If the mass m is displaced and then released, or the rotor in the steam turbine is struck, a fundamental motion will occur in an undamped system. Think of it as a mass hanging on a string or as a swing set in the park. Explaining what caused a failure, along with the proposed solution, to those not well versed in vibration and metal fatigue can be a challenge. This is true for all vibration systems. Next on the speed increase of the machine is the 2× resonance peak, which is due to misalignment and peaks at 2000 rpm. Others can be found in structural steel catalogs. As mentioned earlier, velocity and displacement are available from acceleration through electronic integration.
Many are reduced to two-mass systems, but multimass systems are also evaluated. In Chapter 7 we analyze piping and pressure vessel vibration. You can eliminate some possibilities if the original system was running well. Soft foot is a term used when one mounting point or foot of a motor or pump pulls down more than the others. As it passes through, the amplitude drops off just as quickly. Since metal fatigue is caused by cycling forces and moments, vibration is introduced.
In Chapter 5 we review problems that vibration can cause and the sources of the problems. There are many formulas in vibration books e. Case Histories in Vibration Analysis and Metal Fatigue for the Practicing Engineer, First Edition. As mentioned earlier, various failure events have frequency signatures associated with them. Talking with those who use the device everyday and making contacts in industry will usually pay for itself if you can predict one failure before teardown. Therefore, load combinations were a part of the testing plan.
In Chapter 9 rotor dyna- mics are discussed, but here only the actual startup vibration is shown. It takes a simple, analytical approach to the subject, placing emphasis on practical applicability over theory, and covers both fixed and rotating equipment, as well as pressure vessels. Although much vibration testing was done, this analysis looks at understanding the cause and explaining the nomenclature along the way. Chemical Engineering Progress, 1 May 2013 In all, this most recent Sofronas text is readable, practical and valuable throughout. M values are established Case Histories in Vibration Analysis and Metal Fatigue for the Practicing Engineer, First Edition. .
Depending on their magnitude, with the present system, balancing and realignment could be required. However, it is useful for explaining simple harmonic motion. It takes a simple, analytical approach to the subject, placing emphasis on practical applicability over theory, and covers both fixed and rotating equipment, as well as pressure vessels. The piezoelectric accelerometer shown in Figure 3. Jerk During Slow Roll 10. The spring supports were such that they were at nodal points of the beam and were very soft relative to the platform, so can be neglected in this analysis. A locomotive was being designed that required two engines instead of one in the center of the platform structure, as shown in Figure 2.
It is important to have some baseline value with a good running machine; however, in this case a problem is obvious. Case Histories in Vibration Analysis and Metal Fatigue for the Practicing Engineer Chapter 1 Introduction Chapter 2 Basics of Vibration 2. When two pieces of metal in motion contact each other, such as a ball on a race, two interrelated yet distinct processes occur. An example will show this relative effect. Covers the basic principles of weld fracture and fatigue. She has been extremely helpful in suggesting better wording for many of the sections.
The locomotive platform was essentially two long I-beams boxed in on the top and bottom as shown, although these details are not important for this frequency calculation. These are vibrating at X displacement, and K is the spring constant, that is, how much the load statically displaces the springs. This is a problem with single-degree-of- freedom models of which the analyst must be aware. The subject of metal fatigue is in the book simply because excessive vibration often results in fatigue failures. The rod would be free to swing. Since this could be false 60-cps electrical noise, a check that is some- times used is to cut the electrical power and watch the coast-down.
This represents a vertical pump shaft and impeller hanging from the motor. A Holzer analysis is shown for spreadsheet use and can be used to analyze the frequencies, mode shapes, and relative torques and forces for torsional and linear multimass systems. The 1 × rpm, 2 × rpm, and so on, lines are drawn as shown. Library of Congress Cataloging-in-Publication Data: Sofronas, Anthony. This would be the case if a spectrum analyzer were used to collect the vibration data.
Comparing the spectrum analysis data with the mesh frequencies may not always produce the correct answer unless the time domain is also reviewed. If it was present since installation, it may be a basic system problem such as a resonance problem, poorly designed shaft, poor balance, an installation problem, or just the wrong equipment selection for the service. This fairly simple multistage steam turbine will be reduced to a simple system so that the fundamental natural frequency can be determined. In a design review meeting a question arose regarding whether the two engines might excite the platform enough to cause a disturbance. Another reason for analyzing this type of transducer is that all the quantities i. The importance of this is that the measurement of one quantity at a given fre- quency can be used to calculate the other two. The engine is vibrating considerably, but no damage is being done to the engine.