Mekanik gürültünün modellenmesi ve kontrol tedbirlerinin değerlendirilmesi: Dizel enerji santrali örneği
Modelling of mechanical noise and evaluation of its control measures: Case of diesel power plant
Yazar: GÖKTUĞ ÖZDEMİR
Danışman: PROF. DR. İSMAİL TORÖZ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Enerji = Energy ; Mühendislik Bilimleri = Engineering Sciences ; Çevre Mühendisliği = Environmental Engineering
Dizin: Dizel yakıtlar = Diesel fuels ; Enerji santralleri = Power plants ; Mekanik = Mechanics ; Mekanik modelleme = Mechanical modelling

Özet:
İstenmeyen sesler literatürde gürültü olarak tarif edilir. Fiziksel açıdan nesnel parametrelerle ortaya konabilen gürültü; algısal açıdan kişi, zaman, ortam ve kültüre özgü şartlara göre değişebilen öznel bir kavramdır. Gürültü meydana geldiği yer açısından kentsel ve yapı içi gürültüler şeklinde kategorize edilir. İçerik açısından ise spektral ve zamansal özelliklerine göre değişen gürültü türleri vardır. Hızlı endüstriyel gelişim ve mekanizasyon, yoğun nüfus artışı ve beraberinde getirdiği plansız kentleşme, ulaşım sistemlerinin gelişmesi ve yaygınlaşması, yapıların hafiflemesi, yasal düzenleme ve idari denetim uygulamalarının yetersizliği gibi sebeplerle gürültü ciddi bir çevresel kirlilik unsuru haline gelmiştir. Gürültünün diğer çevresel kirleticiler gibi görme ve koklama duyularına hitap etmeyişi onun uzun vadede bilinçli olarak fark edilmesini zorlaştırmaktadır. Bu sebeple insan sağlığı üzerindeki fizyolojik, psikolojik ve performans etkileri dikkatle takip edilmeli ve bunların minimize edilmesi için gereken kamusal ve idari tedbirler alınmalıdır. Gürültüyle mücadele makro ölçekte kentsel planlama aşamasında ve mikro ölçekte yapısal planlama aşamasında yapılmalıdır. Gürültünün, bir problem haline dönüştükten sonra kontrol edilmesi zor ve masraflıdır. Gürültü kontrol planlaması, mümkünse gürültünün ortaya çıkışının önüne geçilmesi, değilse kaynak ve iletim yolunda engellenmesi ya da alıcı tarafından algılanmasının önüne geçecek tedbirler setinin sistematik olarak alınması prensibine dayanır. Mekanik gürültülerin kontrolüyle alakalı mühendislik uygulamaları da bu aşamaların herhangi birinde ya da şartlara bağlı olarak tamamında söz konusu olabilir. Mekanik gürültülerin kontrolü için, bu gürültüyü doğuran mekanizma kaynak ölçeğinde iyi bilinmelidir. Bu sayede muhtemel bir gürültü probleminin önüne geçilmesi ya da kaynakta kontrol edilmesi mümkün hale gelir. Benzer şekilde iletim yolunda ve alıcıda gürültü kontrolü için alınabilecek tedbirler çok çeşitli olup bunların uygulanabilirliğine ait değerlendirme ve fayda-maliyet analizleri gürültü kontrol mühendisi tarafından yapılmalıdır.
Bu çalışma kapsamında gürültüye hassas kullanımların bulunduğu bir alanda yer alan 20 MW kurulu güce sahip bir dizel enerji santralinde standartlara uygun kaynak ses gücü seviyesi tayini ve çevresel gürültü ölçümleri yapılmış, elde edilen sonuçlar SoundPLAN gürültü simülasyon programına aktarılarak iki farklı konfigürasyona sahip dizel jeneratörlere ait emisyon verileri tespit edilmiş, ardından gürültü maruziyeti bulunan geniş bir alanı kapsayan modelleme çalışmasıyla gürültüye hassas alıcı noktalardaki gürültü seviyeleri tespit edilmiştir. Bu seviyeler, Çevresel Gürültünün Değerlendirilmesi ve Yönetimi Yönetmeliği'nde verilen limit değerlerle mukayese edilerek aşım değerleri tespit edilmiştir. Limitlere uygunluğu sağlamak ve akustik konfor şartlarını iyileştirmek için egzoz susturucuları ve farklı uzunluklardaki gürültü bariyerlerinden oluşan 2 izolasyon senaryosu önerilmiş ve modellenerek simüle edilmiştir. Elde edilen sonuçlara ait gürültü haritaları hazırlanmış ve gürültü izolasyon tedbirlerinin performansları mukayese edilerek değerlendirilmiştir.

Abstract:
In literature, noise is defined as undesired sound. While it can be physically characterized by objective parameters, cognitively it is a subjective term and depend upon person and various concerning aspects such as cultural background as well as feelings and target of him at that point, the time and the ambient where the noise phenomena take place. In terms of where it arises, the noise can be categorized as environmental and indoor noise. The noise emerged by transportation, industrial activity, construction site operations, entertainment venues and outdoor activities is defined environmental whereas the those noise taking place as a consequence of indoor mechanical systems (e.g., heating, ventilation and air conditioning systems, and water installations), circulation systems such as elevator or refuse chute, electrical equipment like lighting or computer systems, and last but not least the noise caused by human activities (e.g., loud shouting of people, impact noise such as footsteps on stair, household appliances noise, noise from shared spaces etc.) is described as indoor noise. In addition, the noise may exist in different forms and classified accordingly. It is termed according to its spectral character as wideband and narrowband noise as well as to its temporal properties as steady and unsteady noise (further categorized as intermittent and impulsive).
Rapid industrial development and mechanization, rapid population growth and consequent unplanned urbanization, broadening of transportation system and increased spectrum of mode of transport, lightweight structures, inadequacy of legislative regulations and administrative supervision can be considered among those reasons why noise becoming one of the most serious environmental pollutants in modern world. The noise is invisible, odorless and has no tactual property, which makes it more difficult in the long term to perceive the noise and to take necessary precautions. Therefore, physiological, psychological and productivity effects of noise on human health should be followed carefully and the administrative principles and practices should be carried out in order to mitigate the risk of numerous health problems.
Strategic and protective response against noise should be made within urban planning phase on macro scale and structural planning on micro scale. It is difficult and expensive the control noise after it has already become a complicated problem. Noise control planning is based on the principle of systematically taking a set of measures to prevent the occurrence of noise, if possible, or to control it in the source and transmission path, respectively or lastly preclude the receiver from noise by means of personnel protective equipment and enhancement the sound insulation performance of building envelope. Engineering applications related to the control of mechanical noises may also be involved in any of these stages or all of them depending on the conditions and complexity of case. In order to the control the mechanical noises, the mechanism within the sound source that the noise originating from should be analyzed and understood well, which in turn it becomes possible to prevent the occurrence of any noise problem or to control it at the source. In a similar manner, the measures that can be taken for noise control in the transmission path and at the receiver have a wide range and the feasibility evaluation and cost-benefit analysis of these applications should be done by the noise control engineer.
There is a series of applications to control the noise and vibration emerged from industrial activities. Acoustic enclosures, barriers, cladding methods, reactive exhaust silencers, dissipative attenuators, acoustic louvres, expansion chambers, side branch attenuators, plenum chambers, and room acoustic treatment can be considered among those of common noise control methods. Furthermore, inertia blocks, steel springs, air springs, elastomeric mounts, pads and area mounts made up of rubber, glass fiber, cork, felt, steel mesh etc. are utilized in vibration control.
In this thesis, it is aimed to measure the noise originating from mechanical equipment in accordance with international standards as well as to systematically evaluate the possible noise control engineering techniques to be implemented. 
Within the scope of the study, the sound power level of 30 containerized generator sets in a 20 MW diesel power plant operating uninterruptedly and located in an area with noise-sensitive uses was determined within the framework of the rules specified in the TS ISO 8297 Standard (Acoustics — Determination of sound power levels of multisource industrial plants for evaluation of sound pressure levels in the environment — Engineering method). In addition, continuous noise measurements were made at two receiving points where noise exposure level and disturbance were of the highest magnitude, which was used to calibrate and investigate the accuracy of the noise simulation model to be created. Then, the noise levels of all receiving points around the diesel generator power station and of outlying dispersed settlements have been calculated on a large scale using the SoundPLAN noise modelling software.
In the current situation where noise reduction applications don't exist, the limit values specified in the relevant regulation are exceeded by 33 dBA on the facades of the onsite buildings where the personnel work within and by 29 dBA in the residential areas around the power plant where the noise exposure is the most, posing a serious problem.
Various acoustic treatment measures have been designed to improve acoustic comfort conditions, the feasibility of these alternatives has been investigated and the efficiencies have been compared. In this context, grid, facade, cross-section and difference noise maps are created for the current situation where noise treatment doesn't exist as well as for 2 different acoustic treatment scenarios within the power plant of interest. Secondary dissipative exhaust silencers have been designed with the purpose of controlling the noise at the source as well as noise barriers at different heights have been proposed for the control of noise in transmission path. Accordingly, façade noise levels of determined receptor points and exceedance values of day, evening, and night noise limits specified by regulations are tabulated.
According to the proposed noise reduction measures, noise barrier application should be conducted on the north, west and south facades of the facility. Barriers should be aligned as close as possible to the containerized gensets, providing suitable clearance for the hot air discharge of the generator radiators. The surface of the barrier facing the generator sets should have sound absorbing lining and the absorption coefficient of the lining material should be selected to fulfil at least A4 class requirements according to the TS EN 1793-1 Standard (Road traffic noise reducing devices - Test method for determining the acoustic performance - Part 1: Intrinsic characteristics of sound absorption under diffuse sound field conditions). Sound transmission loss performance of the barrier section should be above 35 dB. In the application phase of noise barriers; flexible materials should be preferred, which will provide decoupling at the points where the modular panels of noise barrier come into contact with each other and other structural members. It should be ensured that there is no aperture within the barrier section and no gap along the application line. The height of the noise barrier to be applied should be at least 6.5-meters, with 6 meters of linear and 0.5 meters of 30° inclined section at the top. As a consequence of the noise simulations performed for 30°, 45° and 60° alternatives to determine the optimum angle between top section of the noise barrier and vertical axis, the highest noise reduction efficiency was obtained when the top of the barrier was inclined to make an angle of 30° with the vertical axis. On the other hand, proposed secondary dissipative pod silencers must not exceed the maximum back pressure level allowed by the engine manufacturer of the generator. Secondary exhaust silencers should be located on the ceiling of the container. These silencers should be flexibly connected to avoid possible vibration bridges. The silencer body should be made up of steel sheet of appropriate thickness, preferably its outer surface should be cladded, in order to prevent the possibility of noise break-in due to the intensity of the airborne sound field within the power plant. Exhaust silencer outlet pipe should be positioned to be parallel to the horizontal axis. 
The cost-benefit ratio of 2st acoustic treatment scenario, which is considered as the most feasible alternative, involve 6.5-meter-height noise barrier and the addition of a secondary dissipative pod silencers to 15 gensets whose noise emissions are relatively high in comparison with remaining ones. In this scenario, in terms of day-evening-night noise level indicator (Lden), there is a reduction of up to 24 dBA in the noise levels predicted on the facades of the accommodation units close to the facility when compared to the current situation with acoustically untreated sound sources. In this scenario, although the compliance with the limit values specified by the regulation for day-evening-night noise level indicator is largely achieved for the noise sensitive areas around the facility, night-time noise level indicator still has limit exceedances of up to 14 dBA in some buildings. Furthermore, 3rd acoustic treatment scenario including the noise barrier of 8.5-meter-height and the addition of secondary dissipative pod silencers has the highest noise reduction efficiency and ratio of compliance with the limit values for day, evening, night, and Lden noise indicators in all the noise sensitive areas around the facility, with a few exceptions on the north façade. Nevertheless, if evaluated in terms of feasibility, it can be said that the 3rd scenario drops behind the 2nd one in terms of convenience of assembly.
As a result of the proposed acoustic treatment applications, although the noise exposure has been significantly reduced and the auditory comfort has been increased, it has been determined that limit exceedances may still be experienced in the noise-sensitive receiver points especially for night-time noise levels and in general, within onsite buildings. Accordingly, in cases where noise is likely to become a problem, it can be said that the most cost-effective and suitable way of controlling it is to intervene at the urban planning stage before the troublesome situation arises.