Circle the best answer Mark eci 1. In inverse FFT operation on a frequency respo
ID: 2250326 • Letter: C
Question
Circle the best answer Mark eci 1. In inverse FFT operation on a frequency response function will give which of the following a) Time domain of response over excitation ratio b) Time domain of motion over force ratio & c) Impulse response function O d) All of the above e) None of the above 2. Given an idealephericaly radiating noise source, what would the sound level reduction be if the distance between the and receiver is decreased by a decade assuming the far field? a) 3 dB b) 10 dB c) 6 dB d) 20 dB e) None of the above A larger vibration accelerometer has the advantage of a) Lower sensitivity b) Greater mass loading 3. c) Higher sensitivity Od) Higher resonate frequency Greater choices for mounting e) 4. Which of the following are normally used to excite a system during a modal test D a) Shaker b) Hammer c) Accelerometer d)Both b) and c) e) Both a) and b) 5. Which of the following parameters can be determined through modal testing and not FEA. Ob) Mode shape a) Natural frequency c) Damping d) None of the above e) All of a), b) and c) Which of the following FEM parameter is equivalent to a system's natural frequency O a) Eigenvector 6. b) Domain analysis c) FRF d Eigenvalue e) None of the above 7. Which of the following does not have a resonate frequency a) Eyeball b) Rubber bal O c) Coil spring d) All of the above e) None of the aboveExplanation / Answer
1) Option-C
In inverse FFT operation on a frequency response function will give Impulse response function. Fourier Transform (FT) is used to convert a signal into its corresponding frequency domain.
In short, we could say that The Fourier transform is used to convert the signals from time domain to frequency domain and the inverse Fourier transform is used to convert the signal back from the frequency domain to the time domain
2) option - D
the sound level reduction is 20 dB
3) Option - B
An accelerometer is an electromechanical device used to measure acceleration forces
Accelerometers should weigh significantly less than the structure you are monitoring. A larger vibration Accelerometer has the advantage of greater mass loading. All remaining parameters like sensitivity remain same irrespective of weight and size of the accelerometer.
4) Option- B
In a modal test, the system is exited using Hammer. The structure is fixed at one end and the load is applied on the other end with the help of a hammer. We can not use a shaker for model excitation of the system to find natural frequencies and mode shapes.
5) Option - E
Modal testing is used objectives includes modal frequencies, modal masses, mode shapes and modal damping ratios.
6) Option- D
In the dynamic analysis of the system using FEM methods, Eigenvalues are considered as Natural frequencies. Eigenvectors are mode shapes.
7) Option - E
when the frequency of the forced vibration and the natural frequency becomes the same then the superposition of the waves occur and the amplitude of the vibration becomes maximum. So this frequency is known to be the resonance frequency. Naturally, the natural frequency and the resonance frequency are equal. So this is the reason that each and everybody in the universe has resonance frequency because it has a natural frequency.