Date of Award

5-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Civil Engineering

First Advisor

Howell H. Heck

Second Advisor

Paul J. Cosentino

Third Advisor

Geoffrey Swain

Fourth Advisor

Luis D. Otero

Abstract

The major impact of water hammer on force mains integrity include excessive pressure oscillation that is usually accompanied by pipe vibrations. Models for simulating force main water hammer response have been developed. All of these models were based on the method of characteristics (MOC) and most of them were not calibrated for the lack of efficient field data. Although predicting maximum pressure during the first wave cycle is sufficient in most applications, some applications require precise prediction of pressure damping. One-dimensional models usually over predict pressure oscillation beyond the first cycle since they are based on steady friction expressions. It is also not well understood how pipes vibrate during water hammer events. The objectives were to: i) predict transient pressure of a force main system by a water hammer model based on the wave characteristics method (WCM) using Surge 2012 software and that model would be calibrated, validated and then used to perform surge analysis, ii) apply a one-dimensional water hammer model to predict surge pressure beyond the first cycle, and iii) determine the vibration characteristics of a pipeline subjected to water hammer conditions induced by rapid valve closure. A data acquisition system coded by LabVIEW software was built to collect field data. The WCM-based Surge 2012 software was used to model the South Beaches Force Main Sewer System (SBFSS). The model was calibrated, validated, and used to conduct surge analysis. An experimental small scale pipeline system was built. Valve closure experiments at different pipe material types, lengths, flowrates, and closure speeds were conducted and the induced transient pressure and acceleration were measured. The pipeline was modeled using Surge 2012 and a sensitivity analysis was conducted to determine the parameters affecting damping of pressure waves. The SBFSS model predicted field pressure during steady and transient states. Existing surge control devices were predicted to be sufficient to protect the pipeline under the worst case operational scenario. Sensitivity analysis determined the parameters that affect the sufficiency of a one-dimensional model to address the pressure damping issue. Water hammer-induced vibration was found to occur simultaneously with and correlate to surge pressure rise for different pipe materials. A pipe with lower modulus of elasticity was found to vibrate with higher amplitude and lower frequency than one with lower modulus of elasticity under the same conditions. Reducing pipe length for the same material type resulted in lower surge pressures and vibration levels but higher frequency.

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