The spoilers on an aircraft are responsible for several tasks, including execution of roll maneuvers, lift dumping (aerodynamic "spoiling"), and braking. The examined spoiler is manufactured from carbon fiber reinforced composite material and is attached to the wing by four bearing hinges and one actuator hinge. Correct spoiler design involves knowledge of the loads acting on the spoiler, calculation of stresses and strains, and examination of possible failures. Additionally, the fatigue and damage tolerance evaluation of such a spoiler has to follow established certification protocols. This study defines a load cycle based on in-service loadings, including aerodynamic loading, wing bending, inertial loading, and actuator loading. A finite element model of the spoiler is used to calculate the reaction forces in the hinges and the strain in the carbon fiber components occurring during the load cycle. The Miner Rule is used to calculate the fatigue life of the hinges based on the computed stress. A damage tolerance evaluation is then performed assuming that different hinges have failed. Finally, a certification test for fatigue and damage tolerance evaluation of a spoiler is discussed.
In the fields of high-resolution metrology and manufacturing, effective anti-vibration measures are required to obtain precise and repeatable results. This is particularly true when the amplitudes of ambient vibration and the dimensions of the investigated or manufactured structure are comparable, e.g. in sub-micron semiconductor chip production, holographic interferometry, confocal optical imaging, and scanning probe microscopy. In the active anti-vibration system examined, signals are acquired by extremely sensitive vibration detectors, and the vibration is reduced using a feedback controller to drive electrodynamic actuators. This paper deals with the modeling of this anti-vibration system. First, a six-degree-of-freedom rigid body model of the system is developed. The unknown parameters of the unloaded system, including actuator transduction constants, spring stiffness, damping, moments of inertia, and the location of the center of mass, are determined by comparing measured transfer functions to those calculated using the updated model. The model is then re-updated for the case of an arbitrarily loaded system. The responses predicted by the final updated model agree well with the experimental measurements, thereby giving confidence in the model and the updating procedure.
KEYWORDS: Resistance, Resistors, Signal processing, Electronics, Digital signal processing, Linear filtering, Sensors, Piezoelectric effects, Amplifiers, Electrodes
This work presents a semi-passive concept to reduce structural vibrations over a wide frequency regime. Therefore, a purely resistive passive electrical network is designed and connected to a piezoelectric element. This concept allows an enhancement in structural damping without using sensitive sensor electronics and amplifiers. Furthermore, it yields constant vibration reduction over a wide temperature range; limitations arise for temperatures above the Curie temperature. Firstly, the damping capabilities of a resistively shunted piezoelectric element are discussed and the optimal resistance for the passive electrical network is outlined. Next, a design concept for optimal placement of the piezoelectric elements is presented. This concept is designed for placement on two dimensional structures, such as plates. It is based on an energy ratio, which is defined for each structural mode. In this context, the effective strain energy of a two dimensional piezoelectric element is introduced. It allows calculation of the electrical energy, generated by the piezoelectric element as it is mechanically loaded. Adaption of the shunt resistor, and thus, maximal reduction of structural vibrations, is obtained by a new concept, which uses digital potentiometers in combination with a feedforward control concept. Depending on the excitation signal, two different resistances can be realized by the adaptive passive electrical network. In this manner two structural modes can be optimally damped. Finally, experiments are conducted, in which fixed resistors as well as adaptive resistors are implemented. Results show the advantage of using adaptive resistors for the passive electrical network in terms of enhanced vibration reduction capabilities.
The low structural damping of large space structures and the stringent positioning requirements in missions demand effective vibration suppression. The semi-active approach at hand is based on friction damping due to interfacial slip in semi-active joints which can be controlled by varying the normal pressure in the contact area using a piezo-stack actuator. This paper focuses on the modeling, identification and model reduction of a large space structure with semi-active joints. For the purpose of model identification and model reduction, the nonlinear friction forces transmitted in the joints are considered as external forces acting on the linear tress structure. Experimental Modal Analysis results are used to update the FE model of the truss structure and the parameters of the nonlinear friction model are identified from measured responses of an isolated joint. The model of the linear subsystem is reduced by a combination of balanced reduction and matching moments method. The modal truncation is based on controllability and observability gramians. To improve the fidelity locations conventional connections are replaced by adaptive joints, each with a local feedback controller for the adaptation of the normal force. Simulation results of a 10-bay truss structure with semi-active joints show the potential of the present approach.
The low structural damping of large space structures and the stringent positioning requirements in missions demand effective vibration suppression. The semi-active approach at hand is based on friction damping due to interfacial slip in semi-active joints which can be controlled by varying the normal pressure in the contact area using a piezo-disc actuator. This paper focuses on the optimal placement of semi-active joints for vibration suppression. The proposed method uses optimality criteria for actuator and sensor locations based on eigenvalues of the controllability and observability gramians. It is stated as a nonlinear multicriteria optimization problem with discrete variables which is solved by a stochastic search algorithm. As final step in the design procedure, parameters of the local feedback controllers assigned to each adaptive joint are optimized with respect to transient response of the structure. The present method is applied to a 10-bay truss structure. Simulation runs of the controlled structure are used to verify the optimization results.
Measurements performed using a double pulse ESPI (Electronic Speckle Pattern Interferometry) are used to estimate the power flow maps in a square plate excited harmonically. The pulse ESPI was equipped with one camera providing no information about the phase of the measured displacement field. A procedure based on the solution of a system of transcendental equations which corresponds to two measurements with a known time delay is used to determine the magnitude and phase. In order to spatially smooth the operational modes and reduce the noise spikes, a smoothing technique and a median filter are used, respectively. The active power flow is estimated for two frequencies. The reactive power flow due to the bending moments, twisting moments and shear forces are obtained separately. A finite element model based on the theory of thin plates is used for qualitative comparison of the reactive power flow maps.
A smart structure system which uses the piezoelectric materials as sensors to identify harmonic external loads and as actuators to suppress the structure vibration is proposed. Signal estimation subprogram and load estimation subprogram use the piezoelectric materials as sensors to estimate the frequencies, amplitudes and phases of the harmonic external loads based on the dynamic responses of structures. After the load estimation procedure, the optimal voltages of actuators are determined by requiring minimization of deflection amplitude of structure. The piezoelectric materials can also be used as actuators to suppress harmonic vibrations of the structure under the estimated external harmonic loads. The method has been applied for beams containing distributed piezoelectric materials. The simulation results validate that the method is effective for suppression of harmonic vibration.
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