Military

May 2002 Excerpt

Understanding Piping Systems and Noise Flanking Paths

By Dr. Ed Graesser and Leslie Spaulding

PHILADELPHIA—Stealth is one of the primary considerations in design and operation of ships and submarines in the Navy Fleet. Machinery silencing is a key technology in this endeavor. Research and development into making U.S. Navy ships quieter is an ongoing process that takes into account all noises produced by the ship. One very important aspect is the so-called “flanking path.”

Interconnections between machinery noise sources and the hull are called flanking paths for noise transmission, because they often flank out physically in many directions. These may consist of structural connections, piping, bulkheads, and so on. The air inside the ship is also considered to be a flanking path, as airborne noise within the machinery space can (at certain frequencies) propagate through the hull to become a transmitted noise. A program of work started by the Office of Naval Research (ONR), within the Submarine HM&E Technology Program, is primarily focused on study and characterization of selected piping components found in typical flanking paths, with some endeavors into the study of airborne flanking pathways also. The program has expanded and evolved, and has recently been spun-off under NAVSEA sponsorship to address piping system arrangements of practical interest, plus larger piping systems and components, which are within propagation pathways of machinery noise sources.

The ONR program has set forth a technical foundation for measurement and experimental methods, along with required prediction methodologies. The final product is the ability to make piping arrangement designs and analyses concurrently with accurate acoustic predictions of sound and vibration, along any given piping pathway. In the NAVSEA sponsored programs that have followed, these foundation technologies are being used in conjunction with more specific piping system and component noise studies. The work to date has been a cooperative endeavor involving ONR, NAVSEA, NSWC, and private industry partners. ONR has provided direction and funding for focused studies and technology development. NAVSEA subsequently provided funds and direction in follow-on efforts.

“Concerning piping systems and components, we take into account the propagation of vibration along the structural wall of the pipe, as well as the propagation of sound pressure in the fluid column,” said Dr. Ed Graesser (842). “We are also interested in how they originate at the source, how they transmit along the pathways, and how they interact with components. We are particularly interested in what reflection, transmission, and scattering characteristics exist at connections with components.”

The methodology being used involves a relatively new means of experimental characterization, known as array processing, to discriminate propagating noise according to distinct wave types. Array processing tests make use of many hundred small accelerometers that permit discrimination of the sound and vibration into distinctly quantified levels according to frequency and wave type. The advent of large-channel high-speed acquisition and data processing hardware, plus miniature sensors has permitted the development of the current level of technology. “This is a level of sophistication in study of noise and vibration that has not been brought to bear previously for machinery piping/flanking pathways.” It is noted that advanced hardware, software, instrumentation, and sensors for the program were purchased under the Capital Procurement Program (CPP).

The program began in late 1996 at the Annapolis Laboratory and was transitioned to Philadelphia in 1999 when Code 84 was moved as a result of BRAC ‘95. Testing and characterization began with a carefully selected set of shipboard components. “We chose a variety of components that are fairly common and representative of those actually aboard ship,” said Graesser.

Tests were first conducted on single components and then (later) on a variety of piping system arrangements. For example, tests were conducted on a bend in a 3” pipe, as well as a typical shipboard 3” valve, and also on a 3” pipe hanger. Other components were also evaluated in other various pipe sizes. “For any component, we generally characterize the reflection, transmission, and scattering of both structural vibration and fluidborne sound pressure,” explained Graesser. “But, many times we will also characterize the noise generation of the component itself, in the presence of fluid flow. Imagine high flow rates of water flowing through a pipe and going through a sudden restriction or change in direction. We are interested in measuring the noise generated by that phenomena, as well as determining what physical mechanisms cause it.”

After working through a series of single components, attention was also paid to a variety of more complex piping set-ups, which included a complex multi-component test in a 3-dimensional system arrangement. These took place in the Machinery Silencing Facilities in Philadelphia (Bldg. 87).

The specially designed laboratories at Philadelphia provide a unique setting with very quiet background for such work. The site offers extensive support and infrastructure facilities including very low noise laboratory areas having high capacity overhead cranes, generation and storage capacity for very large volumes of clean (deareated) water, isolated floors with very high load ratings, sump and drain facilities, and an extensive high capacity cooling water system.

In addition to tests for quantification of acoustic energy reflection, transmission, and scattering properties of piping components, methods for prediction of noise propagation on more extensive shipboard pipe systems have been developed. A transmission line modeling and prediction code was developed and delivered by Anteon Corporation of Mystic, Conn., under contract to the ONR Flanking Path project. This code will enable engineers to design and/or analyze a piping system using a hybrid combination of theoretically characterized and experimentally measured components. For example, plain pipes and simple symmetric components will be analytically represented to gain required properties needed for input to the transmission line model. More complex devices (such as valves, hangers, bends, tees, damping treatments, etc.) will be characterized in the array-measurement test. Transmission line models (from matrix-based formulations) of complete piping system layouts will enable the design engineer to assess the implications of component arrangements from a noise and vibration perspective. Elegant low-cost design studies will be easier and more convenient to conduct with accuracy. This will permit effective and efficient arrangement of equipment in piping system designs. It will also allow for evaluation of noise reduction ideas and designs, by employing information from finite element models.

It is estimated that knowledge gained from flanking path work will lead to modeling and prediction refinements that will permit highly effective design and arrangement rules. These will enable savings in terms of design and analysis costs, as well as ship construction costs. “Reduction in vessel weight is also an intended outcome, since noise mitigating treatments will be able to be applied more efficiently and effectively.”

Sponsorship originated at the Office of Naval Research under 6.2 and 6.3 efforts. The program was initially executed by Dr. Vern Simmons, and is now sponsored by Steve Shreppler (ONR Code 33, for 6.2 task phases) and Gary Jebsen (Code 33, for 6.3 task phases). William Martin (Code 7014) is the program’s execution manager. The ONR-sponsored pipe/ flanking path work has been transitioned to new NAVSEA sponsorship, which will be a more focused development effort, under the Internal Transmission Paths and SeaCAST programs.

Personnel involved in the Flanking Path program include: Fred Flickinger (8403) as present POC and program coordinator for Code 80; David Larrabee (8409) as previous POC and program coordinator for Code 80; Dr. Graesser (842), Dr. Debra Kenny (841), Kevin Crouchley (843), and Scot Palmer (842) provided senior engineering and technical leadership for Code 84. Engineering and technical laboratory support was provided by Michael Grady (842), James Meriwether (842), Robert Valtos (842), Larry Smith (842), and Jeff Biscardi (842) among many others. Piping system fabrication was provided by Tim Jackson (914) and Howard Feinstein (91414). Electrical installations were provided by Mike Sweeney (91412) and Naz Thomasetti (3632).

The important aspects of data acquisition methods and signal processing tools were primarily developed by ANTEON/ Engineering Technology Center (ETC) of Mystic, Conn., and Cambridge, Mass. Key members involved in array processing development, test design, data analysis, and prediction methodology also included Anteon/ETC staff—in particular: Dr. Chick Corrado, Dr. Matt Conti, Dr. Bruce Abraham, Dr. Anne Stokes, and Dr. Michael Dignan.