Known flows are a special type of fixed load. Known flows remain constant as they progress downstream, and combine directly as a simple sum similar to additional loads. The overwrite behavior of known loads is special. When another known load is specified at a downstream inlet, the local known load replaces the upstream known load, rather than the local known load adding directly to the upstream known load. If the local known flow is left equal to 0, the upstream flow is propagated downstream without being overwritten. A non-zero flow input at any inlet will be used regardless of the magnitude of the combined incoming known flow loads.