Hi Rob,nI am simulating unsteady flow (Re <1) in a 0.3 mm dia. pipe. The flow is driven by a pressure-gradient in x-direction. The inlet-outlet boundary conditions are set to periodic. The walls are set to no-slip boundary condition.nThe first 5 iterations are exact zero. The absolute convergence was set to 1e-5. The convergence criteria fails as the first iteration is zero. Please suggest how can I solve this problem.n