Transient surge modeling remains to be a specialized task and therefore quite unfamiliar to many engineers and designers. The process for discerning when to conduct a model can be vague. The process for how to conduct a model can be even more unclear and quite daunting. This paper serves as an introductory guide to an engineer or reviewing project manager new to surge modeling. The content within covers a brief overview of the physics behind transients, what information is required to create a computer surge model, the content within a surge report and how to interpret it.

The methods for understanding the surge modeling process can be broken down into stages, the first beginning with a general understanding of the physics behind transient pressure waves. Transient pressures also known as surge or water-hammer exist in all systems where there is a change in the fluid velocity. The magnitude of pressure rise, or pressure drop, depends greatly on how abruptly the velocity was changed as well as the system’s wave speed. The wave speed is a function of the elasticity of the fluid as well as the elasticity of the pipe. A rigid system with a sudden velocity change will experience a greater change in pressure than a flexible system with a slower change in velocity.

The next stage is to understand how the model is built and what information is required. A surge modeler will request numerous information including piping layouts, pump curves, valve characteristics and more. The inputs are used to build a transient model that mostly accurately reflects reality.

After verifying the model with steady state operations, the modeler works with the system engineer to understand the various modes of operation and will create a set of case scenarios. Additional scenarios for worst case “events” such as emergency shutdowns will also be established.

A rather tedious stage for a modeler is sizing an all-encompassing solution. It is not uncommon for a solution to be ideal for one scenario and quite problematic for another. A modeler must be keenly aware of the physics to appropriately size and locate an effective solution.

The final stage of modeling consists of summarizing the structure of the model and the results.  A surge report will include numerous key plots for review.

A project manager or reviewing engineering will read a report with numerous objectives in mind ranging from confirming inputs to most importantly understanding the transient risk. Finally, the reviewer will be discerning whether any design modifications suggested are viable and necessary.

Included within this paper are several references and detailed plots derived from actual projects.


The Process of Creating and Reviewing a Transient Surge Computer Model

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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