Example50 Harmonic Analysis of A Tower with Mechanical Loss

General

  • A tower which has certain mechanical loss is forced to oscillate.
     

  • The relation between the oscillation amplitude and the mechanical loss is examined.
     

  • Unless specified in the list below, the default conditions will be applied.
     

 

Analysis Space

Item

Settings

Analysis Space

3D

Model unit

m

 

Analysis Conditions

The analysis type is harmonic analysis.

Item

Settings

Solvers

Mechanical Stress Analysis [Galileo]

Analysis Type

Harmonic analysis

The harmonics analysis tab is set up as follows.

Item

Settings

Sweep Type

Linear step by frequency

Setting

Minimum frequency : 0.8[Hz]

Maximum frequency : 1.0[Hz]

interval : 0.01[Hz]

Model

The forced oscillations are applied on the bottom of the tower. The applied amplitude is set to 0.1[m] on the bottom as boundary condition.

Body Attributes and Materials

Body Number/Type

Body Attribute Name

Material Name

0/Solid

Tower

002_Polycarbonate(PC) *

* Available in Material DB. However the mechanical loss tanδ is set to 0.1 without any bases.

Boundary Conditions

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

Move/Face

Mechanical

Displacement

Select all X/Y/Z components.

UX=0.1, UY=0, UZ=0 [m]

Results

If the loss is considered, the displacement might not be the maximum at the phase 0° due to the phase shift. To prevent it, [Absolute] is selected to show the maximum displacement.

 

 

The relation between the displacement amplitude at the top of the tower and the oscillation frequency is shown in the following graph.

Three curves shown in this graph are obtained by different tanδ values (0.05, 0.1, 0.2).

 

 

When smaller tanδ value is set, the shape of the curve becomes steeper.

 

The displacement shown below is when 0.88[Hz] oscillation is applied. The tanδ value is set to 0.1.

While the amplitude applied on the bottom of the tower is 0.1[m], the amplitude of the generated oscillation is 2.2[m] at the top of the tower.

 

 

(Note) Resonant analysis is available by changing the analysis type to resonant analysis. In this case, however, the displacement setting (0.1[m]) on the bottom of the tower will be ignored. (In resonant analyses, oscillation amplitude can not be specified.)