Two-dimensional Geometric Model Research Articles

Influence of chamber structure on arc quenching in multigap system

In order to improve the arc quenching ability of the multigap system, it is important to know the principle of arc quenching and how the chamber structure affects the arc development process in the multigap system. In this study, the two-dimensional geometric model of the multigap system is established based on the magnetohydrodynamics theory in COMSOL multiphysics simulation platform. The principle of arc quenching in the multigap system is explained in detail by analysing the physical characteristics of the arc in the multigap system. The simulation result shows that the arc is compressed at large scales in the semi-closed chambers of the multigap system, which results in an instantaneous temperature rise of the arc, thus, forming the self-expanding airflow. The strong self-expanding airflow cuts off the arc channel and blocks the energy supply of the arc. The influence of the chamber structure on arc quenching in the multigap system is manifested in the fact that proper improvement of the width and depth of the chamber subserves arc cooling, the reduction of the deflection angle and the increment of the number of the chambers are conductive to arc extinction.

Simulating an Object’s Altitude for Two-Position Systems

A simulation problem for echo signals of two-position radar systems is considered. A four-point configuration of the two-dimensional geometric model is proposed to solve it. Relations are obtained for the arrangement of radiators of the model provided that the signals at both reception points are cophased. Based on these relations, we design an iteration algorithm to form the matrix of radiators to extend the range of possible locations of the simulated object. The obtained theoretical results are confirmed by numerical simulation methods.

Correction Method for Hydraulic Conductivity Measurements Made Using a Fixed Wall Permeameter

Hydraulic conductivity measurement through a fixed wall permeameter is a common practice to obtain the fluid transmissibility characteristics of soil matrix; however, sidewall leakage due to rigid wall effect may significantly influence the observed values for coarse-grained soils. In this study, the boundary flow error was identified through characterizing the geometrical properties of voids adjacent to the sidewall, and a parameter known as the boundary void ratio (eb) was proposed to account for this effect. The findings suggest that a fixed wall cell containing coarse soils would unavoidably generate extra voids at the interface between soil grains and inner rigid wall, contributing to a larger eb at the wall than void ratio within the soil bed; the measured hydraulic conductivity is increased primarily due to the apparatus-induced error. A two-dimensional geometric model was then established to estimate the eb value for uniformly sized coarse soils confined by a rigid permeameter wall, based on which a method was obtained for eliminating the boundary flow error from a fixed wall cell. The mathematical method was finally validated against experimental data from existing literature. It can be concluded that the boundary condition at sidewall featuring unwanted gaps lead to overestimation of the coefficient of permeability; however, the proposed correction method could adequately eliminate the boundary flow error for uniformly sized coarse-grained soils tested within a rigid wall cell.

Analysis of VIP-BWR reactor core physics experiments on UO2 and MOX mockup fuel assemblies - part 2: analysis with SIMULATE5

ABSTRACT Analysis of the three test cores in the VIP-BWR program was performed in a two-dimensional geometrical model with CASMO5 coupled with the JENDL-4.0-based neutron data library, and reported in the previous paper. Following the study, interpretation of the experiments were carried out in a three-dimensional geometrical model with SIMULATE5 for the code validation study. The nuclear libraries for the SIMULATE5 calculations were generated with CASMO5 with the JENDL-4.0-based neutron data library. The effective multiplication factors of the critical cores ranged from 0.9983 to 1.0023 with measurement uncertainties of 0.0003 to 0.0004 (one σ). The root mean squares of (the calculated/the measured-1) for the fission rates at the core-mid plain of all the measured fuel rods were about 3% for the three cores. It was noticed that the calculations underestimated the fission rates of the UO2 fuel rods and overestimated those of the MOX fuel rods for the test cores loaded with MOX fuel rods, which was consistent with trends in the preceding analysis studies of the VIP-BWR program and other MOX core experiments, and the biases were confirmed in the calculation results of power distributions in MOX-fueled light water reactor cores.

Simulation of air-void system in hardened concrete using a geometrical model

In this paper, a two-dimensional geometric model is developed to characterise the air-void system in hardened cement paste. This model consists of non-overlapping circular voids of different size classes randomly placed in the cementitious matrix of a specific size. The major output of this model is the distance of a specific void from its nearest neighbour (void–void spacing). The cumulative distribution function of the nearest void–void spacing fits well the Rosin–Rammler model, from which the probability distribution function is derived. The number and distribution of the voids is obtained from the chord length measurement based on the linear-traverse method. The effect of paste content and air-void saturation on the void spacing is investigated to illustrate gradual increase in void spacing with a higher paste content or the partial filling of air voids. This model is validated by the good correlation between the calculated spacing factor and the tensile strain capacity of concrete from length-change measurement.

ABOUT INVARIANCE OF ANGLE NOISE DISTRIBUTION PARAMETERS BY AN ARBITRARY N-POINT GEOMETRIC MODEL TO VIEWING ANGLE

In this article we consider a problem of reliable modeling of echo signals and angle noise of distributed objects using twodimensional geometric models with random statistically unrelated signals. The conditions that ensure the invariance of distribution parameters of the angle noise generated by an arbitrary N-point configuration of a two-dimensional geometric model are obtained. In the particular case of a model whose emitters are supplied with signals of equal power, the conditions of invariance are reduced to the location of the model points on the plane in the form of a regular polygon. These results can be used to synthesize mathematical models used for simulating reflections from distributed objects and for developing a hardware-software complex for the simulation of electromagnetic fields reflected from the Earth surface, atmospheric inhomogeneities, the sea surface, etc.

An efficient GUI update for BEM-FEM mixed mesh generation

In this paper, it is proposed an efficient GUI for the treatment of two-dimensional physical geometric models and the generation of mixed meshes of boundary and finite elements, respectively, BEM and FEM. The methodology adopted is to use the BEMLBA2D GUI, a special purpose educational program, aiming to illustrate the functionality and main characteristics of the hybrid modeling. The idea is to generate the FEM mesh, using Delaunay triangles, from the BEM mesh. The verification of the methodology is attested by specific examples of complex geometry with holes, inclusions, and cracks, aiming to validate the use of mixed meshes.

The two-dimensional distributed object four-point model based on correlated signals emitters

The paper considers methods for modeling fluctuations of the phase front of an electromagnetic wave reflected from a radar object (reflections) using models that emit statistically related signals. Previously, such models were considered only in relation to objects distributed over a single angular coordinate. A two-dimensional geometric model, emitting statistically related signals, was proposed for replacement of reflections from radar objects distributed over two angular coordinates. The emitters of the model are located at the vertices of the square. Expressions are obtained for determining the characteristics of signals supplied to the emitters of such model, at which the model provides the required parameters of the probability distribution density of the angular noise of the distributed object. Within the framework of the model under study, it is proved that it is possible to control the parameters of the probability density distribution of angular noise along two coordinate axes independently. The equivalence of the four-point partially coherent model and the five-point incoherent in terms of providing the probability characteristics of the angular noise is shown, and the limits of this equivalence are also determined. The proven equivalence of models allows developing an apparatus for the synthesis of spectral-correlation characteristics.

A SPECTRAL APPROACH TO THE SYNTHESIS OF GEOMETRIC MODELS OF DISTRIBUTED OBJECTS

In this article we consider a problem of reliable modeling of echo signals and angle noise of distributed objects using twodimensional geometric models with random statistically unrelated signals. A method for determining the spectral power density of signals applied to emitters of a geometric model, which makes it possible to reliably model angle noise of a distributed object, is proposed. Analytical relations are obtained for calculating the spectral power density of signals applied to the emitters of the five-point model for a number of typical situations that arise when modeling reflections of distributed objects. The proposed approach is applicable for any number of emitters of the model and makes it possible to synthesize models with the given spectral-correlation characteristics of angle noise of both one-dimensional and multidimensional objects equally conveniently.

A raytracing method to create inhomogeneous wave fields for collaborative virtual reality systems

A new rapid, raytracing method was developed and implemented for collaborative virtual reality systems. The goal of the method was to auralize historic acoustic venues in Rensselaer’s Collaborative-Research Augmented Immersive Virtual Environment Laboratory (CRAIVE-Lab). The CRAIVE-Lab provides a physical/digital environment for collaborative tasks using seamless video from multiple projectors and a 128-channel wave-field system with 6 additional ceiling loudspeakers. For the raytracing method, scanned floor plans are marked up by the user to create a two-dimensional geometric room model to calculate the temporal and spatial early-reflection pattern for the horizontal array of 128 loudspeakers resulting in an individual impulse response for each of the 128 loudspeakers. For this purpose, the loudspeaker array is virtually placed within the floor plan to calculate the impulse responses at each loudspeaker position considering the angles of incidence. The user can define wall materials and a directivity pattern for each sound source. The late reverberation tail is generated using a stochastic model based on the volume and surface characteristics of the space. An individual exponentially decaying reverberation tail is computed for each of the 134 loudspeakers with frequency-specific decay times. [Work supported by NSF Grant Nos. #1229391 and CISL.]

Improving the performance of finite element simulations on the wheel-rail interaction by using a coupling strategy.

Over the past few years, a number of implicit/explicit finite element models have been introduced for the purpose of tackling the problems of wheel–rail interaction. Yet, most of those finite element models encounter common numerical difficulties. For instance, initial gaps/penetrations between two contact bodies, which easily occur when realistic wheel–rail profiles are accounted for, would trigger the problems of divergence in implicit finite element simulations. Also, redundant, insufficient or mismatched mesh refinements in the vicinity of areas in contact can lead to either prohibitive calculation expenses or inaccurate implicit/explicit finite element solutions. To address the abovementioned problems and to improve the performance of finite element simulations, a novel modelling strategy has been proposed. In this strategy, the three-dimensional explicit finite element analysis is seamlessly coupled with the two-dimensional geometrical contact analysis. The contact properties in the three-dimensional finite element analyses, such as the initial “Just-in-contact” point, the exact wheel local rolling radius, etc., which are usually a priori unknown, are determined using the two-dimensional geometrical contact model. As part of the coupling strategy, a technique has been developed for adaptive mesh refinement. The mesh and mesh density of wheel–rail finite element models change adaptively depending on the exact location of the contact areas and the local geometry of contact bodies. By this means, a good balance between the calculation efficiency and accuracy can be achieved. Last, but not least, the advantage of the coupling strategy has been demonstrated in studies on the relationship between the initial slips and the steady frictional rolling state. Finally, the results of the simulations are presented and discussed.

Calculation of Iron Loss of Medium-sized High Voltage Motor which Have Axial Ventilation Holes in Rotor

When optimizing the ventilation and cooling system of medium-sized high power density asynchronous motor, it is found that the temperature rise of the motor can be greatly reduced after punching the axial ventilation holes in the rotor yoke, but the traditional method based on the magnetic circuit method cannot accurately calculate the motor iron loss of this new structure. In this paper combined with the finite element field-circuit-motion coupled analysis method, taking YXKK355-4, 355kW and YKK400-4, 400kW medium-sized high voltage asynchronous motor for example, a two-dimensional geometric model and mathematical model of the motor are established, then the iron loss calculation method is improved. Using this method not only the iron loss value of the whole motor can be obtained, but also the specific distribution of iron loss in different areas of the motor can be known, and the correctness of the simulation results is proved by experiments.

ANALYSIS OF MAGNETIC FIELD DISTRIBUTION IN MATRIX OF MAGNETIC SEPARATOR WITH LAMELLAR POLYGRADIENT MEDIUM

The distribution of the magnetic field in the working zones of synthesized polygradient media is studied using a computational experiment. The distribution of the magnetic field is carried out by the numerical finite element method, realized with the help of the ELCUT program complex. It is substantiated that instead of studying the field distribution in the entire interpolar zone of arbitrary structure, it can limited by the field studies in a characteristic, periodically repeating region, taking into account its symmetry. For the studied structural compositions of polygradient media using the ELCUT program tools, two-dimensional geometric models of the working interpolar zones have been developed, taking into account generally accepted engineering assumptions. A comparative analysis of the distribution of induction and force function of the magnetic field in the working gaps of the synthesized structures of a lamellar polygradient medium of a given configuration is performed

Change propagation prediction: A formal model for two-dimensional geometrical models of products

A product is redesigned by integrating structural or functional modifications to satisfy new needs or requirements. Iterations are also necessary to fine-tune product definition during the initial design process. In both cases, engineering changes are the means by which the product evolves. However, changes are propagated from component to components and from function to functions, leading to nonvalue development activities with extra costs and delays. These engineering changes may have harmful impacts on industrialization and manufacturing; they can drastically hinder efforts to ensure faster time-to-market. Research works currently seek to model, predict, analyze, and assess the impacts of engineering changes and their propagations. This article focuses on changes in a two-dimensional geometrical product model and proposes a new change prediction approach based on two steps. First, the dependencies between the parameters of structural components are identified through experiments. These dependencies are characterized qualitatively, quantitatively, and by formal equations. The changes are then propagated through the network of dependencies, and their consequences are computed. A geometric two-dimensional model of a bicycle is used to illustrate the approach. The results are discussed, and the main contributions of the approach are highlighted while further research paths are presented at the end of this article.

Computational Fluid Dynamics Simulation of High Speed Jet Under Different Input Pressures

The aim of this study is to execute the computational fluid dynamics (CFD) simulation of high speed jet under different input pressures (i.e., 80, 120, 160, 200, and 240 MPa). In particular, this study focuses on the pressure distributions and streamlines of the orifice in high speed jet, primarily because the orifice plays a role in accelerating the flow of liquid, having significant effects on the working performance of high speed jet. Firstly, the two-dimensional geometric model of high speed jet is established on the basis of the actual operational conditions. Next, the unstructured grids of high speed jet are generated by means of ICEM CFD 16.0. Virtually, the computational fluid dynamics simulation of high speed jet is a two-phase flow (gas-liquid) problem, so the homogeneous (Eulerian-Eulerian) two-phase model is employed to carry out the gas-liquid interaction. Particularly, the turbulent flow computation of high speed jet is carried out with procedures based on the Reynolds-averaged Navier-Stokes (RANS) equations. As the flow of high speed jet is highly turbulent, the RNG k-ɛ turbulence model derived by Yakhot et al. (1992) is utilized in this study. Finally, the computational fluid dynamics (CFD) simulation of high speed jet is implemented by using the CFX-Solver in ANSYS CFX 16.0. The simulation results show that when liquid flows through the orifice, the pressure of flows decreases swiftly, whereas the velocity of flows skyrockets to the maximum value and then decreases slightly. In addition, the relationship between the working pressure and input pressure and the relationship between the working velocity and input pressure are achieved, which could provide certain theoretical guidance for predicting the working pressure and velocity of high speed jet based on real input pressures.

The Influence of Thermal Radiation on Effective Thermal Conductivity in Porous Material

Effective thermal conductivity is an important parameter of porous materials for measurement of heat insulation performance. Two-dimensional geometrical models based on micrographs of real material were constructed in this paper and the finite element approach was applied for thermal analysis, the effective thermal conductivity was calculated. The influence of radiation heat transfer, temperature, and porosity on thermal conductivity were analyzed. The results show that conduction heat transfer plays an important role in total heat transfer and the influence of radiation heat transfer was small at low temperature. Because of the increase in radiation heat transfer, the temperature gradient decreased obviously at high temperature and the heat flux lines passed through the pores and became relatively smooth; thus the radiation heat transfer plays an important role in total heat transfer at high temperature and the influence of radiation heat transfer cannot be ignored. Thermal conductivity for a high porosity value will be greater than thermal conductivity for a low porosity value at high temperature. This paper provides guidance for predicting thermal conductivity and reducing the heat transfer efficiency of porous materials at high temperature.

The tip point feature of pakchoi recognition and virtual plant modelling based on image processing

Abstract: Image processing is one of the key technologies in virtual agriculture. In this paper, the image processing technology is combined in pakchoi virtual modeling. By extracting the contour curve, the minimum circumscribed plants and the feature of tip points of the pakchoi, a virtual two-dimensional geometric model of pakchoi was established. This modelling method is simple and the model can reflect the number of leafs, leaf relative size and the growth of plant. This study has important significance in researching the growth model of pakchoi, image feature point recognition and virtual modelling.

Numerical Simulation of Closing Process of Shuttle Check Valve

For studying the kinetic characteristics of passive shuttle check valve at the moment that it closes its valve core on the condition of high pressure differences, this paper first constructs the equation of motion of the valve core and twodimensional geometrical model by using computation fluid dynamics method, then with the help of the calculation method and physical model provided by Fluent software, employing the dynamic mesh and user-defined functions, simulates the unsteady flow in the valve core’s closing process under the different pressure fluctuations, and obtains the stress nephogram, the velocity vector diagram, the speed curve, and pressure curve of the interior flow field of the valve. The results show that the bigger the value of valve fluctuation is, the larger the fluid pressure that the valve core is subjected to, the openness of the core and the speed fluctuation of the core are, and that in the case of sudden decompression at the entrance, the core can be shut down quickly with the steady speed field and pressure field. The simulation results are conducive to the design and optimization of structure parameter of shuttle check valve.

A Map for Social Navigation in the Human Brain

Deciphering the neural mechanisms of social behavior has propelled the growth of social neuroscience. The exact computations of the social brain, however, remain elusive. Here we investigated how the human brain tracks ongoing changes in social relationships using functional neuroimaging. Participants were lead characters in a role-playing game in which they were to find a new home and a job through interactions with virtual cartoon characters. We found that a two-dimensional geometric model of social relationships, a "social space" framed by power and affiliation, predicted hippocampal activity. Moreover, participants who reported better social skills showed stronger covariance between hippocampal activity and "movement" through "social space." The results suggest that the hippocampus is crucial for social cognition, and imply that beyond framing physical locations, the hippocampus computes a more general, inclusive, abstract, and multidimensional cognitive map consistent with its role in episodic memory.

Methods of integrated computer-aided design of structural elements of the aircraft

Previously applied methods of designing aircraft based on two-dimensional geometric models that made it impossible to take into account all the necessary design and technological features. It was a prerequisite for the development of an integrated methodology that includes design and computer simulation of three-dimensional parametric design of the aircraft as a whole and its individual parts [2-5]. In this paper, the method of computer-aided design stringer at the master model geometry and space allocation wing aircraft.In article approaches to integrated computer-aided design. These types of problems preliminary design and the method of calculation of typical aircraft structural elements for example longitudinal force element sets as stringer. Also, the algorithm constructs a fully stringer system aided design of integrated Siemens NX. What can shorten the design time and use it as a reference for the calculation and further change just values for other dimensions stringers.Methods integrated design ensure the application of standard parametric analytical stringers in the calculation of aerodynamics and strength, life and vitality, weight of the aircraft and its alignment, safety of structures, as well as technological preparation of production and quality control, maintenance and repair.Considered aided design techniques can be extended to other than the stringers typical elements airframe.