流体-结构耦合的node复位问题？

shuizs

本人看ansys 的帮助，其中有一个例子，是流体和结构耦合
The example in this section illustrates a steady-state fluid-structure interaction problem. This problem demonstrates the use of nonlinear large-deflection structural coupling for a fluid domain as well as the use of the "null" element type in a physics environment setting. It also demonstrates mesh morphing.
在进行耦合分析时说：
After each structural analysis, mesh morphing is executed to move the nodes in the small fluid region around the gasket to conform to the structural displacements. These new node locations are inputs for the subsequent flow analysis. For a proper structural solution and further morphing, all nodes must be returned to their original positions before applying the updated pressures from a flow analysis.
我想了很久，还是不明白为什么所有的节点在施加流体计算的压力前都要回到原来的位置？哪位高手能够解释一下？