Pressure wave

The technique presented above has been extensively evaluated experimentally using ultrasonic data acquired from a test block made of cast stainless steel with cotirse material structure. Here we briefly present selected results obtained using two pressure wave transducers, with refraction angles of 45° and 0°. The -lOdB frequency ranges of the transducers were 1.4-2.8 MHz and 0.7-1.4 MHz, respectively. The ultrasonic response signals were sampled at a rate of 40 MHz, with a resolution of 8 bits, prior to computer processing. 

There have been a few other experimental set-ups developed for the IR characterization of surfaces. Photoacoustic (PAS), or, more generally, photothemial IR spectroscopy relies on temperature fluctuations caused by irradiating the sample with a modulated monocliromatic beam the acoustic pressure wave created in the gas layer adjacent to the solid by the adsorption of light is measured as a fiinction of photon wavelength... 

As long as AT, Ax and Ax remain small, they will be proportional to the sinusoidal pressure wave. In... 

Absence of ignition peaks or reinforcing pressure waves Minimum gun smoke, flash, and blast pressure Detonation-free in event of malfunction... 

J. MaiUette and co-workers, "Pressure Wave Generation in Three Inch/50 Gun," in Proceedings of the 10th International Symposium on Ballistics, American Defense Preparedness Association, (ADPA), San Diego, Calif., 1987. 

An explosion model is used to predict the overpressure resulting from the explosion of a given mass of material. The overpressure is the pressure wave emanating from a explosion. The pressure wave creates most of the damage. The overpressure is calculated using a TNT equivalency technique. The result is dependent on the mass of material and the distance away from the explosion. Suitable correlations are available (2). A detailed discussion of source and consequence models may be found in References 2, 8, and 9. 

Fig. 3. Stressing mechanisms (a) single particles or (b) a bed of particles cmshed between two solid surfaces impact of a particle against (c) a solid surface or (d) another particle (e) cutting (f) shearing forces or pressure waves and (g) plasma reaction, an example of size reduction by nonmechanical energy.

Stressing by the Surrounding Medium. Size reduction is effected by shearing forces or pressure waves (Fig. 3f). The amount of energy that can be transferred is very limited and this method is used mainly to break agglomerates. 

V/c is the ratio of fluid velocity to the speed of sound or aeoustie veloeity, c. The speed of sound is the propagation velocity of infinitesimal pressure disturbances and is derived from a momentum balance. The compression caused by the pressure wave is adiabatic and frictionless, and therefore isentropic. 

Water Hammer When hquid flowing in a pipe is suddenly decelerated to zero velocity by a fast-closing valve, a pressure wave propagates upstream to the pipe inlet, where it is reflected a pounding of the hne commonly known as water hammer is often produced. For an instantaneous flow stoppage of a truly incompressible fluid in an inelastic pipe, the pressure rise would be infinite. Finite compressibility of the flmd and elasticity of the pipe limit the pressure rise to a finite value. The Joukowstd formula gives the maximum pressure... 

AV = change in liquid velocity a = pressure wave velocity... 

The maximum pressure surge is obtained when the valve closes in less time than the period T required for the pressure wave to travel from the valve to the pipe inlet and back, a total distance of 2L. 

Successive reflections of the pressure wave between the pipe inlet and the closed valve result in alternating pressure increases and decreases, which are gradually attenuated by fluid friction and imperfect elasticity of the pipe. Periods of reduced pressure occur while the reflected pressure wave is travehng from inlet to valve. Degassing of the liquid may occur, as may vaporization if the pressure drops below the vapor pressure of the liquid. Gas and vapor bubbles decrease the wave velocity. Vaporization may lead to what is often called liquid column separation subsequent collapse of the vapor pocket can result in pipe rupture. 

Noise Control Sound is a fluctuation of air pressure that can be detected by the human ear. Sound travels through any fluid (e.g., the air) as a compression/expansion wave. This wave travels radially outward in all directions from the sound source. The pressure wave induces an oscillating motion in the transmitting medium that is superimposed on any other net motion it may have. These waves are reflec ted, refracted, scattered, and absorbed as they encounter solid objects. Sound is transmitted through sohds in a complex array of types of elastic waves. Sound is charac terized by its amplitude, frequency, phase, and direction of propagation. 

Cavitation has three negative side effects in valves—noise and vibration, material removal, and reduced flow. The bubble-collapse process is a violent asymmetrical implosion that forms a high-speed microjet and induces pressure waves in the fluid. This hydrodynamic noise and the mechanical vibration that it can produce are far stronger than other noise-generation sources in liquid flows. If implosions occur adjacent to a solid component, minute pieces of material can be removed, which, over time, will leave a rough, cinderlike surface. 

The hot gases expand and produce pressure waves, which travel ahead of the flame. Any dust lying on surfaces in the path of the pressure waves will be thrown into the air and could cause a secondary explosion more violent and extensive than the first. 

Explosions are either deflagrations or detonations. The difference depends on the speed of the shock wave emanating from the explosion. If the pressure wave moves at a speed less than or equal to the speed of sound in the unreacted medium, it is a deflagration if it moves faster than the speed of sound, the explosion is a detonation. 

Uneonfined vapour eloud explosion a large flammable gas or vapour-air eloud burns in free spaee with suffleient rapidity to generate pressure waves, whieh propagate through the eloud and into the suiTounding atmosphere. Sueh events are extremely rare. 

Explosive hazards are reduced by using similar techniques and by structures for explosions through the use of blow-out doors to direct the pressure wave in harmless directions,... 

This pressure variation can be considered as the transfer of a pressure wave in space. In the same w ay, w hen a stone is thrown into a lake, the ripples generated move radially from the point of entry of the stone. But this observation is only apparent, because a floating buoy will stay in the same horizontal position. It does not move radially in the space the perturbation, however, moves. 

Shock wave A pressure wave resulting from the rapid closure of a valve or damper in a pipeline or ductwork system, or from an explosion. 

In extreme cases, very high pressure waves are encountered in which the time to achieve peak pressure may be less than one nanosecond. Study of solids under the influence of these high pressure shock waves can be the source of information on high pressure equations of states of solids within the framework of specific assumptions, and of mechanical, physical, and chemical properties under unusually high pressure. 

The effect of such a transformation on a pressure-volume relation and on wave profiles is shown in Fig. 2.12. Above the transformation, its characteristics dominate the wave profile. At sufficiently high pressure, the peak pressure wave will move at higher speeds and a strong shock regime can be encountered. 

When a toroidal ferromagnetic sample is subjected to shock loading, a pressure wave of pressure P moves through the sample with a velocity U and produces a change in magnetization AM. An N-turn detection coil with inductance L is wound around the sample and connected to a resistive circuit in which the L/R time constant is longer than the time required for the shock wave to traverse the sample thickness. The current i in the coil is then... 

For the two explosive loading systems used, the initial pressure wave into the powder is relatively low, varying from perhaps 1.5-4 GPa. In such cases the most relevant compression characteristic of the powder compact is its crush strength , i.e., the pressure required to compress the porous compact to solid density. In the simulations, this strength can be varied over a wide range with the P-a model. The wavespeed of the initial waves was modeled on the basis of shock-compression data on rutile at densities from 44% to 61% of solid density [74T02]. 

As shown in Fig. 6.7, typical temperature histories show a quite different behavior from that observed with pressure in that the initial low pressure wave produces the major portion of the increase in temperature. This behavior is the expected consequence of the large volume compression of the powder compact. 

Dust filter of special ceramic-fiber mat with special pressure-wave absorbing coils... 

Flame Front Diverter A device that opens in response to the pressure wave preceding the flame front of the deflagration, venting the flame front and pressure wave. 

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