D. Knezevic, N. Jovancevic, A. M. Sukhovoj and L.V. Mitsyna
The spectrum of random functions of level density as well as radiative strength functions of dipole E1- and M1-transitions of 28Al were determined. Obtained functions can reproduce very precisely the intensity of the two-step cascade following the radiative capture of thermal neutrons for a given energy of the primary transitions. The density of the observed intermediate levels can be reproduced correctly using the mean value of these functions. In this work we proposed a new hypothesis about the dependence of radiative strength functions for gamma-transitions in heated nucleus on the energy of excited levels. The results provide a solid basis that this new hypothesis allows to get realistic estimation on the parameters of nuclear structure in any nucleus, including the light ones.
M. A. Grado-Caffaro and M. Grado-Caffaro
The exchange interaction in itinerant-electron metamagnetism is investigated theoretically. In fact, by considering spin-up and spin-down electrons in an itinerant-electron metamagnetic gas in the presence of an external magnetic field, we show that the difference between the Fermi energies of the spin-up and spin-down electrons equals, up to a multiplicative constant, the absolute value of the matrix element of the Hamiltonian operator relative to the interaction in question. Furthermore, the Stoner formula for the electronic energy of the gas is used to study the size of the exchange interaction.
Marek Grodzicki and Marek Rotkegel
The article presents a comparison of the roadway supports currently used in mines in the Soma basin in Turkey with new one proposed by Huta Łabędy and Central Mining Institute (GIG) in terms of resistance parameters and work in conditions of specific loads. The strength analysis of the frame was carried out using the finite element method, using the COSMOS/M program, based on the methodology developed and applied in GIG.
The frame models were built corresponding to their geometry and cross-sectional parameters of the sections used. Beam elements (BEAM3D) were used for building models, which were given cross-sectional parameters of the V36 section. This resulted in three frame models that were loaded in three ways (three load variants). The first option included roof load, acting on the roof bar in a uniform manner, at a length of about 3.0 m. In the second variant, the same load was adopted but the resistance of the side wall was omitted. However, in the third variant, the same roof load was assumed in addition to a side load, acting on the sliding arch, at a length of about 3.0 m, a value corresponding to half the load of the roof. As a result of the calculations carried out, the distribution of reduced stresses in the analysed frames and the maximum load values were obtained.
The proposed roadway supports retain the functionality of the previously used frames in terms of width, height, cross-sectional area of the support and the number of elements. They are characterised by the same weight and at the same time, they have up to 24% more load capacity because of the replacement of straight sections of curved side sections. This treatment was possible by forming individual elements of the arch with two bending radii. The additional load increase was obtained by using S550W steel.
Krzysztof Sternik and Katarzyna Dołżyk-Szypcio
Calculation of pullout capacity of anchoring concrete cylindrical block by finite element method is carried out. 3D model of the block assumes its free rotation. Alternative solutions with one and two pulling forces attached at different heights of the block are considered. Dependency of the ultimate pulling force on the points of its application, the block’s embedment depth as well as contact friction are investigated. Results of FE analysis and simple engineering estimations are compared. The maximum pullout resistance results from FE analysis when the rotation of the block is prevented.
Tomasz Strzelecki, Anna Uciechowska-Grakowicz, Michał Strzelecki, Eugeniusz Sawicki and Łukasz Maniecki
This article presents the results of numerical simulations of seepage through the body of the dam and the reservoir bed. The purpose of this study was to analyse the seepage stability during a flood as well as the impact on seepage stability of the diaphragm wall and gravel columns, on which the dam body is founded in selected segments. Simulations were conducted for three different locations, and the following 3D models of the dum were prepared:
a model containing the front and right-bank part of the dam, for which no diaphragm wall, gravel columns and drainage ditch were provided for
a model of a segment of the right-bank dam including a diaphragm wall, drainage ditch and gravel columns under the dam (two variants with differing diaphragm wall lengths)
a model of the water dam segment accounting for gravel columns and a drainage ditch, but without a diaphragm wall. In the case of founding on gravel columns, the base was modelled as an anisotropic medium in terms of seepage properties, macroscopically equivalent to the actual soil medium.
The numerical model utilises the finite element method. The geometry of the dam and geological substrate was defined in the GIS tools in the form of a 3D model of the terrain and geology of the substrate.
Zygmunt Meyer and Krzysztof Żarkiewicz
This article shows the mathematical method to determine the lateral stress on the shaft and toe resistance of pile using the new approach. The method was originally invented by Meyer and Kowalow for the static load test. The approximation curve was used for the estimation of both settlement curve and toe resistance curve of the pile. The load applied at the head of the pile is balanced by the sum of two components: the resistance under the toe of the pile and the skin friction. Therefore, the settlement curve is compilation of two factors: the skin friction curve and the resistance under toe curve. The analysis was based on the verification of the methods using laboratory experiments, that is, static load tests. The results of the research allowed to determine the relationship between parameters of the Meyer–Kowalow curve. On the basis of the relationships, it was possible to determine the skin friction and the toe resistance of the pile. Mathematical analysis of curve parameters allowed to determine the influence of the toe resistance on the settlement.
M. Muthtamilselvan and S. Sureshkumar
This paper is intended to investigate the effects of an inclined magnetic field on the mixed convection flow in a lid-driven porous enclosure filled with nanofluid. Both the left and right vertical walls of the cavity are thermally insulated while the bottom and top horizontal walls are maintained at constant but different temperatures. The governing equations are solved numerically by using finite volume method on a uniformly staggered grid system. The computational results are obtained for various combinations of Richardson number, Darcy number, Hartmann number, inclination angle of magnetic field, and solid volume fraction. It is found that the presence of magnetic field deteriorates the fluid flow, which leads to a significant reduction in the overall heat transfer rate. The inclination angle of magnetic field plays a major role in controlling the magnetic field strength and the overall heat transfer rate is enhanced with the increase of inclination angle of magnetic field. Adding the nanoparticles in the base fluid significantly increases the overall heat transfer rate in the porous medium whether the magnetic field is considered or not.
Duraisamy Velmurugan, Masilamany Santha Alphin and Benedict Jain AR Tony
Background: Implant thread profile plays a vital role in magnitude and distribution of contact stresses at the implant-bone interface. The main goal of this study was to evaluate the biomechanical effects of four distinct thread profiles of a dental implant in the mandibular premolar region.
Methods: The dental implant represented the biocompatible Zirconia material and the bone block was modelled as transversely isotropic and elastic material. Three-dimensional finite element simulations were conducted for four distinct thread profiles of a dental implant at 50%, 75%, and 100% osseointegration. An axial static load of 500 N was applied on the abutment surface to estimate the stresses acting within the bones surrounding the implant.
Results: Regions of stress concentration were seen mostly along the mesiodistal direction compared to that in the buccolingual direction. The cortical bone close to the cervical region of the implant and the cortical bone next to the first thread of the implant experienced peak stress concentration. Increasing the degree of osseointegration resulted in increased von-Mises stresses on the implant-cortical transition region, the implant-cancellous transition region, the cortical bone, and the cancellous bone.
Conclusion: The results show that the application of distinct thread profiles at different degrees of osseointegration had significant effect on the stresses distribution contours in the surrounding bony structure. Comparing all four thread profiles, a dental implant with V-thread profile induced lower values of von-Mises stresses and shear stresses on the implant-cortical transition region, implant-cancellous transition region, cortical bone, and cancellous bone.