# Vibration Damping

Vibration damping is the dissipation of energy in a system, either through time or distance. Damping will reduce the vibration amplitude. Hence reducing the radiated sound or reducing the vibration and hence improving the tactile quality.

The term is generally applied to the vibration of a structure owing to the internal dissipative properties of the structure. However, damping can also be applied to acoustic waves in the form of fibrous sound absorbing material.

In a vehicle we use shock absorbers or dampers. In simple terms these consist of a piston that fits poorly in a cylinder full of oil. The movement of the piston is inhibited by the oil. At low speed the motion is not really inhibited, but at high speed this motion is turned into heat in the oil.

Shock Absorber

Characteristic Equation – the mathematical equation whose solution defines the dynamic characteristics of the structure in terms of its natural frequencies, damping, and mode shapes. The mathematical formulation of the characteristic equation is called the Eigenvalue problem. The characteristic equation is obtained from the equations of motion for the structure.

Constrained-layer damper – a treatment to control the vibration of a structure by bonding a layer of damping material between the structure’s surface and an additional elastic layer (that is, the constraining layer), whose relative stiffness is greater than that of the damping material, so that energy is dissipated through cyclic deformation of the damping material, primarily in shear.

Damping Factor – the ratio of actual damping in a system to its critical damping.

Damping Pad – material applied to add damping to another material to reduce structural vibrations. This layer may be constrained or unconstrained.

Eigenvalue Problem – the mathematical formulation and solution of the characteristic equation is called the Eigenvalue problem.

Free-layer damper – a treatment to control the vibration of a structural by bonding a layer of damping material to the structure’s surface so that energy is dissipated through cyclic deformation of the damping material, primarily in tension-compression.

Glassy region of a damping material – a temperature region where a damping material is characterized by a relatively high modulus and a loss factor that increases from extremely low to moderate as temperature increases.

Nonlinear Damping – damping due to a damping force that is not proportional to velocity.

Rubbery region of a damping material – a temperature region where a damping material is characterized by a relatively low modulus and a loss factor that decreases from moderate to low as temperature increases.

Transition region of a damping material – a temperature region between the glassy region and the rubbery region where a damping material is characterized by the loss factor passing through a maximum and the modulus rapidly decreasing as temperature increases.

Viscous Damping – viscous damping is the dissipation of energy that occurs when a particle in a vibrating system is resisted by a force proportional to the velocity of the particle particle and direction opposite to the direction of the particle.

Viscous damping is used largely for system modeling since it is linear.