Seher Eken

Computational analysis of orbital debris impact on spacecraft shields

In this study we present the results of numerical simulation of orbital debris impact on spacecraft shields. The impact response of the stuffed Whipple shield is computed using forward finite difference method. Fragment simulating projectile hitting the crimp composite fabric at an angle 90° is analyzed. The yarn segments between hinged joints at crossovers are modeled using discrete mass-spring-damper in pin-joint systems consisting of planar square lattices. After a certain time of impact; displacement of the fabric, change in the velocities and the failure in the material is computed and depicted graphically. The effect of crimp and areal density on the ballistic performance of the fabric of the stuffed Whipple shield is examined and discussed.

Active Vibration Control Applications for Adaptive Aircraft Wings Modelled as Thin-Walled Composite Beams

In this study the closed-loop vibrational behavior of aircraft wing is investigated. The wing is modeled as an adaptive thin-walled composite beam with a kite type cross section. Several non-classical effects inherently exist in this beam model resulting from thin-walled beam theory such as material anisotropy, transverse shear deformation and warping restraint. In this case, anti-symmetric lay-up configuration i.e. Circumferentially Uniform Stiffness (CUS) is employed to form transverse-lateral bending and transverse shear coupled motion from amongst numerous other elastic couplings due to directionality property of thin-walled composite beams. Adaptive materials chosen as piezoelectric ceramics are used to achieve active vibration control and inserted into structures as layers. They are located symmetrically in host structure and spread over the entire beam span. As a result, a boundary moment is induced at the beam tip and in this case, the control is achieved via the boundary moment feedback control, yielding an adaptive change in the dynamical characteristics of the beam. Three different control applications are implemented namely proportional and velocity feedback and optimal control and the effect of slenderness ratio on the fundamental frequencies are investigated, enhanced and discussed.

Optimal Control Procedure Application for Dynamic Response of Adaptive Aircraft Wings Modeled as Thin-Walled Composite Beams

In this study we investigated the dynamical behavior of aircraft wings and using piezoelectric actuation we implemented active vibration control. The aircraft wing is modeled as a thin-walled composite beam having a cross section of diamond shaped. The dynamic response of the beam under varying proportional and velocity feedback gain parameters is obtained and shown to be enhanced with optimal control procedure, minimizing the control effort and response.

Effect of the Transverse Shear Deformation on the Free Vibration of Rotating Blades Modeled as Thin-Walled Composite Beams

In this paper, vibration analysis of a blade modeled as an anisotropic composite thin-walled beam is carried out. The analytical formulation of the beam is derived for the flapwise bending, chordwise bending and transverse shear deformations. The equations of motion are solved by applying the extended Galerkin method (EGM) for anti-symmetric lay-up configuration that is also referred as Circumferentially Uniform Stiffness (CUS). Consequently, the natural frequencies are validated by making comparisons with the results in literature and it is observed that there is a good agreement between the results. Combined effects of transverse shear, fiber orientation, and rotational speed on the natural frequencies are further investigated.

Aerolelastic Analysis of a Thin-Walled Composite Aircraft Wing With an External Store Subjected to a Follower Force

This study reports dynamic aeroelastic analyses of an aircraft wing with an attached mass subjected a lateral follower force in an incompressible flow. A swept thin-walled composite beam with a biconvex cross-section is used as the structural model that incorporates a number of non-classical effects such as material anisotropy, transverse shear deformation and warping restraint. A symmetric lay-up configuration i.e. circumferentially asymmetric stiffness (CAS) is further adapted to this model to generate the coupled motion of flapwise bending-torsion-transverse shear. For this beam model, the unsteady aerodynamic loads are expressed using Wagners function in the time-domain as well as using Theodorsen function in the frequency-domain. The flutter speeds are evaluated for several ply angles and the effects of follower force, transverse shear, fiber-orientation and sweep angle on the aeroelastic instabilities are further discussed.Copyright

Dynamic and Aeroelastic Analyses of a Wind Turbine Blade Modeled as a Thin-Walled Composite Beam

In this paper, dynamic and aeroelastic analysis of a wind turbine blade modeled as an anisotropic composite thin-walled box beam is carried out. The analytical formulation of the beam is derived for the flapwise bending, chordwise bending and transverse shear deformations. The derivation of both strain and kinetic energy expressions are made and the equations of motion are obtained by applying the Hamilton’s principle. The equations of motion are solved by applying the extended Galerkin method (EGM) for anti-symmetric lay-up configuration that is also referred as Circumferentially Uniform Stiffness (CUS). As a result various coupled vibration modes are exhibited. This type of beam features two sets of independent couplings: i) extension-torsion coupling, ii) flapwise/chordwise bending-flapwise/chorwise transverse shear coupling. For both cases, the natural frequencies are validated by making comparisons with the results in literature and effects of coupling, transverse shear, ply-angle orientation, and rotational speed on the natural frequencies are examined and the mode shapes of the rotating thin-walled composite beams are further obtained. Blade element momentum theory (BEMT) is utilized to model the wind turbine blade aerodynamics. After combining the structural and the aerodynamic models, the aeroelastic analysis are performed and flutter boundaries are obtained.Copyright