Frequency critical

Increase Sound- Transmission Loss. The only significant iacreases ia sound-transmission loss that can be achieved by the appHcation of dampiag treatments to a panel occur at and above the critical frequency, which is the frequency at which the speed of bending wave propagation ia the panel matches the speed of sound ia air. AppHcation of dampiag treatment to 16 ga metal panel can improve the TL at frequencies of about 2000 H2 and above. This may or may not be helpful, depending on the appHcation of the panel. 

The Nyquist critical frequency or critical angular frequency is... 

To avoid operating difficulties, the torsional critical frequencies of the combined engine and driven equipment should be calculated or measured to assure that operating speeds are removed from these criticals or that vibration dampers are provided or that the equipment is designed for the resulting cyclic stresses. 

The speed of the controller is adjusted by the proportional band and reset rate (proportional and integral gains). These parameters also influence the stability of the control loop. All control loops are limited to a gain of less than one at their critical frequency. Higher closed-loop gain will make the loop unstable. 

This speed becomes critical when the frequency of excitation is equal to one of the natural frequencies of the system. In forced vibration, the system is a function of the frequencies. These frequencies can also be multiples of rotor speed excited by frequencies other than the speed frequency such as blade passing frequencies, gear mesh frequencies, and other component frequencies. Figure 5-20 shows that for forced vibration, the critical frequency remains constant at any shaft speed. The critical speeds occur at one-half, one, and two times the rotor speed. The effect of damping in forced vibration reduces the amplitude, but it does not affect the frequency at which this phenomenon occurs. 

Earlier experiments indicate clearly that a lowered sound pressure level can be an effective measure to reduce the inconvenience reactions due to a ventilation noise, provided that it is targeted at the most critical frequency range from the point of view of influence or that the measure results in a general lowering over the entire spectral range of the ventilation noise. 

The degree of attenuation at the critical frequency can be very large, but this type of silencer has a very narrow bandwidth. This device may be suitable when the machine being dealt with emits sound predominantly of a single wavelength. Lining the chamber with absorbers can expand the absorber bandwidth of a Helmholtz resonator, but this has the effect of reducing the efficiency. The perforated absorber, which forms the basis of many acoustic enclosures and silencers, is a development of the resonator principle. 

Of particular interest are measurements on a vibrating sphere in forced flow by Gibert and Angelino (G3) because of the careful experimental execution and wide range of frequencies and Re numbers investigated. Below a certain critical frequency, the mass-transfer rate to the sphere is not affected by vibration. 

No a priori knowledge of the system time constants is needed. The method automatically results in a sustained oscillation at the critical frequency of the process. The only parameter that has to be specified is the height of the relay step. This would typically be set at 2 to 10 percent of the manipulated variable range. 

From the definition of cOint follows that the quasireversible maximum can be also determined by varying the frequency, while keeping 0 constant. In analogy to (2.105), it is obvious that the critical frequency, associated with the position of the maximum, depends on the interaction product a. The relationship between the critical frequency and the interaction product is given by the following equation ... 

Table 4.1 Analysis of the quasireversible maxima measured for three different concentrations of the transferring ion in the aqueous phase. The other experimental conditions are the same as in Fig. 4.11. The standard rate constants have been estimated from the critical frequencies measured...

Critical frequency of quasireversible maximnm, Hz Faraday constant, C mol ... 

The critical energy required for a photon to remove an electron is then hvc = q>, where Vc is the critical frequency of the photon and h is Planck s constant. When the frequency of the incident radiation is less than the critical frequency, electrons will not be ejected. Similarly, when the wavelength of the incident radiation is greater than the critical wavelength, Xc, electrons will also not be emitted (recall that V = c/X, where c is the speed of light in vacuum). This relationship between... 

Geometry and Torsional Properties of Candidate Materials. From a mechanics standpoint, a driveshaft can be approximated as a thin, rotating tube. The first critical frequency, Ncr, in units of rev/min (rpm), of a simply supported thin rotating tube is given by... 

Work in groups of three. Each person should select one of the three composite candidate materials listed in Table 8.11. Using the data in Table 8.11 and the geometric data in Table 8.10, calculate the critical frequency of rotation, Wr, for each type of vehicle listed in Table 8.10 for your composite. Using this criterion only, how many of the vehicles will your composite be suitable for Compare your answers with the other group members for their composites. 

Some time ago we measured the dielectric dispersion of a plant virus particle and found a critical frequency in the kHz region, therefore in a region that may well correspond to the eventual maximum of your ultrasonic absorption. We were able to describe the mechanism leading to this dispersion in terms of the rotation of the complete virus particle and of the motion of associated (or bound) counterions on the elongated surface of the particle. 

Fig. 38. Helix-coil transition of a PBLG sample (Mw = 59000) in a DCA-CHa3 mixture (70 30) detected by ORD ( ) and by dielectric dispersion (O). (+) (US). Here d and e represent the quantities defined by Eq. (E-6) and Eq. (E-7), respectively, and tj f. denotes the critical frequency of the dispersion corrected for solvent viscosity...

The activation energy of absorption I is reported in Table I for Na-F86.5 at different hydration levels. It increases with increasing water content. Because of the rapid shift of the critical frequency with water content relevant activation energies for the other samples cannot be given. 

Figure 4- Logarithms of the critical frequencies for absorptions A and B vs. the inverse of the absolute temperature for the four Na+ zeolites...

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