Xie, Chen (2009-08). Statistical Estimation of Two-Body Hydrodynamic Properties Using System Identification. Doctoral Dissertation. Thesis uri icon

abstract

  • A basic understanding of the hydrodynamic response behavior of the two-body system is important for a wide variety of offshore operations. This is a complex problem and model tests can provide data that in turn can be used to retrieve key information concerning the response characteristics of such systems. The current study demonstrates that the analysis of these data using a combination of statistical tools and system identification techniques can efficiently recover the main hydrodynamic parameters useful in design. The computation of the statistical parameters, spectral densities and coherence functions provides an overview of the general response behavior of the system. The statistical analysis also guides the selection of the nonlinear terms that will be used in the reverse multi-input / single-output (R-MI/SO) system identification method in this study. With appropriate linear and nonlinear terms included in the equation of motion, the R-MISO technique is able to estimate the main hydrodynamic parameters that characterize the offshore system. In the past, the R-MISO method was primarily applied to single body systems, while in the current study a ship moored to a fixed barge was investigated. The formulation included frequency-dependant hydrodynamic parameters which were evaluated from the experimental measurements. Several issues specific to this extension were addressed including the computation load, the interpretation of the results and the validation of the model. Only the most important cross-coupling terms were chosen to be kept based on the estimation of their energy. It is shown that both the heading and the loading condition can influence system motion behavior and that the impact of the wave in the gap between the two vessels is important. The coherence was computed to verify goodness-of-fit of the model, the results were overall satisfying.
  • A basic understanding of the hydrodynamic response behavior of the two-body system is
    important for a wide variety of offshore operations. This is a complex problem and
    model tests can provide data that in turn can be used to retrieve key information
    concerning the response characteristics of such systems. The current study demonstrates
    that the analysis of these data using a combination of statistical tools and system
    identification techniques can efficiently recover the main hydrodynamic parameters
    useful in design.
    The computation of the statistical parameters, spectral densities and coherence functions
    provides an overview of the general response behavior of the system. The statistical
    analysis also guides the selection of the nonlinear terms that will be used in the reverse
    multi-input / single-output (R-MI/SO) system identification method in this study. With
    appropriate linear and nonlinear terms included in the equation of motion, the R-MISO
    technique is able to estimate the main hydrodynamic parameters that characterize the
    offshore system. In the past, the R-MISO method was primarily applied to single body
    systems, while in the current study a ship moored to a fixed barge was investigated. The formulation included frequency-dependant hydrodynamic parameters which were
    evaluated from the experimental measurements. Several issues specific to this extension
    were addressed including the computation load, the interpretation of the results and the
    validation of the model. Only the most important cross-coupling terms were chosen to
    be kept based on the estimation of their energy. It is shown that both the heading and the
    loading condition can influence system motion behavior and that the impact of the wave
    in the gap between the two vessels is important. The coherence was computed to verify
    goodness-of-fit of the model, the results were overall satisfying.

publication date

  • August 2009