10CrMo9-10
2011年5月2日 by admin
As we know, vortex-induced vibration (VIV) can cause large stress and fatigue damage of slender marine structures. With the increasing interest in worldwide deep-water petroleum production, more efforts have been put on the research activities on VIV. Base on tracing the recent direction in the worldwide research on VIV and summarizing the research productions, the real scale Reynolds number flexible riser has been chosen as the subject investigated in this thesis, and the main contents including experimental investigations base on similar model and real scale model.The main contents and contributions of this thesis can be summatized as follows:1.A test system which can conduct VIV experiment of real scale Reynolds number flexible riser in different flow fields with a longer valid test period is developed. The test system incude a rotate T-type test rig, a new method of making real scale riser model,and a new method of making helical strakes which is a kind of VIV suppression device. The work theory of the test rig is as the following description, the riser model is installed on the T-type test rig , and the test rig rotate in the ocean engineering basin to make a relative water flow. The real scale riser model will be installed with fiber optic bragg grating strain sensor, which can be used without electromagnetic interference and structural damage. By the new method of making helical strakes which is based on the helix line theoy, the experimentation cost is saved, and helical strakes with many different sizes can be achived.2.To study the re10CrMo9-10
lationship between the model test results and the full scale responses of the VIV of the riser, in this part, the strategies of the modification of the model test velocity are investigated. Base on the numerical VIV prediction theory, similarity theory analysis of the model test, the modification strategies of the model test velocity are found and verified by plenty of numerical simulation cases.3.A real scale Reynolds number VIV test in shear current was performed in the State Key Laboratory of Ocean Engneering of SJTU using the tset system developed in the thesis. Two risers with the diameters 30mm and 168.3mm were tested. And the bare riser was tested for benchmarking, and the performance of 8 strake geometries was then evaluated.From the above-mentioned works, it can be concluded that:1.The test system was proved to be stable and reliable by the real scale Reynolds number VIV test performed in SKLOE of SJTU.2.The result of the experimental investigation base on similarity model shows that, mode number and response RMS (A/D) of the riser model will have a good agreement with those of the full scale riser, if we modify the model test velocity, and therefore increase the Re number in the model test. As a study case, the relationship of the full scale velocity and model test velocity is finally given out by a curve fitting function.3.In the real scale Reynolds number VIV test, both CF (cross-flow) and IL (in-line) responses were recorded in terms of strain. Riser displacements were reconstructed by decomposing instantaneous strain signal into structural modal contribution. Test results shows that: 1) In shear current, all strake geometries were effective in suppressing VIV; 2) There is no obvious difference between different strake geometries in suppressing VIV in shear current field. For NO.1 riser, the suppression efficiency of all strake geometries up to 96.25%, and for the NO.2 riser, the number is93.96%; 3) The height of the strke shows minor impact on the suppression efficiency in shear cureent; 4) The drag force of the riser during the test increasing with the height of the strake, but shows no significant change with the pitch of the strake; 5) Scale effect is not obviously for the VIV test of helical strakes in shear current.
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