1. Assoc. Prof., Dept. of Hydr. Engrg., Tsinghua Univ., Beijing 100084, China. E-mail: jmma@hydr.tsinghua,edu.cn
2. Grad. Student, Dept. of Hydr. Engrg., Tsinghua Univ., Beijing, China. E-mail: liangyuanbo@chinaren.com
3. Prof., Dept. of Hydr. Engrg., Tsinghua Univ., Beijing, China.