ABSTRACT

Vibroacoustics is a relatively new area in the field of engineering science. It consists of elements of vibration theory, acoustics, and the theory of measurement of dynamic quantities. Typical applications include problems of noise and vibration control, dynamic model identification, manufactured parts identification, and diagnostics of manufacturing machines. This field, characterized by rich empirical achievements but with less well-developed theory, has numerous applications to manufacturing engineering.

In the past, vibration and noise have tended to be treated as separate problems. It is important, however, to begin training engineers to recognize that noise and vibration are an integrated problem, a matter of cause and effect.

The technology program at the bachelor's and master's level at SIU Carbondale focuses on manufacturing. A course in vibroacoustics will be offered as a technical elective in the program to be taken by students during their senior year or during graduate study.

This paper outlines a designed course that includes class and laboratory sessions that emphasize the principles and concepts of noise and vibration phenomena. Students will have an opportunity to learn in the classroom as well as in the laboratory, about passive and active noise and vibration control, acoustics absorption and transmission loss of materials, and diagnostics of machines and machine components.

INTRODUCTION

In recent years scientists have observed the rise of a separate branch of science and engineering called "vibroacoustics." It is a combination of the elements of sonics, theories of vibration and measurements of dynamic processes and techniques of technical diagnostics. This field, characterized by rich empirical achievements but with less well-developed theory, has numerous applications to manufacturing engineering [1, 2, 3].

At the present time, we observe the trend of designing and manufacturing products with lightweight, material-saving construction, which are as a result characterized by relatively low stiffness and a tendency to vibrate at low frequencies. At the same time, consumers are increasingly conscious of noise and seek quieter products. In addition, there is the controversy of an expanding trend to reduce noise levels not only in the workplace but also in the environment. To reduce workplace, or industrial, noise the vibroacoustic behavior of manufacturing equipment assumes a special importance. It should also be noted that vibration and noise processes are related to the quality of manufacturing and the operational condition of the manufacturing machine. Therefore machine noise and vibrational analysis may serve as a diagnostic measure of the state of the machine and also the quality of the product [3, 4].

All of the above mentioned factors make the measurement and analysis of vibration and noise in manufacturing machines as well as consumer products an object of intensive engineering and scientific research and point out the necessity of developing a new generation of engineering professionals. They should be trained to handle vibroacoustics problems in manufacturing operations and in the development of new products and consumer goods.

Vibration and noise have tended to be treated as separate problems. It is important, however, to begin to train engineers to recognize that noise and vibration are an integrated problem, a matter of cause and effect. Laboratory training is an essential element in the teaching of engineering students to solve vibroacoustical problems.

PROPOSED COURSE BACKGROUND

The technology program at the bachelor's and master's levels focuses on manufacturing. In addition, Southern Illinois University at Carbondale has proposed and developed a Bachelor of Science program in Manufacturing Engineering and is currently seeking final approval by the Illinois Board of Higher Education. A course in vibroacoustics will be offered as a technical elective in this program and is designed to be taken by students in their senior year or during graduate study. Two factors guide the conduct and content of the course: (1) needs of industry for our manufacturing-oriented graduates and (2) the proper preparation of students trained in that technical field.

Students not going to graduate school will move directly into entry-level engineering jobs. Our B.S. graduates often work in organizations that are highly structured and where new engineering employees are supervised by senior technical staff. When new graduates are given assignments requiring analysis testing or design of dynamic systems, they tend to work on engineering teams which include experienced professionals in these areas. Our graduates will be expected to have a broad knowledge in noise and vibration and should bring specialized training on the theoretical and experimental aspects of vibration and noise, as a unified problem, into the group.

Students enrolled in vibroacoustics will be required to have completed calculus and the equivalent of eight semester hours of statics, dynamics and strength of materials. Students will also be required to have completed physics, material sciences and a course on the design of mechanical components in manufacturing.

COURSE DEVELOPMENT

Considering the academic background and the needs of our future bachelor degree seeking students, we have designed a course in vibroacoustics that emphasizes basic principles and concepts of noise and vibration phenomena. A partial list of topics and laboratory experiments anticipated in vibroacoustics includes:

1) Course topics:

• Review of statics, dynamics, strength of materials, and physics
• Nomenclature in both vibration and sound areas
• Single waves, transverse, longitudinal, and torsional periodic motions
• Single tone, acoustical field, normal and diffused signals, property of sound in a reverberation room
• Time and frequency domains, representation for periodic and transient motion
• Simplified models
• One degree of freedom vibrations (free, forced, undampened, dampened)
• Vibrations of continuous systems
• Vibration isolation and control (passive and active)
• Energy transfer
• Introduction to smart materials
• Noise control, passive and active designs (transmission loss through barriers and absorption of barriers)
• Generated noise and vibrations versus the state of manufacturing machines and product quality
• Examples of noise and vibration spectrums generated by new and worn machine parts
• Detection and identification of immediate defects of machines parts

2) Laboratory experiments

1. Vibration and sound basic phenomena
   • Computer simulation of one and two degrees of freedom vibration, including passive control. Several IBM workstations located at the Department's main building classroom will be used.
   • Vibrations developed by sound wave and sound waves generated by vibrations of plate
   • Active control of one-degree-of-freedom vibration experiment
   • Active control of single acoustical waves in a channel experiment
2. Property of materials
   • Absorption measurements using an impedance tube and the Sabine method (reverberation time measurements)
   • Transmission loss measurements
3. Diagnostics of machine components
   • Measurements of the vibration and noise spectra (sound intensity) in frequency and time domains of new and worn out anti-friction bearings
   • The same for gears

   EXISTING LABORATORY POTENTIAL

   Currently the Vibration and Acoustic Laboratory located in the College of Engineering at Southern Illinois University at Carbondale is one of the largest in the state with a value of over $300,000 in instrumentation alone. It allows us to perform vibroacoustical property measurements in both the areas of frequency domain and time domain. We are measuring, on almost a daily basis, the physical properties of vibrating systems and acoustical products such as transmission loss, absorption property, rate of sound pressure decay, dynamic response of structure and characteristic acoustics impedance. Almost half the student experiments in a vibroacoustics laboratory, during the time of writing this paper, are related to the above mentioned frequency and time dependent measurements of dynamic properties of the system.

   SUMMARY

   A course in vibroacoustics in manufacturing will be offered as an undergraduate technical elective for senior year students in the Manufacturing Engineering Department at Southern Illinois University at Carbondale. In vibroacoustics, mechanical vibrations and noise are treated as processes which have similar causes and properties. Students are required to have completed calculus through differential equations and the equivalent of eight semester hours of statics, dynamics and strength of materials.

   Integral to the course is a short design project and laboratory sessions. Laboratory experiments are divided into three groups. At the beginning, students learn vibrations and sound phenomena and conduct experiments with adequate simulating programs. Several workstations will be used. In two other laboratory experiments, "properties of materials" and diagnostics of machines," measurements will be carried out in a vibration and acoustics laboratory. Some of the most important experiments are related to passive and active vibration and noise control, the use of smart materials, generated noise and vibration versus the state of the manufacturing machine, product quality, and detection and identification of defective machine parts. Although the Vibration and Acoustics Laboratory at SIU is one of the largest in Illinois, with a value of over $300,000, the facility and instrumentation is not adequate for all of the above mentioned modern teaching tasks in the vibroacoustics field. With additional instrumentation support, we will better prepare our students to face new technologies, modern designs and manufacturing problems.

   REFERENCES

   [1] William Tyrell Thomson. "Theory of Vibration with Applications." Prentice Hall, Englewood Cliffs, New Jersey, 1988.

   [2] M.L. James, G.M. Smith, J.C. Wolford, and P.W. Whaley. "Vibration of Mechanical and Structural Systems: With Microcomputer Applications." Harper & Row, Publishers, Inc., New York, 1989.

   [3] Lewis H. Bell. "Industrial Noise Control." Marcel Dekker, Inc., 1993.

   [4] Charles E. Wilson. "Noise Control." Krieger publishing Company, Inc., Malaber, Florida, 1994.

   MAREK L. SZARY

   Dr. Marek L. Szary is an Assistant Professor in the College of Engineering at Southern Illinois University at Carbondale. He has extensive knowledge and long-term experience in the field of noise and vibration. The author currently directs a research project supported by United Technologies-Automo-tive (UT-A). He also has long term experi-ence in industrial noise and vibration control. Other projects include noise surveys in manu-facturing plants, study and measurement of noise generated by hydraulic and pneumatic components, and noise surveys and design of new acoustical absorbers for local clients.

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