This paper presents fatigue characteristic analysis of a deepwater steel catenary riser （SCR） under ambient excitations. The SCR involves complex nonlinear dynamic behaviors, especially at the touchdown point （TDP...This paper presents fatigue characteristic analysis of a deepwater steel catenary riser （SCR） under ambient excitations. The SCR involves complex nonlinear dynamic behaviors, especially at the touchdown point （TDP） where the riser first touches the seafloor. Owing to the significant interaction with soil, the touchdown zone is difficnlt to be modeled. Based on Lumped-Mass method and P-y curve, nonlinear springs are used to simulate the SCR-seabed coupled interaction. In case studies, an SCR＇s dynamic features have been obtained by transient analysis and the structure fatigue assessment has been carried out by S-N approach. The comparative analysis shows that the TDP is the key location where soil-riser interaction rises steeply and minimum fatigue life occurs. Parameters such as ocean environment loads, vessel motions, riser material and geometric parameters are discussed. The results indicate that the vessel motion is the principal factor for the structure fatigue life distribution.展开更多
A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at t...A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point （TDP）. The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.展开更多
The application of fracture in three-point bending to blanking of bearing steel is studied in this paper. Several mechanical models of stress blanking are discussed at first. And then the experiments have been made in...The application of fracture in three-point bending to blanking of bearing steel is studied in this paper. Several mechanical models of stress blanking are discussed at first. And then the experiments have been made in special equipment of three-point bending designed by us. Several problems, such as the suitable span, the relations between bending and tension bending complex, the ratio of blanking length to the diameter, the relations of blank length to force, the feature of fracture, are studied through the experiments. The suitable parameters of three-point bending to blanking, depth and tip radius of notch and the ratio between blanking length and stick diameter have been proposed.展开更多
With the development of technology for earthquake resistant,the research of the low yield point(LYP) steel which used for the fabrication of energy dissipation damper were paid more and more attention.The common studi...With the development of technology for earthquake resistant,the research of the low yield point(LYP) steel which used for the fabrication of energy dissipation damper were paid more and more attention.The common studies of the low yield point steel is mainly about the performance with constant amplitude and constant frequency.The low cycle fatigue properties of low yield piont steel were studied by series of test with continuous varying amplitude and varying frequency with the materials testing system by us.The test results showed that low yield point steel of Baosteel have excellent low cycle fatigue properties,which meet the requirement for steel used for the fabrication of energy dissipation damper completely.The low cycle fatigue performance of low yield point steel of Baosteel mainly depended on the amplitude in test.And the effect of varying frequency for the low yield point steel was more less than varying amplitude.展开更多
Background: Among elderly people, rehabilitation is important for reducing the risk of falls and hospitalization and to maintain an independent life for longer. Motivation is a factor for elderly people to lead an act...Background: Among elderly people, rehabilitation is important for reducing the risk of falls and hospitalization and to maintain an independent life for longer. Motivation is a factor for elderly people to lead an active daily life and leave home more frequently. Purpose: The purposes of this study were to determine the optimal cut-off point in the Scale for Achievement Motive in Geriatrics (SAMG) that could identify individuals as inactive or active, based on the Frenchay Activities Index (FAI), and to compare characteristics between active and inactive groups classified by the cut-off point. Methods: A cross-sectional study of 285 community-dwelling elderly people measured SAMG and FAI and physical function. Receiver operating characteristic (ROC) analysis was used to calculate the area under the curve (AUC) that was the optimal cut-off point for the SAMG total score, with the associated sensitivity and 1-specificity when compared with the FAI results. Demographic parameters and physical function were compared between two groups defined by cut-off point. Results: The AUC was 0.78, the optimal cut-off for SAMG total score for indicating inactivity was ≤48, the sensitivity was 77.98% and the 1-specificity was 75.00%. The group with SAMG score >48 was characterized by a significantly higher proportion of women, fewer people sharing a house, and participation in more hobbies. Discussion: A cut-off point of 48 in the SAMG could be a predictive index of motivation toward goals for individuals with inactive daily activities. The group with score higher than the cut-off was characterized by more women, fewer people living together, and more hobbies than the group with lower scores.展开更多
A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and v...A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and valid for high strength high fracture toughness steels. The values of JIC and KIC measured by this method are in good agreement with those measured by standard test method.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50739004)
文摘This paper presents fatigue characteristic analysis of a deepwater steel catenary riser （SCR） under ambient excitations. The SCR involves complex nonlinear dynamic behaviors, especially at the touchdown point （TDP） where the riser first touches the seafloor. Owing to the significant interaction with soil, the touchdown zone is difficnlt to be modeled. Based on Lumped-Mass method and P-y curve, nonlinear springs are used to simulate the SCR-seabed coupled interaction. In case studies, an SCR＇s dynamic features have been obtained by transient analysis and the structure fatigue assessment has been carried out by S-N approach. The comparative analysis shows that the TDP is the key location where soil-riser interaction rises steeply and minimum fatigue life occurs. Parameters such as ocean environment loads, vessel motions, riser material and geometric parameters are discussed. The results indicate that the vessel motion is the principal factor for the structure fatigue life distribution.
基金supported by the National Natural Science Foundation of China(Grant No.51009089)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20100073120017)
文摘A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point （TDP）. The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.
文摘The application of fracture in three-point bending to blanking of bearing steel is studied in this paper. Several mechanical models of stress blanking are discussed at first. And then the experiments have been made in special equipment of three-point bending designed by us. Several problems, such as the suitable span, the relations between bending and tension bending complex, the ratio of blanking length to the diameter, the relations of blank length to force, the feature of fracture, are studied through the experiments. The suitable parameters of three-point bending to blanking, depth and tip radius of notch and the ratio between blanking length and stick diameter have been proposed.
文摘With the development of technology for earthquake resistant,the research of the low yield point(LYP) steel which used for the fabrication of energy dissipation damper were paid more and more attention.The common studies of the low yield point steel is mainly about the performance with constant amplitude and constant frequency.The low cycle fatigue properties of low yield piont steel were studied by series of test with continuous varying amplitude and varying frequency with the materials testing system by us.The test results showed that low yield point steel of Baosteel have excellent low cycle fatigue properties,which meet the requirement for steel used for the fabrication of energy dissipation damper completely.The low cycle fatigue performance of low yield point steel of Baosteel mainly depended on the amplitude in test.And the effect of varying frequency for the low yield point steel was more less than varying amplitude.
文摘Background: Among elderly people, rehabilitation is important for reducing the risk of falls and hospitalization and to maintain an independent life for longer. Motivation is a factor for elderly people to lead an active daily life and leave home more frequently. Purpose: The purposes of this study were to determine the optimal cut-off point in the Scale for Achievement Motive in Geriatrics (SAMG) that could identify individuals as inactive or active, based on the Frenchay Activities Index (FAI), and to compare characteristics between active and inactive groups classified by the cut-off point. Methods: A cross-sectional study of 285 community-dwelling elderly people measured SAMG and FAI and physical function. Receiver operating characteristic (ROC) analysis was used to calculate the area under the curve (AUC) that was the optimal cut-off point for the SAMG total score, with the associated sensitivity and 1-specificity when compared with the FAI results. Demographic parameters and physical function were compared between two groups defined by cut-off point. Results: The AUC was 0.78, the optimal cut-off for SAMG total score for indicating inactivity was ≤48, the sensitivity was 77.98% and the 1-specificity was 75.00%. The group with SAMG score >48 was characterized by a significantly higher proportion of women, fewer people sharing a house, and participation in more hobbies. Discussion: A cut-off point of 48 in the SAMG could be a predictive index of motivation toward goals for individuals with inactive daily activities. The group with score higher than the cut-off was characterized by more women, fewer people living together, and more hobbies than the group with lower scores.
文摘A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and valid for high strength high fracture toughness steels. The values of JIC and KIC measured by this method are in good agreement with those measured by standard test method.
