Theory Quiz

Linear Dynamics using Ansys Mechanical - Theory Quiz

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1 / 47

Which of the following statements are TRUE regarding the expected frequency in the Response PSD results? Select the two best options.

This gives us an indication of whether the output of the response is occurring at a dominant natural frequency.

This value is used in Fatigue calculations of a random vibration simulation.

It is the point in the Response PSD curve where the slope is minimum with respect to frequency.

It is the centroid of the area under the Response PSD probe with respect to frequency.

2 / 47

What are the factors associated with extracting a number of modes equal to a number of nodal DOFs? Select the three best options.

It leads to exact results with no numerical errors.

It is a computationally expensive task.

It leads to less accurate results with numerical errors.

It is a time-consuming task.

3 / 47

Which of the following statements are TRUE regarding the Response PSD tool in Random Vibration analysis? Select the two best options.

The option of Clustering frequency points is available for the Response PSD tool, but not available for the Response PSD probe.

We cannot change the frequency range for the Response PSD tool.

The Response PSD can be scoped for surface areas and the complete geometry of the model.

The response PSD tool is preferred over the Response PSD probe since it provides more options.

4 / 47

What possible scenarios do we wish to achieve for the structure by performing Harmonic Response Analysis? Select the best option.

To make sure that the structure’s output has the same amplitude and phase as the input loading.

To avoid extracting too many modes for upstream Modal Analysis.

To make sure that the structure will not experience excessive displacements or stresses, especially at the structure’s natural frequencies where resonance may occur.

To reduce the random output behavior of the structure for a given sinusoidal input loading.

5 / 47

Which of the following statements is TRUE regarding the Mode Superposition Method for Transient Analysis? Select the best option.

It solves coupled equations directly with no assumptions.

Modal Analysis is a pre-requisite for this method.

Uses a quadratic combination of mode shapes.

Supports can be directly added to the Transient Analysis.

6 / 47

In Random Vibration Analysis, what do we mean by 'fidelity of the PSD curve'? Select the best two options.

It tells us the accuracy of the PSD curve in representing the time signal.

It tells us the accuracy of the solution results obtained from the input PSD curve.

It tells us if the solver can properly represent the input PSD curve as input.

It gives us an estimation of the time taken to solve the analysis with the given input PSD curve.

7 / 47

What is the needed input for using the Missing Mass effect in Ansys Mechanical? Select the best option.

A frequency range.

The acceleration value at zero period acceleration.

The acceleration value at peak frequency.

The frequency at zero period acceleration.

8 / 47

Which of the following statements hold true for loads — F1 and F2 as shown below? Select the two best options.

Both loads have the same phase.

Both loads have the same amplitude.

Both loads have different amplitudes.

Both loads have different phases.

9 / 47

Consider a case where a Cricket player hits the ball with a Cricket bat. The bat is thus hit by a force of a large magnitude for a very short period. Which of the following type of analysis would be the ideal choice to carry out the problem statement defined above? Select the best option.

Static Analysis

Harmonic Analysis

MSUP Transient Analysis

Full Solution Transient Analysis

10 / 47

How to resolve Grounding in Ansys Mechanical? Select the best option.

Ignore the rigid-body modes with non-zero frequencies.

Grounding cannot be removed or improved if there is contact with a non-uniform gap.

For each rigid-body mode, in the direction of the mode shape, add sufficient boundary conditions to eliminate rigid motion.

Try different contact methods to reach zero or near zero frequencies for all rigid-body modes.

11 / 47

Typically, how many modes should be included in the Modal solution of MSUP Transient, to get accurate results? Select the best option.

Sufficient modes such that the ratio of effective mass to the total mass in the direction of interest is at least 0.9.

30

Sufficient modes such that the cumulative mass fraction in the direction of interest is 1.

Sufficient modes such that the ratio of effective mass to the total mass in all coordinate directions is at least 0.9.

12 / 47

Which of the following types of damping is directly proportional to the frequency? Select the best option.

Beta Damping

Constant Damping

Rayleigh Damping

Alpha Damping

13 / 47

When analyzing the response of a structure, many closely spaced modes were observed. Thus, the user decides to go for CQC mode combination Method. Identify the options from which the value of the coupling coefficient can be calculated. Select the best option.

The program calculates the value of the coupling coefficient.

For the CQC method, the coupling coefficient is not accounted for.

The user needs to choose it arbitrarily till the desired response is obtained.

The user needs to calculate the value using the general SRSS equation of the mode combination method.

14 / 47

Consider a hypothetical situation where the given response spectrum with acceleration input, needs to be converted to a new spectrum with velocity as input. Which of the following options suits the best for operation? Select the best option.

Input values raised to 2*Pi*f.

Input values can be directly used.

Input values divided with 2*Pi*f.

Input values multiplied with 2*Pi*f.

15 / 47

Which of the following change will decrease the frequency of a structure? Select the two best options.

Increase young’s modulus of the material.

Remove material from the structure.

Add more constraints to the system.

Increase the density of the material.

16 / 47

Identify the characteristics of the SRSS (Square Root Sum of Squares) mode combination method. Select the two best options.

Suitable for closely spaced modes.

Suitable for sufficiently spaced modes.

Accounts for uncorrelated modes.

Accounts for co-related modes.

17 / 47

Consider a case of two MSUP Harmonic analyses, A1 and A2, wherein A1 has a constant damping of 3%, whereas in A2 a beta damping of 4% at 250 Hz is used. Select the two correct options based on the present case.

The frequency response output value at 200 Hz will be higher for A2 than A1.

The frequency response output value at 150 Hz will be higher for A1 than A2.

The frequency response output value at 300 Hz will be higher for A1 than A2.

The frequency response output value at 150 Hz will be higher for A2 than A1.

18 / 47

In linear perturbation analysis, the contact status can _____. Select the two best options.

NOT be changed by the user

NOT be defined as "Force Sticking" by the user

be defined as "Use True Status" by the user

be changed by the user

19 / 47

The results in a Random Vibration analysis output are _____ in nature since the input of the loads/boundary conditions is _____ in nature. Select the best option that completes the statement.

statistical, statistical

precise, precise

precise, statistical

statistical, precise

20 / 47

Which of the following statements on damping are TRUE regarding different linear dynamic analysis types? Select the two best options.

In transient analysis, numerical damping minimizes noise caused by high frequency.

Defining Damping is not necessarily important in linear dynamic analysis since it is very negligible and does not affect the accuracy of solution.

In Random Vibration Analysis, if no damping is defined, the Ansys Mechanical automatically takes a global default value of 0.01.

Response Spectrum Analysis supports constant damping but not alpha and beta damping in global level.

21 / 47

Overall Damage calculated by using Miner’s rule is equal to? Select the best option.

Damage for maximum stress level

Damage at the last cycle

Damage per cycle of the load

Sum of damage per cycle of the load

22 / 47

What can be the source of Grounding in Ansys Mechanical? Select the best option.

Nonlinear elements

Extra boundary condition in a system

Bonded contact with non-uniform gap

23 / 47

Which of the following types of input spectrum does the Missing Mass effect support? Select the best option.

All of the mentioned.

Acceleration Spectrum

Displacement spectrum

Velocity Spectrum

24 / 47

Which of the following statement is TRUE about geometric nonlinearity and mesh in pre-stressed modal analysis? Select the best option.

If base analysis uses a large deformation formulation, the modal analysis is performed using an undeformed mesh.

Undeformed mesh is used in modal analysis no matter whether the base analysis uses small deformation or large deformation formulation.

Deformed mesh is used in modal analysis no matter whether the base analysis uses small deformation or large deformation formulation.

If base analysis uses a large deformation formulation, the modal analysis is performed using a deformed mesh.

25 / 47

How would you know if you have extracted enough modes? Select the best option.

When you have extracted all the modes up to 500 Hz.

The results do not change based on the number of modes extracted.

When you have extracted the first 10 modes.

When the sum of effective mass/ total mass is greater than 0.9 for all the modes in the direction of excitation.

26 / 47

Consider a system whose operating frequency is 600 Hz. For this system, the default 6 mode shapes ranging between 0 Hz to 500 Hz frequency are extracted using a Modal analysis. Which of the following statements hold true for determining peak response for the operating frequency using mode superposition harmonic analysis? Select the best option.

Since the default 6 modes have been extracted, there is no need to extract additional modes.

Only one additional mode needs to be extracted for incorporating the operating frequency.

Since the default 6 modes have been extracted which doesn’t cover operating frequency, the harmonic analysis should be performed using Full Method.

One or more modes need to be additionally extracted such that the operating frequency falls within the range of extracted modes.

27 / 47

Which of the following methods is correct for obtaining the damping value for a given system? Select the best option.

It can be directly measured with the help of a gauge.

Default damping values are present for each material, hence the summation of them will give us the exact damping value.

Damping cannot be directly measured but can only be estimated via testing.

We can determine the precise damping value by taking a simple RMS of all the damping values of the various materials used to build the structure.

28 / 47

A structure was analyzed for modal analysis and the user needs to perform a response spectrum analysis with the given input spectrum in acceleration data. For analyzing the effects of the missing mass, what will be the input acceleration in mm/s^2 in Ansys Mechanical? Select the option closest to the obtained answer.

500

150

800

400

29 / 47

Which of the following statements are TRUE regarding the results obtained from a Random analysis? Select the best option.

Only the location of the maximum deformation is obtained, but not the shape of the deformation.

Only the deformed shape is obtained, but not the location of maximum deformation.

We only get the magnitude, but neither the deformed shape nor the location of maximum deformation is obtained.

Both the deformed shape and the location of the maximum deformation are obtained.

30 / 47

Which of the following options are NOT permitted when solving a prestressed model using the MSUP Transient method? Select the best option.

Setting Include Residual Vectors to Yes in Analysis Settings of the Transient System.

Setting Auto Time Stepping to ON in the Step Controls of the Transient System.

Setting Nodal Forces in Output Controls of Transient Analysis Settings to Yes.

Setting Modal Environment to Modal in the Definition of Initial Conditions of the Transient System.

31 / 47

In an MSUP workflow, which of the following cells are shared between the Modal Analysis and the downstream Analysis? Select the three best options.

Model cell

Solution cell

Geometry cell

Engineering data cell

32 / 47

What limitations do we need to keep in mind while using the Mode Superposition Method for Transient Analysis? Select the two best options.

Constant Time steps cannot be used.

It cannot account for structural non-linearities in the solution.

It is not an ideal method for analyzing transient vibrations of structures.

The numerical accuracy is influenced by the number of modes being used.

33 / 47

Which of the following factors does NOT influence the number of modes to be extracted from the Modal solution to get accurate results? Select the best option.

Rate of Loading

Magnitude of loading

Computational Cost

Nature of Deformation

34 / 47

Which of the below statement is TRUE about resonance for a structural under dynamic loading? Select the best option.

Resonance is one of the dynamic characteristics of a structure, which can not be altered.

Resonance should always be avoided for a structure.

Resonance should always be included for a structure.

Depending on the applications of a structure, resonance should be avoided or included.

35 / 47

Which of the following degrees of freedom responses are calculated by default in Ansys Mechanical? Select the best option.

Acceleration

Displacement

Velocity

Circular velocity

36 / 47

You have done a PSD analysis of a bridge. Your customer asked about the effect of self-weight on the PSD results. You did a static analysis under gravity and then decide to add the results. Select the best option.

Add together the 3-sigma equivalent stress and 3 times the static stress.

Just take the maximum 1-sigma equivalent stress and add the equivalent stress from static analysis.

Add the displacements from the PSD analysis and the Static analysis and recompute the stresses based on this displacement.

The static analysis results are deterministic. The PSD analysis results are statistical. They cannot be added.

37 / 47

Which of the following statement is TRUE about the deformation of base analysis and the following modal analysis? Select the best option.

The deformation of base analysis is relative values, but the deformation of the modal analysis is real values.

The deformation of base analysis is true values, but the deformation of the modal analysis is relative values.

The deformation of the base analysis and the modal analysis are all real values.

The deformation of the base analysis and the modal analysis are all relative values.

38 / 47

What is the cyclic frequency if the circular frequency is 63 rad/s? Choose the option closest to the obtained value.

15 Hz

2 Hz

5 Hz

10 Hz

39 / 47

In Random Vibration analysis, many excitation plots follow _____ distribution. Select the best option

Gaussian/Normal

Poisson

Uniform

Exponential

40 / 47

Which of the following statement is TRUE about the ROSE method? Select the two best options.

If 0 damping is defined, the ROSE method calculates a damping coefficient internally and applies it to the system.

The ROSE method has a distinct equation to calculate the coupling coefficient different from CQC.

The ROSE method always leads to a larger response compared to the SRSS method.

The ROSE method follows the same method to calculate the coupling coefficient as the CQC.

41 / 47

Response spectrum analysis is a _____ type of analysis with constant _____ and mass. Select the two best options that complete the statement.

Damping

Non-linear

Linear

Stiffness

42 / 47

In the Frequency Response Details panel, the “Use Minimum” and “Use Maximum” settings of the Spatial Resolution are based on ________. Select the best option.

All of the mentioned.

Frequency

Amplitude

Phase Angle

43 / 47

Consider an S-N curve whose last data point is located at 1e6 cycles for 60 MPa. While evaluating fatigue results for a single frequency, what value of total cycles to failure would be considered for an alternating stress value of 40 MPa, if not defined directly on the S-N curve? Select the best option.

1e8 cycles

1e4 cycles

1e32 cycles

1e6 cycles

44 / 47

The Stress-Life method assumes that fatigue failure is caused by ______. Select the best option.

Mean stress

Alternating stress

Minimum stress

Maximum stress

45 / 47

If a Modal analysis of a structure was to be performed with no constraints, the first _____ modes would be zero or near zero. Select the best option.

2

3

6

5

46 / 47

Damping can be specified in Mode-superposition harmonic analysis using ______. Select the best option.

Stiffness Coefficient

Damping Ratio

Cluster Number

Cluster Results

47 / 47

Geometric nonlinearities in a model can be introduced due to _____. Select the two best options.

the stress stiffening effect

the complex geometry

a coarse mesh

large rotation

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Linear Dynamics Using Ansys Mechanical

Total Available Time - 90 mins

Total Number of Questions - 45