Journal of Waterway, Port, Coastal, and Ocean Engineering

Sediment remediation involves restricted activities in the dredging process in order to minimize environmental risk. Operational constraints add significant capital cost to the overall project. This paper presents an example of the special conditions for a typical environmental dredging operation. REMSIM software, which simulates the sediment remediation processes, aids in planning for environmental dredging by reducing uncertainties in cost and performance estimations. The scow and bucket capacities, number of scows, and effective working time are parameters that improve productivity significantly as they are increased. The purpose of this paper is to help dredging contractors use their navigational dredging knowledge base to estimate costs, performance, and equipment selection for future environmental dredging projects where contaminant dispersion is a concern. REMSIM is used to obtain cost and productivity comparisons between environmental dredging and typical navigational dredging situations. Equipment and performance parameters can be adjusted in order to compensate for environmental dredging limitations while improving productivity and minimizing costs.

The flow behavior of turbulent wave boundary layers with weak currents was described using a numerical model. Horizontal velocities, shear stresses, turbulent eddy viscosities, and apparent roughnesses were described. The numerical model is based upon the fluid continuity and momentum equations in the vertical plane. The momentum equations retain the advection terms with vertical orbital velocity in contrast to previous numerical models. The horizontal velocities were calculated from the momentum equations, and the vertical orbital velocity distribution was obtained from the continuity equation. The Reynolds terms were modeled by a mixing length hypothesis. The model was compared with existing models for the wave friction factor by switching off the advection terms and produced similar answers to two existing models. Next, the model was applied to a wave-only flow case with the advection terms retained. The model reproduced the measured mass transport profile by van Doorn and Godefroy reasonably well. The model was then applied to wave-current flow cases with arbitrary intersection angles. The model results for 0°, 180°, and 90° agreed well with measurements by van Doorn and Godefroy and van der Stel and Visser, respectively. The model produced significant differences between the following and opposing current cases for the same wave condition. The model results suggest that the wave boundary layer flows for relatively strong waves and weak currents can be accurately described by taking account of the nonlinear advection terms by means of the vertical wave orbital velocity.

Different types of second-order superharmonic wave forces acting on jack-up platforms are studied. The nonlinear effect of variable wave surface (i.e., the inundation effect) is found to be the most significant. It is shown that a concentrated force acting at the mean water level of the structure can be used to represent the effect of the variable wave surface. The nonlinear transfer function of the modal wave force, with the inundation effect included, is derived. Frequency-domain analyses of the nonlinear wave force and structural response of a jack-up platform, modeled as a linear structure, are carried out to show the effect of inundation. The response spectral density functions obtained from the frequency-domain analysis are also compared with the spectra of time-domain simulations based on wave kinematics predicted by the Wheeler stretching and vertical uniform extrapolation methods.

Several accidents in which vessels impacted bridges have led to significant improvement of design procedures for impact protection of bridge piers. However, the guidelines usually call for such expensive solutions as piers that can withstand a design force derived from local waterway standards. This paper presents an idea for retrofitting a certain class of existing bridge fenders to serve more efficiently as protective structures against such impacts. Computational analysis was conducted using the nonlinear, dynamic computer code LS-DYNA. The research concentrated on analysis of a collision of a Jumbo Hopper barge with a bridge fender consisting of concrete piles. Several impact scenarios were considered, and four different retrofit solutions were compared with the original design. The analyses performed were used to assess the crashworthiness performance of the fender system, and specific retrofit recommendations, allowing for more efficient kinetic energy absorption, were developed and compared with the original design. The numerical results from 3D computational mechanics were also compared and interpreted using a simple special-case, two-body analytical approach.

This paper reports on extensive experiments on nonlinear wave groups that evolve in a hydrodynamic laboratory over long distances (200 m) from the generation of simple bichromatic waves. The deepwater experiments show large deformations of the wave group, with large increase of wave heights, depending on the value for the quotient of wave amplitude and frequency difference. The experimental results show little dissipation and reflections are virtually absent. A very efficient and accurate numerical code based on the full nonlinear surface wave equations, which has been developed for this purpose, reconstructs the experiments and enables one to investigate the evolution over much longer distances (reported here until 1,200 m) than in the laboratory.

Small floating objects do not alter the ocean wave characteristics. They are passively driven by waves. This is a theoretical study of the drift pattern of a small floating object in a monochromatic wave field. Small amplitude and deepwater conditions are assumed. Extension to intermediate water depth is straightforward. The effect of added mass and drag coefficients of the object, as well as the presence of wave reflection, is investigated. It is found that approximate analytic solutions exist for the two special cases where either the added mass coefficient or the drag coefficient vanishes. In general, the long-term motion of the floating object is oscillatory with the wave frequency but superimposed with a net drift. For the case when the drag coefficient vanishes, the net drift depends on the initial condition. Both forward and backward drifts are possible. For realistic added mass and drag coefficients, the motion is retarded. Sensitive dependence on the initial condition is still present. If a reflective wave is present, the motion of the object can be arrested. The higher the reflection, the more likely it is to trap the floating object. The critical reflection coefficient to trap the object is dependent on the added mass and the drag coefficient of the object.