Steps Toward Redeeming the Physical and Practical Insights of the Often-neglected "rigid column" Approach to Transient Analysis

There is a natural tendency over time toward adopting progressively more sophisticated numerical models for transient flow analysis. Yet, the systems themselves are complex, the range of loadings they experience broad, and the need for practical and operational insight great. These competing realities in the realm of practical decision making (whether in design or operation) have a tendency of rewarding simpler rather than more complex insights and understanding. It is the contention of this paper that the rigid column approach (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 and those with problematic response.

Indeed, the paper argues that as the system is moved away from particularly extreme events, like sudden and complex valve closures, into the domain of better managed and controlled systems, the degree of approximation associated with incompressible transient models tends to progressively improve, with huge improvements in computational efficiency and thus the ability to consider a broader range of loadings and responses. These ideas will be illustrated in the paper for both large and small hydraulic systems displaying a range of transient behaviour. Moreover, 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.