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2. Optimization methods for solving transportation problems on networksKatja Prnaver, 2011, doktorska disertacija Opis: In this thesis we study problems from real situations, which can be applied to network
graphs and solved using mathematical graph theory.
We start with the problem of oriented network design. The problem originates from
networks, where the flow over the arcs is important and many times limited with the capacity
of the networks. There are several techniques and results on the problem of assigning the
flow through the network channels. In our problem, we try to find the optimal network
structure, which could be used in the design phase of the network. With metaheuristics,
we search for optimal network structures for a given number of nodes. We define triangle
neighborhood and compare the results of the algorithm with the conjecture by Choplin et
al. [8].
Further, we study the problem of order picking and order batching in block structured
warehouses. For order picking problem, we present the extension of a dynamic programming
algorithm by Ratliff and Rosenthal [42], which enables the development of an algorithm for
an unlimited number of blocks. In order to achieve this, a new presentation of states and
transitions of dynamic programming algorithm is given. We prove that the resulting path is
optimal for the given structure. We compare the optimal path lengths to the results found in
literature and also investigate the impact of warehouse layout parameters onto the routing.
Closely related to the problem of order picking, we investigate the order batching problem.
We discuss the variation of the order batching problem with time windows and present
the algorithmic approach to solving the problem. The previously presented optimal path
algorithm is applied in the algorithm to ensure even better quality of results. We introduce
the evaluation function of a batch and compare the results of the algorithm with the test
data from the literature as well as with data from the real warehouse.
We conclude by summarizing the results and stating some possible extensions and further
work.
Ključne besede: graph theory, networks, optimization, shortest path problem, traveling salesman problem, algorithms, metaheuristics, order batching
Objavljeno: 03.06.2011; Ogledov: 3366; Prenosov: 131
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3. Optimization of cultivation conditions for mammalian cell lines producing complex biosimilarsJure Strnad, 2011, doktorska disertacija Opis: EXTENDED ABSTRACT
The possibility to replace standard single use 250 mL shake flasks with single use 50 mL spin tubes was investigated using the design of experiments methodology. Experimental throughput could be tripled to a maximum of 120 spin tubes per shaker-incubator unit if similar process performance could be proven in shake flasks and spin tubes. A D-optimal response surface design was used to model titer values in a seven day batch process producing recombinant erythropoietin. Shaking rate and working volume in spin tubes were adjusted to simulate titers that are produced in shake flasks at the reference setting. Research results indicated that equivalent titers as in shake flasks at the reference setting can be produced in spin tubes; moreover, even higher titers are possible. The maximal titers in spin tubes reached values as observed in 6 L bioreactors. Furthermore, a comparison of process performance and product quality attributes between two spin tube settings, the reference shake flask setting, a standard bioreactor run and a bioreactor run without pH control was made. Process performance and product quality attributes in spin tubes at the equality setting (shaking rate of 180 rpm and 30 mL working volume) were comparable to the ones derived from the reference shake flask setting. Results derived for both bioreactor runs were not fully comparable to the spin tube and shake flask systems. The statistical model for calculating titers on day seven of a batch process in spin tubes was successfully validated and can be used for titer prediction in the proposed design space.
The optimized spin tube settings were further used in a repetitive batch process where in the harvest phase of the process medium was daily exchanged to prevent component depletion or build-up of inhibitors. Spin tubes and shake flasks were used to simulate the industrial process of erythropoietin production. The effect of process mode change from seven-day batch to repetitive batch was investigated on process performance and product quality attributes, such as isoform distribution and glycan group distribution. Spin tube performance at the equality setting was comparable to the shake flask performance also in the repetitive batch process. Performance, especially titers at the maximal titer spin tube setting was, however, not fully comparable to the results obtained in previous optimization experiments.
The spin tube equality setting was also used for cultivating two cell lines producing different monoclonal antibodies. The goal was to investigate how different cell lines influence process performance and product quality attributes, such as monoclonal antibody charge variant distribution and glycan group distribution. Both cell lines were derived from a Chinese hamster ovary parental cell line, therefore, it was proposed that maybe the optimal spin tube setting derived for the erythropoietin producing cell line, which was also derived from the Chinese hamster ovary parental cell line, could also be used for these subtypes. Cell growth of the monoclonal antibody producing cell lines was extensively better as observed for the erythropoietin producing cell line, which meant that culture demands were more pronounced, such as oxygen transfer or mass transfer. It was observed that the erythropoietin derived equality spin tube setting did not produce similar process responses as shake flask at the reference setting for both monoclonal antibodies. The foremost difference was that the metabolite lactate was being consumed in shake flasks after it reached a maximum value but was not consumed in spin tubes for both monoclonal antibody producing cell lines. In these experiments also amino acid time profiles during a seven day batch process were monitored and subsequently compared. It was seen that several amino acids seemed to be in excess as most of them were only half way consumed. Product quality attributes also differed between the spin tube and the shake flask setting. The conclusion of the experimental work was that some fine tuning of th
Ključne besede: design of experiments, spin tube, shake flask, optimization, erythropoietin, monoclonal antibodies
Objavljeno: 22.12.2011; Ogledov: 2003; Prenosov: 105
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4. Numerical optimisation of a waste-to-energy plant's operating parameters using CFDMiran Kapitler, Niko Samec, Filip Kokalj, 2011, izvirni znanstveni članek Opis: The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output parameters such as the temperatures or mass-flow rates of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieving optimal combustible conditions with minimal pollutant emissions, during the plant-design phase. in order to meet these goals, a waste-to-energy plant with bed combustion was investigated by using computational fluid-dynamics approach. The adequate variable input boundary conditions based on the real measurement are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion, or heat transfer models. The operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the combustible products were predicted and visualized. Finally, the response charts and matrix among the input and output parameters during the optimization process are presented, which monitored the dependence among these parameters.
Ključne besede: municipal solid waste, bed combustion, computational fluid dynamics, numerical optimization, goal driven optimization, trade-off study, parameters correlation
Objavljeno: 01.06.2012; Ogledov: 798; Prenosov: 9
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5. Kefir grains production - An approach for volume optimization of two stage bioreactor systemAndreja Goršek, Marko Tramšek, 2008, izvirni znanstveni članek Opis: The main objective of the present study was to design a continuous two-stage bioreactor system for kefir grains production. Based on the experimental data of time-depended kefir grain mass increase and average pH profile during kefir grains batch propagation, parameters of predictive growth and exponential pH models were initially estimated. Afterwards, the non-linear programming (NLP) optimization problem for estimating the optimal volumes of two unequal in series connected continuously stirred tank bioreactors (CSTB) has been developed. The NLP problem is based on criterion of minimal total holding time (MTHT), kefir grain mass balances in CSTB and parameters of the growth and pH models. The results showed that novel kefir grains production plant with two-stage continuous operation, at capacity, qm,KG,pr=3 kgh-1 and conversion, Xo,2=0.980, would primarily require investment in two CSTB with V1=5.93 m3 and V2=5.62 m3, respectively. Technological and economical authorization for a two-stage continuous bioreactor system was mainly confirmed with a more than five times lower total bioreactor volume compared to one-stage plant.
Ključne besede: chemical processing, bioprocesses, milk products, kefir grains production, bioreactor design, modeling, optimization
Objavljeno: 31.05.2012; Ogledov: 1409; Prenosov: 20
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6. Development of a mathematical model for the dynamic optimization of batch reactors, and MINLP synthesis of plug-flow reactors in complex networksMarcel Ropotar, Zdravko Kravanja, 2007, izvirni znanstveni članek Opis: This paper describes the development of a robust and efficient reactor model suitable for representing batch and plugflow reactors (PFRs) in different applications. These would range from the nonlinear (NLP) dynamic optimization of a stand-alone batch reactor up to the mixed-integer nonlinear (MINLP) synthesis of a complex reactor network in overall process schemes. Different schemes for the Orthogonal Collocation on Finite Element (OCFE) and various model formulations, in the case of MINLP model, were studied in order to increase the robustness and efficiency of the model. A deterministic model for known kinetics was obtained for batch and PFR reactors and extended for uncertainties in process parameters and reaction kinetics when the kinetics is unknown. Different variations of the developed model were applied to certain problems, as examples. The first motivating example was the dynamic optimization of batch reactor and the second the MINLP synthesis of a process scheme for the production of allyl chloride. The NLP version of the model with moving finite elements was found to be the most efficient for representing a batch reactor in the dynamic optimization example, and PFR trains in the process synthesis example.
Ključne besede: batch reactor, orthogonal collocation, off-line optimization, on-line optimization, flexibility, uncertainty
Objavljeno: 31.05.2012; Ogledov: 1220; Prenosov: 6
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7. An intelligent system for monitoring and optimization of ball-end milling processFranc Čuš, Matjaž Milfelner, Jože Balič, 2006, izvirni znanstveni članek Opis: The paper presents an intelligent system for on-line monitoring and optimization of the cutting process on the model of the ball-end milling. An intelligent system for monitoring and optimization in ball-end milling is developed both in hardware and software. It is based on a PC, which is connected to the CNC main processor module through a serial-port so that control and communication can be realised. The monitoring system is based on LabVIEW software, the data acquisition system and the measuring devices (sensors) for the cutting force measuring. The system collects the variables of the cutting process by means of sensors. The measured values are delivered to the computer program through the data acquisition system for data processing and analysis. The optimization technique is based on genetic algorithms for the determination of the cutting conditions in machining operations. In metal cutting processes, cutting conditions have an influence on reducing the production cost and time and deciding the quality of a final product. Experimental results show that the proposed genetic algorithm-based procedure for solving the optimization problem is effective and efficient, and can be integrated into a real-time intelligent manufacturing system for solving complex machining optimization problems.
Ključne besede: ball-end milling, cutting forces, monitoring, optimization
Objavljeno: 30.05.2012; Ogledov: 809; Prenosov: 7
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8. Heat integration in a speciality product processMajda Krajnc, Anita Kovač Kralj, Peter Glavič, 2006, izvirni znanstveni članek Opis: The essence of effective process designing is to use methods which are efficient to engineers in practice and not only to scientists. The proposed design procedure is composed of two steps: conceptual one and optimization one. At the conceptual step, pinch design analysis is used. In the optimization step pinch analysis and mixed-integer nonlinear programming method are applied. In the case study analysed, a speciality product is to beproduced in continuous chemical process with a capacity which causes smallerheat flow rates and needs smaller heat exchanger areas than usual. Therefore, an equation for cost estimation of heat exchangers with areas smaller than 7 m2 was developed and used in the optimization procedure. Using thermodynamic pinch analysis and mathematical programming method, the heat integrated structures were synthesized and compared with the base process flowsheet. Finally, the optimal structure was determined.
Ključne besede: načrtovanje procesov, načrtovanje procesov, ekonomska analiza, prenos toplote, optimizacija, chemical process design, economic analysis, heat integration, optimization
Objavljeno: 30.05.2012; Ogledov: 1010; Prenosov: 4
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9. Approach to optimization of cutting conditions by using artificial neural networksFranc Čuš, Uroš Župerl, 2006, izvirni znanstveni članek Opis: Optimum selection of cutting conditions importantly contribute to the increase of productivity and the reduction of costs, therefore utmost attention is paid to this problem in this contribution. In this paper, a neural network-based approach to complex optimization of cutting parameters is proposed. It describes the multi-objective technique of optimization of cutting conditions by means of the neural networks taking into consideration the technological, economic and organizational limitations. To reach higher precision of the predicted results, a neural optimization algorithm is developed and presented to ensure simple, fast and efficient optimization of all important turning parameters. The approach is suitable for fast determination of optimum cutting parameters during machining, where there is not enough time for deep analysis. To demonstrate the procedure and performance of the neural network approach, an illustrative example is discussed in detail.
Ključne besede: optimization, cutting parameter optimization, genetic algorithm, cutting parameters, neural network algorithm, machining, metal cutting
Objavljeno: 30.05.2012; Ogledov: 976; Prenosov: 11
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10. Design of the optimal total site heat recovery system using SSSP approachAndreja Goršek, Peter Glavič, Miloš Bogataj, 2006, izvirni znanstveni članek Opis: Site expansions or changes in production capacities are usually related with changes of utilities demands andžor utility system design. Despite several available and well established techniques for process synthesis and integration, very often, changes in process designs are made on the basis of intuition and experiences of engineers. In this paper possibilities of rational energy consumption and energy integration in an existing site for production of specialty chemicals were studied. On the basis of real process parameters and computer simulation results energy integration was re-examined.Total site analysis using modified Site Sink Source Profiles, which gives a profound insight into the site utility system configuration, heating-cooling demands and cogeneration design was performed. The existing site was found to be very well designed. With only few modifications additional 9% of hot utilities and 5% of cold utilities savings are possible.
Ključne besede: chemical engineering, process design, optimization, heat integration, cogeneration, pinch method, energy retrofit
Objavljeno: 30.05.2012; Ogledov: 1418; Prenosov: 10
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