ISVR Consulting - Annual report 2008

Every year the Institute of Sound and Vibration Research publishes an Annual Report. This is the entry for ISVR Consulting covering the calendar year 2008.



Group Developments

ISVR Consulting, the commercial consultancy division of the ISVR, provides services direct to industry and the public sector over a wide range of acoustics and vibration topics. Our team of 18 includes consulting engineers, and technical and clerical support staff. Our service includes environmental acoustics, expert witness services (particularly for hearing loss claims and audio tape analysis), specialist measurements, workplace noise, aeroacoustics, noise and vibration control and automotive design. Although much of our work is client confidential, we are often able to make a contribution to the research profile of the ISVR by reporting on analogous problems or by removing sensitive information. We also make a contribution to learning by teaching topics within our expertise on short courses and on the undergraduate and MSc programmes, and by supervising some of the acoustics measurements laboratories. We celebrated the 40th anniversary of the foundation of ISVR Consulting as the Wolfson Unit for Noise and Vibration Control with an event for current and many former unit members during the summer.

Two factors were of great significance for the unit during the reporting year. First was the relocation of the Chilworth automotive and marine division of the unit to newly refurbished laboratories adjoining the Rayleigh Building at Highfield; and the second factor is the economic downturn that has adversely affected many of our clients.

Several factors contributed to the decision to move from Chilworth. The building attracted high estate charges from the University yet was poorly maintained and out of character with other buildings on the Science Park. A one-site operation is less complex to manage and provides opportunities for greater collaborative work within the unit, and for closer integration with the rest of the ISVR for automotive work. The relocation also marks the end of a series of moves that were made possible by the construction of Building 19. We have been able to move into space that was refurbished for us after being vacated by the Dynamics Group. The new space includes a large vehicle lab with acoustically treated walls, a workshop/preparation area and an acoustically treated test area that can accommodate the “Banger Rig” and may yet be used for running-engine work. Nevertheless many facilities have been lost as a result of the move, including engine test cells, vehicle labs and large areas of space both outdoors and under cover. A simply enormous volume of equipment, materials and components has been scrapped, sold, returned or passed to museums, in some instances involving difficult decisions, and sheer hard work in others. It is appropriate to acknowledge the support of the ISVR technical staff and the whole Chilworth team who have devoted many weeks of effort to this activity, yet continued to make progress with client work over the same period.

Meanwhile, the economic downturn has created challenging trading conditions particularly in the automotive, construction and industrial manufacturing sectors that have been among our traditional client-base. We are fortunate in having a very experienced and flexible team that can react quickly to changes in topic areas for consultancy support and project work. However, the volume of enquiries is currently falling and it seems likely that conditions for our clients may yet deteriorate further. We are tackling this with a series of business development initiatives that should ensure that we can survive the recession and so be well-placed to take advantage of trading improvements when economy eventually recovers.

In the remainder of this report we describe some of the projects that we have been involved with over the reporting year. Further details about some of these and about our services and facilities generally are given on the ISVR Consulting website www.isvr.co.uk

 

Research and project work

Automotive engineering

Development has continued on both EngWaves (real-time measurement) and the Inca (noise prediction) software projects: fundamental studies into the transmission of diesel engine impulsive noise are underway in order to support the next phase of the Inca project. Meanwhile, training material for the Inca software has been developed and two initial training courses presented in the UK and Europe in conjunction with experts from Ford and Jaguar-Land Rover. These courses were received well. A highlight of this year was the presentation of a Jaguar-Land Rover Technology Award to the Inca team comprising four members from Jaguar-Land Rover and Dave Rhodes from the ISVR.

Sound source manufacture has continued with both high- and low-frequency sources produced for export to Europe and China. Work has begun on a major re-design of the sound source electronics to achieve updating and improvements in both flexibility and acoustic output.

We have worked on a project involving testing and development work for a manufacturer of multilayer brake shim materials. The study involved investigating the use of their products and processes as constrained layer damping or isolation treatments to reduce noise in numerous applications from automotive oil pans to computer hard drives.

The source of an intermittent knock associated with the suspension of a luxury off-road vehicle was investigated. Although rather subtle and only associated with certain speeds and bump profiles, customer complaints had highlighted that noise quality is of paramount importance, even for an off-road vehicle.

The “Banger Rig” was kept very busy throughout the year evaluating the combustion noise attenuation characteristics of engines from both Europe and North America. As well as providing the broad band radiated noise and structural vibration responses for the engines, there was a healthy demand for more specific modal information. The “Banger Rig” was also used as a finite element model validation tool.

 

Marine acoustics

Marine activities continued to grow. Projects ranged from new-build support for a 24 metre explorer-style yacht, through to noise reduction of a new concept of stabiliser system. The majority of small power craft rely on water injection to attenuate exhaust noise. Although this method is very effective in most cases, little is known about the detailed science behind this phenomenon. An engine-based rig has been commissioned that allows gas flow, gas temperature and water injection flow to be controlled independently; the effect of these three parameters on the attenuation afforded by various spray heads has been studied.

We have continued work on noise and vibration issues associated with a large luxury yacht, and have worked on transmission loss testing of composite bulkhead materials and performance testing of shock-absorbing matting for deck structures. The deck matting has the feature of a relatively rigid surface underfoot during normal loads from standing or walking, but deforms and absorbs the shock loads associated with bouncing over waves.

In February 2008, the Merchant Shipping and Fishing Vessel (Control of Noise at Work) Regulations 2007 came into force, to mirror similar regulations for land-based industry. The Maritime and Coastguard Agency commissioned an updated code of practice for noise on ships, to provide guidance for those concerned with designing, building, owning, or managing ships; the new code was aimed at protecting the seafarer from the harmful effects of noise. ISVR Consulting provided the noise code of practice.

John Dixon's work for Halyard was recognised by the CBI in their report Stepping Higher: workforce development through employer-higher education partnership” (page 78). The report provides case study evidence to show how employers and universities can and do work effectively together and cites the ISVR Consulting work as a leading example of such collaboration.

 

Aeroacoustics

Work on control of airframe noise in collaboration with Airbus has continued as a major activity, with a variety of long term projects at various stages of completion. Many of the projects are co-funded by the DTI (ANDANTE and Integrated Wing projects) or the EU (TIMPAN, NACRE and HISSAC projects). The focus of these studies is design and testing of noise control features on landing gears, with ISVR Consulting participating in the design work, predicting anticipated noise reductions and interpreting wind tunnel test data.

 

Firearms and explosives

We are frequently asked to measure the noise exposures from conventional firearms but two projects this year were unusual. In one case we were asked to measure the sound characteristics of the impulse noise generated by detonating cord and explosive charges of various sizes and at a number of distances. The purpose of the tests was to measure the sound spectrum of each explosion, to classify the individual noises as Type 1 (low-frequency) or Type 2 (mid- to high-frequency) and to measure the peak sound levels. This information was then used to determine combinations of safe distances with appropriate hearing protection to minimise risk of hearing damage to personnel involved. The measured peak sound levels were in the range from 160 dB(C) to 186 dB(C). BS EN 458:2004 gives a method of estimating hearing protector attenuation for impulse noise. The method relies on the classification of the impulse noise as one of three types, Type 1, 2 or 3. The method is endorsed by the Health & Safety Executive in its guidance on the Control of Noise at Work Regulations 2005. Our tests were designed to classify noise under the BS EN 458 scheme, rather than to validate the scheme.

In another unconventional weapon noise project, we measured the noise produced by a range of firearms using a Kemar Manikin: recordings from the trials are to be used in studies on source localisation in combat situations.

 

Hearing loss due to occupational noise

Unit staff have worked on several hearing loss claims during the reporting year. Increasingly we find that we are appointed as a single joint expert under the civil procedure rules, reducing the scope for adversarial challenges by other experts, but increasing the significance of our reports for both the complainant and the defendant. The cases dealt with this year include a worker at a double glazing factory who sought compensation from his employer for hearing loss attributed to occupational noise. An inspection yielded noise data suggesting an LEP,d of 89 dB(A) over 10 years with the company; such a daily exposure would be potentially harmful. However, the Claimant stated that he had always worn the hearing protectors provided by his employer; in the end, the claim was dropped.

A more complex case considered how to apportion a claimant’s noise-induced hearing loss between several employers: those who provided no hearing protection, or those who provided inadequate protection.

ISVR Consulting was instructed to analyse existing noise data for a major annual carnival from 2001 to 2007. One major intention was to characterise the noise exposures of police officers assigned to accompany individual floats along the carnival parade route, and also the exposures of officers assigned to static positions as the floats passed along the route. Carnival duty at static locations was shown to produce lower noise exposures than for some of the float-followers. This means that exposure reduction through duty assignment was potentially useful, but not the full solution. Consideration was given to the hearing protection provided by the earplugs used by police officers. Consideration was also given to the possible noise exposures of those officers equipped with radios. Such communications officers were provided with individually-moulded ear inserts for use with their radios, the output of which were limited to pre-set maximum values. These officers have reported that the present radio system does not perform well in the high noise levels found along the carnival parade route.

 

Laboratory testing

In the Anechoic Chamber we have carried out sound power testing on a varied range of products including computer backup devices, mobile telecommunication network hubs, ventilation units, pumps, motors, hair dryers and vacuum cleaners. We have also used the anechoic chamber to evaluate products such as Fire Alarm Sounders, Ultrasonic Pest Deterrents and Acoustic Enclosures.

In the Reverberation Chambers, we have carried out transmission loss testing on acoustic sliding and folding partitions and have helped the Building Services Research and Information Association (BSRIA) in their quest to develop alternative building materials that still meet the current requirements for sound transmission between dwellings.

The Reverberation Chambers have also been used for sound absorption testing including work carried out with the Furniture Industry Research Association (FIRA) who are interested in developing ‘acoustic’ furniture to improve working environments in large open plan offices.

We have continued to carry out high-intensity acoustic fatigue testing, mainly on aircraft components. All of the components survived the testing (which is a pity in some ways as failures lead to retests!)

 

Building acoustics

ISVR Consulting continues to provide advice, measurement and consultancy in the area of building acoustics. These activities cover the Sound Insulation between newly built residential properties (Building Regulations Approved Document E), and the planning requirements related to residential properties (PPG 24) and industrial facilities (BS 4142). Projects completed over the past year have included a large expansion of a packaging plant in Havant, and the design of nightclub ventilation systems in Chester. An on-going project involves advice on noise insulation between apartments for a development on Park Lane in London.

Control of vibration and structure-borne noise in buildings has again generated a useful amount of work. Projects include a finite element study to assess an unusual building design that was thought might be vulnerable to ground-borne vibration from underground trains, and the design of a two-stage vibration isolation system to suppress structure-borne noise from a water pumping station in a residential area.

The year has also seen introduction of an exercise intended to enhance the learning and future employability of ISVR students; this project had funding support from the University Learning and Teaching Enhancement Unit (LATEU). A very successful series of consultancy schemes took place, bringing the students into more direct involvement with the “real world” . The individual projects involved real problems where the client had no funding, such as schools and community groups. A total of nine students from the MSc and BEng course were able to benefit from the training opportunity. The projects ranged from problems in room acoustics, to environment noise prediction. The programme was cited as an example of good practice in the latest Learning and Teaching Enhancement Review and Action Plan review of the ISVR.

 

Industrial noise and vibration

There has been a considerable increase in work in the field of vibration measurement and visualisation. The work has included projects using both modal analysis and operational deflection shape analysis. A series of projects has been carried out analysing the natural frequencies of stator end windings in the generators of a power station. This involved testing a “basket” of windings at each end of the generator to ensure the mechanical integrity of the windings during the lifetime of the generator.

In another project, measurements were used to produce an animation of the deflection of the structural supports of a very large-scale but vibration sensitive experimental facility. These vibration amplitudes are as low as 10 nm and yet useful animations of the operating vibrational deflection can be obtained.

Other projects involved support in statutory noise nuisance cases, with several staff called to act as expert witnesses during the reporting year.

ISVR Consulting has recently been commissioned to predict the noise levels from condenser units, to be used downstream of the turbines in coal-fired power stations, under different operating conditions. In the bypass condition, the steam is released inside the condenser casing via a set of perforated pipes. This process produces noise similar to a jet or valve, which will be transmitted acoustically through the walls of the condenser. The temperature in the condenser is kept as low as possible to achieve the lowest possible pressure in the condensing steam. For this reason, the condenser works under near-vacuum conditions where the pressure of the vapour is much less than atmospheric pressure. Because the ratio of the pressure inside the bypass flow pipes to the pressure inside the condenser is very high, the flow through the perforations is choked, causing significant increases in the noise of the jets due to the formation of shock waves. On the other hand, during the normal operation of the condenser, the steam vapour from the turbine steam passes over bundles of water filled heat-exchanger pipes. Ultimately, the condensate is collected in the hotwell. This will cause vortex shedding noise, the level of which has been predicted using published models of noise from the struts of aircraft landing gears. This model that is used assumes that the pipes are effectively rigid, so that feedback mechanisms between vibration and the vortex shedding process that could cause resonance are avoided.

Measurement of ground-borne vibration caused by railways continues to be of interest. A particular example has shown that structural damage to a new build has been caused directly by the vibration from heavy goods trains. This has confirmed the perspicacity of measurements made before planning permission has been granted on other sites. In other work, ground-borne noise predictions due to the construction and operation of metro-rail systems have been made in collaboration with Chris Jones in the Dynamics Group.

Publications

Karatsovis, C  and  Dyne, S J C
Instrument for soundscape recognition, identification and evaluation: an overview and potential uses in legislative applications. 
Proceedings of the Institute of Acoustics, Vol. 30(2), 602-608, April 2008

*Ma, Z; *Zhang, X; and Smith, M G
Broadband slat noise attenuation potential with acoustic liner treatment.
Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, Canada, 5-7 May 2008. Paper AIAA-2008-2964, 18pp

* indicates authors who are not in the ISVR


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