2.当L>Sr 则d1=V2R1h2 则d2=√2Rh2 2R 2R Sn=d1+d2=√2R(Vh+√h2 R 2(√h+Vh2)2 ST R d. L2．当L>ST : 1 1 2 1 1 2 2 d Rh R d h = ，则 = 2 2 2 2 2 2 2 d Rh R d h = ，则 = 2 ( ) ST = d1 + d2 = R h1 + h2 2( ) 4 2 2 1 2 2 min T  ST  h h S L = + = 2( ) 1 2 2 h h S R T + =