Bottom Inclination Research Articles

The Effects of Sampling Depth on Benthic Testate Amoeba Assemblages in Freshwater Lakes: A Case Study in Lake Valdayskoe (the East European Plain)

Testate amoebae are widely used as proxies in paleoecological reconstructions of lacustrine environments; however, our knowledge on their distribution along depth gradients are limited. This study investigates the distribution of benthic testate amoebae along a sampling depth gradient (0 to 57 m) and related environmental characteristics in Lake Valdayskoe, Russia. In total, 101 species belonging to twenty-one genera were identified. Four types of testate amoeba assemblages (littoral, sublittoral, bottom slope and profundal) were distinguished that corresponded well to the bottom zones of the lake. The results of redundancy analysis indicated that sampling depth, temperature, pH and bottom inclination significantly explained 40.2% of the total variance in the species composition. Temperature and sampling depth had the largest individual contributions of 19.2 and 7.4% (p < 0.001), respectively. The minimal values of species diversity were observed on the littoral and at the lower boundary of the thermocline. We estimated depth optima and ranges for the species with high occurrences and distinguish stenobathic and eurybathic species. These data might improve the interpretations of paleoecological records of subfossil testate amoeba assemblages in lacustrine surface sediments and serve as basis for the development of a transfer function for reconstruction of lake depths.

Estimate of energy loss from internal solitary waves breaking on slopes

Abstract. Internal solitary waves (ISWs) emerge in the ocean and seas in various forms and break on the shelf zones in a variety of ways. This results in intensive mixing that affects processes such as biological productivity and sediment transport. As ISWs of depression propagate in a two-layer ocean, from the deep part onto a shelf, two mechanisms are significant: (1) the breaking of internal waves over bottom topography when fluid velocities exceed the wave phase speed that causes overturning of the rear face of the wave, and (2) the changing of polarity at the turning point where the depths of the upper and lower layers are equal. We assume that the parameters that describe the process of the interaction of ISWs in a two-layer fluid with an idealized shelf-slope topography are (1) the nondimensional wave amplitude, normalized on the upper-layer thickness; (2) the ratio of the height of the bottom layer on the shelf to the incident wave amplitude; and (3) the angle of the bottom inclination. Based on a proposed three-dimensional classification diagram, four types of wave propagation over the slopes are distinguished: the ISW propagates over the slope without changing polarity and wave breaking, the ISW changes polarity over the slope without wave breaking, the ISW breaks over the slope without changing polarity, and the ISW both breaks and changes polarity over the slope. The energy loss during ISW transformation over slopes with various angles was estimated using the results of 85 numerical experiments. “Hot spots” of high levels of energy loss were highlighted for an idealized bottom configuration that mimics the continental shelf in the Lufeng region in the South China Sea.

Effects of flow condition and chute geometry on the shockwaves formed on chute spillway

Abstract Shock waves have undesirable effects, such as excessive dynamic pressure on spillway walls and the extension of flow beyond spillway conduits. To eliminate these detrimental impacts, designers have attempted to detect the characteristics of these waves. Flow interaction with chute piers generates triple waves in the middle walls and sidewalls of spillway conduits. The present study quantitatively investigated the characteristics of these waves with respect to variations in the bottom inclination angle (θ), wall contraction (φ), and Fr numbers (). The results indicated that with the increment of θ, , (φ, ), and (θ, ), the height () and distance () of the first wave increased, which can be helpful for flow aeration. Furthermore, owing to a boost in θ, , (φ, ), and (θ, ), the height of the second wave was decreased. Therefore, the amount of dynamic pressure on the spillway walls was reduced. Moreover, the distance of decreased with a rise in θ, φ and increased with the increment of and (φ, ). As for , raising φ and (φ, ) elevated the height of this wave and declined its distance. An increase in the height of boosted the flow turbulence and aeration.

A simplified approach to assess the resistance of a ship sliding on elliptic paraboloïd rock

This paper presents a simplified method for predicting the resistance of a ship bottom structure sliding over a rock idealised as an elliptic paraboloid. The derived analytical model may be considered as an extension of a previous work by the authors on the response of such structure in raking condition. The approach consist in splitting the structure into several independent super-elements and to derive closed-form expressions giving the plastic resistance force of each of them. Theoretical developments are based on plastic limit analysis with the objective to capture the main deformation modes of the outer shell plating, transverse floors, and longitudinal girders. Situations where the rock impacts the structure between two girders and below one girder are investigated as well as the general case where the ship bottom is not horizontal but inclined. For each situation, the proposed analytical formulations are confronted to numerical simulations performed with Ls-Dyna finite element solver, considering different rocks, friction coefficients and penetration heights. A good correlation between analytical predictions and numerical simulations is found for the majority of the sliding scenarios investigated but some limitations of the proposed model are also highlighted, more specifically when the grounding event involves a very sharp rock. Finally, it is shown that both the ship bottom inclination and its friction with the rock have a significant influence on the results.

Defining a single set of calibration parameters and prestorm bathymetry in the modeling of volumetric changes on the southern Baltic Sea dune coast

The studies described herein aimed to estimate the accuracy of determination of the volumetric changes on the dune coast of the southern Baltic Sea through the application of the XBeach numerical model, which is crucial for coastal engineering. In the first phase of the study, the profile (1D) mode of the model was adapted to 19 cross-shore profiles located along the Dziwnów Spit.The model was calibrated with a storm event in 2009 that caused significant changes to dunes and beaches. Cross-shore profiles were measured approximately one and a half months before and after the storm. An evaluation of model performance was made based on the Brier skill score (BSS), the visual match of the profile shape (VMS), the absolute volumetric change error (m3/m) and the relative volumetric change error (%). In this study, parameters related to the asymmetry transport (facua) and the dune erosion algorithm (wetslp) were taken into account.The best results for model calibration on all 19 cross-shore profiles were obtained with facua values ranging from 0.16 to 0.40 and wetslp values from 0.35 to 0.60. The calibration of individual profiles yielded good results, with an average absolute error of approximately 4 m3/m and an average relative error of ca. 20%. The poorest results were collected for the profiles situated near coastal engineering structures, where the average absolute error was 10 m3/m and the relative error was 60%. The possibility of accepting one set of parameter values for all the profiles at once was also investigated. These studies revealed that the application of one set of facua and wetslp values for all profiles simultaneously resulted in a relative volumetric change error of ca. 25% on average, with the maximum of about 40%.Due to the difficulty of collecting data just before and after the storm event, complex studies using all available bathymetric data were performed. Using a joint dataset composed of prestorm topography recorded before that storm and bathymetry from different years, a simulation of the 2009 storm event was carried out. The studies revealed that the prestorm bathymetry and the randomness of the selection of calibration parameters have similar effects on the accuracy of volumetric changes.Moreover, the impact of the nearshore bathymetry (to a depth of 2 m) on modeling the volumetric changes in the terrestrial part of the shore is evident. A change in the sea bottom inclination and a successive change in the nearshore sediment volume can increase the difference between modeled and actual volumetric changes.

Результаты моделирования зависимости высоты изгибно-гравитационных волн в плавающей пластине с заделанной кромкой от наклонности дна водоема

На основании проведенных автором экспериментов по разрушению льда амфибийными судами на воздушной подушке (СВП) резонансным методом при их движении в сторону берега, их крупномасштабных моделей в полевых условиях, а также известных случаев разрушения ледяного покрова движущимися в сторону берега транспортными средствами показана возможность существенного увеличения толщины льда, разрушаемого у его береговой кромки. Приведены данные экспериментов, выполненных в опытовом бассейне на моделирующих ледяной покров упругих пленках, подтверждающие эти возможности. В работе представлены результаты моделирования зависимости высоты изгибно-гравитационных волн (ИГВ), возбуждаемых в плавающей пластине движущейся в направлении ее заделанной кромки нагрузкой, от угла наклона дна бассейна. Также приведены рекомендации по использованию наклонности дна для повышения эффективности разрушения ледяного покрова (увеличения толщины разрушаемого льда) путем возбуждения резонансных ИГВ. На основании выполненных экспериментов показано, что приближение к берегу ИГВ, возбуждаемых СВП с последующим их выходом на него, может значительно увеличить толщину разрушаемого льда за счет отрыва от берега его кромки. Отмечена возможность увеличения ледоразрушающей способности ИГВ благодаря последующим проходам судна вдоль нее из-за роста деформаций ослабленного таким образом льда, т.е повышения ледоразрушающей способности СВП. Based on the experiments conducted by the author on ice destruction by amphibious hovercraft using the resonant method when they move towards the shore, their large-scale models in the field, as well as known cases of ice cover destruction by vehicles moving towards the shore, the possibility of a significant increase in the thickness of ice destroyed at its coastal edge is shown. The data of experiments performed in the experimental pool on elastic films modeling the ice cover are presented, confirming these possibilities. The paper presents the results of modeling the dependence of the height of Flexural-gravitational waves excited in a floating plate by a load moving in the direction of its embedded edge on the angle of inclination of the pool bottom. Recommendations are also given for using the bottom slope to increase the efficiency of ice cover destruction (increasing the thickness of the destroyed ice) by exciting resonant Flexural-gravitational waves. Based on the performed experiments, it is shown that the approach to the shore of Flexural-gravitational waves excited by hovercraft with their subsequent exit to it can significantly increase the thickness of the destroyed ice due to the separation of its edge from the shore. The possibility of increasing laboratree the ability of the Flexural-gravitational waves during the next passages of the ship along it due to the growth of deformations weakened the ice.

Downslope migration of free-living corals (Scleractinia: Fungiidae) in typhoon-exposed reef habitats at Okinawa, Japan

Offshore Onna Village, Okinawa Island, Japan, there is a large and densely covered coral assemblage of free-living mushroom corals (Scleractinia: Fungiidae) on a reef slope at depths from 20 m to 32 m, covering an area of approximately 350 × 40 m2. From previous research, it is known that migration distances of mushroom corals may depend on coral shapes, coral sizes, substrate, and bottom inclination. However, until now there have been no published examples of regular Fungiidae movement and behavior from typhoon-exposed coastlines, such as those in the western Pacific Ocean. Our surveys across three years offshore Onna Village show that mushroom corals always move in down-slope direction from shallow to deeper reef zones. The results indicated that mushroom corals migrated faster in autumn than in other seasons, and that oval-elongate fungiids, and particularly those with a smooth underside, migrated more quickly than species with other shapes. Surprisingly, we observed a negative relationship between the presence of typhoons and migration rates. We also observed active migration by fungiid individuals to escape situations in which they were threatened to become overgrown by Acropora corals, or when they needed to escape from burial underneath coral debris.

Impact of sloping porous seabed on the efficiency of an OWC against oblique waves

The study examines the influence of a sloping porous bed on the efficiency of an oscillating water column (OWC) device facing oblique water waves. A vertical, surface piercing, thin plate near a rigid wall approximates the OWC. The system is simulated using a multi-domain boundary element method assuming the linear potential theory. The impact of varying sloping bed structural parameters and influence of the incident wave angle on the performance of the OWC is evaluated and discussed. The significance of this model to act as a breakwater protecting near-shore marine facilities is also highlighted. The OWC efficiency is found to be highly sensitive to the slope of the porous seabed, and seabed porosity is found to stabilize the resonant frequency against changes in water levels. OWCs are found to be more efficient over porous seabeds with higher frictional coefficients and lower values of porosity. The results indicate the optimum values of the sloping bottom inclination, the porosity and the frictional coefficient for the porous sloping bottom that can be used for the design and implementation of an efficient OWC device.

Mathematical Modeling the Dynamics of the Bottom Sediments Granulometric Composition in the Balaklava Bay Affected by the Wind Waves

Purpose. Based on the mathematical modeling methods, influence of the wind waves on redistribution of the sand fractions in the semi-closed estuary-type water area is estimated using the Balaklava Bay as an example. Methods and Results. A two-dimensional version of the XBeach model with a constant grid spacing 10 m was used. The characteristics of wind waves were preset using the JONSWAP spectrum. The calculations were carried out for a storm event lasting about 12 hours once a year. The in-situ data on the particle size distribution in the bottom sediments resulted from the monitoring observations in the Balaklava Bay region was used in the numerical experiments. Conclusions. The results of modeling showed that the basic determining factors regulating the sediments movement were the depth and the bottom slope. It is noted that changing of the bottom inclination angle between the isobaths 6–7 and 7–8 m leads to deposition of the large and medium fractions, and in the area between the isobaths 9–10 and 10–12 m – to accumulation of fine sand. It was revealed that in the Balaklava Bay water area, the main redistribution of sand material caused by the storm waves took place within the southern basin, as well as at the bay exit in the coastal zone of the Megalo-Yalo Gulf. This is primarily determined by the features of the Balaklava Bay coast orography, namely, the knee-shaped narrowness separating the northern and southern basins. Nevertheless, in the isolated northern part of the Balaklava Bay being affected by the storm waves, insignificant dynamics of sand material was observed. The fractions of bottom sediments are redistributed from the western coast to the central part of the basin and to the eastern coast of the bay.

Matematicheskoye modelirovaniye dinamiki granulometricheskogo sostava donnykh otlozheniy Balaklavskoy bukhty pod vozdeystviyem shtormovogo volneniya

Purpose. Based on the mathematical modeling methods, influence of the wind waves on redistribution of the sand fractions in the semi-closed estuary-type water area is estimated using the Balaklava Bay as an example. Methods and Results. A two-dimensional version of the XBeach model with a constant grid spacing 10 m was used. The characteristics of wind waves were preset using the JONSWAP spectrum implying fixed height, wave period and various combinations of the wave direction. The calculations were carried out for a storm event lasting about 12 hours once a year. The in-situ data on the particle size distribution in the bottom sediments resulted from the monitoring observations performed by the Marine Hydrophysical Institute, Russian Academy of Sciences, in the Balaklava Bay region was used in the numerical experiments. Conclusions. The results of modeling showed that the basic determining factors regulating the sediments movement were the depth and the bottom slope. It is noted that changing of the bottom inclination angle between the isobaths 6–7 and 7–8 m leads to deposition of the large and medium fractions, and in the area between the isobaths 9–10 and 10–12 m – to accumulation of fine sand. It was revealed that in the Balaklava Bay water area, the main redistribution of sand material caused by the storm waves took place within the southern basin, as well as at the bay exit in the coastal zone of the Megalo-Yalo Bay. This is primarily determined by the features of the Balaklava Bay coast orography, namely, the knee-shaped narrowness separating the northern and southern basins. Nevertheless, in the isolated northern part of the Balaklava Bay being affected by the storm waves, insignificant dynamics of sand material was observed. The fractions of bottom sediments are redistributed from the western coast to the central part of the basin and to the eastern coast of the bay.

CONJUGATE NATURAL CONVECTION IN A POROUS ENCLOSURE SANDWICHED BY FINITE WALLS AND SUBJECTED TO CONVECTION COOLING CONDITION

Steady conjugate natural convection heat transfers in a two-dimensional enclosure filled with fluid saturated porous medium is studied numerically. The two vertical boundaries of the enclosure are kept isothermally at same temperature, the horizontal upper wall is adiabatic, and the horizontal lower wall is partially heated. The Darcy extended Brinkman Forcheimer model is used as the momentum equation and Ansys Fluent software is utilized to solve the governing equations. Rayleigh number (1.38 ≤ Ra ≤ 2.32), Darcy number (3.9 * 10-8), the ratio of conjugate wall thickness to its height (0.025 ≤ W ≤ 0.1), heater length to the bottom wall ratio (1/4 ≤  ≤ 3/4) and inclination angle (0°, 30° and 60°) are the main considered parameters. The presented results show the effect of these parameters on the heat transfer and fluid flow characteristics. These results include streamlines, isotherm patterns, and local and average Nusselt number for different values of the governing parameters. It is found that either increasing the Rayleigh number and the ratio of conjugate wall thickness to its height (d/H) or decreasing the ratio of heat source width to bottom wall (l/L), the average Nusselt number is increased. Also, it was observed that the average Nusselt number does not change substantially with inclination angle.

Discharge of a silo through a lateral orifice: Role of the bottom inclination versus friction.

In this work we propose to identify the relative role of the inclination of gravitational acceleration and friction on the discharge flow rate of a granular media from a rectangular silo by varying the silo geometry thanks to an inclined bottom which ends up at a lateral outlet. The study is motivated by a nuclear safety problem: a fuel rod (modeled by an elongated silo) accidentally releases fuel fragments (modeled by grains). We performed experiments where we independently measured the mass flow rate and the velocity profiles, together with discrete particle simulations and continuum simulations with a frictional rheology described by a μ(I) constitutive law and taking into account the wall friction. We study monolayer flows and three-dimensional flows, and we propose an analytical model that predicts the discharge flow rate of particles from a rectangular silo with an inclined bottom according to its outlet aspect ratio and the bottom inclination angle.

Mitigation of hunchbacked gravity quay wall displacement due to dynamic loading using shaking table tests

Five reduced-scale shaking table tests have been performed to investigate the deformation behavior of a block type quay wall under strong earthquakes. The quay wall was resting on a high relative density inclined seabed. The underlying seabed inclination and bottom block slopes have been considered as two parameters for mitigating the wall displacement. The experimental results indicated that the dominant mode of the wall failure under strong base acceleration was the sliding of the wall. Increasing the bottom block inclination (from 0 to 10°) significantly decreased the lateral displacement and the backfill settlements, which can increase the safety of port facilities. Since the high bottom inclination can cause the wall to overturn, a 7-degree angle was selected as the optimal degree for the presented wall model. Furthermore, it was observed that, making the bottom block inclined, without the seabed being inclined, did not effectively reduce the wall displacement.

A quantitative assessment of the diel influence on the cryptobenthic fish assemblage of the shallow Mediterranean infralittoral zone

Cryptobenthic fishes are an underestimated and probably important component of coastal marine ecosystems that are usually overlooked by standard methods for collecting and studying benthic fishes. Studies focusing on cryptobenthic fishes have been rare and all have been based on samples taken during daytime. The present study tested the difference in epibenthic and cryptobenthic fish composition, diel differences in cryptobenthic fish assemblage and diel shifts of infralittoral fish species between hidden and open bottom spaces. It also looked for the significant habitat variables structuring the cryptobenthic fish assemblage. The daylight, sunset and night samples of epibenthic and cryptobenthic fish assemblages were collected from 78 squares of 1 m2 shallow water plots (0.5 to 3 m) on Brač island in the eastern Adriatic. The study recorded 27 species, among which the family Gobiidae dominated fish diversity with 14 species. Cryptobenthic specimens highly outnumbered epibenthic specimens, with a ratio of 7.5 to 1. Species composition of cryptobenthic and epibenthic fish assemblages differed significantly. No diel variation in composition, species richness or abundance of the cryptobenthic fish assemblage was detected. Occurrence frequencies in hidden and open bottom spaces of ambivalent species did not change significantly between times of day, so no dial switches between open and hidden places were apparent. In combination, these results suggest that the cryptobenthic fish assemblage has diel stability and is mostly composed of permanent inhabitants of hidden spaces with domination of miniature gobies. Significant habitat variables for species occurrence were the presence of multiple layers, bottom inclination and the presence of cobbles, while depth also had a large but not significant effect.

Influence of the angle of the bath bottom inclination in ergot isolation device on grain immersion in a liquid

For the mechanization of the allocation of toxic ergot from the rye seeds in a wet way, the urgent issue is the development of a device containing a bath with an aqueous solution of salt. The aim of the study is to determine the influence of the angle of inclination of the bottom of the bath on the rate of immersion of grains in the fluid of the device for separating ergot from rye seeds, which will ensure the efficiency of the process. Theoretically, we consider the movement of individual rye grains along the inclined surface of the bottom of the bath of the ergot extraction device. Rye grains have a density ρz = (1.2...1.5)·103 kg/m3, a length lz = (5.0. 10.0)·10-3 m, a width b = (1.4...3.6)·10-3 m, and a thickness δ = (1.2 3.5)·10-3 m. Geometric models of these grains are presented in the form of cylindrical and spheroidal grains. The movement of grain on the surface of the bottom of the bath of an ergot extraction device is considered at angles of inclination α = 27, 30, 40, 50, 60, 70, 80, and 90 degrees by the methods of mathematical modeling, classical mechanics using the laws of hydrodynamics. It was established that the angle α of the slope of the surface of the bottom of the bathtub to the horizontal should be taken at least 650, at which accumulation is excluded due to the rapid rolling of the grain and a decrease in the thickness of its layer.

CO2 sorption and sorbent depressurized regeneration in circulating-turbulent fluidized bed regime

The circulating fluidized bed reactor can be used to capture CO2 continuously by performing three different processes: CO2 sorption in riser, gas-solid separation in cyclone, and sorbent regeneration in downer. The semi-continuous mode of the reactor is employed to screen out the effect of operating parameters by ANOVA analysis. Superficial gas velocity is the crucial operating parameter, which provides a significant positive trend on CO2 sorption capacity. Due to the interaction between operating parameters, the solid recirculating rate must be optimized to achieve high sorption capacity. The inclination of downer bottom should be greater than the angle of repose of the sorbent particle. Depressurized regenerator downer is the most important part to complete circulating sorption and regeneration as a continuous mode. One of the poor operations at 47.21 mg-CO2/g-sorbent (Ug of 1.0 m/s and Gs of 100 kg/m2.s) is selected as a task for performing continuous mode. The result shows that CO2 capture capacity improves by three times. The concentration profile of the treated gas is constant about a half of the breakthrough concentration and no trend reaching the breakthrough point.

Comparative Study of Continuous Wave and Pulse Wave Electromagnetic Acoustic Resonance for the Measurement of Pipe Wall Thickness

This paper describes the measurement of wall thinning by continuous wave electromagnetic acoustic resonance (CW-EMAR) and pulse wave electromagnetic acoustic resonance (PW-EMAR). Simulated pipe wall thinning specimens are measured. The two methods show accurate results in the areas with a low variation of thickness, and the accuracy decreases when the thickness changes drastically. The two methods are analyzed by using the finite element method. The results show that with the increase of the bottom inclination, the accuracy of the two methods is reduced. For thin specimens, the reason for the larger error of CW-EMAR method is due to that CW-EMAR method is more easily affected by ultrasonic scattering and nonuniform distribution of static magnetic field.

Solitary wave run-up: wave breaking and bore propagation

ABSTRACTThe run-up features of breaking solitary waves over a plane sloping beach are described using both high-speed images and a systematic data analysis. Experiments were conducted in a smooth, rectangular and prismatic channel. The main hydraulic parameters investigated include relative wave height, stillwater depth, and channel bottom inclination. The various types of wave breaking are discussed, including the plunging, spilling, and surging breaker types in addition to the amplitude evolution due to wave shoaling. Furthermore, the generation and propagation of bores is examined. A detailed data analysis, based on hydraulic similitude, allows for deriving mathematical expressions that are considered to represent the observed wave features. The research includes film-like image series describing the wave run-up features, allowing for a description of the flow complexities observed and the beauties associated with wave run-up. This research excludes a numerical analysis, given the complexities due to turbulence generation and air entrainment.

An Investigation of Forces during Roller Forming Process

The tubular sections or shells for forming channels, drums, tanks or pressure vessel are manufactured by bending plates generally through three-roller bending machine and then welding the ends of bent plate to form a cylinder or cone. Force exerted on rollers during bending is one of the important criteria which must not exceed the capacity of bending machine. Secondly, Total bender capacity must be utilised during bending of desired curvature, which reduces number of passes and hence time required to attain desired curvature. Thus, it necessary to estimate the forces during bending, based on the roller position, so that it does not exceeds the bender capacity and simultaneously reduces number of passes. In this regards, some analytical models are available to predict the forces during three roller bending process with assumption of constant bend radius during bending. In fact, the radius continuously changes during bending operation which affects the magnitude and the direction of the forces exerted on the roller. An attempt is made to simulate the roller bending using FEA. Variation of curvature of plate and effect of various parameters such as plate thickness, bottom roller inclination and top roller inclination on bending forces during cylindrical and conical bending operation are studied using FEA analysis.

Comparison of Analytical Models of Force Prediction during Dynamic Bending Stage for 3-Roller Conical Bending Process

Conical bending process using three rollers with different configurations is a widely used process for manufacturing conical sections and shells in the industries. The process involves static as well dynamic stages. For optimum design of the machine, accurate analytical model of the force prediction is required for static as well dynamic bending stages. In this paper the analytical models considering three different stress conditions have been compared with the experimental results. The observations of the comparison have been reported. It is concluded that for higher bottom roller inclination, the shear stress has to be considered for evaluation of bending force whereas for lower bottom roller inclination it can be neglected.