https://rjav.sra.ro/index.php/rjav/issue/feedRomanian Journal of Acoustics and Vibration2022-06-23T13:20:55+03:00Ovidiu 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>https://rjav.sra.ro/index.php/rjav/article/view/271Impedance Boundary Conditions on The Optimal Design of the H-Type Cylinder Resonator Using Transmission Matrix Method and Genetic Algorithm2022-03-28T15:02:32+03:00Yosi Aprian SARIryosia@uny.ac.idAgung Bambang Setio UTOMO, Prof.agungbambang@ugm.ac.idMitrayana MITRAYANA, Dr.mitrayana@ugm.ac.idDanang LELONO, Dr.danang@ugm.ac.id<p>Optimization of the H-type cylinder resonator design is very important in order to obtain maximum acoustic wave signal in photoacoustic. Geometrically, this resonator is in the form of three cylinders arranged axis-symmetric where the middle cylinder (resonator) is flanked by two other cylinders (buffer) giving sudden contraction and expansion. Impedance boundary conditions are used to analyze the waves propagating in this resonator. The method used in this optimization is the transmission matrix method (TMM) and genetic algorithm (GA), in which the transmission loss (TL) at a certain frequency and quality factor ( ) are treated as optimization objectives for the cell performance, whereas the resonator geometry dimensions are treated as optimization. Optimization of the H-type cylinder resonator design is very important in order to obtain maximum acoustic wave signal in photoacoustic. Geometrically, this resonator is in the form of three cylinders arranged axis-symmetric where the middle cylinder (resonator) is flanked by two other cylinders (buffer) giving sudden contraction and expansion. Impedance boundary conditions are used to analyze the waves propagating in this resonator. The method used in this optimization is the transmission matrix method (TMM) and genetic algorithm (GA), in which the transmission loss (TL) at a certain frequency and quality factor ( ) are treated as optimization objectives for the cell performance, whereas the resonator geometry dimensions are treated as optimization.</p>2022-03-28T15:01:45+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/287Evaluation of the Dynamic Regime Upon Trial of An Elastic Beam Excited by Vibrodyne2022-03-28T15:14:49+03:00Nicusor DRĂGANndragan@ugal.roGigel Florin CĂPĂȚÂNĂgcapatana@ugal.roAurora Maria POTÎRNICHEaurora.potirniche@ugal.ro<p>There are presented the outcomes of the research on the dynamic behavior for an elastic beam dynamically excited by an inertial vibrator placed in the middle of it.</p> <p>In this case the dynamic load inertial vibrator is called vibrodyne and has a rotating inertial force with known static moment of the eccentric mass of dynamic imbalance.</p>2022-03-28T15:14:49+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/260Sensitivity of Progressive Collapse of MRF to Redundancy Factor2022-03-28T15:39:03+03:00Amin GHANNADIASL, Assistant Professoraghannadiasl@uma.ac.irSaeed MORTAZAVIm.saeedmortazavi@gmail.comHassan REZAEI DOLAGHhassan7205@yahoo.com<p>Progressive collapse mainly refers to a chain failure in a structure. That is, if one of the structural members gets a local collapse, it will lead to the other member's failure and eventually an additional collapse in the building. Over the past few decades, the assessment problems of the potential for progressive collapse, as well as improving the performance of structures against this type of failure, are widely discussed among the researchers. Several studies have been carried out on this field in the structures, but the effects of the redundancy factor of the structure, which is considered as one of the effective parameters in the progressive collapse, is not assessed. In this study, the effects of redundancy factor on improving the performance of the structure with moment frame system against progressive failure are investigated, also the adequacy of the numerical value of the recommended redundancy factor of Standard No. 2800 is worked out. Due to the positive effect of redundancy degree on the load redistribution of the collapsed member to other structural members, if the structure is not sufficient in terms of redundancy degree, the designing problem can be acceptably solved by considering the redundancy factor. In this paper, some structures with a moment frame system are studied in two groups with various spans. In the selected models, the effects of redundancy are studied by increasing the number of spans and floors. Furthermore, the redundancy factor with both regular and irregular plans are modeled. The selected structures are studied with and without considering the redundancy factor, and as well as by removing the columns which are more susceptible to progressive collapse. Finally, the results of the nonlinear static analysis of the models obtained.</p>2022-03-28T15:19:27+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/289The Effect of The Symmetrical Elastic Nonlinearity on Structural Vibrations Transmitted by Dynamic Equipment on The Construction Envelope2022-03-28T15:25:41+03:00Polidor BRATUicecon@icecon.roGeorge Lucian NICOLAEnicolaegeorgelucian91@gmail.comSamir IACOVESCUsamir.iacovescu@upit.roDan IONdan.ion@icecon.roAndrei COTOBANandrei.cotoban@gmail.com<p>The results of the research carried out for elastic systems with symmetrical nonlinearity have been systematized in this article so that they can be disseminated for real models of dynamic equipment in construction endowment. Thus, the ventilation - conditioning systems, water pumping systems, main and interior piping systems from nuclear power plants, platforms with optoelectronic equipment are supported on elastic devices that can have a non-linear behavior.</p> <p> In this case, it is highlighted that under certain functional and constructive conditions it is possible the occurrence of subharmonic vibrations of order 1/3 of the excitation pulsation. This leads to the generation of structural noise with consequences for the people inside it.</p>2022-03-28T15:25:41+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/250Study on the Influence of Magnetorheological Fluid Damper on Vibration in Rotating Machinery2022-03-28T15:38:25+03:00Sam Paul P.psam_paul@rediffmail.comLawrance Glawrancedevaraj@gmail.comShylu D.S.mail2shylu@yahoo.com<p>In day-to-day life, the concept of rotary machines appears everywhere in diverse engineering applications. In rotating machinery, the safety and performance of the entire system are considered as the significant factors which has to be monitored continuously. As the speed of the motor increases, the amplitude of vibration varies rapidly, and the excitation is due to the elements of rotating structure. There are various parameters that affect the vibration in the rotor during different rotating speed. In this paper, rotor made of mild steel and supporting structure made of cork, synthetic rubber was considered, and these parameters were tested for similar condition with and without magnetorheological fluid damper. This damper is used to reduce the vibration in the shaft due to whirling of shaft at critical speeds. The vibration characteristics of the rotary machinery were studied with change in the base material of the supporting structure. From experimental result, it was observed that the rubber base material reduces vibration much better when compared to cork material. The percentage of reduction in the shaft vibration shows that it is better to use rubber base material with Magnetorheological fluid damper rather than the cork material even though vibration was reduced considerably when both base materials was attached to the setup with MR damper.</p>2022-03-28T15:27:54+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/297Modal Analysis of a Mechanical System Modeled as a 6 Degrees-of-Freedom Solid Body with Elastic Bearings and Structural Symmetries2022-03-28T15:32:29+03:00Aurora Maria POTÎRNICHEaurora.potirniche@ugal.roOvidiu VASILEovidiu_vasile2002@yahoo.co.ukGigel Florin CĂPĂȚÂNĂgcapatana@ugal.ro<p>The paper presents the physical model and the mathematical model of a mechanical system modeled as a solid body with 6 degrees of dynamic freedom and elastic bearings. Considering that the system has constructive symmetries (masses and inertia, elastic support elements), simpler physical and mathematical models are obtained, the systems of differential equations of motion being decoupled in subsystems with fewer equations. The systems of decoupled equations of motion describe the dynamic behavior of subsystems with coupled motions in certain directions (translational and/or rotational motions). The paper also presents a case study: a modal analysis of an 6DOF elastic mechanical system with a vertical plane of symmetry.</p>2022-03-28T15:32:29+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/284Evaluating the Thermo-acoustic Performance of Composite Panels Made of Oil Palm Fibers with Latex2022-06-23T13:06:15+03:00Lamyaa Abdulrahman JAWAD, Dr.lamyaeng@gmail.comTawfeeq Wasmi MOHAMMEDtawfeeqwasmi@uomustansiriyah.edu.iq<p>In this study, composite panels made of natural oil palm fibers (OPFs) mixed with latex are manufactured and tested to evaluate the thermo-acoustic performance as sound insulation panels. The involving of OPFs in the manufacturing would be a contribution to green technology and optimal usage due the accumulation of deposits thus non-useful ways of removal wastes by burning. The study has included theoretical and experimental investigation to determine the acoustic absorption coefficient (AAC) of composites made of OPFs with latex. Allard approach is used for calculating the values of AAC theoretically in a range of frequencies between 100 Hz to 5000 Hz. In the experimental works, different composite panels of 20, 30, 40, and 50 mm thickness have manufactured. The measurement of AAC has done using an impedance tube instrument. The results show that the value of AAC has increased by increasing the thickness and bulk density for a certain range. Peak AAC values are pointed at high frequencies (more than 1600 Hz) and they have reached up to 0.8. Where, an improving in the value of the AAC between 10-20% could be obtained by increasing the thickness by 10 mm. However, the experimental values show a slight deviation in contrast to theoretical values by ±20% as a consequent to experimental regards as well as some approximated assumptions.</p>2022-06-23T13:05:07+03:00##submission.copyrightStatement##https://rjav.sra.ro/index.php/rjav/article/view/305Frequency Estimation using Spectral Techniques with the Support of a Deep Learning Method2022-06-23T13:20:55+03:00Cristian TUFISIcristian.tufisi@ubbcluj.roAndrea Amalia MINDAandrea.minda@ubbcluj.roDaniela-Giorgiana BURTEAdaniela.burtea@stud.ubbcluj.roGilbert-Rainer GILLICHgilbert.gillich@ubbcluj.ro<p>In the case of damage detection, it is important to estimate the frequencies accurately. DFT-based methods provide us with amplitude-frequency pairs, but displayed frequencies carry important errors in the case of short signals. On the other hand, the amplitudes displayed for a sinusoidal signal with different time lengths describe approximately a <em>sinc</em> function. When involving interpolation to find the maxima of the <em>sinc</em> function, to which the real amplitude of the signal corresponds, it is necessary to ensure the existence of at least three points on the main lobe of the <em>sinc</em> function. To this aim, we apply zero-padding to the original signal in such a way that its length is doubled. The frequency estimation method proposed in this paper involves an artificial neural network (ANN). The three amplitudes taken from the main lobe determined for all considered signal lengths are the input values used to train the network. The correction term that allows us to evaluate the frequency will be the target. Following the simulations made, it is found that using normalized data sets we can estimate any frequencies, irrespective of the frequency with which the network was trained. It applies to any signal length, and any signal amplitude.</p>2022-06-23T13:20:55+03:00##submission.copyrightStatement##