Papers by Keyword: Structural Control

Abstract: Structural health monitoring and control (SHMC) for Post-earthquake realignment and repairs (PERR) is one of the most challenging issues facing earthquake engineers worldwide. Currently, neither SHMC nor PERR are parts of contemporary curricula and codes of practice. The ultimate aim of SHMC is to help achieve a viable degree of structural sustainability (SS) under predictable environmental conditions. In the present context SHMC refers to the effort that aims at achieving structural operability before and after severe earthquakes. SHMC is generally associated with the use of piezoelectric sensors to measure changes in stresses and strains of critical elements of important engineering structures. Regardless of the effectiveness of the SHMC systems no structure can lend itself well to PERR or remain seismically sustainable unless it has been designed specifically for the purpose, otherwise it would be disposable with no gains from the SHMC effort. A SS structure is one that can be designed to prevent actual collapse, overcome residual effects and lend itself well to PERR. All indications are that the use of multifunction design in conjunction with SHMC can lead to the evolution of viable SS archetypes. The purpose of the current article is to introduce a practical basis for efficient use of SHMC concepts in multi-objective earthquake resisting structures (ERSs). Replaceable energy dissipating moment connections (REDMC), rigid rocking cores (RRCs), high strength tendons, built-in stressing devices and support level grade beams have been introduced as natural instruments of structural control. The use of monitoring devices has been directed towards evaluation of the effects of formations or elimination of plastic hinges and the variations of the global drift of the system. The proposed methodologies impose and control the desired modes of lateral response and facilitate the PERR operations. Key words: Health monitoring; structural control; earthquakes; recentering; repairs.

Abstract: Beams in lightweight truss structures are subject to axial and lateral loads that may lead to undesired structural vibration or failure by buckling. The axial and lateral forces may be transferred via the truss supports that offer possibilities for state control of single beams and larger structures. In earlier own studies, the concept of a piezo-elastic support for active buckling control and resonant shunt damping has been investigated. An elastic spring element is used to allow a rotation in the beam's bearing in any plane perpendicular to the beam's longitudinal axis. The rotation is laterally transferred to an axial displacement of piezoelectric stack transducers that are either used to generate active lateral forces for active buckling control or to attenuate vibrations with a resonant shunt. In this paper, the model verification and validation of the elastic properties of the piezo-elastic support for passive and active structural control of beams with circular cross-section is presented. The rotational and lateral spring element stiffness is investigated numerically and experimentally and the existing models are updated in the verification process. The model is validated by comparing the numerical results and experimental ability for vibration attenuation.

Abstract: This paper concerns the design of robust controller for a linear system with time-varying state and input delay. The new adaptive sliding mode control algorithm of the system with multiple delays in system states and control inputs are proposed. The delay dependent conditions of the closed loop system are formulated and the equivalent gain of the adaptive sliding mode controller is obtained in the form of linear matrix inequalities (LMI). Finally, simulation results of a numerical example based on a practical inverted pendulum shows both the feasibility and efficiency of the proposed controller.

Abstract: The application of tuned mass dampers (TMDs) to offshore wind turbines has a huge potential to suppress the large vibration responses of these systems. Control module of TMDs is added into the wind turbine structural dynamics simulation code FAST and fully coupled aero-hydro-TMD-structural dynamics model of the 5MW Barge-type floating wind turbine by National Renewable Energy Laboratory (NREL) is established. A multi-parameter optimization study is performed to determine the optimal parameters of a fore-aft TMD system in the Barge-type model. The wind turbine model equipped with the optimal TMD is then simulated under five typical load conditions and the performance of the new system is evaluated. The results show that longitudinal loads at tower base and deflections at tower top reductions of up to 50% and longitudinal loads at blade root and deflections at blade tip reductions of up to 40% are achieved, which indicates that the optimal TMD can be used to suppress the vibration response of offshore wind turbines and also demonstrates the potential for TMD structural control approaches.

Abstract: Traditional tuned mass damper (TMD) can reduce the dynamic response of structure under earthquake, but the traditional tuned mass damper is not effective to reduce translation-torsion coupled vibration. A two-directional horizontal and torsional tuned mass damper, which includes tuned mass blocks, torsional blocks and rotation lever, is proposed. The horizontal and torsional response of the building structure is controlled by the movement and the rotation of the multi-dimensional tuned mass damper (MDTMD) in different directions. According to the movement mechanism of the MDTMD, the dynamic equation for the control system considering eccentric torsion effect is established. An eccentric structure with MDTMD is analyzed to verify the control effctive for the horizontal and torsional coupled system under earthquake, and the reduction effect is compared with the traditional TMD. The results show that the coupled response can be reduced effectively by MDTMD and the vibration reduction ration is much higher than traditional TMD.

Abstract: The aim of this paper is to develop an active structural control scheme to control wind turbine nacelle/tower out-of-plane vibration. An active tuned mass damper (ATMD) is designed an placed inside the turbine nacelle. An EulerLagrangian wind turbine model based on energy formulation is developed for this purpose, which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations. Also, the interaction between the blades and the tower including the ATMD is considered. The wind turbine is subjected to gravity and turbulent aerodynamic loadings. A three-dimensional (3D) model of a wind turbine foundation is designed and analysed in the finite element geotechnical code PLAXIS. The rotation of the foundation is measured and used to calculate a rotational spring constant for use in wind turbine models to describe the soil-structure interaction (SSI) between the wind turbine foundation and the underlying soil medium. Damage is induced in the soil medium by a loss in foundation stiffness. The active control scheme is shown to reduce nacelle/tower vibration when damage occurs.

Abstract: Yielding can be emulated in a structural system by adding an adaptive “negative stiffness device” (NSD) and shifting the “yielding” away from the main structural system-leading to the new idea of “apparent weakening” that occurs ensuring structural stability at all displacement amplitudes. This is achieved through an adaptive negative stiffness system (ANSS), a combination of NSD and a viscous damper. By engaging the NSD at an appropriate displacement (apparent yield displacement that is well below the actual yield displacement of the structural system) the composite structure-device assembly behaves like a yielding structure. The combined NSD-structure system presented in this study has a re-centering mechanism thereby avoids permanent deformation in the composite structure-device assembly unless, the main structure itself yields. Essentially, a yielding-structure is “mimicked” without any, or with minimal permanent deformation or yielding in the main structure. As a result, the main structural system suffers less accelerations, less displacements and less base shear, while the ANSS “absorbs” them. This paper presents comprehensive details on development and study of the ANSS/NSD. Through numerical simulations, the effectiveness and the superior performance of the ANSS/NSD as compared to a structural system with supplemental passive dampers is presented. A companion paper presents the NSD and its mechanics in detail.

Abstract: Model Order Reduction (MOR) denotes the theory by which one tries to catch a model of order lower than that of the real model, in view of the design of an efficient structural control scheme. When the nonlinear response of the reference structural system affects the nature of the reduced model making it dependent on the visited subset of the input-output space, standard MOR techniques do not apply. The mathematical theory offers some specific alternatives. One of them is applied, in this paper, to a case study focused on a multi-bay, multi-storey plane frame with assigned locations for the potential plastic hinges.

Abstract: The present contribution gives an overview on own research that has been performed from 2008 to 2011 in Area 2, Mechanics and Model Based Control, of the COMET K2 Austrian Center of Competence in Mechatronics (ACCM), which is situated at the Science Park of the Johannes Kepler University of Linz. Area 2 is motivated by the fact that mechanics and control both are rapidly expanding scientific fields, which share demanding mathematical and/or system-theoretic formulations and methods. The goal of Area 2 has been to utilize and extend these relations, with special emphasis on solid mechanics and control methods based on physical models. Some corresponding results will be reviewed subsequently with respect to the mechanical modelling of structures, robots and machines, and with respect to the corresponding model based control as linear/non-linear lumped/distributed parameter systems. Due to limitations in space, the present review restricts itself to work of Area 2 that has been directly performed at the University of Linz. The review contains 118 references to works on mechanics and model based control.

Abstract: Smart structural systems are emerging as a vehicle for implementing semi active control algorithms. Sensors, processors and actuators are the generic basic components of any smart structural system. Sensors are employed in gathering information that could be used by a smart shape identifier in order to define a real-time abstract deformed shape of the system at any given point in time. This information could be employed in proposing a suitable smart control algorithm to suppress the vibration of a given structural system. In this paper, a generic framework for abstract shape identification is developed. The proposed framework employs predefined potential deformed patterns, for a given structural system, in training and/or designing the smart shape identifier. Two applications were developed which employ neural network and fuzzy logic as two potential smart technologies. Both models are capable of indentifying and/or classifying the abstract deformed shape of a three degree-of-freedom structural system in real-time. The neural network model was developed and trained by a single earthquake record then tested using five unseen earthquake records. The fuzzy inference system employed a rule-base that was developed to capture all potential combinations of inter-story deformations then tested using all six earthquake records. The performance of both models was measured by the statistical and geometrical properties of a linear compliance graph. The developed systems were initially designed and tested to model a three-degree-of-freedom system and are now being expanded to model a multi-degree-of-freedom system.