Impulsive Sources

The impulsive noise of a helicopter leads to several effects with pulsing characteristic and high amphtudes at discrete frequencies. Again, we are concerned with the higher harmonics of the blade passage frequency. These types of noise occur in different flight situations and are recognized by the human ear 

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The loops primary device has backup indication with separate impulses sources... 

After introduction of an impulsive source U <5(R — R ) <5(f) of momentum into the suspension at position R = R (with R = Rn- + r ), at time t = 0 and vector strength U, subsequent transport of this momentum tracer through the suspension (the latter assumed to be initially at rest) is governed by the system of equations (Mauri and Brenner, 1991a,b)... 

The Greens function G = G x,Xo) describes the scalar field at a position a as a result of a unit impulsive source at some other position Xo- Hence, G is a function of an observer system x and a source system Xo. If Xo is chosen within the same interval as for x. Equations A-2 and A-3 can be rewritten in terms of the source coordinate system simply by replacing X by Xo- Then multiplying Equation A-2 by G and Equation A-3 by F, subtracting the products, and integrating over the source coordinate, oCo, from Xi to X2 gives ... 

I will illustrate the basic idea of geometrical migration by considering a simple example of zero-offset scattered wavefield data generated by an impulsive source and... 

In reality, impulse sources do not exist under PEB conditions. An impulse source can be approximated as having a concentration Cq over some small distance Ax centered at Xq, with zero concentrations outside this range. Using this modified impulse source as a boundary condition, the solution of Eq. (12.69) can be approximated as... 

Equation (12.72) is fairly accurate if Ax < 3o-. In the simation where there are two impulse sources located at xi and X2, with initial concentrations Ci and C2, each over a range Ax, the concentration of A at x after diffusion is given by ... 

Given the durations, we ean ealculate the source signal for the utterance. We use an impulse source for sonorant phones, a noise source for unvoiced consonants, and a combined impulse and noise souree for voiced obstruents. The source characteristies are switched at phone boundaries. For voiced sounds, the impulse sequence is created by plaeing impulses at a separation distanee determined by 1 /FO at that point. Finally we feed the souree signal into the filter coefficients to generate the final speech waveform for the sentence. 

There are some minor modifications that we can make to this basic model. Firstly, it is possible to lessen the switching character of the sound source at phone boundaries by appropriate use of amphtude control on the noise and impulse source. This is motivated... 

One type of sonar transducer, primarily used in the surveillance community, is a low-frequency active source. The tonpilz design is commonly used for such projectors at frequencies down to about 2 kHz (a tonpilz at this frequency is almost 0.75-m long). For frequencies below 2 kHz, other types of transducer technology are employed, including mechanical transformers such as flexing shells, moving coil (loud speaker) devices, hydraulic sources, and even impulse sources such as spark gap and air. Explosives are a common source for surveillance, and when used with towed arrays make a very sophisticated system. 

Keywords Shallow water equations Wave front amplitude Impulse source Eikonal equation Finite difference method... 

Figure 20 shows typical waveforms of LMEs at the Sechilieime DSGSD. One type corresponds to impulsive sources similar to small explosions, while another event tyqDe shows mostly emergent onsets and represents source-time functions lasting 5 s, either relatively broadband or low frequency. The LMEs cluster either in the... 

Each receiver is connected to a common multichannel recording instrument (i.e., a seismograph). This is the most significant difference between the CSW and the MASW techniques, as CSW is usually based on a two-receiver approach. Also the MASW method generally uses an impulsive source, such as a sledgehammer, to produce surface waves, whereas the CSW technique makes use of a frequency-controlled vibrator. 

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