Presentation on shock waves
- 2. In descriptive terms Shock wave is a very sharp, thin, wave front. At sea level shock wave in air has a thickness of about one micro inch or 10-6 inches. A shock wave is generated when energy is suddenly released or deposited in a material, thereby causing an explosion. When a strong shock wave travels through an undisturbed material the pressure, temperature and density of disturbed state is increased many- fold. Examples : Natural : Thunder, Earthquake, Meteor Strike, Solar Wind. Man Made Inventions: Bull-Whip, Gunpowder, Bombs. Shock Wave generated by an exploding copper wire.
- 3. Simplest way of how shock way is generated is by observing a moving piston in a cylinder. At time t1, a gentle push generates a Mach Wave. At time t2, another gentle push generates another Mach Wave. At time t3, both Mach Waves unite to form a Weak Shock. If a piston is impulsively accelerated from rest to a finite velocity, a shock wave is instantly generated. Generating a Shock Wave with a Piston.
- 4. Although the shock wave photographically have finite width, they are very thin. Ambient molecules after getting hit by shock front undergo collisions to achieve a new equilibrium state behind the shock wave. Apparent thickness of Shock Wave.
- 5. Man progressively learned how to generate and increase the strength of shock waves by inventing the bull whip, gun power, chemical and nuclear weapons. BULL WHIP One of the earliest method of generating shock waves. Cracks like bull whip can be produced by bursting pressurized balloon or paper bag. The operation requires considerable skill in transferring man’s muscular energy into traveling loop. Shock Waves from a flick of a Whip.
- 6. CHEMICAL EXPLOSIONS AND SHOCK WAVES. With the invention of gunpowder and modern chemical explosives, man was able to increase his capacity for generating ever stronger shock waves for destructive or peaceful purpose. In military field, explosives and propellants with slow burning rates are used as initiators and accelerators in all type of ammunition for rifles, guns, rocket launchers, bombs etc. In industrial applications for peaceful purposes, explosions are used extensively in mining, civil engineering, mechanical engineering and in space programs. In figure it is seen under varying condition of pressure and blast radius, the shock wave decay does not take place at constant rate. The decay is greatest at early times and least at late times.
- 7. CHEMICAL EXPLOSIONS AND SHOCK WAVES. (contd.) Figure shows the detonation of 20-ton hemispherical charge. The turbulent white explosive gas can be seen driving the shock. Figure shows the aerial photograph of 500- ton charge of TNT. The aerial photograph was taken 0+0.7 seconds.
- 8. CHEMICAL EXPLOSIONS AND SHOCK WAVES. (contd.) The production of explosion and implosion is seen in the picture. The framing camera took a sequence the sequence of 15 pictures at a rate of 600,000 frames per second with an exposure time of 0.6 microseconds.
- 9. BULLETS AND SHOCK WAVES. (contd.) Seen in the figure: the explosive gases 250 microseconds after firing. Seen the figure: the bullet outraces the decaying blast waves at 400 microseconds .
- 10. SONIC BOOM The supersonic flights have transformed long, tiring journey into a relatively short, comfortable journey. It will also bring about the frequent exposure of man, creatures and structures to sonic boom. Pressure levels with reference to atmosphere produced during normal conversations are about one-millionth of an atmosphere or 0.002 pounds per square foot (psf). Sonic booms from the supersonic aircrafts are 1000 times greater or 2psf.
- 11. SONIC BOOM (contd.) When aircraft goes supersonic the pressure pulses pile up to form two conical shock waves. The bow shock has its apex at the head of aircraft and tail shock is at rear of aircraft. These waves strike the ground and are reflected back into the atmosphere. The strength of the boom depends on altitude of aircraft, its lift distribution and the slenderness of profile. Wave pattern from a supersonic aircraft.
- 12. ATMOSPHERIC RE-ENTRY PHENOMENON. The re-entry of a space capsule into the denser layers of our atmosphere is just as spectacular as a meteoroid entry or an explosion. The whole vehicle gets engulfed in a spectacular plume of fire. In front of this plume there is a glowing bow shock wave. About 99% of energy expended by plunging capsule is dissipated through shock wave by compressing and heating the gas around it up to 6500 degree C. Artist's concept: Apollo Capsule Re-Entry. (Source FAA)
- 13. In space the shock wave phenomenon which occur among countless stars nebulae and galaxies, can be observed by men with a sense of awe, wonder and excitement but without the concern for possible cataclysmic effects on earth. The great masses of gas in our sun and in the stars are heated by nuclear reactions to interior temperatures of hundreds of millions of degrees at enormous pressure and incredibly high densities. Exploding shock waves, generated from the rapid heat addition of the nuclear reactions can move from dense interior to the rarefied gas at the outer surface of a star. SOLAR WIND The solar furnace radiates energy at rate of 4x1026 watts therefore the sun every second emits energy with a TNT equivalent of 1011 megaton bomb blasts. Of this the earth receives a energy of a 50Megaton bomb blast per second. This is quite sufficient to supply energy required to generate thunderstorms, winds and other thermal phenomenon on earth.
- 14. SOLAR WINDS (contd.) The sun issues a steady solar wind stream of fully ionized particles consisting of electrons , and nucleons of hydrogen. The solar wind blows with a supersonic velocity of about 250 miles per second. Figure shows interaction of solar wind with earth and its magnetic field.
- 15. Our eyes cannot normally distinguish a shock wave in a gas, liquid or solid, because air is invisible to us whether it is at low or high pressure. However as density of gas increases, the refractive index also increases. This makes it possible to visualize shock waves by means of relatively simple techniques such as shadow photography. How many times since infancy have we been startled from our sleep by crash of thunder? How often during our waking hours have we been awed by blinding flashes of lightening ? THUNDER It is probably the most prevalent example of shock waves that man encounters during his span on earth. A dramatic presentation of lightening strokes over Arizona. VOLCANICERUPTIONS The ejected steam, burning gases and solid material in volcanic eruptions can be spectacular and shock waves generated by this fast moving can be heard over a greater distance. https://www.youtube.com/watch?v=2XlDa3WxVJ0
- 16. The scientific and technological study of cosmic and terrestrial shock waves can be fascinating. Unfortunately, it is bound up with a threat to human life from firearms, chemical explosions and nuclear weapons on a scale that extends from individual tragedy to a possible world catastrophe involving millions of people. SHOCK WAVES AND SURVIVAL. The foregoing overview of shock wave phenomenon in Space and on Earth has illustrated their universal importance. We are just now beginning to understand their cosmic roles. Is man safe on Earth? Ultimately it is the individual who has the power to decide how the knife shall be used: to sustain life or to take life.