טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGov Favel
SubjectDynamic Response to Gust Excitation of Air Vehicles
with Very Flexible Wings
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Mordechay Karpel


Abstract


The tools necessary for the aeroelastic design of very flexible aircraft with geometric nonlinearities are limited. The present dissertation describes a novel method that uses modal formulation to construct three-dimensional nonlinear structural dynamic models, for effective studies of very flexible aircraft structures under impulsive loads, such as abrupt gusts, that cause large displacements. The presented modal formulation links linear segments with nonlinear coupling terms. The model nonlinearity is captured by dividing the wing structure into several spanwise segments, each having large rigid-body displacements but may be assumed to have linear elastic deformations. The required number of segmental modes is reduced significantly by using fictitious masses at the segment interfaces. A structural dynamic model based on co-rotational linear frameworks is also developed, matching the modal formulation characteristics. The framework follows the segmental geometry of the structure using Euler angles defined as Cardan angles sequence formulation. The simulation stability is improved, introducing an energy conservation enforcement approach. The modified strip theory is used for the aerodynamics of the simulation, including extension of the thin airfoil theory, finite-wing effect based on Vortex Lattice Method (VLM), unsteady aerodynamic lag function and a static stall model. The modal formulation was validated and demonstrated, showing very good performance as a candidate for the dynamic response to gust excitation of air vehicles with very flexible wings.