203219018 - OFFSHORE STRUCTURES by taraka rama Kalyan

WAVE

tksatuluri29 — 2020-05-21 06:44:13 UTC

They usually occur on the free surface of a water body.

GENERATION OF WAVES

tksatuluri29 — 2020-05-21 06:54:03 UTC

They are generated due to:
1)Wind action
2)Gravitational pull of sun and moon
3)Catastrophic events

WIND MOVEMENT

tksatuluri29 — 2020-05-21 06:55:54 UTC

Wind deflection due to pressure gradient and Coriollis force.

BEAUFORT SCALE

tksatuluri29 — 2020-05-21 07:02:46 UTC

Gives the type of wind and its velocity.
Ranges from 1 to 17.

CYCLONES

tksatuluri29 — 2020-05-21 07:08:12 UTC

Intensity of cyclone is defined by the distance from its eye to he periphery.
Cyclones caused due to:
1)Temperature difference are called tropical cyclones.
2)pressure difference are called extratropical cyclones.

WIND VELOCITY

tksatuluri29 — 2020-05-21 07:38:08 UTC

Given by various scientists.

INTERACTION OF WIND WITH OCEAN

tksatuluri29 — 2020-05-21 07:42:13 UTC

Due to wind system and earth rotation.

COMPONENTS OF STORM SURGES

tksatuluri29 — 2020-05-21 07:45:52 UTC

These are the components.

ABOUT WAVES

tksatuluri29 — 2020-05-21 07:52:13 UTC

Fetch is the are of zone over which the wind blows.
Beyond the fetch,the continued waves are called swell waves.(type of spilling breaking)
Surfing is a type of plunging breaking.

CLASSIFICATION OF WAVES

tksatuluri29 — 2020-05-21 08:11:15 UTC

Waves are classified as follows.

WAVE PROFILE

tksatuluri29 — 2020-05-21 08:21:38 UTC

This is wave profile, where:
H - Wave height
T - Wave period

L - Wave length
These 3 are the fundamental components of wave.

η - Wave surface elevation
h - Water depth
a - Wave amplitude
C - Celerity
u,w - water particle orbital velocities in x and z directions.

VELOCITY POTENTIAL AND DISPERSION EQUATIONS

tksatuluri29 — 2020-05-21 10:22:51 UTC

We use equations and relations among velocity potential and other parameters for finding out the required characterstics of the wave.
We use the velocity, laplace and bernoulis equation to get the final amplitude formula.
We obtain dispersion relation to have a relation between wavelength,wave period and water depth.
φ - Velocity potential
σ - Wave angular frequency
k - Wave number

OCEAN WAVES ACCORDING TO WATER DEPTH

tksatuluri29 — 2020-05-21 10:51:29 UTC

According to d/L ratio,ocean waves are classified.

CELERITY AT DIFFERENT WATER DEPTHS

tksatuluri29 — 2020-05-21 10:55:15 UTC

The relation between d/L and d/L_o is obtained form the graph.
where L_o - wavelength in deep waters.

PARTICLE ORBITAL DISPLACEMENT, VELOCITY AND ACCELERATION

tksatuluri29 — 2020-05-21 11:08:58 UTC

The following expressions give the particle orbital displacement,velocity and accelerations for the given progressive sine wave.
where,
D - Semi major axis
B - Semi minor axis

DISPLACEMENTS UNDER VARIOUS DEPTHS

tksatuluri29 — 2020-05-21 11:27:39 UTC

For shallow waters,the particles take elliptical shape.
For deep waters,the particles take circular shape.

GROUP CELERITY

tksatuluri29 — 2020-05-21 11:35:19 UTC

When group of waves travel, the velocity of the group is not the direct superimposition of velocities of individual waves.
This group velocity is called group celerity.
C_G - Group celerity

MASS TRANSPORT VELOCITY

tksatuluri29 — 2020-05-21 12:08:44 UTC

When waves are in motion, the particles upon completion of each nearly an elliptical or circular motion would have advanced a short distance in the direction of propagation.
Consequently there is a mass transport in the direction of progress of the wave.
The mass transport velocity at any depth z below S.W.L is given.

WAVE TRANSFORMATIONS

tksatuluri29 — 2020-05-21 12:14:50 UTC

When a crest line approches the coast it will slowly be changing its angle parallel to the shore.
This process is called wave refraction.
Diffraction is the process that occurs when the moving water encounters a break water.
The diffracted water will move into the shadow region from the light region.
The water which directly hits the breakwater reflects back.

WAVE ENERGY

tksatuluri29 — 2020-05-21 12:39:25 UTC

Total energy is sum of potential and kinetic energy

WAVE THEORIES

tksatuluri29 — 2020-05-21 12:45:38 UTC

They are classified as:
1)Small amplitude waves - Airy's wave theory
2)Finite amplitude waves :
- Stokes theory : d/L > 0.1
- Cnoidal theory: d/L € (0.02,0.1)
- Solitary theory: d/L < 0.02
Waves are classified according to this dimensionless number.
Solitary waves are no periodic with no definite wavelength.

CLASSIFICATION OF WAVE LOADS

tksatuluri29 — 2020-05-21 12:48:46 UTC

Loads on off-shore structures can be mainly classified into two categories.
1)Functional loads - all static and dynamic loads during installation.
2)Environmental loads - wind,wave currents,ice etc.
The force regimes are given.

DESIGN WAVE APPROACH

tksatuluri29 — 2020-05-21 13:01:19 UTC

100 year wave is taken as the design wave for survival condition.
The wave forces on the submerged member are determined using Morison's equation.
This equation is applicable for D/L<0.2 only.
The total force in such case is the sum of particle orbital velocity dependent drag force and particle acceleration dependent inertial force.

MORISON'S EQUATION

tksatuluri29 — 2020-05-21 13:09:54 UTC

The concept involved is the water particle moving with a velocity carries a momentum.
The value of the total force on cylinder, overturning moment and θ_max are obtained.

KEULEGAN AND CARPENTER(KC) NUMBER

tksatuluri29 — 2020-05-21 13:21:43 UTC

Keulegan and Carpenter studied the forces of sinusoidally oscillating 2 dimensional flow.
They found that C_D and C_Mwere smoothly varying functions of a non dimensional parameter called KC number.

WAVE DECAY

tksatuluri29 — 2020-05-22 02:36:48 UTC

As the waves enters the coastal region, the wave which was symmetric in deep waters becomes unsymmetric and tries to break.
This is called breaking of wave or wave decay.
The limited conditions for the wave to break are given.
1) H/L > 0.142 * tanh(k*d)
2)Wave height greater than 0.178
3)Wave crest angle less than 120^o