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Journal Cover Facta Universitatis, Series : Mechanical Engineering
  [2 followers]  Follow
    
  This is an Open Access Journal Open Access journal
   ISSN (Print) 0354-2025 - ISSN (Online) 2335-0164
   Published by U of Niš Homepage  [11 journals]
  • APPLICATION OF THE PERFORMANCE SELECTION INDEX METHOD FOR SOLVING
           MACHINING MCDM PROBLEMS

    • Authors: Dušan Petković, Miloš Madić, Miroslav Radovanović, Valentina Gečevska
      Abstract: Complex nature of machining processes requires the use of different methods and techniques for process optimization. Over the past few years a number of different optimization methods have been proposed for solving continuous machining optimization problems. In manufacturing environment, engineers are also facing a number of discrete machining optimization problems. In order to help decision makers in solving this type of optimization problems a number of multi criteria decision making (MCDM) methods have been proposed. This paper introduces the use of an almost unexplored MCDM method, i.e. performance selection index (PSI) method for solving machining MCDM problems. The main motivation for using the PSI method is that it is not necessary to determine criteria weights as in other MCDM methods. Applicability and effectiveness of the PSI method have been demonstrated while solving two case studies dealing with machinability of materials and selection of the most suitable cutting fluid for the given machining application. The obtained rankings have good correlation with those derived by the past researchers using other MCDM methods which validate the usefulness of this method for solving machining MCDM problems.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • AN APPLICATION OF MULTICRITERIA OPTIMIZATION TO THE TWO-CARRIER TWO-SPEED
           PLANETARY GEAR TRAINS

    • Authors: Jelena Stefanović-Marinović, Sanjin Troha, Miloš Milovančević
      Abstract: The objective of this study is the application of multi-criteria optimization to the two-carrier two-speed planetary gear trains. In order to determine mathematical model of multi-criteria optimization, variables, objective functions and conditions should be determined. The subject of the paper is two-carrier two-speed planetary gears with brakes on single shafts. Apart from the determination of the set of the Pareto optimal solutions, the weighted coefficient method for choosing an optimal solution from this set is also included in the mathematical model.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • FUNCTION K - AS A LINK BETWEEN FUEL FLOW VELOCITY AND FUEL PRESSURE,
           DEPENDING ON THE TYPE OF FUEL

    • Authors: Boban Nikolić, Miloš Jovanović, Miloš Milošević, Saša Milanović
      Abstract: Regarding the application of vegetable oil based fuels in diesel engines, it is necessary to fully examine and understand the processes which take place in fuel delivery systems, namely, the processes of injection, mixture formation and combustion as well as emission characteristics. The paper provides an analysis of fuel flow in high pressure tubes of the fuel injection system, with the aim of determining function K as a link between fuel flow velocity and fuel pressure, and observing the influence of certain physical characteristics of the fuel upon the given function. The analysis presents the speed of sound and density, as fuel characteristics which affect the K function. The paper determines the speed of sound, density and bulk modulus for four fuels (pure rapeseed oil RO, biodiesel B100, a mixture of biodiesel and diesel B50, and diesel D), and forms appropriate K functions for each fuel in the pressure range from the atmospheric one to 1600 bar.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • IMPLANT MATERIAL SELECTION USING EXPERT SYSTEM

    • Authors: Miloš Ristić, Miodrag Manić, Dragan Mišić, Miloš Kosanović, Milorad Mitković
      Abstract: Most certainly, in the field of medicine there is a great contribution of new techniques and technologies, which is reflected in an entire system of health care services. Customized implants are both fully geometrically and topologically adjusted so as to meet the needs of individual patients, thus making each implant unique. Their production requires joint efforts of a multidisciplinary team of different profile experts who combine their knowledge in the Implant knowledge model. Thus, we develop an expert system which should help or replace humans in the process of Implant material selection. This paper gives an overview of the expert system concept for the given problem. Its task is to carry out a selection of biomaterial (or class of material) for a customized implant. The model significantly improves the efficiency of preoperative planning in orthopaedics.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • DEEP DRAWING TECHNOLOGY WITH WALL IRONING IN MASS PACKAGING INDUSTRY

    • Authors: Saša Ranđelović, Mladomir Milutinović, Vladislav Blagojević
      Abstract: Aluminum is a metal that is being increasingly used in the packaging industry in the modern metal forming technology, but it also provides a good opportunity for effective advertising and product promotion. Processing technologies for aluminum plastic deformation ensure superior packaging that meets the most rigorous demands in the food, pharmaceutical, chemical, and other industries. It is the case of mass production with very little material loss that offers the possibility of multiple recycling. On the other hand, today's products for general purpose consumers cannot be imagined without aggressive advertising that has a major impact on customers. Modern graphics techniques for printing images and different basic surfaces offer great opportunities that manufacturers use widely in the promotion and sale of their products.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • A THEORETICAL-EXPERIMENTAL APPROACH FOR ELASTO-DAMPING PARAMETERS
           ESTIMATION OF CONE INERTIAL CRUSHER MOUNTING

    • Authors: Rosen Mitrev, Simeon Savov
      Abstract: The present paper deals with estimation of the elasto-damping parameters of a cone inertial crusher mounting. The numerical values of these parameters are crucial for accurate reproduction of the machine vibrational behavior and dynamical model adequacy. Due to the significant difficulties arising during the purely theoretical determination of the stiffness and damping parameters of the rubber vibroisolators it is well-suited to use a theoretical-experimental approach. The developed approach is based on the theoretical determination of the mounting stiffness parameters as a function of two experimentally measured natural frequencies of the mechanical system. The crusher is represented as a six degrees of freedom system with two planes of symmetry. By using the system characteristic polynomial, the theoretical derivation of mathematical relationships for the mechanical system natural frequencies as a function of stiffness, inertial and geometrical parameters is performed. A good agreement is shown when comparing the experimental and the theoretical results for the system kinematical characteristics.
      PubDate: 2017-02-02
      Issue No: Vol. 14, No. 3 (2017)
       
  • FOREWORD

    • Authors: Dragan Marinković
      Abstract: Foreword to the thematic issue entitled:TRIBOLOGY AND CONTACT MECHANICS IN BIOLOGICAL AND MEDICAL APPLICATIONS
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • INDENTATION OF FLAT-ENDED AND TAPERED INDENTERS WITH POLYGONAL
           CROSS-SECTIONS

    • Authors: Qiang Li, Valentin L. Popov
      Pages: 241 - 249
      Abstract: Using the Boundary Element Method, we numerically study the indentation of prismatic and tapered indenters with polygonal cross-sections. The contact stiffness of punches with flat bases in the form of a triangle and a square as well as a number of higher-order polygons is determined. In particular, the classical results of King (1987) for indenters with triangle and square base shapes are revised and more precise numerical results are provided. For tapered indenters, the equivalent transformed profile used in the Method of Dimensionality Reduction (MDR) is determined. It is shown that the MDR-transformed profile of polygon-based indenters with power function side is given by the power function with the same power; it differs from the 3D profile only by a constant coefficient. These coefficients are listed in the paper for various types of indenters, in particular for pyramidal and paraboloid ones. The determined MDR-transformed profiles can be used for study of other contact problems such as tangential contact, normal contact with elastomers, and, in an approximate way, to adhesive contacts.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • METHOD OF DIMENSIONALITY REDUCTION IN CONTACT MECHANICS AND FRICTION: A
           USER'S HANDBOOK. II. POWER-LAW GRADED MATERIALS

    • Authors: Markus Hess, Valentin L. Popov
      Pages: 251 - 268
      Abstract: Until recently, the only way of solving contact problems was to applythree-dimensional contact theories. However, this presupposes higher mathematical and nu-merical knowledge, which usually only research groups possess. This has changed drastically with the development of the method of dimensionality reduction (MDR), which allows every practically oriented engineer an access to the solution of contact problems. The simple and contact-type dependent rules are summarized in the first part of the user manual; they require contacts between elastically homogeneous materials. The present paper forms the second part of the user handbook and is dedicated to the solution of contact problems between power-law graded materials. All the MDR-rules are listed with which normal, tangential and adhesive contacts between such high-performance materials can be calculated in a simple manner.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • ADHESION EFFECTS WITHIN THE HARD MATTER – SOFT MATTER INTERFACE:
           MOLECULAR DYNAMICS

    • Authors: Alexey Tsukanov, Sergey Psakhie
      Pages: 269 - 280
      Abstract: In the present study three soft matter – hard matter systems consisting of different nanomaterials and organic molecules were studied using the steered molecular dynamics approach in order to reveal regularities in the formation of organic-inorganic hybrids and the stability of multimolecular complexes, as well as to analyze the energy aspects of adhesion between bio-molecules and layered ceramics. The combined process free energy estimation (COPFEE) procedure was used for quantitative and qualitative assessment of the considered heterogeneous systems. Interaction of anionic and cationic amino acids with the surface of a [Mg4Al2(OH)122+ 2Cl–] layered double hydroxide (LDH) nanosheet was considered. In both cases, strong adhesion was observed despite the opposite signs of electric charge. The free energy of the aspartic amino acid anion, which has two deprotonated carboxylic groups, was determined to be –45 kJ/mol for adsorption on the LDH surface. For the cationic arginine, with only one carboxylic group and a positive net charge, the energy of adsorption was –26 kJ/mol, which is twice higher than that of chloride anion adsorption on the same cationic nanosheet. This fact clearly demonstrates the capability of “soft matter” species to adjust themselves and fit into the surface, minimizing energy of the system. The adsorption of protonated histamine, having no carboxylic groups, on a boehmite nanosheet is also energetically favorable, but the depth of free energy well is quite small at 3.6 kJ/mol. In the adsorbed state the protonated amino-group of histamine plays the role of proton donor, while the hydroxyl oxygens of the layered hydroxide have the role of proton acceptor, which is unusual. The obtained results represent a small step towards further understanding of the adhesion effects within the hard matter – soft matter contact zone.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • THE JKR-ADHESIVE NORMAL CONTACT PROBLEM OF AXISYMMETRIC RIGID PUNCHES WITH
           A FLAT ANNULAR SHAPE OR CONCAVE PROFILES

    • Authors: Emanuel Willert, Qiang Li, Valentin L. Popov
      Pages: 281 - 292
      Abstract: The JKR-adhesive frictionless normal contact problem is solved for the flat annular and the conical or spherical concave rigid punch indenting an elastic half space. The adhesive solution can be derived analytically from the non-adhesive one, the latter one being calculated by the boundary element method. It is found that the annular flat punch will always start to detach at the outer boundary. The pull-off forces for both concave punch shapes almost do not depend on the pull-off boundary regime and can be significantly larger than the pull-off force for the cylindrical flat punch.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • THE BOUNDARY ELEMENT METHOD FOR VISCOELASTIC MATERIAL APPLIED TO THE
           OBLIQUE IMPACT OF SPHERES

    • Authors: Stephan Kusche
      Pages: 293 - 300
      Abstract: The Boundary Element Method (BEM) for elastic materials is extended to deal with viscoelastic media. This is obtained by making use of a similar form of the fundamental solution for both the materials. Some considerations are attributed to the difference of the normal and the tangential contact problem. Both normal and tangential problems are furthermore assumed to be decoupled. Then the oblique impact of hard spheres with an incompressible viscoelastic half-space (linear standard-model) is studied. By assuming stick conditions during impact, one obtains the dependence of the two coefficients of restitution as functions of two input parameters. This result is expressed in an elegant and compact form of the fitting function.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • MODIFYING AND EXPANDING THE SIMULATION OF WEAR IN THE SPHERICAL JOINT WITH
           A POLYMERIC COMPONENT OF THE TOTAL HIP PROSTHESIS

    • Authors: Vladimir Pakhaliuk, Aleksandr Poliakov, Mikhail Kalinin, Yevgenii Pashkov, Pavel Gadkov
      Pages: 301 - 312
      Abstract: The existing model of wear, based on the classical Archard equation, in the spherical joint of a total hip prosthesis comprising an acetabular cup of ultra-high molecular weight polyethylene (UHMWPE) in combination with a metal or ceramic femoral head is modified and expanded. With this model, studies are conducted using the finite element analysis in terms of cumulative linear and volumetric wear for the ISO 14242-1 demands and additionally for the conditions during walking gait. Also they are carried out for the head diameter of 28 mm at the constant and the variable wear factor, where the variable wear factor is adopted from the modified formula for the dependence on the contact pressure.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • TANGENTIAL DISPLACEMENT INFLUENCE ON THE CRITICAL NORMAL FORCE OF ADHESIVE
           CONTACT BREAKAGE IN BIOLOGICAL SYSTEMS

    • Authors: Iakov A. Lyashenko
      Pages: 313 - 320
      Abstract: The dependencies of the critical components of normal and tangential forces corresponding to the contact breakage between a parabolic indenter and an elastic half-space have been determined taking into account adhesive interaction. In order to describe the adhesive contact, the method of dimensionality reduction (MDR) and the modified rule of Heß taking into account tangential displacements have been used. The influence of the surface energy depending on the indenter separation angle has been studied.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • BIOSIMILAR ARTIFICIAL KNEE FOR TRANSFEMORAL PROSTHESES AND EXOSKELETONS

    • Authors: Aleksandr Poliakov, Vladimir Pakhaliuk, Nikolay Lozinskiy, Marina Kolesova, Pavel Bugayov, Petro Shtanko
      Pages: 321 - 328
      Abstract: Artificial knees play an important role in transfemoral prostheses, lower extremity exoskeletons and walking robots. Their designs must provide natural kinematics, high strength and stiffness required in the stance phase of gait. Additionally, modern artificial knee is the principal module by means of which the prosthesis control is performed. This paper presents a prototype of an artificial polycentric knee, designed on the basis of the hinge mechanism with cross links. In order to increase strength and stiffness, the elements of the joint have curved supporting surfaces formed in the shape of centroids in relative motion of links of the hinge mechanism. Such construction is a mechanical system with redundant links but it allows for providing desirable characteristics of the artificial knee. Synthesis of the hinge mechanism is made by a method of systematic study of the parameter space, uniformly distributed in a finite dimensional cube. Stiffness of bearing surfaces elements of knee was determined by solving the contact problem with slippage of surfaces relative to each other.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • NUMERICAL STUDY OF STRESS-STRAIN LOCALIZATION IN THE TITANIUM SURFACE
           MODIFIED BY AN ELECTRON BEAM TREATMENT

    • Authors: Ruslan Balokhonov, Varvara Romanova, Alexey Panin, Sergey Martynov, Marina Kazachenok
      Pages: 329 - 334
      Abstract: Numerical simulation is performed to investigate the mesoscale stress-strain localization in a surface-modified commercial titanium alloy. The calculated crystalline microstructure corresponds to that observed in experiments and is accounted for in an explicit way as initial conditions of a dynamic boundary-value problem. The latter is stated in terms of plane strain developing in microstructure subjected to tension and is solved numerically by the finite-difference method. Elastic-plastic constitutive models were built to describe the experimental mechanical response both of the substrate and of the modified layer. Plastic strain localization is found to depend on the grain yield strength.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • CRITICAL VELOCITY OF CONTROLLABILITY OF SLIDING FRICTION BY NORMAL
           OSCILLATIONS IN VISCOELASTIC CONTACTS

    • Authors: Mikhail Popov
      Pages: 335 - 341
      Abstract: Sliding friction can be reduced substantially by applying ultrasonic vibration in the sliding plane or in the normal direction. This effect is well known and used in many applications ranging from press forming to ultrasonic actuators. One of the characteristics of the phenomenon is that, at a given frequency and amplitude of oscillation, the observed friction reduction diminishes with increasing sliding velocity. Beyond a certain critical sliding velocity, there is no longer any difference between the coefficients of friction with or without vibration. This critical velocity depends on material and kinematic parameters and is a key characteristic that must be accounted for by any theory of influence of vibration on friction. Recently, the critical sliding velocity has been interpreted as the transition point from periodic stick-slip to pure sliding and was calculated for purely elastic contacts under uniform sliding with periodic normal loading. Here we perform a similar analysis of the critical velocity in viscoelastic contacts using a Kelvin material to describe viscoelasticity. A closed-form solution is presented, which contains previously reported results as special cases. This paves the way for more detailed studies of active control of friction in viscoelastic systems, a previously neglected topic with possible applications in elastomer technology and in medicine.
      PubDate: 2016-12-08
      Issue No: Vol. 14, No. 3 (2016)
       
  • NON-FRAGILE ROBUST H∞ CONTROLLER FOR HALF-CAR ACTIVE SUSPENSION SYSTEMS
           CONSIDERING DRIVER’S BIODYNAMICS

    • Authors: Mohammad Gudarzi
      Pages: 121 - 134
      Abstract: The paper investigates a non-fragile robust control strategy for a half-car active suspension system considering human-body dynamics. A 4-DoF uncertain vibration model of the driver’s body is combined with the car’s model in order to make the controller design procedure more accurate. The desired controller is obtained by solving a linear matrix inequality formulation. Then the performance of the active suspension system with the designed controller is compared to the passive one in both frequency and time domain simulations. Finally, the effect of the controller gain variations on the closed-loop system performance is investigated numerically.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • SOFTWARE TOOL FOR LASER CUTTING PROCESS CONTROL – SOLVING REAL
           INDUSTRIAL CASE STUDIES

    • Authors: Miloš Madić, Marko Kovačević, Miroslav Radovanović, Vladislav Blagojević
      Pages: 135 - 145
      Abstract: Laser cutting is one of the leading non-conventional machining technologies with a wide spectrum of application in modern industry. It order to exploit a number of advantages that this technology offers for contour cutting of materials, it is necessary to carefully select laser cutting conditions for each given workpiece material, thickness and desired cut qualities. In other words, there is a need for process control of laser cutting. After a comprehensive analysis of the main laser cutting parameters and process performance characteristics, the application of the developed software tool “BRUTOMIZER” for off-line control of CO2 laser cutting process of three different workpiece materials (mild steel, stainless steel and aluminum) is illustrated. Advantages and abilities of the developed software tool are also illustrated.

      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • CAD/CAM DESIGN AND GENETIC OPTIMIZATION OF FEEDERS FOR SAND CASTING
           PROCESS

    • Authors: Nedeljko Dučić, Žarko Ćojbašić, Radomir Radiša, Radomir Slavković, Ivan Milićević
      Pages: 147 - 158
      Abstract: The paper proposes methodology of feeder design and optimization for sand casting process. Casting part is a part of excavator buckets, i.e. holder of the cutting tooth. Process of design and optimization is based on the application of the rules, which are the result of many years of work researchers in the field of metal casting. Computer Aided Design (CAD) is used as a methodology in the design of feeders. Genetic Algorithm (GA) as an artificial intelligence technique is used in the optimization process of the feeder geometry. Computer Aided Manufacturing (CAM) is used as methodology that involves numerical simulation of the casting process. Numerical simulation is used to verify the validity of the optimized geometry of the feeding system.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • REDUCTION OF RESIDUAL SHEAR STRESS IN THE LOADED CONTACT USING FRICTION
           HYSTERESIS

    • Authors: Adrian Kraft, Roman Pohrt
      Pages: 159 - 168
      Abstract: We investigate the tangential contact problem of a spherical indenter at constant normal force. When the indenter is subjected to tangential movement, frictional shear stresses arise at the interface and do not vanish when it is moved backwards. We study the evolution of shear stress when the indenter is moved back and forth at falling amplitude. The method of dimensionality reduction (MDR) is employed for obtaining the distribution of stick and slip zones as well as external forces and the final stress distribution. We find that the shear stress decreases. For the special case of linearly falling amplitude of the movement, we observe uniform peaks in the shear stress. The absolute value of the shear stress peaks is reduced best for a high number of back-and-forth-movements with slowly decreasing amplitude.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • BROWNIAN HEAT TRANSFER ENHANCEMENT IN THE TURBULENT REGIME

    • Authors: Suresh Chandrasekhar, Vaarin Majumdar Sharma
      Pages: 169 - 177
      Abstract: The paper presents convection heat transfer of a turbulent flow Al2O3/water nanofluid in a circular duct. The duct is a under constant and uniform heat flux. The paper computationally investigates the system’s thermal behavior in a wide range of Reynolds number and also volume concentration up to 6%. To obtain the nanofluid thermophysical properties, the Hamilton-Crosser model along with the Brownian motion effect are utilized. Then the thermal performance of the system with the nanofluid is compared to the conventional systems which use water as the working fluid. The results indicate that the use of nanofluid of 6% improves the heat transfer rate up to 36.8% with respect to pure water. Therefore, using the Al2O3/water nanofluid instead of water can be a great choice when better heat transfer is needed.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • INSTABILITY OF THE RAYLEIGH-BENARD CONVECTION FOR INCLINED LOWER WALL WITH
           TEMPERATURE VARIATION

    • Authors: Sadoon Ayed, Gradimir Ilić, Predrag Živković, Mića Vukić, Mladen Tomić
      Pages: 179 - 197
      Abstract: This paper deals with an analysis of a two-dimensional viscous fluid flow between the two parallel plates inclined with respect to the horizontal plane, where the lower plate is heated and the upper one is cooled. The temperature difference between the plates is gradually increased during a certain time period after which it is temporarily constant. The temperature distribution on the lower plate is not constant in x-direction, there is a longitudinal sinusoidal temperature variation imposed on the mean temperature. We have investigated the wave number and amplitude influence of this variation on the subcritical stability and the onset of the Rayleigh-Bénard convective cells, by direct numerical simulation of 2D Navier-Stokes and energy equation.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • SPLITTING THE TOTAL EXERGY DESTRUCTION INTO THE ENDOGENOUS AND EXOGENOUS
           PARTS OF THE THERMAL PROCESSES IN A REAL INDUSTRIAL PLANT

    • Authors: Goran Vučković, Mića Vukić, Mirko Stojiljković, Miloš Simonović
      Pages: 199 - 208
      Abstract: The total exergy destruction occurring in a component is not only due to the component itself (endogenous exergy destruction) but is also caused by the inefficiencies of the remaining system components (exogenous exergy destruction). Hence care must be taken in using the total exergy destruction of a component for making decisions to optimize the overall energy system. In this paper, a complex industrial plant is analyzed by splitting the component’s exergy destruction into its endogenous part (the part resulting totally from the component’s irreversibilities) and its exogenous part (resulting from the irreversibilities of the other components within the system). It is observed that the steam generator has the dominant effect. From the total exergy destruction in the steam generator, 1,097.63 kW or 96.95% come from internal irreversibilities in the component, while the influence of other components on the loss of useful work in the steam generator is only 3.05%.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • ADAPTIVE NEURO-FUZZY COMPUTING TECHNIQUE FOR PRECIPITATION ESTIMATION

    • Authors: Dalibor Petković, Milan Gocić, Shahaboddin Shamshirband
      Pages: 209 - 218
      Abstract: The paper investigates the accuracy of an adaptive neuro-fuzzy computing technique in precipitation estimation. The monthly precipitation data from 29 synoptic stations in Serbia during 1946-2012 are used as case studies. Even though a number of mathematical functions have been proposed for modeling the precipitation estimation, these models still suffer from the disadvantages such as their being very demanding in terms of calculation time. Artificial neural network (ANN) can be used as an alternative to the analytical approach since it offers advantages such as no required knowledge of internal system parameters, compact solution for multi-variable problems and fast calculation. Due to its being a crucial problem, this paper presents a process constructed so as to simulate precipitation with an adaptive neuro-fuzzy inference (ANFIS) method. ANFIS is a specific type of the ANN family and shows very good learning and prediction capabilities, which makes it an efficient tool for dealing with encountered uncertainties in any system such as precipitation. Neural network in ANFIS adjusts parameters of membership function in the fuzzy logic of the fuzzy inference system (FIS). This intelligent algorithm is implemented using Matlab/Simulink and the performances are investigated.  The simulation results presented in this paper show the effectiveness of the developed method.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • THE PATH TOWARDS ACHIEVING A LEAN SIX SIGMA COMPANY USING THE EXAMPLE OF
           THE SHINWON COMPANY IN SERBIA

    • Authors: Srđan Mladenović, Peđa Milosavljević, Nevena Milojević, Dragan Pavlović, Milena Todorović
      Pages: 219 - 226
      Abstract: In the last twenty years, many companies have realized that the demands of the global market, including more demanding and receptive customers, have set new standards for production flexibility. Gradual reduction of mass production, characteristic of a large number of companies, has opened space for the introduction of a new system which focuses exclusively on the customer. The customer-oriented system was created with the idea that process optimization would lead to the production of a relatively cheap product, delivered on time and with the best possible quality. Such a system is achieved by applying the Lean Six Sigma concept. The aim of this paper is to identify all of the defects that occur as losses and complicate the process of production in order to achieve the Lean Six Sigma level in the Shinwon Company. The original data from the Shinwon company were identified, collected and analyzed, using the methods and tools of the Lean Six Sigma concept (Process Mapping, 5S audit, Pareto diagram, Ishikawa diagram, Seven basic wastes and SPC analysis), in order to present the effectiveness of the quality management system and to evaluate the possibility of its continuous improvement.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • AN EFFICIENT CO-ROTATIONAL FEM FORMULATION USING A PROJECTOR MATRIX

    • Authors: Viet Anh Nguyen, Manfred Zehn, Dragan Marinković
      Pages: 227 - 240
      Abstract: Co-rotational finite element (FE) formulations can be seen as a very efficient approach to resolving geometrically nonlinear problems in the field of structural mechanics. A number of co-rotational FE formulations have been well documented for shell and beam structures in the available literature. The purpose of this paper is to present a co-rotational FEM formulation for fast and highly efficient computation of large three-dimensional elastic deformations. On the one hand, the approach aims at a simple way of separating the element rigid-body rotation and the elastic deformational part by means of the polar decomposition of deformation gradient. On the other hand, a consistent linearization is introduced to derive the internal force vector and the tangent stiffness matrix based on the total Lagrangian formulation. It results in a non-linear projector matrix. In this way, it ensures the force equilibrium of each element and enables a relatively straightforward upgrade of the finite elements for linear analysis to the finite elements for geometrically non-linear analysis. In this work, a simple 4-node tetrahedral element is used. To demonstrate the efficiency and accuracy of the proposed formulation, nonlinear results from ABAQUS are used as a reference.
      PubDate: 2016-08-02
      Issue No: Vol. 14, No. 2 (2016)
       
  • MODELS FOR INTRALAMINAR DAMAGE AND FAILURE OF FIBER COMPOSITES - A REVIEW

    • Authors: Klaus Rohwer
      Pages: 1 - 19
      Abstract: In order to fully exploit the potential of structures made from fiber composites, designers need to know how damage occurs and develops and under what conditions the structure finally fails. Anisotropy and inhomogeneity cause a rather complex process of damage development which may be one reason for an exceptionally large number of existing models. This paper intends to provide an overview over those models and give some hints about current developments. As such it is an updated version of a recent publication [1]. The survey is limited to laminates from unidirectional layers out of straight continuous fiber polymer composites under quasi-static loading. Furthermore, focus is laid on intralaminar damage.
      Many failure models smear out the inhomogeneity between fibers and the matrix. Simply limiting each stress component separately can lead to surprisingly good results as documented in the first World-Wide Failure Exercise. Interpolation criteria consider mutual influence of normal and shear stresses, predominantly through a quadratic failure condition. Traditionally one distinguishes between interpolation criteria and physically based ones. As an important physical effect the difference between fiber failure and inter-fiber failure is considered. Furthermore, stress invariants are taken as a basis, increased shear strength under compression is accounted for, and characteristic failure modes are captured. Fibers and the matrix material are characterized by a large disparity in stiffness and strength. Micromechanical models consider this inhomogeneity but suffer from the difficulty to determine relevant material properties. Compressive strength in fiber direction has attracted special attention. However, the role of kink band formation, which is observed in the failure process, seems to be not yet fully understood.
      In summary it must be concluded that despite the tremendous effort which has been put into the model development the damage and failure simulation of fiber composites are not in a fully satisfying state. That is partly due to lack of accurate and reliable test results. 
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • MODAL TRIGGERED NONLINEARITIES FOR DAMAGE LOCALIZATION IN THIN WALLED FRC
           STRUCTURES – A NUMERICAL STUDY

    • Authors: Tobias Rademacher, Manfred Zehn
      Pages: 21 - 36
      Abstract: This paper presents a novel method for detecting locations of damages in thin walled structural components made of fiber reinforced composites (FRC). Therefore, the change of harmonic distortion, which is found by current research to be very sensitive to delamination, under resonant excitation will be derived from FEM-simulation. Based on the linear modal description of the undamaged structure and the damage-induced nonlinearities represented by a nonlinear measure, two spatial damage indexes have been formulated.
      The main advantage of this novel approach is that the information about the defect is represented mainly by changes in the modal harmonic distortion (MHD), which just needs to be measured in one (or few) structural points. The spatial resolution is given by the pairwise coupling of the MHD with the corresponding mode shapes.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • MU-SYNTHESIS BASED ACTIVE ROBUST VIBRATION CONTROL OF AN MRI INLET

    • Authors: Atta Oveisi, Tamara Nestorović
      Pages: 37 - 53
      Abstract: In this paper, a robust control technique based on μ-synthesis is employed in order to investigate the vibration control of a funnel-shaped structure that is used as the inlet of a magnetic resonance imaging (MRI) device. MRI devices are widely subjected to the vibration of the magnetic gradient coil which then propagates to acoustic noise and leads to a series of clinical and mechanical problems. In order to address this issue and as a part of noise cancellation study in MRI devices, distributed piezo-transducers are bounded on the top surface of the funnel as functional sensor/actuator modules. Then, a reduced order linear time-invariant (LTI) model of the piezolaminated structure in the state-space representation is estimated by means of a predictive error minimization (PEM) algorithm as a subspace identification method based on the trust-region-reflective technique. The reduced order model is expanded by the introduction of appropriate frequency-dependent weighting functions that address the unmodeled dynamics and the augmented multiplicative modeling uncertainties of the system. Then, the standard D-K iteration algorithm as an output-feedback control method is used based on the nominal model with the subordinate uncertainty elements from the previous step. Finally, the proposed control system implemented experimentally on the real structure is to evaluate the robust vibration attenuation performance of the closed-loop system.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • LIMITING PROFILE OF AXISYMMETRIC INDENTER DUE TO THE INITIALLY DISPLACED
           DUAL-MOTION FRETTING WEAR

    • Authors: Qiang Li
      Pages: 55 - 61
      Abstract: Recently the final worn shape of elastic indenters due to fretting wear was analytically solved using the method of dimensionality reduction. In this paper we extend this model to dual-motion fretting wear and take into account that the indenter is initially pressed with constant indentation depth and moved horizontally with constant displacement. Two key parameters, the maximal indentation depth during oscillation and the stick area radius in the final state as well as the liming shape of indenter are analytically calculated. It is shown that the oscillation amplitudes and the initially indented or moved displacements have an influence on the final shaking-down shape.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • AN ADVANCED COARSE-FINE SEARCH APPROACH FOR DIGITAL IMAGE CORRELATION
           APPLICATIONS

    • Authors: Samo Simončič, Melita Kompolšek, Primož Podržaj
      Pages: 63 - 73
      Abstract: The paper presents a newly developed fine search algorithm used in the application of digital correlation. In order to evaluate its performance a special purpose application was developed using C# programming language. The algorithm was then tested on a pre-prepared set of the computer generated speckled images. It turned out to be much faster than the conventional fine search algorithm. Consequently, it is a major step forward in a never ending quest for a fast digital correlation execution with sub pixel accuracy.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • BENDING VIBRATION AND STABILITY OF A MULTIPLE-NANOBEAM SYSTEM INFLUENCED
           BY TEMPERATURE CHANGE

    • Authors: Danilo Karličić, Sanja Ožvat, Milan Cajić, Predrag Kozić, Ratko Pavlović
      Pages: 75 - 88
      Abstract: In this study, we analyzed the bending vibration and stability of a multiple-nanobeam system (MNBS) coupled in elastic medium and influenced by temperature change and compressive axial load. The MNBS is modeled as the system consisting of a set of m identical and simply supported nanobeams mutually connected by Winkler’s type elastic layers. According to the Euler - Bernoulli beam and nonlocal thermo-elasticity theory, the system of m coupled partial differential equations is derived and solved by means of the method of separation of variables as well as the trigonometric one. Analytical solutions for natural frequencies and critical buckling loads of elastic MNBS are obtained. The effects of nonlocal parameter, temperature change and the number of nanobeams on the natural frequencies and the buckling loads are investigated through numerical examples. Thus, this work can represent a starting point to examine dynamical behavior and design of complex nanobeam structures, nanocomposites and nanodevices under the influence of various physical fields.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • A STUDY OF THIN FILM LUBRICATION AT NANOSCALE FOR A FERROFLUID BASED
           INFINITELY LONG ROUGH POROUS SLIDER BEARING

    • Authors: Jimit R. Patel, Gunamani M. Deheri
      Pages: 89 - 99
      Abstract: The study aims at analyzing the performance of a ferrofluid-based infinitely long rough porous slider bearing which makes use of thin film lubrication at nanoscale. The stochastic model of Christensen and Tonder has been employed to analyze the effect of surface roughness while the Neuringer-Rosensweig’s model has been adopted to study the magnetization effect. The pressure distribution in the bearing system has been obtained by solving the associated stochastically averaged Reynolds type equation. The results indicate that although the transverse roughness is supposed to affect the bearing system adversely, the situation remains fairly better in the case of thin film lubrication at nanoscale. In fact, the consideration of thin film lubrication at nanoscale results in an all round improved performance, even for lower strength of the magnetic intensity. However, the couple stress adds a little more to this positive effect.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • EXPERIMENTAL FORCED SOLAR THIN LAYER GINGER DRYING

    • Authors: Mahesh Kumar
      Pages: 101 - 111
      Abstract: In this research paper, the convective and the evaporative heat transfer coefficients of ginger (zingiber officinale) drying in an indirect solar cabinet dryer under the induced forced convection mode is presented. Experiments were conducted during the month of March 2015 under the climatic conditions of Hisar, India (29°5’5”N latitude and 75°45’55”E longitude). The experimental data obtained for solar drying of a constant ginger mass of 150 g has been used to determine constants ‘C’ and ‘n’ in the Nusselt number expression using linear regression analysis; consequently, the convective and the evaporative heat transfer coefficients have been evaluated. The average value of constants ‘C’ and ‘n’ were evaluated as 0.999 and 0.318, respectively. The average values of the convective and the evaporative heat transfer coefficients were found to be 3.95 W/m2 °C and 160.47 W/m2 °C, respectively, for the given mass samples of ginger. The average collector efficiency was observed to be 14.5%. The experimental error in terms of percentage uncertainty was found to be 20.87%.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
  • SOLAR VACUUM TUBE INTEGRATED SEAWATER DISTILLATION - AN EXPERIMENTAL STUDY

    • Authors: Selcuk Selimli, Ziyaddin Recebli, Semra Ulker
      Pages: 113 - 120
      Abstract: The subject of this study is the seawater distillation process enhancement through integration of the solar vacuum tube into the system. Positive effects on the rate of distillated freshwater achieved by means of the enhanced system have been investigated experimentally. Experiments were done in the Turkish city of Samsun in the Black Sea region. A distillation pond setup having the volume of 0.015m3 and a water surface area of 0.24m2 was constructed. The distillation pond is covered with a condensation glass and also equipped with a 0.15m solar vacuum tube that is inclined at an angle of 30o to the ground, a feed water tank connected with a ball cock, and distillated fresh water tank. Experimental results have shown that the rate of distilled fresh water was enhanced for about 62.5% by integrating the solar vacuum tube and the natural distillation pond. Isolation of the condensation glass not only prevents the light transmission to the pond but also heat loss from the pond; hence the rate of the distillated fresh water is increased for about 137.5% due to the natural distillation.
      PubDate: 2016-04-01
      Issue No: Vol. 14, No. 1 (2016)
       
 
 
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