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.

Main Page

Submit a paper | Submission terms | Paper format

 


Volume 13, 2019


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.