Supported by the National Natural Science Foundation of China (Grant Nos. 50539030, 50609004) and the National Basic Research Program of China ("973" Program) (Grant No. 2007CB714104)
[1]Department of Engineering Mechanics, Hohai University, Nanjing 210098, China [2]College of River and Ocean Engineering, Chongqing Jiaotong University, Chongqing 400074, China