Showing papers in "Journal of the Waterways, Harbors and Coastal Engineering Division in 1975"

Friction Factor under Oscillatory Waves

Abstract: Tests were performed in an oscillating water tunnel to determine the relationships between wave parameters and resulting bottom friction and shear stresses. The test results are presented in Stanton-type wave friction factor diagrams and results are compared with existing semitheoretical expressions. Transitions between flow regimes are also defined.

Wave Induced Pressures in Permeable Seabeds

Abstract: A theoretical investigation on the transmission of wave induced pressures into a permeable sea bottom has been performed. Assuming that the soil water is compressible, while the grain skeleton is assumed rigid, the resulting theoretical model describes an effective mechanism by which the soil permeability affects the pressure transmission.

Computation of wave heights due to refraction and friction.

Abstract: The equations for the wave orthogonals and the wave heights are presented for depth refraction of regular, long-crested, small amplitude surface gravity waves over an arbitrary bottom, using time as the independent variable. The effect of turbulent bottom friction on the wave height is included. The computer outputs are in the form of automatically plotted wave orthogonals with the wave heights written at discrete points along these paths. Systematic tests are presented for water areas with straight and parallel bottom contours. The errors inherently connected with the introduction of a grid plus a set of formulas for the differentiation and interpolation are examined for a horizontal bottom with an infinite long sinusoidal threshold. For one plane sloping bottom, information is given for the influence of the initial curvature of the wave front, bottom roughness, and initial wave height.

Man-Induced Changes of Middle Mississippi River

Abstract: The objectives of the 150 yrs of development along the Middle Mississippi River have been to provide flood protection to people and property on the flood plain and to provide a suitable channel for navigation. The River has been leveed to protect the people and property from floods and it has been contracted to provide the navigation channel. The objectives of flood protection and year-round river navigation have been met to a great extent in the Middle Mississippi River. However, the developments for flood protection and river navigation have produced a new river morphology and a different river behavior. The history of channel positions, riverbed areas, cross-sectional areas, and channel bed elevations describe how the river morphology has been changing. The variations in water and sediment discharge, stages, and stage versus discharge indicate how the river behavior has been changing.

Dynamic effects of ship passage on moored vessels

Abstract: A moored ship may experience strong disturbances even in a calm basin when other ships pass along at a sufficiently close range. These disturbances may be so strong in some instances that the sustained stress on the mooring lines might possibly exceed their breaking strength and result in breakage. The objective of this paper is to provide an engineering guide in estimating these loadings on moored ships, as this information should be of utmost value to harbor and ship engineers in securing berthing and mooring safety. The problem is investigated by using slender body theory approach. The effect of hydrodynamic interaction due to a steadily moving ship on a fixed vessel is derived. The resulting surge force, sway force and yaw moment acting on the moored ship are shown as a function of the passing-ship speed, the geometrical particulars of the two ships, their separation distance between ship centerlines, and the harbor water depth. Calculated results are presented graphically.

Effects of Entrance Loss on Harbor Oscillations

Abstract: By assuming a head loss across the harbor entrance the wave-induced response in a rectangular model harbor is studied theoretically. The loss is assumed to be quadratic in local velocity with a constant friction coefficient. Bottom and side-wall dissipation are not considered. It is shown that odd higher harmonics are present. The resonance characteristics of the fundamental harmonic response in the harbor are significantly influenced by the additional damping due to friction, especially for the lowest peaks. While in the perfect fluid theory these peaks heighten with diminishing entrance width, in the presence of friction the opposite is true for sufficiently narrow mouth.

Tide-Induced Mass Transport in Lagoons

Abstract: This paper examines the tide-induced mass transport in coastal lagoons which are connected to the ocean by more than one opening. An approximate analytic expression for the tide-induced mass transport in a lagoon of uniform width and depth at each end freely connected to a tidal basin is derived, assuming one-dimensional homogeneous flow. Analytic results are compared with numerically computed values of the mass transport. It is shown that the tide-induced mass transport can be an important factor in the renewal of the waters of shallow lagoons.

Second-Order Wave Force on Large Vertical Cylinder

Abstract: The purpose of this note is to analyze their second-order solution and to compare it with the approximate solution presented earlier by the writer. Plots are presented to show the effect and importance of nonlinear terms. The second-order theory is correlated against laboratory data.

Wave Height Distribution around Vertical Cylinder

Abstract: In the present study, wave heights and dynamic pressures at the still-water level on half of a vertical cylinder surface are measured Since the height is measured only between 0° and 180°, the symmetry of the distribution cannot be shown However, Galvin and Hallermeier established in their study that symmetry existed in all cases tested The purpose of this study is to show further that the height distribution follows crest distribution and dynamic pressure distribution which, in turn, suggests that even the pressure transducers around the structure may be used to establish direction of the wave

Anchor-Last Deployment Simulation by Lumped Masses

Abstract: Often the anchor is deployed as the final action in the mooring of buoys in the water. It has not been economical to calculate the transient conditions in the mooring line until a predictor-corrector technique was developed, which calculates the positions of the anchor and mooring line, the accompanying velocities, and the tensions throughout the line, all as a function of time. This study is based on a numerical lumped mass model representation of a single continuous nylon line 5,000 ft (1,525 m) long.

Wave Induced Pressures on Submerged Plates

Abstract: In the analysis, the plate is imagined to be rigidly suspended at an arbitrary fixed depth and then replaced by a vortex sheet the strength of which varies both temporarily and spatially. The velocity potential of this sheet is adjusted such that, when combined with the potential of the oncoming waves, boundary conditions on the plate, the free surface, and the bottom are approximately satisfied. The final vortex strength distribution can be determined allowing the velocity field and thus the pressure distribution on each side of the plate to be calculated. The experimental program was conducted using a 4x4x40ft (1.2x1.2x12-m) flume with a generator capable of producing waves having a broad frequency and amplitude spectrum in varying water depths. A flat plate of sandwich type construction was instrumented with small pressure transducers with outputs that were processed and recorded on an oscillographic recorder. Results are presented as instantaneous differential pressure distributions for associated wave positions, sequentially as the wave progresses. An advantage of the analytic approach is that pressure distributions as well as total forces may be readily obtained.

Statistics of Random Wave Field

Abstract: The effects of free surface fluctuations on the probability density function and spectrum of fluid particle velocities and pressure of a random gravity wave field are examined. The waves are assumed to be unidirectional, stationary, Gaussian, and in deep water. These are the usual assumptions of incompressible inviscid fluid and irrotational motion and wave. Expressions of the probability density function and spectrum of velocities and pressure are derived, and numerical results are obtained and presented graphically. Comparisons are made with the case in which the free surface fluctuations phenomenon is ignored. Results indicate that the quantities are all non-Gaussian. Pressure and horizontal velocity is unskewed and zero-mean. With and without the free surface fluctuations phenomenon considered, the spectra of the velocities and pressure differ appreciably; the difference being most pronounced at points above and around the mean water level.

Wave Forces on Bottom-Mounted Large-Diameter Cylinder

Abstract: A systematic set of experimental results for the wave force acting on a large horizontal bottom-mounted circular cylinder is presented and compared with a simple theory based on an unseparated flow model. The horizontal force is represented as an inertial component while the uplift force is represented by a lift force arising from the flow velocity plus a Froude-Krilov component. The test results show agreement with the theory.

Effect of Structures on Irregular Waves Compared to Regular Waves

Abstract: The transfer functions of two different types of structures were determined from measurements of incident and transmitted wave characteristics.The two structures, which consist of a fixed barrier and of A-shape floating breakwater, were submitted to the attack of irregular wave trains mechanically generated by a programming device. The effect of structures on waves were compared from the simulation of four types of wave spectra. Test conditions for the structures were also made variable by changing the depth of immersion and by varying the distance between the cylinders for the floating breakwater. Results indicate that under corresponding conditions the fixed barrier is more efficient to stop waves; however results for the floating A frame are less dispersive. These results were then compared to those obtained by subjecting the given structures to regular wave attack.

Waves of maximum height on uniform currents.

Abstract: Offshore design often involves the use of maximum wave height for a given water depth, yet the presence of a current is usually neglected. A constant current, having the same magnitude over the water depth, can be simply included in design by relating the wave propagating on a current to an equivalent wave propagating in still water. By relating the maximum height values for still water to those on a current, a breaking index curve is generated for waves on uniform currents. The effect of the current on the wave crest displacement is also examined. Finally, a curve is presented to show the magnitude of the maximum opposing currents for which wave groups can propagate upstream. Two examples are provided to illustrate the use of the results.

Optimum Dredged Depth in Inland Waterway

Abstract: Criteria for optimum depths in the inland waterway network is minimized value of the sum: cost of tow industry plus cost of waterway structures, in the open rivers mainly cost of dredging. Volume of dredging may be estimated by use of the relationships between the most important hydrological and morphological parameters that determine the degree of stability of riverbed. If extensive dredging is planned, it is necessary to take into account a change of hydraulic parameters of river that will be followed by a lowering of the water level and depth in the channels. In the reaches of open river with sufficient large seasonal oscillation of water levels, it is important to calculate average usable (seasonal or annual) depth and draft on base of relationships between water level and controlling depth. The plan described in the paper represents a simple way for solution to the problem of optimal channel depth, useful for planning purposes and economic estimates.

Computation of Flow through Masonboro Inlet, N.C.

Abstract: The Masonboro Inlet system is a complex arrangement of channels connecting the coastal waterways to the Atlantic Ocean. The flow through the system was computed by means of a numerical model based on the equations of unsteady flow which represent the laws for the conservation of mass and momentum. An implicit method was used to find the solutions for the finite difference equations. The method requires that the basic equations be satisfied at all locations simultaneously. A comparison of the computed results with the field observations demonstrates the accuracy, reliability, and efficiency of the method. It is believed that the simulation model can handle other inlets with little difficulty, because other inlets are generally much simpler than the Masonboro Inlet.

Physicochemical Properties of Dredge Spoil

Abstract: Physicochemical changes resulting from the subaerial exposure of dredge spoil during land disposal were investigated using five fine-grain bottom sediment samples from the lower Great Lakes. Air-drying of unoxidized postglacial sediments increased cation exchange capacity and decreased plasticity. Air-drying of a Pleistocene oxidized sediment did not affect these parameters appreciably. The difference is attributed to an irreversible collapse of weathered swelling minerals and the oxidation of ferrous and manganous ions in postglacial sediments. Mineralogical composition and changes caused by citrate-dithionite extraction were examined by X-ray diffraction, infrared absorption, electron-optical, and surface area measurements.

Spartina Revegetation on Dredge Spoil in SE Marshes

Abstract: Spoil from the dredging of harbors, rivers, and the Inland Waterway when deposited on salt marshes often permanently destroy these important natural resources. Portions of destroyed marsh can be restored through transplantation of the major marsh plant Spartina alterniflora. This was accomplished in a typical silt-clay spoil site along the Intra-coastal Waterway in Georgia for less than –100/acre. Thirty percent of the transplants survived and are continuing to spread 18 months after planting. Elevation of the spoil is of prime importance for transplants and at lower elevations survival rates are as high as 75%. The use of seeds and nursery grown seedlings was not as successful; only 13% of the seeds germinated and none of the seedlings survived.

Analytical Model of Hydraulic Pipeline Dredge

Abstract: A hydraulic pipeline dredge system is a complicated combination of mechanical equipment, operational variables, and soil-water interactions. Of primary interest is knowledge of the maximum solids o...

Wave Motion in Rockfill

Abstract: A mathematical model, coupling an external nonlinear wave and the resulting internal flow in a rockfill embankment with an impervious core is presented. The method of characteristics along with a f...

Energy and Pollution Concerns in Dredging

Abstract: Dredging equipment in the United States should be augmented for a more versatile dredging fleet by the addition of the mechanical bucket ladder dredge for channel work. The addition of the bucket ladder dredge is especially desired in view of the relatively new concerns of energy conservation and pollution abatement. From these concerns, the former is well defined but the latter is not. In most cases, both concerns oppose each other and interfere with the conventional concept of economy. The new concerns are expected to shift the conventional concept of economy toward efficiency in terms of amount of bottom density material dredged, transported, and deposited per unit of fuel. This shift is expected to be accompanied by a change in emphasis from maximum solid flow rate toward maximum effluent density. Bucket ladder dredges are inherently well suited to satisfy the new concerns, especially at long transport distances.

Engineering Challenges of Dredged Material Disposal

Abstract: In fulfilling its mission, the Corps has been responsible for the annual dredging of approx 380,000,000 cu impacts of the disposal of these materials. The U. S. Army Engineer Waterways Experiment Station is conducting a nationwide research program to develop environmentally compatible, technically satisfactory, and economically feasible disposal alternatives, including consideration of dredged material as a manageable resource. Problem identification and assessments are summarized, and program progress with emphasis on engineering aspects of the study is examined.

Strategic Approach to Estuarine Environmental Management

Abstract: It is reasoned that ecological systems must be examined from a spectrum of views ranging from those of high perspective-low detail to those of low perspective-high detail. Such a spectrum should provide complimentary views of real world systems the “true” nature of which is beyond our capacity to perceive. A high perspective low detail view is employed to examine the organization, function, and requirements of whole estuarine systems. A number of concerns pertinent to comprehensive environmental planning of estuaries are identified. A planning approach is presented that calls for the uneven distribution of development activities among Oregon’s estuarine systems. This approach places a high value on environmental variety, including a wide range of undeveloped ecosystems. Cluster communities with intervening open space are called for within systems selected for development. A number of methods, concerns, and problems related to the implementation of this approach are identified. Although the approach is recommended for Oregon’s estuaries, emphasis is given to general concepts that have wider applicability.