Iranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-476112220260701Stress estimation in fifth wheel coupling system using finite element model validated by experimental modal test73580710.22064/tava.2026.2066958.1271ENRezaEbrahimiMechanical Engineering, Faculty of Engineering, Yasouj University, Yasouj, Iran0000-0002-0118-437XAlirezaShafieiResearch and Development Department, Espahan Koosha Company, Isfahan 81611-98371, IranSeyed MasoudFatemiResearch and Development Department, Espahan Koosha Company, Isfahan 81611-98371, IranJournal Article20250803In the heavy vehicle transport industry, the fifth wheel coupling system is used as important component for connecting the semi-trailer with the tractor. Misfunction, corrosion or fracture of the fifth wheel can affect the stability and consequently the safety of the heavy vehicles. During operation, the fifth wheel experiences different loading conditions. So, a reliable model which represents stresses due to acting forces on the fifth wheel coupling system plays a significant role. For this purpose, first, controlled vibration experiments are conducted on a JOST’s fifth wheel coupling system and modal parameters of the system is obtained. Moreover, a finite element model (FEM) is constructed in ABAQUS software and successfully validated by the results of the experimental modal analysis (EMA). Then, the validated FEM is used to achieve the stress distribution in the system for accelerating and breaking conditions. Also, it is found that stresses in the JOST’s fifth wheel coupling system remain below the mechanical strength limit of the material.https://tava.isav.ir/article_735807_9340113410887504dbba05a37f589592.pdfIranian Society of Acoustics and Vibration and AvecinaJournal of Theoretical and Applied Vibration and Acoustics2423-476112220260701Vibration Analysis of Pre-Twisted Blades with Symmetric and Asymmetric Airfoils Using the Ritz Method73624410.22064/tava.2026.2074533.1277ENSaeedShokrollahiMalek E Ashtar University of TechnologyAlirezaNorouziMalek Ashtar university of Technology, Aerospace Engineering DepartmentSalmanShafaghatMalek Ashtar university of Technology, Aerospace Engineering DepartmentJournal Article20251023This study performs a theoretical free vibration analysis of pre-twisted rectangular and airfoil-section blades using a global Ritz-based continuous classical beam–shaft reduced-order model (ROM), demonstrating its applicability in gas turbine design workflows. The framework incorporates pre-twist effects and static imbalance (CG–EA offset), which is horizontal in symmetric airfoils and also vertical in cambered or asymmetric airfoil sections. Validation is performed against finite element method (FEM) analyses using MSC Nastran and results from an advanced finite difference method (FDM) reported in the literature. The results show strong agreement with other works while maintaining computational efficiency. The proposed framework provides a basis or ROM-based tools capable of performing computationally efficient aeroelastic analyses of continuous blade models, blade rows, and integrated gas turbines. Torsional, flapwise, and chordwise bending modes—including their couplings induced by pre-twist and static imbalances—are examined, and natural frequency trends for different imbalance configurations are presented as functions of pre-twist anglehttps://tava.isav.ir/article_736244_40f026b93649be43bce0f7794c268b96.pdf