ETD

• dynamic analysis
• gear
• torsional vibration

This thesis work is part of the development project for the NGTR (Next Generation Test Rig), a mechanical power recirculation facility intended for the advanced testing of aeronautical transmissions. The activity performed constitutes an integral part of the Preliminary Design Review (PDR), a critical phase of the engineering process aimed at validating preliminary design choices through computational analysis and functional checks before the final design freeze.
In the aerospace sector, mechanical transmissions are subject to increasingly stringent requirements regarding efficiency, power density, and reliability. To meet these needs, the design of a new test rig became necessary, capable of exceeding the operational limits of the pre-existing RENK facility by extending the operating range up to speeds of 20,000 rpm and torques of 1,200 Nm. The main objective of this work is the dynamic and static validation of the NGTR kinematic chain. Given the complex system architecture, characterized by high rotation speeds and multiple gear meshes, torsional vibration analysis assumes a pivotal role in ensuring structural integrity and testing quality.
The work begins with an analysis of the state of the art and a system description, presenting an overview of test rig types, with particular reference to back-to-back mechanical recirculation systems, followed by a detailed description of the NGTR architecture and its operating configurations (R=0 and R=-1). Subsequently, the theoretical approach to dynamic modeling and the creation of a lumped parameter model are illustrated. This methodology was chosen for its effectiveness in representing the torsional dynamics of complex systems by distinguishing between inertial and elastic elements. The model allows for the calculation of natural frequencies and mode shapes, which are essential for identifying potential critical issues within the operating range, and the results obtained were validated through comparison with a parallel FEM model.
The paper proceeds with the characterization of the loading system, analyzing the operation of the hydraulic servo-actuator responsible for torque application via the translation of double helical gears. The analysis focuses on the relationship between axial displacement and torque, taking into account backlash recovery and chain stiffness, to verify compatibility with the actuator stroke. Finally, to support the preliminary sizing, bearing life checks in critical zones (Test and Slave) and dissipated power calculations for the sizing of the lubrication and cooling system (HTO) are presented. The results of these analyses provide the necessary data to confirm the feasibility of the proposed architecture and guide the subsequent detailed design phases.