Mandic, Danilo P.

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Mandic, Danilo P.
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Mandic, Danilo P.

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  • Publication
    A comprehensive study of the delay vector variance method for quantification of nonlinearity in dynamical systems
    (The Royal Society, 2016-01-01)
    Jaksic, Vesna 
    ;
    Mandic, Danilo P. 
    ;
    Ryan, Kevin M. 
    ;
    Basu, Biswajit 
    ;
    Pakrashi, Vikram 
    Although vibration monitoring is a popular method to monitor and assess dynamic structures, quantification of linearity or nonlinearity of the dynamic responses remains a challenging problem. We investigate the delay vector variance (DVV) method in this regard in a comprehensive manner to establish the degree to which a change in signal nonlinearity can be related to system nonlinearity and how a change in system parameters affects the nonlinearity in the dynamic response of the system. A wide range of theoretical situations are considered in this regard using a single degree of freedom (SDOF) system to obtain numerical benchmarks. A number of experiments are then carried out using a physical SDOF model in the laboratory. Finally, a composite wind turbine blade is tested for different excitations and the dynamic responses are measured at a number of points to extend the investigation to continuum structures. The dynamic responses were measured using accelerometers, strain gauges and a Laser Doppler vibrometer. This comprehensive study creates a numerical and experimental benchmark for structurally dynamical systems where output-only information is typically available, especially in the context of DVV. The study also allows for comparative analysis between different systems driven by the similar input.
      543Scopus© Citations 16
  • Publication
    A Delay Vector Variance based Marker for an Output-Only Assessment of Structural Changes in Tension Leg Platforms
    (IOP Publishing, 2015-07-09)
    Jaksic, Vesna 
    ;
    Wright, C.S. 
    ;
    Mandic, Danilo P. 
    ;
    Murphy, Jeremiah G. 
    ;
    Pakrashi, Vikram 
    Although aspects of power generation of many offshore renewable devices are well understood, their dynamic responses under high wind and wave conditions are still to be investigated to a great detail. Output only statistical markers are important for these offshore devices, since access to the device is limited and information about the exposure conditions and the true behaviour of the devices are generally partial, limited, and vague or even absent. The markers can summarise and characterise the behaviour of these devices from their dynamic response available as time series data. The behaviour may be linear or nonlinear and consequently a marker that can track the changes in structural situations can be quite important. These markers can then be helpful in assessing the current condition of the structure and can indicate possible intervention, monitoring or assessment. This paper considers a Delay Vector Variance based marker for changes in a tension leg platform tested in an ocean wave basin for structural changes brought about by single column dampers. The approach is based on dynamic outputs of the device alone and is based on the estimation of the nonlinearity of the output signal. The advantages of the selected marker and its response with changing structural properties are discussed. The marker is observed to be important for monitoring the as- deployed structural condition and is sensitive to changes in such conditions. Influence of exposure conditions of wave loading is also discussed in this study based only on experimental data.
      267Scopus© Citations 2
  • Publication
    Estimation of nonlinearities from pseudodynamic and dynamic responses of bridge structures using the Delay Vector Variance method
    (Elsevier, 2016-01-01)
    Jaksic, Vesna 
    ;
    Mandic, Danilo P. 
    ;
    Karoumi, Raid 
    ;
    Basu, Biswajit 
    ;
    Pakrashi, Vikram 
    Analysis of the variability in the responses of large structural systems and quantification of their linearity or nonlinearity as a potential non-invasive means of structural system assessment from output-only condition remains a challenging problem. In this study, the Delay Vector Variance (DVV) method is used for full scale testing of both pseudo-dynamic and dynamic responses of two bridges, in order to study the degree of nonlinearity of their measured response signals. The DVV detects the presence of determinism and nonlinearity in a time series and is based upon the examination of local predictability of a signal. The pseudo-dynamic data is obtained from a concrete bridge during repair while the dynamic data is obtained from a steel railway bridge traversed by a train. We show that DVV is promising as a marker in establishing the degree to which a change in the signal nonlinearity reflects the change in the real behaviour of a structure. It is also useful in establishing the sensitivity of instruments or sensors deployed to monitor such changes.
      418Scopus© Citations 9