calculate the values of hydrodynamic coefficients, breakwater motions, 

 and the wave field. Input variables include: 



(a) The body contour, C , represented by a series of points on 

 the contour. 



(b) The physical properties of the body; mass, mass moment of 

 inertia, and position of the center of gravity. 



(c) The mooring system spring constants. 



(d) The hydrostatic restoring spring constants. 



(e) The incident wave frequency, w. 



In this program the exciting forces and moments appearing in the equa- 

 tions of motion and the fixed-body parts of the transmitted and reflect- 

 ed waves are found by computing the forces, moments, and waves which 

 result when a rigidly fixed body is struck by a sinusoidal incident wave 

 of frequency ^. Motions are found by computing the steady-state solu- 

 tion to the three equations of motion. The hydrodynamic coefficients 

 and the waves generated by the body motions are found by computing the 

 forces, moments, and waves which result when the body is forced to os- 

 cillate in Stillwater in pure sway, pure heave, or pure roll. 



The physical properties used in the performance calculations for 

 the various breakwaters are collected in Appendix F. 



a. Wave Transmission . To assess the performance of a floating 

 breakwater, one quantity which is commonly used is the transmission 

 coefficient. This is simply the transmitted wave amplitude divided by 

 the incident wave amplitude, |riT(x,t) |/ |ni(x,t) | for monochromatic inci- 

 dent waves . 



(1) Proposed Oak Harbor Breakwater . At one time the Corps of 

 Engineers was considering a marina and floating breakwater at Oak Har- 

 bor, Washington. Model experiments were carried out by Davidson (1971) 

 to determine transmission characteristics and mooring forces. The break- 

 water itself had a catamaran- type cross section. A comparison between 

 the theoretically predicted and experimentally measured transmission 

 coefficient is shown in Figure 5. This figure as well as the others 

 plotted in this section and Section IV were drawn using a CALCOMP plot- 

 ter. The plotting program uses a parabolic fit to determine additional 

 points between the given data. Varying numbers of data points were used 

 to describe each curve depending on its behavior. Data points were 

 closely spaced in regions where the theoretical predictions indicated 

 large changes in curvature. Wavelength is calculated in all the figures 

 using the relationship between wavelength and period for waves in deep 

 water. 



In this case, the results compare reasonably well except for the 



23 



