Pier Marzocca

Multi-Input/Multi-Output Adaptive Output Feedback Control Design for Aeroelastic Vibration Suppression

Via the use of leading- and trailing-edge control surface actuation, an adaptive output feedback controller is designed for suppressing aeroelastic vibrations on a nonlinear wing section. Although a single flap under adaptive control can suppress vibrations, the response rate is limited by the system zero dynamics. Under the restriction that only pitching and plunging variables are available for measurement but their rates are not, the proposed algorithm addresses the problem of designing a singularity-free adaptive output feedback controller when the control inputs are coupled via an input gain matrix for which the parameters are uncertain. The stability result achieved is global asymptotic tracking. Simulation results demonstrate the efficacy of the multi-input/multi-output control toward suppressing flutter and limit-cycle oscillations, as well as reducing the vibrational level in the subcritical flight-speed range. Pertinent conclusions are outlined.

Development of a FBG based distributed strain sensor system for wind turbine structural health monitoring

The development of a fiber Bragg grating (FBG) based distributed strain sensor system for real time structural health monitoring of a wind turbine rotor and its validation under a laboratory scale test setup is discussed in this paper. A 1 kW, 1.6 m diameter rotor, horizontal axis wind turbine with three instrumented blades is used in this study. The sensor system consists of strain sensors, surface mounted at various locations on the blade. At first the sensors are calibrated under static loading conditions to validate the FBG mounting and the proposed data collection techniques. Then, the capability of the sensor system coupled with the operational modal analysis (OMA) methods to capture natural frequencies and corresponding mode shapes in terms of distributed strains are validated under various non-rotating dynamic loading conditions. Finally, the sensor system is tested under rotating conditions using the wind flow from an open-jet wind tunnel, for both a baseline wind turbine and a wind turbine with a structurally modified blade. The blade was modified by attaching a lumped mass at the blade tip simulating structural damage or ice accretion. The dynamic characteristics of the baseline (healthy) blade and modified (altered) blade are compared to validate the sensor systems ability for real time structural health monitoring of the rotor.

Conceptual Approach to Unconventional Airship Design and Synthesis

This paper presents a novel design methodology to be used in the evaluation of the main features of advanced unconventional airship configuration. Similar to the process used in aircraft design, the concept of volume fractions (VF) is introduced to estimate airship weights, dimensions, and performances, in an early design phase. The paper presents the complete methodology, with tables and constants to help unconventional airship designers with preliminary design considerations. Volumes and weights of candidate solutions are obtained through an iterative method within a user-friendly tool requiring graphical and straightforward mathematical operations. The solutions are ranked based on procedures aiming at satisfying customer needs and expectations provided as inputs. A case study highlighting a step-by-step methodology process is presented, and the approach followed to select the final solution is documented. The method is easy to use and implement, rapidly providing a significant amount of data. A parametric approach is used such that the evolution in materials and technology, new configurations, and modern power and energetic solutions can be considered by simply performing a parameter sweep to perform sensitivity analysis.

Aerodynamics and Static Aeroelastic Behavior of Low–Reynolds Number Deformable Membrane Wings

AbstractA modern class of micro aerial vehicles (MAVs) uses deformable membrane wings (DMWs), which comprise rigid or rigidizable structural elements that guarantee stiffness, as well as flexible membranes that provide an aerodynamic shape, all in a compact and lightweight form. To contribute to the body of knowledge about DMWs, this paper presents extensive numerical simulations, accompanied by experiments that substantiate the findings pertinent to the aerodynamics and static aeroelastic behavior of these unconventional wings. The performance characteristics of canonical, untapered, and untwisted rectangular DMWs are studied using a parametric physical-based two-dimensional (2D) fluid structure interaction (FSI) model adopting a two-way coupled FSI algorithm. The effect of geometrical, material, and flow properties is investigated, and the results obtained show that the material Young’s modulus is the most influential parameter affecting the aerodynamic characteristics of the studied DMWs, with their hi...

Unsteady aerodynamic modeling and flutter analysis of long-span suspension bridges

A parametric one-dimensional model of suspension bridges is employed to investigate their static and dynamic aeroelastic behavior in response to a gust load and at the onset of flutter. The equilibrium equations are obtained via a direct total Lagrangian formulation where the kinematics for the deck, assumed to be linear, feature the vertical and the chord-wise displacements of the deck mean axis and the torsional rotations of the deck cross sections, while preserving their shape during rotation. The cables elasto-geometric stiffness contribution is obtained by condensing the equilibrium in the longitudinal direction assuming small horizontal displacements and neglecting the cable kinematics along the bridge chord-wise direction. The equations of motion are linearized about the prestressed static aeroelastic configuration and are obtained via an updated Lagrangian formulation.The equations of motion governing the structural dynamics of the bridge are coupled with the incompressible unsteady aero-dynamic model obtained by a set of reduced-order indicial functions developed for the cross section of a suspension bridge, here represented by a rectangular cross-section. The space dependence of the governing equations is treated using the Galerkin approach borrowing as set of trial functions, the eigenbasis of the modal space. The time integration is subsequently performed by using a numerical scheme that includes the modal reduced dynamic aeroelastic Ordinary Differential Equations (ODEs) and the added aerodynamic states also represented in ODE form, the latter being associated with the lag-state formulation pertinent to the unsteady wind-induced loads.The model is suitable to analyze the effect of a time and space non uniform gust load distributed on the bridge span. The obtained aeroelastic system is also suitable to study the onset of flutter and to investigate the sensitivity of the flutter condition on geometrical and aerodynamic parameters. The flutter instability is evaluated using appropriate frequency and time domain characteristics. The parametric continuum model is exploited to perform dynamic aeroelastic flutter analysis and gust response of the Runyang Suspension Bridge over the Yangtze river in China.Copyright

Advanced System Identification of Plates Using a Higher-Order-Spectral Approach: Theory and Experiment

A nonlinear system identification technique exploiting the dynamic response features of fully nonlinear physics-based plate models extracted by Higher-Order Spectral (HOS) analysis tools is developed. The changes induced by an imperfection in the dynamics through the structural nonlinearities are used as key detection mechanism. The differences in dynamic response of a baseline and a modified/imperfect structure are enhanced by the local nonlinearities induced by the structural modification which thus represent the specific objective of identification. The validation of the procedure and the developed algorithms is carried out through extensive experimental testing employing various plates, including isotropic and composite lay-ups, and excitation sources, including White Gaussian Noise and a train of impulses.Copyright

Dynamic Response Control of Rotating Composite Booms Under Solar Radiation

This paper deals with the thermally induced dynamic response analysis of a composite blade rotating at a constant speed. Fiber-reinforced composite thin-walled beam are used in a variety of aerospace applications, including helicopter rotor blades, tilt rotor aircraft, turbine engines, compressor blades, only to name a few. The composite beam is modeled as a tapered thin-walled beam which is subjected to a temperature field. A number of non-classical features such as transverse shear, secondary warping, anisotropy of constituent materials, and rotary inertias have been included in the model. The structure of the blade consists of a host graphite epoxy laminate with spanwise distributed transversely isotropic (PZT-4) sensors and actuators. The discussed results reveal that the thermal environment has a detrimental effect on the blade dynamic response. The active controller is implemented via the combined displacement and velocity feedback control methodology, which can alleviate the deleterious effect associated with the thermally induced dynamic response.

About the Aerothermoelastic Stability of Panels in Supersonic Flows

This article provides new insights into the aerothermoelastic stability of thin plates. Particularly, the issue of loss of stability of an isotropic plate-strip of constant thickness immersed in a supersonic flow field and subjected to a variable temperature field through the thickness is examined. Using the basic principles of the theory of aerothermoelasticity of isotropic bodies, the theories of flexible panels, and the linear law of temperature field through the thickness of the panel, the stability equations and associated boundary conditions are obtained. As expected, the coefficients of the aerothermoelastic governing equations depend on the thermal load, and consequently the panel-flutter critical speed depends on temperature. The model takes into account quadratic and cubic aerodynamic non-linearities as well as cubic geometric non-linearities. Due to the inhomogeneity of the temperature field distribution across the thickness plate buckling instability occurs. This instability accounts for the deformed shape of the plate and the stability boundary depends on the variables characterizing the flow speed, the temperature of the middle plane and the temperature gradient in the direction normal to the plane. It is shown that the combined effect of the temperature field and free-stream regulates the process of stability and the temperature field can significantly change the flutter critical speed and flutter behavior. The problem of stability is also considered in the non-linear framework. The existence and behavior of flutter-type vibrations is investigated at pre- and post-critical speeds. The influence of the temperature field on the dependency of the limit cycle amplitude as a function of speed is studied. Results and discussions are presented along with pertinent concluding remarks.

Dynamic Response Analysis of Rotating Functionally Graded Thin-Walled Blades Exposed to Steady Temperature and External Excitation

This paper focus on the thermoelastic modeling and dynamic response of a rotating blade made of functionally graded ceramic-metal based materials. The blade is modeled as non-uniform thin walled beams which are fixed at the hub with various selected values of setting angles and pre-twisted angles. In this study, the blade rotates with a constant angular velocity and is exposed to a steady temperature field and external excitation. The effect of the temperature gradient through the blade thickness is also considered. Material properties are graded across the blades thickness according to the volume fraction power law distribution. Numerical results highlighting the effects of the volume fraction, temperature gradient, taper ratio, setting angle and pre-twisted angle on the dynamic response of bending-bending coupled beam characteristics are provided for the case of a biconvex cross-section and pertinent conclusions are outlined.

Comparative analysis of control performances applied to a 3-DOFs nonlinear supersonic lifting surface

This paper presents a comparative analysis of control strategies applied to a nonlinear 2-D wing-flap system operating in supersonic/hypersonic flight speed regimes. Open and closed-loop aeroelastic response and flutter of 2-D supersonic lifting surfaces are investigated. In this context, the implications of aerodynamic and structural nonlinearities on the aeroelastic response in the post-flutter range are presented and various robust control methodologies, such as sliding mode control, H∞ and fuzzy logic control, are compared. The controls’ effectiveness in reducing the aeroelastic vibrations in the various flight speed ranges and in suppressing flutter is demonstrated.