On the optimal design of water distribution networks: a practical MINLP approach

We propose a practical solution method for real-world instances of a water-network optimization problem with fixed topology using a nonconvex continuous NLP (NonLinear Programming) relaxation and a MINLP (Mixed Integer NonLinear Programming) search. Our approach employs a relatively simple and accurate model that pays some attention to the requirements of the solvers that we employ. Our view is that in doing so, with the goal of calculating only good feasible solutions, complicated algorithmics can be confined to the MINLP solver. We report successful computational experience using available open-source MINLP software on problems from the literature and on difficult real-world instances. An important contribution of this paper is that the solutions obtained, besides being low cost, are immediately usable in practice because they are characterized by an allocation of diameters to pipes that leads to a correct hydraulic operation of the network. This is not the case for most of the other methods presented in the literature.     

Development of a MINLP model for the optimization of a large industrial water system

This paper presents the design of a large water system within the production and packaging areas of a brewery. In order to accomplish the task, mathematical models were developed based on a Mixed Integer Nonlinear Programming (MINLP) formulation from the open literature. These models enable the investigation of several integration options: a) direct water re-use between batch and semi-continuous consumers operating within the same time interval and b) regeneration re-use options, by designing and scheduling an on-site wastewater treatment system. A multilevel strategy was applied for this large-scale industrial problem, which firstly decomposes design problem into several smaller integration problems concerning water consumers within each section of the brewery. At the following level, water re-use and regeneration re-use opportunities between the brewhouse and the packaging areas were explored for each working day. Finally, the design of an integrated water system was performed over the entire working week by fixing identified intra-daily matches between sections. An optimum water integration scheme is proposed based on the results obtained.     

Optimum synthesis of a slider-crank mechanism using geometric programming

Geometric programming is a powerful technique and its application to mechanism synthesis has not been fully explored. In this paper, slider-crank mechanism is chosen since the objective function consists of a large number of terms while there are only two design variables. Thus the degree of difficulty is more and does not lend itself to easy application of the geometric programming. Here, modification of the objective function is suggested so that the degree of difficulty reduces to zero even when the working space constraint is imposed. This results in a near optimum solution. Application of signomial geometric programming is illustrated through a numerical example.     

The analysis of an inventory control model using posynomial geometric programming

We consider a generalization of the well-known ‘sawtooth’ inventory control model which is used to determine optimal policies for stocking a single item under certain conditions. The case where several items are to be stocked simultaneously and subject to a number of constraints give rise to the generalization that is of interest. We show that the problem of analysing the model may he viewed as a problem in posynomial Geometric Programming. We then point out some of the advantages to be realized from viewing it this way and from using Geometric Programming techniques to solve it. These include, the ability to obtain feasible solutions with known upper bounds on the difference between their associated costs and the minimum cost, a capability for performing an analysis of the sensitivity of the values of the optimized parameters to variations in input parameters, availability of a solution method that is computationally more attractive than methods previously known and, arising out of this last benefit, an ability to deal with much more complicated problems to which the model is applied than previously seemed practical. A simple example problem is solved in detail to illustrate many of these benefits and results are presented for a much more complex case. In addition some possible extensions of the model, which can also be dealt with in this framework, are pointed out.     

Simulation of static recrystallization in non-isothermal annealing using a coupled cellular automata and finite element model

A coupled cellular automata and finite element model has been proposed to evaluate static recrystallization kinetics during non-isothermal annealing of cold deformed low carbon steels. The effects of various factors including heating rate, annealing temperature, and initial microstructures have been considered in the model to accurately predict the static recrystallization kinetics and the final microstructures. In order to examine the employed algorithm, the predicted results have been compared with the experimental observations and a good agreement was found between the two sets of results.     

Photometry and colorimetry of reference LEDs by using a compact goniophotometer

In the development, production control, quality assurance and during the selection of appropriate LEDs for very different applications, it is essential to know their photometric and colorimetric quantities very precisely. The calibration of the measuring devices required for this purpose is performed via LED transfer standards. These LED standards transfer photometric, spectroradiometric and colorimetric units and characteristics, from the National Metrology Institute (NMI) to the user. Finally, LED standards serve as references for the user. Usually a set of LED reference standards consists of at least four different LED colours (blue, green, red and white), sometimes even more. Further more it is very often necessary to have more than only one set of reference standards as a backup. This generally causes a large number of calibrations. To handle this work load, a special reference standard and a compact goniophotometer prove to be a considerable advantage. PTB developed a special LED transfer standard which operates under controlled conditions: a controlled LED chip temperature and a controlled chip current help to keep the photometric and colorimetric properties constant. On the other hand, a compact goniophotometer was designed to measure luminous flux, luminous intensity and colorimetric quantities of LED transfer standards in a relatively short time with low measurement uncertainties.     

Mathematical model of contact heat exchange of a gas and water during adiabatic evaporation

It is shown that the gas temperature distribution in a contact heat exchanger is characterized by the presence of two zones during adiabatic evaporation — an initial zone with a reduced temperature and a final zone with an elevated temperature — as compared with the heat exchange through a separating surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 6, pp. 1098–1100, December, 1979.     

Optimal cost design of water distribution networks using a decomposition approach

Water distribution network decomposition, which is an engineering approach, is adopted to increase the efficiency of obtaining the optimal cost design of a water distribution network using an optimization algorithm. This study applied the source tracing tool in EPANET, which is a hydraulic and water quality analysis model, to the decomposition of a network to improve the efficiency of the optimal design process. The proposed approach was tested by carrying out the optimal cost design of two water distribution networks, and the results were compared with other optimal cost designs derived from previously proposed optimization algorithms. The proposed decomposition approach using the source tracing technique enables the efficient decomposition of an actual large-scale network, and the results can be combined with the optimal cost design process using an optimization algorithm. This proves that the final design in this study is better than those obtained with other previously proposed optimization algorithms.     

Complete electrolysis using a microflow cell with an oil/water interface

A novel microflow cell with a nitrobenzene (NB)/water (W) interface was developed. A poly(tetrafluoroethylene) membrane filter was employed to prepare the NB/W interface which was formed over a thin channel (0.1 mm thick, 48 cm long) on a silver plate. The silver plate was electrolyzed in advance and served as an Ag/AgCl electrode for controlling the Galvani potential difference across the NB/W interface as well as detecting the current flowing through the interface. Using the microflow cell, complete electrolysis was accomplished for the interfacial transfer of a representative ion (i.e., tetramethylammonium ion). Thus, the present microflow cell was shown to be promising for coulometric (i.e., absolute quantitative) analysis of ions. Also, the microflow cell was shown to be useful for determination of the number of electrons for complicated charge-transfer processes at the oil/water interface.     

Facile solution synthesis and characterization of porous cubic-shaped superstructure of ZnAl2O4

Porous and cubic-shaped superstructure of ZnAl₂O₄ was successfully synthesized by a facile wet chemical solution-phase method. The structural properties of the samples were systematically investigated by X-ray powder diffraction (XRD), Brunauer-Emmet-Teller (BET), scanning electron microscopy (SEM), energy-dispersive spectra (EDS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The characterization results revealed that the structure of the cubic-shaped ZnAl₂O₄ was an inverse spinel structure. The sample prepared by a solution-phase chemical method has a higher surface area and monomodal pore size distributions. Furthermore, the valence states and the surface chemical compositions of ZnAl₂O₄ were further identified by X-ray photoelectron spectroscopy (XPS). This study provides a simple method to prepare cubic-shaped ZnAl₂O₄ in large scale, which broadens their practical applications.     

Application of a real-world university-course timetabling model solved by integer programming

In this case study, we describe an integer programming (IP) approach, which has been implemented at the School of Economics and Management at Hannover University, Germany, to create the complete timetable of all courses for a term. Approximately 150 different weekly lectures, tutorials and seminars ranging from 5 to 650 students are taught by about 100 teachers. The decision problem is to assign these teaching groups to time slots and rooms so that several soft and hard constraints are met. It is modeled as an assignment problem with numerous types of constraints and about 100,000 binary or integer variables. An open source mixed-integer solver can be used to solve the problem to optimality within minutes whereas the commercial CPLEX solver takes only seconds. We also describe the implementation process and report results from an anonymous satisfaction survey among the faculty with respect to the new planning approach.     

Mathematical model of an air-to-air heat pump equipped with a capillary tube

This paper described in general a computer model for simulation of steady-state performance of a split, residential, air-to-air heat pump. Organization of the model is discussed and approach to modelling of main heat pump components is explained. The modelling effort emphasis was on the local phenomena to be described by fundamental thermodynamic, heat transfer and fluid mechanic relationships. The model has been verified in a wide range of operating conditions from high temperature cooling to low temperature heating.     

Analysis of perchlorate in water by reversed-phase LC/ESI-MS/MS using an internal standard technique

A new method was developed for the analysis of perchlorate in water by using reversed-phase liquid chromatograhy/electrospray ionization-mass spectrometry/mass spectrometry (LC/ESI-MS/MS) in the negative ESI mode. Selective and sensitive perchlorate detection was obtained by monitoring the 35ClO4- --> 35ClO3- and 37ClO4- --> 37ClO3- mass transitions. The 35ClO4- --> 35ClO3- transition was quantitated against the internal standard oxygen-labeled sodium perchlorate (NaCl18O4). Sample pretreatment for the removal of major common anions and dissolved metal ions along with internal standard quantitation sufficiently compensated for ion suppression caused by the matrix. The 37ClO4- --> 37ClO3- transition was examined to provide additional specificity. The method sensitivity, accuracy, and precision were investigated by analyzing fortified blank samples, field samples, and performance evaluation samples. The results (1.01-13.5 microg/L) for the proficiency evaluation samples differed from the certified values (1.04-14.1 microg/L) by 3-18%. The developed reversed-phase LC/ESI-MS/MS method was rapid, accurate, and reproducible. The calculated method detection limits were 0.007 microg/L for deionized reagent water and 0.009 microg/L for synthesized reagent water, respectively. The minimum reporting limit was conservatively set to 0.05 microg/L.     

溶剂热法制备Fe_3O_4/氧化石墨烯复合材料及其性能研究

以氧化石墨和二茂铁为原料,采用溶剂热法原位一步合成了Fe3O4/还原氧化石墨烯(Fe3O4/RGO)复合物,通过X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、扫描电镜(SEM)、透射电镜(TEM)、振动样品磁强计(VSM)、循环伏安测试等手段对复合材料的形貌、结构、磁性能和电化学性能进行了表征。结果表明,该方法具有简单、可控的优点,通过调变前驱物中氧化石墨和二茂铁的比例,可以控制复合物中Fe3O4纳米粒子的负载量。所制备Fe3O4/RGO复合材料由平均粒径约20nm的Fe3O4纳米颗粒高度分散在还原氧化石墨烯片层上组成,具有较好的超顺磁性,电化学稳定性和良好的倍率性能。     

Mathematical model and experimental results for cryogenic densification and sub-cooling using a submerged cooling source

Among the many factors that determine overall rocket performance, propellant density is important because it affects the size of the rocket. Thus, in order to decrease the size of a rocket, it may be desirable to increase the density of propellants. This study analyzes the concept of increasing the propellant density by employing a cooling source submerged in the liquid propellant. A simple, mathematical model was developed to predict the rate of densification and the propellant temperature profile. The mathematical model is generic and applicable to multiple propellants. The densification rate was determined experimentally by submerging a cooling source in liquid oxygen at constant positive pressure, and measuring the time rate of change in temperature with respect to vertical position. The results from the mathematical model provided a reasonable fit compared to experimental results.     

Loss-efficiency model of single and variable-speed compressors using neural networks

Compressor is the critical component to the performance of a vapor-compression refrigeration system. The loss-efficiency model including the volumetric efficiency and the isentropic efficiency is widely used for representing the compressor performance. A neural network loss-efficiency model is developed to simulate the performance of positive displacement compressors like the reciprocating, screw and scroll compressors. With one more input, frequency, it can be easily extended to the variable speed compressors. The three-layer polynomial perceptron network is developed because the polynomial transfer function is found very effective in training and free of over-learning. The selection of input parameters of neural networks is also found critical to the network prediction accuracy. The proposed neural networks give less than 0.4% standard deviations and ±1.3% maximum deviations against the manufacturer data.     

Surfactant-assisted synthesis of reduced graphene oxide/polyaniline composites by gamma irradiation for supercapacitors

A series of graphene materials are prepared by intercalation of graphene oxide (GO) with different surfactants, cetyltrimethylammonium bromide (CTAB), n-octyltrimethylammonium bromide, tetramethylammonium bromide, and sodium dodecylbenzene sulfonate, subsequently by γ-ray induced reduction in N-methyl-2-pyrrolidone (NMP) at room temperature. GO can be reduced by the electrons generated from the radiolysis of NMP under γ-ray irradiation, and reduced GO is simultaneously functionalized by the radiolytic product of NMP. Cationic surfactant CTAB with longer alkyl chains can effectively promote the reduction process of GO by preventing the aggregation of graphene sheets, which has been testified by X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy analyses. Furthermore, when the as-prepared graphene/polyaniline composites are used for supercapacitor electrode materials, there is a highest specific capacitance of 484 F g^?1 at a current density of 0.1 A g^?1 for the graphene produced in the presence of cationic surfactant CTAB.     

Mathematical model of heat and mass transfer in a geothermal reservoir upon extraction of steam and water mixture

A mathematical model of heat and mass transfer in a geothermal reservoir saturated with steam and water mixture upon the extraction of heat carrier through a single well is considered. The exact solution of the time-independent and quasi-time-independent nonlinear problems is obtained. Typical water saturation, temperature, and pressure distributions around a well are shown. Conditions for the regimes of heat and mass transfer, the violation of which leads to the formation of a region saturated with either pure fluid of pure steam, are found. Parametric studies are performed.     

An optimization approach for the synthesis of recycle and reuse water integration networks

This paper presents a convex mathematical programming model for the global optimization of recycle/reuse water networks. The model is based on a general superstructure that includes the major configurations of interest such as segregation, mixing, recycle, bypass, and treatment of streams needed to satisfy the process and environmental constraints. The basic idea of the model formulation is to consider component balances, treating as optimization variables the individual flowrates. This formulation avoids the bilinear terms that appear when the compositions and total flowrates are considered as optimization variables. The objective function consists in the minimization of the total annual cost including the fresh sources costs, the treatment units costs (which are reformulated as convex functions) and the piping costs. Four examples problems are solved to show the applicability of the proposed model.     

Mathematical model of an angular velocity transducer utilizing a laser with a fiber-optic ring resonator

An angular velocity transducer based on a laser with a fiber-optic ring resonator is considered. A relationship is obtained linking the amplitude and phase characteristics of the radiation with the parameters of the resonator and the rotational velocity of the transducer. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 6–8, March, 1996.