Gallery_of_mitochondria.pdf

Transmission electron micrographs of muscle mitochondria of Chymomyza costata.</p

T. MAUDER et al.: A FUZZY-BASED OPTIMAL CONTROL ALGORITHM FOR A CONTINUOUS CASTING PROCESS A FUZZY-BASED OPTIMAL CONTROL ALGORITHM FOR A CONTINUOUS CASTING PROCESS ALGORITEM, KI TEMELJI NA MEHKI LOGIKI, ZA OPTIMALNI NADZOR KONTINUIRNEGA PROCESA ULIVANJA

Nowadays, continuous casting is used for processing almost one hundred percent of liquid steel into an intermediate shape. Steel with a poor structure and many defects is not acceptable to final customers, and therefore the producers must put strong emphases on its quality. Many serious steel defects can be eliminated by a preceding computer simulation, optimization and a proper control of the casting process. This paper describes an algorithm that optimizes the control parameters to ensure both a high production rate and a high quality of the products. These controlled parameters are the casting speed and all the cooling rates in the secondary cooling zone. The main principle of the algorithm is to get the surface and core temperatures to the prescribed values corresponding to the required ductility of steel. The whole optimization procedure consists of two separate parts, i.e., the numerical simulation of the process and the decision-making part based on fuzzy logic for modifying the control parameters. By incorporating the fuzzy logic into the optimization process, the algorithm has a very robust behaviour and an easy adaptation for different grades of steel. This algorithm runs in an off-line version and can be used as a preparation tool for a real casting process where the proper setting of the casting parameters is crucial for achieving high-quality products at an economical price. Keywords: fuzzy optimization, heuristic optimization, temperature field, continuous casting Postopek kontinuirnega ulivanja za pridobivanje vmesne oblike se danes uporablja pri obdelavi skoraj stoodstotnega dele`a teko~ega jekla. Jeklo s slabo strukturo in {tevilnimi napakami ni sprejemljivo za kon~ne kupce, zato morajo proizvajalci veliko pozornosti posvetiti kakovosti jekla. S predhodnimi ra~unalni{kimi simulacijami, z optimizacijo in ustreznim nadzorom procesa ulivanja se lahko odpravijo mnoge resne napake jekla. V tem prispevku je opisan algoritem za optimizacijo parametrov nadzora, ki zagotavlja visoko stopnjo proizvodnje ter visoko kakovost izdelkov. Med omenjene parametre nadzora spadata hitrost ulivanja in hitrost ohlajevanja v sekundarni coni ohlajanja. Glavno na~elo algoritma je, da povr{ina in temperatura sredice dose`eta dolo~ene vrednosti, ki ustrezajo zahtevani razteznosti jekla. Celoten postopek optimizacije obsega dva med seboj lo~ena dela -numeri~no simulacijo postopka in pa del, namenjen odlo~anju, ki temelji na mehki logiki za spreminjanje parametrov nadzora. Z integracijo mehke logike v postopek optimizacije algoritem dose`e zelo robustno vedenje in enostavno prilagoditev razli~nim vrstam jekla. Ta algoritem deluje v razli~ici »off-line« in se lahko uporablja kot pripravljalno orodje za dejanski proces ulivanja, kjer je ustrezna nastavitev parametrov ulivanja klju~nega pomena za proizvodnjo visokokakovostnih izdelkov po ekonomi~ni ceni. Klju~ne besede: mehka optimizacija, hevristi~na optimizacija, temperaturno polje, kontinuirno ulivanj

The Importance of Thermophysical Properties of Steels for the Numerical Simulation of a Concasting Process

The thermophysical properties of steels have significant influence on the actual concasting process, and on the accuracy of its numerical simulation and optimization. The determination of these properties (heat conductivity, specific heat capacity and density in the solid and liquid states) often requires more time than the actual numerical calculation of the temperature fields of a continuously cast steel billet, cylinder or slab (generally a concasting). The influence of individual properties should be neither under- nor over-estimated. Therefore, an analysis/parametric study of these thermophysical properties was conducted. The order of importance within the actual process and the accuracy of simulation and optimization were also determined. Individual properties, which, in some cases, were obtained from tables, and in others experimentally, were substituted by an approximation using orthogonal polynomials. The accuracy of each polynomial is dependent on the precision of individual values. The order of significance of individual thermophysical properties was determined with respect to the metallurgical length. The analysis was performed by means of a so-called calculation experiment, i.e. by means of the original and universal numerical concasting model developed by the authors of this paper. It is convenient to conduct such an analysis in order to facilitate the simulation of each individual case of concasting, thus enhancing the process of optimization

Melting front propagation in a paraffin-based phase change material: Lab-scale experiment and simulations

The paper reports experimental and numerical investigation of the melting front propagation in a paraffin-based phase change material (PCM). The investigated case was a block of PCM with a heat flux introduced at one of its sides. The PCM block was contained in a transparent container and thus the propagation of the melting front could be monitored with a camera. The melting temperature of the PCM was 28 °C and the container was located in an environmental chamber where the ambient temperature was maintained at 27 °C during the experiment. The natural convection in the melted PCM played an important role and it had to be considered in the heat transfer models. The numerical models taking into account natural convection in liquid PCM require long computation times, and therefore they are impractical if the fast computation of the melting front position is needed. The effective heat conductivity approach can be used to overcome this issue. Two numerical models were compared: an in-house heat transfer model using effective conductivity approach developed in MATLAB and a more advanced model created in the off-the-shelf simulation tool COMSOL, which accounts for the natural convection in liquid PCM

Numerical optimization of the taper a vertically cast plate

The temperature field of the studied plate was analyzed with different angles of widening in its cross section (in the range from 0° to 4.4°). From the inclined side, the plate was either insulated or uninsulated. Plastizol was used as an insulator. An uninsulated plate has a calculated optimum angular expansion of 3°. A widening of 2° is the minimum angle at which internal defects (e.g. shrinkage voids) begin to disappear. The insulated plate has an optimum angle of 2°. Using numerical calculations, it is possible to predict that after crystallization without insulation, the plate itself with a widening of 3° will have the same internal quality as a widening of 2° with insulation. The knowledge gained from this study can lead to a reduction in the volume of liquid metal used and also to a reduction in machining costs. These research results have already been successfully applied to the design of the technology for casting nodular cast iron cylinder liners

Physiological basis for low-temperature survival and storage of quiescent larvae of the fruit fly Drosophila melanogaster

International audienceThe cryopreservation techniques proposed for embryos of the fruit fly Drosophila melanogaster are not yet ready for practical use. Alternative methods for long-term storage of D. melanogaster strains, although urgently needed, do not exist. Herein, we describe a narrow interval of low temperatures under which the larvae of D. melanogaster can be stored in quiescence for up to two months. The development of larvae was arrested at the pre-wandering stage under fluctuating thermal regime (FTR), which simultaneously resulted in diminishing the accumulation of indirect chill injuries. Our physiological, metabolomic, and transcriptomic analyses revealed that compared to larvae stored at constant low temperatures, the larvae stored under FTR conditions were able to decrease the rates of depletion of energy substrates, exploited brief warm episodes of FTR for homeostatic control of metabolite levels, and more efficiently exerted protection against oxidative damage