International Journal of Mechanics

ISSN: 1998-4448
Volume 13, 2019

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 13, 2019

Title of the Paper: Multiscale Modeling of Composite Materials With Decm Approach: Shape Effect of Inclusions


Authors: E. Ferretti

Pages: 104-113

Abstract: This paper addresses the study of the stress field in composites continua with the multiscale approach of the DECM (Discrete Element modeling with the Cell Method). The analysis focuses on composites consisting of a matrix with inclusions of various shapes, to investigate whether and how the shape of the inclusions changes the stress field. The purpose is to provide a numerical explanation for some of the main failure mechanisms of concrete, which is precisely a composite consisting of a cementbased matrix and aggregates of various shapes. Actually, while extensive experimental campaigns detailed the shape effect of concrete aggregates in the past, so far it has not been possible to model the stress field within the inclusions and on the interfaces accurately. The reason for this lies in the limits of the differential formulation, which is the basis of the most commonly used numerical methods. The Cell Method (CM), on the contrary, is an algebraic method that provides descriptions up to the micro-scale, independently of the presence of rheological discontinuities or concentrated sources. This makes the CM useful for describing the shape effect of the inclusions, on the micro-scale. When used together with a multiscale approach, it also models the macro-scale behavior of periodic composite continua, without losing accuracy on the micro-scale. The DECM uses discrete elements precisely to provide the CM with a multiscale approach.

Title of the Paper: Post-processing of 2d Fem Q1 Models for Fracture Mechanics by Radial Basis Functions and Balance Equations


Authors: Andrea Chiappa, Corrado Groth, Carlo Brutti, Pietro Salvini, Marco E. Biancolini

Pages: 104-113

Abstract: In this paper a method to improve the stress state on a 2D finite element (FE) Q1 coarse mesh for fracture mechanics applications is shown. Radial Basis Functions (RBF) are employed synergically with balance equations to reduce the interpolation error and improve results extracted from the coarse FEM models. In addition to FE nodes, RBF interpolation embeds a certain number of additional points, for which displacements satisfy a minimization procedure of the error on balance equations. Derived fields (strain, stress) yield analytically from the constructed interpolator. Proposed method is validated with two 2D structural cases involving strong stress concentrations and applied on a mode I crack opening simulation in which the J-integral is extracted. Described procedure can be employed as a post-processing tool on meshes not suitable to be employed for fracture mechanics applications

Title of the Paper: 3D Vector Field Approximation and Critical Points Reduction using Radial Basis Functions


Authors: Michal Smolik, Vaclav Skala, Zuzana Majdisova

Pages: 100-103

Abstract: Vector field simplification aims to reduce the complexity of the flow by removing features according to their relevance and importance. However, the important features as critical points with a large range of influence should be preserved. We present a new approach for vector field simplification and approximation using Radial basis functions. The experiments proved the ability to approximate complex 3D tornado data set. In addition, a significant contribution of the proposed method is also an analytical form of the vector field which can be used in further processing. The abstract goes here.

Title of the Paper: Improvement of 2D Finite Element Analysis Stress Results by Radial Basis Functions and Balance Equations


Authors: Andrea Chiappa, Corrado Groth, Marco E. Biancolini

Pages: 90-99

Abstract: This paper presents a method able to upscale finite element (FE) results obtained for coarse meshes of 2D models at a higher resolution, using both radial basis functions (RBF) and balance equations. RBF supply a smooth function from nodal displacements. In addition to FE nodes, RBF interpolation embeds a certain number of additional points, for which displacements satisfy a minimization procedure of the error on balance equations. Derived fields (strain, stress) yield analytically from the constructed interpolator. We tested the method with two 2D structural cases where strong stress concentrations were included. As regards the stress field, an error reduction with respect to validated test benches was observed in all cases.

Title of the Paper: The Behavior of Composite Dowels Subjected to Four-Point Bending Test


Authors: Veronika Václavíková, Michal Štrba

Pages: 84-89

Abstract: The article constitutes one of the modern methods of shear connection of composite steel-concrete beams, which is mainly used in bridge engineering where strength and fatigue durability is required. Such method using combination of rolled girders encased in a concrete slab and pcb (precast composite beam) technology is called pcb-W (precast composite beam – coupled in web) technology. This solution has been developing since 2003 in Germany and is widely used in many European countries (including Poland, Germany, France and Czech Republic). The longitudinal shear force is transformed by composite dowels instead of headed studs. The behavior of composite dowels is extremely complex. These connectors constitutes an integral part of composite beam, they are not only subjected to the global effects of bending and axial loading but to the local longitudinal shear acting between steel and concrete part as well. In order to understand the failure mechanism and verify the bearing capacity of composite dowels theoretical and experimental researches were carried out at the authors’ workplace.

Title of the Paper: Impact of Concrete´s Curing Process on its Biocorrossive Resistance


Authors: V. Ondrejka Harbulakova, A. Estokova, A. Luptakova, M. Smolakova

Pages: 79-83

Abstract: The properties of the concrete are influenced by many factors. Selection of the proper curing of the concrete and cement mortars belong to the very important determinative factor of the required characteristics of the construction material. The air-treated concrete samples (XCA) and in water-treated concrete samples (XCW) were exposed to the concentrated and diluted bacterial environment. The comparative study proceeded also with control media without bacteria. Both sets of samples were immersed in three types of liquid media (medium with sulfur-oxidizing bacteria Acidithiobacillus thiooxidans, diluted bacterial medium and control medium). Experiment run in laboratory condition during 270 days when a set of concrete samples were exposed to the different impact of bacterial aggressive media and evaluation of its properties at the end of the experiment were assessed in accordance to curing condition of the sets of samples. The results indicated a better resistance of the air-treated concrete samples compared to the in water-treated concrete samples to the concentrated bacterial environment. Any significant difference between the variable treated samples was observed in case of samples in control media (without bacteria). The findings are linked to the well-known positive concrete process of hydration proceeded in concrete matrix exposed to the liquid environments.

Title of the Paper: Identification of Variation Coefficient of Equivalent Stress Range of Steel Girders with Cracks


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

Pages: 69-78

Abstract: A steel bridge in operation is subjected to multiple variable stress range spectrum from the passage of axles of vehicles of different weights. The fatigue reliability assessment of steel bridges can be performed using the equivalent stress range, which is converted from the variable stress range spectrum. The paper presents a case study of the identification of the coefficient of variation of the equivalent stress range of steel girders. The histogram of equivalent stress range is statistically evaluated with consideration to uncertainties resulting from the statistical evaluation of the histogram of stress range spectrum from field monitoring. It is shown that the equivalent stress range can be rationally considered as a random variable with Gauss probability density function with coefficient of variation of 0.1. The case study is evaluated using the Latin Hypercube Sampling statistical method. The results are exploitable in the probabilistic analyses of reliability and lifetime of bridges using linear elastic fracture mechanics.

Title of the Paper: New Dual Parameter Quasi-Newton Methods


Authors: Issam A. R. Moghrabi

Pages: 64-68

Abstract: We develop a framework model for the development of multi-step quasi-Newton methods which utilizes values of the objective function. The model developed here is constructed using iteration genereted data from the m+1 most recent iterates/gradient evaluations. The model hosts double free parameters which introduce a certain degree of flexibility. This permits the interpolating polynomials to exploit available computed function values which are otherwise discarded and left unused. Two new algorithms are derived for which function values are incorporated in the update of the inverse Hessian approximation at each iteration, in an attempt to accelerate convergence. The idea of incorporating function values is not new within the context of quasi-Newton methods but the presentation made in this paper constitutes a new approach for such algorithms. It has been shown in several earlier works that Including function values data in the update of the Hessian approximation numerically improves the convergence of Secant-like methods. The numerical scores of the new methods are reported with promising performance results.

Title of the Paper: Identification of Nonparametric Linear Systems


Authors: M. Benyassi, A. Brouri, T. Rabyi, A. Ouannou

Pages: 60-63

Abstract: Identifying nonlinear systems is a much more rich and demanding problem area, especially in mechanical systems. In this presentation, some major approaches and concepts are outlined. The aim of the considered problem in this work is the modelling and identification of nonlinear systems based on spectral approach. Presently, the studied nonlinear system can be nonparametric, i.e. not necessarily described by a limited number of parameters and structured by Hammerstein models. These systems consist of nonlinear element followed by a linear block. This latter (the linear subsystem) is not necessarily parametric and the nonlinear function can be nonparametric smooth nonlinearity. The developed identification problem of these nonlinear models is studied in the presence of possibly infinite-order linear dynamics. The determination of linear and nonlinear block can be done using a unique stage.

Title of the Paper: A Novel Adaptative Mesh-Free Method using Prandtl’s Equation in the Boundary Layer


Authors: Asmae Mnebhi-Loudyi, El Mostapha Boudi, Driss Ouazar

Pages: 52-59

Abstract: In this paper,we propose a new adaptative Meshfree Method applied in the boundary layer. Traditional methods such as MEF (Finite Elements Method), VFM (Volume Finite Method), and FD(Finite Difference Method) are based on the extraction of too many parameters, that have an influence in the resulting accuracy and also in time processing. Only one parameter is used in the proposed method to compute Meshless nodes which is related to a local RBF method. Generation of nodes is done using a so- called ”Prandtl equations”. Furthermore, by means of Radial Basis Function in Finite Difference method(RBF-FD) the generated nodes will be modeled into independent models: flat plate, and circular disk. This last, will provide nodes and fluid flow velocity. Experimental results demonstrate that the proposed Meshless method surpass traditional methods.

Title of the Paper: Novel Fluid Dynamic Nonlinear Numerical Models of Servovalves for Aerospace


Authors: Matteo D. L. Dalla Vedova, Parid Alimhillaj

Pages: 39-51

Abstract: Modern flight control system often requires the development of more and more highly detailed numerical simulation models in order to analyze their specific behavior as a whole or related to their components and subsystems. Especially during preliminary design activities or in the development of diagnostic or prognostic algorithms, it is often required to implement simplified numerical models able to simulate the actual behavior of the considered system, combining appropriate levels of accuracy and reliability with low calculation times and moderate computational efforts. In this work, authors investigated the feasibility of new simplified numerical models, aiming to provide faster models able to analyze the dynamic behavior of entire systems and, at the same time, able to guarantee a suitable level of accuracy. In particular, this paper concerns novel fluid-dynamics numerical models simulating the performance of servovalves. These algorithms are based upon a semiempirical formulation and, although simplified, they are able to take calculate the effects of variable supply pressure and leakages (which is related to the control ports connecting the valve to the motor elements). Two new models are proposed and compared with a detailed reference. This comparison is performed by evaluating the performance of the different models and their ability to describe the fluid dynamic behavior of the considered valve.

Title of the Paper: Modeling and Thermal Control of Elastic Abrasive Cutting Process


Authors: Anna Stoynova, Irina Aleksandrova, Anatoliy Aleksandrov

Pages: 31-38

Abstract: The paper considers the results from the application of a thermography approach to the analysis of heat fluxes and the determination of the temperature of the work piece, cut-off wheel and cut piece in elastic abrasive cutting. The thermal distribution upon changing the cut-off wheel diameter, compression force and workpiece rotation frequency has been investigated for different materials by means of an infrared camera. The complex effect of the conditions of elastic abrasive cutting on the cut-off wheel, cut piece and workpiece has been modelled by using the multiple regression analysis method. The optimal conditions ensuring minimal values for temperature parameters have been defined by applying multi-objective optimization and a genetic algorithm. The achieved results could be used for thermal control and appear a precondition for increasing tool durability, process intensity and the quality of surfaces being processed.

Title of the Paper: Optimization Algorithms for Prognostics of Electrohydraulic on-board Servomechanisms


Authors: Matteo D. L. Dalla Vedova, Marco Borghetto

Pages: 21-30

Abstract: This paper studies the response of an electrohydraulic actuator (EHA) subjected to three different progressive failures (demagnetization of the torque motor, increment of the jack static friction and presence of backlash); in particular, it is focused on the identification of failure precursors able to give an early identification of progressive failures affecting the system, in order to provide tools that can be used to predict its remaining useful life. This kind of analysis belongs to a new discipline, called Prognostics and Health Management (PHM), that focuses on predicting the time at which a system or a component will no longer perform its intended function, estimating its Remaining Useful Life (RUL) and, then, providing an effective diagnostic tool that allows them to exploit a component until it is safe, saving money. In order to conceive an effective prognostic algorithm authors studied the failures effects on the system behaviors, identifying some details in the monitored time-history signals that exclusively got evidence of a particular failure, avoiding confounding each other and allowing pointing out the fault level of the system. For this purpose, the authors developed a new EHA Monitor Model able to reproduce the dynamic response of the actual system in terms of position, speed and equivalent current, even with the presence of incipient faults. Starting from this Monitor Model, the authors propose a new model-based fault detection and identification (FDI) method, based on Genetic Algorithms (GAs) optimization approach and parallelized calculations, investigating its ability to timely identify symptoms alerting that a component is degrading.

Title of the Paper: Mathematical Modeling of the Coal Activation Process in Rotary Cylindrical Kiln


Authors: Carlos Z. Oliva, Enrique Torres Tamayo, Alexandra O. Pazmiño, Edwin R. Pozo, Marco A. Ordoñez, Sócrates M. Aquino, Luis S. Choto

Pages: 15-20

Abstract: The activation of coal applying physical or thermal method is carried out under an atmosphere in the presence of air, dioxide carbon or water vapor, at temperatures between 800 °C and 900 °C. In this research, it get the mathematical modeling of the coal activation process in order to predict the behavior of the gas and coal temperature distribution inside a rotary cylindrical kiln. The proposed model aims for acquiring useful information to select operating conditions and design parameters. The model groups a non-linear differential equations system, the equations to determine the temperature of the cylinder inner wall and the heat transfer coefficients. The Runge-Kutta fourth order numerical method was used. The comparison of the results obtained from the modeling of the gas temperature inside the cylinder with the experimental data showed that the variation is negligible, with an error less than 5 %.

Title of the Paper: Three-Dimensional Numerical Simulation of the Velocity Fields Induced by Submerged Breakwaters


Authors: G. Cannata, F. Gallerano, F. Palleschi, C. Petrelli, L. Barsi

Pages: 1-14

Abstract: We propose a three-dimensional numerical model for non-hydrostatic free surface flows in which the Navier-Stokes equations are expressed in integral form on a coordinate system in which the vertical coordinate is varying in time. By a time-dependent coordinate transformation, the irregular time varying physical domain is transformed into a uniform fixed computational domain, in which the equations of motion are numerically integrated by a shock-capturing scheme based on WENO reconstruction and an approximate HLL Riemann Solver. The proposed model is used to simulate free surface elevation and three-dimensional velocity fields induced by normally incident waves on a beach with submerged breakwaters. The three-dimensional numerical results are compared with experimental measurements and with the numerical results obtained by a depth-averaged horizontal two-dimensional model. This comparison shows that features of three-dimensionality in the fluid flow induced by wave-structure interaction, as the undertow, can be correctly simulated by the proposed non-hydrostatic three-dimensional model.