PPT PRESENTATION ON COULOMB DAMPING AND VISCOUS DAMPING

PPT PRESENTATION ON
COULOMB DAMPING AND VISCOUS DAMPING

1. PPT PRESENTATION ON COULOMB DAMPING AND VISCOUS DAMPING SRINIVAS REDDY . S

2. DAMPING It is the resistance to the motion of vibrating body These are of 2 types 1 Coulomb damping 2 Viscous damping

3. Coulomb damping is a type of constant mechanical damping in which energy is absorbed via sliding friction. The friction generated when a body is allowed to slide over the another body surface , The surface of the body offers some resistance to the movement of the other body. This resistance force is called as force of friction or dry force. In general, damping is the dissipation of energy from a vibrating system where the kinetic energy is converted into heat by the friction. COULOMB DAMPING

4. Modes of Coulomb damping Coulomb damping absorbs energy with friction, which converts that kinetic energy into thermal energy or heat. The Coulomb friction law is associated with two aspects. Static and kinetic frictions occur in a vibrating system undergoing Coulomb damping Static friction  occurs when the two objects are stationary or undergoing no relative motion . For static friction, the friction force  F  exerted between the surfaces having no relative motion cannot exceed a value that is proportional to the product of the normal force  R  and the coefficient of static friction  μ s : F s = µ s R Where F s = frictional force µ s = coefficient of static friction R= normal force

5. Modes of Coulomb damping Kinetic friction  occurs when the two objects are undergoing relative motion and they are sliding against each other. The friction force  F  exerted between the moving surfaces is equal to a value that is proportional to the product of the normal force  R  and the coefficient of kinetic friction  μ k : F k = µ k R Where F k = frictional force µ k = coefficient of kinetic friction R= normal force In both of these cases, the frictional force (F) always opposes the direction of motion of the object. The normal force (R) is perpendicular to the direction of motion of the object and equal to the weight of the object sliding.

6. Newton's Second Law states that the equation of motion of the block is  m {x’’} = -kx-F or m{x}=- kx’+F   depending on the direction of motion of the block. In this equation {x} is the acceleration of the block and {x’} is the position of the block. A real-life example of Coulomb damping occurs in large structures with non-welded joints such as airplane wings.

7. VISCOUS DAMPING Viscous damping is the dissipation of energy that occurs when a particle in a vibrating system is resisted by a force the magnitude of which is a constant, independent of displacement and velocity, and the direction of which is opposite to the direction of the velocity of the particle. Viscous damping is caused by such energy losses as occur in liquid lubrication between moving parts These can be applied for liquids as well as solids Liquids observes the energy so energy dissipates Example : 2 plates with oil in between

8. Viscous Damping Viscous damping force is a formulation of the damping phenomena, in which the source of damping force is modeled as a function of the volume, shape, and velocity of an object traversing through a real fluid with viscosity. Typical examples of viscous damping in mechanical systems include: Fluid films between surfaces Fluid flow around a piston in a cylinder Fluid flow through an orifice Fluid flow within a journal bearing

9. S.NO Viscous damping Coulomb damping 1 In case of viscous damping, the ratio of 2 successive amplitudes was constant and envelope of maxims of displacement time curve was exponential curve. In case of coulomb damping, the difference between any 2 successive amplitudes is constant and envelope of maxims of displacement time curve was straight line. 2 In viscous damping, the system once disturbed from mean equilibrium position then finally it comes to rest in equilibrium position only and theoretically it takes  ∞∞  time. In coulomb damping, the body may finally come to rest in equilibrium or in displaced position depending upon the initial amplitude and amount of friction present. 3 Damping force is proportional to the velocity. Coulomb's damping force is independent of velocity but depends on the co efficient of friction. 4 In viscous under damping system mass oscillates about the same mean position.  Mean position about which mass oscillates varies with each half cycle. 5 Applied for both liquids and solids Applied only for solids 6 Liquid observes energy so energy dissipation takes place Energy dissipates because of friction between 2 solid surfaces

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