Journal of Waterway, Port, Coastal, and Ocean Engineering

A simple methodology is presented to examine the effects of fixed and floating structures on seabed stability. Liquefaction potential is estimated using Biot consolidation theory to model the dynamic soil response. Scour potential and stable grain sizes are determined from a simple incipient motion model. For a fixed structure, the potential for liquefaction and scour may be estimated from the incident wave conditions and the reflection coefficient. In general, the floating‐structure soil responses are smaller than those for the fixed case, except when the wave frequency is near the natural frequency of the structure. At the natural frequency, the liquefaction potential may be twice that of the fixed case and the stable grain size, an order of magnitude larger.

Capping is the controlled, accurate placement of contaminated dredged material at a disposal site which is covered by a cap of clean isolating material. Capping projects are typically categorized as either level‐bottom placement or contained aquatic disposal. Field experience with subaqueous capping is limited, but 11 sites have been identified where the technique has been applied. Site selection considerations for capping projects are similar to those for any open‐water disposal. The influences of several site characteristics on capping have been identified and discussed. Modeling methods are available to aid in evaluating sites and designs. Additional information on cap materials, placement, and monitoring techniques are provided.

The in‐line hydrodynamic forces on submerged tubular members have been investigated experimentally for different positional depths (z/h), relative clearances (e/D), diameter‐to‐water depth ratios (D/h), and horizontal gap‐to‐diameter ratios (G/D). The forces due to wave‐current interaction on the tubular members near the free surface show an increase of about 40% for $D/h=0.20\text{,}$ compared with the force due to wave action only. For the tubular members located near the bed, the increase is on the order of 80%, irrespective of D/h. The results indicate that tubular members behave as an independent unit for $G/D>2.7\text{,}$ and the varation of dimensionless force $F_{\mathrm{DIM}}$ with z/h, instead of in terms of e/D, is a unique approach. Variation of drag and inertia coefficients indicate that these coefficients are functions of z/h, D/h, and G/D, in addition to Reynolds number. Scale effects on the prototype prediction of force are also critically discussed.

A method of analysis of the nonproportionally damped motions of fixed offshore structures in waves is presented. The damping considered is that due only to radiation, and is assumed to be linear. Since both the radiation damping and the added mass are frequency dependent, the damping is, by nature, nonproportional. Hence, the standard normal‐mode analysis cannot be used. To isolate the modes, the matrix equation of motion of the assumed lumped‐mass system is first transformed into a first‐order equation. The complex eigenvectors and eigenvalues for the underdamped system are then obtained through matrix iteration, The displacement of each mass is obtained in deterministic seas. One of the most important results of this analysis is the demonstration of the ability of the technique to predict the movement of the nodal points over time. That is, the nodal points move up and down the centerline of the structure over each period. This means that the analyst can predict the positions of maximum stresses and strains over each cycle, a capability that the standard normal‐mode technique lacks.

A comprehensive list of wave parameters and wave‐related functions is developed to accommodate modern laboratory and field programs and to help investigators clarify symbols, nomenclature, and definitions used. The list is suggested as a reference with the aim of promoting uniformity and reducing the confusion of present usage. Parameters in the list are grouped for easier reference. The list was originally published by the International Association for Hydraulic Research (IAHR) and Permanent International Association of Navigation Congresses (PIANC). It is provided here to increase its accessibility and use by ASCE members, readers, and contributors.

A complete second‐order solution is presented for the hydrodynamic forces on a bottom‐mounted, surface‐piercing vertical cylinder of arbitrary cross section in water of uniform, finite depth. Exploiting the constant structural cross section, the vertical dependency of the linearized potentials is expressed in terms of eigenfunction expansions. The first‐order problem is solved using a two‐dimensional Green's function approach. Through application of Green's second identity, the second‐order forces due to the second‐order potential are expressed in terms of free‐surface and structural integrals involving first‐order quantities and associated linearized radiation potentials obtained by oscillating the structure at the second‐order wave frequency. An efficient numerical technique treats the oscillatory free‐surface integral appearing in the second‐order force formulation. Integration of this term in the far‐field utilizes the asymptotic behavior of the potential components, eliminating need to define a truncation boundary specifying the extent of a finite, free‐surface computational domain. Numerical results are presented for a cylinder of elliptical cross section that illustrate the relative importance of secondorder effects for a range of wave frequencies and incident wave directions.

The geometry of arrested thermal wedges is studied on the basis of Schijf and Schoenfeld's one‐dimensional model. The derived equations for the dimensionless length and shape of the wedge are also given in graphic form in terms of the Darcy‐Weisbach interfacial‐friction coefficient, $f_i\text{,}$ and easily measured gross flow and density parameters. However, $f_i$ cannot be estimated analytically. The difficulty of estimating $f_i$ is bypassed by approximation of previously known relations or by new analytical forms that contain the free‐surface slope instead of $f_i\text{.}$