Elastic lateral-torsional buckling analysis of permanent means of access structure

International Maritime Organization (IMO) adopted a new regulation to request permanent means of access (PMA) for a regular inspection of ship structure. Horizontal platforms for an inspector to walk on should be provided at specified locations. The platform is attached perpendicular to longitudinal bulkheads or side shell like a common longitudinal stiffener. Since the platform is much wider than ordinary stiffeners, a mid-flat-bar is welded in the middle of the platform. The wide platform (i.e. the tall web plate) makes PMA structure prone to lateral torsional buckling prior to overall flexural Euler buckling subjected to axial compression. This study employs the Rayleigh-Ritz method to treat the elastic lateral-torsional buckling of the PMA structure. The deformation of the cross-section can be expressed using six independant parameters. Compared to the previous research for an ordinary stiffened plate (Hughes and Ma, 1996a), two additional parameters are employed to model the deformation of the mid flat bar. This study also proposes a new strain distribution of lateral bending introducing two respective neutral axes for the flange and the mid-flat-bar. Two mathematical models are developed for two cases; one without associated plating, and the other with both the plating and its rotational restraint. In the former, the coupling between the lateral torsional buckling (“tripping”) and the Euler buckling is investigated. In the latter, a plate rotational spring constant is suggested based on extended deformed shape of the plating. For each model, the validity of the proposed method is verified by a comparison with a number of linear buckling analyses carried out using the NASTRAN finite-element program.     

基于可预报模态分析方法的青藏高原东部夏季降水统计预测模型

利用国家气象信息中心提供的降水资料、NCEP/NCAR再分析月平均资料以及Hadley中心提供的海温资料,基于可预报模态分析(PMA)方法,从观测数据中提取青藏高原东部夏季降水具有物理意义的可预报模态,根据已有研究选取合适的预报因子并建立了物理-经验(P-E)模型,从而对青藏高原东部夏季降水进行统计预测。结果表明:南北反向型、一致型、中部型和东北型这4个主导模态反映了降水的异常变化,具有一定的物理意义,为可预报模态;超前0个月和超前1个月的区域平均的预报技巧分别为0.44和0.36,其中青藏高原东南部地区的预报技巧较高;超前0个月和超前1个月的模态相关系数分别为0.46和0.42,预报最好的年份都是1998年,预报最差的年份分别是1980年和2009年。