代写CENV6175 COASTAL AND MARITIME ENGINEERING调试数据库编程

CENV6175W1

COASTAL AND MARITIME ENGINEERING

SEMESTER 1 ASSESSMENT PAPER 2020/21

Section A

A1. A 5 m wide wave power station is designed using physical model  tests with a scale of 1:10. The full scale incident wave height is Hi   = 1.5 m, the wave period T = 11 seconds, the water depth is 3 m.  Determine the wave parameters and the available wave power for the model scale. Assume shallow water conditions. Formulas are  given on pages 9 and 10.   [  8  ]

A2. Describe a simple model for depth induced wave breaking,

including a sketch and formulas. Compare the model with the general assumption for shallow water wave breaking.    [  8  ]

A3. In many harbours there are vertical quay walls which reflect waves and may make standing waves possible. Briefly describe a standing wave using sketches. Can a standing wave be higher than the waves outside the harbour? Briefly describe two methods to avoid the build-up of standing waves in harbours.      [ 9 ]

NOTE:

Wave Tables are given on page 8.

Formulas are given on pages 9 and 10.

SECTION B

B1. A  tsunami  wave  at  breaking  has  an  estimated  wave

height of H1  = 3.0 m (from observations). The tsunami consists of a wave train with a period of  T  =  1,200 seconds. The epicentre of the earthquake which caused the tsunami is located at a water depth of d0  = 1,800 m. The incoming tsunami at landfall is idealised as a bore traveling with a near vertical front, which has a height of hB  = 3.0 m, and a velocity of vB  = 7 m/s.

(i) Determine the offshore wave height H0  of the tsunami in 1,800 m depth (Eq.’s B1.1 and 1.2).    [ 5 ]

(ii) The land has a gentle slope with a friction free surface, determine the maximum run-up height.    [ 5 ]

(iii) It is planned to build a vertical tsunami wall close to  the shoreline. Determine the maximum run-up height tW at the wall, assuming the tsunami to constitute a reflected bore of initial height tB  = 3.0 m. Use an iterative procedure (hint: start with water depth tW  at the wall of tW  = 2.5 tB , where tB  = 3.0m). Three iteration steps are sufficient. [ 10 ]

(iv) Comment on the result, considering the height of the total energy line of the incoming tsunami wave.   [ 5 ]

NOTE:

Wave Tables are given on page 8.

Formulae are given on pages 9 and 10.

B2. Wave theory:

(i)     A 200 m long harbour basin has a depth of 7 m depth, and a width 50 m. The harbour walls are vertical. Estimate the longest wave periods for standing waves in both directions, using linear wave theory. Which wave is more critical, and why?   [ 9 ]

(ii)    A lake has a fetch length of 20 km, and a depth of 9 m. The wind speed for 1 hour duration was measured as 30 m/s, at 5 m height.

(a)    Determine the wave height, period and length in

9 m water depth. Hint : Use Fig. B2.1.     [ 4 ]

(b)    At the windward end of the lake, there is a

beach. Determine the wave height and length of the wave in 3.0 water depth.    [ 5 ]

(iii)    From the formulas from linear wave theory for wave

length and wave energy, derive a shoaling coefficient ks for the change in wave height when the wave travels from deep water into shallow water. ks  is the ratio of shallow water wave height Hi to deep water wave height H0 , ks = Hi/H0  (see Eq. B2.2). [ 7 ]

NOTE:

Wave Tables are given on page 8.

Formulae are given on pages 9 and 10

Fig. B2.1 : Wave generation nomogram, d = 9.0 m

B3. Wave diffraction: The harbour shown in Fig B3.1 has to be designed for (1) a wave period of T1 = 6 seconds and an offshore wave height of H01  = 2.3 m, and (2) for a wave with a period of T2  = 12 seconds and a deep water wave height of H02  = 1.8 m. The water depth d inside and outside of the harbour is constant, with d = 10.0 m.

(i) Determine the maximum wave height / surface elevations at points ‘1’ at the harbour wall, and point ‘2’ in the harbour basin for T1  = 6 seconds. Use Fig. B3.2. [ 8 ]

(ii) Determine the wave height at point ‘2’ for T2  = 12 seconds. Use Fig. B3.2.   [ 6 ]

(iii) Define the critical design wave for point ‘2’ . Use Fig. B3.2.      [ 6 ]

(iv) What could be done to reduce the wave height at point ‘1’?     [ 5 ]

NOTE:

Wave Tables are given on page 8.

Formulas are given on pages 9 and 10.

Fig. B3.1: Plan view of harbour

Fig. B3.2: Diffraction diagram