Oblique-wave generation

Fig. 6. MR wave image of acoustic refraction. Shear waves generated in the upper part of an agar gel phantom (horizontal motion) propagate vertically in the stiff part of the phantom (/i 50 kPa cT 7.5 cm/s) and are refracted by the oblique lower part of soft gel (fi 15 kPa cT 4 cm/s). Note the marked reduction of wavelength in the softer medium. From Ref. 23, reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley Sons, Inc.

The velocity vector field pattern presented in Fig. 10.32b is useful for understanding the details of the explosion products displacement. Due to the products expansion behind the attached oblique wave, the upstream flow of gas is generated in the central part and is the reason for a typical mushroom-shape cloud formation in the final stage of an explosion. The behavior in the vicinity of the explosion products cloud can be described using the models from [56, 57]. 

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

The formation of a shock wave is dependent on the objects that affect the flow field. The conservation of mass, momentum, and energy must be satisfied at any location. This is manifested in the formation of a shock wave at a certain location in the flow field to meet the conservahon equations. In the case of a blunt body in a supersonic flow, the pressure increases in front of the body. The increased pressure generates a detached shock wave to satisfy the conservation equations in the flow field to match the conserved properties between the inflow and outflow in front of the body. The velocity then becomes a subsonic flow behind the detached shock wave. However, the shock wave distant from the blunt body is less affected and the detached shock wave becomes an oblique shock wave. Thus, the shock wave appears to be curved in shape, and is termed a bow shock wave, as illustrated in Fig. C-1. 

However, (a) infarction of the inferobasal segment (posterior wall) does not usually generate a Q wave because it depolarises after 40 milliseconds (Durrer et al., 1970) (Figure 9.5). (b) Furthermore, the CMR correlations have demonstrated that the posterior wall often does not exist, because usually the basal part of the inferoposterior wall does not bend upwards (Figure 1.13). (c) In cases that the inferoposterior wall bends upwards, even if the most part of inferior wall is posterior, as may be rarely seen in very lean individuals, as the heart is located in an oblique... 

Finally, solitary waves are characterized by their collisions. There exist two main types of wave collisions, oblique and head-on collisions, which generate different patterns in the liquid surface. Head-on collisions are better analyzed in a space-time diagram, whereas oblique collisions can be easily analyzed in real space. 

The viscosity coefficients may also be determined by studying the reflexion of ultrasonic shear waves at a solid-nematic interface. The technique was developed by Martinoty and Candau. A thin film of a nematic liquid crystal is taken on the surface of a fused quartz rod with obliquely cut ends (fig. 3.7.1). A quartz crystal bonded to one of the ends generates a transverse wave. At the solid-nematic interface there is a transmitted wave, which is rapidly attenuated, and a reflected wave which is received at the other end by a second quartz crystal. The reflexion coefficient, obtained by measuring the amplitudes of reflexion with and without the nematic sample, directly yields the effective coefficient of viscosity. 

Oblique ultrasonic waves sent to a composite at frequencies that excite plate wave modes induce the leaky lamb wave phenomenon. When the leaky Lamb wave is generated, the specular reflection is distorted. When the specular reflection and the leaky Lamb wave interfere, a phase cancellation occurs, and two components are generated with a phase between them. Because each type of defect has a unique response, this technique can be used to determine material eleastic constants and to estimate the volume content of resin as well as porosity content. Detection of transverse cracking and delamination in a 24-layer unidirectional graphite-epoxy laminate has also been reported [140], and oblique incidenee back-scattering techniques give accurate fiber orientation of the first composite layers [15],... 

A thin nematic layer is formed on top of a fused quartz rod with obliquely cut ends to which a quartz generator and receiver are glued. The transducer generates waves at its frindamratal frequency and its odd harmonics. The wave transmitted to the nematic layer is rapidly damped, while the reflected wave is detected by the receiver. Multiple reflection at the interface and both ends leads to a pulse echo pattern at the detector, from which the reflection coefficient can be determined [90,91]. The accurai of the determination of the viscosity coefficients is about 6% to 15%. Use of a mechanical wave method was also reported in [93]. 

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