Archive for August, 2009

The Source, Of Course

Wednesday, August 19th, 2009

by Lance Meister

(The first in an occasional series on the basics of noise and vibration as they relate to trains and transit.)

One of the basic things we do in our business is help to reduce noise or vibration levels from transportation sources.  At times, this can seem like a very daunting challenge, but it’s very helpful to look at all noise or vibration problems in a very simple framework.

The Source-path-receiver Concept

The Source-path-receiver Concept

When Carl Hanson and I teach the FTA Transit Noise and Vibration course around the country, we emphasize this concept to our classes, and try to show how any noise or vibration scenario contains all three pieces.

The first piece of the framework is the source, and that’s what I’m going to discuss in this post.  I’ll cover the path and receiver later, and also cover what to do with each piece of the framework to reduce the noise or vibration.

The source is what is generating the noise vibration.  And yes, this is very basic and obvious, you may be saying to yourself (quietly, I hope), but it is important.  To properly diagnose the problem, you need to understand the source of the noise or vibration.  (And really, noise and vibration are essentially the same phenomenon, just in different materials: noise  – air, vibration – ground.)

Think for a minute about taking your car in to a mechanic because you hear a noise.  What questions does the mechanic ask you?

  • Where is the noise coming from?
  • What does it sound like?
  • When does it occur?
  • How loud is it?

There are the same types of questions we ask in a noise or vibration assessment.  They may be a little bit more detailed, but we basically ask the same questions.  And just like with your car, the answers to those questions are very important, and help determine what needs to be done.

Here is a source I am very familiar with: a train.  There are many potential sources of noise and vibration on a train, and if you want to reduce the noise or vibration from a train, you need to understand where it is coming from.  Just like with your car, to say “the noise is coming from the train” may not be enough.  Depending on the type of train, there are many potential sources of noise and/or vibration, including:

Noise

  • Wheel/rail interaction
  • Brakes
  • Wheel squeal on curves
  • Horns and bells at grade crossings
  • Diesel exhaust and fans

Vibration

  • Vehicle suspension
  • Wheel type and condition
  • Track surface
  • Track support system
  • Transit structure
  • Depth of vibration source

And in addition to all of these, speed can have a dramatic effect on the source of noise or vibration.  In general, noise and vibration increase with increasing speed.  Certain sources increase more or less quickly with speed (and some not at all!), so knowing the speed is important for the source of noise and vibration.

Here’s something really interesting: with High Speed Rail (HSR), the speed actually changes the type of dominant source of noise!  At lower speeds, the power sources on the train dominate the noise (engines, cooling units, etc.).  At higher speeds, the wheel/rail noise dominates and at the highest speeds, (don’t worry, we’re not there yet in the US!) aerodynamics noise (airflow over the train itself) is the biggest source.

In addition to where the noise or vibration is coming from, you need to understand which sources of noise or vibration are contributing most to the specific scenario you are dealing with.  Knowing this helps to understand how you can address the problem for the maximum benefit.  Once you know what the source of the noise or vibration is, you need to know where it is going.

Next time: The Path “Where do we go from here?”

TRB Noise and Vibration Committee Visits Home of the Pop-top

Wednesday, August 12th, 2009

by Doug Barrett

During the last week in July, transportation noise enthusiasts convened in Dayton, Ohio for the Transportation Research Board’s Committee on Transportation-related Noise and Vibration (TRB Committee ADC40) annual summer meeting.

2009_0307_MiniConceptA

The mission of the Transportation Research Board, one of six branches of the National Research Council, is to “provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multi-modal.”  With 31 technical presentations, a tour of the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, vendor/sponsor displays, a chance to meet state DOT representatives one-on-one during a 90-minute “Speed Stating” session, and the official Committee meeting itself, this summer’s gathering was right on target with TRB’s mission statement.

ADC40 has long been an active committee, and I’m always impressed by how much valuable information is exchanged at these summer meetings.  With a total attendance of somewhere around  100 individuals, a large percentage of the attendees also are presenters, sponsors, exhibitors, or organizers.   The technical sessions are uniformly well attended, and the follow-up questions show that this crowd knows its audience well and presents topics that are pertinent to many in the group.  HMMH gave four presentations covering the range from a new ANSI standard for estimating noise-induced awakenings, to issues regarding highway noise barrier studies, to a noise-barrier design contest at Amsterdam’s Schiphol Airport.  As in years past, other hot topics included research on tire/pavement noise, news on FHWA’s  updated version of the Traffic Noise Model (TNM 3.0), and policy updates from FHWA and state DOTs.

There was time for some fun too, including a chance to see the Dayton Dragons take on the Peoria Chiefs (Class “A” baseball) on Tuesday evening.  For aviation buffs though, a visit to the National Museum of the U.S. Air Forcewas a stand-out treat.  The museum covers the history of aviation, from the Wright Flyer to moon landings and beyond, with as impressive an assortment of vintage aircraft as you’re going to find under one roof – ok, actually three enormous roofs.  On the bus ride back from the museum, the driver treated us to a bonus monologue of Dayton history and trivia.  One got the feeling that the driver was readily capable of expanding our 15-minute version to a much more complete history, with the level of detail dictated by the length of the ride.  At any rate, if not for this, I may never have known that Dayton gave birth not only to the Wright Flyer, but also to the step ladder and pop-top can.

A final note, many thanks to the Organizing Committee for all their efforts, and congratulations to the successful meeting!

People, Noise, People

Tuesday, August 11th, 2009

by Nick Miller

So when I started my career in acoustics, the Noise Control Act of 1972 had just passed, the “Levels Document” was being researched by the heavies of acoustics, and the concept of Ldn (DNL to some of you) was being proposed.  Passing through the work room, Ted Schultz (God rest his soul) was pasting up some report or other: “Hi Meatball.  Did you know the architect thought building this wall in the shape of a sine wave would reduce the traffic noise?  Good thing it was built of bricks, long and tall.”

It was the early days of trying to understand acoustics.  The concept of Ldn and setting some sort of compatibility level was pretty innovative and a good start, it seemed to me.  I carefully read and marked up Appendix D of said “Levels Document.”

Then came the public meetings and field work.  Measuring aircraft taxi noise levels in Jeffries Point (East Boston) under the watchful eye of several residents, Mary Ellen Welch says, “But it can’t be Ldn 65.  That number is just too small.  The aircraft make much more noise than that.”  And so began my struggles of trying to figure out how to 1.) explain Ldn and 2.) relate noise levels to the way people reacted.

But now the International Civil Aviation Organization (ICAO ) Committee on Aviation Environmental Protection (CAEP) has issued a report recommending that rather than counting the number of people exposed to significant noise as measured by DNL, the focus should be on specific health effects or outcomes.  More significantly for us in the U.S., the Federal Aviation Administration (FAA) is considering whether DNL 65 and percent highly annoyed is the best way to characterize impact, and is planning an international forum to discuss noise research needs.  Finally (and here I have to pause and take a deep breath as well as cross my fingers), the FAA and the National Park Service (NPS) seem like they’re about to cooperatively work on figuring out how aircraft noise affects park visitors.

To many of us on the front lines of aircraft noise assessment, these developments are a wonder and welcome beyond words (well, not beyond words, but pretty welcome anyhow).  The motivations for these thoughtful, long needed efforts are probably many – maybe partly the effort of specific personalities, maybe Vision 100 and its requirement for the creation of a plan to design the Next Generation Air Transportation System that reduces the impact of aviation on community noise.  Well, whatever the motiviation, it’s great to think that the time has finally come to update and upgrade the ways we examine and reduce the effects of aircraft noise on people.  “O frabjous day!  Callooh!  Callay!”  I’ll keep you posted.

Look out, Virginia! Here we come!

Monday, August 10th, 2009

by Steve Barrett

I think we all struggle to grasp the threat of climate change.  Believers issue the clarion call of melting glaciers and drowning polar bears when few of us have ever seen a polar bear beyond the technicolor of TV.  Cynics say we can’t risk our economic health (I can hear the wheezing) worrying about science fiction of the distant future.  Listen, the year 2050 seems a long way off and many of us will be well beyond the pale in some form by that point.  Leave the problem to the ingenuity of future generations who will have larger brains and more sophisticated tools to remake the third rock from the sun or create a new paradise in some other neighborhood in the universe.  Heck – I could be swayed to just kick back, crank up the air-conditioning and drive a Winnebago around the world, ignorant to the subtle signs reported on NPR as I drive the ribbon of highway soon to connect the purple mountains majesty with the Tierra del fuego.  But then there is that slow train coming heading south to Virginia.

Emissions Scenario

Emissions Scenario

As a native New Englander, the thought of Massachusetts migrating south to Virginia makes me sweat.  It’s not that I dislike Virginia or think it somehow uncultured when compared to my elitist home (hub of the universe, Athens of America, yada yada).  In fact, I spent 5 years living with southern “Commonwealth” cousins, and I can tell you, there aren’t more welcoming people.  It’s just that I am partial to the combination of mountains with the brilliance of fall from the maples and birches, coastline of rocks and sand, and rivers all nice and clean thanks to successful environmental regulation. 

Cape Cod forms an amazing eco-boundary between the humpback whales and sea turtles of the south and the cod and lobster of the north; all of that great bounty for us New Englanders to plunder and restore for 400 years – which we have done well.  But none of these wonderful creatures will be here in 2050 if we don’t take action today.  Well, a few mutants will survive and create populations closer to the arctic, but isn’t there a better way?  Do we really want to induce such environmental havoc where humans live with the likes of poison ivy and Asian long-horned beetles? 

I say sprinkle some wind turbines amongst the glory of fall foliage (head north on I-93 to I-89 to Route 10 and the small town of Lempster NH for your first glimpse)

 

Lempster

Lempster

and throw a few more in the ocean off Nantucket.  Not only will it put some speed bumps along the eastern seaboard to slow our advance on Virginia, but it will also give us elitists of New England another “first” to crow about besides Harvard and the Industrial Revolution.