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WorksheetsMEAVS - English
Total questions: 12
Worksheet time: 16mins
Let us consider a beam in bending vibration. At x=0, the beam is clamped. At x=L, a spring is fixed to the beam in transversal direction.
What could be the shape of the first mode shape of the beam is stiffness K of the spring tends to infinity ?
Let us consider a beam with a rectangular cross-section (h>b). We distinguish bending vibration in plane (0xy) and the one in plane (0xz).
The natural frequencies of mode shapes in plane (0xy)...
...are higher than those in plane (0xz).
...are identical to those in plane (0xz).
...are lower than those in plane (0xz).
Which sentences are true when considering the direct method for computation of a frequency response using Finite Element Method?
It is faster than modal summation method
It allows taking into account frequency dependent parameters (as Young's modulus, damping...)
It is necessary to assume a proportional damping (Rayleigh damping) so that the system of equations becomes diagonal.
The quality of the result depends on the number of modes used in the computation (modal truncation)
What is mandatory to determine the natural frequencies and mode shapes of a structure?
Equation of motion
Boundary Conditions
Initial Conditions
External force distribution applied on the structure
The direction of propagation of waves in the medium
Let us consider a 3D space. A structure is coupled to a fixed frame with a ball joint (without friction). How many rigid body modes appear when computing the modal basis of the structure?
0
1
3
6
How many natural frequencies can be seen in this phase plot of a transfer function?
None, one has to look at the amplitude rather than phase
4
7
An infinity
The Experimental Modal Analysis (EMA) allows determining...
...modal damping
...mode shapes
...natural frequencies
...material properties
What are the effects of damping on vibration of a structure?
It decreases the vibration level at every frequency.
It dissipates a part of the power injected in the structure by the external force distribution.
It shifts the natural frequencies of the structure.
It avoids resonance problems.
What are the possible reasons a system is nonlinear?
The material itself is nonlinear.
The presence of gap, bolting, coupling joint.
The presence of friction or contact.
The presence of large amplitude vibration
Which displacement field exhibits the smallest wavelength?
Some piano strings are spun with copper wires. The interest is to...
...increase the stiffness of the string to increase its natural frequencies.
...increase the stiffness of the string to decrease its natural frequencies.
...increase the mass of the string to increase its natural frequencies.
...increase the mass of the string to decrease its natural frequencies.
What are the conditions for having a resonance problem?
The excitation frequency has to match all the natural frequencies of the structure.
The structure must be excited by an impact hammer.
The excitation frequency has to match at least one of the natural frequencies of the structure.
The applied force distribution has to have a non negligible spatial coincidence with one of the mode shapes of the structure.
The modal mass has to be equal to the modal stiffness.
