OC4213 LAB 1

Wave Forces

OBJECTIVE:

To compute wave forces on a cylinder using linear wave theory and to observe how the forces vary with depth of water, wave height, wave period, the diameter of the cylinder, and the distance below the water surface.

PROCEDURE:

1. Before beginning this lab, you may wish to create a subdirectory called "oc4213" in which you can store all the programs and outputs you will generate. Also, you may find it useful to examine and/or print out this supplemental information.

2. In the directory you will use for oc4213, create soft links to the following oc4213 files required for this lab. You will need the m-file called "wforces" as well as the compiled fortran code called "wforce". You can link to these files with the unix command immediately below:

ln -s ~orzech/oc4213/Forces/* ~/oc4213

3. If you now type "ls", you should see the files "wforces.m" and "wforce" listed, along with the file "signature.m". (Alternatively, you can go to the main OC4213 Lab web page and link to "Programs for download to PC". Select and download the appropriate "tar" file to your PC, then unzip the enclosed files using a utility like WinZip.)

4. Enter the matlab environment by typing "matlab" at the unix prompt.

5. Run the wave force program by typing "wforces" at the matlab prompt. The input values you use for this program should fit within the following ranges:

h, water depth 1 - 100 m, h > L/10

H, wave height 1 - 10 m, H/h < ½

T, wave period 3 - 20 sec

D, pile diameter 0.1 - 2 m, D/L < 0.01

z, depth of force evaluation 0 - h

EXERCISES:

1. Hold H, T, h, and D constant while varying the depth of evaluation, z (z = 0, h/10, h/5, h/2). Use the programs to calculate the forces and maximum total force and the phase angle at which it occurs (e.g., at wave crest, trough, or elsewhere). Turn in the four plots you obtain from these calculations. How do the forces (Total = Ft, Drag = Fd, and Internal = Fi) vary with depth and why?

2. This time, run the programs holding H, h, and D constant, and setting z to h/50. Vary the wave period, T (T = 5, 10, 15, 20). Again calculate forces and phase angle of maximum total force and submit the four plots generated.

3. Finally, hold H, h, and D constant, and set z to h/2. Again vary the wave period, T (T = 5, 10, 15, 20) and generate four more plots for submission. In 2 and 3, how do the forces vary with an increasing wave period and why? Explain carefully for each case.