Iranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-47619220230829Acoustical simulation, design and experimental investigation of a classroom: A case study12070728310.22064/tava.2023.563390.1213ENMohammad RezaTorabiBSc Student, Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, IranAliLoghmaniAssistant Professor, Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, IranJournal Article20220912To improve teaching and learning conditions, room acoustics tries to adjust the educational environment. This research addresses the room acoustics of a small classroom in the Department of Mechanical Engineering at Isfahan University of Technology. It has been studied by modeling and simulating the classroom in the COMSOL software using the ray tracing method, and the reverberation time has been calculated. The model is validated by field measurements and using the impulse response function according to ISO 3382-2 in terms of the reverberation time. Then, it is compared with Eyring's and Sabin's empirical relationships, as well. The acoustics modes of the classroom have been obtained using the modal analysis in the COMSOL software. ANSI/ASA S12.60 is employed to design a suitable acoustical environment for the classroom and absorption panels and bass traps are utilized to reach the desired condition. After applying the adjustments, the reverberation time reached the recommended standard value, which increases the sound quality. Other acoustical parameters such as Definition (D_50), Clarity (C_50) and Sound Transmission Index (STI) have been calculated before and after the acoustic correction. Results revealed that speech intelligibility has fallen in the acceptable range.https://tava.isav.ir/article_707283_7f3c42ee0ee6930ddaefce7c69f4257e.pdfIranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-47619220231126Experimental study on the impact of variations in the friction material properties on the vibration behaviour of brake pads213870904910.22064/tava.2023.2009608.1226ENMohammadRavanbodAutomotive Research Centre, Department of Mechanical and Energy Systems Engineering, University of Bradford, Bradford, UK0000-0002-6944-5847SalmanEbrahimi-NejadAssistant Professor, School of Automotive Engineering, Iran University of Science & Technology, Tehran, Iran0000-0002-1591-023XJournal Article20230819Brake noise is often caused by the coupling of the natural frequencies of the disc and pad. To prevent this, it is important to control the natural frequencies of these components, hence, the dispersion of natural frequency values is a critical factor in brake noise determination. This paper examines how the brake pad's natural frequencies and mode shapes are affected by its friction material properties, such as Poisson's ratio, Young's modulus, and shear modulus in different directions. Two brake pad designs from Land Rover are modelled and analysed using finite element analysis (FEA) and experimental modal analysis (EMA). A machine learning algorithm based on multiple-features linear regression is used to identify the main friction material parameters and their relationship to the natural frequencies. The results show that increasing the transverse Young's modulus or decreasing the longitudinal Young's modulus, shear modulus, or Poisson's ratio in all directions can increase the natural frequencies. Consequently, the paper suggests that Poisson's ratio and transverse Young's modulus should be considered when selecting friction compounds for brake pads.https://tava.isav.ir/article_709049_ec6de61492a27913151d2f080529dbe1.pdfIranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-47619220231101Investigating the vibration of cracked micro-cantilever beam with concentrated mass and rotary inertia based on MCST395371150610.22064/tava.2023.556982.1208ENHamedPetoftPh.D. Candidate, Faculty of Mechanical & Energy Engineering, Shahid Beheshti University, Tehran, Iran0000-0003-4356-7130AbbasRahiAssociate Professor, Faculty of Mechanical & Energy Engineering, Shahid Beheshti University, Tehran, IranJournal Article20230214The current paper proposes the vibrational behavior of a cracked micro-cantilever Euler-Bernoulli beam with a concentrated mass and its moment of inertia at the free-end boundary condition based on the Modified Couple Stress Theory (MCST). We model the open-edge crack and calculate its stiffness. We also consider The Stress Intensity Factor (SIF). Using Hamilton’s principle, the associated boundary conditions followed by the system’s dynamic equations are derived based on MCST. Afterward, the natural frequencies of the cracked micro-cantilever beam are semi-analytically determined. In the numerical results, we obtain the first three natural frequencies of the system versus various parameters containing the crack depth and location changes and the material length scale parameter with the different mass ratios. The results are verified with similar previous research. The calculated results indicate that increasing the crack depth, approaching the crack location to the concentrated mass and the node points, and increasing the mass ratio cause a decrease in frequencies. However, increasing the material length scale parameter causes an increase in the natural frequencies due to raising the total strain energy of the system.https://tava.isav.ir/article_711506_b0a04c35d4f2165c1c5ccf030554002e.pdfIranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-47619220230920Optimisation, development and evaluation of a tractor seat suspension via artificial intelligent method546470956310.22064/tava.2023.555480.1205ENMohamadGohariFaculty of Mechanical Engineering, Arak University of Technology, Arak, IRAN0000-0001-6744-2151MonaTahmasebiAgricultural Engineering Research Department, Markazi Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Arak, IRANFarzadRafieianFaculty of Mechanical Engineering, Arak University of Technology, Arak, IRAN0000-0003-1595-466XAbbasPakFaculty of Mechanical Engineering, Engineering School, Bu-Ali Sina University, Hamedan, IRAN0000-0002-4099-982XJournal Article20220619Tractor drivers’ health is so important and some injuries can develop in the long run such as lower back pain or spinal column disorder resulting from low-frequency vibrations. Seat suspension plays a crucial role in the reduction of harmful vibrations in off-road vehicles. Passive suspension design parameters should be tuned properly to remove vibrations efficiently. Lumped parameter models have been widely used in seat suspension optimization to simulate human body responses. In this study, a tractor seat suspension was designed based on an artificial neural network biodynamic model instead of a lumped model. In the optimisation step, a novel approximation approach via an artificial neural network was employed to minimise seat-to-spine vibration transmissibility. Then, a seat suspension was modified based on the optimisation results, and an outdoor dynamic test was carried out to evaluate suspension in vibration transmissibility attenuation. The gathered data were processed and analyzed in terms of vibration transmissibility, mobility, and apparent mass. The transmitted vibration from floor to spine was measured between 0.2 and 0.4 at 4 to 6 Hz (spine dominant frequency range) on bumpy and smooth roads at various traveling speeds. The effect of seat suspension modification showed the changes in the performance of seat suspension in regard to vibration transmissibility. Thus, this passive suspension may decrease the risk of lower back pain for tractor drivers. So, this modification can be considered by the tractor manufacturer for future designed models to provide more comfort for operators in the daily use of this device.https://tava.isav.ir/article_709563_bdff8fef4bf06e7bd4d9297da98d31fd.pdfIranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-47619220240110Analytical determination of Iwan and Maxwell slip models of an elastic frictional rough interface6610271652110.22064/tava.2024.2012100.1228ENHosseinJamshidiPh.D., Department of Mechanical Engineering, Iran University of Science and Technology, Tehran, IRANHamidAhmadianProfessor, School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran0000-0002-2383-672XJournal Article20230922This paper analytically derives the Maxwell slip model associated with a frictional rough contact interface using the multi-asperity contact theory in the elastic region. The multi-asperity contact theory based on the Mindlin solution relates interface roughness, material properties, and preload to the contact interface Jenkins element parameters of the discrete Maxwell slip model and continuous Iwan model distribution function. The rough surface properties are obtained from the measured roughness profile of two contacting surfaces. The main advantage of the proposed analytical Maxwell slip model is there is no need to update or identify any parameter using experimental test data. In achieving a rough interface discrete Maxwell slip model, the interface contacting asperities are grouped based on their heights, called a height-region element group of the contact interface model. Each height-region asperities' contact area is divided into annular areas; the number of annular areas determines sliding motion states. Using the classical Mindlin solution, a Jenkins element is assigned to each specified annular area using the Hertzian normal pressure distribution function of the contact area and contribution to the tangential contact stiffness. The Iwan and Maxwell slip model's resultant hysteresis curves are compared with the analytical multi-asperity contact model to verify the proposed contact model procedure's accuracy. Model predictions of the proposed procedure are also validated against measured frictional contact behavior, resulting in good agreements with experimental observations.https://tava.isav.ir/article_716521_6588b9ba8f4dcba327712fdcfb45d7e2.pdf