Technology & Engineering
Vibration Isolation
Vibration isolation is a technique used to reduce the transmission of vibrations from a source to its surroundings or from the surroundings to the source. This is achieved by using various materials and mechanisms to absorb, dampen, or redirect the vibrations. Vibration isolation is important in engineering to protect sensitive equipment, improve performance, and enhance comfort.
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10 Key excerpts on "Vibration Isolation"
- Frank Fahy, John Walker, Frank Fahy, John Walker(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
12.3 Vibration Isolation Vibration Isolation is the dynamic decoupling of two connecting systems and is usually achieved by placing a resilient element (isolator) in the trans-mission path. In practice, two common situations occur: (a) isolation of a vibrating machine from its surroundings; (b) isolation of a delicate piece of equipment from a vibrating host structure. Vibration control 545 At relatively low frequencies, when flexural wavelengths in the source and receiving structures are long compared to their dimensions, vibration isola-tion can be considered using simple lumped parameter models, and this is now reviewed. This elementary analysis has some merits, but it also has various deficiencies when considering high-frequency Vibration Isolation. In this context the term ‘high frequency’ is used when the vibrating source or the isolator or the receiving structure exhibits resonant behaviour. An alternative modelling approach, which enables the high-frequency dynamics of the system to be accounted for, is also described in this section. Finally, some issues, such as moment excitation and isolator placement are briefly mentioned with references to further reading on these subjects. 12.3.1 Simple approach The simple approach to the problem of Vibration Isolation is to view the system as a single-degree-of-freedom system and to examine its frequency response. Cases (a) and (b) in Section 12.3 are depicted in Figure 12.14 where F e F t X e X b the complex amplitudes. The machine and the equip-ment are assumed to be point masses and the isolators are modelled as massless springs with hysteretic damping.
eBook - PDF- Clarence W. de Silva(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
7.3 Vibration Isolation The purpose of Vibration Isolation is to “isolate” the system of interest from vibration excitations by introducing an isolator in between them. Examples of isolators are machine mounts and vehicle suspension systems. Two general types of isolation can be identified: 1. Force isolation (related to force transmissibility) 2. Motion isolation (related to motion transmissibility) In force isolation, vibration forces that would be ordinarily transmitted directly from a source to a supporting structure (isolated system) are filtered out by an isolator through its flexibility (spring) and dissipation (damping) so that part of the force is routed through an inertial path. Clearly, the concepts of force transmissibility are applicable here. In motion isolation, vibration motions that are applied at a moving platform of a mechanical system (isolated system) are absorbed by an isolator through its flexibility and dissipation so that the motion that is transmitted to the system of interest is weakened. 8 Motion Sickness Region 4 2 30 min. Trips 1.0 0.8 0.6 0.4 2 hr Trips 8 hr Trips 0 .2 0.1 0 .2 0 .4 0 .6 0 .8 1.0 Frequency (Hz) RMS Acceleration (m/s 2 ) FIGURE 7.3 A severe-discomfort vibration specification for ground transit vehicles. Vibration Design and Control 7 -5 The concepts of motion transmissibility are applicable in this case. The design problem in both cases is to select applicable parameters for the isolator so that the vibrations entering the system are below specified values within a frequency band of interest (the operating frequency range). Let us revisit the main concepts of force transmissibility and motion transmissibility. Figure 7.4(a) gives a schematic model of force transmissibility through an isolator. Vibration force at the source is f ð t Þ : In view of the isolator, the source system (with impedance Z m ) is made to move at the same speed as the isolator (with impedance Z s ).
eBook - PDFVibration
Fundamentals and Practice, Second Edition
- Clarence W. de Silva(Author)
- 2006(Publication Date)
- CRC Press(Publisher)
Before completing this section it should be noted that the specifications we are con-cerned with in the present context of design and control are upper bounds of vibration. The system should perform below (within) these specifications under normal operating conditions. Test specifications are lower bounds. The test should be conducted at or above these vibration levels so that the system would meet the test specifications. Some consid-erations of vibration engineering are summarized in Box 12.1 12.3 Vibration Isolation The purpose of Vibration Isolation is to ‘‘isolate’’ the system of interest from vibration excitations by introducing an isolator in between them. Examples of isolators are machine mounts and vehicle suspension systems. Two general types of isolation can be identified: 1. Force isolation (related to force transmissibility) 2. Motion isolation (related to motion transmissibility) Motion sickness region 30 min trips 2 h trips 8 h trips rms acceleration (m/s 2 ) 0 .2 0 .4 0 .6 0 .8 1.0 Frequency (Hz) 8 4 2 1.0 0.8 0.6 0.4 0.2 0.1 FIGURE 12.3 A severe-discomfort vibration specification for ground transit vehicles. Vibration Design and Control 765 In force isolation, vibration forces that would be ordinarily transmitted directly from a source to a supporting structure (isolated system) are filtered out by an isolator through its flexibility (spring) and dissipation (damping) so that part of the force is routed through an inertial path. Clearly, the concepts of force transmissibility are applicable here. In motion isolation, vibration motions that are applied at a moving platform of a mechanical system (isolated system) are absorbed by an isolator through its flexibility and dissipation so that the motion that is transmitted to the system of interest is weakened. The concepts of motion transmissibility are applicable in this case.
eBook - PDF- Ernest Doebelin(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
31 2 Vibration Isolation for Sensitive Instruments and Machines 2.1 Introduction Measurement and/or control systems whose performance would be adversely affected by vibration may require a mounting system that “filters out” the existing vibrational force or motion of the structure to which the system is attached. Optical systems are a good example, as testified to by the inclu-sion of a section on anti-vibration mounts in almost every optical company’s catalog. Some laser and holography measurement techniques cannot toler-ate base motions more than a small fraction of the wavelength of the light being used, but the existing and unavoidable floor vibrations greatly exceed these levels. This means that the optical table must include some kind of vibration-isolating system. Similar requirements exist in some manufactur-ing processes, particularly those used for producing microelectronic circuits or microelectromechanical systems (MEMS). Here, the exceedingly small dimensions and tolerances of the parts being produced require close control of spurious vibrations. Over the years, engineers have invented and developed a number of tech-nologies for implementing Vibration Isolation. In this chapter, we will explore six of these approaches: 1. Simple passive spring/mass systems using metal or elastomer springs 2. Passive air-spring systems 3. Active air-spring systems 4. Low-frequency isolation using negative-spring-constant devices 5. Active electromechanical systems 6. Tuned vibration absorbers and input-shaping methods 32 Instrumentation Design Studies Our approach will be conventional but you should be aware that uncon-ventional methods* are worthy of consideration.
eBook - PDF- Colin Hansen, Scott Snyder, Xiaojun Qiu, Laura Brooks, Danielle Moreau(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
CHAPTER 12 Vibration Isolation 12.1 INTRODUCTION Active Vibration Isolation involves the use of an active system to reduce the transmission of vibration from one body or structure to another. A broader definition would also include the reduction of vibration of a machine or structure by an active vibration absorber. Passive Vibration Isolation is covered adequately in many textbooks (see, for example, Bies and Hansen, 2009) and will not be discussed here. In the analyses discussed in this chapter, a constant force (or infinite impedance) source is assumed. That is, it is assumed that the driving force is independent of the structure and does not change significantly if the dynamics of the structure change. Although this idealised case is not often found in practice, the constant force assumption simplifies complex analyses, and the results obtained are indicative of what can be achieved in many practical cases. Active Vibration Isolation systems are usually significantly more complex and expensive than their passive counterparts, which consist of steel or rubber springs and dashpots (illustrated diagrammatically in Figure 12.1(a)) and which have been in use for many years. One may well ask what advantages are offered by active systems which justify their increased cost and complexity. Of course, the main advantages are better static stability of the supported equipment and better performance, especially at low frequencies, which in many cases makes an active system the only feasible choice. Active systems can also be used to minimise vibration at critical locations on a flexible support structure, at some distance from the isolator attachment point and for some applications this is a distinct advantage. Active systems also have the capability of adjusting to changes in machine operating conditions (and thus vibration excitation frequencies) without any outside intervention.
eBook - PDFNoise Control in Building Services
Sound Research Laboratories Ltd
- A. Fry(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 6 Vibration Isolation 6.1 INTRODUCTION Just as the acoustics designer plans his strategy for dealing with the effects of machinery noise upon the building containing or adjacent to the equipment, his solutions will invariably be centred upon one, or possibly more, of three main considerations - the source - the transmission path - the receiver Similarly when we consider the effects of disturbing vibration, there are two scenarios which may apply. 1 .To protect the building or a part of its structure from the vibration effects of the machinery operation. 2.To protect equipment or people from the vibration effects of the building. The interplay between the machinery as a source or receiver and the building structure as the transmission path provides the basic link which results in the designer needing to include a programme of vibration control or isolation as part of the overall acoustic strategy. When considering transmitted vibration, we are essentially concerned with frequencies at the very low end of the spectrum normally below 200 Hz. Within the frequency band between 0 and 200 Hz there is a further split which takes account of the difference between those vibrations which are felt, on the one hand, and those which are audible on the other. The point in the frequency spectrum at which this difference becomes apparent is between 30 and 35 Hz. The upper band or audible spectrum of vibration, when considered, leads the designer to reviewing methods of acoustic isolation. Clearly, the perception of vibration in terms of human subjective response is by other body senses and not just the ear. 131 132 NOISE CONTROL IN BUILDING SERVICES With the ever increasing use of lighter weight methods of building construction and materials in the last 10 to 15 years, the acoustic designer has seen that instances of inadequate or non-existent Vibration Isolation provisions result in major acoustic problems.
- Peter R Saulson(Author)
- 1994(Publication Date)
- World Scientific(Publisher)
132 Seismic Noise and Vibration Isolation In both cases, the damping gives a bounded value for the transfer function at the resonant frequency (x/z,(/o) = Q). instead of the unphysical divergence predicted by Eq. 8.3. There are many different kinds of mechanical realization of the required spring. They range from coils of metal wire to metal cantilevers, from blocks of rubber to a magnetic field to the wire holding the mass in a pendulum. No matter what their shape is and what material they are made of, all springs isolate a mass from vibration for the same reason: they give a soft connection to the outside world, so that there exists a resonant frequency above which the mass can't be pulled strongly enough to keep up with the motion of the outside world. 8.4 M y t h s A b o u t V i b r a t i o n Isolation There are many misleading hand-waving explanations of vibration isolators in the folklore of physics, a remarkable fact considering they are such simple devices. Peo-ple will sometimes assert that isolation comes from vibration damping, that is from absorption of vibrational energy. Energy is absorbed if the spring constant has an imaginary part, or if a dashpot is attached to the mass. For example, a car has dashpots, called shock absorbers, in parallel with the springs that isolate the body from the vibration imparted to the wheels as they roll along a bumpy road. But the isolation has no necessary connection with the dissipation. We were able to derive the high frequency response of an isolator (its stop-band response, in filter terminology) without reference to the strength of damping present. A car's shock absorbers are there to mini.;iize the amplification of the noise near the resonant frequency by the isolator. Another folk explanation of Vibration Isolation is that it arises from a mismatch in impedance between the spring material and the mass material.
eBook - PDF- Mickael Lallart(Author)
- 2010(Publication Date)
- IntechOpen(Publisher)
4 Vibration Isolation System Using Negative Stiffness Taksehi Mizuno Saitama University Japan 1. Introduction Vibration Isolation plays an important role in the operation of many advanced production and measurement systems such as semiconductor manufacturing and high-precision measuring. Rapid technological developments in these fields have increased the need for higher-performance Vibration Isolation systems. There are two kinds of vibration that must be reduced by a Vibration Isolation system: 1. vibration transmitted from the ground through the suspension (ground vibration), 2. vibration caused by disturbances acting on an isolation table (direct disturbance). A suspension with less stiffness is better for reducing the former because dynamic coupling between the vibration source and the isolation table is weakened; thus, zero stiffness is ideal. However, higher stiffness is better for suppressing the latter because it reduces displacement of the isolation table from its desired position; thus, infinite stiffness is ideal. In conventional passive-type Vibration Isolation systems, a trade-off between lower and higher stiffness is inevitable, so that performance is limited. In contrast, active-type Vibration Isolation systems do not suffer from such performance limitations (Rivin, 2003). In particular, the performance limitations of passive-type Vibration Isolation systems can be effectively overcome by two-degrees-of-freedom control (Yasuda et al ., 1996). There are also various control methods applied according to required performance and acceptable cost. One of the fundamental control strategies is to provide feedback regarding the absolute velocity of the isolation table, which is often referred to as skyhook damping (Fuller et al ., 1996). State feedback (Miyazaki et al. , 1994), feedforward (Mohamed et al. , 2005) and active acceleration control (Zhu et al. , 2006) have also been applied.
- Cheuk Ming Mak, Kuen Wai Ma, Hai Ming Wong(Authors)
- 2023(Publication Date)
- CRC Press(Publisher)
Chapter 4 Assessment of Vibration Isolation for machinery of ventilation systemsDOI: 10.1201/9781003201168-44.1 Introduction
Despite their benefits, ventilation ductwork systems produce airborne, duct-borne, and structure-borne sounds. Sounds are generated because the systems have vibrating mechanical machines, such as ventilation fans and motor-driven equipment. These machines may cause the roof or floor of the electrical and mechanical (E&M) equipment room to vibrate sufficiently high, rendering the spaces they serve unusable. Thus, satisfactory acoustic design plays an important role in the design of ventilation systems. Building acoustics is focused on the audio frequency range (or audible frequency range) 20–20 kHz as well as the octave or 1/3 octave scale and Bark scale for the frequency analysis in acoustic and psychoacoustic measurements, respectively. However, vibration or structure-borne sound analyses are typically centred on low frequencies (e.g., 0–200 Hz). This range includes frequencies from 20 to 200 Hz that humans may be able to hear and vibrations below 20 Hz that can be felt but are inaudible. The human perception of vibration and sound differs because our senses include hearing and touch. In addition, vibrations or structure-borne sound problems are typically analysed in a single-hertz band instead of the octave or 1/3 octave band.Figure 4.1 shows a schematic of a simple vibratory system for modelling a machine resting on a floor/roof. It includes a simple vibration isolator in relation to a vibrating source, structure-borne sound transmission path, and receiver. It also demonstrates several important aspects in the study of structure-borne sound transmission in buildings such as:- Structure-borne sound source characterisation,
- Vibration Isolation (assessment of performance using transmissibility),
- Vibrational waves produced in the floor/roof, and
- Coupling with air at the hearing end.
- Bob Peters (Chair), Alan Fry Salex, Richard Galbraith, Peter Henson, Alex Krasnic, John Lloyd, John Shelton, Peter Tucker(Authors)
- 2016(Publication Date)
— Ensure that vibration isolators are loaded to give equal deflections and installed to maintain vertical alignment of their springs and other components. — Remember that misaligned isolators are a source of many problems. — Check support bolts for integrity and free movement. — Do not neglect vibration from pipes and ducts; use flexible attachments to the structure. Further advice is given by Schaffer (1992). References ASHRAE (2011) HVAC Applications ASHRAE Handbook (Atlanta GA: ASHRAE) ASHRAE (2013) Fundamentals ASHRAE Handbook (Atlanta GA: ASHRAE) Beranek LL and Ver IL (eds.) (1992) Noise and Vibration Control Engineering 1st edn. (Chichester: Wiley Intersci ence) Beranek LL and Ver IL (eds.) (2005) Noise and Vibration Control Engineering 2nd edn. (Chichester: Wiley Interscience ) BSI (1987) BS 6841: 1987: Gui de to measurement and evaluation of human exposure to whole-body mechanical vibration and repeated shock (London: British Standards Institution) BSI (1994) BS EN 60651: 1994, IEC 60651: 1979: Specification for sound level meters (London: British Standards Institution) [withdrawn] BSI (1997a) BS EN ISO 11690-1: 1997: Acoustics. Recommended practice for the design of low-noise workplaces containing machinery. Noise control strategies (London: British Standards Institution) BSI (1997b) BS EN ISO 11690-2: 1997: Acoustics. Recommended practice for the design of low-noise workplaces containing machinery. Noise control measures (London: British Standards Institution) BSI (1998) BS EN ISO 14163: 1998: Acoustics. Guidelines for noise control by silencers (London: British Standards Institution) BSI (1999) BS EN ISO 11690-3: 1999: Acoustics. Recommended practice for the design of low-noise workplaces containing machinery. Sound propagation and noise prediction in workrooms (London: British Standards Institution) BSI (2000a) BS EN 12354-4: 2000: Building acoustics. Estimation of acoustic performance in buildings from the performance of elements.
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