Effects of vertical central stabilizers on nonlinear wind-induced stabilization of a closed-box girder suspension bridge with various aspect ratios

The aerodynamic shape of a closed-box girder plays an important role in the wind-induced stabilization of long-span suspension bridges. The purpose of this study is to investigate the effects of the combination of five aspect ratios and a downward vertical central stabilizer (DVCS) on nonlinear flutter and aerostatic behaviors of a super long-span suspension bridge with closed-box girders. Through conducting a series of wind-tunnel tests and nonlinear finite element analysis, the results show that the nonlinear self-excited forces and the critical wind speed (U_cr) gradually increase as the increase of the aspect ratio (i.e. the width to depth ratios). Furthermore, the application of 20% deck depth DVCS could significantly increase the nonlinear self-excited forces and U_cr for small aspect ratios of 7.9 and 7.1. Particularly, the installation of the DVCS could change the flutter divergence patterns of the bridge from soft flutter to hard flutter, especially for a relatively small aspect ratio. In addition, the aerostatic force coefficients and torsional divergence critical wind speeds of the larger aspect ratio with DVCS are significantly larger than that without DVCS. A relatively small aspect ratio of the bridge has better aerostatic performance than that with a larger aspect ratio.

     

动态对等群上的基于身份的认证密钥协商协议

针对DB08协议(Dutta和Barua的动态群密钥协商协议)不满足密钥独立性的缺陷,利用SK(Sakai和Kasahara)的密钥构造方法,提出了一个动态对等群上的基于身份的认证密钥协商协议.在新协议中计算子密钥时,利用Hash运算和增加会话标识,来避免不同会话中子密钥的关联性,因此新协议满足密钥独立性.同时新协议满足完善的前向安全性、主密钥前向安全性,以及抗主动和被动攻击等安全性.与DB08协议相比较,新协议大大降低了计算开销和通信开销,因此更适用于动态的对等网络.