Category: Engineering

Wind turbines

Wind turbines 02/23/16

Wind turbines are one of my favorite parts of Engineering. Wind turbines work by transferring energy from the wind into a spinning shaft (mechanical energy) which rotates a generator which converts all of that into electrical energy. There are two types of wind turbines, vertical axis and horizontal axis. In the latter, the larger profile allows it to catch more wind but the tower is higher and it is more complicated to build, while the former is easier to build/design/maintain but catches less energy as an offset. The part of the turbine that catches wind with blades and converts it to mechanical energy is called the rotor. One possible design for a wind turbine is known as the drag design, which uses a turbine whose axis of rotation is perpendicular is to the movement of the wind to catch the drag force provided by the wind as energy. This design is slower moving but provides a heavier torque, making it useful for tasks such as lifting water or hay 9 your stereotypical dutch farm activities) A more modern design is the lift design, which uses a rotor facing the wind movement to use the lift force caused by an asymmetric blade profile. Lift based mechanisms have a much higher rotation speed than drag types and therefore make excellent candidates for electricity generation.

The number of blades on a wind turbine can have a multitude of effects on a wind generation system. Increasing the number of blades increases efficiency at a diminishing rate. Going from one to two blades gives us a 6% increase in efficiency while going from two to three blades gives us a 3 percent efficiency. typically, the less amount of blades, the lower material and torque needed. Rotor blades are always twisted to account for a changing angle of attack, explaining the curved structure. The theoretical power generated by a wind turbine is given by the equation Power = 1/2**A*v3, with being the wind density Abeing the area of the profile andvbeing the wind velocity. The Betz limit is the theoretical efficiency of a wind turbine, given at 59.3 percent. However, most commercial systems operate at around 10-30 percent.
Wind turbines have contain a generator which converts mechanical energy into electrical energy, and transmission which increases the rotation rate of a generator to accomplish an efficient electricity generation rate. The cut in speed is the speed in which a turbine will generate usable power, typically between 7 -15 mph. The Rated speed is the speed in which a wind turbine will generate it’s designated power, typically at around 25-25 mph. To account for dangerously high wind speeds at around 45-80 mph, most wind turbines have a cut out speed feature which shuts down the wind turbine using a versatile repertory of methods. Tower heights are usually two to three times the blade diameter to account for efficiency.

Energy Efficiency

Energy Efficiency 02/21/16

As a result of the second law of thermodynamics, the phenomena of a one hundred percent energy efficient system exists in human imagination only. Consequently, the energy efficiency of systems can be measured. If you take the percentage difference between the input power of a system and the amount of work it does, then you have just measured the energy efficiency. This has a pertinent application to the field of Engineering, where maximum efficiency is paramount. For example, the energy efficiency of most commercial solar cells is between 15-20%, so 15-20 percent of the energy taken in from the sun is transferred into usable work.

CAD software

CAD software 02/18/16

In my humble opinion, CAD software is one of the single greatest inventions created by the human species. CAD is short for Computer Aided Design, and this software allows for humans to accomplish one very important goal, the geometric design of Engineering systems. For all of human history, humans were limited to simple 2-dimensional sketches which required abstract visualization and therefore was more taxing on the brain. CAD software, however, allows a user to edit a 3-D model of an object with a repertory of different tools, Which consequently allows Engineers to be more free form and dynamic in image generation. One starts by making a 2-dimensional “sketch” and then protruding to create a 3-dimensional image.One can also sweep and revolve an sketch for other forms of 3-dimensional manipulation. CAD software really brings out the creative side of Engineering in designing parts and tools for use. CAD software also lets users simulate stresses to test ut different parts of an element.

P N type semiconductors

P N type semiconductors 02/13/16
Silicon has an octet structure chemical structure, which means that it’s outer shell has four valence electrons. When sunlight strikes silicon, one of the electrons are jettisoned from the outer shell and is free to move around randomly within the material. However, for practical purposes, humans want it to move in one direction. This is accomplishable with the use of P and N type semiconductors. There are two types, N and P type semiconductors. With the latter, a paltry amount of elements with 5 outer electrons are added, forming a bond with silicon as well as leaving one electron free. This free electron can be knocked in in a perfunctory manner by sunlight. P type semiconductors are bonded with elements that are one electron short ( a hole), therefore allowing for easy acceptance of an extra electron. N-type semiconductors conduct electric current through the transfer of electrons, while P-type conducts current through the transfer of “holes”. P and N types can then be amalgamated to create a P-N junction. In P-N junctions, the two types are put right next to each other, first causing an electrical exchange (the P-type will receive electrons and become negative and vice versa for N-types). When sunlight strikes the material, the free electron will be repulsed by the negatively charged P-type and be attracted to the positive N-type. And that is how solar panels work

Air resistance

Air resistance 02/12/16
An interesting conundrums appears for students of physics when considering Newton’s first law. If objects are supposed to go on forever in the vacuity of a net force, then why do objects on Earth slow down in the horizontal direction? The answer lies in the fact that when objects move through Earth’s atmosphere, they experience a phenomena called air resistance. Because air is a fluid, solid objects can be suffused in it as a surrounding medium. Analogous to objects moving in water, when one moves through the atmosphere, it comes into contact with air particles, causing minor but emergent impinging effects on an object’s motion. When all of these collisions amalgamate, a phenomena known as a drag force appears. This drag force is what causes all of the impinging effects. Because drag force is based off collisions with air particles which in turn are based off Newton’s third law, the drag force is contingent on an object’s velocity, so the faster one moves, the more resistance one experiences. An application of this is terminal velocity in free fall, a peculiar phenomena that all objects in free fall experience. When an object is in free fall, it accelerates which in turn causes it’s velocity to rise, However, as it’s velocity rises, so does it’s drag force, and consequently the velocity of the object will reach an apex, with the drag force balancing out the gravitational force, therefore causing constant velocity as a result of Newton’s first law.

Molniya orbit

Molniya orbit 02/08/16
Molniya orbits are of of the most peculiar discoveries made by the old Soviet Union. As shown below, Molniya orbits have a highly eccentric Apogee and Perigee, and consequently they spend a large amount of time in orbit around certain latitudes (north being the most common ones). Molniya orbits were used by the Soviet union for communication satellites since the highly eccentric orbit meant that it spent a large amount of time in the Northern hemisphere, allowing for excellent communications coverage for the Soviet’s geographic position.

Space elevators part II

Space elevators part II 02/06/16
Space elevators were conceptualized by the legendary Russian Scientist and Enginner Konstantin Tsiolkovsky. Space elevators can possibly work on less gravity intensive celestial bodies such as Mercury and Earth’s moon. Kevlar is one possible material to be used for this application. A space elevator can put objects in geostationary orbit, which means that objects can orbit the earth at the earth’s rotation speed.

Space elevators part I

Space elevators part I 02/05/16
Space elevators are some of the most riveting concepts in the field of Mechanical Engineering. Imagine if there was an elevator so tall that it broke the ionosphere and into geostationary orbit. Transporting objects across this medium would make rockets completely unavailing, and consequently would save an inordinate amount of energy. There is only one issue with this. In respect to earth’s gravity, there is no known material extant that is strong enough to support it’s own tensile weight.