| This work focuses on the development of Finite element Based methodologies for mass, stiffness, and damping modifications of practical airframe structures. This preliminary design type of engineering methodology of analysis and optimization allows rapid and accurate engineering prediction and placement of responses while guiding the structural designer-dynamicist in determining the location, type and quantity of structural modifications when the airframe is sustaining severe forced vibrations. For new airframe structures, minimum weight structures can be designed with proper placement of airframe natural frequencies and subject to constraints on forced response displacements and dynamic stresses by systematic nonlinear programming-based modifications of mass, stiffness and damping of the structure. In the case of an existing design, when significant mass and stiffness modifications cannot be affected, the designer can resort to viscoelastic type energy-dissipation damping treatments and determine their efficacy. Furthermore, should the change of excitation frequency bring about modal resonance, damping treatments can control response due to resonating modes, without resorting to stiffness or mass changes.;This work focuses on the development of necessary computational tools for airframe structural optimization and implements the sensitivity analysis procedures for the various design constraints encountered in vibration and fatigue design of structures. The application of the optimization procedure is demonstrated using both an elastic-line as well as a built-up finite element model of the Bell AH-1G helicopter airframe structure. |
