bluuebunny/crossref_metadata_2025 huggingface dataset:
3-D Knee Biomechanics
Authors: Caruntu Dumitru I.
Published: August 2009

This is a survey on 3-D dynamic and quasi-static human knee joint modeling. Anatomical surface representation, contact modeling, ligament structure, and solution algorithm are reviewed. Understanding knee joint biomechanics is important for total knee replacement and rehabilitation exercise design, ligament reconstruction, and cartilage damage. Knee models were proposed mostly in the last two decades. They aimed normal activities and rehabilitation exercises, and sought muscle, ligament, and joint contact forces. Consisting of two joints, tibio-femoral (TF) and patello-femoral (PF), the human knee 3-D models were PF, TF [1–3], and both TF and PF [4–7]. Models were static, quasi-static, and dynamic, including the entire, partial, or none of the ligament structure. Contact models of the knee were rigid or deformable. Both natural knees and replacement models were reported. Different groups of muscles were considered.
Rheology of a Suspension of 1000 Liquid Capsules in Channel Flow
Authors: Bagchi Prosenjit , Kalluri R. Murthy , Doddi Sai K.
Published: August 2009

Three-dimensional numerical simulations are presented on the motion of large ensembles of deformable particles (up to 1096 in number) in a channel flow at small inertia. Particles are modeled as capsules, that is, liquid drops surrounded by elastic membranes. Unlike liquid drops where the fluid-fluid interface is characterized by isotropic surface tension, that of a capsule is governed by more complex constitutive laws. Here we assume that the capsule membrane follows the neo-Hookean constitutive law. The particle volume fraction considered is up to 29%. The numerical methodology is based on a mixed finite-difference/Fourier transform method for the flow solver and a front-tracking method for fluid/membrane interaction. In the simulations, the flow field is resolved using up to 288×288×288 grid points, and each particle surface is resolved by 1280 triangular elements. The simulations are computation- and data-intensive, and the first of their kind in the context of deformable capsule suspension. The database generated from the simulations provides a wealth of information on the dynamics of semi-dense suspension of liquid capsules, in particular, and of deformable particles, in general. Preliminary results on flow visualization, particle trajectory, deformation, mean velocity and suspension viscosity are presented.
Effect of Sorbent Physical Structure—Pore Size Distribution and Surface Morphology—on the Limestone Capability for Sulfation
Authors: Crnkovic Paula M. , A´vila Ivonete , Milioli Fernando E. , Pagliuso Josmar D.
Published: August 2009

Sulfur oxides are present in the gases from burning coals and these pollutants are harmful to the environment. Sulfur removal in the fluidized bed reactor applying limestones is an efficient technology. During sulfation, the formation of CaSO4 leads to the partial or complete blockade of the particle interior, resulting in a low efficiency of the use of limestones. As the desulphurization capacities of the sorbents are strongly affected by thermal condition, this paper focuses on the study of the development of the particles’ physical structure before and during sulfation reaction. The experiments were performed for two Brazilian limestones, a calcite and a dolomite. The particles were well characterized by BET analysis and mercury porosimetry and the behavior of the sorbents was observed through thermogravimetry analysis (TGA). The morphological analysis of the surface of both raw calcite and dolomite particles indicated that dolomite was a less compact sorbent. However, after calcination and sulfation, the change in pore and voids distributions showed that for dolomite both swelling and partial pore filling could take place, whereas for calcite the spaces between particles were maintained constant, possibly owing to a less intense swelling. In 30 min of reaction under air atmosphere TGA measurements provided conversions of 0.40 ±0.061 for the calcite, and 0.55 ±0.089 for the dolomite. The results showed strong dependence on meso and macropores region with high conversion of the sorbents. The reactivity differences between calcite and dolomite can also be explained based on the swelling of the particles.
Buoyancy Driven Effects in Formation of Mixing Zones
Authors: Banerjee Arindam
Published: August 2009

The release of a mass of hydrogen fuel (gas) into the ambient atmosphere results in the transient formation of flammable mixture zones that represent potential fire, explosion and toxic hazards. The formation of mixing zones of air and hydrogen for this simple geometry follows the classical Rayleigh Taylor (R-T) instability, which is induced when a heavy fluid is placed over a light fluid in a gravitational field. Buoyancy driven mixing in such flow configurations is studied by using the Boussinesq approximation and considering the flow to be laminar. However, this approximation is valid only at low Atwood numbers (non-dimensional density differences). As Atwood number increases (>0.1, i.e. large density differences) the Boussinesq approximation is no longer valid and a distinct bubble and spike geometry of Rayleigh-Taylor buoyant plumes is formed. Aside from asymmetry in the flow the Atwood number also affects key parameters such as the growth constants and molecular mix. The effect of initial conditions on the growth rate of turbulent Rayleigh-Taylor (RT) mixing has been studied using carefully formulated numerical simulations. A monotone integrated large-eddy simulation (MILES) using a finite-volume technique was employed to solve the three-dimensional incompressible Euler equations with numerical dissipation for air and hydrogen mixing at Atwood number 0.875. The study also provides preliminary guidelines for reducing the fire and explosion hazards in enclosures where such situations are present.
Soret Effect on Double-Diffusive Laminar Convection in a Square Cavity Filled With Porous Material
Authors: Mesquita Maximilian S. , de Lemos Marcelo J. S.
Published: August 2009

This paper reports a numerical study of the Soret effect on steady-state flows, which are induced by double-diffusion in an enclosure. Convection takes place in a square cavity filled with a porous medium. Horizontal walls are impermeable and subjected to a vertical gradient of temperature. Vertical surfaces are adiabatic and subjected to a horizontal gradient of concentration. The physical model for momentum conservation equation makes use of the Forchheimer extension of the classical Darcy model. Governing parameters of the problem under study are thermal and solutal Rayleigh (Ra), Buoyancy ratio (N), Lewis numbers (Le) and Soret parameters (M). Computations using the finite-volume method cover the range 100 < Ra < 1000, −40 < M < 40 for N = 0.1.
An Efficient Method for Predicting Fracture of Hard Food Source
Authors: Patel Nirdesh D. , Grosse Ian , Sweeney Dan , Strait David S. , Lucas Peter W. , Wright Barth , Godfrey Laurie R.
Published: August 2009

In this paper we present a fast and reliable method for estimating the bite force required to fracture hard foods. The process involves complementary physical testing and finite element modeling. For physical testing, metal castings of upper or lower teeth are prepared. Metal tooth castings are mounted on a pivoting fixture interfaced to an Instron machine to simulate bite mechanics and thus to fracture hard food specimens. For the finite element model the tooth surfaces are modeled as rigid surface bodies in a nonlinear multi-load step contact analysis, while the food item is modeled as an elastic body. However, because only tooth surface information is needed in the model, we are able to automatically develop the geometry of the tooth surface using a tactile digitizing stylus with stereo lithographic surface profile information directly exported and subsequently imported into the FEA tool. We therefore avoid the need to laser scan tooth geometry which introduces significant “noise” into the surface model representation that must be painstakingly “cleaned” manually using software tools. The physical testing provides the force required to fracture the food item, while the finite element model provides the complete stress and strain state of the food item at the moment of fracture. Using this approach we have simulated the tooth biting mechanics of fossil primates to estimate biting force required to initiate a crack in a hard food source such as a macadamia nut. These analyses are designed to measure how occlusal morphology affects feeding performance, as the bite force needed to initiate a crack may vary according to tooth shape. The bite forces found using this approach will be used as an input for full-skull finite element models of early hominids (extinct fossil relatives of humans). The results of this work will be useful in testing the hypothesis that derived craniodental features in some of these hominids are adaptations for feeding on hard, brittle, seasonally available foods.
Verification of a New Principle of Automatic Transmission
Authors: Dong Janet , Hong Shane Y.
Published: August 2009

From 1877, the continuously variable transmission (CVT) showed up and became popular in the transmission market, and it is expected to be the main stream of transmission in the future. This paper attempts to verify a new principle of CVT which is achieved by elastic deformation of an elastic belt. Unlike traditional transmission, this new approach does not rely on the gear ratio or the radius of the driving and driven wheel to change the speed ratio. The speed change is achieved by an elastic belt on two fixed-diameter pulleys. The belt elongates in proportion to the load applied, and the driving pulley has to rotate more to accommodate the increased length of the belt due to the load increase, consequently reduces the speed of driven pulley. This self-sensing, self-adjusting, and fully automatic drive system is pure mechanical without the need of electrical or hydraulic control, and greatly simplifies the current transmission system. This paper will introduce the new principle of automatic transmission and discuss the experimental results of the speed changes, and therefore prove the feasibility of the new principle of automatic transmission.
Prepare Electrolyte and Electrolyte/Anode Bi-Layers for Solid Oxide Fuel Cells With Novel Gel-Casting Method
Authors: Xu Zhigang , Rajaram Gukan , Sankar Jag
Published: August 2009

A novel gel-casting method has been developed from general slurry tape casting technique to prepare electrolyte films and bi-layers of electrolyte and anode. This method permits to fabricate electrolyte layer as thin as 10–30 microns after sintering. In the study, a factorial experiment design was performed on the quantities of the gelling agent and the binders for the gel casting of electrolyte thin films and fuel cell bi-layers. The quality of the green films was assessed to determine the optimal amount of the gelling agent and the binders. The films were sintered at different temperatures from 1200°C to 1450°C to test the sinterability of the films. The sintering were also performed with impregnation of Bi(NO3)3 resulting in a great improvement in densification at lower temperature.
A Novel Device for Nonmagnetic Particle Navigation Using Ferrofluids Manipulated by Magnetic Fields
Authors: Forte James A. , Sipahi Rifat , Ozturk Alper
Published: August 2009

Particle navigation is performed for a variety of reasons including but not limited to drug delivery, cell isolation, sorting and filtering, and cell counting. Current methods accomplish these tasks by ‘tagging’ which has many benefits but also limitations in some cases. This paper proposes a novel device for nonmagnetic non-contact in-vitro particle navigation. The device is based on an idea that utilizes ferrofluids in connection with magnetic fields while effectively removing carriers as required by tagging methods and thus eliminating challenges associated with them. Analytic solution approaches and preliminary results show that this technology has promising potential to profoundly impact the field.
Introducing Temperature Measurement and Control Techniques to Engineering Undergraduate Students in the Gulf Region
Authors: Rodgers Peter , Molki Arman
Published: August 2009

Hands-on laboratory skills play a vital role in providing students with a sound understanding of the scientific fundamentals and their application in solving real-life engineering problems. One of the essential laboratory based courses taught at our Institute is Introduction to Measurements and Instrumentation. The design and implementation of such a course has been well documented in Western engineering education, but presents specific challenges in the Gulf region due to economical, social and cultural factors. This paper discusses the adaptation of corresponding Western courses to undergraduate mechanical engineering studies in the Gulf region. Laboratory exercises for temperature measurement and control are described, which consist of four modules, each building upon the other. In each module, students learn how to design an accurate measuring system, and process and interpret collected data. In the first module, the students are required to build a thermocouple reader using an AD620 instrumentation amplifier and to compare measurements with NIST reference tables. The second module is an introduction to LabVIEW, a graphical data acquisition programming language. The students are required to write a LabVIEW program to record multiple thermocouple signals from a heated plate under varying convective cooling conditions, using a high resolution temperature logger with on-board signal conditioning. The third and fourth modules focus on temperature control techniques. In the third laboratory exercise, the students are required to construct an electrical circuit using a low-power PCB relay and NPN bipolar transistor to develop a bang-bang linear temperature controller. The program created in module two is modified to have the heater operation automatically controlled for a fixed temperature set point. In module four, the students replace the bang-bang controller built in the previous lab with a commercially available PID controller and explore the differences between PID and linear temperature control systems. For each module, students are required to submit a formal report covering the theoretical background, the experimental procedure employed, uncertainty analysis, and conclusions and recommendations. An effective teaching strategy is outlined that covers the fundamental concepts of temperature measurement and control through carefully designed experiments, with sample results presented. Emphasis is placed on the tailoring of the course topics to engineering education in the Gulf region.
Ab Initio Calculations of Vibrational Energy Levels and Transition Dipole Moments of CO2 Molecules
Authors: Liang Zhi , Tsai Hai-Lung
Published: August 2009

Ab initio MD simulation of laser-matter interactions is a hot area in the study of the mechanisms of photo-dissociation, photo-ionization and laser induced chemical reactions. The major problems in the study of laser-molecule interactions are to determine the energies and wave functions of molecular vibration states and the molecular transition dipole moments. An efficient method is presented to calculate the intramolecular potential energies and electrical dipole moments of CO2 molecules at the electronic ground state by solving the Kohn-Sham (KS) equation for a total of 101,992 nuclear configurations. The Projector-Augmented Wave (PAW) exchange-correlation potential functionals and Plane Wave (PW) basis functions were used in solving the KS equation. The calculated intra-molecular potential function was then included in the pure vibrational Schro¨dinger equation to determine the vibrational energy eigen values and eigen functions. The vibrational wave functions combined with the calculated dipole moment function were used to determine the transition dipole moments. The calculated results have a good agreement with experimental values. These results can be further used to determinations of molecular spectroscopy and laser absorption coefficients.
Transient Multi-Field FEA Model for Predicting Current Density Distribution When Deforming Sheet Metal Under a Direct Current
Authors: Roth John T. , Khalilollahi Amir , Jageman Daniel J.
Published: August 2009

Previous investigations have been performed that involve developing new ways in which to deform a material while minimizing the energy required to do so. More recent research involves applying an electric current to the workpiece to achieve superplasticity. However, those investigations only utilized uniaxial workpieces and lack the ability to be used for more common geometries. The research presented herein, however, the effect is investigated under three-dimensional conditions so that the results could be projected to more realistic sheet metal geometries. A working finite element analysis (FEA) model has been developed to analyze these more complicated three-dimensional flow fields and will be presented as a part of this research. The model was used to solve for the temperature and current density distributions across the workpiece. The results from the FEA model are compared to results obtained from experimental tests. In the experimental setup, the two dome heights were separately tested under the same conditions that the FEA model simulated, however, only a temperature distribution was obtained here. The comparison of the FEA results and the experimental results related the temperature distribution to the current density distribution across the workpiece. From here, the individual effects of certain parameters on the distributions were found. The parameters included: duration of current, amount of current, electrode placement, and dome height geometry. The results showed that the current density distribution can be manipulated by varying the above parameters. This capability can be used to delay tearing/necking of a sheet metal workpiece under deformation.
Showerhead Film Cooling Performance of a Transonic Turbine Vane at High Freestream Turbulence (Tu = 16%): 3-D CFD and Comparison With Experiment
Authors: Wu Hong , Nasir S. , Ng W. F. , Moon H. K.
Published: August 2009

The main objective of the study reported here is to use 3-D CFD to calculate and explain adiabatic film cooling effectiveness and Nusselt number distributions downstream of the showerhead film cooling rows of a turbine vane at high freestream turbulence and realistic exit Reynolds number/Mach number condition. The paper discusses a three-simulations technique to calculate vane surface recovery temperature, adiabatic wall temperature, and surface Nusselt number to completely characterize film cooling performance in a high speed flow. The RANS based ν2-f turbulence model, originally suggested by Durbin [1], is used in all numerical predictions. The vane midspan numerical calculations are compared with the experimental results obtained with the showerhead film cooled vane instrumented with single-sided platinum thin film gauges at the midspan and arranged in a two-dimensional, linear cascade in a heated, transonic, blow-down wind tunnel. Exit Mach number of Mex = 0.76—corresponding to exit Reynolds numbers based on vane chord of 1.1 × 106—was tested with an inlet free stream turbulence intensity (Tu) of 16% and an integral length scale normalized by vane pitch (Λx/P) of 0.23. A showerhead cooling scheme with five rows of cooling holes was tested at blowing ratios of BR = 0 and 1.5, and a density ratio of DR = 1.3. CFD predictions performed with experiment-matched boundary conditions show an overall good trend agreement with experimental adiabatic film cooling effectiveness and Nusselt number distributions downstream of the showerhead film cooling rows of the vane. For the experimental data, the primary effects of coolant injection are to augment Nusselt number and reduce adiabatic wall temperature downstream of the injection on the vane surface as compared to no film injection case (BR = 0) at Mex = 0.76. Similar to experimental results, the adiabatic film cooling effectiveness prediction on the suction surface at BR = 1.5 is found to be influenced by favorable pressure gradient due to Mach number through changes in local adiabatic wall and recovery temperature. The Nusselt number prediction on the suction surface shows a peak and a valley downstream of the film cooling rows in a favorable pressure gradient region for both tested blowing ratio conditions. This trend is also observed in the experimental results.
Determination of Equilibrium Wire Feed Speeds for a Stable GMAW Process
Authors: Rao Z. H. , Hu J. , Liao S. M. , Tsai H. L.
Published: August 2009

In gas metal arc welding (GMAW), for given welding conditions (e.g., current, electrode diameter, electrode material, etc.), the consumable electrode wire must be fed in such a speed that it dynamically balances the electrode melting speed in order to achieve a stable welding. In this article, a comprehensive model for GMAW was developed to study the interplay between the transport phenomena including the electrode melting and plasma arc, and the dynamically equilibrium wire feed speeds (WFSs) under different welding conditions. The predicted WFSs are in excellent agreement with published data that were obtained through the trial-and-error procedure.
Microscale Thermoelectric Cooler Assembled From Bulk Materials for Thermal Management of Electronics
Authors: Mishra Pradeep , Crane Nathan
Published: August 2009

Electronic device thermal management improvements are critical to continued increases in computing performance. Thermoelectric coolers (TECs) show promise in meeting this need. This paper compares the performance of Bismuth Telluride (BiTe) in three different forms: thin film, bulk, and a hypothetical nanostructured bulk material. This hypothetical materials is based on recent experimental demonstrations in Lead Telluride. Performances of the TEC based on the three different BiTe forms are compared with respect to heat pumping capacity and optimum thickness. The simulations are based on 1-D models that include the effects of thermal and electrical contact resistance. Simulated results show a significant enhancement in maximum heat pumping capacity of ‘Nanostrutured-Bulk TEC’. Modified definitions of heat pumping capacity and coefficient of performance (COP) are proposed for evaluating TECs used to cool objects with temperatures above ambient temperature. It is observed that the appropriate heat sink selection is key factor for achieving the improved TEC performance while maintaining minimum thickness.
A Dynamic Model Incorporating Thermal Effect for Piezoelectric Stick-Slip Actuators
Authors: Li J. W. , Zhang W. J. , Zhang Q. S. , Chen X. B. , Tu S. D.
Published: August 2009

It was found experimentally from our previous study that the operation of the piezoelectric actuator (PEA) and the friction in the piezoelectric stick-slip actuator (PE-SSA) can cause significant rise in temperature, thereby degrading the performance of the actuator. This paper presents a dynamic model for the PE-SSA by taking into account thermal effect. In particular, the dynamic model is developed by integrating the PEA model proposed by Adriaens et al. [1] and the LuGre friction model proposed by De Wit et al. [2]; the parameters involved in the models are determined using a system identification approach. Experiments are carried out to verify the effectiveness of the model. It is shown that the simulation and experimental results are in a good agreement. This study provides a new way to model thermal effect for other micro motion systems.
Characterization of Aortic Root Compliance at Different Heights
Authors: Sirois Eric M. , Chiu Tsuicheng , Fox Martin , Sun Wei
Published: August 2009

Aortic valve stenosis is a significant cause of morbidity and mortality [1]. Currently, the preferred treatment of severe aortic stenosis is aortic valve replacement, which carries a significant risk for patients with comorbidities [2]. Recently, percutaneous aortic valve (PHV) replacement represents an endovascular alternative to conventional open heart surgery without the need for sternotomy, aortotomy, or cardiopulmonary bypass [3]. However, there are significant serious adverse events associated with the percutaneous procedure, such as myocardial infarction, peripheral embolism, injury to the aorta, perivalvular leak and access site injury [3–5]. Furthermore, long-term durability and safety of these valves need to be evaluated and studied carefully. We hypothesize that the device (dys)function could be more accurately predicted if a better understanding of the biomechanical interaction between the native aortic valve/root and the PHV were available. In this study, our objective is to characterize the mechanical properties of the aortic root such that its interaction with the PHV device can be quantified.
Nanohole Arrays as Optical and Fluidic Elements for Sensing
Authors: Escobedo Carlos , Eftekhari Fatemeh , Ferreira Jacqueline , Wood Paul , Gordon Reuven , Brolo Alexandre G. , Sinton David
Published: August 2009

Arrays of nanoholes in metal films present several opportunities as surface based sensors in lab-on-chip systems. Metallic nanohole arrays support surface electromagnetic waves that enable enhanced transmission through the holes and have been harnessed for chemical and biological sensing. Nanohole array based sensing performed to date has involved nanoholes that end shortly beyond the metallic film layer on a substrate such as glass. Such dead-ended holes fail to harness the potential of through-hole nanohole arrays including enhanced transport of reactants to the active area and a solution sieving action that is unique among surface-based sensing methods. In this work we investigate the potential of a flow-through-array sensing format.
Simulated Compensatory Motion of Transradial Prostheses
Authors: Lura Derek , Dubey Rajiv , Carey Stephanie L. , Highsmith M. Jason
Published: August 2009

The prostheses used by the majority of persons with hand/arm amputations today have a very limited range of motion. Transradial (below the elbow) amputees lose the three degrees of freedom provided by the wrist and forearm. Some myoeletric prostheses currently allow for forearm pronation and supination (rotation about an axis parallel to the forearm) and the operation of a powered prosthetic hand. Older body-powered prostheses, incorporating hooks and other cable driven terminal devices, have even fewer degrees of freedom. In order to perform activities of daily living (ADL), a person with amputation(s) must use a greater than normal range of movement from other body joints to compensate for the loss of movement caused by the amputation. By studying the compensatory motion of prosthetic users we can understand the mechanics of how they adapt to the loss of range of motion in a given limb for select tasks. The purpose of this study is to create a biomechanical model that can predict the compensatory motion using given subject data. The simulation can then be used to select the best prosthesis for a given user, or to design prostheses that are more effective at selected tasks, once enough data has been analyzed. Joint locations necessary to accomplish the task with a given configuration are calculated by the simulation for a set of prostheses and tasks. The simulation contains a set of prosthetic configurations that are represented by parameters that consist of the degrees of freedom provided by the selected prosthesis. The simulation also contains a set of task information that includes joint constraints, and trajectories which the hand or prosthesis follows to perform the task. The simulation allows for movement in the wrist and forearm, which is dependent on the prosthetic configuration, elbow flexion, three degrees of rotation at the shoulder joint, movement of the shoulder joint about the sternoclavicular joint, and translation and rotation of the torso. All joints have definable restrictions determined by the prosthesis, and task.
MEMS Pressure Sensor Array for Aeroacoustic Analysis of the Turbulent Boundary Layer
Authors: Krause Joshua S. , White Robert D. , Moeller Mark J. , Gallman Judith M. , De Jong Richard
Published: August 2009

The design, fabrication, and characterization of a surface micromachined, front-vented, 64 channel (8×8), capacitively sensed pressure sensor array is described. The array was fabricated using the MEMSCAP PolyMUMPs® process, a three layer polysilicon surface micromachining process. An acoustic lumped element circuit model was used to design the system. The results of our computations for the design, including mechanical components, environmental loading, fluid damping, and other acoustic elements are detailed. Theory predicts single element sensitivity of 1 mV/Pa at the gain stage output in the 400–40,000 Hz band. A laser Doppler velocimetry (LDV) system has been used to map the spatial motion of the elements in response to electrostatic excitation. A strong resonance appears at 480 kHz for electrostatic excitation, in good agreement with mathematical models. Static stiffness measured electrostatically using an interferometer is 0.1 nm/V2, similar to the expected stiffness. Preliminary acoustic sensitivity studies show single element acoustic sensitivity (as a function of frequency) increasing from 0.01 mV/Pa at 200 Hz to 0.16 mV/Pa at 2 kHz. A more in depth analysis of acoustic sensitivity is ongoing.
Computational Modeling and Experimental Investigation of Static Straight-Through Labyrinth Seals
Authors: Untaroiu Alexandrina , Goyne Christopher P. , Untaroiu Costin D. , Wood Houston G. , Rockwell Robert , Allaire Paul E.
Published: August 2009

To design highly efficient and stable turbomachines, engineers require accurate methods to model seal flows and calculate clearance-excitation forces generated by the eccentric position of the rotor. One of the most widely used methods to predict leakage flow and dynamic coefficients is the use of computer codes developed based on bulk flow theory. In recent years, computational fluid dynamics (CFD) modeling is increasingly being recognized as an accurate assessment tool for flow parameters and dynamic coefficients evaluation as compared to the bulk flow codes. This paper presents computational and experimental investigations that were carried out to calculate flow parameters in a stationary straight-through model labyrinth seal. The main objective of this study is to explore the capabilities of Ansys-CFX, a commercially available state of the art 3D numerical code, to accurately model compressible flow through the seals. The flow behavior is analyzed using CFD and the flow parameters calculated by CFD are validated against experimental data taken for the same seal configuration. The integrated values of leakage flow rates estimated from the computational results agree with the experimental data within 7.6%. This study serves as a benchmark case that supports further efforts in applying CFD analysis in conjunction with automatic design optimization techniques for seals used for compressible media. It was shown that optimization algorithms combined with CFD simulations have good potential for improving seal design.
Impact of Altering Aspect Ratio of the Loading Particles on a Suspension’s Thermal Conductivity
Authors: Cherkasova A. S. , Shan J. W.
Published: August 2009

It has been recognized that heat-transfer fluids used to convey thermal energy produced by one device to another can exhibit significant increases in thermal conductivity with the addition of highly conductive particles. Suspensions of nano- and micro-particles have attracted the most recent interest because of their enhanced stability against sedimentation, reduction in potential for clogging a flow system, as well as the tantalizing possibility of unexpected enhancements in thermal conductivity that have been reported in some experiments. Among various suspensions, considerable attention has focused on those containing large-aspect-ratio particles, such as carbon nanotubes. Although recent experiments have demonstrated enormous heat-transfer enhancements in these fluids, such increases were reportedly not in agreement with existing macroscale theories [1–3]. In this research we report on an experimental study of the effects of particle aspect ratio on the effective thermal conductivity of micro- and nano-particle suspensions. The influence of particle aspect ratio on the thermal properties of suspensions was first studied in dispersions of micron-sized, silicon-carbide particles with varying aspect ratio. To carry out a detailed comparison with theoretical predictions, particle aspect ratio and size distributions were measured. It is shown that the conductivity of the silicon-carbide suspensions can be quantitatively predicted by an effective-medium theory (EMT), provided the volume-weighted aspect ratio of the particles is used. The particle-aspect-ratio effect was further studied in the suspensions of multi-walled carbon nanotubes. Experimental data on the thermal conductivity of nanotube suspensions could also be interpreted in terms of the aspect-ratio dependence predicted by EMT if the additional nanoscale effect of interfacial resistance was considered.
Study of Whole Blood Viscosity Using a Microfluidic Device
Authors: Zeng Hansong , Zhao Yi
Published: August 2009

Cardiovascular diseases include a wide range of disorders that affect heart and blood vessels, and are the leading cause of death in the United States. Whole blood viscosity, a parameter to describe the rheologic properties of blood, is an important measure of various cardiovascular diseases. It is used clinically to assess the risks of heart attack, hypertension, thrombosis and strokes. Currently used viscometers measure whole blood viscosity by inducing Couette flow to drive the blood at a certain shear rate. The blood viscosity is derived from the resistance toque measured by the toque sensor integrated within the shaft. Although effective, this method is limited due to the expensive toque sensor and the relatively large amount of blood required. More important, the fluidic conditions within the viscometer are vastly different from those in natural blood vessels (Poiseuille flow), which makes this method inappropriate to predict actual blood viscosity and its effect under natural conditions. In this work, we demonstrate whole blood viscosity measurement from the electrical resistance of the blood sample using a microfluidic device. Since the predominant parameters of the blood viscosity also determine the electrical impedance of the blood sample, the microdevice can be used as a new route of measure for blood viscosity. Blood samples with different hematocrit levels were flowed through a microchannel at different velocities that correspond to different shear rates. The electrical resistance at 20 kHz AC stimulation was recorded and compared with the viscosities measured by a commercialized rheometer. The results showed that the representative rheologic parameters (hematocrit and shear rate) are measurable by the electrical impedance. The correlation between the blood viscosity and the electrical resistance was quantitatively determined by regression analysis with a high determination coefficient. This study provides a solution for low cost, quick measurement of blood viscosity with minimal blood consumption. It also enables the in-depth investigation of blood rheology under in vivo like conditions.
Numerical Simulation of Random Packing of Spherical Particles for Selective Laser Sintering Applications
Authors: Zhou Jianhua , Zhang Yuwen , Chen J. K.
Published: August 2009

Selective Laser Sintering (SLS) is an efficient and rapid manufacturing technique because it allows for making complex parts that are often unobtainable by traditional manufacturing processes. However, the application of such technique is quite limited by the balling phenomenon, for which it largely reduces the manufacturing quality. Eliminating the structural defects is crucial to overcome the balling phenomenon. Therefore, a better understanding of the packing structure details is urgently needed for the SLS applications. In this study, the sequential addition packing algorithm is employed to investigate the random packing of spherical particles with and without shaking effect. The 3-D random packing structures are demonstrated by illustrative pictures and quantified in terms of pair distribution function, coordination number and packing density. The results are presented and discussed aiming to produce the optimal packing parameters for the SLS manufacturing process.
Flow Regime Observations in a Vertical Annulus With an Inner Roughened Tube
Authors: Harvel G. D. , Torica B.
Published: August 2009

The efficiency and safe performance of a nuclear power plant is often reliant upon a solid understanding of the multiphase flow phenomena that occurs in various components and piping networks throughout the heat transport loops. Depending upon the conditions, various flow regimes can be observed and each of these flow regimes would have a different impact upon the heat transfer and pressure drop of the component or piping that the two-phase mixture is traveling in. Thus, many researchers have performed significant studies to predict flow regime. Over the past several years, the maintenance and inspection efforts at various nuclear power plants have shown that ageing phenomena are occurring including corrosion, cracking, erosion phenomena, and deposition of materials. One of the effects of such phenomena is the roughening of the surface which would impact the nature of fluid behaviour, heat transfer behaviour, and mass transfer at the surface. Relationships for surface conditions and pressure drop/heat transfer are already established for single phase flow conditions albeit with significant uncertainty. Yet, the relationships for multiphase flow have not been established and it is assumed that the surface effects are covered through the single phase component. In this work, experimental studies are performed for a vertical annulus geometry. The apparatus consists of glass tubing to allow visualization of the flow regime inside the tubes. The glass tube material is also a reference case for the smooth tube. Experiments are performed in a bubble column mode for superficial gas velocities up to 0.5 m/s. Observations are taken at various developing lengths and varied water inventories. The results are compared to previous work which shows that the smooth tube results match previous measurements. The inner surface of the tube is modified by forming a thin layer of material over the glass surface. The material is initially moldable and allows for the imprinting of different surface shapes and roughnesses. The material cures in a few hours and is resistant to erosion or dissolution in water. Thus, the surface conditions are changed on the inner tube. The experiments indicate that the flow regime transition from bubbly to slug flow and from slug to churn flow occur at lower superficial gas velocities.
Simultaneous Water Droplet Formation and Sorting Using an Electric Field
Authors: Ahn Byungwook , Panchapakesan Rajagopal , Lee Kangsun , Oh Kwang W.
Published: August 2009

The droplet-based microfluidic technology has a potent high throughput platform for biomedical research and applications [1]. Recently, Link et al. showed that an electric field can be very useful to control water droplet in carrier oil [2]. In this research, simultaneous droplet formation and sorting has been demonstrated using an electric field, allowing very precise droplet sorting to different outlets depending on the electrical actuation.
Special Matrices and Shape Factors for Linear Empirical Similitude Method
Authors: Tadepalli Srikanth , Wood Kristin L.
Published: August 2009

Empirical Similitude Method (ESM) is a technique developed to enhance the applicability of similarity methods to incorporate more realistic experimental data and scaling effects. Much of the development has been motivated by the premise of forging a relationship between experiential information and physical systems that have inherent non–linear variables and factors affecting their response. We augment this procedure by incorporating the Toeplitz and Hankel matrices, and solve the modified linear ESM problem using the conjugate gradient method, highlighting the potential benefits in the process. A simple deflection example is illustrated for lucidity and a comparison is made between all the available methods for contrast. A final extension into the use of shape factors is made using a numerical example.
A Gravity Balanced Test Stand for Flight Testing of Small/Micro Unmanned Aerial Vehicles
Authors: Lu Qi , Ortega Carlos E. , Ma Ou
Published: August 2009

For the purpose of safety, test stands are usually needed for testing unmanned aerial vehicles (UAVs), especially in the early test stage. Although a test stand can prevent the tested vehicle from flying away or crashing, it adds extra burden to the vehicle due to the weight of its moving mechanism. This can be a major problem for micro aerial vehicles (MAVs) because of their tiny lifting or payload capability. This paper presents an innovative solution to this problem by designing a passive gravity balanced test stand. The stand is capable of completely compensating its own weight, so that the tested vehicle will not have the extra burden from the weight of the test stand. To verify the feasibility of the design, a simulation study has been conducted, which demonstrated the benefits of the new design.
A Dynamic Relationship Between Vegetation and Erosion
Authors: Zhang Huayong , Han Lu
Published: August 2009

In order to give a comprehensive view about the essential relationship between vegetation and erosion, we employ an analysis of systemic dynamic stability based on vegetation-erosion equation raised by Thornes, and the further simulation about the equilibriums (fixed points) of the dynamic system can be given. We get four different types of the real equilibriums of the system. As well as this, the stability about all equilibriums is determined by systematic differential equation qualitative theory -Jacobi method. As a development of the original work of J.B.Thornes, this theoretical study highlights the insight to the interactive competition between vegetation and erosion.
Effect of Preheating on the Delamination and Crack Formation in Laser Solid Freeform Fabrication Process
Authors: Alimardani Masoud , Toyserkani Ehsan , Huissoon Jan Paul
Published: August 2009

This paper presents a numerical-experimental investigation on the effects of preheating the substrate on the potential delamination and crack formation across the parts fabricated using the Laser Solid Freeform Fabrication (LSFF) process. For this purpose, the temperature distributions and stress fields induced during the multilayer LSFF process, and their correlation with the delamination and crack formation are studied throughout the numerical analysis and the experimental fabrication of a four-layer thin wall of SS304L. A 3D time-dependent numerical approach is used to simulate the LSFF process, and also interpret the experimental results in terms of the temperature distribution and the thermal stress fields. The numerical results show that by preheating the substrate prior to the fabrication process, the thermal stresses throughout the process domain substantially reduce. Accordingly, this can result in the reduction of potential micro-cracks formation across the fabricated part. Preheating also decreases the transient time for the development of a proper melt pool which is an important factor to prevent poor bonding between deposited layers. The experimental results are used to verify the numerical findings as well as the feasibility of preheating on the reduction of the micro-cracks formed throughout the fabrication process.
Modeling of Droplet-Based Processing for the Production of High-Performance Particulate Materials Using Level Set Method
Authors: Wang Pengtao , Sun Hongwei , Wong Peter Y. , Fukuda Hiroki , Ando Teiichi
Published: August 2009

This research is focused on a numerical investigation of dynamic and thermal processes of single droplet in the uniform droplet spray (UDS) process. The level set method (LSM) is used to assist in tracking the liquid-gas and solid-liquid interfaces during droplet’s impingement and solidification. UDS process generates mono-size droplets of desired diameter, permits stringent control of the thermal state of the droplet, and produces deposits and materials with distinctly different microstructures including Icosahedral quasicrystalline phase (I-phase) in the Mg-Zn-Y system. The conservative level set function, combined with the Navier-Stokes and energy equations have been adopted to study the deformation and heat transfer of liquid metal droplet when impacting on the substrate under supercooling condition. The effects of surface tension and contact angle on droplet’s deformation are taken into consideration. The developed simulation technique is validated both analytically and experimentally. A rapid solidification model has been integrated with LSM to simulate the rapid solidification within the deformed Mg-Zn-Y droplet predicted in the former model. It is found that the initial temperature fields and latent heat releasing during solidification have significant impact on the solidification process.
Electromechanical Coupling and Signal Distribution of a Circular Cylindrical Shell Coupled With Segmented Sensors
Authors: Huang Shih-Lin , Chu Chin-Chou , Chang Chien C. , Tzou H. S.
Published: August 2009

The direct piezoelectric effect has long been recognized as an effective electromechanical coupling effect applied to designs of various transducers. Conventional sensor design usually follows three design principles: 1) the tension/compression design, 2) the bending or flexible design and 3) the shear design. These are mostly point-type transducers monitoring responses of discrete locations and, thus, they are not suitable to dynamic spatial monitoring of large-scale distributed structures, such as shells and plates. Accordingly, distributed designs and configurations, such as the segmentation and shaping techniques, have been proposed and evaluated in the last two decades. This study is to evaluate electromechanical coupling and signal generations of a coupled piezoelectric/elastic circular shell structure. A generic open-circuit signal equation of electromechanical coupling and signal generation is presented first, followed by a simplification to signal generation of a circular cylindrical shell case. The total signal generation and its contributing components are analyzed in the modal domain. Spatially distributed modal signals of various shell modes are calculated and the spatial signal distribution illustrates distinct modal characteristics resulting from microscopic modal strain behaviors. Thus, the optimal sensor location(s) for specific shell modes can be identified from the modal signal distribution plots.