Modal Analysis

Intro to Modal Analysis — Lesson 1

Governing Equations of Modal Analysis — Lesson 2

An Eigenvalue Problem — Lesson 3

Mode Participation Factor and Effective Mass — Lesson 4

Free-free Modal and Pre-stressed Modal Analysis — Lesson 5

Applications of Modal Analysis — Lesson 6

Homework, Quizzes, Simulation Examples — Lesson 7

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Quiz — Modal Analysis

Summary — Modal Analysis — Lesson 8

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Quiz — Modal Analysis

Modal Analysis Homework, Quizzes, Simulation Examples — Lesson 7 Quiz — Modal Analysis

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Question 1 of 9

1. Question
Modal analysis tells an engineer
- 1) Maximum deflection of a structure under certain dynamic load
- 2) Relative deformations at natural frequencies
- 3) Most critical natural frequency of a structure
- 4) All of the above
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Question 2 of 9

2. Question
For SDOF spring-mass system, the governing equation for modal analysis is Ma+Ku = 0, where mass is M, spring stiffness is K. Find out correct statements from below options. (Select all applicable)
- 1) The stiffer the spring, the higher the natural frequency of the system is.
- 2) The system has multiple natural frequencies and mode shapes
- 3) Mass does not affect the natural frequency of the system
- 4) Natural frequency of the system is proportional to sqrt(K/M)
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Question 3 of 9

3. Question
For modal analysis of a 3D structure, it is found that there are repeated natural frequencies in the results. The reason for this could be:
- 1) Numerical error. Repeat natural frequencies can be ignored.
- 2) Symmetric behavior of the structure in 3D space. Same natural frequency value in different direction.
- 3) Too many natural frequencies are requested.
- 4) All of the above
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Question 4 of 9

4. Question
In the homework problem for the lightweight aircraft which of the following mode represent the mode like the first mode of a cantilever beam made of Aluminum Alloy?
- 1) Mode 6
- 2) Mode 7
- 3) Mode 8
- 4) Both Mode 7 and 8
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Question 5 of 9

5. Question
Considering the example of 'Recreational Drone', which of the following frequencies have the maximum ratio of effective mass to total mass in the X direction? (Select the option closest to the obtained value)
- 1) 44 Hz
- 2) 59 Hz
- 3) 90 Hz
- 4) 170 Hz
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Question 6 of 9

6. Question
In the "Guitar String" problem in the homework, based on that problem, which of the following is a correct statement?
- Tightening a string via the tuning knob increases the stress in the string, which leads to lower natural frequencies.
- Tightening a string via the tuning knob decreases the stress in the string, which leads to higher natural frequencies.
- Tightening a string via the tuning knob increases the stress in the string, which leads to higher natural frequencies.
- Tightening a string via the tuning knob decreases the stress in the string, which leads to lower natural frequencies.
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Question 7 of 9

7. Question
Which of the below systems is/are suitable for free-free modal analysis (Select all applicable):
- 1) Solar panel attached to the ground
- 2) Recreational Drone hovering in air
- 3) Magnetic levitation train
- 4) Suspension bridge
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Question 8 of 9

8. Question
For a pre-stressed modal analysis, find correct statements:
- 1) Natural frequencies of a pre-stressed structure are always increased compared to original system, because stiffness matrix is augmented by stress stiffness [S]
- 2) Participation factor of pre-stressed modal analysis remain the same compared to the original structure
- 3) Although value of natural frequencies are changed, the mode shapes always remains same pattern for pre-stressed modal analysis
- 4. To have consistent results, boundary condition needs to be the same in the static analysis and in the modal analysis for pres-stressed modal analysis.
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Question 9 of 9

9. Question
Which of the following statements are correct regarding the Burj Khalifa?
- 1) It has a buttressed core (Y-design)
- 2) It has low natural frequencies
- 3) Bending and Torsion are two of the significant modes
- 4) All the above
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