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APPLIED and THEORETICAL MECHANICS

 Volume 3, 2008
Print ISSN: 1991-8747
E-ISSN: 2224-3429

Issue 1, Volume 3, January 2008

Title of the Paper: Consideration on Stainless Steel Plate Plastic Deformed by Fluid Impact Substances and Pressured Nitrogen Blasting

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Authors: Adrian Rosca, Daniel Rosca, Vasile Nastasescu

Abstract: The paper presents a plastic deformation method for thin plates made of stainless steel, plastic deformed by pressured nitrogen blasting combined with impact fluid substances. There are presented experimental results for comparative values of deformation velocities obtained by different initial pressured nitrogen blasting, respectively by pressured nitrogen blasting combined with several quantities of impact fluid substances.

Keywords: Pressured nitrogen blasting, Plastic deformation, Stainless steel thin plates

Title of the Paper: Homogenisation Procedure to Evaluate the Effectiveness of Masonry Strengthening by CFRP Repointing Technique

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Authors: A. Cecchi, A. Barbieri

Abstract: In this work masonry walls, made of clay bricks and mortar joints, have been investigated and in particular the effectiveness of CFRP repointing technique is analysed by homogenisation procedure. Masonry walls - typical of historical buildings and churches – are subject to in plane or/and out of plane loading and, due to the low tensile strength of mortar joint (assumed zero in terms of safety), need strengthening procedure to bearing seismic loads or new service loads related to restoration design. The homogenisation procedure has been carried out taking into account several geometrical and mechanical parameters of masonry and CFRP strengthening. The difficulty in modelling masonry lies in its heterogeneous character, since it is composed by blocks between which mortar joints are laid. Here a linear elastic analysis is performed that is significant under service loads, and may be a starting point for non linear and collapse analysis. The masonry has been identified with a standard elastic continuum by means of homogenisation method. Two homogenisation approaches are proposed: an analytical approach and a numerical approach. Both of them allow to determine values of homogenised in plane moduli, for running bond texture, strengthened by CFRP, taking into account the effective micro-structure of masonry and FRP An extensive numerical analysis has been carried out to investigate the reliability of homogenisation methods to take into account the geometrical and mechanical parameters in the analysis of masonry walls considering different FRP Young moduli. The sensitivity of strain field to strengthening material is investigated on a meaningful case such as a masonry wall loaded by horizontal and vertical displacement respectively along horizontal joints or vertical ones. This case is of practical interest for the partition masonry walls: infill walls.

Keywords: Masonry, CFRP repointing, Homogenisation, in plane moduli.

Title of the Paper: Calculation of Dynamic Stresses using Finite Element Method and Prediction of Fatigue Failure for Wind Turbine Rotor

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Authors: Z. I. Mahri, M. S. Rouabah

Abstract: The aim of this work is the calculation of the dynamic loads and stresses acting on wind turbine blades in order to predict fatigue. The prediction of the dynamic behaviour of the rotor constitutes one of the most important processes in the design of wind turbine, this analysis is useful in estimating the energetic performance of this machine, as well as in predicting the structural problems such as fatigue failure, which is the major cause of wind turbine breakdown. In the first part of this work the blade element theory is used to calculate aerodynamic loads for small wind turbine blades. This method can also estimate the power coefficient and the total power extracted by the turbine. In the next part of the work, modal analysis of the blades is carried out in order to compute frequencies and mode shapes. These parameters are useful for dynamic load estimation. At last, dynamic stresses are computed for the root region of the blades, using finite element modelling. The resulting curves of stress vs. time, obtained for different wind speeds, are used for fatigue analysis in order to make an optimal choice of blades resistant to fatigue and being energetically efficient. In both modal and stress analysis two different approaches are utilized and their results are compared.

Keywords: Wind Energy, structural dynamics, Aerodynamics, fluid mechanics and Numerical Analysis.

Issue 2, Volume 3, February 2008

Title of the Paper: Optimum Determination of Partial Transmission Ratios of Three-Step Helical Gearboxes

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Authors: Vu Ngoc Pi

Abstract: In this paper, a new study on the applications of the optimization and regression techniques for optimum determination of partial ratios of three-step helical gearboxes in order to get different objectives including the minimum gearbox length, the minimum gearbox cross section dimension and the minimum mass of gears is presented. From the moment equilibrium condition of a mechanic system which includes three gear units and their regular resistance condition, three optimization problems for getting the minimum gearbox length, the minimum gearbox cross section dimension and the minimum mass of gears were conducted. In addition, explicit models for the prediction of the partial ratios of the gearbox were given by using regression analysis technique. With these models, the calculation of the partial ratios becomes accurate and simple.

Keywords: Gearbox design; Optimum design; Helical gearbox; Transmission ratio.

Title of the Paper: An Original Approach of Tensile Behaviour and Elastic Properties of Multiphase Pre-Impregnated Composite Materials

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Authors: Horatiu Teodorescu, Sorin Vlase, Luminita Scutaru, Florin Teodorescu

Abstract: An original approach to compute the longitudinal tensile break stress of multiphase composite materials with short fibers reinforcement is presented. The most obvious mechanical model which reflects a multiphase composite material is a pre-impregnated material, known as prepreg. In the class of prepregs the most known are Sheet- and Bulk Molding Compounds (SMCs and BMCs). The model is seen as consisting of three phase compounds: resin, filler and fibers, model that is reduced to two phase compounds: substitute matrix and fibers. The Sheet Moulding Compounds reinforced with discontinuous and almost parallel fibers, subjected to longitudinal tensile loads, presents a specific note by the existence of a shear mechanism between fibers and matrix. This shear mechanism transfers the tensile load through the fibers. The Young’s moduli for the substitute matrix and for the entire composite are computed and a comparison between the theoretical approach and the experimental data is accomplished. The paper presents also an original homogenization method to predict the elastic properties of these materials. The upper and lower limits of the homogenized coefficients for a 27% fibers volume fraction SMC are computed. It is presented a comparison between the upper and lower limits of the homogenized elastic coefficients of a SMC material and the experimental data. The estimation model used as a homogenization method of these heterogeneous composite materials, gave emphasis to a good agreement between this theoretical approach and experimental data.

Keywords: Prepregs, Sheet Molding Compounds, Substitute matrix, Homogenization, Heterogeneity, Estimation method, Elliptic equations, Elastic coefficients.

Title of the Paper: Consideration Concerning the Static and Dynamic Stability of Metallic Bunker on Environmental Engineering

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Authors: Adrian Rosca, Daniela Rosca

Abstract: The paper presents considerations concerning static and dynamic stability of metallic bunker on environmental engineering. There are presented theoretical considerations and experimental results concerning the shock wave velocity / dynamic pressure, the shock wave influence on the bunker’s walls deformation and long term stability.

Keywords: metallic bunker, static/dynamic stability, air shock waves, environment engineering

Issue 3, Volume 3, March 2008

Title of the Paper: Finite Element Analysis of Tunnel-Soil-Building Interaction using Displacement Controlled Model

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Authors: Ma Keshuan, Ding Lieyun

Abstract: Using some building affected by the river-crossing highway tunnels of Wuhan as engineering background, this paper investigates the interaction between the tunneling in soft soils and adjacent structures. A full three-dimensional finite element model, which takes into account the presence of the building during the excavation of the tunnel, is well analyzed. The soil behavior discussed in this paper is assumed to be governed by an elastic perfectly-plastic constitutive relation based on the widely adopted Mohr-Coulomb criterion with a non-associative flow rule. The paper consists of three parts. The first part presents the 3-D finite element numerical model, and the second part provides a full analysis of the construction of a shallow tunnel close to a five level building. Comparison between the full couple model analysis and the full 3D free-field analysis is given in the final part. The corresponding comparison results provide a fundamental guidance for the shield tunnel design and construction.

Keywords: Finite Element; Three-dimensional; Slurry shield tunneling; Structure; Excavation; Settlement

Title of the Paper: Development of a Spiral Trajectory for High Speed Roughing of Light Alloy Aerospace Components

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Authors: Jean-Francois Chatelain, Rejean Roy, Rene Mayer

Abstract: A new spiral cutting method and its implementation within a CAD/CAM application software is proposed to save more than 16% in the roughing process of pockets for light alloy aerospace parts. The application prototype developed automatically generates the tool paths related to specific pocket profile geometry. It is shown, through experimentation using the prototype, that the parameters which define the spiral tool path geometry have a direct and important impact on cutting times. During the roughing operation, the proposed tool path takes into consideration the slant of the walls but also allows maximizing the quantity of material to be removed. The approach developed indicates great potential for roughing optimization of parts having multiple pockets.

Keywords: CAD, CAM, roughing, spiral trajectories, tool path, machining.

Title of the Paper: Die Attach Film Performance in 3D QFN Stacked Die

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Authors: A. Jalar, M. F. Rosle, M. A. A. Hamid

Abstract: Consumer demand for smaller and lighter products in wiresless application with maximum functionality had drive the semiconductor industries toward the developement of 3-dimensional stacked die. One of the key technology is relies on die stacking process. A suitable bonding condition and material set are essential to achieve required reliability performance. This study is to relate the effects of variables bonding parameter on the mechanical adhesion and delamination of the die attach film in QFN stacked die. Samples are deliberately built with nine combination sets of die attach parameters including bonding temperature, force and time to achieve a minimum reliability performance under IPC/JEDEC Moisture Sensitivity Level 3 at reflow 260°C. Characterisation of die attach film was carried out using differential scanning calorimetry whereas it performance was carried out using shear testing machine and scanning acoustic test (SAT) is used to detect the interfacial delamination between DAF and die. The best die attach process is characterized by stable values of die attach film thermal resistance properties and optimum touch area between die/die attach film and die attach film/die.

Keywords: Die attach film, QFN, delamination

Issue 4, Volume 3, April 2008

Title of the Paper: Finite Element Analysis of Micro – Electro – Mechanical Systems: Towards the Integration of MEMS in Design and Robust Optimal Control Schemes of Smart Microstructures

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Authors: John K. Sakellaris

Abstract: Microelectromechanical Systems (MEMS) is the technology of the very small, and merges at the nano-scale into "Nanoelectromechanical" Systems (NEMS) and Nanotechnology. MEMS are also referred to as micro machines, or Micro Systems Technology (MST). MEMS are separate and distinct from the hypothetical vision of Molecular nanotechnology or Molecular Electronics. MEMS generally range in size from a micrometer (a millionth of a meter) to a millimeter (thousandth of a meter). At these size scales, the standard constructs of classical physics do not always hold true. Due to MEMS' large surface area to volume ratio, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass. Finite element analysis is an important part of MEMS design. The paper presents the design of a vibration control mechanism for a beam with bonded piezoelectric sensors and actuators and an application of the arising smart structure for vibrations suppression too. The mechanical modelling of the structure and the subsequent finite element approximation are based on Hamilton’s principle and classical engineering theory for bending of beams in connection with simplified modelling of piezoelectric sensors and actuators. Two control schemes LQR and H2 are considered. The latter robust controller takes into account uncertainties of the dynamical system and moreover incompleteness of the measured information, it therefore leads to applicable design of smart structures. The numerical simulation shows that sufficient vibration suppression can be achieved by means of the proposed general methods. It is given as a perspective to the MEMS technology towards the direction of integrating MEMS in design and robust optimal control schemes.

Keywords: Finite Element Analysis, Micro – Electro – Mechanical Systems, ANSYS software, Coupled problems, Micro - actuator, Bi - stable electromagnetic actuation, UV-LIGA technology, Simulation, Active structural control, Smart beam, Composite structure, Piezoelectric layer.

Title of the Paper: Spectral Distribution of a Star-Shaped Coupled Network

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Authors: Xu Gen Qi, Nikos E. Mastorakis

Abstract: In this paper we study a star-shaped coupled network of strings and Euler-Bernoulli beams with damping. Suppose that the exterior vertices of the coupled network are clamped and at common node there is a damping. In the present note, our attention concentrate on the spectral distribution of an operator determined by the system. Under certain condition we show that the spectrum of the operator distributes in a strip parallel the imaginary axis.

Keywords: Star shape network stabilization string beam

Title of the Paper: Nonlinear Effects in Seismic Base Isolations

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Authors: Dinu Bratosin

Abstract: By interposing a layer with low horizontal stiffness but with high damping characteristics between the structure and his foundation, an aseismic isolation system partly decouples the building structure from the horizontal components of the earthquake ground motion and thus diminishes the structural demand. As a result of the lateral flexibilization, the natural period of the former fixed-base structure undergoes a jump and the new base-isolation structure has a new and larger natural period. This “period-shift” can extract a structure away from the dominant period of the earthquake ground motion and thus can avoid the destructive effects given by the system resonance. The dynamic behavior of the materials and devices of the isolating layer governs the performance of base-isolation system. The dynamic properties, such as horizontal stiffness and damping capacity determine the filtering role of the isolating layer and, finally, the structural dynamic response. But all of materials and devices used in an isolating layer systems exhibit, more or less, a nonlinear behavior. In addition, all site soils materials have the well-known nonlinear mechanical characteristics, which affect the dynamic structural response. Thus, in the dynamic response evaluation of a base-isolated system the nonlinear behavior of both isolator and site layers must taken into account. This paper presents a method for the necessary period-shift determination by using the dynamic linear or/and nonlinear magnification functions. For the nonlinear magnification functions determination we shall use a nonlinear Kelvin-Voigt model (NKV model) for base-isolated structure, which is able to model the effects of the soils and isolating layer nonlinearity on the shape and resonant magnitude of the magnification functions. Thus, we shall obtain a proper tool for modeling the resonant peak dispersion, which is a very important condition for a correct period-shift evaluation and therefore for a correct isolation design.

Keywords: Earthquake engineering, Nonlinear dynamics, Seismic base-isolation

Title of the Paper: Dynamical Behavior of Foundations in Linear and Nonlinear Elastic Characteristic Hypothesis

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Authors: Adrian Leopa, Silviu Nastac

Abstract: This study presents a viewpoint regarding dynamic behavior of the technological equipment foundation who works in the production process with shocks and vibration. In this way was analyzed the variations of three cinematically parameters acceleration, velocity and movement, as well as a frequency response of the vertical movement of the foundation. These analyses were made by comparison for the two considerate hypotheses: linear and non-linear elastic characteristic of the viscous-elastic system.

Keywords: vibration, non-linear, linear, detect, damage, frequency

Issue 5, Volume 3, May 2008

Title of the Paper: New Structural Configurations for Vibroisolation Devices with High Isolation Performances

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Authors: Silviu Nastac, Adrian Leopa

Abstract: This paper is a summary of the large study regarding the isolation performances improvement of the vibration isolation devices. The main area of this study was framed by the passive isolation, using different structural configurations, based on the compressing and torsion rubber elements. First, it is present the few theoretical aspects regarding the dynamic analysis of the passive elastic anti-vibrational devices and their isolation degree evaluation. It have to be mentioned that in this paper there are presented only the final structural configurations of passive isolation devices, obtained by a selection procedure based on the numerical simulation and instrumental tests of dynamic behaviour for each type. Taking into account the structure of the basic compressing and torsion elastic elements, their working principle, and their functional restraints, there was tested a lot of possible configurations, both from the structural, and from the functional points of view. Through the comparative analysis of the acquired results, it was fixed two final and operational structural configuration. All the theoretical suppositions, completed by the computer simulation on the numerical models, was entirety validated through the experimental tests on realistic models. Concluding the ensemble of numerical and instrumental tests, it could be mentioned that the major advantages of these special structural and functional configuration, with a view to the increasing of the isolation degree and to the passive anti-vibrational elastic devices performances incrementation, point at the high isolation performance, relative to a simple and robust structure. Using of these innovative anti-vibrational devices leads to high values of the isolation degree for a large area of technical and industrial applications, and also for vibration sensitive embedded equipments. As it could be see on the paper, the basic structural configuration could be easy modified, on call, as a function of a practical application service requirements, by changing a spatial distribution of the elastics components.

Keywords: isolation efficacy, passive elastic devices, rubber elements

Title of the Paper: Enhancement of Panel zone (PZ) Contribution to the Ductility of post-Northridge Welded Connections

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Authors: Amir A. Hedayat, Murude Celikag

Abstract: In welded connections, beam-end and panel zone (PZ) are the only sources to dissipate the seismic energy released during an earthquake. Energy dissipation at the PZ is accompanied by the inelastic shear deformation at PZ. In seismic codes, in order to reach to the maximum plastic rotation capacity of connection, the inelastic shear deformation is controlled by a balance condition with respect to the initiation of flexural yielding of beam flanges. Hence, connections are classified as weak, balance and strong panel zone connections. In the case of weak PZ, balance condition can be obtained by increasing the thickness of the column’s PZ or using doubler plates. This study was aimed to obtain balance condition for connections with strong panel zones. Therefore, a circular hole was opened at the column web in the PZ region. A pre-tested post-Northridge connection which has a strong panel zone was modeled using finite element analysis. Then the effects of different diameter holes on the behavior of this type of connection were investigated. Further, a function was proposed to determine the PZ shear yielding resistance in the presence of a circular hole in PZ. Analytical results showed that the column with a PZ hole ratio (hole diameter divided by PZ height) of 18% associated with a PZ hole of 50 mm radius and balance ratio of 0.81 appears to be the best configuration for increasing the PZ plastic rotation from 0.05% to 0.2%. This increase in plastic rotation capacity of PZ would only increase the total plastic rotation capacity of the connection by 10%. This indicates that a connection of this type also require modifications at the beam-end to increase both the total plastic rotation capacity and contribution of panel zone to the inelastic behavior of connection.

Keywords: Post-Northridge connections; Panel zone; Ductility; Inelastic shear deformation

Title of the Paper: The Influence of the Lubricant from a Rectilinear Pair above the Work Accuracy of the Elastic Elements from the High Precision Mechanisms

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Authors: Madalina Calbureanu, Raluca Malciu, Mihai Lungu, Dan Calbureanu

Abstract: The paper presents the determination by experiment of the vibration of a long elastic cinematic element with a mobile rectilinear pair, lubricated by two kinds of oil with low and high values for lubrication properties and cinematic viscosity. The lubricant pressures’ field is analyzed by using the finite element method (COSMOSM program), starting with the datum obtained by experiment in the analysis of the elastic cinematic element vibration. The vibration acceleration for the elastic element was measured and the spectrum analysis was attached for each case separately. The efficacy acceleration and the power spectral density for different kinds of oil were comparatively presented. More actions are proposed for the high accuracy mechanism in order to obtain less vibration on the elastic cinematic elements.

Keywords: Lubricated rectilinear pair, elastic element, pressures field, film breaking phenomenon, spectral analysis

Title of the Paper: Advanced Computational Concepts about Projecting a Multiple Designs of Self-Supporting Metallic Structure using Finite Element Method in Determination the Buckling Factor and Running the Stress Analysis

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Authors: Madalina Calbureanu, Emil Albota, Raluca Malciu, Romulus Lungu, Dan Calbureanu

Abstract: The paper presents the fully and correctly computation of a self-supporting metallic structure by using the capabilities of NISA-program and Finite Element Method. The stress and buckling analysis using SHELL and TRUSS Elements are performed for optimizing the design of the structure. The system of loading forces includes all the types of loads specified by the international standards for the civil buildings. The values of loads depend on the structure location zone. Permanent, temporary (quasi-permanent and variable) loads and the extremity loads are considered. It is been also realized a designing of the structure based on the obtained results. The advanced computational concept used in designing multiple shapes for the metallic structures were introduced by MACRO program. This program can realize automatically modeling of the structure introducing in a parametrical way the dimensions of the metallic building.

Keywords: Self-supporting metallic structure, design, buckling factor, stress analysis

Issue 6, Volume 3, June 2008

Title of the Paper: A Strain-based Non-linear Elastic Model for Geomaterials

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Authors: Andrew Heath

Abstract: The non-linear elastic behaviour of geomaterials has traditionally been modeled using stressdependent elastic models. The approach used by many researchers is not rigorous where the “elastic” models can create energy and can predict permanent deformation under certain circumstances. Other researchers have used rigorous hyperelastic models where energy is conserved by the elastic portion of the model, but these models have stress-dependent stiffness which can slow computation and lead to iterative solutions in finiteelement or other strain-based computation techniques. To overcome these problems a rigorous elastic model is investigated which predicts similar behaviour to hyperelastic models, but has the advantage of being elastic strain based which allows more direct solution in strain-based finite-element or other computational codes.

Keywords: Elasticity, Geomaterials, Non-linear, Finite Element, Elastic strain

Title of the Paper: On the Eigenvalues Optimization of Beams with Damping Patches

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Authors: Veturia Chiroiu

Abstract: The paper discusses the behavior of beams with external nonlocal damping patches made from traditional and auxetic materials. Unlike ordinary local damping models, the nonlocal damping force is modeled as a weighted average of the velocity field over the spatial domain, determined by a kernel function based on distance measures. The performance with respect to eigenvalues is discussed in order to avoid resonance. The optimization is performed by determining the location of patches from maximizing eigenvalues or gap between them.

Keywords: eigenvalues, optimization, damping patches, Euler-Bernoulli beam, nonlocal theory, auxetic material

Issue 7, Volume 3, July 2008

Title of the Paper: Mechanical Behavior Analysis with the Finite Elements Method of Solar Collector’s Tracking Systems

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Authors: Mihai Tiberiu Lates

Abstract: The paper presents the finite elements analysis of the mechanical behavior for three main solar collector tracking systems: for plate, for dish and for trough solar collectors; There are presented the modeling algorithm by using FEM, the characteristics of the loads and of the restrictions. Finally, the aim is to find out the critical position of the tracking systems, when the equivalent stresses and the displacements have a maximum value and to identify the free oscillations characteristics (modes, frequencies, accelerations). According to the conclusions can be compared, as mechanical behavior, the analyzed structure of the tracking systems.

Keywords: Solar collector, Tracking system, FEM, Stresses, Displacements, Vibrations.

Title of the Paper: Bending Beams, a Computer-Aided Approach

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Authors: Carmen E. Eisinger-Borcia

Abstract: This paper presents a new general computer-aided (CA) way for optimization of bending beams that is an example of using the CA capabilities to obtain a large quantity of data to receive new qualitative information. Our method is obtained combining two new results based on the CA approach: (1) the computer-aided method of obtaining the influence coefficients for bending a beam and (2) the State Matrix Strategy- a quasi-optimization tool. The CA method of obtaining the influence coefficients stands for any statically determined or undetermined straight beam of a constant cross section under all the combinations of loading and boundary conditions. The extension to a non-constant cross section is easy to obtain. The adopted model for the bending beam is an n-lumped beam unrelated to how big is n. The flexibility of this mathematical model synergistically completed by the Mathematica® software symbolic calculus capabilities, allows us to determine the values of the design parameters that optimize the elasto-dynamic behavior of bending beams, according to predefined criteria, static and dynamic as well.

Keywords: bending, lumped beam, influence coefficients, computer-aided optimization, Mathematica®.

Title of the Paper: The Effect of Frequency and Amplitude of Vibration on the Coefficient of Friction for Metals

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Authors: Jamil Abdo, Mahmoud Tahat

Abstract: Experiments were conducted to determine the effects of frequency and amplitude of vibration on friction. The experimental analysis also seeks to take into account a variety of factors influencing the coefficient of friction such as normal load and surface roughness. An in-house pin-on-disc apparatus was constructed with a spindle speed control and applied forced-feedback to perform the tests. The response surface methodology is utilized to investigate the effects of the factors and their cross influence on the coefficient of friction for the Steel C1020 and Aluminum 7079. The analysis of variance is done on the experimental data to evaluate the statistical significance of the model. The response equation for the coefficient of friction of Steel C1020 and Aluminum 7079 were determined. The ranges of frequency and amplitude of vibration were 120 – 600 Hz and 15 – 225 μm, respectively. Studies have shown that the coefficient of friction decreases with the increase of frequency and amplitude of vibration within the observed ranges for both metals whereas the in case of Aluminum 7079 the coefficient of friction is about 13 % when it compares with the coefficient of friction of Steel C1020.

Keywords: Frequency and amplitude of vibration, Coefficient of friction, Pin on disc.

Title of the Paper: Creep Analysis of Thin Rotating Disc under Plane Stress with no Edge load

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Authors: Sanjeev Sharma, Manoj Sahni

Abstract: - Creep stresses and strain rates for a transversely isotropic and isotropic materials have been obtained for a thin rotating disc using Seth’s transition theory. Results obtained have been discussed numerically and depicted graphically. It is seen that a disc made of transversely isotropic material rotating with higher angular speed increases the possibility of fracture at the bore as compared to a disc made of isotropic material and possibility of fracture further decreases with the increase in measure N. The deformation is significant for transversely isotropic disc for the measure N =7.

 Key words: Creep, Transition, Stresses, Strain Rates, Transversely Isotropic and Rotating Disc

Title of the Paper: Intelligent Modular Design of Automatic Dimensional Inspection Systems

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Authors: Luciana Cristea, Mihai Manescu

Abstract: The new production has to undertake a continuous quality improvement due to its major economic involvement; the consequence consists in high performances in the quality assurance. Therefore the author of this work wants to present some concerns in the automatic dimensional inspection systems field. The new production has to undertake a continuous quality improvement due to its major economic involvement; the consequence consists in high performances in the quality assurance. Therefore the author of this work wants to present some concerns in the automatic control system field. This paper presents aspects of the design for an intelligent modular inspection system. The performed researches aimed at an original method of grouping the parts based on the relation between dimensional inspection process characteristics and modular design of all inspection equipments with a high universality and flexibility degree.

Keywords: Inspection, mechatronics, modular design, automation, dimension.

Issue 8, Volume 3, August 2008

Title of the Paper: A Hierarchical Relevance Feedback Algorithm for Improving the Precision of Virtual Tutoring Assistant Systems

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Authors: Ji-Wei Wu, Judy C. R. Tseng

Abstract: In recent years, several virtual tutoring assistant systems had been proposed based on question-answering systems. These virtual tutoring assistant systems are very helpful for the students to get instant helps when the teachers are not available. Pedagogic scholars think that when a student is stuck on a certain problem while learning, an instant tutoring assistant is very helpful to promote his/her study. Therefore, the qualities (precision) of the answers of virtual tutoring assistant systems are very important. It determines the effectiveness of these systems. In practices, some students are suffered from not being able to properly express their need; some may not even know exactly what information they need. As a result, some problems do not match any existing solutions, even if they do contain some clues for finding solutions. That makes the effectiveness of the virtual tutoring assistant systems not being acceptable. In the literatures, researchers found that relevance feedback information are quite useful for information retrieval systems to improve their effectiveness. Among them, the Rocchio’s Relevance Feedback (RRF) algorithm is the most well-known and have been employed in several information retrieval systems. In this paper, we proposed a novel pseudo relevance feedback algorithm, called Hierarchical Relevance Feedback (HRF) algorithm. The HRF algorithm is used for improving the precision of virtual tutoring assistant systems. After a query is submitted by some student, the new virtual tutoring assistant system will automatically modify the student’s query according to the HRF algorithm and re-submit it to the system. Experimental results showed that the effectiveness of the system is improved by automatically modifying user’s query using the HRF algorithm. Moreover, the HRF algorithm is also outperformed the famous RRF algorithm.

Keywords: E-learning, Tutoring assistant, Information Retrieval, Question-answering, Relevance feedback

Title of the Paper: Variational Formulations and Extended Thermodynamics for Resting Irreversible Fluids with Heat Flow

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Authors: Stanislaw Sieniutycz, Piotr Kuran

Abstract: Nonequilibrium statistical mechanics helps to estimate corrections to the entropy and energy of the fluid with heat flux in terms of the nonequilibrium distribution function, f. This leads to the coefficients of wave model of heat: relaxation time, propagation speed and thermal inertia. With these data a quadratic Lagrangian and a variational principle of Hamilton’s type follows for the fluid in the field representation of fluid’s motion. We analyze canonical conservation laws and show the satisfaction of the second law under the constraint of these conservation laws.

Keywords: Grad solution, variational calculus, wave equations, conservation laws, entropy

Title of the Paper: Sub-Optimal Orbital Maneuvers for Artificial Satellites

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Authors: Bruno Nunes Vaz, Antonio Fernando Bertachini De Almeida Prado

Abstract: The determination of a specific orbit and the procedure to calculate orbital maneuvers for artificial satellites are problems of extreme importance in the study of orbital mechanics. Therefore, the transferring problem of a spaceship from one orbit to another, and the attention to this subject has increased during the last years. Many applications can be found in several space activities, for example, to put a satellite in a geostationary orbit, to change the position of a spaceship, to maintain a specific satellite’s orbit, in the design of an interplanetary mission, and others. The orbit and the general data of the Brazilian Satellite SCD-1 (Data Collecting Satellite) will be used as example in this paper. It is the first satellite developed entirely in Brazil, and it remains in operation to this date. SCD-1 was designed, developed, built, and tested by Brazilian scientists, engineers, and technicians working at INPE (National Institute for Space Research) and in Brazilian Industries. During its lifetime we will study its orbital behavior and we will perform some orbital maneuvers that could be necessary, being this one either an orbital transferring, or just to make periodical corrections. The purpose of the transferring problem is to change the position, velocity and the satellite’s mass to a new pre-determined state. This transfer can be totally linked (in the case of “Rendezvous”) or partially free (free time, free final velocity, etc). In the global case, the direction, the orientation and the magnitude of the thrust to be applied must be chosen, respecting the equipment’s limit. In order to make this transferring, either sub-optimal or optimal maneuvers may be used. In the present study, only the sub-optimal will be shown, since we want to study an algorithm for this type of maneuver. Hence, this method will simplify the direction of thrust application, to allow a fast calculation that may be used in real time, with a very fast processing. The thrust application direction to be applied will be assumed small and constant, and the purpose of this paper is to find the time interval that the thrust is applied. This paper is basically divided into three parts: during the first one the sub-optimal maneuver is explained and detailed, the second presents the Satellite SCD-1, and finally the last part shows the results using the sub-optimal maneuver applied to the Brazilian Satellite.

Keywords: Astrodynamics, Spatial Mechanics, Brazilian Satellites, Orbital Maneuvers, Space Trajectories

Title of the Paper: Modeling the Nonlinear Vibration Response of a Cracked Rotor by Time Delay and Embedding Technique

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Authors: Alfayo A. Alugongo

Abstract: In this paper, a non-linear model for a cracked rotor is established based on constitutive equations and local flexibility due to a transverse breathing crack on a rotor shaft. The crack is characterized by a switching function and change in shaft stiffness, whose variation and value defines the closing-opening or breathing condition of the crack during rotation of the shaft. The model accounts for the rotor shaft weakening parallel and perpendicular to the direction of the crack opening. The system equation bears discontinuity, and its numerical solution exhibits bifurcation and chaos. The model is used to investigate the dynamics of the vibrating rotor system, and the crack force reconstructed’ by Time delay and Embedding Technique. The crack force manifests the action of the crack on the rotor. It is observed that the largest computed Lyapunov exponent of the simulated time series is a good and sufficient indicator of the system’s chaotic state. Various scenarios of the system at sub-critical and super-critical speeds have been simulated and discussed.

Keywords: Bifurcation, Chaos, Lyapunov exponent, Cracked rotor dynamics, Switching function

Issue 9, Volume 3, September 2008

Title of the Paper: The Application of Computational Fluid Dynamic (CFD) on the Design of High Subsonic Wing

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Authors: Prasetyo Edi, Nukman Yusoff, Aznijar Ahmad Yazid

Abstract: This paper intends to present the application of Computational Fluid Dynamic (CFD) on the design of high subsonic wing of transport aircraft. The computation was performed using RAMPANT, an unstructured, multigrid flow solver. A 2-D and 3-D model of the wing was created using CATIA (2D and 3D modeling). A corresponding grid was created using preBFC and TGrid. The paper describes the technique of creating the grid and using the CFD on the wing design process. It then discusses the benefits and penalties of using the above tools. Description is then given in using the aerodynamic analysis result to optimize the wing. It concludes with a discussion of the results and recommendations for future work.

Keywords: Computational fluid dynamic (CFD), wing design, aircraft design, aerodynamic configuration

Title of the Paper: New Design Approach of Compound Helicopter

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Authors: Prasetyo Edi, Nukman Yusoff, Aznijar Ahmad Yazid, Catur Setyawan K., Nurkas W., Suyono W. A.

Abstract: Current trends in the design of helicopter have shown that in order to be economically viable and competitive it is necessary to investigate new design concept which may give an improvement in performance and operational flexibility goal and expanding the flight envelope of rotorcraft, but must be shown to be cost-effective. The helicopter has carved a niche for itself as an efficient vertical take-off and landing aircraft, but have limitation on its cruising speed due to restrictions of retreating blade stall and advancing blade compressibility on the rotor in edgewise flight. This is a challenging task, which might be solved by the use of new design approach. It is believed that the application of a compound helicopter design concept would assist in achieving such a task. This paper describes an investigation aimed to examine the suitability of a compound helicopter design concept, allowing for the use of a combined conventional fix-wing aircraft with single propeller in the nose and conventional helicopter to satisfy the above objectives. The paper describes the phenomenon of presents VTOL (vertical take-off and landing) aircraft. It then discusses the benefits and penalties of the presents concept. Description is then given of the concept proposed compound helicopter which incorporated combines main rotor-wing-auxiliary propeller. It concludes with a discussion of the results and recommendations for future work.

Keywords: Compound helicopter, VTOL (vertical take-off and landing), high speed helicopter, aircraft design

Title of the Paper: The Design Improvement of Airfoil for Flying Wing UAV

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Authors: Prasetyo Edi, Nukman Yusoff, Aznijar Ahmad Yazid

Abstract: This paper intends to presents the design improvement of airfoil for flying wing UAV (Unmanned Aerial Vehicle) when the Author works with Universiti Putra Malaysia. The design was performed using XFOIL code (an interactive program for the design and analysis of subsonic isolated airfoils) and the wind tunnel test results for verification. Eppler E334 (thickness to chord ratio, t/c = 11.93%) is used as a based airfoil. The final design was using Eppler E334 with t/c = 13.5%. It was shown from this work that the result from XFOIL is fairly accurate.

Keywords: Airfoil design, flying wing, UAV (Unmanned Aerial Vehicle), aerodynamic design

Title of the Paper: Development of a Mathematical Model for Analysis on Ship Collision Dynamics

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Authors: M. Rafiqul Islam, Zobair Ibn Awal, Adi Maimun

Abstract: This research work attempts to develop a model for ship to ship collision. The collision model is fundamentally divided into two segments namely, model for simulation before collision and model for simulation after collision. In the first part, mathematical formulations are derived for finding the possibility of a collision, determining the spatial location of collision and identification of the contact points on the ships. In the later part, a mathematical model is developed to study the kinetic energy losses, collision forces and dynamic responses with respect to different variables such as coefficient of restitution, ship speed, angle of attack, location of hitting, added mass for sway force and others. In the model, expressions for collision forces are derived based on changes in linear momentum. By incorporating the collision force into the equation of motion, which is a linear differential equation with constant coefficients, the dynamic responses are calculated for different collision scenarios. The study considered two different vessels of length 46 meter and 32 meter for conducting the simulations. Results obtained from the mathematical model suggest that collision forces can be reduced significantly by altering the considered variables; e.g. motion amplitudes can be reduced very significantly (as high as eighty five percent) by using materials with lower coefficient of restitution in the fenders and may save ships from capsizing in severe cases. Finally, a number of recommendations have been put forward and further investigations on such models are also proposed.

Keywords: Collision Dynamics, Coefficient of Restitution, Collision Forces, Ship Capsizing, Mathematical Model

Title of the Paper: Research Regarding the Establishment of Force and Energetic Characteristics of the Bucket Wheel Excavator in given Working Conditions

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Authors: Marin Silviu Nan, Iosif Kovacs, Iosif Andras, Dumitru Jula

Abstract: This paper presents the power and energy characteristics whit the view to defining and analyzing the working mode of the rotor excavators in operation at Oltenia lignite open casts, for lignite mining and for mining of the predominantly overburden rock, i.e. the sandy clay. The forces which act on a bucket and wheel, the force needed for the excavation and for lifting the material, as well as the force necessary for turning around the superior platform of the excavator during operation will be calculated. The calculus method applies to bucket wheel excavators type EsRc 1400 and SRs 1300. A software for the study of force and energetic excavation parameters is presented.

Keywords: Rotor excavator, Working mode, Forces, Power, Power consumption, Excavation capacity, Case study, Software

Issue 10, Volume 3, October 2008

Title of the Paper: Physical Modelling of a Continuous Casting Tundish: a Parametric Study of Residence Time Distribution Curves

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Authors: Amel Ferial Boudjabi, Ahmed Bellaouar, Mohammed Lachi, Nadim Elwakil

Abstract: More than 94% steelmaking and ironmaking are released in continuous casting process. Product quality is closely related to metal cleanness and non-metallic inclusions removal. So, lliquid metal flow in ladles, tundishes and moulds is recognised to be of great importance in the quality of these products. The metal jet from the ladle to tundish tends to induce turbulent motions which can play important roles in non-metallic inclusions removal at the slag surface, thereby helping in the production of cleaner steel. To improve particle decantation, flow control devices such as dams and weirs are used. The present work is an experimental study released using similarity criteria, through Reynolds and Froude numbers. A reduced scale (1/4) water model of an industrial tundish is used to visualise and measure different parameters of a tracer flow injected in water. The analysis of residence time distribution curves (RTD) by the combined model for different configurations is carried out to establish the interest of placing weirs in the amelioration of inclusions flotation and decantation.

Keywords: Continuous casting, Non-metallic inclusions decantation, Similarity criteria, Water model, Residence time, Combined model

Title of the Paper: Low Thrust Maneuvers for Artificial Satellites

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Authors: Vivian Martins Gomes, Antonio F. B. A. Prado, Helio Koiti Kuga

Abstract: An orbital maneuver is an important phase of a space mission. The idea is to change the orbit of a spacecraft, in order to be able to complete the mission goals required. It can be done to insert a spacecraft in its nominal orbit or during the mission to compensate undesired effects of perturbations. To perform the orbital maneuvers, a software that calculates an optimal maneuver is developed. This method will be used as a reference for comparison and analises of the suboptimal methods to be used on board. This method id based on an analytical development that generate equations that can be computed in a shorter time, allowing real time applications. In all the simulations, low thrust is used to make the maneuvers.

Keywords: Orbital maneuvers, low thrust, astrodynamics, artificial satellites, orbital dynamics

Issue 11, Volume 3, November 2008

Title of the Paper: Swing-By Maneuvers for a Cloud of Particles with Planets of the Solar System

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Authors: Vivian Martins Gomes, Antonio F. B. A. Prado

Abstract: The idea of the present paper is to study the swing-by maneuver between one of the planets of the Solar System and a cloud of particles. This is what happens when a fragmented comet crosses the orbit of a planet like Jupiter, Saturn, etc. We used the dynamical system that is formed by two main bodies (the Sun and one of the planets of the Solar System) and we assumed that they are in circular orbits around their center of mass and a cloud of particles is moving under the gravitational attraction of these two primaries. The motion is assumed to be planar for all the particles and the dynamics given by the “patched-conic” approximation is used, which means that a series of two-body problems are used to generate analytical equations that describe the problem. The main obejctive is to understand the change of the orbit of this cloud of particles after the close approach with the planet. It is assumed that all the particles that belong to the cloud have semi-major axis a ± da and eccentricity e ± de before the close approach with the planet. It is desired to known those values after the close approach. In particular, we will study the effects of the periapsis distance in this maneuver.

Keywords: Astrodynamics, Orbital maneuvers, Swing-By, Gravity assisted maneuvers, Orbital motion

Title of the Paper: On the Mechanics of the Particle on a Curve

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Authors: Nicolae–Doru Stanescu, Stefan Tabacu

Abstract: In this paper we present a new method to study the mechanics of a particle on a curve without friction. Two aspects are discussed. First is the static developed in linear independent co-ordinates, not necessary orthogonal. The second aspect treats the dynamics in intrinsic co-ordinates, obtaining not only the speed but also the components of the acceleration and the time variation of the generalized co-ordinate on the curve. The theory is applied in practical situations.

Keywords: Linear independent co-ordinates, static, dynamics

Issue 12, Volume 3, December 2008

Title of the Paper: Analysis of a Drainage Efficiency in Stratified Porous Media

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Authors: Chakib Seladji

Abstract: The oil recovery from reservoirs formed of more subsurface rock formations can be hindered by the variability of the rocks permeability. This element can strongly influence the oil recovery and the efficiency of the drainage process. In order to understand this phenomenon and to propose a technical solution thereafter, the simulation of an ascending air phase flow in a saturated vertical porous channel, composed of two layers with different permeabilities is done. The numerical study is performed in order to evaluate the effect of injected air mass flow rate, the effect of the porous column width and their permeability variations. The results show that some regions in the channel are not correctly drained due to high pressure losses in those regions.

Keywords: Inertial two-phase flow, pressure drop, recovery process, stratified porous matrix, saturation behavior

Title of the Paper: Design and Analysis of Modular Mobile Robot with Magnetic Wheels

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Authors: Fei Yanqiong, Song Libo

Abstract: In the paper, a modular climbing-wall mobile robot with four magnetic wheels is presented. It can move on the vertical steel wall and inspect the weld seam. First, the structure of the mobile robot is analyzed. It is modular, which consists of a light manipulator module, an ultrasonic probes module and a weld testing sensors module. Then, the magnetic wheels are designed and analysed. One magnetic wheel consists of two pieces of magnet and three pieces of pure steel plates. Second, the motion of the robot on the vertical cylindrical vessel is analysed in detail. The position deviation and angle deviation are adjusted with the geometric method. At last, the experiments of the modular climbing-wall robot on real vertical steel vessel are shown to verify the above motion analysis and design requirements at Nanjing refinery factory in China. It is of high reliability and simple control.

Keywords: Mobile robot, Magnetic wheel, Motion, Modular, Structure