Circular Segments Research Articles

Numerical simulations of the aerodynamic response of circular segments with different corner angles by means of 2D URANS. Impact of turbulence modeling approaches

ABSTRACTThis paper presents the results of numerical and experimental investigations on the force coefficients and Strouhal numbers of circular segments considering different corner angles or chord to sagitta ratios. The research is motivated because these geometries are becoming increasingly popular in several engineering disciplines. The so-called D-section (semi-circular cylinder with a corner angle of ) has been experimentally studied in the past, since it is a galloping prone geometry. However, there is a lack of research for cases with different corner angles, and the numerical investigations related to this topic are particularly scarce. In this work, a 2D Unsteady Reynolds Averaged Navier–Stokes approach has been adopted aiming to study the circular segments at the sub-critical regime, considering corner angles from to , and the flow parallel to the rectilinear side. These sections were found to be particularly challenging since they present massive flow separation on the rectilinear side, alongside the inherent difficulties related to modeling the flow along curved surfaces at high Reynolds numbers. The impact of introducing low-Reynolds-number and curvature corrections in the SST turbulence model and the performance of the Transition SST model have been extensively studied.

Free space-planning solutions in the architecture of multi-storey buildings

Here some aspects of the development of steel frame structure design from the standpoint of geometry and morphogenesis of bearing steel structures of civil engineering objects. An alternative approach to forming constructive schemes may be application of curved steel elements in the main load-bearing system. As an example, it may be circular and parabolic arches or segments of varying outline and orientation. The considered approach implies creating large internal volumes without loss in the load-bearing capacity of the frame. The basic concept makes possible a wide variety of layout and design solutions. The presence of free internal spaces of large volume in buildings of a "skyscraper" type contributes to resolving a great number of problems, including those of communicative nature.

Contemporary approach to the design of circular form tools for complex-geometry part manufacture

Form tools have been used in industry for a number of decades. Their use is booming and such growing popularity can be attributed to minimized manufacturing costs and shorter manufacturing time. On the other side, one of the major drawbacks is the method of their design. It reflects in the constraints present in the machining of straight-line and circular arc segments of a workpiece. For each segment the rake angle has a different value, which imposes an additional constraint. In case it is necessary to use form tools to manufacture complex-geometry parts, the value of the rake angle would require to be zero. The paper presents contemporary design method of circular form tools by implementing CAD system. This way, it is not only provided a constant value of the rake angle across the entire cutting edge, which can be different from zero too, but also optimum tool geometry for machining a desired material. Additionally, the geometry of a form tool designed using a new method was experimentally tested.

Ex vivo culture of human atherosclerotic plaques: A model to study immune cells in atherogenesis

Background and aimsThe mechanisms that drive atherosclerotic plaque progression and destabilization in humans remain largely unknown. Laboratory models are needed to study these mechanisms under controlled conditions. The aim of this study was to establish a new ex vivo model of human atherosclerotic plaques that preserves the main cell types in plaques and the extracellular components in the context of native cytoarchitecture. MethodsAtherosclerotic plaques from carotid arteries of 28 patients undergoing carotid endarterectomy were dissected and cultured. At various time-points, samples were collected and analysed histologically. After enzymatic digestion, single cells were analysed with flow cytometry. Moreover, tissue cytokine production was evaluated. ResultsWe optimised the plaque dissection protocol by cutting plaques into circular segments that we cultured on collagen rafts at the medium–air interface, thus keeping them well oxygenated. With this technique, the relative presence of T and B lymphocytes did not change significantly during culture, and the sizes of lymphocyte subsets remained stable after day 4 of culture. Macrophages, smooth muscle cells, and fibroblasts with collagen fibres, as well as T and B lymphocyte subsets and CD16 natural killer cells, remained largely preserved for 19 days of culture, with a continuous production of inflammatory cytokines and chemokines. ConclusionsOur new model of ex vivo human atherosclerotic plaques, which preserves the main subsets of immune cells in the context of tissue cytoarchitecture, may be used to investigate important aspects of atherogenesis, in particular, the functions of immune cells under controlled laboratory conditions.

Particle swarm optimization for constrained circular-arc/line-segment fitting of discrete data points

In this paper, a new non-gradient-based optimization scheme is designed for constrained circle–circle/circle–line fitting of discrete data points. It contains two important technical components: (a) constrained least-squares fitting of circular arcs and line segments, and (b) specially designed particle swarm algorithm for optimal corner/edge points. Our approach is developed for both two-dimensional and three-dimensional cases. The results of numerical computation demonstrate the better performance of the proposed approach, compared to the conventional methods. It can be used for the accurate determination of sharp edges in the form of circular arcs and/or line segments measured in high-precision inspection and manufacturing.

The ultimate limit state of the underground circular tunnel segment lining

Circular tunnel segment lining with staggered joints in track tunnels of Prague Underground was found to be on the ultimate limit state; static analysis (mathematical modeling) is used to determine the causes which led to such situation. This situation is signalized by cracks and related deformations; lining load-limit coefficient can be used to determine the cause. Analysis is performed in the form of parametric study, where the variables are the values of geotechnical figures, the rigidity of the lining with staggered joints and the load of the lining. This paper focuses on analysis of reinforced concrete segmental lining Ø5.3 / 5.8 m (5 + 1 element) and cast iron Ø5.1 / 5.5 m (9 + 1 element). Parametric study using coefficient of loading limit for both of these cases in the Prague Underground leads to fast and relatively easy determination of the cause of the reaching of the ultimate limit state.

Deducing the form factors for shear used in the calculus of the displacements based on strain energy methods. Mathematical approach for currently used shapes

The paper presents an initial study concerning the form factors for shear, for a rectangular and for a circular cross section, being used an analytical method and a numerical study. The numerical study considers a division of the cross section in small areas and uses the power of the definitions in order to compute the according integrals. The accurate values of the form factors are increasing the accuracy of the displacements computed by the use of the strain energy methods. The knowledge resulted from this study will be used for several directions of development: calculus of the form factors for a ring-type cross section of variable ratio of the inner and outer diameters, calculus of the geometrical characteristics of an inclined circular segment and, using a Bool algebra that operates with geometrical shapes, for an inclined circular ring segment. These shapes may be used to analytically define the geometrical model of a complex composite section, i.e. a ship hull cross section. The according calculus relations are also useful for the development of customized design commands in CAD commercial applications. The paper is a result of the long run development of original computer based instruments in engineering of the authors.

Research on parametric modeling and grinding methods of bottom edge of toroid-shaped end-milling cutter

For a toroid-shaped end-milling cutter to have multi-structure features of tooth offset center and introversion of bottom edge, this article proposes a generalized parametric modeling method of the bottom edge, including a straight edge segment and a circular arc edge segment. And based on the parametric model, this article also deduces the corresponding tool path for grinding of the bottom edge’s rake and flank faces. The parametric modeling method is based on the geometric analytic equations while the grinding method is driven by the proposed parametric model and the parameters of rake and flank faces. The two methods can be applied to a bottom edge of a cutter with multi-structure features to guarantee G1 continuity at the two joints for connecting a circular arc edge with a straight edge and a conical helix edge, respectively. In order to verify the accuracy of proposed methods, experiments were carried out. The modeling and grinding experimental results verified the accuracy and utility of the methods.

Mechanical behavior of natural fiber-based isogrid lattice cylinder

This paper explores the compression behavior of eco-friendly natural fiber-based isogrid lattice cylinder made of pineapple leaf fibers and phenol formaldehyde resin matrix. The filament winding method and an appropriate curing system was used to prepare specimens. The mechanical behavior of the structure was determined by axial compressive test. The interfacial adhesions between pineapple leaf fibers and phenol formaldehyde resin contain physical and chemical bonding by analyzing Fourier transform infrared spectroscopy. For the lattice cylinder, corresponding theoretical and finite element models were proposed to simulate the mechanical properties. Compared with the measured values, the predicted values for the theory and the finite element method were approximately 77–96% of the values of the experimental data. The failure forms of lattice cylinders focus on delamination and fracture of circular rib segments adjacent to the crossover, in agreement with the analytical position of shear failure based on the finite element method, indicating the validity of the predicted model. After that, an orthogonal test was designed to explore the impacts of structural parameters on the mechanical behavior of the lattice cylinder. The results indicated that the main influence factor of special load and stiffness is the number of equal divisions of the circumference. The lattice cylinder can be treated as a truss core combined with skins to manufacture a hierarchical sandwich structure, for use in the construction of some parts of buildings, like the floor.

The influence of geometric imperfections in cardiovascular FSI simulations

We present a study of the fluid–structure interaction in an idealized end-to-end anastomosis of a vascular bypass-graft and an artery. Special attention is paid to the impact of geometric imperfections in the artery and the flow path of the upstream vessel segment on the hemodynamics. A partitioned solution approach is applied and developed further to solve the coupled problem in an implicit manner. To stabilize and accelerate the convergence of the staggered coupling iterations, an interface quasi-Newton least squares method is applied. While the finite volume method is used for the fluid mechanics subproblem, high-order finite elements serve to discretize the structural subproblem. A convergence study shows the efficiency of the high-order elements in the context of nearly incompressible, anisotropic materials used to model circular and irregular-shaped segments of an artery. The fluid–structure interaction simulations reveal a dominant influence of the upstream vessel’s curvature, which, however, decays rapidly in straight sections where the influence of geometric imperfections is dominant. Based on the proposed simulation approach, hemodynamic parameters such as the oscillating shear index can be directly linked to the shape and the intensity of the imperfections.

Modelling of energy demand from computer numerical control (CNC) toolpaths

It is important to accurately model the total electrical energy requirements in order to compare and select the least energy consumption toolpath in a manufacturing process. To enable this goal in this study, a feed axes energy demand model (which incorporates the weights of feed axes, machine vice, and workpiece) proposed in previous work by the authors was integrated and used to refine the energy consumption models for machine tools to analytically estimate the power and processing time, and hence energy required to execute a CNC toolpath. Furthermore, an algorithm for establishing energy prediction software with regards to numerical control (NC) codes was developed based on the proposed energy consumption model. The NC-code based analytical model and energy prediction software were both validated by undertaking slot milling of a 2D half bottle toolpath. Results show that shorter linear path lengths (i.e. G01) and circular path segments (i.e. G02 and G03 codes) were highly energy intensive. This is because for short length segments, the maximum feedrate may not be reached due to constraints imposed by acceleration and deceleration; the weights carried take a higher share of the load, and therefore increase the inertia effects on the drive. Thus, energy intensity in machining could be significantly reduced by selecting toolpaths with longer linear path segments. The knowledge obtained in this study would enable machining engineers to predict the electrical energy for toolpaths and hence enable selection of toolpaths for reduction of electrical energy demand in machining.

Spiral modes supported by circular dielectric tubes and tube segments

The modal properties of curved dielectric slab waveguides are investigated. We consider quasi-confined, attenuated modes that propagate at oblique angles with respect to the axis through the center of curvature. Our analytical model describes the transition from scalar 2-D TE/TM bend modes to lossless spiral waves at near-axis propagation angles, with a continuum of vectorial attenuated spiral modes in between. Modal solutions are characterized in terms of directional wavenumbers and attenuation constants. Examples for vectorial mode profiles illustrate the effects of oblique wave propagation along the curved slab segments. For the regime of lossless spiral waves, the relation with the guided modes of corresponding dielectric tubes is demonstrated.

Research Review on the Manufacturing Technology of Large-span Spatial Pipe Truss Structures of the Tongling Stadium

Aiming at the large cantilever triangle spatial pipe truss structure system of Tngling stadium, from the perspective of component processing technology, studying of machining technology for complex steel structure components, combining the new steel tube with existing commonly used hydraulic press, the smaller investment in equipment will meet the production requirements. In view of the small curvature angle bend, proposing the more straight pipe shrimp tube instead of the circular arc segment has solved the intersecting node production problems of the two small Angle steel pipes. In this paper, the results for complex pipe truss structure was processed for the future similar structure construction with popularization and application value.

A rapid and intelligent approach to design forming shape model for precise manufacturing of flanged part

Adjusting the part shape with complex flanges to compensate springback deformation is key to forming shape design for manufacturing rapidly and precisely. Classical forming shape design by displacement adjustment (DA) method using finite element (FE) simulation is usually time-consuming and not accurate enough for complex surface part in industrial application. In this paper, the forming shape is modeled by changing the relations of geometric features of part model with the new flange control surfaces directly. Control surface processing (CSP) method is presented including control surface trimming, cross section division, springback compensation, and extending to design forming shape model of doubly curved flange part with joggles rapidly. The algorithms of cross section curves division of control surfaces and subsequent subdivision of each curve with circular arc and line segments are proposed. A case-based reasoning (CBR) technique and gray relation analysis (GRA) are used to support the intelligent springback prediction of each bending segment of the cross section curve. The geometric data of control surface is expressed in XML format to realize the integration of the CAD-based tools of control surface division and compensation with the Web-based springback prediction system. The approach is demonstrated on an industrial aircraft wing rib part. The forming shape model could be designed rapidly by comparison with DA method. The part shape deviations of flange angle (−0.465° ~ 0.528°) and surface position (−0.3 mm ~ 0.3 mm) were detected by comparing the desired geometry with the actual digital formed part shape, and the results indicate that the approach can achieve the industrial part manufacturing rapidly and precisely.

Sulodexide Promotes Venous Contraction in Rat Inferior Vena Cava

Sulodexide (SDX) is a highly purified glycosaminoglycan composed of fast-moving heparin (80%) and dermatan sulfate (20%). SDX has both antithrombotic and profibrinolytic properties with reported benefits in chronic venous disease and other thrombotic and atherosclerotic vascular disorders. However, the effects of SDX on the vein wall structure and function are unclear. We have previously shown that matrix metalloproteinases 2 and 9 cause venous relaxation, and other studies have suggested that SDX may inhibit matrix metalloproteinase 9. The purpose of this study was to test whether SDX affects venous function and whether its venous effects are different from those in the arteries. Male rat inferior vena cava (IVC), abdominal aorta, and mesenteric artery were harvested and 3-mm circular segments were equilibrated under 0.5g, 2g, and 1g basal tension, respectively, in a tissue bath containing Krebs solution bubbled with 95% O2 5% CO2 at 37°C, and the changes in isometric contraction were recorded. Vessel segments were precontracted with the α-adrenergic receptor agonist phenylephrine (PHE, 3 × 10−7 M), and the changes in the vessel response to SDX (0.001-1 mg/mL) were measured. The % venous/arterial contraction or relaxation was calculated, and the data were presented as means ± standard error of the mean and analyzed with t-test, with P < .05 significant. In the IVC, aorta, and mesenteric artery, PHE (3 × 10−7 M) caused submaximal contraction that remained steady for at least 1 hour. In PHE-precontracted IVC, SDX caused concentration-dependent increases in contraction that reached a maximum at 1 mg/mL (SDX 62.8 ± 3.9 vs control 0.0; P < .01). In contrast, in PHE-precontracted aorta and mesenteric artery, SDX caused concentration-dependent relaxation compared with control (maximum 45.4 ± 6.0 vs 6.7 ± 6.6; 39.3 ± 6.2 vs 0.0, respectively; P < .05). SDX potentiates contraction in veins while causing relaxation in arteries. The mechanisms may involve differential effects of SDX on different matrix metalloproteinase subtypes, protease-activated receptors, and integrins in the veins vs arteries and need to be further examined. The results may have clinical implications as SDX may be helpful as a venotonic agent for chronic venous disease while promoting arterial dilation and decreasing arterial pressure.

A Novel Control Strategy for Roundabout System with Origin-Destination Flow Pattern

Abstract This study proposes and evaluates a novel control strategy that aims to regulate the roundabout approach inflow by taking into consideration its origin-destination demand pattern. The average density of the circular segment is controlled at a pre-defined range of optimal density which is derived using the Macroscopic Fundamental Diagram (MFD). A case study of a two-lane roundabout in Selangor, Malaysia, is developed in a microscopic simulation environment to study and test the effectiveness of the proposed control strategy. It is shown that the proposed control strategy could reduce the system travel time and increase throughput especially during medium to high level of demand. In addition, the sensitivity analysis reveals that its effectiveness is sensitive to the parameters’ setting such as: the roundabout lane geometry, origin-destination demand level, and traffic congestion level.

Improvement of point spread function (PSF) using linear- quadratic aperture

Since each of the modulated linear and quadratic apertures give better resolution as compared with that obtained in case of circular aperture. Hence, we believe that a combination of both linear and quadratic multilayer concentric circular aperture will give further improvement in resolution and contrast. Consequently, the following two models are assumed. The 1st aperture model is composed of successive quadratic, linear, and constant circular transmission segments from the center. In this model, the central quadratic distributed segment from the aperture is chosen in order to attenuate the low spatial frequencies. The 2nd aperture model is composed of four concentric segments. In this aperture, starting from the center, the 1st segment is dark central disk followed by a higher order, ρ 6, distribution, the next is linear, and the last has constant transmission segment. In this model, further spatial frequency attenuation is attained by the selection of the central dark disk followed by the ρ 6 distribution.The point spread function (PSF) of the described apertures is computed and compared with the corresponding annular and circular apertures. In addition, the coherent transfer function of the confocal microscope is computed using the two models of multilayer arrangement. The effect of the pinhole diameter upon the PSF of a standard CSLM using the two models of apertures is discussed. A MATLAB code is organized to perform all the numerical computations and plots.

An approach to consider the arterial residual stresses in modelling of a patient-specific artery

In this work, the residual stress state of a human common carotid artery is predicted using the so-called thermomechanical analogy approach. The purpose of the approach is to enable consistent mapping of residual stresses and the respective configuration from a circular arterial segment to a patient-specific arterial geometry. This is achieved by applying proper volumetric dilatations to the actual arterial stress-free in vivo geometry, which makes use of the analogy that states that the bending stresses can be obtained on an equivalent manner by applying proper thermal dilatations. The common carotid artery data are obtained in vivo from a healthy 28-year-old man using non-invasive methods. The predicted residual stresses of the common carotid artery are in good quantitative agreement with the data from prior work in this field. The approach is validated by predicting the common carotid artery zero-stress state configuration, where a sector-like (cut-open) state is obtained. With this approach, it is thus possible to predict the residual stresses as well as the configuration of patient-specific arterial geometry without the need to model its cut-open zero-stress configuration.

Layout problems for arc objects in convex domains

We introduce a new methodology for solving layout problems. Our objects and containers are bounded by circular arcs and line segments. We allow continuous object translations and rotations as well as minimal allowable distances between objects. For describing non-overlapping, containment and distance constraints the phi-function technique is used. We provide a general mathematical model as nonlinear programming problem with nonsmooth functions. We propose here the automatic feasible region generator, using phi-trees. The generator allows us to form ready-to-use systems of inequalities with smooth functions in order to apply efficient nonlinear optimisation procedures. We develop an efficient solution algorithm and original solver for layout problems which uses the core representation of inequlities in a sybmol form and provides exact calculation of Jacobian and Hessian matrixes. The search for local minima of NLP-problems is performed by IPOPT algorithm. An essential part of our local optimisation scheme is LORA algorithm that simplifies description of feasible region of the problem and reduces the runtime of local optimisation. It is due to this reduction our strategy can work efficiently with collections of composed objects and search for “good” local-optimal solutions for layout problems in reasonable time.

3-D thermo-mechanical modeling of plume-induced subduction initiation

Here, we study the 3-D subduction initiation process induced by the interaction between a hot thermo-chemical mantle plume and oceanic lithosphere using thermo-mechanical viscoplastic finite difference marker-in-cell models. Our numerical modeling results show that self-sustaining subduction is induced by plume–lithosphere interaction when the plume is sufficiently buoyant, the oceanic lithosphere is sufficiently old and the plate is weak enough to allow the buoyant plume to pass through it. Subduction initiation occurs following penetration of the lithosphere by the hot plume and the downward displacement of broken, nearly circular segments of lithosphere (proto-slabs) as a result of partially molten plume rocks overriding the proto-slabs. Our experiments show four different deformation regimes in response to plume–lithosphere interaction: a) self-sustaining subduction initiation, in which subduction becomes self-sustaining; b) frozen subduction initiation, in which subduction stops at shallow depths; c) slab break-off, in which the subducting circular slab breaks off soon after formation; and d) plume underplating, in which the plume does not pass through the lithosphere and instead spreads beneath it (i.e., failed subduction initiation). These regimes depend on several parameters, such as the size, composition, and temperature of the plume, the brittle/plastic strength and age of the oceanic lithosphere, and the presence/absence of lithospheric heterogeneities. The results show that subduction initiates and becomes self-sustaining when the lithosphere is older than 10 Myr and the non-dimensional ratio of the plume buoyancy force and lithospheric strength above the plume is higher than approximately 2. The outcomes of our numerical experiments are applicable for subduction initiation in the modern and Precambrian Earth and for the origin of plume-related corona structures on Venus.