Mid-Term Exam OCEN 201 March 04, 2013

General Instruction: Please show all your steps in your computation. It is your responsibility not only to get the correct answer, but also to show that you understand the technique. During your computation, please keep at least three significantfigures behind the decimal point.

Each (Problems 1 – 15) carries 2 points.

  1. Wavelength is the horizontal distance between

a. a trough to a crest b. two neighboring crests c. ab both d. all of them

  1. Which chemical element is the most in sea water?

a. magnesium b. sodium c. sulfate d. chlorine

  1. The line of the ocean contacting the land is known as

a. surf zone b. shoreline c. coastal zone d. none of them

  1. If the ratio of the water depth to the wavelength is equal to 0.4, it is considered as

a. deep water b. shallow water c. intermediate depth water d. none of them

  1. The trajectory of water particles underneath a regular wave train in intermediate depth water is approximately

a. a circleb. an ellipse c. a straight line d. all of them

  1. Which of the following oil production platforms is likely used in the water depth of 100 ft?

a. a steel jacket platform b. a SPAR c. a TLP d. all of them

  1. A tide day is roughly….. long.

a. 24 hoursb. 24.55 hours c. 24.84 hours d.23.80 hours

  1. Waves propagating from deep water towards the shoreline may result in

a. shorter wavelength b. loner wavelength c. longer wave period d. none of them

  1. The average height of the highest one third waves in a wave field is known as

a. average wave height b. significant wave height c. standard deviation of wave height d. root-mean-square wave height

  1. The average ocean water depth is close to

a. 10,800 mb. 1,800 m c. 6,800 m d. 3,800 m

  1. Which of the force or forces is related to the earth’s rotation?

a. Buoyancy forceb. Gravity force c. Coriolis force d. all of them

  1. Coastal structures built parallel to the beach for trapping sediments are known as

a. Groins b. Jetties c. Break water d. all of them

  1. Bending of wave crests (crest lines) due to sea bathymetry (water depth) change is known as wave

a. Diffraction b. Refraction c. Reflection d. Scattering

  1. Energy of incident waves may transport laterally to the wave direction due to the presence of surface piercing structures, which is known as wave

a. Diffraction b. Refraction c. Reflection d. None of them

  1. Which of the following metals is the most active?

a. Silver b. High strength steel c. Copper d. Aluminum

  1. (6%) Write down the full words of the following acronym (offshore structure or vehicle related).

(i)ROV

(ii)MODU

(iii)TLP

  1. (6%) Write down the full words of the following acronym (related top professional engineering society).

(i)MTS

(ii)ASCE

(iii)SNAME

  1. (6%) Four OE students compute the wavelength of a regular wave train of 8 s period in water depth of 50 m using the dispersion relationship. Please find which of the following solution is correct.(Please conduct at least 3 iterations)
  1. 9.052m b. 101.52m c. 99.23m

d. If none of them are correct, please write your own solution

  1. (4%) They also compute the phase velocity of the same wave train motioned above. Please find which one is correct.
  1. 11.32 m/s b. 12.69 m/s c. 12.40 m/s

d. If none of them are correct, please write your own solution

20 (4%) How about their computation on the group velocity.

  1. 6.439 m/s b. 6.283 m/s c. 5.625 m/s

d. If none of them are correct, please write your own solution

21(14%) A pier is supported by 0.28 m diameter cylindrical piles in 5 m water. The maximum current in the vicinity of the pier is 5 m/s. Using the Morrison equation, please estimate the drag force on the pile. (waterproperties are and ).

22 (6%) An incident wave in deep water has a wave height of 20 ft. When it travels toward the shallow water, based on the wave period, water depth and bathymetry, a coastal engineer did the computation and found that at this location the shoaling coefficient and the refraction coefficient . Based on his/her results, please determine the wave height at this location of shallow water.

23(14%) Determine the buoyancy index for sand with a in seawater with a specific weight of 10.1 and a kinematic viscosity . The specific gravity of sand is 2.66 and the specific weight of (fresh) water is 9.8. Based on the buoyancy index, using the following formula to compute the fall velocity of the sand.

24 (10 %) A periodic (or regular) wave train of period 5 seconds and amplitude 2 m travels in deep water. Please compute

a)Its energy density (the density of water,).

b)Its energy flux