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Asia Noise News Building Accoustics

Railway Noise

Rail transport or train transport is one of the main transportation modes these days, both for transferring passengers and goods. Every day people commute to work and back home using trains in a form of subway systems, light rail transits and other types of rail transport. These types of system can create noise both to the passengers inside of the train as well as to the environment. In this article, we will discuss about noise source components that we hear daily both inside and outside of the train.

If we pay attention to the noise when we are on board of a train, there are more than one noise source that we can hear. The main sources for interior noise in a train are turbulent boundary layer, air conditioning noise, engine/auxiliary equipment, rolling noise and aerodynamic noise from bogie, as illustrated in the following figure.

By the way, we wrote and recorded the sound of Jakarta MRT. You can see the link below to help you imagine the train situation better.

Exploring Jakartan Public Transportation Through The Sound

Rolling noise is caused by wheel and rail vibrations induced at the wheel/rain contact and is one of the most important components in railway noise. This type of noise depends on both wheel and rail’s roughness. The rougher the surface of both components will create higher noise level both inside and outside of the train. To be able to estimate the airborne component from the rolling noise, we must consider wheel and track characteristics and roughness.

Another noise component that contributes a lot to railway noise is aerodynamic noise which can be caused by more than one sources. These types of sources may contribute differently to internal noise and external noise. For example, aerodynamic noise contributes quite significantly at lower speeds to internal noise while for external noise, it doesn’t contribute as much if the train speed is relatively low. For example, on the report written by Federal Railroad Administration (US Department of Transportation), it is stated that aerodynamic sources start to generate significant noise at speeds of approximately 180 mph (around 290 km/h). Below that speed, only rolling noise and propulsion/machinery noise is taken into consideration for external noise calculation. In addition to external noise, machinery noise also contributes to the interior noise levels. This category includes engines, electric motors, air-conditioning equipment, and so on. 

To perform the measurements of railway noise, there are several procedures that are commonly followed. For measurement of train pass-by noise, ISO 3095 Acoustics – Railway applications – measurement of noise emitted by rail bound vehicles, is commonly used. This standard has 3 editions with the first published in 1975, and then modified and approved in 2005 and again in 2013. The commonly used measures for train pass-by are Maximum Level (LAmax), Sound Exposure Level (SEL) and Transit Exposure Level (TEL).

For interior noise, the commonly used test procedure is specified in ISO 3381 Railway applications – Acoustics – Measurement of noise inside rail bound vehicles. This procedure specifies measurements in few different conditions such as measurement on trains with constant speed, accelerating trains from standstill, decelerating vehicles, and stationary vehicles. 

Written by:

Hizkia Natanael

Acoustical Design Engineer

Geonoise Indonesia

hizkia@geonoise.asia

Reference:

D. J. Thompson. Railway noise and vibration: mechanisms, modelling and means of control. Elsevier, Amsterdam, 2008

Federal Railroad Administration – U.S. Department of Transportation, High-Speed Ground Transportation Noise and Vibration Impact Assessment. DOT/FRA/ORD-12/15. 2012

Categories
Building Accoustics

Researchers Develop ‘Acoustic Metamaterial’

Boston University researchers, Xin Zhang, a professor at the College of Engineering, and Reza Ghaffarivardavagh, a Ph.D. student in the Department of Mechanical Engineering, released a paper in Physical Review B demonstrating it’s possible to silence noise using an open, ring-like structure, created to mathematically perfect specifications, for cutting out sounds while maintaining airflow.

They calculated the dimensions and specifications that the metamaterial would need to have in order to interfere with the transmitted sound waves, preventing sound—but not air—from being radiated through the open structure. The basic premise is that the metamaterial needs to be shaped in such a way that it sends incoming sounds back to where they came from, they say.

As a test case, they decided to create a structure that could silence sound from a loudspeaker. Based on their calculations, they modeled the physical dimensions that would most effectively silence noises. Bringing those models to life, they used 3-D printing to materialize an open, noise-canceling structure made of plastic.

Trying it out in the lab, the researchers sealed the loudspeaker into one end of a PVC pipe. On the other end, the tailor-made acoustic metamaterial was fastened into the opening. With the hit of the play button, the experimental loudspeaker set-up came oh-so-quietly to life in the lab. Standing in the room, based on your sense of hearing alone, you’d never know that the loudspeaker was blasting an irritatingly high-pitched note. If, however, you peered into the PVC pipe, you would see the loudspeaker’s subwoofers thrumming away.

The metamaterial, ringing around the internal perimeter of the pipe’s mouth, worked like a mute button incarnate until the moment when Ghaffarivardavagh reached down and pulled it free. The lab suddenly echoed with the screeching of the loudspeaker’s tune.

How acoustic metamaterial works – Geonoise Instruments
How acoustic metamaterial works – Geonoise Instruments

Now that their prototype has proved so effective, the researchers have some big ideas about how their acoustic-silencing metamaterial could go to work making the real world quieter.

Closer to home—or the office—fans and HVAC systems could benefit from acoustic metamaterials that render them silent yet still enable hot or cold air to be circulated unencumbered throughout a building.

Ghaffarivardavagh and Zhang also point to the unsightliness of the sound barriers used today to reduce noise pollution from traffic and see room for an aesthetic upgrade. “Our structure is super lightweight, open, and beautiful. Each piece could be used as a tile or brick to scale up and build a sound-canceling, permeable wall,” they say.

The shape of acoustic-silencing metamaterials, based on their method, is also completely customizable, Ghaffarivardavagh says. The outer part doesn’t need to be a round ring shape in order to function.

“We can design the outer shape as a cube or hexagon, anything really,” he says. “When we want to create a wall, we will go to a hexagonal shape” that can fit together like an open-air honeycomb structure.

Such walls could help contain many types of noises. Even those from the intense vibrations of an MRI machine, Zhang says.

According to Stephan Anderson, a professor of radiology at BU School of Medicine and a coauthor of the study, the acoustic metamaterial could potentially be scaled “to fit inside the central bore of an MRI machine,” shielding patients from the sound during the imaging process.

Zhang says the possibilities are endless, since the noise mitigation method can be customized to suit nearly any environment: “The idea is that we can now mathematically design an object that can block the sounds of anything”.

Source:

https://phys.org/news/2019-03-acoustic-metamaterial-cancels.html

Categories
Asia Noise News Building Accoustics

Noise and Vibration Monitoring for Construction Sites

In a densely populated city like Bangkok, most of the construction projects are surrounded by condominiums, offices or residential areas. The construction sites must control the noise and vibration that may affect the surroundings. Construction sites need to control the noise and vibration levels that they produce following the EIA standard.

To manage this, noise and vibration instruments are installed which automatically will send alarms to the construction company if the thresholds are exceeded.

Noise Monitoring Station

Sound level meter class 2 according to IEC61672-1 standard which can collect the data of SPL, LEQ and LMAX. These instruments are calibrated before they are installed at a construction site. The system has a LED display and warning light when noise levels in the site are over a trigger level, which is referred to in the standards for maximum sound levels around construction sites.

According to the announcement of National Environment Board no.15 BE.2540 (1997) in the topic of “Standard loudness”, the average sound 24 hour must not exceed 70 dBA and the maximum peak level must not exceed 115 dBA.

Sound level meter are designed to be used outdoors and an additional LED display was added by Geonoise which is a professional sound and vibration company. Sound level meter with LED display also can analyse the loudness in percentile (Statistical,Ln) or analyse the frequencies in 1/1 and 1/3 octave bands. In addition to storing vibration data, you can also create level notifications in Alarm Alert format before vibration levels exceed the standard value for monitoring the activities being performed.

Vibration Monitoring

In the construction industry, transportation Industry and most large industries vibrations will occur.
High vibration levels will cause structural damage to buildings, bridges, structures as well as nuisance or health risks to occupants in exposed (residential) buildings.

Therefore, it is necessary to comply with the standard of vibration in a building according to the Announcement of the National Environment Board Announcement No. 37, BE 2553 (2010) Re: Determination of Standard Vibration to Prevent Impact on Buildings and the measuring instruments need to comply with DIN45699-1.

At construction projects in Bangkok, most cause a lot of unwanted noise and vibrations. Vibration caused by construction projects are caused by piling work as well as the increased traffic of large trucks that enter and exit the construction site. To prevent that vibration levels will be exceeded, a vibration monitoring system will have to be installed.

The Announcement of the National Environment Board No. 37, BE 2553 Vibration standards to prevent impacts on buildings is the main regulation to comply with for construction sites in Thailand. The vibration standards are derived from DIN 4150-3 whereas buildings are classified into 3 types.

Building types according to DIN 4150-3:

  • Type 1 buildings such as commercial buildings, public buildings, large buildings, etc.
  • Type 2 buildings such as residential buildings, dormitories, hospitals, educational institutions, etc.
  • Type 3 buildings, such as archaeological sites or buildings that cultural values but not strong, etc.

In addition to storing vibration data, you can also create level notifications in Alarm Alert format before vibration level exceed the standard value for monitoring the activities being performed.

Categories
Asia Noise News

Delhi’s RTR Flyover May Get Noise Barrier Costing INR 20 Cr

Delhi’s RTR Flyover May Get Noise Barrier Costing INR 20 Cr

Jugaad is the exact word when we find a temporary solution for the not-so-temporary problem. And, if a necessary step is not taken in time, someone suffers. So, after years of ‘juggad’, the residents of the RTR flyover area finally have some good news coming.

The existing 900-metre flyover ( which was built in 2009), was a single carriageway till it was decided (in 2014) to construct a parallel one to decongest the existing one. But, the construction kept getting delayed sometimes due to residents moving to court and other hindrances. So, to be precise this new flyover will be 2.7-km-long and the project is expected to be completed by June 2018.

So here is the problematic scenario,

To construct this parallel flyover, the Public Works Department (PWD) sought  Central Road Research Institute’s (CRRI) help. They asked them to study the noise pattern in the nearby areas.

According to the research, it was concluded that noise was loudest during the day at 78-82 dB and further by 10 dB during the night. And this would continue happening if they kept using the current noise barrier, which costs around Rs 1.5 Cr. But, as per standards, the noise limit is 55db in residential areas during the day and 45db in the night. Vasant Vihar, West End and Anand Niketan, Munirka and other areas near Rao Tula Ram Flyover will be affected.

The good news is the CRRI has suggested installing the micro-perforated noise barriers which will absorb noise, unlike the reflective ones which just reflects it and then install them in the nearby areas too.

Here is what Nasim Akhtar, a scientist with CRRI, who has performed the study has to say on the subject.

CSIR-Central Road Research Institute (CRRI)

He said, “We have recommended noise barrier at the flyover as it passes through residential areas. Such noise barriers are used in Taiwan, China and we recently got them installed at BR Ambedkar flyover in Mumbai. This barrier will reduce the noise by 18db-20 dB. It has small holes and the noise from the traffic will go to a box and be absorbed there. The height of the barrier should be 3.5 meters.”

As per their report, “Various traffic surveys in tandem with noise and vibration monitoring were conducted at four locations falling on the flyover corridor to understand the traffic scenario and the noise generated. Due to joints in flyover span, an approximately 10db noise will increase at flyover in the night time. Maximum noise level can even cross 100db.”

“A good noise barrier should be lightweight yet strong and durable, and should also be water/fire resistant. It should also be easy to maintain and assemble and disintegrate,” the report further said. This what a PWD official had to say on after the study has been conducted.

He said, “We have got the study conducted to understand the pattern. They have recommended the high-quality barriers and it is up to the government to decide.”

FYI, Block, concrete, wood or metal, without any added treatment or design behave like the reflective wall. And here is a look at how Absorptive Noise Barrier Walls are a better solution than the Reflective Barrier Walls.

Source

Categories
Asia Noise News

Mumbai, India, Govt builds flyovers over homes, but cites fund crunch for not installing noise barriers

Mumbai: In a city with over 50 flyovers, most of which run past residential areas, barely half a dozen have been fitted with the mandated barriers which can bring noise levels down. This, despite repeated complaints by residents in various areas and an amendment to Development Control rules (DCR), which makes it compulsory to install them.
The barriers have to be installed by the Mumbai Metropolitan Region Development Authority (MMRDA) and the Maharashtra State Road Development Corporation (MSRDC), which built most of the flyovers. Both cite shortage of funds as the main reason for the violation. Considering that barriers would cost roughly Rs 6-7 crore per flyover—a fraction of the cost of building a flyover—the explanation does seem odd.
In Mumbai, noise barriers for flyovers first became a reality after BMC and MMRDA officials travelled to Italy in 2011 to study the concept of noise reduction. Apart from flyovers, a 1,500-metre noise barrier was also erected by MMRDA along the Indian Institute of Technology campus perimeter in 2012 and on the Kalanagar stretch at Bandra-Kurla Complex. These were panels of pre-galvanized sheets, painted in keeping with the aesthetics of the surroundings and mounted on the flyovers. If placed correctly, they lower noise by up to 17 decibels, according to studies done by Awaaz Foundation (TOI’s campaign against noise is in association with this NGO).
Some more have been erected on Sion Hospital, King’s Circle, Hindmata and Dahisar flyovers. On the 16.8km Eastern Freeway, which connects P D’Mello Road in south Mumbai with Eastern Express Highway at Ghatkopar, too, there are stretches where barriers are visible. A few of them are of inferior material though, and serve only to block the view into nearby areas while others may be in inappropriate locations.
Anti-noise activist Sumaira Abdulali said there is an urgent need for scientific studies to be done before erecting barriers. “For example, noise barriers have been erected on the Sion flyover. Instead, these should have been erected near the Sion Circle junction where there is continuous movement of vehicles. There is a need for a noise-mapping study or else the infrastructure may not prove to be useful at all. Noise barriers are more helpful when erected at heavy traffic junctions. In case of BKC, barriers were put at the request of the residents and they are happy with it. This is what the authorities should look at doing instead of randomly placing them on any flyover,” said Abdulali.
MMRDA officials said there are plans to install them on two more flyovers on the Eastern Expressway, but there are no deadlines as of now and there is no clarity on whether studies are being undertaken.
In case of MSRDC, of the 23 flyovers it built in the Mumbai metropolitan region, only one in Thane at Kapurbawadi has noise barriers at present—residents and commercial establishments along the remaining 22 have to cope with the sound pollution that easily goes beyond the permissible 45-65 decibels range.
The agency, which has a budget of a few hundred crores, though, says it is now in the process of finalizing a proposal to build barriers on JJ flyover more than 15 years after its completion.
“People living along JJ flyover have demanded such barriers but it all depends on the state and financially sound agencies like MMRDA who can make funds available for the purpose,” a senior MSRDC engineer told TOI .

Mumbai flyoverws noise nuisance
Mumbai flyoverws noise nuisance

MSRDC, which built the Bandra-Worli sea link, cites poor finances as the reason for lack of initiative on its part. The agency has scores of important flyovers to maintain such as the ones at Sion, J J, Vakola, JVLR, Duttapada, Aaarey Colony, Kandivli, Borivli National Park, Nitin Cadbury, Teen Hath Naka and Golden Dyes. It has contracted work of maintenance of these flyovers and certain subways to Mumbai Entry Point Toll, which collects toll against their maintenance at five toll posts—Vashi, Airoli, Mulund, LBS and Dahisar—on the city’s fringes.
According to MSRDC officials, only flyovers within a 30-metre distance from residential buildings need barriers; those who live beyond may not get disturbed. They said barriers on flyovers only cut the sound emanating from vehicles taking the flyovers. Noise from those zooming below the viaducts remains unchecked. To make residential areas fully sound-proof, such barriers are needed along building boundaries as well. Mumbai has two road stretches—one at BKC along Matoshree in Kalanagar and the other at IIT, Powai campus on JVLR—which have barriers erected by MMRDA along the road to obstruct noise of vehicles entering these areas.
Sion resident G R Vora from the F-North Ward Citizens’ Federation said authorities need to analyze and do research before erecting noise barriers. “In case residential buildings are near flyovers, these barriers has helped but in case of barriers which have been erected on the Sion hospital flyover the buildings and the hospital are located at a distance and therefore it is not proving to be very useful,” said Vora.

Source: http://www.indiatimes.com