Pressure-impulse diagrams

Figure B-1. Pressure impulse diagrams for damage to brick houses. Line 1 Threshold for light damage. Line 2 Threshold or moderate damage partial collapse of roof some bearing wall failures. Line 3 Threshold for severe damage 50 to 75 percent of bearing wall destruction. P, side-on overpressure. /, side-on impulse (Baker et al. 1983).

Most of the criteria found in literature are extracted from Bowen et al. (1968). Diagrams of pressure versus duration are presented for various body positions in relation to the blast wave, from which the chance of survivability can be calculated. Those diagrams were combined in a pressure-impulse diagram, which is depicted in Figure C-1. The scaled overpressure P equals Plp, in which P is the actual pressure acting on the body, and po is the ambient pressure. The scaled impulse i equals ... 

Figure C-1. Pressure-impulse diagram for lung injury. P scaled overpressure. / scaled impulse. (Bowen et al. 1968).

Generalization of data for cylinder blast parameters obtained in the close in zone was not allowed to approach the HAM-air boundary, while analysis of a hemispherical explosion makes it possible to complete the pressure/impulse diagrams at 0.1 [Pg.221]

The pressure/impulse diagrams in Fig. 10.8 illustrate the respective changes recorded for a detonation (line 1), a constant volume explosion (line 2) and a deflagration with 200 m/s velocity (line 3) and 150 m/s (line 4). Accounting for the finite duration of the blast wave is of crucial importance because of the potential reduction of dangerous distances. 

Gibson method. The mean velocity in a penstock leading from a reservoir can be determined by rapidly closing a valve at the lower end and recording a pressure-time diagram at a point just upstream from the valve. The principle that impulse equals change of momentum can be applied to the mass of liquid between the reservoir and the point of measurement. The impulse is given by the area under the recorded pressuretime curve, and from this the initial velocity can be determined [10]. 

Fig. 10.8 Diagram of blast wave pressure/impulse resulting from H2 + air cloud explosion ( H2 - 100 kg) for various combustion modes line 1 - detonation line 2 - constant volume explosion line 3 — deflagration with 200 m/s velocity line 4 - deflagration with 100 m/s velocity 5 - boundary of deflagration regimes...

The calculation data [41] for detonation of gas layers (curve 1), columns (curve 2) and spheres (curve 3) can be presented by the damage diagram in pressure-impulse coordinates (Fig. 10.24). It is easy to compare the dangerous effect resulting from gas clouds of various shapes if one of the targets has a boundary of equi-probable destruction corresponding to curve 4. It is seen that the plane explosion causes a destructive blast wave pressure of the lowest level (position data of intersection points of curves 1, 2, 3 with curve 4). 

The parameter data for an underwater gas explosion from [45, 46] allows comparison of the damage diagram (lines 1-3) in the pressure-impulse plane with the underwater TNT explosion damage diagram (lines 4-6), see Fig. 10.30. Additionally, the 50% probable lethal threshold for fish [53] is plotted in the diagram. It is seen that none of the lines 1,2 or 3 cross the lethal threshold. But lines 4,5 and 6, for all three variants of TNT explosions, cross the boundary of the dangerous area. 

The two conditions that vary the most in a turbine are the inlet pressure and temperature. Two diagrams are needed to show their characteristics. Figure 3-12 is a performance map that shows the effect of turbine inlet temperature and pressure, while power is dependent on the efficiency of the unit, the flow rate, and the available energy (turbine inlet temperature). The effect of efficiency with speed is shown in Figure 3-13. Figure 3-13 also shows the difference between an impulse and a 50% reaction turbine. An impulse turbine is a zero-reaction turbine. 

Figure 9-6 shows a diagram of a single-stage impulse turbine. The statie pressure deereases in the nozzle with a eorresponding inerease in the absolute veloeity. The absolute veloeity is then redueed in the rotor, but the statie pressure and the relative veloeity remain eonstant. To get the maximum energy transfer, the blades must rotate at about one-half the veloeity of the gas jet veloeity. Two or more rows of moving blades are sometimes used in eonjunetion with one nozzle to obtain wheels with low blade tip speeds and stresses. In-between the moving rows of blades are guide vanes that redireet the gas from one row of moving blades to another as shown in Figure 9-7. This type of turbine is sometimes ealled a Curtis turbine.

Figure 17. Impulse Versus Pressure Diagram for Constant Levels of Building Damage. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)...

A schematic diagram, Figure 6, shows a typical underwater test configuration and oscilloscope record used to determine shock wave impulse. The pressure vs. time is displayed both at fast and slow scope speeds and the impulse vs. time at the faster scope speed. The impulse vs. time is electronically integrated from the pressure vs. time signal from the pressure gauge. 

The determination of the thrust of a rocket motor involves recording the time diagram of the force (tons, kp, or newtons) during combustion. The force is allowed to act on a support, with a pick-up element thrust cell interposed between them. The measurement is carried out by the aid of a strain gauge element (variation of resistance with pressure) or of a piezo-quartz element, and the results are recorded on an oscillograph connected in a compensation circuit. Modern measuring and computation techniques yield the total thrust time (impulse) immediately. 

Fig. 18.8. Calculation diagram of impulsive pressure coefficient. ai = aioaii,...

Detailed investigation of observation and measurement methods [23, 78-80] has shown that the standard approach to Tj = Tj (P, T) measurements using pressure-time, concentration-time, impulse-time / = I(t) diagrams might result in potential errors. 

Figure 9.31 presents the relative pressure wave intensity ahead of the wall and behind it and the scaled positive impulse value versus the reduced distance. The diagrams in Figs. 9.31 and 9.8 illustrate noticeable blast wave attenuation by the wall at distance equal to the double wall height [18]. 

Pressure and impulse in the pressure wave determine the danger level resulting from an explosion of hydrogenous combustible mixtures. The main measurable blast wave parameters are presented in the diagram (Fig. 10.1). The blast wave pressure in a gas explosion is a function of the energy release rate and it reaches a maximum at the detonation mode of combustion [1 ]. 

Fig. 10.17 Generalized diagram of damage caused by gas detonation in pressure amplitude-impulse coordinates cwve 1 - positive pressure phase damage curve 2 - rarefaction phase damage...

The spherical blast diagram is presented in Fig. 10.23c. Figure 10.23 illustrates the change (calculations in [21, 22, 32, 41]) in the relative pressure amplitude and the blast wave impulse with distance. The particular non-dimensional impulse coordinate is used for plotting the blast wave impulse relation... 

Fig. 10.23 Relative pressure amplitude and non-dimensional impulse of a compression phase versus the relative distance for gas mixture detonations (plane detonation - cwve 1, diagram (a) cylindrical detonation -cwve 2, diagram (b) spherical detonation - cwve 3, diagram (c)). BW - blast wave...

Fig. 11.31 Diagram of the impulse high-pressure injection of a combustible gas into the air [40, 46] ...

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