This paper introduces the 3D Peskin problem: a two-dimensional elastic membrane immersed in a three-dimensional steady Stokes flow. We obtain the equations that model this free boundary problem and show that they admit a boundary integral reduction, providing an evolution equation for the elastic interface. We consider general nonlinear elastic laws, i.e., the fully nonlinear Peskin problem, and prove that the problem is well-posed in low-regularity Hölder spaces. Moreover, we prove that the elastic membrane becomes smooth instantly in time.
Contents1. Introduction 2 2. Formulation and Boundary Integral Reduction 9 3. Preliminaries 12 4. Nonlinear decomposition 18 5. Calculus estimates 24 6. Frozen-coefficient Semigroup 39 7. Local well-posedness 56 8. Higher Regularity 66 Appendix A. Besov Spaces and Fourier Multiplier Theorems 75 Appendix B. Estimates for the semigroup e ´tLApξq 77 References 90