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MINLP optimization of a single-storey industrial steel building
Tomaž Žula, Zdravko Kravanja, Stojan Kravanja, 2008, izvirni znanstveni članek

Opis: The paper presents the topology and standard sizes optimization of a single-storey industrial steel building, made from standard hot rolled I sections. The structure consists of main portal frames, connected with purlins. The structural optimization is performed by the Mixed-Integer Non-linear programming approach (MINLP). The MINLP performs a discrete topology and standard dimension optimization simultaneously with continuous parameters. Since the discrete/continuous optimization problem of the industrial building is non-convex and highly non-linear, the Modified Outer- Approximation/Equality-Relaxation (OA/ER) algorithm has been used for the optimization. Alongside the optimum structure mass, the optimum topology with the optimum number of portal frames and purlins as well as all standard cross-section sizes have been obtained. The paper includes the theoretical basis and a practical example with the results of the optimization.
Ključne besede: civil engineering, topology optimization, sizing optimization, nonlinear programming, MINLP
Objavljeno v DKUM: 31.05.2012; Ogledov: 2366; Prenosov: 65
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Heat integration between two biodiesel processes using a simple method
Anita Kovač Kralj, 2008, izvirni znanstveni članek

Opis: Biodiesel is a clean-burning alternative fuel, produced from domestic, renewable resources. Biodiesel can be blended at any level with petroleum diesel to create a biodiesel blend. It can be used in compression-ignition (diesel) engines with little or no modification. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics. This paper presents heat integration between two biodiesel processes. Biodiesel can be produced by the esterification of different fatty acids (high and low boiling point) with alcohols. This simple method for heat integration is based on three possible steps. Simultaneous integration between processes can be performed using a stagewise model with a mixed integer nonlinear programming (MINLP) algorithm (step 3), which can include alternatives suggested by pinch analysis of heat transfer between the processes (step 2). The internal integration of individual processes can be performed in step 1. The fraction can be calculated for maximum integration between processes. Integration between the processes can be carried out using all three steps or by the first and third steps or by the last step only, depending on the problems' complexities. This method includes streams of different processes which are heated or cooled using a utility only. The existing heaters and coolers can be left unchanged in their original processes or can be used for integrating heat between processes, with hot and cold utilities being saved. This approach is illustrated by integrating two simulated biodiesel processes.The objective was to maximize additional annual profit for integration between processes by USD8300/a.
Ključne besede: chemical processing, biodiesel producing, heat integration, nonlinear programming
Objavljeno v DKUM: 31.05.2012; Ogledov: 1988; Prenosov: 127
URL Povezava na celotno besedilo

H2 separation and use in fuel cells and CO2 separation and reuse as a reactant in the existing methanol process
Anita Kovač Kralj, Peter Glavič, 2007, izvirni znanstveni članek

Opis: Fuel-cell efficiencies yield substantial reductions in the emissions of climate-change gases and promise an end to exclusive reliance on carbon fuels for energy. Fuel cells, CO2 reuse, process heat integration, and open gas turbine electricity cogeneration can be optimized simultaneously, using a nonlinear programming (NLP) algorithm. The simplified NLP model contains equations of structural and parametric optimization. This NLP model is used tooptimize complex and energy-intensive continuous processes. This procedure does not guarantee a global cost optimum, but it does lead to good, perhaps near-optimum, designs. The plant, which produces methanol, has a surplus of hydrogen (H2) and CO2 flow rates in purge gas. H2 is separated from the purge gas by an existing pressure swing adsorption (PSA) column. Pure H2 can be usedas fuel in fuel cells. CO2 can be separated from the outlet stream (purge gas) by a membrane or absorption system (absorber and regenerator) or an adsorption system and reused as a reactant in a reactor system. Therefore, theproduct yield can be increased and CO2 emissions can be reduced, simultaneously. CO2 emissions can then be reduced at the source. The retrofitted process can be operated within existing parameters. Using a methanol process as a case study, the CO2 emission flow rate can be reduced by4800 t/a. The additional electricity cogeneration in the gas turbine and in fuel cells and additional flow rates of the raw material could generate an additional profit of 2.54 MEUR/a.
Ključne besede: chemical processing, methanol production, optimization, nonlinear programming, CO2 reuse, fuel cells, heat integration, energy cogeneration
Objavljeno v DKUM: 31.05.2012; Ogledov: 2528; Prenosov: 119
URL Povezava na celotno besedilo

CO2 separation from purge gas and flue gas in the methanol process, using NLP model optimization
Anita Kovač Kralj, Peter Glavič, 2007, izvirni znanstveni članek

Opis: The concentration of CO2 in the atmosphere has to be stabilized, requiring a reduction in current emission rates in existing plants. This will be done by reducing the environmental burden imposed in such areas as materials input andCO2 emission reduction and using cleaner production, resources, and energy recycling. Any opportunities for emission reduction and CO2 reuse largely depend on existing plant and energy systems. CO2 can be separated from the outlet stream (purge gas) and from flue gas by a membrane or absorption system(absorber and regenerator) or adsorption system and reused as a reactantin a reactor system. Therefore, product yield can be increased and CO2emissions reduced, simultaneously. CO2 emissions can be reduced at the source. The authors of this paper studied CO2 reuse in a methanol process, in which electricity can be generated using an open gas turbine, followed by a separator. Simultaneous optimization of a process structure and its parametersusing simplified nonlinear programming (NLP) ensures an additional annual profit, influenced by reusing the flow rate of CO2. The additional electricity cogeneration and additional flow rates of the raw material could generate an additional profit of 2.79 MEUR/a.
Ključne besede: chemical processing, methanol production, optimization, nonlinear programming, CO2 emissions, CO2 reuse
Objavljeno v DKUM: 31.05.2012; Ogledov: 2064; Prenosov: 91
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Selection of the economic objective function for the optimization of process flow sheets
Zorka Novak-Pintarič, Zdravko Kravanja, 2006, izvirni znanstveni članek

Opis: This paper highlights the problem of selecting the most suitable economic optimization criteria for mathematical programming approaches to the synthesis, design, and optimization of chemical process flow sheets or their subsystems. Minimization of costs and maximization of profit are the most frequently used economic criteria in technical papers. However, there are manyother financial measures which can lead to different optimal solutions if applied in the objective function. This paper describes the characteristics ofthe optimal solutions obtained with various optimization criteria like the total annual cost, the profit, the payback time, the equivalent annual cost, the net present worth, and the internal rate of return. It was concluded that the maximization of the net present worth (NPW) with a discount rate equal to the minimum acceptable rate of return (MARR) is probably the most appropriate method for the optimization of process flow sheets or their subsystems. Similar or equal solutions can be obtained by simpler criteria of minimum equivalent annual cost or maximum profit if the annual investment cost is calculated by using the MARR instead of the straight-line depreciation method.These criteria represent a thorough compromise between quantitative andqualitative measures, because they consider the absolute terms of future cash flows of investments equally important as profitability through the life cycle of the project. The uncertainty related to the value of the MARR was considered by the generation of Pareto optimal solutions for the NPW and by the stochastic analyses of two design example problems.
Ključne besede: chemical processing, optimization, mathematical programming, flow sheets
Objavljeno v DKUM: 31.05.2012; Ogledov: 1909; Prenosov: 160
URL Povezava na celotno besedilo

Energy saving and modifications in the methanol process, using the NLP model optimization
Anita Kovač Kralj, Peter Glavič, 2006, objavljeni znanstveni prispevek na konferenci

Opis: The opportunities for additional profit depend very much on the existing plant and energy system. Heat and power integration can reduce fuel usage in chemical processes. Nonlinear programming contains equations which enable structural and parametric optimization. The NLP model is formulated using an optimum energy target of process integration and electricity generation using a gas turbine with separator. The reactor acts as a combustion chamber of the gas turbine plant, producing a lot of energy. The simultaneous NLP approach can account for capital cost, integration of combined heat and power, process modification and additional production of trade-offs, and can thus yield a better solution. The combined production of electricity, heat and chemical products can lead to better process efficiency. The methanol plant was optimized using a mathematical nonlinear programming model by including an additional flowrate of hydrogen in crude methanol recycle and increasing the methanol production by 2,5%. The electricity can be generated in methanol recycle using a gas turbine. The total additional profit is 2,5 MEUR/a.
Ključne besede: chemical engineering, methanol production, simultaneous process optimization, nonlinear programming, cogeneration, product increase
Objavljeno v DKUM: 30.05.2012; Ogledov: 2426; Prenosov: 46
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Intelligent programming of CNC turning operations using genetic algorithm
Jože Balič, Miha Kovačič, Boštjan Vaupotič, 2006, izvirni znanstveni članek

Opis: CAD/CAM systems are nowadays tightly connected to ensure that CAD data can be used for optimal tool path determination and generation of CNC programs for machine tools. The aim of our research is the design of a computer-aided, intelligent and genetic algorithm(GA) based programming system for CNC cutting tools selection, tool sequences planning and optimisation of cutting conditions. The first step is geometrical feature recognition and classification. On the basis of recognised features the module for GA-based determination of technological data determine cutting tools, cutting parameters (according to work piece material and cutting tool material) and detailed tool sequence planning. Material, which will be removed, is split into several cuts, each consisting of a number of basic tool movements. In thenext step, GA operations such as reproduction, crossover and mutation are applied. The process of GA-based optimisation runs in cycles in which new generations of individuals are created with increased average fitness of a population. During the evaluation of calculated results (generated NC programmes) several rules and constraints like rapid and cutting tool movement, collision, clamping and minimum machining time, which represent the fitness function, were taken into account. A case study was made for the turning operation of a rotational part. The results show that the GA-based programming has a higher efficiency. The total machining time was reduced by 16%. The demand for a high skilled worker on CAD/CAM systems and CNC machine tools was also reduced.
Ključne besede: CNC programming, genetic algorithm, intelligent CAM, turning, tool path generation
Objavljeno v DKUM: 30.05.2012; Ogledov: 2834; Prenosov: 96
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Study of crosslinking efficiency of cotton cellulose by different physical-chemical methods and genetic programming
Olivera Šauperl, Miran Brezočnik, 2006, izvirni znanstveni članek

Opis: We have investigated the crosslinking effect of unmercerized and mercerized cotton celluose crosslinked with different BTCA mass fractions in the impregnation bath. Crosslinking efficiency was analyzed using FT-IR spectroscopy, water retention capacity method, tensiometry and the methylene blue method. On the basis of the experimental data which was obtained with theseparate physical-chemical methods, different prediction models for crosslinking efficiency was developed. Modelling was taken out with the genetic programming method. Research shows good accordance of the experimentaldata with the genetic models.
Ključne besede: textile fibres, cotton, cellulose, crosslinking, FTIR spectroscopy, methylene blue method, water retention capacity, tensiometry, genetic programming
Objavljeno v DKUM: 30.05.2012; Ogledov: 2030; Prenosov: 79
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Modeling of impact toughness of cold formed material by genetic programming
Leo Gusel, Miran Brezočnik, 2006, izvirni znanstveni članek

Opis: In the paper, an approach completely different from the conventional methods for determination of accurate models for the change of properties of cold formed material, is presented. This approach is genetic programming (GP) method which is based on imitation of natural evolution of living organisms. The main characteristic of GP is its non-deterministic way of computing. No assumptions about the form and size of expressions were made in advance, but they were left to the self organization and intelligence of evolutionary process. First, copper alloy rods were cold drawn under different conditions and then impact toughness of cold drawn specimens was determined by Charpy tests. The values of independent variables (effective strain, coefficient of friction) influence the value of the dependent variable, impact toughness. On the basis of training data, different prediction models for impact toughness were developed by GP. Only the best models, gained by genetic programming were presented in the paper. Accuracy of the best models was proved with the testing data set. The comparison between deviation of genetic model results and regression model results concerning the experimental results has showed that genetic models are more precise and more varied then regression models.
Ključne besede: metal forming, genetic programming, evolutionary computing, impact toughness, copper alloy, modelling
Objavljeno v DKUM: 30.05.2012; Ogledov: 2320; Prenosov: 106
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