Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 Thermal performance assessment of two side-by-side natural draft dry cooling towers with circular and elliptical periphery radiator arrangements Thermal performance assessment of two side-by-side natural draft dry cooling towers with circular and elliptical periphery radiator arrangements 1239 1262 6021 10.22060/mej.2026.25198.7927 FA Yaser Farahani Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran 0009-0006-5461-3891 Mohsen Goodarzi Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran Journal Article 2025 12 02 Wind significantly deteriorates thermal performance of natural draft dry cooling towers (NDDCTs). Although various approaches have been proposed to enhance the performance of single and multiple cooling towers, the effect of modifying the geometric arrangement of the radiators has not been comprehensively investigated. In this study, the thermal performance of two side-by-side natural draft dry cooling towers with an elliptical radiator arrangement was numerically compared with that of a conventional circular arrangement using three-dimensional CFD simulations. Results revealed that the presence of an adjacent tower leads to a reduction in the heat transfer rate of each individual tower compared to the isolated (single-tower) condition, highlighting the significant impact of flow interference between the towers. However, at wind speeds of 7 and 10 m/s, the elliptical arrangement outperformed the circular layout. Under high-wind conditions, the elliptical tower improves the thermal efficiency by approximately 18.2% to 29.5% compared to the conventional circular tower. Detailed flow field analysis revealed that the enhanced passage of warm air over the rear radiators in the elliptical arrangement increased the average temperature gradient along the lateral surfaces of these radiators, thereby improving their heat transfer rate. The optimal radiator arrangement depends on the prevailing wind conditions at the site and plays a critical role in improving the thermal performance of the cooling towers. Wind significantly deteriorates thermal performance of natural draft dry cooling towers (NDDCTs). Although various approaches have been proposed to enhance the performance of single and multiple cooling towers, the effect of modifying the geometric arrangement of the radiators has not been comprehensively investigated. In this study, the thermal performance of two side-by-side natural draft dry cooling towers with an elliptical radiator arrangement was numerically compared with that of a conventional circular arrangement using three-dimensional CFD simulations. Results revealed that the presence of an adjacent tower leads to a reduction in the heat transfer rate of each individual tower compared to the isolated (single-tower) condition, highlighting the significant impact of flow interference between the towers. However, at wind speeds of 7 and 10 m/s, the elliptical arrangement outperformed the circular layout. Under high-wind conditions, the elliptical tower improves the thermal efficiency by approximately 18.2% to 29.5% compared to the conventional circular tower. Detailed flow field analysis revealed that the enhanced passage of warm air over the rear radiators in the elliptical arrangement increased the average temperature gradient along the lateral surfaces of these radiators, thereby improving their heat transfer rate. The optimal radiator arrangement depends on the prevailing wind conditions at the site and plays a critical role in improving the thermal performance of the cooling towers. https://mej.aut.ac.ir/article_6021_b075703bbe07a50ddcccfaac424bb6d9.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 A data-driven framework for wind turbine power curve cleaning and abnormal data detection based on binning and quantiles A data-driven framework for wind turbine power curve cleaning and abnormal data detection based on binning and quantiles 1263 1286 6028 10.22060/mej.2026.24688.7894 FA Alireza Aghajani Mobarakeh Control Group, Department of Electrical Engineering, Iran University of Science and Technology, Tehran, Iran Javad Poshtan Control Group, Department of Electrical Engineering, Iran University of Science and Technology, Tehran, Iran Journal Article 2025 09 05 In this study, a preprocessing approach is proposed to improve training accuracy and computational efficiency by leveraging SCADA data and integrating machine learning algorithms with statistical techniques for unlabeled data. The method reduces the training dataset substantially by partitioning the data into equal points intervals and selecting representative samples based on quantiles, a procedure referred to as RD. Using this strategy, only 0.2% of the original dataset is required for model training in this study. Subsequently, abnormal data points are identified using a power curve model with quantile thresholds. The RD method is evaluated against DBSCAN and a KNN-based model. Experimental results obtained from real-world wind farm data indicate that RD combined with KNN outperforms DBSCAN. Specifically, both MAE and RMSE are reduced by approximately 15%, reflecting improved predictive accuracy. From a computational perspective, the execution time of RD is about 0.15 seconds, compared to 0.99 seconds for DBSCAN, corresponding to a reduction in runtime exceeding 50%. Moreover, unlike DBSCAN, which requires precise parameter tuning or additional constraints tailored to the power curve structure when dealing with dense or linear outliers, the proposed approach is capable of automatically eliminating outlier data points from the wind turbine power curve without the need for predefined filters or explicit boundary definitions prior to the cleaning process. In this study, a preprocessing approach is proposed to improve training accuracy and computational efficiency by leveraging SCADA data and integrating machine learning algorithms with statistical techniques for unlabeled data. The method reduces the training dataset substantially by partitioning the data into equal points intervals and selecting representative samples based on quantiles, a procedure referred to as RD. Using this strategy, only 0.2% of the original dataset is required for model training in this study. Subsequently, abnormal data points are identified using a power curve model with quantile thresholds. The RD method is evaluated against DBSCAN and a KNN-based model. Experimental results obtained from real-world wind farm data indicate that RD combined with KNN outperforms DBSCAN. Specifically, both MAE and RMSE are reduced by approximately 15%, reflecting improved predictive accuracy. From a computational perspective, the execution time of RD is about 0.15 seconds, compared to 0.99 seconds for DBSCAN, corresponding to a reduction in runtime exceeding 50%. Moreover, unlike DBSCAN, which requires precise parameter tuning or additional constraints tailored to the power curve structure when dealing with dense or linear outliers, the proposed approach is capable of automatically eliminating outlier data points from the wind turbine power curve without the need for predefined filters or explicit boundary definitions prior to the cleaning process. https://mej.aut.ac.ir/article_6028_2c60e40b399dc55d8b755ec6b5d09f8a.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 Adjoint-Based Sensitivity Analysis of a Fixed Cross-Section Fin with Temperature-Dependent Conductivity Adjoint-Based Sensitivity Analysis of a Fixed Cross-Section Fin with Temperature-Dependent Conductivity 1287 1306 6039 10.22060/mej.2026.25461.7948 FA Behzad Baghapour Mechanical Engineering Department, Amirkabir University of Technology, Iran 0000-0003-0235-0605 Journal Article 2026 01 29 In this paper, the sensitivity of the efficiency of a fixed cross-sectional fin with temperature-dependent thermal conductivity to various parameters is investigated using the adjoint equation. A one-dimensional steady-state formulation is assumed for both the governing energy equation and the corresponding adjoint equation. The appropriate boundary condition for a convective fin tip is derived for the adjoint variable. The energy and adjoint equations are solved numerically using a finite-difference scheme. The results indicate that a slight increase in certain parameters, such as the cross-sectional area and the base thermal conductivity, leads to an improvement in fin efficiency. In contrast, increasing parameters such as the fluid heat transfer coefficient and the fin length results in a reduction in efficiency. The slope factor in the linear thermal conductivity model exhibits a non-monotonic effect: for negative values, increasing the slope reduces fin efficiency, whereas for positive values, it enhances the efficiency. Furthermore, the Biot number defined along the fin length shows a pronounced negative influence on fin efficiency as it increases. Its most significant impact occurs around a Biot number of 0.1, corresponding to the transition from a nearly uniform temperature distribution to a regime with a pronounced internal temperature gradient. In this paper, the sensitivity of the efficiency of a fixed cross-sectional fin with temperature-dependent thermal conductivity to various parameters is investigated using the adjoint equation. A one-dimensional steady-state formulation is assumed for both the governing energy equation and the corresponding adjoint equation. The appropriate boundary condition for a convective fin tip is derived for the adjoint variable. The energy and adjoint equations are solved numerically using a finite-difference scheme. The results indicate that a slight increase in certain parameters, such as the cross-sectional area and the base thermal conductivity, leads to an improvement in fin efficiency. In contrast, increasing parameters such as the fluid heat transfer coefficient and the fin length results in a reduction in efficiency. The slope factor in the linear thermal conductivity model exhibits a non-monotonic effect: for negative values, increasing the slope reduces fin efficiency, whereas for positive values, it enhances the efficiency. Furthermore, the Biot number defined along the fin length shows a pronounced negative influence on fin efficiency as it increases. Its most significant impact occurs around a Biot number of 0.1, corresponding to the transition from a nearly uniform temperature distribution to a regime with a pronounced internal temperature gradient. https://mej.aut.ac.ir/article_6039_eb2e9dffe58d635b7d72e99c8e61b5f2.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 Experimental Investigation of the Simultaneous Effect of Temperature and Aging on Mechanical Safety and Failure Behavior of Cylindrical Lithium-Ion Batteries Under Dynamic Impact Experimental Investigation of the Simultaneous Effect of Temperature and Aging on Mechanical Safety and Failure Behavior of Cylindrical Lithium-Ion Batteries Under Dynamic Impact 1307 1322 6040 10.22060/mej.2026.24433.7868 FA Mohammad Ali Ehteram Mechanical and Energy Engineering, Shahid Beheshti University Amir Nezhadsafar Faculty of Mechanical and Energy Engineering, Shahid Beheshti University Journal Article 2025 07 21 The present research aims to experimentally evaluate the safety behavior and failure mechanism of 18650 cylindrical lithium-ion battery cells under dynamic impact loading. To this end, a pneumatic impact testing apparatus was developed in accordance with the SAE J2464 standard to assess the simultaneous effects of initial temperature (25, 0, and -25 °C), state of charge (10% and 100%), and state of health (fresh and aged over 400 cycles). Experimental results derived from high-speed imaging and thermal data analysis indicated that at ambient temperature, impact with a critical velocity of 9.23 m/s on fully charged samples led to immediate separator rupture and extensive internal short circuit. Under these conditions, the cell voltage dropped to zero within 290 ms, and explosive thermal runaway occurred with a severe temperature rise reaching 662 °C. In contrast, the most significant finding of this study reveals a substantial enhancement in the cell's mechanical resistance at sub-zero temperatures; remarkably, at -25 °C, no penetration or exothermic reaction was recorded even at high impact velocities. Further analysis suggests that the partial solidification and increased viscosity of the electrolyte at low temperatures act as an internal support with quasi-solid behavior, thereby preventing local stress concentration and separator tearing. The present research aims to experimentally evaluate the safety behavior and failure mechanism of 18650 cylindrical lithium-ion battery cells under dynamic impact loading. To this end, a pneumatic impact testing apparatus was developed in accordance with the SAE J2464 standard to assess the simultaneous effects of initial temperature (25, 0, and -25 °C), state of charge (10% and 100%), and state of health (fresh and aged over 400 cycles). Experimental results derived from high-speed imaging and thermal data analysis indicated that at ambient temperature, impact with a critical velocity of 9.23 m/s on fully charged samples led to immediate separator rupture and extensive internal short circuit. Under these conditions, the cell voltage dropped to zero within 290 ms, and explosive thermal runaway occurred with a severe temperature rise reaching 662 °C. In contrast, the most significant finding of this study reveals a substantial enhancement in the cell's mechanical resistance at sub-zero temperatures; remarkably, at -25 °C, no penetration or exothermic reaction was recorded even at high impact velocities. Further analysis suggests that the partial solidification and increased viscosity of the electrolyte at low temperatures act as an internal support with quasi-solid behavior, thereby preventing local stress concentration and separator tearing. https://mej.aut.ac.ir/article_6040_4c9d1fbce4890fc2731b6a61262313b1.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 Dynamic Sensitivity Analysis of a Free-Free Aluminum Beam Under Transient Multi-Point Impact Excitation Using Experimental Modal Analysis, Numerical Simulation, and Analytical Modeling Dynamic Sensitivity Analysis of a Free-Free Aluminum Beam Under Transient Multi-Point Impact Excitation Using Experimental Modal Analysis, Numerical Simulation, and Analytical Modeling 1323 1358 6041 10.22060/mej.2026.24330.7861 FA Mehrdad Karimi Aerospace, Faculty of Postgraduate Studies, Shahid Sattari University, Tehran, Iran Masoud Javadi Assistant Professor, Faculty of Aerospace, Shahid Sattari University, Tehran, Iran 0000-0003-0280-3643 Journal Article 2025 07 08 Dynamic analysis plays a crucial role in predicting the vibrational behavior of structural systems. This study aims to accurately extract the modal characteristics of a free-free aluminum beam through a synergistic integration of experimental, analytical, and numerical approaches. In the experimental phase, calibrated modal hammer tests were conducted at six nodal positions, and the dynamic responses were captured using precision signal analyzers. The acquired data were processed in the specialized Star software using advanced signal processing algorithms to extract modal parameters with minimal systematic error. In the analytical phase, a mathematical model based on the governing differential equations of elastic structures—accounting for structural damping—was developed in MATLAB. Natural frequencies and mode shapes were identified using Peak Picking and Circle Fitting techniques. Additionally, finite element analysis was carried out in Abaqus, utilizing fine rectangular meshing and high-order hexahedral elements, which demonstrated excellent performance in simulating the system’s vibrational behavior under resonant conditions. Comparison of the results showed strong agreement in the frequency range of 0 to 1700 Hz, with deviations of less than 0.01% when considering the first mode as a rigid-body mode. This study highlights the importance of selecting appropriate excitation points to ensure accurate modal identification and confirms the proposed framework’s potential for analyzing more complex engineering structures. Dynamic analysis plays a crucial role in predicting the vibrational behavior of structural systems. This study aims to accurately extract the modal characteristics of a free-free aluminum beam through a synergistic integration of experimental, analytical, and numerical approaches. In the experimental phase, calibrated modal hammer tests were conducted at six nodal positions, and the dynamic responses were captured using precision signal analyzers. The acquired data were processed in the specialized Star software using advanced signal processing algorithms to extract modal parameters with minimal systematic error. In the analytical phase, a mathematical model based on the governing differential equations of elastic structures—accounting for structural damping—was developed in MATLAB. Natural frequencies and mode shapes were identified using Peak Picking and Circle Fitting techniques. Additionally, finite element analysis was carried out in Abaqus, utilizing fine rectangular meshing and high-order hexahedral elements, which demonstrated excellent performance in simulating the system’s vibrational behavior under resonant conditions. Comparison of the results showed strong agreement in the frequency range of 0 to 1700 Hz, with deviations of less than 0.01% when considering the first mode as a rigid-body mode. This study highlights the importance of selecting appropriate excitation points to ensure accurate modal identification and confirms the proposed framework’s potential for analyzing more complex engineering structures. https://mej.aut.ac.ir/article_6041_58ee2794cc87707943624dc8db2ff5a0.pdf

Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 57 10 2025 12 22 Optimizing the Distance-to-Diameter Ratio in a Marine Ducted Propeller Using CFD and Genetic Algorithm, with Comparison to the KP505 Reference Propeller Optimizing the Distance-to-Diameter Ratio in a Marine Ducted Propeller Using CFD and Genetic Algorithm, with Comparison to the KP505 Reference Propeller 1359 1386 6044 10.22060/mej.2026.25245.7933 FA MohammadHasan Ahmadi Sea-Based Energy research group, Babol Noshirvani University of Technology Rouzbeh Shafaghat Department of Mechanical Engineering, Babol Noshirvani University of Technology Mohsen Zamani Sea-Based Energy research group, Babol Noshirvani University of Technology Behrad Alizadeh Kharkeshi Faculty of Mechanical Engineering, Babol Noshirvani University of Technology 0000-0001-6522-6914 Journal Article 2025 12 09 Numerical simulations were performed using STAR-CCM+ software, and optimization was carried out with a genetic algorithm. The ducted propellers were innovatively designed based on the KP505 propeller. Simulations were conducted at six pitch ratios. To evaluate the results and perform optimization, thrust, torque, and efficiency coefficients were considered as objective functions. The results showed that the thrust coefficient exhibited a decreasing trend at low advance ratios, a non-linear behavior at medium advance ratios, and an increasing trend at high advance ratios as the pitch ratio increased. A comparative analysis revealed that before optimization, the ducted propeller's thrust coefficient was at best 15% higher than that of the KP505 propeller at an advance ratio of 0.8. The optimal pitch ratio obtained after optimization was 0.2641, corresponding to a maximum efficiency of 45.35% for the ducted propeller. Performance comparison between the optimized ducted propeller and the KP505 propeller showed that the optimized ducted propeller could increase thrust by up to 26% (at an advance ratio of 0.8) and improve efficiency by 7.84% at an advance ratio of 1.0. Flow analysis also indicated that increased velocity behind the propeller and an improved pressure pattern in the optimized ducted propeller contribute to higher thrust and reduced cavitation risk. Numerical simulations were performed using STAR-CCM+ software, and optimization was carried out with a genetic algorithm. The ducted propellers were innovatively designed based on the KP505 propeller. Simulations were conducted at six pitch ratios. To evaluate the results and perform optimization, thrust, torque, and efficiency coefficients were considered as objective functions. The results showed that the thrust coefficient exhibited a decreasing trend at low advance ratios, a non-linear behavior at medium advance ratios, and an increasing trend at high advance ratios as the pitch ratio increased. A comparative analysis revealed that before optimization, the ducted propeller's thrust coefficient was at best 15% higher than that of the KP505 propeller at an advance ratio of 0.8. The optimal pitch ratio obtained after optimization was 0.2641, corresponding to a maximum efficiency of 45.35% for the ducted propeller. Performance comparison between the optimized ducted propeller and the KP505 propeller showed that the optimized ducted propeller could increase thrust by up to 26% (at an advance ratio of 0.8) and improve efficiency by 7.84% at an advance ratio of 1.0. Flow analysis also indicated that increased velocity behind the propeller and an improved pressure pattern in the optimized ducted propeller contribute to higher thrust and reduced cavitation risk. https://mej.aut.ac.ir/article_6044_6b39183e7053a0106e4376f4e9c5c74d.pdf