Fluid and Machinery Dynamics

Test data from simulated pipeline ruptures were used to evaluate new rupture detection and control systems and to validate computer models of pipeline flow dynamics.

The Institute's fluid and machinery dynamics program encompasses machinery and piping technology, structural dynamics, acoustics, multiphase/multicomponent flow, microgravity fluid dynamics, hydrodynamics, gas dynamics, fluid/thermal systems diagnostics, and computational fluid dynamics. Investigations range from the development of space fluid systems, to research with gas industry consortia on advanced technology, to solving noise and vibration problems for automotive manufacturers and other industries.

The centerpiece of the Institute's gas flow metering research program is the Gas Research Institute (GRI)-owned Metering Research Facility located at SwRI. Research at the facility this year was funded primarily by GRI, but significant cofunding was provided by the American Petroleum Institute (API), the U.S. Department of Energy, and individual gas companies. Ongoing activities include the evaluation of piping installation effects on orifice and turbine meter accuracy and assessments of the performance of ultrasonic flow, rotary flow, and compact gas meters.

SwRI research has demonstrated that advanced computational methods provide key data regarding time-evolving flow fields in complex problems. Here, natural gas flow around pipeline orifice meters is simulated at 0.1-second intervals using computational fluid dynamics techniques and parallel computing. Orifice plates cause pressure oscillations that can affect metering accuracy. In these simulations, red areas indicate positive vorticity (counterclockwise rotation) and blue areas indicate negative vorticity (clockwise rotation). Analyses of simulated flow phenomena can contribute to more accurate methods of pipeline metering.

In a program for GRI, Institute engineers are investigating better ways of sampling pipeline gas to determine its composition, one variable that can significantly affect flow measurement accuracy. To transfer results of this and other projects from the laboratory to the field, SwRI conducts field studies to help individual gas companies solve measurement problems and teaches measurement short courses to gas company personnel. Routine flow meter calibrations for commercial clients are also provided, along with a number of programs to help manufacturers with prototype meter research and development.

A flow loop is being constructed to study multiphase transport of solids such as sand, paraffins, and hydrates that can block flow or cause erosion in pipelines. The solids and liquids of interest flow continuously through the loop without degradation, allowing simulation of many miles of pipeline.

Improved gas purging practices, as outlined in the American Gas Association's (A.G.A.) Purging Principles and Practices manual, were the goal of a recently completed project sponsored by GRI in cooperation with the A.G.A. The purpose of the project was to develop the scientific principles upon which safe, practical gas pipeline purging practices can be based. These principles, which were proven through field studies on various gas pipeline configurations, have been integrated into computer software that will help operators plan safe and cost-effective pipeline purges.

An important safety feature of many high-pressure, interstate gas pipelines is the automatic detection and isolation of pipeline ruptures using mainline block valves. While such breaks are rare, computer simulation studies conducted by SwRI, under contract to GRI, confirmed industry field experience that existing technology and equipment are sometimes unreliable in detecting and isolating mainline ruptures, and that normal pipeline operations can trigger unnecessary valve closures, thereby disrupting customer service. As a result of the studies, guidelines were written to aid industry in the selection, location, and adjustment of existing protective equipment, and computer models of pipeline flow dynamics were developed to improve rupture detection system reliability while minimizing false indications of line breaks.

The Institute continues to provide worldwide rapid response consulting and field testing services to assist machinery and piping system operators in obtaining safe, reliable, efficient performance from their plant equipment. An SwRI engineer recently traveled to the Tarim Basin of western China to investigate excessive vibrations in newly installed reciprocating oil field water injection pumps. These pumps are critical to oil field production. Prior to installation, the pumps met performance and vibration requirements. After installation of multiple pumps in the field piping system, system vibrations occurred, causing excessive downtime. The Institute was asked to identify the cause of the vibrations and develop a solution to the system problem. Data from an on-site survey of dynamic pressure pulsation and vibration were used to model the system in the Pipeline and Compressor Research Council (PCRC) Design Facility at SwRI. The model achieved excellent correlation with measured pulsations. Piping modifications were then developed, fabricated in the U.S., shipped to the site, and installed, solving the vibration problem.

This reciprocating oil field pump is part of a piping system located in western China. The pump installation recently experienced system vibration problems that resulted in pipeline attachment failures. SwRI engineers diagnosed the source of the vibration through field measurements and solved the problem using PCRC Design Facility modeling capabilities.

A multiyear research effort is under way for the PCRC to examine factors related to large reciprocating compressor foundation- and mounting-related problems, which have been identified as a major maintenance cost for gas pipeline companies. The study is developing a better understanding of foundation performance as well as methods to extend foundation life and properly design new foundations. Deteriorated foundations permit excessive movement of the compressor frame that can result in bearing and crankshaft failures. Research efforts in the past year have focused on aspects of the compressor mounting system. The as-built friction coefficients of various chock mounting materials are being determined experimentally in a specially configured test apparatus that uses near-full-scale mounting chocks. Information gained from these experiments will enable designers to specify more accurately the anchor bolt preloads necessary to hold the compressor in place.

A customized laboratory test apparatus is being used to study foundation-related problems for large reciprocating compressors. Test results should enable a better understanding of compressor tie-down requirements to withstand the large shaking forces produced by these machines.

Catastrophic failures in reciprocating compressors, while rare, can seriously affect refinery productivity and profitability. To address the problem, SwRI engineers have combined expertise in compressor technology, instrumentation, digital signal processing, statistical analysis, and pattern recognition to develop a smart transmitter. The device continuously acquires time-varying pressure readings from a compressor cylinder and extracts key characteristics such as maximum, minimum, and mean values. In real time, the transmitter looks for statistically anomalous patterns that immediately reveal the occurrence of a catastrophic fault, such as total loss of a cylinder valve or rod packing, and provides for an automatic shutdown or alarm. The transmitter can also relay the pressure record to a host computer, as a basis for detailed performance calculation, observable trends, and diagnostics. The project team has tested the device in the laboratory and plans to demonstrate and evaluate its capabilities in a new refinery compressor installation in 1997.

An internally funded research initiative was launched this year to aid the oil and gas industry in deep water production flow. High pressure and near freezing temperatures in the deep water environment enhance the formation of hydrate and paraffin blockages in pipelines, which can reduce or stop oil and gas flow. A unique multiphase flow test facility under construction at SwRI will be used to simulate field conditions and to test solutions for preventing and remediating hydrate blockages. Under contract to the oil company consortium DeepStar, SwRI will also perform field trials to create hydrate blockages and then test methods to remove them on a production pipeline in Wyoming during the winter of 1996-97.

The Institute continues development of an experiment to investigate how liquid motions in the propellant tanks of spinning spacecraft affect the stability and control of the spacecraft. Part of NASA's In-Space Technology Experiment Program, the SwRI payload will be housed in the mid-deck lockers of the space shuttle on a 1997 flight. The experimental hardware and electronics have been constructed and are undergoing qualification testing. Representatives from spacecraft manufacturers serve on an advisory panel for the experiment, to ensure that the experiment design and results meet national space program requirements. In a related internal research program, analytical models of liquid motion in spinning tanks are being developed to predict and better understand the results of the NASA flight experiments.

SwRI investigates the effects of adverse environments on the functional integrity of mechanical and electromechanical components. Institute engineers recently updated a bearing test stand for the U.S. Air Force with state-of-the-art mechanical and electrical components. SwRI is using the test stand to determine the reliability of flight-critical bearings used in T-38 aircraft by testing the bearings, as installed in the subsystem of the aircraft, under simulated operational load conditions. Methods to increase the mean time-to-failure of these components are being determined that will improve the reliability of the T-38 and extend periods between maintenance.

The gas transmission industry operates thousands of reciprocating compressors driven by large (3,000-10,000 horsepower), gas-fueled, two-cycle engines. Small fluctuations in fuel gas delivery and combustion result in wide variations between the peak firing pressures in different cylinders. For years, operators have manually balanced these engines by making small adjustments in the fuel flow to each cylinder until the peak firing pressure in all cylinders falls within an acceptable tolerance band. Recently, a commercial company introduced an automatic balancing fuel flow system that helps control emissions and reduce fuel consumption. Institute engineers are working with a group of pipeline companies and the system manufacturer to determine whether autobalancing can also improve compressor mechanical integrity by reducing damage-causing mechanisms such as vibration and crankshaft speed variation.

1996 Annual Report SwRI Home