Harbour and Coastal Assignment

8/12/2019 Harbour and Coastal Assignment

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CE 4013: Harbour and Coastal Engineering Denis OSullivan, 108348006

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Name: Eoghan ODriscoll

Collins

Student Number:

109326049

April 2013

Dr. Jimmy Murphy

CE 4013:

Harbour

and Coastal

Engineering

University College CorkColiste na hOllscoile Corcaigh

Department of Civil and Environmental Engineering.


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Table of ContentsExperiment 1: Wave Celerity .................................................................................................................. 3

1.1 Introduction ............................................................................................................................ 3

1.2 Apparatus ................................................................................................................................ 3

1.3 Method ................................................................................................................................... 4

1.4 Formulae ................................................................................................................................. 4

1.5 Results and Calculations ......................................................................................................... 5

1.6 Discussion and Conclusion ...................................................................................................... 7

Experiment2: Observation of Different Wave Types, Wave Run-up and Interaction with Obstacles .... 8

2.1 Observation of Different Wave Types ..................................................................................... 8

2.1.1 Regular Waves ................................................................................................................ 8

2.1.2 Irregular Waves ............................................................................................................... 8

2.1.3 Bulls Eye Wave ................................................................................................................ 8

2.1.4 Freak Wave ..................................................................................................................... 8

2.1.5 Observation of Wave Period and Wavelength ............................................................... 9

2.2 Observation of Reaction with Obstructions ............................................................................ 9

2.2.1 Interaction with Rubble Mound Breakwater (Beach) ..................................................... 9

2.2.2 Interaction with Vertical Wall ....................................................................................... 102.2.3 Interaction with Partial Depth Fixed Wave Barrier ....................................................... 10

Experiment 3: Stability of a Floating Body ............................................................................................ 11

3.1 Introduction .......................................................................................................................... 11

3.2 Apparatus .............................................................................................................................. 11

3.3 Method ................................................................................................................................. 12

3.4 Formulae ............................................................................................................................... 13

3.4.1 Theoretical Metacentric Height .................................................................................... 13

3.4.2 Experimental Metacentric Height ................................................................................. 14

3.5 Results and Calculations ....................................................................................................... 14

3.6 Graph for Determination of Experimental Metacentric Height ........................................... 16

3.7 Discussion of Results and Conclusion ................................................................................... 17

Experiment 4: Sediment Transfer ......................................................................................................... 18

4.1 What is happening? .............................................................................................................. 18

4.2 How is it happening? ............................................................................................................. 18

4.3 Why are we studying it? ....................................................................................................... 19


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Experiment 1: Wave Celerity

1.1 Introduction

This experiment investigates linear water wave theory with respect to real waves. Linear

wave theory models wave behavious. It is only an approximate method of analysis but

results can be suprisingly accurate and consistent.

The experiments to compare real waves and linear wave theory were carried out in the UCC

Hydraulics and Maritime Research Centre (HMRC) in Pouladuff, Cork City in the specialised

18 x 25 x 1 metre wave tank in which the waves are generated by 40 centrally controlled

flap type wedge shaped aluminium paddles. The wave tank in this facility is capable

generating waves up to a significant wave height of 0.18 metres at a period of 2.5 seconds.

In this experiment, it was decided to investigate the agreement with theoretical values for

wave periods varying from 0.8 to 2 seconds. The wave height in this case was selected as

50mm. This was however varied in order to enable the easy observation of the waves.

1.2 Apparatus

The only apparatus required in this experiment were a stopwatch and the aforementioned

HMRC wave tank: a picture and a schematic of which is shown in Figure 1.1 and Figure 1.2.

Figure 1.1: HMRC Wave Tank


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Figure 1.2: Schematic of HMRC Wave Tank

1.3 Method

1. For a particular wave period, measure the time taken for ten waves to pass a point

and divide it by ten to determine the experimental wave period. Repeat this and

take the average figure.

2. Measure the time it takes for a wave to pass between the two marks on the side of

the tank (8 metres apart). Divide 8 by this value to determine the experimental

celerity of the wave.

3. Repeat steps 1 and two for wave periods of 0.8, 1, 1.1, 1.14, 1.33, 1.6 and 2 seconds.

4. Use the data collected to calculate C0, C Theory, 0, Theory and Measured. Plot these

values against Period, T.

1.4 Formulae

The waves are classified as either deep water waves or transitional waves. The relevant

formulae are as follows:

Parameter Deep Water Transitional Water

Wave Velocity (c)

(

)Wave Length ()

(

)Limits of Application

Table 1.1: Formulae of Linear Wave Theory

The shallow water equations are omitted as none of the waves were shallow water waves.


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1.5 Results and Calculations

The data collected and the calculated C0, C Theory, 0, Theoryand Measuredare shown in Table

1.2 below.

Period

(T)TMeasured C0 0 CTheory Theory CMeasured Measured Classification

0.8 0.8 1.25 1.00 1.25 1.00 1.27 0.99 Deep

1 1 1.56 1.56 1.56 1.56 1.54 1.60 Deep

1.14 1.144 1.78 2.03 1.77 2.02 1.75 2.01 Transitional

1.33 1.32 2.08 2.76 2.04 2.71 1.91 2.58 Transitional

1.6 1.62 2.50 4.00 2.33 3.73 2.24 3.63 Transitional

2 1.99 3.12 6.25 2.61 5.22 2.38 4.78 Transitional

Table 1.2: Results and Calculations

The variation of C0, C Theory and C Measuredwith Period (T) is shown in Figure 1.3 while thevariation of 0, Theoryand Measuredwith Period (T) is shown in Figure 1.4.


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Figure 1.3: Variation of Wave Celerity with Period (T).

Figure 1.4: Variation of Wavelength with Period (T).

Celerity,c/(m/s)

Period, T / (sec)

Plot of C0, CMeasured& CTheoryAgainst Period (T)

C Measured C Theory C0

Wavelen

gth,

/

(m)

Period, T / (sec)

Plot of 0, Measured& TheoryAgainst Period (T)

Measured Theory 0


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1.6 Discussion and Conclusion

Based on this experiment, it is possible to deduce that, for a given wave height, both the

wave celerity (c) and the wavelength () increase with increasing Period (T), as is illustrated

by Figures 1.3 and 1.4 respectively.

It is apparent that the TMeasuredis nearly always greater than the actual Period (T). This can

be attributed to human error, resulting in a delay in turning off the stopwatch after the

wave passes the mark.

It can be seen that the linear water wave theory agrees reasonably well with real waves.

The agreement is very good for low periods. However, as the period increases, the

wavelengths and wave celerities recorded (I love cock) from the real waves deviate fromthe values predicted by the linear water wave theory.

For each measurement of wavelength and wave celerity, the measured figure is lower than

that predicted by the linear wave theory. It is possible that this could be attributed to

experimental error. This is unlikely however as the any experimental error would have been

minimised by choosing a large number of waves (ten) over which to record the times. It is

more likely that the discrepancy occurs as a result of the fact that the linear water wave

theory is less accurate for periods over approximately 1.4 seconds.


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Experiment2: Observation of Different

Wave Types, Wave Run-up and

Interaction with Obstacles

2.1 Observation of Different Wave Types

2.1.1 Regular Waves

Both long and short crested regular waves were observed in the wave tank. Regular waves

are waves which travel from one end of the tank to the other without changing or meeting

other waves. These waves are ultimately absorbed by the artificial Enkamat absorption

beach at the other end of the wave tank and hence, are not reflected back along the tank.

2.1.2 Irregular Waves

Irregular waves were then observed in the wave tank. These types of wave simulate the

conditions likely to be found offshore. They are the types of wave which commonly occur in

the ocean. Waves come randomly from different directions, meet and break at different

locations and spread and diffract in different directions. The result is a choppy surface,

similar to that found when wind blows across an open stretch of water.

2.1.3 Bulls Eye Wave

Bulls Eye waves were then observed in the tank. These occur when a series of similar waves

travel towards each other at an angle and intersect at a central point. At this point, the

wave height increases. A bulls eye formation then occurs propagating from this point. This

type of wave is rarely occurs in reality.

2.1.4 Freak Wave

Finally, freak waves were created in the tank. These occur when a series of waves with

varying height and period are created. Firstly, waves with a low celerity are created. These

are then followed by waves with a higher celerity. The waves with the higher celerity move

faster than those with the low celerity and therefore catch the slow moving waves. At the

point when the fast moving waves catch the slow moving waves, a breaking wave with a

large amplitude known as a freak wave is formed.


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2.1.5 Observation of Wave Period and Wavelength

Several different types of waves were observed in the 26 metre wave flume. Firstly, waves

with a height of 50 mm, a Period (T) of 0.7 seconds and a wavelength () of 0.76 metres

were observed. Following this, waves with a similar height a Period (T) of 1.75 seconds and

a wavelength () of 4.78 metres were observed. It was noticed that the second group of

waves (with the greater Period and Wavelength) seemed much smaller owing to the fact

that they were less steep and more spread out as a result of their longer wavelength.

2.2 Observation of Reaction with Obstructions

The elevation and plan view of the obstructions to which the waves were subjected in the

wave flume are shown below in Figure 2.1.

Figure 2.1: Layout of Obstructions in Wave Flume

2.2.1 Interaction with Rubble Mound Breakwater (Beach)

At one end of the wave flume, a sloped rubble mound breakwater had been constructed

from loose granular material. The interaction of the waves with this obstruction was

observed. As the waves approached the beach, they changed from deep water waves (d >

0.5 L) to transitional waves (0.05 L d 0.5 L) and ultimately to shallow water waves (d

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