Two solution methods for dynamic game in reservoir operation

During the last decade, a number of models have been developed to consider the conflict in dynamic reservoir operation. Most of these models are discrete dynamic models which are developed based on game theory. In this study, a continuous model of dynamic game and its corresponding solutions are developed for reservoir operation. Two solution methods are used to solve the model of continuous dynamic game, namely the Ricatti equations and collocation methods. The Ricatti equations method is a closed form solution, requiring less computational efforts compared with discrete models. The collocation solution method applies Newton's method or a quasi-Newton method to find the problem solution. These approaches are able to generate operating policies for dynamic reservoir operation. The Zayandeh-Rud river basin in central Iran is used as a case study and the results are compared with alternative water allocation models. The results show that the proposed solution methods are quite capable of providing appropriate reservoir operating policies, while requiring rather short computational times due to continuous formulation of state and decision variables. Reliability indices are used to compare the overall performance of the proposed models. Based on the results from this study, the collocation method leads to improved values of the reliability indices for total reservoir system and utility satisfaction of water users, compared to the Ricatti equations method. This is attributed to the flexible structure of the collocation model. When compared to alternative water allocation models, lower values of reliability indices are achieved by the collocation method.     

Capabilities of satellite precipitation datasets to estimate heavy precipitation rates at different temporal accumulations

The importance of satellite datasets as alternative sources of precipitation information has been argued in numerous studies. Future developments in satellite precipitation algorithms as well as utilization of satellite data in operational applications rely on a more in‐depth understanding of satellite errors and biases across different spatial and temporal scales. This paper investigates the capability of satellite precipitation data sets with respect to detecting heavy precipitation rates over different temporal accumulations. In this study, the performance of Tropical Rainfall Measuring Mission real time (TRMM‐RT), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks and CPC MORPHing (CMORPH) is compared against radar‐based gauge‐adjusted Stage IV data. The results show that none of the high temporal resolution (3‐h) datasets are ideal for detecting heavy precipitation rates. In fact, the detection skill of all products drops as the precipitation thresholds (i.e. 75 and 90 percentiles) increase. At higher temporal accumulations (6, 12 and 24 h), the detection skill improves for all precipitation products, with CMORPH showing a better detection skill compared to all other products. On the other hand, all precipitation products exhibit high false alarm ratios above the heavy precipitation thresholds, although TRMM‐RT lead to a relatively smaller level of false alarms. These results indicate that further efforts are necessary to improve the precipitation algorithms so that they can capture heavy precipitation rates more reliably. Copyright © 2013 John Wiley & Sons, Ltd.     

Dust acoustic shock waves in suprathermal dusty plasma in the presence of ion streaming with dust charge fluctuations

Dust acoustic (DA) shock waves are investigated in a dusty plasma having a high-energy-tail electron distribution. The effects of ion streaming, charge variation and electron deviation from the Maxwellian distribution on the DA shock wave are then considered. It is shown that as the suprathermal character of the plasma is increased, the potential amplitude enhances. It is also found that the ion temperature may be destructive for the formation of DA shock waves. Their strength decreases with increasing ion streaming speed. Our results may be useful in understanding the basic nonlinear features of the DA wave propagation that may occur in space dusty plasmas, especially those including a relative motion between species (comet tails, solar wind streams, etc.).     

Dust acoustic localized structures in an electron depleted dusty plasma with two-suprathermal ion-temperature

We consider Brans-Dicke theory with a self-interacting potential in Einstein conformal frame. We introduce a class of solutions in which an accelerating expansion is possible in a spatially flat universe for positive and large values of the Brans-Dicke parameter consistent with local gravity experiments. In this Einstein frame formulation, the theory appears as an interacting quintessence model in which the interaction term is given by the conformal transformation. In such an interacting model, we shall show that the solutions lead simultaneously to a constant ratio of energy densities of matter and the scalar field.     

Spherical electron acoustic solitary waves in plasma with suprathermal electrons

A reductive perturbation technique is employed to solve the fluid-Poisson equations in spherical geometry describing a weakly nonlinear electron–acoustic (EA) waves in unmagnetized plasma consisting of stationary ions, cold electrons and kappa distributed hot electrons. It is shown that a variable coefficient Kadomtsev–Petviashvili (KP) equation governs the evolution of scalar potential describing propagation of EA waves. The influence of suprathermality and geometry effects on propagation of EA solitary waves is investigated. We found that when electrons evolve toward their thermodynamic equilibrium, EA solitons are generated with large amplitudes. Also it is shown that EA solitary structures can be significantly modified by transverse perturbations.     

Validation of Hyperbolic Model by the Results of Triaxial and Direct Shear Tests of Municipal Solid Waste

The increasing demand of engineering landfills requires that designers propose a framework for landfill design, construction, repair and maintenance. As municipal solid waste (MSW) is a major part of a landfill, the analysis should consider MSW mechanical behavior using a constitutive model. To investigate this, 18 direct shear (DS) and triaxial (TX) tests were conducted on MSW samples with different fiber contents. Different shearing mechanisms lead to understand effects of fibers on stress–strain response. Based on obtained results the hyperbolic model Duncan and Chang (J Soil Mech Found Div 96(5):1629–1653, 1970) has been employed to simulate the TX results indicating the ability of the model to predict stress–strain behavior of MSW. This model could also be employed to the DS test results with some assumptions. The model can capture DS stress–strain response well whereas for TX tests the predictions were just enough. The experimental results and two sets of proposed MSW parameters of hyperbolic model have been compared and discussed.     

An improved methodology for estimation of two-phase relative permeability functions for heavy oil displacement involving compositional effects and instability

In heavy oil recovery by immiscible gas injection, adverse mobility ratio and gravity segregation along with influential mass transfer are the most crucial factors controlling displacement efficiencies. Obtaining relative permeability functions using conventional techniques that are based on a stable displacement front could be highly misleading. In this work, an improved methodology was proposed for estimating relative permeability curves under simultaneous effects of frontal instability and mass transfer using history-matching techniques. The compositional analysis of produced oil from a coreflood experiment was employed, which represents dynamic interactions more realistically. For the history matching, an optimum, high-resolution, two-dimensional core model was used, as opposed to the industry standard use of a one-dimensional model. The results of the simulation were then verified by a semi-empirical approach using the Koval model, which was then used to predict a similar experiment but in a vertical orientation. A good match was obtained between the forward simulation and the experiment. To highlight the effect of mass transfer on the shape of relative permeabilities, the simulation results from two immiscible gas injection corefloods were compared: CO₂ injection with mass transfer and N₂ injection without mass transfer. The results showed that the two estimated functions were quite similar, indicating that instability levels would determine the displacement pattern rather than local mass transfer. This integrated approach, therefore, highlights the importance of employing the right fluid model and an appropriate 2D-grid model in estimating relative permeabilities in displacement with instability and mass transfer against the current industry practice.     

Determination of Two-phase Relative Permeability from a Displacement with Safman-Rayleigh Instability Using a Coarse-Scale Model History Matching Approach

Computational Geosciences - In heavy oil displacement by fluid injection, severe instability can occur due to the adverse mobility ratio, gravity segregation or compositional effects. However, when...     

Influence of random heterogeneity of the friction angle on bearing capacity factor Nγ

ABSTRACT

Probabilistic methods in geotechnical engineering have received a lot of attention during the last decade and different methodologies are used to capture the inherent variability of soil in different geotechnical engineering problems. In this paper, numerical simulations are conducted to obtain the bearing capacity factor, N_γ, for a purely frictional heterogenous soil where the friction angle is modelled as randomly distributed throughout the domain and the effect of its spatial variability on N_γ is investigated. A finite element method, based on the upper bound limit analysis was combined with random field theory and linear programming to develop a probabilistic analysis. Monte Carlo simulations were performed and the effect of the variability of the friction angle defined by statistical parameters on the bearing capacity factor was investigated. Results show that the mean bearing capacity factor N_γ of a footing on a spatially variable cohesionless soil is generally higher than the deterministic N_γ obtained from a constant mean value. Increasing the heterogeneity of the friction angle by an increase in the coefficient of variation generally increases this deviation. This can be explained by the nonlinearity of the relationship between N_γ and the friction angle.     

Propagation properties of ion acoustic waves in a magnetized superthermal bi-ion plasma

A theoretical investigation is carried out to analyse the propagation of ion acoustic (IA) waves in a magnetized bi-ion plasma having two populations of fluid ions and kappa-distributed electrons. The propagation properties of all possible modes (in the linear regime) are investigated. The nonlinear evolution of the IA solitary waves is governed by a Korteweg-de Vries (KdV)-like equation. The influence of obliqueness, magnitude of the magnetic field, ion polarity and electron superthermality on the IA waves is then examined. Our findings should aid in understanding the nonlinear electrostatic excitations that may propagate in spatial magnetized plasmas.