Now showing 1 - 10 of 20
  • Publication
    LASER ABLATION OF PAINT COATINGS IN INDUSTRY
    A comparison is made between the laser and sandblasting methods for removing paint from industrial facilities. The advantages of laser ablation are discussed. The possibilities of laser paint removal systems - stationary and moving - are shown. The main factors influencing the laser ablation process and the indicators that determine the quality of the obtained surface are systematized. Researchers' publications on this technological process are analyzed.
  • Publication
    Processing composite materials with lasers
    Composite materials, consisting of fibers and binders of natural and artificial origin, are increasingly used in various fields of industry. Processing of the obtained materials into finished forms is often difficult and expensive. Treatment of composite materials, such as milling, cutting, or grinding, is currently dominant. At present, lasers are increasingly used in production processes. It should be noted that modern industrial production is unthinkable without the use of laser equipment. However, when using lasers, initial adjustment of their laser parameters is required for optimal material processing. When considering different lasers and materials to be processed, the setting parameters are different and the obtained processing quality is varied. In the research, samples of composite materials have been made, consisting of epoxy resin as a binder and hemp, flax, and carbon fibers as reinforcing materials. The obtained composite materials have been studied with fiber laser for their processing quality.
  • Publication
    ON MATHEMATICAL MODELLING OF THE 2-D FILTRATION PROBLEM IN POROUS AXIAL SYMMETRICAL CYLINDER
    In this paper we study diffusion and convection filtration problem of one substance through the pores of a porous material which may absorb and immobilize some of the diffusing substances. As an example we consider round cylinder with filtration process in the axial direction. The cylinder is filled with sorbent i.e. absorbent material that passed through dirty water or liquid solutions. We can derive the system of two partial differential equations (PDEs). One equation is expressing the rate of change of concentration of water in the pores of the sorbent and the other - the rate of change of concentration in the sorbent or kinetically equation for absorption. The approximation of corresponding initial boundary value problem of the system of PDEs is based on the conservative averaging method (CAM). This procedure allows reducing the 2-D axis-symmetrical mass transfer problem described by a system of PDEs to initial value problem for a system of ordinary differential equations (ODEs) of the first order.
  • Publication
    PRELIMINARY NUMERICAL ANALYSIS FOR THE ROLE OF SPEED ONTO LASER TECHNOLOGICAL PROCESSES
    Studying the impact of speed on a number of laser processes such as marking, engraving, cutting, welding and others is crucial for the optimization of these technological processes. The processing speed, along with the frequency of laser pulses and their duration, also determines the time of action in the processing area and hence the absorbed quantity of electromagnetic energy. Based on numerical experiments with specialized software TEMPERATURFELD3D, the report analyzes the temperature variation in the processing area as a function of speed. The researches were analyzed for processing with two types of lasers emitting in the visible and infrared areas of the electromagnetic spectrum and two types of steels (tool and structural). From the course of the obtained temperature fields the dependence of temperature on the speed at two power densities was obtained. The obtained results help to make a preliminary assessment the speed work intervals for the processes as laser marking, laser engraving, laser cutting, laser welding and others. In this way, it is assisted in building an optimal concept for the passing of a particular technological process in function of the laser source, the material and the type of the technological operation.
    Scopus© Citations 13
  • Publication
    SPECIAL SPLINE APPROXIMATION FOR THE SOLUTION OF THE NON-STATIONARY 3-D MASS TRANSFER PROBLEM
    In this paper we consider the conservative averaging method (CAM) with special spline approximation for solving the non-stationary 3-D mass transfer problem. The special hyperbolic type spline, which interpolates the middle integral values of piece-wise smooth function is used. With the help of these splines the initial-boundary value problem (IBVP) of mathematical physics in 3-D domain with respect to one coordinate is reduced to problems for system of equations in 2-D domain. This procedure allows reduce also the 2-D problem to a 1-D problem and thus the solution of the approximated problem can be obtained analytically. The accuracy of the approximated solution for the special 1-D IBVP is compared with the exact solution of the studied problem obtained with the Fourier series method. The numerical solution is compared with the spline solution. The above-mentioned method has extensive physical applications, related to mass and heat transfer problems in 3-D domains.
  • Publication
    SPECIAL HPERBOLIC TYPE APPROXIMATION FOR SOLVING OF 3-D TWO LAYER STATIONARY DIFFUSION PROBLEM
    In this paper we examine the conservative averaging method (CAM) along the vertical z-coordinate for solving the 3-D boundary-value 2 layers diffusion problem. The special parabolic and hyperbolic type approximation (splines), that interpolate the middle integral values of piece-wise smooth function, is investigated. With the help of these splines the problems of mathematical physics in 3-D with respect to one coordinate are reduced to problems for system of equations in 2-D in every layer. This procedure allows reduce also the 2-D problem to a 1-D problem and the solution of the approximated problem can be obtained analytically. As the practical application of the created mathematical model, we are studying the calculation of the concentration of heavy metal calcium (Ca) in a two-layer peat block.
    Scopus© Citations 1
  • Publication
    Distribution of iron and iron compounds in the Kemeri - Jaunkemeri occurence of sulphide water
    Iron concentrations, distribution and migration forms, depending on pH and oxidation – reduction potential, were analyzed in case of the Kemeri-Jaunkemeri occurrence (area about 240 km2) of sulphide containing water (maximal sulphides concentration – 74 mg/l), located in Latvia. Iron content was investigated in 457 wells located within all area of occurrence. Those wells were installed to two aquifers: the Quarternary multi-aquifer and Salaspils aquifer, where occurrence of sulphide containing groundwater is distributed. All groundwater of occurrence is classified in four types depending on oxygen, sulphides and organic matter content in the groundwater.  Modeling of groundwater migration forms was carried out, and it is stated that iron migrates basically as Fe2 in oxygen and suphides non-containing water. Migration forms are influenced by concentration of organic matter in the aquifer. The portion of Fe2 migrating in a form of free decreases due to formation of complexes with fulvic and humic acids, which can reach 36.5% of all migration forms. Iron migrates as Fe(OH)3  in oxygen containing water (more than 99% of determined forms). Presence of iron is ascertained also in sulphides containing water, where iron migrates basically as (98.8% of determined forms).  This occurs due to formation of complexes with sulphydes – FeHS- and Fe(HS)2o.
  • Publication
    The Mathematical Modeling of Metals Mass Transfer in Three Layer Peat Blocks
    The mathematical model for calculation of concentration of metals for 3 layers peat blocks is developed due to solving the 3-D boundary-value problem in multilayered domain-averaging and finite difference methods are considered. As an example, mathematical models for calculation of Fe and Ca concentrations have been analyzed.
  • Publication
    THE APPLICATION OF HEMP IN BIOECONOMY
    (2021) ;
    Dagnija Blumberga
    ;
    Global trends in the world are currently representing a serious incentive to bring ‘green thinking’ to life. This is the case of replacing synthetic materials derived from fossil resources with natural-origin, renewable resources. In the automotive industry and other segments of the manufacturing industry, increasing attention is being paid to the use of natural fibers in the manufacturing of composite materials. For example, flax and hemp fiber, as reinforcing material, is starting to widely replace carbon fiber. It is not just an ecological benefit, but also an important product protecting human health, since the amount of emissions that pollute the environment is minimized. Consequently, that lead to reduced intake by human being of harmful substances that would affect its health status. Existing composite materials used in motor vehicles, produced from carbon fibers, are creating very sharp fracture areas in the event of accidents causing human injury, while materials from natural fiber plants in this case are free from sharp edges at the place of fracture. Raw materials derived from hemp processing are used in the automotive, textile industry, construction (hemp concrete, heat insulation material), energy, biofuel production, arts and design, paper production, food, medicine, etc. This paper covers the main types of products derived from hemp.
  • Publication
    INVESTIGATIONS OF MUNICIPAL SOLID WASLE LANDFILLS LEACHALE TREATMENT
    (2007) ;
    Līga Bērziņa-Cimdiņa
    ;
    Juris Mālers
    ;
    Gatis Pelčers
    ;
    Municipal solid waste landfills are one of the most dangerous environment “point" polluters. The main polluter in landfills is leachate, which arise mainly of waste moisture and precipitations. Leachate is very contaminated wastewater and all landfills operators have problems in leachate treatment sector, because composition of leachate contaminants and concentrations very changed in time. It is very problematic task for selection of leachate treatment method or methods. Normally, in leachate treatment practice combination of different treatment methods are used. In this paper composition of leachate in two biggest Latvia landfills are described. Leachate treatment investigations were achieved with coagulation and sorbtion methods. In researches leachate with coagulants Al2(SOf3 and FeCl3 and peat as sorbent are treated. Researches showed that peat is very effective sorbent for heavy metals removing from leachate.