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S5-1 SECTION 5 DAMPING OVERVIEW. S5-2 DAMPING IN DYNAMIC ANALYSIS n n Damping is present in all...
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Transcript of S5-1 SECTION 5 DAMPING OVERVIEW. S5-2 DAMPING IN DYNAMIC ANALYSIS n n Damping is present in all...
S5-1
SECTION 5
DAMPING OVERVIEW
S5-2
DAMPING IN DYNAMIC ANALYSIS Damping is present in all oscillatory systems
Damping removes energy from a system
Possible energy dissipation via:
Heat
Sound waves
Fluid motion
Resulting effect:
Free Vibration gives decay in amplitude
Mechanisms include:
Internal Molecular friction - raw material (structural damping)
Sliding Friction - joints, plies
Fluid Resistance - dampers, air or water environment (viscous damping)
S5-3
DAMPING IN DYNAMIC ANALYSIS (Cont.) What levels of damping should I use?
There is no one good answer to this question!
For a particular structural configuration and material look at:
Test results
Industry standards
Company experience
Remember in General lowest levels of damping are most conservative:
Use a range of damping values in presenting results
Peak response is difficult to capture
Typical values (NOT TO BE QUOTED!):
NC machined components – 2% to 5% critical
Fabricated metal components – 4% to 10% critical
Composites – 6% to 20% critical
S5-4
Damping Model – Discrete Dashpots
S5-5
Damping Model – Viscous Material Damping
S5-6
Damping Model – Modal Damping
S5-7
Damping Model – Modal Damping
Damping in Modal transient Analysis
Direct Damping
• Allows definition of damping as a fraction of critical damping.
• Typical value is between 1% and 10% of the critical damping.
• The same damping values is applied to different modes.
S5-8
Damping Model – Rayleigh Damping
S5-9
Damping Model – Rayleigh DampingHarmonic Response
S5-10
Damping Model – Rayleigh DampingHarmonic Response
S5-11
Damping Model – Structural Damping
Part of this energy dissipation is caused by internal friction in the material.
S5-12
Damping Model – Structural DampingHarmonic Response
S5-13
Damping Model – Structural DampingHarmonic Response
S5-14
Damping Model – Structural DampingHarmonic Response
S5-15
Damping Model – Numerical DampingTransient Response