bluuebunny/crossref_metadata_2025 huggingface dataset:
Nested Ripple Down Rules (NRDR) as a Design Assistant in Mechanical Dimensional Tolerancing
Authors: Hamade Ramsey F. , Ammouri Ali H. , Beydoun G.
Published: May 2012

The dimensional tolerancing knowledge management system presented in this paper uses Nested Ripple down Rules (NRDR) targeted towards incrementally capturing expert design knowledge. A demonstrated example of such captured knowledge is that which human designers utilize in order to specify dimensional tolerances on shafts and mating holes in order to meet desired classes of fit as set by relevant engineering standards. In doing so, NRDR interface was designed to receive mathematical functions with their specifications prior and during the KA process. This is necessary to be able to exploit relationships among several classes with respect to certain numerical features of the cases in order to accelerate the convergence of the NRDR knowledge acquisition process by generating artificial cases which are likely to trigger the addition of exception rules. The incorporation of equations constitutes a novel contribution to the field of knowledge acquisition with NRDR. The developed dimensional tolerancing knowledge management system would help mechanical designers become more effective in the time-consuming tolerancing process of their designs in the future.
Risk Based Estimate: Keep It Simple...
Authors: Cretu Ovidiu , Cretu Vlad , Berends Terry , Stewart Robert
Published: May 2012

The project cost and schedule estimate is a very subtle effort that needs to be repeated throughout the entire project’s life. The relatively new method of including risk events into the project cost estimate makes this effort more sensitive to subtleness. The authors have noticed during their work with other professionals that it is a tendency to make the processes of cost risk analysis (Risk Based Estimate (RBE)) more complicated than they should be. The authors call this tendency as “professional sophistication” when the RBE includes too many activities, too many uncertainties, and too many risk events. The “professional sophistication” usually is detrimental to the entire cost and schedule risk analysis and it constitutes a significant source of the analysis’ failure. The paper presents few cases when so called “professional sophistication” led to the initial analysis failure and if not caught in time to the project cost and schedule misrepresentation. The paper presents the reasons why the “Keep It Simple Smarty (KISS)” principle is critical for a robust and reliable cost and schedule risk analysis. The papers evaluate the impact of having too many variables included into RBE. It makes recommendation about the optimum number of variable that may be incorporated in the cost risk analysis. The ultimate recommendation is about being sure that the Risk Based Estimate includes only the uncertainties or risk events that may change significant the project cost or schedule.
On Chip Micropumping for Biofluids by Temperature Biased AC Electrothermal Effect
Authors: Wu Jie , Yang Kai , Yuan Quan
Published: May 2012

For biofluids, very limited voltage can be applied without causing reactions, even with AC voltages, so conventional electrokinetic pumps cannot function effectively. Here two innovative ACEK micropump designs are proposed, which are expected to solve the long-standing problem of on-chip pumping for biofluids. This work focuses on exploiting external heat flux or temperature bias to enhance micropumping by AC electrothermal effect. AC electrothermal effect is ubiquitous as long as electric current flows through fluid. Investigating the interplay between electric field and temperature field will be useful for the research area of electrokinetics as a whole. New methods to enhance on chip micorpumping have been presented in this paper. Inhomogenous electric fields can cause uneven Joule heating of the fluid, which generates thermal gradients and leads to mobile charges in fluid bulk. The two pumping schemes circumvent the voltage problem by introducing extra thermal gradient to generate mobile charges. The free charges then move under the electric field and induce microflows due to viscosity. Numerical simulation and preliminary experiments have successfully demonstrated the improvement in flow velocity. It enriches the repertoire for the design of ACEK micropump, and affords us more flexibility when dealing with micropumping tasks. The micropumping mechanisms proposed here are simple, robust, of small form factor, can be readily integrated into microsystems at low cost. The proposed fabrication and micropump integration process is highly manufacturable with various materials and can be easily incorporated into a fully integrated biochip. The added design flexibility from this project will lend the pump design well towards many lab-on-a-chip applications.
Fatigue Strengthening of Cracked Steel Beams With CFRP Plates
Authors: Fernando D. , Schumacher A. , Motavalli M. , Teng J. G. , Yu T. , Ghafoori E.
Published: May 2012

Externally bonded FRP systems offer an attractive method to improve the fatigue life of steel beams. The fatigue performance of such a strengthened beam can be further enhanced by prestressing the bonded FRP reinforcement. While a number of studies have been conducted on the fatigue strengthening of steel beams using FRP, they have generally been concerned with the overall performance of the strengthened beam, with limited attention to the behaviour of the FRP-to-steel interface and its effects. Against this background, this paper presents the preliminary results of an ongoing experimental program aiming at investigating the behaviour and fatigue failure mechanism of FRP-strengthened cracked steel beams under fatigue cyclic loading, with particular emphasis on the debonding process of the FRP reinforcement and the effect of debonding on crack propagation. The effects of prestressing and debonding on the fatigue performance of the strengthened beam are clearly demonstrated by the test results.
Study the Transverse Vibration in a Pushrod of a Diesel Engine Valvetrain Using Contact Element in Flexible Multibody Dynamics
Authors: Mehrgou Mehdi
Published: May 2012

Dynamic simulations of the engine valvetrain and detailed studies on the operating mechanisms have long been a centre of attention. In heavy duty diesel engines, heavier valvetrain parts lead to higher inertia force. On the other hand, the opening and closing of valves is very fast and high overlap in Valves lifts and necessity for increase the exhaust and inlet valve opening time by dwelling, individuates cam design basis of these engines, which cause to increase in inertia forces. A common practice in valvetrain dynamic analysis is to use rigid multibody dynamics model. However, some assumptions are to be considered to simplify the model, especially in attachments and joints. In this paper, an under development heavy duty medium speed diesel engine valvetrain system has been studied. The valvetrain mechanism has been modeled using ADAMS commercial software. The flexible valvetrain parts have been considered by means of Component Mode Synthesis (CMS) method. Instead of using simple joint assumption of rigid multibody dynamics model, contact has been employed to study the exact interaction between each two parts. In this method the clearances in the system could easily considered. The dynamic behavior of valvetrain has been investigated and the forces for the parts have been obtained and compared with rigid multibody dynamics model.
Mechanical Properties of Open-Cell Cellular Structures With Rhombic Dodecahedron Cells
Authors: Babaee Sahab , Jahromi Babak Haghpanah , Ajdari Amin , Nayeb-Hashemi Hamid , Vaziri Ashkan
Published: May 2012

We present a series of analytical models and finite element results (FE) for special 3-D open cellular foam to determine the effective material properties of a 3D rhombic dedecahedron open-cell cellular structure. The analytical approach is based on minimizing the total energy associated with small deformation of a single unit cell of the cellular structure. The finite element models were developed for both a single unit cell and three dimensional foam structure and used to obtain the mechanical properties in all three principal directions.
Sensorless Simultaneous Rotary-Translational Axis Motion Error Measurement and Trace Based on Virtual Bar
Authors: Zhou Yuqing , Mei Xuesong , Jiang Gedong , Sun Nuogang , Shao Bai
Published: May 2012

Simultaneous rotary-translational (R-T) axis motion error has significant influence on multi-axis machine tool precision. To improve multi-axis machine tool precision, axis motion error measurement and trace method are investigated in this study. A sensorless R-T axis motion error measurement and trace technology based on virtual bar is proposed. Firstly, the fundamental sensorless test principle is discussed. Then, the virtual-bar-based test path of a circular test though a rotary axis and two translational axes motion is scheduled. The mathematical model of motion error is established. Furthermore, to identify the error source, spatial error charts and some advanced signal processing and feature extraction technologies, such as wavelet transform and frequency analysis, are used. The analysis of experimental results shows that it is practical and efficient to use the virtual bar and the sensorless information to estimate motion error.
Effects of Shallow-Angle Jet Impingement and Free Stream Velocity on Heat Transfer
Authors: Wang Lei , Sunde´n Bengt , Andreas Borg , Abrahamsson Hans
Published: May 2012

Experimental studies are carried out to investigate the heat transfer characteristics involving an impinging jet with a shallow-angle in a crossflow. Liquid crystal technique is employed to measure the wall temperature and obtain the heat transfer coefficients. In the study, the Reynolds number for the crossflow is range from 80,000 to 160,000 and the Reynolds number for the jet varies from 20,000 to 40,000. The jet-to-crossflow velocity ratio changes from 2.4 to 4.9. For a constant velocity ratio R = 3.5, it is found that the structure of heat transfer changes in nature as both Reynolds number increases. In addition, it is observed that the heat transfer in the wall jet region is uniquely determined by the jet and is independent of the crossflow. A correlation is constructed to fit data and predict the Nusselt number in this region.
Thermal and Structural Response of Pin Fins for Different Interface Conditions
Authors: Arif Abul Fazal M. , Pashah Sulaman , Zubair Syed M. , Inam M.
Published: May 2012

Thermal management of electronic products relies on the effective dissipation of heat. Heat sink elements (e.g. a pin fin) are used for any effective heat dissipation network. Despite much optimized design of the heat sink element, the heat transfer may not be effective because the interface between power device and heat sink element is critical in the heat dissipation network. Thermal Interface Materials TIM (e.g. adhesive, solder, pads, or pastes) are employed at interface between power device and heat sink element to minimize the interface thermal resistance. However, several challenges need to be addressed before they can be successfully utilized because depending on the thermal interface conditions, the thermal stress level can attain undesirable values. This issue can be addressed by the optimization of the system design with the help of simulation methods. Generally the effects of interface conditions are studied on the thermal performance of the heat sink system whereas in this paper, a coupled-field (thermal-structural) analysis using FEM is performed to study the thermal as well as structural behavior of the heat sink system. Temperature variation and stress fields in the region of interface between pin fin and base plate are analyzed. Effects of various parameters (such as contact pressure, surface roughness, TIM thickness, and operating conditions) on the resulting thermal and structural response at the interface are presented. It has been found that different interface conditions may have comparable thermal performance with significant different stress fields at the interface. Therefore stress state must be known to ensure the structural integrity of the heat sink system for a given operating condition.
Consistency Considerations for Integrated Thermodynamics and Fluid Mechanics Instruction
Authors: Boettner Daisie D. , Crawford Bobby G.
Published: May 2012

As a result of mechanical engineering curriculum revision at the United States Military Academy at West Point, separate courses in thermodynamics and fluid mechanics were integrated into a two-course sequence, Thermal-fluid Systems I and II, in academic year 2005–2006. After four years of instruction using available text books from publishers, the mechanical engineering faculty developed a text tailored specifically to the integrated two-course sequence. The experience in writing a text that integrates concepts in thermodynamics and fluid mechanics highlights the need for consistency between the two disciplines. Issues identified include logical organization of topics, selection of appropriate variables, consistent use of sign convention throughout all topics, recognition of various forms of the same fundamental principle, and definition of performance parameters. This paper explores these issues and how they were addressed for integrated instruction of thermodynamics and fluid mechanics.
Development of a Measuring System of Contact Force for Braille Reading Using a Six-Axis Force Sensor
Authors: Saadeh Mohammad , Trabia Mohamed
Published: May 2012

The objective of the recent research effort on tactile sensation is to provide the blind or visually impaired (BVI) persons with a more natural handling of their surrounding environment. To generate natural fingertip stimulations, the forces felt by the fingertip should be characterized. This work presents an approach to measure the fingertip forces while reading Braille characters. In the proposed experimental procedure, a subject is asked to identify five individual Braille characters that are hidden from view. Each Braille character is mounted on top of a six–axis force sensor. The experiment requires that each subject places a fingertip normal to a Braille character until the character is identified. The same experiment is repeated but with the subject applying pressure in the tangential direction. A new approach is proposed to identify these forces to ensure the validity of the readings. The subject is then asked to identify the letter out of images of the Braille characters. Twenty-eight subjects participated in the experiment so far. Data are statistically analyzed to obtain a general form of force-time history during the phase of Braille character identification. Normalization of the data is explored by identifying the equivalent fingertip pressure.
Micromechanical Hyperelastic Modeling of Bi-Directional Oriented Axons in Brain White Matter
Authors: Karami Ghodrat , Shankar Saurav , Ziejewski Mariusz , Azarmi Fardad
Published: May 2012

The white matter of the brain constitutes axonal elements simulating fibrous elements through the extracellular matrix of the brain anatomy. Brain injury caused due to failure of axons under incidents such as falls, accidents and blasts where sudden motion or mechanical loads might impact the brain to cause traumatic brain injury. The axons within the white matter of the brain elongate due to brain injury and hence the axonal fibers fail to retain their original state. This paper deals with the modeling of the brain tissue in the white matter assuming the unidirectional or bi-directional orientations for axons with and without undulation. A unit cell of the representative volume element of the material is composed of extracellular matrix and axons. Micromechanical principals are used with the unit cell under periodic boundary conditions. The material properties of Corona radiata in a porcine brain tissue with bi-directional orientation of axonal fibers within the base matrix will be considered. Hyperelastic material data and behavior will be assumed for the constitutive materials of the unit cell. The unit cell will be exposed to various types of normal and shear loading to examine the load transfer to the axons, and to examine the extent of the axonal stresses and deformation. The results in a multiscale analysis point to the extent of damage as well as to the response of the white matter under impact mechanical loadings or sudden head motions.
Metal Cutting Theory Applied to Thermal Mapping of the Friction Stir Welding Process
Authors: Payton Lewis N. , Chandrasekaran Vishnuvardhan
Published: May 2012

Friction Stir Welding is a solid state “green” welding method developed by The Welding Institute (UK). An internal thermal mapping instrument has been developed which allows for symmetrical mapping of the thermal fields developed by a Friction Stir Welding tool as it passes through the material being welded. This symmetrical mapping conclusively documents statistically the asymmetrical nature of the heat sources within the friction stir welding process. The various models in the literature are compared against these results. A model developed by the authors using classic metal cutting theory predicts the observed thermal fields. A successful predictive model will facilitate tool optimization and welding schedules, while optimizing the mechanical properties of the weld.
Modeling and Optimization of an Elliptical Shape Ultrasonic Motor Using Combination of Finite Element Method and Design of Experiments
Authors: Sanikhani Hamed , Akbari Javad , Shahidi Ali Reza , Darki Ali Akbar
Published: May 2012

Standing-wave ultrasonic motors are a modern class of positioning systems, which are used to deliver a high precision linear or rotary motion with an unlimited stroke. The design process should be performed through an effective optimization algorithm in order to guaranty proper and efficient function of these motors. An optimization method of ultrasonic motors is proposed based on the combination of finite element method and factorial design as a design of experiments in this study. The results show the ability of this method in optimal design of ultrasonic motors especially those which have a complex structure and multi modes operation principle.
Dynamic Analysis and Sliding Mode Impedance Control of a Robot Manipulator Subject to Impact/Contact With an Arbitrary Environment
Authors: Mahmoodi Masih , Farid Mehrdad , Eghtesad Mohammad
Published: May 2012

In this paper, dynamic equations of a robot manipulator subject to compliant contact/impact with the environment are derived using nonlinear elastodynamic approach. Then, a sliding mode impedance algorithm is proposed to control compliant impact/contact dynamics of the robot manipulator with an arbitrary environment. Impact/contact phenomenon can be regarded as a perturbation due to an abrupt change of system’s velocity. Thus the need to have robust characteristics in such systems especially after impact seems to be evident. The performance of the proposed controller is compared against standard second order impedance controller through numerical simulation studies. Finally, simulation results are provided to show the effectiveness of the proposed algorithm.
Tribological Performance Study of HVOF-Sprayed Microstructured and Nanostructured WC-17wt.%Co Coatings
Authors: Saha Gobinda C. , Mateen A. , Khan Tahir I.
Published: May 2012

Abrasive and erosive wear of components and machinery is an ongoing challenge in the oil sands industry in northern Alberta, Canada. To improve the wear resistance by increasing surface hardness of steels, heat treatments and deposition of hard layers of metal alloys (such as stellite) by fusion welding techniques are traditionally used. However, these deposition techniques are not applicable to all shapes and add considerable weight to the final component. Thermal spraying techniques such as the use of high velocity oxy-fuel (HVOF) composite coatings based on WC-Co cermet system offer better wear resistance and greater flexibility in applications. This study presents work on two feedstock powders, namely nanocrystalline and microcrystalline WC-Co cermets, with identical matrix phase content: WC-17wt.%Co. The novelty of the research is that an engineered duplex Co coated WC-17wt.%Co cermet particle designed to withstand coating spalling under elevated loads as well as to limit abrasive debridement during wear is introduced for the first time to produce a more homogeneously-dispersed coating microstructure. The engineered particle has 6wt.% of the ductile phase material mixed into the core to insure that the reinforcement WC phase is discontinuous to limit the debridement during wear, while remainder (11wt.%) of the Co is applied as a coating on the particle to improve the ductility. The mechanical properties of the overall particle are further improved by controlling the size of the reinforcing phase (WC) in the matrix (Co). This resulted in a WC-17wt.%Co particle containing a characteristic WC grain in the order of 350 nm in the core with the Co outer coating of 1–2 μm thick, making the powder particle as nanocrystalline. HVOF deposited coatings of the nanocrystalline and microcrystalline powders were examined for microhardness, fracture toughness, sliding abrasion (ASTM G133-05) and dry-sand rubber wheel abrasion (ASTM G65-04) wear performance. The wear rate under various loads and sliding distances was studied. In both the coatings, it was found that the wear rate increased with increasing applied loads, while it decreased with increasing sliding distances. 3D surface analysis of the wear tracks using atomic force microscopy (AFM) revealed two distinctive mechanisms associated with the two coatings after abrasive wear. The improved wear resistance was attributed to the higher hardness value of the nanostructured WC-17wt.%Co coating. It was also found that the nanostructured WC-17wt.%Co coating has about twice the toughness of the conventional microstructured coating counterpart. The extent of the WC decarburization and the dissolution of Co in the coatings were also studied.
Acoustical Scattering by Spherical Objects Containing Electrorheological Fluid Layers
Authors: Cai Liang-Wu , Orris Gregory J. , Calvo David C. , Nicholas Michael
Published: May 2012

In an effort to explore the mechanism to exert control over the band gap in phononic structures or acoustic metamaterials, a layer of electrorheological (ER) fluid is introduced into a spherical scatterer. The ER fluids have the capability of changing the mechanical properties from fluid-like into a solid-like material in a matter of milliseconds. It is expected that such significant changes in the material properties would afford a range of significant opportunities for tuning the band gap. In this study, numerical analysis of acoustical scattering characteristics of such scatterers in a underwater environment is explored. The ER fluid layer is encased between a solid steel core and a steel shell, which provide electrodes to electrify the ER fluid. The ER fluid, both before and after the electrification is modeled as viscoelastic solid in order to account for its capability for sustaining the shear wave. Effects of externally applied electric field on the scattering characteristics are observed.
Fatigue Strength Evaluation Methods Using Stress Distributions
Authors: Hattori T. , Yamashita M.
Published: May 2012

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ and developed a method of formulating critical stress-singularity parameter Hth for each order of stress singularity λ by utilizing critical distance stress theories (point method and line method), which can be derived from two typical strength parameters, namely, fatigue limit σw0 and threshold stress-intensity factor range ΔKth. These estimated critical Hth (λ) value agreed well with the experimentally measured value. Using these simple critical distance stress approach we estimated the fatigue strength of general stress concentration structures such as, round hole, elliptical hole, V notch and contact edge structures. Then these critical distance stress approaches are applied to estimate the size effects of structures. And the eligibility of these estimated results are confirmed by comparing these estimated results with the experimental results. Finally these estimated results and experimental results are compared with the estimated results by other researchers such as, Neuber, Siebel, Ishibashi and Heywood. And we can confirm the superiority of this critical distance stress approach.
Performance of Solar Driven Vuilleumier Cycle Heat Pump
Authors: Xie Yingbai , Li Bing , Wang Shaoheng , Tang Jiancheng
Published: May 2012

By using low grade solar energy, the utilization of heat energy can be increased more than 50%.The solar energy is cleanliness without any pollution, and can be used unboundedly. For our present energy structure is not proper, we have to use low grade energy instead of high grade energy. Vuilleumier (VM) cycle system include two Isochoric and isothermal processes [1], it has many advantages, such as low requirement for seal, low noise and pollution levels, long life and so on. This paper analyzes the performance of solar driven VM heat pump, and calculates an example of the system, points the advantages of solar-driven.
The 5-Coordinate Simultaneous NC Machining of the Vane Wheel Leaf With Cylindrical Cutter
Authors: Ran Liuhu , Yi Lou , Liu Quanhong
Published: May 2012

The concept of contact is applied into the machining of the complex surface. If the contact line along the straight line of cutter, the contact line should along the asymptotic direction of the surface being machined. For the undeveloped ruled surface, the directions of the normal vectors are different, while the directions of the normal vectors on the straight line of cylinder are the same, so that there may be some over cutting on the surface. With the theory of this paper, the best cutter postural can be determined when the contact line not along the straight line of the cutter. And further more, with the concept of third order contact, both the best cutter postural and contact direction can be determined at same time. This paper showed how to use this method for the machining of impeller leaf. This project is supposed by the natural scientific foundation of Zhejiang province, China, No. Y106047 and Y1080093.3.
Numerical Modelling of Turbulent Flow in Vortex Tube
Authors: Khazaei Hossein , Mirzaii Iman , Teymourtash Ali reza
Published: May 2012

In this paper, energy separation effect in a vortex tube has been investigated using a CFD model. The numerical simulation has been done due to the complex structure of flow. The governing equations have been solved by FLUENT™ code in 2D compressible and turbulent model. The effects of geometrical parameters have been investigated. The results have shown that the hot outlet size and its shape, does not affect the energy distribution in vortex tube and very small diameter will decrease the temperature separation.
Interaction Between Multiple Solid Objects and Bubbles
Authors: Iwata Ryuichi , Kajishima Takeo , Takeuchi Shintaro
Published: May 2012

In the present study, bubble-particle interactions in suspensions are investigated by a coupled immersed-boundary and volume-of-fluid method (IB-VOF method), which is proposed by the present authors. The validity of the numerical method is examined through simulations of a rising bubble in a liquid and a falling particle in a liquid. Dilute particle-laden flows and a gas-liquid-solid flow involving solid particles and bubbles of comparable sizes to one another (Db/Dp = 1) are simulated. Drag coefficients of particles in particle-laden flows are estimated and flow fields involving multiple particles and a bubble are demonstrated.
Material Optimization for Design Improvement of Crash Energy Absorbers
Authors: Ibrahim Hesham
Published: May 2012

Crash energy absorbers in the form of thin walled tubes play a significant role in mitigating the harmful effects of frontal vehicles accidents on occupants. Specific energy absorbed (SEA), which is the ratio of impact energy absorbed to mass, is usually used to evaluate the efficiency of crash energy absorbers. A good design of a crash energy absorber must maximize the amount of impact energy that can be absorbed with a certain weight. The formal approach that has been used to improve the design of crash energy absorbers is to employ optimization to search for the optimum thickness distribution that maximizes SEA. This approach can be conceptualized as searching the design space in only one dimension (thickness). In this paper, a new dimension is added to the design space (material type). The proposed approach considers the type of material as a variable. An optimum design is then found by not only searching for the optimum thickness distribution, but also by selecting the optimum material type. The approach is demonstrated to the design improvement of a crash energy absorber in the form of a thin walled tube of square cross section. Steel and magnesium have been used as the two material alternatives. Magnesium has been selected due to its low density that had made it a promising candidate for use as a structural material in the automobile manufacturing. The results have shown that following the proposed technique, SEA has been increased by 54% compared to the value obtained through following the formal design optimization approach.
Use of Parametric Resonance, Subharmonics and Wavelet in Diagnostics of a Breathing Crack on a Two-Disc Balanced Rotor in Torsion
Authors: Alugongo Alfayo A.
Published: May 2012

A diagnostic model of a crack in macro state based on analysis of parametric resonance and a wavelet transform is proposed in this paper. Parametric resonance and sub-harmonics are deliberately adopted into the model and treated by a Harmonic Wavelet. The model is considered for analysis of torsional vibration. A parallel and suitable harmonic time series is derived to simulate the dynamics of the crack and consequently the influence of breathing on the system. The model is analytically demonstrated to be good for investigating a balanced cracked rotor in torsional vibration.
A Rapid Computational Method for Reducing the Search Space Required in Nuclear Reactor Optimization
Authors: Osborne Andrew G. , Deinert Mark R.
Published: May 2012

Reactor optimization is central to increasing the efficiency of nuclear fuel cycles and critical for making meaningful comparisons between different design options. Optimization algorithms work by generating trial parameter sets which can be used as inputs to reactor physics models. Unfortunately, many reactor physics codes require substantial CPU time, making optimization of large parameter sets impractical. We have developed a method for finding optima within an N-dimensional parameter space using a fast, flexible reactor physics model that is capable of performing fuel burnup calculations on the order of once per second. Global optima found in this way can then be verified using a high fidelity reactor physics code. We demonstrate our approach by considering a simple fuel pin pitch optimization for a light-water reactor, and we find our code executes in 5 minutes. Repeating this approach using a high-fidelity Monte Carlo simulation requires approximately 15 days of runtime by contrast.
Minimum-Order System Identification by Subspace Method and Frequency-Domain Least-Squares Approximation for Vibration Isolation Tables
Authors: Hoshino Yohei , Kobayashi Yukinori , Chinda Hiroshi , Takahashi Masaki
Published: May 2012

A system identification technique to obtain the minimum-order model for a vibration isolation table is studied in this paper. The vibration isolation table is supported by four pneumatic actuators at corners of the square rigid table. A 3DOF mathematical model of the vibration isolation table is constructed. The regulator for the pneumatic actuator is driven by a stepping motor. Proposed procedure is described as follows: First, the state space model is identified from input-output data by subspace method. Next, the low-order curve fitted model is calculated by Frequency-Domain Least-Squares Approximation (FDLSA). And then, the characteristic eigenvalues near the eigenvalues of FDLSA model is picked out from the N4SID model, and the minimum-order system that has the characteristic eigenvalues of N4SID model is reconstructed. And the procedure can be fully automated. Availability and usefulness of this approach is illustrated by experiments.
Flow of a PTT Fluid Through Planar Contractions: Vortex Inhibition Using Rounded Corners
Authors: Khodadadi Yazdi M. , Ramazani S. A. A. , Hosseini Amoli H. , Behrang A. , Kamyabi A.
Published: May 2012

Contraction flow is one of important geometries in fluid flow both in Newtonian and non-Newtonian fluids. In this study, flow of a viscoelastic fluid through a planar 4:1 contraction with rounded corners was investigated. Six different rounding ratios (RR = 0, 0.125, 0.25, 0.375, 0.438, 0.475, 0.488) was examined using the linear PTT constitutive equation at creeping flow and isothermal condition. Then the resulting PDE set including continuity, momentum, and PTT constitutive equations were implemented to the OpenFOAM software. The results clearly show vortex deterioration with increasing rounding diameter, so that when rounding corner exceeds a critical value, the vortex disappears completely. This phenomenon was also observed at different upstream widths. Furthermore, by increasing rounding diameter, the diminishing vortex approaches to the re-entrant corner.
On the Friction Coefficient in the Numerical Simulation of Tidal Wave Propagation
Authors: Song Z. Y. , Cheng C. , Xu F. M. , Kong J.
Published: May 2012

Based on the analytical solution of one-dimensional simplified equation of damping tidal wave and Heuristic stability analysis, the precision of numerical solution, computational time and the relationship between the numerical dissipation and the friction dissipation are discussed with different numerical schemes in this paper. The results show that (1) when Courant number is less than unity, the explicit solution of tidal wave propagation has higher precision and requires less computational time than the implicit one; (2) large time step is allowed in the implicit scheme in order to reduce the computational time, but the precision of the solution also reduce and the calculation precision should be guaranteed by reducing the friction factor: (3) the friction factor in the implicit solution is related to Courant number, presented as the determined friction factor is smaller than the natural value when Courant number is larger than unity, and their relationship formula is given from the theoretical analysis and the numerical experiments. These results have important application value for the numerical simulation of the tidal wave.
Teaching the Concept of Bernoulli Equation Using Particle Image Velocimetry (PIV)
Authors: Goharzadeh Afshin , Molki Arman , Wang Liang , Rodgers Peter , Bojanampati Shrinivas
Published: May 2012

Particle Image Velocimetry (PIV), a state-of-the-art flow visualization technique, is used in this paper to demonstrate the concept of the Bernoulli equation which is one the oldest and most widely used equations in fluid mechanics. The experiment is based on the venturi effect to permit application of the Bernoulli equation to a laboratory scale test facility. The experimental set-up consists of a horizontal, straight transparent pipe with a venturi tube (contraction and expansion of the pipe diameter). Both water and air pipe flows are characterized. Students are required to measure and predict the average velocities and pressure upstream and downstream of the expansion region, using combined Bernoulli and Continuity equations. The averaged velocities are obtained using a flowmeter and compared with their corresponding two dimensional velocity distribution measured by the PIV system. Pressure difference over the expansion is measured using wall mounted static pressure taps and compared with predicted quantities. The paper includes the cost of the experimental setup and various teaching strategies.
Numerical and Experimental Investigations on Mini Channel Liquid Metal Coolers for Power Semiconductor Devices
Authors: Tawk M. , Avenas Y. , Kedous-Lebouc A. , Petit M.
Published: May 2012

The need to adopt new cooling techniques arouse because of the continuous increase in power dissipation of electronic parts and systems. Due to the low thermal conductivity of classical liquids (water, alcohols, dielectric fluid, etc.), in many cases, the standard liquid cooling techniques cannot achieve the required cooling performances. This paper deals with power semi conductor devices (IGBT, MOSFET or diodes) cooling. The major problem of those power components is that they can easily dissipate several hundreds W.cm−2. Thus their cooling needs very high heat transfer coefficients. Therefore we introduce the use of liquid Ga alloys whose thermal conductivity (approx. 28Wm−1K−1) is 40 times greater than thermal conductivity of water. In this paper a numerical modeling and an experimental study of liquid metal mini channel coolers are presented. In the experimental cooling loop the working fluid (Ga alloy) is moved via an electromagnetic pump. The values of the convection coefficient obtained by the numerical model are compared with the correlations founded in the bibliography and the experimental data.
Experimental Characterization of EHD Flow in an Electrostatic Air-Oil Droplets Separator Using Particle Image Velocimetry
Authors: Kong Xiangling , Alshehhi Mohamed , Goharzadeh Afshin , Shooshtari Amir , Dessiatoun Serguei , Ohadi Michael
Published: May 2012

In the present work, results of electrohydrodynamic (EHD) flow field in a wire-plate air-oil droplets electrostatic separator under positive polarity are presented. Using Particle Image Velocimetry (PIV), the structure of EHD flow under fully developed primary laminar gas flow is investigated and corresponding flow patterns are studied. Velocity distribution results show that the transverse velocity induced by EHD flow depends significantly on applied voltage and the cross-section plane position of the separator. Detailed transverse velocity distribution profiles under different ratio between electrostatic force and inertial force of droplets (Ehd/Re2) are presented. Oscillating jets are observed under a relatively low Ehd/Re2 ∼ 4 and counter rotating vortices around the wire for large Ehd/Re2 > 90 are characterized in this experiment. Contrary to EHD flow patterns for fine solid particles, no von Karman vortex was observed downstream of the charged electrode wire.
Cohesive Model in Prediction of Multi-Axial Fatigue
Authors: Jha Deepak K. , Banerjee Anuradha
Published: May 2012

A fatigue failure model for life assessment of a structure that incorporates the stress-state dependence and irreversible nature of fatigue damage is presented. In the frame work of cohesive zone model, a stress state dependent traction separation law for plane strain is taken to represent an undamaged ferritic steel. The evolution of damage has two additional fatigue parameters: a stress and a length parameter. Initially a parametric study is done to show that the model is able to reproduce a typical uniaxial fatigue response to stress based cyclic load, that of a stress-life curve and reduction in life due to positive mean stress. The effect of the cohesive fatigue parameters on the characteristics of the stress-life curve is then established. The model is further applied for a range of sinusoidally varying in-phase stress states which are characterised by a fixed bi-axiality ratio. The initiation and growth of damage is shown to be more rapid for higher bi-axiality. Except for stress amplitudes in which the lower bi-axiality case has conditions close to monotonic failure, the effect of bi-axiality is shown to be detrimental to the life expectancy of the material as observed in available experimental literature.
Plastic Flow Establishment in Circular Pipes Under the Effect of a Magnetic Field
Authors: Stockle Juan S. , Letelier Mario F. , Siginer Dennis A. , Maria Jesus A.
Published: May 2012

In many biological, chemical and industrial applications the time for discharging a pipe in a process is very important in order to obtain optimal mixing. Particulary in the case of stationary rate processes it may mean lower cost and improved optimization. In this paper a new method to compute the velocity profile in established plastic flow in circular pipes under the effect of a magnetic field is presented. Results are presented for a variety of pressure gradients and yield stresses for different values of the Hartmann number.
Finite Element Analysis of a Thin Walled Composite Wing by Including Warping Effects
Authors: Ozdemir Ozgumus Ozge , Durmaz Seher , Kaya Metin Orhan
Published: May 2012

The purpose of the present paper is to develop a finite element code to model a thin-walled composite beam. The beam is modeled as a thin-walled composite beam with a single-cell, rectangular cross-section featuring both CAS and CUS lay-up configurations. Analytical and finite element formulations of the flapwise bending, chordwise bending and torsional displacements of the beam are derived. Effect of the ply orientation on the natural frequencies is investigated and it is noticed that the obtained results are in good agreement with the ones in open literature.
Optimum Design of Fibre Orientation Angles in Composite Laminate Plates for Minimum Thickness
Authors: Khandan Rasoul , Noroozi Siamak , Sewell Philip , Vinney John , Ramazani Mohammad Reza
Published: May 2012

Previous studies have shown that composite fibre orientation angles can be optimised for specific load cases such as longitudinal or in-plane loading. However, the methodologies utilised in these studies cannot be used for general analysis of such problems. This research presents a methodology whereby the thickness of laminated composite plates is minimised by optimising the fibre orientation angles for different load cases. Therefore, the effect of transverse shear forces is considered in this study. Simulated annealing (SA), which is a type of stochastic optimisation method, is used to search for the optimal design. This optimisation algorithm has been shown to be reliable as it is not based on the starting point and it can escape from the local optimum points. In accordance with the annealing process where temperature decreases gradually, this algorithm converges to the global minimum. In this research, the Tsai-Wu failure and maximum stress criteria for composite laminate are chosen. Tsai-Wu failure is operationally simple and readily amenable to computational procedures. In addition, this criterion shows the difference between tensile and compressive strengths clearly, through its linear terms. By applying two failure criteria at the same time the results are more reliable. Finally, the numerical results are obtained and compared to the results of previous research with specific loadings to validate the methodology. Additionally the ply angles of composite plate are optimised by considering the effect of transverse shear force and induced twist angles.
An Array of Nitrogen Producing Cells for Microthrusters
Authors: Godin Kyle A. , Huang Po-Hao A.
Published: May 2012

Presented here is a method for selectively depositing solid sodium azide (NaN3) upon a substrate. An array of nitrogen producing cells fabricated using this method can be sequentially activated to produce small quanta of nitrogen gas. This is of interest in creating microscale thrusters for positioning and aligning pico-, nano-, and micro-satellites, which require minimum thrust impulses on the order of 10μN·s and thrust levels of 1–10mN. A 1cm × 1cm thruster chip is expected to provide 34mN·s of thrust impulse.
Designing Gear-Shift Pattern for an Electric Vehicle to Optimize Energy Consumption
Authors: Rahimi Mohammad A. , Salehi Rasoul , Alasty Aria
Published: May 2012

In this paper optimization of energy consumption in an electric vehicle is presented. The main idea of this optimization is based on selecting the best gear level in driving the vehicle. Two algorithms for optimization are introduced which are based on fuzzy rules and fuzzy controllers. In first algorithm, fuzzy controller simulates energy consumption in different gear levels, and chooses the optimum gear level. While in second method, fuzzy controller detects the optimum gear level by measuring the vehicle’s average speed and acceleration. To investigate the performance of these controllers, a model of TOSAN vehicle is developed and the controllers outputs are checked in simulation of TOSAN being driven within drive cycles in the city of Tehran. It is shown that both algorithms are able to improve efficiency in typical city driving cycles.
A Lumped Parameter Vibration Model Developed Based on a Realistic Kinematic Description of the Hand-Arm System
Authors: Pattnaik Shrikant , Kim Jay
Published: May 2012

Prolonged exposure of hand to vibration causes vascular, neurological and musculoskeletal abnormalities, which are collectively known as hand-arm vibration syndrome (HAVS). A significant number of construction workers, miners and even dentists are affected by HAVS. The precise mechanism or pathogenesis of the syndrome is still not clearly understood. Accurate analysis of hand-arm vibration response is very difficult due to the complexity of the hand-arm structure such as redundancy of the musculo-tendon unit, active participation from central nervous system, inherent non-linearity and heavy damping effect. Various types of lumped parameter models have been developed, typically by matching response characteristics of the model with the measurement. Not being based on the actual physics of the hand-arm, such a model has limited applications such as qualitative, relative analysis of the hand-arm response. A new lumped parameter model is developed in this work retaining as much actual kinematic characteristics of the hand and arm system as possible. The model includes descriptions of relevant musculo-tendon systems and the effect of the gripping force to enable calculation of the forces transmitted through the musculo-tendon system and joints.
Numerical Study of Film Cooling Scheme on a Blunt-Nosed Body in Hypersonic Flow
Authors: Kim Sung In , Hassan Ibrahim
Published: May 2012

In hypersonic flights, the prediction of aerodynamic heating and the construction of a proper thermal protection system (TPS) are significantly important. In this study, the method of a film cooling technique, which is already the state of the art in cooling gas turbine engine, is proposed for a fully reusable and active TPS. Effectiveness of the film cooling scheme to reduce convective heating rates for a blunt nosed spacecraft flying at Mach number 6.56 and 40 degree angle of attack is investigated numerically. The inflow boundary conditions used the standard values at an altitude of 30 km. Computational domain consists of infinite rows of film cooling holes on the bottom of a blunt-nosed slab. Laminar and several turbulent calculations have been performed and compared each other. The influence of blowing ratios on the film cooling effectiveness is investigated. The results exhibit that the film cooling technique could be an effective method for an active cooling of blunt-nosed bodies in hypersonic flows.