Defence Research & Development Organisation Design Engineer Interview Questions and Answers

1 hr and various apti topics

Q1. What are your strengths
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Q2. How do gas turbine engines work
Ans. 
Gas turbine engines work by compressing air, mixing it with fuel, igniting the mixture, and using the hot exhaust gases to spin a turbine.
• Air is drawn into the engine and compressed by a compressor

• Fuel is injected and mixed with the compressed air

• The mixture is ignited, causing a rapid expansion of gases

• The hot exhaust gases are used to spin a turbine, which drives the compressor and generates thrust

• Examples: Jet engin
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Q1. Why the brittle material fail as spiral fracture surface under torsion
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Brittle materials fail as spiral fracture surface under torsion due to their inability to deform plastically.
• Brittle materials lack ductility and are unable to deform plastically under stress

• Under torsion, the material experiences shear stress which leads to the formation of spiral fracture surfaces

• The lack of plastic deformation causes the material to fail catastrophically along these spiral paths

• Examples of brittle m...read more
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Q2. What is entropy
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Entropy is a measure of disorder or randomness in a system.
• Entropy is a thermodynamic property that quantifies the amount of energy in a physical system that is not available to do work.

• It is a measure of the number of possible arrangements of particles in a system.

• Entropy tends to increase in isolated systems over time, leading to a state of maximum disorder or equilibrium.

• An example of entropy is the melting of ice -...read more
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Q3. How to find natural frequency practically
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Natural frequency can be found practically by conducting modal analysis or using specialized equipment like accelerometers.
• Conduct modal analysis by applying a force or impulse to the structure and measuring the resulting vibrations.

• Use specialized equipment like accelerometers to measure the vibrations of the structure.

• Calculate the natural frequency using the formula: f = 1 / (2π√(k/m)), where f is the natural freque...read more
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Q4. What is Fast Fourier transform
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Fast Fourier Transform (FFT) is an algorithm used to compute the Discrete Fourier Transform (DFT) of a sequence or signal.
• FFT is used to analyze the frequency content of a signal by decomposing it into its constituent frequencies.

• It is commonly used in signal processing, image processing, audio analysis, and many other fields.

• FFT algorithms are much faster than the naive DFT computation, making it practical for real-ti...read more
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Q5. How FFT is different from DFT
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FFT is a faster algorithm for calculating DFT
• FFT is faster than DFT in terms of computation time

• FFT uses a divide-and-conquer approach to reduce the number of operations

• DFT computes all frequencies while FFT only computes the frequencies of interest

• FFT is commonly used in signal processing applications
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