bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictive Maintenance System for 2 Stroke Diesel Engines
Authors: Jime´nez-Espadafor Aguilar Francisco J. , Becerra Villanueva Jose´ A. , Torres Garci´a Miguel , Carvajal Trujillo Elisa , Chacartegui Rami´rez Ricardo
Published: May 2012

Maintenance cost and unexpected failures can be drastically reduced in low speed diesel engines using vibro-acoustic condition monitoring. This methodology has presented as a reliable method for detection of manufacturing faults, running damages and other abnormalities in engine and its components. Continuous trending keeping deviations of monitored parameter allows also reduction of fuel consumption, optimize exhaust emissions, and increase components life time and increase safety. This paper describes a methodology for vibration monitoring and fault diagnosis based on time-windowing and frequency analysis. The effectiveness is demonstrated based on the results of two year operation on a large two stroke power plant diesel engine located in Mahon, Spain.
Numerical Study of Flow Fields and Heat Transfer Characteristics in an Impinging Slot Jet With Buckling Phenomenon
Authors: So Hongyun , Yoon Hyun Gi , Chung Myung Kyoon
Published: May 2012

Plane impinging slot jet is widely used in a variety of industrial fields such as the cooling and coating system. In these systems, flow stability of the jet is the most important factor to obtain good products. But, in some operating cases it was found that there are alternating plane-wise vortices near the impinging stagnation region, and that such alternating vortices move almost periodically to the right and left sides along the stagnation line due to the jet flow instability and the pressure force balance, and then high and low temperature points are appeared periodically along the stagnation line. This instability is closely related to buckling of the jet center sheet. And, this instability of the flow fields causes the non-uniform heat transfer characteristic in the impinging region. In order to verify these flow fields and heat transfer characteristic, impinging slot jet system has been investigated numerically by using a commercial 3-D flow analysis code, FLUENT. At here, Reynolds number is about 10,000 and L/d is 6.67 as geometric conditions where d is the nozzle width and L is the nozzle-to-plate distance. LES turbulent model is used to obtain instantaneous flow fields near the jet exit and on the plate.
An Investigation of Friction Dynamic of Two Coupled Mass-Spring-Damper System With Visco-Elastic Contact
Authors: El-Butch A. M. A. , Fahim A. F.
Published: May 2012

The friction force between coupled machine members in relative motion exerts sometimes significant influence on system dynamic behavior, giving rise to undesirable friction-induced vibrations. The aim of this paper is to investigate the contribution of each design parameter and operating conditions on the system dynamic performance of a metallic mass sliding on a polymeric lower base, the mass is excited from its support by a harmonic input velocity. The governing equations are solved numerically and results showed that, for high excitation amplitude, an increase in the negative slope of the friction-velocity curve which leads to an increase in the friction-induced vibrations. Also system with high natural frequency of the lower mass has lower self-excited vibrations.
Development of an Interactive Graphical User Interface (GUI) for EnergyPlus
Authors: Pan Yiqun , Li Qiqiang , Zhou Hui , Huang Joe , Huang Sen , Huang Zhizhong , He Zongjian
Published: May 2012

In order to make EnergyPlus easier to use in China, VisualEPlus, a Chinese graphical user interface for the program, has been developed. VisualEPlus is designed to be generic, so that it can be used in any country, as well as be linked to other modeling tools and interfaces for EnergyPlus. VisualEPlus has three main modules: (1) a Building Loads Module for defining the building geometry, envelope, and space conditions that has been adapted from an existing DOE-2 interface (DOE2IN); (2) a HVAC System Module with a drag-and-drop feature for defining the HVAC system; and (3) a View Report Module with a reporting and visualization tool for EnergyPlus reports and outputs. This paper presents the background and development of VisualEPlus, describes its main functions and features as compared to other existing interfaces for EnergyPlus, and discusses plans for the further development of VisualEPlus.
Study on Micro Piezoelectric Actuator by Using Longitudinal Wave Energy for Catheter Application
Authors: Ajoudanian M. , Morita M. , Jiang Z.
Published: May 2012

The cerebral stroke is one of the diseases which many aged people are being to suffer. It occurs due to a thrombus created in a blood vessel, which blocks a blood flow in a brain and induces a brain cell necrosis. This study is the part of a research project that aims to develop high performance and amplitude micro stirrer for dissolution of cerebral thrombus. This paper presents the fundamental study on of a Novel actuator for creating vertically fluctuation to effective dissolution of cerebral thrombus or blood clot. By stirring the blood around the thrombus after the infusion of the agent, the quick dissolution can be obtained. This actuator was supported one side and the other side is free. The longitudinal wave excited by transducer from support side, traveling throw catheter and before reach to tip of beam impinges to skewed surface and reflect to shear wave and longitudinal wave. Thus the stirrer moves transversely due to transverse wave and reflected longitudinal wave.
Elliptic Airfoil Stall Analysis With Trailing Edge Slots
Authors: Kweder Jonathan , Clarke Mary Ann , Smith James E.
Published: May 2012

Circulation control (CC) is a high-lift methodology that can be used on a variety of aerodynamic applications. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft where the early models were referred to as “blown flaps”. Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a lifting surface This phenomenon keeps the boundary layer jet attached to the wing surface thus increasing the lift generated on the surface. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient. It should be noted that due to the trailing edge location of the circulation control exit jet, a “virtual” camber is created with the free stream air adding length to the overall airfoil. Due to this phenomena, the actual stall angle measured increased from eight degrees on the un-augmented airfoil, to a maximum of twelve degrees.
Specification of Prosthetic Knee Kinematic Design Parameters Using a Three-Position, Instant-Center Specification Approach
Authors: Thompson Thomas J.
Published: May 2012

The large number of above-knee amputations world-wide creates a need for prosthetic knees with kinematic characteristics fit to individual users. Prosthetists use a number of parameters to fit an individual: leg length in zero and 65 degree flexion, cosmetic advantage in 90 degree flexion, and location of the coupler instant center of rotation both above the knee joint and behind its axis in the first position. Designers use four-bar and similar mechanisms to provide acceptable motion. The first three design requirements point to three-position motion synthesis, a well-studied kinematic synthesis approach for which a four-bar designer exercises two free choices. However, specification of the instant center location adds constraints which may force the designer to iterate or compromise in order to satisfy space and other constraints. The three-position, instant-center specification problem is generally applicable to a number of other situations. It is shown that the addition of the instant center requirement reduces the number of free choices available to the designer to only one, so that pivot locations may be located along a locus similar to a Burmester curve. Results of work to produce such curves graphically and computationally is presented.
3D Analysis of a New Radial Channel for PEMFCs and Comparison With a Traditional Channeled System
Authors: Perez-Raya I. , Hernandez-Guerrero A. , Elizalde-Blancas F. , Juarez-Robles D. , Almanza-Huerta L.
Published: May 2012

The present study shows a 3D analysis of a new radial geometry for a PEM fuel cell flow field. The objective of this study is to understand the effects of this configuration on the fuel cell performance. The geometry is proposed with the objective to increase the fuel cell performance while reducing the pressure drop. In order to compare the results, a conventional commercial geometry was also analyzed and then both geometries were compared via polarization and power curves. The geometry proposed in this work shows quite a good improvement with respect to conventional geometries reducing the pressure drop and generating also a good power.
Improved Mechanical Design for a Fully Variable Electromechanical Valve Actuation System for Internal Combustion Engines
Authors: Rokni Damavandi Taher Hossein , Seethaler Rudolf J. , Milani Abbas S.
Published: May 2012

This study aims to improve the mechanical design of a fully flexible valve actuation system (FFVA) for intake valves of internal combustion engines. Optimization procedures for increasing the reliability and efficiency of the mechanical design of the FFVA system are presented. Simulations and experimental tests are carried out in order to validate the system performance. It is shown that position, velocity and acceleration of the valve obtained by simulations are consistent with those observed experimentally. Furthermore, it is observed that the mechanical vibrations are considerably reduced in the redesigned FFVA system. As a result, current levels and ohmic losses in the electric motor are also reduced. The present redesigned FFVA system then provides more reliable valve motion and better efficiency than the previously shown design [25].
Stiffening of Sheet Metal With Failure-Free Bead Patterns
Authors: Albers Albert , Majic Neven , Kro¨nauer Benedikt , Hoffmann Hartmut
Published: May 2012

In this study, the methodology of ManuBeadOpt (Manufacturing based Bead Optimization) including new functionalities for a failure-free based bead optimization of sheet metal is presented. The objective of this optimization strategy is to design automatically a beaded sheet metal which is both optimal for stiffness and manufacturing. In this context, shape optimization is combined with a forming simulation based on an inverse approach to evaluate formability. Two types of shape optimization methods are considered: A bead optimization until failure identification and a shape optimization with local modifications to guarantee failure-free geometries. So, this optimization tool makes an important contribution considering manufacturing aspects in bead optimization processes. Hence, product development cycles can be reduced by increasing quality of beaded sheet metal components. As example, a flat round plate as initial geometry is used to demonstrate the new iterative procedure of ManuBeadOpt.
Thermal Conductivity Prediction for Thermal Barrier Coatings
Authors: Silva Monica B. , Guo S. M. , Mensah Patrick F. , Diwan Ravinder
Published: May 2012

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a higher working temperature and thus lead to a better efficiency. Yttria-Stabilized-Zirconia (YSZ), a material with low thermal conductivity, is commonly used as the TBC top coat to provide the thermal barrier effect. In this paper, an analytical model is proposed to estimate the effective thermal conductivity of the TBCs based on the microstructures. This model includes the micro structure details, such as grain size, pore size, volume fraction of pores, and the interfacial resistance. To validate the model, two sets of TBC samples were fabricated and tested for thermal conductivity and associated microstructures. The first set of samples were disk shaped YSZ-Al2O3 samples fabricated using a pressing machine. The YSZ-Al2O3 powder mixture was 0, 1, 2, 3, 4 and 5 wt% Al2O3/YSZ powder ratio. The second set of samples were fabricated by Atmospheric Plasma Spray process for two different microstructure configurations, standard (STD) and vertically cracked (VC), at two different thicknesses, 400 and 700 urn respectively. A laser flash system was used to measure the thermal conductivity of the coatings. Experiments were performed over the temperature range from 100°C to 800°C. The porosity of the YSZ samples was measured using a mercury porosimetry analyzer, POREMASTER 33 system. A Scanning Electron Microscope (SEM) was used to study the microstructure of the samples. It is observed that the microstructure and the porosity are directly linked with the thermal conductivity values. The relationship of the properties to the real microstructure determines the validity of the proposed model.
A Numerical Model to Simulate Diffuse Effects in Microfluidic Fuel Cells
Authors: Sprague Isaac B. , Dutta Prashanta
Published: May 2012

A 2D numerical model is developed for a laminar flow fuel cell considering ion transport and the electric double layer around the electrodes. The Frumkin-Butler-Volmer equation is used for the fuel cell kinetics. The finite volume method is used to form algebraic equations from governing partial differential equations. The numerical solution was obtained using Newton’s method and a block TDMA solver. The model accounts for the coupling of charged ion transport with the electric field and is able to fully resolve the diffuse regions of the electric double layer in both the stream-wise and cross-channel directions. Different operating phenomena, such as laminar flow separation and the development of the depletion boundary layers and electric double layers are obtained. These numerical results demonstrate the model’s ability to capture the complex behavior of a microfluidic fuel cell which has been ignored in previous 1D models.
CAE in Automotive Engine Mount Development
Authors: Lu Min
Published: May 2012

The desire for more quiet and comfortable cars from consumers requires better engineering in the process of engine mount development. The fact that no physical vehicle exists at the time when the project launches, the design guidance relying on computer-aided engineering is essential. This paper discusses an engine mount development approach relying on computer-aided engineering with the assumption that the initial powertrain data, which include the powertrain mass, mass center, mass moment of inertia and engine power, are available. The mount placement strategy is discussed after the torque roll axis is introduced. To achieve the decoupled vibration modes for the mounting system, the computer simulated powertrain rigid body modal analysis is employed. As a result, the mount linear portion of the load-deflection curve is determined while the nonlinear portion is chosen by static analysis, whose constraint is the maximum powertrain roll angle under the condition of the maximum torque input. Also, the reaction forces in the three orthogonal directions are able to be estimated under the various loading conditions which reflect the vehicle driving conditions. Finally, finite element analysis is employed in the designs of the metallic and rubber components to meet the durability and performance requirements.
State of the Art in Power Storage Composites
Authors: Gallagher Tanya M. , Ciocanel Constantin
Published: May 2012

This paper presents a review on the latest developments in power storage composites. During the last decade, the need for multifunctional materials has grown steadily and has become a major priority as the demand for weight and, consequently, fuel consumption reduction, in ground and aerial vehicles, became critical. Accordingly, attempts have been made to develop structural materials that could incorporate specific devices, which would perform as sensors, for structural health monitoring, as actuators, for structural morphing capabilities, or as power harvesters, for supplementing existing power sources. Attempts have also been made to develop power storage composites, by embedding fuel cells, thin film lithium batteries, or capacitors in their structures. While it has been proven that these technologies are viable, the resulting structural materials exhibit significantly lower structural properties. To date, the most promising approach in power storage composites seems to be the development of structural load carrying capacitors. Such composites have the potential to provide good structural and electrical characteristics and can be easily manufactured.
Ultrasonic Measurement of Helium Bubble Rise and Group Velocity Using 1-D and 2-D Methods in Water and Mercury
Authors: Nakamura Hiraku , Ruggles Arthur E. , Sparger Johnathan
Published: May 2012

Single element ultrasonic Doppler velocimeter flow measurement instruments are available (Metflow) that allow velocity measurement along the main lobe of the transducer through gated processing of Doppler shift from echoes from targets in the flow. Correlation of target migration through the time gates has been used to supplement the Doppler data, and to measure void wave speeds when the targets are bubbles in the liquid flow. These methods are developed using helium bubbles in water flow with optical verification, and then used with helium bubbles in mercury. A second method for bubble rise velocity is presented using conventional 2-D medical ultrasound imaging equipment by Terason, with a 12L5V transducer, to develop an ultrasonic imaging analogue to conventional Particle Image Velocimetry. This system is also first tested in the water with helium bubbles using optical verification, and then in the mercury with helium bubbles.
Hybrid-Nuclear Energy: An Unexpected Assist to Compressed Air Storage
Authors: Keller Michael F.
Published: May 2012

A long sought but elusive goal of the energy industry has been the use of stored compressed air to support utility power production during periods of high electrical demand. While only limited success has been achieved, an emerging hybrid technology may offer an unexpected assist. Hybrid-nuclear energy marries the helium gas reactor with a combined-cycle power plant. This unique and highly flexible combination readily supports a distinctive adaptation of the basic compressed air technology, with the union poised to overcome the shortfalls that have long hampered the wide-scale deployment of the energy storage facilities.
Automating Risk Assessments of Hazardous Material Shipments for Transportation Routes and Mode Selection
Authors: Dolphin B. H. , Richins W. D. , Novascone S. R.
Published: May 2012

The METEOR (Model to Evaluate Transportation Effects of Risk) project at Idaho National Laboratory (INL) successfully addresses the difficult problem in risk assessment analyses of combining the results from bounding deterministic simulation results with probabilistic (Monte Carlo) risk assessment techniques. This paper describes a software suite designed to perform sensitivity and cost/benefit analyses on selected transportation routes and vehicles to minimize risk associated with the shipment of hazardous materials. METEOR uses Monte Carlo techniques to estimate the probability of an accidental release of a hazardous substance along a proposed transportation route. A METEOR user selects the mode of transportation, origin and destination points, and charts the route using interactive graphics. Inputs to METEOR (many selections built in) include crash rates for the specific aircraft, soil/rock type and population densities over the proposed route, and bounding limits for potential accident types (velocity, temperature, etc.). New vehicle, materials, and location data are added when available. If the risk estimates are unacceptable, the risks associated with alternate transportation modes or routes can be quickly evaluated and compared. Systematic optimizing methods will provide the user with the route and vehicle selection identified with the lowest risk of hazardous material release. The effects of a selected range of potential accidents such as vehicle impact, fire, fuel explosions, excessive containment pressure, flooding, etc. are evaluated primarily using hydrocodes capable of accurately simulating the material response of critical containment components. Bounding conditions that represent credible accidents (i.e., for an impact event, velocity, orientations, and soil conditions) are used as input parameters to the hydrocode models yielding correlation functions relating accident parameters to component damage. The Monte Carlo algorithms use random number generators to make selections at the various decision points such as crash, location, etc. For each pass through the routines, when a crash is randomly selected, crash parameters are then used to determine if failure has occurred using either external look up tables, correlations functions from deterministic calculations, or built in data libraries. The effectiveness of the software was recently demonstrated in safety analyses of the transportation of radioisotope systems for the US Dept. of Energy. These methods are readily adaptable to estimating risks associated with a variety of hazardous shipments such as spent nuclear fuel, explosives, and chemicals.
Modeling of Particle Formation via Emulsion Combustion Spray Method
Authors: Eslamian Morteza , Ahmed Mahmoud
Published: May 2012

In this paper, a theoretical model is developed to simulate the process of vaporization and burning of emulsion droplets and the evolution and the formation of micro- and nano-particles via the Emulsion Combustion Method (ECM). In ECM, a precursor solution is mixed and stirred with a fuel to form an emulsion of micro-solution droplets suspended in the oil phase. The emulsion liquid is sprayed into in emulsion droplets that are therefore composed of a fuel and tiny micro solution droplets. Spray droplets are ignited and burn to form final micro- or nanoparticles. In this paper, the principles of the method and the main governing equations of the developed model are discussed. Model equations are solved numerically and the results will be presented. The model predicts that depending on the operating and processing conditions, such as the initial size and concentration of the suspended micro solution droplets in emulsion droplets, the fuel fraction of the emulsion droplets, and the fuel combustion enthalpy, the final particles may be mono-dispersed nanoparticles, or larger agglomerate particles. Due to the similarity of the emulsion combustion method with spray pyrolysis and flame spray pyrolysis, most of the equations presented here are applicable to those methods, as well.
Eulerian FEA With Volume of Solid (VOS) Application in Metal Forming
Authors: Al-Athel K. S. , Gadala M. S.
Published: May 2012

The adaptation of the volume of fluid method (VOF) to solid mechanics (VOS) is presented in this work with the focus on metal forming applications. The method is discussed for a general non-uniform mesh with Eulerian finite element formulation. The implementation of the VOS method in metal forming applications is presented by focusing on topics such as the contact between the tool and the workpiece, tracking of the free surface of the material flow and the connectivity of the free surface during the whole process. Improvement on the connectivity of the free surface and the representation of curves is achieved by considering the mechanics of different metal forming processes. Different applications are simulated and discussed to highlight the capability of the VOS method.
NanoFIBrication of Ultra High Aspect Ratio Vias in Silicon
Authors: Goettler Drew , Su Mehmet , Olsson Roy , Burckel D. Bruce , El-Kady Ihab , Leseman Zayd
Published: May 2012

In this paper we present both experimental and theoretical results showing the effective use of material shaping to fabricate ultra-high-aspect-ratio (UHAR) vias with a focused ion beam (FIB). With this technique, one can create vias with aspect ratios of 20:1 and higher. This is achieved by placing a ‘lower sputter rate’ material on top of a ‘higher sputter rate’ material. We model the FIB as a Gaussian beam with an angular dependent sputter rate. With our model we predict a high sputter rate ratio (high/low) can achieve vias with aspect ratios near 20:1. Experimental results support this prediction. By placing a thin layer of pyrolyzed carbon on top of silicon, we fabricated UHAR vias with diameters of 75 nm.
NanoFIBrication of a Two-Dimensional Phononic Crystal in a Free Standing Membrane
Authors: Goettler Drew , Su Mehmet , Olsson Roy , El-Kady Ihab , Leseman Zayd
Published: May 2012

A two-dimensional phononic crystal (PnC) that can operate in the GHz range is created in a freestanding silicon substrate using NanoFIBrication (using a focused ion beam (FIB) to fabricate nanostructures). First, a simple cubic 6.75 × 6.75 μm array of vias with 150 nm spacing is generated. After patterning the vias, they are backfilled with void-free tungsten scatterers. Each via has a diameter of 48 nm. Numerical calculations predict this 2D PnC will generate a band gap near 22 GHz. A protective layer of chromium on top of the thin (100 nm) silicon membrane confines the surface damage to the chromium, which can be removed at a later time. Inspection of the underside of the membrane shows the vias flaring out at the exit, which we are dubbing the ‘trumpet effect’. The trumpet effect is explained by modeling the lateral damage in a freestanding membrane.
Reliability Failure Analysis to Characterize Time-Directed Maintenance Inspection Interval
Authors: Wessels William R. , Farrington Seth , Henstock Tim
Published: May 2012

Reliability failure analysis is performed to implement Reliability-Centered Maintenance, RCM. RCM is implemented by Condition-based Maintenance, CBM, or Time-directed Maintenance, TDM. This paper defines the approach to characterize the time-directed inspection interval for fielded systems in sustainment. The limitation of resources available to the field engineer dictates that neither the incidence nor costs of part failure are sufficient criteria to identify which parts will be selected for transition from unscheduled repair maintenance to RCM. Application of fault tree analysis combined with failure modes, effects and criticality analysis enable a selection process that optimizes the efficiency of operating capital. The FTA and FMECA hypothesize the physical, thermal, and chemical failure mechanisms that act on the part. The hypothesized failure mechanisms are evaluated by math models and simulation to isolate the statistically significant failure mechanisms — the relevant few. Empirical investigation of the statistically significant failure mechanisms begin with nondestructive investigation of control sample parts, to include: visual, microscopic, X-ray, acoustical, and modal inspections. Small scale ‘coupon’ or ‘part’ experiments are designed and performed to model failure behavior for ambient and operational sources of stress loads using accelerated and highly accelerated life test methods. Stress testing is performed on selected test articles at specified intervals to characterize the component strength properties. Data from all tests are fit to a failure model to characterize a time-interval stress-strength frequency distribution from which the reliability functions are inferred using interference theory. The reliability and hazard functions are compared to the specified risk thre4shold to characterize the Time-Directed Maintenance Inspection Interval.
A Particle-Based Model for Prediction of Cement Diffusion During Osteoporotic Hip Augmentation Surgery: Theory and Validation
Authors: Basafa E. , Otake Y. , Kutzer M. D. , Armiger R. S. , Armand M.
Published: May 2012

Elderly patients with preexisting osteoporotic hip fracture are at high risk of a subsequent fracture in their contralateral hip. Current preventive approaches commonly have a long delay in restoring bone strength leaving patients at continued risk despite preventive efforts. Femoroplasty — injection of bone cement into the proximal femur — has been proposed as a potential preventive approach. However, it can cause complications because of extravasation of the cement into unwanted regions of the bone and an increased pressure within the bone, if not controlled and planned carefully. Therefore, precise modeling of the diffusion of the bone cement in osteoporotic bone and control over the injection process is of substantial importance. This paper presents a patient-specific fluid dynamics model to simulate the diffusion of the bone cement inside femur. The model is based on the smoothed particle hydrodynamics (SPH) method for particle-based modeling of fluids. The Navier-Stokes equations were built into the SPH formulations and viscosity effects were added to model the flow of cement inside porous media. To validate the model, a new prototype automatic injection device was used to inject acrylic silicone into a porous foam block. Results of simulation of the injection show close matching with experimental data. The model is therefore promising for further development of optimized and fully controlled femoroplasty procedures.
Young’s Modulus and Hardness of Zr0.5Hf0.5CoxRh1−xSb0.99Sn0.01 and Zr0.5Hf0.5CoxIr1−xSb0.99Sn0.01 Half-Heusler Alloys
Authors: Verges Melody A. , Schilling Paul J. , Germond Jeffrey D. , Upadyhay Puja , Miller William K. , Maji Pramathesh , Takas Nathan J. , Poudeu Pierre F. P.
Published: May 2012

Mechanical testing was performed to determine the influence of compositional changes on the Young’s modulus and hardness of half-Heusler compounds of the base composition Zr0.5Hf0.5CoSb0.99Sn0.01. In the efforts to decrease the thermal conductivity of the composition toward the development of thermoelectric materials with high thermal conversion efficiencies, specimens were fabricated with varying amounts of rhodium and iridium at the cobalt site. In addition to the general Zr0.5Hf0.5CoSb0.99Sn0.01 composition, six hot-pressed samples of the Zr0.5Hf0.5CoxRh1−xSb0.99Sn0.01 (0.0≤x≤1.0) composition and four hot-pressed samples of the Zr0.5Hf0.5CoxIr1−xSb0.99Sn0.01 (0.0≤x≤0.7) composition were synthesized. Indentation measurements were obtained using both microhardness testing and depth-sensing nanoindentation. The general Zr0.5Hf0.5CoSb0.99Sn0.01 composition was observed to have a hardness and elastic modulus around 896HV0.2 and 247GPa, respectively. For all of the compositions tested the hardness range was observed to lie between 347HV0.2 and 951HV0.2. The elastic moduli for these compositions were found to range between 97GPa and 247GPa. The effects of the rhodium substitution and iridium substitution at the cobalt site on the elastic stiffness and hardness are examined.
Field Assisted Sintering Technology (FAST) Model for Prediction of Final Properties
Authors: Paul Rajiv , Kulkarni Anil K. , Singh Jogender
Published: May 2012

Sintering is the process of making materials from powder form by heating the powder below its melting point until the particles fuse to each other. Field assisted sintering technology (FAST), also sometimes known as spark plasma sintering (SPS), uses a pulsed and/or continuous electric current along with the simultaneous application of compressive pressure which leads to extremely high heating rates and short processing durations. A high relative density and small grain size promote superior properties such as greater hardness and electrical breakdown. Hence, selection of the proper sintering parameters is of paramount importance and a predictive model would be extremely useful in narrowing the range of experimental parameters. This will drastically reduce the number of extra attempts at obtaining certain properties in a material and save experimentation time, effort and material to name a few. Four of the most important FAST parameters: target temperature, holding time, heating rate and initial particle size, have been reviewed to assess their effect on the densification, hardening and grain growth of Alumina, Copper, Silicon Carbide, Tungsten and Tungsten Carbide through extensive literature survey. The relationship between each has been incorporated in a Microsoft Excel program which acts as a predictive tool to determine an estimate of the final properties based on the initial parameters chosen. This is done by curve fitting a polynomial onto the existing data points as closely as possible and using the polynomial to obtain final properties as a function of the initial parameters. The model was verified against an existing paper which sought to obtain the optimum sintering parameters for Copper. While the actual experimentation range was 400°C to 800°C, the program would have suggested a much narrower range from 650°C to 800°C and hence saved unnecessary additional efforts.
Investigation of Heat Transfer in Microchannels With Asymmetric and Periodic Slip at the Walls
Authors: Gunde Akshay C. , Chakraborty Suman , Mitra Sushanta K.
Published: May 2012

Recent development of microfluidic applications in various areas like cooling of silicon chips, VLSI, aircraft avionics, X-Ray and laser equipments has led to an increased study of coupled fluid flow and heat transfer in microchannels. A major issue in the mathematical modeling of these phenomena is the applicability of the no-slip boundary condition at solid-fluid interfaces. Most of such micro-scale investigations consider a slip velocity at solid boundaries, which has been observed in a number of experiemntal studies [1], [2]. In cases involving the heating of substrate and/or transport fluid, definite formation of nanobubbles from the fluid has been established [3]. These bubbles migrate to the channel walls and deposit on them in the form of random clusters. As a result, due to the minimized shear resistance offered by the surfaces of such bubbles to the fluid, variation in slip length is observed along the channel walls. Hence, in order that theoretical studies lead to physically acceptable results required for the fabrication of microfluidic devices, such variation of slip length encountered by a fluid in a microchannel must be included in these analysis.
Design of Microstructure Response Using a Complex Step Plasticity Approach
Authors: Rangarajan Aswath , Sundararaghavan Veera
Published: May 2012

Microstructure-sensitive design is performed using a newly developed Multiscale Complex Step Method. Algorithmic implementation of the complex-step method is based on conventional multiscale Taylor or FE2 direct model, with the difference being that the microstructural deformation gradient is modeled as a complex number with a small imaginary component. We introduce methods to calculate derivatives of microstructural fields with respect to loading parameters. The sensitivities are used to identify optimal microstructures with desired elastic and plastic properties.
Comparative Study on the Effect of Filler Size on the Mechanical Properties of Poly(DL-Lactide-Co-Glycolide) Acid – Hydroxyapatite Composite Scaffolds
Authors: Leung Linus H. , Mortazavi Saba , Dick Sheldon M. , Naguib Hani E.
Published: May 2012

Tissue engineering is an emerging alternative treatment for various diseases and injuries. The use of hydroxapatite composites for bioscaffolds has shown to improve the osteoconductivity. Studies in the literature have been performed to examine the advantages of using this composite in the biological aspects of tissue engineering; however, few studies have been on the synthesis and mechanical properties of these bioscaffolds. These properties are especially important in load bearing applications like in bone tissue engineering. In this study, poly(DL-lactide-co-glycolide) acid (PLGA) and hydroxyapatite (HA) were used to fabricate gas-foamed/salt leached scaffolds. Micro and nano-scaled HA particles were melt-compounded with PLGA using a twin-screw compounder. The composite material was dry blended with salt particles at a salt-to-polymer mass ratio of 5:1. From observations of micrographs taken with a scanning electron microscope, both the micro and nano-HA particles were shown to be well dispersed within the polymer matrix. The thermal properties were examined using differential scanning calorimetry, and the effect of the compositions on the glass transition temperature, Tg, was studied. The Tg was not significantly changed with the addition of HA particles from 0 to 20 wt%. Similarly, thermogravimetric analysis showed that the thermal degradation temperature remained at approximately 320 °C. The mechanical properties of the scaffolds were tested in compression. At the same composition, the scaffolds fabricated with the nano-HA showed an increase in modulus and strength. The results found in this study are important in developing novel biodegradable scaffolds with a focus on improving the mechanical properties of the scaffolds for bone tissue engineering applications.
Uncertainty Reduction on the Identification of the Inertial Parameters Based on a Complex 3D Motion
Authors: Barreto M. Juan P. , Munoz C. Luis E.
Published: May 2012

The uncertainty on the identification of the inertial parameters of rigid bodies can be reduced by studying the motion for the identification experiments. This paper presents a method for measuring the center of mass and the inertia tensor of a rigid body by generating a complex 3D motion. The proposed method is intended to reduce the time consumed by the experiment and the post-processing of the data. This reduction on the time is achieved by using the same assembly for the center of mass and inertia tensor identification experiments as well as an algebraic method for the identification. The experimental setup consists on a Stewart Platform for the generation of the motion, a load cell and an inertial measuring unit. A study on the reduction of the uncertainty was developed. It was found that the uncertainty on the identification of the center of mass can be reduced with a static experiment that takes the object to different orientations, improving the numerical condition of the identification system. The uncertainty on the inertia tensor identification is reduced when the motion of the body is generated relative to different axes in space. The method was first tested on simulations to estimate the uncertainty and then validated experimentally.
Blast Response of Protective Armor Concepts Using an Arm Surrogate
Authors: Simmonds K. E. , Bagchi A. , Matic P. , Leung A. C. , Pogue W. M. , Thompson A. K. , Strain J. C. , Gauvin J. E.
Published: May 2012

Protection and comfort are two key armor requirements to the US warfighter. NRL has supported this effort by developing QuadGard extremity protection [1], and instrumented surrogate torso and brain to assess armor and helmet systems performance [2, 3], among others. Surrogate systems for analyzing personal protection equipment for torso and brain have also been developed by other researchers in US, Australia and Canada and are reported in the literature, but no publications were found on assessment of extremity armors.
Circulation Control Applied to Wind Turbines
Authors: McGrain David , Angle Gerald M. , Graham Henry , Pertl Emily , Smith James E.
Published: May 2012

This research effort provided a process and results for the prediction of the pressure gradient in the vicinity for a circulation controlled vertical axis wind turbine (CC-VAWT). The pressure gradient was determined using the Computational Fluid Dynamics (CFD) software, Fluent. The pressure gradient was then compared to the current commercial standard horizontal axis wind turbine (HAWT) the CC-VAWT and was shown to produce a much lower pressure drop within its immediate vicinity of the wind turbine. This difference shows evidence towards a potential solution for the current negative effects that the wind turbine industry is having on bat populations, namely barotrauma.
A Design Method of Radial Fans Considering the Torque-Speed-Characteristic of the Motor
Authors: Epple Philipp , Miclea Mihai , Pfannschmidt Klaus , Grobeis Detlev , Delgado Antonio
Published: May 2012

The use of high speed radial impellers is very common in fans for industrial applications. The most common design case is the one with constant speed. In that case, one assigns the corresponding value to the speed n, hence the speed no longer matters in the further design procedure: it is given and it is constant. However, in many cases the speed is not constant, since it is governed by the torque-speed characteristic of the driving motor. In such a case it is necessary to consider the motor characteristic already at the design stage. In the present work a design method was developed in order to perfectly match the torque-speed characteristic of the radial impeller to the torque-speed characteristic of the driving motor. In such a way it is possible to design an impeller-motor unit with maximum efficiency. The extended impeller mean-line-design formulas presented in Epple [6] were complemented with the equations describing the motor torque-speed-characteristic. Both sets of equations where combined and solved in order to achieve a prescribed operating range at a maximum efficiency. In order to validate the design method, it was applied to an industrial fan which should be improved. That radial fan with spiral casing consisted of the main radial fan and a motor cooling axial fan at the other end of the shaft. This later fan was rotating at a too low speed leading to cooling problems of the motor. Hence, a new fan had to be designed which had to deliver the same hydraulic performance but at higher rotating speeds. This had to be done, however, on the given motor. That could only be done when properly designing an impeller matching its torque-speed characteristic to the torque-speed characteristic of the motor: it was an excellent task to validate the combined impeller-motor design procedure. Under these constrains six designs where performed and validated with a commercial CFD solver. The three best designs according to the CFD results were built as prototypes and measured at a standard test rig. The best design delivered the prescribed head-flow characteristic at an even improved hydraulic efficiency. The higher speed was also properly achieved. The design procedure is described and explained in detail and a detailed CFD analysis is presented, complemented by the experimental data obtained at the test rig. A final comparative analysis of the combined impeller-motor design method, the CFD analysis and the measurements is presented.
Statistically Consistent Generation of Random Fields for Multiphase Materials
Authors: Lloyd George M.
Published: May 2012

A methodology is presented which facilitates the generation of high-fidelity realizations of stochastic fields for multiphase materials (such as a matrix with embedded inclusions), and thus allows consistent and realistic computational discretizations to be created in a straightforward manner. Examples of such random fields are concrete (in which aggregate particles are mixed with cement), geological substrata as modeled in reservoir and groundshock simulations, and modern rocket propellants, which consist of high energy constituents suspended in relatively homogeneous binders. The properties of such stochastic materials may include short-range orientational phenomena, mid-range spatial correlations, global geometric properties such as the marginal size distributions of the inclusions, and perhaps long-range orderings. While ad-hoc methodologies exist that can mimic certain of these stochastic properties through “tuning”, they can do so only in a limited way, are computationally expensive in their right, and cannot replicate measured stochastic properties in a direct and constructive way. The method described here is general in nature and computationally tractable, and allows an analyst to directly incorporate knowledge of empirical stochastic features of arbitrary form thought to be of greatest interest, as well as their cross-dependencies into a stochastic model.
Steady State Heat Transfer Models of CO2 Condensing in a Vertical U-Tube
Authors: Hu Yang , Archer David H.
Published: May 2012

Two distinct steady state models have been programmed to calculate heat transfer and pressure loss from a saturated CO2 vapor in a vertical U-tube to the surrounding grout and earth. The work began with calculations of the individual heat transfer coefficients from vapor, from the condensing vapor, and from the liquid to the tube, and then from the U-tube to the surrounding grout and earth. According to computations for the tube to the earth reviewed in the ASHARE Handbook and relevant literature on the coefficients inside the tube, all reviewed in the paper, the internal heat transfer coefficient area products, hA, for CO2 condensing in a 3/4 inch tube diameter are much higher than the ground heat transfer coefficient; the ground heat transfer coefficient limits the heat transfer in the U-tube. A homogeneous model assumed that the vapor-liquid mixture in the tube is represented by a fluid whose properties and heat transfer coefficients are a weighted average between those of the vapor and the liquid present at the point. The homogeneous model has been developed by the mass balance, momentum balance, energy balance, enthalpy property, equation of state, and phase equilibrium of liquid and vapor CO2. The equations of the model have been numerically calculated in Matlab by solver ODE4 (Runge-Kutta). Measured values of heat transfer were closed to values calculated by the model. Measurements of the pressure loss over the U-tube were significantly higher than those predicted by the model. Based on the assumption that the pressure differences in the U-tube between the inlet and outlet are mainly due to the presence of liquid CO2 in the up and down legs, a new simplified model has been created and the simulation results have been compared with the experimental results. Greater agreement between measured and predicted pressure losses was achieved. This study is useful in understanding heat transfer and pressure loss of CO2 condensing in a vertical U-tube transferring heat to the earth.