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| Honors Marine ECE 2012/2013
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| Upcoming Events and Homework |
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answer the review questions and problems at the end of the chapter (homework)
Due Date: May 20, 2013
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try the questions and problems first and then check the answers here.
Chapter 11: Answers to Study Questions
1.
a) A diurnal tide has one tidal cycle per tidal day. A semidiurnal tide has two tidal cycles per tidal day.
b) The tidal day is the time between two successive diurnal lunar high tides or three successive semidiurnal lunar high tides. The tidal period is the time between two successive high tides whether lunar or solar for semidiurnal and diurnal tides.
c) Spring tides are the large-amplitude tides created at the new and full moons when the lunar and solar tide waves are in phase with each other. Neap tides are the small-amplitude tides at the moon's first and third quarters when the lunar and solar tide waves are out of phase.
d) The flood tide is the tidal phase of increasing water level. The ebb tide is the tidal phase of decreasing water level.
e) Cotidal lines show successive simultaneous positions of the high tide crest. Corange lines denote positions where tidal range is the same.
2. Add an arrow 1 nm in length and pointing due south to each of the vectors shown in figure 11.14.
3. Because the water is not confined, the work output of a waterwheel may create a resistance against the moving water, causing the water to flow around the waterwheel blades instead of turning them. Water in a tidal dam system is confined in a pipe and cannot escape around the turbine blades. The height differential across a tidal dam can be maintained for an extended period of time to produce a uniform current. The current in a tidal stream changes magnitude over time, which would affect the power production.
4. Table 11.1 indicates that natural periods of oscillation in a basin can match the tidal periods. If an ocean basin has both large width and length, depths need to be great to produce natural periods of oscillation matching tidal periods. In smaller coastal basins where width and length are small, the depth must be less to have comparable periods.
5. The large tidal range (about 7 m) is necessary to generate the pressure difference through the turbine path that gives the water passing through the turbine its speed. If the stored volume is small, the fast volume flow through the turbine will drain the reservoir and lower the height too rapidly, allowing electrical generation for only a short time period.
6. See figure 11.1. Watch for appropriate labeling of tide type, tidal stages, length of tidal day, and tidal datum.
7. A tide's wave form can be explained by using the equilibrium tidal model of a water-covered earth. When the tide crests are at opposite sides of the earth's equatorial plane (a semidiurnal tide), the wavelength is approximately one-half the circumference of the earth. When a declinational or diurnal tide is formed, the wavelength of the tide at a mid- to low-latitude position is approximately equal to the earth's circumference. The earth turns eastward within the tidal envelope and this is equivalent to the tide wave moving westward relative to the earth. The wavelength is so long that the tide wave in midocean moves as a shallow water wave. The tide wave can be a progressive type or it can be a standing type. The tide wave also has wave height (tidal range) and wave period (based on a 24 hour, 50 minute tidal day or one-half the tidal day). In some cases the tide wave does not travel as a free wave but is forced to move across a basin at a speed faster than that determined by C = . For example, at the equator the crest of the tide waves moves westward about 1000 mph to stay centered under the moon as the earth turns eastward (see fig. 11.10).
8. The tide is the regular rise and fall of water associated with the movement of the tide wave in an ocean basin. Tidal currents are the flows of water required to increase or decrease the volume of water required locally as the water level changes. In a standing type tide, the maximum flow of water occurs at midtide and is zero at high or low water. In a progressive type tide, the horizontal component of the orbital velocity associated with an open ocean tide wave generates the tidal current. In this case maximum current coincides with high or low water. In inshore embayments and channels, the tidal current is the horizontal flow of water that is required to add water on the rising tide or remove water on the falling tide.
9. Using average oceanic depths, the free speed of a shallow water wave is approximately 400–500 mph. At the equator the speed of the seafloor under the crest of the tide is about 1000 mph. If the tide crest is to remain in a nearly fixed position relative to the moon, then the tide wave must be forced to move across the sea at a speed equal to the eastward speed of the seafloor.
10. Progressive tides show a linear progression of the crest of the tide wave across the ocean. If a progressive tide is reflected in an oceanic basin, a standing rotary tide results; the tide rotates about the amphidromic point.
11. A tidal bore is produced when the approaching tide wave undergoes a sudden decrease in forward speed due to the shallowing of the water or an opposing downriver current. Tide height increases rapidly but the wave does not move forward as rapidly. A breaking or plunging wave face forms and moves slowly inshore or upstream. This discontinuity in water level is known as a tidal bore.
12. If there was no centrifugal force counteracting the sun's gravitational force on the center of mass of the earth-moon system, the earth and the moon would be drawn into the sun.
13. When the sun is above the Tropic of Capricorn during the Northern Hemisphere winter, a high tide crest is displaced north of the equator according to the equilibrium tidal model and a more declinational solar tide is produced with corresponding higher high tides. These then combine with the lunar tides. Low atmospheric pressure due to winter storm systems, and less dense coastal water due to precipitation and river runoff, also allow the water along the coast to rise.
14. The moon moves between its latitudes of highest and lowest declination (28½° N and 28½° S) and back over a period of 18.6 years. Records must be kept for approximately 19 years to determine the full cycle of the moon's influence on the tides at any location.
15. Satellite altimetry over the entire ocean surface allows observations to be made of the uneven surface of the ocean. The unevenness of the ocean surface is due to currents, bottom topography, changing tide levels, atmospheric pressure effect, earth's gravity, and wind stress. These direct observations and measurements of sea surface topography cannot be accurately observed from a vessel at sea.
Chapter 11: Answers to Study Problems
1. In the case of a lunar diurnal tide, there are 24.8 hours between successive high tides and the high tide advances by 0.8 hours per day; 24 hours divided by 0.8 hours/day yields 30 days. A semidiurnal tide requires 29½ days for a specific high tide crest to repeat its clock time but only half this time for the other crest to move to the time position of the first crest.
2. The San Diego tide is a mixed semidiurnal tide.
3. The listed water levels are referenced to Mean Lower Low Water (MLLW). Hence, MLLW should correspond to the x axis of the plot.
4. The maximum tidal range is 7.63 feet from 19:59 on July 8 to 03:27 on July 9. The minimum tidal range is 0.73 feet from 07:42 on July 6 to 11:47 on July 6.
5. You should arrive at 14:57 when slack water occurs just as ebb tide begins.
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read ch 11 quiz on tides
May 20, 2013
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| Downloads |
 Document 1 (51.2 KB)
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Field Trip
May 28, 2013
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| Downloads |
 slip (16.58 KB)
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Project Final Portion (homework)
Due Date: June 13, 2013
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Have a presentation prepared for your project. This should include info from the background research, a plan of action for the applied project, data collected and any photos you have taken. If you have not started the field portion of your project, we need to meet before this date. This presentation may be one that you are presenting or have presented to an interest group or your classmates may end up being your interest group. Ideally, you have found someone trhat wants the information you have gathered. If not, that will impact the grade.
The presentation can be powerpoint, active inspire, video, poster based or any other media that seems appropriate for the subject.
Along with the presentation should be a binder with the background articles, your final paper - which should include:
1. the background summary
2. a summary of your action plan
3. results summarized
4. a reflective piece on the project
We will discuss the specifics in class |
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ECE open ended and essays (homework)
Due Date: June 24, 2013
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| Have this completed before the exam. This will count as 40% of the grade. |
| Downloads |
essays and open ended (58.88 KB)
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advanced intro letter and reading list2012.doc
Examples of possible project ideas.docx
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Waterford High School
Michael O'Connor
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