available surface meaning in English

有效表面
有效表面积
自由表面

So you can make docking ports more or less big depending on the size of your ship , and the available surface on the front
那么你可以根据船的大小和前端面积来决定对接口的大小。
Greatly increases the available surface area for the essential bacteria to live in . this greatly increases the level of biological filtration
增大硝化细菌居住空间，促进硝化细菌繁殖，使生物过滤能力倍增。