S5-1 SECTION 5 DAMPING OVERVIEW

S5-2 DAMPING IN DYNAMIC ANALYSIS n n Damping is present in all oscillatory systems n n Damping removes energy from a system n n Possible energy dissipation via: u u Heat u u Sound waves u u Fluid motion n n Resulting effect: u u Free Vibration gives decay in amplitude n n Mechanisms include: u u Internal Molecular friction - raw material (structural damping) u u Sliding Friction - joints, plies u u Fluid Resistance - dampers, air or water environment (viscous damping)

S5-3 DAMPING IN DYNAMIC ANALYSIS (Cont.) n n What levels of damping should I use? n n There is no one good answer to this question! n n For a particular structural configuration and material look at: u u Test results u u Industry standards u u Company experience n n Remember in General lowest levels of damping are most conservative: u u Use a range of damping values in presenting results u u Peak response is difficult to capture n n Typical values (NOT TO BE QUOTED!): u u NC machined components – 2% to 5% critical u u Fabricated metal components – 4% to 10% critical u u 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 n 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 Damping Harmonic Response

S5-10 Damping Model – Rayleigh Damping Harmonic Response

S5-11 Damping Model – Structural Damping n Part of this energy dissipation is caused by internal friction in the material.

S5-12 Damping Model – Structural Damping Harmonic Response

S5-13 Damping Model – Structural Damping Harmonic Response

S5-14 Damping Model – Structural Damping Harmonic Response

S5-15 Damping Model – Numerical Damping Transient Response