This paper proposes a new methodology to select an optimal threshold level to be used in the peak over threshold （POT） method for the prediction of short-term distributions of load extremes of offshore wind turbines...This paper proposes a new methodology to select an optimal threshold level to be used in the peak over threshold （POT） method for the prediction of short-term distributions of load extremes of offshore wind turbines. Such an optimal threshold level is found based on the estimation of the variance-to-mean ratio for the occurrence of peak values, which characterizes the Poisson assumption. A generalized Pareto distribution is then fitted to the extracted peaks over the optimal threshold level and the distribution parameters are estimated by the method of the maximum spacing estimation. This methodology is applied to estimate the short-term distributions of load extremes of the blade bending moment and the tower base bending moment at the mudline of a monopile-supported 5MW offshore wind turbine as an example. The accuracy of the POT method using the optimal threshold level is shown to be better, in terms of the distribution fitting, than that of the POT methods using empirical threshold levels. The comparisons among the short-term extreme response values predicted by using the POT method with the optimal threshold levels and with the empirical threshold levels and by using direct simulation results further substantiate the validity of the proposed new methodology.展开更多
<span style="font-family:Verdana;">As the new demands on curriculum teaching in the information age, the application of various technologies is profoundly affecting classroom teaching today. The techno...<span style="font-family:Verdana;">As the new demands on curriculum teaching in the information age, the application of various technologies is profoundly affecting classroom teaching today. The technology-embedded classroom approach includes technology-</span><span style="font-family:""> </span><span style="font-family:Verdana;">assisted teaching, technology-integrated teaching, and technology-based</span><span style="font-family:""><span style="font-family:Verdana;"> teach</span><span style="font-family:Verdana;">ing. There are still some deficiencies in the technological embedding of</span><span style="font-family:Verdana;"> course teaching, the technological presentation of knowledge destroys the ecosystem of classroom, the technological controlled teaching hinders the development of teacher-student relationship, and the value orientation under technological efficiency neglects the integrated development of students. It is recommended </span><span style="font-family:Verdana;">to develop an ecological view of technological development, a pedago</span><span style="font-family:Verdana;">gical system focused on teacher-student interaction and an evaluation system with a multi-valued orientation.</span></span>展开更多
Co-seismic responses of the groundwater level and temperature in the Tayuan well of 68 earthquakes （Ms ≥ 7.0） from January 2004 to September 2007 were analyzed. Results show that the Tayuan well has a strong abilit...Co-seismic responses of the groundwater level and temperature in the Tayuan well of 68 earthquakes （Ms ≥ 7.0） from January 2004 to September 2007 were analyzed. Results show that the Tayuan well has a strong ability to record large earthquakes worldwide, and the coseismic response shows a pattern of water level oscillation →temperature decrease→ oscillation stop → temperature resumption. Further analyses indicate that the amplitude of the water level and temperature change is not ouly concerned with the epicenter distance and magnitude, but is also related to the temporal state of aquifer while the seismic wave arrives. Mechanisms of water level oscillation, temperature decrease, water level oscillation stop and temperature resumption are discussed, with the results from previous research on the co-seismic response mechanisms analyzed. These include gas escape, heat diffusion and cold water seepage. Results show that a single mechanism could not explain the co-seismic response of the Tayuan well water level to multiple earthquakes; the results were garnered from a variety of jointly acting mechanisms.展开更多
基金supported by the funding of an independent research project from the Chinese State Key Laboratory of Ocean Engineering(Grant No.GKZD010038)
文摘This paper proposes a new methodology to select an optimal threshold level to be used in the peak over threshold （POT） method for the prediction of short-term distributions of load extremes of offshore wind turbines. Such an optimal threshold level is found based on the estimation of the variance-to-mean ratio for the occurrence of peak values, which characterizes the Poisson assumption. A generalized Pareto distribution is then fitted to the extracted peaks over the optimal threshold level and the distribution parameters are estimated by the method of the maximum spacing estimation. This methodology is applied to estimate the short-term distributions of load extremes of the blade bending moment and the tower base bending moment at the mudline of a monopile-supported 5MW offshore wind turbine as an example. The accuracy of the POT method using the optimal threshold level is shown to be better, in terms of the distribution fitting, than that of the POT methods using empirical threshold levels. The comparisons among the short-term extreme response values predicted by using the POT method with the optimal threshold levels and with the empirical threshold levels and by using direct simulation results further substantiate the validity of the proposed new methodology.
文摘<span style="font-family:Verdana;">As the new demands on curriculum teaching in the information age, the application of various technologies is profoundly affecting classroom teaching today. The technology-embedded classroom approach includes technology-</span><span style="font-family:""> </span><span style="font-family:Verdana;">assisted teaching, technology-integrated teaching, and technology-based</span><span style="font-family:""><span style="font-family:Verdana;"> teach</span><span style="font-family:Verdana;">ing. There are still some deficiencies in the technological embedding of</span><span style="font-family:Verdana;"> course teaching, the technological presentation of knowledge destroys the ecosystem of classroom, the technological controlled teaching hinders the development of teacher-student relationship, and the value orientation under technological efficiency neglects the integrated development of students. It is recommended </span><span style="font-family:Verdana;">to develop an ecological view of technological development, a pedago</span><span style="font-family:Verdana;">gical system focused on teacher-student interaction and an evaluation system with a multi-valued orientation.</span></span>
基金Research Grant from the Institute of Crustal Dynamics,CEA under the Contract No.ZDJ2008-04the Joint Earthquake Science Foundation (A07084),China
文摘Co-seismic responses of the groundwater level and temperature in the Tayuan well of 68 earthquakes （Ms ≥ 7.0） from January 2004 to September 2007 were analyzed. Results show that the Tayuan well has a strong ability to record large earthquakes worldwide, and the coseismic response shows a pattern of water level oscillation →temperature decrease→ oscillation stop → temperature resumption. Further analyses indicate that the amplitude of the water level and temperature change is not ouly concerned with the epicenter distance and magnitude, but is also related to the temporal state of aquifer while the seismic wave arrives. Mechanisms of water level oscillation, temperature decrease, water level oscillation stop and temperature resumption are discussed, with the results from previous research on the co-seismic response mechanisms analyzed. These include gas escape, heat diffusion and cold water seepage. Results show that a single mechanism could not explain the co-seismic response of the Tayuan well water level to multiple earthquakes; the results were garnered from a variety of jointly acting mechanisms.
