Shock and Vibration - Volume 19, issue 5

Authors: Lallart, M. | Guyomar, D.

Article Type: Research Article

Abstract: Recent trends in Structural Health Monitoring (SHM) systems have demonstrated the growing interest in autonomous, embeddable devices able to perform in-situ inspection and to work conjointly and wirelessly in a global sensor network. Hence, the energy aspect is of prior importance when dealing with such systems. However, most signal processing methods for assessing the integrity of a structure still rely on linear transforms or operators, such as Fourier or amplitude analysis, which for example require analog-to-digital …converters that consume a lot of energy. As well, in addition of optimizing the signal processing, another important part is the use of a proper energy management for the whole system. Hence, the purpose of this paper is twofold. First, it aims at reviewing a particular set of low energy cost methods for Structural Health Monitoring consisting of deriving a Damage Index (DI) obtained from the comparison of the LW signature with a reference signal using logical operators that greatly reduce the required computational energy. A particular emphasis will be placed not only on the performance of the exposed techniques, but also on their energy consumption as well as their sensitivity and robustness facing environmental drifts. It will therefore be shown that the use of non-linear operators for the comparison permits ultra-low energy requirements while allowing detection abilities similar to classical approaches. The second objective of this paper is to discuss the implementation of the whole system in an efficient way using proper management strategies. This issue will be discussed through an example of a self-powered SHM scheme powered using ambient vibrations. Show more

Keywords: Structural Health Monitoring, damage index, Lamb wave, low-power, self-powered

DOI: 10.3233/SAV-2012-0695

Citation: Shock and Vibration, vol. 19, no. 5, pp. 867-877, 2012

Authors: Lee, Young-Sup | Lee, Sang-Kwon | Shin, Kihong

Article Type: Research Article

Abstract: A piezoelectric cantilever type sensor for locating the precise weak-impact or touch position on a plate is presented in this paper. Since the importance of human-computer interface such as a touch panel system has been rapidly increasing recently, this study could suggest an appropriate sensor for the detection of a weak-impact point effectively and accurately for such a system. This sensor detects the out-of-plane vibration of a panel when a touch with a finger or pen …is applied on it. The sensor is made with a steel beam and a single crystal PMN-PT patch is bonded on the beam, which is designed to detect the base vibration of the panel. The sensor was designed, manufactured to verify the detect ability of a weak-impact and attached on two different plates of a glass of 400 × 400 × 4 mm and a wooden MDF of 600 × 600 × 9 mm. The experiment result of the sensor was compared with that of an accelerometer which can also be used for the same purpose and shows clear weak-impact responses with a narrow-band property at its resonant frequency. It is expected that the cantilever type sensor in this study could be applied to make a simple flat plate into a touch panel when the time difference of arrivals method is used to locate the weak-impact point. Show more

Keywords: Piezoelectric cantilever sensor, weak-impact locating, wave dispersion, narrow-band response, time difference of arrivals

DOI: 10.3233/SAV-2012-0696

Citation: Shock and Vibration, vol. 19, no. 5, pp. 879-890, 2012

Authors: Yalciner, Hakan | Sensoy, Serhan | Eren, Ozgur

Article Type: Research Article

Abstract: Corrosion is a long-term process resulting in the deterioration of the reinforced concrete (RC) structures. Most of the structural problems observed under the impact of either earthquakes or service loads might occur due to corrosion. Therefore, prediction of the remaining service life of a corroding RC structure plays an important role to prevent serious premature damage. In this study, a corroded, 25-year-old high school building which has been demolished at an earlier time was analyzed as …a function of corrosion rate. Bond-slip relationships were taken into account in nonlinear analyses as a function of corrosion rate for different time periods (i.e., non-corroded (t: 0), existing (t: 25) and 50 years after construction); and they were used to ensure the effect of time-dependent slip rotation on the global structural behaviour by modifying the target post-yield stiffness of each structural member. Nonlinear push-over analyses were performed by defining the time-dependent plastic hinge properties as a consequence of corrosion effects. In order to define the performance levels of three different time periods, nonlinear incremental dynamic analyses (IDA) were performed for 20 earthquake ground motion records as a function of corrosion rate. Results showed that bond-slip relationship between concrete and steel is very important in evaluating the non-linear behaviour of corroded RC structures. Show more

Keywords: Incremental dynamic analysis, corrosion, bond-slip, performance level

DOI: 10.3233/SAV-2012-0697

Citation: Shock and Vibration, vol. 19, no. 5, pp. 891-902, 2012

Authors: Lopes, H.M. | Oliveira, C.S.

Article Type: Research Article

Abstract: Before establishing the priority settings for the reduction of seismic risk of water supply infrastructures, it is necessary to understand the dynamic behavior of elevated water tanks, which are components of those infrastructures. Among other information, the main frequencies of vibration of these structures must be estimated and the analytical models used in their analysis and design should reproduce the frequency values obtained by in-situ dynamic tests. This work focuses exclusively on reinforced concrete (RC) …elevated water tanks (200–750 m^3 of water at heights of 30–40 m), which are very common structures in the water supply systems in Portugal since the mid XXth century. This type of structures can also be seen in many regions around the world. First, a nationwide survey was conducted to determine the most common typologies in the country in terms of structural layout. Second, an in-situ campaign using ambient vibration as input was performed for a group of selected structures to determine the main frequencies of vibration and to identify modal shapes and damping values. Third, a finite element model of several different typologies was developed using the water simply as a concentrated mass at the top; the elastic properties of the model of the structure including the foundation were calibrated, so that the frequencies of various mode shapes obtained by the analytical model would match the frequencies of the real structure. Finally, an expression was derived to estimate the fundamental frequency of a group of elevated water tank typologies based on the total mass at the top of the supporting structure, which include the water, the global lateral stiffness, and the height of the tank. This study, providing important information on the frequencies of vibration of RC-elevated water tanks, contributes in a definite way to the analysis and design of such water tanks. Show more

Keywords: Dynamic analysis, RC elevated water tanks, identification of frequencies, analytical modeling

DOI: 10.3233/SAV-2012-0698

Citation: Shock and Vibration, vol. 19, no. 5, pp. 903-914, 2012

Authors: Leopa, A. | Nastac, S. | Debeleac, C.

Article Type: Research Article

Abstract: A highly efficient seismic protection of bridges have been demonstrated by the passive control systems with mechanical links with selective viscoelastic energy dissipation through viscous friction and dry friction. These systems are able to take over the deformations and movements caused by temperature variations, those due to seismic activities and from road traffic. A number of natural factors such as atmospheric and anthropogenic parameters, such as shock and vibration from road traffic, lead to the …degradation of the viscoelastic bonds of passive control systems based on rubber molding. The presence of the elastic and dissipative nonlinear forces in the functioning of antiseismic systems inevitably leads to quantitative and qualitative changes of the structural responses of bridges and viaducts both in time and spectral domains. The implications of these changes on the integrity and stability of the bridge or viaduct sections may be from the simplest to the most severe depending on the type of seismic excitation to which they are subjected. For these reasons, it is imperative that we should identify and quantify the degree of nonlinearity of antiseismic systems embedded in the structure of bridges and viaducts in order to prevent accidents with severe socioeconomic implications. In this way can determine the dependence of the nonlinear behavior of the bearing system and the degree of degradation of their viscoelastic links. From a theoretical point of view the following parameters of the vibration of the system will be comparatively analyzed: the displacement and acceleration of the bridge deck in time and frequency domains, the hysteretic loop, the representation in the plane of phases, the power spectral density and the spectrograms of the acceleration signals. From an experimental point of view there will be identified and plotted the parameters able to provide information regarding the abnormal operation of the bearings from the elastomer: system acceleration, representations in time and frequency and its spectrogram. Show more

Keywords: Dynamic, viscoelastic, vibration, nonlinear, rubber

DOI: 10.3233/SAV-2012-0699

Citation: Shock and Vibration, vol. 19, no. 5, pp. 915-928, 2012

Authors: Enss, G.C. | Platz, R. | Hanselka, H.

Article Type: Research Article

Abstract: Buckling of load-carrying column structures is an important design constraint in light-weight structures as it may result in the collapse of an entire structure. When a column is loaded by an axial compressive load equal to its individual critical buckling load, a critically stable equilibrium occurs. When loaded above its critical buckling load, the passive column may buckle. If the actual loading during usage is not fully known, stability becomes highly uncertain. This paper …presents an approach to control uncertainty in a slender flat column structure critical to buckling by actively stabilising the structure. The active stabilisation is based on controlling the first buckling mode by controlled counteracting lateral forces. This results in a bearable axial compressive load which can be theoretically almost three times higher than the actual critical buckling load of the considered system. Finally, the sensitivity of the presented system will be discussed for the design of an appropriate controller for stabilising the active column. Show more

Keywords: Uncertainty, buckling, active stabilisation

DOI: 10.3233/SAV-2012-0700

Citation: Shock and Vibration, vol. 19, no. 5, pp. 929-937, 2012

Authors: Souza, L.C.G. | Gonzáles, R.G.

Article Type: Research Article

Abstract: Design of Satellite Attitude Control System (ACS) that involves plant uncertainties and large angle manoeuvres following a stringent pointing control, may require new non-linear control techniques in order to have adequate stability, good performance and robustness. In that context, experimental validation of new non-linear control techniques through prototypes is the way to increase confidence in the controller designed. The Space Mechanics and Control Division (DMC) of INPE is constructing a 3-D simulator to …supply the conditions for implementing and testing satellite ACS hardware and software. The 3-D simulator can accommodate various satellites components; like sensors, actuators, computers and its respective interface and electronic. Depending on the manoeuvre the 3-D simulator plant can be highly non-linear and if the simulator inertia parameters are not well determined the plant also can present some kind of uncertainty. As a result, controller designed by linear control technique can have its performance and robustness degraded, therefore controllers designed by new non-linear approach must be considered. This paper presents the application of the State-Dependent Riccati Equation (SDRE) method in conjunction with Kalman filter technique to design a controller for the DMC 3-D satellite simulator. The SDRE can be considered as the non-linear counterpart of Linear Quadratic Regulator (LQR) control technique. Initially, a simple comparison between the LQR and SDRE controller is performed. After that, practical applications are presented to address problems like presence of noise in process and measurements and incomplete state information. Kalman filter is considered as state observer to address these issues. The effects of the plant non-linearities and noises (uncertainties) are considered in the performance and robustness of the controller designed by the SDRE and Kalman filter. The 3-D simulator simulink-based model has been developed to perform the simulations examples to investigate the SDRE controller performance using the states estimated by the Kalman filter. Simulations have demonstrated the validity of the proposed approach, once the SDRE controller has presented good stability margin, great performance and robustness. Show more

Keywords: Satellite simulator, SDRE methodology, robust control

DOI: 10.3233/SAV-2012-0701

Citation: Shock and Vibration, vol. 19, no. 5, pp. 939-946, 2012

Authors: Mainenti-Lopes, I. | Souza, L.C.G. | De Sousa, F.L.

Article Type: Research Article

Abstract: The Attitude Control System (ACS) for Flexible Space Structures (FSS) like rigid-flexible satellite and solar sails demands great reliability, autonomy and robustness. The association of flexible motion and large angle maneuver imply that the FSS dynamics is only captured by complex non-linear mathematical model. As a result, FSS controller performance designed by linear control technique under the hypothesis of rigid dynamic can be degraded. Although vibrations can be suppressed rapidly, the flexibility effect can …introduce a tracking error resulting in a minimum attitude acquisition time. On the other hand, faster manoeuvres can excite flexible modes in such a way to make the FSS lose the required pointing accuracy. In the present work, it is shown that a new multi-objective optimization algorithm, called M-GEOreal (Multi-objective Generalized Extremal Optimization with real codification), is a good tool to be used in such kind of problems. The M-GEOreal is a real coded version of the M-GEO evolutionary algorithm. Its performance on finding the gains of a non linear control law is evaluated through its application to the problem of controlling a large angle attitude manoeuvre of a rigid-flexible satellite.. The satellite non-linear model consists of a rigid central hub with a clamped free flexible beam. The multi-objective approach allows optimizing conflicting objective functions like time and energy. As a result, one can find a trade-off solution (non-dominated solutions). These solutions become available to the designer for posterior choice of an individual solution to be implemented. The non-dominated solutions are represented in the design space (Pareto set) and in the objective functions space (Pareto front). Having in mind the complexity of implementing a control algorithm in onboard satellite computer, this preliminary investigation has shown that the non-linear controller based on the M-GEOreal algorithm is a promising technique, since it has satisfied all the ACS requirements. A great advantage of the M-GEOreal procedure is its capacity to deal with non-linear system and designing non-linear controller with constant gains facilitating the on board computer implementation. Show more

Keywords: Nonlinear controller, flexible satellite, multi-objective optimization, Generalized Extremal Optimization

DOI: 10.3233/SAV-2012-0702

Citation: Shock and Vibration, vol. 19, no. 5, pp. 947-956, 2012

Authors: Hamdin, H.A.M. Ben | Tanner, G.

Article Type: Research Article

Abstract: We describe a multi-component boundary element method for predicting wave energy distributions in a complex built-up system with material properties changing discontinuously at boundaries between sub-components. We point out that depending on the boundary conditions and the number of interfaces between sub-components, it may be advantageous to use a normal derivative method to set up the integral kernels. We describe how the resulting hypersingular integral kernels can be regularised. The method can be used to minimise …the number of weakly singular integrals thus leading to BEM formulations which are easier to handle. Show more

Keywords: Multi-component boundary element method, hypersingular integral, Helmholtz equation, green function

DOI: 10.3233/SAV-2012-0703

Citation: Shock and Vibration, vol. 19, no. 5, pp. 957-967, 2012

Authors: Bellino, A. | Marchesiello, S. | Garibaldi, L.

Article Type: Research Article

Abstract: It is well known that nonlinear systems, as well as linear time-varying systems, are characterized by non-stationary response signals. In this sense, they both show natural frequencies that are not constant over time; this variation has however different origins: for a time-varying system the mass, and possibly the stiffness distributions, are changing over time, while for a nonlinear system the natural frequencies are amplitude-dependent. An interesting case of time-varying system occurs when analyzing the transit of …a train over a railway bridge, easily simulated by the crossing of a moving load over a beam. In this case, the presence of a nonlinearity in the beam behaviour can cause a significant alteration of the modal parameters extracted from the linearized model, such that the contributions of the two effects are no more distinguishable. For this study, some reinforced concrete beams have been tested in the framework of a vast project: these beams show a clear softening nonlinear behaviour, well detectable when the excitation is produced by a hammer (free response). If the passage of a carriage is considered, moreover, the variation of natural frequencies is always larger than expected because of this softening nonlinearity. The article first analyzes theoretically the two effects on the natural frequencies of a simply supported beam, then a numerical and an experimental tests are presented. The identification procedure is conducted with a linear algorithm called ST-SSI, which has been demonstrated to be appropriate for the analysis of non-stationary signals, in particular in presence of moving masses. The article shows that the nonlinear contribution can be well estimated by using this linear tool but, on the contrary, when also moving masses are present, it is difficult to separate the nonlinear effects from the time varying ones. Show more

Keywords: Moving load, nonlinear behaviour, Short Time Stochastic Subspace Identification, concrete reinforced beams

DOI: 10.3233/SAV-2012-0704

Citation: Shock and Vibration, vol. 19, no. 5, pp. 969-978, 2012