bluuebunny/crossref_metadata_2025 huggingface dataset:
Guided Wave Propagation in Tubular Section With Multi-Layered Viscoelastic Coating: Part II — Circumferential Waves
Authors: Kuo Chi-Wei , Suh C. Steve
Published: April 2014

Propagating waves physically admissible in a tubular section are derived to establish their dispersion characteristics in response to the presence of multi-layered viscoelastic coatings. Shear and longitudinal waves along the circumferential direction were investigated. To characterize the hollow cylinder with coating layers, wave dispersion and attenuation are studied using the “global matrix” technique. Since each layer is considered to be perfectly bonded to each other, displacement and strain continuity are imposed as the interfacial boundary conditions. Viscoelastic coating materials such as bitumen and epoxy serve to improve pipeline reliability, but they also dampen and dissipate wave energy. The viscoelastic materials are studied as well. By replacing the real material constants with complex material constants in the characteristic equation, the impact of the viscoelastic coatings on wave dispersion is established. Bisection method is followed to find the real and complex roots of the three characteristic equations derived. Roots thus obtained are manipulated to allow the phase velocity and attenuation dispersion to be plotted against frequency. The dispersion of phase velocity and wave attenuation for coated pipes are evaluated against a baseline model which is the bare, uncoated tubing to establish the propagation characteristics of the guided shear and longitudinal waves in the presence of multiple coating layers.
A Study on the Development of Slip Form System With Lightweight GFRP Panel
Authors: Yoon Hyejin , Chin Won Jong , Kim Hee Seok , Kim Young Jin
Published: April 2014

Nowadays, many countries are competing in the erection of long-span bridges with main span longer than 2,000 m owing to the tremendous innovations realized in the domain of high performance and high strength materials as well as in the design and construction technologies. The near future will see a boom in the market of suspension bridges with main span longer than 3,000 m. Since three-dimensionally shaped high concrete pylons would be unavoidably required to construct these super long-span bridges, need is to develop advanced slip form systems for their erection. This paper presents the development of a slip form system applying lightweight GFRP panel. Improved slip form management technology is secured by introducing a slip-up technique using GPS-based verticality control and wireless early strength estimation. A mock-up test is conducted by designing and fabricating the slip form system based on the developed techniques.
Structural and Mechanical Properties of Mg/MgO and Mg/Al2O3 Nanolaminate Coating for Implant Applications
Authors: Kotoka Ruben , Neralla Sudheer , Yarmolenko Sergey , Pai Devdas , Sankar Jag
Published: April 2014

Nanostructured magnesium coatings have the potential of enhancing the integration of implant to bone tissues due to their ability to regulate the functions of integrin, which modulates cell proliferation and differentiation. However, they are soft, ductile and have low wear resistance. These limitations prevent the practical use of Mg coatings for this application. However, application of Mg thin films in the form of nanolaminate coatings has been found to improve hardness as well as wear properties. In this study, Mg/MgO and Mg/Al2O3 nanolaminates with bilayer thicknesses (Λ) 10, 20, 40, 100, 200, 1000 nm were deposited on glass substrate using the reactive pulsed DC magnetron sputtering process. The Mg/MgO nanolaminates were developed from an Mg target. Λ was controlled by the duration of oxygen flow during the sputtering process. Values of Λ were obtained from low angle-XRD. We found that the rate of MgO deposition significantly depends on water vapor content in the chamber and that a partial base pressure of water below 10−8 Torr is required to achieve repeatable results. Structure and properties of multilayered coatings were studied by X-ray diffractometry, nanoindentation, SEM and AFM. At Λ < 100 nm, MgO and Mg have preferred orientations <200> and <002> respectively, while at higher Λ, other orientations are present in the XRD patterns. The nanoindentation results showed slightly higher hardness of Mg/MgO and Mg/Al2O3 nanolaminate coatings compared to that of pure Mg. Nanolaminates have high ductility compared to MgO and Al2O3. Nanolaminate coatings at Λ < 100 nm exhibit an improvement in the mechanical properties due to the presence of interfaces which act as barrier to dislocation movement.
Simultaneous Time-Frequency Control of Active Magnetic Bearing
Authors: Liu Meng-Kun , Suh C. Steve
Published: April 2014

Active magnetic bearings enable greater spindle dynamic stiffness through higher attainable bearing surface speeds. However, the active magnetic bearing system is highly nonlinear due to the interaction between electromagnetic field and rotor dynamics. Its nonlinear character becomes prominent when rotating in high speed. The operation undergoes route-to-chaos and is vulnerable to external excitation, which eventually leads to detrimental failure. A novel simultaneous time-frequency control theory is developed for controlling the active magnetic bearing at high speed. The control theory is able to tolerate the uncertainties in the system due to on-line identification and the deterioration in both time and frequency domain can be restrained.
Simplified Procedure to Estimate the Wind Turbine Blade Aerodynamic Loadings Without Using CFD
Authors: Mohammad Fouad , Ayorinde Emmanuel
Published: April 2014

The aerodynamic loadings that act on the blade of a horizontal axis wind turbine change as a function of time due to the instantaneous change of the wind speed, the wind direction and the blade position. The new contribution in this study is the introduction of a simplified non CFD based procedure for the calculation of all the aerodynamic loadings acting on a wind turbine blade. The premise of the current simplified model is that (a) the forces can be modeled by a set of point loads rather than distributed pressures, and (b) the magnitudes of these point loads can be estimated using the below load formulas, (c) an interpolation scheme needed to have all computed forces and moments as a function of the blade lengthwise x. Considering a 14m blade length and utilizing a time dependent set of parameters such as angle of attack, material and air density, wind and blade speed, flow angle, yaw, pitch angles, the centrifugal forces (along x-direction of the blade length), the cross-sectional forces (Fy and Fz) and the twisting moment of the blade (about the x-direction) were calculated for each of all the given time steps. After that the authors explain how to interpolate the calculated loadings (forces and twisting moment) and the right formulas to compute the aerodynamic load vector (the right side of the dynamic equations of motion).
Design and Evaluation of a Multi-Sensor Unit for Measuring Physiological Stressors of Medical Transport
Authors: Kaloutsakis Georgios , Reimer Andrew , Jeong Donghwa , Lee Kiju
Published: April 2014

Patients who undergo inter-hospital transfer experience increased relative mortality, ranging from 10 to 100% higher than non-transferred patients. The high-cost, increased risk of complications and poor outcomes of transferred patients warrant the critical examination of potential causes. One of the major causes may be the external stressors that patients are exposed to during medical transport. To realize simultaneous measurements of external stressors, we developed a multi-sensor unit for measuring vibration, noise, ambient temperature, and barometric pressure. For preliminary evaluation, the sensor unit was tested on 29 medical transports, 11 air transports by a helicopter and 18 ground missions by an ambulance. The average whole-body vibration for each air and ground transport was calculated at 0.3510m/s2 and 0.5871m/s2 respectively. Air transports produced much higher level of noise than the ground transports. We found no significant difference between two modes in terms of average temperature and the temperature changes. Barometric pressure drops significantly during air transport, indicating potential use of this data for automatic mode classification.
Determining Optimal Assembly Sequences for a Robotic Autonomous Assembly Task
Authors: Guo Bin , Zhang Tao , Wang Xinwei , Wang Ying
Published: April 2014

This paper proposes a genetic algorithm to determine the optimal assembly sequence for a robotic autonomous assembly task. The coding rule of chromosomes, the selection, crossover and mutation operations are presented. In order to avoid invalid chromosomes, a modified crossover operation is suggested. In addition, a specific fitness table is created to evaluate a random assembly sequence. Some simulation results are employed to validate the effectiveness and accuracy of the proposed approach.
A New Method for the Generation of Tool Paths for Finishing Near Net Shape Components
Authors: Mendoza López Edgar A. , Medellín Castillo Hugo I. , de Lange Dirk F. , Lim Theo
Published: April 2014

The CNC machining has been one of the most recurrent processes used for finishing NNS components. This paper presents a new method for the generation of tool paths for machining 3D NNS models. The proposed approach comprises two machining stages: rough cut and finish cut, and three types of cutting tools: ball-end mill, flat-end mill and fillet-end mill. The proposed tool path generation algorithm is based on: (1) approximation of the model surfaces by points using slice planes and visibility analysis, (2) accessibility analysis of the tool, (3) approximation error and tolerance evaluation, (4) collision analysis of tool and tool holder. The tools paths generated are exported as a CNC program. The implementation was carried out in C++ using the ACIS® geometric modeling kernel to support the required geometric operations. To prove the effectiveness of the system several models with variable geometric complexity were tested. The results have shown that the proposed system is effective and therefore can be used to generate the tool paths required for finishing 3D NNS components.
Multi-Objective Optimal Control Design With the Simple Cell Mapping Method
Authors: Sardahi Yousef , Naranjani Yousef , Liang Wei , Sun Jian-Qiao , Hernandez Carlos , Schuetze Oliver
Published: April 2014

Controls are often designed to meet different and conflicting goals. Consider the well-known LQR optimal control. The performance index contains a response measure and a control penalty, which are conflicting requirements. Proper linear or nonlinear combinations of the conflicting objective functions have led to single objective optimization problems. However, such a single objective optimization is dependent on the combination algorithm, and only provides a narrow window of all possible optimal solutions that a system may have.

Multi-objective optimization provides a set of optimal solutions, known as Pareto set. There have been many studies of search algorithms for Pareto sets of multi-objective optimization problems for complex dynamical systems. Recently, the simple cell mapping (SCM) method due to C.S. Hsu has been found to be a highly effective tool to compute Pareto sets. This paper applies the SCM method to several control design problems of linear and nonlinear dynamical systems. The results of the work are very exciting to report.
Improvement of Mechanical Reliability of 3D Electronic Packaging by Controlling the Mechanical Properties of Electroplated Materials
Authors: Suzuki Ken , Miura Hideo
Published: April 2014

Three-dimensional (3D) integration of silicon microelectronic devices improves the electronic functions of devices and minimizes packaging density drastically. A through-silicon via (TSV) structure is indispensable for maximizing the density of interconnections among the stacked silicon chips. However, since the TSV structure is surrounded by silicon, and there is large mismatch in materials properties between metallic materials used for the TSV structure and silicon, thermal stress is essentially generated around the TSV structure during their fabrication process and operating conditions. Recently, electroplated copper thin films have started to be applied to the interconnection material in the TSV structure because of its low electric resistivity and high thermal conductivity. However, the electrical resistivity of the electroplated copper thin films surrounded by SiO2 was found to vary drastically comparing with those of the conventional bulk material. This was because that the electroplated copper thin films consisted of grains with low crystallinity and grain boundaries, in other words, abnormally high defect density. Thus, both the crystallinity and electrical properties of the TSV structure was investigated quantitatively by changing their electroplating conditions and thermal history after the electroplating. It was observed that many voids and hillocks appeared in the TSV structures depending on the electroplating conditions. It was also found that the stress-induced migration occurred after the high temperature annealing which was introduced for improving the crystallinity of the electroplated films. Therefore, it is very important to evaluate the crystallographic quality of the electroplated copper thin films after electroplating to assure both the mechanical and electrical properties of the films.
CFD Conjugate Analysis of a Jet-Impingement Configuration With Sudden Changes in Heating and Cooling Loads
Authors: Lee C.-S. , Shih T. I-P. , Bryden K. M.
Published: April 2014

The temperature in a material could exceed the maximum allowable during transients when the heat load is suddenly increased despite a corresponding increase in cooling. This is because there is a time lag in the response of the material. Unsteady RANS based on the shear-stress transport model with conjugate analysis were used to study the unsteady heating and cooling of a superalloy flat plate with a thickness of 1 mm. The flat plate was initially at steady-state conditions, heated on one side by a constant heat flux of 10 W/cm2 and cooled on the other side by impingement of air jets such that the maximum temperature in the plate was just below 900 °C, where 900 °C was taken to be the maximum allowable material temperature. Suddenly, the heating load was increased from 10 W/cm2 to 68 W/cm2 with a corresponding increase in the cooling such that the maximum temperature in the plate remains just below 900 °C when steady state is reached. Results obtained show that though the maximum temperatures at the two steady states are just below 900 °C, the highest temperature in the material can exceed 900 °C by up to 14 seconds during the transient from one steady state to the other. Thus, the minimum cooling flow based on steady-state conditions are inadequate during the transient process if the sudden heating and cooling occurred simultaneously. However, if the increase in cooling preceded the sudden increase in heating by a sufficient amount of time (i.e., pre-cooling), then over temperature was found to not occur during the transient. This paper presents results that show the unsteady flow and heat transfer in the fluid phase and the transients in the solid phase with and without pre-cooling.
The Effects of Longitudinal and Circumferential Cracks on the Torsional Dynamic Response of Shafts
Authors: Nabian M. , Vaziri A. , Olia M. , Nayeb-Hashemi H.
Published: April 2014

Turbo generator shafts are manufactured through the extrusion process. This results in formation of weak planes along the extrusion direction. Under service loading (e.g. cyclic torsion due to electrical line faults), large longitudinal cracks often form in these shafts before the appearance of any circumferential cracks. The presence of these cracks could severely compromise the shaft resonance frequencies. Here, we investigated the dynamic response of solid turbo generator shafts with longitudinal and circumferential cracks. The longitudinal cracked section of the shaft section was modeled as a shaft with reduced effective torsional rigidity. The effective torsional rigidity was found to be a function of ratio of crack depth to the shaft radius only. The circumferential cracked section was modeled as a torsional spring, with the torsional spring constant determined using fracture mechanics principles. It was found that the resonance frequency of the shaft may be little affected by the presence of a longitudinal crack. The resonance frequencies of the shaft with the circumferential crack depend on the crack length and its location. The effects of crack surface interactions for both longitudinal and circumferential cracks were also investigated. For circumferential cracked shafts, the sever crack surface interaction results in the peak response frequency approaches to that of un-cracked shafts. However the frequency where the peak response occurs for a longitudinally-cracked shaft generally exceeds that of un-cracked shaft first resonance frequency.
Multifunctional Hierarchical Nanocomposites: A Review
Authors: Ghasemi-Nejhad Mehrdad N.
Published: April 2014

Nanocomposites; including nano-materials such as nano-particles, nanoclays, nanofibers, nanotubes, and nanosheets; are of significant importance in the rapidly developing field of nanotechnology. Due to the nanometer size of these inclusions, their physicochemical characteristics differ significantly from those of micron size and bulk materials. The field of nanocomposites involves the study of multiphase materials where at least one of the constituent phases has one dimension less than 100 nm. This is the range where the phenomena associated with the atomic and molecular interaction strongly influence the macroscopic properties of materials. Since the building blocks of nanocomposites are at nanoscale, they have an enormous surface area with numerous interfaces between the two intermix phases. The special properties of the nanocomposite arise from the interaction of its phases at the interface and/or interphase regions. By contrast, in a conventional composite based on micrometer sized filler such as carbon fibers, the interfaces between the filler and matrix constitutes have a much smaller surface-to-volume fraction of the bulk materials, and hence influence the properties of the host structure to a much smaller extent. The optimum amount of nanomaterials in the nanocomposites depends on the filler size, shape, homogeneity of particles distribution, and the interfacial bonding properties between the fillers and matrix. The promise of nanocomposites lies in their multifunctionality, i.e., the possibility of realizing unique combination of properties unachievable with traditional materials. The challenges in reaching this promise are tremendous. They include control over the distribution in size and dispersion of the nanosize constituents, and tailoring and understanding the role of interfaces between structurally or chemically dissimilar phases on bulk properties. While the properties of the matrix can be improved by the inclusions of nanomaterials, the properties of the fibers can also be improved by the growth of nanotubes on the fibers. The combination of the two will produce super-performing materials, not currently available. Since the improvement of fiber starts with carbon nanotube grown on micron-size fibers (and matrix with a nanomaterial) to give the macro-composite, this process is a bottom-up “hierarchical” advanced manufacturing process, and since the resulting nanocomposites will have “multifunctionality” with improve properties in various functional areas such as chemical and fire resistance, damping, stiffness, strength, fracture toughness, EMI shielding, and electrical and thermal conductivity, the resulting nanocomposites are in fact “multifunctional hierarchical nanocomposites.” In this paper, the current state of knowledge in processing, performance, and characterization of these materials are addressed.
Storytelling - A Most Powerful Tool in Shaping Lesson Plans in Engineering Education
Authors: Kobus Chris J.
Published: April 2014

Most engineering instructors are put into the classroom by virtue of simply holding a Ph.D. in their field of study. Very few have any formal training in education or more specifically in engineering education, which would include a knowledge of various learning styles and how to engage them. Even knowing learning styles, one of the tools that is almost not utilized at all in engineering education is weaving in anecdotal evidence (ie — storytelling) into what is typically a logic-only lesson plan. Research shows that integrating right-brain activities (emotional, imaginative) into left-brain lesson (logical) very much increased student retention of material. Examples are given for how this can be done in mechanical engineering lessons specifically.
Effect of Externally Applied Stresses on the Moisture Diffusion Characteristics of Epoxy Glass Composites
Authors: Stoffels Mark T. , Miller David A.
Published: April 2014

A model is proposed which relates externally applied tensile stresses to changes in absorption capacity as well as diffusion rate. The model postulates that changes seen in the diffusion process are the result of stress-dependent changes in the free volume of the epoxy resin. The free volume changes of the resin are calculated through laminate plate theory, which itself becomes a function of fiber angle as well as a host of elastic properties of the constituents. Consequently, according to the proposed model, changes in diffusion parameters are dependent upon the magnitude of applied stress, the loading angle, as well as elastic properties of the constituents.

Additionally, a finite element model is presented. The proposed finite element model establishes an analogy between thermal and mass diffusion for use in solving the moisture diffusion problems, both in free and stressed states. Input parameters for the FE model are found through use of the previously established mathematical diffusion model.

In order to experimentally verify the proposed models, a series of epoxy glass laminate samples were manufactured at varying fiber angles and immersed in a moist environment while subjected to varying levels of tensile loading. Weight gain measurements were recorded throughout the diffusion process until full saturation was achieved. The experimental values exhibited excellent agreement with both the suggested theoretical model and the finite element model.
Influences of Silicon Crystal Anisotropy in Nano-Machining Processes Using AFM
Authors: Wang Yachao , Shi Jing , Wang Xinnan
Published: April 2014

Atomic force microscope (AFM) machining has the potential to become an essential technology for manufacturing micro/nano-scale devices. In literature, this technique has been successfully employed to machine various types of materials, including semiconductor materials and metals. However, the effect of material anisotropy in terms of crystal direction is rarely considered in the existing studies. In this paper, we conduct nano-scratching experiments on the (1 0 0) plane of single crystal silicon surface with a diamond tip in an AFM machine. Three levels of crystal direction of nano-scratching are considered. Four levels of normal loading are applied. Machining performances are mainly evaluated by the groove morphology. Also, the wear coefficients and scratch ratio are calculated to the anti-wear performance. Based on the pile up volume and cutting volume respectively, the presence of the ploughing and cutting mechanisms is determined. The experiment results indicate that the applied normal load significantly affect the groove depth and debris morphology. The scratching direction has a pronounced effect on the friction coefficient and the calculated scratching hardness. By observing the debris morphology and cracks formation, the dependence of ductile to brittle transformation mechanism of silicon machining on the crystal direction is also discussed.
Mechanical Properties of a Photopolymerizable Hydrogel for Intervertebral Disc Replacement
Authors: Schmocker Andreas , Khoushabi Azadeh , Pioletti Dominique P. , Bourban Pierre-Etienne , Manson Jan A. , Moser Christophe
Published: April 2014

We report on the modeling and experimental validation of a photopolymerizable hydrogel for the replacement of the interior of the intervertebral disc (so called Nucleus Pulposus).

The hydrogel is initially injected in its liquid form and then photopolymerized inside via a small catheter. The light necessary for the photopolymerization is constrained to a small light guide to keep the surgical procedure as minimally invasive as possible.

During polymerization, the material’s absorption and scattering coefficients change and directly influence local polymerization rates and hence the mechanical properties. Quantitative scattering and absorption values as well as monomer conversion rates of the hydrogel sample were validated using a Monte Carlo model for photopolymerization. By controlling the input light pattern, local material properties can be engineered, such as elastic modulus and swelling ratio to match the set of requirements for the implant.

Experiments were conducted by polymerizing a hydrogel in a column-like volume using an optical fiber for light delivery. Quantitative scattering and absorption values as well as monomer conversion rates of the hydrogel sample were validated using a newly established Monte Carlo model for photopolymerization. The results were used to study and predict 3D polymerization patterns for different illumination configurations. Swelling ratio and elastic modulus were measured as a function of monomer conversion. Preliminary results on hydrogel fatigue tests in an in-vitro bovine disc will be shown.
Nonlinear Planar Dynamics of Fluid-Conveying Cantilevered Extensible Pipes
Authors: Ghayesh Mergen H. , Païdoussis Michael P. , Amabili Marco
Published: April 2014

This paper for the first time investigates the nonlinear planar dynamics of a cantilevered extensible pipe conveying fluid; the centreline of the pipe is considered to be extensible resulting in coupled longitudinal and transverse equations of motion; specifically, the kinetic and potential energies are obtained in terms of longitudinal and transverse displacements and then the extended version of the Lagrange equations for systems containing non-material volumes is employed to derive the equations of motion. Direct time integration along with the pseudo-arclength continuation method are employed to solve the discretized equations of motion. Bifurcation diagrams of the system are constructed as the flow velocity is increased as the bifurcation parameter. As opposed to the case of an inextensible pipe, an extensible pipe elongates in the axial direction as the flow velocity is increased from zero. At the critical flow velocity, the stability of the system is lost via a supercritical Hopf bifurcation, emerging from the trivial solution for the transverse displacement and non-trivial solution for the longitudinal displacement and leading to a flutter.
Development of an Experimental Method to Estimate the Operating Force of a Hand-Held Power Tool Utilizing Measured Transfer Functions
Authors: Lim Alvin , Kim Jay , Zechmann Edward
Published: April 2014

Hand-arm vibration syndrome (HAVS) collectively refers to diseases caused by prolonged exposure to intensive hand-transmitted vibration, which has been affecting millions of workers who use hand-held power tools. The force interacting between a hand-held power tool and the work-piece is valuable basic information in studying hand-arm vibration problems, however cannot be measured directly. An experimental method is developed to estimate this tool force by utilizing the input point impedance of the hand and measured transfer functions of the tool. The developed method is applied to calculate the tool force of a hand-held grinder and a circular saw to demonstrate and validate the method. Possible applications of the method to study hand-arm vibration or tool design are explained.
Analyzing of Impact, Vibration Response and Stability of Artificial Upper Limb
Authors: Bedaiwi Bashar A.
Published: April 2014

Investigation of impact and stability effects on an artificial upper limb due to external disturbance is made and the findings analyzed. For this purpose an experimental rig was suggested and constructed. The experimental rig consists of a special impact hammer to simulate the disturbance occurred and a special measuring device (accelometer, power amplifier and two Chanel vibration analyzer). The vibration response of human was measured at different points along the hand by using specified selected points. A suitable finite element model using ANSYS14 was suggested and the results are compared with those obtained from experimental work. This study aims to investigate the effects of vibration and impact on upper prosthetic limbs and is also aimed at mitigating vibration to the human body for greater comfort of the amputee.
Improved Image Registration Technique Using Demons and B-Spline
Authors: Tang Chao , Xie Xiaohui , Du Ruxu
Published: April 2014

Non-rigid image registration is an important and challenge work in image processing. The demons algorithm is one of the most effective non-rigid image registration methods. However, it is only suitable for images with small deformation. In recent years, many improving techniques are proposed. The free form deformation method based on B-spline function is widely employed in non-rigid image registration and is good at dealing with large deformation image registration. However, the performance of the demons algorithm is better than that of the B-spline method in dealing with small deformation registration. Therefore, in this paper, we propose to combine the demons algorithm and the B-spline method. The new method consists of two steps: First, it applies the B-spline method to deal with the large deformation. Then, it uses the demons algorithm to treat the small deformation. The testing results show that the new method is effective in dealing images with both small and large deformations. Comparing to the demons algorithm as well as the B-spline method, the new method has the smallest registration error and hence, is the best.
Computational Study of Single-Sided Ventilation Through a 3-Dimensional Room With Rounded Edges
Authors: Idris A. , Huynh B. P.
Published: April 2014

A commercial Computational Fluid Dynamics (CFD) software package is used to investigate numerically a 3-dimensional rectangular-box room with rounded edges. The room has all its window openings located on one wall only. The standard K-ε turbulence model is used. Air’s flow rate and flow pattern are considered in terms of wind speed and the openings’ characteristics, such as their number, location, size and shape. Especially, comparison with ventilation rate corresponding to when the room edges are sharp is made; and thereby the effects of the edges being rounded are examined.
Damage Quantification Using Wave Propagation Data With Integrated Numerical and Experimental Approach
Authors: Heidary Zahra , Ozevin Didem
Published: April 2014

Acoustic Emission (AE) has been studied as a nondestructive testing method for real time damage detection and location studies. The method relies on the propagation of the elastic waves due to the formation of new crack faces. While the method is capable of detecting damage initiation and location with an array of sensors, the variations in geometries and material properties, which change the output response, limit the capabilities of the method in further quantifications in terms of damage size and orientation. The ability to accurately model elastic waves offers significant potential for understanding the AE data; however, the oscillatory nature of wave equation requires very fine meshing and small time step for a stable numerical solution. In this paper, the AE signature of the damage initiation is predetermined using effective numerical models. The numerical model reduces the required degrees of freedom about 60% as compared to conventional finite element formulation and the computational time. Through studying different geometries and materials, it is demonstrated that the crack size and orientation can be identified if the magnitude and the phase of the surface motion are preserved without any modifications due to data acquisition electronics. When the AE sensors are positioned properly, the phase difference of two sensors indicates the crack orientation and direction. The numerical results are validated on monotonic testing of aluminum coupon samples with induced notches at different angles. Understanding the crack orientation provides the directions of the acoustic wave patterns, which improves the source location accuracy with proper wave velocity selection.
Analytical Model for Estimating Knee Loads During Ladder Climbing
Authors: Giachetti Robert S. , Danek Kari A.
Published: April 2014

We present a simple two-dimensional analytical model that estimates the knee joint loading during vertical ladder climbing. By developing a model with simplification assumptions, such as vertical ascent with no whole-body angular acceleration, we can grossly estimate knee loads under dynamic conditions using posture and whole-body acceleration. The model presented demonstrates that upward whole-body acceleration influences the knee load on the leading leg of the climber during ladder mounting and climbing.

In an effort to define the preferential departure acceleration during ladder ascent for use with the model presented, we also present preliminary data of the initial step onto a fixed ladder. These data are combined with the model at the moment of initial stance foot departure to generate preliminary knee loading estimates. Where appropriate and possible, the authors have attempted to compare and validate the analytical model with published knee loading.
System and Method for Analysis of Involving Factors in the Demisting Cyclone Efficiency
Authors: Najafabadi Masoud Molaei , Ehteram Mohammad Ali , Ahmadian Mohammad Taghi , Barari Ahmad
Published: April 2014

In this study a system for real-time analysis of some involving factors in the efficiency of gas-liquid separators is developed based on the weighing method. An ultrasonic atomizer generates water drops in a size range of 1–10 μm with the same frequency during the test. A cyclone separator is selected and effect of the developing flow rate and shape of the mini-riser as a part of connecting assembly to the cyclone separator is investigated. Further an efficient electrostatic precipitator (ESP) with outcome of single-phase airflow is employed in the downstream of the cyclone to separate remaining droplets and produce the same pressure loss during the test. Circular, triangular, rectangular and square cross section areas with the same hydraulic diameter of 14 mm were examined. The highest cyclone efficiency was recorded for the triangular and rectangular risers comparing to the circular riser at the same length and hydraulic diameter, so the connecting risers with corner could improve the separation efficiency.
Numerical Analysis on Nanofluid Mixed Convection in Triangular Ducts Heated by a Constant Heat Flux
Authors: Manca O. , Ricci D. , Tamburrino S.
Published: April 2014

The enhancement of heat transfer represents a very important issue regarding several industrial heating or cooling equipments. This goal can be achieved by means of different techniques; for example, by adopting passive methods like changing flow geometries or by enhancing the thermal conductivity of the working fluids. Thus, an innovative way of improving the thermal conductivity of base fluids consists into introduce suspended small solid nanoparticles.

In this paper a numerical investigation on laminar mixed convection with Al2O3/water based nanofluids in a triangular channel is presented. Duct surfaces were heated by means of a constant and uniform heat flux. The analysis was performed in laminar steady state regime for particle size in nanofluids equal to 38 nm, by adopting a single-phase model approach. The base fluid was water and alumina (Al2O3) nanoparticles were dispersed at different concentrations. Different Richardson number values were considered in order to solve a 3-D model of triangular duct. Results are presented for the fully developed regime flow in terms of surface shear stress and heat transfer convective coefficient, Nusselt number and required pumping power profiles. Comparisons with results related to the fluid dynamic and thermal behaviors are carried out in order to evaluate the enhancement due to the presence of nanoparticles in terms of volumetric concentration. The increase of average convective heat transfer coefficients and Nusselt number values for increasing values of Richardson number and particle concentration is observed by analyzing the obtained results. However, also wall shear stress and required pumping power profiles increase as expected.
Dimensionless Optimization of Thermoelectric Cooler Performance When Integrated Within a Thermal Resistance Network
Authors: Pearson Matthew R. , Lents Charles E.
Published: April 2014

Thermoelectric coolers are solid-state cooling devices which, in certain applications, can be used to reduce the operating temperature of electronics or increase their heat dissipation. However, the performance of the cooler is strongly influenced by the thermal system into which it is placed, and the cooler design should be optimized for a given system. In this work, the possible benefits of a thermoelectric cooler implemented within a realistic thermal system are quantified. Finite thermal conductances between the cooled device and the thermoelectric cooler, and between the thermoelectric cooler and the heat sink are considered. The entire problem is treated using dimensionless parameters, which reduces the number of independent parameters and enables generalized performance maps which clearly show the maximum benefit (in terms of a reduced device temperature or increased device heat dissipation) that a prescribed thermoelectric cooler can deliver to a particular application. The use of these dimensionless parameters also allows for optimization of thermoelectric cooler parameters without considering the cooler detailed design geometry.
Computational Study of Air Cooled Data Centers Assisted With Locally Distributed Water to Air Heat Exchangers
Authors: Gao Tianyi , Sammakia Bahgat , Schmidt Roger
Published: April 2014

The heat dissipated by data center equipment continues to increase due to the growing server power year by year. Thermal management continually becomes a challenging problem both from the standpoint of maintaining the equipment within a proper and reliable operation environment, as well as from a total energy cost perspective. With the total heat load increasing, as well as local high density heat fluxes, more cooling air flow rates may be needed by the racks which cannot be sufficiently provided by CRAC units. This may occur during peak periods of operation and may also occur in isolated aisles in the data center. Under such circumstances, just changing the air flow rates to specific aisles may cause unanticipated hot air recirculation into cold aisles which may happen during the transients that arise as the load and air flow rates are changing; henceforth, it may even occur in steady state. This could reduce the reliability of the data center equipment. A hybrid cooling strategy, which uses water to air heat exchangers located at the rear of specific racks to assist the air cooling, can be very effective in solving this problem by removing heat from the rack before it is exhausted into the room. This study describes the impact of this heat exchanger strategy on the thermal management of a data center. In this analytical study, the heat removal percentage and working efficiency of the heat exchanger are presented under different water flowrates and water inlet temperatures. Different case studies are conducted, showing that this method can significantly assist the data center air cooling under scenarios such as, power increases or CRAC unit failure. Detailed function of the heat exchanger on impacting the rack inlet temperatures are also discussed in this paper.
A Study on Doppler Weighting Factor for Control Element Assembly Ejection Accident by Using Newly Developed Nuclear Design Code and Non-LOCA Methodology
Authors: Yoon Kyungmin , Jang Chansu , Yoon Jooil
Published: April 2014

Among Reactivity Initiated Accidents (RIAs) for Pressurized Water Reactor (PWR), Control Element Assembly Ejection (CEAE) accident causes the rapid positive reactivity insertion to the core. It causes an asymmetric power distortion which results in the rising of local fuel temperature, fuel pellet thermal expansion and cladding ballooning or rupture. In the CEAE accident, Doppler feedback has a profound effect because the negative reactivity insertion due to the rise of fuel temperature reduces the core power after rapid power excursion. But the Doppler reactivity can’t be calculated properly in the safety analysis code, using point kinetics model, because the point kinetics model is not able to consider spatial-time effect of the sudden rise in local fuel temperature on Doppler feedback calculation during CEAE accident. And then the excessively high core power which results from the underestimated Doppler feedback would make more severe results such as PCMI fuel failure, fuel cladding rupture and serious DNB fuel failure. Therefore, Doppler Weighting Factor (DWF) is needed for the safety analysis of CEAE accident to compensate a missing spatial-time effect on Doppler feedback calculation. In this study, the adequacy of the application of DWF for APR1400 was evaluated by using nuclear design code called ASTRA (Advanced Static and Transient Reactor Analyzer)[1] and a methodology called ISAM (Integrated Safety Analysis Methodology)[2]. ASTRA is the 3D nuclear design code newly developed by KNF and has various functions such as the static core design, the transient core analysis and the operational support. ISAM is the methodology which is newly developed by KNF to perform the Non-LOCA safety analysis by using RETRAN[3] code which is widely used in the transient analysis and based on the point kinetics model.
Smoke and Heat Propagation Modeling in Transportation Interchange Stations Using LES and RANS Methods
Authors: Zanzi Claudio , Mozas Alberto , Hernández Julio , García-Hortelano Antonio , Aldecoa Javier
Published: April 2014

A numerical study of smoke and heat transport from fires occurring in a large interchange bus station is presented. The ultimate goal of this type of study is to increase the fire safety level of the station by improving the design of fire protection systems and evacuation procedures. The phenomena involved in the fire are highly transient and three dimensional, and their modeling requires large computational resources. In the present work, we introduce several simplifications in the numerical model, mainly related to turbulence modeling and the boundary conditions used to reproduce the effects of the combustion process, which allow us capturing the essential features of the fire while keeping the memory requirements and the CPU time at a reasonable level. In particular, we are interested in describing in a realistic way the spread of smoke and heat in a typical fire scenario in the lobby of an interchange bus station. The numerical analysis is carried out with the aid of a general-purpose computer code, using two different approaches for turbulence modeling (RANS and LES) and several discretization schemes. The fire effects are reproduced in a simple way, describing the fire focus as a source of mass, heat and chemical species. Boundary conditions are imposed at the fire focus, by setting the inlet velocity, temperature and gas composition (combustion products) at a section of appropriate area. The values of these quantities are chosen to be consistent with the prescribed heat release rate, type of fuel (heptane) and fire spread area. A comparison of the results obtained with the different methods, along with the CPU time consumption and dependence on the computational mesh, is presented. The capabilities and limitations of unsteady RANS and LES methods to reproduce the main features of the smoke and heat propagation patterns are analyzed.
On the Safety of Heating Pads
Authors: Barnett Ralph L. , Wingfield James R.
Published: April 2014

The electric heating pad represents one of the medical devices that escaped the FDA safety net by a “grandfather” exemption. An amazing number of philosophical safety issues are introduced by this relatively innocuous commodity. Pain relief is a major attribute of heating pads followed by a minor in actual medical efficacy associated with the improvement of local blood circulation. By contrast, the historic downside is very dramatic featuring electrocution, fire, and skin burns. This paper begins with a brief introduction to current protocol for placing new medical devices into the stream of commerce. In the case of heating pads, it is fortunate that the Underwriters Laboratories Inc. developed and promulgated design rules that effectively mitigated the dangers of shock/electrocution and fire. On the other hand, UL has not undertaken a technical program that addresses the skin burn problem that is the focus of this paper. Nevertheless, many heating pad manufacturers are under the impression that their compliance with UL 130 has ameliorated the skin burn propensity of their pads. Heating pad manufacturers have attempted to control skin burn injuries exclusively through the means of on-product and in-manual warnings that have been promulgated by UL, FDA, and CPSC. This approach has tenaciously maintained a burn rate of 1600 cases per year. A different approach to the skin burn problem is automatically orchestrated by invoking the “Safety Hierarchy.” For example, falling asleep and causing prolonged skin exposures to a heated pad can be eliminated by a dead-man control. Exposure to extreme temperatures that arise when both faces of the pad are concurrently covered is perhaps the most prevalent cause of skin burns. This paper exploits the notion of monitoring both face temperatures and shutting off the pad when they are almost the same. We also explored shutting down the pad when the cycle rate of the bang-bang controls was sufficiently slow; higher heating rates are associated with an uncovered face.