Drilling Riser Model Tests for Software Verification

Abstract

Marine drilling riser is subject to complicated environmental loads which include top motions due to Mobile Offshore Drilling Unit (MODU), wave loads and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling riser system, especially at the subsea well head (WH). Statoil and BP have carried out a comprehensive model test program on drilling riser in MARINTEK’s Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling riser behaviour under various environmental conditions by use of model test data. Six drilling riser configurations were tested, including different components such as Upper Flex Joint (UFJ), tensioner, marine riser, Lower Marine Riser Package (LMRP), Blow-Out Preventer (BOP), Lower Flex Joint (LFJ), buoyancy elements and seabed boundary model. The drilling riser models were tested in different load conditions: 1. Forced top motion tests 2. Regular wave test 3. Combined regular wave and towing test 4. Irregular wave test 5. Combined irregular wave and towing test 6. Towing test (VIV) Measurements were made of micro bending strains and accelerations along the riser in both In-Line (IL) and Cross-Flow (CF) directions. Video recordings were made both above and under water. In this paper, the test set-up and test program are presented. Comparisons of results between model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling riser model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between model test and RIFLEX simulation is promising.

Effectiveness of the segment method in absolute and joint coordinates when modelling risers

“…It can be seen that the differences, as in the case of using the Riflex package, are smaller than 10.5%. In summary, the validation process has proved that the results obtained during the analysis of both free and forced vibrations are compatible with experimental measurements and the calculation results presented in [66] and [67]. Formulation of the segment method in joint coordinates has been used, and in order to calculate frequencies of free vibrations a procedure presented in [60] has been applied.…”

“…Validation of the segment method is carried out on the basis of well-documented results of experimental measurements and numerical calculations presented in [66,67]. The model of the riser analysed is shown in Fig.…”

“…Table 8 presents the first three frequencies of free vibrations of the riser from Fig. 16a obtained by experimental measurements (E), the Riflex program (R) as in [66], the segment method (S), and calculated analytically (A) from the following formula: where L is the length of the riser, i is the number of the free frequency. Using this formula, it is assumed that buoyancy forces act along the whole length of the riser.…”