bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparisons of Different Wind Power Forecasting Systems
Authors: De Giorgi Maria Grazia , Tarantino Marco , Ficarella Antonio
Published: January 2011

Wind forecasting models are divided in two main categories, physical and statistical. The former are based on Numerical Weather Prediction (NWP). The statistical models, on the other hand, use on-line measurements. In this paper we use hybrid models, which combine elements of both types. In particular three forecast systems based on Artificial Neural Networks have been developed in order to predict power production of a wind farm in different time horizons: 1, 3, 6, 12 and 24 hours. In the first forecast system, the neural network has been used only as a statistic model based on time series of on-line measured wind power, while in the second and third forecast systems different combinations of measured data and numerical weather predictions have been used, improving the performance in the predictions, especially over long time horizons. The error of the different forecast systems is investigated for various forecasting horizons and statistical distributions of the error are calculated and presented.
Design of a New Test Rig to Evaluate Under-Platform Damper Performance
Authors: Gola Muzio M. , Braga dos Santos Marcelo , Tong Liu
Published: January 2011

This work presents the development of a test rig capable of measuring the forces transferred between the blade platforms through the under-platform damper. This test rig is composed of two distinct parts each one representing a platform. The static part contains the load cells, which measure the forces in two perpendicular directions; the moving part controlled using two piezoelectric actuators reproduces any in-plane relative displacement between two adjacent platforms. In this scheme, the damper is placed between these two platforms and loaded by dead weights that reproduce the effects of centrifugal force. The hysteresis cycle, of the damper system, is obtained using the measured forces and the imposed displacement. In addition, two laser beams can be used to measure the damper displacement and its tilt angle, which allows validating dynamic models of the damper. Moreover, the test rig is designed to allow heating the specimens up to temperatures which are normally found in real operation. Finally, the test rig provides necessary variables to study the damper performance and to evaluate some contact models used to simulate under-platform dampers.
Scalar and Vector Time Series Methods for Vibration Based Damage Diagnosis in an Aircraft Scale Skeleton Structure
Authors: Kopsaftopoulos Fotis P. , Magripis Spiros G. , Amplianitis Aris D. , Fassois Spilios D.
Published: January 2011

A comparative assessment of several vibration based statistical time series methods for Structural Health Monitoring (SHM) is presented via their application to an aircraft scale skeleton structure. A concise overview of some of the main scalar and vector time series methods is provided, encompassing both non–parametric and parametric as well as response–only and excitation–response schemes. Damage detection and identification, collectively referred to as damage diagnosis, is based on single and multiple vibration response signals. The methods’ effectiveness is assessed via multiple experiments under various damage scenarios (loosened bolts). The results of the study confirm the global damage detection capability and effectiveness of scalar and vector statistical time series methods for SHM.
The Effect of Surface Roughness and Shaft Speed on the Frictional Characteristics of Radial Lip Seals
Authors: O¨zperk Hacer , Temiz Vedat
Published: January 2011

The purpose of this study is to investigate the effects of shaft surface roughness, speed, seal inner diameter, and lip geometry on the rotary lip seal’s performance. For this reason, a test system was developed. In this test system, a cylinder block is placed on four load cells to monitor the friction torque generated between seal and counter face. Radial lip geometry was taken as the prior criteria to group the seals for experiments. Two different profiles (with and without dust lip) and three different inner diameters (30-35-40 mm) were selected for the tests. Three shaft surface roughness values for each diameter were also tested. One shaft surface roughness value is between the limits that are recommended in standards, and two others are greater and less than that limits. At the end of the systematical experiments, variations of friction torque with respect to shaft surface roughness, lip profile and shaft diameter have been determined.
Effect of Specimen Dimensions on Mechanical Behavior of Resistant Spot Welded Aluminium Lap Joints
Authors: Han L. , Thornton M. , Chandrasekar C. , Maggs S. , Shergold M.
Published: January 2011

A study was carried out to examine the effect of specimen dimensions on mechanical behavior of RSW welded joints. A full factorial Design of Experiment (DOE) approach was applied to the experimental process and analysis stages. Aluminium alloy AA5754 sheet in various thicknesses was used to form symmetrical and asymmetrical joints. Single lap shear test geometry with three dimensional changes; width, length and overlap at two-level, was tested throughout the project. The results demonstrated that for both symmetric and asymmetric stacks, the width of the specimen had a statistically significant effect on both failure mechanism and shear strength value of such joints; a strong interaction effect between length and overlap of the specimen on joint shear strength was observed. Although the strength variation is not substantial in engineering terms, the change in failure mechanism is significant and the results are useful in optimization of lap shear test standards and in comparison of joint strength obtained from different investigations with different specimen dimensions. It is also helpful in assisting structural and manufacturing engineers in design and development of RSW of aluminium for application.
Process Feasibility Analysis of Self-Pierce Riveting High Strength Low Alloy Steel
Authors: Han L. , Thornton M. , Hewitt R. , Chrysanthou A. , Shergold M.
Published: January 2011

Self-Piercing Riveting (SPR) has been widely used in automotive Body in White (BIW) assembly as an alternative to Resistance Spot Welding (RSW), in particular for joining of dissimilar materials, for example Steels to Aluminium. A study examining the process feasibility of SPR of Aluminium alloy AA5754 and High Strength Low Alloy (HSLA) steel in various thicknesses has been conducted. It has been shown that the process is capable of joining the two materials together. However, it was also observed that the selection of rivet and die is limited when joining HSLA. The setting force required to drive the rivet into the sheet material to be joined tends to be high. This leads to potential tooling life concerns. It was also shown that the arrangement of the high strength steel joined to aluminium can have a significant effect on the process feasibility.
Testing and Modelling of an Advanced Motorcycle Shock Absorber
Authors: Cossalter Vittore , Doria Alberto , Pegoraro Roberto , Trombetta Luca
Published: January 2011

In shock absorbers damper-rod force not only depends on damper-rod velocity, but also on position and acceleration. Since hydraulic losses are responsible for velocity-dependent forces, other phenomena are responsible for the dependence of force on position and acceleration, they are: compliances of the chambers and of the seals, compressibility of oil and gas and inertia of oil. The presence of position and/or acceleration-dependent terms in the force causes a hysteresis loop in the force-velocity diagram and a delay between force and velocity in the force-time diagram, which affect the performance of the shock absorber. Usually test benches measure only the damper-rod force, hence, it is difficult to recognize the physical phenomena that generate the hysteresis loop. This paper deals with a research program in which a high performance motorcycle shock absorber was tested by means of a specific test bench which includes the measurement of pressures inside the cambers during harmonic tests (frequency range 1–7 Hz). The experimental results with proper mathematical models made it possible to analyze the hysteresis loops of the pressures in the various chambers and the generation of the hysteresis loop and time delay of damper-rod force. First some experimental results dealing with pressures inside compression, rebound and compensation chambers are shown. Then a simplified mathematical model is presented, it is able to capture the most relevant physical phenomena that generate the hysteresis loop of the total force. Finally a complete model of the shock absorber is described, it takes into account details of oil motion inside the valves and it is able to predict the behavior of the shock absorber for a wide range of working conditions. Some numerical results obtained with the complete model are presented and compared with experimental results.
Instability of Viscoelastic Fluids in Blasius Flow
Authors: Doostmohammadi Amin , Mortazavi Seyyedeh Negin
Published: January 2011

In this paper, we study the hydrodynamic stability of a viscoelastic Walters B liquid in the Blasius flow. A linearized stability analysis is used and orthogonal polynomials which are related to de Moivre’s formula are implemented to solve Orr–Sommerfeld eigenvalue equation. An analytical approach is used in order to find the conditions of instability for Blasius flow and Critical Reynolds number is found for various combinations of the elasticity number. Based on the results, the destabilizing effect of elasticity on Blasius flow is determined and interpreted.
A Novel Hybrid Approach for Unstructured Viscous Grid Generation
Authors: Bahrainian Seyed Saied , Mehrdoost Zahra
Published: January 2011

Accurate solution of boundary layer and wake flow require generation of high aspect ratio grids in these regions. A hybrid approach for the efficient generation of inviscid and viscous unstructured grids has been introduced. A novel feature of the current work is its ability to produce boundary layer and wake grids that enables accurate flow solutions in viscous flow regions. The grid generation algorithm starts with a very coarse initial grid. In the inviscid region, isotropic cells of excellent quality are produced using a combination of point insertion and cell subdivision techniques. Simultaneously, a directional grid refinement strategy is used to construct highly stretched triangular cells in viscous regions. First, anisotropic unstructured grids are produced in the stream wise direction. Then, cells close to the solid surface are refined to highly stretched layer of triangles suitable for boundary layer region. Smooth transition between the boundary layer grid and the outer isotropic grid is easily obtained with a user specified cell size and stretch. The accuracy of the current grid generation approach is assessed by laminar and turbulent compressible flow solutions around NACA0012 and RAE2822 airfoils. The results of the numerical flow simulations are compared with published experimental and numerical data. Comparisons point to the ability of the proposed unstructured boundary layer and wake grid generation procedure.
3-D Free Vibration Analysis of Functionally Graded Thick Circular and Annular Plates on Elastic Foundation
Authors: Tajeddini Vahid , Ohadi Abdolreza , Sadighi Mojtaba
Published: January 2011

This paper describes a study of three-dimensional free vibration analysis of thick circular and annular functionally graded (FG) plates resting on Pasternak foundation. The formulation is based on the linear, small strain and exact elasticity theory. Plates with different boundary conditions are considered and the material properties of the FG plate are assumed to vary continuously through the thickness according to power law. The kinematic and the potential energy of the plate-foundation system are formulated and the polynomial-Ritz method is used to solve the eigenvalue problem. Convergence and comparison studies are done to demonstrate the correctness and accuracy of the present method. With respect to geometric parameters, elastic coefficients of foundation and different boundary conditions some new results are reported which maybe used as a benchmark solution for future researches.
Vision System Based Lane Keeping Assistance Evaluated in a Hardware-in-the-Loop Simulator
Authors: Cos¸kun Fuat , Tuncer O¨zgu¨r , Karslıgil Elif , Gu¨venc¸ Levent
Published: January 2011

Lane keeping assistance systems help the driver in following the lane centerline. While lane keeping assistance systems are available in some mass production vehicles, they have not found widespread use and are not as common as ESP or ACC at the moment. Lane keeping assistance systems still need further development. Previously available systems have to be continuously adapted to newer vehicle models and fully tested after this adaptation. An image processing algorithm for lane detection and tracking, a lane keeping assistance controller design and a real time hardware-in-the-loop (HiL) simulator developed for testing the designed lane keeping assistance system are therefore presented in this paper. The high fidelity, high order, realistic and nonlinear vehicle model in Carmaker HiL runs as software in a real time simulation on a dSpace compact simulator with the DS1005 and DS2210 boards. A PC is used for processing video frames coming from an in-vehicle camera pointed towards the road ahead. Lane detection and tracking computations including fitting of composite Bezier curves to curved lanes are carried out on this PC. In the present setup, the camera used is a virtual camera attached to the virtual vehicle in Carmaker and provides video frames from the Carmaker animation screen. A dSpace microautobox is available for obtaining the lane data from the PC and the Carmaker vehicle data from the dSpace compact simulator and calculating the required steering actions and sending them to the Carmaker vehicle model. The lane keeping controller is designed in the Matlab toolbox COMES using parameter space techniques. The motivation behind this approach is to develop the lane keeping assistance system as much as possible in a laboratory hardware-in-the-loop setting before time consuming, expensive and potentially dangerous road testing. Lane detection, tracking and curved lane fit results, hardware-in-the-loop simulation results of the lane keeping controller with the image processing system are are used to demonstrate the effectiveness of the proposed method.
Numerical and Experimental Investigation of Thermodynamic Behavior of Positive Displacement Compressor
Authors: Paknezhad Morad , Yousefi Tooraj , Sadeghi Sajjad , Ahmadi Mehran
Published: January 2011

A numerical model, based on dynamic mesh, has been developed by FLUENT software, to simulate behavior of a positive displacement compressor. Only first compression stage of compressor was modeled. Modeling was done, by dividing the domain to three areas with different type meshes. Some relations were presented for volumetric, mechanical, isothermal, and overall isothermal performance, and thermodynamic analysis has been performed in term of these relations. Effects of outlet pressure and crankshaft’s angular velocity have been investigated on work, polytropic factor of compression, and efficiency. Numerical and experimental results have been compared, and a good agreement was seen between them.
A Mechatronic Design Process for Three Axis Robots
Authors: Karagulle Hira , Akdag Murat , Malgaca Levent
Published: January 2011

Three axis serial robots with different sizes are widely used for pick and place, welding and various operations in industry. Developments in mechatronics, which is the synergistic integration of mechanism, electronics and computer control to achieve a functional system, offer effective solutions for the design of such robots. The mechatronic design process involves solid modeling, assembly, rigid body dynamics, finite element rigidity analysis, motion control and computer programming. In this study, SolidWorks, CosmosMotion, CosmosWorks and PC-based motion control programs are used with an integrated approach. The integration software is developed in VisualBASIC by using the application programming interface (API) capabilities of these programs. An experimental three axis serial robot with a reach distance of 790 mm has been produced to develop and test the process.
Effect of Roller Profile and Misalignment in EHL of Finite Line Contacts
Authors: Park Tae-Jo
Published: January 2011

All the rollers of cylindrical and tapered roller bearing are axially profiled to relieve high edge stress concentration caused by mainly their finite length and by misalignment. In this paper, a numerical solution of the EHL of finite line contacts is presented for axially profiled and misaligned (tilted) cylindrical roller. Applying a finite difference method with non-uniform grids and the Newton-Raphson method, the highly nonlinear problems are systematically solved. Physically consistent solutions are obtained for moderate load and material parameters, and very small misalignment. For two different dub-off radii and various misalignment angles, contours and sectional plots of pressure and film shape near edge regions are compared, and variations of the minimum film thicknesses are showed. The effect of misalignment on the EHL pressure distribution is much higher than the film shapes. The absolute minimum film thickness decreases highly with misalignment angle and profile radius while the central minimum film thickness at the footprint center is nearly constant.
Singularity Reduction of a 3-UPS Mechanism With 6 DOF for Haptic Applications
Authors: Vossoughi G. R. , Khodabakhsh M.
Published: January 2011

A method for singularity reduction in a triangular 3-UPS mechanism is discussed. This mechanism usually has singularity near the origin. Changing the active joint angle can arrive at a suitable workspace near the origin without any singularity. Moreover, a 4-UPS mechanism, based on adding one additional leg to the 3-UPS mechanism, has a larger singular free workspace. Moreover, force analysis of two different mechanisms shows a reasonable and consistent force distribution between the different actuators. Singular free workspace is one of the characteristics which makes this mechanism ideal for haptic applications.
Modeling and Simulation of Non-Contact Atomic Force Microscope
Authors: Bahrami Mohammadreza , Ramezani Asghar , Osquie Kambiz Ghaemi
Published: January 2011

The Atomic force microscope in non-contact mode of operation is modeled as a lumped parameter system. The interaction of the cantilever tip with the sample surface through the van der Waals force introduces the nonlinearity to the model. The model is analyzed by the method of multiple scales and the frequency response equation is obtained. The effects of the nonlinearity, amplitude of excitation, and damping coefficient on the frequency response are studied.
On the Stress Singularities and Boundary Layer in Moderately Thick Functionally Graded Sectorial Plates
Authors: Saidi A. R. , Hejripour F. , Jomehzadeh E.
Published: January 2011

In this paper, the stress analysis of moderately thick functionally graded (FG) sector plate is developed for studying the singularities in vicinity of the vertex. Based on the first-order shear deformation plate theory, the governing partial differential equations are obtained. Using an analytical method and defining some new functions, the stretching and bending equilibrium equations are decoupled. Also, introducing a function, called boundary layer function, the three bending equations are converted into two decoupled equations called edge-zone and interior equations. These equations are solved analytically for the sector plate with the simply supported radial edges and arbitrary boundary condition along the circular edge. The singularities of shear force and moment resultants are discussed for both salient and re-entrant sectorial plates. Also, the effects of power of the FGM, thickness to length ratio on the stress singularities of the FG sector plates are investigated.
A Theoretical Approach for Free Vibration Analysis of the Nano-Plates Considering the Small Scale Effect
Authors: Jomehzadeh Emad , Saidi Ali Reza
Published: January 2011

The free vibration analysis of a nano-plate is investigated based on the first order shear deformation theory considering the small scale effect. The governing equations of motion are obtained using Hamilton’s principle by considering the nonlocal constitutive equations of Eringen. These coupled partial differential equations are reformulated into two new equations called the edge-zone and interior equations. Analytical solutions are obtained for a nano-plate with Levy boundary conditions. In order to find the natural frequencies of the nano-plate, the various boundary conditions at one direction of the plate should be imposed. Applying these conditions and setting the determinant of the six order coefficient matrix equal to zero, the natural frequencies of the nano-plate are evaluated. Non-dimensional frequency parameters are presented for over a wide range of nonlocal parameters and different boundary conditions. In addition, the effects of nonlocal parameter on the natural frequency of a nano-plate are discussed in details.
Transient Flow Simulation in Natural Gas Pipelines Using the State Space Model
Authors: Behbahani-Nejad M. , Ghanbarzadeh A. , Alamian R.
Published: January 2011

A transient flow simulation for gas pipelines and networks is proposed. The proposed transient flow simulation is based on the state space equations. The equivalent transfer functions of the nonlinear governing equations are derived for different boundary conditions types. Next, the state space equations are derived from the transfer functions. To verify the accuracy of the proposed simulation, the results obtained are compared with those of the conventional finite difference schemes (such as total variation diminishing algorithms, method of lines, and other finite difference implicit and explicit schemes). The effect of the flow inertia is incorporated in this simulation. The accuracy and computational efficiency of the proposed method are discussed for a single gas pipeline and a sample gas network.
The Stability and Chaos Analysis of a Nonlinear Wheeled Vehicle Model Under Road Excitation
Authors: Samandari Hamed , Rezaee Mousa
Published: January 2011

In this paper, the dynamic behavior of a quarter-car with two degree-of-freedom which consists of sprung mass and unsprung mass is examined. Nonlinearity occurred due to nonlinear hysteretic suspension damper and spring. Vehicle tire is modeled as a nonlinear hardening spring. The disturbance of road assumed to be sinusoid. Frequency response diagram of the model has been obtained. Results show that the dynamic response of the vehicle can be chaotic. Influence of road roughness amplitude on vehicle vibration is investigated and critical amplitude of the road surface profile is found, above which the system can vibrate chaotically. The comparison between the results obtained from the proposed model and those from the single degree-of-freedom quarter-car model shows that the unsprung mass has great influence on the dynamical behavior of the system, which cannot be ignored.
On Measuring Dynamic Properties of Damping Materials Using Oberst Beam Method
Authors: Koruk Hasan , Sanliturk Kenan Y.
Published: January 2011

The Oberst Beam Method is widely used for the measurement of the mechanical properties of damping materials. This method is a classical method based on a multilayer cantilever beam which consists of a base beam and one or two layers of other materials. The base beam is almost always made of a lightly damped material such as steel and aluminum. If the Oberst Beam Method (OBM) is to be used, it is essential to establish a very accurate measurement methodology. In this respect, the response and the excitation sensors in the Oberst test rig are generally non-contact type. Although the drawbacks of contacting type of transducers are eliminated by this way, there are other critical issues when OBM is used. It is therefore essential to be aware of the parameters that might adversely affect the measured data and also to avoid them as much as possible. Consequently, all the parameters affecting the result need to be optimized in order to obtain the material properties with high accuracy. Although the OBM is referenced in some standards and widely used in scientific studies, detailed information in the literature on how to perform a successful Oberst Beam experiment is very limited. This is the main subject this paper aims to address. In this paper, after setting up the Oberst test rig the effects of various parameters on measured data using an Oberst test rig are examined in an attempt to improve the accuracy of the estimated material properties. Then repeatability measurements are performed and the main parameters affecting the quality of the measured data are identified. After that, extensive tests are performed so as to determine the effect of the amplitude of the excitation force, adverse effects of electromagnetic excitation and the effects of length of the test specimen. Furthermore, it is found that the small differences between individual samples may also affect the results significantly. Finally, some suggestions are given to the potential users of the OBM so as to avoid undesirable effects of certain parameters during such measurements.
Bifurcations in the Response of a Jeffcott Rotor With Rotor-to-Stator Rub
Authors: Inayat-Hussain Jawaid I.
Published: January 2011

In the design of rotating machines the clearances between the rotating and stationary parts are often made smaller in order to increase their efficiency. Although the smaller clearance provides an advantage from the performance point of view, it is however not the case when viewed from the dynamics perspective as the possibility of rotor-to-stator rub to occur increases significantly. Rubbing in rotating machines is a highly nonlinear phenomenon and therefore it is very important to understand its dynamics. In this work the bifurcations in the response of a Jeffcott rotor subjected to rotor-to-stator rub is numerically investigated. In particular the influence of the rotor imbalance, contact stiffness and friction coefficient on the response of the rotor is examined for a range of operating speed. For the range of parameters investigated in this work, numerical results revealed the occurrence of sub-synchronous, quasi-periodic and chaotic vibrations in the response of the rotor. The range of operating speed where sub-synchronous and non-synchronous vibrations were found in the rotor’s response was seen to increase as a result of increasing the magnitudes of the rotor imbalance and contact stiffness. The response of the rotor was generally found to be invariant to the variation of the friction coefficient magnitude except for the combination of the largest values of rotor eccentricity and contact stiffness, whereby the range of sub-synchronous and non-synchronous vibrations was observed to increase as the magnitude of the friction coefficient became larger. For these particular magnitudes of rotor eccentricity and contact stiffness, the rotor response exhibited hysteresis phenomena resulting in the presence of multiple attractors for the same set of parameter values.
Experimental Investigation on the Heat Transfer of a Portable Forced-Convection Solar Air Heater
Authors: Fakoor Pakdaman Mohammad , Zohorian Izadi Pejman , Javadinia Azari Mohammad , Lashkari Amir
Published: January 2011

A cross-corrugated portable forced-convection solar air heater has been designed, fabricated, and developed. A wavelike bottom plate has been positioned crosswise to the air flow while rectangular baffles have been attached to the flat-plate absorber. The relative corrugation height, (e/Dh) ranges between 0.24 and 0.4, and relative baffles distance (l/L) varies between 0.21 and 0.48. The air flow rate in the heater duct has been varied in the range of 0.001 kgs−1 to 0.01kgs−1 (Reynolds number ranges from 350 to 3500), while other thermal specifications such as inlet, outlet, and plate temperatures have varied due to weather changes. Results of this study have been compared with those related to smooth ducts and other literatures, and the maximum enhancement in Nusselt number is observed to be approximately five times of that of the smooth duct under similar flow conditions. Finally, thermal efficiency of the device for different case studies has been determined and compared with other researches.
Experimental Analysis of Internal Heat Exchanger for Automotive A/C System
Authors: Bahrami Salman , Beigi Hasan Mohammad , Sabour Mohammad Hosein
Published: January 2011

In this paper, a new designed internal heat exchanger (suction-liquid line heat exchanger) for R134a automotive air conditioning system is proposed, and is studied experimentally. The approval is done by calorimeter test apparatus, which provides conditions close to real automotive A/C system operation. In this design, the high-pressure liquid passes through central channel and the low-pressure vapor flows in several parallel channels in the opposite direction. The results show that in all conditions, internal heat exchanger adoption will increase the condenser real capacity. Therefore, smaller condensers can be used to reach the same capacities. Using the designed internal heat exchanger will decrease the needed mass flow rate. In a constant mass flow rate, internal heat exchanger adoption will increase evaporator capacity. In all concluded tests, the compressor power consumption was decreasing by internal heat exchanger adoption; it was intensifying at higher air temperature passing through the condenser. Using this internal heat exchanger will decrease compressor power consumption up to 6%, and will increase mostly the coefficient of performance. The condenser higher air temperature will increase the coefficient of performance and its improvement with internal heat exchanger. In this case the coefficient of performance can increase up to 8.4%, and will enhance subcooled degree at expansion valve inlet up to 12.8°C.
Construction of a Rational Tire Model for High Fidelity Vehicle Dynamics Simulation Under Extreme Driving and Environmental Conditions
Authors: Bas¸lamıs¸lı S. C¸ag˘lar , Solmaz Selim
Published: January 2011

In this paper, a control oriented rational tire model is developed and incorporated in a two-track vehicle dynamics model for the prospective design of vehicle dynamics controllers. The tire model proposed in this paper is an enhancement over previous rational models which have taken into account only the peaking and saturation behavior disregarding all other force generation characteristics. Simulation results have been conducted to compare the dynamics of a vehicle model equipped with a Magic Formula tire model, a rational tire model available in the literature and the present rational tire model. It has been observed that the proposed tire model results in vehicle responses that closely follow those obtained with the Magic Formula even for extreme driving scenarios conducted on roads with low adhesion coefficient.
Development of Competitive Skills in Future Mechanical Engineers
Authors: Lino F. Jorge , Duarte Teresa P.
Published: January 2011

Nowadays, the Web is a common tool for students searching information about the subjects taught in the different university courses. Although this is a good tool for the first rapid knowledge, a more deep study is usually demanded. After many years of teaching one course about ceramic and composite materials, the authors, used the Bologna reformulation of the mechanical engineering course to introduce new teaching methodologies based on continuous evaluation. One of the main innovations is one practical work that comprises the study of a recent ceramic scientific article, using all the actual available tools, elaboration of a scientific report, present the work and participate in a debate. With this innovative teaching method the enrolment of the students was enhanced with a better knowledge about the ceramics subject and the skills related with the CDIO competences.
Historical Progression of Mathematizing Vibro-Acoustic Problems
Authors: O¨g˘u¨c¸ Mete
Published: January 2011

Some of celebrated geometers whom are acknowledged as to be the pioneers of scientific revolution have worked on acoustics and modeling of vibration of structures. They made great contributions on both the physical understanding and the mathematical modeling of these phenomena. The historical stream of physical understanding of sound propagation, foundations of the mathematical background of vibration mechanics and the instruments that reinforced the conceived theory of acoustics led to the advanced concept of modern vibro-acoustic engineering. A historical investigation is made on the early engineering approaches on vibro-acoustic engineering problems to comprehend the evolution of acoustic engineering and its place in modern era.
Effect of Material Properties and Thickness of Die Attach on Delamination of Die Attach/Die Paddle Interface in Electronic Package
Authors: Chang Chia-Lung , Li Po-Hsien
Published: January 2011

The electronic package is a multi-layered structure that is consisted of several materials. Under the temperature loadings, the interfacial stresses between layered components are generated due to the CTE (coefficient of thermal expansion) mismatch between different materials. In die bonding process, the void or defect might exist at the die attach/die paddle interface. The void cause further delamination on the interface during the encapsulation process. In this study, the finite element method is used to construct the model of electronic package with a void on the die attach/die paddle interface. The energy release rate based on J integration, which is calculated by the stress and strain around the tip of crack, is used as a damage parameter to predict the tendency of further delamination during encapsulation. Effect of material properties (Young’s modulus and CTE) and die attach thickness on delamination of die attach/die paddle interface in package during encapsulation is studied.
A Numerical Investigation on Pulsatile Blood Flow Through Consecutive Axi-Symmetric Stenosis in Coronary Artery
Authors: Mahmoudzadeh Akherat Seyed Mohammad Javid , Kimiaghalam Morteza
Published: January 2011

The objective of this research is the determination of the wall shear stress (WSS) and velocity distribution patterns in axi-symmetric single or repeated stenoses in coronary arteries. The blood flow is modeled as an incompressible laminar flow with Re = 500 and the analysis is performed for both Newtonian and non-Newtonian blood behaviors. For the single stenosis cases, the area reduction of 25%, 64% and 75% are considered, while for the consecutive stenosis cases two sets of 64%, 25%, and 75%, 64% for the first and second stenosis are examined numerically respectively. Single stenosis cases are also employed for validation purposes, since experimental data are available for them. Present results indicate that regions of high and low shear stress may play an important role in the rupture of atherosclerotic lesions. Both sides of the stenotic area with high WSS and intense WSSG (Wall Shear Stress Gradient) are the most vulnerable sites of plaques. For the cases of consecutive stenoses, results show that displacement of the secondary plauque does not have any effect on the flow pattern. Moreover, the effect of the progression and the area reduction percentage of the consecutive stenoses were studied numerically. It was concluded that the progression of the first and the second stenoses creates high alterations in WSS and velocity distribution and increases the vulnerability of creation of new plaques. Furthermore, the pulsatile property of blood was considered. An accurate velocity waveform was implemented to predict the pulsatile behavior of blood. Results significantly vary from those of the laminar analysis in terms of velocity distribution and the magnitude of the maximum velocity. The flow patterns are studied for several time sections in one period.
Experimental Evaluation of Cavitating Venturi as a Passive Flow Controller in Different Sizes
Authors: Farshi Fasih Hamidreza , Ghassemi Hojat
Published: January 2011

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. A cavitating venturi is a converging-diverging nozzle with a suitable throat area for passing flow. The flow rate is a function of the upstream pressure, the throat area, the density and saturated pressure of the liquid. An experimental setup with the capability of supplying constant water flow rate, upstream pressure and temperature was designed and manufactured. Three cavitating venturies were designed and built to investigate the effect of cavitating venturi size on its mass flow rate and capability of performance venturi in wide ranges of flow rates. Three different sets of experiments were conducted to ensure the performance of the venturi to keep constant mass flow rate independent of downstream pressure. In the experiments, under different downstream and upstream pressure conditions, the mass flow rates were examined. The results show that if the ratio of downstream pressure to upstream pressure is less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever pressure ratio exceeds from 0.8, the venturi acts like an orifice.
Densification Behavior of Metal Powder Under Uniaxial Cold Compaction
Authors: Darroudi Mostafa , Ghassemi Hojat , Akbari Baseri Mahmoud
Published: January 2011

Metal powder compaction is a quite important process in Powder Metallurgy (PM) industry and it is widely applied in the manufacturing of key components in different fields. During metal powder compaction, the solid volume fraction changes and many mechanical characteristics become different. The Finite Element simulation provides a flexible and efficient approach for the researches of this process and its complicated mechanical behaviors. In this paper, several 2D finite element spherical powder compaction models are generated. Different particle arrangements are build up and different friction coefficients are set to the inter-particle contacts and die wall contact for a certain arrangement. The Von Mises yield surface with isotropic hardening plasticity model is applied in the simulation and the displacement controlled load is used to compress the structure up to 25% of die height. Results show that the die wall friction increases compaction pressure but inter-particle friction has negligible effect.
A New Structural Optimization Method Based on Group Hunting of Animals: Hunting Search (HuS)
Authors: Oftadeh R. , Mahjoob M. J.
Published: January 2011

This paper presents a novel structural optimization algorithm based on group hunting of animals such as lions, wolves, and dolphins. Although these hunters have differences in the way of hunting but they are common in that all of them look for a prey in a group. The hunters encircle the prey and gradually tighten the ring of siege until they catch the prey. In addition, each member of the group corrects its position based on its own position and the position of other members. If the prey escapes from the ring, the hunters reorganize the group to siege the prey again. A benchmark numerical optimization problems is presented to show how the algorithm works. Three benchmark structural optimization problems are also presented to demonstrate the effectiveness and robustness of the proposed Hunting Search (HuS) algorithm for structural optimization. The objective in these problems is to minimize the weight of bar trusses. Both sizing and layout optimization variables are included, too. The proposed algorithm is compared with other global optimization methods such as CMLPSA (Corrected Multi-Level & Multi-Point Simulated Annealing) and HS (Harmony Search). The results indicate that the proposed method is a powerful search and optimization technique. It yields comparable and in some cases, better solutions compared to those obtained using current algorithms when applied to structural optimization problems.
Dynamic Analysis of Functionally Graded Piezoelectric Material Beam Using the Hybrid Fourier-Laplace Transform Method
Authors: Doroushi A. , Akbarzadeh A. H. , Eslami M. R.
Published: January 2011

This paper presents an analytical solution for transient response of a simply supported functionally graded piezoelectric material (FGPM) beam under mechanical loads. The beam’s material properties are assumed to vary through the thickness direction following a power law distribution in terms of the volume fractions of the constituent materials. Based on higher-order shear deformation theory the governing equations, equations of motion and Maxwell equation, are derived using Hamilton’s principle. The resulting system of differential equations of vibration is solved using the finite Fourier transformation method. Using the Laplace transform, the unknown variables are obtained in the Laplace domain. Applying the analytical Laplace inverse method, the solution in the time domain is derived. Initially the efficiency of the proposed method is investigated by comparing present results with FEM and Newmark method. Then the effects of material composition, slenderness ratio, and shear deformation on the transient response are investigated.
Modeling of Surfaces Subject to Orientation Tolerances
Authors: Petro` Stefano , Moroni Giovanni
Published: January 2011

Most of products may be manufactured by different processes. However, different process will yield slightly different products. In particular, similar geometric deviations will characterize parts produced by a specific process. It may then be stated that parts show a “manufacturing signature”, i.e. parts manufactured by the same manufacturing process will show similar, but not identical, local geometric deviations. Signature analysis has several applications, including process monitoring, tolerancing, inspection strategy planning for geometric tolerance verification, and failure identification. In past years, several signature models have been proposed for form error. However, models proposed so far are not adequate to describe the signature when orientation, location and run-out tolerances are of interest. These geometric tolerances involve a toleranced feature, plus at least one datum feature, so relation between these feature is relevant. In this work, a methodology for simultaneously modeling both toleranced and datum features will be proposed. The overall model will be constituted by a model for the toleranced feature, a model for the datum feature(s), and a model for the relation between toleranced and datum feature. A case study will be proposed involving orientation tolerances.
Design and Analysis of a Foot Contact Sensor for Posture Control of a Biped Robot
Authors: S¸afak Koray K. , Baturalp T. Batuhan
Published: January 2011

Development of a planar biped robot is currently underway at Yeditepe University. The robot consists of lower extremities with a torso that are designed at anthropomorphic dimensions. This study describes the design and testing of a foot contact sensor for the biped robot. Dynamic stability of a biped robot is commonly measured by the zero moment point (ZMP) method. Experimentally, ZMP is measured by multi-component force/torque sensors. Due to their low cost and ease of use, force sensitive resistors (FSR) are used to build a foot contact sensor for the biped robot. Four FSRs are mounted at the corners of the robot’s foot to measure the ground reaction force and its moment. Hence, by utilizing the data from the foot contact sensors, a real-time ZMP computation scheme can be implemented. The performance of the designed foot contact sensor is presented by numerical simulations of a planar biped robot’s postural stability control. Results indicate that reaction force computation by the FSR based force sensors is a viable method to monitor postural stability of biped robots. Force sensors and their electronics are currently being built to be used for the actual tests.
Modelling and Validation of a Rotor System With Ball Bearings
Authors: Cakmak Onur , Sanliturk Kenan Y.
Published: January 2011

In this paper, a dynamic model of a rotor-ball bearing system is developed in Msc. ADAMS commercial software. Contacts between the balls and the rings are modelled according to Hertzian theory. The bearing model is capable of representing the effects of bearing defects and internal clearances. When they are coupled with the rotor structures, bearings without any defect can also cause excessive vibrations due to the resonance characteristics of the system. In order to demonstrate these characteristics the rotor itself is modelled as a flexible shaft and a disc positioned at the free end of the shaft. The rotor-ball bearing model developed here is capable of representing the gyroscopic effects and the behaviour of the system under different unbalance conditions. Various case studies are performed and Campbell diagrams are obtained by using short-time Fourier transform method. A test rig consisting of two ball bearings, a shaft and a disc is also designed and developed so as to validate the theoretical model using experimental data. The test rig is developed in such a way that all of the elements are easy to assemble/disassamble, allowing quick observation of the system’s dynamic behaviour for different parameters including imbalance, internal clearance and bearing defects. Modal analysis and order tracking analysis were carried out using the test rig. Both the modal results and Campbell diagrams obtained using experimental data are compared with their theoretical counterparts. In the light of the experimental data, the theoretical model is validated for the purpose of further analyses and research.
Optimal Fiducial Configuration in Image-Guided Neurosurgery Using a Genetic Algorithm
Authors: Gastaldi Laura , Battezzato Alessandro , Bernucci Claudio , Mannino Marco , Pastorelli Stefano
Published: January 2011

Image Guided Neurosurgery allows surgeons to navigate and localize lesion through the patient’s cranium with a 3D image guidance. The model of the head is reconstructed using pre-operative Computed Tomography (CT) or Magnetic Resonance (MR) images and real and virtual spaces are aligned by means of fiducial markers placed on the patient. In the paper a new method for the optimal placement of the fiducial markers in order to reduce misalignment is presented. Using routine diagnostic images a customized 3D model of the patient’s cranium is reconstructed. A genetic algorithm calculates optimal positions of the marker in order to minimize the Target Registration Error (TRE). The fiducial set is shown to the surgeons on the 3D model to help him/her in placement of them.
Application of the Nonlinear Energy Sink Systems in Vibration Suppression of Railway Bridges
Authors: Younesian Davood , Nankali Amir , Motieyan M. Emad
Published: January 2011

Vibration suppression of railway bridges using nonlinear energy sink systems (NES) is studied in this paper. Train is modeled as a set of successive moving loads traveling on an Euler-Bernoulli beam. Energy sink as a new passive control strategy is employed as the suppression system. Galerkin method here is adopted as the solution technique. Within a parametric study, series of numerical simulations are carried out and performance of the passive control system is investigated. It is numerically found that an appropriately designed NES can passively reduce the displacement of the bridge up to 43%.