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Showing posts with label Mechanical Engineering. Show all posts
Showing posts with label Mechanical Engineering. Show all posts

Monday, 10 February 2020

How will a driverless car hear a siren?

Teaching cars to listen: The acoustic sensor system includes microphones, which go outside the car, a control unit and the software.

Cars with Ears 

There have been concerns about the silence of electric cars, which can pose a risk to pedestrians.

But, electric or not, when the cars become autonomous - that is, when they dispense with the drivers to guide them - those vehicles that self-drive will need to be "aware" of the traffic noise around them.

Be it the siren of an ambulance or a fire truck, the whistle of a guard, or even a danger call from a passerby, cars without a driver will definitely need to have ears.

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A team from the Institute of Technology of Digital Media, in Germany, has already anticipated this need, and has just built the first prototype of a "vehicle hearing system". In addition to traditional microphones, the device includes a processing center, whose software is already able to identify the most common noise in traffic, such as sirens.

"Despite the enormous potential of such applications, no autonomous vehicle has yet been equipped with a system capable of perceiving external noise," said engineer Danilo Hollosi, head of the acoustic event recognition group at the German institute. "These systems will be able to immediately recognize the siren of an oncoming emergency vehicle, for example, so that the autonomous vehicle then knows how to move to one side of the highway and form an access lane for rescue services."

To filter out continuous city and highway noise, the team used artificial intelligence techniques to train the algorithm that runs in the "automotive ear". "We use machine learning. And to train the algorithms, we use a whole range of archived noise," explained Hollosi.

The team believes that the first cars with ears are unlikely to reach the market before 2025 - the processing system will still need to be optimized - but they bet their technology will be used in many other areas, such as safety systems, quality control in the industry, personal care and consumer products.


Wednesday, 26 June 2019

All electric cars may use the same engine

The big challenge is to build a unique platform that serves different classes of hybrid and electric cars. [Image: Drivemode / Disclosure]

Generic propellant

In pursuit of increased efficiency and lower costs, the auto industry has shown an interest in avoiding the mistakes and problems of its first century, based on internal combustion engines.

Taking advantage of the migration to electric motors, efforts have focused on creating basic motorization platforms from which different car models can be built by each company.

This is precisely the purpose of the Drivemode project , funded by the European Union.

The multi-institutional team is developing a scalable, distributed, integrated transmission module (IDM) for all types of mass-produced electric and hybrid cars, from light-duty vehicles to high-performance utility vehicles.

At their last meeting last month in Brussels, Belgium, the team has proven to have reached a critical point in their research and development: they have discovered ways of integrating a high-speed gearbox (achieving 97% efficiency around the (75kW, 100Nm and more than 20,000rpm) and a SiC inverter (20kHz switching, 140A rms current) in efficient and economical transmission modules.

The next step is to start building and testing the propulsion modules. [Image: Drivemode / Disclosure]

Integrated propulsion module

The main advantages of the integrated module come from reduced material usage, simplified installation and optimum synergy between components. In addition, the distributed power concept opens the door to a unique design to fit a variety of vehicles.

The next step will be to start manufacturing these modular cars.

Among the goals set for this next stage are achieving a 30% increase in specific torque and power, a 50% increase in electric motor speed, an increase in voltage (800V) to further reduce the materials used and a 50% loss of materials, and faster battery recharging.

Sunday, 23 June 2019

Sound and heat are put to flow in a single direction

A flexible membrane (gray square) serves as an acoustic resonator, placed between two mirrors. When the laser light gets stuck between the mirrors, it repeatedly passes through the membrane. The force exerted by laser light is used to control membrane vibrations. [Image: Harris Lab / Yale University]

Reversible acoustic diode

A few days ago, you heard of the creation of a tube-shaped acoustic shield that promises things like ending the drone's buzz.

A team from Yale University in the USA has just presented something with similar effect - but not in tube format and with greater versatility.

It is a resonator coupling structure that is essentially a reversible acoustic diode, a structure that allows sound to only go in one direction - in the direction you want it to go.

"This is an experiment in which we make a one-way route for sound waves." Specifically, we have two acoustic resonators, the sound stored in the first resonator can leak to the second resonator, but not vice versa, "said Professor Jack Harris.

Reversible thermal diode

Since heat also consists basically of vibrations, the team repeated the experiments not with sound, but with heat, and the thing worked.

"Using our unidirectional sound trick, we can make heat flow from point A to point B, or from point B to point A, regardless of which one is colder or hotter. hot water and let the ice cubes get colder as the water around them gets warmer and hotter. So by changing a single setting on our laser, we make the heat flow in the usual way, and the cubes of ice gradually cool and melt while the liquid water cools a bit.While in our experiments are not ice cubes and water that are exchanging heat but two acoustic resonators, "Harris detailed.

Steering wheel for heat and sound

While some of the most basic examples of acoustic resonators are found in musical instruments or even automobile silencers, they are also found in a variety of electronic devices, being used as sensors, filters and transducers because of their compatibility with a wide variety of materials , frequencies and manufacturing processes.

With this, the new device can be interesting not only to isolate acoustically environments, but also to guide the heat inside the electronics, all with the turn of a button - in fact, with the adjustment of a laser.

The team now intends to move from its laboratory configuration to more suitable apparatus for practical applications.


 Nonreciprocal control and cooling of phonon modes in an optomechanical system
H. Xu, Luyao Jiang, AA Clerk, JGE Harris
 Nature Vol .: 568, pages 65-69
 DOI: 10.1038 / s41586-019-1061-2

Saturday, 22 June 2019

Thermodynamic magic promises refrigerators that do not expend energy

Chilling out: in principle, a thermal inductor could help convert boiling water to ice without using any external energy. (Courtesy: A Schilling and AC Mangham)

Not for the Law of Thermodynamics

Physicists at the University of Zurich in Switzerland have developed an incredibly simple device that allows heat to temporarily flow from a cold object to another hot object without requiring an external power source, as it does in traditional refrigerators.

Curiously, the process seems at first glance to contradict the fundamental laws of physics, more specifically the Second Law of Thermodynamics , which states that the entropy of a closed natural system must increase with time. Or, more simply, the heat will flow itself from a warmer object to a colder one, not the other way around.

Andreas Schilling and his colleagues were able to cool a nine-gram piece of copper from over 100 ° C to a level significantly below room temperature without any external power supply, which seems at first glance to challenge this Second Law of Thermodynamics.

"Theoretically, this experimental device can turn boiling water into ice without using any energy," says Schilling.

The arrows represent the direction of the heat flux from light / yellow or dark / purple to the respective hottest object. [Image: A. Schilling et al. - 10.1126 / sciadv.aat9953]

Cooling without energy consumption

To do this, the team used a Peltier element , a commonly used component, for example, to cool minibars in hotel rooms or in solid-state (non-gaseous) refrigerators used in automobiles. These thermoelectric elements can transform electrical currents into temperature differences.

The team had already used a Peltier plate, along with a coil, to create an oscillating heat chain in which the heat flow between two bodies perpetually changes direction. In that experiment, the heat also temporarily flows from an object colder to a warmer one, so that the colder object is cooled further. This type of "thermal oscillating circuit" contains a "thermal inductor", functioning in the same way as an electric oscillating circuit, in which the voltage oscillates with a constantly changing signal.

However, until then, these thermal oscillating circuits - essentially thermal diodes - only operated using an external source of energy.

Now, for the first time, Schilling has shown that this type of thermal oscillating circuit can also operate "passively", ie without external power supply. Thermal oscillations still occur and after some time the heat flows directly from the coldest copper to a warmer solution with a temperature of 22 ° C, without the heat being transformed into another form of energy in the way.

Despite this, the team made the calculations to show that the apparatus does not contradict the laws of physics. To prove this, they considered the change in entropy of the whole system and showed that it increases over time - fully according to the Second Law of Thermodynamics.

Another team has already found that the Second Law of Thermodynamics fails on an atomic scale . In fact, there seem to be several Second Laws of Nanoscale Thermodynamics . [Image: Iñaki Gonzalez / Jan Gieseler]

Applications depend on additional developments

Although the team recorded a difference of only about 2 ° C compared to the ambient temperature in the experiment, this was mainly due to the performance limitations of the used Peltier element, which was purchased commercially. According to Schilling, it would be possible in theory to achieve a cooling down to -47 ° C, under the same conditions, if Peltier's "ideal" element - still to be invented - could be used.

Another factor that leaves large-scale applications of this technique still distant in the future is that the current configuration requires the use of superconducting inductors to minimize electrical losses.

But this does not seem to make the team discourage or even dislike their experiment.

"With this very simple technology, large amounts of solid, liquid or gaseous materials can be cooled to a temperature well below room temperature without any energy consumption. At first glance, the experiments seem to be a kind of thermodynamic magic, challenging our perceptions heat flow, "said Schilling.


Heat flow from hot to cold without external intervention by using a thermal inductor
A. Schilling, X. Zhang, O. Bossen 
 Science Advances 
 Vol .: 5, no. 4, eaat9953 
 DOI: 10.1126 / sciadv.aat9953 

 LC-circuit calorimetry 
O. Bossen, A. Schilling 
 Review of Scientific Instruments 
 Vol .: 82, 094901 
 DOI: 10.1063 / 1.3632116

NASA tests new type of airplane wing

Artistic view of an airplane using the new wing structure. [Image: Eli Gershenfeld / NASA Ames]

Flying wing

NASA announced the results of the first wind tunnel tests done with a new type of airplane wing.

It is a wing that becomes the very body of the airplane, a concept known as flying wing or airplane-wing .

Instead of several separate movable surfaces, such as ailerons to control longitudinal and transverse angulation, such as conventional wings, the concept makes it possible to deform the entire wing, or parts thereof, by incorporating a mixture of rigid and flexible components into its structure.

The tiny subassemblies, which are screwed to form an open and light truss structure, are then covered with a thin layer of polymeric material.

The result is a wing that is much lighter and therefore much more energy efficient than conventional designs made of metal or composites, says the team at NASA's Ames Research Center and MIT.

The wing is assembled from hundreds of identical subunits. It was tested in a NASA wind tunnel. [Image: Kenny Cheung / NASA Ames]

Metamaterial handle

The wing structure is made up of thousands of tiny triangles with phosphor stick-like supports.

As it consists mainly of void spaces, it forms a mechanical metamaterial that combines the structural rigidity of a polymer similar to rubber with the lightness and low density of an airgel.

The wing has a density of 5.6 kilograms per cubic meter - for comparison, the rubber has a density of about 1,500 kilograms per cubic meter.

The expectation is that this concept will allow a significant increase in flight efficiency, reduced maintenance and increased aircraft production, say researchers.

This initial prototype was assembled by hand, but future versions could be assembled by miniature robots. [Image: Kenny Cheung / NASA Ames]

Aircraft Efficiency

Each of the phases of the flight - takeoff and landing, cruise, maneuvers and so on - has its own different set of optimal wing parameters. Therefore, a conventional rigid wing is necessarily a compromise that is not optimized for any of them, sacrificing efficiency. A constantly deformable wing can provide a much better approximation of the best configuration for each stage.

"We can gain efficiency by combining shape with loads at different angles of attack. We can produce exactly the same behavior that you would do actively, but we did it passively," said Nicholas Cramer, one of the makers of the morphological wing prototype.
Artistic concept of an airplane-wing. [Image: MIT / NASA]

New aircraft formats

This wing-fuselage concept will also allow aircraft to change shape.

The fact that most aircraft have the same shape - essentially a winged tube - is due to costs. It is not always the most efficient way, but massive investments in design, tools and processes. easy to maintain long-established configurations, "said team member Benjamin Jenett.


Elastic shape morphing of ultralight structures by programmable assembly
Nicholas B. Cramer, Daniel W. Cellucci, Olivia B. Formoso, Christine E. Gregg, Benjamin E. Jenett, Joseph H. Kim, Martynas Lendraitis, Sean S. Swei, Greenfield T. Trinh, Khanh V. Trinh, Kenneth C. Cheung
 Smart Materials and Structures
 Vol .: 28, Number 5
 DOI: 10.1088 / 1361-665X / ab0ea2

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