The computer code TFSIM simulates transient and steady flow in networks defined by any combination of explicit pipes, implicit pipes, implicit open channels, and various other implicit components. Flow in explicit pipes is modeled using the fixed-grid method of characteristics. Flow in implicit pipes and open channels is modeled using Preissmann’s weighted four-point scheme. For solution at each time step, a network is organized into explicit components and implicit clusters, where an implicit cluster is defined as a grouping of implicit components bounded by explicit components and external boundary conditions. Each implicit cluster is solved using the Newton-Raphson technique with the double-sweep method, modified for loops, used to solve the matrix of linearized equations at each iteration. While the explicit method of characteristics is the preferred numerical method for transient analysis of pipe flow, the implicit Preissmann’s scheme can provide nearly identical solutions for slower transients while allowing larger time steps. By using a mix of implicit and explicit pipes, large, complex networks with many pipes of many different lengths can be analyzed using a time step based on resolving the time-varying boundary conditions rather than solely on satisfying the Courant condition in every pipe segment.

This content is only available via PDF.
You do not currently have access to this content.