Abstract
Owl wing inspires reduction in turbine noise
Many species of owl are able to hunt in effective silence by suppressing their noise at sound frequencies above 1.6 kHz—over the range that can be heard by humans.
A team of researchers studying the acoustics of owl flight—including Justin W. Jaworski, assistant professor of mechanical engineering and mechanics at Lehigh’s P.C. Rossin College of Engineering and Applied Science—are working to pinpoint the mechanisms that accomplish this virtual silence to improve human-made aerodynamic design of wind turbines, aircraft, naval ships and, even, automobiles.
Now, the team has succeeded—through physical experiments and theoretical modeling—in using the downy canopy of owl feathers as a model to inspire the design of a three-dimensional (3D) printed, wing attachment that reduces wind turbine noise by a remarkable 10 dB, without impacting aerodynamics. They have further investigated how such a design can reduce roughness and trailing-edge noise. In particular, trailing-edge noise is prevalent in low-speed applications and sets their minimum noise level. The ability to reduce wing noise has implications beyond wind turbines, as it can be applied to other aerodynamic situations such as the noise created by air seeping through automobile door and window spaces.
For more information, follow the link: https://www.sciencedaily.com/releases/2016/11/161116123404.htm
Documenting crowd noise effects
How loud was the crowd at Beaver Stadium on Saturday?
“They were a lot louder earlier in the game”, said Andrew Barnard—and he has more than anecdotal evidence to back up his assertion. While Joe Paterno led the Nittany Lions on the field, Barnard, a doctoral candidate in acoustics and research assistant in the Applied Research Laboratory’s structural acoustics department, led a team of his own on the sidelines, measuring the noise levels throughout the game.
“The loudest level we recorded was a peak sound pressure level (SPL) of 122 decibels (dB). That is loud enough to cause physical pain on the ear drum”, Barnard said. “The crowd only achieved these levels for very short bursts, on the order of 10 milliseconds. The loudest SPL we recorded averaged over a second or more was about 110 dB”.
By the fourth quarter, with Penn State trailing the Buckeyes, noise readings were down around the 80–90 dB range, roughly equivalent to a noisy vacuum cleaner or a motorcycle. At that level, the Buckeyes were able to communicate fairly easily with raised or very loud voices at distances up to 32 feet. The highest noise reading recorded in the fourth quarter was 100 dB, which is equivalent to a riding lawn mower and makes communication difficult, but possible by shouting.
The acoustics exercise, while interesting, also serves some practical purposes for Penn State.
For more information, follow the link: http://news.psu.edu/story/192796/2007/10/29/acoustics-team-documents-crowd-noise-effect-opposition
Rating the loudest college basketball arenas
University Park, PA—Who’s got the loudest college basketball arena in the country? ESPN The Magazine recently asked engineers from Penn State’s graduate acoustics program to help answer the question.
The results appear in the magazine’s 15 November issue, which is available on newsstands.
Micah Shepherd, a doctoral candidate in acoustics and a research assistant at the Applied Research Laboratory (ARL) who led the effort, said the magazine heard about the crowd noise measurements conducted at Penn State football games at Beaver Stadium.
“One of their writers contacted Stephen Hambric, professor of acoustics, and asked him about doing this type of analysis, figuring out which basketball arena is the loudest”, Shepherd said.
Hambric then asked Shepherd to see if he was interested in leading the project.
With a tight deadline, Shepherd and a group of acoustics graduate students quickly went to work. Shepherd’s team included Andy Christian, Bryan Cranage, Dan Domme, Neal Evans, Michael Gardner, Andrew Orr, and Kieran Poulain.
“We had a relatively short time frame”, he said. “It wasn’t feasible to go out into every arena and do measurements anyway. So, I looked back in some textbooks on acoustics and found equations for sound buildup in large rooms—large meaning arenas, concert halls, things like that”.
Those equations served as the starting point for the Penn State acoustics team.
For more information, follow the link: http://news.psu.edu/story/162878/2010/11/16/acoustics-engineers-help-espn-rate-loudest-college-basketball-arenas#nw63
Acoustic levitation of a large sphere
When placed in an acoustic field, small objects experience a net force that can be used to levitate the objects in air. In a new study, researchers have experimentally demonstrated the acoustic levitation of a 50-mm (2-in) solid polystyrene sphere using ultrasound–acoustic waves that are above the frequency of human hearing.
The demonstration is one of the first times that an object larger than the wavelength of the acoustic wave has been acoustically levitated. Previously, this has been achieved only for a few specific cases, such as wire-like and planar objects. In the new study, the levitated sphere is 3.6 times larger than the 14-mm acoustic wavelength used here.
The researchers, Marco Andrade and Julio Adamowski at the University of São Paulo in Brazil, along with Anne Bernassau at Heriot-Watt University in Edinburgh, UK, have published a paper on the acoustic levitation demonstration in a recent issue of Applied Physics Letters.
“Acoustic levitation of small particles at the acoustic pressure nodes of a standing wave is well-known, but the maximum particle size that can be levitated at the pressure nodes is around one quarter of the acoustic wavelength”, Andrade told Phys.org: This means that, for a transducer operating at the ultrasonic range (frequency above 20 kHz), the maximum particle size that can be levitated is around 4 mm. In our paper, we demonstrate that we can combine multiple ultrasonic transducers to levitate an object significantly larger than the acoustic wavelength. In our experiment, we could increase the maximum object size from one quarter of the wavelength to 50 mm, which is approximately 3.6 times the acoustic wavelength.
Although there are several different ways to acoustically levitate an object, most methods use an ultrasonic transducer, which converts electrical signals into ultrasonic waves. The current setup uses three ultrasonic transducers arranged in a tripod fashion around the sphere.
For more information, follow the link: http://phys.org/news/2016-08-acoustic-levitation-large-sphere.html
Manipulating nanoparticles using low-frequency vibrations
The world of science and technology has been in hot pursuit of the nanoparticle for the last few decades bridging the gap between the atomic and the bulk levels, nanoparticles of all materials possess unique properties. These open up an almost endless array of new possibilities for applications in practically every field of human endeavor. The sustained efforts of the scientific community, driven by enormous investments in time and resources, have yielded great advances in the knowledge of the how and why of nanoparticle properties and behavior.
However, for all the possibilities that this new body of knowledge throws open, it would be next to impossible to employ any of it in practical applications without the ability and the tools to select, sort, arrange, and manipulate specific particles as needed. Much work has been done to identify, develop, and refine methods for this purpose.
For example, nanoparticle manipulation (in the range of 100 nm) has been achieved through the use of external magnetic and electric fields to position and sort selective particles. These have also been integrated with electrostatically actuated micro-grippers to “pick and place” particles. In microfluidic systems, methods such as di-electrophoresis, optical trapping, and magnetic tweezers have been used.
Each of these methods has its merits and demerits in terms of technique and implementation for particle manipulation in microfluidic systems. For example, in the case of optical tweezers, the diffraction which occurs at the interfaces between different media will complicate the production of highly focused laser beams. For di-electrophoresis, the force field produced diminishes rapidly as distance from the electrodes is increased.
For more information, follow the link: http://www.iitbmonash.org/story-45/
Bee-culture utilizes vibrations
Before eating your next meal, pause for a moment to thank the humble honeybee. Farmers of almonds, broccoli, cantaloupe, and many other nuts, vegetables, and fruits rely heavily on managed honeybees to pollinate their crops each year.
Recently, honeybees have been under stress from a mysterious threat called colony collapse disorder, which causes the majority of worker bees to abandon the hive. While scientists are still investigating the causes of the phenomenon, beekeepers could benefit from technologies that help them keep tabs on the health of their hives.
Researchers from Nottingham Trent University, in the United Kingdom, have now developed and tested a new prototype device that can remotely monitor hive activity without disturbing the bees. The device picks up and analyzes vibrations from special types of bee vocalizations, such as the common one called a “begging signal”. It has successfully tracked changes in bee activity from day to night, and seasonally, by monitoring the occurrences of this specific signal.
The team will present their results at the 170th meeting of the Acoustical Society of America (ASA), held 2–6 November, in Jacksonville, Florida.
“We want to develop a tool to find out the status of honeybee colonies—if the colony is starving, if there is a lot of foraging going on, or if the bees are preparing to swarm”, said Martin Bencsik, a researcher in the School of Science & Technology at Nottingham Trent University.
For more information, follow the link: http://www.beeculture.com/catch-the-buzz-vibrations-in-a-colony-tell-a-story/
Solving unwanted engine noise and vibration using Maple
When an engine stops, several engine components take part in the process. Components can produce unwanted noise and vibrations when the engine slows down, which can lead to their deterioration. Jean-Louis Ligier, a Research and Development manager at Renault, and his team were tasked with determining the sources of these noises and vibrations in a 2.2-L 4-cylinder turbo diesel engine. They found Maple™ to be the most efficient tool to model the engine and determine the source of the unwanted noise. More importantly, they also used Maple to determine a solution to the problem.
Ligier, who has a PhD in Mechanical Engineering, has been using Maple for over 20 years. He has used the software in several applied research projects, such as time-varying thermal analysis in gearbox components, engine friction optimization, and vibration analysis. He has been with Renault for over 12 years, managing thermal behaviors and mechanic fatigue on engine components, as well as determining new simulation methodology for them. His primary goal in using Maple was to write equations that control the engine components very easily.
When creating mathematical models of various components, different software can be implemented. Ligier has found through his experiences that Maple is the easiest and fastest software for his tasks. “In comparison with others, Maple can do in a couple of hours what other software can take days to compute”, he said: The natural math notation allows me to enter the equations as if I were writing them by hand. The fact that I can do symbolic calculations allows me to do optimizations that are virtually impossible with other software. What’s more, the results are extremely accurate.
For more information, follow the link: http://www.maplesoft.com/company/casestudies/stories/19216.aspx