Design of Offshore Structures Padlet by Praveen(203219008) by praveen kumar

WAVE THEORIES:

princepraveen000 — 2020-05-21 15:16:26 UTC

WAVE:
Wave is generated due to
1. Wind
2. Gravitational forces of sun,moon
3.Catastrophic events like earthquakes
The above factors are without considering earth's rotation.

When we are considering rotation of earth, two factors are present:
1. Pressure Gradient
2. Coriolis Effect

BEAUFORT SCALE:

princepraveen000 — 2020-05-21 15:16:26 UTC

It gives a description about wind in terms of strength and numbered from 0 to 17.

CYCLONE:

princepraveen000 — 2020-05-21 15:41:21 UTC

There are two types of cyclone
1. Due to temperature gradient i.e.,Tropical cyclone.
2. Due to pressure gardient i.e, Extra tropical cyclone.

OCEAN WAVES AND THEIR CLASSIFICATION:

princepraveen000 — 2020-05-21 15:42:27 UTC

A variety of waves ranging fromripples monster waves are generated and are classified based on their wave period.

WIND VELOCITY FOR OPEN SEA CONDITION:

princepraveen000 — 2020-05-21 15:43:06 UTC

This profile is given by Sheppard, Wind velocities varies from maximum at higher elevations to minimum as it reaches the ocean surface.

INTERACTION OF WIND WITH OCEAN WATER MASS:

princepraveen000 — 2020-05-21 15:44:32 UTC

ma= Pgf+Grf+Fcf+Ff+Cf
where,
Pgf - force due to pressure gradient
Grf - fprce due to gravitation
Fcf - force due to centrifugal action
Cf - coriolis force
Ff - frictional force which can appear on surface(in the form of shear)

STORM SURGE:

princepraveen000 — 2020-05-21 15:45:04 UTC

Storm surge or simoly rise in water level due to storm is caused predominantly by
1. Large pressure variations between the centre of the and its periphery
2. Wind stress directed fromcontinental shelftowards shallow waters.

COMPONENTS OF STORM SURGES:
1. Initial setuo
2. Pressure setup
3. Long wave setup
4. Wave setup
5. Wind stress setup
6. Coriolis setup

WAVE CHARACTERISTICS:

princepraveen000 — 2020-05-21 15:50:18 UTC

1.Flow is said to be irrotational.
2. Fluid is ideal.
3. Surface tension is neglected.
4. Pressure at the free surface is uniform and constant.
5. The seabed is rigid, horizontal and impermeable.
6.Wave height is small compared to its length.
7. Potential flow theory is applicable.

CLASSIFICATION OF WAVES:

princepraveen000 — 2020-05-21 15:50:56 UTC

AIRY'S WAVE THEORY:

princepraveen000 — 2020-05-21 15:51:40 UTC

Airy wave theory (often referred to as linear wave theory) gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer and the equation is given as:

DISPERSION RELATIONSHIP:

princepraveen000 — 2020-05-21 15:53:03 UTC

The relationship between wavelength, period and water depth is obtained as given below.

CLASSIFICATION OF OCEAN WAVES ACCORDING TO WATER DEPTH:

princepraveen000 — 2020-05-21 15:53:53 UTC

CELERITY:

princepraveen000 — 2020-05-21 15:54:33 UTC

C=L/T
Where, L =length of wave
T = Wave period

CELERITY IN DIFFERENT WATER DEPTH CONDITIONS:
1. Deep water conditions:
Co =sqrt((gLo)/2*pi))
where, Lo = 1.56T^2

2. Shallow water conditions:
C=sqrt(g*D)

WATER PARTICLE DISPLACEMENT UNDER PROGRESSIVE WAVES:

princepraveen000 — 2020-05-21 15:55:44 UTC

The expression for individual and vertical water displacements is obtained as follows

WATER PARTICLE DISPLACEMENT EQUATION FOR SHALLOW WATER CONDITION:

princepraveen000 — 2020-05-21 15:57:18 UTC

WATER PARTICLE DISPLACEMENT FOR DEEP WATER CONDITIONS:

princepraveen000 — 2020-05-21 15:59:20 UTC

MASS TRANSPORT VELOCITY:

princepraveen000 — 2020-05-21 15:59:45 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 32 Basics of wave motion.Consequently there is a mass transport in the direction of progress of the wave.

WAVE TRANSFORMATIONS:

princepraveen000 — 2020-05-21 16:00:28 UTC

* Swell waves leaving the generation area propagate along the wind direction and reach coastal waters after travelling thousands of kilometers.
* Wave height may increase or decrease depending on the configuration of coast and sea bed topography.
* where there is a vertical barrier resulting in
- fanning of wave crest on leeside barrier is called WAVE DIFRACTION.
- Total reflection from barrier is known as WAVE REFLECTION.
- Change in wave alignment of wave crest line as wave advances from deep to shallow is known as WAVE REFRACTION.

URSELLS DIMENSIONLESS NUMBER:

princepraveen000 — 2020-05-21 16:01:24 UTC

There are four theories in this,
1. Airy's wave theory
C < sqrt(g*d)
2. Stoke's wave theory
C < = sqrt(g*d)
3. Cnoidal wave theory
C >= sqrt(g*d)
4. Solitary wave theory
C = 1.33*sqrt(g*d)

WAVE LOADS:

princepraveen000 — 2020-05-21 16:02:04 UTC

These are of two types,
1. FUNCTIONAL LOADS - Loads due to existence , use and treatment of structure under ideal circumstances for each design condition. Such loads may be constant, static or dynamic.
2. ENVIRONMENTAL LOADS - Loads are due to wind, wave currents , ice etc.

MORISON EQUATION:

princepraveen000 — 2020-05-21 16:02:44 UTC

In this morison equation,
Total force = drag force due to velocity + inertia force due to partical acceleration

KEULEGAN AND CARPENTER NUMBER:

princepraveen000 — 2020-05-21 16:03:24 UTC

Umax = maximum in-line orbital velocity
U = current velocity
D = cylinder diameter
T = time period

FROUDE KRYLOV FORCE:

princepraveen000 — 2020-05-21 16:04:10 UTC

Morison equation is applicable if during passage of wave, flow seperation occurs and low pressure region develops downstream of the cylinder.
whereas, Froude krylove theory can be applied if flow seperation is not significant , reflection from the cylinder is minimum and diameter of structure is not very small when compared with wavelenght.

GENERATION PROCESS OF TROPICAL CYCLONE:

princepraveen000 — 2020-05-21 17:20:17 UTC

Warm heated oean air raising above the water surface and creating a low pressure region, depicts spiralling of cool air around the circular column of warm air. With continuous displacement of warm air, an increase in influx of cool air occurs causing pressure to drop further and, in this process , spiralling wind system gains strenght.

GENERATION PROCESS OF EXTRA-TROPICAL CYCLONE:

princepraveen000 — 2020-05-21 17:30:17 UTC

There are three stages in the development of a cyclone.
1. Development of an initial disturbance.
2. Development of polar wave front.
3. Development of a fully matured storm.