All posts by Wei Song Lim

Radar: Luftwaffe’s Nemesis

Figure 1
Figure 1

Ever since Louis Bleriot made the first flight across the English Channel, the Britons realized that the possibility of being attacked from the air became a reality. It is this historical event that caused the Ministry of Defense to start developing an air defense system known as the “Chain Home Network”. The primitive stages of this defense network comprise of large ‘hearing blocks’ where the Royal Air Force (RAF) would have someone sit in front of the concrete blocks (above Figure 1) and listen for the sound of approaching airplane armadas. This method did produce results, however, by the time the personnel was able to hear the airplanes and relay it to command center, it was already too late for the RAF to launch an effective counter response. Hence, the Ministry of Defense decided to use another system, which they named the “object-detection system”, but little did they know that it is precisely this system that would turn the tides in favour of the Brits and change the fate of the war during the Battle for Britain. Many historians throughout the world till this day believe that the United Kingdom was key to putting Hitler’s ‘unstoppable’ Blitzkrieg (or lightning war) to a halt in Western Europe. Although what many previously did not realize is that the key component in stopping the infamous Luftwaffe during the Battle of Britain and effectively preventing the invasion of Britain was in fact an intangible system. This system had a classified name: “Radio Detecting and Ranging” object-detection system; or in today’s terms, it’s commonly known as RADAR.

Figure 2
Figure 2

I knew that the RADAR aided the British in stopping the Luftwaffe from my previous knowledge in the history of World War Two, but how did the RADAR do it?  Well, the RADAR transmits pulses of radio waves or microwaves with very long wavelength that bounces off (or reflects off) of any object in their path. Regardless of the size of the object, it returns a tiny part of the wave energy to a radar dish or antenna (shown above) that’s usually located at the same site as the transmitter. The components of RADAR are actually quite simple; it has a transmitter, a waveguide, a duplexer, a receiver, and an electronic station. The transmitter generates the radio signal with an oscillator, which emits the pulses from a radar (similar to that of a sonar sound you hear in the submarines) and the duration is controlled by a modulator (charges up with high voltage to release the pulse which is sent out through the antenna). The waveguide links the transmitter to the antenna, which broadcasts the radio signal. The duplexer is a switch between the antenna and the receiver or transmitter for the signal when the antenna is used in both situations. The radar receiver, receives the signal that is reflected off the object hit by the pulse emitted from the transmitter. This signal is then sent back to the electronic station for interpretation (commonly a visual image of that object on a circular screen showing the location of that object in Figure 3 shown below). I know this to be true because in my Phyiscs class I’ve learned that this concept of radar is valid and proven. So, by being able to detect the German bombers way before they reached Britain, the RAF was able to effectively assemble a counter-attack strike force against the bombers.

Figure 4
Figure 3
Figure 3
Figure 4

In figure 4, it shows the radar (mounted on the top of the AWAC airplane). The radar emits radios waves 360 degrees and when these radio waves ‘hit’ an object (e.g. airplane, flock of birds, etc.) the radio waves are reflected back to the airplane. The amount of time the radio waves take to travel back to the airplane is how far the object is from the radar source. This was the basic functioning of radar. The invention of radar is important then and now because if it weren’t for the development and use of RADAR in World War Two, then a lot more British civilians in London would have been killed and potentially the Luftwaffe might not have been harassed by the RAF on their bombing runs to London, and the Germans could’ve potentially invaded Britain. So, from a British military perspective, the invention of radar not only helped the RAF defend the British mainland but also aided them in bombing runs by methods of triangulation or honing in on a target to get the British bombers on track and hit their targets during blackouts at night. On the contrary however, from a German military perspective, the invention of the radar by the British became a nuisance and a great cost to the Luftwaffe. This is because they now no longer have the advantage of a surprise attack, due to the long detection ranges of the radar, and they have to defend the German cities not only from the American daylight bombing runs, but now from the British night bombing runs as well.

This knowledge and use of radar is also important to modern day times because little do we know that we actually rely on radar almost every single day. Radar has expanded its usage by being placed on airplanes and used for detecting the position of airplanes by air traffic control. Otherwise without radar and with thousands of airplanes flying over the continental US at the same time, it is very likely to crash into another airplane. Another use of radar today is to detect weather patterns and climate change, e.g. formation of a tropical storm/ hurricane, or seeing the position of storm clouds, etc. Now the technology of radar has gotten so advanced that it’s now instead of just detecting objects, radar has now been used to jam other radar in order to make an object become ‘invisible’. So, a major implication from this is that even though radar was designed intentionally for military purposes, throughout the century it has expanded into other areas. This goes to show how such a major invention in World War Two that potentially changed the tide in the Battle for Britain, has found new purposes and adapted in today’s world.

Works Cited:

Brain, Marshall. How Radar Works. HowStuffWorks. Web. 9 Oct. 2011.

How does radar and the Doppler system work?. RADARS. Web. 9 Oct. 2011.

Radar Modulator. Radar Basics. Web. 10 Oct. 2011.

Reply to Ian’s Post: Shake or Stand?

After reading Ian’s blog post ‘Shake or Stand?’, I suddenly made a connection to my physics class. This is because in his post he had mentioned the words ‘natural frequency’ and coincidentally, we’re learning about waves and natural frequencies in physics. So, what is natural frequency? A frequency that’s natural? No, it is the frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed, or somehow disturbed is known as the natural frequency (the Physics classroom). In simple English, it’s a frequency that causes an object to vibrate back and forth. In his post he also mentions that each building has it’s own unique natural frequency. I did a bit of research and found that the natural frequencies of vibration of a building depend on its mass and how stiff the building is. So, a taller building will have a lower natural frequency because it’s heavier and taller which makes it more flexible (IDEERS). Why is this important? It is important to determine a building’s natural frequency so then you know how the object vibrates, which in turn you can counteract that vibration by using a damper. A damper is a heavy weight that vibrates in the opposite direction of the building thus effectively canceling out any vibrations caused by the building.

The Damper that engineers use in Taipei 101 to counteract any vibrations in the building.
(Figure 1: The Damper that engineers use in Taipei 101 to counteract any vibrations in the building.)

Ian’s post mentions a building reaching it’s natural frequency potentially from vibrations from earthquakes, but a natural frequency of a building doesn’t occur just from earthquakes. It’s also possible for the natural frequency of a building to be reached from wind. As stated in the post, an earthquake causes the ground to vibrate, which in turn sends shockwaves up to the building that causes it to vibrate. The same principle applies to wind, except this time the vibrations start from the top. Wind is weaker at lower elevations because friction (e.g. mountains, hills, buildings, trees) will cause the wind to slow down, and wind is stronger at higher elevations because there is little to no friction. (Air Pressure and Wind). So the higher the building, the more susceptible it is to strong winds. Now, in the present day, engineers have revolutionized their thinking when it comes to buildings, instead of fighting against nature, why not work with nature? The Shanghai World Financial Centre (SWFC) applies this concept. At 492 meters all, the SWFC is the third tallest building in the World. At this height, it means that it is very susceptible to strong winds and it has a huge surface area at the top, which could then lead to the possibility of the building tipping over.

(Figure 2: Picture showing how the wind flows around a building.)
(Figure 2: Picture showing how the wind flows around a building.)

Think of an empty water bottle, it you blow towards the bottom of the bottle it requires a lot of strength to knock it over, however, if you blow towards the top of the water bottle, it tips over very easily. This is the same concept for a building. Which is why engineers have decided to put a big opening at the top of the SWFC, to allow the wind to flow through the building, effectively decreasing the possibility of the building tipping over and vibrating as a result from strong winds.

Figure 2: Picture of the Shanghai World Financial Center
(Figure 3: Picture of the Shanghai World Financial Center)

But wind doesn’t just affect buildings; it also affects other structures such as bridges. A famous example is the Tacoma Narrows Bridge in Washington State. On an early morning of November 7th, 1940, under strong wind conditions, the bridge began to twist and turn in a vertical motion (transverse vibration) (Wikipedia). As the wind became stronger and stronger, it caused the amplitude of the vibrations to increase because the wind was ‘putting in’ more energy then the flexing of the structure can dissipate. The Tacoma Narrows Bridge (aka Galloping Gertie) soon reached its natural frequency and snapped in half. The bridge was rebuilt and this time, the engineers were much more careful and regarded wind with the respect it deserves. A local camera store clerk recorded the collapse of the bridge on film and to this day, it serves to engineering, architecture, and physics students as a warning that nature is not to be underestimated.

Figure 3: Picture showing the collapse of the Tacoma Narrows Bridge in Washington State
(Figure 4: Picture showing the collapse of the Tacoma Narrows Bridge in Washington State)

Click here to see footage of the collapse of the Tacoma Bridge.

Click here to learn more about Resonance and Natural Frequencies.

Click here to learn more about Natural Frequencies and Simple Harmonic Motion

Works Cited:

Resistant Buildings – Vibrating – The Natural Frequency of a Building. IDEERS from Bristol University, 2008. Sun. 27 Feb. 2011.

Resonance and Standing Wave – Natural Frequency. the Physics Classroom, 2011. Sun. 27 Feb. 2011.

Tacoma Narrows Bridge (1940). Wikipedia, 2011. Sun. 27 Feb. 2011.

Wind. Air Pressure and Wind, 2003. Sun. 27 Feb. 2011.

Shocked by a Dam

After being let off from work or school, people go home and turn on numerous appliances in their everyday life that require electricity. The population of Shanghai is about 19.3 million (True Knowledge) people as of November 2010. At night, when all of these people return from work and turn on their lights, there is a huge increase in the demand of electricity. The electricity company, Shanghai Power, has to meet those demands. But how on earth are the electricity suppliers able to meet the demands of 19.3 million people? This was the first question that came into my mind whilst we were building circuits in my physics class. This is because in my physics class the circuits we built are powered by batteries, which was our source of electricity; so that made me think on a larger scale, where does all the electricity that is required to power our appliances come from? Having done some research, I realized that such an enormous demand for electricity is met with a single dam. A dam that will create a 400 mile long reservoir, produce electricity 8 times (18.2 million kWh, Kennedy, CNN) that of US’s Hoover Dam, costing $35 billion USD, taking 17 years to build (Neville, Discover Yangtze), and is China’s largest civil engineering project since the Great Wall. Ladies and gentlemen, the Three Gorges Dam.

Picture of the World's largest dam, Three Gorges.
(Figure 1: Picture of the World's largest dam, Three Gorges.)

The Three Gorges Dam is constructed on China’s Yangzi (Yangtze) River, the third longest river in the world. This idea of constructing the Three Gorges Dam was conceived by Mao Tse Dong in the 1950’s after numerous floods along the Yangzi River, but construction of the dam only began in the 1990’s. The construction of the dam was not only meant to meet the increasing demands of electricity but also to control the notorious flood-prone Yangzi. So how does that work? Well, by damming the Yangzi, it already effectively slows down the river’s powerful, and strong currents downstream where there are farmlands and villages. The water from the upper and higher part of the dam will flow down the spillway to the lower portion of the river should the water level of the dam be too high. So how does a hydroelectric dam work? Water flows through the penstock, or a tunnel that carries water to the turbines (Figure 2). The turbines of the dam are turned by the powerful force of the water flowing from the penstock onto the blades. The turbines, attached to a generator, turns the generator, thus producing the electricity carried by power lines to cities.

(Figure 2) Picture of how a Hydroelectric dam works.
(Figure 2: Picture of how a Hydroelectric dam works.)

The only output from hydroelectric dams is just electricity and water, unlike coal plants where the burning of coal produces carbon dioxide one of the main contributors to global warming. This is why building a hydroelectric power plant is much greener, or more environmentally friendly than a coal plant. Or is it? A scientific concern arising from the Three Gorges project is whether the dam will reap more than it destroys, meaning will the dam be more beneficial than harmful. Looking at this project from an engineer’s point of view, the Three Gorges is undoubtedly China’s greatest project undertaken since the Great Wall. My personal bias is that I want to become an engineer when I grow up. This is considered a personal bias because I will be looking at the Three Gorges Project from an engineer’s point of view rather than an environmentalist’s perspective. Which would put me more in favor of the construction of the dam than against it.

Nonetheless, different perspectives must be taken into consideration. So, putting on your environmentalist glasses and looking at this project from their perspective, the Three Gorges Dam would seem to be a catastrophe on nature. This is because the dam will inundate approximately ‘632 square kilometers’ of land, which is a little short of the size of Singapore, or 17 times the area of Manhattan. Such a huge area being submerged (Figure 3) creates a lot of concern because of the lack of attempts to remove toxic materials and other pollutants from industrial sites that are being inundated. The toxic materials could potentially pollute the reservoir causing harm to the 177 species of fish that live in the Yangzi. But the concerns don’t stop there. There is also a huge problem about the plants that will be affected as a result of the Three Gorges Dam.

(Figure 3) Satellite picture of before and after image of the Yangzi River.
(Figure 3: Satellite picture of before and after image of the Yangzi River.)

The area that will be inundated accounts for 6000 plant species, which is 20 percent of China’s plant species (Hvistendahl, Scientific American). Therefore, it is important that we know all of this because in the future, should there be any more projects as monumental as the Three Gorges, we will know that many factors and effects of the dam must be kept in mind and taken into consideration. Although there has been a lot of research about the effects of damming up a river, much is still unknown as damming a river on such a monumental scale is still at its primitive stages. Meaning, there isn’t much knowledge about the effects of damming the third longest river in the world on such a humongous scale. So, was building the Three Gorges dam a correct decision? As an old quote goes: “The only way to know whether you’ve chosen the right path to follow is after you’ve reached the end of it.” Which means that only time can tell us whether the decision to build the Three Gorges Dam was a correct or erroneous one.

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Video Link: Three Gorges Dam

For further inquiries: Three Gorges Project

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Works Cited

What is the population of Shanghai 2010?” trueknowledge.com. True Knowledge, n.d. Web. 19 Nov. 2010.

Kennedy, Bruce. “Visions of China- Asian Superpower: China’s Three Gorges Dam.CNN.com. CNN, n.d. Web. 20 Nov. 2010.

Hvistendahl, Mara. “China’s Three Gorges Dam: An Environmental Catastrophe?scientificamerican.com. Scientific American, 25 Mar. 2008. Web. 20 Nov. 2010.

Neville, Peter. “THE THREE GORGES DAM.discoveryangtze.com. Discover Yangtze, n.d. Web. 19 Nov. 2010.