bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Studying Human Embryonic Stem Cell Culture Conditions in Pulsed Flow Micro-Reactors
Authors: Korin Natanel , Bransky Avishay , Dinnar Uri , Levenberg Shulamit
Published: July 2009

Embryonic stem (ES) cells research is a promising field for tissue engineering due to their proliferative capacity and differentiation abilities. The culture of Human Embryonic Stem Cells (hESC) in microchannel bioreactors can be valuable for hESC cell biology studies and hESC tissue engineering applications. We have previously demonstrated the long-term culture of mammalian (HFF-Human Foreskin Fibroblasts) cells in a microchannel (130μm) bioreactor under constant perfusion in a simple approach. However, hESC were found to be highly sensitive to flow and did not grow under flow rates which were proper for HFF long-term culture. Here, we propose the use of a novel automated periodic perfusion system to co-culture hESC with HFF in a microchannel bioreactor. The method is based on short temporal pulsed flows of medium renewal followed by long static incubation periods. The short pulsed exposure to shear enables shear sensitive cells (e.g., hESC) to withstand the medium flow. The present work studies experimentally and via numerical simulations the conditions required for hESC culture in a microchannel bioreactor using the periodic perfusion method. Conventional soft-lithography techniques were used to fabricate PDMS microchannels (100 μm) sealed reversibly with glass cover slides. HESC were seeded in the microchannel with HFF, incubated for several hours and then connected to a perfusion system which contained: a syringe pump, a permeable tube oxygenator, and waste container. The ability of the periodic perfusion protocols to prevent hESC de-attachment and maintain their culture was examined. Mass transport and fluid mechanics models were used to evaluate the culture conditions within the micro-bioreactor (shear stress, oxygen level, nutritious etc.). 3D finite element mass transport analysis (Comsol 3.3) was preformed to examine the oxygen levels in the microchannel as a function of time and design parameters. Altogether, the experimental results and the theoretical model indicate that the use of a periodic perfusion bioreactor is a suitable and promising method to culture hESC in a microreactor. Culturing undifferentiated human ES cell colonies in a micro-bioreactor is an initial step toward utilizing microfluidic techniques to investigate embryonic stem cell biology.
Adaptive Motor Control During Experiments With Brain Machine Interfaces
Authors: Beiser Koren , Zacksenhouse Miriam
Published: July 2009

Recent experiments with Brain Machine Interfaces indicate that the extent of neural modulations increases abruptly upon starting to operate the interface. In contrast, neural modulations due to the trajectory profile remain relatively unchanged. Furthermore, the enhanced modulations subside with further training, mirroring the trend in task performance, which degraded upon starting to operate the interface and improved gradually with training. Here we investigate the hypothesis that the enhanced modulations reflect internal representation of trajectory errors, which results in corrective commands in the short term and adaptive modifications of internal models in the long term. A simplified uni-dimensional model is analyzed to demonstrate the observed transient enhancement in neural modulations during the operation of Brain machine Interfaces. Identifying the source of the transient enhancement in neural modulation would provide insight into adaptive motor control and facilitate the improvement of future Brain Machine Interfaces.
Preventing Breakthroughs From Breakdowns
Authors: Reich Yoram
Published: July 2009

Breakthrough products are essential to the sustainability of manufacturers. Yet, their success statistics is disturbing. Rather than trying to correlate project success with its characteristics — a familiar endeavor whose results are seldom used by industry, we present a paradox in product development and use it to drive an approach implemented in a suite of five tools for supporting critical product development decisions. Some of the tools have been tested in industry and some are taught to students. We anticipate that the evolution of such tools and their adoption by industry would improve the fate of breakthrough product development projects.
Digital Imaging Exposure-Time Optimisation of Tripod-Camera Vibrating Systems Based on MTF
Authors: Fanti Giulio , Basso Roberto
Published: July 2009

The problem of exposure-time optimization in digital images acquired by a tripod-camera vibrating system is examined in this paper and an initial analysis is presented. The different noise sources concerning both the acquisition sensor in the camera and external vibrations were studied and quantified in some specific cases. The digital image quality is then discussed in terms of the MTF function evaluated at 50% level in order to define what the optimum ranges of exposure-times are.
A Robotic Prototype for Spraying and Pollinating Date Palm Trees
Authors: Shapiro Amir , Korkidi Eran , Rotenberg Amit , Furst Gilad , Namdar Harel , Sapir Barak , Mishkin Maor , Ben-Shahar Ohad , Edan Yael
Published: July 2009

Spraying and pollinating date palm trees is currently done manually by a team of three workers from a platform lifted 18 meters or more above the ground. This method is extremely unsafe and many accidents have happened due to lack of stability when the platform is in a lifted position. Alternatively, date clusters are occasionally sprayed by a large pressurized sprayer directly from the ground, a method that is highly unselective and environmentally harmful. In this paper we present the concept of an automatic apparatus that can effectively and accurately spray and pollinate date clusters from a robotic apparatus mounted to a standard tractor operated by a single driver. The apparatus consists of a robotic arm and computer controlled sprayer, guided by a computer vision system that detects and localizes date clusters with a camera. This system will minimize risk of injury, significantly save manpower (from three to one person per team), and deliver the spray with maximum accuracy thereby reducing chemical disposure. A small scaled prototype has been built and is currently under preliminary experiments.
A New Non-Parametric Model Based on Neural Network for a MR Damper
Authors: Boada Mari´a Jesu´s L. , Calvo Jose´ Antonio , Boada Beatriz L. , Di´az Vicente
Published: July 2009

Currently dampers based on magnetorheological (MR) fluids are being used in many applications such as construction, biomechanical and semi-active suspension to improve their behaviour. The main advantage of MR dampers is its very low time response (≈ 10 ms). In many cases, it is necessary to establish a suitable model of MR damper which characterizes its behaviour so that this model can be used in the simulation stage. In this paper, a new non-parametric model is proposed based on neural networks using a recursive lazy learning to model the MR damper behaviour. The proposed method is validated by comparison with experimental obtained responses. Results show that the estimated model correlates very well with the data obtained experimentally and learns quickly.
Effect of Fin Pitch and Height on Pin-Fin Heat Sink Performance
Authors: Sahray D. , Shmueli H. , Segal N. , Ziskind G. , Letan R.
Published: July 2009

In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. The sinks have the same base dimensions whereas the fin height and pitch vary. The fins have a constant square cross-section. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6.3 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights.
HSM Machining Stability During Hardened Steels Milling Process
Authors: Twardowski Paweł
Published: July 2009

In this paper HSM analysis of milling hardened steels is presented. All cutting parameters under process stability are described as well. The process stability is showing from point of view of self-excited chatter of machined system, assessed basis on signals of the chatter accelerations and components of resultant force.
Knowledge Based Approach to Assembly System Reuse
Authors: Harms Robert , Fleschutz Timo , Seliger Gu¨nther
Published: July 2009

The reuse of assembly equipment allows the exploitation of its unused potential, thus complying with both the economic objective of a high level of cost efficiency and the ecological objective of a high level of resource efficiency. Surveys have revealed manifold challenges for practitioners. Lack of experiences with the reuse process, the insufficiently designed and prepared equipment, missing life-cycle documentation as well as missing holistic planning concepts for the reuse where identified as main obstacles. In order to meet these challenges, a framework consisting of methods, tools and business process reference models for assembly equipment reuse is proposed. The core element is a computer aided reuse planning application that allows planners to generate reuse options and provides decision support during the planning process. The knowledge based approach, including its structure and core inference processes, which support the application is explained. The service oriented architecture for the realization of the framework is presented.
Effect of Counterface Roughness on the Wear of Polyoximethylene and Polypropylene
Authors: Aksulu Murat , Palabiyik Mehmet
Published: July 2009

In this study, effect of counterface roughness on dry sliding wear of polyoximethylene (POM) and polypropylene (PP) against stainless steel discs (HRC 52) is investigated. A pad on disc tribotester was used. Cylindrical surfaces of discs were used as wearing surfaces. Polymer specimens were produced as cylindrical pins. One of end faces of each pin was formed in the same radius of the discs. Normal force and sliding speed were constant. Roughness of the discs was produced by cylindrical grinding. Very low roughness values (mean of profile deviations Ra < 0.15 μm) were produced by using SiC emery paper after grinding. Ra parameters of the discs were measured both in axial (perpandicular to grinding traces) and circumferential direction (parallel to grinding traces). Average radius of curvature of the asperities Rav was computed by numerical analysis using raw surface profile data obtained from roughness measurements. Axial roughness measurements were chosen to illustrate the variation of wear rate and coefficient of friction with counterface roughness. Axial Ra values were varying from almost 0.1 – 3 μm. Disc surfaces were observed using an optical microscope. Worn polymer pin surfaces were observed by a Scanning electron microscope (SEM) to investigate wear mechanisms. SEM micro-photographs of the pins which worked against counterfaces with an axial roughness Ra = 0.3 μm and Ra = 3 μm were taken. As a result, it was seen that steady state wear rates of POM and PP increase with increasing disc surface roughness, and that circumferential Ra parameter may be effective to explain the interesting variation of wear rate with axial Ra, for axial Ra = 1–2.5 μm. PP and POM were observed to form no transfer film on the counterfaces. According to the SEM micro-photographs, for axial Ra = 0.3 μm some fatigue cracks were observed on the wear surface of the POM pins. For axial Ra = 3 μm, for both polymers, traces which were evident of abrasive wear, tearing and wear debris which was irregularly shaped particles were observed. It was investigated whether the relationship between wear rate and Rav conforms to the “fatigue wear model” of Hollander and Lancaster. In this investigation, asperities on the disc surfaces were assumed to have hemi-cylindrical shape and the radius of the hemi-cylinder is taken as Rav calculated from axial roughness profiles. It was seen that the results obtained for axial Ra = 0.1–1 μm, conform to the fatigue wear model.
Design and Control of Capstan-Pulley Draw System for Optical Fiber Manufacturing
Authors: Jenkins Hodge E. , Nagurka Mark L.
Published: July 2009

Optical fiber for data communication is manufactured by the draw process, which involves heating and pulling high purity glass cylinders to diameters of 125 μm. The diameter of the glass fiber and its light-guide core must remain constant to create a product capable of transmitting high-bandwidth optical data. The draw capstan design has a significant impact on the optical fiber quality. As the draw speed is used to control the fiber diameter, the ability of the draw capstan to follow velocity commands directly affects the resulting fiber diameter. To improve the control of the optical fiber diameter, the design of the overall system was revisited. A lumped-parameter model of the capstan drive was developed. It accounts for disturbances in the draw process that arise from sources such as the variation in the diameter of the input glass cylinder and the draw tension control, affecting the glass temperature and viscosity. The selection of the motor and the design of the speed controller in the optical fiber draw capstan pulley system were studied. Simulation studies over a range of parameters demonstrate that speed regulation, necessary to manufacture optical fiber within allowable diameter tolerances, can be achieved in the presence of estimated process disturbances without motor current saturation. The model predictions suggest that an effective draw capstan system can be synthesized and controlled. This case study has broad applications for the design of practical engineering systems that include control, electrical, and mechanical subsystems, typical in modern manufacturing. The paper highlights the use of mechanical and electrical modeling, system identification, and control design as necessary parts of product and process improvement.
CAE Tools as Valid Opportunity to Improve Quality Control Systems Performances for Sheet Metal Formed Components
Authors: Del Prete Antonio , Primo Teresa , Elia Alfredo
Published: July 2009

The numerical simulation of the forming process is a consolidated technique to verify, a priori, the effectiveness of the designed “method” to realize components obtained by sheet metal forming. As it is used in the industrial field at present, the limit of the forming simulation is that simulation results are based on an initial hypothesis that isn’t really true, that is on the hypothesis that the forming process is deterministic. Facts prove such affirmation is wrong considering that each input variable/datum of the simulation is non-deterministic by definition [1]. Therefore, a more realistic approach that uses the process simulation should consider this uncertainty by treating the process parameters as uncertain in an admissible domain. The authors are, at the moment, engaged in the development of an on line control and test system based on acquisition modules composed by a laser and two CCD video cameras. Its aim is to allow the statistical monitoring of the forming process through the investigation of the produced parts, and to point out, with a sufficient confidence level, situations of incipient process drift. The sampling frequency is 1, 2 parts per minute depending on the part main dimensions, therefore an express loading system of the part has been designed without clamps adoption [2]. The support provided by the non-deterministic simulation to the on line control system is very important. In fact, in the first phase of the production screening, for each produced part it allows to verify the areas that have a higher “risk” of defect on the basis of the simulation results. Moreover, as well as the simulation supplies useful suggestions on the areas of each piece at top priority where the quality control is executed, the quality control system can also provide interesting information for the non-deterministic process simulation system, thanks to the data and the measurements carried out on line, in order to increase the numerical-experimental correlation of the designed control system.
Stress State of Shells With Residual Strains: Refined Model and Matrizant Method
Authors: Maksymuk Alexander V. , Shcherbyna Natalie N. , Shlapak Lyubomyr S.
Published: July 2009

An axisymmetric problem on determination of the stress state for limited cylindrical shells caused by residual strains is considered. Using of suggested matrizant numerical-analytical method the solution of this problem in refined statement is given. The theoretical model allows taking into account of the effect of transversal shear deformation and the compression of normal. Numerical analysis of the stress state is presented.
Infinite Dimensional Slow Modulations in a Delayed Model for Orthogonal Cutting Vibrations
Authors: Nandakumar K. , Wahi Pankaj , Chatterjee Anindya
Published: July 2009

We apply the method of multiple scales (MMS) to a well known model of regenerative cutting vibrations in the large delay regime. By “large” we mean the delay is much larger than the time scale of typical cutting tool oscillations. The MMS upto second order for such systems has been developed recently, and is applied here to study tool dynamics in the large delay regime. The second order analysis is found to be much more accurate than first order analysis. Numerical integration of the MMS slow flow is much faster than for the original equation, yet shows excellent accuracy. The main advantage of the present analysis is that infinite dimensional dynamics is retained in the slow flow, while the more usual center manifold reduction gives a planar phase space. Lower-dimensional dynamical features, such as Hopf bifurcations and families of periodic solutions, are also captured by the MMS. Finally, the strong sensitivity of the dynamics to small changes in parameter values is seen clearly.
Noninvasive Electromagnetic Evaluation of Bjo¨rk-Shiley Heart Valves: Lifetime Prediction
Authors: Grimberg Raimond , Savin Adriana , Chan Shiu C. , Steigmann Rozina , Udpa Lalita , Udpa Satish S.
Published: July 2009

Prosthetic heart valves of the Bjork-Shiley Convexo-Concave (BSCC) type have long been used extensively in implants; however, there have been reports of cases where one component of the valves failed, leading to the demise of the patient. This paper presents a new method for noninvasive electromagnetic evaluation for this type of valve, using an eddy current transducer with orthogonal coils. In vitro experiments have shown that discontinuities of outlet strut with depths equal or larger than 0.4mm can be detected with a probability of detection (POD) of 86.4%, and in the case of discontinuities with depth equal or larger than 0.6mm with POD of 97%.
Rigid-Body Motion Estimation Using Statistical Solid Dynamics Method and Dynamic Method
Authors: Mor M. , Wolf A.
Published: July 2009

The most frequently used method in three dimensional human gait analysis involves placing markers on the skin of the analyzed segment. This introduces a significant artifact which strongly influences the bone position and orientation and joint kinematics estimates. The benefit in developing a method to reduce soft tissue artifacts is significant, resulting in the prevention, better diagnosis, and treatment of joint disorders and in the design of better prosthetic devices with longer mean times to failure. In this work we approached the problem of soft tissue artifacts from both a dynamic method and a statistical solid dynamics method. The dynamic method is based on the implementation of a Lagrangian approach to drive model based procedure for the estimation of the rigid body (bone) motion for the measurements of markers attached to the skin. The statistical solid dynamics method is a combination of several existent tools. It is based on a least squares optimization of markers position and orientation. Both methods were tested and evaluated using computer simulation and similar dynamics systems.
On Some Information Metrics of Intelligent Material Systems
Authors: Bonsignorio Fabio P.
Published: July 2009

In this paper it is proposed a theoretical model of an ‘intelligent material’ system. An ‘intelligent material’ body is seen as a flexible body capable to manage energy, deformations and information. In any finite element dynamical, material and information processing properties are coexisting and interacting. On the basis of some Shannon and Kolgomorov theory and network statistical physics relations, it is shown how such a material is actually able to store and process information in itself physical structure. Some relations linking the dynamical characteristics to the information metrics are shown. A finite element model for intelligent materials is outlined. The aim of this approach is, on one side, to explain why the payload ratio of, for example, an human arm is much higher than that of a (current) robotic arm, on the other end, to suggest that deeper relations between material dynamics computational models, information and control theory could help design new artifacts with new improved performance, closer to what we can see in natural biological examples.
Performance Comparison for a Constructal-Based Flow Field Pattern in a Single PEMFC
Authors: Damia´n-Ascencio C. E. , Herna´ndez Guerrero A. , Escobar Vargas J. A. , Cano-Adrade S. , Elizalde Blancas F.
Published: July 2009

The present work shows a three-dimensional numerical simulation of a Single Proton Exchange Membrane Fuel Cell (PEMFC) with a constructal-based pattern as a gas distributor. The models are classified according to the proposed angle and bifurcation level. The numerical model considers a complete solution of the Navier-Stokes equations, the species transport equation and two potential field equations; the model is solved using a finite-volume technique assuming isothermal and steady state conditions. The three-dimensional simulation includes nine control volumes: two current collectors, two flow channels, two gas diffusion layers, two catalyst layers and a membrane between the two catalyst layers. The results show that larger values of current density can be obtained in order if the bifurcation levels are increased. This suggests that a better performance is reached when the structure is closer to those structures found in the natural world.
A Simple Flow Model for Amorphous Molecular Solids
Authors: Diaconescu E. N. , Zegrean V. F.
Published: July 2009

Theoretical and experimental investigations suggest that EHD oil films exhibit amorphous solid properties. Therefore, oil EHD traction properties may be found by the shear of corresponding molecular solids, such as amorphous paraffin. To check this possibility, the viscosity of solid paraffin under controlled pressure and temperature is measured on a computer assisted shear device. Experimental results indicate that some viscosity properties in amorphous solids do not match those found in liquids. AFM investigations show that solid paraffin structure is a mixture of clusters and simple molecules. A possible mechanism of flow in molecular amorphous solid was advanced which explains the observed discrepancies.
Comparison Between Traditional Microchannels Heat Sinks and Microchannels Heat Sinks Based on Biomimical Tendencies
Authors: Rubio-Jimenez Carlos A. , Hernandez-Guerrero Abel , Rubio-Arana Cuauhtemoc , Popescu Daniela
Published: July 2009

In the last few years high-tendency electronic devices have improved to a larger processing capability with smaller physical dimensions. This fact coupled to traditional cooling mechanisms, are not able to dissipate the high heat fluxes generated by these devices (around 200 W/cm2.) Microchannel heat sinks are the new tendency in heat dissipation. Many of the studies done before had used single-phase water as cooling fluid in laminar flow. Operating within this regimen, and using water as the cooling fluid, the dissipated heat flux is not enough to keep optimal operational conditions in the electronic devices. Therefore, this work presents a thermal and hydraulic numerical analysis for a microchannel heat sink with circular cross section, fabricated in a silicon substrate. The channel cross section is variable, being a function of the heat sink longitudinal position, decreasing as the cooling fluid passes through the channel. The ratio between the inlet and outlet diameters is given as a function of the Biomimic tendency. These theories are based on the behavior that nature has for the mass transport in circular ducts. The cooling fluid used in this study is water in single-phase. These microchannels heat sink arrangements are based in the operational and geometrical parameters of previous works developed by several authors on microchannels heat sinks with constant and conventional cross sections.
Friction of Rubber Wheels on Wet Asphalt Surfaces
Authors: Bouzid Noamen , Heimann Bodo
Published: July 2009

A reliable online prognosis of the grip between tire and road is a feature with a big potential for further improvements of the automotive safety. Existing grip potential prognosis systems for wet conditions are able only to describe the hydrodynamic decrease of friction at high speeds which depends on vehicle velocity, water film thickness and drainage properties both of the road surface and the tire. The present work deals with the friction at low speeds which depends on the road micro roughness. The experimental investigations are done in laboratory using a small solid rubber wheel and several asphalt samples. All parameters possibly influencing the friction process are varied. The influence of the test surface is found to be related to the micro texture and to be independent of any other parameters.
Health Monitoring of Adhesive Joints Using Magnetostrictive Fillers
Authors: Weber Yarden B. , Schweitzer Daniel , Bar Hedva , Shilo Doron
Published: July 2009

One major application for smart materials is measuring stresses or strains in load bearing structures. The ability to monitor structural health, and observe real time stress levels in load bearing platforms is a field of great interest. In this work, we develop and characterize a method for stress monitoring adhesively bonded joints by incorporating a magnetostrictive filler into the polymeric matrix. Magnetostrictive materials create a change in their surrounding magnetic field when subjected to strain, and thus serve as natural strain sensors, that require neither power supply nor any kind of wiring. A clear correlation between the stress and the magnetic field, which is measured at a distance of 20–60 mm from the specimen, is observed under both shear and compression loads. Moreover, there is a significant stress region in which the relationship between the stress and the magnetic field is approximately linear. This behavior demonstrates the possibility of monitoring the average stress in a specimen by a single magnetic sensor mounted at a distance from the specimen. Additionally, complete three dimensional mapping of the magnetic field around loaded specimens reveals that the specimen magnetization is not uniform and implies the existence of a correlation between the specimen magnetization and the stress field which was numerically computed. This behavior indicates the potential of mapping the local stress profile within a specimen by using an array of several magnetic sensors. The effects of magnetostrictive particle size and of applying a magnetic field during specimen polymerization are also discussed.
Freedom of Micro Manufacturing Tool-Free Series Production in Industrial Applications of Micro- and Nanotechnology
Authors: Go¨tzen Reiner
Published: July 2009

RMPD®, which stands for Rapid Micro Product Development, is a family of technologies designed to generate with a parallel batch process, microstructures, microsystems and/or MEMS or MOEMS in a parallel batch process. Photo polymerized monomer, oligomere and hybrismaterial (sol-gel) polymerized with uv-light and generate the system. The technology’s 3D-CSP (tree dimensional chip sice packaging), RMPD®-multimat (volume specific material propertys), RMPD®-stick2 (mechanical parts directly to a foil, wafer and so on) and RMPD®-nanoface (surface roughness in sub-nm range) have since 1996 been key elements in this worldwide-patented family of technologies, which has allowed System in Packing SiP to develop into a virtually tool-free production process. Additive and parallel processes give these technologies a costefficient and customer oriented strategic direction.
Industrial Constraints Handling With a GA Approach in Multiobjective Optimization of a Composite Material
Authors: Bassir David H. , Zhang WeiHong , Zapico Jose´ L.
Published: July 2009

In this article, complexities related to the multicriteria (multiobjective) optimization of laminated composite structures subjected to technological constraints we will be presented. So, various technological constraints will be presented and a strategy of handling each constraint (in order to use the multiobjective optimization tools based on genetic algorithms) will be also introduced.
Performance Assessment of an Active Noise Reduction System
Authors: Wolf Kai , Han Soong-Oh , Doll Torsten , Kurtze Lothar , Bein Thilo , Hanselka Holger
Published: July 2009

In the past decade the field of smart structures and intelligent material systems received a lot of scientific attention. Numerous publications deal with the modeling, design, optimization and performance evaluation of such systems, in which beams, plates or truss structures are often considered as test cases. In the application of this promising new technology to real systems, the designer is often confronted with problem specific issues, e.g. proper formulation of the desired output function, integration of the actuators, sensors made of multifunctional materials and the control scheme to the system model, etc. As an example, the performance assessment of an active fac¸ade system is presented in this paper. The fac¸ade system consists of distributed piezoelectric sensors and actuators bonded to the surface of the doubleglazed windows. An adaptive feedforward control scheme was implemented to reduce the noise transmission via the active fac¸ade. The performance of the active system with four sensor/actuator pairs was first demonstrated in a numerical simulation. A Digital Signal Processing System was used to validate the performance of the system with the help of a demonstrator fac¸ade, showing the reduction of the ambient noise experimentally for different types of harmonic and transient excitation.
Mesh Segmentation for CAD Applications
Authors: Tal Ayellet
Published: July 2009

Segmentation of meshes has received a lot of attention in recent years, due to its growing number of applications. In this paper, we discuss properties that have been used in the literature to evaluate segmentation algorithms. Then, we describe some applications of segmentation in CAD. For each application, we review one of our segmentation algorithms that is suitable for the problem. We focus on four applications: modeling by example, shape-based retrieval, skeleton extraction, and paper crafting.
Improvement of Integrity Concepts for NPP Primary Circuit Piping
Authors: Arzhaev Alexey , Butorin Sergey
Published: July 2009

Operating NPPs license extension activities in Russia produced strong demand for safety improvement of plants build according to earlier standards. Installation of additional supports as pipe whip restraints is one of requirement in acting regulatory documentation which should be followed or compensated by appropriate measures like Leak Before Break (LBB) analyses and improvement of In-Service Inspection (ISI) and Leak Detecting System (LDS). Basic document for LBB concept application to Russian NPP piping is RD 95 10547-99. Its requirements correspond to classical LBB principles used in many countries in Europe, USA and Japan. In many real cases requirements of RD 95 10547-99 could not be applied to safety important NPP piping systems due to the presence of specific features of operational degradation due to some corrosion mechanisms: for example, erosion-corrosion (E-C) for carbon steel piping and intergranular stress corrosion cracking (IGSSC) for heat affected zones of austenitic piping weldments. For special case of RBMK piping with outer diameter 325 mm (potentially susceptible to IGSCC) special Break Preclusion Concept has been developed in Russia after IAEA Extrabudgetary Program in 2000–2002. Contrary to LBB Concept demanding for all four basic principles to be completely fulfilled BP Concept accepts some principles to be fulfilled in a balanced way with demonstration of monitored degradation effectively achieved in operation. Special BP Concept is being developed now to support integrity assessment of RBMK carbon steel steam and feed water piping potentially susceptible to E-C which requires another set of measures to demonstrate principle of controlled degradation in operation then in case of austenitic steel piping. General scheme of piping integrity analyses according to LBB and BP Concepts is discussed and examples of specific approaches to achieve controlled degradation are illustrated in paper. As result of LBB and BP Concepts application it is possible to substantiate reject of additional piping whip restraints implementation on-site. Examples of similar safety methodology development in other countries have been reported at IAEA Specialists Meeting on LBB in Kiev, Ukraine in November 2006.
In-Situ Observations of Dislocation Patterning in Deformed Polycrystalline Aluminum
Authors: Landau Peri , Shneck Roni Z. , Makov Guy , Venkert Arie
Published: July 2009

The formation and evolution of dislocation patterns in pure polycrystalline aluminum was examined using transmission electron microscopy. The conventional characterization of the deformed samples was combined with in-situ tensile tests of prestrained samples which were carried out in order to get a better understanding of dislocation motion during deformation. The role of different types of boundaries was studied and it was found that while dense dislocation walls have an ordered structure since they are geometrically necessary, incidental dislocation boundaries can change their configuration from tangled to ordered.
Cavitation Intensity Measurement by Analysis of Pump Structure Oscillation: A New Parametric Method Approach
Authors: Arjmandi Tash Hadi , Sadeghi Morteza , Shervani Tabar Mohammad T. , Ettefagh M. Mohammad
Published: July 2009

One of the sources of instability in pumps is cavitation phenomenon. Cavitation in a pump can cause some undesirable effects, such as deterioration of the hydraulic performance (drop in head-capacity and efficiency curves), damage of the pump by pitting and erosion, structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore its occurrence inside a pump and its intensity must, by all means, be identified. In the present study, alternations in the velocity of an axial flow pump structure, for the first time used to investigate Cavitation. An average energy method for identification cavitation occurrence and measurement its intensity has been developed. This is called the Logarithmic Cavitation Intensity (LCI). To establish the pump cavitation conditions, a statistical analysis has been undertaken in a real-time and an LCI has been recommended as a proper criterion for defining the cavitation intensity. The results also showed the proposed method besides some other advantages comparing other detection methods, is feasible by simple hardware with low sampling frequency resulting in reducing the computational time as well as hardware complexity and cost.
Volume Particle Tracking in Three-Dimensional Micro-Channel Flows
Authors: Homeniuk Darren L. N. , Nobes David S. , Molla Shahnawaz , Bhattacharjee Subir
Published: July 2009

A micro-fluidic technique has been developed that uses a combination of dielectorphoresis and tangential flow to remove particles from a filter membrane. To assess the characteristics of particle motion at the membrane surface, a volume scanning imaging system has been developed to track the three-dimensional motion of particles in this micro-channel flow. The development of the image and tracking system is described and results highlighting experimental application of the technique are presented.
Large-Eddy Turbulent Flow Simulation of a KOMAX Static Mixer
Authors: Rahmani Ramin K. , Keith Theo G. , Ayasoufi Anahita
Published: July 2009

Viscous liquids have to be homogenized in continuous operations in many branches of processing industries; and therefore, fluid mixing plays a critical role in the success or failure of many industrial processes. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality, resulting in the need for more elaborate downstream processes and increased costs. The range of practical flow Reynolds numbers for KOMAX static mixers in industry is usually from moderate values (Re ≈ 0) to very large values (e.g. Re ≈ 5,000,000). However, most of industrial applicants have a very small flow to moderate Reynolds numbers (e.g. Re ≈ 5,000). This paper presents an improved understanding of the turbulent flow pattern for single-phase liquids through the mixer. Large-Eddy Simulation (LES) model is applied to the flow in a KOMAX static mixer to calculate the flow velocities, pressure drops, etc. Using a variety of predictive tools, the mixing results are obtained.
A Comparative Study Between the Various Methods of Measuring Void Fraction in Air-Water Two-Phase Flow
Authors: Kendoush Abdullah Abbas , Yaqob Banipal N.
Published: July 2009

This paper contains measurement of local void fraction by using the capacitance and the auto-transformer techniques in bubbly air-water two-phase simulation flow. The uncertainty in void fraction measurement by the two techniques was compared with those measured by nuclear radiation techniques used by Kendoush (1992) and Kendoush and Sarkis (2002). It was found that the auto-transformer and the capacitance techniques have more accurate results than the γ-ray attenuation and neutron transmission techniques. The X-rays technique has less uncertainty in void fraction measurement as compared to the auto-transformer and the capacitance techniques.
Gas-Liquid-Solid Three-Phase Flows Through Pipes: Particle Velocity Measurement and Prediction
Authors: Bello O. O. , Reinicke K. M. , Teodoriu C. , Liu M.-Y.
Published: July 2009

Particle transport issues in three-phase gas-liquid-solid flow systems continue to challenge petroleum as well as mining, petrochemical, biochemical, pharmaceutical, food, nuclear, pulp and paper industries. The poor knowledge of particle transport processes associated with three-phase gas-liquid-solid pipe flow has greatly hampered the design and cost-effectiveness of these systems. This paper presents experimental and computational studies on three-phase gas-liquid-solid pipe flow systems in order to increase the understanding of particle transport and dispersion behaviour as well as the conditions for solid particle deposition and erosion risk initiation. The non-invasive high-speed charge coupled device (CCD) measuring technique is used in this work to study the particle velocities in three-phase gas-liquid-solid pipe flow systems. A calculation method to predict particle velocity in the three-phase gas-liquid-solid pipe flow systems is proposed. The model is based on the fundamentals of the particle mechanics in the three-phase gas-liquid-solid pipe flow systems. A good agreement between experiment and prediction is obtained.
3D Numerical Simulation of a Parachute With Two Air Vented Canopies in a Top-to-Top Formation
Authors: Izadi Mohammad J. , Razzaz Reza Baradaran
Published: July 2009

In a parachute, an increase of drag force occurs when the frontal area or the area of its canopy is increased. To prevent the technical problem in deployment of large parachutes, designing parachutes consisting of more than one canopy with smaller frontal area with an air vent at the top of each one is suggested. In this investigation, several formations of canopies are considered, and all are set as concentric and is placed at the top of each other with some distances apart. The canopies are taken as solid bluff bodies (Hemi-spherical cups) for simplicity. The effect of two variables on drag is the main idea of this study. All the formations of the two canopies (Two bluff bodies) are based on two variables; the diameter ratio (The diameter of the upper canopy to the lower canopy), and the distance between the canopies. The drag force is found at maximum, when the upper and the lower canopies have equal diameters, and for when the distance between the canopies is twice the upper canopy diameter.
Flow Control in Serpentine Inlet Duct Using Vortex Generator Jets
Authors: Sullerey R. K. , Chandra S.
Published: July 2009

The objective of the present research is to study the effectiveness of steady and pulsed vortex generator jets in reducing inlet flow distortion and in improving pressure recovery by effective secondary flow control in uniform inflow Serpentine duct diffuser. The measurements were carried out in at a test Reynolds number of 6.5×105 based on the diffuser inlet width. Serpentine duct diffuser consisted of two main portions namely square to circular constant area followed by a circular diffusing duct. Investigations show that the flow in the serpentine diffusing duct suffers from stall on the inner wall and the outflow at AIP has considerable flow distortion due the combined effect of secondary flow and the inner wall stall. It is observed that the use of vortex generator jets both in steady and pulsed modes improve the performance substantially. The number of jets, location of jets, velocity ratios and the pulse frequency are some of the variables that are studied. The results obtained so far suggest that use of pulsed jet not only gives better performance but also reduces the amount of air that need to be injected through the jets in comparison to steady jets for similar velocity ratios.
Prediction of Surface Roughness Effects on Centrifugal Compressor Performance
Authors: Kawakubo Tomoki , Numakura Ryusuke , Majima Kanji
Published: July 2009

The present paper deals with the effect of the surface roughness on the performance of centrifugal compressors and the applicability of the Computational Fluid Dynamics (CFD) for the purpose of the quantitatively accurate prediction of the performance deterioration due to the surface roughness. Commercial CFD solver FLUENT was applied in the current research. High Reynolds number turbulence model was used with the wall function corrections to the rough walls. In the initial phase, CFD analyses were conducted on an axial compressor and an axial turbine cascades, those geometrical and experimental data on the effect of the surface roughness are publicly available. The comparison of the CFD results with the experimental data showed reasonable agreement in view of the increase in the cascade loss coefficient at the cascade design conditions, although less satisfactory agreements were obtained at some off-design conditions. In the next step, a series of performance testing was conducted on the centrifugal compressor stages, whose wetted surfaces are intentionally roughened by sand-blasting surface treatment. Corresponding CFD analyses were conducted. In these analyses the intensity and extent of the surface roughness were appropriately modeled based on the observations and measurements of the surface texture. Efficiency decrements were compared and good agreements were confirmed between them. In this case, good agreements were obtained not only for the design conditions but also for the wide range of the off-design conditions. Based on the above analyses and comparisons with experimental data, following conclusions were obtained. Reasonable quantitative agreements between experimental data and CFD analyses were obtained on axial compressor and turbine cascades and centrifugal compressor stages. CFD analyses with wall roughness can be used to estimate the detrimental effect of the surface roughness.
CFD Modeling of Slurry Flows in Horizontal Pipes
Authors: Herna´ndez Franz H. , Blanco Armando J. , Rojas-Solo´rzano Luis
Published: July 2009

Liquid-solid two-phase flows are found in numerous operations in the chemical, petroleum, pharmaceutical and many other industries. In numerous cases, the mixture or slurry that flows is composed by a suspension of solid particles (dispersed phase) transported by a liquid (continuum phase). However, the large number and range of variables encountered in slurry flows, in the case of pipelines, cause the flow behavior of these slurry systems to vary over a wide range of conditions, and consequently, different approaches have been used to describe the behavior of different flow regimes. Therefore, there are numerous studies of particular cases that cover limited ranges of conditions. In consequence, the experimental approach is necessarily limited by geometric and physical scale factors. For these reasons, Computational Fluid Dynamics, CFD, constitutes an ideal technique for predicting the general flow behavior of these systems. CFD models in this area can be divided in two different classes: Eulerian-Eulerian and Lagrangian-Eulerian models. Differences between these models are related to the way the solid phase flow is represented. Lagrangian-Eulerian models calculate the path and motion of each particle, while Eulerian-Eulerian models treat the particle phase as a continuum and average out motion on the scale of individual particles. This work focuses on the Eulerian-Eulerian approach for modeling the flow of a mixture of sand particles and water in a horizontal pipe. Homogeneous and heterogeneous flow regimes are considered. The k-ε model was used for modeling turbulent effects. Additionally, closure of solid-phase momentum equations requires a description for the solid-phase stress. Constitutive relations for the solid-phase stress considering the inelastic nature of particle collisions based on the Gas Kinetic Theory concepts have been used. Governing equations are solved numerically using the control volume-based finite element method. An unstructured non-uniform grid was chosen to discretize the entire computational domain. A second-order scheme in space and time was used. Numerical solutions in fully developed turbulent flow were found. Results show that flow predictions are very sensitive to the restitution coefficient and pseudo-viscosity of the solid phase. The mean pressure gradients from numerical solutions were compared with results obtained using the correlations of Einstein, Thomas and Krieger for homogeneous cases and with experimental data found in the open literature for heterogeneous cases. The solutions were found to be in good agreement with both correlations and experimental data. In addition, these numerical results were closer to experimental data than results obtained using other numerical models.