A marine riser,one of the most important components of offshore oil/gas transportation,needs to be designed to eliminate the risks caused by complex ocean environments,platform displacement and internal corrosion,etc....A marine riser,one of the most important components of offshore oil/gas transportation,needs to be designed to eliminate the risks caused by complex ocean environments,platform displacement and internal corrosion,etc.In this study,a new analytical-numerical assessment approach is proposed in order to quantitatively investigate the reliability of internally corroded risers under combined loads including axial tension and internal pressure.First,an analytical solution of the limit state function of intact risers under combined loads is obtained,which is further modified by the non-dimensional corrosion depth （d/ t） for the risers with a narrow and long corrosion defect.The relationship between d/t and limited internal pressure is obtained by finite element analysis and nonlinear regression.Through an advanced first-order reliability method （HL-RF） algorithm,reliability analysis is performed to obtain the failure probability,the reliability index and the sensitivity.These results are further verified by Monte-Carlo importance sampling.The proposed approach of reliability analysis provides an accurate and effective way to estimate the reliability of marine risers with narrow and long corrosion defects under combined loads.展开更多
Automatic weld seam tracking technology to be used in hyperbaric underwater damaged pipeline repair welding is much more important,because of poor bevel preparation and severe working condition.A weld seam tracking sy...Automatic weld seam tracking technology to be used in hyperbaric underwater damaged pipeline repair welding is much more important,because of poor bevel preparation and severe working condition.A weld seam tracking system based on digital signal processing(DSP)passive light weld image processing technology has been established.A convenient charge coupled device(CCD)camera system was used in the high pressure environment with the help of an aperture and focus altering mechanism to guarantee overall image visibility in the scope of pressure below 0.7 MPa.The system can be used in the hyperbaric environment to pick up the real welding image of both the welding arc and the welding pool.The newly developed DSP technology was adopted to achieve the goal of system real time characteristics.An effective weld groove edge recognition technique including narrow interesting window opening,middle value wave filtering,Sobel operator weld edge detecting and edge searching in a defined narrow area was proposed to remove the guide error and system accuracy was ensured.The results of tracking simulation and real tracking application with arc striking have proved the validity and the accuracy of the mentioned system and the image processing method.展开更多
基金the National Basic Research Program of China(973 Program,Grant No.2011CB013702)the Beijing Natural Science Foundation(Grant No.KZ201210017017)
文摘A marine riser,one of the most important components of offshore oil/gas transportation,needs to be designed to eliminate the risks caused by complex ocean environments,platform displacement and internal corrosion,etc.In this study,a new analytical-numerical assessment approach is proposed in order to quantitatively investigate the reliability of internally corroded risers under combined loads including axial tension and internal pressure.First,an analytical solution of the limit state function of intact risers under combined loads is obtained,which is further modified by the non-dimensional corrosion depth （d/ t） for the risers with a narrow and long corrosion defect.The relationship between d/t and limited internal pressure is obtained by finite element analysis and nonlinear regression.Through an advanced first-order reliability method （HL-RF） algorithm,reliability analysis is performed to obtain the failure probability,the reliability index and the sensitivity.These results are further verified by Monte-Carlo importance sampling.The proposed approach of reliability analysis provides an accurate and effective way to estimate the reliability of marine risers with narrow and long corrosion defects under combined loads.
基金supported by National Hi-tech Research and Development Program of China(863 program,Grant No.2002AA602012)National Natural Science Foundation of China(Grant No.40776054)Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality of China
文摘Automatic weld seam tracking technology to be used in hyperbaric underwater damaged pipeline repair welding is much more important,because of poor bevel preparation and severe working condition.A weld seam tracking system based on digital signal processing(DSP)passive light weld image processing technology has been established.A convenient charge coupled device(CCD)camera system was used in the high pressure environment with the help of an aperture and focus altering mechanism to guarantee overall image visibility in the scope of pressure below 0.7 MPa.The system can be used in the hyperbaric environment to pick up the real welding image of both the welding arc and the welding pool.The newly developed DSP technology was adopted to achieve the goal of system real time characteristics.An effective weld groove edge recognition technique including narrow interesting window opening,middle value wave filtering,Sobel operator weld edge detecting and edge searching in a defined narrow area was proposed to remove the guide error and system accuracy was ensured.The results of tracking simulation and real tracking application with arc striking have proved the validity and the accuracy of the mentioned system and the image processing method.
