Papers by William McDougal
Coastal Engineering 1986, Nov 30, 1987
A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring ... more A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring lines is modeled analytically and experimentally. The system behavior is described theoretically utilizing an eigenseries representation of linear wave theory in the vicinity of the breakwater. The structure dynamics are modeled in terms of structure weight, inertia, buoyancy, damping, mooring line tension and the wave pressure field. The mechanically coupled system provides shelter by reflecting incident waves and by attenuating wave energy through structural and viscous damping. The structure can be tuned to minimize wave transmission within a particular frequency range by changing the flap spacing and adjusting the mass and equilibrium position of the mooring line weights. The theory is validated with experimental results for models fabricated from inflatable, parallel-tube membranes. Buoyancy and inertia are changed by filling tubes with air and/or water. Single and double flaps are examined with and without mooring lines. Incident, reflected, and transmitted waves are measured as well as flap motion. Theoretical results are corroborated by the experiments and the importance of including damping in the model is demonstrated.
24th International Conference on Coastal Engineering, Aug 11, 1995
25th International Conference on Coastal Engineering, Aug 5, 1997
A combined BEM-FEM model has been developed to study the nonlinear dynamic interaction between a ... more A combined BEM-FEM model has been developed to study the nonlinear dynamic interaction between a submerged breakwater and waves. The resistance coefficients in the equations of motion inside the porous media have been experimentally determined based on measured values of the wave forces on spherical armor units in a submerged breakwater. Comparisons of the numerical model results with the experimental measurements indicate that this modification has improved the model accuracy in simulating the wave deformation and the energy dissipation due to a submerged breakwater. Results also show that the model gives good estimates for the wave kinematics inside and around the breakwater which are necessary to compute the stable armor stone weight. INTRODUCTION: Submerged breakwaters have several advantages over the conventional surface piercing structures including aesthetics, less impact on the near shore water quality and ability to trigger early wave breaking. Their use is also recommended on recreational beaches to ensure safe conditions. They are usually constructed from rubble and may be protected by an armor layer of large stones or concrete blocks. Earlier researchers focused on wave deformation and energy dissipation due to submerged breakwaters, but less interest was given to their internal properties and shape. Driscoll et al. (1992) studied the harmonic generation and transmission past
Coastal Engineering, 1989
ABSTRACT
American Society of Civil Engineers eBooks, 1999
Ocean Engineering, 1989
An eigenfunction expansion technique is utilized to investigate the linear wave field produced by... more An eigenfunction expansion technique is utilized to investigate the linear wave field produced by a spiral wavemaker consisting of an eccentrically-mounted, right circular cylinder rotating at a constant angular velocity in a basin of arbitrary uniform depth. In the present study the effect of a finite gap which exists between the underside of the wavemaker and the floor of the basin is included in a mathematially consistent manner. Numerical results are presented which illustrate the influence of this gap on the generated waves and on the hydrodynamic loads experienced by the wavemaker.
Advances in Water Resources, 1992
Abstract A linear hyperbolic groundwater model (a damped wave equation) based on the unsteady Dar... more Abstract A linear hyperbolic groundwater model (a damped wave equation) based on the unsteady Darcy equation is developed for pressure waves in a saturated, porous medium. The field equations in this formulation include the time-dependent fluid flux which is characterized by a small parameter referred to as the relaxation time. The equations are solved analytically by standard integral transform techniques. Numerical results are presented to demonstrate the behavior of the analytical solution. After an initial start-up time, the damped wave equation problem reduces to the classical diffusive problem. The motivation for using the hyperbolic model is that it allows an estimate of the transmissivity and storativity from the long-term response and the porosity based on the lag time of the head response.
Coastal Engineering, May 1, 1983
ABSTRACT
Journal of offshore mechanics and Arctic engineering, May 1, 1992
A numerical technique is utilized to investigate the dynamics of a submerged compliant breakwater... more A numerical technique is utilized to investigate the dynamics of a submerged compliant breakwater consisting of a flexible, beamlike structure anchored to the seabed and kept under tension by a small buoyancy chamber at the tip. The fluid motion is idealized as linearized, two-dimensional potential flow and the equation of motion of the breakwater is taken to be that of a one-dimensional beam of uniform flexural rigidity and mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the fluid domain, modifications are made to the basic formulation to account for the zero thickness of the idealized structure and the singularity in the fluid velocity which occurs at the breakwater tip. The dynamic behavior of the breakwater is described through an appropriate Green function. Numerical results are presented which illustrate the global influence of the tip singularity on the solution and the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. Small-scale physical model tests were also carried out to validate the foregoing theory. In general, the agreement between experimental and numerical results was reasonable, but with considerable scatter.
Journal of Coastal Research, Jan 20, 1994
The overall form of many beach profiles has an exponential shape where the depth h is given by h ... more The overall form of many beach profiles has an exponential shape where the depth h is given by h = (Sj k)(l e b) with S,. the beach-face slope at x = 0 and k is an adjustable coefficient that determines the degree of concavity. The cross-shore variation in beach slope is then S = S"e "or S = S"-kh. Beach profiles can be analyzed in terms of both the cross-shore variations in hand S. Based on previous studies, the beach-face slope S" is predictable as a function of the sediment grain size and wave parameters. The evaluation of k can be based on best-fit comparisons with the measured profile depths or from bottomslope variations across the profile. Equations are derived for the evaluation of k from the offshore closure depth of the envelope of profile changes, or from some arbitrarily selected coordinate of the profile. An example of the analysis approach is provided by a beach profile from the Nile Delta coast of Egypt. This measured profile shows good agreement with the exponential form for cross-shore variations in both the absolute depth h and local bottom slope S. There is poor agreement with the h = Ax profile relationship. in part because this Nile Delta profile is more reflective and has a greater concavity than allowed by the x dependence. The failure of the x profile form is still more evident in analyzing the beach-slope variations since it predicts an infinite slope at the shoreline. The exponential beach profile is a convenient mathematical relationship that should be useful in many applications.
Journal of Coastal Research, Apr 27, 2001
A model has been developed to evaluate the susceptibility of coastal properties to wave induced e... more A model has been developed to evaluate the susceptibility of coastal properties to wave induced erosion. The model includes analyses of the probabilities of extreme water levels due to tides affected by various oceanographic and atmospheric processes, and the runup elevations of storm waves on beaches. The application is to the Oregon coast where measured tides often exceed predicted astronomical tides by tens of centimeters, especially during the occurrence of an EI Nino. The measurements of wave runup on dissipative beaches typical of the Oregon coast depend primarily on the deep-water significant wave height, but when combined with other data sets show some dependence on the wave period and beach slope. Predicted extreme water elevations due to the combined processes are compared with measured elevations of the junctions between the beach face and the toe of foredunes or sea cliffs. The objective is to evaluate the frequency with which water can reach the property, providing an evaluation of the susceptibility to potential erosion. Application is made to a number of sites along the Oregon coast, revealing differences between the various littoral cells depending on the quantity of sand on the beach and its capacity to act as a buffer from wave attack. A more detailed application is made to the Newport Littoral Cell, demonstrating how this type of analysis can aid in making coastal management decisions. Although the application here is to the Oregon coast, the model can be used on other coastlines with evaluations of extreme tides and storm-wave runup specific to those locations.
The paper discusses a one-dimensional circulation model for the marina. Tides are modeled as long... more The paper discusses a one-dimensional circulation model for the marina. Tides are modeled as long waves and are assumed to be much longer than the marina. This circulation model is coupled to a conservation of mass model for a conservative pollutant. The pollutant model allows an examination of the marina flushing characteristics as well as the response to point, uniform, and time dependent sources of pollution. A numerical sedimentation model is also coupled to the circulation model. A suspended sediment model is developed based on the settling velocities of the sediment. Deposition is determined from conservation of sediment mass and residence times.
Ocean Engineering, 1991
Concrete armor units are commonly employed for the protection of shorelines and rubble structures... more Concrete armor units are commonly employed for the protection of shorelines and rubble structures. Their design is based primarily on hydrodynamic stability. However, several recent breakwater failures indicate that unreinforced concrete armor units are susceptible to structural failure for hydraulically stable wave conditions. The structural stability of 42-ton dolos armor units, both unreinforced and pre-stressed and subject to wave-induced pulsating loads, are examined in this paper.
Civil-Comp press eBooks, Dec 1, 2000
Proceedings of ... Conference on Coastal Engineering, Jan 29, 1986
A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring ... more A system composed of two buoyant flaps hinged at the sea floor and coupled with weighted mooring lines is modeled analytically and experimentally. The system behavior is described theoretically utilizing an eigenseries representation of linear wave theory in the vicinity of the breakwater. The structure dynamics are modeled in terms of structure weight, inertia, buoyancy, damping, mooring line tension and the wave pressure field. The mechanically coupled system provides shelter by reflecting incident waves and by attenuating wave energy through structural and viscous damping. The structure can be tuned to minimize wave transmission within a particular frequency range by changing the flap spacing and adjusting the mass and equilibrium position of the mooring line weights. The theory is validated with experimental results for models fabricated from inflatable, parallel-tube membranes. Buoyancy and inertia are changed by filling tubes with air and/or water. Single and double flaps are examined with and without mooring lines. Incident, reflected, and transmitted waves are measured as well as flap motion. Theoretical results are corroborated by the experiments and the importance of including damping in the model is demonstrated.
Journal of offshore mechanics and Arctic engineering, Feb 1, 1989
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Papers by William McDougal