Original Article
Structure/mechanics of solids/dynamics of solids/vibrations/aeroelasticity/...
Aliasghar Naderi; Hadi Teymouri; Mehdi Pourseifi
Volume 4, Issue 2 , October 2025
Abstract
The security and survivability of defensive structures against extreme dynamic loads such as blast waves and impacts is a fundamental priority in modern design. Sandwich panels, due to their exceptional strength-to-weight ratio and high energy absorption capacity, are among the primary candidate materials ...
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The security and survivability of defensive structures against extreme dynamic loads such as blast waves and impacts is a fundamental priority in modern design. Sandwich panels, due to their exceptional strength-to-weight ratio and high energy absorption capacity, are among the primary candidate materials in this field. This research investigates and compares the influence of two widely used core types the porous core and the viscoelastic core on the natural frequencies of a sandwich beam structure. The main objective of this study is to assess the potential of these cores to enhance the strength and safety of defensive structures through the analysis of their vibrational behavior. The present research employs analytical modeling to perform the natural frequency analysis. Using three-layer sandwich beam theory and applying Hamilton's principle, the governing equations of the system are derived. The resulting equations are complex partial differential equations (PDEs). To solve these equilibrium equations, the semi-analytical Navier method is utilized in the spatial domain. To validate the accuracy of the obtained results, comparisons are made with existing solutions for specific cases. Finally, the influence of various parameters such as carbon nanotube volume fraction, porosity coefficient, porosity distribution pattern, geometric and dimensional ratios on the natural frequencies of the sandwich structure is examined. This investigation covers structures with both porous and viscoelastic cores and nanocomposite face sheets. A key finding of this research is that, in most instances, the viscoelastic core exhibits higher natural frequencies and greater strength compared to the porous core.
Original Article
Seyed Ali Salari; Fathollah Ommi
Volume 4, Issue 2 , October 2025
Abstract
The performance of naturally aspirated aircraft engines declines significantly with increasing altitude due to reduced air pressure and density, affecting power, torque, in-cylinder pressure, and combustion temperature. This study presents a comparative analysis of the carbureted (Rotax 912 ULS) and ...
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The performance of naturally aspirated aircraft engines declines significantly with increasing altitude due to reduced air pressure and density, affecting power, torque, in-cylinder pressure, and combustion temperature. This study presents a comparative analysis of the carbureted (Rotax 912 ULS) and fuel-injected (Rotax 912iS) versions of the Rotax 912 engine using GT-SUITE simulations across altitudes up to 9,150 meters. Results indicate that the carbureted engine suffers an 80% reduction in power at high altitudes due to its fixed fuel-air mixture, while the fuel-injected engine maintains more stable performance by dynamically adjusting fuel delivery. The EFI system also preserves higher in-cylinder pressure and combustion stability under oxygen-scarce conditions. Although EFI mitigates performance loss more effectively than carburetion, both configurations exhibit significant degradation at high altitudes, highlighting the inherent limitations of naturally aspirated engines. These findings underscore the importance of advanced altitude compensation methods—such as turbocharging or optimized EFI mapping—for enhancing reliability and efficiency in high-altitude aviation operations.
Original Article
Defense mechanics/navigation/control/...
Aliasghar Moazzen; Ramazan Havangi
Volume 4, Issue 2 , October 2025
Abstract
Accurate estimation of attitude and heading in UAVs is one of the key challenges in autonomous navigation systems, playing a vital role in the control and guidance of these vehicles. In this paper, a quaternion-based particle filter with a specific sampling method and an extended Kalman filter (EKF) ...
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Accurate estimation of attitude and heading in UAVs is one of the key challenges in autonomous navigation systems, playing a vital role in the control and guidance of these vehicles. In this paper, a quaternion-based particle filter with a specific sampling method and an extended Kalman filter (EKF) are employed for UAV attitude estimation. By integrating data from inertial sensors (including gyroscopes, accelerometers, and magnetometers) and applying filtering techniques, the proposed methods significantly enhance the accuracy of roll, pitch, and yaw angle estimation. The innovation of this study lies in the comprehensive comparison of the particle filter and EKF performance across two scenarios: simulated data and real-world data collected from a specific attitude and heading reference system (AHRS). The results demonstrate that the particle filter achieves remarkable improvements of over 99.99% in simulated data and over 88.48% in real-world data for roll and yaw angle estimation. Additionally, the analysis of variance and standard deviation of errors confirms that the particle filter outperforms in reducing error dispersion, with the error variance for yaw angle being approximately 100 times lower than that of the EKF. On the other hand, the EKF shows slightly better performance in pitch angle estimation. These findings suggest that a combination of these two filters can serve as an effective solution for precise navigation systems in UAVs. The resampling method implemented in the particle filter also significantly enhances the accuracy of roll and yaw angle estimation.
Original Article
Jalil Fereidooni; mahmoud adami; abbas mohammadian
Volume 4, Issue 2 , October 2025
Abstract
This study focuses on the thermal analysis of the cooling system for a specific type of enclosed motor pump. According to the IEC standard, the winding insulation has a specific temperature tolerance; exceeding this limit can damage the insulation and impair motor function. A crucial component of the ...
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This study focuses on the thermal analysis of the cooling system for a specific type of enclosed motor pump. According to the IEC standard, the winding insulation has a specific temperature tolerance; exceeding this limit can damage the insulation and impair motor function. A crucial component of the motor's cooling system is the waterjacket, which serves two purposes: cooling the motor housing and cooling the flow passing through the motor interior. Reducing the motor housing temperature ultimately lowers the winding temperature. To simplify calculations, a thermal analysis of the enclosed motor housing was performed, considering temperature and thermal boundary conditions. The effect of the waterjacket at various flow rates 0.1, 0.3, and 0.5 kg/s and the coil flow at flow rates of 0.05, 0.1, and 0.15 kg/s, along with different diameters, were investigated to determine temperature and pressure drop. The heat generated in different motor components was applied as a heat flux on the inner surface of the motor housing. The results show that increasing the waterjacket flow rate consistently reduces the housing temperature and the coil outlet fluid temperature. Conversely, increasing the coil flow rate increases the coil outlet temperature. Using a water-antifreeze mixture compared to pure water slightly increases the minimum housing temperature. The minimum housing temperature consistently occurs at a coil flow rate of 0.05 kg/s and a waterjacket flow rate of 0.5 kg/s. The pressure drop always increases with increasing waterjaket flow rate
