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 μs:
Fs = µsR
Where
Fs = frictional force
µs = 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 μk:
Fk = µkR
Where
Fk = frictional force
µk = 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

10. THANKYOU