Drilling Riser Model Test for Software Verification

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 wellhead (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. 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.acceptedVersio

Experimental and numerical study of a top tensioned drilling riser subjected to vessel motion

Model tests of a top tensioned riser (TTR) model were carried out as a part of a joint industry project, with the purpose of better understanding the dynamic behaviour of drilling riser and verifying the calculations of the riser analysis tools. Sinusoidal motion in one direction was imposed at the top end of the riser model to simulate vessel motion. The tests were carried out in still water, accelerations and bending strains were measured along the riser model. Numerical simulations were performed using RIFLEX and the predicted global responses were compared with the model tests. This paper discusses interesting aspects of this comparison as well as the general dynamic behaviour of the top tensioned riser. It was found that the dynamic responses of a TTR with vessel motion can consist of not only the in-line (IL) responses due to vessel motion at the riser top end, but also cross-flow (CF) vortex-induced vibrations (VIV) under conditions when Keulegan-Carpenter (KC) number is relatively small. CF VIV response is estimated using a time domain VIV prediction model and compared to the measured response. The main conclusion is that the IL global dynamic responses and CF VIV responses are predicted sufficiently well.acceptedVersio

Dynamic response of a top-tensioned riser under vessel motion

Model tests of a top-tensioned riser model were carried out as a part of a joint industry project, with the purpose of verifying the calculations of the riser analysis program RIFLEX. Sinusoidal motion in one direction was imposed at the top end of the riser model to simulate vessel motion. The tests were carried out in still water. Bending strain and acceleration were measured in both in-line (IL) and cross-flow (CF) directions along the riser model, so that the global response could be obtained through post-processing of the measured signals. Numerical simulations were performed and the results were compared with results from the model tests. This paper discusses interesting aspects of this comparison as well as the general dynamic behaviour of the top tensioned riser. It was found that the dynamic responses of a top tensioned riser with vessel motion can consist of not only the in-line responses due to vessel motion at the riser top end, but also cross-flow vortex-induced vibrations (VIV) under conditions when Keulegan–Carpenter number is relatively small. Cross-flow VIV response is estimated using the VIVANA software and compared to the measured response. The main conclusion is however that the riser analysis program RIFLEX can predict the global dynamic responses sufficiently well.acceptedVersio

Time Domain VIV Analysis Tool VIVANA-TD: Validations and Improvements

An empirical time-domain (TD) vortex-induced vibration (VIV) prediction model has been implemented in a software called VIVANA-TD based on its earlier development by Thorsen at NTNU. It models the synchronization of VIV loads and structural responses with a set of empirical parameters generalized from model tests. Combining this time domain hydrodynamic load model with a non-linear finite element structural model makes it possible to account for structural non-linearities and time-varying flow. A joint industry project (JIP), i.e., Lazy Wave Riser JIP has been organized to improve the design basis for SLWRs. This JIP is executed by SINTEF Ocean with support from NTNU. The industry participants are Equinor, BP, Subsea7, Kongsberg Maritime and Aker Solutions. The overall objective of this JIP is to systematically validate VIVANA-TD, in order to establish it as an industrial tool for VIV prediction. It is also aimed to improve the empirical basis and methods for calculation of VIV of deep-water steel lazy wave risers (SLWRs). In the present paper, the validation study is presented for selected model tests in constant flow conditions with uniform and sheared profiles. The test model includes bare pipe, pipe with partial strake coverage and riser model with staggered buoyancy elements. The empirical parameters have been generalized based on extensive model test data. Limitations and improvement of the model have been also been explored. The results show that the present TD model can represent reasonably the VIV loads and that the prediction has good agreement with measurements in general