State of the Art of Machine Noise Identification and Control

Transcription

1 International Conference on rends in Mechanical and Industrial Engineering (ICMIE') Bangkok Dec., State of the Art of Machine Noise Identification and Control Chandrakant Ramesh Patil, Vaishali Prakash Choudhari and Deepak.S. Dhote Abstract his paper presents state-of-the-art of noise pollution generated by generator set, design and development of acoustic enclosure. A procedure of noise mapping has been developed. Design and development of acoustic enclosure are often complex and costly to manage as it involves design of complex structures, an integration of various systems and technologies. his paper demonstrates the establishing of design criteria to get at least of 5 db (A) reduction in sound level and to determine the corresponding acoustical performance required of the enclosure to meet the criteria. An enclosure is designed according to the criteria such as available space, size and shape of source etc. Calculations like transmission loss, heat generated and air flow required is effectively applied for the design and development stages of a new acoustic enclosure. Keywords acoustical enclosure, insertion loss, noise mapping, transmission loss. I. INRODUCION HE sound produced in the diesel generator/ Alternator (DA) is a major source of noise pollution, so this research is being developed to encounter this lethal threat for the environment and human habitability. he study was developed and designed for effective sound mapping and thereby minimize the noise to the levels at audible control by adopting noise control method at transmitting path and by use of an acoustic material. here are basically three types of methods, which are used to control the noise radiated by any source i.e. Methods applied at source, on the noise transmission path, and at the receivers end. he term Enclosure in the context of noise control may be taken as a generic term for almost any method of artificially impeding the free flow of acoustic energy away from the source. It includes, at one extreme end, simple screens and plain barriers, through partial enclosure such as side sheds, on to acoustically sealed enclosure of the source. II. MEHODOLOGY he evaluation of noise generated by DA is carried out through experimentation at site location of Diesel Engine Wing shown in figure. [] Chandrakant Ramesh Patil is Associate Professor, Mechanical Engineering Department, elephone Number crpatil@rediffmail.com. Vaishali Prakash Choudhari is Lecturer, Physics Department, HVPM College of Engineering, Amravati (India) 66. Deepak.S.Dhote is Professor, Electronics Department, Brijlal Biyani Science College, Amravati (India) 66. Instrumentations Used For Measurement. Bruel and Kjaer`s 6 investigator M sound level meter.. Hygrometer is used to measure relative humidity (Range to %).. Anemometer is used to measure air flow velocity (Range to 5 m/s).. hermometer is used to measure environment temperature (Range to 8 degree centigrade). 5. Stop watch is used to measure time in seconds. he experiment is carried out in two stages i.e. with DA running and when DA is not running. he following readings have been recorded during experiment: i) Pulse rate. ii)air flow velocity. iii)relative Humidity. iv)emperature of ooms/working environment. [] Measurements before Installation of Acoustic Enclosure the Sound measurements of the DA were carried out by using the grid method over the surfaces. Grid method depicts the noise level at various coordinates as mentioned in figure to figure 9. he noise readings, when the DA is running were compared with the readings when the DA is not running. It is found that the maximum noise level is db (A) at live bay site as shown in table.he location of various floor wise rooms are shown in figure. Fig.. Depicts the vertical floor wise cross section of the study site building where the noise mappings of DA is carried. When DA is not running: he readings are shown in the 5

2 International Conference on rends in Mechanical and Industrial Engineering (ICMIE') Bangkok Dec., following table. Location Noise level, db(a) emperature (t), ABLE I READINGS WHEN DA IS NO RUNNING Relative Humidity (%) Air Velocity (v), m/sec Geometric variable of distance from DA, feet Average Pulse Rate Performance of students % Class I Class II Class III Class Live Bay A sound spectrum is usually presented as a graph of either power or pressure as a function of frequency. he power or pressure is measured in decibels and the frequency is measured in vibrations per second (or hertz, abbreviation Hz) or thousands of vibrations per second. he spectrum shows frequency on the x axis and sound level (on a decibel scale) on the y axis. In the spectrum, the harmonics, which appear as equally spaced components (vertical lines Note that the pitch doesn't change, so the frequencies of the spectral lines are constant. However the power of every harmonic increases with time, so the sound becomes louder. he higher harmonics increase more than do the lower, which makes the timbre 'brassier' or brighter and also makes it louder. [] db 9 8 Excluded band Dynamic Capability 8.stp Row:, Column: A L Power Lin Cursor: (A) Status code Power. db Fig.. otal sound power spectrum prior to installation of enclosure When DA is running: he readings are shown in the following table. he noise level on each surface at each corners are shown in figures to 8.he total noise level of all five surfaces is mentioned in figure 9 Hz ABLE.II READINGS WHEN DA IS RUNNING. Location Noise level, db(a) emperature (t), Relative Humidity (%) Air Velocity (v), m/sec Geometric variableof distance from DA, feet Average Pulse Rate. Performance of students % Class I Class II Class III Live Bay.5 8 Class III

3 International Conference on rends in Mechanical and Industrial Engineering (ICMIE') Bangkok Dec., IntensityA-w PressureA-w Statuscode PowerA-w Row: Column: IntensityA-w87.5dBPressureA-w9.dB StatuscodePowerA-w9.dB Fig. Five surfaces enclosing the DA D IntensityA-w PressureA-w Statuscode PowerA-w Row:Column:8IntensityA-w87.9dBPressureA-w9.dBStatuscodePowerA-w8.9dB Fig. op surface grid (maximum level at column 8, row) DR 86.5 D 86. D D (-) D D Row: Column: IntensityA-w7.9 db Pressure A-w9.8 db Status codedr Power A-w(-)6.6 db Fig.5 Front surface grid (maximum level at column, row) D D D Row: Column: 7 IntensityA-w9. db Pressure A-w9.9 db Status code Power A-w8.8 db Fig.6 Back surface grid (maximum level at column 7, row) Row: Column: IntensityA-w9.8 db Pressure A-w95. db Status code Power A-w86.6 db Fig.7 Left surface grid (maximum level at column, row) Row: Column: IntensityA-w85.9 db Pressure A-w9. db Status code Power A-w8.7 db Fig.8 Right surface grid (maximum level at Column, row) Intensity A-w khz Pressure A-w khz Status code Power A-w Row: Column: Intensity A-w khz75. db Pressure A-w khz79. db Status code Power A-w. db Fig.9 otal of all five surface grid III. DESIGNS AND DEVELOPMEN OF AN ACOUSIC ENCLOSURE In the context of noise control, the term enclosure is almost any method of artificially impending the free flow of acoustic energy away from the source. [] he design and development consists of following steps: a) Dimensions of the enclosure panels are to be calculated. b) Developing initial design rules for considering noise control. he Initial step is to establish design norms and determine the performance of the enclosure to meet the criteria. Here our aim is to get noise reduction up to 85dB (A). c) Determine the octave band sound pressure level of the equipment by using 6 investigator. d) Design according to the criteria available such as space, size and shape of the source. e) Developing the methods of noise control of each component of the equipment. f) Determination of acoustical properties of different exposed surfaces. g) Carrying out actual methods of the installation of acoustic enclosure to check its effectiveness, reduction of noise thereby providing habitability for undergoing trainees and instructors. he two thumb rules of acoustic design :(a) he distance between the source and the enclosure should be at least half the wavelength of the lowest frequency of interest.(b)he distance between the source and the enclosure should be more than the largest dimension of the source.[5] 7

4 International Conference on rends in Mechanical and Industrial Engineering (ICMIE') Bangkok Dec., Calculations: For to find transmission loss ( L ), R R logσ W n And, K πf C Where,σ Radiationefficiency [ ln( s )].5. +., Where, C m/s (speed of sound in air), f Frequency Hz And, s L max X Lmin So, K 6.9 R n (Normal incident transmission loss) Where, f Hz, ρ m h πf log + ρ C K Air flow requirement (Q), units) Q H ρ Here, Q H C p volume of air flow required in m³/s Heat generated in watts 55-5 ºC (emperature differential between the external ambient and the maximum permissible inside) ρ.8 kg/m³ (Density of air) C p m²sˉ² ºC ˉ¹ (Specific heat of the air in SI Q.7 (.8 ).9 m³/s 7. m³/s ρ m. kg/m³, Density of Steel, ρ 77 kg/m³density of air and R n h mm (thickness of steel) 7.5 db 77. π log +. σ.5[. ln( ) ] L R W db (A) 7.5 log (.9) otal sound power spectrum after installation of acoustic enclosure.stp Row:, Column: Excluded band Dy namic Capability Repeatability db A L Power Lin Cursor: (A) Status codedr Power8. db It is observed that by comparing total sound power spectrum after installation of acoustic enclosure with total sound power spectrum prior to installation of enclosure the Fig. otal sound power spectrum after installation of acoustic enclosure noise level reduced from db(a) to 9 db(a) at live bay site.[6] Hz 8

5 International Conference on rends in Mechanical and Industrial Engineering (ICMIE') Bangkok Dec., IV. CONCLUSION At the design stage, the aim was to achieve an insertion loss of above 5dB (A) in the overall sound power reduction. he figure was closely achieved as can be observed in the readings. he Panels were especially very effective in reducing the sound intensity in the - Hz region, as the entire design was around frequency of Hz. he spectrum shows a significant reduction in the high frequency region. he low frequency region also has been attenuated due the incorporation of the perforated sheet in the design. Overall, a considerable amount of noise reduction has taken place and the DA is now acoustically enclosed as per the necessary standards and the air borne noise levels at m distance from the enclosure has been reduced by db (A). ACKNOWLEDGMEN he authors of paper are pleased to Dr.V..Ingole, Principal, Prof.Ram Meghe Institute of echnology and Research, Badnera-Amravati and he Secretary, Ministry of Environmental Department, Maharashtra Government- Mumbai (India) for permitting, encouraging and providing crucial facilities to carry out the present work. REFERENCES [] Allan M eplizky (985), Electric utility noise emissions, Proceedings of the ASME convention in Denver, Colorado, Page. [] Anderson, S (98), Acoustical measurements of outdoor noise barriers: Progress on standardization, Proceedings of the 98 International conference on noise control engineering, Poughkeepsie NY. [] Andrew S Harris (985), he noise mitigation plan for Stapleton airport, Proceedings of the ASME convention in Denver, Colorado, Page 9-9. [] Bell Lewis H. (988), Industrial Noise Control, Harmony publications. [5] Beranek (99), Noise and Vibration Control, John Wiley Publications. [6] J.S.Rao (), Solid Rotor Dynamics, Advances in vibration engineering, Vol., No., Oct. - Dec.. 9