Sector Geometry Research Articles

Effect of swirl ratio on charge convection, temperature stratification, and combustion in gasoline compression ignition engine

Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.

Study of orbit properties and intense beam dynamics in a high current separated sector proton cyclotron

This paper outlines a simple method based on analytical formulations to find out the physics design of a separated sector cyclotron. Formulations are developed to determine the magnet sector shape and equilibrium orbit properties for a chosen orbital frequency and a peak magnetic field in the magnet sector. Stability analysis of single particle motion without space charge effect has been performed and allowed values of sector angles are determined. The dynamics of space charge dominated beam in the separated sector proton cyclotron are explored by using beam envelope equations that includes radial and longitudinal coupling. Evolution of the rms beam envelopes and emittances has been studied as a function of the beam current for various sector geometry. The envelope equations and perturbed equations of motion around the matched beam envelopes have been utilized to obtain the matched beam conditions at different values of the beam current.

Starting Darcy–Brinkman Flow in a Sector Duct Using the Method of Eigenfuction Superposition

The powerful method of eigenfunction superposition is applied to the starting flow in a sector duct filled with a porous medium. Using analytic eigenfunctions and eigenvalues of the Helmholtz equation, the solution can be expressed in a simple series. The properties of the velocity and the transient flow rate are found to depend on the sector geometry and a porous medium factor. The starting solution is then used to construct the solution to arbitrary unsteady flows.

Systemic Congestion Propagation in the Airspace Network

To be different from the traditional concept of congestion, congestion propagation based on the correlation between aircraft is given. And the main resource shared and competed for in airspace is the air route network, especially the intersection linking the multiroute. The system composed of congestion propagation units operates in airspace network, which is limited by the network geometry and the correlation between aircraft. This paper presents models based on the congestion and propagation characteristics in complex network, predicting the trend of congestion propagation and the peak of congestion size. By analyzing the relationships between system parameters and congestion propagation and accounting for the effects of propagation across networks, this paper enhances the current dynamics models of congestion propagation in airspace. Firstly, a heterogeneous network model is introduced to reveal the propagation process of aircraft with different degrees of correlation. This is followed by the specification of two simplified models for short-term prediction, just taking the sector capacity, propagation rate, and dissipation rate into account. And the propagation rate and dissipation rate depend on the sector geometry and aircraft distribution. Using them (sector capacity, propagation rate, and dissipation rate), the prediction models are accurate in predicting the evolution of congestion peak and propagation trend in comparison with the sample data of intersections in the sector. Of them, the model with capacity limitation is more accurate on busy hour. And on non-busy hour, capacity is insensitive in predicting congestion clusters. Furthermore, the computing method of propagation rate and dissipation rate is given in our paper. Finally, a numerical analysis is performed, in which it is demonstrated that system capacity, propagation rate, and dissipation rate have different effects on congestion propagation in airspace. The results show that low propagation and high dissipation rates not only are nonlinear but also decrease the level of congestion in the propagation of congestion. In particular, of the three parameters, system capacity affects the rate of convergence, with a low-capacity system reaching a stable state quickly and therefore providing a basis for sector partitioning. The method proposed in this paper should enable air traffic controllers to better understand the characteristics of congestion and its propagation for the benefits of both congestion management and improvement of efficiency. Significantly, airspace designers can take congestion propagation into consideration for optimizing the airspace structure in the future.

Band Sedimentation Experiment in Analytical Ultracentrifugation Revisited.

The band sedimentation experiment in analytical ultracentrifugation (AUC) allows for the performance of a chemical reaction inside the AUC and also offers separation of individual pure components in a sedimentation velocity experiment. Although this experiment offers exciting possibilities for application, it is barely used. This is related to the bad definition of the initial conditions. Both the duration and the time of the solution overlay during rotor acceleration are not known. In this study, we investigate these conditions under the variation of the overlay volume using recording of interference patterns in a continuous mode during the acceleration of the rotor. It was found that the overlay occurs at rotor speeds between 770 and 2000 rpm, which is very low compared to typical experimental rotor speeds from 3 000 to 60 000 rpm and therefore elucidates that the generated reaction products, respectively, overlaid species are subject to the centrifugal force almost from the beginning. Also, the duration of the overlay is less than 1.2 s, which is very fast compared to hours of centrifugation time for an experiment and we demonstrated that the overlay compartment is completely emptied during overlay allowing for the precise calculation of the meniscus using the known sample sector geometry. Our results show that the initial conditions of the experiment are defined and should make an adapted analysis possible if the interdiffusion of the two solvents is taken into account, which lead to a dynamic density gradient.

Stability Analysis of Composite Perforated Annular Sector Plates Under Thermomechanical Loading by Finite Element Method

This paper presents the stability analysis of a perforated plate with sector geometry made of composite materials. The sector of concern is a compound of graphite-epoxy and glass-epoxy with identical ply thickness but different fiber angles for each layer. The mechanical load conditions considered include uniform axial, circumferential, and biaxial pressure, while the thermal loading is specified to be uniform temperature increase over the whole sector. The existence of one or two circular holes has increased the complexity of analysis. To obtain solutions of high accuracy, the three-dimensional elasticity theory relations have been employed. Using the finite element method along with the stability condition of Trefftz, the buckling equation of the structure is derived. Green nonlinear strain-displacement relations are used to form the geometrical stiffness matrix. Unlike the finite element method used by other researches, a novel curved 3D B-Splined element is used to more accurately trace the displacement and stress variations of the structure. This element can be used in solution domains with geometric discontinuities, such as perforated plates and also meshed in the thickness direction. Moreover, instead of using the common von Karman assumptions, the most general form of the strain tensors in the curvilinear coordinates is adopted. The buckling load is obtained by extremizing the second variations of the total potential energy. The finite element formulation is coded in the MATLAB software. The effects of various parameters such as sector dimensions, dimensions of the hole, mechanical load directions, and fiber angles of each layer on the thermomechanical buckling is investigated.

COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF FLOW AND COMBUSTION OF A DIESEL ENGINE

Efficient usage of fossil fuels and reduction of CO2 emissions are very important priorities for the automotive industry. Without increasing contributions from diesel engines and newer diesel technologies, it would not be possible to successfully meet fuel consumption and CO2 emission reduction targets. Therefore, new regulations and applications have been put into action to address exhaust gas emission problems. Some exhaust gases have become prominent with regard to strong effects, such as NOx and soot. NOx contributes to acid rain, which has deteriorating effects on the ozone layer. In this study, flow and combustion characteristics of a diesel engine are investigated by using Computational Fluid Dynamics (CFD). Whole engine components are modeled and analyses are performed for entire speed range of the engine. Calculated crank angle dependent pressure and temperature values are used as boundary condition for reactive 3D CFD simulations. Reactive CFD simulations are performed with 45° sector geometry for the period that both valves are closed. In reactive simulations, RNG k-ε and Standard k- ε models are used to characterize turbulence flow field. A lagrangian approach is used for two-phase flow computations to simulate the liquid fuel injection. Commercially available CFD code called Forte Reaction Design and its sub-module Chemkin are used for three dimensional reactive simulations, moving grid generation and problem setup. Predicted in-cylinder pressure and apparent heat release rate are validated with experimental results. NOx and Soot formations as a result of combustion process are also investigated. Optimum level of NOx and Soot formation obtained with 8.5% EGR usage.

EN-ROUTE AIRSPACE CAPACITY AND TRAFFIC FLOW ENHANCEMENT USING GENETIC ALGORITHMS

Air transportation industry has gone under a rapid and continuous growth for the last four decades. International Civil Aviation Organization (ICAO) and airlines anticipate that annual growth rate of air traffic will be 4.5-5.1% until 2030. Airspace capacity management becomes more critical for the safety, efficiency and sustainable growth of the industry. En-route areas cover the largest portion of the controlled airspace and are subdivided into small segments referred to as ‘en-route sectors’ usually monitored and controlled by a single air traffic controller in the relevant Area Control Center (ACC). When air traffic demand reaches or exceeds the available en-route sector capacity, serious aircraft delays occur at airports or in airspace and lead to system-wide congestions and interruptions in air traffic services, airline flight schedules and airport operations, and therefore result in increased operational costs, passenger dissatisfaction and air traffic controller workload. This study presents a multiple entry point assignment model based on a genetic algorithm to minimize delays and increase throughput of a generic high-altitude en-route sector. The proposed approach intends to use more flexible direct route configuration without changing the sector geometry and provide a framework for a decision support system for air traffic flow and capacity planning and management. The available single entry point sector configuration and its multiple entry point assignment alternatives were compared for various traffic scenarios. Multiple entry point configurations provided up to 10% increase in throughput and significant reductions in average delay per aircraft compared to the single point entry configuration.

Modeling of Internal State and Performance of an Ironmaking Blast Furnace: Slot vs Sector Geometries

Mathematical modeling is a cost-effective method to understand internal state and predict performance of ironmaking blast furnace (BF) for improving productivity and maintaining stability. In the past studies, both slot and sector geometries were used for BF modeling. In this paper, a mathematical model is described for simulating the complex behaviors of solid, gas and liquid multiphase flow, heat and mass transfers, and chemical reactions in a BF. Then the model is used to compare different model configurations, viz. slot and sector geometries by investigating their effects on predicted behaviors, in terms of two aspects: (i) internal state including cohesive zone, velocity, temperature, components concentration, reduction degree, gas utilization, and (ii) performance indicators including liquid output at the bottom and gas utilization rate at the furnace top. The comparisons show that on one hand, predictions of internal state of the furnace such as fluid flow and thermo-chemical phenomena using the slot and sector geometries are qualitatively comparable but quantitatively different. Both sector and slot geometries give a similar cohesive zone shape but the sector geometry gives a higher cohesive zone near the wall and faster reduction. On the other hand, the two geometries can produce similar performance indicators including gas utilization at the furnace top and liquid output at the bottom. Such a study is useful in selecting geometry for numerically examining BF operation with respect to different needs.

Attenuation of rotating disk vibrations with sector-shaped plates in disk storage devices

A parametric study has been conducted to understand the mass loading contribution to rotating disk vibrations in disk storage devices. With sector-shaped plates retaining air between the two plates and a rotating disk, results have shown frequency crossing of disk flutter modes with non-zero nodal diameters where significant modal pattern switching is observed. Extending the range of the analysis to sector geometries provides insight into the disk vibrations on the degree of frequency separation and mode switching as a span angle of the sector-shaped plates and disk rotating speed. Design guidelines are formulated to minimize this mode crossing phenomenon and thus minimize the number of spindle disturbances present during track follow or the servotrack writing process.

Wind-stress feedback amplification of abrupt millennial-scale climate changes

The influence of changes in surface wind-stress on the properties (amplitude and period) and domain of existence of thermohaline millennial oscillations is studied by means of a coupled model of intermediate complexity set up in an idealized spherical sector geometry of the Atlantic basin. Using the atmospheric CO2 concentration as the control parameter, bifurcation diagrams of the model are built to show that the influence of wind-stress changes on glacial abrupt variability is threefold. First, millennial-scale oscillations are significantly amplified through wind-feedback-induced changes in both northern sea ice export and oceanic heat transport. Changes in surface wind-stress more than double the amplitude of the strong warming events that punctuate glacial abrupt variability obtained under prescribed winds in the model. Second, the average duration of both stadials and interstadials is significantly lengthened and the temporal structure of observed variability is better captured under interactive winds. Third, the generation of millennial-scale oscillations is shown to occur for significantly colder climates when wind-stress feedback is enabled. This behaviour results from the strengthening of the negative temperature-advection feedback associated with stronger northward oceanic heat transport under interactive winds.

Dynamic Airspace Configuration Using Approximate Dynamic Programming

On the basis of weather and high traffic, the Next Generation Air Transportation System envisions an airspace that is adaptable, flexible, controller friendly, and dynamic. Sector geometries, developed with average traffic patterns, have remained structurally static with occasional changes in geometry due to limited forming of sectors. Dynamic airspace configuration aims at migrating from a rigid to a more flexible airspace structure. Efficient management of airspace capacity is important to ensure safe and systematic operation of the U.S. National Airspace System and maximum benefit to stakeholders. The primary initiative is to strike a balance between airspace capacity and air traffic demand. Imbalances in capacity and demand are resolved by initiatives such as the ground delay program and rerouting, often resulting in systemwide delays. This paper, a proof of concept for the dynamic programming approach to dynamic airspace configuration by static forming of sectors, addresses static forming of sectors by partitioning airspace according to controller workload. The paper applies the dynamic programming technique to generate sectors in the Fort Worth, Texas, Air Route Traffic Control Center; compares it with current sectors; and lays a foundation for future work. Initial results of the dynamic programming methodology are promising in terms of sector shapes and the number of sectors that are comparable to current operations.

A multi-objective approach for Dynamic Airspace Sectorization using agent based and geometric models

A key limitation when accommodating the continuing air traffic growth is the fixed airspace structure including sector boundaries. The geometry of sectors has stayed relatively constant despite the fact that route structures and demand have changed dramatically over the past decade. Dynamic Airspace Sectorization is a concept where the airspace is redesigned dynamically to accommodate changing traffic demands. Various methods have been proposed to dynamically partition the airspace to accommodate the traffic growth while satisfying other sector constraints and efficiency metrics. However, these approaches suffer from several operational drawbacks, and their computational complexity increases fast as the airspace size and traffic volume increase. In this paper, we evaluate and identify the gaps in existing 3D sectorization methods, and propose an improved Agent Based Model (iABM) to address these gaps. We also propose three additional models using KD-Tree, Bisection and Voronoi Diagrams in 3D, to partition the airspace to satisfy the convexity constraint and reduce computational cost. We then augment these methods with a multi-objective optimization approach that uses four objectives: minimizing the variance of controller workload across the sectors, maximizing the average sector flight time, and minimizing the distance between sector boundaries and the traffic flow crossing points. Experimental results show that iABM has the best performance on workload balancing, but it is restrictive when it comes to the convexity constraint. Bisection- and Voronoi Diagram-based models perform worse than iABM on workload balancing but better on average sector flight time, and they can satisfy the convexity constraint. The KD-tree-based model has a lower computational cost, but with a poor performance on the given objectives.

Optimization of sector geometry of a compact cyclotron by random search and matrixmethods

We have developed two iterative techniques to optimize the pole profile of the hill of a cyclotron magnet. One of the optimization method is based on random search technique and in another method we have found out the unknown parameters by using the matrix method. In both these methods we have approximated the sector shape by a polynomial function of radius and the coefficients of polynomial are optimized to get the isochronous magnetic field. Compared with the previous shimming scheme, this method gives smooth pole shape of the hill and takes less computation time for optimization. The proposed optimization method has been used to design the magnet of a high current compact cyclotron where valleys are deep and the effect of fringe field is dominant at lower radii; however, it can be used for the low flutter magnet geometry as well. In the random search method we can also give the constraint on the coil current of the magnet.

Fractal structure of Hastings–Levitov patterns restricted in a sector geometry

A generalized form of the Hastings and Levitov algorithm for the simulation of diffusion-limited aggregation (DLA) restricted in a sector geometry is studied. It is found that this generalization with uniform measure produces ‘wedge-like’ fractal patterns in the physical space, whose fractal dimension and anisotropy exponent depend significantly on the opening angle β of the sector. The morphological properties and the overall shape of the patterns are analyzed by computing the angular two-point density correlation function of the patterns. We also find that the fractal dimension of the patterns with sinusoidal distributed measure depends weakly on β with almost the same dimension as the radial DLA cluster. The anisotropy exponent and the visual appearance of the patterns in this case are shown to be compatible with those of the advection-diffusion-limited aggregation clusters.

Extract and infer quickly

The modern hard disk drive is a complex and complicated device. It consists of 2--4 heads, thousands of sectors per track, several hundred thousands of tracks, and tens of zones. The beginnings of adjacent tracks are placed with a certain angular offset. Sectors are placed on the tracks and accessed in some order. Angular offset and sector placement order vary widely subject to vendors and models. The success of an efficient file and storage subsystem design relies on the proper understanding of the underlying storage device characteristics. The characterization of hard disk drives has been a subject of intense research for more than a decade. The scale and complexity of state-of-the-art hard disk drive technology calls for a new way of extracting and analyzing the characteristics of the hard disk drive. In this work, we develop a novel disk characterization suite, DIG (Disk Geometry Analyzer), which allows us to rapidly extract and characterize the key performance metrics of the modern hard disk drive. Development of this tool is accompanied by thorough examination of four off-the-shelf hard disk drives. DIG consists of three key ingredients: O (1) a track boundary detection algorithm; O (log n ) a zone boundary detection algorithm; and hybrid sampling based seek time profiling. We particularly focus on addressing the scalability aspect of disk characterization. With DIG, we are able to extract key metrics of hard disk drives, for example, track sizes, zone information, sector geometry and so on, within 3--20 minutes. DIG allows us to determine the sector layout mechanism of the underlying hard disk drive, for example, hybrid serpentine, cylinder serpentine, and surface serpentine, and to a build complete sector map from LBN to the three dimensional space of (Cylinder, Head, Sector). Examining the hard disk drives with DIG, we made a number of important observations. In modern hard disk drives, head switch overhead is far greater than track switch overhead. It seems that hard disk drive vendors put greater emphasis on reducing the number of head switches for data access. Most disk vendors use surface serpentine, cylinder serpentine, or hybrid serpentine schemes in laying sectors on the platters. The legacy seek time model, which takes the form of a + b √ d leaves much to be desired for use in modern hard disk drives especially for short seeks (less than 5000 tracks). We compare the performance of the DIG against the existing state-of-the-art disk profiling algorithm. Compared to the existing state-of-the-art disk characterization algorithm, the DIG algorithm significantly decreases the time to extract comprehensive sector geometry information from 1920 minutes to 7 minutes and 1927 minutes to 180 minutes in best and worst case scenarios, respectively.

Forecasting workload and airspace configuration with neural networks and tree search methods

The aim of the research presented in this paper is to forecast air traffic controller workload and required airspace configuration changes with enough lead time and with a good degree of realism. For this purpose, tree search methods were combined with a neural network. The neural network takes relevant air traffic complexity metrics as input and provides a workload indication (high, normal, or low) for any given air traffic control (ATC) sector. It was trained on historical data, i.e. archived sector operations, considering that ATC sectors made up of several airspace modules are usually split into several smaller sectors when the workload is excessive, or merged with other sectors when the workload is low. The input metrics are computed from the sector geometry and from simulated or real aircraft trajectories. The tree search methods explore all possible combinations of elementary airspace modules in order to build an optimal airspace partition where the workload is balanced as well as possible across the ATC sectors. The results are compared both to the real airspace configurations and to the forecast made by flow management operators in a French en-route air traffic control centre.

Reduced Stability of the Atlantic Meridional Overturning Circulation due to Wind Stress Feedback during Glacial Times

Abstract A previous study by Mikolajewicz suggested that the wind stress feedback stabilizes the Atlantic thermohaline circulation. This result was obtained under modern climate conditions, for which the presence of the massive continental ice sheets characteristic of glacial times is missing. Here a coupled ocean–atmosphere–sea ice model of intermediate complexity, set up in an idealized spherical sector geometry of the Atlantic basin, is used to show that, under glacial climate conditions, wind stress feedback actually reduces the stability of the meridional overturning circulation (MOC). The analysis reveals that the influence of the wind stress feedback on the glacial MOC response to an external source of freshwater applied at high northern latitudes is controlled by the following two distinct processes: 1) the interactions between the wind field and the sea ice export in the Northern Hemisphere (NH), and 2) the northward Ekman transport in the tropics and upward Ekman pumping in the core of the NH subpolar gyre. The former dominates the response of the coupled system; it delays the recovery of the MOC, and in some cases even stabilizes collapsed MOC states achieved during the hosing period. The latter plays a minor role and mitigates the impact of the former process by reducing the upper-ocean freshening in deep-water formation regions. Hence, the wind stress feedback delays the recovery of the glacial MOC, which is the opposite of what occurs under modern climate conditions. Close to the critical transition threshold beyond which the circulation collapses, the glacial MOC appears to be very sensitive to changes in surface wind stress forcing and exhibits, in the aftermath of the freshwater pulse, a nonlinear dependence upon the wind stress feedback magnitude: a complete and irreversible MOC shutdown occurs only for intermediate wind stress feedback magnitudes. This behavior results from the competitive effects of processes 1 and 2 on the midlatitude upper-ocean salinity during the shutdown phase of the MOC. The mechanisms presented here may be relevant to the large meltwater pulses that punctuated the last glacial period.

Study of the ATLAS MDT spectrometer using high energy CERN combined test beam data

In 2004, a combined system test was performed in the H8 beam line at the CERN SPS with a setup reproducing the geometry of sectors of the ATLAS Muon Spectrometer, formed by three stations of Monitored Drift Tubes (MDT). The full ATLAS analysis chain was used to obtain the results presented in this paper. The basic design performances of the Muon Spectrometer were verified. The stability of MDT calibration constants, the alignment system using optical devices and high energy tracks, as well as the intrinsic sagitta resolution of the Muon Spectrometer were studied and found to agree with expectations. The reconstruction of muon tracks using the combined information from both the Inner Detector and the Muon Spectrometer are also presented.

Electromagnetic design of superconducting dipoles based on sector coils

We study the coil layouts of superconducting dipoles for particle accelerators based on the sector geometry. We show that a simple model based on a sector coil with a wedge allows us to derive an equation giving the short sample field as a function of the aperture, coil width, cable properties, and superconducting material. The equation agrees well with the actual results of several dipole coils that have been built in the past 30 years. The improvements due to the grading technique and the iron yoke are also studied. The proposed equation can be used as a benchmark to judge the efficiency of the coil design, and to carry out a global optimization of an accelerator layout.