Charles Erklin Seeley

A higher order theory for modeling composite laminates with induced strain actuators

A refined higher order laminate theory is developed to analyze smart materials, surface bonded or embedded, in composite laminates. The analysis uses a refined displacement field which accounts for transverse shear stresses through the thickness. All boundary conditions are satisfied at the free surfaces. Non-linearities are introduced through the strain dependent piezoelectric coupling coefficients and the assumed strain distribution through the thickness. The analysis is implemented using the finite element method. The procedure is computationally efficient and allows for a detailed investigation of both the local and global effects due to the presence of actuators. The finite element model is shown to agree well with published experimental results. Numerical examples are presented for composite laminates of various thicknesses and the results are compared with those obtained using classical laminate theory. The refined theory captures important higher order effects which are not modeled by the classical laminate theory, resulting in significant deviations.

Modeling of adaptive composites including debonding

Abstract Debonding of piezoelectric actuators for use in composite structures can result insignificant changes to the static and dynamic response. This important issue is studied in thecurrent work. The refined higher order theory for composite laminates with embedded⧹surfacebonded piezoelectric sensors and actuators is extended to incorporate debonding of transducersby partitioning the laminate into debonded and nondebonded regions. The stress free boundaryconditions at the free surfaces are satisfied in the analytical formulation. Continuity conditionsbetween the debonded and the nondebonded regions, which are nontrivial for the higher ordertheory, are formulated and implemented using a penalty approach in the finite element model.The computational model is efficient and correlation with experimental results is very good.Numerical results are presented which indicate significant changes in the natural frequencies andmode shapes due to debonded transducers.

Experimental investigation of composite beams with piezoelectric actuation and debonding

Piezoelectric transducers can be used as sensors and actuators for vibration reduction in composite structures. Debonding at the transducer-laminate interface results in significant changes to the dynamic response and control authority. This important issue is studied in the current work. Composite specimens with surface bonded piezoelectric transducers were constructed with varying stacking sequences and debonding lengths. Closed loop control was implemented using an analog circuit. Experimental results were obtained for both open and closed loop frequencies and damping ratios. The results correlate well with a newly developed higher order based theory for modeling composites with debonded piezoelectric transducers. Significant changes are observed in the open and closed loop frequencies and damping ratios as a result of debonding.

A simulated annealing technique for multiobjective optimization of intelligent structures

A multiobjective optimization procedure is developed to address the combined problems of the synthesis of structures/controls and the actuator-location problem for the design of intelligent structures. Continuous and discrete variables are treated equally in the formulation. Multiple and conflicting design objectives such as vibration reduction, dissipated energy, power and a performance index are included by utilizing an efficient multiobjective optimization formulation. Piezoelectric materials are used as actuators in the control system. A simulated annealing algorithm is used for optimization and an approximation technique is used to reduce computational effort. A numerical example using a cantilever box beam demonstrates the utility of the optimization procedure when compared with a previous nonlinear programming technique.

Aeroelastic tailoring using piezoelectric actuation and hybrid optimization

Active control of fixed wing aircraft using piezoelectric materials has the potential to improve its aeroelastic response while reducing weight penalties. However, the design of active aircraft wings is a complex optimization problem requiring the use of formal optimization techniques. In this paper, a hybrid optimization procedure is applied to the design of a scaled airplane wing model, represented by a flat composite plate, with piezoelectric actuation to improve the aeroelastic response. Design objectives include reduced static displacements, improved passenger comfort during gust and increased damping. Constraints are imposed on the electric power consumption and ply stresses. Design variables include composite stacking sequence, actuator/sensor locations and controller gain. Numerical results indicate significant improvements in the design objectives and physically meaningful optimal designs.

Coupled Acoustic and Heat Transfer Modeling of a Synthetic Jet

Synthetic jets based on acoustic resonators have recently been applied to the active cooling of small, heat generating components such as microelectronics. The synthetic jets considered in this study are constructed using two piezoelectric bimorph disks separated by a donut shaped elastomeric wall with a small orifice in the wall. The piezo disks are energized to actuate out of phase at high frequency to alternately entrain and expel surrounding air. The resulting pulsating jet of air enhances local heat transfer by a factor of at least 3X, and exceeds 8x for small surfaces, compared to natural convection. These synthetic jets also create substantial noise at certain operating conditions that may be objectionable for some applications. This paper develops an analytical model that captures the coupled structural dynamic, acoustic and heat transfer physics, but is also simple enough to investigate the underlying physical behavior of the parameters that govern the jet’s performance and run many trade-o studies. Detailed comparison with experimental results is also discussed. Despite issues with the comparison of some parameters impacting jet performance, such as disk velocity and exit velocity, the predicted sound intensity and heat transfer coecient agree well with experimental test data.

The development of an optimization procedure for the design of intelligent structures

Intelligent structures are structures which can actively react to an unpredictable environmental disturbance in a controlled manner. Piezoelectric materials are an excellent choice for the development of sensors and actuators for these structures due to their special properties. It is important to locate these discrete actuators optimally on the structure in order to achieve the most efficient implementation of their special properties. It is also necessary to design the structure to be controlled for optimum performance. This leads to a combined problem which includes the discrete actuator location problem and the continuous optimization problem involving control and structure interaction. A multiobjective optimization technique is used to formulate the problem. Optimum piezoelectric actuator thicknesses for the static case are determined for the active piezoelectric elements development in this work. An optimization procedure is then presented which includes actuator locations, vibration reduction, power consumption, minimization of dissipated energy and maximization of the natural frequency as design objectives. The procedure is demonstrated through a cantilever beam problem. Results obtained indicate that improved structural and control performance can be obtained with only a few optimally placed actuators.

Design of a smart flap using polymeric C-block actuators and a hybrid optimization technique

The concept of a rotor blade with a smart flap has received considerable attention lately due to the potential for vibration suppression using individual blade control (IBC). In this paper, curved polymeric piezoelectric actuators, called C-block actuators, which exhibit significant advantages over other types of actuators are proposed to drive a smart flap for IBC. The efficient implementation involves the design of both the actuators and the flap. Therefore, it is appropriate to use a formal optimization technique to address this problem. The optimization problem is complex since it includes both continuous (flap size) and discrete (number of actuators) design variables. Therefore, a newly developed hybrid optimization procedure, which can include both types of design variable, is used to maximize flap performance using the C-block actuators. Optimization results indicate that the C-block actuators provide comparable control authority without some of the drawbacks, such as brittleness, of conventional bimorph actuators.

A Multiobjective Design Optimization Procedure for Control of Structures Using Piezoelectric Materials

Piezoelectric materials can be used as sensors and actuators for structures that re quire active vibration control and lack sufficient stiffness or passive damping. Efficient implementa tion of these actuators requires that their optimal locations on the structure be determined and that the structure be designed to best utilize the properties of the actuators. A formal optimization pro cedure has been developed to address both of these issues. A gradient based multiobjective optimiza tion technique is used to minimize multiple and conflicting design objectives associated with both the structure and the control system design which is also coupled with the actuator location problem. Objective functions such as the fundamental natural frequency of the structure and energy dissipated by the piezoelectric actuators are included in this study. Constraints are placed on the mass of the structure, displacements and applied voltage to the piezoelectric actuators. Design variables include parameters defining both the control system and the structure. The finite element method is used to model active damping elements which are piezoelectric actuators bonded to a box beam. The op timization procedure is implemented on a flexible 2-D frame.

Fluid-Structure Interaction Model for Low-Frequency Synthetic Jets

Advancements in microelectronics have increased circuit board heat densities to the point where active cooling is required. Synthetic jets offer interesting capabilities for localized active cooling of electronics due to their compact size, low cost, and substantial cooling effectiveness. The design of synthetic jets for specific applications requires practical design tools that capture the strong fluid-structure interaction without computationally long run times. There is particular interest in synthetic jets that have a low operating frequency to reduce noise levels. This paper describes how common finite elements and codes can be used to calculate parameters for a synthetic jet fluid- structure interaction model that only requires a limited number of degrees of freedom and is solved using a direct approach for low-frequency synthetic jets. Extensive tests are performed with the synthetic jet in vacuum to measure deflection, in ambient air to measure pressure and exit velocity, and impinging on a heated surface to measure heat transfer enhancement. The test results are compared with the fluid-structure interaction model results for validation, and agreement is found to be good in the frequency range of interest from 200 to 500 Hz.