Author(s): Bryan Karney, Johnathan Nault
Linked Author(s): Bryan W. Karney
Keywords: Water hammer; Transient flow; Incompressible models; Rigid water column;
Abstract: There is a natural tendency toward advocating progressively more sophisticated numerical models for both network and transient flow analysis. Yet, this can compound complexity in decision making since the systems themselves are invariably physically complex, the range of loadings they experience broad and evolving, and the need for practical and operational insight great. These realities in the context of practical decision making (whether decisions in design or operation) create a counter tendency that often rewards simpler, but still valid, insights and understanding. This paper argues that the rigid column (or incompressible) approach to unsteady flow model has important and often poorly understood advantages when dealing with large and uncertain transient flow phenomena particularly in complex branched and networked systems. Indeed, the paper argues that as the system moves away from particularly extreme (and undesirable) events, like sudden and valve closures or unprotected pump trips, into the domain of better managed and controlled systems, the degree of approximation associated with incompressible transient models progressively improves. Moreover such an approach leads to huge improvement in computational effectiveness and thus in the ability of the analyst to consider a broader range of loadings and system responses. These ideas are illustrated here for both large and small hydraulic systems displaying a range of transient behaviour. Specifically, it is shown that a well-formulated incompressible model can bridge the gap between quasi steady (i.e., extended period simulation) and full water hammer analysis.