Shallow Water Effects Research Articles

Numerical Stability Verification of a Two-Dimensional Time-Dependent Nonlinear Shallow Water System Using Multidimensional Wave Digital Filtering Network

This paper aims to study the stability effects of a two-dimensional time-dependent nonlinear shallow water (NLSW) system based on the concordance analysis of necessary and sufficient conditions derived from a multidimensional wave digital filtering (MDWDF) network. Approximating the differential equations used to describe elements of a MD passive electrical circuit by grid-based difference equations, the satisfactory Courant–Friedrichs–Levy condition usually known to be necessary are derived with various initial conditions to provide theoretical support for the existence of a MD passive dynamical system and thus stability of the discrete equivalent. Together with the evaluation of the system’s energy and hence solution error propagation that both arise directly and sufficiently to the stability of MDWDF networks, the numerical convergence of the network can be fully established. As a consequence, all instability related aspects in relation to computational errors and overflow corrections are fully excluded leading to uniquely a high degree of robustness of MDWDF architecture. Feasible comparisons are made with a finite element method implemented in the COMSOL Multiphysics to confirm the verification process.

Fabrication and testing of a self-propelled, miniaturized PDMS flotilla

In this work, we developed a miniaturized PDMS flotilla, which was capable of moving on a water surface. The flotilla consisted of five mm-scaled PDMS boats that were linked together through μm-scaled PDMS bars. We explored its design, fabrication, propulsion, and motions in straight and circular channels. The flotilla was fabricated using a molding approach with two-layer SU-8 structures as the mold, and actuated by the difference between fore-and-aft surface tensions. It was tested in straight and circular channels at water levels of 2.0, 3.0, 6.0 and 9.0 mm, respectively. No collisions were observed between neighboring boats in all the tests. Travel distances ranged from 385 to 1,128 mm. Average speeds varied from 38.5 to 102.5 mm/s, and increased with the increase in water depth. Dramatic squat and trim phenomena were directly observed in the two types of tests conducted in the straight channel. They were mainly induced by the difference between surface tensions of water and flotilla propellant. Simple models were further developed to interpret driving mechanisms of the flotilla, and to extract its resistance coefficients in different motions. These coefficients ranged from 0.1 to 0.7 in the 2-, 3-, 6- and 9-mm tests performed in the straight channel. The two ends of the flotilla had direct contact with the outer sidewall of the circular channel during a circular motion. The supporting forces of the outer sidewall at these contact points provided the centripetal force needed for the circular motions. In the four tests conducted in either the straight or the circular channel, water resistances increased with the decrease in water depth. Furthermore, the flotilla suffered much larger resistances in the 2-mm test than in another three, implying that, to avoid the effect of shallow water, water is preferred to be deeper than 2 mm in the applications of the miniaturized flotilla. The results presented in this work indicate that the water flotilla was capable of traveling reasonably long distances in straight and circular channels at fast speeds. Due to its mobility on a liquid surface, such a miniaturized flotilla would have the capability of delivering different materials and sensors on demand in small-scale fluidic applications.

Deep and Shallow Water Effects on Developing Preschoolers' Aquatic Skills

The aim of the study was to assess deep and shallow water teaching methods in swimming lessons for preschool children and identify variations in the basic aquatic skills acquired. The study sample included 32 swimming instructors (16 from deep water programs and 16 from shallow water programs) and 98 preschool children (50 from deep water swimming pool and 48 from shallow water swimming pool). The children were also studied regarding their previous experience in swimming (6, 12 and 18 months or practice). Chi-Square test and Fisher’s exact test were used to compare the teaching methodology. A discriminant analysis was conducted with Λ wilk’s method to predict under what conditions students are better or worse (aquatic competence).Results suggest that regardless of the non-significant variations found in teaching methods, the water depth can affect aquatic skill acquisition - shallow water lessons seem to impose greater water competence particularly after 6 months of practice. The discriminant function revealed a significant association between groups and all predictors for 6 months of swimming practice (p<0.001). Body position in gliding and leg displacements were the main predictors. For 12 and 18 months of practice, the discriminant function do not revealed any significant association between groups. As a conclusion, it seems that the teaching methodology of aquatic readiness based on deep and shallow water programs for preschoolers is not significantly different. However, shallow water lessons could be preferable for the development of basic aquatic skills.

Tides, moonlight, machines, and D-Day

Bruce Parker’s article in the September 2011 issue of PHYSICS TODAY (page 35) presented a clear and thorough account of the important role of tide predictions for the Normandy invasion on 6 June 1944. The exceptionally rapid rise of the water level that morning meant that the engineers had only a short time to blow up beach obstacles while they were exposed just after low water. We can verify Parker’s statement that the water-level rise was “at least a meter per hour—perhaps even faster due to shallow-water effects.”Our calculation of the tide curve for the Normandy coast near Omaha Beach includes shallow-water constituents and gives a rate of rise of 1.5 meters per hour while the demolition teams were struggling to blow up the beach obstacles; the rate of rise exceeded 1.9 meters per hour shortly thereafter.11. D. W. Olson, R. L. Doescher,Sky Telesc. 87 (6), 84 (1994). Perhaps less clear is Parker’s comment about the time of moonrise. Parker states that the paratroopers needed to see their drop zones during the preceding night and therefore “there had to be a late-rising Moon.”According to our astronomical calculations for Omaha Beach (49°22’ N, 0°52’ W), the Moon had risen about 1.5 hours before sunset on the preceding day (5 June). It then arced across the sky during the night of 5–6 June and reached its highest point for that night just as the airborne assault began, about five hours after moonrise.11. D. W. Olson, R. L. Doescher,Sky Telesc. 87 (6), 84 (1994). We calculate that moonrise on 5 June occurred at 18:33 Greenwich Mean Time (GMT), that sunset at 20:04 GMT marked the beginning of civil twilight, and that the period of brightest moonlight fell near 23:22 GMT. Our calculations agree well with the approximate times determined by reading down the left edge of the official 1944 tidal and illumination diagram reproduced as Parker’s figure 4.General Dwight Eisenhower later explained that the Allied forces “wanted a moon for our airborne assaults,”22. D. D. Eisenhower, Crusade in Europe, Doubleday, Garden City, NY (1948), p. 239. and Winston Churchill agreed that “moonlight . . . would help . . . our airborne troops.”33. W. S. Churchill, Closing the Ring, Houghton Mifflin, Boston (1951), p. 591. Brigadier General James Gavin of the 82nd Airborne gives an eyewitness account. As his C-47 military transport aircraft approached a drop zone west of Sainte-Mère-Église, Gavin could clearly see that “the roads and the small clusters of houses in the Normandy villages stood out sharply in the moonlight.”44. J. M. Gavin, Airborne Warfare, Infantry Journal Press, Washington, DC (1947), p. 57. REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. D. W. Olson, R. L. Doescher,Sky Telesc. 87 (6), 84 (1994). Google Scholar2. D. D. Eisenhower, Crusade in Europe, Doubleday, Garden City, NY (1948), p. 239. Google Scholar3. W. S. Churchill, Closing the Ring, Houghton Mifflin, Boston (1951), p. 591. Google Scholar4. J. M. Gavin, Airborne Warfare, Infantry Journal Press, Washington, DC (1947), p. 57. Google Scholar© 2012 American Institute of Physics.

Adapting a model of heat and mass exchange between a water body and the atmosphere taking into account the effect of shallows: Case study of the Ivankovo Reservoir

The paper is based on a box model of heat and mass exchange with the incorporation of a block for calculating latent heat flux, supplemented by parameterization of heat and mass exchange between shallow water area and the atmosphere. The results of calculation of evaporation from the water area of the Ivankovo Reservoir, with allowance made for more intense evaporation from shallows, are given. The latent heat fluxes from shallow and deep-water zones of the water body are shown to differ, depending on weather conditions and water level; the increase in the evaporated-water volume due to taking into account the shallow-water effect is evaluated.

The tide predictions for D-Day

Based on the physics of Newton and Laplace, the big brass tide-predicting machine designed by Lord Kelvin was crucial for the success of the Normandy invasion in World War II.

Realistic evaluation of hull performance for rowing shells, canoes, and kayaks in unsteady flow

In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic performance of rowing shells as well as canoes and kayaks. An approach was developed to generate data in a towing tank using a test rig capable of reproducing realistic speed profiles. The impact of unsteady shallow-water effects on wave-making resistance was examined via experimental measurements on a benchmark hull. The data generated were used to explore the validity of a computational approach developed to predict unsteady shallow-water wave resistance. Comparison of measured and predicted results showed that the computational approach correctly predicted complex unsteady wave-resistance phenomena at low oscillation frequency and speed, but that total resistance was substantially under-predicted at moderate oscillation frequency and speed. It was postulated that this discrepancy arose from unsteady viscous effects. This was investigated via hot-film measurements for a full-scale single scull in unsteady flow in both towing-tank and field-trial conditions. Results suggested a strong link between acceleration and turbulence and demonstrated that the measured real-world viscous-flow behaviour could be successfully reproduced in the tank. Thus a suitable tank-test approach could provide a reliable guide to hull performance characterization in unsteady flow.

MARÉS ASTRONÔMICAS NA BAÍA DA BABITONGA, SC

Tidal harmonic constituents for Praia da Enseada (# PE) and Port of Sao Francisco do Sul (# PSFS) were assessed to characterize the local astronomical tide, as well to evaluate the shallow water effects on the tidal propagation to the interior of the Babitonga Bay. The sea level at # PE were monitored with a pressure tide gauge during June to December, 1996. From this data set, 48 tidal harmonic constituents was determined using the harmonic method for tidal analysis. The 32 harmonic constituents for the # PSFS were obtained with the Diretoria de Hidrografia e Navegacao. Considering these information, the tide at the Babitonga Bay is classified as mixed, with semidiurnal dominance and diurnal inequalities, with Form Number of 0.32 for # PE and 0,29 for # PSFS. Nonlinear effects results in the amplification of the astronomical constituents towards the interior of the bay, showing hypersynchronous behavior. Some harmonic constituents increased about 2 to 7 times, and all presented around of 40 minute phase shift. Despite of the astronomical constituents amplification, there are also an asymmetry on the wave propagation, with flood dominate in bay. The role of the channel constriction effects over the bottom friction was clearly observed by the harmonic constituents speed increase towards the bay. The Babitonga Bay presents a natural oscillation period about 3,6 hours resonance with some of shallow water components. This effect can be a significant processes in the increasing of the astronomical components.

The hydrodynamic model for simulating the motions of a ship moored near the quay in waves

In this study, a hydrodynamic mathematical model for simulating the motions of a ship moored near the quay in waves is presented. The related hydrodynamic coefficients such as the added mass, damping coefficient and wave exciting force are calculated by the two-dimensional source distribution method. The strip theory is then applied to integrate the whole ship hydrodynamic characteristics along the ship length and the ship motion behaviors in waves can be obtained through the equations of motions. The bank effects are treated by using the image method which is similar to the treatments of the twin hull ship except the differences on some coupled hydrodynamic forces. The time domain simulation technique is made to analyze the motions deeply by using the 4th order Runge-Kutta method. Different wave conditions are considered with respect to different clearances between the ship and bank and shallow water effect is neglected for simplicity. The present results will be helpful for the design on the ship mooring system arrangement near the quay or the wharf.

Tide‐surge Interaction Intensified by the Taiwan Strait

The Taiwan Strait is a long and wide shelf‐channel where the hydrodynamics is extremely complex, being characterized by strong tides, and where storm surges frequently occur during the typhoon season. Obvious oscillations due to tide‐surge interaction were observed by tide gauges along the northern Fujian coast, the west bank of the Taiwan Strait, during Typhoon Dan (1999). Numerical experiments indicate that nonlinear bottom friction (described by the quadratic formula) is a major factor to predict these oscillations while the nonlinear advective terms and the shallow water effect have little contribution. It is found that the tide‐surge interaction in the northern portion of the Taiwan Strait is intensified by the strait. Simulations based on simplified topographies with and without the island of Taiwan show that, in the presence of the island, the channel effect strengthens tidal currents and tends to align the major axes of tidal ellipses along the channel direction. Storm‐induced currents are also strengthened by the channel. The pattern of strong tidal currents and storm‐induced currents along the channel direction enhances tide‐surge interaction via the nonlinear bottom friction, resulting in the obvious oscillations along the northern Fujian coast.

Extraction of Structural Curves, Regression Relations and Structural Regression Relations in the Tidal Limit of the Karun River

The Karun River is the most important tidal river in Iran. Two factors are governing of hydraulic conditions of tidal rivers (fluvial flows and tidal flows). Fluvial flow concerns hydrologic and physiographic conditions of watershed and characteristics of rainfall while tidal flows are produced by gravity of moon and sun, reflection wave from beach, effects of shallow water in estuaries and the shape of beach. Because tidal flows move to upstream and fluvial flows go toward downstream in the tidal limit of the tidal rivers, hydraulic conditions of this part are very complex. The measurement of discharge and velocity of current is impossible in this part. For determination of discharge-stage curve in tidal limit, an especial approach was applied in this research. Structural curves (an especial type of discharge-stage curve) were developed by using of discharge of fluvial flow in the upstream and tidal height in the downstream. For convenience of using of structural curves, these curves converted to regression relations. For determination of correlated water surface elevations to different return periods, structural regression relations were extracted by regression relations, joint probability method and combination coefficient. In this research, four methods made used of determination of combination coefficient. These methods are conventional method, desk study joint probability method, analytic joint probability method and developed analytic joint probability method by researcher. The results of developed analytic joint probability method by researcher have the best fitness by observed data in the Karun River. At the end structural regression relations showed correlated water surface elevation to each combined return period of fluvial flow and tidal flow.

Extraction of structural curves, regression relations and structural regression relations in the tidal limit of the Karun River

The Karun River is the most important tidal river in Iran. Two factors are governing of hydraulic conditions of tidal rivers (fluvial flows and tidal flows). Fluvial flow concerns hydrologic and physiographic conditions of watershed and characteristics of rainfall while tidal flows are produced by gravity of moon and sun, reflection wave from beach, effects of shallow water in estuaries and the shape of beach. Because tidal flows move to upstream and fluvial flows go toward downstream in the tidal limit of the tidal rivers, hydraulic conditions of this part are very complex. The measurement of discharge and velocity of current is impossible in this part. For determination of discharge-stage curve in tidal limit, an especial approach was applied in this research. Structural curves (an especial type of discharge-stage curve) were developed by using of discharge of fluvial flow in the upstream and tidal height in the downstream. For convenience of using of structural curves, these curves converted to regression relations. For determination of correlated water surface elevations to different return periods, structural regression relations were extracted by regression relations, joint probability method and combination coefficient. In this research, four methods made used of determination of combination coefficient. These methods are conventional method, desk study joint probability method, analytic joint probability method and developed analytic joint probability method by researcher. The results of developed analytic joint probability method by researcher have the best fitness by observed data in the Karun River. At the end structural regression relations showed correlated water surface elevation to each combined return period of fluvial flow and tidal flow.

Overall hearing abilities of manatees and ecological acoustical challanges.

A comprehensive series of underwater psychoacoustic tests was conducted to measure the hearing abilities of West Indian manatees. Pure tones, complex and real world sounds were presented to manatees under controlled acoustical conditions. The results from 30 000 threshold trials measured their audiogram, temporal integration, critical ratios, MMAs and directional hearing. Complementing these investigations, underwater acoustical measurements of manatee habitats and vessel noise propagation were conducted to evaluate acoustical factors that render Florida manatees vulnerable to repeated collisions with vessels. Both low‐frequency cutoffs in shallow water and near surface boundary effects limit the propagation of the dominant low‐frequency spectra from slow moving boats. Slow speed zones implemented to protect manatees do not address this underlying acoustical challenge. Ironically, the strategy can be counter‐productive in turbid waters and can exacerbate the problem, making vessels more difficult or impos...

HF Radar Sea-echo from Shallow Water.

HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information) far more than first-order (which gives information on current velocities), the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements.

천수 영역에서 저속 운항하는 선박의 조종성능 추정에 관한 연구

In this paper, a mathematical model for a ship manoeuvring with low forward speed in shallow water was suggested. Based on the cross flow model with low forward speed in deep sea, hull, propeller and rudder models were modified to consider the shallow water effects. Static drift and PMM tests were performed to obtain the cross flow drag coefficients and hydrodynamic coefficients. To validate suggested mathematical model, numerical simulation results were compared with those of sea-trials. Through comparisons, it was concluded that suggested mathematical model could give proper estimation on turning test results.

Assessment of ship squat in shallow water using CFD

In the recent years much research effort in ship hydromechanics is devoted to the practical navigation problems in getting larger ships safely into existing harbours or to the appropriate design of expansion of harbours for safe accommodation of larger ships. Both these problems are directly related to the safety of navigation and therefore they receive high attention from ship designers, harbour designers, ship operators and maritime administration. The starting point of any navigational or design analysis lies in the accurate determination of the hydrodynamic forces generated on the ship hull moving in confined waters. The analysis of such ship motion should include the effects of shallow water, horizontal restrictions, asymmetric channels, muddy bottoms, ship squat, ship to ship interactions etc. It is natural to use advanced Computational Fluid Dynamics methods for this purpose. The paper includes a wide introduction into the problems of modelling of the restricted water effects on ship motion using CFD. This presentation is illustrated with the examples of calculations performed using the commercial system Fluent.

Modeling the Maneuvering Behavior of Container Carriers in Shallow Water

Due to the expansion of the dimensions of container vessels, the available maneuvering space in harbor areas and their access channels is decreasing as waterway authorities are often unable to increase the channel dimensions at the same pace. The under keel clearance is an especially important parameter for ship maneuver-ability and controllability. After an overview of the shallow water effects on ship maneuvering, a new mathematical maneuvering model based on captive model tests is introduced. The mathematical model is valid in a large under keel clearance range and is applicable in four quadrants of forward speed: propeller rate combinations, drift angles, and yaw angles. The mathematical model has been validated by means of an independent set of captive model tests.

C103 回流水槽における模型船の造る浅水波の可視化

It is important to consider shallow water effect for design of ships, because there are several differences when the ship is sailing in shallow water and in deep water. Many studies have been done, however few experiments have been done because a special device is necessary to simulate the shallow water condition and visualize shallow water waves. In this study, a device for shallow water effect in a circulating water channel is developed. Experiments are carried out to study the performance of the device for shallow water effect. For these purposes, relationship between rotation of impeller and flow velocity and uniformity of flow velocity in the device should be investigated. Experimental visualizations of the shallow water wave using this device are carried out, and crest angles of the diverging wave are measured and discussed.

Role of water in the formation of the Late Cretaceous Wetumpka impact structure, inner Gulf Coastal Plain of Alabama, USA

Abstract— The effect of shallow marine water (˜30–100 m deep) in the late excavation and early modification stages of a marine‐target crater 5 km in diameter, as exemplified by the Late Cretaceous Wetumpka impact structure in Alabama, USA, is manifest in the early collapse of a weak part of the rim. Excavation flow and connate marine water are interpreted to be factors in this collapse. This partial rim collapse catastrophically emplaced an upper‐structure‐filling unit of broken and redistributed sedimentary target formations, which presently mantles the deeper fallback breccia deposits within the structure. Furthermore, rim collapse flow facilitated the formation of a structurally modified, extrastructure terrain, which is located outside and adjacent to the collapsed rim segment. This extrastructure terrain appears to be the product of extensive slumping of poorly consolidated target sedimentary formations.

Variation in Cutoff Effect and Sound Field Caused by Geometrical Structures near the Coast

The mysterious mass stranding of whales often arises in specific areas in the world. Moreover, vibrational noise, suspected to originate from large-scale construction in coastal areas, is problem. These problems could be considered to be related to sound propagation near coastal areas with a special geometrical structure and an ambient noise environment. We set up a propagation model in a coastal area, and simulated low-frequency sound propagation near the coast using the parabolic equation method (PE method) and the normal mode method. It has been shown that low-frequency sound cannot propagate from the ocean to the coast owing to the cutoff effect of shallow water that occurs when there is a water layer with a basement half space. However, when the water layer has a sediment layer, mode coupling occurs between the water layer and the sediment layer and propagation attenuation rapidly decreases. Sound can propagate to the coast in this case.