Active vibration control of helicopter fuselage shell structures by experimental analysis methods

This thesis study includes scientific approaches towards active vibration control with piezoelectric actuator placement determined by applying a new experimental modal analysis method to shell structures. Numerical and experimental applications are carried out in order to provide high vibration control performance. In the application of the methodology to shell structures, validation is performed on the UH1H helicopter cargo doors (main and auxiliary). In order to obtain the dynamic characteristics of the helicopter cargo doors, a new experimental modal analysis method, which has not been presented before in the literature, and which is applied for the first time using inertial modal shaker, is presented within the scope of this thesis. The superiority of the roving shaker method over traditional experimental modal analysis methods is investigated through modal analysis validation methods, especially due to the unstable behavior of shell structures under load. The roving shaker method is proven to be more successful in determining modal parameters in a nonlinear modal matrix. After obtaining the experimental dynamic behaviors of the structures, the mode combination method is used to place the optimal actuator/sensor pairs on the helicopter cargo doors according to the experimental/numerical modal correlation values. This method is a new method applied with finite element package program and it is a fast and practical solution compared to similar studies. To investigate its performance, this method is tested in two different works in the literature and the results are compared. With the Adaptive Response Frequency Compensator developed for experimental active vibration control of helicopter cargo doors within the scope of the Positive Position Feedback (PPF) controller design methodology, the dominant frequencies of the vibrations, generated under the excitation which is obtained from the UH1H helicopter flight data, are suppressed by detecting with spectrum analysis on the system. According to the experimental control results, an average of 37% vibration reduction for the auxiliary cargo door and 30% for the main cargo door is achieved in the laboratory environment. In addition, in order to use in numerical active vibration control studies, the state space models are obtained by using the first three, first five and first ten modes of the auxiliary cargo door and the modes with high experimental/numerical modal correlation percentage for the main cargo door. Positive Position Feedback (PPF) controller design is used in the control of all numerical models, and the most effective vibration reduction is achieved by optimizing the scalar gain and damping ratio coefficients in the compensators.