Journal of Waterway, Port, Coastal, and Ocean Engineering

In the present engineering practice, direct formulas are not given for the preliminary hydraulic design of Jarlan‐type breakwaters: Only qualitative observations and heuristic considerations are reported. The writers analyze the wave attenuation produced by the permeable structure and propose design formulas that can be used for the optimized hydraulic design of Jarlan‐type breakwaters. The proposed model, based on the linear wave theory, is validated by comparison of the theoretical results with the experimental measurements of other authors. The results show that the Jarlan‐type breakwater with a single chamber gives the most effective wave reduction in the range of practical applications and that no particular configuration of the porous wall can be suggested as the best one. The size of the breakwater cannot be standardized, since the optimum hydraulic design of the structure is linked to the parameters of the design wave. Moreover, the proposed design formulas may be used to approximately predict the response of the structure to incident irregular waves.

This paper presents the results of an experimental investigation on scour around piles exposed to waves. In addition to the actual scour tests, bed shear‐stress measurements and a flow visualization study are carried out. The effects of lee wake and horseshoe vortex are demonstrated to be the two key elements in the scour process. The development of these flow structures mainly depends on the Keulegan‐Carpenter (KC) number that hereby becomes the main parameter that governs the equilibrium scour depth on a live bed. Based on the present data, a design equation is established, relating the scour depth to the Keulegan‐Carpenter number. For the values of the Keulegan‐Carpenter number below six, the scour around the pile practically ceases to exist. The scour depth normalized by the pile diameter is found to increase with increasing Keulegan‐Carpenter number and approaches its steady‐current value for Keulegan‐Carpenter numbers above approximately 100.

This paper presents a new design methodology for long, offshore piles. The paper defines the soil‐pile “reserve capacity” available after cyclic degradation due to storm wave loading. The reserve capacity design method (RCDM) involves (1) Definition of the static and cyclic soil‐pile, load‐deflection behavior; (2) evaluation of the initial static and the cyclically degraded pile capacities; and (3) determination of the reserve capacity of the pile to resist the design loads. The use of the method is demonstrated in the paper through an example problem for a typical tension leg platform located at a deepwater Gulf of Mexico soft‐clay site.

The process of reflection, transmission, and propagation of long waves past a step and onto a horizontal shelf is examined analytically and experimentally using solitary waves. It is found that reflection can be described well by a linear theory for relatively small incident waves and/or relative depths, but nonlinear effects become important as wave heights and relative depths increase. A nonlinear analytical approach must be used to evaluate the transmission process onto the shelf, except for small‐amplitude waves. Although the propagation of the waves on the shelf can be treated linearly close to the step, nonlinear effects soon become important and eventually, in the far field, dispersion also becomes important.

It has been suggested that Bragg reflection, the combined coherent wave reflection from a few low‐lying shore‐parallel bars, might be used to protect a beach against storm‐wave attack. Numerical models are used to examine two issues relating to the feasibility of this concept: the degree of erosion protection provided by reflecting a portion of the incident wave energy, and the degree of wave reflection that can be generated by a bar field of varying geometry. The results show that a Bragg‐reflection bar field must reflect about one‐quarter of the incident wave energy to provide a significant measure of storm erosion protection. Bar fields with uniform spacing are capable of producing the required magnitude of wave reflection, but lack sufficient bandwidth. Bandwidth can be increased by staggering the spacings between bars, however, this produces a concurrent decrease in wave‐reflection magnitude. Bragg‐reflection bar fields appear capable of providing a limited measure of storm erosion protection along U.S. Gulf Coast and Atlantic Coast beaches, but their bandwidth may be too limited for use along Pacific Coast beaches.

Due to ever‐increasing demands on our ports and harbors from both industrial and recreational users, conflicts of interest concerning anchorages, marinas, and water‐dependent industrial plants will become more and more common as our economies grow. This paper develops a theoretical methodology to study the economic impact of eliminating anchorage space in a deep‐draft anchorage system. The theoretical framework consists of a standard queueing model adapted to an anchorage system with random arrivals and departures and a stochastically formulated cost function. The model structure is applied to the Lower Mississippi anchorage system under various assumptions related to arrivals, staying times, and other basic cost additions that might occur.

Field observations of a shoaling, nonbreaking, directionally spread wave field are simulated in a laboratory basin to determine whether laboratory artifacts cause significant distortions of the shoaling process. The laboratory wave field is measured with scaled arrays of surface‐elevation sensors similar to the arrays used for the field observations. However, differences in the laboratory and field beach slopes (0.033 and 0.025, respectively) do not allow precise replication of the field conditions in the laboratory. Therefore, a nonlinear wave propagation model with no adjustable parameters (previously successfully compared to a wide range of field data) is used to show that differences between the laboratory and field data sets are caused primarily by the different beach slopes. The observations demonstrate, in agreement with the model, that it is possible to compensate partially for differences in beach slope by altering the initial conditions. With such compensation, the evolution of surface‐elevation power spectra, bispectra, and skewness and asymmetry are remarkably similar in the laboratory and field. Frequency‐directional spectra measured just outside the surf zone also show similar nonlinear effects in both field and laboratory data. Based on this case study, the laboratory directional wave basin appears to be useful for investigating the linear and nonlinear evolution of random, two‐dimensional waves on beaches.

Results of an experimental and theoretical study of the positive drift of a 1.7-m model of a backward-bent duct barge (BBDB) wave energy conversion system are presented. The results show that the positive drift of the BBDB model is experienced over a rather wide range of wave frequencies. This frequency range depends on a number of parameters that include the water depth and the weight distribution of the barge. The driving force for the positive drift is at the 90° bend in the internal water-column duct located at the bow, while the direction of the drift is a function of the phase difference between the water-column oscillations and the external wave at the bow.

Stokes-mode edge waves in an inviscid-fluid and irrotational-flow domain have simmlar characteristics as deep-water waves. The mathematical presentations of edge waves are identical, except the coefficients, to those of deep-water waves when the coordinate axes are rotated so that one of the axes points along the beach surface in the offshore direction. Although the similarities appear to exist in their nonlinear wave solutions, the second-harmonic component on the runup wave profile of edge waves arises from the first higher-order solution whereas, in deep-water waves, such a characteristic appears in the second higher-order solution. This early appearance of the nonlinear effect in the runup profile is due to the flow restriction caused by the beach geometry. On the other hand, the vertical water-surface displacement of edge waves has no second-harmonic component at the first-order solution, instead has the characteristic of the set-down of mean water level.