Bifurcation of Water Column Oscillator Behavior Simulating Reactor Safety System: 2nd Report, Analytical Model

2002 ◽  
Author(s):  
K. Kawamata ◽  
Y. Morimoto ◽  
Haruki Madarame ◽  
Koji Okamoto
Keyword(s):  
Water Column ◽  
Abrupt Change ◽  
Free Water ◽  
Reactor Safety ◽  
System Behavior ◽  
Analysis Model ◽  
Constant Rate ◽  
Gas System ◽  
Analytical Result ◽  
Closed Period

Behavior of a water column oscillator with a cover gas system was studied experimentally and analytically. One of the free water surfaces was sealed with the cover gas, while the other was open to the atmosphere. The cover gas was supplied with a constant rate, and it was ejected through a valve when the water level reached a certain point. As soon as the level reached another point, the valve closed and the cover gas quantity increased again. In the experiment, a bifurcation-like phenomenon was observed; the valve closed period usually had a single value, while it took two values under certain conditions. In order to examine the cause of this bifurcation-like phenomenon, a numerical analysis model was developed which described the system behavior precisely. The analytical result revealed that the bifurcation-like phenomenon was not bifurcation but an abrupt change of the value dimmed by superimposed noise. Finally the numerical model predicts that the water column oscillator behaves chaotically at certain conditions.

Numerical Investigation of Bifurcation in Water Column Oscillator

2002 ◽  
Author(s):  
K. Kawamata ◽  
Y. Morimoto ◽  
K. Okamoto ◽  
H. Madarame
Keyword(s):  
Water Column ◽  
Free Water ◽  
Slight Variation ◽  
System Behavior ◽  
Analysis Model ◽  
Small Noise ◽  
Constant Rate ◽  
Gas System ◽  
Analytical Result ◽  
Closed Period

Behavior of a water column oscillator with a cover gas system was studied experimentally and analytically. One of the free water surfaces was sealed with the cover gas, while the other was open to the atmosphere. The cover gas was supplied with a constant rate, and it was ejected through a valve when the water level reached a certain point. As soon as the level reached another point, the valve closed and the cover gas quantity increased again. In the experiment, a bifurcation-like phenomenon was observed; the valve closed period usually had single value, while it took two values under certain conditions. In order to examine the cause of this bifurcation-like phenomenon, a numerical analysis model was developed which described the system behavior precisely. The analytical result revealed that the bifurcation-like phenomenon was not bifurcation. Very small noise superimposed on the singular characteristic of the system was found to cause the two duration values under the conditions; the duration changed abruptly by an uncontrollable slight variation of the system conditions. It is likely to be confused with bifurcation by observers who could not perceive the uncontrollable noise.

scholarly journals Advanced experimental approaches to marine water-column biogeochemical processes

2017 ◽  
Vol 75 (1) ◽  
pp. 30-42 ◽  
Author(s):  
Louis Legendre ◽  
Richard B Rivkin ◽  
Nianzhi Jiao
Keyword(s):  
Water Column ◽  
Numerical Models ◽  
Free Water ◽  
Sea Surface ◽  
Biogeochemical Processes ◽  
In Situ Experiments ◽  
Technological Developments ◽  
Approaches To Study ◽  
Experimental Approaches

Abstract This “Food for Thought” article examines the potential uses of several novel scientific and technological developments, which are currently available or being developed, to significantly advance or supplement existing experimental approaches to study water-column biogeochemical processes (WCB-processes). After examining the complementary roles of observation, experiments and numerical models to study WCB-processes, we focus on the main experimental approaches of free-water in situ experiments, and at-sea and on-land meso- and macrocosms. We identify some of the incompletely resolved aspects of marine WCB-processes, and explore advanced experimental approaches that could be used to reduce their uncertainties. We examine three such approaches: free-water experiments of lengthened duration using bioArgo floats and gliders, at-sea mesocosms deployed several 100s m below the sea-surface using new biogeochemical sensors, and 50 m-tall on-land macrocosms. These approaches could lead to significant progress in concepts related to marine WCB-processes.

Net Environmental - Economic Benefit Analysis Model

2003 ◽  
Vol 2003 (1) ◽  
pp. 995-1002 ◽  
Author(s):  
W. Koops ◽  
M.G.D. Smit ◽  
R. de Vos
Keyword(s):  
Environmental Economic ◽  
Water Column ◽  
Food Chain ◽  
Economic Benefit ◽  
Water Surface ◽  
Ecological Effect ◽  
Benefit Analysis ◽  
Analysis Model ◽  
Response Option ◽  
Response Options

ABSTRACT To be able to compare various response strategies for oil spill response a Net Environmental – Economic Benefit Analysis model (NEEBA) has been developed by TNO. This model consists of an oil behaviour module, a response module and an ecological effect module. In the oil behaviour module a quantitative division of the oil volume over the different compartments (air, water surface and water column) is determined on the basis of spreading, transport and weathering. This module determines also the fate of the remaining oil after one of the response options has been applied. With the ecological effect module the effects on organisms at the water surface, in the water column and on the sea floor are determined. In order to come up with one benefit score a simplified weighing method has been chosen to compare the effects on different species. The NEEBA score is therefore expressed in costs, using the costs of fish as basis. The “costs” of the other organisms in relation to fish are dependent on their place in the food chain. For each step in the food chain a factor ten has been applied. In other words 1 kg of birds equals 10 kg of fish and 100 kg of Zooplankton. To account for seasonal fluctuations the model can be adjusted by changing the densities of the different organisms over the year. The methodology, developed in MS excel, can be used by policy makers and decision takers to assist in choosing the most appropriate response option. The model interface consists of an input window, a default window with several variables and defaults and two output windows. In the input window parameters such as volume, density and viscosity of the oil but also meteorological and hydrological information can be filled in. In the default window parameters like the densities of the different organisms, weighing factors, costs, water type, etc, can be varied. The response option can be varied with respect to mobilization time, number of units deployed and capacity. The NEEBA model is a valuable tool to support decision-making and gives insight in the environmental effects related to a particular response option. The NEEBA model shows that there is a specific role for the different response options. Each option has a window of opportunity in which the use is most optimal. The tool can be used for preplanning as well as during actual spills. The model will be developed further to increase its value and realism

scholarly journals Permeability Evaluation of Clay-quartz Mixtures Based on Low-Field NMR and Fractal Analysis

2020 ◽  
Vol 10 (5) ◽  
pp. 1585 ◽  
Author(s):  
Zhen Lu ◽  
Aimin Sha ◽  
Wentong Wang
Keyword(s):  
Prediction Model ◽  
Decay Rate ◽  
Fractal Analysis ◽  
Bound Water ◽  
Free Water ◽  
Evaporation Process ◽  
Permeability Coefficients ◽  
Constant Rate ◽  
Saturated Mixture ◽  
Two Stages

Nuclear magnetic resonance (NMR) technology has been widely used for predicting permeability coefficients of porous medium, such as shales, sandstones, and coals. However, there have been limited studies on the prediction model of clay-quartz mixtures based on NMR technology. In this study, evaporation tests at 40 °C and NMR tests were simultaneously performed on eight clay-quartz mixtures with different mineral compositions. The results show that during the evaporation process, the decay rate of T2 total signal amplitudes was constant at first, and then decreased to 0 after a period of time. Based on the decay rate, the evaporation process was divided into two stages: the constant rate stage and the falling rate stage. Based on the two stages, the T2 cut-offs of eight mixtures were determined. The water in the mixture was divided into two parts by the T2 cut-off: the free water and the bound water. The prediction model of permeability coefficients of clay-quartz mixtures was established based on the Timur-Coates model. In order to simplify the process of predicting the permeability coefficient, fractal analysis was used to develop the relationship between the T2 cut-off and fractal dimension of the T2 spectrum of saturated mixture. A simplified method for predicting permeability coefficients of clay-quartz mixtures based on NMR technology without centrifugal and evaporation experiments was also proposed.

Distribution and retention of faecal coliforms in the Nakivubo wetland in Kampala, Uganda

2001 ◽  
Vol 44 (11-12) ◽  
pp. 199-206 ◽  
Author(s):  
F. Kansiime ◽  
J.J.A. van Bruggen
Keyword(s):  
Water Column ◽  
Free Water ◽  
Vertical Transport ◽  
Laboratory Studies ◽  
Faecal Coliforms ◽  
Cyperus Papyrus ◽  
Plant Debris ◽  
Flow Through

Nakivubo wetland, which has been receiving wastewater from the capital of Uganda for more than 40 years is a tropical wetland dominated by Cyperus papyrus and Miscanthidium violaceum. Field, pilot and laboratory studies were carried out to assess the distribution of faecal coliforms and factors responsible for their retention in different compartments of the two macrophytes in the wetland. There were higher coliform numbers in the free water column below the mat of zones dominated by Miscanthidium (1.1±0.6×105 MPN/100 ml) compared to those dominated by papyrus (8.9±3.1×104 MPN /100 ml). The thick (1.3 m) and compact mat of Miscanthidium restricts vertical transport of wastewater into the mat, resulting in flow-through of wastewater under the mat. The papyrus mat is loose, open and thin (0.5 m) and allows easy vertical penetration of wastewater into the mat. The unrestricted interaction between the wastewater in the water column and that in the mat of papyrus in addition to plant debris and detritus continuously sedimenting out of the mat to the wetland bottom are responsible for the retention of coliforms in the papyrus dominated zones. Attachment, sedimentation and natural die-off were found to be important mechanisms responsible for the retention of coliforms in the Nakivubo wetland.

Confluences and Land Cover As Agents of Change: Temporal Habitat Variability Modifies the Movement and Assemblage Change of Headwater Fishes

2021 ◽  
Author(s):  
Joshua P. Hubbell ◽  
Jacob F. Schaefer
Keyword(s):  
Land Cover ◽  
Water Column ◽  
Anthropogenic Disturbance ◽  
Fish Assemblages ◽  
Gulf Coastal Plain ◽  
Habitat Variability ◽  
Habitat Stability ◽  
Constant Rate ◽  
Agents Of Change ◽  
Stream Fish Assemblages

Abstract Interspersed inputs of wood and sediment brings about morphological change at confluences and the extent to which these processes are modified by anthropogenic disturbance has ramifications for stream fish assemblages. In this study, we use three functional groups of headwater fishes to assess the influences of confluence size and land cover on habitat stability, distance moved, movement rate, and assemblage change in a Gulf Coastal Plain drainage in the southeastern United States using a 2X2 design. Our results suggest that differences in habitat stability were described by a hydrogeomorphic gradient, and urban reaches characterized by a confluence size > 0.6 displayed the greatest habitat instability. Water-column specialists in urban reaches were more likely to move when habitat change was limited, whereas movement by this functional group in forested reaches was more likely in response to greater habitat instability. Therefore, the distance moved by water-column specialists was related to land cover. Assemblage change also occurred at a more constant rate in urban reaches in response to habitat instability. There was little evidence that confluence size influenced movement or assemblage stability in these headwater assemblages. Our understanding of the extent to which land cover alters the geomorphic and ecological gradients associated with headwater confluences will be critical to ensure the conservation of sensitive species whose fitness is dependent on the integrity of these habitats.

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