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Sound and Wave Phenomena
Published in David M. Scott, Industrial Process Sensors, 2018
The frequency of a wave refers to the rapidity with which the medium (in this case, air) oscillates. The unit of frequency is the hertz (defined to be one cycle per second), which is abbreviated as Hz.1 A continuous wave at a single frequency is shown in Figure 3.4. The top part of Figure 3.4a shows the time evolution of what happens at a fixed position when the wave passes by it. As a specific example, the y-axis could represent the elevation of a cork in a pond as it rides over ripples on the surface of the water. The bottom part of Figure 3.4b shows a picture of the spatial extent of the wave, recorded at a single instant in time. Both waveforms are identical in shape; the time it takes to complete a full cycle of the wave (i.e., the duration) is called the period (as shown in Figure 3.4a), and the corresponding spatial quantity (shown in Figure 3.4b) is the wavelength. The frequency f, in hertz, is determined from the period T: () f=1T
Frequency Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
As noted previously, stability measurements can tell us something about the inherent quality of an oscillator, and the stability of an oscillator is closely related to its quality factor, or Q. The Q of an oscillator is its resonance frequency divided by its resonance width. The resonance frequency is the natural frequency of the oscillator. The resonance width is the range of possible values where the oscillator will run. Obviously, a high resonance frequency and a narrow resonance width are both advantages when seeking a high Q. Stability and Q are generally correlated, because a high Q means that an oscillator has to stay close to its natural resonance frequency.
Noise and Vibration in Switched Reluctance Machines
Published in Berker Bilgin, James Weisheng Jiang, Ali Emadi, Switched Reluctance Motor Drives, 2019
James Weisheng Jiang, Jianbin Liang, Jianning Dong, Brock Howey, Alan Dorneles Callegaro
As discussed in Chapter 12, vibrational resonance, in the form of increasing amplitude of oscillation for a system, happens when the natural frequencies of a system are close to forcing frequencies acting on the structure. The natural frequency is defined as the frequency at which a system’s main mode of vibration oscillates without any external frequential forces. In a motor system, the stator-frame structure acts as the major source of noise. If the forcing frequencies of the radial force harmonics approach the natural frequencies of the stator-frame structure for a certain mode shape, resonance occurs in the stator-frame structure, causing a buildup of noise and vibration.
Effects of frequency and CSR on dynamic properties of marine clay in drained condition
Published in Marine Georesources & Geotechnology, 2022
Hao Liu, Si Yan, Jie Yin, Jiang-Qiao Fan, Yong-Hong Miao, Fan-Bo Zhou
Figure 8 shows the variation of the area S of hysteresis loop with log N for specimens dynamically loaded at different frequencies under a given CSR. Generally, a significant increase in S can be observed for almost all soft marine clay specimens within N = 1000. S reflects the energy dissipation capacity of the clay, so it can be said for this clay sample, major absorbed energy change occurs within the first 1000 cycles. As N continues to increase, the value of S tends to increase insignificantly at a lower frequency yet decreases at a higher frequency. Frequency is the number of complete cycles that occur per second. Soil skeleton experiences many more vibrations from dynamic loads at high frequency in a certain period, thereby causing much more rapid soil structure destruction with the propagation of micro-cracks (Lei et al. 2017). Moreover, the S-log N curve for specimens with lower frequency lies above that with higher frequency. That is, the clay sample exhibits a higher energy dissipation capacity at a lower frequency at a given N. The resonance effect where the natural frequency of the clay is close to 1 Hz may be causing this. Therefore, in geotechnical engineering applications, a lower value of frequency is anticipated to achieve greater energy dissipation capacity.
A novel control strategy of virtual synchronous generator in island micro-grids
Published in Systems Science & Control Engineering, 2018
Yong-jin Yu, Li-ke Cao, Xingmin Zhao
On the basis of the above researches, the main contribution of this paper is to propose the hybrid control of J and D of virtual synchronous generator (VSG) in island micro-grids. The control strategies are composed by three steps: firstly, if the frequency is less than the set value, the traditional control strategy (fixed inertia and damping) is used, and the values of inertia and damping are determined by the stability of the system at this point; secondly, supposing the frequency is more than the set value, the control strategy includes adaptive inertial control and constant damping, and the value of damping are determined by the steady state of the system at this moment; thirdly, assuming that the rate of frequency change is reverse, the control strategy is adaptive damping control and constant inertial. In addition, this paper also proposed a pre-synchronized control for the VSG to connect the micro-grids. By deploying the control strategy, the flexibility of power electronic devices is well demonstrated, and the curve of the frequency in island micro-grids is optimized. Hence, the dynamic and steady-state stability of the system has been greatly enhanced.
Development and analysis of high density poly ethylene (HDPE) nano SiO2 and wood powder reinforced polymer matrix hybrid nano composites
Published in Journal of Experimental Nanoscience, 2018
Tanya Buddi, B. Nageswara Rao, Swadesh Kumar Singh, Rajesh Purohit, R. S. Rana
Natural frequency is the frequency at which a system tends to oscillate in the absence of any driving or damping force. In general, the frequencies identified from the microtremor measurements correspond to the analytically determined frequencies for the situation where the heavy hanging masses in the structure are not active in the dynamic response, the test readings are shown in Table 2 and the frequency vs amplitude for samples c1,c2,c3 are shown in Figures 2–4. The typical tools of identification of dynamic systems, available in the Toolbox of Dynamic Systems Identification of Matlab (Math Works [6]) and other routines specially prepared for this effect were used (also based in Matlab)Figure 3.