Considering the dependent relationship among wave height,wind speed,and current velocity,we construct novel trivariate joint probability distributions via Archimedean copula functions.Total 30-year data of wave height...Considering the dependent relationship among wave height,wind speed,and current velocity,we construct novel trivariate joint probability distributions via Archimedean copula functions.Total 30-year data of wave height,wind speed,and current velocity in the Bohai Sea are hindcast and sampled for case study.Four kinds of distributions,namely,Gumbel distribution,lognormal distribution,Weibull distribution,and Pearson Type III distribution,are candidate models for marginal distributions of wave height,wind speed,and current velocity.The Pearson Type III distribution is selected as the optimal model.Bivariate and trivariate probability distributions of these environmental conditions are established based on four bivariate and trivariate Archimedean copulas,namely,Clayton,Frank,Gumbel-Hougaard,and Ali-Mikhail-Haq copulas.These joint probability models can maximize marginal information and the dependence among the three variables.The design return values of these three variables can be obtained by three methods:univariate probability,conditional probability,and joint probability.The joint return periods of different load combinations are estimated by the proposed models.Platform responses(including base shear,overturning moment,and deck displacement) are further calculated.For the same return period,the design values of wave height,wind speed,and current velocity obtained by the conditional and joint probability models are much smaller than those by univariate probability.Considering the dependence among variables,the multivariate probability distributions provide close design parameters to actual sea state for ocean platform design.展开更多
A novel modeling technique based on the coupled Eulerian-Lagrangian(CEL) method is provided to solve the geotechnical problems with large deformations. The technique is intended to solve the update problem of soil mec...A novel modeling technique based on the coupled Eulerian-Lagrangian(CEL) method is provided to solve the geotechnical problems with large deformations. The technique is intended to solve the update problem of soil mechanical properties during spudcan penetration in normally consolidated clay soil. In the CEL model, the normal method of assigning an increasing shear strength profile with depth(NA) is defective due to its Eulerian framework. In this paper, a new technique is proposed to update soil material properties by introducing thermo-mechanical coupled analysis(TMCA) to the CEL models. During establishment of the CEL models, the optimal penetration velocity and minimum mesh size are determined through parametric studies. Reasonability and accuracy are then verified through comparison of the preliminary results with the soil flow configuration and penetration resistance(Fv) of a centrifuge test, and the results of the proposed method are compared with those of the remeshing and interpolation technique with small strain(RITSS) method. To achieve a CEL model with satisfactory accuracy, the NA and TMCA methods implemented in the CEL models and the RITSS method are first adopted in weightless soil. Comparison of the findings with those obtained in previous studies shows that the TMCA method can update material properties and predict Fv. The TMCA method is then applied to soils with self-weight and different shear strength profiles. Results show that the proposed method is capable of accurately modeling the large deformation problem of spudcan penetration in non-homogeneous clay.展开更多
An extreme sea storm process can lead to a jack-up rig under the combined loading condition of vertical load(V), horizontal load(H), and moment(M) to have stability problems. This paper presents the analysis of combin...An extreme sea storm process can lead to a jack-up rig under the combined loading condition of vertical load(V), horizontal load(H), and moment(M) to have stability problems. This paper presents the analysis of combined bearing capacities of a circular spudcan on layered clays with a strong layer overlying a comparatively weaker layer. Numerical models combined with displacement-based load tests, swipe tests, and constant ratio displacement probe tests are adopted to calculate the uniaxial bearing capacities, failure envelopes in combined V-H, V-M planes, and failure envelopes in a combined V-H-M load space, respectively. A parametric study on the effects of vertical load level V, the layer strength ratio s_(u,t)/s_(u,b), and the hard layer thickness t_1 on the bearing capacities is then performed. Results show that the vertical load level is a key factor that influences the values of H and M and the size of the H-M failure envelope. The existence of the underlying weak clay decreases the bearing capacities in all directions, and the vertical capacity Vult is affected more than the horizontal(H_(ult)) and moment(M_(ult)) capacities based on a single uniform deposit. The influence of the underlying weak clay on H-M failure envelope is mainly shown where H and M are coupled in the same direction. In contrast, little difference is observed when H and M are coupled in opposite directions.展开更多
基金partially supported by the National Natural Science Foundation of China(No.51479183)the National Key Research and Development Program,China(Nos.2016YFC0302301 and 2016YFC0803401)the Fundamental Research Funds for the Central University(No.201564003)
文摘Considering the dependent relationship among wave height,wind speed,and current velocity,we construct novel trivariate joint probability distributions via Archimedean copula functions.Total 30-year data of wave height,wind speed,and current velocity in the Bohai Sea are hindcast and sampled for case study.Four kinds of distributions,namely,Gumbel distribution,lognormal distribution,Weibull distribution,and Pearson Type III distribution,are candidate models for marginal distributions of wave height,wind speed,and current velocity.The Pearson Type III distribution is selected as the optimal model.Bivariate and trivariate probability distributions of these environmental conditions are established based on four bivariate and trivariate Archimedean copulas,namely,Clayton,Frank,Gumbel-Hougaard,and Ali-Mikhail-Haq copulas.These joint probability models can maximize marginal information and the dependence among the three variables.The design return values of these three variables can be obtained by three methods:univariate probability,conditional probability,and joint probability.The joint return periods of different load combinations are estimated by the proposed models.Platform responses(including base shear,overturning moment,and deck displacement) are further calculated.For the same return period,the design values of wave height,wind speed,and current velocity obtained by the conditional and joint probability models are much smaller than those by univariate probability.Considering the dependence among variables,the multivariate probability distributions provide close design parameters to actual sea state for ocean platform design.
基金supported by the National Natural Science Foundation of China (No. 51779236)the NSFC-Shandong Joint Fund Project (No. U1706226)funded by the China Scholarship Council (No. 201606330049)
文摘A novel modeling technique based on the coupled Eulerian-Lagrangian(CEL) method is provided to solve the geotechnical problems with large deformations. The technique is intended to solve the update problem of soil mechanical properties during spudcan penetration in normally consolidated clay soil. In the CEL model, the normal method of assigning an increasing shear strength profile with depth(NA) is defective due to its Eulerian framework. In this paper, a new technique is proposed to update soil material properties by introducing thermo-mechanical coupled analysis(TMCA) to the CEL models. During establishment of the CEL models, the optimal penetration velocity and minimum mesh size are determined through parametric studies. Reasonability and accuracy are then verified through comparison of the preliminary results with the soil flow configuration and penetration resistance(Fv) of a centrifuge test, and the results of the proposed method are compared with those of the remeshing and interpolation technique with small strain(RITSS) method. To achieve a CEL model with satisfactory accuracy, the NA and TMCA methods implemented in the CEL models and the RITSS method are first adopted in weightless soil. Comparison of the findings with those obtained in previous studies shows that the TMCA method can update material properties and predict Fv. The TMCA method is then applied to soils with self-weight and different shear strength profiles. Results show that the proposed method is capable of accurately modeling the large deformation problem of spudcan penetration in non-homogeneous clay.
基金supported by the National Key R&D Program of China (No. 2016YFC0302301)the National Natural Science Foundation of China (No. 51479183)
文摘An extreme sea storm process can lead to a jack-up rig under the combined loading condition of vertical load(V), horizontal load(H), and moment(M) to have stability problems. This paper presents the analysis of combined bearing capacities of a circular spudcan on layered clays with a strong layer overlying a comparatively weaker layer. Numerical models combined with displacement-based load tests, swipe tests, and constant ratio displacement probe tests are adopted to calculate the uniaxial bearing capacities, failure envelopes in combined V-H, V-M planes, and failure envelopes in a combined V-H-M load space, respectively. A parametric study on the effects of vertical load level V, the layer strength ratio s_(u,t)/s_(u,b), and the hard layer thickness t_1 on the bearing capacities is then performed. Results show that the vertical load level is a key factor that influences the values of H and M and the size of the H-M failure envelope. The existence of the underlying weak clay decreases the bearing capacities in all directions, and the vertical capacity Vult is affected more than the horizontal(H_(ult)) and moment(M_(ult)) capacities based on a single uniform deposit. The influence of the underlying weak clay on H-M failure envelope is mainly shown where H and M are coupled in the same direction. In contrast, little difference is observed when H and M are coupled in opposite directions.
