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Number of results: 9
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Abstract

The paper presents a numerical model of the novel design of the axial magnetic bearing with six cylindrical poles. The motivation behind this idea was to eliminate vibrations in rotating machinery due to the axial load. Common conception of such a bearing provides a single component of the electromagnetic force, which is not enough to reduce transverse and lateral vibrations of the armature. The proposed design allows for avoiding wobbling of the disc with the use of a few axial force components that are able to actively compensate the axial load and stabilise the disc in a balanced position. Before a real device is manufactured, a virtual prototype should be prepared. The accurate numerical model will provide essential knowledge about the performance of the axial magnetic bearing.
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Abstract

The use of periodic structures as noise abatement devices has already been the object of considerable research seeking to understand its efficiency and see to what extent they can provide a functional solu- tion in mitigating noise from different sources. The specific case of sonic crystals consisting of different materials has received special attention in studying the influence of different variables on its acoustic performance. The present work seeks to contribute to a better understanding of the behavior of these structures by implementing an approach based on the numerical method of fundamental solutions (MFS) to model the acoustic behavior of two-dimensional sonic crystals. The MFS formulation proposed here is used to evaluate the performance of crystals composed of circular elements, studying the effect of varying dimen- sions and spacing of the crystal elements as well as their acoustic absorption in the sound attenuation provided by the global structure, in what concerns typical traffic noise sources, and establishing some broad indications for the use of those structures.
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Abstract

The aim of the present work is to verify a numerical implementation of a binary fluid, heat conduction dominated solidification model with a novel semi-analytical solution to the heat diffusion equation. The semi-analytical solution put forward by Chakaraborty and Dutta (2002) is extended by taking into account variable in the mushy region solid/liquid mixture heat conduction coefficient. Subsequently, the range in which the extended semi-analytical solution can be used to verify numerical solutions is investigated and determined. It has been found that linearization introduced to analytically integrate the heat diffusion equation impairs its ability to predict solidus and liquidus line positions whenever the magnitude of latent heat of fusion exceeds a certain value.
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Abstract

Several methods can be applied for analyses of the acoustic field in enclosed rooms namely: wave propagation, geometrical or statistical analysis. The paper presents problems related to application of the boundary elements method to modelling of acoustic field parameters. Experimental and numerical studies have been combined for evaluation of acoustic impedance of the material used for the walls of a model room. The experimental studies have been carried out by implementing a multichannel measuring system inside the constructed model of an industrial room. The measuring system allowed simultaneous measurements of the source parameters - the loudspeaker membrane vibration speed, the acoustic pressure values in reception points located inside the model space as well as phase shifts between signals registered in various reception points. The numerical modelling making use of the acoustic pressure values measured inside the analyzed space allowed determination of requested parameters of the surface at the space boundary.
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Abstract

The impact of the transversely-oriented sinusoidal wall corrugation on the hydraulic drag is investigated numerically for the flow through the channel of finite width and with flat sidewalls. The numerical method, based on the domain transformation and Chebyshev-Galerkin discretization, is used to investigate the flow resistance of the laminar, parallel and pressure-driven flow. The obtained results are compared to the reference case, i.e., to the flow through the channel with rectangular cross section of the same aspect ratio. Simple explanation of the gain in the volumetric flow rate observed in the flow through spanwise-periodic channel with long-wave transversely-oriented wall corrugation is provided. In the further analysis, pressure drop in the flows with larger Reynolds numbers are studied numerically by means of the finite-volume commercial package Fluent. Preliminary experimental results confirm the predicted tendency.
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Abstract

For solving a partial different equation by a numerical method, a possible alternative may be either to use a mesh method or a meshless method. A flexible computational procedure for solving 1D linear elastic beam problems is presented that currently uses two forms of approximation function (moving least squares and kernel approximation functions) and two types of formulations, namely the weak form and collocation technique, respectively, to reproduce Element Free Galerkin (EFG) and Smooth Particle Hydrodynamics (SPH) meshless methods. The numerical implementation for beam problems of these two formulations is discussed and numerical tests are presented to illustrate the difference between the formulations.
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Abstract

This work focuses on finding a numerical solution for vehicle acoustic studies and improving the usefulness of the numerical experimental parameters for the development stage of a new automotive project. Specifically, this research addresses the importance of modal cavity damping for vehicle exerts during numerical studies. It then seeks to suggest standardized parameter values of modal cavity damping in vehicular acoustic studies. The standardized value of modal cavity damping is of great importance for the study of vehicular acoustics in the automotive industry because it would allow the industry to begin studies of the acoustic performance of a new vehicle early in the conception phase with a reliable estimation that would be close to the final value measured in the design phase. It is common for the automotive industry to achieve good levels of numerical-experimental correlation in acoustic studies after the prototyping phase because this phase can be studied with feedback from the simulation and experimental modal parameters. Thus, this research suggests values for modal cavity damping, which are divided into two parts due to their behaviour: ξ(x) = -0.0126(x − 100) + 6.15 as a variable function to analyse up to 100 Hz and 6.15% of modal cavity damping constant for studies between 30 Hz and 100 Hz. The sequence of this study shows how we arrived at these values.
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Abstract

High-alloy corrosion-resistant ferritic-austenitic steels and cast steels are a group of high potential construction materials. This is evidenced by the development of new alloys both low alloys grades such as the ASTM 2101 series or high alloy like super or hyper duplex series 2507 or 2707 [1-5]. The potential of these materials is also presented by the increasing frequency of sintered components made both from duplex steel powders as well as mixtures of austenitic and ferritic steels [6, 7]. This article is a continuation of the problems presented in earlier works [5, 8, 9] and its inspiration were technological observed problems related to the production of duplex cast steel. The analyzed AISI A3 type cast steel is widely used in both wet exhaust gas desulphurisation systems in coal fired power plants as well as in aggressive working environments. Technological problems such as hot cracking presented in works [5, 8], with are effects of the rich chemical composition and phenomena occurring during crystallization, must be known to the technologists. The presented in this work phenomena which occur during the crystallization and cooling of ferritic-austenitic cast steel were investigated using numerical methods with use of the ThermoCalc and FactSage® software, as well with use of experimental thermal-derivative analysis.
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Abstract

Mathematical description of alloys solidification in a macro scale can be formulated using the one domain method (fixed domain approach). The energy equation corresponding to this model contains the parameter called a substitute thermal capacity (STC). The analytical form of STC results from the assumption concerning the course of the function fS = fS (T) describing the changes of solid state volumetric fraction and the temperature at the point considered. Between border temperatures TS , TL the function fS changes from 1 to 0. In this paper the volumetric fraction fS (more precisely fL = 1- fS ) is found using the simple models of macrosegregation (the lever arm rule, the Scheil model). In this way one obtains the formulas determining the course of STC resulting from the certain physical considerations and this approach seems to be closer to the real course of thermal processes proceeding in domain of solidifying alloy.
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