Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Free Vibration analysis of a rotating cylindrical shell made of FG-GPLR porous core and MEE face with uncertain parameters in thermal environment Free Vibration analysis of a rotating cylindrical shell made of FG-GPLR porous core and MEE face with uncertain parameters in thermal environment 623 650 5533 10.22060/mej.2024.22228.7586 FA Mohsen Khanahmadi Department of Mechanic, central Tehran Branch, Islamic Azad University, Tehran, Iran Armen Adamian Islamic Azad University Tehran Central Branch Ahmad Hosseini-Sianaki Mechanical Engineering, Islamic Azad University, Central Tehran Branch Journal Article 2023 03 02 In this study, free vibration analysis of a rotating composite double-layer cylindrical shell has been carried out using first-order shear deformation theory. The shell is made of a thin magneto-electroelastic (MEE) top layer bonded to the functionally graded graphene platelet reinforced (FG-GPLR) porous layer and is subjected to the thermal environment. The two ends of the shell can be considered as pinned boundary conditions due to the presence of bearings that prevent transverse movement. At first, natural frequencies of the forward and backward modes for the rotating composite shell were obtained and verified by the literature results. Then the effect of rotational speed, mode numbers, temperature change, porosity and GPLs mass fraction on the frequencies were investigated. This study then seeks to investigate the effect of uncertainties in the MEE layer properties on the free vibration of a rotating composite shell exposed to electric and magnetic potentials. In this case, the uncertainties in the elastic modulus, piezoelectric and piezomagnetic coefficient of the smart layer, are introduced using a symmetric Gaussian fuzzy number. The governing equations for the uncertain system are obtained by combining Hamilton's principle and the dual parametric form of fuzzy numbers; Then the natural frequencies of the uncertain model are calculated using Navier's approach. Free vibration is also investigated by obtaining the natural frequency borders with respect to the various uncertain parameters. The results have shown that the porosity increased the frequencies. In the case of uncertain properties, with increasing of the electric potential, the frequency bounds decreased slightly, but they increased intensely with increasing of the magnetic potential. In this study, free vibration analysis of a rotating composite double-layer cylindrical shell has been carried out using first-order shear deformation theory. The shell is made of a thin magneto-electroelastic (MEE) top layer bonded to the functionally graded graphene platelet reinforced (FG-GPLR) porous layer and is subjected to the thermal environment. The two ends of the shell can be considered as pinned boundary conditions due to the presence of bearings that prevent transverse movement. At first, natural frequencies of the forward and backward modes for the rotating composite shell were obtained and verified by the literature results. Then the effect of rotational speed, mode numbers, temperature change, porosity and GPLs mass fraction on the frequencies were investigated. This study then seeks to investigate the effect of uncertainties in the MEE layer properties on the free vibration of a rotating composite shell exposed to electric and magnetic potentials. In this case, the uncertainties in the elastic modulus, piezoelectric and piezomagnetic coefficient of the smart layer, are introduced using a symmetric Gaussian fuzzy number. The governing equations for the uncertain system are obtained by combining Hamilton's principle and the dual parametric form of fuzzy numbers; Then the natural frequencies of the uncertain model are calculated using Navier's approach. Free vibration is also investigated by obtaining the natural frequency borders with respect to the various uncertain parameters. The results have shown that the porosity increased the frequencies. In the case of uncertain properties, with increasing of the electric potential, the frequency bounds decreased slightly, but they increased intensely with increasing of the magnetic potential.

https://mej.aut.ac.ir/article_5533_8965f76632d7672e7d3cf29c87ecaa0c.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Redesign of energy recovery device to keep the production recovery constant Redesign of energy recovery device to keep the production recovery constant 651 678 5534 10.22060/mej.2024.22968.7705 FA Abdollah Eskandari Payame Noor University - Faculty of Engineering 0000-0003-4441-6473 Journal Article 2024 02 09 One of the problems of producing fresh water by reverse osmosis is its sensitivity to process conditions. In this article, a method for redesigning the hydraulic turbocharger rotor as an energy Recovery device in desalination units has been discussed. For this purpose, firstly, the performance of a desalination unit in operation is investigated. Then, using turbomachinery similarity relations and CFD, two new rotors have been designed for two high- and low-pressure modes and replaced with the primary rotor. The validated results with the test show that despite changing membrane inlet pressure, the amount of produced water was not changed, the total efficiency has increased by more than 4% and the energy recovery has increased by about 2% in the high-pressure mode, which shows that this method can be used in situations where the pressure change of the membranes is noticeably higher or lower than the initial design pressure. One of the problems of producing fresh water by reverse osmosis is its sensitivity to process conditions. In this article, a method for redesigning the hydraulic turbocharger rotor as an energy Recovery device in desalination units has been discussed. For this purpose, firstly, the performance of a desalination unit in operation is investigated. Then, using turbomachinery similarity relations and CFD, two new rotors have been designed for two high- and low-pressure modes and replaced with the primary rotor. The validated results with the test show that despite changing membrane inlet pressure, the amount of produced water was not changed, the total efficiency has increased by more than 4% and the energy recovery has increased by about 2% in the high-pressure mode, which shows that this method can be used in situations where the pressure change of the membranes is noticeably higher or lower than the initial design pressure.

https://mej.aut.ac.ir/article_5534_de6b1cf3fb0a3aa1244d30f7b8c29c41.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Experimental Investigation of the Frequency Spectra of Vortex Shedding from a Triangular Bluff Body at Different Flow Angles Experimental Investigation of the Frequency Spectra of Vortex Shedding from a Triangular Bluff Body at Different Flow Angles 679 698 5544 10.22060/mej.2024.23245.7733 FA Ehsan Ardekani Department of Mechanical Engineering, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Foad Farhani Department of Mechanical Engineering, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Mohammad Ali Ardakani Department of Mechanical Engineering, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Journal Article 2024 06 03 The base of the vortex flowmeter is the linear relationship ( is a constant and is vortex shedding frequency). Therefore, the accuracy of the flow meter is only a function of the vortex shedding frequency measurement accuracy. To determine the frequency measurement accuracy, it is necessary to investigate its frequency spectrum. In this research, vortex shedding and its frequency spectrum downstream of an equilateral triangular model of 10 mm side have been investigated experimentally in a closed-type wind tunnel using a hot-wire anemometer. The vortex shedding frequency spectra were fitted using the normal Gauss distribution, and based on the expected confidence level, the accuracy of the frequency measurement was evaluated and its changes were quantified using the standard deviation of the normal distribution. Results show for Re >1200, the Strouhal number variation is independent of the Re number, and it is only a function of the flow angle. Also, for a 95% confidence level, the maximum frequency measurement error for the triangular model is 1.53% for and 2.46% for . The standard deviation of the frequency spectra has an increasing trend streamwise, however, it is constant spanwise outside the wake region. When the flow angle is in the range of , the measurement error increases to about 9%. The base of the vortex flowmeter is the linear relationship ( is a constant and is vortex shedding frequency). Therefore, the accuracy of the flow meter is only a function of the vortex shedding frequency measurement accuracy. To determine the frequency measurement accuracy, it is necessary to investigate its frequency spectrum. In this research, vortex shedding and its frequency spectrum downstream of an equilateral triangular model of 10 mm side have been investigated experimentally in a closed-type wind tunnel using a hot-wire anemometer. The vortex shedding frequency spectra were fitted using the normal Gauss distribution, and based on the expected confidence level, the accuracy of the frequency measurement was evaluated and its changes were quantified using the standard deviation of the normal distribution. Results show for Re >1200, the Strouhal number variation is independent of the Re number, and it is only a function of the flow angle. Also, for a 95% confidence level, the maximum frequency measurement error for the triangular model is 1.53% for and 2.46% for . The standard deviation of the frequency spectra has an increasing trend streamwise, however, it is constant spanwise outside the wake region. When the flow angle is in the range of , the measurement error increases to about 9%.

https://mej.aut.ac.ir/article_5544_97785e0500ad16c18574c64189ccf4b4.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Comparison of Perceptron and Radial Basis Function Neural Networks in Modeling Heat Exchangers with Rectangular Helical Channels Comparison of Perceptron and Radial Basis Function Neural Networks in Modeling Heat Exchangers with Rectangular Helical Channels 699 716 5561 10.22060/mej.2024.22833.7684 FA Reza Beigzadeh Department of Chemical Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran Journal Article 2023 12 02 In this research, computational fluid dynamics method was used to investigate the effect of geometrical parameters of rectangular spiral channels on heat transfer coefficient. Two artificial neural networks including perceptron (MLP) and radial basis function (RBF) models were used to model the heat transfer in helical channels. The model inputs included the Reynolds number and geometric parameters of the channels, and output was the Nusselt number. 135 data were generated by Computational Fluid Dynamics (CFD) simulation and after validation were used for training and evaluation of neural network models. The results of the research showed that the accuracy of MLP was slightly higher than RBF, however, both models were acceptable. Due to the high and acceptable accuracy of these two models, they can be well used in future research and applications. In this research, the main innovation is comparing two different methods for modelling the heat exchanger with a rectangular helical channel. This research shows that the use of perceptron neural network and radial basis function can both be effective in improving the performance and efficiency of the heat exchanger. This research can be used as a guide to choose the appropriate method for modeling heat exchangers and help to improve technologies related to this field. In this research, computational fluid dynamics method was used to investigate the effect of geometrical parameters of rectangular spiral channels on heat transfer coefficient. Two artificial neural networks including perceptron (MLP) and radial basis function (RBF) models were used to model the heat transfer in helical channels. The model inputs included the Reynolds number and geometric parameters of the channels, and output was the Nusselt number. 135 data were generated by Computational Fluid Dynamics (CFD) simulation and after validation were used for training and evaluation of neural network models. The results of the research showed that the accuracy of MLP was slightly higher than RBF, however, both models were acceptable. Due to the high and acceptable accuracy of these two models, they can be well used in future research and applications. In this research, the main innovation is comparing two different methods for modelling the heat exchanger with a rectangular helical channel. This research shows that the use of perceptron neural network and radial basis function can both be effective in improving the performance and efficiency of the heat exchanger. This research can be used as a guide to choose the appropriate method for modeling heat exchangers and help to improve technologies related to this field.

https://mej.aut.ac.ir/article_5561_5cb22b6ada9b860235e5e20975f23de3.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Development of a novel multi-cellular origami metastructure and investigation into numerical and experimental energy absorption behaviour Development of a novel multi-cellular origami metastructure and investigation into numerical and experimental energy absorption behaviour 717 740 5562 10.22060/mej.2024.22928.7694 FA Mohammad Mazaheri K. N. Toosi University of Technology Mohammad Khalajzadeh K. N. Toosi University of technology Masood Asgari هیات علمی 0000-0002-2063-8699 Journal Article 2024 01 16 Nowadays, the use of additive manufacturing provides a unique opportunity to create complex structures. One such structure that is currently garnering attention in various fields, such as energy absorption, is origami structures. In this paper, novel multi-cellular origami structures are introduced to improve energy absorption performance under quasi-static compression loading. The control of these structures is determined by two key parameters: the number of layers and the ratio between the length of the top side and the bottom side. The effects of these structures on crashworthiness were simulated using Abaqus software and validated through experimental tests with models built using additive manufacturing. Additionally, a simple structure was designed and tested to facilitate a comparison between origami and non-origami structures. The results of this study showed that geometric parameters play an important role in increasing energy absorption behaviour, with origami structures exhibiting a 97 percent increase in specific energy absorption (SEA) compared to non-origami structures. Finally, based on the complex proportional assessment method, the best structure was determined among those designed according to energy absorption criteria. Nowadays, the use of additive manufacturing provides a unique opportunity to create complex structures. One such structure that is currently garnering attention in various fields, such as energy absorption, is origami structures. In this paper, novel multi-cellular origami structures are introduced to improve energy absorption performance under quasi-static compression loading. The control of these structures is determined by two key parameters: the number of layers and the ratio between the length of the top side and the bottom side. The effects of these structures on crashworthiness were simulated using Abaqus software and validated through experimental tests with models built using additive manufacturing. Additionally, a simple structure was designed and tested to facilitate a comparison between origami and non-origami structures. The results of this study showed that geometric parameters play an important role in increasing energy absorption behaviour, with origami structures exhibiting a 97 percent increase in specific energy absorption (SEA) compared to non-origami structures. Finally, based on the complex proportional assessment method, the best structure was determined among those designed according to energy absorption criteria.

https://mej.aut.ac.ir/article_5562_e84401ad27c4cfb9815776eb9432ff17.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 56 5 2024 07 22 Experimental Study of Nano-Oils Containing Iron Oxide, multi-walled carbon nanotubes, and Aluminum Oxide in Reducing the Hot Spot Temperature of Transformers Experimental Study of Nano-Oils Containing Iron Oxide, multi-walled carbon nanotubes, and Aluminum Oxide in Reducing the Hot Spot Temperature of Transformers 741 762 5566 10.22060/mej.2024.22976.7702 FA Fateme Tavakoli Dastjerd Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran Amirhossein Joveini Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran 0009-0004-2807-5044 Mohammad Derayatifar Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran Hamid Niazmand Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran Journal Article 2024 02 09 In tropical regions, particularly during the summer, the rise in ambient temperature causes a significant increase in the hot spot temperature of transformers, which can result in the early failure of transformers and cause irreparable damage to the power grid. Therefore, efforts to reduce the hot spot temperature of transformers are of great importance. One method of thermal management for oil-immersed transformers is to enhance the heat transfer properties of the oil with additives, allowing for the effective and rapid dissipation of heat from the windings and core to the surrounding environment. In this study, the experimental performance of three nan-oil aluminium oxide, iron oxide, and multi-walled carbon nanotubes was evaluated in a laboratory-scale oil-immersed transformer with a maximum rated power of 150 watts. To this end, the aforementioned nanoparticles were mixed with transformer mineral oil at a concentration of 0.5 g/L and tested in the transformer. The results showed that adding nanoparticles to the oil, within the permissible range for various parameters, improved the physical properties of the nano-oil, which could play a significant role in the thermal management of transformer oil. For example, at 100% of the transformer's full power, the aluminium oxide, iron oxide, and multi-walled carbon nanotube nano-oils reduced the hot spot temperature by 2.1°C, 1.3°C, and 5.4°C, respectively, compared to the baseline test with mineral oil. The primary reason for this improvement is the enhanced thermal conductivity of the nano-oil. In tropical regions, particularly during the summer, the rise in ambient temperature causes a significant increase in the hot spot temperature of transformers, which can result in the early failure of transformers and cause irreparable damage to the power grid. Therefore, efforts to reduce the hot spot temperature of transformers are of great importance. One method of thermal management for oil-immersed transformers is to enhance the heat transfer properties of the oil with additives, allowing for the effective and rapid dissipation of heat from the windings and core to the surrounding environment. In this study, the experimental performance of three nan-oil aluminium oxide, iron oxide, and multi-walled carbon nanotubes was evaluated in a laboratory-scale oil-immersed transformer with a maximum rated power of 150 watts. To this end, the aforementioned nanoparticles were mixed with transformer mineral oil at a concentration of 0.5 g/L and tested in the transformer. The results showed that adding nanoparticles to the oil, within the permissible range for various parameters, improved the physical properties of the nano-oil, which could play a significant role in the thermal management of transformer oil. For example, at 100% of the transformer's full power, the aluminium oxide, iron oxide, and multi-walled carbon nanotube nano-oils reduced the hot spot temperature by 2.1°C, 1.3°C, and 5.4°C, respectively, compared to the baseline test with mineral oil. The primary reason for this improvement is the enhanced thermal conductivity of the nano-oil.

https://mej.aut.ac.ir/article_5566_b0c7ae2316c7e8214fd659e4bc8a0dea.pdf