Search results

Filters

  • Journals
  • Authors
  • Keywords
  • Date
  • Type

Search results

Number of results: 11
items per page: 25 50 75
Sort by:

Abstract

The flow of the investigated fluid in a measuring system of a rheometer – a capillary or a slit between rotating parts – may be disturbed by anisotropic behavior of the fluid near the wall. This phenomenon, so-called wall slip, often takes place in concentrated suspensions and solutions of linear polymers and introduces experimental errors to measurement results. There are methods of correction of these errors in the case of capillary and coaxial cylinders measuring systems. In the cone and plate system the correction seems to be more difficult because the width of the gap between cone and plate changes along the radius and thus the influence of the wall slip on the shear stress varies along the radius in an unpredictable and complicated manner. This dependency of the shear stress on the distance from the axis underlies the presented method of correction of experimental results obtained in the cone and plate system. The method requires several series of measurements of shear stress vs. shear rate performed using one measuring set, at various degrees of filling the gap.
Go to article

Abstract

Development of high-performance finite elements for thick, moderately thick, as well as thin shells and plates, was one of the active areas of the finite element technology for 40 years, followed by hundreds of publications. A variety of shell elements exist in the FE codes, but “the best” finite element is still to be discovered. The paper deals with an evaluation of some existing shell finite elements, from the point of view of the third of three requirements to be satisfied by theelement: ellipticity, consistency and inf-sup condition. It is difficult to prove the inf-sup condition analytically, so, a numerical verification is proposed. A set of numerical tests is considered for shell and plate problems. Two norm matrices and a selection of the stiffness matrices (bending, shear and membrane dominated) are analysed. Finite elements from various computer systems can be evaluated and compared with the use of the proposed tests.
Go to article

Abstract

Geometry of plate heat exchangers (PHE) is characterized by a complex net of narrow channels. It enhances turbulence and results in better heat transfer performance. Theoretically, larger number of channels (plates) should proportionally increase the PHE heat power capacity. In practice a nonuniform massflow distribution in consecutive flow channels can significantly deteriorate the overall heat exchange performance. The flow maldistribution is one of the most commonly reported exploitation problems and is present in PHE with and without phase-change flows. The presented paper investigates numerically a flow pattern in PHE with evaporation of R410A refrigerant. Various sizes of PHE are considered. The paper introduces a robust methodology to transform the complicated geometry of a real 3D PHE to its 2D representation. It results in orders of magnitude faster calculations and allows for fast evaluation of different geometrical changes of PHE and their effect on flow maldistribution.
Go to article

Abstract

Most of sound sources are complex vibroacoustic objects consist of numerous elements. Some coupled vibrating plates of different shapes and sizes can be easily found in urban environments. The main aim of this study is to determine the sound radiation of coupled plates system of practical importance. The investigated vibroacoustic system consist of a thin circular plate coupled with a thick flat baffle with a circular hole. The circular plate has been mounted to the baffle’s hole using screws and two steel rings. The measurement setup was located inside a semi-anechoic chamber to assure the free field conditions. It was necessary to take into account the whole system surface to obtain the radiation efficiency based on the Hashimoto’s method. Such an approach can be troublesome and time-consuming. Therefore, the criterion has been proposed which allows the vibration velocity measurements and calculations to be performed only for the thin plate’s area. An alternative approach has been proposed based on the classical Rayleigh integral formula. Its advantage is a simpler implementation in a computer code. The obtained results have been compared with the theoretical results obtained for the elastically supported circular plate. A good agreement has been obtained at low frequencies.
Go to article

Abstract

This paper deals with the problem of the effect of discretization level and certain other parameters characterizing the measurement setup on accuracy of the process of determination of the sound radiation efficiency by means of the Discrete Calculation Method (DCM) described by Hashimoto (2001). The idea behind DCM consists in virtual division of an examined sound radiating structure into rectangular elements each of which is further assumed to contribute to the total radiation effect in the same way as a rigid circular piston having the surface area equal to this of the corresponding virtual element and vibrating in an infinite rigid baffle. The advantage of the method over conventional sound radiation efficiency measurement techniques consists in the fact that instead of acoustic pressure values, source (plate) vibration velocity amplitude values are measured in a selected number of regularly distributed points. In many cases, this allows to determine the sound radiation efficiency with sufficient accuracy, especially for the low frequency regime. The key part of the paper is an analysis of the effect of discretization level (i.e. the choice of the number of points at which vibration amplitude measurements are to be taken with the use of accelerometers) on results obtained with the use of the method and their accuracy. The problem of determining an optimum level of discretization for given excitation frequency range is a very important issue as the labor intensity (time-consuming aspect) of the method is one of its main flaws. As far as the technical aspect of the method is concerned, two different geometrical configurations of the measurement setup were tested.
Go to article

Abstract

The study presents the results of theoretical investigations into lateral torsional buckling (LTB) of bi-symmetric I-beams, elastically restrained against warping at supports. Beam loading schemes commonly used in practice are taken into account. The whole range of stiffness of the support joints, from free warping to warping fully restrained, is considered. To determine the critical moment, the energy method is used. The function of the beam twist angle is described with power polynomials that have simple physical interpretation. Computer programs written in symbolic language for numerical analysis are developed. General approximation formulas are devised. Detailed calculations are performed for beams with end-plate joints. Critical moments determined with programs and approximation formulas are compared with the results obtained by other researchers and with those produced by FEM. Very good accuracy of results is obtained.
Go to article

Abstract

The lithospheric transect South Shetland Islands (SSI) — Antarctic Peninsula (AP) includes: the Shetland Trench (subductional) and the adjacent portion of the SE Pacific oceanic crust; the South Shetland Microplate (younger magmatic arc superimposed on continental crust); the Bransfield Rift and Platform (younger back-arc basin); the Trinity Horst (older magmatic arc superimposed on continental crust); the Gustav Rift (Late Cenozoic) and James Ross Platform (older back-arc basin). Deep seismic sounding allowed to trace the Moho discontinuity at about 30 km under South Shetlands and at 38—42 km in the northern part of Antarctic Peninsula (Trinity Horst), under typical continental crust. Modified crust was recognized under Bransfield Strait. Geological interpretation based on deep seismic refraction and multichannel reflection soundings, and surface geological data, is presented.
Go to article

Abstract

The objective of this article is to present the funerary eye and mouth plates use as a funeral custom from the 10th century in the Carpathian Basin. Presented artefacts, which were interpreted as funerary eye and mouth plates, were sewn onto the shroud used to cover the skull or were placed on the eye cavity and on the mouth of the deceased person. The collected artefacts were divided into four parts, based on the formal aspect. Their characteristics were examined. These artefacts show strong connections with specimens known from eastern Europe, especially with the ones known from the Ural. The ancient Hungarians brought this funeral custom to the Carpathian Basin in the course of their conquest. Ethnic studies are needed to understand the discussed custom, and the subject requires further research.
Go to article

Abstract

The subject of this article is the fragmentary silver plate of a gilded silver sheet braid ornament decorated with palmette motifs, which was deposited in the storage of the Gorgippia Archaeological Museum (Krasnodar Krai, Russia) in 2015, together with several other finds. The finds had been discovered at a site named Andreyevskaya Shhel, located a few kilometres south-east of the town, at the north-western hill area of the Caucasus. Among the artefacts deposited in the storage in 2015, there were other finds related to the 9–10th centuries (e.g. silver plate of a sabretache, gilded bronze belt mounts, bronze strap end, sabre, bow case or sabretache mount, fingering, etc). The braid ornament, with many analogies in the Carpathian Basin, could have reached the North Caucasian region by means of long-distance trade. This hypothesis is sustained by the considerable dirham-finds in the Carpathian Basin, which indicate the integration of this region – and of early Hungarian commerce as a whole – into the Eastern, Muslim trade network.
Go to article

Abstract

The authors developed a simple and efficient method, called the Coupled Displacement method, to study the linear free vibration behavior of the moderately thick rectangular plates in which a single-term trigonometric/algebraic admissible displacement, such as total rotations, are assumed for one of the variables (in both X,Y directions), and the other displacement field, such as transverse displacement, is derived by making use of the coupling equations. The coupled displacement method makes the energy formulation to contain half the number of unknown independent coefficients in the case of a moderately thick plate, contrary to the conventional Rayleigh-Ritz method. The smaller number of undetermined coefficients significantly simplifies the vibration problem. The closed form expression in the form of fundamental frequency parameter is derived for all edges of simply supported moderately thick rectangular plate resting on Pasternak foundation. The results obtained by the present coupled displacement method are compared with existing open literature values wherever possible for various plate boundary conditions such as all edges simply supported, clamped and two opposite edges simply supported and clamped and the agreement found is good.
Go to article

Abstract

The paper presents the results of studies on the development of manufacturing technologies to cast hearth plates operating in chamber furnaces for heat treatment. Castings made from the heat-resistant G-X40CrNiSi27-4 steel were poured in hand-made green sand molds. The following operations were performed: computer simulation to predict the distribution of internal defects in castings produced by the above mentioned technology with risers bare and coated with exothermic and insulating sleeves, analysis of each variant of the technology, and manufacture of experimental castings. As a result of the conducted studies and analysis it was found that the use of risers with exothermic sleeves does not affect to a significant degree the quality of the produced castings of hearth plates, but it significantly improves the metal yield.
Go to article

This page uses 'cookies'. Learn more