Simulation Quiz 2

Understanding the Physics of Structural Mechanics - Simulation Quiz 2

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1 / 15

What is the frequency of the tenth mode for the copper tuning fork in System B (“Copper”)? Pick the closest option.

~ 4000 Hz

~ 3000 Hz

~ 1000 Hz

~ 2000 Hz

2 / 15

What is the first frequency of vibration for the copper tuning fork in System B (“Copper”)?

~ 140 Hz

~ 240 Hz

~ 190 Hz

~ 90 Hz

3 / 15

The Cumulative Mass Fraction reported for the highest extracted mode should _____. Select the best option to complete this sentence.

always add up to 1.0, regardless of the number of modes extracted

be give the same value as the ratio of effective mass to total mass

give the highest value in the direction of interest if a suitable number of modes have been extracted

get closer to but never equal 1.0 as more modes are extracted

4 / 15

What is the frequency of the tenth mode for the steel tuning fork in System A (“Steel”)? Pick the closest option.

~ 3000 Hz

~ 4000 Hz

~ 2000 Hz

~ 1000 Hz

5 / 15

For System B (“Copper”), select two statements which are correct concerning the system response in the global y-direction.

The first 10 modes are not enough to characterize the dynamic response in the y-direction.

The ratio of effective mass to total mass in the y-direction is greater than 0.9

The ratio of effective mass to total mass in the y-direction is less than 0.1

The first 10 modes sufficiently characterize the dynamic response in the y-direction.

6 / 15

Consider System B (“Copper”). For this tuning fork, the desired mode shape is shown below, where the tines (prongs) are vibrating in opposite motions toward/away each other. Select the correct statement below:

This mode shape is represented by the 2nd mode

This mode shape is represented by the 4th mode

This mode shape is represented by the 3rd mode

There is no mode shape that is similar to the desired mode shape in the first 10 frequencies.

7 / 15

For this tuning fork, the desired mode shape is shown below, where the tines (prongs) are vibrating in opposite motions toward/away each other. The desired frequency is 440 Hz. Select the correct statement below:

Copper is a better material than Steel for this application.

Neither the copper nor steel tuning fork has a frequency within +/- 10 Hz of the desired frequency.

Steel is a better material than Copper for this application.

Both copper and steel are suitable materials for this application.

8 / 15

Compare the first four modes of System A (“Steel”) with System B (“Copper”). Select the correct statement below:

The mode shapes are very similar but frequencies are lower for the Copper tuning fork.

The mode shapes and frequencies are the same for both cases.

The mode shapes are very similar but frequencies are lower for the Steel tuning fork.

The frequencies are very similar but mode shapes are different for the two cases.

9 / 15

Consider System A (“Steel”). For this tuning fork, a region of interest for the 6th mode is highlighted in a dotted red oval below. Select the correct statement below:

In practice, the region of interest will only have zero deformation if there is a Fixed Support applied there since a mode shape is not “real”.

The region of interest has the largest negative deformation for the 6th mode.

The region of interest has very small amplitude for the 6th mode.

The region of interest will undergo deformation from zero to maximum amplitude for the 6th mode.

10 / 15

For System A (“Steel”), select two statements which are correct concerning the system response in the global z-direction.

The first 10 modes are not enough to characterize the dynamic response in the z-direction.

The ratio of effective mass to total mass in the z-direction is greater than 0.9

The first 10 modes sufficiently characterize the dynamic response in the z-direction.

The ratio of effective mass to total mass in the z-direction is less than 0.1

11 / 15

Review the third and sixth modes in System B (“Copper”). Select the correct statement below:

The sixth mode has a significantly higher participation factor than the third mode in the global y-direction.

The third and sixth modes both have relatively high participation factors in the global y-direction.

The third and sixth modes both have relatively high participation factors in the global x-direction.

The sixth mode has a significantly higher participation factor than the third mode in the global x-direction.

12 / 15

Compare the modes of System A (“Steel”) with System B (“Copper”). Select the correct statement below:

The Steel tuning fork has larger displacements than the Copper tuning fork because it will vibrate longer.

The Steel tuning fork has larger mode shapes than the Copper tuning fork since Steel has a higher elastic modulus and lower density than Steel.

The Copper tuning fork has lower frequencies than the Steel tuning fork since Copper has lower elastic modulus and higher density than Steel.

The magnitude of deformation is higher in the Steel tuning fork since Steel has a higher elastic modulus than Copper.

13 / 15

In System A (“Steel”), which direction does not have its dynamic response properly characterized with 10 modes?

Global Y direction

Rotation about Global Y direction

Global Z direction

Global X direction

14 / 15

Consider System A (“Steel”). For this tuning fork, a mode shape of interest is shown below. Select the correct statement below:

This mode shape is represented by the 8th mode

There is no mode shape that is similar to the mode shape of interest in the first 10 frequencies.

This mode shape is represented by the 7th mode

This mode shape is represented by the 9th mode

15 / 15

What is the first frequency of vibration for the steel tuning fork in System A (“Steel”)?

~ 240 Hz

~ 190 Hz

~ 90 Hz

~ 140 Hz

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Physics of Structural Mechanics

Modal Analysis of a Tuning Fork

Total Available Time - 45 mins

Total Number of Questions - 15