Structural modification with additional degrees of freedom in large systems


Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Approval Date: 2009

Thesis Language: English

Student: Güvenç Canbaloğlu

Supervisor: HASAN NEVZAT ÖZGÜVEN

Abstract:

In the design and development stages of mechanical structures, it is important to predict the dynamic characteristics of modified structures. Since time and cost are critical in design and development stage, structural modification methods predicting the dynamic responses of modified structures from those of the original structure and modification properties are very important, especially for large systems. In this thesis structural modification methods are investigated and an effective structural modification method for modifications with additional degrees of freedom is adapted to structures with distributed modifications and the performance of the method is investigated. A software program is developed in order to apply the structural modification method with additional degrees of freedom. In the software, the dynamic response of the modified structure is predicted by using the modal analysis results of ANSYS for the original structure and dynamic stiffness matrix of the modifying structure. In order to validate the approach used and the program developed, the dynamic analysis results obtained for modified structures by ANSYS are compared with those obtained by using the software. In order to investigate the performance of the structural modification method in real applications, the method is applied to a scaled aircraft model, and the results are compared with experimental results. In order to demonstrate the importance of using the structural modification method with additional degrees of freedom for distributed modification, lumped and distributed models are used for a distributed modification and results are compared. It is concluded in this study that using structural modification methods with additional degrees of freedom for a distributed modification increases the accuracy of the results, and it is observed that the method adapted is efficient for local modifications.