Free-flow tunnel used more round arch straightwall form cross-section.
无压隧洞多采用圆拱直墙形断面。
2
The hardest thing to build is a plain straightwall. The dimensions must be absolute.
最难砌的是一堵简朴笔直的墙，尺寸必须一丝不差。
3
By taking a duct of an aircraft as an example, ultra long and ultra thin al alloy straightwall special-shaped part machining process is analyzed and discussed.