Falko Seeger

Overall design of actively controlled smart structures by the finite element method

The design process of engineering smart structures requires a virtual overall model, which includes the main functional parts such as the passive structure, the actuators and sensors as well as the control algorithm. The objective of the paper is to pre-sent such a design concept for vibration suppression of thin-walled shell structures controlled by piezoelectric wafers and fi-bers. This concept is based on a recently developed finite element package for the simulation of multi-physics problems. At first a rough design of actuator and sensor distributions is estimated which is based on the controllability and observabilty indices. Then the Matlab/Simulink software tool is used for controller design. From the finite element model all required data and information are transferred to Matlab/Simulink via a data exchange interface. After having designed the controller the result in form of the controller matrices or as C-codes can be transferred back into the finite element simulation package. Within the finite element code the controlled structural behavior can be studied under different disturbances. The structural design can be improved in an iterative way, e.g. by changing the actuator and sensor positions based on a sensitivity analy-sis. As an example an actively controlled smart plate structure is designed and tested to demonstrate the proposed procedure.

On Finite Element Analysis of Piezoelectric Controlled Smart Structures

The increasing engineering activities in the development and industrial application of piezoelectric smart structures require effective and reliable simulation and design tools [9]. Even if significant progress has been observed over the past years most of such developments are restricted to special requirements and applications [2]. In our opinion the finite element method (FEM) is an excellent basis to develop overall software tools which meet the engineering requirements. Consequently, such a general purpose software tool has been designed by the authors and realized step by step over the last few years [1], [3], [4]. Recently, this tool was completed by new thin shell type elements as well as a data interface to connect controller design tools with our finite element analysis tool. In the paper the focus is on these new developments. First the theoretical basis of our finite element software tool is presented briefly. Then the new electromechanical coupled layered thin shell elements are prescribed which are very efficient to simulate the global structural behavior of thin-walled structures controlled by piezoelectric wafers and fibers. After that our concept to connect finite element analysis and controller design is given which result in an computer based overall design and simulation strategy for smart structure. Finally, the active vibration suppression of an excited plate structure is presented as a test example to demonstrate the applicability of our finite element based overall design and simulation software.

Modeling of smart composites controlled by thin piezoelectric fibers

Recently, thin piezoelectric fibers with diameters between 10 micrometer and 30 micrometer have been manufactured and used as sensor/actuator components of smart composite structures. The paper deals with the mathematical analysis, numerical simulation and optimal design of smart structures controlled by such thin piezoelectric fibers, where two different approaches are investigated. At first a smeared concept is applied. Each active layer consisting of piezoelectric fibers embedded in a matrix material is modeled as an anisotropic coupled electro-mechanical continuum and analyzed by recently developed special finite shell elements. At second a discrete concept is used, where the piezoelectric fibers are modeled as one-dimensional truss like finite elements which are embedded into conventional finite elements by a penalty technique. These two approaches are discussed and compared.

Analysis and design of thin-walled smart structures in industrial applications

The utilization of the smart structures technology gains increasing attention in engineering and industrial applications, especially in the wide field of noise and vibration reduction of thin-walled structures. The application of distributed sensors and actuators - e.g. piezoelectric wafer or fiber arrays - directly attached at the structure or laminated into a composite structure results in a highly integrated smart structural system. An optimal exploitation of such facilities of piezoelectric materials requires effective and robust numerical tools for an optimal overall design. In our opinion the finite element approximation based on multi-field thin shell elements provides an excellent method for the simulation and the design of complex smart structures. In the paper a brief introduction in our finite element simulation and design tool is given where the focus is on the recently developed multi-field finite shell elements. These elements have been created on the basis of the classical SemiLoof element family by introducing additional degrees of freedom to approximate the electromechanical coupling. One central point in the design process is the distribution of the active material at the passive base structure to fulfill the design criteria. In the paper a design concept based on controllability and observability indices is presented, which results in an acceptable first design even in complex industrial applications. In connection with a flexible automatic meshing, which generates the overall model for structures with any amount and distribution of active wafers, the overall behavior of a smart structure can be simulated quite accurate. To underline the capability of the design and simulation tool two examples with references to mechanical and automotive applications are discussed.

Overall Design and Simulation of Smart Structures

Increasing engineering activities in the development and industrial application of piezoelectric smart structures require effective and reliable simulation methods and design tools [2], [9], [14]. In our opinion, the finite element method (FEM) is an excellent approach to develop a tool, which meets the relevant engineering requirements. Recently, an overall simulation and design tool for piezoelectric controlled smart structures has been developed, containing both a suitable controller design and the appropriate actuator/sensor placement. To model complex engineering structures, a library of multi-field finite elements has been developed with coupled electric and mechanical degrees of freedom for 1D, 2D and 3D continua as well as for thin-walled layered structures [4].