Showing papers in "Journal of Waterway Port Coastal and Ocean Engineering-asce in 1997"

Breaking criterion and characteristics for solitary waves on slopes

Abstract: ABST.RACT: Sho~ling and breaki,ng of solitary waves is computed on slopes from 1:100 to 1:8 using an expenmentally validated fully nonhnear wave model based on potential flow equations. Characteristics of waves are computed at and beyond the breaking point, and geometric self-similarities of breakers are discussed as a fun?tion of w~ve height and bottom slope. No wave breaks for slopes steeper than 12°. A breaking criterion is denved for rmlde.r slopes, based on val~es of a nondimensional slope parameter So' This criterion predicts both whethe~ waves wIll bre~ or ~ot and which type of breaking will occur (spilling, plunging, or surging). Empirical expressIOns for the bre~ng mdex and for t~e depth and celerity at breaking are derived based on computations. All resul~s agree ~ell With laboratory expenments. The nonlinear shallow water equations fail to predict these results w~th sUfficle~t accuracy at the breaking point. Prebreaking shoaling rates follow a more complex path ~han prevlOus!y reah~ed. Postbreaking beha~iors exhibit a rapid (nondissipative) decay, also observed in exper­ Iments, associated With a transfer of potential energy into kinetic energy. Wave celerity decreases in this zone of rapid decay.

Numerical Simulation of Submarine Landslides and Their Hydraulic Effects

Abstract: The submarine flow slides and their hydraulic effects are studied by numerical means. These types of landslides are assumed to separate into a dense flow close to the bed and a turbulent dispersion above it. A two-dimensional fluid mechanics mixture model based on Navier-Stokes' equations has been developed to study water waves generated by these landslides. The dense part is considered as a viscoplastic fluid, whereas the dispersed part is modeled by an ideal fluid. The rheological parameters of the model comprise a diffusion coefficient, a Bingham yield stress, a viscosity coefficient, and friction on the slope. First, the numerical model is validated with an analytical solution for a viscous and a Bingham flow. Then, it has been tested for a rigid box sliding into water along an inclined plane. The results of this simulation have been compared with experiments conducted in a channel. Finally, laboratory experiments consisting in the slide of a gravel mass have been carried out. The results of these experiments have shown the importance of the sediment rheology and the diffusion. The model parameters are adjusted by trial and error to match the observed landslide flow.

Performance of Cage Floating Breakwater

Abstract: Conventional floating breakwaters are examined and the feasibility of developing a cage floating breakwater is explored. Earlier studies on floating breakwaters reveal that, to achieve a transmission coefficient (\iK\i\dt) less than 0.5, the breakwater width to wave length ratio (\IW/L\N) should necessarily be greater than 0.4 for most of the configurations. Recent studies on cost-effective floating breakwaters indicate that by fixing a row of pipes below the floating body, the \IW/L\N requirement can be reduced to 0.15 without any compromise in the performance. This concept has been adopted in developing a new configuration to serve as: (1) a floating breakwater; and (2) as a possible shallow water cage culture unit. Experiments were conducted to study the performance of the cage floating breakwater under wave and wave-current environment. The results on transmission and reflection coefficients are presented and compared with those reported in the literature. The variation of water surface oscillations and velocities within the cage, the effect of mooring line stiffness, and initial tension on transmission characteristics are also discussed.

Analytical Solutions of One-Line Model for Shoreline Change near Coastal Structures

Abstract: Analytical solutions provide a simple and economical means of quickly estimating qualitative and quantitative responses of the shoreline to a wide range of environmental and engineering conditions. This paper presents analytical solutions for shoreline evolution in the vicinity of coastal structures, including detached breakwaters, seawalls, and jetties with and without wave diffraction. The solution for a detached breakwater illustrates the growth of a salient with time behind the breakwater and the associated initial shoreline retreat at locations across from the breakwater tips. A simple solution describing flanking of a seawall is obtained by using two different solution areas where the longshore sand transport rate and breaking-wave angle vary. A similar technique is used to model diffraction downdrift of a groin or jetty by allowing the wave angle to vary with the distance alongshore according to a specified function or by employing a large number of solution areas. Cases are also presented for the accumulation updrift a groin and the shoreline response in a groin compartment with a breaking wave angle that varies sinusoidally in time. A solution for a single groin illustrates the impact of bypassing on the updrift accumulation.

Predicting Caspian Sea Surface Water Level by ANN and ARIMA Models

Abstract: Fluctuations of the Caspian Sea's mean monthly surface water level for the period of January 1986 to December 1993 were studied. The time series data showed an increasing trend and seasonal variations. Artificial neural network (ANN) and multiplicative autoregressive integrated moving average (ARIMA) modeling were used to predict the time series data. The ANN's input and output consisted of the last 12 months and the current month surface water levels, respectively. The selected ARIMA model required one-month regular differencing, 12-month seasonal differencing, and had a moving average component of lag 12. The ANN and ARIMA predictions for the period of January to December 1993 were very reasonable when compared with the recorded levels. On average, the ANN model underestimated the sea level by three cm, whereas the ARIMA model overestimated it by three cm. The monthly predictions for January to December 1994 presented a continuation of the Caspian Sea water surface level rise that would have various adv...

Absorbing-Generating Boundary Condition for Shallow Water Models

Abstract: An absorbing-generating boundary condition is derived for the two-dimensional-horizontal nonlinear shallow equations using the method of characteristics. It assumes local superposition of the incoming and outgoing long waves at the boundary, and uses a relationship between the flux and surface elevation of the waves. This boundary condition allows the outgoing waves to leave the computational domain through the boundaries with a minimum of reflection, while specifying incoming waves at the same boundaries. The boundary condition's absorbing properties are tested for both linear and nonlinear waves for a range of amplitudes and of angles of incidence. Its performance is compared to the classical Sommerfeld radiation condition for the linear case and is shown to cause significantly less reflection errors, especially for oblique angles. Also, a case of simultaneous absorption and generation of waves at the same boundary is analyzed where it is shown that the errors are of the same order as for the case of ab...

Extended Linear Refraction-Diffraction Model

Abstract: An alternative derivation of the extended refraction-diffraction equation is presented. The bottom curvature and slope-squared terms ignored in the mild-slope equation are included to account for relatively steep and rapidly undulating bathymetry. The linear elliptic partial differential equation is solved by the hybrid element method and applied to three-dimensional bedforms. Quadratic triangular elements are used in the model so that the curvature can be calculated directly from the water depth defined at the nodes. The model is illustrated by simulating wave reflection from a ripple bed and wave transformation over a circular shoal in which previous experimental and numerical results exist. The relative effects of the additional terms and their significance in the model prediction are examined in a numerical experiment.

Numerical Simulation of Sheetflow as Granular Material

Abstract: In the sheetflow regime, the concentration of the sediment is so high that particle/particle interaction plays an important role. In this study, a numerical simulation of the sediment transport in the sheetflow regime is performed on the basis of the Distinct Element Method (DEM) with a focus on particle/particle interaction. The characteristics of the vertical velocity profile of sediment particles in the sheetflow regime, which were reported in previous experiments, are reproduced well by the present simulation. Furthermore, the mechanism to determine the velocity profile of the sediment particles is clarified from the viewpoint of the granular material dynamics. Finally, the half-cycle averaged sediment transport rate under an action of sinusoidal oscillating flow is estimated from the result of the simulation under the quasi-steady assumption and is compared with the result of previous experiments.

Oblique Wave Diffraction by Parallel Thin Vertical Barriers with Gaps

Abstract: The problem of oblique water wave diffraction by two equal thin, parallel, fixed vertical barriers with gaps present in uniform finite-depth water is investigated here. Three types of barrier configurations are considered. A one-term Galerkin approximation is used to evaluate upper and lower bounds for reflection and transmission coefficients for each configuration. These bounds are seen to be very close numerically for all wave numbers and as such their averages produce good numerical estimates for these coefficients. Only the bounds for the reflection coefficient are numerically computed. These are also numerically compared with the results obtained by using multiterm Galerkin approximations involving Chebyshev polynomials for a wide range of parameters. Numerical results for the reflection coefficients for the three barrier configurations are presented graphically. It is seen that total reflection occurs only for the surface-piercing barriers while total transmission occurs for all the three configurations considered here. It is also observed that the introduction of an equal second barrier to a submerged barrier increases the reflection coefficient considerably in some frequency bands and as such submerged double barrier configurations are preferable to a submerged single barrier for the purpose of reflecting more wave energy into the open sea.

Model for severity of hurricanes in gulf of mexico

Abstract: Observational and theoretical evidence suggests hurricane severity can be affected by local oceanographic features. The most important of these features in the Gulf of Mexico are the Loop current and its associated eddies. These features are large bodies of warm subsurface water that, theory suggests, can act as an energy source for passing hurricanes. Present design standards for the offshore oil industry assume no spatial variability, so these findings have substantial financial implications for design of new structures and requalification of thousands of existing ones. We propose a statistical model and an estimation procedure that accounts for the spatial variation of the probability distribution function of hurricane severity. The model is based on the representation of the hurricane process as a marked line process where the hurricane tracks are idealized as linear segments with respect to a given location, and where the marks measure the severity of hurricanes. The efficiency of the estimation procedure is evaluated through simulations for different types of spatially dependent probability distribution functions. The procedure is finally applied to a data set comprising the 100 most severe hurricanes in the Gulf of Mexico from 1900 to 1989.

Seismic risk reduction at ports: case studies and acceptable risk evaluation

Abstract: Japan's Kobe Port was severely damaged during the Hyogoken Nanbu Earthquake of January 17, 1995, suffering a nearly total loss of operations and direct losses estimated to be about $5.5 billion. This paper summarizes the causes of this damage, and uses this experience as a case study to show that the economic benefits of including seismic risk reduction methods in the design and construction of ports in areas of moderate-to-high seismicity can far exceed the increases in initial construction costs. The paper also describes and illustrates an “acceptable seismic risk” evaluation procedure for assessing the viability of alternative seismic risk reduction strategies for a given port.

Occurrence Properties of Giant Freak Waves in Sea Area around Japan

Abstract: Wave data on \iH\d1\d/\d3, \iH\dm\da\dx, etc. observed in the sea area around Japan are analyzed to investigate the probability distribution of \iH\dm\da\dx/\iH\d1\d/\d3 and the occurrence properties of giant freak waves with wave heights exceeding 2\iH\d1\d/\d3 and 10 m. The analyzed results show that the occurrence probability of the giant freak waves could be argued generally under the Rayleigh extreme distribution, although it varies from area to area. Four-ninths of the extreme waves having the largest maximum individual wave height (\iH\dm\da\dx)\dm\da\dx at each observation point are occupied by the giant freak waves and moreover, they occur in lower sea states rather than in the severest one.

Flexible Membrane Wave Barrier. II: Floating/Submerged Buoy-Membrane System

Abstract: The interaction of water waves with a tensioned, inextensible, vertical flexible membrane hinged at the sea floor and attached to a solid cylindrical buoy at its top, was investigated in the context of two-dimensional linear wave-body interaction theory. Both submerged and surface-piercing buoy/membrane wave barriers were considered. A two-domain boundary element program was developed based on a discrete-membrane dynamic model and simple-source distribution over the entire fluid boundaries. Since the boundary condition on the membrane is not known in advance, the membrane motion and velocity potentials were solved simultaneously. The accuracy and convergence of the developed program were checked using the energy-conservation formula. The numerical results were further verified by checking several limiting cases and through comparison with the experiments conducted in a 2D wave tank. Using the developed computer program, the performance of surface-piercing or submerged buoy/membrane wave barriers was tested with varying buoy radius and draft, water depth, membrane length, and mooring-line stiffness. The performance of the three different mooring types was also investigated. From our numerical examples, it can be concluded that the buoy/membrane wave barrier can function as a very effective breakwater if it is properly designed.

Cross-Shore Variation of Wave Reflection from Beaches

Abstract: The cross-shore variation of the local reflection coefficient R is examined under the assumptions of normally incident wind waves on beaches with alongshore uniform bathymetry. The existing three-gauge method is modified to estimate R for the sloping bottom. A new method is developed to estimate the incident and reflected root-mean-square (RMS) wave heights from the measured RMS wave height and wave setup. These methods are used to analyze six runs from the large-scale SUPERTANK data set. The estimated values of R are affected little by the formation of a bar and increase shoreward with the increased percentage of breaking waves. One set of the DELILAH field data on a barred beach is also analyzed using collocated pressure and velocity measurements. This data set confirms the negligible effect of the bar on the variation of R over the bar in the absence of wave-breaking on the bar crest. These crude estimates of R suggest that the reflected wind waves may not be negligibly small in comparison to the incid...

Salinity Control in Mississippi River under Drought Flows

Abstract: Record low flow on the Mississippi River in 1988 created a potential for record prior movement of the saltwater wedge from the Gulf of Mexico, threatening water supply for the city of New Orleans and nearby communities. The U.S. Army Corps of Engineers employed one-dimensional and two-dimensional numerical models to design temporary underwater sill that would limit upstream salinity intrusion. The sill was constructed and successfully protected the freshwater supplies of the New Orleans area with cost savings of over $50,000,000. Postdrought analysis showed that the models accurately predicted behavior of the salt wedge and the sill.

Kinematic Undertow Model with Logarithmic Boundary Layer

Abstract: A new kinematic undertow profile model is developed to relate the mean horizontal velocity, bottom shear stress, and boundary layer thickness in a simple but general manner. The model combines a logarithmic profile in the bottom boundary layer with a parabolic profile in the interior layer. Use of a logarithmic profile is justified using our laboratory measurements for regular waves spilling on a rough, impermeable slope. Two forms of the model are presented, each with one calibration coefficient associated with the mean bottom shear stress. By adjusting the calibration coefficient at each measuring line, the model is shown to be capable of predicting the measured undertow profiles both inside and outside the surf zone for our rough slope case and for smooth slope cases from the literature. The model does not predict the overshoot in the bottom boundary layer for the rough slope case outside the surf zone. The predicted velocity profile for the smooth slope case in the bottom boundary could not be verifie...

Model for recurrence rate of hurricanes in gulf of mexico

Abstract: A model and estimation procedure are proposed for the recurrence rate of hurricanes in the Gulf of Mexico. The model and the estimation procedure are based on the representation of the hurricane tracks as a locally linear line process. The spatial variation of the intensity of the process is estimated through a kernel estimation procedure. The optimal degree of smoothness is selected through a resampling procedure and good­ ness-of-fit statistics. Simulations demonstrate that the model and estimation procedures can detect statistically significant spatial variations in the rate of occurrence of hurricanes. The emphasis of the study is on storms that have affected the offshore areas between the northwest Florida panhandle and the Texas coast. The optimal model indicates that the spatial variation of the recurrence rate is statistically significant and that the highest frequency of hurricanes occurs offshore west of New Orleans. The implications from a hurricane hazard point of view are most significant for deepwater offshore projects, while the recurrence rate appears to be almost constant along the western coast of the Gulf in shallower waters. ABSTRACT: A model and estimation procedure are proposed for the recurrence rate of hurricanes in the Gulf of Mexico. The model and the estimation procedure are based on the representation of the hurricane tracks as a locally linear line process. The spatial variation of the intensity of the process is estimated through a kernel estimation procedure. The optimal degree of smoothness is selected through a resampling procedure and good­ ness-of-fit statistics. Simulations demonstrate that the model and estimation procedures can detect statistically significant spatial variations in the rate of occurrence of hurricanes. The emphasis of the study is on storms that have affected the offshore areas between the northwest Florida panhandle and the Texas coast. The optimal model indicates that the spatial variation of the recurrence rate is statistically significant and that the highest frequency of hurricanes occurs offshore west of New Orleans. The implications from a hurricane hazard point of view are most significant for deepwater offshore projects, while the recurrence rate appears to be almost constant along the western coast of the Gulf in shallower waters.

Hydrodynamic Forces on Piggyback Pipeline Configurations

Abstract: The external hydrodynamic loading exerted by steady incident flows on submarine pipelines is investigated. Of particular interest are the hydrodynamic interactions between pipeline and seabed, and between two pipelines of different diameters. The latter gives rise to the “piggyback” configuration, where one cylinder (the piggyback) is situated either on top of, or slightly above, a larger diameter cylinder (the main pipeline). Drag and lift coefficients, \IC\N\DD\N and \IC\N\DL\N, are obtained experimentally for Reynolds numbers R between 9×10\u4 and 3×10\u5, corresponding to currents of 0.5–1 m/s (1–2 knots) and main pipelines of diameter 400–600 mm (16–24 in.). For piggyback configurations typical of those used by the offshore industry, the proximity of the two pipelines to each other can increase the values of \IC\N\DD\N for single cylinders by 50%–100%. The direction of the transverse lift force is also of practical importance, as it determines whether the pipelines have a tendency to self-bury or free-span. This appears to depend on R and the gap ratio \Ie/D\N between the seabed and (main) pipeline. The characteristics of both a single pipeline and a piggyback configuration near the seabed are discussed. For the piggyback configuration at subcritical R, it is found that \IC\N\DL\N 0 at higher (critical) R and this may increase the likelihood of generating free-spans along the pipeline.

2d numerical study on tidal circulation in strait of dover

Abstract: A two-dimensional numerical study of the tidal circulation in the Strait of Dover is presented. In this study, a depth-averaged model, which employs a finite-difference, splitting technique was used. The present model was calibrated with observed spring tides, and then verified by observed neap tides. Using a fine computing mesh, we obtained detailed information on the hydrodynamic structure of tidal circulation in the Strait of Dover. Several eddy cells due to complex topography and morphology of the studied domain are detected for the first time. The model results show: (1) the residual-transport current field is characterized by two currents, one flowing closely to the French coastline and another coming from the western English Channel, flowing along the English coast and then meeting the former to pass through the strait; and (2) under the effect of the Earth's rotation, sea-surface gradients as well as velocity vectors are rotary counterclockwise.

Dynamic coupling of wave and surge models by eulerian-lagrangian method

Abstract: An Eulerian-Lagrangian method is employed in a third-generation ocean wave model and a two­ dimensional storm surge model that are dynamically coupled. The stability, accuracy, and consistency of the synchronously coupled models are first verified using an idealized case of waves on a Gulf Stream Ring by comparing the computed results with that by others. Application of the coupled models to two hindcastings of storms occurred in the northern South China Sea under different forcing conditions, taking into account the mutual influences of waves and currents, gives satisfactory results in comparison with observations. Calculations show that the surface wave-dependent drag has significant effects on the surges, but the wave radiation stress has only slight effects. For prediction of wave heights, the inclusion of both the wave-dependent drag and the wave radiation stress in the storm surge model has a very small effect on the computed results. The coupled models can be easily applied to prediction or hindcasting of ocean waves and storm surges without the need for further treatment. ABSTRACT: An Eulerian-Lagrangian method is employed in a third-generation ocean wave model and a two­ dimensional storm surge model that are dynamically coupled. The stability, accuracy, and consistency of the synchronously coupled models are first verified using an idealized case of waves on a Gulf Stream Ring by comparing the computed results with that by others. Application of the coupled models to two hindcastings of storms occurred in the northern South China Sea under different forcing conditions, taking into account the mutual influences of waves and currents, gives satisfactory results in comparison with observations. Calculations show that the surface wave-dependent drag has significant effects on the surges, but the wave radiation stress has only slight effects. For prediction of wave heights, the inclusion of both the wave-dependent drag and the wave radiation stress in the storm surge model has a very small effect on the computed results. The coupled models can be easily applied to prediction or hindcasting of ocean waves and storm surges without the need for further treatment. numerically been proved useful and successful by many au­ thors, but physically, a process usually needs to be split into several steps, and thus noninherently conservative errors are raised (Leonard et al. 1995). Compared with the piecewise ray method, the full ray method requires the computation to be conducted separately and independently at each position, and, hence, is less advantageous for the evaluation of horizontal distribution of wave characteristics (Yamaguchi and Hatada 1990). Casulli (1990) developed a semiimplicit finite difference scheme for the solution of the two-dimensional shallow water equations with a Eulerian-Lagrangian method for the approx­ imation of the convective terms, which was proved to be sta­ ble, accurate, and conservative. The Eulerian-Lagrangian method has advantages over other commonly used numerical methods, such as upwind method, ADI method, time-splitting or operator-splitting techniques, and the mode-splitting tech­ nique. The scheme was subsequently extended to three di­

Dispersion Effects on Longshore Currents in Surf Zones

Abstract: A time-dependent model for obliquely incident shallow-water waves with small incident angles is developed to elucidate the dispersion effects due to the vertical variations of instantaneous horizontal fluid velocities on the cross-shore variations of the wave height, setup, and longshore current in surf zones. The three equations for the cross-shore continuity, momentum, and momentum flux correction are solved numerically to predict the water depth and the cross-shore depth-averaged and near-bottom velocities. The two equations for the alongshore momentum and momentum flux correction are derived and solved to predict the alongshore depth-averaged and near-bottom velocities. The developed model is compared with laboratory and field data for planar beaches. The dispersion effects on the wave height and setup are shown to be minor. The dispersion effects on the longshore current are significant for regular waves but secondary for irregular waves. The model is also shown to predict the vertical shape of the longshore current in the surf zone but not outside the surf zone.

Wave kinematics at steep slopes : Second-order model

Abstract: This paper presents an experimental study investigating the relevant characteristics of the flow field induced by a regular wave acting on a uniform steep slope. Due to their uniqueness, the experimental data are of paramount importance and give a contribution toward the rational definition of wave-structure interaction. In the first part of the paper, attention is focused on the flow field characteristics, i.e., temporal and spatial behavior of surface elevation and vertical distribution of the horizontal component of the local velocity. In the second part, it is shown that the main characteristics of the velocity distributions may be represented by the variance of the distribution itself. Furthermore, it has been verified that the temporal behavior of the variance is well reproduced by a Fourier series truncated to the first three even harmonics. Relationships are presented between the coefficients of the Fourier series and some global quantities of the wave motion. Due to the relationship between the variance of velocity distribution and the momentum flux correction coefficient, the proposed second-order model allows the actual shape of the velocity profiles to be accounted for in one-dimensional numerical models describing the flow field due to the action of a wave on a steep slope.

Interaction between Solitary Wave and Floating Elastic Plate

Abstract: The interaction between a solitary wave and a two-dimensional floating elastic plate is studied in this paper The modified Boussinesq equations that represent long waves beneath a floating elastic plate are derived These equations do not take the mass of the plate into account because of the long wave assumption Applying the matched asymptotic expansion method, conditions for a connection between the solution of the ordinary Boussinesq equations that represent long water waves and the modified Boussinesq equations are obtained These sets of equations are solved by the finite-difference method Numerical results demonstrate that the higher-order terms are important for the prediction of the wave celerity of a solitary wave traveling beneath a floating elastic plate They also play an important role in the prediction of the bending moment of the floating elastic plate The rigidity of the floating elastic plate greatly affects the bending moment due to the solitary wave A floating elastic plate whose rigidity is low leads to a weak bending moment and vice versa

Effect of wave-enhanced bottom friction on storm-driven circulation in Massachusetts Bay

Abstract: Massachusetts Bay is a shallow (35 m average depth) semienclosed embayment, roughly 100 × 50 km, which opens into the Gulf of Maine at its eastern boundary. Surface waves associated with winter storm winds from the northeast cause large sediment resuspension events, and wave and circulation fields during these events have a quasi-steady response to the wind stress. Coupled wave, circulation, and boundary layer models indicate that wave-enhanced bottom friction has a significant damping effect on storm-driven circulation in Massachusetts Bay. The simulated response exhibits significant three-dimensional structure, but still can be fundamentally understood using idealized models. The depth-integrated momentum balance is dominated by along-bay stress, pressure gradient, and bottom stress. The effective bottom drag coefficient during typical storm conditions is increased by a factor of 2–5 when wave effects are included, but the mean bottom stress is relatively unaffected by wave effects due to a reduction in...

Effects of Reflective Vertical Structures Permeability on Random Wave Kinematics

Abstract: Two simple numerical models are presented to estimate the root-mean-squared velocity for random nonbreaking waves obliquely incident on partially reflecting coastal structures. The structures considered are vertical permeable structures with a free surface or crowned. The models are also capable of simulating the case of an impermeable vertical wall. Results depend on the input spectrum, breakwater geometry, and porous material characteristics. All this information is considered in the calculated complex reflection coefficient, which has information not only on the modulus of the reflection for each of the wave components, but also on the reflection-induced phase shift.

Wave Loads on Caisson Founded on Multilayered Rubble Base

Abstract: The solution to the problem of the interaction of linear waves with a composite breakwater is presented and is applied to determine wave reflection and transmission as well as wave loads on a caisson founded on a multilayered rubble base. The results show that the bench width has little effect, whereas the rubble base height has a significant effect of wave reflection and transmission and on wave loads on the caisson. The results also show that complex, thick, or less permeable armor layers increase the effect of rubble base. Moreover, the results show that the rubble damping properties should be included in the analysis of wave reflection and transmission, and wave loads on a caisson, and that the damping can be described satisfactorily by the Darcy damping law. The present method can be applied in a straightforward manner to an excitation provided by wind waves and, before a more advanced approach is attempted, some cases associated with nonlinear wave excitation may partially be analyzed with a modification to the present approach. Theoretical results are in fairly good agreement with experimental data.

Fluidization Response of Sediment Bed to Rapidly Falling Water Surface

Abstract: A strain-based criterion for sediment fluidization under transient pressure loading is presented. The criterion predicts that fluidization can be spontaneous, as opposed to incremental, and that it is triggered by a lowering—rather than a buildup—of the pore pressure. The criterion is examined and verified experimentally. A dam break is simulated in a laboratory flume, and a sediment bed is included in the half of the flume initially containing water. Both visual observation and extensive pressure measurements within the bed indicate the occurrence of a massive fluidization failure throughout the entire depth and length of the bed. The fluidization failure is shown to occur on an extremely short timescale. The results from several successive runs, allowing the bed to consolidate overnight between runs, demonstrate the tendency of a bed to repeatedly refluidize.

Noisy Nonlinear Motions of Moored System. Part I: Analysis and Simulations

Abstract: Nonlinear responses of a submerged moored structure are investigated taking into account the presence of environment random noise. Sources of nonlinearity of the system include a quadratic Morison hydrodynamic damping and a geometrically nonlinear restoring force. The random perturbations are modeled by a white-noise process to examine their effects on nonlinear responses analytically and numerically. The analysis procedure includes a generalized Melnikov process to study response stabilities in a global sense and the Fokker-Planck equation to demonstrate response characteristics from a probabilistic perspective. Rich non­ linear phenomena including bifurcations. coexistence of attractors. and chaos are identified and demonstrated. Probability density functions solved from the Fokker-Planck equation are used to depict (co)existing response attractors on the Poincare section and demonstrate their probabilistic properties. Noise effects on responses are shown via a generalized Melnikov criterion and the probability density function. It is found that the presence of noise may expand the chaotic domain in the parameter space and also cause transitions between coexisting responses. ABSTRACT: Nonlinear responses of a submerged moored structure are investigated taking into account the presence of environment random noise. Sources of nonlinearity of the system include a quadratic Morison hydrodynamic damping and a geometrically nonlinear restoring force. The random perturbations are modeled by a white-noise process to examine their effects on nonlinear responses analytically and numerically. The analysis procedure includes a generalized Melnikov process to study response stabilities in a global sense and the Fokker-Planck equation to demonstrate response characteristics from a probabilistic perspective. Rich non­ linear phenomena including bifurcations. coexistence of attractors. and chaos are identified and demonstrated. Probability density functions solved from the Fokker-Planck equation are used to depict (co)existing response attractors on the Poincare section and demonstrate their probabilistic properties. Noise effects on responses are shown via a generalized Melnikov criterion and the probability density function. It is found that the presence of noise may expand the chaotic domain in the parameter space and also cause transitions between coexisting responses.

Solitary Wave Solution to Boussinesq Equations

Abstract: The exact solitary wave solution to the Boussinesq equations, which was given in an implicit integral form, is further studied in the present note. Through numerical curve fitting, an explicit closed-form empirical solution whose profile is nearly identical to the exact solution is obtained. Discussion and comparison between solitary wave solutions based on the Boussinesq model and higher-order theories of the Euler equation are presented.