Dr. Craig Hunter of NASA Langley has developed a software package called Jet3D, that simulates flow out of a jet engine and calculates how much noise it makes from the standpoint of a microphone on the ground.
Read the full story on the apple web site
The hard disks inside every desktop and laptop are designed to emit low noise and generate, and also to be relatively insensitive to vibration.
Two important designs features that enable this are fluidic bearings and winglets on the head of the arm.
Hard disks were once made with tiny rolling element ball bearings, however nowadays almost all hard disks are made with fluidic (journal) bearings. These bearings are more reliable, quieter, generate less vibration, and cheaper than the ball bearings.
Another important design feature are the winglets on the end of the read / write head. The hard disks spin at 4200rpm or higher which causes the air to move. Small wings attached to the sides of the hard disk head enables the head to “fly” precisely above the rotating disk. This design makes the hard disk less sensitive to vibration.
BBC news has an article about the effects of low frequency sound. Church organs emit infra-sound which causes mood changes in the congregation. Elephants use infra-sound to communicate.
Read the story on the BBC news web site.
New book titled Acoustic interaction with submerged elastic structures, Part 5: Nondestructive Testing, Acoustic Wave Propagation and Scattering, edited by Ardéshir Guran, Anders Boström, Oswald Leroy and Gérard Maze.
508pp Pub. date: Jul 2002
ISBN 981-02-4271-9 US$100 / £67
Read the full review here.
Industrial Research has developed an active vibration control system to reduce vibration from headrig bandsaws, that enables thinner saw blades to be used.
A feedback system applies control forces using non-contact electromagnetic guides.
Read the full article here.
Engineers at Penn State University have developed a novel method of extracting power from vibration. The method uses a rectified piezo-electric device to generate electricity.
Read the full article on the Penn State web site.
Newport, a manufacturer of vibration isolation and optical components, will become a preferred supplier for EM4 for all test and assembly equipment to support the company’s optical manufacturing business.
Read the full article here.
Pistachio nuts can be sorted using the difference in impact noise between a nut with an open and closed shell. It was found that upon impact with a steel plate, nuts with closed shells emit sound with higher signal magnitudes than do nuts with open shells.
The classification accuracy of this system is approximately 97%, and the cost of the system is about $7k per channel, which is less than conventional sorters that use color of the nuts. Increased sorting accuracy of the acoustic sorter, coupled with low cost, enables a payback period of less than one year.
Reference: “Detection of pistachio nuts with closed shells using impact acoustics”, Pearson, T.C., USDA ARS GMPRC, Manhattan, KS 66502, United States, Applied Engineering in Agriculture v 17 n 2 March 2001. p 249-253 , 2001.
Tires for vehicles have various tread patterns, usually to balance the amount of traction to the road surface during dry and wet weather. As most people know, a solid soft tyre has the greatest surface area in contact with the road and hence has the most amount of traction. The tread pattern allows water to escape when the tire is on wet roads.
When the tread is in contact with the road surface, volumes of air are formed between the road and the tread pattern in the tire, which is compressed as the tire rotates. The volumes of air are a network of small Helmholtz resonators that generate noise.
In addition, the interaction of the tread pattern with the road vibrates the body of the tire and causes the walls of the tire to radiate noise.
Read an article on tire noise by Stuart Bolton.
I’ve added a new topic called, “Did you know …” where posts about interesting facts on acoustics and vibration are welcome.
Click here to read all the articles.