Dynamic response analysis of nonlinear secondary oscillators to idealised seismic pulses

The paper deals with the seismic response analysis of nonlinear secondary oscillators. Bilinear, sliding and rocking single-degree-of-freedom dynamic systems are analysed as representative of a wide spectrum of secondary structures and nonstructural components. In the first stage, the equations governing their full dynamic interaction with linear multi-degree-of-freedom primary structures are formulated, and then conveniently simplified using primary-secondary two-degree-of-freedom systems and dimensionless coefficients. In the second stage, the cascade approximation is applied, whereby the feedback action of the secondary oscillator on the primary structure is neglected. Owing to the piecewise linearity of the secondary systems being considered, efficient semi-analytical and step-by-step numerical solutions are presented. The semi-analytical solutions allow the direct evaluation of the seismic response under pulse-type ground excitations and are also used to validate step-by-step numerical schemes, which in turn can be used for general-type seismic excitations. In the third stage, a set of decoupling criteria are proposed for the pulse-type base excitations, identifying the conditions under which a cascade analysis is admissible from an engineering standpoint. Finally, the influence and relative dependencies between the input parameters of the ground motion and the primary-secondary assembly are quantified on the response of the secondary systems through nonlinear floor response spectra, and general trends are identified and discussed.     

基于声相关计程仪(ACL)的海底散射模型研究

为了进行声相关计程仪(ACL)仿真研究,结合K irchhoff近似和R ay le igh-R ice近似散射模型,根据ACL垂直发射波束的特点,在掠射角90°附近,利用已发表的海底散射实验数据与APL-UW散射模型及L am bert公式的理论计算结果相比较,基于K irchhoff近似的散射模型与实验数据具有很好的一致性,仿真结果证明,由于不同类型海底沉积物引起的体积散射在上述情况下是可以被忽略的,这将大大简化进行声相关测速仿真研究的海底建模过程。     

Wave-induced mean flows in vertical rubble mound structures

Waves impinging on rubble mound breakwaters and seawalls induce a mean flow within the breakwater, analogous to the so-called undertow within the surf zone. Here, using a plane wave approximation (kh<1.5), a second-order problem is solved for an idealized breakwater with a rectangular cross-section to show the origin and the nature of the mean flow within the porous structure. The mean flow is expressed in terms of a mean stream function analytically derived, obtained based on the mass flux balance between the incident, reflected and transmitted waves. Furthermore, the evolution of other second-order magnitudes such as mean water level and mass flux is analyzed under different incident wave conditions, structure geometry and porous material characteristics. Results show that the evolution of the different mean quantities is controlled mainly by reflection and consequently depends highly on structure geometry and porous material characteristics. Furthermore, it is shown that the return flow is stronger with increasing mass flux decay. Some qualitative experiments to show the described mechanism are also presented.     

基于T-matrix的非线性参数估计方法

全波形反演可提供高精度的地下介质参数空间分布,但传统的全波形反演方法建立在Born近似的基础上,对初始模型具有一定的依赖性.为了摆脱Born近似的束缚,本文基于二维常密度声波方程,在De Wolf近似的前提下,借助传输矩阵(T-matrix)方法,深入研究了逆薄板传播算子(Inverse Thin-Slab Propagator,ITSP),实现了速度扰动的非线性估计.ITSP方法避免了Born级数方法在扰动较强、扰动区域较大时的发散性问题,且只经过一次扫描校正,计算效率较高.二维模拟数据分析验证了本文方法的可行性以及有效性.     

快速确定扰动引力的广域多项式逼近方法的模拟实验

飞行器在飞行过程中时刻受到地球重力场的作用,地球外部空间扰动引力会对飞行器的运行轨迹和姿态等方面产生影响,因此,研究地球重力场信息并实时快速的计算出飞行器运行处的扰动引力,对飞行器轨迹和姿态等方面的调节具有重要的作用。利用模拟数据,本文基于广域多项式逼近方法来快速逼近扰动引力,该法在单元边界点上满足插值条件,而又利用插值单元周围节点信息,实现拟合过程。试验表明,这一方法在高度方向的步长为30km的条件下可达到1mgal的计算精度。     

非共振二阶椭圆型方程解的存在唯一性

利用Galerkin逼近方法和minimax原理，证明了非线性非共振椭圆型方程弱解的存在唯一性。     

球锥扁椭球冰粒后向散射实验与DDA计算研究

采用实验室观测和DDA法理论计算，分别获得了球锥扁椭球形冰粒对3.2、5.6和10.7cm三种波长极化波的后向散射特性数据。结果表明，测量资料和计算数据具有很好的一致性。球锥扁椭球形冰粒的后向散射截面大小不仅依赖于其尺寸（等容半径）而且受其形状影响，“差反射率雷因子ZDR”与粒子形状参数“水平-垂直尺度比”呈很好的线性正相关。这是利用双偏振雷达探测识别球锥扁椭球形冰雹的依据。     

陕西省精细化网格预报业务系统技术方法

精细化网格预报不仅是目前中国气象局主推的预报业务,而且是未来天气预报的发展方向。本文详细阐述了陕西省精细化网格预报业务系统中数据产品的技术方法。主要包括4个方面:(1)建立了陕西网格预报技术框架,提出"动态交叉最优要素预报"(DCOEF)的方法来建立基础网格预报场。(2)提出"站点订正值向格点场传递"的格点连续性要素订正方法,交叉检验表明该方法在格点场上24h最低、最高温度2℃的准确率较模式降尺度数据分别提高34%和23%,此外,该方法在背景场协同,主观站点预报和客观格点预报要素值融合一致方面有较好的应用价值。(3)基于"偏差订正"方法订正格点降水,结果表明通过计算预报偏差Bias,来"消空"小雨频率,"补漏"暴雨频率,ECMWF降水预报24h小雨、暴雨TS评分较原模式分别提高2.5%和4.82%。(4)提出"反向离差数据归一化"算法,处理因客观方法或主观订正后数据在时间序列上的矛盾问题,该方法不改变原模式对要素的预报趋势,同时使得要素在时间上协同一致,很好地解决了网格要素预报的时间协同性问题。     

逻辑算子集与模糊粗糙近似算子集的性质及相关性

定义了逻辑算子集与模糊粗糙近似算子集之间的映射,并讨论其性质。特别地给出了由模糊粗糙近似算子构造相应的t范算子以及由连续的严格单调实函数构造相应的negator算子的方法。所得结论对各种特色的粗糙近似模型的建立有指导意义。     

Numerical storm surge model with higher order finite difference method of lines for the coast of Bangladesh

In this study, the method of lines (MOLs) with higher order central difference approximation method coupled with the classical fourth order Runge-Kutta (RK(4,4)) method is used in solving shallow water equations (SWEs) in Cartesian coordinates to foresee water levels associated with a storm accurately along the coast of Bangladesh. In doing so, the partial derivatives of the SWEs with respect to the space variables were discretized with 5-point central difference, as a test case, to obtain a system of ordinary differential equations with time as an independent variable for every spatial grid point, which with initial conditions were solved by the RK(4,4) method. The complex land-sea interface and bottom topographic details were incorporated closely using nested schemes. The coastal and island boundaries were rectangularized through proper stair step representation, and the storing positions of the scalar and momentum variables were specified according to the rules of structured C-grid. A stable tidal regime was made over the model domain considering the effect of the major tidal constituent, M₂ along the southern open boundary of the outermost parent scheme. The Meghna River fresh water discharge was taken into account for the inner most child scheme. To take into account the dynamic interaction of tide and surge, the generated tidal regime was introduced as the initial state of the sea, and the surge was then made to come over it through computer simulation. Numerical experiments were performed with the cyclone April 1991 to simulate water levels due to tide, surge, and their interaction at different stations along the coast of Bangladesh. Our computed results were found to compare reasonable well with the limited observed data obtained from Bangladesh Inland Water Transport Authority (BIWTA) and were found to be better in comparison with the results obtained through the regular finite difference method and the 3-point central difference MOLs coupled with the RK(4,4) method with regard to the root mean square error values.