Reliability Improved Stochastic Dynamic Programming for Reservoir Operation Optimization

Stochastic Dynamic Programming (SDP) is widely used in reservoir operation problems. Besides its advantages, a few drawbacks have leaded many studies to improve its structure. Handling the infeasible conditions and curse of dimensionality are two major challenges in this method. The main goal of this paper is proposing a new method to avoid infeasible conditions and enhance the solution efficiency with new discretization procedure. For this purpose, an optimization module is incorporated into regular SDP structure, so that, near optimal values of state variables are determined based on the available constraints. The new method (RISDP) employs reliability concept to maximize the reservoir releases to satisfy the downstream demands. Applying the proposed technique improves the reservoir operating policies compared to regular SDP policies with the same assumptions of discretization. Simulation of reservoir operation in a real case study indicates about 15% improvement in objective function value and elimination of infeasible conditions by using RISDP operating policies.     

Increasing Water Security: An Algorithm to Improve Water Distribution Performance

Water Distribution Systems (WDSs) are indispensable infrastructures for urban societies. Due to vitality of continuous supply of drinking water in urban areas, it is necessary to have a performance evaluation and monitoring system to provide the expected level of security in water distribution systems. A main weakness point of these systems is the physical break of pipes which results in high level of water loss, pollution risk and public unsatisfactory. In this study, a framework is developed to increase physical water supply security in urban areas. For this purpose, a physical vulnerability index (PVI) is developed for evaluation of physical statues of water mains. In quantifying PVI, pipe characteristics and bedding soil specifications are considered. The importance of these factors on PVI is determined using Analytical Hierarchy Process (AHP). In system performance evaluation, the pipe role in system performance is incorporated regarding pipe location in WDS, distance of pipe from reservoir and average pressure of pipe. Then, System Physical Performance Index (SPVI) is evaluated. An optimization algorithm is employed to determine ways to improve the system performance through enhancing the physical condition of the pipe in the system at a minimum cost. The genetic algorithm is employed for solving the optimization model. A global sensitivity analysis method named FAST, is used for sensitivity analysis to incorporate the correlation between different parameters in analysis. The proposed framework is applied to a case study located in Tehran metropolitan area. The results of this study show the significant value of the proposed algorithm in supporting decision makers to better choose vulnerable pipes for rehabilitation practices in order to decrease system vulnerability against physical failures.     

Optimal Design of Concrete Canal Section for Minimizing Costs of Water Loss,Lining and Earthworks

Canal section design with minimum cost, which can be considered as an objective function, involves minimization of total costs per unit length of the canal, including direct costs of per cubic meter earthworks and per meter canal lining and indirect costs of water losses through canal seepage and evaporation. Since the costs (both direct and indirect) are associated with the canal geometry and dimensions, it is possible to lower them by optimization of the mentioned objective function. For this purpose, some constraints were subjected and considered to solve the problem. Flow discharge, as the main constraint, was considered in addition to the minimum permissible velocity and Froude’s number, as subsidiary constraints. MATLAB programming software was used to demonstrate and run the optimization algorithm. The results finally were illustrated in forms of dimensionless graphs, which simplify the optimum design of canal dimensions with minimum cost per meter length. Comparing the results with other similar studies, however show the importance and role of earthworks and lining costs, as well as including the subsidiary constraints in the optimization process.     

Temporal and Spatial Assessment of Supply and Demand of the Water-yield Ecosystem Service for Water Scarcity Management in Arid to Semi-arid Ecosystems

Water scarcity is one of the problems affecting people’s livelihoods in arid and semi-arid areas, requiring a sustainable balance between water demands and water resources. This study was carried out to assess temporal and spatial distribution of water supply and demand in order to help managers to overcome water scarcity in Jiroft basin, southeastern Iran. Spatial supply and demand of water were mapped and standardized rainfall index (SPI) was used to assess drought for a 20 years period (1994–2014). Supply and demand of water were matched in 23% of the basin area, mostly concentrated in the cold zones. Water supply was reduced up to 80% during dry years, declining water supply-demand matching to 5% of the basin area. Shrub-grass rangelands and deciduous woodlands were the most valuable land covers for conservation with $ 1,100 and $ 936 per hectare water prices respectively. Water value dropped more than 72% in mismanaged ecosystems (p?<?0.01). Our finding showed that water supply-demand ratio can be used as a proxy of ecosystem health and water-yield, which can provide a good information for water resources managers to reduce the threats of water scarcity in arid and semi-arid regions.

     

An Approximate Model of Multistage Automatic Transfer Lines with Possible Scrapping Of Workpieces

We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.     

Identification of time-varying linear and bilinear systems via Fourier series

A method for identification of time-varying linear systems and bilinear systems is proposed. The method is based upon expanding various time functions in the system as their truncated Fourier series, using the operational matrices for integration and product and hence reducing the problem into a set of algebraic equations. The method is computationally attractive, and applications are demonstrated through illustrative examples.     

Design and experimental testing of a tactile sensor for self-compensation of contact error in soft tissue stiffness measurement

The measurement of viscoelastic properties of soft tissues has become a research interest with applications in the stiffness estimation of soft tissues, sorting and quality control of postharvest fruit, and fruit ripeness estimation. This paper presents a tactile sensor configuration to estimate the stiffness properties of soft tissues, using fruit as case study. Previous stiffness-measuring tactile sensor models suffer from unstable and infinite sensor outputs due to irregularities and inclination angles of soft tissue surfaces. The proposed configuration introduces two low stiffness springs at the extreme ends of the sensor with one high stiffness spring in-between. This study also presents a closed form mathematical model that considers the maximum inclination angle of the tissue’s (fruit) surface, and a finite element analysis to verify the mathematical model, which yielded stable sensor outputs. A prototype of the proposed configuration was fabricated and tested on kiwifruit samples. The experimental tests revealed that the sensor’s output remained stable, finite, and independent on both the inclination angle of the fruit surface and applied displacement of the sensor. The sensor distinguished between kiwifruit at various stiffness and ripeness levels with an output error ranging between 0.18 % and 3.50 %, and a maximum accuracy of 99.81 %, which is reasonable and competitive compared to previous design concepts.

     

A comparative study of CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> adsorption using activated carbon prepared from pine cone by phosphoric acid activation

Adsorption of pure carbon dioxide and methane was examined on activated carbon prepared from pine cone by chemical activation with H₃PO₄ to determine the potential for the separation of CO₂ from CH₄. The prepared adsorbent was characterized by N₂ adsorption-desorption, elemental analysis, FTIR, SEM and TEM. The equilibrium adsorption of CO₂ and CH₄ on AC was determined at 298, 308 and 318 K and pressure range of 1–16 bar. The experimental data of both gases were analyzed using Langmuir and Freundlich models. For CO₂, the Langmuir isotherm presented a perfect fit, whereas the isotherm of CH₄ was well described by Freundlich model. The selectivity of CO₂ over CH₄ by AC (CO₂: CH₄=50: 50, 298K, 5 bar), predicted by ideal adsorbed solution theory (IAST) model, was achieved at 1.68. These data demonstrated that pine cone-based AC prepared in this study can be successfully used in separation of CO₂ from CH₄.     

Aluminum Pitting Corrosion in Halide Media: A Quantum Model and Empirical Evidence

The phenomenon of localized damage of aluminum oxide surface in the presence of halide anions was scrutinized at an atomistic level, through the cluster approach and density functional theory. The phenomenon was also investigated empirically through Tafel polarization plots and scanning electron microscopy. A distinct behavior witnessed in the fluoride medium was justified through the hard-soft acid-base principle. The atomistic investigations revealed the greatest potency for chloride entrance into the metal oxide lattice and rationalized to the severity of damage. The interaction of halide anions with the oxide surface causing some displacements on the position of Al atoms provides a mechanistic insight of the phenomenon.     

Experimental characterization of the small strain shear modulus of soft clay stabilized with cement and nano-SiO2 using bender element tests

Bulletin of Engineering Geology and the Environment - The accurate and efficient modification of the static and dynamic properties of problematic soils is a primary concern in geotechnical...