Friday, June 18, 2021

Semi-Permanent Noise Monitoring

Jonathan Chui and Azar Sagiyev, Stantec Consulting Ltd.

Semi-permanent noise monitoring equipment with remote access has been available for at least a decade, but the technology has evolved with advances in internet speed and wireless connectivity.  Early on, we spent considerable time setting up an account with the wireless service provider and many hours struggling with the cell modem IP configuration.  This has improved recently.
While permanent noise monitoring systems are common for airport authorities and marine port authorities in large Canadian cities, semi-permanent systems have been effective for noise monitoring in short-term construction and operation industrial activities. Most semi-permanent noise monitoring systems consist of the following main components:
  • Sound level meter, pre-amp and microphone
  • Weather station
  • Power source (i.e., AC and/or DC power)
  • Cell modem
  • Data storage
Semi-permanent systems have many advantages, which include
  • Providing continuous noise monitoring for intermittent events with unplanned schedules (e.g., construction activities)
  • Reducing multiple visits to the monitoring site, especially for remote locations
  • Giving easy access to real-time noise monitoring results for users (e.g., clients, consultants, other stakeholders) via the internet
  • Providing a noise threshold exceedance alert (i.e., SNS message) for immediate corrective action
  • Providing sufficient data-sampling
  • Automating the reporting process
Challenges associated with semi-permanent systems include
  • Data transmission is limited by cell coverage (satellite data providers are available but at significantly higher cost)
  • Connectivity can be intermittent in remote locations
  • Remote (e.g., cloud) data storage of audio recording is limited by connectivity
  • Continuous power sources may be required in some systems
  • Post-processing and data management can be labour-intensive due to the large amount of collected data
Semi-permanent systems come at higher cost; however, they provide versatility and functions not available with portable systems. The use of semi-permanent systems may be justified for long-term (e.g., multiple months) monitoring programs where intermittent and unplanned site activities may occur. Semi-permanent-to-permanent systems are also an indispensable tool for major infrastructure projects that require long-term data trends, such as large airports, marine ports and highways that undergo major operational changes or are expected to receive steady increase in traffic in long-term.

Are Electric Cars Quieter than Gas-Powered Cars on the Road?

The number of electric vehicles (EV) is increasing in Alberta and across the globe. While this will positively impact greenhouse gas emissions in our cities, the impact EVs may have on road noise is less well known. EVs are undeniably quieter than their internal combustion engine (ICE) counterparts at start-up and while “idling.” However, road-pavement noise becomes dominant at highway speeds, making EVs and ICEs similar. 

Patching Associates Acoustical Engineering (PAAE) measured pass-by noise levels of locally available compact SUVs, comparing EV and ICE models on a local Alberta highway at various speeds. The results are shown below and indicate that at the tested speeds of 20+ km/h, pass-by noise emissions of EVs and ICEs on typical local pavement did not differ significantly.

While electric vehicles have the potential to reduce noise with very slow speeds (under 20 kph) and during idling and acceleration from standstill—where engine-generated noise dominates, such as in very congested city centres—these data show that the rise of EVs is not going to drastically change the situation for Alberta residents who are currently most affected by roadway noise—those living near busy arterial and highway road infrastructure.

Thursday, June 17, 2021

Paradise Lost: The Wilderness is Not What it Used to Be

Henk de Haan & Virgini Senden

Freshly vaccinated, we decided it was time for a change of scenery, so we packed our recently-acquired second-hand travel trailer and hit the road. The trailer, like any other trailer, is packed with amenities to turn it into our home away from home—heating, cooling, cooking facilities (an oven and a microwave), a fridge with freezer, and a bed with a real memory foam mattress and a bedside reading light. After a lifetime of camping in small, portable tents and sleeping on wafer-thin camping mattresses not worthy of the name—the epitome of luxury.  All these amenities require electric power, of course, either supplied via batteries or via a hookup at the camping spot.

Our first camp site was not equipped with power at all. To prevent draining his batteries, a neighbouring camper schlepped a transportable generator in and ran the generator for about an hour each day around lunch time. The first time, I was sitting outside reading, enjoying the beautiful weather, the songbirds, the busybody squirrel—it was heaven! The generator in question was not equipped with any noise-mitigating features, and it showed. The birds, the squirrels, the rustling leaves—all gone. I sighed, went inside and closed the door.

When camping, you’re more exposed to the weather, and it can turn nasty. We had a spot of rain overnight, and when I woke up early the next morning, everything inside felt a bit damp. I sneaked out of bed and decided to try out the heating system to get rid of the dampness, thus making getting up a more pleasurable experience for my significant other (she’s sensitive that way). The furnace came on, and so did the fan. It turns out the fan is a small, high-performance fan, tearing the peaceful slumber of my beloved to pieces. I tried to restore peace by offering breakfast in bed, which was (thankfully) gracefully accepted. A golden rule for both camping and staying in hotels: bring earplugs!

Our next campsite, located in a popular National Park, had it all—or almost everything in the eyes of management. Opposite from our campsite, a construction crew was working to erect a new building quite close to an existing, also fairly new, one. The crew put in admirable hours, even on Saturday and Sunday—twelve-hour shifts at least. For their power, they relied on a generator, not on the outlets of the building less than 25 metres away. When we pointed out the option of plugging in their equipment to the camp operator, the young man stared at me and said that generators were allowed between 7 AM and 11 PM, completely missing the point.

The weather on this camping trip was warm. Neighbours a few sites over invested in an RV the size of a city bus, equipped with at least three AC units. Obviously, they liked it cool, including overnight. We reached for the ear plugs once more. Did I mention the grass mowers? Management likes the grass on the campsite short.

All in all, we had a lovely outing, but not a quiet one. Thankfully, we were not confronted with rowdy neighbours playing their favourite music over the outdoor sound system that any decent trailer comes with. I’m sure, however, we will in the not-too-distant future. I want to go home.

Wednesday, June 16, 2021

When Condos “Sing”: Assessing Wind-Induced Balcony Railing Noise

Condo balcony railings can generate noise in high-speed winds
Modern condo towers can be prone to unwelcome noise outcomes. Mysterious ringing sounds that rattled residents in central Edmonton, Alberta were suspected to be caused by strong winds acting on balcony railings from a new residential hi-rise. Condo towers can be wrapped in balcony railing panels of countless styles, shapes, and materials. At the height of the top floors of tall towers, wind shear produces wind at several times the speed at ground height, and the wind speed can be extreme.
Some perforated aluminum balcony railing designs can generate wind-induced noise
Some perforated aluminum balcony railing designs can generate wind-induced noise

In general, there are two types of balcony railing panel designs: a solid material (usually glass) or a perforated material (usually aluminum). While it may be possible for a solid glass railing to generate noise, it is not typically a concern we are called on to assess and/or mitigate. On the other hand, when it comes to perforated aluminum railing designs on condo balconies, there are many possible combinations of wind speeds and angles of attack that can induce unwelcome sound.

The Benefits of Acoustically Assessing Balcony Railing Design Early on in a Project

Given the complexity of the mechanism that produces tonal sound from balcony panels, and given the cost of retrofitting existing panels, it is important to consider how a balcony railing panel will behave in the wind before the panels are installed, during the design phase.

Aeolian excitation (a.k.a. the wind) can cause a structure to vibrate, which under certain conditions and within a certain range of frequencies can lead to unwelcome sound. Thin, flat surfaces, like balcony railing panels are particularly good at converting vibration to sound, much like the diaphragm of a speaker.

There are two dominant mechanisms that can produce wind-generated noise at the perforations: vortex shedding, where the wind passes along the face of the railing over a repeating pattern of holes or slots, and jet noise due to wind flowing through the perforations. A third mechanism relates to the Helmholtz resonator effect, similar to blowing over the top of a bottle, but the lack of a defined volume behind the balcony panels renders this mechanism inapplicable.

The likelihood for a balcony railing panel to generate noise is dependent on many factors, including but not limited to the wind speed, the angle of attack of the wind, and the size and shape of the perforations. Because the flow of the wind over a small area is extremely difficult to predict or to model accurately, the interaction between the balcony railing panels and the wind is also difficult to predict. Therefore, we have found the most comprehensive way to evaluate how a balcony railing panel will behave is to test it in a wind tunnel.

Wind tunnel testing balcony railing design for possible wind-induced noise generation
Wind tunnel testing balcony railing design for possible wind-induced noise generation

Wind-Tunnel Testing of Balcony Railing Design Mock-ups for Noise

HGC Engineering has been called on by several developers during the design phase of a project to test full-sized balcony railing mock-ups inside of a wind tunnel. The wind tunnel environment allows us to measure the behaviour of a balcony panel design at any wind speed and angle of attack in a controlled and predictable environment, and to evaluate several perforation designs for their potential ability to generate sound under varying wind conditions. Wind speeds of up to hurricane strength can be tested with the proper setup.

Acoustical results of wind tunnel testing on balcony railing panel design
Acoustical results of wind tunnel testing on balcony railing panel design

During wind tunnel testing our acoustical consultants measure sound, vibration, and wind speed data in high-resolution in a variety of locations on and near the mock-up, using state-of-the-art acoustical instrumentation. The complex interactions between the balcony railing panel and the wind is analyzed to ensure that no wind-induced tonal noise is present. Should tonal noise be detected, we can then assess the cause and recommend various options to the project development team, including changes to the panel design or retrofit options for an existing panel. In many cases, these options can be tested and verified within hours.

Excerpted with permission of HGC Engineering.

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