Correlation study between ground motion intensity measure parameters and deformation demands for bilinear SDOF systems

The correlation between ground motion intensity measures （IM） and single-degree-of-freedom （SDOF） deformation demands is described in this study. Peak ground acceleration （APG）, peak ground velocity （VPG）, peak ground displacement （DPG）, spectral acceleration at the first-mode period of vibration [As（T1）] and ratio of VPG to APG are used as IM parameters, and the correlation is characterized by correlation coefficients p. The numerical results obtained by nonlinear dynamic analyses have shown good correlation between As（T1） or VPG and deformation demands. Furthermore, the effect of As（T1） and VPG as IM on the dispersion of the mean value of deformation demands is also investigated for SDOF systems with three different periods T=0.3 s, 1.0 s, 3.0 s respectively.     

Elastic-plastic analysis for pile-anchor supporting system of deep foundation pit

By using numerical analysis methods to simulate the deep excavation, a lot of analyses are established on the basis of two-dimensional plane strain, ignoring the fact that foundation pit possesses three dimensions. For soil constitutive relation, people always take linear and nonlinear model, without considering the plastic behavior of soil. Using plastic-elastic hardening model to simulate constitutive relation of soil characteristics, the authors carried out mechanical analysis for pit excavation and support. The results show that the analysis for the stress state of pile anchor system is an effective way which provides theoretical basis for calculation of soil displacement.     

回顾与展望

数学系创建于1977年。在完成全院各专业的数学教学任务的同时，积极开展了科学研究。在常微分方程、随机微分方程、偏微分方程、生物数学等基础数学和应用数学分支中取得了一批成果，并结合海浪、海流、潮汐、海洋工程、海洋气象、海洋地质、海洋生物及水产科学的研究获得了一些具有实用价值的成果。     

海底三维声学图像实时处理系统设计

结合多核CPU硬件PC平台,设计了一种海底三维声学图像实时处理系统,主要包括声学前端信号处理子系统、数据传输控制子系统和PC客户端图像处理系统三个部分。声学前端信号处理子系统统根据接收到的多路声学换能器信号,通过两级FPGA信号处理,采集多通道水声信号,进行实时电子聚焦波束形成。为了解决海量声学数据快速传输问题,数据传输控制子系统未采用传统用户空间TCP/IP传输机制,而是直接通过嵌入式PowerPC处理器在Linux内核态采用DMA通道进行声学数据转发,减少系统调用和数据拷贝开销,有效提高网络传输效率。针对海量声学数据实时处理需求,PC客户端图像处理系统通过对复杂、耗时的单帧重建和数据拼接算法模块根据声学数据点的角度范围进行等分分割,对每个子范围声纳数据采用多线程并行处理,均衡多个CPU核之间负载,实现高性能三维声学图像实时处理。通过室内水池和湖试实验,结果表明该系统能够实时高效地进行三维声学图像采集、传输与处理。     

Ensemble retrieval of atmospheric temperature profiles from AIRS

ABSTRACT Satellite-based observations provide great opportunities for improving weather forecasting. Physical retrieval of atmo spheric profiles from satellite observations is sensitive to the uncertainty of the first guess and other factors. In order to improve the accuracy of the physical retrieval, an ensemble methodology was developed with an emphasis on perturbing the first guess. In the methodology, a normal probability density function （PDF） is used to select the optimal profile from the ensemble retrievals. The ensemble retrieval algorithm contains four steps： （1） regression retrieval for original first guess; （2） perturbation of the original first guess to generate new first guesses （ensemble first guesses）; （3） using the ensemble first guesses and nonlinear iterative physical retrieval to generate ensemble physical results; and （4） the final optimal profile is selected from the ensemble physical results by using PDE Temperature eigenvectors （EVs） were used to generate the pertur- bation and generate the ensemble first guess. Compared with the regular temperature profile retrievals from the Atmospheric InfraRed Sounder （AIRS）, the ensemble retrievals RMSE of temperature profiles selected by the PDF was reduced between 150 and 320 hPa and below 400 hPa, with a maximum improvement of 0.3 K at 400 hPa. The bias was also reduced in many layers, with a maximum improvement of 0.69 K at 460 hPa. The combined optimal （CombOpt） profile and a mean optimal （MeanOpt） profile of all ensemble physical results were improved below 150 hPa. The MeanOpt profile was better than the CombOpt profile, and was regarded as the final optimal （FinOpt） profile. This study lays the foundation for improving temperature retrievals from hyper-spectral infrared radiance measurements.     

GPS基线向量的非线性解算及精度分析

根据GPS基本观测方程,导出了顾及二次项含XY,XZ,YZ的非线性双差观测模型,根据展开至二次项含XY,XZ,YZ的基线向量模型,推导了法方程的直接解算方法,分析了基线长度的精度估计,并给出了简明的估计公式,为GPS基线非线性解算的精度评定提供了直接的评定公式.     

地震作用下高墩连续T形梁桥梁端碰撞分析

针对高墩连续梁桥伸缩缝位置处的碰撞现象,建立考虑单边碰撞空间有限元简化分析模型,采用非线性时程分析方法研究了高墩连续梁桥伸缩缝处碰撞发生的规律.总结了梁端碰撞发生时各个桥墩、台位置处梁墩相对位移及墩底内力的变化规律,以及影响梁端碰撞的因素.研究成果对同类型桥梁抗震设计时具有一定的参考价值.     

EIV模型参数求解的超球体单行采样法

EIV模型实际上是一种非线性模型,其参数估值是有偏的。引入可以使参数解达到二阶精度的超球体单行采样法,通过特定的采样策略近似非线性函数的概率密度分布,无需计算非线性函数的Jacobi矩阵和Hessen矩阵。在一定程度上降低了求非线性函数达到二阶精度的参数解的难度。通过算例表明,该方法可以得到比TLS迭代方法更为合理的结果,验证了本文方法的可行性和有效性。     

A nonlinear coupled soil moisture-vegetation model

Based on the physical analysis that the soil moisture and vegetation depend mainly on the precipitation and evaporation as well as the growth, decay and consumption of vegetation a nonlinear dynamic coupled system of soil moisture-vegetation is established. Using this model, the stabilities of the steady states of vegetation are analyzed. This paper focuses on the research of the vegetation catastrophe point which represents the transition between aridness and wetness to a great extent. It is shown that the catastrophe point of steady states of vegetation depends mainly on the rainfall P and saturation value v0, which is selected to balance the growth and decay of vegetation. In addition, when the consumption of vegetation remains constant, the analytic solution of the vegetation equation is obtained.