Comparison of Laboratory and Field Spar Platform Response Behavior

The design of deepwater offshore structures is often significantly influenced by the analysis of model basin data from large scale physical model tests. In these tests, great care is taken in the design, construction and verification of the model details. A test matrix typically includes regular waves, white noise spectrum tests and multiple realizations combining wind, wave and current conditions to simulate realistic design environments at a proposed offshore site. The objective clearly being to obtain enough quality data sets under well controlled laboratory conditions to reliably predict the extreme platform response statistics of interest. Great care is taken in selecting and executing the tests for each design environment, especially with regards to the specification of site specific conditions and assuring an adequate number of time series realizations are obtained. In sharp contrast, field data is obtained using the ambient environment with particular interest on the response of the ocean structure during events such as storms and eddy events. Those measurements reflect the often directional nature of the environmental excitation. This of course is quite different from the model basin tests data where the wind, wave and current environments are developed under controlled conditions. The measurement systems deployed offshore are generally keyed to sample at regularly scheduled intervals and are expected to capture samples from major design events including the build up and decay of a storm or other site specific events. This article focuses upon the statistical characterization and graphical interpretation needed to compare and contrast laboratory data with field measurements. Both single and sequenced data sets are analyzed and particular attention is directed at a time delayed sequence of field measurements.