is modeled as two-dimensional body and numerical analysis is carried out with and without trailing jets. A commercial code is used for this purpose. Unsteady computation is performed in case of rectangular cylinders with no trailing jets where as steady state computation is performed when jet is introduced. It is found that drag can be reduced by introducing jets with small intensity in rear stagnation region of the rectangular cylinders.
Coupled Electro-Thermal Mechanical Analyses for SMM Actuators Development
Authors: Wong C. Channy , Lober Randy R. , Hales Jason D.
Published: April 2008

A coupled-physics analysis code has been developed to simulate the electrical, thermal, and mechanical responses of surface micromachined (SMM) actuators. Our objective is to optimize the design and performance of these micro actuators. Since many new designs of these electro-thermal actuators have shuttles or platforms between beams, calculating the local Joule heating requires a multi-dimensional electrostatics analysis. Moreover, the electrical solution is strongly coupled to the temperature distribution since the electrical resistivity is temperature dependent. Thus, it is essential to perform a more comprehensive simulation that solves the coupled electrostatics, thermal, and mechanical equations. Results of the coupled-physics analyses will be presented.
Impeller Design for Radial and Mixed Flow Compressors
Authors: Pauer Reinhard , Mu¨ller Norbert
Published: April 2008

An impeller design algorithm implemented in a computer code is presented. It can be used for designing radial and mixed flow impellers for compressors, blowers and fans. The implemented algorithm allows finding suitable impeller geometries considering fluid mechanical and technological aspects. Based on the input of main design parameters for the stage (like tip diameter, rotational speed, through flow, and specific energy transfer), first the feasibility of the given combination of input values is checked, and possible design ranges are determined (like for outlet blade angles, inlet diameter, and outlet width). After choosing the final design parameter within the possible range, a mean line blading is generated. Then the algorithm allows optimizing the blading geometry, velocity distribution, and blade loading by changing the mean streamline. The mean line blading then serves as a basis for generating the complete 3D blading, distributing the blade loading in a way that favorable velocity distributions are obtained throughout the impeller and that the obtained blade geometry is acceptable. Finally the blading generated according to fluid mechanical aspects can be adapted to technological constrains by changing geometric parameters and overlaying a thickness distribution. During this process the velocity distributions are always re-evaluated using the streamline curvature algorithm by Stanitz und Prain. Despite friction is neglected, experience has shown that the obtained results allow a good evaluation of the aerodynamic quality of the impeller design.
Effect of Interosseous Membrane on Load Transfer in Rat Forelimb Using Finite Element Analysis
Authors: Tami A. E. , Suresh G. , Patel R. B. , Knothe Tate M. L.
Published: April 2008

Due to the curvature of the ulna and the complex geometry of the ulna and radius as well and their interaction with and possible transfer of load through the interosseous membrane that joins them, an understanding of the loading situation is not trivial. The IOM might counteract the bending effect resulting from the curvature of the ulna, therefore stabilizing the lateral displacement of the ulna and decreasing the ratio between bending and compression. Thus, in order to understand the mechanisms underlying effects of the mechanical stimulation applied using the end-loading model of the ulna, it is necessary to have a fundamental understanding of the loading mechanics and strain distribution. Hence, the goals of this study were: i) to develop a three dimensional finite element mesh of a mature rat ulna, ii) to measure experimental surface strain values of rat forelimbs with intact and non-intact interosseous membranes, iii) to compare experimental and computational strain distribution data, and iv) to analyze for the first time the effect of the radius and interosseous membrane on axial load distribution through the ulna.
Development of a Sophomore Manufacturing Laboratory Course to Streamline the Manufacturing Education Within Mechanical Engineering Curriculum
Authors: Atiqullah Mir M. , Cowin Aaron R. , Ising Ed M. , Kelly Terrance K. , Ravindra K.
Published: April 2008

A basic shop course was typical in the early days of mechanical engineering studies. However, in the late seventies, the shop course was dropped from the engineering curriculum in most schools for various reasons. The need for a preparatory manufacturing course became apparent after recognizing the lack of modest shop skills exhibited by our students in design-build projects which are routinely assigned in several junior and senior level courses. The traditional manufacturing course, that all students are required to take during the senior year, requires higher-level prerequisites. In addition, being a senior level course, it provides very little opportunity for the students to utilize those skills in other courses. To address this void, a new engineering workshop course has been objectively designed and implemented for the sophomore mechanical and aerospace engineering students, beginning fall 2003. The goals of the course are to develop an appreciation for manufacturing in engineering design, prepare students for follow-up manufacturing course, and develop necessary skills for design-build projects at various levels of the curriculum. The engineering shop course is designed around nine laboratory content modules that introduce the students to the fundamentals of shop safety, measurement, and manufacturing. The present paper describes the development and implementation of the course. The effectiveness of the course in meeting the goals is also assessed through surveys conducted both before and after the course is completed. Long-term success will be measured in the future by a survey of graduating seniors to assess the effectiveness of the engineering shop course in the students’ ability to successfully complete design-build projects assigned in other courses. The modular design would allow this course to be adapted for achieving similar objectives elsewhere.
Validation of ASHRAE Equation to Find Evaporation Rates in Humid Cavity
Authors: Kuravi Suma , Agonafer Dereje
Published: April 2008

Presence of Humidity has many undesired effects in many applications. Moisture balance of the air has become an important task and dehumidification has become a necessity for many applications in many industries. This paper discusses about the study of the factors affecting the evaporation rate of water in cavities exposed to humid conditions. The ASHRAE equation to find the evaporation rate in swimming pools is considered and validated for a small pool of water in humid conditions in humid cavity with fixed dimensions. The equation states that, the evaporation rate, W = (95+0.425*V)*(Pw-Pa)/Y, where W is the Evaporation rate in lb/h-ft2; V is the air velocity at water surface; ft/min; Pw is the saturation vapor pressure at water temperature, in. Hg; Pa is saturation vapor pressure at air dew point, in. Hg; and Y is latent at water temperature, Btu/lb. The evaporation rate inside the humid cavity is found and compared with that of the equation. The evaporation rate obtained inside the humid cavity is 95% of the evaporation rate obtained by the use equation. The factors responsible for the low evaporation rate are identified. A CFD Model is developed using FLUENT to represent the time averaged steady state condition of the humid cavity. The temperature and velocity values at particular points are probed in CFD model and are obtained. The results are compared with the actual physical model. These values are used to find the evaporation rate occurring inside the cavity using the ASHRAE equation. The evaporation rate found in the humid cavity is found to be 76% of the evaporation rate that is calculated from the values of the CFD model, using the equation. Factors affecting the evaporation rate inside the humid cavity are discussed and the effects of these factors are illustrated using the CFD Model. Propositions are made to improve the evaporation rates inside the humid cavity. Future studies are planned to do a multi species modeling to include humidity in the CFD analysis for humid cavity.
Numerical Analysis of Local Heat Transfer From a Flat Plate to a Pair of Circular Air Impingining Jets
Authors: Yan X. Terry , Saravanan Yavaraj
Published: April 2008

Local heat transfer from a flat plate to a pair of circular air impinging jets is investigated numerically. A pair of impinging jets from fully-developed pipe flows are used for the numerical simulations. The Reynolds Averaged Navier-Stokes equations(RANS) and energy equation are solved for the three dimensional flow. Eddy-viscocity based turbulence models, RNG k-epsilon and V2F models, are used. Hybrid meshes are used for the three dimensional flows and mesh independent solutions are obtained. The flow Reynolds number, which is based on the jet diameter, is kept at 23,000. In the analysis, local heat transfer coefficients are obtained for the jet-to-plate distance, L/D, ranging from 2 to 10 and the jet-to-jet spacing, S/D, in the range of 1.75 to 7.0. Both local and average heat transfer coefficients are evaluated and compared with available experimental data under same flow conditions. The effect of using different turbulence models in the numerical analysis is evaluated and the selection of proper turbulence models under such a flow condition is suggested.
Flight Control of a Variable Span Cruise Missile
Authors: Seigler T. Michael , Bae Jae-Sung , Inman Daniel J.
Published: April 2008

In this work the benefits of variable span morphing are considered, specifically with regards to the increased maneuverability of bank-to-turn cruise missiles. Along with an increase in range associated with variable span aircraft-in the case where both wings are equally extended-there is also the possibility of an additional advantage of higher control authority over both pitch and roll motions. In the case of roll control, one wing is extended while the other is contracted thus producing a moment about the longitudinal axis of the missile. Compared to conventional tail surface control, this moment can be substantial depending on the flight conditions. There is, however, some complexity involved in flight control of variable span aircraft; namely the shift of the missile’s center of mass and the dependence of the roll producing moment on the angle of attack. The following work attempts to address these complexities through nonlinear control. First, a full nonlinear model of the missile is presented that includes aerodynamic effects and changes in weight distribution. Nonlinear methods are then used to control the trajectory of the missile via the roll angle, angle of attack, and sideslip angle. The results show that, in comparison with conventional missile configurations, the addition of variable span morphing has the capability of increasing overall flight performance.
Robust Repetitive Control System With On-Line Identification of the Period of Periodic Disturbances
Authors: Yamada Manabu , Tomizuka Masayoshi
Published: April 2008

Repetitive control system is a servo system that achieves zero steady-state tracking error for any periodic desired outputs and any periodic disturbance inputs with a known period. This paper deals with a repetitive control problem for the case where the plant has a norm-bounded uncertainty and the period of periodic disturbances is unknown but is within known lower and upper bounds. A new robust repetitive controller is proposed not only to guarantee the robust stability against the uncertainty but also to estimate the unknown period and to reject any periodic disturbances with the period. It is shown that the design problem is reduced to a simple and feasible l1 norm minimization problem. The controller can be obtained easily by solving a simple linear programming problem. Simulation results show the effectiveness of the proposed controller for rejection of periodic disturbances with uncertain periods.
A Multi-Cylinder HCCI Engine Model for Control
Authors: Souder Jason S. , Mehresh Parag , Hedrick J. Karl , Dibble Robert W.
Published: April 2008

Homogeneous charge compression ignition (HCCI) engines are a promising engine technology due to their low emissions and high efficiencies. Controlling the combustion timing is one of the significant challenges to practical HCCI engine implementations. In a spark-ignited engine, the combustion timing is controlled by the spark timing. In a Diesel engine, the timing of the direct fuel injection controls the combustion timing. HCCI engines lack such direct in-cylinder mechanisms. Many actuation methods for affecting the combustion timing have been proposed. These include intake air heating, variable valve timing, variable compression ratios, and exhaust throttling. On a multi-cylinder engine, the combustion timing may have to be adjusted on each cylinder independently. However, the cylinders are coupled through the intake and exhaust manifolds. For some of the proposed actuation methods, affecting the combustion timing on one cylinder influences the combustion timing of the other cylinders. In order to implement one of these actuation methods on a multi-cylinder engine, the engine controller must account for the cylinder-to-cylinder coupling effects. A multi-cylinder HCCI engine model for use in the control design process is presented. The model is comprehensive enough to capture the cylinder-to-cylinder coupling effects, yet simple enough for the rapid simulations required by the control design process. Although the model could be used for controller synthesis, the model is most useful as a starting point for generating a reduced-order model, or as a plant model for evaluating potential controllers. Specifically, the model includes the dynamics for affecting the combustion timing through exhaust throttling. The model is readily applicable to many of the other actuation methods, such as variable valve timing. Experimental results validating the model are also presented.
Developments and Applications of Structural Optimization and Robustness Methods in Vehicle Impacts
Authors: Yang R. J. , Gu L. , Soto C. , Li G. , Tyan T.
Published: April 2008

Finite element based full vehicle structural crash simulation is an analysis tool commonly used in automotive industry to evaluate vehicle impact performance. As the simulations are computation intensive, special optimization methods and processes are often required. This paper presents recent developments and applications of structural safety optimization and robustness methods for vehicle crashworthiness. It addresses advanced methods in gauge, size, shape, topology optimization, and robust, reliability-based design optimization methods. Recent applications in vehicle safety design are presented and discussed.
Developing an Appreciation of the Basic Principles in Earth Sciences, Physics, and Mathematics Supporting Careers of the Future Through Workshops for Pre-College Teachers
Authors: Williams W. B. , DeJarnette Fred , Craft W. J. , Grossman B. M.
Published: April 2008

On September 26, 2002, the National Institute of Aerospace, NIA, was created near NASA’s Langley Research Center in Hampton, VA as a result of a winning proposal submitted from the AIAA and a 6-university team in response to a broad agency announcement. Our proposal emphasized these four imperatives to: • Conduct leading edge aerospace & atmospheric science research and develop revolutionary new technologies by creating innovative, collaborative, synergistic partnerships among NASA’s Langley Research Center, academia, and industry; • Provide comprehensive graduate and continuing education in science and engineering by using both a local campus and exploiting innovative distance-learning concepts; • Incubate and stimulate the commercialization of new intellectual property developed through the Institute’s activities, including radical ideas and disruptive technologies; and • Promote aerospace science and engineering and provide outreach to the region and nation. As part of the fourth imperative, we specifically proposed to develop and conduct summer workshops for grade 6–12 teachers. This paper describes our experiences in planning and conducting our first teacher workshop in July, 2003.
Nanoscale Indentation of Simulated Soft Tissues
Authors: Gupta Shikha , Carrillo Fernando , Pruitt Lisa , Puttlitz Christian
Published: April 2008

The use of small animal models, such as murine and rabbit models, are currently being explored to help elucidate the mechanobiological mechanisms of clinically relevant orthopaedic conditions such as fracture healing and osteoarthritis progression, with the goal of developing a comprehensive view of the biomechanical structure-function relationships at the tissue and cellular level. In addition to the heterogeneous nature of these tissues, the miniature size of the test specimens from these small animal models precludes the use of conventional bulk mechanical testing procedures to obtain material properties. Nanoindentation is a technique that is used to assess mechanical properties on a cellular scale. Though traditionally used to study hard, elastic-plastic materials, it has been effectively utilized to measure the material properties of mineralized biological materials [1, 2]. More recently, there have been some preliminary studies on soft, hydrated tissues, such as demineralized dentin, cartilage, and vascular tissues [3, 4]. However, this technique has not been validated for measuring the properties of tissues with extremely small, time- dependent tissue matrices (elastic moduli below 5 MPa). A finite element model (FE) of the nanoscale indentation process has been developed to assess some of the experimental issues associated with using nanoindentation on physical tissue specimens. In addition, we have used this FE model to predict the distribution of stresses and strains within the indenting substrate (tissue sample), mechanical parameters that cannot be mapped using currently-available experimental methods.
Development of Problem-Based Learning Modules for Engineering Thermodynamics
Authors: Nasr Karim J. , Ramadan Bassem , Ahire Prashant
Published: April 2008

Problem-Based Learning (PBL) is an instructional approach that fosters active learning, supports knowledge construction, integrates disciplines, and naturally combines classroom learning with real-life applications. This approach can be described as student-centered and concept-embedded. This paper presents the development of curricular materials in Engineering Thermodynamics that are founded on PBL, supported by technology through simulations, and target higher levels of Bloom’s Taxonomy of Learning. Thermodynamics is restructured as modules presenting practical applications first whereas principles are introduced just-in-time and as encountered. Theoretical information is presented to support the understanding of knowledge as students apply inquiry-based learning. These modules are carefully designed to reflect traditional concepts but made more exciting as students discover the need for the laws and principles. The classroom format is interactive, cooperative and revolves around students’ needs. Formative and summative assessment tools are designed to examine the effectiveness of created modules.
Compliant Stress-Engineered Interconnects for Next-Generation Packaging
Authors: Klein Kevin M. , Sitaraman Suresh K.
Published: April 2008

Future demands of microelectronic packing include increasing input/output (I/O) densities, providing high frequency capabilities, and maintaining sufficient reliability while keeping costs minimal. Organic materials with Coefficients of Thermal Expansions (CTE) over four times greater than silicon will continue to be used as future substrate materials because of their low cost. Consistent with the International Technology Roadmap for Semiconductors (ITRS, 2003), chip-to-substrate interconnects will need to have a pitch approximately equal to 40μm by the year 2012 and be able to accommodate the silicon and organic CTE mismatch without resorting to expensive reliability solutions. The demand for fine pitch chip-to-substrate interconnects combined with the CTE mismatch, creates significant demands for overall interconnect compliance as means to ensure reliability, through increasing fatigue life. Stress-engineered compliant off-chip interconnects are capable meeting future interconnect demands. Such interconnects are fabricated from stress-engineered metal thin-films using traditional IC fabrication methods and can be integrated with wafer level packing. A systematic design approach has been used to optimize interconnect geometry for use with estimated operational conditions. Finite Element Analysis (FEA) and Regression modeling have been used to create macro-models of interconnect behavior to assist in the optimization of the geometric design. Copper and Copper-Molybdenum are considered as interconnect material and the development intrinsic stress within copper is investigated via sputter deposition.
Using Genetic Algorithms to Identify Initial Operating Conditions for a Transient CVT Model
Authors: Srivastava Nilabh , Blouin Vincent Y. , Haque Imtiaz U.
Published: April 2008

A Continuously Variable Transmission (CVT) provides a continuum of gear ratios between desired limits. CVT is a promising automotive technology and a sundry of models has been researched to realize the potential benefits of a CVT. CVT, being a highly nonlinear system, has a definite operating regime where it is able to maximize the torque transmission. The numerical model presented in this paper is difficult to solve because of its sensitivity with respect to the initial operating conditions such as initial belt tension, axial forces, and driven preload. The present research focuses on using Genetic Algorithms (GA) to identify these operating conditions and to understand the various dynamic interactions in a metal pushing V-belt CVT. This paper uses continuous Coulomb friction approximation theory to model friction between the belt and the pulleys. The computational scheme, the mathematical models, and the results corresponding to different loading scenarios are discussed.
Effect of Microprocessor Features in Control Loops Modeled in Simulink
Authors: Zavala Jose Carlos , Hedrick J. Karl
Published: April 2008

The intensive use of simulation tools, such as simulink has made possible the development of embedded controllers using a plant model as a base. The performance in the simulation environment does not account however for the details of the hardware architecture. In this paper, a way to approximate some of the effects of the features of a particular microprocessor is derived for the Simulink environment. Worst-case execution time of the given control algorithm is performed as the first step. The computation error is also estimated for that particular algorithm. A block in the Simulink model could then express the computation latency due to hardware processing and the error due to computation accuracy. An automatic way of estimating these effects is presented here in order to achieve a higher integrability of software tools available for the designer. In particular, controller design involves deciding what hardware platform to choose for a particular application. Analysis and experimental results of a particular microprocessor are discussed.
AC Electrokinetics for Biosensors
Authors: Sigurdson M. , Meinhart C. , Wang D.
Published: April 2008

We develop here tools for speeding up binding in a biosensor device through augmenting diffusive transport, applicable to immunoassays as well as DNA hybridization, and to a variety of formats, from microfluidic to microarray. AC electric fields generate the fluid motion through the well documented but unexploited phenomenon, Electrothermal Flow, where the circulating flow redirects or stirs the fluid, providing more binding opportunities between suspended and wall-immobilized molecules. Numerical simulations predict a factor of up to 8 increase in binding rate for an immunoassay under reasonable conditions. Preliminary experiments show qualitatively higher binding after 15 minutes. In certain applications, dielectrophoretic capture of passing molecules, when combined with electrothermal flow, can increase local analyte concentration and further enhance binding.
Cutter Engagement Feature Extraction From Solid Models for End Milling
Authors: Yip-Hoi Derek , Huang Xuemei
Published: April 2008

Accurate process modeling requires the calculation of cutter/workpiece engagement (CWE) geometry. This is challenging when the geometry of the workpiece is changing un-predictably as is the case for most machined components of moderate complexity. Solid modelers are increasingly being considered as a computational engine for performing these calculations. This is largely due to increased robustness and computing efficiency that is evolving within this technology. The vast majority of reported research using solid modelers focuses on the domain of 2 1/2 D machining with flat end mills. While significant there remain restrictions in the types of inprocess workpiece geometry that can be processed with these approaches. In particular, they assume a constant axial engagement for a connected set of tool paths. This assumption cannot be made when the initial workpiece geometry is non-rectangular prismatic stock, when multiple setups are machined and when tool changes introduce tools of different diameters. In these cases the depth of engagement can vary over a single rotation of the cutter even though there is no axial feed motion. In this paper a solid modeling based solution is presented for calculating these engagements when multiple setups and tool changes are considered. Orthogonal setups and flat end mills are assumed so as to preclude cutter engagement on inclined workpiece faces. Classes of Cutter Engagement Features (ceFs) are defined to support this approach. Algorithms for ceF extraction are provided and validated using a test part. This research introduces the use of features and extends the capabilities of solid modeling techniques for cutting force prediction.