Home / Examples / Stress Analysis [Galileo] / Example 75: Transient Analysis of Standing Bars

Example 75: Transient Analysis of Standing Bars

General

Forced oscillation is applied to two standing bars with different heights. Perform a transient analysis of the standing bars.
Refer to Example 16: Harmonic Analysis of Standing Bars for the result of the harmonic analysis.
It is observed that the frequency of the forced oscillation affects the vibration.
Unless specified in the list below, the default conditions will be applied.
The oscillation amplitude near the resonant frequency depends on the mechanical loss of material. Adjust the mechanical loss if needed. (See Example 50)
Obtain this session's project file. (Right-click and choose 'Save link as')
Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

The analysis type is the transient analysis.

Item	Settings
Solver	Stress Analysis [Galileo]
Analysis Type	Transient Analysis
Analysis Options	None

The resonant frequencies of each tower are 1250 [Hz] and 1650 [Hz], which have been acquired in the harmonic analysis in advance.

The bars vibrated at 1250 [Hz] are analyzed here.

The transient analysis is set on the transient analysis tab as follows.

By selecting [Automatic] for the timestep and [Adjust referring to time-dependent condition] in the detailed automatic timestep setting, the timestep for analysis can be set based on the specified boundary conditions.

When the waveform is defined using the [Input Waveform] function in a boundary condition, one-tenth of a period of the waveform is applied as the timestep.

Tab	Setting Item	Settings
Transient Analysis	Timestep	Automatic
	Finish Time	10 [ms]
	Maximum Number of Calculation Steps	1000
	Detailed Automatic Timestep Setting	Select [Adjust referring to time-dependent condition]

Model

Two bars (TOWER) with different heights are standing on a plate (GROUND).

internal ports. The amplitude of forced vibration is applied to the Y-direction displacement boundary condition (VIBE_Y) on the face topology of the bottom face of GROUND.

Body Attribute and Material Property Setting

Body Number/Type	Body Attribute Name	Material Name
0/Solid	TOWER	001_Al *
1/Solid	TOWER	001_Al *
2/Solid	GROUND	001_Al *

* Available from the material DB

Boundary Conditions

The forced vibration involves the vibration of the bottom face, GROUND, in the Y direction and the concurrently fixed displacement in the X and Z directions.
For it, the following boundary conditions are set.

The setting below means the vibration having an amplitude of 1 [mm] in the Y direction is applied to the bottom face, GROUND.

It is conditioned to vibrate five times and then stop.

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

VIBE_Y/Face

Mechanical

Displacement

Select all X/Y/Z components.

UX=UX=0.0, UY=1×10-3 [m]

Select [Time Dependency]

Weight Function

Input using [Input Waveform]

Item	Settings
Select waveform	Sine Wave
Frequency/Period	Frequency
Magnitude (Weight）	P-P Amplitude 1 Offset 0
Wavenumber	Select [Set wavenumber] Wavenumber 5
Frequency	1250 [Hz]

Results

The displacement diagrams below show the displacement at 1.6 [ms], 4 [ms], and 10 [ms], respectively.

The contour diagrams show the displacement in the Y direction.

1.6 [mm] (At 2 Cycles)

4 [mm] (At 5 Cycles)

10 [ms] (Finish Time of Calculation)

The right tower is vibrating more.

The temporal change in Y-displacement at the tip point (0, 30, 80) of the right tower is plotted.

It is observed that the amplitude of the tower vibration increases while the forced vibration is applied up to 4 [ms]. After 4 [ms], the forced vibration ends and the amplitude remains constant.