Thanks for your reply!

Yeah,the lines can be ignored or just delete them, I'm just curious about it. Thank you though.

But how about the first problem, the shattered surface, which puzzles me a lot.

In fact I desire to make a 2D simulation about a rectangle wing, I thought it was rather simple, so I just set up the geometry by ICEM.But it always goes shattered while segmenting the surface with a  rectangle, I tried a small circle instead, but it still goes wrong like the picture showed below.

As to spaceclaim, thanks for reminding, I'll check later.

Best regards.

simple 2D surface segment, always shattered.