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analisis modal en midas nfx
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Modal Analysis
Modal Analysis 2
Step
00 Modal Analysis
Modal Analysis Summary
The presence of resonance and displacement caused by the vibration of a structure are predicted using Modal Analysis.
Through the analysis, the dynamic characteristics such as natural frequencies and mode shapes of the structure are
determined.
Important Terminology
Natural Frequency and Natural Period
• Natural Frequency: The number of times a structure oscillates (moves back and forth) in a unit time (Hz)
• Natural Period: The reciprocal of the Frequency (1/f), which represents the time required to oscillate one full cycle (sec)
• Natural Mode Shape: The shape of a vibrating structure at the state of removed external force. The lowest mode represents the most easily
deformable shape.
• Resonance occurs when the frequency of the oscillation applied to the structure is close to the natural frequency of vibration.
1st mode 2nd mode 3rd mode
• Natural mode shapes of a cantilever
A.
B.
• Although the amplitudes of A and B are different, their frequencies
and periods are the same.
• The frequency and period depend on the length.
• The number of full cycles of motion of the pendulum in one second
is referred to as natural frequency, and the time required to
complete one full cycle of motion is referred to as natural period.
• The natural frequency of a structure is directly proportional to its
stiffness and inversely proportional to its mass. If a concentrated
mass is located farther away from the boundary of the structure, a
decrease in the natural frequency will result due to the inertia effect. <Pendulums having
different amplitudes>
Modal Analysis 3
Step
00 Free Vibration
Overview of Modal Analysis
• Without any external forces acting on the structure, the structure vibrates due to its inertia force, damping and restoring forces.
Thus, the structure vibrates with a natural frequency and is not subjected to any external effects.
• Although the structure is not subjected to any load, free vibration takes place because of a non-zero initial condition.
Static
equilibrium Initial
condition
Free
vibration
Initial
displacement: A
Free vibration
Time
Period : T
Modal Analysis 4
Step
• Number of Modes:
Input the number of natural frequencies to be calculated.
• Lowest/Highest Values:
Set the range of frequencies.
The frequencies are calculated only within the range.
• Sturm Sequence Check:
Calculate the missing eigenvalues through an iterative process.
• Total Mass Calculation:
Calculate the properties corresponding to the nodal mass.
The properties include total mass, center of gravity and mass inertia moment.
• Global Mass Scaling Factor:
The parameter is used when the material density is defined by the weight instead of the mass.
The mass density is calculated by the following:
• Coupled Mass Calculation:
If this option is checked on, a distributed mass matrix is calculated instead of a general mass matrix.
It represents the values of coupled masses.
wmg )
1(
00 Overview of Modal Analysis
Modal Analysis Options
Modal 5
Step
Modal
Summary
Summary 00 Modal Analysis
- Unit: N, mm
- Geometrical Model: Modal.x_t
Material
- Cast Alloy Steel
Boundary and Load Condition
- Fixed (Holes inner part)
Results Verification
- Displacements
- Eigenvalues
- Modes Shapes
Modal 6
Step
00 Analysis Summary
Use Midas NFX (Designer) to perform the basic Modal Analysis and understand the features
- Understanding the purpose of Modal Analysis
Modal analysis is performed for the design verification of parts subjected to vibrations and periodic loads.
The analysis calculates the resonance frequency and evaluates the mode shapes of a constrained structure.
Therefore, the natural frequency determined through the analysis can be used so as not to approach the operational frequency or to coincide with the operational
frequency in certain cases (ex: ultra sonic welding)
Objectives of Tutorial
Analysis Summary
Target Model Boundary Condition (Fixed) Finite Elements Model (Tetra Mesher)
Fixed
The boundary conditions are not absolutely
required for modal analysis, but any existing
constraints must be reflected into the boundary
conditions. If the model is not fully constrained, the
Rigid Body Mode will appear (frequency near zero).
Modal 7
Step
00 Analysis Summary
Important Terminology
(Circular Frequency, ) Number of revolutions in one second
(Period, T) Time required to vibrate one full cycle (inverse of frequency)
(Frequency, f) Number of full cycles of vibration in a unit time
(Resonance) It occurs when the frequency of external forcing vibration coincides with the natural frequency of a structure or
machine.
(Mode Shape)
Mode shapes represent the shape components of free vibration of a structure without being subjected to any
external load. The most easily deformable shape component is the first mode. The higher the mode, the lesser
the contribution toward the deformation of the structure due to the corresponding mode.
Free Vibration
Time
Period: T
θ
ω t
A
m
k
Tf n
2
1
2
1
Modal 8
Step
Procedure
Model & LBC > Geometry > Import
5
3
01 Click [ ] (New).
Click [Geometry] - [Import].
Model: Select Modal.x_t.
Check [Search Contact Faces].
Click [Open].
Note: Tutorial models are included
in the folder, Manuals / Tutorials /
Files, in the installed program
folder.
1
2
3
4
Click [New], then all the menus will be
activated.
If the option [Search Contact Faces]
is checked on when importing the
CAD model, all the faces in contact
will be automatically defined as
welded contacts.
5
4
Check File type and Length Unit
1
2
Modal 9
Step
Procedure
Model & LBC > Geometry > Material 02 Click [Geometry] - [Material].
In the Material Library, select the
Group Steel.
Select Cast Alloy Steel.
Click [OK].
1
2
4
2 3 1
3
4
Modal 10
Step
Procedure
Model & LBC > Geometry > Material (Material-Cast Alloy Steel) 03 After selecting the model in the work
window, right-click Geometry.
Select [Material] > [Cast Alloy Steel]
1
2 1
2
Right-click each part under Geometry
to assign them with different materials.
To assign the same material on all the
parts, simply right-click Geometry and
select the material.
Modal 11
Step
Procedure
Model & LBC > Boundary > Support 04 Click [Boundary] - [Support].
Name: Enter Fix.
Target: Select 4 Planes.
(Refer To picture).
Condition: Select Fixed.
Click [OK].
1
2
3
4
3
3
5
2
4
5
1
Modal 12
Step
Procedure
Model & LBC > Mesh > Auto Mesh 05 Click [Mesh] - [Auto Mesh].
Select the entire model as the target.
Select High Speed Tetra Mesher.
Click [Option] button.
Verify that High-Order Element is
checked on.
Click [OK].
1
2
3
2
3
6
Click [ ] (Select All) Icon to select
the total model displayed on the work
window.
4
4
5
6
5
1
2
Modal 13
Step
Procedure
Analysis & Results > Analysis Case > General 06 Click [Analysis Case] - [General].
Name: Enter “Modal”.
Analysis type: Select [Modal].
Click [OK].
1
2
3
2
3
1
Modal 14
Step
Procedure
Analysis & Results > Analysis > Perform 07 Click [Analysis] - [Perform].
Click [OK].
Save As:
Enter “Modal”.
Click [Save(S)].
1
2
3
4
Once midas NFX is executed, the
solver becomes engaged. Click “Stop
Execution!” to interrupt the calculation.
1
2
3
4
Modal 15
Step
Procedure
Analysis & Results Works Tree > Modal > Modal Analysis > MODE 1 08 Click [ ] (Isometric2) Icon.
Select Deform > Deform+Undeform
(Transparent).
In the Analysis & Results Works
Tree, double-click
MODE 1, TOTAL DISPLACEMENT.
1
2
3
1
2
Natural Frequency
of Mode 1
The total displacements from the
results of modal analysis do not
represent “real” values. Therefore,
ignore the total displacements, and
check only the natural frequencies
and the modal shapes.
3
Modal 16
Step
Procedure
09 In the Analysis & Results Works
Tree, double-click
MODE 3, TOTAL DISPLACEMENT.
1
Analysis & Results Works Tree > Modal > Modal Analysis > MODE 3
Natural Frequency
of Mode 3
1
Modal 17
Step
Modal
Summary
Summary 00 Modal Analysis
- Unit: N, mm
- Geometrical Model:
Hanger.x_t
Boundary Condition
- Pinned
Results Verification
- Mode Analysis Results
- Mode Shapes
- Natural frequencies
Modal 18
Step
00 Analysis Summary
Understanding the basics of Modal Analysis
- Define the basically required conditions for performing modal analysis (Material-Mass density, Boundary Condition)
- Define the number of modes in Analysis Case – General - Analysis Control option.
- In order to avoid resonance of a structure to which a vibrating part is attached, modal analysis is performed to check the natural frequencies and mode shapes.
Objectives of Tutorial
Analysis Summary
Target Model Boundary Condition (Pinned) Finite Elements Model (Tetra Mesher)
Modal 19
Step
Procedure
Model & LBC > Geometry > Import 01 Click [ ] (New)
Click [Geometry] - [Import].
Model: Select Hanger.x_t.
Click [Open].
Note: Tutorial models are included in
the folder, Manuals / Tutorials / Files,
in the installed program folder.
1
2
3
4
Click [New], then all the menus will be
activated.
4
3
Check File type and Length Unit
1
2
Modal 20
Step
Procedure
Model & LBC > Geometry > Simplify
1
02 Click [Geometry] – [Simplify]
Target: Select the total Model.
Fillet (Radius): Enter “1”.
Click [Find].
Click [Select All].
Click [Remove].
Click [Close].
1
2
3
4
5
6
Delete holes and fillets unnecessary
for analysis.
Upon entering values and clicking
[Find], all the fillets/holes to be
deleted will be displayed by colors.
7
2
3
4
5 6 7
Modal 21
Step
Procedure
Model & LBC > Geometry > Material 03 Click [Geometry] - [Material].
ID: “2”, Name: Enter “Steel”.
Elastic Modulus: Enter “2.1e5”.
Poisson's Ration: Enter “0.3”.
Mass Density: Enter “7.9e-6”.
Click [OK].
1
2
3
“Mass Density” must be specified to
perform Modal Analysis.
4
2 2
3
4
1
Modal 22
Step
Procedure
Model & LBC > Geometry > Material (Material Assignment) 04 After selecting the model in the work
window, right-click the mouse.
Select [Material] > [Steel].
1
1
2
2
Modal 23
Step
Procedure
Model & LBC > Boundary > Support 05 Click [Boundary] - [Support].
Name: Enter “Support”.
Target: Select the 8 surfaces.
(Refer to Picture)
Condition: Select [Pinned].
Click [OK].
1
2
3
4
1
5
2
3
4
5
3
Select the 8 cylindrical surfaces of the
two holes.
Modal 24
Step
Procedure
Model & LBC > Mesh > Auto Mesh
3
06 Click [Mesh] - [Auto Mesh].
Target: Select the total Model. (Refer
to Picture)
Click [OK].
1
2
3
2
1
Modal 25
Step
Procedure
Analysis and Results > Analysis Case > General 07 Click [Analysis Case] – [General].
Name: Enter “Hanger”.
Analysis Type: Select [Modal].
1
2
2
1
Modal 26
Step
Procedure
Analysis & Results > Analysis > Modeling 08 Click [ ] (Analysis Control) Icon.
In the [Analysis Control] window,
open the tab [Eigenvalue] and in
Eigenvectors > Number of Modes:
Enter “20”.
Click [OK].
Click [OK].
1
2
3
4
2 1
3
4
Number of modes: Entering “20” will
automatically calculate the modes
from 1 to 20.
Modal 27
Step
Procedure
Analysis & Results > Analysis > Perform 09 Click [Analysis] - [Perform].
Click [OK].
Save As: Enter “Hanger”.
Click [Save(S)].
1
2
3
4
2
3
4
1
Once midas NFX ix executed, the
solver becomes engaged. Click
“Stop Execution!” to interrupt the
calculation.
Modal 28
Step
Procedure
Analysis & Results Works Tree > Hanger > Modal Analysis > MODE 1 10 Click [ ] (Isometric1) Icon.
Select Deform> Deform+Undeform
(Transparent).
In the Analysis & Results Works
Tree, double-click
MODE 1, TOTAL DISPLACEMENTS.
1
2
1
2
3 3
Natural Frequency
of Mode 1
The total displacements from the
results of modal analysis do not
represent “real” values. Therefore,
ignore the total displacements,
and check only the natural
frequencies and the modal
shapes.
Modal 29
Step
Procedure
Analysis & Results Works Tree > Hanger > Modal Analysis > MODE 3 11 In the Analysis & Results Works
Tree, double-click
MODE 3, TOTAL DISPLACEMENTS.
1
Natural Frequency
of Mode 3
1