Global instability phenomenon as a physical mechanism controlling dynamics of a nitrogen-diluted hydrogen flame

We investigate the dynamics of counter-current reacting flow under varying strengths of the counterflow and report the occurrence of global instability phenomena. This clarifies the role of global instability in the transition between attached and lifted flames. The research is performed with the help of the Large Eddy Simulation method using a high-order numerical method. The combustion process is modelled by applying detailed chemical kinetics for hydrogen combustion with chemical reaction terms computed from the resolved scale. The flow configuration consists of a central jet of nitrogen-diluted hydrogen fuel surrounded by an annular nozzle with a suction slot enforcing counterflow in the vicinity of the fuel stream. Suction strength is controlled by the ratio between the velocity in the suction slot (Usuc) and the velocity of the fuel jet (Uj) (I=Usuc/Uj). The Reynolds number based on the fuel parameters and the central nozzle diameter is Re=1600. Two values of the suction strength are considered (I=0.1,0.2) as well as the case without suction (I=0.0). A hot oxidizer (air) provided in the region outside the co-axial nozzle causes fuel auto-ignition far from the injection system after which the flame propagates downstream. It is shown that increasing the suction strength postpones the ignition and shifts its axial location downstream. Depending on the I parameter the flame stabilizes as attached (I=0.0,0.1) or lifted (I=0.2). It is shown that the flames in the cases with I=0.0,0.1 are very similar to each other appearing as laminar non-premixed flames both in the nozzle vicinity and far downstream. The flame in case I=0.2 is turbulent and much more dynamic. Its lifting is the result of global instability appearing at increased suction in the region of counter-current flow. It is shown that the global instability induces strong toroidal vortices that create a premixed reaction zone at the flame base. This flow structuring prevents upstream flame propagation and intensifies the mixing process ensuring almost complete fuel burning in a short distance from the nozzle.</p

Real-Time Jerk Limited Feedrate Profiling and Interpolation for Linear Motor Multiaxis Machines Using NURBS Toolpaths

In this article, a NURBS toolpath feedrate profile generation algorithm for a biaxial linear motor control system is presented. High achievable velocities and accelerations of linear motor machines present new computational challenges in implementing feedrate generation and toolpath interpolation algorithms in real-time controllers. The proposed algorithm is capable of online generation of the feedrate profile with axial acceleration and jerk constraints. Each stage of the feedrate profiling algorithm is described with attention being given to both performance and implementation aspects. Furthermore, an alternative to the commonly used Taylor series interpolation method is also tested to ensure minimal interpolation errors. The feedrate profiling and interpolation algorithms’ implementation in a PC-based controller with real-time Linux kernel is described. Experimental results are presented that confirm that the algorithm is capable of limiting acceleration and jerk in the machine’s axes and it is low computation time enables real-time on-line operation in a PC-based CNC controller

LES of a non-premixed hydrogen flame stabilized by bluff-bodies of various shapes

Dynamics of flames stabilized downstream of different shape bluff-bodies (cylindrical, square, star) with different wall topologies (flat, wavy) is investigated using large-eddy simulations (LES). A two-stage computational procedure involving the ANSYS software and an in-house academic high-order code is combined to model a flow in the vicinity of the bluff-bodies and a flame formed downstream. The fuel is nitrogen-diluted hydrogen and the oxidizer is hot air in which the fuel auto-ignites. After the ignition, the flame propagates towards the bluff-body surfaces and stabilizes in their vicinity. It is shown that the flames reflect the bluff-body shape due to large-scale strong vortices induced in the shear layer formed between the main recirculation zone and the oxidizer stream. The influence of the acute corners of the bluff-bodies on the flame dynamics is quantified by analysing instantaneous and time-averaged results. Compared to the classical conical bluff-body the largest differences in the temperature and velocity distributions are observed in the configuration with the square bluff-body. The main recirculation zone is shortened by approximately 15% and at its end temperature in the axis of the flame is almost 200~K larger. Simultaneously, their fluctuations are slightly larger than in the remaining cases. The influence of the wall topology (flat vs. wavy) in the configuration with the classical conical bluff-body turned out to be very small and it resulted in modifications of the flow and flame structures only in the direct vicinity of the bluff-body surface

In pursuit of tax equity: lessons from VAT rate structure adjustment in Poland

In 2011, in the aftermath of the economic crisis, Poland increased its value added tax rates. Despite an already large VAT policy gap, further rate differentiation was used to address distributional concerns and to protect the most vulnerable households. We find that the changes to the VAT rate structure hardly improved the overall progressivity of the VAT and the tax system as a whole. While providing only minimal relief to the poor, taxation of food products at a super reduced rate greatly subsidized the richer households. With a small change to the income tax structure, the government could have secured more progressivity at a lower cost in terms of revenue foregone

Piękne i szkaradne. Motyw maski na drodze rozwoju i transmisji nowożytnej groteski

In 1555, the serie of masks by Cornelius Floris was edited in Antwerp. This well known and a comprehensive artist, designed Maski fantastyczne (The Fantastic Masks) and then he separated a motive which was the element of ancient and modern grotesque. His style and projects exerted the significant influence on art, especially in the north of Europe. The origin of grotesque ornament can be found in the ancient paintings. In the second half of XVth century, inside Nero’s House in Rome, were discovered some interior decorations – mostly strange and fantastic creatures like the sea monsters, hybrids, girlands of flowers and masks, covering the walls of ancient interior which delighted some the late Reneissance artists. The mask was connected with the theatre, coming from the rituals in honour of Dionisos and it was not only the symbol of vegetation or rebirth but also the oncoming end of life. In medieval times the apotropaic properties were attributed to it. The grotesque ornaments thanks to printing – houses and graphic artists and also – thanks to many XVI th artists’ journeys, expanded quickly and they used by architects, sculptors, carvers, goldsmiths and especially –by graphic artists. The activity of the artists from Raphael’s School in Rome had the main influence on a grotesque ornament expansion in the whole Europe. They transferred the themes from Nero’s House and their work was willingly engraved by well – known Italian, German and Netherlander graphic artists. The important moment for the spread of grotesque ornament was the invitation from Francis the First to Italian artists to the work of Fontainebleau Castle decorations. The monumental wall decorations, joined a picture and relief, figural and abstract composition with the elements of grotesque, two – way exchange of patterns, Italian mannerism connected with ancient , with the French gothic tradition. It involved to a grotesque reduction from strange forms to dominant cartouche, made mainly by Netherlanders. Within the north grotesque the mask achieved an unusual, fantastic shape of mascaron, mostly in Floris’s and Bos’s art. But, most of all, The Floris’s patterns, by graphic artists and his students, got to the north Europe, also to Gdańsk and Toruń – the main protestant centres in the territory of Royal Prussia.

PSO based feedrate optimization with contour error constraints for NURBS toolpaths

Paper presented at MMAR 2016 conference (Międzyzdroje, Poland, 29 Aug.-1 Sept. 2016)Generation of a time-optimal feedrate profile for CNC machines has received significant attention in recent years. Most methods focus on achieving maximum allowable feedrate with constrained axial acceleration and jerk without considering manufacturing precision. Manufacturing precision is often defined as contour error which is the distance between desired and actual toolpaths. This paper presents a method of determining the maximum feedrate for NURBS toolpaths while constraining velocity, acceleration, jerk and contour error. Contour error is predicted during optimization by using an artificial neural-network. Optimization is performed by Particle Swarm Optimization with Augmented Lagrangian constraint handling technique. Results of a time-optimal feedrate profile generated for an example toolpath are presented to illustrate the capabilities of the proposed method

Neural Network Contour Error Predictor in CNC Control Systems

Paper presented as poster presentation at MMAR 2016 conference (Międzyzdroje,Poland, 29 Aug.-1 Sept. 2016)This article presents a method for predicting contour error using artificial neural networks. Contour error is defined as the minimum distance between actual position and reference toolpath and is commonly used to measure machining precision of Computerized Numerically Controlled (CNC) machine tools. Offline trained Nonlinear Autoregressive networks with exogenous inputs (NARX) are used to predict following error in each axis. These values and information about toolpath geometry obtained from the interpolator are then used to compute the contour error. The method used for effective off-line training of the dynamic recurrent NARX neural networks is presented. Tests are performed that verify the contour error prediction accuracy using a biaxial CNC machine in a real-time CNC control system. The presented neural network based contour error predictor was used in a predictive feedrate optimization algorithm with constrained contour error

Stanowisko badawcze układów sterowania wieloosiowego napędami liniowymi poprzez magistralę EtherCAT

W artykule przedstawiono stanowisko badawcze przeznaczone do badania wieloosiowych układów sterowania z serwonapędami liniowymi. Stanowisko składa się z komputera pełniącego rolę sterownika nadrzędnego, serwosterowników oraz silników liniowych. Sterownik pracuje pod kontrolą systemu Linux z jądrem czasu rzeczywistego. Zaimplementowano również programowy stos EtherCAT do komunikacji z napędami. Przedstawiono budowę układu sterowania oraz strukturę oprogramowania sterownika. Przedstawiono również planowane badania, które będą realizowane na stanowisku dotyczące metod generacji optymalnych trajektorii ruchu, implementacji algorytmów regulacji położenia i prędkości w sterowniku oraz wpływu magistrali EtherCAT na jakość sterowania

Application of Ethernet Powerlink for communication in a Linux RTAI open CNC control system

In computerized numerical control (CNC) systems, the communication bus between the controller and axis servo drives must offer high bandwidth, noise immunity, and time determinism. More and more CNC systems use real-time Ethernet protocols such as Ethernet Powerlink (EPL). Many modern controllers are closed costly hardware-based solutions. In this paper, the implementation of EPL communication bus in a PC-based CNC system is presented. The CNC system includes a PC, a software CNC controller running under Linux Real-Time Application Interface real-time operating system and servo drives communicating via EPL. The EPL stack was implemented as a real-time kernel module. Due to software-only implementation, this system is a cost-effective solution for a broad range of applications in machine control. All software systems are based on GNU General Public License or Berkeley Software Distribution licenses. Necessary modifications to the EPL stack, Linux configurations, computer basic input/output system, and motherboard configurations were presented. Experimental results of EPL communication cycle jitter on three different PCs were presented. The results confirm good performance of the presented system

Monomeric and dimeric forms of cholesterol esterase from Candida cylindracea Primary structure, identity in peptide patterns, and additional microheterogeneity

AbstractCholesterol esterase from Candida cylindracea was separated into two fractions, corresponding to a dimeric and a monomeric form. Fingerprint analysis after lysine cleavages shows identical patterns, suggesting lack of primary differences. Crystals obtained from the two proteins differ and suggest the possibility of an equilibrium between the two forms, influenced by the substrate cholesterol linoleate, which appears to stabilize the more active, dimeric form. All crystals have dimers as the asymmetric unit. The primary structure of the enzyme was determined at the peptide level and shows only one difference, Leu-350 instead of Ile, from a DNA-deduced amino acid sequence, and conservation of features typical for cholesterol esterases characterized