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.
