Ohseop Song

On the static aeroelastic tailoring of composite aircraft swept wings modelled as thin-walled beam structures

Abstract The sub-critical static aeroelastic response and the divergence instability of swept-forward aircraft wing structures constructed of anisotropic composite materials is analyzed. The new element distinguishing this study from the previous, existing ones is the structural model in which framework this problem is treated. In this sense, in contrast to the classical plate-beam or solid-beam models traditionally used in the study of these problems, the thin-walled anisotropic composite beam model is adopted here. The model used incorporates a number of non-classical effects. Among these are the anisotropy of the material of the constituent layers, the transverse shear deformation and the primary and secondary warping effects. Within the framework of this study, in addition to an assessment of the influence of the previously mentioned effects, the aeroelastic tailoring technique is applied and as a result, a series of conclusions concerning the enhancement of the static aeroelastic response characteristics of aeronautical wing structures made of advanced composite materials are outlined.

Behavior of Thin-Walled Beams Made of Advanced Composite Materials and Incorporating Non-Classical Effects

Several results concerning the refined theory of thin-walled beams of arbitrary closed cross-section incorporating non-classical effects are presented. These effects are related both with the exotic properties characterizing the advanced composite material structures and the non-uniform torsional model. A special case of the general equations is used to study several problems of cantilevered thin-walled beams and to assess the influence of the incorporated effects. The results presented in this paper could be useful towards a more rational design of aeronautical or aerospace constructions, as well as of helicopter or tilt rotor blades constructed of advanced composite materials.

Adaptive vibrational behavior of cantilevered structures modeled as composite thin-walled beams☆

Abstract An integrated distributed actuator design methodology based upon the converse piezoelectric effect and aimed at actively controlling the vertical and lateral eigenvibration characteristics of cantilevered thin-walled beams is presented. The system of piezoelectric actuators bonded or embedded into the structure produces a localized strain field when an electric field is injected and, as a result, it yields an adaptive change of dynamic response characteristics. The numerical results which concern the eigenvibration properties suggest that this technology could play a major role in the control of dynamic instability and flutter of aircraft wings and helicopter blades, in particular, and in the improvement of the dynamic response behavior of cantilevered structures, in general.

Application of adaptive technology to static aeroelastic control of wing structures

The static aeroelastic behavior of adaptive swept-forward wing structures modeled as thin-walled beams and incorporating piezoelectric effects is investigated. Based on the converse piezoelectric effect, the system of piezoelectric layers, embedded or bonded to the wing, yields control of both divergence instability and, in the subcritical speed range, of aeroelastic lift distribution.

Thermoelastic Modeling and Vibration of Functionally Graded Thin-Walled Rotating Blades

Thermoelastic modeling and vibration of turbomachinery thin-walled rotating blades made of functionally graded ceramic-metal based materials are studied. In this context, the case of pretwisted and tapered thin-walled beams, rotating with a constant angular velocity and exposed to a steady temperature field of a prescribed gradient through the blade wall thickness, is considered. The study is achieved by varying the volume fraction of the ceramic and metallic constituents with the help of a simple power law distribution and by accounting for the temperature-dependent material properties. The governing dynamic equations that are established are expressed in terms of one-dimensional displacement measures. Because of their general character, static and dynamic problems involving rotating blades operating in the conditions of a high-temperature environment can be solved. The numerical results highlight the effects of the volume fraction, temperature gradient, taper ratio, and pretwist on the bending-bending coupled/uncoupled free-vibration characteristics, and pertinent conclusions are outlined.

Vibration of Pretwisted Adaptive Rotating Blades Modeled as Anisotropic Thin-Walled Beams

Problems related to mathematical modeling and dynamic behavior of pretwisted adaptive rotating blades are considered. The blade is modeled as a thin-wall, single-cell beam encompassing nonclassical effects such as anisotropy, transverse shear, and warping restraint. The adaptive capabilities provided by a system of piezoactuators bonded or embedded into the structure are also implemented in the system. Based on the converse piezoelectric effect and of out-of-phase activation, boundary control moments are piezoelectrically induced at the beam tip. Two feedback control laws relating the induced bending moments with the appropriately selected kinematical response quantities are used, and the beneficial effects of the implementation of the active feedback control, considered in conjunction with that of the structural tailoring on the eigenvibration characteristics, are highlighted.

Bending vibration of cantilevered thin‐walled beams subjected to time‐dependent external excitations

The bending vibration of cantilevered thin‐walled beams of arbitrary closed cross section exposed to time‐dependent external excitations is investigated. The beam model used in this study incorporates a number of nonclassical effects, namely, transverse shear, secondary warping, anisotropy of constituent materials, and heterogeneity of the construction. An exact methodology based on the Laplace transform technique aiming at determining the frequency‐response characteristics is used, and numerical illustrations emphasizing the effects of a number of geometrical and mechanical parameters on the frequency response behavior are displayed.

Adaptive Response Control of Cantilevered Thin-Walled Beams Carrying Heavy Concentrated Masses

An integrated distributed actuator design is presented, based on the converse piezoelectric effect and aimed at actively controlling the excessive deflections and large bending mo ments at the root section of a cantilevered thin-walled beam carrying a system of heavy concentrated masses. The numerical illustrations reveal the great capabilities of the adaptive technology to alleviate, without weight penalties, these undesirable effects.

Dynamics of pretwisted rotating thin-walled beams operating in a temperature environment

The effects of a steady temperature gradient on eigenvibration characteristics of a rotating pretwisted thin-walled beam is addressed. The analysis is carried out in the framework of a refined theory of thin-walled anisotropic composite beams encompassing a number of nonclassical features. The displayed results reveal that the deterioration of material properties induced by the temperature rise yields a decay of eigenfrequencies and modification of natural modes, a fact that is likely to have detrimental repercussions upon their dynamic response and flutter instability characteristics. Moreover, as it was highlighted, the proper use of the tailoring technique can overcome the deleterious effect associated with the thermal degradation of material properties of blade structures.The effects of a steady temperature gradient on eigenvibration characteristics of a rotating pretwisted thin-walled beam is addressed. The analysis is carried out in the framework of a refined theory of thin-walled anisotropic composite beams encompassing a number of nonclassical features. The displayed results reveal that the deterioration of material properties induced by the temperature rise yields a decay of eigenfrequencies and modification of natural modes, a fact that is likely to have detrimental repercussions upon their dynamic response and flutter instability characteristics. Moreover, as it was highlighted, the proper use of the tailoring technique can overcome the deleterious effect associated with the thermal degradation of material properties of blade structures.

Bending vibrations of adaptive cantilevers with external stores

Abstract The vibrational behavior of cantilevers carrying externally mounted stores and featuring adaptive capabilities is investigated. The structure is modeled as a thin-walled beam, and the adaptive capabilities are provided by a system of piezoactuators bonded or embedded into the structure. Based on the converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied electric field and, as a result, an adaptive change in the dynamic response characteristics is achieved. Implementation of a control law relating the applied electrical field to one of the mechanical quantities characterizing the motion of the beam, enables one to obtain the free vibration characteristics as a function of the applied voltage (or in other terms, of the feedback gain). The obtained numerical results suggest that the application of this technology can play a major role in the enhancement of the dynamic response and the control of free vibration characteristics of this type of structures.