全跨和半跨荷载组合下荷载效应函数模型研究

研究了全跨和半跨荷载组合下荷载效应函数的特性.首先分析了荷载效应函数为非线性的原因.然后在多个实例分析的基础上,提出了一个全跨和半跨荷载组合作用下荷载效应函数的一般模型.该模型无论是在构件层次上还是在体系层次上都具有较高的精度.最后根据此函数模型,讨论了荷载效应曲线的非线性程度.结果表明荷载效应曲线为抛物线或双曲线.这...     

风动力效应对斜拉网壳结构承载性能的影响分析

为将风致响应分析与承载安全性能评估结合起来,引入了一种简化的极限承载能力风振系数.通过计算出风荷载动力效应下与静风作用下结构整体极限承载能力的比值,较方便地实现了考虑风动力效应的斜拉网壳结构承载安全评估.然后讨论了网格厚度、荷载组合比例值和预应力水平等参数对简化风振系数的影响规律.结果表明:结构刚度越柔,屋面质量越轻,预应力水平越高,风动力效应的影响越显著一些.     

考虑相位角的脉动风场模拟

为克服考虑相位角后风谱密度矩阵可能不正定而无法进行Cholesky分解的困难,提出了一种基于插值技术的改进风场模拟方法。首先依据风谱密度矩阵的正定性或不正定性将模拟风频范围划分为正定区间和不正定区间。在正定区间内,可直接将风谱密度矩阵进行Cholesky分解。而在不正定区间内,可采用插值技术获得风谱密度矩阵的分解式。然后运用谐波合成法模拟出全部风频范围内的脉动风速。数值算例表明:该方法具有较高的精度,且模拟结果能较好地符合自然风的基本特性。     

Modeling the Evolution of Chorus Waves into Hiss Waves in the Magnetosphere

In this study, we analyze Cluster observations of whistler-mode chorus and hiss waves during the event of August 19-21, 2006. Chorus is present outside the plasmasphere and hiss occurs inside the plasmasphere. Using a recently constructed plasma boundary layer model, we perform a ray-tracing study on the propagation of chorus. Numerical results show that chorus can penetrate into the plasmasphere through the plasma boundary layer, evolving into hiss. The current data analysis and modeling provide a further observational support for the previous findings that chorus is the origin of plasmaspheric hiss.     

Observation and Modeling of Geostationary Orbit Electron Energization Induced by Enhanced Dayside Whistler-Mode Waves

We provide correlated observations of enhanced dayside whistler-mode waves and energetic electron acceleration collected by the CLUSTER and GOES satellites during the 23~24 September 2001 storm.Energetic(>0.6 MeV) electron fluxes are found to increase significantly during the recovery phase and the main phase,by a factor of ~50 higher than the prestorm level.These high electron fluxes occur when strong dayside whistler-mode waves are present.Two-dimensional(2D) numerical simulations are carried out and the results demonstrate that the dayside whistler-mode wave can contribute to such enhancements in electron flux within 24 h,consistent with the observation.     

结构稳定性课程采用五星教学模式的探索

分析了现行结构稳定性课程教学中存在的问题,然后在此基础上采用五星教学模式进行了教学改革的探索。通过具体的教学案例,给出了五星教学模式实施的过程。教学实践表明,按该模式进行教学能达到较好效果。这为课程教学改革提供了新的思路。     

Ray Tracing Study of Electromagnetic Ion Cyclotron Waves Associated with Bi-Ion Frequencies

Ray tracing study of electromagnetic ion cyclotron （EMIC） waves is conducted based on a realistic plasma density model. The simulation result shows that EMIC waves propagate away from the equatorial source region to higher latitudes basically along geomagnetic field lines, and are reflected at the region where their frequency matches the local bi-ion frequency. H＋ band suffers H＋-He＋ bi-ion frequency reflection at lower latitudes, whereas He＋ band suffers He＋-O＋ bi-ion frequency reflection at higher latitudes. Moreover, the concentration of heavy ions slightly affects the bi-ion frequencies and then slightly determines the reflection location of ray paths of EMIC waves. The current results present the first detailed study on the propagation characteristics of EMIC waves associated with bi-ion frequencies.