University of Architecture, Civil Engineering and Geodesy

About: University of Architecture, Civil Engineering and Geodesy is a education organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Finite element method & Beam (structure). The organization has 3808 authors who have published 3822 publications receiving 30736 citations. The organization is also known as: Sofia Polytechnic.

Seismic wave fields in continuously inhomogeneous media with variable wave velocity profiles

Abstract: In this work, elastic wave motion in a continuously inhomogeneous geological medium under anti-plane strain conditions is numerically investigated using the boundary integral equation method (BIEM). More specifically, the geological medium possesses a variable velocity profile, in addition to the presence of either parallel or non-parallel graded layers, of surface relief, and of buried cavities and tunnels. This complex continuum is swept either by time-harmonic, free-traveling horizontally polarized shear waves or by incoming waves radiating from an embedded seismic source. The BIEM employs a novel type of analytically derived fundamental solution to the equation of motion defined in the frequency domain, by assuming a position-dependent shear modulus and a density of arbitrary variation in terms of the depth coordinate. This fundamental solution, and its spatial derivatives and asymptotic forms, are all derived in a closed-form by using an appropriate algebraic transformation for the displacement vector. The accuracy of the present BIEM numerical implementation is gauged by comparison with available results drawn from examples that appear in the literature. Following that, a series of parametric studies are conducted and numerical results are generated in the form of synthetic seismic signals for a number of geological deposits. This allows for an investigation of the seismic wave field sensitivity to the material gradient and the wave velocity variation in the medium, to the presence of layers, canyons and cavities, and to the frequency content of the incoming signal.

Influence of Whistler Turbulence on Fast Electron Distribution and Their Microwave Emissions in a Flare Loop

Abstract: The influence of whistlers on the distribution and gyrosynchrotron radiation of fast electrons injected into a coronal magnetic trap is considered. The kinetic equation in the Fokker–Planck approximation with consideration of fast electron scattering, both on background plasma particles and on whistlers, is solved for an inhomogeneous trap. It is supposed that the source of whistlers is a nonstationary process of flare energy release. Having found the fast electron distribution, we can calculate their gyrosynchrotron microwave emission. The influence of nonthermal electron scattering on whistlers are compared with the effects of scattering on Coulomb collisions. It is shown that whistlers considerably modify the emission characteristics of a loop at a certain energy density; in particular, they steepen the frequency spectrum. This is useful for microwave diagnostics of plasma turbulence in the flare loop.

An experimental investigation on the particle breakage and strength properties of soil-rock mixture

Abstract: The soil-rock mixture (S-RM) is widely used as a kind of geotechnical material in some construction engineering. When analyzing the stability of the engineering, the strength properties of S-RM are used as crucial input parameters. In this paper, to improve the understanding of strength properties of S-RM, a series of large-scale direct shear tests were conducted on S-RM with two volumetric rock block contents (VBCs), each with three types of block lithology. The particle breakage after each test and its relationship with strength properties were also analyzed. The results reveal that the influences of VBC and block lithology on particle breakage are slight when VBC is low, while significant as VBC increases. Compared with the traditional M-C strength criterion, a modified M-C nonlinear strength criterion is more suitable for the S-RM. When VBC is low, the influences of VBC and block lithology on the strength properties are slight. However, when VBC is high, their impacts will become greater, especially on the nonlinear strength parameter Δφ. The nonlinear strength characteristics become more obvious with an increase in relative breakage index Br, which are mainly caused by the particle breakage during the shearing process.

Longitudinal fracture analysis of continuously inhomogeneous beam in torsion with stress relaxation

Abstract: The present paper deals with longitudinal fracture analysis of a continuously inhomogeneous beam with stress relaxation. The beam is loaded in torsion. The stress relaxation behavior is treated by using two linear viscoelastic models under constant applied shear strain. The cross-section of the beam is a circle of linearly varying radius along the beam length. The longitudinal crack is a circular cylindrical surface. The beam is continuously inhomogeneous in both radial and length directions. The shear modulii and the coefficients of viscosity are distributed exponentially along the radius and along the length of the beam. The longitudinal fracture behavior is analyzed in terms of the strain energy release rate. A solution to the strain energy release rate is obtained by differentiating the strain energy. The solution is verified by considering the balance of the energy. The influence of the varying radius of the cross-section on the longitudinal fracture is studied. The effects of the varying shear modulii and coefficients of viscosity in radial and length directions of the beam on the longitudinal fracture behavior are evaluated. The change of the strain energy release rate with the time is analyzed.

Role of Clay Minerals Content and Calcite in Alkali Activation of Low-Grade Multimineral Clays

Abstract: The increased contribution of science-intensive clean materials and technologies to the total industrial production is one of the essential prerequisites for the future of sustainable indus...