气辅成型中如何设置溢流井？

如题。想做一个试试，可惜不知道如何来做。我在原有的模型的末端做了一个柱状的实体，想把它作为溢流井，可是划分网格出现问题，显示 ** ERROR 99780 ** Zero diameter/thickness for element <element_number>. An element must have a non-zero value for the diameter or thickness. Identify this element and use an appropriate value for the diameter or thickness, re-mesh the part, and re-run the analysis.