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The paper describes the practical way and security conditions of realizing the demolition of an industrial chimney located in an oil refinery platform, having in the immediate vicinity sensitive equipment and constructions. The chimney has a height of 150 m and consists of the outer tubular structure of reinforced concrete and an inner chimney made of refractory brick masonry. In order to establish the possible secondary effects generated by the blasting works, a risk assessment was made with reference to seismic wave, air shock wave, noise, dust and the level of shock generated by the impact of chimney construction with the soil. The demolition work was carried out successfully and due to protection and safety measures no unwanted events were recorded, and the measured values of the seismic wave generated by the impact with the ground of the chimney were non-dangerous, being below the values estimated in the risk assessment.

A plume model is used to describe the variation of the salt concentration at the discharge of a river into a saline water. The integral model of the plume behavior consists of a set of ordinary differential equations derived from conservation of mass, momentum and salt concentration. The temperatures of the plume and ambient saline water are considered equal. The concentration of the salt in the river water is null. The saline water is assumed motionless. After release from the river, the concentration of the salt in the plume increases by mixing with the ambient saline water. The rate of mixing depends upon the local plume and ambient fluid properties such as velocity and salt concentration.

Methane is one of the most common gaseous fuels that also exist in nature as the main part of the natural gas, the flammable part of biogas or as part of the reaction products from biomass pyrolysis. In this respect, the biogas and biomass installations are always subjected to explosion hazards due to methane. Simple methods for evaluating the explosion hazards are of great importance, at least in the preliminary stage. The paper describes such a method based on an elementary analysis of the cubic law of pressure rise during the early stages of flame propagation in a symmetrical cylindrical vessel of small volume (0.17 L). The pressure–time curves for lean, stoichiometric and rich methane–air mixtures were recorded and analyzed. From the early stages of pressure–time history, when the pressure increase is equal to or less than the initial pressure, normal burning velocities were evaluated and discussed. Qualitative experiments were performed in the presence of a radioactive source of 60Co in order to highlight its influence over the explosivity parameters, such as minimum ignition energy, maximum rate of pressure rise, maximum explosion pressure and normal burning velocity. The results are in agreement with the literature data.

Particles in suspension come mainly from pollutant emissions generated by industry, traffic, home heating, etc. Due to these particles, various diseases can occur, such as lung cancer, asthma, cardiovascular diseases. An important problem is represented by the particles with an aerodynamic diameter of less than 10 micrometers, which pass through the nose and throat and enter the alveoli of the lungs causing inflammation and intoxication. This paper aimed to establish the chemical composition of residual powders in a production hall from the automotive industry, to identify the source of release. For this, the infrared spectrometry (FTIR) method, the inductively coupled plasma optical emission spectrometry (ICP-OES) method, and the x-ray spectrometry (XRF) method were used. Two samples of dust from different locations of the production hall were analyzed, as well as a substance used in the process, to determine whether the dust came from its use. A series of safety data sheets for substances used in the technological process was also analyzed. The results obtained from the qualitative and quantitative determinations were evaluated considering the chemical composition of all substances involved, leading to the identification of the residual dust release source.

3D representations using assisted design and computer simulations allow determining the geometric characteristics of critical sections needed for analytical calculation. Also, these representations form the basis of meshing necessary for the finite element calculation. The purpose of this paper is to perform the metal structure verification, both by classical analytical calculation and by the finite element method, as well as to validate these calculations by computerized simulation. The calculation performed on this metallic structure involves the analytical determination of stresses and, implicitly, of safety coefficients, which constitute a verification of metal structure.

Today, due to the diversity of the conditions in which the blasting works are executed, they often require a special organization regarding the transportation and storage of the explosive goods near the blasting field. If for explosive storage arranged for long-term use such as those of the producers, there are detailed regulations regarding the constructive and security requirements that they must meet, for the temporary storage facilities, there are not enough details regarding the constructive requirements that they must comply with. One of the most important aspects taken into account when designing and arranging a mobile explosive depot is the limitation to the maximum of the dynamic action and the throw effect of pieces of material under the pression of an accidental detonation. The paper describes the results obtained after testing a container prototype designed for the storage of explosives. Following the tests performed and the evaluation of the dynamic effects of explosions inside and outside the container as well as the analysis of the measurement regarding the pressure generated by the detonation of explosive charges, it turned out that the construction and detonation behavior of the tested container complies with the purpose and safety requirements for setting up a mobile explosive depot.

Rising prices and the desire to reduce pollution by replacing traditional fuels (benzine and diesel) in the transport system require solutions to make this sector more economically efficient. The use of LPG, CNG and H2 implies, from the point of view of explosion risks, additional features compared to conventional filling stations to increase safety and environmental protection. Thus, this paper presents the effects caused by each fuel analysed (LPG, CNG and H2), in the worst case, the initiation case. The analysis performed is based on simulation using ANSYS – Computational Fluid Dynamics (CFD) software, and the result is particularly useful for adopting optimal measures to minimise the risk of explosion.

In a multi-component system the diffusion of a certain species is dictated not only by its own concentration gradient but also by the concentration gradient of the other species. In this case, the mathematical model is a system of strongly coupled second order elliptic/parabolic partial differential equations. In this paper, we adapt the splitting method for numerical solution of multi-component mass transfer equations, with emphasis on the linear ternary systems. We prove the positive definiteness assumptions for the discrete problem matrices which ensure the stability of the method. The numerical experiments performed confirmed the theoretical results, and the results obtained show good numerical performances.

The splitting method used in a previous study for the numerical solution of mass transfer equations in ternary systems is generalized to mixtures with n-components. The diffusion coefficients are considered constant. Theoretical results about the stability of the method are presented, as well as numerical simulations for mixtures with n = 4, 5, and 6. The numerical experiments confirmed the theoretical results and show good numerical performances. Moreover, multicomponent diffusion effects without an imposed concentration gradient are investigated for mixtures with n = 4, 5, and 6 components.

In an earlier paper [J. of Appl. Math. and Informatics, 29(3-4)(2011), 697-712] we proposed a general projection-type algorithm with corrections and proved its convergence under a set of special assumptions. In this paper we prove convergence of this algorithm under a much weaker set of assumptions. This new framework gives us the possibility to obtain as a particular case of our method the two-step algorithm analysed in [B I T, 38(2)(1998), 275-282].

This work continues our previous analysis concerning the performances of the nonlinear multigrid (the Full Approximation Storage algorithm) method and modified Picard preconditioned conjugate gradient methods for the numerical solution of the two-dimensional, steady-state, multicomponent mass transfer equations. The present test problems are steady-state, linear and nonlinear, convection-diffusion-reaction equations. The upwind finite difference method was used to discretize the mathematical model equations. The numerical results obtained show good numerical performances.

Algebraic reconstruction techniques (ARTs), on both their successive and simultaneous formulations, have been developed since the early 1970s as efficient ‘row-action methods’ for solving the image-reconstruction problem in computerized tomography. In this respect, two important development directions were concerned with, first, their extension to the inconsistent case of the reconstruction problem and, second, their combination with constraining strategies, imposed by the particularities of the reconstructed image. In the first part of this paper, we introduce extending and constraining procedures for a general iterative method of an ART type and we propose a set of sufficient assumptions that ensure the convergence of the corresponding algorithms. As an application of this approach, we prove that Cimmino's simultaneous reflection method satisfies this set of assumptions, and we derive extended and constrained versions for it. Numerical experiments with all these versions are presented on a head phantom ...

Picard and Newton iterations are widely used to solve numerically the nonlinear Richards’ equation (RE) governing water flow in unsaturated porous media. When solving RE in two space dimensions, direct methods applied to the linearized problem in the Newton/Picard iterations are inefficient. The numerical solving of RE in 2D with a nonlinear multigrid (MG) method that avoids Picard/Newton iterations is the focus of this work. The numerical approach is based on an implicit, second-order accurate time discretization combined with a second-order accurate finite difference spatial discretization. The test problems simulate infiltration of water in 2D unsaturated soils with hydraulic properties described by Broadbridge–White and van Genuchten–Mualem models. The numerical results show that nonlinear MG deserves to be taken into consideration for numerical solving of RE.

In this paper we consider the numerical solution of first-order Hamilton-Jacobi equations using the combination of a discontinuous Galerkin finite element method and an adaptive $r$-refinement (mesh movement) strategy. Particular attention is given to the choice of an appropriate adaptivity criterion when the solution becomes discontinuous. Numerical examples in one and two dimensions are presented to demonstrate the effectiveness of the adaptive procedure.

Friedrich-Alexander University of Erlangen-Nurnberg, Cauerstrasse 6, 91058 Erlangen, GermanyIn algebraic reconstruction of images in computerized tomography we are dealing with rectangular, large, sparse and ill-conditioned linear systems of equations. In this paper we describe a two-grid algorithm for solving such kind of linearsystems, which uses Kaczmarz’s projection method as relaxation. The correction step is performed with a special “local”aggregation / disaggregation type procedure. In this respect, we have to solve a small sized minimization problem associatedto each coarse grid pixel. The information so obtained is then ”distributed” to the neighbour fine grid pixels. Some imagereconstruction experiments are also presented.

In this paper we consider four versions of Kovarik’s iterative orthogonalization algorithm, for approximating the minimal norm solution of symmetric least squares problems. Although the theoretical convergence rate of these algorithms is at least linear, in practical applications we observed that a too big number of iterations can dramatically deteriorate the already obtained approximation. In this respect we analyse the above mentioned Kovarik-like methods according to the modifications they make on the “machine zero” eigenvalues of the problem’s (symmetric) matrix. We establish a theoretical almost optimal formula for the number of iterations necessary to obtain an enough accurate approximation, as well as to avoid the above mentioned troubles. Experiments on collocation discretization of a Fredholm first kind integral equation illustrate the efficiency of our considerations.