EGM 5121C F22 Data Measurement and Analysis
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Data Measurement and Analysis, EGM 5121C, F22
1. Plot the impulse response function h(t ) vs. ωnt for each of the pole locations shown below in the complex plane. Make one plot for each colored line, and identify the line as having a constant damping ratio, time constant, or oscillation frequency.
Im
x x x x
x x 1
x x
x
Re
2. A first-order system with impulse response function h(t ) = e−t/ a is excited by a truncated step function x (t ) = ⎨ where the time constant a = 2 seconds. Determine the following:
a. the system output y (t ) by applying the convolution integral analytically. (HINT: Break the integral into two intervals: 0 ≤ t ≤ 2a and t > 2a .)
b. the system output y (t ) by numerically convoluting the two functions (e.g. in MATLAB).
c. produce a graph (e.g., in MATLAB) that compares the two solutions.
d. interpret your response. Does it make physical sense? Why?
3. A second-order system with impulse response function h (t ) = e−ζωnt sin (ωd t ) is excited by a truncated ramp function x (t ) = ⎨ where ωn = 1 rad/s, T = , ωd = ωn and ζ = damping ratio = 0.05. Determine the following:
a. the system output y (t ) by applying the convolution integral analytically. (HINT: Use superposition to express the truncated ramp as the sum of a ramp with positive slope for t ≥ 0 , a negative step for t ≥ 2T , and a ramp with negative slope for t ≥ 2T .)
b. the system output y (t ) by numerically convoluting the two functions (e.g. in MATLAB).
c. produce a graph (e.g., in MATLAB) that compares the two solutions.
d. interpret your response. Does it make physical sense? Why?
4. Given the convolution integral y (t ) = j u (τ)h (t −τ)dτ and the definition of the Fourier −∞
Transform Y(ω) =j(∞) y (t )e− jωtdt , prove that Y (ω) = U (ω)H (ω) . Hints: (1) Substitute the
−∞
convolution integral into the Fourier transform. (2) Change the order of integration by integrating over t first, then τ . (3) For the inner integral, make the substitution α= t −τ .
5. From Table 2.1 in B&P, derive H (f ) for the case of relative acceleration output and foundation motion acceleration input to show H(f ) = . Also find the phase angle θ(f ) . Plot H (f ) and θ(f ) for ζ= 0.01, 0. 1, 0.5, and 1.0 .
2022-09-17