Deepstar Study on Predicting FPSO Responses - Model Tests VS Numerical Analysis

1. ABSTRACT This paper presents the correlation study of FPSO model tests and numerical analyses sponsored by the DeepStar program. The numerical analysis results of FPSO responses provided by SBM-IMODCO, FMC SOFEC Floating Systems, Inc., MARIN and MARINTEK have been compared with the model test results compiled by MARIN. The study demonstrated that the FPSO global responses can be well captured by the current state of the art analysis tools developed by the offshore industry. However, there are areas where further studies would be required to explain the test and analysis discrepancies. Through a series of sensitivity analyses, the study also highlighted a number of key parameters that can considerably influence the FPSO responses. 2. INTRODUCTION The DeepStar Program sponsored a series of tasks to evaluate the current industry capability in predicting the responses of deepwater theme structures, namely FPSO, TLP and SPAR. In its Phase IV program, engineering analyses of the theme structures were performed by the participating companies [Ref. 2] prior to the model tests conducted by MARIN [Refs. 3 & 5]. In the Phase V program, engineering companies and model test basins participated in a Post Model Test Study in conjunction with the development of Floater Design Guidelines. The study tasks include (i) evaluating correlation between the model tests and numerical predictions and (ii) conducting sensitivity analyses of key design parameters to support the Floater Design Guidelines development effort. Under the joint coordination of OTRC and DNV, two FPSO designers, SBM-IMOODCO (SBMI) and FMC SOFEC Floating Systems, Inc. (FMC SOFEC), and two deepwater model test basins, MARIN and MARINTEK, participated in the study to evaluate the FPSO system responses. A series of engineering analyses and sensitivity studies have been conducted. The results represent the current state of the art of the industry capability in predicting the FPSO global responses through the means of model tests and numerical analysis. This paper presents an overview of DeepStar's post model test study on FPSOs and covers the following subject areas:Model test setup and test conditions?The state-of-art analytical toolsEvaluation approach, e.g. model the modelKey results of comparisons - tests vs. analysesSensitivities and uncertainties in predicting FPSO responsesAssessment of current industry capabilitiesRecommended areas for future studies 3. STUDY DATA FPSO Model A 200,000 DWT tanker was selected for the purpose of model tests and engineering study. The model test scale is 1:87. The FPSO particulars (full scale) are presented in Table 3.1 and the lines plan is presented in Figure 3.1. Wind and Current Data In the tests, the tanker was provided with a relatively high bulwark and forecastle deck to prevent green water impact. Consequently, the FPSO wind area has been modified from the pre-test analysis. MARIN conducted wind load tests and provided the wind forces and moments data to be used in the study. The current loads were modeled using the OCIMF coefficients. Mooring and Riser System Data Four mooring systems have been developed for the study purpose.