Modelling of Seepage and Slope Stability Analysis of Ribb Embankment Dam, Ethiopia

Safety against seepage is one in all the primary important steps for checking the possibility of failure of embankment dam and the stability of an embankment dam depends on its geometry, its components, materials, properties of every component, and therefore the forces to which it's subjected. This paper presented seepage and slope stability analysis against Ribb dam safety using finite element-based PLAXIS software, and so the result was compared with different standards. PLAXIS is alternative software that will be used for evaluating the protection of embankment dams due to seepage conditions. The simulated results showed the common rate of flow of seepage through the body of the dam at normal pool level was equal to 5.05*10−6 m3/s/m and through the foundation of the dam was 3.00*10−6 m3/s/m. According to Look (2014) recommendation, the seepage results within the tolerable limit. The results of the factor of safety were considered too different loading conditions. The factor of safety results during the end of construction for both static and dynamic stability analysis were 1.3063 and 1.2226, respectively. For steady-state conditions, the factor of safety obtained for static stability analysis was 1.2604, and also the dynamic analysis 1.1803. The rapid drawdown condition is analyzed with a normal pool level of 1940 m lowered to 1900 m or rapidly reduced 57% of the reservoir water. The analysis results showed that the factor of safety for the static, and dynamic analyses were 1.2021 and 1.0662, respectively. Using different recommended design standards: United States Army Corps of Engineers (USACE), British dam society (BDS), and Canadian dam association (CDA) the slope stability analysis of the Ribb embankment dam at all critical loading conditions is safe.

Sediment and morphological changes along Yangtze River’s 500 km between Datong and Xuliujing before and after Three Gorges Dam commissioning

The impoundment of the Three Gorges Dam on the Yangtze River begins in 2003 and a full pool level is first attained in 2010. This process leads to reciprocal adjustments in flow discharge, sediment transport and morphology downstream of the dam. Based on 26-year recorded hydrologic data 1990–2015 and surveyed bathymetries 1998, 2010 and 2015, this study elucidates, before and after the commissioning of the dam, the alterations along the 500-km reach of the river. Two-dimensional numerical simulations are performed to predict future morphological changes by 2025. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. On a multi-year basis, the maximum discharge varies by a factor of 1.3 and the corresponding suspended load concentration and transport rate differ by a factor of 3.0 and 3.8, respectively. Combinations of surveyed and simulated bathymetries reveal its morphological responses to the changes. A general pattern of erosion is observed along the reach. In its upper 120 km, the process slows down towards 2025. In the middle 200 km, the erosion shifts, following the gradual impounding, to slight deposition, which then shifts back to erosion around September 2018. In the final 180 km, erosion continues without any sign of de-escalation, which is presumedly ascribed to tidal actions. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for a while. The combination of the field and numerical investigations provides, with the elapse of time, insight into the morpho-dynamics in the 500 km river reach.

Ice Load Characteristics on Floating Photovoltaic Platform

Nowadays, based upon human needs and preferring perpetual types of energy, photovoltaic system (PV) is a suitable alternative and more frequently used in northern countries, which are recently more attracted by solar power. The new floating type of the structure is installed in the water bodies instead of land. One of the main elements in floating photovoltaic structures is the forces imposed on the panels. In the northern regions, the dominant load is considered to be ice interaction with the structure. This study aims at identifying the loads imposed on a floating PV structure located in the Łapino Reservoir on the Radunia River, which are produced by the wind action on the ice cover. The wind velocity varying between 10 and 26 m/s is implemented, and also the reduction of the pool level was studied. Wind direction plays an important role in the inclination and expansion of ice accumulation. Moreover, the magnitude of wind velocity is a determinative factor in the maximum thickness emerged in various spot of the area. Changes in pool level reduction is not able to cause noticeable changes in ice cover expansion and maximum ice thickness. Additionally, the shoving mechanism is able to originate abrupt changes in ice thickness by means of rising wind velocity.

Lipid metabolic changes in rat brain during permanent cerebral ischemia

With each year, millions of people remain targeted by brain stroke, it still is by all means a global concern of the mankind. Despite all efforts to understand this disease better, there is still a lack of information on pathophysiology of ischemic stroke. Scrutinized data on biochemical changes at early stages of ischemia may help understand the mechanisms of the disorder and possibly reveal ways to finding the cure. The key role in the pathogenesis of stroke belongs to lipids as well as to the molecules associated with their biosynthesis and functionality. On the one hand, stroke evokes a deep oxidative stress leading to damage to biomolecules including lipids while on the other hand, due to the lack of reducing equivalents, the cellular biosynthesis processes are interrupted. The focus of this work was to study the changes taking place in the tissues of rat brain as a result of ischemia including estimation of levels of total cholesterol, FFA, MDA, GSH, and NADP(H). It was shown that in 24 hours from the onset of ischemia, there was a significant decrease in levels of FFA, total cholesterol and GSH, and an increase in the level of MDA, a marker of lipid peroxidation. NADP(H) pool level decreases twice in 6 hours from MCAO.

Agency MBS Prepayment Model Using Neural Networks

The authors apply deep neural networks, a type of machine learning method, to model agency mortgage-backed security (MBS) 30-year, fixed-rate pool prepayment behaviors. The neural networks model (NNM) is able to produce highly accurate model fits to the historical prepayment patterns as well as accurate sensitivities to economic and pool-level risk factors. These results are comparable with model results and intuitions obtained from a traditional agency pool-level prepayment model that is in production and was built via many iterations of trial and error over many months and years. This example shows NNM can process large datasets efficiently, capture very complex prepayment patterns, and model large group of risk factors that are highly nonlinear and interactive. The authors also examine various potential shortcomings of this approach, including nontransparency/“black-box” issues, model overfitting, and regime shift issues.

Effects of experimental pool level reduction on Phylloicus pulchrus (Trichoptera: Calamoceratidae) feeding and conspecific behavior from a tropical rainforest stream

Aumentos en la ocurrencia y persistencia de sequías alrededor del mundo estimulan el entendimiento de sus efectos en las poblaciones naturales y funcionamiento del ecosistema. El principal resultado de las sequías en los ríos es la fragmentación del ecosistema riverino en pozas aisladas a medida que el flujo y la profundidad del agua disminuyen. Hay estudios limitados sobre la respuesta de los tricópteros a reducciones en niveles de agua y su efecto en el funcionamiento del ecosistema. El objetivo de este estudio fue evaluar como reducciones en niveles del agua, similar a las asociadas con sequías, influencian la alimentación y comportamiento conspecífico de Phylloicus pulchrus. Reducciones de pozas en laboratorio simulando condiciones naturales fueron empleadas por dos semanas. Cuatro acuarios plásticos rectangulares fueron llenados a una tercera parte con agua aereada de la quebrada. Dentro de cada acuario se colocaron diez cámaras plásticas circulares (con aperturas de malla) con hojas senescentes de Guarea guidonea. Se simularon dos niveles de pozas (normal y bajo) con dos tratamientos (experimental y control). Las cámaras experimentales (n=20) contenían larvas del cuarto estadío (n=80, 40=normal, 40=bajo) mientras que las del control (n=20) no. Se evaluó el efecto de la reducción de pozas en la pérdida de masa de las hojas, interacciones agresivas (>25 % de su envoltura removida) y mortalidad larval. La reducción en el nivel de las pozas aumentó la pérdida de masa de las hojas (ANOVA: F=5.17, p=0.03), interacciones agresivas (Chi cuadrado: x2=6.24, n=80, p= 0.01), y mortalidad larval (Chi square: x2=4.51, n=80, p= 0.03). Este estudio muestra la respuesta temprana de un tricóptero tropical a una señal abiótica de un cambio ambiental drástico. Esta investigación contribuye al escaso conocimiento sobre el comportamiento de procesamiento de hojarasca en larvas de tricópteros durante etapas tempranas de reducciones de flujo, como las causadas por sequías.

On Subcool Control in Steam-Assisted-Gravity-Drainage Producers— Part I: Stability Envelopes

Summary Steam-assisted-gravity-drainage (SAGD) industry experience indicates that the majority of producer workovers occur because of liners or electrical submersible pumps (ESPs), and both failures appear to result from inefficient “steam-trap control.” Thermodynamic steam-trap control, also termed “subcool control,” is a typical operation strategy for most SAGD wells. Simply, subcool (or reservoir subcool vs. pump subcool) is the temperature difference between the steam chamber (or injected steam) and the produced fluid. The main objective is to keep subcool higher than a set value that varies between 0 to 40° and even higher values. This study presents a method to calculate the liquid-pool level from the temperature profile in observation wells, and liquid-pool shrinkage as a function of time. Unfortunately, it is not practical to monitor the liquid level by having observation wells for every SAGD well pair. For this reason, the algebraic equation for liquid-pool depletion on the basis of wellbore-drawdown, subcool, and emulsion productivity is generated. By use of this equation, the envelopes are suggested to differentiate three different regimes: “stable production,” “liquid-pool depletion,” and “steam-breakthrough limit.” Gas lift operations such as the MacKay River thermal project suggested that envelopes for constant wellbore drawdown are not practical. Therefore, the steam-breakthrough limit is defined for constant rate, which is more consistent in gas lift operations. In this study, the steam-breakthrough limit is validated for operation data from the MacKay River. This study provides a new insight into how factors such as production rate and wellbore drawdown can compromise subcool control and cause steam breakthrough, and how liquid-pool depletion may result in uncontrolled steam coning at long time. As a part of this study, a minimum-subcool concept (or target reservoir subcool) is presented as a function of skin and pressure drawdown. It is shown that the minimum subcool is highly dependent on the maturity of steam-chamber and underburden heat loss especially for zero-skin producers. The results of this work emphasize that the target subcool on the producer should increase slightly with chamber maturity, considering that the skin is nonzero for most SAGD producers.