Using softened contact relationship describing compressible membrane in FEA of spiral case structure

• Modeling the membrane in SCS not in a conventional element-represented way.
• Modeling the membrane by defining a softened contact relationship.
• Governing the penetration behavior of spiral case liner into surrounding concrete.
• Significantly improving the FE modeling efficiency of SCS.
• Considerably simplifying the material description of membrane.

A steel spiral case surrounded with mass concrete in a hydroelectric power plant is what is called a spiral case structure (SCS). The top exterior surface of a steel spiral case is routinely covered with a thin-layer compressible membrane. Unfortunately, the description of membrane in current structural finite element analyses (FEA) of SCS is a tough work in a conventional element-represented way. With the purpose of both accurately and conveniently describing the membrane, we have made a maiden attempt at modeling it by defining a softened contact relationship between the spiral case liner and the surrounding concrete where the membrane works. The novel simulation concept concentrates on governing the penetration behavior of the spiral case liner into the surrounding concrete, by prescribing an appropriate and straightforward dependence of the contact pressure on the penetration (overclosure). Profiting from that the inconvenient and error-prone FE modeling of a thin-layer membrane can be avoided. The simulation technique's reliability in describing the mechanical property of a membrane material was verified. Its applicability and competence have been demonstrated to be valid and satisfactory. Accepting the simulation concept will help to significantly improve the FE modeling efficiency of a SCS and considerably simplify the material description of a membrane. The possibility of contributing to change the way we describe the membrane in structural FEA of SCS is a very exciting proposition.