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Technical Papers

The present study highlights the importance of proper check valve selection to mitigate waterhammer and its associated problems. Two different check valves were installed in a pumping station in a municipal water transfer system: a swing check valve and a nozzle check valve. Measurements were taken of pipeline pressures after a pump trip and resulting check valve closure. The field data was compared to predictions from a model using a commercial waterhammer tool. Commonly accepted methods for estimating reverse liquid velocity at check valve closure were utilized. Results were also compared to previous experimental test from other authors. The calibrated model results matched the field data quite well. Comparisons of inferred valve characteristics to previously published results for swing and nozzle valves were not in close agreement for either tested valve.

Making the world a safer and better place – a plea for more data, validation cases and guidelines for waterhammer simulation
Engineers tend to overdesign systems when uncertainty exists. Overdesign is an important part of the engineering process, but unnecessary overdesign will only increase the cost of systems without enhancing safety. An experience between a major pipeline company,  their engineering design firm, and the waterhammer simulation software products used by both is described. A disagreement between software package results and ultimately the two companies developed into an issue that could significantly increase costs. More and better validation cases would have helped everyone navigate this situation more quickly, easily and inexpensively. More and better application guidelines may have helped the engineering design firm achieve higher certainty in their recommendations with potentially less overdesign.

The transient analysis of reverse flow and rotation in pumps has evolved over the years into modern four quadrant pump waterhammer simulation. Key assumptions are made when mapping manufacturer curves to four quadrant data sets. When operating away from steady-state rated conditions, these assumptions can cause extreme differences in the simulation. If these assumptions are unaddressed, critically incorrect conclusions about the system’s transient behavior may be made, impacting both design and operation. Waterhammer engineers are strongly encouraged to include sensitivity studies to address the uncertainties identified in this study.
 
Surge modeling of complex systems such as marine fuel oil terminals requires the use of accurate computer modeling techniques to help ensure the best possible response to surge events. Various surge mitigation techniques can be pursued that often require information that manufacturers rarely provide and have behavior that is problematic to replicate in a computer model. This paper provides guidance with one such device, the surge relief valve, and offers a case study in how they were used in conjunction with valve stroking to mitigate significant surge events at a terminal in the gulf coast region of the United States. 
 
The Joukowsky equation has been used as a first approximation for more than a century to estimate water hammer pressure surges. However, this practice may provide incorrect, non-conservative, pressure calculations under several conditions. The fundamental goal here is to alert practicing engineers of the cautions that should be applied when using the Joukowsky equation as a first approximation of fluid transient pressures.

A Proposed Guideline for Applying Waterhammer Predictions Under Transient Cavitation Conditions Part 1: Pressures and Part 2: Imbalanced Forces
Part 1 of this paper describes the various safety factors already provided by ASME B31.3 for pressure containment, provides criteria for accepting the results of HTA calculations that show the presence of transient cavitation, and makes recommendations where the user should include additional safety factors based on the transient cavitation results.

Part 2 discusses methods of accounting for uncertainty in HTA imbalanced force predictions due to cavitation. The criteria in this paper assume that cavitation in the HTA has been assessed and accepted per the criteria in Part 1 of this paper.

Pulsation Analysis in Positive Displacement Pump Systems Using Waterhammer, Modal and Animation Software
This paper describes a methodology to computer model pulsation— steady state pressure and flow dynamics— using a combination of general-purpose and readily available, widely used software. The software used includes AFT's waterhammer and surge analysis software, AFT Impulse. Pulsation is a common problem in positive displacement (PD) pump systems, which can cause high vibration, fatigue failures, frequent maintenance outages, and flow uniformity or product quality problems.

Hydraulic Model Calibration of a Nuclear Plant Service Water System
As pipe networks age, build-up (scaling) and corrosion decrease pipe diameter and increase pipe roughness, leading to significant pressure drops and lower flow rates. When modeling the hydraulics of these systems, calibrating the pipes to account for additional scaling and/or fouling can be vital to accurately predict the hydraulic behavior of the system. An automated, multi-variable goal-seeking software, AFT Fathom and its Goal Seek & Control (GSC) Module, was used to calibrate the raw water system of the Duke McGuire Nuclear Station (MNS). This calibration process involved three phases, and the automated goal-seeking software was found to have varying degrees of success in each phase.

Resolving Operational Problems in Pumping Non-Settling Slurries
A case history is presented pertaining to five pumping systems that operated satisfactorily until a new production requirement was imposed on the pumping systems. A new slurry product was introduced for an initial trial run, and problems began to surface immediately. This manufacturing problem had not been anticipated by the team, and without quick resolution, a loss of customer confidence and a significant delay in the new product would have resulted. AFT Fathom was used to model the systems to better understand the hydraulics.

Knocking the SOx Off Emissions
Curbing SOx emissions from thermal power plants remains a challenge for operators, but a project involving the refurbishment of the flue gas desulphurization installation at a Polish power plant offers a way forward. The main goal of this paper is to present results of numerical simulations of flue gas system in the GDF Suez Polaniec power plant carried out in AFT Arrow and to compare them with the measurements collected during actual plant operation.

Cutting Costs in Pump and Pipe Sizing
This paper examines how a new design technology, AFT Mercury, allows plants to achieve more cost-effective designs. Engineers can go beyond specifying their piping systems and identifying pumps that will do the job— now they can bring cost data directly into the pipe and pump-sizing process and access a new intelligent piping system design technology.

Optimizing Pumping Systems to Minimize First or Life-cycle Cost
Recent studies have found that pumping systems account for about 20 percent of world energy usage (Frenning, et al., 2001). With the abundant opportunity for cost and energy reduction in new pumping systems, the need exists for technologies that will allow engineers to optimize pumping system designs to minimize cost and energy usage. The commercial software, AFT Mercury, addresses this need.

X-34 High Pressure Nitrogen Reaction Control System Design and Analysis
The X-34 program is developing a reusable launch vehicle that will be capable of reaching Mach 8 and 250,000 feet. Orbital Sciences Corporation of Dulles, Virginia, has the responsibility for design and performance verification of the system as prime contractor for the X-34 program. AFT Arrow was evaluated, selected and purchased for analyzing the reaction control system performance, and its analysis results confirmed the system is properly configured to meet mission objectives.

Gas-Flow Calculations: Don't Choke
Flow of gases in pipe systems is commonplace in chemical-process plants. Unfortunately, the design and analysis of gas-flow systems are considerably more complicated than for liquid (incompressible) flow, due mainly to pressure-induced variations in the gas-stream density and velocity. This technical paper reviews practical principles and presents some key equations governing gas flow, and assesses several assumptions and rules of thumb that engineers sometimes apply in order to simplify gas-flow analysis and calculations.

Analytical Approaches To Modeling Transient Vaporous Cavitation in Multi-Pipe Fluid Systems
An extension of the Vaporous Cavitation Model method for modeling vapor cavity formation during liquid column separation in transient flows is made to eight common fluid system connecting elements. A comparison to experimental data for three of the elements is made to recent data for a nonstraight pipe. Reasonable agreement with the data is shown, although very large vapor cavities occur in the system.

Rocket Propellant Line Waterhammer Transients In a Variable-G Environment Multi-Pipe Fluid Systems
Waterhammer pressure transients are generated in liquid-filled pipes when the velocity of the liquid is increased or decreased. Rapid velocity changes (such as an instantaneous valve closure) can lead to very high pipe pressures that may damage the piping system. The fundamental equations of waterhammer can be found in standard references (1, 2. ~. and their solution by the method of characteristics has become a straightforward process when performed on a digital computer. 

Optimization of Sea Water Pumping System
Describes the optimization of a high-pressure seawater pipeline being constructed to increase oil production from an oil field in Khurais, Saudi Arabia. Consisting of approximately 145 km of pipeline and several pumping stations, the optimization addressed both initial operational requirements and planned expansions over ten years and included both first and life-cycle costs.