Center Of Cylinder Research Articles

Lattice Boltzmann simulations of flow past a circular cylinder and in simple porous media

The single relaxation time variant of the Lattice-Boltzmann Method (LBM) is applied to the two–dimensional simulations of viscous fluids. Two flow geometries are considered: a single obstacle (circular cylinder) and a system of obstacles making up a simple, computer-created porous medium. A comparative study of two boundary schemes at the fluid–solid interface is performed. Although reasonable results can be achieved with the usage of (non-equilibrium) half-way bounce–back conditions, the interpolation-free scheme is recommended because of its better accuracy and stability. For flow past a circular cylinder, the lift and drag coefficients are computed together with the Strouhal numbers for periodically shedding vortices and validated against empirical relationships for a wide range of Reynolds numbers. The single cylinder case was also used for a novel comparison of two outlet schemes. Next, the system of obstacles that makes up a porous medium is created in two ways: by a regular arrangement of identical obstacles and by a simple randomization of cylinder centres and radii. The pressure loss in function of volumetric flow rate is compared with empirical relationships: the Darcy–Forchheimer law and the Ergun correlation. The impact of the LBM boundary schemes and the Reynolds number on the permeability and Forchheimer coefficients is studied for the two arrangements.

A Through-Dielectric Ultrawideband (UWB) Switched-Antenna-Array Radar Imaging System

A through-dielectric switched-antenna-array radar imaging system is shown that produces near real-time imagery of targets on the opposite side of a lossy dielectric slab. This system operates at S-band, provides a frame rate of 0.5 Hz, and operates at a stand-off range of 6 m or greater. The antenna array synthesizes 44 effective phase centers in a linear array providing <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda/2$</tex></formula> element-to-element spacing by time division multiplexing the radar's transmit and receive ports between 8 receive elements and 13 transmit elements, producing 2D (range vs. cross-range) imagery of what is behind a slab. Laboratory measurements agree with simulations, the air-slab interface is range gated out of the image, and target scenes consisting of cylinders and soda cans are imaged through the slab. A 2D model of a slab, a cylinder, and phase centers shows that blurring due to the slab and bistatic phase centers on the array is negligible when the radar sensor is located at stand-off ranges of 6 m or greater.

New methods for depth determination to horizontal cylinder

Three procedures can be utilized to determine the depth to the center of the horizontal cylinder from gravity profile. Firstly, the gravity profile is subjected to a simple filtering technique. Then, the maximum slope lines are drawn along the flanks of the filtered profile. The horizontal distances between the two slope lines for the positive part are measured at various amplitude levels. A plot of the horizontal distances against amplitude values will give an inclined straight line. The first procedure of depth estimation consists of measuring the distance between the points of intersection of the maximum slope lines at zero level background. This distance, for the positive or negative part, after it is multiplied by the empirical factor, gives directly the depth to the center of the horizontal cylinder. The other two procedures involve fitting a least square line to the inclined straight line of horizontal distances against amplitude values. Then, the maximum amplitude value of the filtered profile multiplied by an empirical factor is used to determine the depth, either graphically or through a simple equation. Accurate results have been achieved with low error percentages for a large number of gravity profiles due to synthetic horizontal cylinders having various depths and radii.

Cycloidal pendulum with a rolling cylinder

Free vibrations of a heavy homogeneous cylinder rolling in a cylindrical cavity whose directing curve is a brachistochrone are considered. The equation of motion of the cylinder is derived and the circular frequency of free vibrations of the cylinder center of mass is determined. An analogy between the cycloidal pendulum with a rolling cylinder and the classical cycloidal pendulum in the form of a material point is obtained.

Thermal stratification in an internal combustion engine due to wall heat transfer measured by laser-induced fluorescence

Laser-induced fluorescence of toluene was used to image spatial fluctuations of gas temperature in an optically accessible engine. These thermal inhomogeneities develop due to wall heat-transfer and convection during the compression stroke. They are known to be important for slowing heat release when operating the engine in compression auto-ignition (CAI) mode. The engine had a pent-roof four-valve head typical for automotive spark-ignited engines and a flat-top piston with a window. Measurements were performed in the central vertical symmetry plane of the cylinder with the engine motored and fed with nitrogen.Toluene was seeded homogeneously into the intake gas. Fluorescence was excited at 248nm and detected spectrally integrated. Toluene fluorescence decreases strongly with increasing temperature. Estimating the absolute in-cylinder temperature from isentropic compression along the measured pressure trace, we found the magnitude of this decrease in the engine to be consistent with literature data from heated flow-cell measurements. This calibration allowed for determination of the spatial fluctuations in temperature against the multi-cycle average temperature. Precision error, mostly from laser mode fluctuations, was between 1.6 and 4.0K depending on crank angle.The results show that the temperature–fluctuation field transitions during the compression stroke from small, evenly distributed inhomogeneities to much greater fluctuations, mostly localized near walls, but convecting into the cylinder center very late in the stroke. There are subtle differences in the spatial structure of the near-wall fluctuation field between cylinder head and piston top. Compiled from the entire imaged area, at top dead-center the standard deviation of the fluctuations was 1.9% of the temperature differential between gas phase and wall, consistent with corresponding literature data.

Lock-on characteristics behind two side-by-side cylinders of diameter ratio two at small gap ratio

The lock-on characteristics, the detailed interactions and downstream evolutions of the wakes behind side-by-side cylinders of unequal diameter (D/d = 2), spaced by a gap ratio 0.75 (G/D = 0.75), are investigated at Reynolds number 600 by the dye flow visualization, laser Doppler anemometry (LDA) and particle image velocimeter (PIV) velocity measurements. The lock-on frequency bands are studied by LDA and PIV at Reynolds number 2,000. The D, d and G are the diameters of the large, the small cylinders and the net gap between two cylinders, respectively. Periodic excitations, in form of rotary oscillation about the cylinder center, are applied to the large cylinder with the same amplitude. It is found that while the large cylinder is excited, two lock-on frequency bands of the wake behind the large cylinder are detected. These two lock-on frequency bands correspond to the primary and the one-third sub-harmonic lock-on of the wake behind large cylinder, respectively. These two lock-on frequency bands distribute symmetrically about the fundamental and the third superharmonic of the natural shedding frequency behind a single cylinder at the same Reynolds number. The left-shifted frequency band (1.8 ≤ fe/fos ≤ 2.0) is not considered as a locked-on frequency band because the phase difference between two excitation frequencies across fe/fos = 2.0 vary significantly. While the wake behind the large cylinder is locked-on at fe/3 (or fos), the gap flow becomes unbiased and the frequency of the wake behind small cylinder remains around the natural shedding frequency. Thus, the frequency band of 3.0 ≤ fe/fos ≤ 3.22 is also not locked-on because the phase difference in the narrow wake excited at fe/fos = 2.93 and 3.07 changes significantly. Note fe and fos denote the excitation frequency and the natural shedding frequency behind a single large cylinder, respectively.

Investigation on Diesel Engine Volume Impact Factors Based on Design of Experiment

In this paper, a parametric experiment model of V-8 diesel engine is developed. The parameters, such as the V-type angle, cylinder centre spacing, connecting rod length, flywheel width, body sinkage, cylinder head height, oil pan height and compression height are selected as research factors and their influences on the engine’s volume are studied by the orthogonal experiment. By each experiment, a new engine model is built by changing these factors’ values and the volume of the new model is calculated. Through analysis of variance, the significant relations between diesel engine volume and factors are given, which provide the criteria for the selection of the design parameters.

Kilovoltage Rotational External Beam Radiotherapy on a Breast Computed Tomography Platform: A Feasibility Study

To demonstrate the feasibility of a dedicated breast computed tomography (bCT) platform to deliver rotational kilovoltage (kV) external beam radiotherapy (RT) for partial breast irradiation, whole breast irradiation, and dose painting. Rotational kV-external beam RT using the geometry of a prototype bCT platform was evaluated using a Monte Carlo simulator. A point source emitting 178 keV photons (approximating a 320-kVp spectrum with 4-mm copper filtration) was rotated around a 14-cm voxelized polyethylene disk (0.1 cm tall) or cylinder (9 cm tall) to simulate primary and primary plus scattered photon interactions, respectively. Simulations were also performed using voxelized bCT patient images. Beam collimation was varied in the x-y plane (1-14 cm) and in the z-direction (0.1-10 cm). Dose painting for multiple foci, line, and ring distributions was demonstrated using multiple rotations with varying beam collimation. Simulations using the scanner's native hardware (120 kVp filtered by 0.2-mm copper) were validated experimentally. As the x-y collimator was narrowed, the two-dimensional dose profiles shifted from a cupped profile with a high edge dose to an increasingly peaked central dose distribution with a sharp dose falloff. Using a 1-cm beam, the cylinder edge dose was <7% of the dose deposition at the cylinder center. Simulations using 120-kVp X-rays showed distributions similar to the experimental measurements. A homogeneous dose distribution (<2.5% dose fluctuation) with a 20% decrease in dose deposition at the cylinder edge (i.e., skin sparing) was demonstrated by weighted summation of four dose profiles using different collimation widths. Simulations using patient bCT images demonstrated the potential for treatment planning and image-guided RT. Rotational kV-external beam RT for partial breast irradiation, dose painting, and whole breast irradiation with skin sparing is feasible on a bCT platform with the potential for high-resolution image-guided RT.

IMPULSIVELY STARTED FLOW TOPOLOGY AROUND TANDEM ARRANGEMENT OF TWO SQUARE CYLINDER AT INCIDENCE

Numerical study of impulsively started flow over two tandem square cylinders where former cylinder is rotated at angles (0-45deg) to main stream flow direction keeping later one inline to flow stream with a separation of twice the side length of square prism between the centers of cylinders is performed using FVM code solver FLUENT 6.3.26. Temporal developments of streamlines around cylinders are studied for laminar flow regime ( Re = 100). Flow pattern formed are categories into Type-1, Type-2, Type-3 &amp; Type-4 as per vortices growth at corresponding angle of incidence which are novel results of present study. Pressure distributions over the surface of cylinders are also monitored.

Bias Estimation and Calibration of a Pair of Laser Range Sensors

Abstract Laser range sensors (LRS) are ubiquitous in mobile robotics. They are usually modeled as having statistical error only, despite some having systematic error (bias) documented. This paper deals with bias estimation for laser range sensors in order to produce better calibration for two LRS. Assuming both LRS sense in the same plane, we propose an algorithm to estimate position and orientation of the second laser in the coordinate frame of the first laser, or vice versa. In order to truly have corresponding points in two LRS scans, we propose a calibration target. We use cylindrical objects of known radius, placed in the field of view of both LRS, perpendicularly to the sensing plane. Centers of circles that result from the intersection of the sensing plane and cylindrical objects then become corresponding points. Our algorithm first estimates cylinder centers, together with their respective uncertainties, and then using those results produces Euclidean transform estimate, together with it's respective uncertainty. The results of this algorithm can be used to gather very precise ground truth for people tracking applications with LRS. In case of occlusions, one has obvious benefits from two or more different viewpoints.

Joule Heating Effect on MHD Combined Convection in a Wavy Chamber Having Conducting Square Cylinder

The current simulation is focused on MHD combined convection flow and heat transfer characteristics in a square lid driven chamber. At the centre of this chamber a heat conducting solid square cylinder is located. Galerkin weighted residual finite element method is used to solve the governing equations of mass, momentum and energy. The left vertical wall of the chamber is mechanically lid driven and having temperature Tcold and velocity V0. But the right wall is sinusoidal wavy pattern and contains more temperature (Thot) than the left lid. The top and bottom surfaces are adiabatic. The behavior of the fluid for the values of Joule heating parameter J (0, 1, 4, 7) and Richardson number Ri (0.1, 1, 10) is described in details. The variations of the average Nusselt number (Nu), the mean temperature of the fluid ( ) and the temperature at cylinder centre ( ) for various Ri and J are also presented. Maximum rate of heat transfer is occurred for the lowest J at each Ri.Keywords: MHD; Wavy chamber; Conducting cylinder; Combined convection; Finite element formulation.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i1.8014J. Sci. Res. 4 (1), 39-49 (2012)

Numerical simulation of flow over two side-by-side circular cylinders

In the present paper, the unsteady, viscous, incompressible and 2-D flow around two side-by-side circular cylinders was simulated using a Cartesian-staggered grid finite volume based method. A great-source term technique was employed to identify the solid bodies (cylinders) located in the flow field and boundary conditions were enforced by applying the ghost-cell technique. Finally, the characteristics of the flow around two side-by-side cylinders were comprehensively obtained through several computational simulations. The computational simulations were performed for different transverse gap ratios (1.5≤ T/ D≤4) in laminar ( Re = 100, 200) and turbulent ( Re = 10 4) regimes, where T and D are the distance between the centers of cylinders and the diameter of cylinders, respectively. The Reynolds number is based on the diameter of cylinders, D. The pressure field and vorticity distributions along with the associated streamlines and the time histories of hydrodynamic forces were also calculated and analyzed for different gap ratios. Generally, different flow patterns were observed as the gap ratio and Reynolds number varied. Accordingly, the hydrodynamic forces showed irregular variations for small gaps while they took a regular pattern at higher spacing ratios.

Spectral Analysis of Magnetic Anomalies Due to a 2-D Horizontal Circular Cylinder: A Hartley Transforms Technique

The spectral analysis of the vertical effect of magnetic anomalies due to a 2-D horizontal circular cylinder is presented using Hartley transform. Hartley transform is an alternative approach to the famous complex Fourier transform. The depth to the center of the horizontal cylinder can be computed by a simple equation as a function of frequency. A synthetic example has been used to illustrate this technique and the validity of this approach has been proved by applying it to real data of a narrow band of quartz-magnetite in Mangampalli near Karimnagar town, India. The noise analyses were tested on the technique and showed a high level of confidence. The results of the field example are in good agreement with the ones published in the literature.

Optimization of block copolymer self-assembly through graphoepitaxy: A defectivity study

In this paper we report a synoptic methodology to evaluate and optimize the long-range order induced by graphoepitaxy of block copolymer (BCP) self-assembly. The authors focus the study on a BCP that produces hexagonally packed arrays of cylinders oriented perpendicular to the substrate with the copolymer film thickness greater than the trench depth. Prepatterned structures used in the graphoepitaxy approach have been generated by e-beam lithography on a commercial hydrogen silesquioxane resist. A suitable surface modification was accomplished by grafting a random polystyrene-r-poly(methyl methacrylate) copolymer on the prepatterned surfaces. The polystyrene-b-poly(methyl methacrylate) was spin-coated and annealed in order to generate the desired self-assembly. Since the self-assembly process is based on a thermodynamic mechanism, the induced defectivity needs to be reassessed with respect to the standard lithographic process. Using the cylinder center coordinates, a Delaunay triangulation is performed to find the nearest neighbors. This triangulation enables us to easily locate the disclinations which are characterized by having a number of nearest neighbors different from six. Thus, the number of defects can be quantified precisely. Additionally, this methodology affords an accurate evaluation of both the optimum mesa and trench critical dimensions yielding defect-free surfaces and may be extended to monitor the robustness of the BCP directed self-assembly process. Such diagnostics are critical in the implementation of large scale industrial processes.

Flow interference between a stationary cylinder and an elastically mounted cylinder arranged in proximity

The flow interference between two circular cylinders, one stationary and the other free to oscillate in the transverse direction, are studied numerically at Re=150. The incompressible Navier–Stokes equation in two space dimensions, an assumption that is expected to be valid at the considered Re, is solved by the characteristic-based-split (CBS) finite element method using the T4/C3 MINI triangular element. The center-to-center spacing between the two cylinders is fixed at 4 D, where D is the cylinder diameter. The angle of incident flow, α, with respect to the line through the two cylinder centers, varies within the range from α=0° to 90°. For the elastically mounted cylinder, the reduced mass considered is M r =2.0; the structural damping coefficient is assigned to be zero, which encourages high amplitude oscillations. For each α, the computations are conducted for a wide range of reduced velocities, U r . The flow interference is examined by scrutinizing (i) the frequency characteristics of the vortex shedding and oscillation; (ii) the dynamic response of the oscillating cylinder, including the amplitude of displacement, the drag and lift force characteristics and the phase relationship between the lift and the displacement series; and (iii) the flow response in terms of the instantaneous vorticity field. It was found that the flow interference type is significantly affected by the angle of the incident flow. As the cylinder is oscillated outside of the region of the wake behind the stationary cylinder ( α≥30°), it behaves similarly to its isolated counterpart. In contrast, if the cylinder is partially or entirely submerged within the upstream wake ( α<30°), then both the flow and body responses are substantially modified due to the vigorous interaction between the upstream wake and the oscillating cylinder; the response therefore belongs to the wake-induced regime. The U r range associated with the higher amplitude response is significantly shifted toward a higher U r . The maximum vibration amplitude builds up to a significantly higher level, even increasing the U r far beyond the resonance regime. In general, the wake flow associated with the wake-induced vibration (WIV) regime appears to be more unperiodic than does that corresponding to the vortex-induced oscillation regime. It is also revealed that both the vortex-cylinder and the shear layer-cylinder interaction mechanisms are responsible for the characteristics of the responses of oscillating cylinder. The larger momentum required for the higher oscillation amplitude is obtained from the duration of the energy transfer from the fluid to the cylinder, which is ascribed to the phase lag between the lift force and the cylinder displacement.

Laminar combined magnetoconvection in a wavy enclosure with the effect of heat conducting cylinder

In the current work, a numerical study of the flow characteristics on combined magnetoconvection in a lid-driven square enclosure, differentially heated, is carried out. This problem is solved by using finite element method of the partial differential equations, which are the heat transfer and stream function in Cartesian coordinates. The tests are performed for different solid–fluid thermal conductivity ratio, cylinder location and Richardson number while the Prandtl number, Reynolds number, magnetic and Joule heating parameters are kept constant. One geometrical configuration is used namely two undulations. The outcome obtained shows that the heat conducting inner square cylinder affects the flow and the heat transfer rate in the enclosure. The trend of the local heat transfer is found to follow a wavy pattern. Results are presented in terms of streamlines, isotherms, average Nusselt number at the heated wavy wall, average temperature of the fluid in the enclosure and dimensionless temperature at the cylinder center for different combinations of the governing parameters.

SU‐E‐J‐73: Preventing Errors in Radiotherapy: A Real‐Time System Using in Vivo EPID Dosimetry

Purpose: In vivo dosimetry using an electronic portal imaging device (EPID) may provide a uniquely effective means for preventing errors and may allow for real‐time beam interlocks. We present graphical processor (GPU)‐based fast EPID dose computation and simulate the sensitivity for detecting errors caused by patient mispositioning. Methods: We implemented an enhanced superposition convolution algorithm to compute the EPID dose. The patient was simulated using a digital cylinder phantom (15cm length and 15cm diameter) with air and bone structure built in. Setup parameters are: SAD 100cm, 12×12‐cm2 open field, 1.5×1.5×1.5‐mm3 dose grid, 6‐MV photon and isocenter at the center of cylinder. 2D dose images were obtained at 1.6‐cm depth of a water slab positioned 60‐cm below the isocenter to simulate the EPID readout. To examine errors caused by mispositioning, we shifted the phantom left‐and‐right and up‐and‐down and compared dose profiles to those with no shifts. Gamma value of each pixel was calculated as an index to identify dose mismatch. Dose failure was determined as gamma &gt; 1 using 3‐mm distance‐to‐agreement and 3% dose difference criteria. Results: Dose failures occur mainly in air‐tissue and bone‐tissue interfaces and in regions with rapid thickness change. Gamma is sensitive to the left‐and‐right shift, with a 3‐mm shift causing dose failure in ∼10% pixels; but is much less sensitive to the up‐and‐down shift, with dose failure detected only after a shift of several centimeters. Analysis with patient CT data sets is underway and will be presented. Conclusions: In vivo EPID dosimetry enabled by GPU‐based dose computation offers the potential for real‐time beam interlocks. Future directions include simulation of other error scenarios, optimization of dose computation, improved EPID modeling and comparison with measured EPID profiles.

Effect of Reynolds and Prandtl Numbers on Mixed Convection in an Obstructed Vented Cavity

A numerical investigation is conducted to analyze the steady flow and thermal fields as well as heat transfer characteristics in a vented square cavity with a built-in heat conducting horizontal solid circular obstruction. Hydrodynamic behavior, thermal characteristics and heat transfer results are obtained by solving the couple of Navier-Stokes and energy equations by using a weighted residuals Finite element method. The computation was made for different Reynolds number, Prandtl number ranging from 50 to 200 and from 0.71 to 7.1 at the three different convective regimes. Three different regimes are observed with increasing Ri: forced convection (with negligible free convection), mixed convection (comparable free and forced convection) and free convection dominated region (with higher free convection). The results are presented to show the effects of the Reynolds number, Prandtl number on flow pattern, thermal field and heat transfer characteristics at the three convective regimes. It is found that the flow and thermal field strongly depend on the Reynolds number, Prandtl number as well as Richardson number. As the Reynolds number and Prandtl number increase, the heat transfer rate increases but average fluid temperature in the cavity and temperature at the cylinder center decrease at the three convective regimes.Keywords: Mixed convection; Finite element method; Obstructed vented cavity; Prandtl number.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i2.4344 J. Sci. Res. 3 (2), 271-281 (2011)

In-cylinder air motion characteristics with variable valve lift in a spark ignition engine. Part 1: swirl flow

While variable valve actuation or variable valve lift (VVL) is used increasingly in spark ignition (SI) engines to improve the volumetric efficiency or to reduce the pumping losses, it is necessary to understand the impact of variable valve lift and timing on the in-cylinder gas motions and mixing processes. In this paper, the in-cylinder flow characteristics for reduced maximum valve lifts (MVLs) were examined in a modified four-valve optical SI test engine in which the combustion system is suitable for gasoline direct-injection (GDI) operations. Three different MVLs of 6.8 mm, 4.0 mm, and 1.7 mm were tested and particle image velocimetry was employed for the measurements. It is expected that the investigation will be helpful in understanding and improving GDI combustion when a VVL system is used. The results showed that a reduced MVL could significantly enhance the in-cylinder swirl motion in all three measured horizontal planes. By comparing the swirl ratios for different MVLs, it can be found that a reduced MLV can considerably increase the swirl ratio during the intake and compression processes. In general, the swirl centre induced by a lower MVL is more stable and can stay closer to the cylinder centre. In addition, the reduction in the MVL can also increase both the high-frequency fluctuating kinetic energy and the low-frequency fluctuating kinetic energy. These may contribute to an improvement in the air-fuel mixing but also to an increase in the cycle-to-cycle variation.

Wear Mechanisms Approach to Ni-P Electroless Plating Applied to Hardening Engine Cylinder

For practical operation conditions of engine cylinder, piston speed and lateral pressure to cylinder wall are determined as experimental factors. According to load and speed on 1mm~8mm below top dead center of cylinder in expansion stroke, the ranges of experimental parameters are chosen. Based on the quadratic regression rotation combination method, wear resistance experiment of hardening material is designed. The wear mathematic models of Ni-P electroless plating is established, and three-dimensional curved surfaces for load-speed-wearing value are drawn. The results show that the Ni-P electroless plating can increase relative wear resistance of cylinder by 5 times. By analysis of wear mechanisms of hardening material and wear resistance, the material is perfect for hardening engine cylinder wall.