Yavuz Yaman

The harmonic response of rectangular sandwich plates with multiple stiffening: A flexural wave analysis

Abstract An exact analytical method is presented for the vibration response of a finite, three-layered, rectangular sandwich plate with a visco-elastic core, subjected to a harmonic line force which varies sinusoidally across the plate. Uniform parallel stiffeners (which may all be different) span the plate between one pair of simply supported edges. The other pair of edges may have any degree or type of uniform constraint. In the analysis the known flexural wave motion in an infinite parallel unstiffened plate subjected to a single harmonic line force or moment is utilized. A matrix equation is set up for the reactions imposed on the plate by the stiffeners and for the amplitudes of wave motion reflected from the ends of a finite plate. The sandwich core may have large or small amounts of damping. Results computed from the theory are presented and are shown to compare well with experimental data. The influence of the stiffener and core properties on the plate harmonic response is readily determined.

THE RESPONSE OF INFINITE PERIODIC BEAMS TO POINT HARMONIC FORCES : A FLEXURAL WAVE ANALYSIS

Abstract An exact analysis is presented of the vibration response of an infinite beam on periodic supports, subjected to a transverse harmonic point force. The supports must all be the same and can be simply supported or be generally linear with elastic, inertial and dissipative properties. The total response is found as the sum of the flexural wave fields generated by the applied force and the infinite number of support reaction forces and moments. The concept of phased arrays of forces and moments is used to sum the support-generated wave fields. This utilizes the propagation constants of free-wave motion in the periodic beam. Equations for either four, six or eight of the unknown complex reactions (depending on the nature of the supports) are set up and solved numerically. This finite number is sufficient to permit the calculation of the beam displacement at any point and of all the other reactions. Some computed values of the beam direct receptance are presented to demonstrate its variation with forcing frequency, the effect of the location of the excitation force and the effect of changing the elastic properties of the supports.

The harmonic response of uniform beams on multiple linear supports: A flexural wave analysis

Abstract A wave approach is developed for the exact analysis of the harmonic response of uniform finite beams on multiple supports. The beam may be excited by single or multi-point harmonic forces or moments; its supports may have general linear characteristics which may include displacement-rotation coupling. Use is made of the harmonic response function for an infinite beam subjected to a single-point harmonic force or moment. The unknowns of the finite beam problem are the support reaction forces/moments and the magnitudes of four waves reflected from the ends of the beam. Equations are presented for the response of a single-bay beam with various support conditions and subjected to single-point harmonic excitation. The same equations, but with the simple addition of further straightforward terms on the right-hand side, are used for multi-point excitation. The effects of damping are easily incorporated. Equations for multi-supported beams are also presented together with illustrative computed frequency-response curves. Natural frequencies have been calculated by finding resonance frequencies of very lightly damped beams. These compare impeccably with the results of other investigators.

Fractional controller design for suppressing smart beam vibrations

Purpose – The purpose of this paper is to detail the design of a fractional controller which was developed for the suppression of the flexural vibrations of the first mode of a smart beam.Design/methodology/approach – During the design of the fractional controller, in addition to the classical control parameters such as the controller gain and the bandwidth; the order of the derivative effect was also included as another design parameter. The controller was then designed by considering the closed loop frequency responses of different fractional orders of Continued Fraction Expansion (CFE) method.Findings – The first, second, third and fourth order approximations of CFE method were studied for the performance analysis of the controller. It was determined that the increase in the order resulted in better vibration level suppression at the resonance. The robustness analysis of the developed controllers was also conducted.Practical implications – The experimentally obtained free and forced vibration results i...

Active Vibration Control of a Smart Fin

This paper summarizes the design and wind tunnel experimental verifications of robust H∞ controllers for active vibration suppression of a dynamically scaled F-18 vertical smart fin. The smart fin consists of a cantilevered aluminium plate structure with surface bonded piezoelectric (Lead-Zirconate-Titanete, PZT) patches, Integrated Circuit Piezoelectric (ICP) type accelerometers and strain gauges. For H∞ controller design, the transfer function of the fin was first estimated outside the wind tunnel. Then, experiments were carried out to determine the aeroelastic characteristics of the smart fin at free flow and vortical (i.e. buffet) flow conditions. Variable air speeds and Angle of Orientations (AoO) were considered in both flow conditions. Significant shifts in vibration frequencies and the damping ratios were observed at the various values of airspeed and AoO. Taking into account these variations, the H∞ controllers were designed to suppress the fin’s buffeting response at the first and second bending and first torsional modes. A second set of wind tunnel experiments was conducted to verify the performance of the designed H∞ controllers at various flow scenarios. Successful vibration suppression levels were obtained within the desired frequency intervals.

A Hybrid Morphing Trailing Edge Designed for Camber Change of the Control Surface

In this study, the design and analyses of a novel morphing trailing edge control surface is presented. The developed control surface is intended to be utilized on an Unmanned Aerial Vehicle (UAV). The morphing features of the control surface was obtained by using different compliant materials, which are able to undergo large in-plane deformations. The design also includes the utilization of the composite materials together with conventional aluminum material hence the design is called a hybrid one. The actuation was applied by using various number of small servo actuators located inside the control surface at different locations. During the design, CATIA V5-6R2012 package program was utilized and the structural analyses were conducted with Finite Element Method by using ANSYS® WorkbenchTM v14.0 package program. First, the design and analyses were done for in-vacuo condition and the relevant aerodynamic loading was later considered. The required aerodynamic loads, which were representing the flight conditions of the UAV, were calculated by Computational Fluid Dynamics analyses. The aerodynamic mesh used was generated by Pointwise® V17.2 R2 package program. The SU2 (Stanford University Unstructured) V3.2.1 open source software was also used in the study as the flow solver. The UAV had a baseline wing with NACA6510 airfoil. The required camber and de-camber characteristics were tried to be achieved for various NACA airfoil targets. By conducting a non-linear Finite Element Analysis it was shown that the control surface can successfully undergo both camber and de-camber morphing, both in-vacuo condition and under aerodynamic loading.

Active Control of Smart Fin Model for Aircraft Buffeting Load Alleviation Applications

Following the program to test a hybrid actuation system for high-agility aircraft buffeting load alleviation on the full-scale F/A-18 vertical fin structure, an investigation has been performed to understand the aerodynamic effects of high-speed vortical flows on the dynamic characteristics of vertical fin structures. Extensive wind-tunnel tests have been conducted on a scaled model fin integrated with piezoelectric actuators and accelerometers to measure the aft-tip vibration responses under various freestream and vortical airflow conditions. Test results demonstrated that the airflow induced considerable damping to the fin structure, which generally increased with airflow speed as well as the vertical fin angle of attack relative to the airflow direction. Moreover, it was observed that at the angle of attack of 10 deg, the high-speed airflow introduced large deflection to the smart fin structure and caused significant frequency shift to the vibration modes due to nonlinear geometrical coupling of bending and torsional modes. These aerodynamic effects may adversely affect the performance and robustness of the closed-loop control laws developed based on vertical fin dynamic model identified without considering the varying aerodynamic effects. To explore this problem, the structured singular values synthesis technique was adopted to develop robust control law using smart fin model identified without aerodynamic excitations, and the aerodynamic effects on the fin structure were assumed as smart fin parametric and dynamic uncertainties. The effectiveness and robust performance of the control law was demonstrated through extensive closed-loop wind-tunnel tests using various airflow conditions. This provided a verified control law design strategy for future flight tests of the full-scale aircraft buffeting load alleviation system.

Structural Health Monitoring System of Composite Beams with Surface Bonded and Embedded Fibre Bragg Grating Sensors

Fibre Bragg Grating (FBG) sensors are frequently being used for Structural Health Monitoring (SHM) of aerospace structures. One of the most important advantages of using FBG sensors is that it is possible to embed them into composites. In this paper, manufacturing methods of composite specimens with embedded FBG sensors are given. To avoid stress concentrations at ingress/egress regions of fibre optic wires, PTFE (Teflon) tubes were used during manufacturing. Moreover, FBG connectors melt at high curing temperatures. Therefore, those connectors were cut and after manufacturing, these connectors were spliced back to the FBG sensors. Embedded FBG’s were then checked and the correct wavelength data were taken. All the sensors were observed as intact and ready for bending tests. Procedure for bending tests is also explained including applied loads, boundary conditions, test setup and the peripheral equipment. Results of bending tests show that the system is an appropriate one for SHM purposes.

Structural and aerodynamic analyses of a hybrid trailing edge control surface of a fully morphing wing

In this article, the design and analysis of a hybrid trailing edge control surface of an unmanned aerial vehicle are presented. The structural design was performed to increase and decrease the camber of the control surface to match selected airfoil profiles. The design was first analyzed with the help of finite element method to assess the morphing capability. The morphed control surface was then analyzed aerodynamically and comparisons with the original target profiles were made. According to the aerodynamic analyses, it was concluded that the control surface can successfully morph into target profiles with very minor changes in the target aerodynamic values while still ensuring the structural integrity and the safety of the control surface.

MDAO for Aerodynamic Assessment of a Morphed Wing for the Loiter Segment of a UAV Flight Mission

In this paper a detailed overview of a framework for an optimization of a morphing wing is presented. The framework presented here aids the design process of a morphing UAV wing which includes the variety of the flight phases and morphing concepts. The framework consists of two main solvers to compute the aerodynamic assessment of the wing: a fast lowfidelity module that solves the aeroelastic problem by coupling a geometrically nonlinear structural model to a potential flow aerodynamic model and a high-fidelity CFD module for detailed RANS simulation. This framework is later applied to the optimization of a morphing UAV wing for the loiter phase of the flight. The wing described in this paper is the focus of the European Union FP7 CHANGE project.