# International Journal of Mechanics

**ISSN: 1998-4448
Volume 11, 2017**

Notice: As of 2014 and for the forthcoming years, the publication frequency/periodicity of NAUN Journals is adapted to the 'continuously updated' model. What this means is that instead of being separated into issues, new papers will be added on a continuous basis, allowing a more regular flow and shorter publication times. The papers will appear in reverse order, therefore the most recent one will be on top.

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**Volume 11, 2017**

Title of the Paper: **Buckling and Free Vibration Analysis of Sandwich Plate**

Authors: **E. Kormanikova, K. Kotrasova**

Pages: **299-304**

Abstract: The paper presents buckling and free vibration analysis of sandwich plate with laminate facings. The sandwich plate is subjected to the Tsai-Wu criterion. Then buckling analysis of the sandwich plate is performed in two steps. First, a finite element method is used to determine the overall buckling load of the sandwich plate. The second part of the analysis is free vibration analysis. The investigated sandwich plate is simply supported at all boundaries and loaded by an uniaxial uniform load.

Title of the Paper: **Fatigue Life Prediction of Titanium Implants with Titanium Dioxide Surface**

Authors: **Stepan Major, Vladimír Kocour, Jan Bryscejn**

Pages: **288-298**

Abstract: Most of mechanical components in the engineering are frequently subjected to multi-axial loading, which also applies to medical engineering. The cyclic-loading can lead to sudden fatigue failure. In present work the fatigue life of cylindrical titanium components of dental implants made from titanium alloys 6Al-4V ELI and 6Al-7Nb were studied. Contrary to surface treatments used in industry, the main goal of titanium dioxide deposition is to improve implants biocompatibility. The effect of surface treatment on fatigue life of implant was tested experimentally. Two sets of experimental samples differed in surface layer thickness, so that its influence can be compared. Its fatigue behaviour was studied and predictive models were tested. Seventeenth different models were applied and analysed in order to obtain the best way to predict fatigue life of implant. Two different types of implants were tested. First type of implant uses abutment screw to fix the crown. This type has four parts. Second type of dental replacement has only three components. This type utilizes abutment polygonal thorn to fix the crown. Experiments show that, the effect of titanium dioxide surfaces on implants mechanical properties is considered negligible. Therefore implants fatigue life is not dependent on dioxide layer thickness. The Gonçalves- Araujo- Mamiya criterion was found the best in implants fatigue prediction. The prediction of fatigue life of polygonal thorn is more complicated, so its prediction is gives inferior results contrary to the first type of implant.

Title of the Paper: **Comparative Study of an Optimal Utilization in Case of Composite Columns of HSS and HPC**

Authors: **Michal Štrba, Marcela Karmazínová**

Pages: **281-287**

Abstract: Several important parameters in the procedure of an optimal design of load-bearing structures exist in a field of civil engineering. As an example of those parameters the using of an efficient and suitable material can be mentioned. In general, the composite steel-concrete columns are usually designed by using of a steel grade S235 or S355 and with a concrete class up to C40/50. The use of high-strength steel seems to be unsuitable, especially in case of buckling, because the utilization of steel is lower (the extreme fiber stress does not reach a yield limit and a modulus of elasticity stays unchanged). However, the high strength materials can be still advantageously used for an increasing of a load-carrying capacity together with a reduction of a self-weight (in comparison to the columns made of an ordinary class of concrete or steel grade). This paper presents some information about a comparative study in the event of using high-strength steel (HSS) and high-performance concrete (HPC) in case of the design of compressed composite columns. The study is partially based on a previous research on the authors’ workplace (Faculty of Civil Engineering at Brno University of Technology) and it deals with the problems of the design especially in case of the composite columns of a circular and partially encased H cross-section under centric compressive loading according to all the rules given by Eurocode.

Title of the Paper: **Numerical Study for Forecasting the Dam Break Flooding Flows Impacts on Different Shaped Obstacles**

Authors: **Issakhov A. A., Mussakulova G.**

Pages: **273-280**

Abstract: This paper presents numerical study for forecasting the dam break flooding flows impacts on different shaped obstacles. A mathematical model for simulation of flooding flow is based on Navier-Stokes equations coupled with the volume-of-fluid (VOF) method. The 2D computational domain is discretized via the finite volume method (FVM). For turbulence modelling, the model is chosen. The interface between air and liquid is captured by CICSAM (compressive interface capturing scheme for arbitrary meshes) scheme, whereas the semi-implicit method for pressure linked equations (SIMPLE) scheme is applied for the pressure-velocity coupling. A second order upwind discretization scheme is used for the momentum equations. The verification of the present results is produced on a single flooding water body. The results show a good agreement with previous simulations and experiments of different authors. Then the simulation is expanded and analysed for cases with two different types of obstacles. Numerical simulation results are illustrated by figures and tables.

Title of the Paper: **Modeling, Regulation and Optimization of Thermal Flux and Temperature to a Radiation Shield Between the Two Planar Surfaces**

Authors: **Sabrije F. Osmanaj, Rexhep A. Selimaj**

Pages: **266-272**

Abstract: The objective of the paper is the analysis about modeling, regulation and optimization of the radiation thermal flux and temperature between two planar surfaces, considering use of a single shield in a two surface enclosure. To this aim, in the second part we present the main contributions to the radiation heat transfer theory, in general, including equations and other data for planar surfaces without shields, with one and n – shields. In the third part we present the equations that describe modeling of the radiation specific thermal flux and temperature by parallel planes with a radiation shield, including two cases for parallel planes - when their emissivity are the same and different. For comparison in terms of heat radiation transfer, for simulation and analysis are used three types of materials where it is shown the impact of the thermal-physical parameters to the shield radiation, temperature and heat flux over time.

Title of the Paper: **CFD Analysis and Numerical Aerodynamic Investigations of Automotive Disc Brake Rotor**

Authors: **A. Belhocine, W. Z. Wan Omar**

Pages: **251-265**

Abstract: Braking system is one of the important control systems of an automotive. For many years, the disc brakes have been used in automobiles for safe retardation of the vehicles. During braking enormous amount of heat will be generated and for effective braking sufficient heat dissipation is essential. The thermal performance of disc brake depends upon the characteristics of the airflow around the brake rotor and hence the aerodynamics is an important in the region of brake components. A CFD analysis is carried out on the braking system as a case study to make out the behaviour of airflow distribution around the disc brake components using ANSYS CFX software. We are interested in the determination of the heat transfer coefficient (HTC) on each surface of a ventilated disc rotor varying with time in a transient state using CFD analysis, and then imported the surface film condition data into a corresponding FEM model for disc temperature analysis.

Title of the Paper: **The Mathematical Model of the Filtration Process in Horizontal Wells for the High Viscosity Oil Fields**

Authors: **Vladimir Astafev, Oksana Shevchenko, Irina Kibalenko**

Pages: **242-250**

Abstract: The main objective of the design of oil fields development is correctly predict the future production rate of a horizontal well. In conditions of heavy oil and horizontal well this forecast is very often inaccurate. Describes a new method for determining the start of the forecast production rate of horizontal wells for heavy oil. Forecast of oil production is the Main indicator of economic efficiency of development of each individual field. The calculations made according to an existing formula showed their complete unsuitability for fields with high-viscosity oil. The calculation error of the flow rate of horizontal wells currently used methods reaches an average of up to 95%, indicating the inadequacy of the proposed solutions to determine the flow rate. Thus, the search for a solution to the problem of maximum approximation of the calculated data flow rate horizontal wells to the actual indicators is a very important task in the modern design of the oil fields. With the aim of finding a reliable formula for determining the flow rate of horizontal wells, drew attention the law of the classical filtration J. Dupui. Based on the assumption by S. Joshua corning to which the drainage area of a horizontal well is an ellipse, the area of the drainage zone of horizontal well were calculated. The definition of the radii of the semi-axes of drainage was determined according to the accepted theory. The namely radius of the minor radius of drainage was defined as half of the thickness of the oil reservoir, and the radius of the larger semi-axis of the drainage as the sum of half the length of the horizontal well and equivalent drainage radius of the imaginary vertical wells, which depends on the reservoir properties. The rate of fluid filtration was determined from the equation A. Krasnopolsky and limit the pressure gradient at which there will be filtering is determined according to the proposed method V. Devlikamova. The result of this work was a new method of calculating the flow rate of horizontal wells in conditions of nonlinear filtering, which significantly reduce the error in the estimated values of almost zero. The new method of calculation considers the following factors influencing at the flow rate of horizontal wells: determined the exact drainage area, the record kept of the rheological properties of filtered liquids, calculated features of the medium through which it filtered. Thanks to all of the above, the calculations made by a new technique performed for the exaltation of the Deposit has shown excellent results, reducing accuracy from 95% to 7%

Title of the Paper: **Water Droplets Effects on an Airfoil Aerodynamic Performance**

Authors: **I. Aramendia, U. Fernandez-Gamiz, A. Lopez-Arraiza, M. A. Gomez-Solaetxe, J. M. Lopez-Guede, J. Sancho**

Pages: **234-241**

Abstract: Wind turbines do not operate only by the effects of the external airflow but with some adverse atmospheric conditions and environmental agents. Surface contamination, erosion, rain or ice accretion are some of them that contribute to an increase of the roughness in the airfoil and therefore to energy losses. We have developed a Computational Fluid Dynamics (CFD) model to evaluate the fluid film formation over the DU91W(2)250 airfoil at three different angles of attack, zero, four and six degrees respectively, through the Lagrangian Multiphase Model (LMP). The fluid film thickness and its total amount of mass were calculated over time. We observed slight differences in the pressure coefficients in light rainy conditions confirming the sensitive of the airfoils to the appearance of a water film layer on them.

Title of the Paper: **How to get Closer to Reality in Pressure Test Simulations with the SPH Method**

Authors: **Martin Hušek, Jiří Kala**

Pages: **226-233**

Abstract: The article describes an algorithm for the generation of the spatial geometry of concrete based on a photograph, and its subsequent use in cylindrical pressure test simulations using the Smoothed Particle Hydrodynamics (SPH) method. The aim of the article is to present several simple steps of the algorithm which enable the achievement of variability in the results of simulated pressure load tests conducted on concrete. The main aim is to achieve the best possible match with reality. The fact is that during real load tests it is never possible to obtain two identical results, e.g. the same stress–strain curves for two concrete specimens. They will always differ slightly. However, this is inconsistent with what happens in the case of numerical simulations, where the result is always the same unless there is a change in the input values. The idea of the algorithm is thus to generate the spatial geometry of the structure of a material based on the utilization of a suitably selected and optimized noise function. In a cutting plane through its space, the noise function is visually identical to the photograph of the material. A unique result can be obtained with every additional photograph of the material. The structure generated in this way can be discretized advantageously using the SPH method while also incorporating numerical heterogeneity, which is used to enhance material heterogeneities, e.g. in the area where aggregate and cement binder are in contact. The article describes the whole procedure via an example of a cylindrical pressure test performed on concrete. The functionality of the algorithm is supported by simulation results.

Title of the Paper: **Cyclic Nonlinear Analysis of Large-Scale Finite Element Meshes Through the Use of Hybrid Modeling (HYMOD)**

Authors: **George Markou, Christos Mourlas, Manolis Papadrakakis**

Pages: **218-225**

Abstract: The simulation of multistory reinforced concrete structures through the use of 3D detail modeling approaches that account for cracking through the smeared crack approach, under ultimate limit state cyclic loading conditions, is currently an approach that is not available in any research or commercial software, due to the excessive computational demand that rises when dealing with this type of large-scale numerical models. Through this research work, the numerical results that were obtained through the use of the simplified hybrid modeling (HYMOD) approach are presented. HYMOD is used herein to illustrate the capabilities of the method in capturing the experimental results of a full-scale 4-storey RC building that was retrofitted with infill walls and carbon fiber polymer jacketing. The adopted modeling approach was found to be able to have a superior computational performance, thus being able to solve the at hand problem thousands of times in an affordable computational time. It is demonstrated that this type of analysis can provide with the ability to study the cyclic mechanical behavior of full-scale structures under ultimate limit state loading conditions, whereas will further utilize scientists to perform parametric investigations towards the optimum retrofitting design of RC structures at a large-scale numerical level.

Title of the Paper: **City Scale Pollutant Dispersion Modelling Utilising a Combination of Computational Fluid Dynamics and Standard Air Quality Simulation**

Authors: **Neihad Hussen Al-Khalidy**

Pages: **210-217**

Abstract: Pollutant dispersion in urban street canyons is usually investigated numerically using Standard Air Quality (AQ) modelling assessment, ie through the application of validated 3-D computer modelling tools such as CALPUFF or Advanced Computational Fluid Dynamic (CFD) for near-field Simulation. This paper presents a road map to use a combination of 3-D standard air quality modelling and Computational Fluid Dynamics (CFD) to reliably simulate air flow and quality in city canyons on the example of emergency ventilation smoke control in roadway tunnels. The local wind rose for a project site was created using The Air Pollution Model (TAPM) and CALMET diagnostic meteorological modelling software, which reconstructs local 3D wind and temperature fields starting from regional meteorological measurements, synoptic weather model outputs, topography and land use data. Emissions from the project site have then been initially modelled using the CALPUFF dispersion model. Boundary conditions (the worst case wind direction, wind speed and ambient temperature) resulting in the highest pollutant concentration predictions were identified through this preliminary CALPUFF dispersion modelling study, which were then used in the detailed microclimate CFD exhaust dispersion modelling. Microclimate CFD modelling is substantially more computationally expensive than preliminary CALPUF simulations. The CFD analysis offers a comprehensive range of output including pollutant concentration, velocity distribution, temperature distribution, pressure profile, turbulent levels, etc. allowing the identification of sources that have unacceptable impact on the city air quality. Downwind pollutant concentrations can be further reduced by optimising the stack dimensions and/or smoke volumes and speeds. It is anticipated that the use of CFD for entire city modelling will be a useful tool to help urban designers and environmental planners. The paper also discusses some of the challenges facing CFD for modelling built environment.

Title of the Paper: **A Hydraulic Cylinder with Variable Power Configuration: Design and Validation of the Fluid-Dynamic Model**

Authors: **C. Abagnale, M. Cardone**

Pages: **204-209**

Abstract: The paper describes the study of a hydraulic actuation system, in terms of design and validation of its fluid-dynamic model. A set of three way manual valves allows to select different cylinder thrust areas, making possible variable power configuration. The activity has been carried out through a combined use of measurements and simulations. The model of the hydraulic actuation system has been developed adopting a commercial code that allows to take several details into account, differently from a typical mathematical model: all the components of the hydraulic circuit have been taken into account for the derivation of the model. In order to characterize the system, the experimental activity has been conducted by open and closed loop tests. The results of numerical simulations have been compared with experimental data to evaluate the validation and the performance of the developed model.

Title of the Paper: **Theoretical Premises of Thermal Wedge Effect in Fluid-Film Bearings Supplied with a Nonhomogeneous Lubricant**

Authors: **Alexey V. Kornaev, Elena P. Kornaeva, Leonid A. Savin**

Pages: **197-203**

Abstract: A computational model of a plain fluid-film bearing with means to create artificial thermal and viscosity wedge effect has been developed. The model of fluid film is based on the numerical solution of the generalized Reynolds equation simultaneously with the energy equation. It is assumed, that the lubricant is supplied to the bearing in the form of a mixture of nonhomogeneous temperature. Thermal boundary condition on the edge of the bearing is a periodic function, which is characterized by the value of temperature drop and the offset. The governing equations have been solved using finite difference method combined with the iteration procedure. A linearized dynamic model of a rigid symmetric rotor has been used to study lateral vibrations. The results have proven efficiency of application of artificial thermal and viscosity wedges to lightly loaded rotors. It is shown, that a correct choice of the offset value significantly influences the effect of loadcarrying capacity’s and damping capacity’s increase. Vice versa, an incorrect choice of the offset could lead to decrease of load-carrying capacity and result in occurrence of unstable oscillations of a rotor.

Title of the Paper: **An Overview of Constrained Fitting Optimization Techniques for Reverse Engineering of Mechanical Parts**

Authors: **Francesco Buonamici, Alessandro Lapini**

Pages: **188-196**

Abstract: Reverse Engineering represents a long-term goal of computer science and engineering; it aims at the reconstruction of digital models from measured data by means of 3D mathematical surfaces and geometrical features representing the geometry of a physical part. In this paper, an overview of constrained fitting optimization methods specifically devised for the reconstruction of mechanical parts is proposed, highlighting the connections between the theoretical problem and some practical solutions. Furthermore, algorithmic procedures are provided in order to underline the main differences between the considered approaches. Critical aspects of constrained fitting and recent trends on Reverse Engineering are finally presented and discussed.

Title of the Paper: **Mathematical Modeling of the Natural Solar Drying Process in Lateritic Mineral Deposits**

Authors: **Enrique T. Tamayo, Jorge L. Guadalupe, Yoalbis R. Mediaceja, Eduardo J. Díaz, Alexandra O. Pazmiño, Jairo R. Jácome, César M. Díaz**

Pages: **182-187**

Abstract: The natural solar drying of lateritic mineral was modeled in order to obtain the moisture distribution and its movement mechanism in the section. In this work we give a physical model of the drying process, based on heat and moisture transport phenomena in porous media. The models that allow calculation of the heat fluxes by radiation, convection and conduction are determined; In addition the global solar radiation that affects the surface of minerals drying; the temperature and humidity distribution experienced by the material during the process; the rate of drying and the mineral moisture on the surface. Natural drying tests were performed and experimental values of material moisture were obtained. The experimental and theoretical results obtained were compared. The validation process was performed by comparing the moisture of the experimentally determined material with the theoretical humidity calculated with the models for the same physical conditions in which the experiment was developed. The mathematical models were obtained by solving, through the variable separation method, the differential equation of moisture exchange in a porous solid for the initial and boundary conditions specific to the natural drying. The results evidenced that during the process, significant changes in the moisture of the material occur until the layers that are separated about 29 and 87 cm from the surface of the east and west slopes of the pile respectively. In addition, it was confirmed that the moisture movement in the ore piles occurs through a mixed transport mechanism; combined effects of vapor diffusion, liquid diffusion and liquid movement.

Title of the Paper: **Analysis and Simulation for the Double Corrugated Cardboard Plates Under Bending and in-Plane Shear Force by Homogenization Method**

Authors: **Pham Tuong Minh Duong**

Pages: **176-181**

Abstract: In this paper, an analytic homogenization model under bending and in-plane shear force for the double corrugated cardboard plates is presented. The proposed model allows us to replace the 3D double corrugated cardboard by a 2D homogenized plate, which reduces a lot of time to calculate as well as time to build the geometry. Based on the theory of stratification and then improved by using the theory of sandwich, we calculated the rigidities of corrugated cardboard plate and then implemented into a 4-node shell element called S4R in Abaqus for an equivalent orthotropic plate. The results obtained by the present model are compared to those given by 3D shell simulations. The comparison shows the efficiency and accuracy of our homogenization model. The homogenization model can be used not only for corrugated cardboard plates, but also for industrial composite structures.

Title of the Paper: **The Effect of Skewness and Kurtosis on the Probability Evaluation of Fatigue Limit States**

Authors: **Z. Kala, A. Omishore, S. Seitl, M. Krejsa, J. Kala**

Pages: **166-175**

Abstract: The article presents the probabilistic analysis of the limit state function of the fatigue resistance of a steel bridge, which is numerically described as the total number of cycles to failure. An example of the evaluation of the histogram of the fatigue resistance of a steel member using the Latin Hypercube sampling method and linear fracture mechanics based on Paris-Erdogan’s law is presented. Probabilistic models of input variables for which the fatigue resistance has a typical log-normal probability density function are described. Differences between the stochastic analyses of one member with one edge crack and the entire steel bridge are discussed. Attention is paid in the limit state function to the effects of skewness and kurtosis of the fatigue resistance on the time-dependent failure probability.

Title of the Paper: **New Results for the A Posteriori Estimates of the Two Dimensional Time Dependent Navier-Stokes Equation**

Authors: **Ghina Nassreddine, Toni Sayah**

Pages: **155-165**

Abstract: In this paper, we study the two dimensional time dependent Navier-Stockes problem. We introduce the discrete problem which is based on the implicit Euler scheme for the time discretization and the finite element method for the space discretization. We establish, by using the Gronwall lemma, an a posteriori error estimation with two types of errors indicators related to the discretization in time and space. The upper bounds is obtained without any restriction to the exact and numerical solutions compared to those obtained by [Bernardi & Sayah (2015)] where the numerical solution must be in a neighborhood of the exact solution providing from the application of Poussin-Rappaz theorem. This is the main advantage of the present work

Title of the Paper: **Reduced Order Modeling of Two-Link Flexible Manipulators Using Finite Element Modal Decomposition**

Authors: **M. Sayahkarajy, E. Supriyanto, Z. Mohamed**

Pages: **145-154**

Abstract: This paper presents dynamic modelling of a two-link planar manipulator with flexible links, using a high order Finite Element (FE) model. First, using sufficiently high number of Euler-Bernoulli beam elements a high order model is derived for the multibody flexible system. The sufficiency of the number of elements is determined based on convergence of the FE model. The global vibration modes of the manipulator are derived from the global mass and stiffness matrices of the system. The gap between the complexity of high order FE models capable of predicting dynamic behavior of a flexible manipulator, and suitability of the FE model for controller design is bridged by a reduced order control scheme based on modal truncation/H∞ techniques.

Title of the Paper: **Mixing in Micro-Scaled Coiled Flow Inverter of Varying Tube Diameter**

Authors: **Joanne Z. E. Soh, Eko Supriyanto**

Pages: **141-144**

Abstract: Coiled Flow Inverter (CFI) is a tubing configuration which facilitates process intensification. In microfluidics domain, the laminar flow due to low Reynolds number (Re) might inhibit effective mixing in Micro-scaled Coiled Flow Inverter (MCFI). Simulation with Computational Fluid Dynamics (CFD) software FLUENT was implemented to investigate the mixing with MCFI with different diameters. Fluid flow of the mixing of two water bodies was simulated. Geometry of the MCFI was designed with tubing diameters of 1.0mm, 0.8mm, and 0.5mm and a fixed curvature ratio (λ) of 10. Fluid flow rate was adjusted to achieve Re of 250 for each tubing size. Simulation results showed skewed velocity profile MCFI, which facilitated secondary flow and flow inversion. MCFI with the tubing diameter of 0.5 mm achieved complete mixing, at 0.69 normalized tube length equivalent to 175mm. MCFI with ID 1.0 mm showed 54.5% mixing, while MCFI with ID 0.8 mm showed 69.6% mixing. Results suggested smaller tubing diameter led to better mixing process in MCFI.

Title of the Paper: **Numerical Simulation of the Coupled Flutter Instability for Closed-Box Bridge Decks**

Authors: **Giovanni Cannata, Luca Barsi, Francesco Gallerano**

Pages: **128-140**

Abstract: In this work a numerical investigation of aeroelastic phenomena for long-span bridge decks is proposed: a simulation model is presented by which the aerodynamic fields and the motion of the structure are simulated simultaneously and in a coupled manner. The structure is represented as a bidimensional elastically suspended rigid body with two degrees of freedom, and the aerodynamic fields are simulated by numerically integrating the ALE formulated 2D URANS equations with a finite volume scheme on moving grids which adapt to the structural motion. The numerical model is validated by the comparison between numerical and experimental results, and is utilised to study the aeroelastic stability of the Forth Road Bridge deck. A deep insight into the onset and the amplification mechanisms of coupled flutter for long span bridge decks is proposed. The numerical model is also used to test the effectiveness of a small aerodynamic modification on the aeroelastic stability of the deck.

Title of the Paper: **Quasi-Resonance Excitation of Stationary Disturbances in Compressible Boundary Layers**

Authors: **Sergey A. Gaponov**

Pages: **120-127**

Abstract: In the paper the resonance theory was used for an explanation of generation reasons of the longitudinal structures in the compressible boundary layer by external vorticities. Researches are conducted as in case of subsonic Mach numbers, and in case of a supersonic flow. As a result of researches Eigen values of a uniform boundary problem have been obtained and the corresponding Eigen functions are constructed. By researches of other authors it has been established that two-dimensional stationary disturbances in a subsonic boundary layer on a flat plate are damped on the longitudinal coordinate by a power law, the exponent is Eigen value of a boundary problem. The present results coincide with their data completely. The researches of three-dimensional disturbances which were conducted for the first time have shown that their fading rate down a stream depends on wave numbers in the lateral direction poorly. However, there are the optimal values of the wave number in the lateral direction, in which perturbations are damped down a stream the most poorly. If in case of subsonic speeds decrements of perturbations of the first mode doesn't depend neither on a Reynolds number, nor on value of a lateral wave number, then in case of M=2 the nature of a perturbations reduction on longitudinal coordinate depends both on a wave number, and on a Reynolds number. Intensive generation of longitudinal structures takes place under a condition when parameters of external waves are close to parameters of Eigen stationary perturbations of a boundary layer. Data of the resonant theory are coordinated with direct calculations of an interaction of external disturbances with a boundary layer satisfactorily.

Title of the Paper: **Simulations of Developing Two-Dimensional Mixing Layers with Particle Dispersion**

Authors: **Altyn Makasheva, Altynshash Naimanova, Nurtoleu Shakhan**

Pages: **115-119**

Abstract: Numerical simulations of particle dispersion in a planar mixing layer formed by two co-flowing streams past a splitter plate are presented. The two-dimensional time-dependent gas-phase equations are solved numerically using the high-order essentially non-oscillatory (ENO) scheme. The particles are traced a Lagrangian approach assuming one-way coupling between the continuous and dispersed phases. The influence of large-scale coherent structures in a spatially-developing mixing layer on the particle dynamics is numerically studied. Detailed analysis reveals that the intermediate size particles are caughted by them, leading to their enhanced dispersion, while the large particles are mostly unaffected by the large eddies. However, the asymmetric entrainment of particles on the periphery of the mixing layer is presented for both cases.

Title of the Paper: **Numerical Solution of a Delay-Advanced Equation from Acoustics**

Authors: **M. Filomena Teodoro**

Pages: **107-114**

Abstract: It is introduced a numerical scheme which approximates the solution of a particular non-linear mixed type functional differential equation from physiology, the mucosal wave model of the vocal oscillation during phonation. The mathematical equation models a superficial wave propagating through the tissues. The numerical scheme is adapted from the work developed previously by the author and collaborators.

Title of the Paper: **Computation of Transverse Injection into Supersonic Crossflow with Various Boundary Layer Thickness**

Authors: **Yekaterina Moisseyeva, Altynshash Naimanova, Asel Beketaeva**

Pages: **101-106**

Abstract: Supersonic turbulent multispecies flow with transverse jet injection is numerically investigated. On the basis of the developed model the pattern of the vortex system formation is studied in detail. As a result, new vortices formed in the recirculation zone ahead of the jet are identified as well as their effect on the mixing layer. The effect of the boundary layer thickness on the vortex system is also studied, and the value of the boundary layer thickness, for which there is an additional multi-structural separation zone ahead of the jet, is determined. The formation of the lateral vortex pairs generated by the upstream vortices, convection of these vortex systems downstream and their effect on the mixing layer are revealed in dependence of the boundary layer thickness.

Title of the Paper: **Modelling of Resonance and Stability of Drill String Nonlinear Dynamics**

Authors: **Askat K. Kudaibergenov, Askar K. Kudaibergenov, Lelya A. Khajiyeva**

Pages: **92-100**

Abstract: This paper studies nonlinear vibrations and stability of a rotating drill string applied in shallow drilling. It is supposed that the drill string is under the effect of a variable compressive axial load with consideration of finite deformations. Taking the drill string as a pinned-pinned rod its lateral vibrations and resonance regimes on basic and higher (the third) frequencies are modelled. The classical Galerkin technique and the method of harmonic balance are utilized. The investigations show considerable nonlinear effects and bifurcation phenomena on the amplitude-frequency characteristics (AFC) of the drill strings that may indicate instability of the studied process. Instability zones of the resonance on the basic frequency, which correspond to a frequency range of bifurcation effects on the AFC, are determined. Numerical analysis of the mathematical model is performed and recommendations for choosing optimal constructive parameters of the drill strings and their operating regimes are provided.

Title of the Paper: **Optimization of the Charge Motion in Sewage Gas-Driven Internal Combustion Engines for Combined Heat and Power Units**

Authors: **Lucas Konstantinoff, Christoph Pfeifer, Martin Pillei, Uwe Trattnig, Thomas Dornauer, Lukas Möltner**

Pages: **82-91**

Abstract: In this study, a goal-oriented optimization of the charge motion in a sewage gas-driven internal combustion engine of a combined heat and power unit was investigated to increase efficiency. The swirl flow influenced by the geometry next to the valve seats was considered in particular. For this purpose, experiments took place on a flow bench to integratively quantify the swirl flow; laser-optical methods were also applied to determine flow patterns in discrete plains inside the cylinder. In detail, we compared two cylinder heads that differ in their geometry in the immediate vicinity to the inlet valve seats. Following the investigations of in-cylinder flow characteristics, combustion analysis on a test engine was conducted via a cylinder pressure indication system for partial and full-load operation points. The framework of the optimization measures consists of the mandatory NOx limit of 500 mg∙m-3 and a limit in the maximum working pressure that could be met. A summary of the results reveals that the new valve seat design has a significant enhancing impact on the swirl motion and, hence, upon the combustion. A comparative consideration between the two cylinder heads shows that the increased swirl motion results in faster combustion and, therefore, higher efficiency. Summing up, the geometrical modifications close to the valve seat result in increased turbulence intensity, and it was proven that this intensification raises the ratio of efficiency by 1.6%.

Title of the Paper: **Single Cavitation Bubble Interaction Close to Hydrophobic Surface**

Authors: **D. Jasikova, M. Kotek, M. Muller, V. Kopecky**

Pages: **73-81**

Abstract: The cavitation bubble has a great potential to be used for local surface hardening. Highly controlled and geometrically placed defined bubbles can easily machine the area of interest modifying the surface of material. However, the effect of pointed pressure hit can be sometimes undesirable. Usage of hydrophobic cover could shield and spread the force in certain part of working. The aim of this project was to design a setup of Laser Induced Breakup and study the effect of cavitation bubble on hydrophobic surface. The main interest was focused on the air film behavior that is created on the surface in interaction with liquids. Here we used 532nm Nd:YAG pulse laser for the cavitation bubble generation. The process and the impact of cavitation bubble was visualized using high speed shadowgraphy. We also measured the air film thickness using microPIV technique and study its behavior under increasing liquid flow impact.

Title of the Paper: **Computational Analysis of High Speed Flow over a Spherical Nose Conical Surface with Varying Mach Number**

Authors: **Khaled Alhussan**

Pages: **69-72**

Abstract: The work to be presented herein is numerical analysis of flow over a 20-degree half angle cone with spherical nose for compressible fluid, with 0 angle of attack and with respect to different values of Mach Numbers. The problem to be solved involves formation of shock waves so that the general characteristics of subsonic, supersonic and hypersonic flows over the spherical nose conical surface are explored through this problem in addition to the analysis of heat transfer taking place during these flows. Shockwaves and slip surfaces are discontinuities in fluid mechanics problems. It is essential to evaluate the ability of numerical technique that can solve problems in which shocks and contact surfaces occurs. The results of contour plots of Pressure, Temperature, Density and Heat flux with respect to Mach number will show that CFD is capable of predicting accurate results and is also able to capture the discontinuities in the flow, e.g. the oblique shock waves. The global comparison between the numerical and analytical values show a good agreement.

Title of the Paper: **Numerically Stable Algorithms for Scattering by Impedance Cylinders**

Authors: **Emrah Sever, Fatih Dikmen, Yury A. Tuchkin, Cumali Sabah**

Pages: **64-68**

Abstract: Electric and Magnetic Field Integral Equations (EFIE&MFIE) on impedance cylinders with smoothly parametrized cross section contours under Transverse Magnetic and Electric (TM&TE) excitations are considered. It is possible to achieve super-algebraic convergence with accurate calculation of the kernels of integral equations. Unless the impedance value is too small or too big, these equations are Fredholm of the second kind and are subject to stable discretization procedures. Otherwise numerical stability requires Analytical Regularization. Numerical results to show evidence for these points are given.

Title of the Paper: **Impact of a Viscoelastic Sphere against an Elastic Kirchhoff-Love Plate Embedded into a Fractional Derivative Kelvin-Voigt Medium**

Authors: **Yury A. Rossikhin, Marina V. Shitikova, Phan Thanh Trung**

Pages: **58-63**

Abstract: In the present paper, we consider the problem on a low-velocity transverse impact of a viscoelastic sphere upon an elastic Kirchhoff-Love plate in a viscoelastic medium, the viscoelastic features of which are described by the fractional derivative Kelvin-Voigt model. Within the contact domain the contact force is defined by the generalized Hertzian contact. The Green function for the target was constructed, what allows us to obtain the integral equation for the contact force and local indentation using the algebra of Rabotnov’s fractional operators. An approximate analytical solution has been found.

Title of the Paper: **Smart Carbon-Epoxy Laminate with High Dissipation Properties for Vibro-Acoustic Optimization in the Turboprop Aircraft**

Authors: **M. Viscardi, M. Arena, G. Barra, L. Guadagno**

Pages: **51-57**

Abstract: The transport industry especially that aviation one is investing in research for innovative technologies to improve the internal comfort both in the design phase and in aircraft already operative. The vibration and noise attenuation is of course among the most relevant target in the aeronautical scientific community actually many research programs which see the cooperation between academic institutions and leading industries are promoting the development and the application of innovative materials: smart composites, SMA, piezoceramics are only few examples of this increasingly emerging field. In this paper, the latest results achieved on the self-healing laminates for their too very appreciable damping performance are presented. The effectiveness of the proposed biomimetic technology has already been assessed in terms of damping capability compared to a standard CFRC specimen. The tests evidence has revealed a really better behavior of the self-healing sample compared to the conventional one in terms of vibrational energy: the average damping coefficient, measured in two different ways has been found to be about four times higher. Therefore, relying upon the results achieved on simple specimens, a numerical model representative of an aircraft fuselage section has been developed in order to predict the levels of noise and vibrations generated by a typical propeller excitation load. A careful investigation of air-structure interaction for internal noise forecast and surface radiated power has been carried out combining the numerical solutions performed within MSC Nastran® and Actran® environments. The Finite Element approach has allowed for emphasizing that the adoption of these smart treatments could led to an average noise reduction of about 3 dB compared to the conventional laminate configuration as well as a surface vibration decrease up to 50%.

Title of the Paper: **A New CFD-Simulink Based Systems Engineering Approach Applied to the Modelling of a Hydraulic Safety Relief Valve**

Authors: **M. D. L. Dalla Vedova, P. Maggiore, G. Riva**

Pages: **43-50**

Abstract: A safety relief valve is a simple hydro-mechanic device, needed to avoid overpressure transients inside hydraulic circuits. Such valves are a critical part of the hydraulic system of aircraft; hence their performances must be adapted to a specific nominal pressure level and design requirements. In the following paragraphs the authors will address the issue of designing and validating a safety valve through a hybrid CFD/MATLAB-Simulink® approach. The main constraints are the geometrical dimensions and the need to limit the weight of the device. A significant part of the work consists of gathering all the possible information available in the literature, dealing with the best design practices to achieve the performance objective. Thanks to a robust computational procedure, it should be possible to reduce the amount of “physical” prototypes required to validate the functionality of a safety relief valve. The process presented uses a numerical computational fluid dynamic (CFD) approach, to define the pressure field inside the valve and the forces acting on it; identifying the force distribution inside the valve is paramount to address the performance evaluation of the valve itself. The first step deals with the definition of a computer aided design (CAD) model of the valve. Then the CFD software uses the above-mentioned CAD model to define the domain of the problem. Once obtained the pressure field, it is possible to integrate it through the surface of the valve, thus obtaining the forces acting on the moving part (poppet). After the numerical scheme has been calibrated, some investigations are done to reduce the computational cost: the main aim is to run a complete simulation (meshing and solving) on a standard computer. Some of the positions (i.e. strokes) of the valve have been simulated as static, hence a steady-state calculation has been applied to solve the motion field. Another important result consists of creating a MATLAB-Simulink® model, capable to reach results comparable to the CFD simulation, but in shorter times. While the CFD model can provide high quality results, the MATLAB-Simulink® calculation should be used to create a “first guess” instrument, useful to address the very first valve geometry. The implementation of the Look-Up Tables (LUTs) links the MATLAB-Simulink® model to the CFD simulation, but increases the time required to obtain a solution: on the other hand, this reduces the amount of equation-modeled quantities, delivering a greater precision to the calculations.

Title of the Paper: **Determination of Soil Parameters in Hydraulic Flow Model for Porous Media**

Authors: **Jozef Kacur, Patrik Mihala, Michal Toth**

Pages: **34-42**

Abstract: Determination of soil parameters (in fundamental flow characteristics) is investigated under new scenario in laboratory experiments with 3D samples. Infiltration into a sample is realized under the gravitation and centrifugal driven forces. Mathematical model for the flow in an unsaturetedsaturated porous media is expressed in terms of Richard’s equation based on the van Genuchten/Mualem experimental capillary-pressure model. Soil parameters characterize the specific porous material and are used as input data in this capillarypressure flow model. Objective of this paper is threefold. The first is to present a direct and inverse efficient solver for governing mathematical model. The second is to apply the inverse solver for parameter estimation using only noninvasive inflow/outflow transient measurements. The third is to avoid resp. significantly reduce the creation of preferred streamlines which shadow reliability in solution of inverse problem. In our setup, a sample of cylindrical shape is submerged in water chamber and the water infiltrates into it. The top of the cylinder is isolated and from its bottom water flows out to the collection chamber. Both chambers except of the sample bottom (resp. its part) are mutually isolated. The flux from lateral boundary into the sample is orthogonal to the driving forces in gravitation and centrifugation mode. This unlike in 1D samples (in the form of thin tubes) the creation of preferred stream lines arising due to small inhomogenities is decreased significantly. Additionally, the isolation of the 1D tube, especially in centrifugation mode, is difficult task. In centrifugation mode we can obtain additional informations from transient monitoring of centrifugal force which is also noninvasive. In our 3D experiments we are able to create more infiltration scenarios by suitable change of boundary conditions and rotational speed. Two different numerical methods have been developed. One is based on finite volume space discretization and flexible time stepping. The obtained nonlinear algebraic system is solved by an quasinewton linearization method. The second one is based only on space discretization and the original problem is reduced to the solution of stiff, nonlinear system of ordinary differential equations.

Title of the Paper: **Homogenisation of a Folded Sandwich Core Structure**

Authors: **Holger Massow, Wilfried Becker**

Pages: **25-33**

Abstract: Folded cores are a not so common kind of sandwich core materials. These folded core structures have properties that make a more detailed examination advisable. Especially some properties make them particularly interesting for the aviation industry. This contribution gives an overview of the possible applications of folded core structures. By applying a numerical homogenisation method mechanical properties of folded sandwich cores are identified. For a selected type of folded core the properties are exemplarily determined. The shown homogenisation procedure is applicable to other types of sandwich cores as well. The mechanical properties presented in this contribution will be similar for other kinds of folded sandwich cores.

Title of the Paper: **Boundary Layer Flow and Heat Transfer of Nanofluids over a Moving Plate with Partial Slip and Thermal Convective Boundary Condition: Stability Analysis**

Authors: **Najwa Najib, Norfifah Bachok, Norihan Md. Arifin, Norazak Senu**

Pages: **18-24**

Abstract: The steady boundary layer flow and heat transfer of nanofluids over a moving plate with partial slip and thermal convective boundary condition is studied. The governing nonlinear partial differential equations are first transformed into a system of nonlinear ordinary equations using a similarity transformation. The system then have been solved numerically using the bvp4c solver in Matlab. The numerical results are presented in tables and graphs for the skin friction coefficient and the local Nusselt number as well as the velocity and the temperature profile for a range of various parameters such as nanoparticles, nanoparticles volume fraction, slip parameter, Biot number and velocity ratio parameter. It is observed that the skin friction coefficient and the local Nusselt number which represents the heat transfer rate at the surface are significantly influenced by these parameters. The results indicate that dual solutions (first and second solutions) exist when the plate and free stream move in the opposite direction. A stability analysis has been performed to show which solutions are stable and physically realizable. Based on the analysis, the results indicate that the first solution is linearly stable, while the second solution is linearly unstable.

Title of the Paper: **Energy Consumption and Simulation of Pneumatic Conveying Lateritic Mineral in Dense and Fluid Phase**

Authors: **Eduardo J. Díaz, Enrique T. Tamayo, Diana M. Vélez, Diego R. Salazar, César M. Díaz, María P. Cedeño**

Pages: **12-17**

Abstract: The mineral pneumatic conveying efficiency depends of different equipment that makes considerable impact on energy-saving. The systems are frequently operated in the dilute-phase regime or in the high air velocity region and cause higher power consumption, pipe erosion and particle degradation. Therefore even small reductions in pressure drop and conveying velocity can obtain improvements in energy-saving, pipe wear and particle degradation. The pneumatic conveying should keep the pressure drop and conveying velocity as low as possible. In order to reach this purpose, some energy-saving techniques have been developed. To observe the relationship between the parameters involved in the pneumatic transport of lateritic mineral and obtain the necessary information about the behavior of the variables, it is necessary to simulate the transport characteristics, for which was used the mathematical model in horizontal and vertical pipes, and the losses in elbows. The simulation of pneumatic conveying systems is developed with the use of experimental - theoretical models to predict areas of lower energy consumption and make the correct selection of the systems. It plays the important role in the research of fluid and dense-phase gas solid flow. This article gave the numerical simulation conclusions based on the experimental and theoretical research. The behavior of the specific energy consumption in function of concentration show the tendency to reduced energy consumption with increased concentration of the mixture and therefore the amount of material transported. This increased concentration is limited by the conveying characteristics depending on the system parameters and air feeder. The consumption values range from 4.23 MJ/t to 14.55 MJ/t, the latter values corresponds with the lower values of gas-solid concentration (10 to 20 kg/kg).

Title of the Paper: **Comparative Analysis of Two Problems of the Impact Interaction of Rigid and Viscoelastic Spherical Shells**

Authors: **Yury A. Rossikhin, Marina V. Shitikova, Duong Tuan Manh**

Pages: **6-11**

Abstract: Two problems of the impact interaction of two spherical shells, one of which is rigid while the second one is viscoelastic, are considered. In the first problem the viscoelastic shell impacts with the velocity V0 against the quiescent rigid shell, while in the second problem, on the contrary, the rigid shell with the velocity V0 bumps the motionless viscoelastic shell. For both problems, integrodifferential equations for the values of local bearing of the material of the viscoelastic shell have been obtained under the assumption that the volume relaxation in viscoelastic shells is negligible. Approximate solutions of the integrodifferential equations allows one to carry out the comparative analysis of the results obtained in the both cases.

Title of the Paper: **Finite Element Model of Fatigue Fracture of Reciprocating Screw in Moulding Machine**

Authors: **Štěpán Major, Pavel Cyrus, Roman Dostál**

Pages: **1-5**

Abstract: This work is devote to the study of fatigue degradation of some parts of moulding machine. The mechanical part of the moulding machine represents the mechanism which injects the molten plastic into the mould. The finite element analysis of fatigue damage of reciprocating screw, i.e screw pump is discussed and compared with results obtained from fractographical analysis of damaged parts of real machine. The process of crack growth in reciprocating screw is example of fatigue of notched bar under biaxial loading. For description of biaxial loading were selected methods based on Smith–Watson–Topper and Fatemi-Socie fatigue criteria. The reciprocating screw used in this study were made from two different steels (P20+Ni and H-13 steel). The theoretical model is in a good agreement with experimental results.