代写CENV6175 COASTAL AND MARITIME ENGINEERING SEMESTER 1 ASSESSMENT PAPER 2020/21代做回归

CENV6175W1

COASTAL AND MARITIME ENGINEERING

SEMESTER 1 ASSESSMENT PAPER 2020/21

Section A

A1.   A developer wants to build a 3 m high reinforced concrete seawall as part of a new hotel. Residents question the sustainability of the approach. Briefly discuss the sustainability aspects of reinforced concrete, and describe a more sustainable design using concrete  as material.   [ 8 ]

A2. Describe an N-wave, its characteristics and give an example where such a wave can occur.   [ 8 ]

A3. There are two wave breaking conditions. Describe both briefly and give the relevant formulas for breaking wave heights.   [ 9 ]

SECTION B

B1. (i)     Figure B1.1 shows a harbour basin for leisure craft.

The harbour has concrete side walls, and a caisson breakwater. There are reports of large waves inside the  harbour  basin, even when there are only moderate waves with a period T of around 10 seconds outside of the harbour. A local offshore service provider company was asked to conduct wave measurements. The company installed a seabed wave height sensor at point ‘1’, Fig. B1.1. Despite further reports from harbour users about high waves, the measurements did not show any significant wave heights. Analyse and comment.

Assume the water depth inside the harbour to be a constant 5.0 m.

Fig. B1.1: Plan view of harbour

[ 10 ]

(ii)          Fig B1.2 shows a seawall with a water depth of 1.5 m. The design wave period is 4.4 seconds, the offshore wave height H0 is 1.5 m. The seawall has to be designed for the current condition, and for an expected sea level  rise (SLR) of 0.30 m. The seabed is smooth, with a bed  slope of 1:10. Assume a density of sea water of ρsw  = 1030 kg/m3 .

Determine:

a)      Type and magnitude of maximum wave load (maximum pressure and force) on the structure without SLR.    [ 5 ]

b)   Type and magnitude of maximum wave load with SLR. Comment on situation.    [ 5 ]

c)    wave condition / load type for max H0   =  1.2 m without and with SLR. Comment on the results.    [ 5 ]

Fig. B1.2: Seawall

B2. Tsunamis:

A tsunami wave with a height H0  = 1.0 m and a wave period of 500 seconds is generated in a water depth of 2,000 m.

(i)          Determine the wave condition (shallow    /

intermediate / deep water) of the tsunami wave at its origin.    [ 5 ]

(ii)         Determine the maximum wave height Hmax  near the coastline, using the conservation of energy and the breaking wave condition.    [ 8 ]

(iii)        The tsunami wave of height H max arrives at the

shoreline as an N-wave, with a preceding trough. Assuming the wave to constitute a boreas shown in Fig. B2.1, and using a small control volume with an energy principle, determine its speed of propagation.   [ 5 ]

(iv)        Compare the  result with the standard formula for

wave celerity in shallow water, comment briefly.    [ 7 ]

Fig. B2.1: Idealised tsunami wave with preceding trough

B3. Wave refraction:

(i)         A developer suggests the construction of a wave power station. There are two possible sites, one on a  headland and one in a bay. At  both sites, the waves approach the coastline with the wave crest in deeper water near parallel to the coast. Which site is preferrable, and why? Explain your answer with sketches.   [ 9 ]

(ii)         Fig. B3.1 shows a wave of height H1   =  1.0 m and

period T  =  5  seconds  propagating  from  a  water depth of d1  = 3.0 m into a water depth of d2  = 5.0 m. The wave crest arrives with an angle of α 1   = 35 degrees with the contour line.

(a)  Determine the wave direction and wave height for the water depth d2 .   [ 8 ]

(b)  The  wave  direction  changes  to  α 1 ’  =  75 degrees,what is the wave height and direction in the deeper water?     [ 8 ]

Assume shallow water conditions throughout.

Fig. B3.1: Wave refraction