Foundations in Linear Dynamics using Ansys Mechanical - Theory Quiz - Ansys Certifications

Foundations in Linear Dynamics using Ansys Mechanical - Theory Quiz

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1 / 45

Which of these applications requires performing a dynamic analysis?

Designing the external case of a headset

Acoustic performance of the vibrating headset speakers

Designing the thermal fatigue of electronics in a headset

Designing comfortable headset ear pads

2 / 45

In a particular jet engine, the turbine blades are not perfectly balanced on the spin axis of the shaft. Choose the statement which describes the cause and effect of this imbalance with a turbine assembly that is in-service. Select the best option.

The imbalance causes lateral forces to develop which leads to an infinite response as the turbine passes thru a nature frequency.

The imbalance causes lateral forces to develop which can lead to excessive displacement especially as the turbine passes thru a nature frequency.

The imbalance causes lateral forces to develop which lead to changes in the nature frequencies of the system.

The imbalance causes lateral forces to develop only at the natural frequency. For all other frequencies the forces are zero.

3 / 45

The displacement vector for a mode superposition solution with three modes is to be computed. The modal coordinate for each mode 1, 2 and 3 is 1 and for each of these modes, let's assume the value from the mode shape vector for a single node of interest is also 1. What will be the value of the nodal displacement calculated for this node of interest using these three modes?

1

6

3

2

4 / 45

Let us assume that there are two materials - "Material A" and "Material B". The stiffness and the density for Material A are both three times that of Material B. The ratio of natural frequencies for a structure made of Material A compared the same structure constructed with Material B will be _____. Complete the sentence with the best option.

9

1

1.732

3

5 / 45

Which of these materials is best suited for a flywheel to store most kinetic energy?

Gray cast iron ($\rho$ = 7200 $kg/m^{-3}$)

HDPE ($\rho$ = 958.5 $kg/m^{-3}$)

Aluminum ($\rho$ = 2770 $kg/m^{-3}$)

Stainless steel ($\rho$ = 7750 $kg/m^{-3}$ )

6 / 45

What is the relationship between displacement, velocity, and acceleration for a dynamic problem? Select the three best options.

Acceleration is the derivative of velocity with respect to time.

Acceleration is the second order derivative of displacement with respect to time.

Velocity is the derivative of displacement with respect to time.

Displacement is the time derivative of velocity respect to time.

7 / 45

Which of these is a time-dependent material behavior?

Viscoelasticity

Linear elasticity

Hyperelasticity

Rate-independent Plasticity

8 / 45

Structural dynamics is the study of _____. Select the best option to complete the sentence.

the response of a structure to very fast loads

the response of a structure to periodic loads

the response of a structure in motion

the response of a structure to very slow loads

9 / 45

Which of the following statements regarding mass scaling in an explicit dynamic analysis are correct? Select the two best options.

If mass scaling is used, the results of the simulation should be scaled proportionally.

Since mass scaling affects only a portion of the model, the global accuracy can be limited to an acceptable range.

Mass scaling is a numerical method to artificially increase the mass of material to reduce the time step size.

Mass scaling uses material with larger mass to replace the current material in the simulation to increase computational efficiency.

10 / 45

Which of these properties dissipates energy from a system? Select the best option.

Elastic strain

Damping

Mass

Stress

11 / 45

Which of the following statements is relevant to using a full method in a harmonic analysis? Select the best option.

The equations are coupled and solving them can be computationally expensive.

The equations are uncoupled and the solution is computationally efficient.

The full method always requires a large amount of memory.

12 / 45

Consider two masses connected by a single spring, and the masses are only allowed movement in a single direction (1D). How many natural frequencies are there in this system?

2

3

1

4

13 / 45

Which of the following is true for participation factor and effective mass?

Participation factor is the square of the effective mass.

Ratio of magnitude of effective mass and participation factor is 1.

Effective mass is the square of Participation factor.

They are independent quantities.

14 / 45

In many cases, modes with frequencies much higher than those of the excitation are neglected because _____. Select the option that best completes the sentence.

mode-superposition techniques have a limit on the number of modes that can be included

high-frequency modes tend to contribute little to the response

doing so yields results that match experimental data more closely

including such modes reduces the accuracy of the solution

15 / 45

The coefficients used for combination of modes in a mode superposition method are called _____? Select the best option.

Mass participation factor

Normalization factor

Modal coefficients

Modal participation Factor

16 / 45

Which three statements are correct about time integration methods?

There are a variety of time integration methods. People choose time integration methods based on the requirements of accuracy, stability and computational characteristics.

Time integration can start from a time-step with an unknown solution and progress to the next time-step.

Time integration method requires an initial condition at time = 0.

At an unknown time-step, time integration methods use known solution at one previous time-step or multiple previous time-steps to progress to the current time-step solution.

17 / 45

For a response spectrum analysis, the mode superposition method is _____. Select the best option.

prerequisite

optional

a post-processing option

essential as per government requirements

18 / 45

A tensile stress state in a pre-stressed modal analysis will tend to _____. Select the best option to complete the sentence.

suppress rigid-body motion

decrease the natural frequency

increase the natural frequency

keep the natural frequency the same

19 / 45

Stress analysis of a part subjected to known, cyclical thermal loads can be performed using a _____. Select the best option to complete the sentence.

dynamic analysis

harmonic analysis

heat transfer analysis

static analysis

20 / 45

A person steps onto a slender wooden plank and begins to oscillate up and down, and eventually the oscillatory motion stops. Which mechanism best models this real world example?

A mass connected to a spring and a damper in parallel

A mass connected to a spring and a damper in series

A mass connected to a spring

A mass connected to two springs in parallel

21 / 45

Which of the following holds true for a cantilever (such as a diving board) excited by a harmonic external force with its frequency matching the second natural frequency? Select the best option.

Most contribution to the deformation will be from the third natural frequency.

Most contribution to the deformation will be from the fourth natural frequency.

Most contribution to the deformation will be from the first natural frequency.

Most contribution to the deformation will be from the second natural frequency.

22 / 45

Which of these NEED NOT be a linear dynamic analysis?

Transient stress analysis

Random vibration analysis

Harmonic analysis

Modal analysis

23 / 45

To maintain numerical stability while using the explicit time integration method, the time-step size should satisfy the CFL condition, which is $\Delta t \leq f \left ( \frac{h}{c} \right )$. Which of the following statements are correct about the CFL condition? Select the two best options.

In the CFL condition, h is the smallest characterize length of all the elements for the simulation.

In the CFL condition, c is the velocity of the structure.

In the CFL condition, h is the average characterize length of all the elements for the simulation.

In the CFL condition, c is the velocity of sound passing through the material.

24 / 45

The damping ratio is defined as:

$\frac{Actual Damping}{Critical Damping}$

$\frac{\sqrt{\frac{k}{m}}}{c}$

$\frac{Critical Damping}{Actual Damping}$

$\frac{c}{\sqrt{\frac{k}{m}}}$

25 / 45

Imagine a body of mass m is resting on a platform of mass $M$. Assuming that there is no friction between them, if we set the platform into motion from rest to a constant velocity, $V$, over a time $T$, what will be the net acceleration of the body?

0

$\frac{m}{m+M} \cdot \frac{V}{T}$

$\frac{V}{T}$

$\frac{m}{M} \cdot \frac{V}{T}$

26 / 45

If a machine component undergoes small, elastic deformations due to time-dependent loads, which analysis is preferred to study such a system?

Harmonic analysis

Static analysis

Nonlinear transient analysis

Linear transient analysis

27 / 45

Which of the following statement is relevant to using the mode superposition method in a harmonic analysis? Select the best option.

The equations are coupled and solving this can be computationally expensive.

The equations are uncoupled and solution is computationally efficient.

For large models, the number of equations to be solved is excessive and prohibits the use of this method.

The mode superposition method always requires a large amount of memory.

28 / 45

Performing a harmonic analysis can serve to _____. Select the two best options.

Maximize structural stiffness

Predict seismic response

Avoid resonance

Help prevent fatigue failure

29 / 45

Which expression characterizes the phase angle of a complex variable?

$\sin^{-1}x$

$\sqrt{x^2+y^2}$

$cos^{-1}x$

$\tan^{-1}\left (\frac{y}{x} \right)$

30 / 45

Which analysis is suitable to calculate the stresses developed in a steam turbine blade due to constant, high-speed rotation?

Harmonic analysis

Transient stress analysis

Modal analysis

Static stress analysis

31 / 45

Which of these are correct statements about time intgeration methods? Select the two best options.

The implicit method can always reach stable results while the explicit method depends on the time step size to have stable results.

The solving speed of the implicit method is faster than the explicit method for one time-step.

The implicit method allows for larger time-step size while the explicit method requires very small time-step size.

For nonlinear problems, both implicit and explicit methods require an iterative solver to find results within one time-step.

32 / 45

A mountain bike has a fluid filled shock absorber with a piston moving in the contained fluid. With regard to the energy dissipation from the damping, one can expect which of the following?

The shock absorber will experience an increase in temperature

Insufficient information to determine the answer

The shock absorber will experience no change in temperature

The shock absorber will experience a decrease in temperature

33 / 45

The velocity derived from the complex displacement function is characterized by which expression?

$-\Omega^2A(\cos \Omega t + i\sin \Omega t)$

$-\Omega^2 A e^{i \Omega t}$

$A(\cos \Omega t + i\sin \Omega t)$

$i\Omega A e^{i \Omega t}$

34 / 45

A large amplification factor Q is associated with a:

zero damping ratio

small damping ratio

independent of damping ratio

large damping ratio

35 / 45

A car is driving at a constant velocity, and the brakes are applied suddenly to stop the car. Which type of physical damping phenomena dominates the energy dissipation due to the braking?

Viscous damping

Rayleigh damping

Material damping

Frictional damping

36 / 45

While simulating the drop test of a circuit board on to a hard ground using an explicit analysis, if the computing time is very long, which of the following options may help reduce the computational time? Select the three best options.

Use mass-scaling to increase the time-step size.

Remove all unnecessary details from the original geometry.

Treat the hard ground as a rigid body.

Treat all the electronic components as rigid bodies.

37 / 45

The peak magnitude of the forcing excitation is typically referred to as _____. Select the best option.

Amplitude

Resonance

Acceleration

Phase angle

38 / 45

The imposed circular frequency in a harmonic analysis is represented by which of the following formulas.

$f=\frac{1}{T_{f}^{2}}$

$f=\frac{1}{T_{f}}$

$\Omega = 2\pi f$

$\Omega = \frac{2\pi }{f}$

39 / 45

A continuous system will have how many natural frequencies?

Infinite

6

>10 and <100

>6 and <10

40 / 45

In the Rayleigh damping equation, how does increasing frequency affect the contribution from the mass and stiffness terms to the damping ratio? Pick the two correct responses.

The contribution from mass damping goes up

The contribution from stiffness damping goes up

The contribution from mass damping goes down

The contribution from stiffness damping goes down

41 / 45

When we clamp and hold a viscoelastic material sample under a constant amount of displacement, what phenomenon do we expect to see?

Strain hardening

Stress stiffening

Stress relaxation

Creep

42 / 45

Damping, and the associated rate of energy dissipation, can be a function of which of these? Pick the three best options.

Material

Velocity

Frequency

Applied force

43 / 45

Which type of analysis is preferred if we wish to study the stresses developed in an electronic device mounted on a moving car's dashboard?

Steady-state analysis

Frequency-domain analysis

Topological Optimization

Time-domain analysis

44 / 45

How can one identify the most important natural frequencies & modes for an excitation in a given direction? Select the best option.

Identify the modes with the highest participation factors in that given direction

It will always be the highest frequencies of the system

Compare the effective mass to the actual mass

Review modeshapes and identify ones with the highest maximum deformation

45 / 45

Harmonic analysis is also referred to as _____. Select the best option.

Modal analysis

Forced frequency response

Response spectrum analysis

Time domain analysis

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Private: Foundations in Linear Dynamics using Ansys Mechanical

Foundations in Linear Dynamics using Ansys Mechanical - Theory Quiz

Total Available Time - 90 mins

Total Number of Questions - 45

Foundations in Linear Dynamics using Ansys Mechanical - Theory Quiz