Nearshore Oceanography SO422, Spring 2009
Wave Calculation Lab
This lab will be individual effort; you will document on the writeup any assistance you receive (if none, explicitly state).
A single Word document will be due Wed 21 Jan at 1330 hours in the Blackboard dropbox (e.g. Guth_Lab1.doc):
From this lab, you will learn the following skills:
Determine wave parameters (height, wavelength) using the d/L tables.
Estimate where a wave will break.
Estimate wave refraction for the simple case of planar offshore topography.
Determine the effect of T, Ho, and ao on the wavelength and height of the wave as it comes ashore, and on where the wave breaks.
All of these skills are testable on quizzes, exams, and the final exam.
You will start with a partially completed Excel spreadsheet (WAVE-422.XLS). This spreadsheet uses iteration and is somewhat particular about how it is set up; you should save it often in case you accidentally do something it does not like.
Nothing here requires you to use the spreadsheet, and with enough brute force calculations you should be able to write an adequate discussion without the graphs the spreadsheet will generate.
If you do use the spreadsheet, take a moment to reflect before blindly starting.
Using a number of columns and verifying the results of intermediate calculations will make it easier to find mistakes than if you create one monster formula which attempts to do it all.
Check that the results in “deep water” are what you would expect, and that they change in the correct direction as the wave comes ashore.
When you need the trigonometric functions, remember that the spreadsheet expects angles to be in radians, and if you use the inverse trig functions, it will return an angle in radians. For conversion the spreadsheet has degrees and radians functions. See the online help if necessary.
Put all the variables at the top of the spreadsheet where you can easily change them; then refer to them as absolute cell addresses (Using $) when you need them in formulas.
If the spreadsheet does not give you the results for a particular depth that you need, you can change the values in column 1 and the spreadsheet will recompute for that depth.
Name __________________
Date___________________
Nearshore Oceanography SO422, Fall 2009
Wave Calculation Lab
You will turn in the following:
1. A consideration of 4 waves (two different periods and two different heights):
|
Period T (sec) |
Ho (m) |
db (m) a0=0 |
db (m) a0=34 |
Shallow d< (m) |
ab (°) |
|
8.5 |
1. 5 |
|
|
|
|
|
6.5 |
1.5 |
|
|
|
|
|
8.5 |
0.5 |
|
|
|
|
|
6.5 |
0.5 |
|
|
|
|
2. Bracket where (to the nearest 0.1 m, such as between 2.1 and 2.0 meters) each wave will break if there is no refraction. (Complete Table above)
3. Bracket where (to the nearest 0.1 m) each wave will break if there is refraction, and a0=41. (Complete Table above)
4. Bracket the depth (to the nearest 0.1 m) at which each wave becomes a shallow water wave (d/L < 0.05). (Complete Table above)
5. Compute the angle of attack to the nearest 0.1º (such as 15.1 to 15.2º) of each wave when it breaks.
Discuss how period and deep water height affect a wave coming ashore and eventually breaking, in particular how they affect changes in the height and wavelength, and the depth where the waves break.
Discuss how (and why) wave period and height affect a wave's refraction, and how the depth of breaking compares to the case without refraction. (Discussion mandatory; graph(s) optional. It may prove difficult to get multiple cases on the same graph, so don't waste time getting that.)