A new ring-pack model has been developed based on the curved beam finite element method. This paper describes the first part of this model: simulating gas pressure in different regions above piston skirt and ring dynamic behavior of two compression rings and a twin-land oil control ring. The curved finite element method separates grid sizes from structural analysis, contact force analysis and gas pressure analysis which enables the model to capture both global and local processes at their proper length scales. The effects of bore distortion, piston secondary motion and groove distortion are considered. Gas flow through ring gap, ring-groove interface, ring-liner interface when ring collapses and drain holes in OCR groove is modeled. Gas pressure force, inertial force, ring-groove interaction and ring-liner interaction are calculated to simulate ring dynamic deformation. Top two rings static twist and expansion force are carefully calculated from their free shape with the consideration of large displacement. Ring dynamics and gas flows are coupled in the formulation and an implicit scheme is implemented. The model is applied to a passenger car engine and a study of local and global effects is conducted.