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Damping.org |
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Vibration Damping Vibration is everywhere. And where there is vibration, there is damping. For most structures, damping is good, vibration is bad. Damping is a complicated subject. In simple terms, vibratory response can lead to cracked structures, defocused optics, or other types of degraded performance. Historically, the damping in a vibratory system has been intrinsic. Damping came from things like bolted joints or air friction. Today, damping is a design parameter. Take a drive in a modern luxury car. What do you hear? What do you feel? Chances are, you mostly hear the radio and other passengers. You feel the motion of the car as it accelerates around corners. You do not feel the bumps of the road or the buffeting of the wind. When an aircraft takes off, there is a lot of noise coming out of the engines. The peak sound level near the exhaust can be as high as 160 dB. There are two paths from the engine exhaust noise to the aircraft structure: one is direct, the other is reflected from the runway. Take-off is typically the highest acoustic environment the structure is exposed to. Skin panels respond to sound pressure like microphones and vibrate. They can vibrate enough to literally crack and break. The skin panels also re-radiate the sound into the interior. Vibratory energy is transmitted from the aircraft skin panels into the substructure-the stringers, frames, and bulkheads. Thus, internal equipment also gets hit with structure-borne vibratory energy at mounting brackets as well as acoustic energy on their surfaces. This can lead to equipment degradation or failure. Vibration is a large problem in Outer Space. Launch vibroacoustics create vibration levels that can break equipment. There are also many vibratory disturbances in orbit. There are always imbalances in reaction wheels, momentum wheels, and control moment gyros used for attitude control. Coolant flow, shifting solar arrays, liquid slosh, gravity gradient, and particle impact are all vibratory disturbances that can degrade the pointing performance of antennas and sensitive optics. This Web site is intended to give basic instruction in the area of modern damping design. For help with structural damping beyond the scope of this Web page, please visit www.csaengineering.com. Click HERE for a brief presentation on the Design and Application of Passive Vibration Suppression. Click HERE for some Damping Terminology. DEFINITIONS Passive Damping-Vibration Control - The structural property which reduces vibrational response to excitation and causes response to stop when the excitation is removed. Passive Damping-Noise Control - The structural property which decreases sound transmission in structures or causes a decrease in radiated sound. Viscous Damping - Damping that is proportional to velocity. Viscoelastic Passive Damping - The conversion of vibrational energy (motion) into heat by properly embedding a viscoelastic (polymeric) material into a structure. Viscous Damping Device - Viscous fluid is forced through a precision orifice. A back pressure is created from a combination of inertia and shearing of the damping fluid. Magnetic Damping - Eddy currents in a moving conductor dissipate energy. Particle Damping - Highly non-linear damping method that uses impact and friction. Below are some graphic plots that demonstrate the effectiveness of Passive Damping.
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