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COASTAL ENGINEERING
WATER RESOURCE ENGINEERING
FACULTY OF ENGINEERING
UNIVERSITY OF BRAWIJAYA
WAVE DIFFRACTION
GROUP 1
• ALIF RAMADHANI MEDISIA PG (135060400111033)
• MUNFARID(135060400111035)
• GANISA ELSINA SALAMENA (135060401111068)
• YUDHISTIRA A Z R (145060400111005)
• FAIZAH FITRIAH (145060400111006)
• TAMI PRATIWI (145060400111007)
• NUR FADHILILLAH A (145060400111008)
INTRODUCING
Coastal area is one of natural resources which has huge potential especially in
tourism sector. In our country coastal area not only popular in tourism sector,
but also in water transportation. Speaking of coast area there must be a
discussion about waves. There are many type of waves. If the wave moving
towards coast area, it may causes a deformation. This phenomenon caused by
a refraction process, diffraction, reflection, and breaking wave. So that coast
area moves in because of abration and sedimentation in this area moves out.
From this problem, a construction is needed to protect coastal area. This
construction has a specific function according to the condition and problem in
the field.
1.1 General Description
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
INTRODUCING
1.2 Purpose and Goal
Purpose and goal from this assignment is to analyze the deformations of wave which occurs in coastal area
especially diffractions wave with formulas that will be used to solve the wave problems.
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
THEORY
2.1 The General Deformation of Waves
Deformation of the wave is a changing of wave characteristic that occurred during the moved of waves
propagating toward the shore. Wave deformation process will determine the wave height and wave crest line
pattern or direction of the wave at somewhere in the coast area. When a row of waves moving towards to the
shore, the wave will changes in shape caused by the refraction and the erosion of the waves, diffraction,
reflection, and wave breaking.
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
THEORY
2.2 Diffraction of Wave
Diffraction happen when the wave height on a point on the crest of a wave larger than a point nearby, which led
to the displacement of energy along the crest of the wave height towards smaller waves. Diffraction happen
when a row of waves resist by restriction such as breaking waves (breakwater) or an island. Wave height and
direction of the waves on the coast area is important, for example, we can use to determining the flow and
sediment transport in coastal areas.
There are parameters that influence the process of diffraction is a wavelength comparison with the end of
distance point of the restriction (r / L), the angle between the barrier and the line joining the end of the
restriction, and the angle between the directions of wave propagation with restriction. The ratio between wave
heights at point being reviewed by the coming wave height is called coefficient of diffraction.
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
THEORY
Figure 2.1 This phenomenon is known as a wave’s
diffraction. In diffraction of wave, there is a transfer
of energy in a vertical direction to the wave sheltered
areas. As seen in Figure 2.1, if there is no diffraction of
waves, the area behind the barrier will stay still. But,
when diffraction process occurs make an area
affected by a wave of energy into the sheltered area.
Transfer of energy to that place causes the formation
of shelter wave.
WATER RESOURCE ENGINEERING
The Shadow area with
diffraction area occurs
The area is not
disturb
The area sharp corners, where
waves come and reflection formed
Figure 2.1 Wave Diffraction behind Obstacles
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THEORY
2.3 Calculation of Diffraction Wave
• If Hi is the height of the waves coming at the end of breakwater and Hd is the height of a wave diffracted at the
reference point in a sheltered area, it can be defined diffraction coefficient :
Kd = Hd / Hi
• Value of Kd depends on the location behind backwater which is defined by r and β, and the direction of the
incoming wave is defined by θ. Or a dimensionless shape :
Kd = f (r/L,,),
• with L is the wavelength in the protected area of backwater. Because wavelengths is a function of the wave
period and water depth, the diffraction coefficient for each component spectrum will depend on the direction of
the wave coming and the period.
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
THEORY
Diffraction Theory for two or more breakwaters with a gap (aperture)
• If there are two or more breakwaters with a gap (aperture) of them, to determine the coefficient used
diffraction chart was developed by Johnson (1952, 1953; in Wiegel, 1964).
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Figure 2.2 Forming an angle of diffraction waves behind obstacles gaps
Sunday, April 10, 2016
THEORY
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Figure 2.3.a Diffraction graph through the Gap (B/L=2)
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THEORY
Example :
The waves come with a period of 6 seconds to the breakwater with the angle of incidence at the end of the
breakwater at θ = 600. The water depth behind or at breakwater protected area is 10 m and assumed to be
constant. Find the wave height at an angle β = 300 from point A breakwater and 99.6m distance from the tip of
the breakwater if the wave coming with a height is 2.2 m.
WATER RESOURCE ENGINEERING
A
THEORY
Answer :
• Lo = 1.56T2 = 1.56 x (6)2 = 56.16 m d/Lo = 6/56.16 = 0.10684
From Figure 2.6 continued Table A-1 can be obtained:
• d/L = 0.1469024 L = 10/0.1469024 = 68.072 m
Distance point A to the end of the hurdles:
• r = 99.6 m r/L = 99.6/68.072 = 1.463 m ≈ 1.5
From the table figure 2.5 Kd table for r/L = 1.5, θ = 600 and β = 300 thus Kd = 0.32
Then the wave height at point A is:
• HA = Kd x Hi = 0.32 x 2.2 = 0.704 m.
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Figure 2.5 and 2.6
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THEORY
VIDEO OF WAVE DIFFRACTION
WATER RESOURCE ENGINEERINGSunday, April 10, 2016
CLOSING
WATER RESOURCE ENGINEERING
3.1 Conclusion
• Deformations wave is one of the change in the nature of the waves that happened at a wave of moving vines
towards the shore. If a row of a wave of moving to the shore, the wave will undergo changes in shape caused
by the process of refraction and shallowed wave, difraction, reflection and brokens wave.
• Difraction happen if high waves one point in the wave crests larger on point in the near, that causing a move
energy on the all the wave crests wave toward the smaller of highers wave. Difraction occurs when a row of
wave of blocked by the obstacles as breakwater or is an island.
• On the breakwater gap or double, diffraction hapens when the wavelength (L) is comparable or larger than
the aperture between the breakwater (B).
Sunday, April 10, 2016
THANK YOU