http://rjav.sra.ro/index.php/rjav/issue/feedRomanian Journal of Acoustics and Vibration2019-01-12T06:29:25+02:00Ovidiu VASILEoffice@sra.roOpen Journal Systems<p>The <strong>Romanian Journal of Acoustics and Vibration (Print ISSN 1584-7284; Online ISSN 2602-0351)</strong> is the referred journal of the Romanian Society of Acoustics (<strong>SRA</strong>).</p>http://rjav.sra.ro/index.php/rjav/article/view/94Collisions of Rigid Bodies – An Open Problem2019-01-10T19:17:47+02:00STANESCU Nicolae Dorus_doru@yahoo.com<p>The problem of the determination of the velocities after collisions and the impulses which appear during the collisions is an old but still open one. All authors agree the following hypotheses: a) only the impulses are considered during the collisions; b) neglect of the rigid displacements; c) the impulses satisfy the principle of action and reaction.</p>2019-01-10T18:35:27+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/19Free Vibration of Initially Deflected Axially Functionally Graded Non-Uniform Timoshenko Beams on Elastic Foundation2019-01-12T06:29:25+02:00Hareram LOHARhr.lohar343@gmail.comAnirban MITRAanirban.mitra@jadavpuruniversity.inSarmila SAHOOsarmila.sahoo@gmail.com<p>The present paper studies the effect of elastic foundation on free vibration of initially deflected non-uniform axially functionally graded (AFG) thick beam on elastic foundation on the basis of Timoshenko beam theory. The elastic foundation is idealized as a set of parallel linear springs. Formulation is carried out through displacement based energy principle. First, the static problem is solved to find out the unknown displacement field by using minimum total potential energy principle. Solution methodology involves an iterative technique known as direct substitution with relaxation scheme. Secondly, subsequent dynamic problem is set up as an eigenvalue problem on the basis of the known displacement field. The governing set of equations in dynamic problem is obtained by using Hamilton’s principle and solved with the help of Matlab’s intrinsic solver. The results of the present method are validated with previously published articles. Frequency vs. displacement curve corresponding to different combinations of system parameters are presented in non-dimensional plane and are capable of serving as benchmark results.</p>2019-01-10T18:40:52+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/27A New Active Control Process Based on Applying Critical Damping Theory in Two Vibration Modes2019-01-10T19:17:47+02:00Javad ALAMATIANalamatian@yahoo.comHamid DAVTALABhamiddavtalab@yahoo.com<p>In this paper, a new active control procedure is presented using the developed critical damping concept. This strategy uses the well-known structural dynamics theories for improving the performance of critical damping (<em>CD</em>) method. In conventional <em>CD</em> algorithm, only the effect of first vibration mode has been incorporated to calculate the actuator force. The proposed method develops the critical damping concept so that the actuator force is formulated by considering the effects of the first and second vibration modes. This strategy improves the efficiency of the critical damping technique. Since the total damping matrix corresponding to the dynamic system should be semi positive definiteness, a novel approach is suggested here for determining the actuator and sensor locations. According to the proposed concepts, a new active control algorithm is obtained. Efficiency and stability of the proposed method is assessed by active control of vibrations of some shear buildings subjected to various dynamic loads. Results demonstrate considerable merit of the proposed active control algorithm compared to the common critical damping method.</p>2019-01-10T18:57:12+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/43Analytical Solution of Dynamic Analysis of Cracked Euler–Bernoulli Beam with Elastic Boundary Condition by G.F.M2019-01-12T06:20:25+02:00Amin GHANNADIASLaghannadiasl@uma.ac.irSaeid Khodapanah AJIRLOUSaeidkhodapanah@yahoo.com<p>The recognition of behavior of the cracked beam causes to find out how can use all capability of beams. Existence crack during the length of the beam makes discontinuity on the beam and leads to reduce local stiffness. This paper presents the dynamic solution of the cracked Euler–Bernoulli beam by Green Function Method (G.F.M). Green function is exhibited for the Euler–Bernoulli beam with various boundary conditions. Also, discontinuity is modeled by rotational spring in this paper. The effects of crack in different locations and depths of cracks with considering various boundary conditions are assessed. In addition, the influence of crack on natural frequency is studied. Finally, several examples are presented to compare the effect of boundary conditions on the dynamic response of the weakened Euler–Bernoulli beam.</p>2019-01-10T19:06:57+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/71Effective Wavenumber of a Random Polydisperse Assembly of Poroelastic Spheres2019-01-12T06:24:20+02:00Hervé FRANKLINherve.franklin@univ-lehavre.fr<p>The effective wavenumber model of Linton and Martin [1] for the dilute monodisperse case (obstacles of identical sizes) is used to calculate the effective modulus and mass density of a polydisperse assembly of poroelastic spheres. We focus on the Rayleigh limit (low frequency regime) where the wavelengths can be considered very large compared to the size of the obstacles. In order to show the influence of the distribution in size of the obstacles, the special case of Schulz probability density function is considered</p>2019-01-10T19:11:54+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/75New Multilayered Composite for Sound Absorbing Applications2019-01-12T06:23:00+02:00Ancuta Elena TIUCancuta.tiuc@yahoo.comOvidiu VASILEovidiu_vasile2002@yahoo.co.ukHoratiu VERMESANHoratiu.Vermesan@imadd.utcluj.roOvidiu NEMESOvidiu.Nemes@imadd.utcluj.roSimona Ioana BORLEA (MURESAN)borleaioana@gmail.com<p><span style="margin: 0px; font-family: 'Times New Roman',serif; font-size: 10pt;">Lightweight structures made of composite materials are increasingly used in many industrial fields for high-technology applications due to their versatile property profile. Waste wood cause both health and environmental problems and this has forced governments to develop laws for recycling. Using fir sawdust in the domain of soundproofing materials is of major importance from technical, economic and ecological point of view. <span style="color: #000000;"><a name="_Hlk528444093"></a>In this paper we determined the sound absorbing ability of each obtained multilayered composite plates by measuring the sound absorption coefficient depending on frequency, using the impedance tubes. Multilayered composite plates were made from layers of composite materials in combination with layers of other <a name="_Hlk527749061"></a><span style="margin: 0px;">materials on the market (cork or felt)</span></span><span style="margin: 0px;">. </span>The composite materials were made from fir sawdust and a polyurethane foam</span></p>2019-01-12T04:52:41+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/72The Disk Radiator for the Influence on the Gas Media2019-01-12T06:03:17+02:00Vladimir KHMELEVvnh@bti.secna.ruAndrey SHALUNOVshalunov@bti.secna.ruRoman GOLYKHgrn@bti.secna.ruViktor NESTEROVnva@bti.secna.ru<p>The article is devoted to the development of efficient ultrasonic disk radiators for the intensification of the processes in the gas media. It is found out, that the main reason of insufficient efficiency of the existing radiators is the reciprocal compensation of vibrations of the opposite phases. The parameters of the radiators developed on the base of the theoretical procedure are revealed experimentally with the help of designed special-purpose test-bench. It is determined; that in near field developed ultrasonic radiators provide maximum level of acoustic pressure of 145 dB, and in far field the level of acoustic pressure is no less than 130 dB.</p>2019-01-12T00:00:00+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/80The Effect of the Friction Coefficient and the Pendulum Radius on the Behavior of Structures Isolated with Simple Friction Pendulums2019-01-12T05:54:38+02:00Gilbert-Rainer GILLICHgr.gillich@uem.roDorian NEDELCUd.nedelcu@uem.roTatian-Cristian MALINmalin_chriss@yahoo.comVasile IANCUv.iancu@uem.roCodruta Oana HAMATc.hamat@uem.roNicoleta GILLICHn.gillich@uem.ro<p>The study presented in this paper shows the results of simulation made on a rigid structure isolated with four simple friction pendulums. We created a model in <em>SolidWorks</em> that was used to find out how the pendulums radii and friction coefficients respectively the frequency of the excitation influences the structural response. It has also been found that the frequency of the structure does not increase with the frequency of excitation if the latter exceeds the natural frequency of the pendulum, but in the post-resonance domain it remains constant taking the value of the natural frequency of the system.</p>2019-01-12T05:01:49+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/73High-frequency Vibration System for Liquid Atomization2019-01-12T05:15:13+02:00Vladimir KHMELEVvnh@bti.secna.ruAndrey SHALUNOVshalunov@bti.secna.ruViktor NESTEROVnva@bti.secna.ru<p><em>The article is devoted to the solution of problem of providing of high-productive fine-dispersed ultrasonic atomization due to the development of the new construction of the piezoelectric vibrating system of the ultrasonic atomizer intended for the operation at the frequencies of 120…250 kHz. The result of the study is the development and practical realization of the ultrasonic vibrating system providing the generation of high-dispersed aerosols with the size of the drops of 10…17 micron at the atomization productivity of 54 ml/min for 120 kHz and 14 ml/min for 250 kHz at consumed power of no more than 10 W for 120 kHz and 3 W for 250 kHz. The essential improvement of the atomization parameters was achieved due to the increase of area of the atomizing surface (2 cm<sup>2</sup> for 120 kHz and 0.5 cm<sup>2</sup> for 250 kHz) and providing of the vibration amplitudes of up to 15 micron at the frequency of 120 kHz and 10 micron at 250 kHz.</em></p>2019-01-12T05:15:13+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/89The Study of Vibration Transmission Using Virtual Instruments2019-01-12T05:22:25+02:00Andrea Amalia MINDAa.minda@uem.roGilbert Rainer GILLICHgr.gillich@uem.roAna Maria BUDAIam.budai@uem.roOvidiu VASILEovidiu_vasile2002@yahoo.co.uk<p>In present, learning through experiments is the preferred studying method for students. Theoretical notions by experimental example offer a high level of understanding on phenomena. Virtual labs represent a method that ensures achieving high performance in designing tool machine. After familiarizing students with theoretical aspects, using Java applets they have carried out a series of experiments which gave them the possibility of a full understanding of the phenomena concerned. The experimental part consisted of successive virtual simulations based on the modification of some functional parameters.</p>2019-01-12T05:22:25+02:00##submission.copyrightStatement##http://rjav.sra.ro/index.php/rjav/article/view/78Computational Assessments on Dragline Bucket Oscillations2019-01-12T06:21:56+02:00Carmen DEBELEACcarmen.debeleac@ugal.roSilviu NASTACsnastac@ugal.ro<p>This paper deals with the transitory dynamics of the dragline bucket during the starting or stopping short periods within various stages of the regular technological cycle. It has supposed the effects of the hoist and drag cables respectively, with bucket unloaded. In addition, it has considered that the bucket has no contact with the ground, meaning this component as a pendulum system with double restricted linkage. The main goal of this research tries to reveal the overloads induced into the dragline structure, especially into the driving and the boom-anchors systems, due to the random dynamics of the bucket oscillations. Computational application has been proposed in order to dignify the correlations of some theoretical approaches with the real-world equipments behaviour. The concluding remarks present the relevant aspects of the transitory tensions inside the drag and the hoist systems with straight influences upon the whole machine system dynamics.</p>2019-01-12T05:40:31+02:00##submission.copyrightStatement##