bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropy Generation in Natural Convection of Water Near Its Density Maximum in a Square Cavity
Authors: Li You-Rong , Deng Nu-Bo , Wu Shuang-Ying , Peng Lan , Zeng Dan-Ling
Published: April 2008

This paper is focused on the entropy generation due to heat transfer and viscous flow in natural convection of water near its density maximum in a square cavity. The present hydrodynamic and temperature fields are obtained by solving numerically the mass, momentum and energy balance equations, using the finite difference method. Local entropy generation distributions are obtained based on the resulting velocity and temperature fields by solving the entropy generation equation. The effect of the Grashof numbers on the total entropy generation is studied. Local entropy generation distribution was found to be dependent on the Grashof number and the dimensionless initial temperature. The results also show that thermal entropy generation is relatively dominant over viscous entropy generation.
Modeling Friction Wedges: Part I — The State-of-the-Art
Authors: Klauser Peter E.
Published: April 2008

The friction wedge is a critical component in the three-piece truck. This paper describes the current approach for modeling friction wedges and compares its implementation in the commercially available NUCARS™ and VAMPIRE® vehicle dynamics codes. NUCARS™ is a software package developed by Transportation Technology Center, Inc., while VAMPIRE® is a package developed by AEA Technology plc. Sample results from both codes are presented based on standalone test cases. Shortcomings of the “state-of-the-art” model are described and directions for future work are proposed.
Guideline for the Dropping Test of the Impact Reliability Study of Solder Joints
Authors: Yu Qiang , Watanabe Keiji , Tsurusawa Toshihiro , Shiratori Masaki , Kakino Manabu , Fujiwara Noriyuki
Published: April 2008

As a result of the miniaturization of mobile electronic devices in recent years, assessing the drop impact reliability of solder joints has become increasingly important. The purpose of the present paper is to establish an experimental method by which to determine the drop impact reliability of solder joint. The drop impact problem consists of various factors, including impact-induced flexural vibration of PCB, collision attitude, and dynamic fracture of solder joints. Numerous methods have been developed for examining the impact reliability of BGA solder joints. Among these is a repeated drop test proposed by the present authors that uses a simple apparatus. The effects of the drop angle on the dynamic behavior of PCB were discussed. In a previous report, it was confirmed that even if the collision angle is very small, the dynamic deformation of the PCB is greatly affected by the collision angle. In this study, the dynamic behavior was dramatically improved by attaching a hemisphere to the bottom of the holder, and the result was equivalent to stable dynamic deformation of the PCB in horizontal collisions. In addition, the relationship between drop height and cycle to failure of the CSP was obtained. The authors also investigated the interaction of the vibration modes of PCB and the specimen holder and the relationship between the holder geometry and its impact strength. Finally, through repeated drop testing, a holder geometry was obtained that did not adversely affect the PCB upon impact.
Analogy Between Heat and Mass Transfer Leads to New Oxygen Transport Equations in Vascularized Biological Tissues
Authors: Liu Jing
Published: April 2008

Mathematical modeling of oxygen transport in living tissues has been an important approach for quantitatively understanding the physiological events. In a vascularized biological tissue, blood flow plays an important role in the local transport of oxygen, nutrients, pharmaceuticals, waste products and heat through the body. However, most of the existing oxygen transport models take few considerations of the anatomical structure. Therefore, disagreements among the theoretical predictions and the experimental measurements are common in those studies. This is because geometrical irregularity of the vascular structure remained to be a major obstacle for the accurate modeling. In fact, it has long been a desirable objective to establish a quantitative and generalized model, which is mathematically tractable in the region of interest and considering the detailed anatomical vascular geometry. In this paper, following the theoretical strategy through analogy between the heat and mass transport, the well-established Pennes equation, Chen-Holmes equation, and Weinbaum-Jiji (W-J) equation, etc. were implemented to develop the basic equations for characterizing the oxygen transport inside a vascularized tissue. These models have collectively included the contributions of the vascular geometry and the blood flow condition. As an illustration, predictions using the new model from W-J equation on several typical oxygen transfer problems were discussed. The theoretical results were applied to interpret some previous experimental observations. Further, uncertainties for the predicted oxygen concentrations of tissues due to approximate parameters and vascular structures were analyzed based on developing a generalized equation. Contributions from each of the thermal parameters such as diffusion coefficient, blood perfusion rate, and oxygen consumption rate of the tissues etc. can all be attributed to a single source term, which would make the model much convenient for practical use. The theoretical route proposed in this paper may provide a feasible way to comprehensively characterize the oxygen transport behaviors in living tissues with complex vasculature. It can also be extended to more wide mass transfer issues such as drug and nutrients delivery etc.
Effects of Large Blood Vessels on Temperature Distributions During Simulated Cryosurgery
Authors: Deng Zhong-Shan , Liu Jing
Published: April 2008

Large blood vessels can produce steep temperature gradients in frozen tissues resulting in inadequate cooling temperatures during cryosurgery. In addition, arresting of blood vessels and bleeding due to rupture of large blood vessels by the iceball may cause undesired damage to healthy tissues. However, such important issues received few attentions up to now. In this article, several typical vascular models are applied to study the effects of large blood vessels to the tissue temperature distributions during cryosurgery. The thermal model combines the Pennes bioheat transfer equation describing for perfused tissues and the energy equation for blood vessels. A finite difference algorithm based on the effective heat capacity method is used to solve this complex heat transfer problems. In the algorithm, the tissues are treated as nonideal materials, freezing over a temperature range. Numerical analyses are then performed to study the influences of the blood vessels to the temperature distributions of tissues. The results indicate that different vascular models produce significantly different temperature responses for a given freezing pattern.
Cooling Penetration Surrounding an Intra-Parenchymal Cooling Probe in Hypothermia Treatment for Ischemia or Head Injury Patients: Theoretical Analyses
Authors: Zhu Liang , Rosengart Axel J.
Published: April 2008

Inducing hypothermia to brain tissue after brain ischemia or head injury has been demonstrated beneficial to the patients. Clinical studies have shown that even 1 or 2°C temperature reduction in brain tissue can be protective [Dietrich 1992]. On the contrary, fever-induced hyperthermia can worsen the neurological outcome in an animal model after cerebral ischemia. It is of clinical importance to understand the temperature distribution in brain during brain hypothermia.
Dynamic Response Predictions of a Truck Tire Using Detailed Finite Element and Rigid Ring Models
Authors: Chae Seokyong , El-Gindy Moustafa , Trivedi Mukesh , Johansson Inge , O¨ijer Fredrik
Published: April 2008

A detailed nonlinear finite element (FE) model of a radial-ply truck tire has been developed using an explicit FE code, PAM-SHOCK. The tire model was constructed to its extreme complexity with three-dimensional solid, layered membrane, and beam elements. In addition to the tire model itself, a rim model was included and rotated with the tire with proper mass and rotational inertial effects. The predicted tire responses, such as vertical stiffness, cornering force, and aligning moment, correlated very well to physical measurements. For complete vehicle simulations, a faster and simplified tire model is required for efficient analysis through-put. The behavior of such a tire model can be verified and improved by comparing responses with the developed FE model. Moreover, the parameters needed for the simplified model can be determined by the developed model instead of having to rely on tire measurements. The in-plane sidewall transitional stiffness and damping constants of the FE tire model were determined by rotating the tire on a cleat-drum. The other constants, such as in-plane rotational stiffness and damping constants, were determined by applying and releasing a tangential force on the rigid tread band of the FE tire model. The tire axle, spindle, and reaction force histories at longitudinal and vertical directions were recorded. In addition, the FFT algorithm was applied to examine the transient response in frequency domain. The tire steering characteristics were also determined. These parameters were used as input for a simplified rigid ring tire model. This study will discuss the results obtained from both the developed tire and the rigid ring tire models while both models are rolling at 12 mph constant linear speed and loading range of 13,345 N (3,000 lbs) to 53,378 N (12,000 lbs). The dynamic responses for the developed FE tire model were compared with the dynamics predicted using the rigid ring model. The results will show a successful attempt to capture the transient response of a tire rolling over a complex road profile.
Effect of a Downstream Ventilated Gas Cavity on the Spectrum of Turbulent Boundary Layer Wall Pressure Fluctuations
Authors: Young Steven D. , Brungart Timothy A. , Lauchle Gerald C.
Published: April 2008

This paper theoretically and experimentally examines the effect of a downstream ventilated gas cavity on the spectrum of turbulent boundary layer wall pressure fluctuations. The theoretical model predicts that the ratio of the point spectrum of the turbulent boundary layer wall pressure fluctuations upstream of a ventilated gas cavity to the blocked point pressure spectrum decays rapidly to zero as the cavity origin is approached and undergoes oscillations in amplitude that relax to unity as the quantity ωx/Uc goes to infinity upstream of the cavity. Here ω is the radian frequency, x is the distance upstream from the cavity origin and Uc is the convection velocity. A water tunnel experiment was performed to investigate the theoretical predictions. Dynamic wall pressure sensors were mounted flush to the surface of a flat plate at various distances upstream from a rearward facing step. Carbon dioxide gas was injected into the separated flow region downstream of the step to form a ventilated cavity. The water tunnel measurements were unable to verify the reduction in the amplitude of the turbulent boundary layer wall pressure fluctuations as the step and cavity were approached but did verify the fundamental oscillation predicted by the theoretical model and its relaxation to unity as ωx/Uc went to infinity upstream of the step and cavity.
Using Super Element and p-Approximation for Free Vibration Analysis of Composite Plates
Authors: Sharafaty Zangeneh M. , Ahmadian M. T. , Ghoreishi Seyed Reza
Published: April 2008

Effective and efficient methods in computational mechanics have been of interest for the designers and engineers in the last decade. A 3D super elements is developed and implemented for the free vibration analysis of the composite plates. These new elements have been constructed by a 2D super elements in the plane direction and p-version finite element in the thickness direction. Results of 2D super elements are comparable to SHELL 63 and results of 3D super elements with cubic polynomial are comparable to SHELL 93. In the thin plates, 2D super element (or SHELL 63) and 3D super elements (or SHELL 93) have same results, but in the thick plates results change drastically. Natural frequencies of thick plates analyzed by one 3D super element in comparison with 25 conventional elements (SHELL 63 and SHELL 93) by ANSYS software indicate good agreement in the results with a maximum 4% deviation.
A Drafting Course for Practicing Engineers
Authors: Mahaney Jack
Published: April 2008

Graphical communication has traditionally been a basic part of the mechanical engineer’s education. The production and reading of drawings have long been considered an attribute of ‘literate’ engineers. Today, that assumption is under attack, as is the very definition of a drafting course. Typical questions include “Why should we teach pencil/paper drawing in an AutoCAD age?” “Why not just teach solids modeling and forget the old-fashioned stuff?” At Mercer University we teach in the sophomore year a single two-semester-hour laboratory course containing three modules: pencil-and-paper drawing, computer-aided drawing, and solids modeling. The course attempts to balance the presentation and mastery of traditional descriptive geometry principles and skills with the need to prepare engineers for practice. The goal in each module is to teach enough skill to provide a base for experience and future learning in both course work and professional practice. The approach in each module is to start with the basic skills of that particular method, and progress to the production of working and assembly drawings. Rationale and learning objectives for the course are presented, as well as representative examples of assignments and projects.
Kinematic Calibration of the Central Linkage of a Wire-Actuated Parallel Robot: A Comparison Between Two Nonlinear Approaches
Authors: Varziri Saeed , Notash Leila
Published: April 2008

In this article kinematic calibration of the central linkage of a wire-actuated parallel robot, which has a parallelogram mechanism in its structure, is discussed. It is shown that the dependency between the parallelogram joint angles affect the conditioning of the identification Jacobian matrix. Through a sensitivity analysis, it is presented that some of the parallelogram link lengths are not identifiable. Two nonlinear calibration approaches, Gauss-Newton and Levenberg-Marquardt, have also been explained and their difference especially when the identification Jacobian matrix is ill-conditioned, are pointed out.
Identifying Common Platform Shape for a Family of Components
Authors: Natarajan Manojkumar , Siddique Zahed
Published: April 2008

To survive in today’s volatile and changing markets, companies are now faced with the problem of providing more customization, greater quality, faster response, more innovative designs and lower prices. New models need to be introduced in the market more frequently, which has given momentum to design product platforms. Use of common components can reduce the design and manufacturing time significantly. Determining commonality among different components is a key to reducing the new product design cycle time. CAD files can be used as a means to measure commonality for a set of similar components. This paper presents a tree-based approach to compare a set of similar 3D CAD models, measure shape commonality and identify the common platform shape. First a mapping of the solid models using the IGES format to IPG (IGES Parametric Graph) has been developed. The IPG, a Labeled Attribute Tree, is used to capture the three dimensional shape and design attributes along with the function of the component. The IPGs are then used to obtain a commonality index and establish a common platform for a set of similar products. The applicability of the method is demonstrated using CAD models of a family of casing. This research can also be applied to identify existing components that can be reused in new products.
Numerical Investigation of the Flow and Heat Transfer Due to a Miniature Piezoelectric Fan
Authors: Acikalin Tolga , Iverson Brian D. , Garimella Suresh V. , Raman Arvind , Petroski James
Published: April 2008

Piezoelectric fans have emerged as a viable alternative for electronics cooling applications requiring low input power and noiseless operation. A piezoelectric fan is a cantilever actuated by a piezoelectric ceramic material bonded to it. The fan oscillates back and forth creating airflow when an alternating electric field is applied to this bonded piezoelectric ceramic. Forced convection induced by such an oscillating fan in an enclosure is numerically investigated. The computational model is capable of sustaining deforming fluid cells that allow large boundary movement. The moving wall boundary, modeled as large-amplitude beam deflection, initiates flow in the fluid domain which enhances convection to varying extents depending on the heat source-to-fan distance and beam deflection amplitude. The effects of these parameters on heat transfer are studied. Transition between distinct convection patterns is observed with changes in the parameters. Results are validated against experimental measurements, with good agreement.
Graphite Intercalation Compounds as Actuation Materials
Authors: Massey Cameron , McKnight Geoffrey , Liu Ping , Barvosa-Carter William
Published: April 2008

The intrinsic electrochemical behavior of Graphite Intercalated Compounds (GICs) during formation offers the potential for high-force, high-strain solid-state actuation applications. To explore this behavior we submitted a “model” system, highly-oriented pyrolytic graphite (HOPG)/sulfuric acid (H2SO4), to axial compressive loads from 0 to 8 MPa, and measured the intercalation response in terms of voltage and displacement. We observed strains greater than 30% between 2 and 6 MPa, confirming the potential of GIC formation as a viable actuating mechanism. Further studies are planned in order to perform more precise analysis and examine alternate GICs.
Vehicle Moonroof Design for Wind Noise
Authors: Gur Yuksel , Agarwal Apoorva , Michnya James
Published: April 2008

A study was undertaken to address excessive moonroof wind noise in some vehicles. Mathematical models were developed to understand noise generation mechanisms associated with the moonroof system, and these models were used to investigate ways to reduce vehicle interior noise levels. Extensive acoustic & vibration testing was performed on vehicles in the wind tunnel and on the test track. The wind tunnel and test track data were analyzed in a sound quality laboratory for root cause analysis. CFD (computational fluid dynamics) simulations were performed to understand flow behavior over the moonroof in both modes of operations (vented and fully retracted). An experimental moonroof deflector optimization study was developed and conducted to identify the necessary design changes to minimize the vehicle interior noise level for fully retracted condition. Variability studies were also performed on the moonroof flushness, deflector height, and retraction distance. Through extensive analyses, using both experimental and analytical techniques, the main causes of wind noise associated with moonroof system were identified. Vehicle moonroof design recommendations were generated for significant wind noise reductions.
A Study on Length Scale Effects on Indentation Delamination of Thin Films
Authors: Li W. , Qu S. , Siegmund T. , Huang Y.
Published: April 2008

Simulations of indentation delamination of ductile films on elastic substrates are performed. A cohesive zone model accounts for initiation and growth of interface delaminations and a strain gradient plasticity framework for the length scale dependence of plastic deformation. With the cohesive zone model and the strain gradient formulation two length scales are introduced in to the analysis.
Laser Scanning Thermal Probe: A Novel Approach to NDE
Authors: Kephart Jacob , Chen John , Zhang Hong
Published: April 2008

Infrared (IR) thermography and, more recently, thermosonics have proven to be viable means of qualitative nondestructive evaluation (NDE). However, structural defects such as cracks observed through thermosonics can only be identified as “hot spots” indicating a general location of a defect without an accurate depiction of the dimensions or shape of the defect. This paper introduces a new technique dubbed Laser Scanning Thermal Probe, LSTP, which combines thermography with the use of heat application in strategic locations to observe the spatial heat flow patterns. LSTP provides the ability to record heat propagation across a defect area with temperature discontinuities forming due to differences in defect thermal diffusivity, thus providing information which can be used to characterize the defect such as crack length.
A “Hands-On” Approach to Teaching Undergraduate Heat Transfer
Authors: Ribando Robert J. , Richards Larry G. , O’Leary Gerald W.
Published: April 2008

Over the last eight years we have converted our undergraduate heat transfer course from a traditional lecture-based format to a “hands-on” environment taught in a room equipped with a computer for each pair of students. For nearly each major topic covered in this third-year survey course we have developed either a “canned” module or a student-implemented project illustrating that topic. The modules are written in Visual Basic and are graphically rich and highly interactive, while modern, research-based algorithms run behind the scenes. Many of these nine modules grew out of demonstrations and student projects developed for use in graduate level courses taught through our outreach program, which for many years has provided a highly supportive environment for instructional innovation. In addition, the student clientele, working engineers who already know and use computation and visualization extensively in their own careers, provides ample incentive for curriculum modernization.
Measurement of Thermally Induced Loads in Back-to-Back Angular Contact Spindle Bearings Using Strain Gauges
Authors: Harder John E. , Stein Jeffrey L.
Published: April 2008

Thermally induced bearing loads can potentially create serious problems for metal cutting spindles when used at high speeds. Proper spindle bearing set-up can minimize, but cannot eliminate this problem. Measuring the thermally induced load can alert the user to a potential problem or can be used to control the load directly. The purpose of this paper is to describe the design of a thermally induced bearing load sensor using strain gauges placed around the outer race. A box spindle with strain gauges on a pair of angular contact ball bearings located in the front of the spindle is used in this analysis. In order to calculate the thermally induced bearing load, the outputs of the strain gauges were recorded over a one second interval, sampled at 7500 Hz from each strain gauge and the root mean square of the deviation of this data from its mean is calculated. This value is a measure of the ball load. This calculated output is calibrated by a quadratic regression of these data to applied axial loads over a range of 0 to 2800 N. Values for each bearing were averaged to yield a front and rear value. The repeatability error for the front bearing sensor is 1.36%, and its accuracy is 98.9%. The repeatability error for the rear bearing sensor is 2.17% and its accuracy is 98.3%. These relatively low repeatability errors are attributable in part to filtering that does reduce the sensors’ bandwidth, but not significantly for measuring the relatively slowly changing thermally induced loads. Sensor design improvements and potential avenues of future research are discussed.
On the Shortcomings of Shape Memory Alloy Phenomenological Models
Authors: Elahinia Mohammad H. , Ahmadian Mehdi
Published: April 2008

The phenomenological models for SMAs, consisting of a thermodynamics based- constitutive and a phase transformation kinetics model, are the most widely used models for engineering applications. The existing phenomenological models are able to predict the behavior of SMA-actuated systems in most cases, except for cases arising from a simultaneous change in temperature and stress of the SMA elements, as is documented in this study. For such cases, the existing models fail to adequately predict the behavior of SMA elements undergoing complex thermomechanical loadings. A rotary SMA-actuated robotic arm is modeled using the existing constitutive models, in order to document the conditions under which the models fail. The model is verified against the experimental results, to document that under certain conditions, the model is not able to predict the behavior of the SMA-actuated manipulator. The phenomenological models discrepancy is also studied experimentally using a dead-weight that is actuated by an SMA wire.
Analytical Modeling of a Loop Heat Pipe at Positive Elevation
Authors: Chuang Po-Ya Abel , Cimbala John M. , Brenizer Jack S. , Conroy C. Thomas
Published: April 2008

A two-phase heat transfer device, a loop heat pipe (LHP), is studied analytically. It is noted that a LHP behaves differently when it is operated against gravity (adverse elevation) or at gravity assisted (positive elevation) conditions. Steady-state modeling of LHP operating characteristics at adverse or zero elevation was broadly studied in the past. This paper presents a steady-state model of a LHP when it is operated at positive elevation based on experimental results. The effects of elevation on the trend of steady-state operating temperature (SSOT) are then studied using the newly developed steady-state model. Experimental results agree with the model predictions at adverse (88.9mm), zero, and positive (88.9mm) elevations. This steady-state model is the only model known to have the capability to predict the operating characteristics at positive elevation. The model will help to design the LHPs utilized in terrestrial applications.
Active Vibration Control of a Rectangular Flexible Wall of an Empty and Fluid-Filled Tank
Authors: Carra S. , Amabili M. , Ohayon R. , Hutin P. M.
Published: April 2008

A rectangular plate bolted to a thick Plexiglas rectangular container is investigated in the case of empty and water-filled tank. A modal analysis is firstly realized in order to verify the effects of different water levels and of the free surface waves on the modal parameters and on the modal shapes. A filtered-x LMS (least mean square) adaptive feedforward algorithm is then applied to the perturbed system realizing structural vibration control in linear field with a SISO approach. Five piezoelectric PZT actuators apply the secondary control input in a nearly-collocated configuration. Their positioning is based on the knowledge on the deformation energy of the plate. The present study investigates primarily the control of the first vibration mode, but second and third modes are also experimentally studied. Satisfactory reductions (up to about 45 dB on the second mode measured on Channel 4) are reached for vibration amplitude of the three modes investigated in absence of water. For each modal shape, a particular effectiveness of the optimally placed actuators clearly appears. The introduction of water in the tank reduces the effectiveness of control of the first mode (maximum 5.5 dB of reduction of the vibration amplitude), but the five control channels show a more global uniform effectiveness.
Development of an Adaptive Helmholtz Resonator for Broadband Noise Control
Authors: Este`ve Simon J. , Johnson Marty E.
Published: April 2008

This paper presents the development of adaptive Helmholtz resonators aimed at controlling broadband disturbance for the reduction of noise transmission into rocket payload fairing. Helmholtz resonators are commonly used for narrow band control application and so are designed to present the lowest amount of damping yielding maximum impedance. For this particular application however, optimal damping ratios usually superior to 4% are required. This relatively high level of damping permits more lightweight and compact design options to be considered that are not possible for low damping applications. Two design solutions are presented. The first tunes the resonator by varying the length of an accordion neck. The second varies the HR opening using an iris diaphragm. The characteristics of these two devices are measured, and a solution to maintain the damping level relatively constant is also proposed. Finally, experimental result obtained in a large cylinder representative of a payload fairing using 8 adaptive resonators is presented.
The Surface Wavelength Composition of Thin Wall Iron Castings and Its Influence on CMM Measurements
Authors: Morse Edward P. , Gopal Krishnakumar , Raja Jayaraman
Published: April 2008

When measuring any mechanical artifact, thickness measurements obtained using a coordinate measuring machine (CMM) are affected by geometric variations having different wavelengths, leading to uncertainty in the reported thickness. These effects can be very pronounced in cast iron products, as the surfaces can be quite rough. This paper presents a methodology for reducing the uncertainty in the thickness measurements by comparing the measurements obtained using profilometry with CMM measurements. The surface data obtained from a profilometer are filtered using standard ISO filter and also using a morphological filter. The different wavelength components — such as the waviness profile and roughness profile — are separated and the thickness values are obtained from the filtered and unfiltered surface profile. The efficacy of different filtering methods is examined, and a procedure for reducing the uncertainty of the reported thicknesses is proposed.
Fatigue Crack Size Estimation From Vibration Induced Acoustic Signals Using Chirp Z-Transform and Neural Net
Authors: Li C. James , Lee Jun-Hee
Published: April 2008

The objective of this research is to develop a practical method to estimate the size of a crack on a rotating beam in a laboratory setting. The effort includes selecting a sensor and a measurement variable, devising a method for crack size estimation and carrying out experimental validations. The study employed a microphone to measure the pressure wave, i.e., acoustic signal, excited by the vibration of the rotating beam, utilized chirp-z transform to extract the 1st and 2nd mode frequencies, and established a diagnostic neural network to map modal frequencies to crack size. Four fatigue tests were conducted to initiate and then propagate a crack. Microphone outputs and crack size were periodically recorded during the four tests. Data from test No. 1 was used to calibrate the neural net and data from the other three tests were used for testing. The experimental results show that the proposed approach can provide reasonably good estimate of the crack size using only the indirect acoustic signal. The root mean square errors ranged from 0.037 mm to 0.124mm over the four tests.
Exact Solutions for Transverse Vibrations of Beams and Plates of Parabolic Thickness Variation
Authors: Caruntu Dumitru I.
Published: April 2008

This paper presents the class of nonuniform beams and nonuniform axisymmetrical circular plates whose boundary value problems of free transverse vibrations and free transverse axisymmetrical vibrations, respectively, have been identified to be eigenvalue singular problems of orthogonal polynomials. Recent published results regarding a fourth order differential equation and eigenvalue singular problem of classical orthogonal polynomials allowed this study, which extends the class of nonuniform beams and circular nonuniform plates having exact solutions for the problem of free transverse vibrations. The geometry of the elements belonging to the class presented in this paper consists of beams convex parabolic thickness variation and polynomial width variation with the axial coordinate, and plates of convex parabolic thickness variation with the radius. Two boundary value problems of transverse vibrations of beams are reported: 1) complete beam (sharp at either end) with free-free boundary conditions, and 2) half-beam, i.e. a half of the symmetric complete beam, with the large end hinged and sharp end free. The boundary value problem of circular complete plate (zero thickness at zero and outer radii) with free-free boundary conditions has been also reported. For all these boundary value problems the exact mode shapes were Jacobi polynomials and the exact dimensionless natural frequencies were found from the eigenvalues of the eigenvalue singular problems of orthogonal polynomials.
Weight Optimized Structural and Acoustic Actuators for the Control of Sound Transmission Into Rocket Payload Compartments
Authors: Johnson Marty , Sacarcelik Ozer , Harris Tony
Published: April 2008

The reduction of sound transmission into rocket payload compartments is a challenging application for active control due to the broadband nature of the disturbance, the large structural and acoustic space and the very high acoustic levels required. The exterior acoustic field that drives the payload fairing at liftoff is typically in the order of 145dB and the active control system must be able to counteract this high drive level using lightweight actuators. This paper is concerned with the development of structural and acoustic actuators for this application with the emphasis on maximum output level in the 60–200Hz bandwidth for a given actuator weight. The electromagnetic structural actuators are based on powerful rare earth magnets in a two degree of freedom arrangement. It is shown that a two degree of freedom arrangement allows the output in the bandwidth of interest to be increased over a simple one degree of freedom arrangement. The design is termed a distributed active vibration absorber or DAVA as the second degree of freedom is provided by a light and distributed foam element that allows easy attachment and low stress concentration on the structure. The two degree of freedom arrangement also acts as a natural low pass filter to naturally remove unwanted spillover at higher frequencies. The acoustic component is also based on powerful rare earth magnets, however the two degree of freedom arrangement used for the structural actuator is no longer of interest. The main concern is in the reduction of the speaker and cabinet weight. It is shown that careful design of the speaker and cabinet can lead to large reductions in weight without loss of performance. Data taken from an active control experiment on a large composite cylinder, coupled with data from the characterization of the actuators will be used to determine the total actuator weight needed for control in a typical launch environment.
A Structural Basis for Anisotropy in Cardiac Fibroblast Populated Collagen Gels
Authors: Thomopoulos Stavros , Holmes Jeffrey W.
Published: April 2008

The development of anisotropic mechanical properties is critical for the successful function of many soft tissues. Load bearing tissues naturally develop varying degrees of anisotropy, presumably in response to their specific loading environment. For example, the scar tissue that forms after a myocardial infarction is structurally and mechanically anisotropic. To better understand the scar mechanics, we first need to develop structure-function relationships for collagen fiber networks. In order to improve the healing after myocardial infarction, a better understanding of the mechanical anisotropy is necessary. An in vitro collagen gel system can be used to control individual fiber network components and to determine the effect of each component on the mechanical properties of the gel. Previously, we demonstrated the ability to promote two different collagen gel structures, with two different levels of mechanical anisotropy [1]. The goal of the current study was to quantitatively relate the observed mechanical anisotropy to the collagen fiber structure. It was hypothesized that the anisotropy could be explained with a simple structural model, where the gel behavior is derived from the behavior of the individual fibers within the gel (i.e., the properties of the fibers, their orientation, and their level of slack).
Model of Eddy Current Damping Mechanism for the Suppression of Beam Vibrations
Authors: Sodano Henry A. , Bae Jae-Sung , Inman Daniel J. , Belvin W. Keith
Published: April 2008

The movement of a conductor through a stationary magnetic field or a time varying magnetic field through a stationary conductor generates electromagnetic forces that can be used to suppress the vibrations of a flexible structure. In the present study, a new electromagnetic damping mechanism is introduced. This mechanism differs from previously developed electromagnetic braking systems and eddy current dampers because the system investigated in the following manuscript uses the radial magnetic flux of a permanent magnet to generate the electromagnetic damping force rather than the flux perpendicular to the magnet’s face as done in other studies. One important advantage of the proposed mechanism is that it is simple and easy to be applied. Additionally, a single magnet can be used to damp the transverse vibrations that are present in many structures. Furthermore, it doesn’t require any electronic devices or external power supplies, therefore functioning as a non-contacting passive damper. A theoretical model of the system is derived using electromagnetic theory, enabling us to estimate the electromagnetic damping force induced on the structure. The proposed eddy current damper was constructed and experiments were performed to verify the precision of the theoretical model. It is found that the proposed eddy current damping mechanism increases the damping ratio by up to 150 times and provides sufficient damping force to quickly suppress the beam’s vibration.
A Multiscale Approach to Multi-Component Wetting
Authors: Grillet Anne M. , Ash Benjamin J. , Brooks Carlton F. , Emerson John A.
Published: April 2008

Laser scanning confocal microscopy has been applied to study segregation in multi-component wetting. By labeling the two components of a blend with contrasting fluorescent dyes, the approximate local concentration can be determined from the relative fluorescence intensities. As a proof of concept, a coarsely blended mixture was imaged and parameters were adjusted to achieve good spectral separation of the two components. The technique was then applied to a well-blended drop of the two components and one component was observed to segregate to the air interface.
Analysis of Steady-State Penetration in Viscoplastic Porous Materials
Authors: Cazacu Oana , Cristescu N. D.
Published: April 2008

A study of the steady-state motion of a porous medium over a rigid wedge-shaped penetrator was conducted. In order to describe the combined effects of strain rate and compaction on yielding, a rigid viscoplastic constitutive equation was used. The deviatoric response was modeled with a non-homogeneous Bingam type equation with shear yield limit dependent on the current density. The system of partial differential equations consisting of the constitutive equation, the continuity equation, and the balance of momentum was solved for different interface conditions. The resistance to penetration as a function of the striking velocity, target properties (density dependent yield, locking pressure, locking density), friction coefficient as well as wedge semi-angle was obtained. The wedge semi- angle corresponding to a minimum in resistance to penetration in mortar for various impact conditions also resulted from this investigation.
Development of a Pre-Clinical Patellar Component Test for Total Knee Arthroplasty
Authors: Kersh Mariana E. , Ploeg Heidi-Lynn
Published: April 2008

Patellar component failure accounts for the majority of complications with total knee arthroplasty procedures [1]. Current patellar component tests involve loads that do not categorize failures as seen in clinical data. The aim of this project is to define the forces that lead to failure and design a test that can predict these failures. Clinical data reveals that the primary mode of failure of patellar components involves polyethylene wear most prominent at the lateral aspect of the component in various types of patella designs. Research on normal knee anatomy, kinematics and forces indicates that quadriceps tension results in a net lateral force exerted on the patella. This force, combined with the lateral to medial motion of the patella and its contact with the femoral condyles during 60° to 140° flexion, is theorized to be the contributing factor that leads to the observed clinical failure.
Application of Aligned Carbon Nanotubes in Micro Shear Stress Sensing
Authors: Clendenin Jason , Rokadia Husein , Tung Steve , Ogburia Konye
Published: April 2008

This paper reports the development of a MEMS based aligned carbon nanotube, thermal surface shear stress sensor for micro shear stress sensing applications. This paper is focused on the theory of alignment of CNTs during sensing element fabrication as well as experimental and calibration results from sensor testing. It is found that CNTs can be routinely aligned between surface micromachined gold electrodes using AC dielectrophoresis to form shear stress sensing elements. In order to fabricate the sensing element, a 25 Vp-p electric field at 3 MHz was used to form a ~150 μm wide line of aligned CNTs. The measured resistance of the sensing element was 580 Ω. The fabricated CNT shear stress sensor has been tested by bonding a Plexiglas channel to the electrode chip in order to create a 2D internal flow. The CNT shear stress sensor was found to have an average TCR of −0.0112%/°C or −0.0691Ω/°C and a current to voltage ratio of 0.07 mA/V.
On Control of a Two-Link Non-Fixed-Base Inverted Pendulum With Guaranteed Uniqueness
Authors: Zeng Hairong , Wu Qiong , Sepehri Nariman
Published: April 2008

A nonlinear controller with guaranteed uniqueness of Filippov’s solution is presented for controlling a two-link non-fixed-base inverted pendulum. The control system is described by differential equations with discontinuous right-hand sides, which violates the requirements of the conventional solution theories to ordinary differential equations, i.e., the vector fields must be at least Lipschitz continuous. It has been shown that Lyapunov’s second method can be used for such non-smooth systems directly under the condition of existence and uniqueness of Filippov’s solution. For this non-smooth control system with three discontinuity surfaces, the uniqueness of the solution is studied using Filippov’s solution concept. The system itself is a nonlinear, non-autonomous dynamic system without an isolated equilibrium point, which violates the assumption of Lyapunov’s stability theory. To analyze the stability of the control system, a Lyapunov-like function is constructed, which satisfies all the requirements for a Lyapunov function. Such a function can serve as an upper bound of the region in which the pendulum can be stabilized. Simulation results are presented to validate the proposed approach.
Performance and Modeling of a Liquid-Fed Direct Methanol Fuel Cell
Authors: Ge Jiabin , Liu Hongtan
Published: April 2008

Systematic experiments have been conducted to study the effects of various operating parameters on the performance of a direct methanol fuel cell (DMFC). The effects of cell operating temperature, anode flow rate, air flow rate, and methanol concentration have been studied. The experimental results showed that the operating parameters have significant effects on the DMFC performances, and some of the effects are complicated and deserve further detailed studies. Selected results are presented in this paper. A three dimensional, single-phase, multi-component model has been developed for liquid-feed DMFC. The traditional continuity, momentum, and species conservation equations are used. At the anode, liquid phase is considered, and at the cathode, only gas phase is considered. In addition to the regular electrochemical kinetics at the anode and cathode, the mixed potential effects due to methanol crossover are also included in the model. The modeling results compared well with our experimental data.
Two-Car Impact Test of Crash-Energy Management Passenger Rail Cars: Analysis of Occupant Protection Measurements
Authors: Severson Kristine J. , Parent Daniel P. , Tyrell David C.
Published: April 2008

As a part of ongoing passenger rail equipment safety research, a full-scale impact test of two cars with energy absorbing end structures was carried out on February 26, 2004. In this test, two coupled cars impacted a rigid barrier at 29 mph. Similar to previous full-scale tests in the series [1,2,3], anthropomorphic test devices (or ATDs) were included on the rail cars to measure the occupant response during the collision. These ATDs were instrumented with accelerometers and load cells to measure the injury risk to the occupants. This paper presents preliminary tests results. Five occupant experiments were included in the two-car test. Three of the experiments were similar to those conducted on the two-car test of conventional equipment that was held on April 4, 2000: forward-facing occupants in inter-city seats, forward-facing occupants in commuter seats, and rear-facing occupants in commuter seats. Two of the experiments examine the interaction of an occupant with a workstation table in a facing-seat configuration. These two tests used experimental ATDs with an increased capacity for recording abdominal impact response. To aid the analysis of this problem, MADYMO computer models were developed for four of the five of the occupant experiments. The models were either modified from earlier simulations, in the case of the commuter seats, or newly developed, in the case of the inter-city seats and table experiment with THOR ATD. The models were validated based on previous tests and/or accident data. Predictions of the ATD response agree closely for the overall kinematics of the ATDs, and for many of the measurements made with the ATDs in the full-scale test.
Band Deformation at a T-Junction While Electrofocusing in a Dog-Leg Microchannel
Authors: Horiuchi Keisuke , Dutta Prashanta , Cui Huanchun , Ivory Cornelius F.
Published: April 2008

On-chip isoelectric focusing (IEF) has been performed in both straight and dog-leg microchannels. Three-dimensional microfluidic chips were fabricated on poly di-methyl-siloxane (PDMS) using soft lithography and multilayer bonding techniques. Plasma oxidized PDMS channel surfaces were dynamically coated with methyl cellulose to discourage electroosmotic flow during separation and purification processes. In a straight microchannel, IEF was completed within 5 minutes at an applied electric field strength of 50 V/cm using broad range ampholytes. The focused bands were generally well-formed with sharp edges and were less than 100 microns across yielding a putative peak capacity in excess of 100 peaks in a 2-cm long channel. However, the conventional IEF protocol shifts the focused bands toward the cathodic well. This cathodic drift can be effectively minimized by placing highly viscous polymer solutions in the electrode reservoirs. In dog-leg microchannels, initially well formed focused band dispersed at the Tee-channel junction, but refocused at the dog-leg channels with relatively lower resolution.