Martinovs, Andris

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Preferred name
Martinovs, Andris
Alternative Name
Andris Martinovs
Martinovs, A
Main Affiliation
Email
andris.martinovs@rta.lv
ORCID
Scopus Author ID
57217029083
Researcher ID
GQW-2280-2022

Research Output

Now showing 1 - 10 of 26
  • Publication
    Lake blue clay - sapropel - flax shive briquettes for water absorption and desorption
    (2018)
    Tretjakova, Rasma 
    ;
    Martinovs, Andris 
    ;
    Avisane, M.
    ;
    Kolčs, Guntis 
    Article Latvian lakes are rich in sapropel sediments and below the sapropel layer there is another valuable natural resource, namely blue clay. Flax shives are formed in large quantities as a waste in flax processing factories. The problem involves processing and rational use of these reso urces. The paper studies the obtaining of briquettes from flax shives using sapropel and lake clay as a binding material. Briquettes are intended for use in cases when problems with regular plant watering occur. For example, provision of plants with water in greenhouses, indoor spaces for a long period of time without human presence. Briquettes are placed into the soil next to the plant roots. Briquettes are initially moistened and absorb a significant amount of water (moisture content to be expressed in co mparison to the sample's dry weight 250 – 380%). The presence of clay in them contributes to slow drying of briquettes and provides a long lasting supply of moisture to the plant roots. The paper deals with the issues of the optimal composition of components and the amount of pressure for the production of briquettes, as well as water absorption and desorption properties of briquettes. The aim of the study is to develop a production method of clay – sapropel – flax shive briquettes with good water absorption and desorption properties.
  • Publication
    New device for air disinfection with a shielded UV radiation and ozone
    (2021)
    Andris Martinovs 
    ;
    Mezule, L.
    ;
    Ritvars Rēvalds 
    ;
    Pizica, V.
    ;
    Denisova, V.
    ;
    Skudra, A.
    ;
    Kolčs, Guntis 
    ;
    Edgars Zaicevs 
    ;
    Juhna, T.
    Indoor air disinfection has become particularly relevant recently because of the Covid-19 pandemics. A shielded device for air and surface disinfection with UV radiation and ozone has been developed. It contains 28 low intensity (11 W) UV lamps (254 nm) in a specially designed three-dimensional grid to provide a large flow cross-sectional area and long path for the air particles to be irradiated. The device can be used in medical institutions, veterinary clinics, manufacturing plants, public premises, poultry, and livestock farms. It does not generate air-ions and ozone concentrations do not exceed the allowed 8-hour average values. The large number of UV lamps and powerful fans ensure air disinfection in large rooms in a relatively short time (400 m3 h -1 ). Simultaneously, the floor surface under the appliance is disinfected. Disinfection efficiency tests demonstrated 99.9999% reduction for Escherichia coli, Staphylococcus aureus and Pseudomonas phage Φ6 aerosols within a single transfer through the system (10 seconds of treatment). The housing of the device protects from direct UV radiation; therefore, people can be in the room during the operation of the device.
  • Publication
    Air ionizer and indoor plants interaction impact on ion concentration
    (2017)
    Natalija Siņicina
    ;
    Martinovs, Andris 
    The plants emit different types of volatile organic compounds (Bio VOC’s) and can improve air quality: they effectively remove organic pollutions and reduce the number of microorganisms in the air by releasing phytoncides. The lack of negative ions in the air can cause deterioration of the health of humans breathing it. At the same time, an air saturated with negative ions can improve the state of health and provide a comfortable environment. In this article, the influence of the plants (Cupressus macrocarpa) on the number of ions is proved, based on a series of experiments performed with applying high-voltage pulses (air ionizer). This work is devoted to the elaboration of the mathematical relationship between the air ions concentration and the factors influencing it. For this purpose an experimental stand was made, consisting of two equal compartments: one contained the plants while another one was used as a control without plants. It was concluded that the plants, in general, are able to stabilize the ion concentration and to reduce its fluctuations. The plants help to increase the concentration of negative ions and to decrease the concentration of positive ones.
  • Publication
    AGING, FATIGUE AND DURABILITY OF RUBBER VIBRATION ISOLATION ELEMENTS
    (2017)
    Svetlana Polukoshko
    ;
    Martinovs, Andris 
    ;
    Svetlana Sokolova
    This paper deal with shock and vibration insulators, which usually are performed from the elastomeric (rubber-like) materials. Elastomeric materials give many engineering advantages due to their capability of absorbing input energy much better than engineering materials, high elasticity, good dynamic properties, low volume compressibility, a linear relationship between stress and strain up to strain of 15% ÷ 20%, resistance to aggressive environmental factors. Elastomeric materials are widely used in machine building, shipbuilding, civil engineering, aviation and aerospace as compensation devices, vibration dampers, shock absorbers. Laminated elastomers, consisting of interleaved thin layers of elastomer and rigid reinforcing layers are also successfully used as bearing, joints, dampers, compensating devices, shock-absorbers. Such structures have many advantages: ability to endure high stress (>200 MPa), ease of maintenance, non- necessity for lubrication, vibration and noise reduction, ability to work in a very dirty, dusty, abrasive environment. The disadvantage of elastomeric material are aging, i.e. changing its properties over time. In this paper the influence of aging of elastomeric materials on the damping properties of shock absorbers is considered based on the mechanical models of elastomers - Maxwell and Burgers modes. Fatigue endurance, i.e. the ability to withstand mechanical actions for a long time is studied based on experiments on dynamic shear with laminated rubber-metal structures. The experiments show that such structures have a very high fatigue life - up to 100 million cycles.
    Scopus© Citations 5
  • Publication
    Laser hardening process optimization using FEM
    (2020)
    Martinovs, Andris 
    ;
    Svetlana Polukoshko
    ;
    Edgars Zaicevs 
    ;
    Rēvalds, Ritvars 
    In given work a method for optimization of the process of laser hardening of steel parts is developed. The approach is based on the finite element method (FEM) using computer program “COMSOL Multiphysics” (module Heat Transfer in Solids) – software for multi-physical processes simulation. This method allows to reduce the number of laser hardening experiments, replacing them with numerical calculations, and to find the optimal parameters of the used laser equipment. To perform the calculations it is necessary to know the hardening temperature range of the particular steel grade, the martensite formation start temperature, the critical value of the cooling rate, the material density, the thermal conductivity k = k(T), the specific heat capacity Cp = Cp(T) and the surface reflectivity R = R(T, λ), where T temperature, λ – wavelength of laser beam. Depending on the laser power, the feed rates of the laser beam, the spot size and the distribution of energy in it, the temperature field is calculated for the steel part in different moments of time. Analysing these data it is possible to determine the thickness of the hardened layer or to predict damage to the material of a given steel part due to heat treatment. The method has been tested experimentally.
  • Publication
    Mechanical and electrical properties of the solid sapropel
    (2015)
    Martinovs, Andris 
    ;
    Josef Timmerberg
    ;
    Tretjakova, Rasma 
    ;
    Paul Beckmann
    ;
    Valentina Popa
    ;
    Regina Wagner
    In this paper are explored the mechanical (ultimate compression strength, ultimate strain, Young’s modulus, hardness) and the electrical (relative permittivity, specific electrical resistance, quality factor, their dependence on the electric field frequency in the range till 1MHz) properties of the solid sapropel. For the researches are used samples from the solid, monolith sapropel (obtained in the drying process) and samples from the sapropel powder that are pressed with a different force; before the measurements, a part of these samples were heated. There is explored the dependence of the relative permittivity on temperature. Are explored the methods for the forming of the products from the solid sapropel powder.
    Scopus© Citations 1
  • Publication
    DAŽI DIELEKTRISKĀS CAURLAIDĪBAS PĒTĪJUMU ASPEKTI GUMIJAS MĀKSLĪGĀS NOVECOŠANAS PROCESOS
    (1999)
    Martinovs, Andris 
    Gumija ekspluatācijas laikā ir pakļauta ilgstošai dabiskai novecošanai, kuras rezultātā izmainās gumijas struktūra, pasliktinās elastīgās īpašības un mehāniskā izturība. Konstruktoram ir nepieciešams zināt, cik ilgi konkrētais gumijas izstrādājums dotajos apstākļos spēs kalpot. To var prognozēt uz paātrināto eksperimentu pamata. Šie eksperimenti ir saistīti ar gumijas mākslīgo novecošanu, kad pētāmajam paraugam papildus tiek pievadīta enerģija, iedarbojoties uz to ar temperatūras lauku, radiāciju, ķīmiski aktīvām vielām, vibrācijām vai kā citādi. Mākslīgajā novecošanā straujāk izmainās gumiju raksturojošie parametri un īsākā laikā sasniedz savas kritiskās vērtības, pie kurām gumijas izstrādājums vairs nav lietojams. Dotajā darbā kā viens no šādiem parametriem ir izvēlēta dielektriskā caurlaidība, mākslīgā novecošana tiek veikta paaugstinātā temperatūrā.
  • Publication
    Specifics of behavior and calculation of elastomeric shock absorber under impact loading
    (2018)
    Svetlana Polukoshko
    ;
    Martinovs, Andris 
    ;
    Vladimirs Gonca
    In this paper the important for the design of shock-absorbers case of a perfectly rigid body impact with a viscoelastic incompressible body is considered. Mathematical apparatus for calculating the parameters of impact of a rigid body with a highly- elastic rod is developed, taking into account the peculiarities of the behavior of elastomers under fast loading. An analytical solution was obtained for longitudinal impact on a vertically disposed rod. The solution was fulfilled by means of the Bubnov- Galerkin variational method, reducing the problem to solving of the integro-differential equation for given boundary and initial conditions The solution is received for the exponential relaxation kernel for the Maxwell model of a highly-elastic material, it describes the process of damped longitudinal vibration, taking into account the effect of creep caused by the instantaneous impact loading. Based on the equation of vibratory motion the equations of velocity and acceleration are received, which are used for stress-strain behavior analysis of rubber damper. A numerical example of an axial tensile impact on a viscoelastic shock-absorber in the form of a cylindrical rod is given with the plots of time dependence of displacement, velocity, and acceleration of the impact end of the rod are provided, the possibility of using them for analyzing the shock absorber is demonstrated.
    Scopus© Citations 1
  • Publication
    IMPACT OF LASER ON MICROORGANISMS IN THE DIGESTATE
    (2017)
    Tretjakova, Rasma 
    ;
    Lazov, Lyubomir 
    ;
    Martinovs, Andris 
    ;
    Samanta Marija Misiņa
    At the biogas plant total of 40 digestate samples have been collected and investigated. The microbiological composition of digestate has been analysed before and after laser processing with wavelength λ 445 nm with power 2 - 4 W. Salmonella spp. has not been stated in any of the samples, Escherichia coli and Enterococcus spp. amount does not correspond Eiropean Union regulation R142/2011 requirements in any of the investigated samples; Staphylococcus aureus has been stated in 24 samples out of 40. By decreasing laser scanning speed and increasing power, the total number of microorganism colonies in digestate has decreased.