Advances in Science and Technology Vol. 83

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: Structural Health Monitoring (SHM) allows to perform a diagnosis on demand which assists the operator to plan his future maintenance or repair activities. Using structural vibrations to extract damage sensitive features, problems can arise due to variations of the dynamical properties with changing environmental and operational conditions (EOC). The dynamic changes due to changing EOCs like variations in temperature, rotational speed, wind speed, etc. may be of the same order of magnitude as the variations due to damage making a reliable damage detection impossible. In this paper, we show a method for the compensation of changing EOC. The well-known null space based fault detection (NSFD) is used for damage detection. In the first stage, a training is performed using data from the undamaged structure under varying EOC. For the compensation of the EOC-e ects the undamaged state is modeled by different reference data corresponding to different representative EOC conditions. Finally, in the application, the influences of one or other EOC on each incoming data is weighted separately by means of a fuzzy-classiffcation algorithm. The theory and algorithm is successfully tested with data sets from a real wind turbine and with data from a laboratory model.

Abstract: This paper includes five parts. The first is the sensing technology, in which ultrasonic-based sensing technology for scour monitoring of bridge piers, electro-chemistry-based distributed concrete cracks and automobile wireless sensors are introduced. The second is the application of compressive sensing technology in structural health monitoring, in which the recovery of lose data for wireless senor networks, spatial distribution of vehicles on the bridge and localization of acoustic emission source by using compressive technique are included. The third is damage monitoring and identification of seismically excited structures, in which data-driven seismic localization approach and nonlinear hysteretic model identification approach are proposed. The fourth is the monitoring for wind and wind effects of long-span bridges, the vortex-induced vibration of deck, suspended cables and stay cables is observed and the buffeting of bridge under Typhoon is also measured. The last one is the data analysis, modeling and safety evaluation of bridges based on structural health monitoring techniques.

Abstract: Integrated actuators and sensors promise significant improvement in structural performance if not being an essential condition for high functionality. But “integration” per se is no added value. For example, actuators have to be sufficiently small and local weakening of the material has to be avoided. So such concepts are specifically apt for actuating and controlling small displacements or low mass / low damping vibrating systems e.g. in opto-mechanical systems or space structures such as large reflectors, solar arrays or telescopes. For large reflectors with high dimensional stability requirements, post-manufacturing improvement of shape accuracy or a certain compensation of in-orbit disturbances is of interest. A further challenge comes into play when such structures have to be drastically morphed in their shapes in order to adapt to modified mission needs, which then calls for micro-actuators with relatively large displacement strokes. The discussion of these aspects will be based on results derived from simulations as well as from laboratory models.

Abstract: Deployable structures have been developed for many different applications from space to mechanical and civil engineering. In the paper the general concepts of deployable structures, combining static and kinematic behaviour are presented first, also discussing their relationships with adaptive and variable geometry structures. Reported applications to civil engineering and architecture are then reviewed and categorized. The characteristics of the following systems are summarized : 1. Pneumatic Structures. 2. Tensegrity Structures. 3. Scissor-like Structures. 4. Rigid Foldable Origami. 5. Mutually Supported Structures. The problems of form finding, direct and inverse kinematics, actuation and self-deployability for some of the most interesting among the above structural types are then discussed in the paper. Some examples involving rigid foldable origami and mutually supported structures are finally presented.

Abstract: This paper describes the concept of monitoring the massive concrete structures based on the inverse problem solution. Properties of young concrete are changing very intensively in the early stage of hydration process, and therefore it is very important to know material constants as a function of age of concrete in order to accurately modeling the phenomena occurring in it. The main idea is to determine the time-dependent thermal properties of concrete on the basis of point temperature measurements in a small laboratory molds. Then, based on these parameters, the coupled thermo-mechanical equations are solved to describe the maturation and aging of concrete. This allows to specify (at the design stage) the potential risk of structural damage (e.g. thermal cracking) and thus prevent them e.g. through the use of intelligent cooling systems. Own, based on finite element method, software TMC (Thermal & Mechanical modeling of Concrete) gives also the possibility of predicting the formation of cracks during the aging of structure, which will be verified by means of electric sensor networks (so called ELGRID). This integration will enable to provide a complete system for monitoring and prediction of the structural stress state and damage development.

Abstract: Composite materials are increasingly used in civil field for structural strengthening. Besides, monitoring the structure during its lifetime is very important, in order to detect possible anomalous situations and to reduce maintenance and inspection costs. Optical fibers represent a promising and increasingly used technique for long-term health monitoring of structures. The aim of this research is to assess the feasibility and reliability of strain measurements by utilizing FBG (Fiber Bragg Grating) optical sensors embedded in FRP (Fiber Reinforced Plastic) packaging. The resulting device is conceived to be applied on the external surface of the structure. The packaging provides the optical fiber with the necessary protection against accidental damage during handling and installation. The mechanical characteristics of the packaging allow the device to be used as a sensorised reinforcement as well. The paper discusses the technology set-up, the physical and the mechanical characterization of the developed smart device.

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.

Abstract: In this study, relative load-carrying capacity (RLC) evaluation system in which the change of load-carrying capacity of a bridge structure can be estimated through the variation of the dynamic property, which is induced by the stiffness change due to the deterioration of the bridge, by using ambient traffic-induced vibration was proposed. The system uses the natural excitation technique in conjunction with the eigensystem realization algorithm for identification of modal parameters. Indoor test using a truss-typed model bridge and field measurement were performed to verify the suggested system and it was shown that the RLC estimation system is suitable for the safety assessment of bridge structures in a simple and efficient manner.

Abstract: The authors have access to an existing laboratory facility which has been used to validate different control schemes. The three-storey steel frame is mounted on a single-axis shaking table simulating the ground excitation. Four single-axis wired accelerometers were mounted on each level (ground and floors of the frame). A mass cart driven by a DC motor, a DC motor position analog controller, and a controller board complete the early bed-test realization. Recently wireless sensor links and a digital position controller were introduced to update the AMD performance. In this paper the frame specimen is simulated by a numerical model allowing the authors to design and test the control laws without any risk of damaging the physical model.