Extended Fourth-Order Depth-Integrated Model for Water Waves and Currents Generated by Submarine Landslides

In this paper, a preexisting higher-order depth-integrated wave propagation model is extended to include a moving seabed. As a result, the extended model can be applied to both wave propagation and the dynamic process of wave generation by a seabed disturbance such as a submarine landslide. The model has the linear dispersion relation in a form of (4,4) Padè approximant, and approximates the water velocity profiles along the water depth with a fourth-order polynomial of the vertical coordinates. The fourth-order model is aimed at extending the validity of the lower-order depth-integrated models from long waves to both long and shorter waves, as well as improving the approximation of the velocity field from the second order to the fourth order. Laboratory experiments are carried out in a wave flume to study wave generation by a submerged landslide model. Both water waves and water velocities are measured by using resistance-type wave gauges and a particle image velocimetry. The experimental data are then compared with the predicted wave height and water current based on the new model and two existing lower-order Boussinesq-type models. The results clearly show that the new model predicts the fluid velocity more accurately and is also able to predict the shorter trailing waves very well where the traditional Boussinesq model may be inadequate, thus validating the improvement provided by the fourth-order model.     

One-Dimensional Model of Shallow Water Surface Waves Generated by Landslides

A numerical model is presented as the basis for the study of surface waves generated by bank and bottom landslides in rivers. The flow is assumed to be properly modeled by the shallow water equations. The solid movement is introduced in the model as an external action, and assumed rigid and impervious. Two situations are identified in the flow subsequent to a solid movement: longitudinal and transversal sliding. A discussion on the modeling difficulties associated with the latter is included. The flow equations are solved by means of an upwind scheme specially adapted to advancing fronts over dry irregular beds.     

Two-Dimensional SPH Simulations of Landslide-Generated Water Waves

Water waves generated by landslides have been of interest to ocean and coastal engineers, as well as to dam engineers. The present study uses a meshless and pure Lagrangian method known as smoothed particle hydrodynamics (SPH) to simulate nonlinear water waves due to landslides, with the aim of an accurate numerical prediction of the generation and propagation of such water waves. Validation is carried out by comparison between the computed prediction and experimental data of water waves generated by a two-dimensional triangular rigid body sliding into water. The calculated results show that the simulated water waves agree well with those observed in the experiment confirming the effectiveness and the accuracy of the proposed scheme.     

Physical Properties of Turbulent Benthic Boundary Layers Generated by Internal Waves

Physical properties of active turbulent benthic boundary layers (TBBL) generated by basin scale internal waves were studied within a Northern hemisphere thermally stratified lake. A microstructure profiler was used to measure the nature of the turbulence within the TBBLs while a series of thermistor chains were used to monitor the thermal structure of the lake. It was observed that a wind-driven anticlockwise diurnal-period vertical mode one Kelvin wave generated large scale motions within the water column, and that the interactions between this wave and the sloping lakebed induced TBBLs. A simple model, based on potential energy change and boundary shearing, was shown to describe the mean TBBL thickness.     

Dynamic compaction of titanium Aluminides by Explosively Generated Shock Waves: Microstructure and Mechanical Properties

A detailed microstructural analysis and evaluation of the mechanical properties of titanium aluminides consolidated by novel shock processes^[131] are presented. Successful consolidation was obtained and was evidenced by strong bonding between individual particles. Additions of Nb and Ti and Al elemental powders resulted in enhanced interparticle bonding through intense plastic deformation of Nb and shock-induced reactions between Ti and Al. Rapid cooling of interparticle molten layers yielded amorphous Ti-Al alloys; this interparticle melting and rapid cooling are a unique feature of shock processing. Embrittlement of individual particles of Ti₃Al-based alloy after exposure to 550 °C and 750 °C was observed. There is evidence of phase transformation after preheating the powder, and this fact can explain the high density of cracks obtained with this alloy after high-temperature shock consolidation. Mechanical properties of the Ti₃Al-based alloy were determined at room temperature and the fracture modes were studied. The microstructural observations are correlated with the mechanical properties.     

Visualization and Simulation of Asphalt Concrete with Randomly Generated Three-Dimensional Models

The objective of this study is to visualize and simulate microscale properties of asphalt concrete with three-dimensional discrete element models under mechanical loading. The microstructure of the asphalt concrete sample was composed of three ingredients: coarse aggregates, sand mastic (a combination of fines, fine aggregates, and asphalt binder), and air voids. Coarse aggregates were represented with the irregular polyhedron particles which were randomly created with an algorithm developed for this study. The gaps among the irregular particles were filled with air voids and discrete elements of sand mastic. The mechanical behaviors of the three ingredients were simulated with specific constitutive models at different contacts of discrete elements. Based on the geometric and mechanical models, visualization and simulation of asphalt mixtures were conducted in this study.     

Numerical Simulations of Nonlinear Short Waves Using a Multilayer Model

The multilayer model developed by Lynett and Liu is used for simulating the evolution of deep-water waves in a constant depth. The computational model is tested with experimental data for nonlinear monochromatic and biharmonic waves with kh values as high as 8.3. The experiments were conducted in a super wave tank with dimensions of 300?m×5?m×5.2?m located at Tainan Hydraulics Laboratory of National Cheng-Kung University. The nonlinearity of the waves tested, ka, range from 0.0627 to 0.1577. The overall comparisons between the multilayer model and the experiments are quite good, indicating that the multilayer model is adequate for both linear and nonlinear deep-water waves.     

Simulation of Bed-Load Dispersion Process

Two general dispersion models suitable for nonequilibrium bed-load transport were constructed. The first one, called the P model, is based on the probability of migration for specific groups of sediment particles. The second one, called the D model, is derived from the advection equation discretized in finite-difference form, which is equivalent to the general dispersion equation. By comparing these models, it is found that the D model can be treated like the P model in some respects. The Courant number, Cr, in the D model has the same physical meaning as the probability of migration, P, in the P model. Although the D model and P model were based on different concepts, the simulated bed-load transport rates, which result from their application, are the same. Therefore, the dispersion equation was replaced by the numerical algorithm of the advection equation (D model) to examine several dispersion phenomena of bed-load transport. To explore further the nonequilibrium dispersion process, a series of flume experiments was conducted by using color-painted fine gravels. Having compared model simulation results and experimental data, it is shown that the models derived in this study have a reasonably good agreement with the experimental results. In summary, this study has indirectly proven that the D model, which is equivalent to the dispersion equation, is capable of simulating the nonequilibrium bed-load transport.     

WAF Method and Splitting Procedure for Simulating Hydro- and Thermal-Peaking Waves in Open-Channel Flows

Hydro- and thermal-peaking waves, generated by hydroelectric power generation, have a strong impact on the ecological integrity of aquatic ecosystems. In order to reduce such effects, mitigation procedure must be studied and implemented. To this end a one-dimensional model which solves the coupling of hydrodynamics with heat transport is developed. The solution is obtained advancing simultaneously the hydrodynamic and thermal module with the same accuracy. For the numerical solution of the governing advection-reaction/diffusion problem a splitting procedure is adopted: the advection-reaction part is solved by means of the weight average flux (WAF) finite volume explicit method, while the diffusion part is solved using a nonlinear version of the implicit Crank-Nicolson method. The WAF method is extended to second-order in the presence of reaction terms. Numerical results are presented for different test examples, which demonstrate the accuracy and robustness of the scheme and its applicability in predicting temperature transport by shallow water flows. Application to the Adige River (Northern Italy) of this framework proves that the model is an effective tool for designing hydro- and thermal-peaking waves mitigation procedures.     

Estimating Uncertainty in the Extreme Value Analysis of Data Generated by a Hurricane Simulation Model

Extreme value analyses of any environmental phenomenon are fraught with difficulties, but the additional difficulty of collecting reliable data during hurricane events makes their analysis even more complicated. A widely accepted procedure is to use calibrated hurricane models to simulate hurricane events. The simulated data can then be subjected to standard extreme value procedures. The estimation uncertainties which arise from such analyses depend upon (1) the extent to which the hurricane models are physically realistic, (2) the length of the simulated series, which consists of about 1,000 or even 10,000 simulated events, and therefore introduces negligible errors, and (3) the length of the historical record on which the simulations are based, which usually consists of about 50 events. In this paper, we propose the use of resampling schemes in an attempt to obtain some reasonable measure of uncertainties due to the relatively short length of the historical record. An intuitive, “naive” procedure is first described, which leads to an alternative approach that has connections with the statistical procedure of bootstrapping. Standard application of these procedures for extremes induces bias, and we propose a simple, though nonstandard method for reducing this effect. The results are illustrated in detail for a dataset of simulated hurricane wind speeds corresponding to a location in Florida and are also summarized for a sequence of 55 locations along the U.S. Gulf and Atlantic coasts.     

Hindsight ≠ hindsight: Experimentally induced dissociations between hindsight components.

Hindsight bias has recently been conceived of not as a unitary phenomenon but as a conglomerate of 3 separate phenomenological manifestations (“hindsight components”; Blank, Nestler, von Collani, & Fischer, 2008): memory distortions, impressions of foreseeability, and impressions of inevitability. These components are thought to be fundamentally different in nature, to be influenced by different processes, and to serve different functions. This article provides strong evidence for the separate components view and its underlying assumptions by demonstrating theoretically predicted dissociations between the components. In Experiment 1, for example, we used a memory encoding manipulation to specifically influence the amount of hindsight memory distortion but not participants' inevitability impressions. Conversely, varying the number of provided reasons for an event outcome affected inevitability impressions but left memory distortion untouched. Similar results—using different theoretically derived manipulations—were obtained between foreseeability impressions and memory distortions (Experiment 2) and between inevitability and foreseeability impressions (Experiment 3). Theoretical and practical consequences of these results and of the separate components view are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coupled Large Strain Consolidation and Solute Transport. II: Model Verification and Simulation Results

The results of numerical simulations for coupled large strain consolidation and solute transport, obtained using the CST1 model, are presented. CST1 accounts for advection, longitudinal and transverse dispersion, first-order decay reactions, and linear equilibrium sorption. Verification checks of CST1 show excellent agreement with analytical solutions for one-dimensional (1D) transport in rigid porous media, including various Peclet numbers and concentration boundary conditions. Similarly excellent agreement is observed for two-dimensional advection-dispersion transport in rigid media and 1D advection-dispersion transport in compressible media undergoing large strain consolidation. CST1 is then used to investigate consolidation-induced solute transport for a single composite liner system and a confined disposal facility for dredged contaminated sediments. In both cases, solute transport was found to be strongly affected by consolidation-induced advection both during and after the consolidation period. Consolidation has a lasting effect on solute migration because transient advective flows change the distribution of solute mass, which then becomes the initial condition for subsequent transport processes.     

Depth-Dependent Dispersion Coefficient for Modeling of Vertical Solute Exchange in a Lake Bed under Surface Waves

Variable pressure at the sediment/water interface due to surface water waves can drive advective flows into or out of the lake bed, thereby enhancing solute transfer between lake water and pore water in the lake bed. To quantify this advective transfer, the two-dimensional (2D) advection-dispersion equation in a lake bed has been solved with spatially and temporally variable pressure at the bed surface. This problem scales with two dimensionless parameters: a “dimensionless wave speed” (W) and a “relative dispersivity” (λ). Solutions of the 2D problem were used to determine a depth-dependent “vertically enhanced dispersion coefficient” (DE) that can be used in a 1D pore-water quality model which in turn can be easily coupled with a lake water quality model. Results of this study include a relationship between DE and the depth below the bed surface for W>50 and λ ? 0.1. The computational results are compared and validated against a set of laboratory measurements. An application shows that surface waves may increase the sediment oxygen uptake rate in a lake by two orders of magnitude.     

Comparison of Measured and Computed Stresses in a Steel Curved Girder Bridge

Steel curved I-girder bridge systems may be more susceptible to instability during construction than bridges constructed of straight I-girders. The primary goal of this research is to study the behavior of the steel superstructure of a curved steel I-girder bridge system during all phases of construction and to ascertain whether the actual stresses in the bridge are represented well by linear elastic analysis software developed for this project and typical of that used for design. Sixty vibrating wire strain gauges were applied to a two-span, four-girder bridge, and elevation measurements were taken by a surveyor's level. The resulting stresses and deflections were compared to computed results for the full construction sequence of the bridge as well as for live loading from up to nine 50-kip trucks. The analyses correlated well with the field measurements, especially for the primary flexural stresses. Stresses due to lateral bending and restraint of warping induced in the girders and the stresses in the cross frames were more erratic but generally showed reasonable correlation. In addition, it is shown that, for the magnitude of live load applied to the bridge, analyses in which composite behavior is assumed in the negative moment region yield better correlation than analyses in which just the bare steel girders are used (no shear connectors were used on the bridge in the negative moment region). It is concluded that the curved girder analysis software captures the general behavior well for these types of curved girder bridge systems at or below the service load level, and that the stresses in these bridges may be relatively low if their design is controlled largely by stiffness.     

Coupled Large Strain Consolidation and Solute Transport. I: Model Development

The development of a numerical model, CST1, for coupled large strain consolidation and solute transport in saturated porous media is presented. The consolidation algorithm is one-dimensional and includes the capabilities of a previous code, CS2, with the addition of time-dependent loading, unload/reload effects, and an externally-applied hydraulic gradient. The solute transport algorithm is two-dimensional and accounts for advection, longitudinal and transverse dispersion, first-order decay reactions, and linear equilibrium sorption. Solute transport is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating layer. The key to the transport model is the definition of two Lagrangian fields of elements that follow the motions of fluid and solid phases separately. This reduces numerical dispersion and simplifies transport calculations to that of dispersion mass flow between contiguous fluid elements. The effect of relative numerical resolution of fluid and solid elements on the accuracy of sorption/desorption is also discussed. This paper presents the theoretical and numerical development of the CST1 model. A companion paper presents verification checks of CST1 and the results of simulations that illustrate the significance of consolidation-induced solute transport for some interesting numeric examples.     

Predictions of Resuspension of Highway Detention Pond Deposits in Interrain Event Periods due to Wind-Induced Currents and Waves

The paper presents a numerical study of resuspension of deposits from highway detention ponds based on a previous experimental study. The resuspension process is evaluated in dry weather periods with baseflow/infiltration flow through the ponds only. The resuspension is caused by the bed-shear stress induced by the return flow near the bed and waves both generated by the wind. Wind statistics for 30 years have been applied for prediction of the annual discharged bulk of suspended solids and associated pollutants; fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene and indeno(1,2,3-cd)pyrene (PAHs) and the heavy metals of cadmium, chromium, copper, lead, nickel, and zinc. The current and wave-generated bed-shear stresses entail a discharged bulk of pollutants corresponding to approximately 10% of the annual accumulation of pollutants in the present pond due to the baseflow in the pond. The mean outlet concentration of suspended solids is well correlated with the wind speed. To reduce the resuspension of deposited materials, two mechanisms are prevailing; either by increase of the water depth of the pond to minimize the effect of the wind in the near-bed region or by reduction of the wind to some degree. The most efficient action for reducing the wind impact on the shallow waters is the establishment of shelterbelts as known from the agriculture. Just a 20% reduction of the yearly wind speeds will reduce the outlet mass with 70% and a 50% reduction with almost 100%. A 50% reduction of the wind speed is far from impossible to achieve with relatively small investments.     

Comparison of SF6 and Fluorescein as Tracers for Measuring Transport Processes in a Large Tidal River

We present the first large-scale comparison of a fluorescent dye [fluorescein (C20H10O5Na2)] and a gas [sulfur hexafluoride (SF6)] as tracers of advection and longitudinal dispersion from a dual tracer release experiment conducted in the tidal Hudson River. At the beginning of the experiment, 36?kg of fluorescein and ～ 4.3?mol of SF6 were injected into the Hudson River at an averaged depth of 9.5?m, ～ 1?m above the bottom, near Hyde Park, N.Y. After injection, fluorescein distributions were surveyed for 4 days (until it became undetectable) and SF6 distributions were surveyed for 10 days. The dye resolves initial vertical mixing on the day of injection, and then net advection and longitudinal dispersion, whereas SF6 provides information on net advection and longitudinal mixing on larger spatial scales and longer time scales. Quantitative estimates of transport processes (net advection and longitudinal dispersion) calculated from the two methods are consistent for the first three days, and start to deviate on the fourth day when the signal-to-noise ratio of the dye deteriorated.     

Morphology and Substrate Control on the Dynamics of Flowlike Landslides

A numerical model set up to simulate rapid flowlike landslide motion across three-dimensional terrain has been used to investigate the capability of various constitutive relationships to model the dynamics of complex events characterized by a changing type of substrate and morphology (e.g., glacier, bends). The numerical procedure is based on a continuum mechanics approach and on depth-averaged St. Venant equations for shallow flows. The developed RASH3D code includes the possibility of using several rheological laws, whose parameter values can vary along the runout path. Two rock avalanche cases, with some morphological peculiarities along the propagation path, have been numerically back-analyzed with both a frictional and a Voellmy rheology. Of the two considered rheologies, the Voellmy model produces the most consistent results in terms of runout area as well as velocity values. The main drawbacks of the frictional model are the tendency to predict excessive spreading of the mass and to overestimate the velocities. The results show that, when a complex problem of runout of rapid flowlike landslides has to be analyzed, it is necessary to have detailed knowledge of the geological and morphological features and to resort to increasingly complex rheologies.