bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Emission Assessment of FRP Composites Delamination
Authors: Hajikhani Milad , Ahmadi Najafabadi Mehdi , Refahi Oskouei Amir , Sharifi Amir , Heidari Mohammad
Published: January 2011

Delamination is one of the most common failure modes of composite materials. It may result from imperfections in the production process or may be caused by service life conditions, such as impact by foreign objects. The presence of delamination in the composite material may reduce the overall stiffness. The geometrical parameters, material properties, loading conditions and mid-plane layouts are important factors which effect the initiation and growth of delamination. In this paper different types of mid-plane layouts are used. Test set up involved double cantilever beam to detect delamination of mode I. Experimental results have obtained from monotonic tests and have been shown good agreement between crack-growth data. Previous studies made on different composite materials have allowed us to set up a schematic model of acoustic emission. At current work, both different levels of absolute energy of acoustic emission signals (Ecum) and mechanical energy (GIcum) are identified for different mid-plane layouts. The experimental method has been applied to this work and allows continuous and alive monitoring of damage growth through delamination tests. Finally, used method by acoustic emission to obtain GIc was not in good agreement with ASTM methods and it is needed to find a new method based on acoustic emission to obtain GIc.
Look-Ahead NURBS-PH Interpolation for High Speed CNC Machining
Authors: Moetakef Imani Behnam , Ghandehariun Amirmohammad
Published: January 2011

Various methods for parametric interpolation of NURBS curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a jerk-limited module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X-Y table confirm that the developed method improves tracking and contour accuracies significantly when compared to previously proposed adaptive-feedrate and curvature-feedrate algorithms.
Walking Gait of a Single-Tetrahedral Robot: Design, Modeling and Implementation
Authors: Izadi M. , Mahjoob M. J. , Soheilypour M.
Published: January 2011

A Tetrahedral Walker (TET Walker) is a robot made to extend space exploration into inaccessible regions. The motion of the tetrahedron is due to the changes in the struts length. This work presents the implementation and walking gait design of a tetrahedron walker robot. A model for walking gait of the robot is developed. A comparison is then made between different computer simulations of the gaits. A navigation algorithm for walking gait of this type of robots is also developed and discussed.
Finite Element Analysis of Full Penetration and Fillet Welds in Cantilever Beams
Authors: Mirzaali M. , Sattarifar I.
Published: January 2011

Beams in engineering structures are mainly jointed together by welding. In general, they are imposed to static and dynamic loads. Thus, analyses of welds are very important to study their behaviours. In this study finite element analyses of welds in the cantilever box beams are performed using the ANSYS program. Two different types of weld are considered; full penetration welds and fillet welds. Stress distributions in different paths are calculated for both types. It is shown that using of full penetration welds in a structure leads to safer welds than using of fillet welds. In addition, effects of different parameters such as fillet weld leg, weld material, thickness of cantilever box beam, and amount of its penetration in beam are studied.
A Newton-Krylov Type Algorithm for an Incompressible Navier-Stokes Solver Using Pseudo Compressibility Technique
Authors: Nejat Amir , Jalali Alireza , Sharbatdar Mahkame
Published: January 2011

A Newton-Krylov type algorithm is designed and implemented for a pseudo compressible Navier-Stokes solver in an incompressible Cavity flow. Both GMRES and BICGSTAB (Krylov-subspace) techniques are employed for the solving the linear solver resulting from the residual linearization. ILU-0 and ILU-1 and Thomas algorithm are used for preconditioning. The results show promising convergence acceleration especially for the GMRES/ILU-1 case compared to the classic Approximate Factorization method.
Coherent Flame Model to Predict Formation Pollutants in Turbulent Premixed Flame
Authors: Bentebbiche Abdelhalim , Veynante Denis
Published: January 2011

The objective of this work is to analyze and to model the turbulent flames in the context of coherent flame model. We present a detailed description of equations and the flamelet regimes in turbulent premixed flame. A surface density models proposed here represents a good issue for numerical simulation. Extension of coherent flame model and homogenous stilled reactor model is proposed to consider the dynamics behavior of flame and pollutants formation. From the results of this work it is concluded that the coherent flame model allows surpassing difficulties of the turbulent reactive flow modeling. Calculations based on a semi-global kinetic scheme and flamelet formulation combined with a well stirred reactor analysis of the burnt gases are used and provided reasonably accurate values of CO and NO formation. Also, we have observed that CO is formed near the reaction zone (front flame) but emission of CO2, H2O and NO are formed in the hot gases.
Variational Principles for the Stability Analysis of Multi-Walled Carbon Nanotubes Based on a Nonlocal Elastic Shell Model
Authors: Asghari Mohsen , Rafati Jacob
Published: January 2011

The nonlocal continuum theories are capable to reflect the small length characteristic of nanostructures. In this work, variational principles are presented for the stability analysis of multi-walled carbon nanotubes under various mechanical loadings based on the nonlocal elastic Donnell’s shell by the semi-inverse method. In this manner, a set of proper essential and natural boundary conditions for each layer of the multi-walled nanotube is derived.
An Aerodynamic Design and Optimization of a Heavy Truck for Drag Reduction
Authors: Selenbas Bugra , Gunes Hasan , Gocmen Kenan , Bahceci Uygar , Bayram Bertan
Published: January 2011

In this paper, a computational fluid dynamics (CFD) study is carried out in an effort to design and optimize the cabin geometry and its various parts for drag reduction that include the side deflectors, the mirrors and the sun visor. For the validation of computational results, an experimental investigation using a 1/5 scale truck model has been carried out in a wind tunnel. The aerodynamic force as well as the surface-pressure point measurements carried out at selected wind speeds. The flow visualizations using smoke and oil were also performed. With the experimental results, the basic characteristics of flow over the cabin geometry (including the flow separation locations) are compared with the CFD results. The both steady and unsteady CFD simulations are performed. The comparison of steady/unsteady results reveals that the time-averaged unsteady flow characteristics are practically the same as the steady calculations for design purposes. In addition to CFD simulations involving the actual (real) truck cabin geometry, for the optimization of the specific cabin accessories, (e.g., side deflectors and mirrors), a generic truck model is also used for CFD analyses. The optimized side deflector geometry (e.g., the ratio of the air inlet and outlet area), and the optimum form of the mirrors for drag reduction have been realized by numerical investigations.
Experimental Study of Natural Gas Fuel Temperature Influence on Radiation Enhancement and Emission
Authors: Javadi S. Mohammad , Nikoueeyan Pourya , Moghiman Mohammad , Feyz M. Ebrahim
Published: January 2011

The enhancement of the flame radiation in gas fueled burners not only improves the thermal efficiency, but also can suppress the rate of NO emission due to reducing the flame temperature. In this experimental investigation, the effect of inlet gas temperature on the flame radiation intensity and the rate of NO formation are studied. To serve this aim, with increasing the temperature of inlet methane to the burner up to 310°C, the variations of CO and NO level in exhaust gases and also the exhaust gas temperature are recorded by gas analyzer device. In each case, the flame radiation intensity was also measured by a photovoltaic module. The results revealed that by increasing the inlet gas temperature up to 250°C, the NO concentration and the exhaust gases temperature are raising. But when the inlet gas temperature exceeds from 250°C and reaches to 310°C, the flame luminosity gradually increases which results in 70 percent growth in flame radiation and 10 percent drop in exhaust gas temperature. The results of the preheating of inlet air also show the same behavior.
Potential for Primary Energy Savings in Telecommunication Centers Through Free Cooling
Authors: Baccino Giorgia , Verda Vittorio , Rossi Gianni , Arena Alessandra , Bernardini Vincenzo , Suino Diego
Published: January 2011

Telecommunication sector is nowadays among the largest electricity consumers. This is fast growing thanks to the increase in the power density of the installed devices: traditional power densities were below 1 kW/m2, while in the case of latest data centers there are power densities of about 11 kW/m2 [1]. Air conditioning represents a significant contribution in the energy balance, as the devices must operate in appropriate ambient conditions. In this paper the potential reduction of primary energy consumption that can be achieved through with free cooling and adiabatic free cooling is examined. Due to the specific requests for the operation (standard ETSI) the analysis must be conducted considering realistic annual temperature and humidity profiles, not only average profiles. For this reason, a probabilistic climate model is developed and tested. Moreover, the effects due to the configuration of the various devices and the characteristics of fresh air supply and extraction systems are evaluated and accounted. This is obtained using both computational and experimental analysis. Several areas in Mediterranean countries are considered.
Study of Shape Memory Effect in NiMnGa Magnetic Shape Memory Alloy Single Crystals by Incremental Modeling
Authors: Khajehsaeid H. , Naghdabadi R. , Sohrabpour S.
Published: January 2011

Magnetic Shape Memory Alloys (MSMAs) are a category of active materials which can be excited by magnetic field. These alloys have been used in sensor and actuator applications recently. MSMAs possess special properties such as large magnetic field-induced strains (up to %10) and high actuation frequency (about 1kHz), while ordinary shape memory alloys can’t act in frequencies above 5Hz due to the time involved with heat transformation. In this paper, MSMAs are modeled by an incremental modeling approach which utilizes different secant moduli for different parts of stress-strain curve. Furthermore, stress-strain curve of MSMAs is approximated using an analytical expression. The incremental model is used in predicting magnetic-field-induced strain either under the influence of mechanical stress or in the absence of stress. In this study, magnetic field equivalent stress is considered to be dependent on the orientation of martensitic variants during variant reorientation while it has been supposed to be a constant value in the previous works. This way, calculation of the magnetic field equivalent stress is modified to predict the superelastic behavior of MSMAs under constant field as well as variable stress. Results obtained from the incremental model are compared with experimental observations as well as other theoretical results available in the literature. This comparison shows a good correlation between the results of the model and experimental observations.
Friction Model for an Intermediate Orientation and Density of Fibres in Dry Cutting of Composites
Authors: Mkaddem Ali , El Mansori Mohamed
Published: January 2011

This paper discusses a numerical analysis of polymer-matrix composites cutting. Focus is put on the sensitivity of friction to both the fibre orientation and fibre volume fraction. Firstly, a theoretical model based on decomposition technique was proposed for predicting the evolution of friction coefficient with the parameters considered. Secondly, the numerical model was built, for orthogonal cutting configuration and equivalent homogeneous material assumption, using Abaqus/Explit FE code. For enhancing the simulation of chip formation, adaptive mesh technique with kill element option was used in the dynamic explicit analysis. The model assumes plane stress state and orthotropic behaviour. Hashin damage model was considered for simulating the damage initiation mechanisms and material failure modes. The results showed an increase of both the thrust and cutting force with fibre volume fraction. The predictions confirmed the high dependency of chip formation on reinforcement percentage. The advantage of adaptive mesh on predicting the damage localization was further proved.
On the Avoidance of Friction Induced Vibrations by Structural Optimization
Authors: Spelsberg-Korspeter Gottfried
Published: January 2011

Rotors show very rich dynamical behavior especially when friction is involved. Due to the interaction of nonconservative, dissipative and gyroscopic forces a very interesting stability behavior can be observed. Instability of the rotor can yield severe problems, for example in the context of brakes and clutches it causes squeal, in the process of paper calendering the duration of the rollers is decreased substantially. This paper deals with the problem of how to design a rotor such that it is robust against friction induced vibrations using structural optimization. The problem is addressed using discrete and continuous models for disk brake squeal. It is shown that a proper design of the brake rotor can passively suppress squeal without introduction of additional damping into the system. Many of the qualitative results carry over to other problems of friction induced vibrations in rotors.
Identification of an IPMC Actuator Model Using Incorporating a Nonlinear With Linear Least Squares Method
Authors: Vahabi Meisam , Mehdizadeh Emad , Kabganian Mansour , Barazandeh Farshad
Published: January 2011

Ionic polymer metal composite is a class of electro-active polymers that are becoming more significant as smart actuators due to their large bending deflection, mechanical flexibility, low excitation voltage, low density, and ease of fabrication process. These properties make IPMCs suitable for a variety of application fields such as robotics, aerospace, biomedicine etc. There are a lot of linear and nonlinear models which describe actuation properties of IPMC. These models’ parameters may be obtained by various identification methods in which only a very few are nonlinear. Besides, there has been no model that explains all the physical phenomena associated with this actuator. In this paper, a new identification method is presented which incorporates a nonlinear with linear least squares method. This method is implemented on a nonlinear model. This model in comprised of two steps; as a first step, nonlinear relationship between the absorbed current and the voltage applied and as a second step relationship between the absorbed current and the blocked force are determined. The first and second steps are identified using a nonlinear and linear least squares methods, respectively.
The Effect of Fiber Arrangement on Stress Concentration Around a Pin in a Laminated Composite Joint
Authors: Shishesaz Mohammad , Attar Mohammad Mehdi , Robati Hosein
Published: January 2011

This paper analytically investigates the effect of fiber arrangements on stress distribution around a pin joint in a laminated composite. It is assumed that all fibers lie in one direction while loaded by a force po at infinity. According to the shear lag model, equilibrium equations are derived for two types of fiber arrangements. In the first model, a square arrangement is selected for the fibers, while in the second; a hexagonal arrangement is used to deduce the equilibrium equations. Upon proper use of boundary and boundness conditions, stress and displacement fields are derived within the laminate and their peak values are determined on the compressive side of the pin periphery. The effect of pin diameter on stress concentration around the pin is well examined. The presence of the pin on shear stress distribution in the laminate is also examined for various pin diameters. According to the results, a square arrangement of fibers results in smaller values of stress concentrations around the pin, as compared to those of a hexagonal arrangement. The pin position and its diameter shows to have noticeable effect on both normal and shear stresses developed within the laminate, as well as pin surrounding.
Analysis of Free Nonlinear Vibration Behavior for Curved Embedded Carbon Nanotubes on Elastic Foundation
Authors: Rezaee M. , Fekrmandi H.
Published: January 2011

Carbon nanotubes (CNTs) are expected to have significant impact on several emerging nanoelectromechanical (NEMS) applications. Vigorous understanding of the dynamic behavior of CNTs is essential for designing novel nanodevices. Recent literature show an increased utilization of models based on elastic continuum mechanics theories for studying the vibration behavior of CNTs. The importance of the continuum models stems from two points; (i) continuum simulations consume much less computational effort than the molecular dynamics simulations, and (ii) predicting nanostructures behavior through continuum simulation is much cheaper than studying their behavior through experimental verification. In numerous recent papers, CNTs were assumed to behave as perfectly straight beams or straight cylindrical shells. However, images taken by transmission electron microscopes for CNTs show that these tiny structures are not usually straight, but rather have certain degree of curvature or waviness along the nanotubes length. The curved morphology is due to process-induced waviness during manufacturing processes, in addition to mechanical properties such as low bending stiffness and large aspect ratio. In this study the free nonlinear oscillations of wavy embedded multi-wall carbon nanotubes (MWCNTs) are investigated. The problem is formulated on the basis of the continuum mechanics theory and the waviness of the MWCNTs is modeled as a sinusoidal curve. The governing equation of motion is derived by using the Hamilton’s principle. The Galerkin approach was utilized to reduce the equation of motion to a second order nonlinear differential equation which involves a quadratic nonlinear term due to the curved geometry of the beam, and a cubic nonlinear term due to the stretching effect. The system response has been obtained using the incremental harmonic balanced method (IHBM). Using this method, the iterative relations describing the interaction between the amplitude and the frequency for the single-wall nanotube and double-wall nanotube are obtained. Also, the influence of the waviness, elastic medium and van der Waals forces on frequency-response curves is researched. Results present some useful information to analyze CNT’s nonlinear dynamic behavior.
Novel Empirical Relations for Accurately Estimating the Eigenfrequencies of Cantilever Beams With Linear Width Variation
Authors: Joglekar M. M. , Joglekar D. M.
Published: January 2011

Dynamic analysis of variable cross-section beams has been the focus of numerous investigations because of its relevance to aeronautical, civil, and mechanical engineering. In this article, we analyze the case of isotropic Euler-Bernoulli cantilever beams having linearly varying width, constant thickness, and classical boundary conditions. The linear width variation is characterized by a taper parameter, which can be varied between zero and unity. The free transverse vibration problem is cast as a fourth order Sturm-Liouville eigenvalue problem, and numerically solved by using the differential transform technique. A five-parameter exponential fitting model is used to develop novel empirical relations to estimate the first five eigenfrequencies as functions of the taper parameter. The proposed empirical relations are able to predict the eigenfrequencies with an error of less than 0.1% with respect to the simulated values, which make them useful for practical design applications. Using the proposed empirical relations, we then examine the sensitivity of each eigenfrequency to the variation in taper parameter near zero and near unity.
Design of a Low-Cost Thermoacoustic Electricity Generator and Its Experimental Verification
Authors: Yu Zhibin , Jaworski Artur J. , Backhaus Scott
Published: January 2011

This paper describes the design and testing of a low cost thermoacoustic generator. A travelling-wave thermoacoustic engine with a configuration of a looped-tube resonator is designed and constructed to convert heat to acoustic power. A commercially available, low-cost loudspeaker is adopted as the alternator to convert the engine’s acoustic power to electricity. The whole system is designed using linear thermoacoustic theory. The optimization of different parts of the thermoacoustic generator, as well as the matching between the thermoacoustic engine and the alternator are discussed in detail. A detailed comparison between the preliminary test results and linear thermoacoustic predictions is provided.
A Methodological Approach to Radical Technological Changes and Improvements in Electron Beam Technology
Authors: Cavallaro Marco , Moroni Giovanni , Zaeh Michael , Lutzmann Stefan , Kahnert Markus
Published: January 2011

Predicting of the optimal machining conditions for experimental results and dimensional accuracy plays an important role in process planning. In addition, whenever there is a new unknown process, great importance has to be placed on the estimation of all operative conditions with rational and logical planning methodologies. The aim of this work is to obtain feasible conditions for Electron Beam (EB) technology, using a welding machine, which is then converted for additive manufacturing processes. At the beginning of the research there was a state of uncertainty about the influencing parameters and the use of EB for rapid manufacturing process; a multi-disciplinary and integrated methodology was then performed in order to carry out the work. The proposed methodology is composed of several techniques, including a method to support multi-decision making problems and a statistical approach.
Investigation of Sectoral Scanning in Selective Laser Melting
Authors: Yasa Evren , Deckers Jan , Kruth Jean-Pierre , Rombouts Marleen , Luyten Jan
Published: January 2011

Selective laser melting (SLM), a powder metallurgical (PM) additive manufacturing (AM) technology, is able to produce fully functional parts directly from standard metal powders without using any intermediate binders or any additional post-processing steps. During the process, a laser beam selectively scans a powder bed according to the CAD data of the part to be produced and completely melts the powder particles together. Stacking and bonding two-dimensional powder layers in this way, allows production of fully dense parts with any geometrical complexity. The scanning of the powder bed by the laser beam can be achieved in several different ways, one of which is island or sectoral scanning. In this way, the area to be scanned is divided in small square areas (‘sectors’) which are scanned in a random order. This study is carried out to explore the influence of sectoral scanning on density, surface quality, mechanical properties and residual stresses formed during SLM. The experiments are carried out on a machine with an Nd:YAG laser source using AISI 316L stainless steel powder. As a result of this experimental study, it is concluded that sectoral scanning has some advantages such as lower residual stresses and better surface quality. However, the selection of parameters related to sectoral scanning is a critical task since it may cause aligned porosity at the edges between sectors or scanned tracks, which is very undesired in terms of mechanical properties.
A Lattice Boltzmann Simulation of Cross-Flow Around Four Cylinders in a Square Arrangement
Authors: Abolfazli Esfahani J. , Vasel Be Hagh A. R.
Published: January 2011

The purpose of the present work is simulating cross flow around four cylinders in a square configuration by using a Lattice Boltzmann method. The effective parameters such as Reynolds number and spacing ratio L/D are chosen on the basis of former researches of other authors which have been done experimentally or by using traditional numerical schemes like finite volume method to provide the opportunity for comparing Lattice Boltzmann results with those obtained from experimental and CFD studies. Hence, the Reynolds number is set at Re = 100 and the spacing ratio is chosen to be 1.5, 2.5, 3.5, 4.5. It is shown that final results such as flow pattern, velocity and vorticity field are in accordance with those obtained by former researchers via experimental efforts or by use of finite volume method. This good agreement beside other important qualities such as efficient code, not having mesh tangling associated with other common numerical approaches, high convergence speed and nondimensional velocity and pressure field indicate this fact that in comparison with other numerical methods, Lattice Boltzmann method is very capable of analyzing a broad variety of fluid flows.
Empirical Comparison of Sliding Friction and Wear Behaviors of Gray and White Cast Iron
Authors: Hashemi Mehdi , Ghajar Rahmatollah
Published: January 2011

In this paper, sliding friction and wear behaviors of gray cast iron A35 and white cast iron manufactured by quenching from the same cast iron in water were studied and compared by employing pin-on-disk wear tests. Microstructure of the worn surfaces before and after the wear tests were investigated by optical microscope observations. These images show that flakes separated from the surface in gray cast iron due to delamination process, while in white cast iron, the separation of materials from its surface is in the form of powder. In addition, the gray cast iron had higher graphite volume fraction with Type-A graphite flake morphology. The results show that white cast iron has less rate of wear than gray cast iron due to the higher hardness. However, gray cast iron because of presenting graphite flakes in its surface (lubricant property) has lower average coefficient of friction.
Application of Modified Discrete Ordinates Method With the Concept of Blocked-Off Region Method to Radiative Heat Transfer Problems in Irregular Geometries
Authors: Amiri H. , Mansouri S. H. , Safavinejad A.
Published: January 2011

The discrete ordinates method (DOM) for the solution of radiative heat transfer problems have received significant attention and development owing to their good compromise between accuracy, flexibility and moderate computational requirement. However, the DOM suffers from the ray effects related to the discretization of the angular distribution of the radiation intensity. The modified discrete ordinate method (MDOM) proved to significantly mitigate ray effects originated from discontinuities or abrupt changes of the wall temperature. This article presents blocked-off region treatment of irregular geometries using a modified discrete ordinates method in Cartesian coordinates. The Cartesian based 2D algorithm can be used to solve radiative heat transfer in irregular geometries by dividing the region into active and inactive regions. It is easier and convenient way of handling 2D irregular geometries than to write an algorithm in curvilinear coordinates. It is capable of handling participating (absorbing, emitting and isotropic or anisotropic scattering) or non participating gray media enclosed by gray diffuse walls. Both radiative and non-radiative equilibrium situations are considered. The walls of the enclosures can have either heat flux or temperature boundary conditions. Cases with curved and obstacle and radiation shield are considered. Some test problems are considered and results are validated with the available results in the literature. Results are found to be accurate for all kinds of situations.
CFD Modelling of Gear Windage Losses: Two Phase Modelling Using Particle Injections
Authors: Webb Thomas , Eastwick Carol , Morvan Herve´
Published: January 2011

This paper presents results for modelling two-phase flows between a rotating spiral bevel gear and a static shroud. The context behind this is a desire to use Computational Fluid Dynamics (CFD) as a tool for reducing heat-to-oil within gas turbine bearing chambers and gearboxes. This paper uses a solid model and mesh technique first presented in [1], and extends it to include visualisation techniques for two-phase flows. A single tooth model of a spiral bevel gear is used with a Discrete Particle Model (DPM) approach to simulate the presence of oil within the domain using FLUENT 12.0.16. Two different injections are used; the inlet to the shroud simulates the ingestion of a suspended mist from the chamber in which a gear is sitting, and the outer diameter of the gear simulates shedding of oil from the rotating gear onto the surface of the shroud. Variation of the injection velocities allows parameterisation of the destination trajectories and locations of the particles. Analysis of the results of particles injected at the inlet to the shrouded gear show that larger droplets are likely to hit the underside of the nose to the shroud, whereas particles of around 3.5 microns diameter or smaller, will travel further into the domain and hit the gear, or pass entirely through the shrouded region. Droplets injected from the outer diameter of the gear show little sensitivity to the initial velocity and strike the surface of the shroud radially outwards from their injection location. This strong concentration of particles hitting the shroud will provide a useful avenue for further two-phase modelling using a thin-film created with the discrete particle model.
Numerical Simulation of Turbulent Heat Transfer on a Rotating Disk With an Impinging Jet
Authors: Saidi M. H. , Karrabi H. , Avval H. B. , Asgarshamsi A.
Published: January 2011

A numerical study has been earned out to investigate the fluid flow structure and convective heat transfer due to a circular jet impinging on a rotating disk. The temperature distribution and convection heat transfer coefficient on the disk are calculated. Flow is considered to be steady, incompressible and turbulent. k-ε RNG model is used to model the turbulent flow. Two new criteria are introduced and used to evaluate the performance of cooling process which are maximum temperature difference on the disk and the average temperature of the disk. The first parameter shows the uniformity of temperature distribution in the disk and the second shows the effect of both thermo physical properties of the disk material and cooling process. In order to verify the numerical approach, results have been compared with the experimental data which shows a good agreement.
Anisotropic Elastic-Plastic Mechanical Properties of Thermally Bonded Bicomponent Fibre Nonwovens
Authors: Demirci Emrah , Acar Memis¸ , Pourdeyhimi Behnam , Silberschmidt Vadim V.
Published: January 2011

Having a unique structure, nonwoven fabrics possess distinct mechanical properties dissimilar to those of woven fabrics and composites. Anisotropic elastic-plastic mechanical properties of core/sheath type thermally bonded bicomponent fibre nonwoven textiles are computed based on manufacturing parameters and fibre properties. Initially, tensile tests are performed on nonwoven fabrics and their single fibres to assess their mechanical behaviour and obtain input parameters for the developed algorithms. Random orientation of individual fibres is introduced into the model in terms of the orientation distribution function (ODF). An algorithm, based on the Hough transform, is developed to determine the ODF and calculate the structure’s anisotropy. The nonwoven fabric is modelled as an assembly of two regions — bond points and a fibre matrix, having distinct mechanical properties. Bond points are treated as a deformable bicomponent composite material composed of the sheath material of fibres as matrix reinforced with the core material as fibres with random orientation of reinforcement. On the other hand, the fibre matrix is treated as a composite membrane structure having low stiffness in thickness direction. A second algorithm is developed to calculate anisotropic material properties of these regions based on fibre characteristics and manufacturing parameters; it can be used in numerical modelling as well as product development and optimization of nonwovens.
Boundary Drag Force Acting on an Impenetrable Nano-Particle
Authors: Karrabi H. , Kebriai M. H. , Meigounpoury M. R.
Published: January 2011

Flow over nano spheres is a fundamental problem encountered in many engineering technical problems and the motion of nano-particles is important in many technical areas, for example nano-organizms motion in aqueous media, super hydrophobic spray for coating materials, nano-capsules for detecting cancer, and additive nano-particles in oil and fuel for automotive engines. In this paper computations are performed to determine the steady flow forces acting on the stationary nano-tube for Reynolds numbers in the range of 0.1<Re<40 and 0.01<Kn<0.1 with the slip boundary condition. A single dimensionless parameter, the so-called slip number (Tr), is defined to account for the slip at the nano-particle boundary., Increasing slip causes to delay of flow separation around the nano-tube surface. Numerical results confirm that slip variations can not affect on the drag coefficient values at low Reynolds regime. At higher Reynolds number increasing slip causes to drag reduction of flow around the Nano-Tube.
Three Dimensional Friction Contact Model and Its Application in Nonlinear Vibration Analysis of Shrouded Blades
Authors: Liu Yalin , Xu Zili , Gu Weiwei , Chen Dexiang
Published: January 2011

Dry friction damping structures are simple and can be used in big range of working temperature, therefore varied kinds of friction contact damping structures have been widely used in turbomachine blades to reduce the forced vibration and improve dynamic stability. However, the dynamic analysis of such structures is still a challenging engineering task because the dry friction damping is a dynamic contact problem with complex boundary condition and strong nonlinear characteristics. A three dimensional numerical model for friction contact has been proposed to investigate the contact kinematics in the contact surfaces between adjacent blade shrouds. Microslip effects taken into account with a discretization of the contact surface with a mesh of contact elements, by altering the number of contact node can consider the effects of the area of the contact surface on forced response of shroud blade. The complex movement in the shroud contact surfaces was described by tracking the trajectory of the relative motion of the contact node. The model can consider the differences between the static friction coefficient and dynamic friction coefficient. The model has the mathematically tractable characteristic and can be easily used, and conforms to the engineering need. In order to decrease time consuming for computing the forced response, a reduced method is employed to condense all nonlinear degrees of freedom (DOF) to the nonlinear DOF on the contact surfaces, hence, iterative procedure of solution is limited in nonlinear degrees of freedoms. An alternating frequency/time domain method (AFT) which takes the advantages of both the time domain method and the frequency domain method is introduced to predict nonlinear vibration of shrouded blade systems. The developed friction model and calculated method of dynamic equation are applied to calculate nonlinear vibration for a real steam turbine blade. The effect of parameters on resonant frequency and response of the blade are investigated and discussed.
Quarter Car Ride Model and Optimization Including a Suspension Mechanism
Authors: Koray Yıldıray , So¨nmez U¨mit
Published: January 2011

In this study, a double wishbone suspension mechanism is modeled attached to a body representing a quarter-car. Quarter car models have been studied extensively in the literature using lumped parameter models usually represented as simple systems made of sprung masses, springs, dampers and unsprung masses. In reality suspension mechanisms consists of control arms, which contribute significantly to the response of the overall system. Considering more complex models system including suspension mechanism usually simulation software are used. The main purpose of this study is to derive and to develop the quarter car’s mathematical model including a suspension mechanism in matrix form, and to use this model simulating and investigating various types of studies. First a mathematical model of the double A arm suspension attached to a car mass is generated and the resulting computer simulations are obtained in MATLAB. Second the same model is created using Adams/View software to validate the mathematical model simulation results. In order to get the realistic responses of the suspension system to the road input, the spectral descriptions are used for generating artificial road profiles. Two types of optimization process are performed, one concerning the dimensional optimization of the mechanism (kinematic/geometric mechanism optimization), the other concerning the nonlinear characteristics of the suspension elements namely coil spring and viscous damper (dynamic ride optimization). In the kinematical optimization, the camber angular deviation and the roll center height are taken into account as the weighted objective function. Considering optimization of the nonlinear characteristics of the damper and the spring, the passenger comfort and the car handling measures are taken into account using ISO 2631 weighting standard. Finally, actuators are included in the model in order to increase the ride comfort by an active control scheme. Two actuators are inserted, one is under the driver seat the other is in the A arm mechanism to form an active suspension. A PID control scheme is used to increase ride comfort. These steps also show that, even though it is cumbersome to obtain the simulations of a realistic mathematical model of a commonly used system; once the simulation model is established, it is easy to perform several types of the studies at once.
Addressing Thermal Challenges in Design of Data Centres
Authors: Fakhim Babak , Nagarathinam Srinarayana , Wong Simon , Behnia Masud , Armfield Steve
Published: January 2011

Aggregation of small networking hardware has led to an ever increasing power density in data centres. The energy consumption of IT systems is continuing to rise substantially owing to the demands of electronic information and storage requirements. Energy consumption of data centres can be severely and unnecessarily high due to inadequate localised cooling and densely packed rack layouts. However, as heat dissipation in data centres rises by orders of magnitude, inefficiencies such as air recirculation causing hot spots, leading to flow short-circuiting will have a significant impact on the thermal manageability and energy efficiency of the cooling infrastructure. Therefore, the thermal management of high-powered electronic components is a significant challenge for cooling of data centres. In this project, an operational data centre has been studied. Field measurements of temperature have been performed. Numerical analysis of flow and temperature fields is conducted in order to evaluate the thermal behaviour of the data centre. A number of undesirable hot spots have been identified. To rectify the problem, a few practical design solutions to improve the cooling effectiveness have been proposed and examined to ensure a reduced air-conditioning power requirement. Therefore, a better understanding of the cooling issues and the respective proposed solutions can lead to an improved design for future data centres.
Workspace Optimization of a Six Degrees of Freedom Parallel Manipulator for Micromachining
Authors: Agaoglu Ahmet , Ciblak Namik , Safak Koray K.
Published: January 2011

This work addresses the optimization of the workspace of a six degrees of freedom parallel manipulator. In this study, The topology of the manipulator is composed of three xy-tables, symmetrically positioned on a circle on a base plane, connected by three legs to a moving platform. Kinematic composition of the manipulator is introduced and kinematic diagram is illustrated. Orientation workspace is investigated using three different orientation representations. XYZ fixed angles representation is selected considering the benefits of its visualization are considered. By using this representation, the orientation workspace is modeled and kinematic circuits of the manipulator are explored. First, optimization is performed without slider limitations. A result table is obtained based on the user defined parameters. Secondly, optimization is performed under slider limitations. The maximal orientation capability is optimized using numerical analysis. The optimized configuration of the manipulator indicates that a 330% increase in orientation capability is achieved, compared to the old configuration.
Non Destructive Testing of Low Profile Light Weight Track System
Authors: Al Nageim Hassan
Published: January 2011

The paper presents the results of the responses of a concrete trough of a new lightweight rail track system (LR55) to full scale non destructive tasting. The system which is made from three main components; low profile steel rail, elastomeric pad and prestressed concrete trough is developed for light rail transits in cities streets, which can significantly help in improving the traffic flow, reducing the traffic congestion and thus providing opportunities for minimising serious environmental problems such as level of noise, vibration and air pollutions and in this regards it can be considered as environmentally friendly means of transport. A mathematical model was developed where the LR55 track system was treated as multilayer beams on elastic foundations, and the model was then validate experimentally through a series of non-destructive tests on full scale model subjected to a full scale service load specified by the current BS codes of practises.
Designing a Novel Controller for Boiler Pressure
Authors: Gharib Mohammad Reza , Dabzadeh Iman , Seyyed Mousavi Seyyed Alireza
Published: January 2011

In this paper, a practical method to design a robust controller for pressure of boiler in Mashhad Power plant using Quantitative Feedback Theory (QFT) is proposed. In reality fuel flow, air flow and pressure of boiler are three dependent parameters which must control in every power plant. The boiler pressure system has uncertain mathematical model. Uncertainties in mentioned model are caused by lack of knowledge about the dynamics of the system, pay load changes, air flow. Thus, application of robust control methods for high precise control of pressure is inevitable. In the first step plant is converted into a group of linear uncertain plants. Then, a controller is designed for tracking problem and disturbance rejection. Finally, nonlinear simulation has been carried out which indicates successful design of controllers and pre-filters. The research demonstrates that applying the proposed technique successfully overcomes obstacles for robust control of pressure of the Power plant.
Sliding Mode Control Application to Amplitude Control of Comb-Actuated Resonant Microscanners
Authors: Abtahi Mansour , Vossoughi Gholamreza
Published: January 2011

MOEMS (Micro-Opto-Electro-Mechanical System) are MEMS in which the optical part plays a dominant role. The use of MOEMS as scanners and projectors has been studied lately. For high speed scanning applications, electrostatic comb drive actuation has several advantages. In this paper, we demonstrate the application of sliding mode control scheme for amplitude control of comb-actuated resonant microscanners. This method that leads to a simple and practical control function is simply extendable for microscanners with other type of actuation and even for any kind of oscillators that need amplitude control. The functionality and performance of the presented scheme is verified using numerical.
Identification and Significance of the First Structural Modes of Vibration of Two Wheeled Vehicles
Authors: Doria Alberto , Trombetta Luca , Pegoraro Roberto
Published: January 2011

In motorcycles and scooters the structural modes of vibration are important because they influence both vehicle’s comfort and vehicle’s stability and handling. Some researchers have shown that instabilities, which may occur when the vehicle is running (weave and wobble), are influenced by the modes of vibration, of the vehicle. At the Motorcycle Dynamics Research Group of Padova University many motorcycles have been tested with the method of modal analysis. The results of this research highlight that the whole motorcycle is a complex system that shows many kinds of modes of vibration: rigid modes, in which the structural components of the vehicle (chassis, fork, handlebars) behave as rigid bodies and deflection is given by tires and suspensions; local modes, in which deflection is concentrated in some subsystem of the vehicle (e.g. handlebars) and the rest of the motorcycle behaves as a system of rigid bodies; global modes with relevant deflection of the whole vehicle. This paper focuses on a specific issue, which is important for motorcycle design: the identifications of the frequencies of the first modes that show relevant deflection of the front fork and swing-arm. First, experimental equipment and testing methods are presented and discussed. Then the modal properties (natural frequencies, damping coefficients and modal shapes) of four motorcycles of different categories are presented, the characteristics of some modes are highlighted. Finally, the paper focuses on the identification of the frequencies that represent the borderline between rigid and elastic behavior of front fork and swing-arm. A method that requires the analysis of the characteristics of a small set of frequency response functions, without carrying out a long and expensive modal analysis of the whole vehicle, is presented. It is based on the properties of rigid modes (variation in vibration amplitude along a set of measurement points).
Effects of Inlet Geometry on the Pressure Drop and Collection Efficiency of Tangential Inlet Cyclones
Authors: Teke Mehmet , Karago¨z I˙rfan
Published: January 2011

This work presents a computational fluid dynamics simulation to investigate the effects of inlet geometry on the pressure drop and particle collection efficiency of a tangential inlet cyclone. Three-dimensional, steady governing equations for the incompressible, turbulent flow inside a tangential inlet cyclone are solved numerically under certain boundary conditions. The continuous gas flow is predicted by solving Navier-Stokes equations using the differential RSM turbulence model. The second phase is modeled based on a Lagrangian approach. The commercial CFD code Fluent was used for numerical analysis. Computational results compared experimental data available in the literature for validation. Various cyclones, each has different geometrical ratio of inlet section, studied in this paper. Detail analyses of the effects of inlet geometry on the flow behavior, pressure drop and collection efficiency were given.