bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Acoustics Behavior of Chiral Truss-Core Beams
Authors: Spadoni Alessandro , Ruzzene Massimo
Published: April 2008

The vibration-reduction and sound-absorption properties of a truss-core sandwich beam are analyzed. The core is composed by the assembly of unit cells across both the length and thickness of the proposed beam. The cells have chiral geometry which features cylinders, or nodes, joined by ligaments, or ribs. The resulting assembly is characterized by a number of interesting properties that can be exploited for the design of alternative honeycomb or cellular topologies to be used in sandwich construction. The vibro-acoustic analysis of the considered beam is performed through a finite element model developed using a commercially available Finite Element package. In the model, the sandwich beam is constrained to a rigid baffle and divides two fluid domains of infinite extent. The dynamic performance of the beam is evaluated through the estimation of the vibration amplitudes of the two constraining layers, while the performance of the beam as an acoustic panel with high insulation characteristics is analyzed through the estimation of the sound transmission loss between the two fluid domains. A sensitivity study to investigate the influence of core configuration and geometry on the beam’s performance is presented. The results indicate the design flexibility offered by the proposed design, which allows modifying and optimizing the structural acoustic performance of the beam through proper selection of the core configuration.
Resonant Dynamics and Saturation in a Coupled System With Quadratic Nonlinearities
Authors: Mankala Reddy , Quinn D. Dane
Published: April 2008

This work examines the behavior of a three-degree-of-freedom weakly coupled system. The system is composed of two components. The first is a two degree-of-freedom translational system that possesses an internal 2 : 1 resonance between the linear normal modes, which are coupled through quadratic nonlinearities. Under external forcing this component exhibits the saturation phenomena. The second is a rotational mass with a small imbalance, supported by the translational component. The angular speed of the rotor is not fixed, rather, the rotor is subject to a small torque and therefore its angular velocity slowly varies in time. A dynamic resonance occurs when the angular velocity of the rotor evolves to a neighborhood of one of the frequencies of the linear normal modes. Each of these resonances has been independently investigated previously in the literature. This work uncovers how the behavior of the dynamic resonance is modified by the mode coupling introduced by the 2 : 1 internal resonance and describes how the amplitudes of the linear normal modes are dependent on the properties of the dynamic resonance.
Vehicle Handling and Stability Enhancement With Active Steering Control Systems
Authors: Chen Shih-Ken , Lin William C. , Chin Yuen-Kwok Steve , Kang Xiaodi
Published: April 2008

This paper presents an analysis and comparison of a vehicle with active front steering and rear-wheel steering. Based on linear analysis of base vehicle characteristics under varying speed and road surfaces, desirable vehicle response characteristics are presented and a set of performance matrices for active steering systems is formulated. Using pole-placement approach, controllability issues under active front wheel steering and rear- wheel steering controls are discussed. A frequency response optimization approach is then used to design the closed-loop controllers.
Pulsed Micro Catalytic Combustor for Use in a Solid Piston Microengine
Authors: Green Darren V. , Miller Christopher G. , Santavicca Domenic A. , Sharp Kendra V.
Published: April 2008

In an effort to develop a novel micro power source, the design of a solid piston microengine is introduced. The operational principle of the Penn State Solid Piston (PSSP) is to employ a pulsed catalytic combustion reaction to thermally expand and contract a solid piston connected to a piezoelectric transducer, and in turn use the piezoelectric transducer to convert the mechanical energy of the periodic expansion and contraction of the solid piston (thermal actuator) into electrical energy. The existence of controlled temperature fluctuations within the combustion chamber is critical to the solid piston microengine design. Therefore, the focus of the microcombustor research presented herein is to obtain a consistent and predictable cyclical process leading to predictable temperature fluctuations within the solid piston. Experiments have been conducted using hydrogen gas in a catalytic combustion test rig to quantify the effect of changes in pulse frequency, pulse duty cycle, and equivalence ratio on overall temperature fluctuation and average temperature within the combustion chamber. The percentage of hydrogen consumed within the reaction is also measured.
An Automated System for Controlling the Laminar Flow Interface in a Microfluidic System
Authors: Kuczenski Brandon , LeDuc Philip R. , Messner William C.
Published: April 2008

The interface between adjacent laminar flow streams in the output channel of a Y-shaped confluent microfluidic network is useful for investigating the response of individual living cells to steep chemical gradients. This paper reports the design and performance of an automated pressure-feedback system for accurately and rapidly changing the position of that interface. The device will be employed to investigate the dynamic response of cells to time-varying chemical stimulation. The system works by controlling the pressure difference between the two adjoining inputs of the microfluidic network, altering the relative flow rate of the laminar streams in the output microchannel. Continuity of incompressible fluids dictates that the plane of the interface between the two streams will move from side to side as the flow rates change. The sample-data control system samples a temperature-compensated monolithic piezoresistive pressure sensor at 1 kilohertz, allowing the control of high-bandwidth microfluidic systems. This automated system enables long-duration, high-precision experiments that involve time-varying parameters to be performed simply, rapidly, and inexpensively.
Design of Over Center Valves Based on Predictable Performance
Authors: Hansen Michael R. , Andersen Torben Ole , Pedersen Peder , Conrad Finn
Published: April 2008

A typical over center valve system and a time domain simulation model is introduced together with a hypothesis that flow force compensation should reduce the inherent oscillatory behavior of such systems. A few results are shown from a parameter study that confirms this assumption and an approach to design over center valve geometries that have negative flow forces is presented with emphasis on predictability. In conclusion it is made clear that negative flow forces in the over center valve cannot solve the instability problem in general, however, it might very well be a method like lowering the pilot ratio, that can be used to application specific instability problems.
Industrial Applications of Advanced Electrochemical Finishing Techniques
Authors: Bonifas A. M. , Taylor E. J. , Sun J. J.
Published: April 2008

Faraday Technology, Inc. has developed electrochemical techniques for the edge and surface finishing of advanced materials, such as titanium alloys, stainless steels, and nickel based superalloys. This technology employs electrochemical metal removal under the influence of a bipolar, pulsed electric field to provide enhanced process control and excellent surface finishes. This process achieves high rates of metal removal in the presence of simple chemistries that are pH neutral, water based, non-toxic, and environmentally benign. This is in contrast to competing technologies that rely on electrolytes that are comprised of concentrated acids or ethylene glycol. This paper will present Faraday’s recent development efforts in a wide variety of industries, including the semiconductor, automotive, and medical industries.
In Vitro Pressure Flow Relationship in Model of Significant Coronary Artery Stenosis
Authors: Roy Abhijit Sinha , Back Lloyd H. , Millard Ronald W. , Khoury Saeb , Banerjee Rupak K.
Published: April 2008

Simultaneous measurement of pressure and flow rate has been found to be helpful in evaluating the physiologic significance of obstructive coronary artery disease and in the diagnosis of microvascular disease. This experimental study seeks to find important pressure-flow relationship in an in-vitro model of significant coronary artery stenoses using a non-Newtonian liquid, similar to blood showing a shear thinning behavior, using significant stenotic in-vitro model (minimal area stenosis = 90%). The geometry for the stenotic model is based on data provided in an in vivo study by Wilson et al., (1988). For 90% area stenosis, the maximum recorded pressure drop for steady flow rate of 55, 79 and 89 are 14, ~24 and ~32 mmHg respectively. The maximum pressure drop at flow rate of 115 ml/min (the physiological limit) is 50.3 mmHg respectively. Using a power law curve fit, the maximum pressure drop (in mmHg) related with flow rate (in ml/min) provided a power law index of 1.72. Shorter distal length than required in the in-vitro model did not allow the recording of complete pressure recovery. This preliminary data provides reference values for further experimentation both in vitro with pulsatile flow as in physiological conditions, and in vivo.
Deposition of Particles on Ocular Tissues and Formation of Krukenberg Spindle, Hyphema and Hypopyon
Authors: Kumar Satish , Acharya Sumanta , Beurman Roger
Published: April 2008

Eye diseases such as Krukenberg Spindle, Hyphema and Hypopyon are related to the deposition of specific particles such as pigmentary cells, leukocytes and erythrocytes. These particles are circulated by the aqueous humor (AH), and tend to deposit in regions of low velocities or high resistance. In the present paper, numerical simulations are reported of the AH flow and particle transport, and the particle concentration predictions are qualitatively compared with clinical images. The particle concentration distributions provide an understanding of the likely sources of deposition, and the origin of the deposited particles. Pigmentary cells are seen to concentrate in a vertical band on the corneal surface consistent with clinical observations of Krukenberg Spindle. Leukocytes and erythrocytes are seen to collect at the bottom of the anterior chamber similar to the observations made for Hypopyon and Hyphema. These results confirm the potential of using numerical calculations in order to obtain a better understanding of the particle transport and deposition patterns in the anterior chamber of the eye.
Statistical Analysis of Assemblies Having Dependent Fitting Conditions
Authors: Morse Edward P.
Published: April 2008

Analysis of the propagation of geometric variability through assemblies is used to estimate the probability that randomly selected components will, in fact, assemble. This process is known as Statistical Tolerance Analysis. One-dimensional analyses utilize a direct root-sum-square composition of the contributing part dimensions (the dimension stack) to estimate the probability that appropriate clearances will be maintained in the assembled configuration. Higher dimensional analyses frequently use the sensitivities of the clearances to dimensional changes based on the kinematics of the assembly. However, commercial tolerance analysis software does not support the analysis of assemblies where more than one dependent variable (a clearance) appears in each dimension stack. This paper describes the extension of a novel modeling method to accommodate statistical variability in assemblies. Assemblies are modeled in terms of their clearance conditions between mating surfaces, and parts are allowed to “float” with respect to one another, rather than being required to have all degrees of freedom removed in the final assembly. Variability in part dimensions is transformed to variation in the clearances, allowing inter-dependent dimension stacks sharing multiple, dependent clearances. The differences in predicted yield — will the parts fit together as designed? — for assemblies whose components can float with respect to one another is compared to similar assemblies where relative motion is fixed by a specified condition of contact or alignment.
Scribe-and-Break for Post Release MEMS Die Separation
Authors: Wallner Thomas W. , Oliver Andrew D. , Bergstrom Paul L.
Published: April 2008

We describe a post release die separation process for polysilicon surface micromachines using a combination of diamond scribing and breaking. The process resulted in yields above 80% for two types of electrostatic actuators. The paper describes the experimental apparatus and optimization of the process using a four parameter design of experiments. We determined that the two key parameters in the scribe-and-break process are the scribe force and the scribe angle. We also examined the theory of crack creation during the scribing process and determined experimentally that the crack depth in silicon is consistent with the theory developed for the scribing of glass.
A Circular Magneto-Hydrodynamic (MHD) Micropump With Electrolyte Solution
Authors: Shen Weidong
Published: April 2008

Linear and circular magneto-hydrodynamic (MHD) micro-pumps that operate with electrolyte solutions were studied experimentally. Each pump consisted of a conduit with a square cross-section. The linear pump consisted of a straight conduit with its inlet and an outlet subjected to different pressures. The circular pump consisted of a conduit bent into a loop. Copper electrodes were aligned along the two opposite walls of the conduits. Experiments were carried out with various electrolyte solutions such as NaCl, FeCl2/FeCl3, and CuSO4 at various concentrations. The device was placed in a uniform magnetic field and a potential difference was applied across the electrodes. The resulting current interacted with the magnetic field to produce a Lorenz force that propelled the liquid. The electric current and the flow rate were measured as functions of the imposed potential difference across the electrodes, the electrolyte composition and concentration, and the adverse pressure head. The feasibility of using the closed-loop MHD pump to transfer heat from a heat source to a heat sink was also explored.
Influence of External Loads on Thin Film Cracking
Authors: Chakravarthy Srinath S. , Jordan Eric H. , Chiu Wilson K. S.
Published: April 2008

Cracking in thin films under the combined influence of residual stress and an external load is examined. An improved accuracy version of the existing solution for substrate cracking absent the external load is provided. A superposition scheme that uses the solution for substrate cracking and other existing published solutions is presented for the determination of the energy release rate. The superposition scheme is validated using finite element analysis, and conditions under which the superposition scheme is valid are discussed. Crack arrest is examined and two parameters that determine the possibility of crack arrest are identified. The influence of external loading on channelling behavior in the substrate is discussed.
Too Hot to Handle? An Investigation Into Safe Touch Temperatures
Authors: Arthur Katie , Anderson Ann M.
Published: April 2008

Thermal burns occur when tissue temperature rises above a threshold value for a finite period of time. The safe touch temperature (STT) is the maximum allowable surface temperature for a material at which no tissue damage or pain occurs when the material is touched for a long enough period to allow safe handling. Current guidelines for the determination of safe touch temperatures are limited. The objective of this study was to determine the effect of material type and thickness on the safe touch temperature. We considered two boundary conditions in our evaluation of safe touch temperatures. Case 1 employed a fixed surface temperature on the surface opposite the contact point (i.e. a single sided contact situation like that encountered touching a pipe carrying a hot fluid) and Case 2 employed an adiabatic surface on the surface opposite the contact point (i.e. a two sided contact situation like that encountered when picking up a hot plate). The study utilized a finite element model to predict skin contact temperature as a function of plate temperature for copper and plastic plates ranging in thickness from 0.1 to 3.0 mm. We applied the damage function model of Xu and Qian [1] and determined that for the single sided contact condition the safe touch temperature increases with thickness from a low of 60 °C to a high of 115 °C for plastic and is invariant with thickness for copper at 60 °C. For the two sided contact condition the safe touch temperature was found to decrease as thickness increases from a high of 160 °C to a low of 110 °C for plastic and a high of 100 °C to a low of 60 °C for copper.
Curriculum Improvement Process in Mechanical Engineering at Penn State
Authors: Pauley Laura L. , Lamancusa John S. , Litzinger Thomas A.
Published: April 2008

This paper describes the process that was used to review and improve the Mechanical Engineering curriculum at Penn State University. The improvement process applied design methodology to review the present curriculum, develop alternate curriculum models, and evaluate those models. The curriculum models that were developed and challenges in implementing this process are also described.
Numerical Computation of the Heat Transfer and Fluid Mechanics in the Laminar Wall Jet and Comparison to the Self-Similar Solutions
Authors: Issa Johnny , Ortega Alfonso
Published: April 2008

Despite its importance as a canonical two-dimensional flow, the laminar wall jet has not been extensively studied using modern computational fluid dynamic methods. As in the laminar boundary layer, existence of analytical self-similar solutions make the problem particularly attractive for validating CFD code, yet we have found little archival work in which it has been used for this purpose. In the present study, we present a numerical investigation of the steady, laminar, and two-dimensional plane wall jet with constant properties. A finite-volume approach is used to solve the governing equations using self-similar inlet boundary conditions for the velocity and temperature profiles. The thermal solution is investigated for isothermal boundary condition at the wall. Velocity and temperature profiles are reported at various locations downstream and show an excellent agreement with the similarity solution obtained by Glauert [1] and Schwarz, et al. [2] respectively. In addition, the skin friction coefficient and the Nusselt number are investigated and compared with the analytical solutions presented by Glauert [1] and Mitachi, et al. [3] respectively, and very good agreement is observed. Despite its simplicity, it is shown that proper convergence of the numerical solutions of the wall jet to the expected analytical solutions requires care in specification of the jet inlet conditions, and the boundary conditions on the computational domain boundaries.
Single-Disk and Double-Disk Viscous Micropump
Authors: Blanchard Daniel B. , Ligrani Phillip M. , Gale Bruce K.
Published: April 2008

The development and testing of two novel micropumps called the single-disk and double-disk viscous pumps are described. A single disk and the top pump housing, or two disks are separated by a small gap that forms a fluid passage. A wiper, that is the height of this gap, is placed between the two disks, or between the single disk and top pump housing, and extends from the outer diameter of the disk(s) to the center region of the disk(s). The movement of the disk(s) induces viscous stresses on the fluid that forces the fluid through the pump area above the single disk, or between the two disks. The wiper acts to “wipe” the fluid from the disk(s) toward the outlet channel. The fluid flow through the double-disk pump is visualized using a red Rhodamine dye that is injected into the fluid passage upstream of the pumping area. Experimental flow rate for the single-disk and double-disk pumps are obtained for a disk diameter of 2.381 mm, and a gap height of 103 μm. The maximum flow rates obtained are 0.74 ml/min and 2.1 ml/min for the single-disk and double-disk pumps, respectively, for a rotational speed of 5000 rpm. Advantages of the disk pumps include simplicity of design, planar structure, continuous flow, well controlled flow rate, and mixing characteristics.
Fault Detection of an Electro-Hydraulic Cylinder Using Adaptive Robust Observers
Authors: Garimella Phanindra , Yao Bin
Published: April 2008

This paper presents the application of an Adaptive Robust Observer (ARO) to the detection of some common faults that occur in hydraulic cylinder drive units such as the lack of sufficient supply pressure, reduced hydraulic compliance and excessive leakage of the hydraulic fluid. All of these faults could contribute to the reduced performance of the system and eventual complete failure. The inherent nonlinear system dynamics, severe parametric uncertainties and model uncertainties make fault detection in hydraulic systems difficult to implement in practice. To tackle these problems, the Adaptive Robust Observer presented in this paper is designed using the nonlinear system dynamics and robust filter structures which attenuate the effect of model uncertainties to give robust estimates of the states. By using on-line parameter adaptation the accuracy of the state-estimate is improved. Also, by estimating the parameters only when certain persistence of excitation conditions are satisfied, bounds on parameter estimation errors can be computed which would help in setting better threshold limits on the residual signals which improves the robustness of the fault detection scheme. Simulation and experimental results on the swing-arm of a three-degree of freedom hydraulic robot arm are presented to demonstrate the effectiveness of the proposed fault detection scheme.
Finite Element Implementation of a Thermoviscoplastic Model for Ratcheting
Authors: Abu Al-Rub Rashid K. , Voyiadjis George Z.
Published: April 2008

A thermoviscoplastic constitutive model is proposed to simulate the uniaxial/multiaxial ratcheting of cyclically stable materials and its finite element implementation is also achieved. The kinematic and isotropic hardening rules used in the proposed model are similar to that developed by Voyiadjis and Abu Al-Rub [1], except for the coupling with temperature and strain-rate effects. The proposed constitutive equations include thermo-elasto-viscoplasticity, a dynamic yield criterion of a von Mises type, the associated flow rules, non-linear strain hardening, strain-rate hardening, and temperature softening. In the finite element implementation of the proposed model new implicit stress integration algorithms are proposed. The proposed unified integration algorithms are extensions of the classical rate-independent radial return scheme to the rate-dependent problems. A new expression of consistent tangent modulus is also derived for rate- and temperature-dependent inelasticity. The proposed model is verified by simulating the uniaxial ratcheting of a metallic material.
Optimization of Droplet Generation by Controlling PDMS Surface Hydrophobicity
Authors: Hung Lung-Hsin , Lee Abraham P.
Published: April 2008

This paper presents an optimized method for droplet generation in PDMS microchannels. With controllable PDMS surface hydrophobicity and hydrophobicity recovery, alternative component droplets can be generated as anticipated. Different surface hydrophobicity results in different droplet generation patterns. Monodispersed water-in-oil and oil-in-water droplets are generated from hydrophilic and hydrophobic surface respectively. Nearly hydrophilic surface (30°<θ<50°) results in long-tailed droplets and less hydrophilic surface (70°<θ<80°) results in stream mixing. Discussion of methods to loss and recovery hydrophobicity of PDMS also included.
Efficiency Characterization of Piezoelectrics for Power
Authors: Cho J. H. , Raupp J. C. , Hayenga P. D. , Richards R. F. , Bahr D. F. , Richards C. D. , Anderson M. J.
Published: April 2008

The efficiency of energy conversion by piezoelectric devices depends upon the quality factor Q, and electromechanical coupling coefficient k2. Efficiency, Q, and k2 were measured for a piezoelectric cantilever and piezoelectric stack, and compared to a model of the efficiency in terms of Q and k2. The model and experiment agree very well.
A Modified Gradient Plasticity Theory for Micro-Bending and Micro-Torsion Size Effects
Authors: Voyiadjis George Z. , Abu Al-Rub Rashid K.
Published: April 2008

The definition and magnitude of the intrinsic length scale are keys to the development of the theory of plasticity that incorporates size effects. Gradient plasticity theory with a material length scale parameter is successfully in capturing the size dependence of material behavior at the micron scale. However, a fixed value of the material length-scale is not always realistic and that different problems could require different values. Moreover, a linear coupling between the local and non-local terms in the gradient plasticity theory is not always realistic and that different problems could require different couplings. A generalized gradient plasticity model with a non-fixed length scale parameter is proposed. This model assesses the sensitivity of predictions in the way in which the local and non-local parts are coupled. The proposed model gives good predictions of the size effect in micro-bending tests of thin films and micro-torsion tests of thin wires.
Investigation of Enhanced Surface Spray Cooling
Authors: Silk Eric A. , Kim Jungho , Kiger Ken
Published: April 2008

Experiments were conducted to study the effects of enhanced surfaces on heat transfer during spray cooling. The surface enhancements consisted of cubic pin fins, pyramids, and straight fins (uniform cross sectional straight fins) machined on the top surface of copper heater blocks. Each had a cross-sectional area of 2.0 cm2. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N2 gas at 101 kPa). The results show that the straight fins had the largest enhancement in heat flux. Critical heat flux (CHF) for this surface showed an increase of 55% in comparison to the flat surface for the nominally degassed condition. The cubic pin finned and pyramid surfaces provided slightly more than half the heat flux enhancement (30%–40% greater than the flat surface) of the straight fins. The gassy case showed that the straight fins again provided the largest enhancement (48%) in CHF relative to the flat surface. This was followed by the cubic pin fins, and pyramids which had increases of 31% and 18% respectively. No significant effect was observed in the surface temperature at which CHF occurs for either portion of the study.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Authors: Luzin Vladimir , Gordon Jeffrey E. , Gnaupel-Herold Thomas , Prask Henry J.
Published: April 2008

Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.
Integrated Dynamic Simulation Model With Supervisory Control Strategy for a PEM Fuel Cell Hybrid Vehicle
Authors: Lin Chan-Chiao , Peng Huei , Kim Min Joong , Grizzle Jessy W.
Published: April 2008

System-level modeling and control strategy development for a hybrid fuel cell vehicle (HFCV) are presented in this paper. A reduced-order fuel cell model is created to accurately predict the fuel cell system efficiency while retaining dynamic effects of important reactant variables. The fuel cell system model is then integrated with a DC/DC converter, a Li-Ion battery, an electric drive and tire/vehicle dynamics to form a HFCV. The supervisory-level control problem of the HFCV is subsequently investigated. A stochastic dynamic programming (SDP) based approach is applied to obtain an optimal power management strategy. Simulations over different driving cycles showed that the SDP control strategy not only saved a significant amount of hydrogen but also produced smoother load for the fuel cell stack—both of which help the long term viability of the fuel cell technology for automotive applications.
Analysis and Modeling of Aortic Tissue Material Properties
Authors: Darvish Kurosh , Lobovsky Libor , Lee Sang-Hyun
Published: April 2008

A hyperelastic material with linear viscoelasticity was used to characterize the mechanical behavior of aortic tissue based on literature and new experimental data. It was shown that the previous data led to contradictory uniaxial and biaxial responses. A set of new material properties were identified which closely described the experimental data for strains below 40%.
The Iowa Interactive Digital-Human Virtual Environment
Authors: Yang Jingzhou , Abdel-Malek Karim , Farrell Kim , Nebel Kyle
Published: April 2008

Proper assessment of human reach posture is one of the essential functions for workspace design and evaluation in a CAD system with a built-in human model. Most existing models have used heuristic methods, which provide only the range of feasible human reaching postures, which may or may not include naturalistic reach posture. We present a multi-objective-optimization (MOO)-based approach for predicting realistic reach postures of digital humans, one based on our belief that humans assume different reach postures depending on different cost functions, i.e., multi-objective functions. In this work, the number of degrees of freedom (DOF) associated with the model is unlimited, and ranges of motion of joints are considered. The problem is formulated as MOO and single-objective optimization (SOO) algorithms where one or all cost functions (joint displacement, energy, effort, etc.) are considered as objective functions that drive the model to a solution set. A real-time simulation of the digital human’s motion is applied in the IOWA digital-human virtual environment.
An Integrated Robust Design Method for Occupant Restraint System
Authors: Fu Yan
Published: April 2008

Computational analysis of occupant safety has become an efficient tool to reduce the development time for a new product. Multi-body computer models (e.g. Madymo models) that simulate vehicle interior, restraint system and occupants in various crash modes have been widely used. To ensure public safety, many important injury numbers, such as head injury criteria, chest G, chest deflection, femur loads, neck load, and neck moment, are monitored. In the past, deterministic optimization methods have been employed to meet various safety regulations. Further emphasis on product quality and the consistency of product performance, uncertainties in modeling, simulation, and manufacturing, need to be considered. There are many difficulties involved in the optimization under uncertainty for occupant restraint systems, such as (1) highly nonlinear and noisy nature of occupant injury numbers; (2) large number of constraints; and (3) computational intensity to obtain the statistic information of injury numbers by the traditional Monte Carlo method. This paper investigates an integrated robust design approach for occupant restraint system by taking advantages of design of experiments, variable screening, stochastic meta-modeling, and genetic algorithm. An occupant restraint system is used as an example to demonstrate the methodology, however, the proposed method is applicable for all occupant restraint system design problems.
The Utilization of Flow Control During Multi-Cavity Injection Molding Processes
Authors: Layser Gregory S. , Coulter John P. , Bielawiec Gregory M.
Published: April 2008

Process control is an important factor for improving the performance and consistency of thermoplastic parts manufactured by injection molding processes. A critical process parameter for manufacturing of high quality plastic parts is cavity pressure. This paper presents a continuation of a numerical based study of the utilization of flow control specifically for cold runner applications in multi-cavity injection molding processes. A cold runner system supplying polymer melt to a multi-cavity mold incorporating several types of mechanical valves in the runner systems was modeled and manufactured. Each valve independently controls the flow and pressure to its portion of the mold. The goal of the numerical simulation phase of the present investigation was to numerically simulate and thus validate a physical capability to modify the filling of individual cavities during injection molding of products utilizing multi-cavity tooling. A decision was made to attempt to do so by physically controlling the flow rate of polymer into each cavity. The tooling set was made adaptive through the incorporation of custom designed control valves into the runner channels leading to each product cavity. Simulations of both the overall adaptive tooling concept and the specific control valve designs were performed with LCP and PPS as a molding material. It was concluded that the flow control concept developed was numerically validated [1–3], and it was shown that the valve system proposed here is applicable to control melt flow through cavities at industrial manufacturing facilities. The adaptive tooling developed and simulated during the current investigation yielded significant variations in both processing parameters and resultant product quality in response to in-tooling control valve adjustments. It was found that by changing valve angle settings, the flow rate to each cavity could be controlled individually without degrading desired material properties. In an attempt to further promote the flow control concept, an experimental mold was developed and forms the basis for this paper. Preliminary experimental results verifying previous work and the future directions for the continuing project are also discussed.
The Adaptive Piezoelectric Microsensoriactuator for Active Control of Microcantilevers
Authors: Burns Steven Robert , Cole Daniel G. , Clark Robert L.
Published: April 2008

The adaptive piezoelectric sensoriactuator is modified for use at the microscale to facilitate non-contact mode imaging of a microcantilever MEMS device in atomic force microscopy. The sensoriactuator is a truly colocated (sensor and actuator occupy exactly the same position on the structure) sensor/actuator device that uses a hybrid digital and analog design to drive a structure while simultaneously sensing the mechanical response. Using a piezoelectric material to both sense and actuate simultaneously is problematic because of the difficulty in resolving the sensory (mechanical) and actuator (electrical) parts of the output signal. Implementation of the adaptive piezoelectric sensoriactuator at the microscale results in a system with electrical quantities that are vastly reduced or increased from typical macroscale values, requiring more precise components and more careful design and construction of analog circuitry. For example, a typical micro-cantilever piezoelectric has a capacitance of on the order of 100 pF with an impedance at 50 kHz nearly 32 kΩ. The signal levels are significantly smaller with a typical piezoelectric current on the order of 100 nA. Thus, environmental noise can overwhelm signals in the system mandating the use of high precision operational amplifiers featuring ultra-low bias currents (±30 fA) and careful guarding or shielding of all circuitry. As reported in this paper, the adaptive piezoelectric microsensoriactuator has been successfully used to simultaneously sense and actuate while imaging using non-contact mode. The self-sensing microcantilever was successfully tested to produce a surface image using the microsensoriactuator to measure the movement of the microcantilever. The RMS value of the microsensoriactuator output is compared with the desired RMS output and the difference is used to drive an active resonance response controller. The active resonance response controller determines the control signal required to augment or attenuate the microcantilever’s motion to match the desired motion.
Consistent Atomic-Scale Finite Element: A Unified Framework for the Multiscale Modeling of Carbon Nanostructures
Authors: Mahdavi Arash , Mockensturm Eric
Published: April 2008

A new multiscale modeling technique called the Consistent Atomic Finite Element (CAFE´) is introduced. Unlike traditional approaches for linking the atomic structure to its equivalent continuum, this method directly connects the atomic degrees of freedom to a reduced set of finite element degrees of freedom without passing through an intermediate homogenized continuum. As a result, there is no need to introduce stress and strain measures at the atomic level. The Tersoff-Brenner interatomic potential is used to calculate the consistent tangent stiffness matrix of the structure. In this finite element formulation, all local and non-local interactions between carbon atoms are taken into account using overlapping finite elements. In addition, a consistent hierarchical finite element modeling technique is developed for adaptively coarsening and refining the mesh over different parts of the model. This process is consistent with the underlying atomic structure and, by refining the mesh, molecular dynamic results will be recovered. This method is valid across the scales and can be used to concurrently model atomistic and continuum phenomena. Applicability of the method is shown with several examples of deformation of a graphite sheet under different loadings and boundary conditions.
Acceleration Methods in the Interactive Design of a Hydraulic Mixing Nozzle Using Virtual Engineering Tools
Authors: Xiao Angran , Bryden Kenneth M. , Englebrecht Josh , McCorkle Douglas S.
Published: April 2008

Product design is a complex decision-making process requiring intensive interactions between designers and the designed product, especially in cases involving complex geometric shape creation and optimization. Virtual engineering is presented as a next-generation product realization system that integrates product models and engineering tools using virtual reality technology as a platform, which extends the application scope of virtual reality from visualization to interaction and decision making. The interaction between designers and product models is enabled by computing the engineering analysis models, wherein most researchers believe that the conflict between analysis accuracy and speed always exists. In this paper, several solution acceleration methods of high-fidelity computational fluid dynamics models are introduced, e.g., idealization, grid reduction, and a new convergence criterion. We have observed that it is possible to improve analysis accuracy and speed concurrently, and designers must consider specific design requirements when compromising these two factors. To demonstrate this idea, a hydraulic mixing nozzle design and analysis scenario is introduced. It has been shown that when conducting engineering analysis, design requirements are the primary factors that should be considered.
Design of Apparatus for Studying Aerodynamics of Voice Production
Authors: Barry Michael
Published: April 2008

The design and testing of an experimental apparatus for in vitro study of phonatory aerodynamics (voice production) in humans is presented. The presentation includes not only the details of apparatus design, but flow visualization and Digital Particle Image Velocimetry (DPIV) measurements of the developing flow that occurs during the opening of the constriction from complete closure. The main features of the phonation process have long been understood. A proper combination of air flow from the lungs and of vocal fold tension initiates a vibration of the vocal folds, which in turn valves the airflow. The resulting periodic acceleration of the airstream through the glottis excites the acoustic modes of the vocal tract. It is further understood that the pressure gradient driving glottal flow is related to flow separation on the downstream side of the vocal folds. However, the details of this process and how it may contribute to effects such as aperiodicity of the voice and energy losses in voiced sound production are still not fully grasped. The experimental apparatus described in this paper is designed to address these issues. The apparatus itself consists of a scaled-up duct in which water flows through a constriction whose width is modulated by motion of the duct wall in a manner mimicking vocal fold vibration. Scaling the duct up 10 times and using water as the working fluid allows temporally and spatially resolved measurements of the dynamically similar flow velocity field using DPIV at video standard framing rates (15Hz). Dynamic similarity is ensured by matching the Reynolds number (based on glottal flow speed and glottis width) of 8000, and by varying the Strouhal number (based on vocal fold length, glottal flow speed, and a time scale characterizing the motion of the vocal folds) ranging from 0.01 to 0.1. The walls of the 28 cm × 28 cm test section and the vocal fold pieces are made of clear cast acrylic to allow optical access. The vocal fold pieces are 12.7 cm × 14 cm × 28 cm and are rectangular in shape, except for the surfaces which form the glottis, which are 6.35 cm radius half-circles. Dye injection slots are placed on the upstream side of both vocal field pieces to allow flow visualization. Prescribed motion of the vocal folds is provided by two linear stages. Linear bearings ensure smooth execution of the motion prescribed using a computer interface. Measurements described here use the Laser-Induced Fluorescence (LIF) flow visualization and DPIV techniques and are performed for two Strouhal numbers to assess the effect of opening time on the development of the glottal jet. These measurements are conducted on a plane oriented perpendicular to the glottis, at the duct midplane. LIF measurements use a 5W Argon ion laser to produce a light sheet, which illuminates the dye injected through a slot in each vocal fold piece. Two dye colors are used, one for each side. Quantitative information about the velocity and vorticity fields are obtained through DPIV measurements at the same location as the LIF measurements.
Effects of DC Current on the Stress-Strain Curve and Hardness of 6061 T6511 Aluminum
Authors: Andrawes Joseph S. , Heigel Jarred C. , Roth John T. , Warley Russell L.
Published: April 2008

The effects of electricity on the mechanical properties of aluminum are investigated with the ultimate goal of establishing a technique by which the mechanical energy associated with cutting a material can be reduced without requiring an increase in the material’s temperature. The effects of the electricity on the mechanical properties of 6061 aluminum are investigated through both tensile and hardness testing. As the electricity is passed through the material, resistive heating occurs within the material. Therefore, the effects of non-stationary temperatures on the stress-strain behavior of 6061 aluminum are investigate with and without the electrical current flowing through the material. How the electrical effect varies based on the aluminum’s temper is also investigated, along with the effects of electrical pre-treatments. The experimental results indicate that the electricity has the potential to substantially reduce the energy required to machine the material without causing significant increases in the workpiece temperature. The testing also indicates that these effects exist regardless of the temper on the material. Finally, the study found that, while not reducing the energy as substantially as when using a continuous current, an electrical pre-treat can be used to reduce the energy below that found from annealing alone.
Superlayer Test for Interfacial Fracture Toughness Measurements
Authors: Zheng Jiantao , Sitaraman Suresh K.
Published: April 2008

Knowledge of the mode-mixity (?) dependent interfacial fracture toughness (Γ) is needed to predict the interface delamination and the component reliability of thin-film structures. Mode-mixity, ?, is a measure of the relative shearing to tensile opening of the interface crack near the tip. Typically, Γ increases as ? increases, such that the delamination is less likely when the loading on the interface is shear-dominated. The measurement of mode-mixity dependent Γ has been a challenge for thin film interfaces. The single-strip superlayer test, developed by the authors, eliminates the shortcomings of current testing methods. This test employs a stress-engineered superlayer to drive the interfacial delamination between the thin-film and the substrate. An innovative aspect of the proposed test is to introduce a release layer of varying width between the interested interfaces to control the amount of energy available for delamination propagation. By designing a decreasing area of the release layer, it is possible to arrest the interfacial delamination at a given location, and the interfacial fracture toughness or critical energy release rate can be found at the location where the delamination ceases to propagate. Design, preparation, and execution of the test are presented. Results are shown for Ti/Si interfaces of different mode mixities.