Shock and Vibration - Volume 19, issue 5

Article Type: Other

DOI: 10.3233/SAV-2012-0725

Citation: Shock and Vibration, vol. 19, no. 5, pp. 763-763, 2012

Authors: Avitabile, Peter | Pingle, Pawan

Article Type: Research Article

Abstract: Dynamic response is an important consideration for design of structures due to operating or occasional loadings. The resulting dynamic stress strain is also of concern for fatigue and structural health monitoring. Typically, the actual loading and structural condition (boundary conditions, environmental condition, geometry, mechanical properties, etc.) are not necessarily known. Much effort is expended in attempting to identify the loads and appropriate model for prediction of these types of events. At best, the …forces and actual boundary conditions are approximate and have an effect on the overall predicted response and resulting stress-strain that is identified for subsequent evaluation. Experimental data can only be obtained from limited sets of points, such as those typically collected with accelerometers. These are normally used in the evaluation the state of a structure in service condition. More recently, Digital Image Correlation (DIC) and Dynamic Photogrammetry (DP) have become very important techniques to measure the surface response. These are non-contact and full-field techniques, which allow that much more simultaneous data to be measure. The sets of limited surface data that are collected can be used in conjunction with an expansion algorithm to obtain full field information. The finite element model mass and stiffness matrices are used to obtain the normal constitutive relations as well as the modal characteristics. This information is used to develop the expansion algorithm and for the stress recovery during the back substitution process typically employed. Show more

Keywords: Full field dynamic strain prediction, response prediction, dynamic response, full field response

DOI: 10.3233/SAV-2012-0686

Citation: Shock and Vibration, vol. 19, no. 5, pp. 765-785, 2012

Authors: Buff, H. | Friedmann, A. | Koch, M. | Bartel, T. | Kauba, M.

Article Type: Research Article

Abstract: Structural Health Monitoring (SHM) has reached a high importance in numerous fields of civil and mechanical engineering. Promising damage detection approaches like the Damage Index Method, Gapped Smoothing Technique and Modal Strain Energy Method require the structure's mode shapes [1]. Long term modal data acquisition on real life structures requires a computational efficient system based on a measuring method that can easily be installed. Systems using the Random Decrement Method (RDM) are composed of a …decentralized network of smart acceleration sensors applied for both, triggering and pure measuring. They allow the reduction of cabling effort and computational costs to a minimum. In order to design a RDM measuring network efficiently, an approved procedure for defining hardware as well as measuring settings is required. In addition, optimal sensor positions have to be defined. However, today those decisions are mostly based on expert's knowledge. In this paper a systematic and analytical procedure for defining the hardware requirements and measuring settings as well as optimal sensor positions is presented. The proposed routine uses the outcome of an Experimental Modal Analysis (EMA). Due to different requirements for triggering and non-triggering sensors in the RDM network a combination of two approaches for sensor placement has to be used in order to find the best distribution of measurement points over the structure. A controllability based technique is used for placing triggering sensors, whereas the Effective Independence (EI) is utilized for the placement of non-triggering sensors. The combination of these two techniques selects the best set of measuring points for a given number of sensors out of all possible sensor positions. Damage detection itself is not considered within the scope of this paper. Show more

Keywords: Structural health monitoring, test planning, effective independence

DOI: 10.3233/SAV-2012-0687

Citation: Shock and Vibration, vol. 19, no. 5, pp. 787-794, 2012

Authors: Nguyen, V.H. | Rutten, C. | Golinval, J.-C.

Article Type: Research Article

Abstract: In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In machine condition monitoring, the number of available vibration sensors is often small and it is not unusual that only one single sensor is used to monitor a machine. The aim of this paper is to propose an extension of fault detection techniques that may be used …when a reduced set of sensors or even one single sensor is available. Fault detection techniques considered here are based on output-only methods coming from the Blind Source Separation (BSS) family, namely Principal Component Analysis (PCA) and Second Order Blind Identification (SOBI). The advantages of PCA or SOBI rely on their rapidity of use and their reliability. Based on these methods, subspace identification may be performed by using the concept of block Hankel matrices which make possible the use of only one single measurement signal. Thus, the problem of fault detection in mechanical systems can be solved by using subspaces built from active principal components or modal vectors. It consists in comparing subspace features between the reference (undamaged) state and a current state. The angular coherence between subspaces is a good indicator of a dynamic change in the system due to the occurrence of faults or damages. The robustness of the methods is illustrated on industrial examples. Show more

Keywords: Fault diagnosis, damage detection, vibration monitoring, Hankel matrices

DOI: 10.3233/SAV-2012-0688

Citation: Shock and Vibration, vol. 19, no. 5, pp. 795-801, 2012

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

Article Type: Research Article

Abstract: This paper deals with the theoretical aspects combined with experimental analysis regarding early damage identification in passive vibro-isolation devices. Basically, this research presents the relevant results obtained for a singular element. Rubber based on elements is discussed especially. This study was a naturally fall-back of the authors large analysis regarding the dynamic behaviour of the passive isolation devices against vibration, shocks and seismic waves. Main hypothesis supposed that on the exploitation time, …all technical devices and systems acquire different levels of wearing because of the dynamic overloads and their derivative influences (aging, fatigue, energy dissipation, external heating or cooling, etc.). Hereby the performance characteristics changes and the system becomes working improperly. Numerical simulations were developed for simple spatial configuration of isolation device. Stochastic approach of essential results was briefly presented nearby the relevant results and discussions. Show more

Keywords: Damage, identification, vibration, isolation, rubber

DOI: 10.3233/SAV-2012-0689

Citation: Shock and Vibration, vol. 19, no. 5, pp. 803-809, 2012

Authors: Palomino, L.V. | Tsuruta, K.M. | Mour, Jr, J.R.V. | Radea, D.A. | Steffen, Jr., V. | Inman, D.J.

Article Type: Research Article

Abstract: Structural Health Monitoring (SHM) is the process of damage identification in mechanical structures that encompasses four main phases: damage detection, damage localization, damage extent evaluation and prognosis of residual life. Among various existing SHM techniques, the one based on electromechanical impedance measurements has been considered as one of the most effective, especially in the identification of incipient damage. This method measures the variation of the electromechanical impedance of the structure as caused …by the presence of damage by using piezoelectric transducers bonded on the surface of the structure (or embedded into it). The most commonly used smart material in the context of the present contribution is the lead zirconate titanate (PZT). Through these piezoceramic sensor-actuators, the electromechanical impedance, which is directly related to the mechanical impedance of the structure, is obtained as a frequency domain dynamic response. Based on the variation of the impedance signals, the presence of damage can be detected. A particular damage metric can be used to quantify the damage. For the success of the monitoring procedure, the measurement system should be robust enough with respect to environmental influences from different sources, in such a way that correct and reliable decisions can be made based on the measurements. The environmental influences become more critical under certain circumstances, especially in aerospace applications, in which extreme conditions are frequently encountered. In this paper, the influence of electromagnetic radiation, temperature and pressure variations, and ionic environment have been examined in laboratory. In this context, the major concern is to determine if the impedance responses are affected by these influences. In addition, the sensitivity of the method with respect to the shape of the PZT patches is evaluated. Conclusions are drawn regarding the monitoring efficiency, stability and precision. Show more

Keywords: Structural health monitoring, damage detection, piezoceramic sensor-actuators

DOI: 10.3233/SAV-2012-0690

Citation: Shock and Vibration, vol. 19, no. 5, pp. 811-823, 2012

Authors: Torres-Arredondo, M.A. | Fritzen, C.-P.

Article Type: Research Article

Abstract: Acoustic Emission (AE) techniques are used for the structural health monitoring of civil, aeronautic and aerospace structures. Recently, these structures are made of composite materials due to their advantages over traditional materials, but this increases the interpretation complexity of the failure modes present. Therefore, in order to make AE a trustworthy technique, reliable source location and damage mechanism characterization must be accomplished. On that account, this work proposes a novel approach based on a …chirplet atomic decomposition, time-frequency energy distribution and dispersion analysis, where the failure-emitted signals are separated from extraneous noise and the detected modes are analyzed according to their dispersive behaviour and angular dependence characteristics. Dispersion relations are obtained by the use of a higher order plate theory on a non-absorbing anisotropic plate model, and then used in conjunction with the previous methodologies for mode identification and localization. The proposed methodology and model are validated, and the capability of the method to overcome practical issues encountered in AE testing is demonstrated experimentally. Show more

Keywords: Structural health monitoring, acoustic emission, structural dynamics, signal processing

DOI: 10.3233/SAV-2012-0691

Citation: Shock and Vibration, vol. 19, no. 5, pp. 825-833, 2012

Authors: Lopes, H. | Ribeiro, J. | Araújo dos Santos, J.V.

Article Type: Research Article

Abstract: This paper describes several interferometric techniques and their applications in structural damage identification. With that objective in mind, damaged aluminum beams with clamped-free and free-free boundary conditions are analyzed. Different damages cases are inflicted by creating small cuts perpendicular to the beams longitudinal axis, being the damage, therefore, characterized by the dimensions of these cuts. The out-of-plane displacement field of modal response is measured with an electronic speckle pattern interferometric system. The …static and dynamic rotation fields, defined as the spatial derivative of the displacement field, are measured with two different speckle shearography systems. Second and third order spatial derivatives of the displacement field, which are related to the bending moment and shear force, are computed by differentiation techniques. The cuts locations are determined by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces. This method is validated by comparing its results with numerical ones, from which the most suitable interferometric technique is chosen. Show more

Keywords: Damage identification, ESPI, speckle shearography, higher order spatial derivatives, beam

DOI: 10.3233/SAV-2012-0692

Citation: Shock and Vibration, vol. 19, no. 5, pp. 835-844, 2012

Authors: Meredith, J. | González, A. | Hester, D.

Article Type: Research Article

Abstract: Empirical Mode Decomposition (EMD) is a technique that converts the measured signal into a number of basic functions known as intrinsic mode functions. The EMD-based damage detection algorithm relies on the principle that a sudden loss of stiffness in a structural member will cause a discontinuity in the measured response that can be detected through a distinctive spike in the filtered intrinsic mode function. Recent studies have shown that applying EMD to the acceleration response, due …to the crossing of a constant load over a beam finite element model, can be used to detect a single damaged location. In this paper, the technique is further tested using the response of a discretized finite element beam with multiple damaged sections modeled as localized losses of stiffness. The ability of the algorithm to detect more than one damaged section is analysed for a variety of scenarios including a range of bridge lengths, speeds of the moving load and noise levels. The use of a moving average filter on the acceleration response, prior to applying EMD, is shown to improve the sensitivity to damage. The influence of the number of measurement points and their distance to the damaged sections on the accuracy of the predicted damage is also discussed. Show more

Keywords: Empirical Mode Decomposition, vibration-based analysis, damage detection, signal decomposition

DOI: 10.3233/SAV-2012-0693

Citation: Shock and Vibration, vol. 19, no. 5, pp. 845-856, 2012

Authors: Moreno-García, P. | Castro, E. | Romo-Melo, L. | Gallego, A. | Roldán, A.

Article Type: Research Article

Abstract: In this paper, two procedures for damage detection in Carbon Fiber-Reinforced Polymer (CFRP) plates are shown. One is based on the use of statistical frequency series to detect the presence of damage. This method was tested experimentally on a CFRP plate with induced damage. The other one is a procedure based on Ritz method and wavelet transform that was applied to the numerical vibration modes of a damaged CFRP plate. The former method can also be …used experimentally, even if the material engineering constants are unknown. Show more

Keywords: CFRP plates, SHM, damage detection, vibration test, Ritz method, wavelet analysis

DOI: 10.3233/SAV-2012-0694

Citation: Shock and Vibration, vol. 19, no. 5, pp. 857-865, 2012

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

Authors: Awrejcewicz, J. | Papkova, I.V. | Krylova, E.U. | Krysko, V.A.

Article Type: Research Article

Abstract: We investigate non-linear dynamics of flexible rectangular plates subjected to external shear harmonic load action. We show that an application of the classical and widely used Fourier analysis does not allow to obtain real picture of the frequency vibration characteristics in each time instant. On the other hand, we show that application of the wavelets approach allows to follow frequency time evolutions. Our numerical results indicate that vibrations in different plate points occur with the same …frequencies set although their power is different. Hence, the vibration characteristics can be represented by one arbitrary taken plate point. Furthermore, using wavelets scenarios of transitions from regular to chaotic dynamics are illustrated and discussed including two novel scenarios not reported so far in the existing literature. Show more

Keywords: Dynamics, plate, chaos, wavelets

DOI: 10.3233/SAV-2012-0705

Citation: Shock and Vibration, vol. 19, no. 5, pp. 979-994, 2012

Authors: Koziol, Piotr | Hryniewicz, Zdzislaw

Article Type: Research Article

Abstract: This paper presents a new semi-analytical solution for the Timoshenko beam subjected to a moving load in case of a nonlinear medium underneath. The finite series of distributed moving loads harmonically varying in time is considered as a representation of a moving train. The solution for vibrations is obtained by using the Adomian's decomposition combined with the Fourier transform and a wavelet-based procedure for its computation. The adapted approximating method uses wavelet filters of Coiflet type …that appeared a very effective tool for vibration analysis in a few earlier papers. The developed approach provides solutions for both transverse displacement and angular rotation of the beam, which allows parametric analysis of the investigated dynamic system to be conducted in an efficient manner. The aim of this article is to present an effective method of approximation for the analysis of complex dynamic nonlinear models related to the moving load problems. Show more

Keywords: Moving load, Timoshenko beam, nonlinear vibrations, wavelet approximation, Adomian's decomposition

DOI: 10.3233/SAV-2012-0706

Citation: Shock and Vibration, vol. 19, no. 5, pp. 995-1007, 2012

Authors: Koziol, Piotr | Neves, M.M.

Article Type: Research Article

Abstract: A wavelet based approach is proposed in this paper for analysis and optimization of the dynamical response of a multilayered medium subject to a moving load with respect to the material properties and thickness of supporting half-space. The investigated model consists of a load moving along a beam resting on a surface of a multilayered medium with infinite thickness and layers with different physical properties. The theoretical model is described by the Euler-Bernoulli equation for the …beam and the Navier's elastodynamic equation of motion for a viscoelastic half-space. The moving load is modelled by a finite series of distributed harmonic loads. A special method based on a wavelet expansion of functions in the transform domain is adopted for calculation of displacements in the physical domain. The interaction between the beam and the multilayered medium is analyzed in order to obtain the vibration response at the surface and the critical velocities associated. The choice of the specific values of the design parameters for each layer, which minimize the vibration response of the multilayered medium, can be seen as a structural optimization problem. A first approach for using optimization techniques to explore the potential of the wavelet model is presented and briefly discussed. Results from the analysis of the vibration response are presented to illustrate the dynamic characterization obtained by using this method. Numerical examples reflecting the results of numerical optimizations with respect to a multilayered medium parameters are also presented. Show more

Keywords: Multilayered half-space, wavelet-based approximation, vibrations, structural optimization, distributed moving load

DOI: 10.3233/SAV-2012-0707

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1009-1018, 2012

Authors: Moita, P.P. | Cardoso, J.B. | Barreiros, A.

Article Type: Research Article

Abstract: This paper presents an integrated approach to optimize for design and control of mechanical systems with random input parameters. Random parameters are represented by probability density functions. A numerical technique defining directly the representative values and the associated probabilities is implemented by modeling the stochastic parameters as generalized Wiener processes. The Monte Carlo¡¯s method is also implemented to deal with correlated parameters. A design and control sensitivity analysis optimization formulation is derived. …A conceptual separation between time variant and time invariant design parameters is presented, this way including the design space into the control space and considering the design variables as control variables not depending on time. By using time integrals through all the derivations, the design and control problems are unified. In the optimization process we can use both types of variables simultaneously or by interdependent levels. The dynamic response is modeled via space and time finite elements, and is integrated either by at-once integration or step-by-step. The formulation is applied to a numerical example. Show more

Keywords: Space-time finite elements, adjoint system, stochastic modeling, wiener processes

DOI: 10.3233/SAV-2012-0708

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1019-1025, 2012

Authors: Spencer, A.B. | Worden, K. | Staszewski, W.J. | Rongong, J.A. | Sims, N.D.

Article Type: Research Article

Abstract: The paper demonstrates the application of guided ultrasonic waves for estimating material elastic properties in multi-layered composite plates. Two-dimensional Lamb wave propagation is modelled using the Local Interaction Simulation Approach (LISA). The wave responses are then used to estimate relevant material properties. This numerical inverse method is based on an optimisation scheme using a Differential Evolution (DE) algorithm. The method is demonstrated on a simulated seven-layered glass fibre-epoxy composite plate. The results …show a good agreement between the exact and reconstructed material properties. Show more

Keywords: Glass fibres, layered structures, mechanical properties, computational modelling, ultrasonics

DOI: 10.3233/SAV-2012-0709

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1027-1040, 2012

Authors: Sall, A.C. | Thouverez, F. | Blanc, L. | Jean, P.

Article Type: Research Article

Abstract: Stator vanes which are found in axial compressors are subject to vibratory fatigue. Their division into monoblock sectors makes the prediction of their vibratory behaviour difficult by deterministic methods due to the loss of the cyclic symmetry properties and also to a high sensitivity to mistuning. The purpose is to present a robust calculation strategy based on a stochastic modelisation of the structure. The methodology has been developed first on a simplified model and then applied …to an industrial case. Polynomial chaos based results are in good agreement with reference Monte Carlo simulations. Show more

Keywords: Blades vibration, mistuning, uncertainties, polynomial chaos

DOI: 10.3233/SAV-2012-0710

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1041-1050, 2012

Authors: Devin, A. | Fanning, P.J.

Article Type: Research Article

Abstract: Structures include elements designated as load bearing and non-load bearing. While non-load bearing elements, such as facades and internal partitions, are acknowledged to add mass to the system, the structural stiffness and strength is generally attributed to load bearing elements only. This paper investigates the contribution of non-load bearing elements to the dynamic response of a new structure, the Charles Institute, in the grounds of University College Dublin (UCD) Ireland. The vertical vibration response of the …first floor and the lateral response at each floor level were recorded at different construction stages. The evolution of the structural response as well as the generation of a finite element (FE) model is discussed. It was found that the addition of the non-load bearing facades increased the first floor natural frequency from 10.7 Hz to 11.4?Hz, a change of approximately +6.5%. Similarly these external facades resulted in the first sway mode having its frequency increased by 6%. The subsequent addition of internal partitions, mechanical services and furnishings resulted in the floor natural frequency reducing to 9.2 Hz. It is concluded that external facades have the net effect of adding stiffness and the effect of internal partitions and furnishings is to add mass. In the context of finite element modelling of structures there is a significant challenge to represent these non-structural elements correctly so as to enable the generation of truly predictive FE models. Show more

Keywords: Operational modal analysis, frequency domain decomposition, non-structural elements

DOI: 10.3233/SAV-2012-0711

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1051-1059, 2012

Authors: Kodama, N. | Komiya, K.

Article Type: Research Article

Abstract: The forces applied to a structure from the soil ground during an earthquake and the dynamic response of a structure are problems that are not well understood. In recent years, seismic design technology aided by numerical simulation is under active development. Successful improvement of the accuracy and reliability of numerically simulated results relies on a clear understanding of the seismic force transmission mechanism between the soil and a structure associated with mechanical properties of soil. …In this study, laboratory shaking tests were conducted using the unique apparatus designed to have a structure move only by its inertial force and the lateral earth pressure that comes from surrounding sandy soils. The earth pressure at the structure surface and the relative displacement between the soil and the structure were measured in the experiments under various conditions. A new Finite Element interface model for sandy soil-structure dynamic interaction is proposed from the experimental results. Estimated seismic responses of a bridge pier calculated by the proposed interface model, conventional linear elastic model and tension cut-off model are compared. Show more

Keywords: Soil-structure dynamic interaction, laboratory shaking test, finite element method, earthquake

DOI: 10.3233/SAV-2012-0712

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1061-1069, 2012

Authors: Devriendt, Christof | De Troyer, Tim | De Sitter, Gert | Guillaume, Patrick

Article Type: Research Article

Abstract: During the recent years several new tools have been introduced by the Vrije Universiteit Brussel in the field of Operational Modal Analysis (OMA) such as the transmissibility based approach and the the frequency-domain OMAX concept. One advantage of the transmissibility based approach is that the ambient forces may be coloured (non-white), if they are fully correlated. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal …Analysis: ambient (unknown) forces as well as artificial (known) forces are processed simultaneously resulting in improved modal parameters. In this paper, the transmissibility based output-only approach is combined with the input/output OMAX concept. This results in a new methodology in the field of operational modal analysis allowing the estimation of (scaled) modal parameters in the presence of arbitrary ambient (unknown) forces and artificial (known) forces. Show more

Keywords: Operational modal analysis, transmissibility, flutter

DOI: 10.3233/SAV-2012-0713

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1071-1083, 2012

Authors: De Sitter, Gert | Devriendt, Christof | Guillaume, Patrick

Article Type: Research Article

Abstract: Recently it has been shown that also transmissibilities can be used to identify the modal parameters. This approach has several advantages: because of the deterministic character of the transmissibility functions, the estimated parameters are more accurate than the results obtained with the power spectra based operational modal analysis techniques. Another advantage is that the transmissibility functions do not depend on the colouring of the unknown forces. A disadvantage of the transmissibility based operational modal analysis …techniques is that non-physical modes show up in the stabilisation diagrams. In this contribution it will first be shown that those non-physical modes will show up when traditional stabilisation diagrams are used. In a second step, a new approach of selecting the physical modes out of a set of estimated modes will be discussed and the new approach will be validated using data generated with an acoustical Finite Element Model. Finally, the approach will be validated using real acoustical data. Show more

Keywords: Operational modal analysis, transmissibilities, stabilisation diagrams

DOI: 10.3233/SAV-2012-0714

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1085-1097, 2012

Authors: Soria, L. | Peeters, B. | Anthonis, J.

Article Type: Research Article

Abstract: Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is of fundamental importance to obtain satisfying results. Operational Modal Analysis allows the experimental structural identification in those that are the real operating conditions: Moving from output-only …data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper two suspension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kinds of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test. Show more

Keywords: Operational Modal Analysis, vehicle suspension systems, semi-active and active dampers

DOI: 10.3233/SAV-2012-0715

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1099-1113, 2012

Authors: Awrejcewicz, J. | Kudra, G.

Article Type: Research Article

Abstract: The integral model of dry friction components is built with assumption of classical Coulomb friction law and with specially developed model of normal stress distribution coupled with rolling resistance for elliptic contact shape. In order to avoid a necessity of numerical integration over the contact area at each the numerical simulation step, few versions of approximate model are developed and then tested numerically. In the numerical experiments the simulation results of the Celtic stone with the …friction forces modelled by the use of approximants of different complexity (from no coupling between friction force and torque to the second order Padé approximation) are compared to results obtained from model with friction approximated in the form of piecewise polynomial functions (based on the Taylor series with hertzian stress distribution). The coefficients of the corresponding approximate models are found by the use of optimization methods, like as in identification process using the real experiment data. Show more

Keywords: Celtic stone, Coulomb-Contensou-Zhuravlev friction model, rolling resistance

DOI: 10.3233/SAV-2012-0716

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1115-1123, 2012

Authors: Schmidt, A. | Bograd, S. | Gaul, L.

Article Type: Research Article

Abstract: The vibration and damping characteristics of an assembled structure made of steel are investigated by an experimental modal analysis and compared with the results of a finite element modal analysis. A generic experiment is carried out to evaluate the stiffness and the damping properties of the structure's join patches. Using these results, an appropriate finite element model of the structure is developed where the join patches are represented by thin-layer elements containing material properties which are …derived from the generic experiment's results. The joint's stiffness is modeled by orthotropic material behavior whereas the damping properties are represented by the model of constant hysteresis, leading to a complex-valued stiffness matrix. A comparison between the experimental and the numerical modal analysis shows good agreement. A more detailed damping model in conjunction with an optimization procedure for the joint's parameters results in an improved correlation between the experimental and the numerical modal quantities and reveals that the results of the generic experiment are sound. Show more

Keywords: Damping, constant hysteresis, finite element method, thin-layer elements

DOI: 10.3233/SAV-2012-0717

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1125-1133, 2012

Authors: Tehrani, M. Ghandchi | Ouyang, H.

Article Type: Research Article

Abstract: Many structures or machines interact with some internal nonconservative forces and present asymmetric systems in which the stiffness and damping matrices are asymmetric. Examples include friction-induced vibration and aeroelastic flutter. Asymmetric systems are prone to flutter instability as a result of the real parts of some poles becoming positive when certain system parameters vary. This paper presents a receptance-based inverse method for assigning a number of complex poles of second-order damped asymmetric …systems while keeping other unassigned poles unchanged. It uses state-feedback (active damping and active stiffness) to shift the poles to desired locations where all poles have negative real parts. Receptances at only a small, limited number of degrees-of-freedom of the underlying symmetric system are required. Simulated numerical examples indicate that this is an effective method and is capable of assigning negative real parts to unstable poles to stabilise an otherwise unstable second-order dynamic system. Show more

Keywords: Partial pole assignment, asymmetric system, friction-induced vibration, flutter instability, receptance, state feedback

DOI: 10.3233/SAV-2012-0718

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1135-1142, 2012

Authors: Carcaterra, A. | Roveri, N.

Article Type: Research Article

Abstract: This paper presents a novel approach to the study of shock in elastic structures. An energy storage property for linear elastic non-dissipative structures is demonstrated, then extrapolated also to damped systems. This property relates locations of energy accumulation along the structure to the form of its stiffness and mass matrices. This result can be profitable used at a design stage of complex structures undergoing shock excitations. On the theoretical ground, the obtained results disclose indeed …general properties of energy distribution in dynamical systems with implications on energy localization as well as on energy equipartitioning. Finally, these findings open a new point of view on energy transmission in structures, with potential application in the context of Statistical Energy Analysis. Show more

Keywords: Shock response, energy flow analysis, localization, equipartitioning, Statistical Energy Analysis

DOI: 10.3233/SAV-2012-0719

Citation: Shock and Vibration, vol. 19, no. 5, pp. 1143-1163, 2012