Showing papers on "Waves and shallow water published in 2008"
TL;DR: The ''effective'' forcing for wave-driven, near-bed processes is defined as the product of the magnitude of forcing times its probability of occurrence, and it is concluded that different bottom orbital velocity statistics may be appropriate for different problems.
223 citations
TL;DR: Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern as discussed by the authors, where the mean depth-averaged flow is equatorward, along-shelf, and increases with increasing water depth.
Abstract: Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern The mean depth-averaged flow is equatorward, alongshelf, and increases with increasing water depth from 3 cm s 1 at the 15-m isobath to 10 cm s 1 at the 100-m isobath The mean cross-shelf circulation exhibits a consistent cross-shelf and vertical structure The near-surface flow is typically offshore (positive, range 3t o 6c m s 1 ) The interior flow is onshore and remarkably constant (02 to 14 cm s 1 ) The near-bottom flow increases linearly with increasing water depth from 1c m s 1 (onshore) in shallow water to 4 cm s 1 (offshore) at the 250-m isobath over the slope, with the direction reversal near the 50-m isobath A steady, two-dimensional model (no along-isobath variations in the flow) reproduces the main features of the observed circulation pattern The depth-averaged alongshelf flow is primarily driven by an alongshelf pressure gradient (sea surface slope of 37 10 8 increasing to the north) and an opposing mean wind stress that also drives the near-surface offshore flow The alongshelf pressure gradient accounts for both the increase in the alongshelf flow with water depth and the geostrophic balance onshore flow in the interior The increase in the near-bottom offshore flow with water depth is due to the change in the relative magnitude of the contributions from the geostrophic onshore flow that dominates in shallow water and the offshore flow driven by the bottom stress that dominates in deeper water
162 citations
TL;DR: Bromirski et al. as discussed by the authors showed that coastal regions having a narrow shelf with irregular and rocky coastlines are known to be especially efficient at radiating secondary microseisms.
Abstract: Microseisms are the most ubiquitous continuous seismic signals on Earth at periods between approximately 5 and 25 s (Peterson 1993; Kedar and Webb 2005). They arise from atmospheric energy converted to (primarily) Rayleigh waves via the intermediary of wind-driven oceanic swell and occupy a period band that is uninfluenced by common anthropogenic and wind-coupled noise processes on land (Wilson et al. 2002; de la Torre et al. 2005). “Primary” microseisms (near 8-s period) are generated in shallow water by breaking waves near the shore and/or the nonlinear interaction of the ocean wave pressure signal with the sloping sea floor (Hasselmann 1963). Secondary microseisms occur at half of the primary period and are especially strongly radiated in source regions where opposing wave components interfere (Longuett-Higgins 1950; Tanimoto 2007), which principally occurs due to the interaction of incident swell and reflected/scattered wave energy from coasts (Bromirski and Duennebier 2002; Bromirski, Duennebier, and Stephen 2005). Coastal regions having a narrow shelf with irregular and rocky coastlines are known to be especially efficient at radiating secondary microseisms (Bromirski, Duennebier, and Stephen 2005; Shulte-Pelkum et al. 2004). The secondary microseism is globally dominant, and its amplitudes proportional to the square of the standing wave height (Longuett-Higgins 1950), which amplifies its sensitivity to large swell events (Astiz and Creager 1994; Webb 2006).
Microseisms have long been recognized as an indicator of large-storm intensity (Gilmore 1946; Gutenberg 1947; Gilmore and Hubert 1948). However, contributions from deep-water open-ocean storms are not generally significant in records from land-based seismometers (Bromirski and Duennebier 2002; Haubrich and McCamy 1969). Rather, microseism levels predominantly measure spatially distributed wave activity associated with wave interactions along coasts. The efficient propagation and ubiquity of short-period microseism Rayleigh waves (Bromirski, Duennebier, and Stephen 2005; Schulte-Pelkum …
124 citations
TL;DR: It is rigorously shown that the periodic wave solutions tend to the soliton solutions under a "small amplitude" limit.
Abstract: Based on a multidimensional Riemann theta function, the Hirota bilinear method is extended to explicitly construct multiperiodic (quasiperiodic) wave solutions for the $(2+1)$-dimensional Bogoyavlenskii breaking soliton equation. Among these periodic waves, the one-periodic waves are well-known cnoidal waves, their surface pattern is one-dimensional, and often they are used as one-dimensional models of periodic waves in shallow water. The two-periodic (biperiodic) waves are a direct generalization of one-periodic waves, their surface pattern is two dimensional, that is, they have two independent spatial periods in two independent horizontal directions. The two-periodic waves may be considered to represent periodic waves in shallow water without the assumption of one dimensionality. A limiting procedure is presented to analyze asymptotic behavior of the one- and two-periodic waves in details. The exact relations between the periodic wave solutions and the well-known soliton solutions are established. It is rigorously shown that the periodic wave solutions tend to the soliton solutions under a ``small amplitude'' limit.
118 citations
TL;DR: In this article, the authors demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the EM signal into modes and using only the mode least affected by interaction with the atmosphere.
Abstract: The marine controlled-source electromagnetic (CSEM) method is being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings. Until recently, its use was confined to deepwater (water depths greater than approximately 300 m ) because of the interaction of signals with the atmosphere in shallower water depths. The purpose of this study was to investigate, using a simple 1D analytical analysis, the physics of CSEM in shallow water. This approach demonstrates that it is difficult to simply decouple signals that have interacted with the earth from those that have interacted with the air using either frequency-domain or time-domain methods. Stepping away from wavelike approaches, which if applied without care can be misleading for the diffusive fields of CSEM, we demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the EM signal into modes and using only the mode least affected by interaction with the atmosphere. Such decompos...
105 citations
TL;DR: The study suggests that tree species of the Edwards Plateau do not commonly reduce aquifer recharge by tapping directly into perched water tables, but more likely by reducing water storage in the epikarst, the transition zone between soil and bedrock.
Abstract: The ecohydrology of karst has not received much attention, despite the disproportionally large contribution of karst aquifers to freshwater supplies Karst savannas, like many savannas elsewhere, are encroached by woody plants, with possibly negative consequences on aquifer recharge However, the role of savanna tree species in hydrological processes remains unclear, not least because the location and water absorption zones of tree roots in the spatially complex subsurface strata are unknown This study examined the water sources and water relations of two savanna trees, Quercus fusiformis (Small) and Juniperus ashei (Buchholz) in the karst region of the eastern Edwards Plateau, Texas (USA) Stable isotope analysis of stem water revealed that both species took up evaporatively enriched water during the warm season, suggesting a relatively shallow water source in the epikarst, the transition zone between soil and bedrock Q fusiformis had consistently higher predawn water potentials than J ashei during drought, and thus was probably deeper-rooted and less capable of maintaining gas exchange at low water potentials Although the water potential of both species recovered after drought-breaking spring and summer rain events, associated shifts in stem water isotope ratios did not indicate significant uptake of rainwater from the shallow soil A hypothesis is developed to explain this phenomenon invoking a piston-flow mechanism that pushes water stored in macropores into the active root zones of the trees Epikarst structure varied greatly with parent material and topography, and had strong effects on seasonal fluctuations in plant water status The study suggests that tree species of the Edwards Plateau do not commonly reduce aquifer recharge by tapping directly into perched water tables, but more likely by reducing water storage in the epikarst A more general conclusion is that models of savanna water relations based on Walter’s two-layer model may not apply unequivocally to karst savannas
97 citations
TL;DR: In this paper, the authors reviewed and analyzed nearshore flows by means of the classic nonlinear shallow water equations with a specific focus on the interdependence between physical phenomena, model equations, and numerical schemes.
Abstract: Modeling of nearshore flows by means of the classic nonlinear shallow water equations is reviewed and analyzed with a specific focus on the interdependence between physical phenomena, model equations, and numerical schemes. Numerical benchmarking solutions for coastal applications are summarized. Strengths and limits of the nonlinear shallow water equations to reproduce the fundamental features of coastal flows are illustrated along with indications on needed improvements.
89 citations
TL;DR: In this paper, the authors estimate a frequency and depth-dependent dissipation rate function for the Gulf of Mexico seafloor using a numerical nonlinear wave model, which accurately simulates the large reduction in wave energy observed in the Gulf.
Abstract: [1] Muddy seafloors cause tremendous dissipation of ocean waves. Here, observations and numerical simulations of waves propagating between 5- and 2-m water depths across the muddy Louisiana continental shelf are used to estimate a frequency- and depth-dependent dissipation rate function. Short-period sea (4 s) and swell (7 s) waves are shown to transfer energy to long-period (14 s) infragravity waves, where, in contrast with theories for fluid mud, the observed dissipation rates are highest. The nonlinear energy transfers are most rapid in shallow water, consistent with the unexpected strong increase of the dissipation rate with decreasing depth. These new results may explain why the southwest coast of India offers protection for fishing (and for the 15th century Portuguese fleet) only after large waves and strong currents at the start of the monsoon move nearshore mud banks from about 5- to 2-m water depth. When used with a numerical nonlinear wave model, the new dissipation rate function accurately simulates the large reduction in wave energy observed in the Gulf of Mexico.
83 citations
TL;DR: This paper highlights the benthic characterization in extracting statistical parameters derived from the bottom backscatter and classifying them in the scanning hydrographic operational airborne light detection and ranging (LiDAR) Survey.
Abstract: The scanning hydrographic operational airborne light detection and ranging (LiDAR) Survey (SHOALS) consists of a bathymetric LiDAR system that provides high-precision measurements of water depth. Although the acquisition is focused on depth accuracy, the return signal, i.e., waveform, contains other relevant information because of integration signatures from the water surface, the water column, and the seabed. This paper highlights the benthic characterization in extracting statistical parameters derived from the bottom backscatter and classifying them. In implementing a specific unsupervised classification, it is significantly proven that the signals derived from habitat, described as statistically homogeneous throughout ground-truth analysis, are similar within an intrahabitat view, whereas they are different between themselves.
82 citations
TL;DR: In this article, the authors simulated the Indian Ocean tsunami moving into the shallow Strait of Malacca and formation of undular bores and solitary waves in the strait using the fully nonlinear dispersive method (FNDM) and the Korteweg-deVries (KdV) equation.
Abstract: [1] Deformation of the Indian Ocean tsunami moving into the shallow Strait of Malacca and formation of undular bores and solitary waves in the strait are simulated in a model study using the fully nonlinear dispersive method (FNDM) and the Korteweg-deVries (KdV) equation. Two different versions of the incoming wave are studied where the waveshape is the same but the amplitude is varied: full amplitude and half amplitude. While moving across three shallow bottom ridges, the back face of the leading depression wave steepens until the wave slope reaches a level of 0.0036–0.0038, when short waves form, resembling an undular bore for both full and half amplitude. The group of short waves has very small amplitude in the beginning, behaving like a linear dispersive wave train, the front moving with the shallow water speed and the tail moving with the linear group velocity. Energy transfer from long to short modes is similar for the two input waves, indicating the fundamental role of the bottom topography to the formation of short waves. The dominant period becomes about 20 s in both cases. The train of short waves, emerging earlier for the larger input wave than for the smaller one, eventually develops into a sequence of rank-ordered solitary waves moving faster than the leading depression wave and resembles a fission of the mother wave. The KdV equation has limited capacity in resolving dispersion compared to FNDM.
76 citations
TL;DR: In this paper, a surface wave model is developed with the intention of coupling it to three-dimensional ocean circulation models, based on a paper by Mellor wherein depth-dependent coupling terms were derived.
Abstract: A surface wave model is developed with the intention of coupling it to three-dimensional ocean circulation models. The model is based on a paper by Mellor wherein depth-dependent coupling terms were derived. To be compatible with circulation models and to be numerically economical, this model is simplified compared to popular third-generation models. However, the model does support depth and current refraction, deep and shallow water, and proper coupling with depth-variable currents. The model is demonstrated for several simple scenarios culminating in comparisons of model calculations with buoy data during Hurricane Katrina and with calculations from the model Simulating Waves Nearshore (SWAN); for these calculations, coupling with the ocean was not activated.
TL;DR: In this paper, the authors focus on the impact of climate warming on eutrophic shallow lakes in the Netherlands, using three representative lakes that cover the full range of lake sizes and depths and apply an existing model to predict water temperatures from air temperatures for shallow, wind exposed and holomictic water bodies.
TL;DR: In this paper, a 3-week field investigation was conducted on a macrotidal beach with intertidal bar morphology with the aim of quantifying cross-shore sediment transport rates and beach response.
TL;DR: In this article, the authors used echo sounding data to assess the distribution and colonization depth of submerged macrophytes in Lake Balaton and found that the influence of light and exposure on plants could be distinguished by considering the complex interplay of site-specific morphometry and the stochastic wind field in a highly simplified manner.
TL;DR: Watanabe et al. as mentioned in this paper proposed a new calculation method for bottom shear stress based on velocity and acceleration terms, theoretical phase difference, φ and the acceleration coefficient, expressing the wave skew-ness effect for saw-tooth waves.
TL;DR: It appears that, in small water bodies, the total amount of incoming long wave radiation is sensitive to the sky view factor, and the intensity of precipitation also appears to have a small effect on the stratification of the water temperature.
Abstract: For aquatic biological processes, diurnal and annual cycles of water temperature are very important to plants as well as to animals and microbes living in the water. An existing one-dimensional model has been extended to simulate the temperature profile within a small water body. A year-round outdoor experiment has been conducted to estimate the model input parameters and to verify the model. Both model simulations and measurements show a strong temperature stratification in the water during daytime. Throughout the night, however, a well-mixed layer starting at the water surface develops. Because the water body is relatively small, it appears that the sediment heat flux has a strong effect on the behaviour of the water temperature throughout the seasons. In spring, the water temperature remains relatively low due to the cold surrounding soil, while in autumn the opposite occurs due to the relatively warm soil. It appears that, in small water bodies, the total amount of incoming long wave radiation is sensitive to the sky view factor. In our experiments, the intensity of precipitation also appears to have a small effect on the stratification of the water temperature.
TL;DR: A detailed analysis of a prodeltaic turbidite unit within the Pennsylvanian Minturn Formation provides insight into the nature of fan-delta deposition, and allows reconstruction of paleogeographic and paleoclimatic conditions within a tectonically active cratonic basin this paper.
Abstract: Detailed sedimentological analysis of a prodeltaic turbidite unit within the Pennsylvanian Minturn Formation provides insight into the nature of fan-delta deposition, and allows reconstruction of paleogeographic and paleoclimatic conditions within a tectonically active cratonic basin. The formation, a thick succession of fan-delta deposits, exhibits a complex stratigraphic architecture of alluvial, fluvial, and deltaic fithofacies that were deposited in the Central Colorado Basin (CCB), U.S.A., a fault-bounded depression within the Ancestral Rockies. An ~ 20 to 35-m-thick, regionally extensive, unconformity-bounded prodelta unit was deposited during a large eustatic sea-level rise that temporarily interrupted coarsegrained fluvial-deltaic deposition. The unit consists of dark-green shale and sandstone event beds with tool marks produced by abundant plant debris. The sandstone event beds were previously interpreted as turbidites because they contain current ripples, parallel lamination, and sole marks consistent with deposition from turbidity currents in the absence of storm-generated surface gravity waves. We have found, however, that proximal prodeltaic deposits contain evidence for combined oscillatory and unidirectional flow (i.e., asymmetric hummocky cross stratification (HCS), quasi-planar lamination, and combined-flow ripple stratification), indicating deposition under large waves in relatively shallow water. Paleohydraulic calculations indicate that formation of the HCS beds requires a fetch of at least 75 km to generate the necessary wave periods. Given the position of the CCB in the lee of the ancestral Front Range relative to the prevailing trade winds, and the narrow seaway to the south, storms either tracked across the Cordilleran seaway from the west or formed in situ within the CCB. The former hypothesis is consistent with paleoclimate models that purport the development of summer monsoonal circulation patterns over western equatorial Pangea during the late Paleozoic, and regional observations of southeastward eolian bedform migration directions.
TL;DR: In this paper, a model combining hydrodynamics, waves and sediment dynamics has been developed to describe a very shallow tidal lagoon, the Venice Lagoon, Italy, in order to evaluate the status of a coastal lagoon environment.
TL;DR: In this paper, the effects of benthic grazing and light attenuation on this shallow, turbid, and nutrient replete system were examined and it was found that grazing by shallow water bivalves was important in determining phytoplankton bloom occurrence throughout the system and that above a shallow-water bivalve grazing threshold, the biomass did not exceed bloom levels.
TL;DR: In this article, a conceptual model in polar coordinates and a numerical model are developed, together with data analysis, to illustrate the dense plume and demonstrate that the northward expansion of the plume occurs under northerly winds.
Abstract: Circular shaped density plumes of low turbidity, low fecal indicator (Escherichia coli and enterococci) concentrations, and high salinity have been observed near the Industrial Canal in Lake Pontchartrain, north of the City of New Orleans. A conceptual model in polar coordinates and a numerical model are developed, together with data analysis, to illustrate the dense plume. It is demonstrated that the northward expansion of the plume occurs under northerly winds. The northward expansion of the plume occurs under northerly winds that drive downwind flow at the surface and upwind radial flow at the bottom. Northerly wind-induced straining, similar to tidal straining, promotes vertical stratification. As a result, the water becomes stratified near a thin bottom layer (<1 m), within which density currents are facilitated. The stability of the stratified plume suppresses wind-induced turbulent mixing inside the plume. The bottom water outside of the plume is more effectively stirred by the wind, the result being that the suspended sediment concentration outside of the plume area is much higher than inside. This contrast in mixing makes the plume visible from the surface by satellites even though the stratification is at the bottom. Laterally, wind stress produces a torque (vorticity) in areas of non-uniform depth such that upwind flow is developed in deep water and downwind flow in shallow water. The continuity requirement produces an upwind flow along the axis of the Industrial Canal (IC). The upwind flow is balanced by the downwind flow over the shallower peripheral areas along the coast.
TL;DR: In this article, a numerical study on dam-break waves over movable beds is presented, where a one-dimensional (1-D) model is built upon the Saint-Venant equations for shallow water waves, the Exner equation of sediment mass conservation and a spatial lag equation for non-equilibrium sediment transport.
Abstract: This paper reports a numerical study on dam-break waves over movable beds. A one-dimensional (1-D) model is built upon the Saint-Venant equations for shallow water waves, the Exner equation of sediment mass conservation and a spatial lag equation for non-equilibrium sediment transport. The set of governing equations is solved using an explicit finite difference scheme. The model is tested in various idealized experimental cases, with fairly good agreement between the numerical predictions and measurements. Discrepancies are observed at the earlier stage of the dam-break wave and around the dam location due to no vertical velocity component being taken into account. Sensitivity tests confirm that the friction coefficient is an important parameter for the evaluation of sediment transport processes operating during a dam-break wave. The influence of the non-equilibrium adaptation length (or the lag distance) is negligible on the wavefront celerity and weak on the free surface and bed profiles, which indicates that one may ignore the spatial lag effect in dam-break wave studies. Finally, the simulation of the Lake Ha!Ha! dyke-break flood event shows that the model can provide relevant results if a convenient formula for computing the sediment transport capacity and an appropriate median grain diameter of riverbed material are selected.
TL;DR: In this article, the time-dependent boundary layer induced by a strongly nonlinear internal wave of depression in shallow water is examined experimentally and it is shown that global instability has a critical threshold dependent on the Reynolds number of the flow and the amplitude of the wave.
Abstract: Experimental evidence is presented in support of the theoretical prediction of Diamessis and Redekopp [J. Phys. Oceanogr. 36, 784 (2006)] for wave-induced vortex shedding at the lower solid boundary of a stratified fluid system as a result of global instability. The time-dependent boundary layer induced by a strongly nonlinear internal wave of depression in shallow water is examined experimentally. Measurements of the velocity field close to the bottom boundary illustrate coherent periodic shedding of vortex structures at the lower boundary in the adverse pressure gradient region aft of the wave. The vortical structures ascend high into the water column and cause significant benthic turbulence. It is shown that global instability has a critical threshold dependent on the Reynolds number of the flow and the amplitude of the wave. The critical amplitudes observed are approximately half that predicted by Diamessis and Redekopp [J. Phys. Oceanogr. 36, 784 (2006)], indicating that internal wave-induced benthic mixing may be even more prominent than previously thought.
TL;DR: In this paper, the spectral characteristics of shallow water waves with significant wave height more than 2m based on the data collected along the Indian coast is examined. But it was found that the Scott spectra underestimate the maximum spectral energy of high waves.
TL;DR: In this article, the ability of one-dimensional hydrodynamic models to reproduce dissipation of turbulent kinetic energy and velocity profiles for conditions of whitecapping waves in a shallow water, tide-and wind-forced environment was assessed.
Abstract: [1] The ability of one-dimensional hydrodynamic models to reproduce dissipation of turbulent kinetic energy and velocity profiles for conditions of whitecapping waves in a shallow water, tide- and wind-forced environment was assessed. The models were forced with the conditions experienced during a month-long field experiment in a shallow estuarine embayment, and the results were compared with the observed dissipation and mean velocity profiles. Three turbulence models were assessed: the k-ω model and two k-l models, with different prescribed bilinear relationships for the turbulent length scale, l. The k-ω turbulence model was found to best replicate the measured decay of dissipation with depth with a surface roughness length, z0s = 1.3Hs, and wave energy parameter, α = 60. The k-l model achieved equally as good reproduction of the observations as the k-ω model when the proportionality constant in the prescribed linear length scale relationship for the upper half of the water column was modified from the traditionally employed von Karman's constant, κ = 0.4, to 0.25. The model results show that the whitecapping waves often supplied the dominant source of turbulent kinetic energy over the majority of the water column in the shallow, tide- and wind-forced system.
TL;DR: In this paper, a numerical model of depth-independent, nondispersive, long-wave dynamics with a forcing from nonlinear interactions among the primary wind waves (including swell) was used to investigate the possible source of seismic free oscillations.
Abstract: [1] Oceanic infragravity waves are investigated as a possible source of seismic free oscillations, often referred to as the “hum” of the Earth, using a numerical model of depth-independent, nondispersive, long-wave dynamics with a forcing from nonlinear interactions among the primary wind waves (including swell) Because of near-resonant amplification, the structure of the primary-wave forcing field in shallow water, and an edge-trapping mechanism, infragravity waves are excited very effectively near the coasts Deep-water infragravity waves are significantly influenced both by offshore leakage and propagation of the coastally generated free waves and by deep-water primary-wave forcing With the inclusion of “mesoscale” variability on top of the more slowly varying primary waves generated in synoptic storms, the deep-water infragravity waves are found to have an amplitude on the order of a millimeter in height, which is consistent with field observations and considered to be sufficient to account for local hum excitation in the middle of the basin
TL;DR: The median crest diameter (MCD) as mentioned in this paper is defined as the distance between the wave flanks under the crest at a level halfway between the crest and trough, which decreases relative to the similarly defined median trough diameter MTD, which remains constant up to the breaking point.
TL;DR: In this article, the influence of non-linear effects upon tides in shallow coastal regions, due to the presence of a significant storm surge is examined using a two-dimensional model of the west coast of Britain.
Abstract: [1] The influence of non-linear effects upon tides in shallow coastal regions, due to the presence of a significant storm surge is examined using a two-dimensional model of the west coast of Britain. The model has an unstructured grid, designed to have a high resolution mesh in the near coastal region of the eastern Irish Sea, the area chosen as the focus of this study. The influence of tide-surge interaction upon the M2, M4 and M6 components of the tide, due to surges produced by steady uniform wind stresses is examined in detail. Calculations show that in deep regions the tide is unaffected by the surge. However, in shallow coastal regions there is significant modification of tidal elevations and currents. This arises because of changes in bottom stress, and the non-linear interaction term in the hydrodynamic equations. In addition the locations of regions that “wet and dry” are changed during the tidal cycle due to the influence of the surge. This gives rise to significant spatial variations and changes in magnitude of the tide and its higher harmonics depending upon wind stress direction and water depth. These results explain why tidal energy remains in the surge residual in shallow water when it is computed by de-tiding the total signal using a tide only calculation; an effect often found in observed surge residuals.
TL;DR: This article presents a non-linear output feedback tracking controller deisgn for autonomous underwater vehicles (AUVs) operating in shallow water area and global exponential stability of overall observer-controller system is proved through Lyapunov stability theory.
Abstract: This article presents a non-linear output feedback tracking controller deisgn for autonomous underwater vehicles (AUVs) operating in shallow water area. In a shallow water environment, significant disturbances due to shallow water waves affect the motion of marine vehicles greatly. Since it is not energy efficient to counteract the oscillatory disturbances due to waves, it is critical to obtain the wave information or wave induced disturbance information and design an energy efficient controller to reduce the action of actuators to counteract wave disturbances to avoid wear and tear on actuators. In this article, a non-linear observer is first designed to estimate the low frequency (LF) motion of AUVs and to filter out wave-frequency (WF) motion of AUVs due to shallow water wave by using position and attitude measurements. Based on the designed observer, a non-linear output feedback controller is subsequently derived by using the observer backstepping technique. By using this approach, the AUV achieves gl...
TL;DR: In this paper, hydrography and currents in the active Storfjorden polynya during fieldwork in April 2004 and 2006 are presented, showing that high-resolution hydrographic data, spacing less than 05 km, are necessary to resolve such downflow.
Abstract: [1] Observations of hydrography and currents in the active Storfjorden polynya during fieldwork in April 2004 and 2006 are presented The polynya adds salt from its efficient ice production, usually increasing the density ∼015 kg m−3 Downflow of dense water from the coastal polynya to the deeper basin enclosed by the Storfjorden sill was captured in both years April 2006 had a period of strong heat loss and intense frazil ice growth in the polynya This created downflow of brine-enriched shelf water (BSW) with a maximum salinity of 3525, ie, an increased density ∼04 kg m−3 above that of the source water In April 2004, the salinity remained lower than BSW (S > 348), reflecting the fresh source water in fall 2003 due to the heavy ice conditions in the western Barents Sea that year A portion (005 Sv) of such source water probably enters Storfjorden through Freemansundet where the mean current transports less saline and warmer water from the northwestern Barents Sea Freemansundet has additionally a strong tidal current peaking at 53 cm s−1, dominated by the M2 component The tidal wave propagates through the narrow sound producing shallow water components and a locally well-mixed water column The estimated ice production in winter 2004, twice as large as that of winter 2006, could not overcome this less saline well-mixed source water BSW downflow within Storfjorden was both observed and modeled to occur in areas with steep bathymetry Our observations show that high-resolution hydrographical data, spacing less than 05 km, are necessary to resolve such downflow Consistent with the observed polynya water salinity, current data at the sill showed weaker overflow in 2004 than in 2006 Overflow of BSW was observed on the eastern part of the Storfjorden sill in April 2006, indicating that overflow occurs across the entire sill width during the freezing period Current, temperature, and salinity data from the overflow indicate a time lag of 12–18 days between the BSW production and the sill This downflow–overflow link is confirmed by a numerical experiment and analytical scaling, making results applicable to other polynyas
TL;DR: In this article, the construction of high-order ADER numerical schemes for solving the one-dimensional shallow water equations with variable bed elevation with variable bottom elevation has been studied, and the resulting schemes can be applied to solve realistic problems characterized by nonuniform bottom geometries.