Andris Jakovics

Andris Jakovics
University of Latvia | LU · Department for Physics

Dr. Phys.

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257
Publications
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1,559
Citations

Publications

Publications (257)
Preprint
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This paper presents the analysis of the particle-laden liquid metal wake flow around a cylindrical obstacle at different obstacle Reynolds numbers. Particles in liquid metal are visualized using dynamic neutron radiography. We present the results of particle tracking velocimetry of the obstacle wake flow using an improved version of our image proce...
Article
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This paper demonstrates particle tracking velocimetry performed for a model system wherein particle-laden liquid metal flow around a cylindrical obstacle was studied. We present the image processing methodology developed for particle detection in images with disparate and often low signal- and contrast-to-noise ratios, and the application of our MH...
Preprint
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Dynamics of liquid metal free surface is an important aspect in many different metallurgical processes, such as cold-crucible melting and continuous casting. AC magnetic field can be used to change the shape of a liquid metal volume. Here, we study experimentally and numerically a rectangular liquid metal layer in transverse AC magnetic field. Depe...
Article
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An efficient and versatile implementation of offline multiple hypothesis tracking with Algorithm X for optimal association search was developed using Python. The code is intended for scientific applications that do not require online processing. Directed graph framework is used and multiple scans with progressively increasing time window width are...
Article
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Hempcrete is a very promising bio-based insulating material with a minor or even negative CO2 footprint and low thermal conductivity. To utilize it efficiently, it must be possible to make predictions regarding hempcrete hygrothermal performance and whether it is up to the modern standards—this requires a verified material model for use in numerica...
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In addition to infection with SARS-CoV-2 via direct droplet transmission or contact with contaminated surfaces, infection via aerosol transport is a predominant pathway in indoor environments. The developed numerical model evaluates the risk of a COVID-19 infection in a particular room based on measurements of temperature, humidity, CO 2 and partic...
Article
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As solar panel technologies become more and more popular and are increasingly used in nearly zero-energy building solutions, one must make sure that the panels are able to achieve performance indicators similar to those determined by manufacturers under standard testing in real-world conditions. To determine the efficiency of poly- and monocrystall...
Article
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Monitoring systems allow operators to accomplish the greatest comfort indoors, but, as a rule, the available parameters are not enough to analyse the epidemiological threat in buildings. Due to the pandemic and increasing incidence of the disease, there is a need for monitoring systems that can provide the necessary information to analyse the risk...
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We demonstrate a new image processing methodology for resolving gas bubbles travelling through liquid metal from dynamic neutron radiography images with an intrinsically low signal-to-noise ratio. Image pre-processing, denoising and bubble segmentation are described in detail, with practical recommendations. Experimental validation is presented-sta...
Preprint
Full-text available
This paper demonstrates particle tracking velocimetry performed for a model system wherein particle-laden liquid metal flow about a cylindrical obstacle was studied. We present the image processing methodology developed for particle detection in images with disparate and often low signal- and contrast-to-noise ratios, and the application of our MHT...
Preprint
Full-text available
We demonstrate a new image processing methodology for resolving gas bubbles travelling through liquid metal from dynamic neutron radiography images with intrinsically low signal-to-noise ratio. Image pre-processing, denoising and bubble segmentation are described in detail, with practical recommendations. Experimental validation is presented - stat...
Article
Full-text available
We demonstrate the first application of dynamic mode decomposition (DMD) to bubble flow with resolved dynamic liquid/gas boundaries. Specifically, we have applied DMD to the output of numerical simulations for a system where chains of bubbles ascend through a rectangular liquid metal vessel. Flow patterns have been investigated in the vessel and bu...
Preprint
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We showcase the dynamic mode decomposition (DMD) code developed for applications in two-phase flow analysis. Vertical bubble chain flow in a rectangular vessel filled with liquid gallium is studied without and with applied static horizontal magnetic field (MF) and DMD is applied to the velocity fields computed via volume of fluid simulations. Flow...
Preprint
Full-text available
An efficient and versatile implementation of offline multiple hypothesis tracking with Algorithm X for optimal association search was developed using Python. The code is intended for scientific applications that do not require online processing. Directed graph framework is used and multiple scans with progressively increasing time window width are...
Article
Full-text available
Electrovortex flow (EVF) of liquid metal in container with submerged electrodes and bifilar current supply relates to problem of melt stirring in electrometallurgical aggregates like welding, electroslag remelting, direct current (DC) electrical arc furnaces (EAF) and others. Maximum values of electromagnetic (EM) force and flow velocity are develo...
Article
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We study liquid metal stirring by rotating permanent magnets in a laboratory-scale rectangular glass container. The main goal is numerical model validation using experimental free surface shape data. We find reasonable agreement between the experiments and coupled liquid metal magnetohydrodynamics simulations. Since the surface tension forces are n...
Article
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We investigate argon bubble flow in liquid gallium within a container large enough to avoid wall effects. Flow with and without applied horizontal magnetic field is studied. We demonstrate the successful capture and quantification of the effects of applied magnetic field using dynamic neutron radiography and the previously developed and validated r...
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This paper presents detailed results of neutron imaging of argon bubble flows in a rectangular liquid gallium vessel with and without the application of external horizontal magnetic field. The developed image processing algorithm is presented and its capability to extract physical information from images of low signal-to-noise ratio is demonstrated...
Preprint
Full-text available
This paper presents detailed results of neutron imaging of argon bubble flows in a rectangular liquid gallium vessel with and without the application of external horizontal magnetic field. The developed image processing algorithm is presented and its capability to extract physical information from images of low signal-to-noise ratio is demonstrated...
Article
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With solar panels increasingly used in nearly zero energy building solutions it is important to clarify if the panels can achieve the efficiency indicators specified by their producers in real operation conditions. To determine the efficiency of poly- and monocrystalline panels depending on their spatial orientation and the seasons a set of test pa...
Article
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Numerical models of heat and moisture transfer for performance forecast of lightweight insulating assemblies require many inputs. These include exterior climate data (i.e. temperature, relative humidity, solar radiation), interior climate data or standard models, transfer coefficients, correct initial conditions, etc. Most importantly, one needs re...
Article
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We study liquid metal free surface deformation in an electrically induced vortical flow system, both numerically and experimentally. A 50 Hz current is applied between a small bottom electrode at the center and a conducting cylindrical side wall, and consequently an upward fluid jet is driven causing a notable free surface deformation. The surface...
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In order to assess the sustainability of buildings with different types of insulating assemblies in the Latvian climate, a long-term test building monitoring experiment has been underway since 2013. There are a total of five test buildings on site with roughly six years’ worth of accumulated temperature and humidity readings in the key parts of ass...
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This paper presents the results of numerical modelling of hygrothermal processes in test buildings situated in the Botanical garden of the University of Latvia. Long-term performance of wall, floor and ceiling insulating assemblies for five different buildings was simulated using WUFI Pro 6.3. On the experimental side, measurements of temperature a...
Article
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In practice, during the design stage of a building, only the initial costs are taken into account. These costs are also discussed with the customer and optimised with the aim of reducing them. It is the global costs over a longer period that show the real difference in the total expenses of living in a particular house, however. In this study, one...
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Building materials contribute a significant amount of CO 2 to overall greenhouse gas emissions and this environmental impact should be reduced to improve the sustainability of the construction industry. Although new and low-carbon materials are emerging, the majority of materials used are still traditionally produced and are highly carbon intensive...
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The article investigates the influence of different ventilation strategies on annual energy consumption and thermal comfort. The method proposed for the study is the analysis of the building model realized in the energy simulation software IDA Indoor Climate and Energy (IDA-ICE) 4.7 - a tool for dynamic simulation of thermal comfort, indoor air qua...
Conference Paper
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This work showcases the complete design pipeline based on COMSOL Multiphysics, a general-purpose physics simulation package, for one of the luminaire models manufactured by Vizulo, the OAK series industrial reflector. Generation of optimization targets, ray tracing models and utilized optimization algorithms are described. The authors also evaluate...
Conference Paper
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Bio-based building materials (3BMs) are one of the solutions for how the construction industry can mitigate its negative environmental impact because of energy consumed in material production and due to the insufficient thermal insulation of buildings, as, in general, these materials sequester CO2 in them and have low thermal conductivity. One of t...
Conference Paper
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Paper presents the comparison of experimental and computation results for velocity of electrovortex flow (EVF) of mercury in cylindrical vessel, which is driven with alternating electrical current (AC), supplied over three non-submerged electrodes or two fully submerged electrodes. Time-averaged velocity of liquid metal, computed with LES model of...
Article
The construction industry (and buildings) is one of the largest energy consuming and CO 2 emitting sectors in the world. To counter this, more lightweight structures are being used and energy saving applications are being developed. Phase change materials (PCM) are materials that can be considered to tackle these new challenges. It has been proven...
Article
The characterization of thermal insulation properties of construction materials represents a fundamental step on the building insulation assessment. In recent years innovative materials have been introduced in the market to fulfill the continuously growing requirements of energy saving and sustainability, and their performance is not so reliable an...
Article
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This manuscript describes the development of a wireless sensor system for long term monitoring of temperature, humidity and heat flux reading within building structural elements, including places that are hard to reach using wired sensors. The system was tested in cold Latvian climate in 3 different buildings. The main objectives during the develop...
Article
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Natural, or ‘green’ insulation materials, have become more popular for the ‘ecologisation’ of construction activities. The ecological aspects for such materials are being widely analysed, but experimental data about their physical properties when installed in building constructions remains lacking. In this study, pressed samples of three locally wi...
Article
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As a rule, during the design stage of a single-family house, only initial costs are taken into account and optimised. Long-term financial calculations are usually not even made. At the same time, total costs to design, build and operate the building show a real difference in expenses while living in this house. In the case of nearly zero energy bui...
Article
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In this work, we study rotating permanent magnet based liquid metal pump. Full 3D model of the pump is created and different approaches to electromagnetic force computation are investigated. First, we seek a possibility to model the permanent magnet block consisting of many separate magnets as a single block with equivalent analytically prescribed...
Article
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In this work, we study electrically induced flows numerically using open-source software and experimentally. Two systems are considered - single and multiphase (free surface) flows driven by axisymmetric DC and AC current injection. We investigate characteristic velocity and free surface deformation dependence on the injected current and validate i...
Article
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In this work, we study liquid gallium stirring by rotating permanent magnets. We demonstrate possibility of easily creating different flow patterns by rotating permanent magnets, which can be industrially important for controlling heat and mass transfer processes in the system. Unlike the typical approach of simulating magnet rotation as a transien...
Article
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Reduction of the CO2 emissions in the atmosphere is one of the goals set forth by the European Union, hence various directives have been adopted, such as the European directive 2012/27/EU on energy efficiency, i.e. ensuring from 2019 the construction of the near-zero energy buildings (nZEB). The construction segment plays a very important part in s...
Article
Building envelopes under various climates behave differently, in this paper the actual thermal transmittance or U-value of five different wall assemblies are evaluated and compared with values, calculated using standard EN ISO 6946. The experiment is carried out in five test buildings with equal spatial orientation, the same ceiling and floor assem...
Article
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A CFD mathematical model for an entrained-flow gasifier is constructed – the model of an actual gasifier is rendered in 3D and appropriately meshed. Then, the turbulent gas flow in the gasifier is modeled with the realizable k-ε approach, taking devolatilization, combustion and coal gasification in account. Various such simulations are conducted, o...
Article
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This work is the study of one particular candidate for white etching crack (WEC) initiation mechanism in wind turbine gearbox bearings: discharge current impulses flowing through bearing steel with associated thermal stresses and material fatigue. Using data/results from previously published works, the authors develop a series of models that are ut...
Article
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Numerical simulation tools for industrial magnetohydrodynamics are rare and in high demand, especially open-source codes that can be run on massively parallel computers. Recently, the finite element multi-physics simulation software Elmer was coupled with the computational fluid dynamics software OpenFOAM using parallel two-way coupler EOF-Library....
Article
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In this work, large-scale electromagnetic levitation melting of metals in two-frequency horizontal fields is investigated. A coupled electromagnetic field and free surface flow problems are solved with a three-dimensional model that incorporates a Large Eddy Simulation turbulence description. The developed numerical model is used to design a pilot...
Article
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The main aim of this study is a comprehensive analysis of long-term monitoring data of thermal comfort and discomfort parameters in small identical test buildings equipped with different heating/cooling systems. Calculations of PPD index expressed the human perception of thermal comfort and such discomfort factors like draught rate and vertical air...
Article
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Five test stands have been built in Riga, Latvia equipped with sensors (temperature, solar radiation, humidity, etc.) to measure energy efficiency and thermal comfort conditions. Roof and floor constructions are made the same. For the walls building envelopes differ and typical materials used in Latvia (aerated concrete, ceramic building blocks, wo...
Article
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This paper focuses on the long-term monitoring of thermal comfort and discomfort parameters in five small test buildings equipped with different heating and cooling systems. Calculations of predicted percentage of dissatisfied people (PPD) index and discomfort factors are provided for the room in winter season running three different heating system...
Article
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The usage of phase change materials (PCMs) is a way to store excess energy produced during the hot time of the day and release it during the night thereby reducing the overheating problem. While, in Latvian climate conditions overheating is not a big issue in traditional buildings since it happens only a couple of weeks per year air conditioners mu...
Article
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Development of new, more efficient thermal insulation materials is a key to reduction of heat losses and contribution to greenhouse gas emissions. Two innovative materials developed at Thermeko LLC are Izoprok and Izopearl. This research is devoted to experimental study of thermal insulation properties of both materials as well as their mixture. Re...
Conference Paper
Recently, the finite element multi-physics simulation software Elmer was coupled with the computational fluid dynamics software OpenFOAM using parallel two-way coupler EOFLibrary. In order to verify the software is applicable to magnetohydrodynamics (MHD) problems involving alternating electromagnetic fields and conductive fluids with a free surfac...
Conference Paper
Full-text available
A new technology for large scale electromagnetic (EM) levitation melting and casting of metals is presented. In conventional axisymmetric approaches for EM levitation melting the charge weight is rather limited because the required Lorentz forces vanish on the symmetry axis and therefore leakage of the molten metal can be avoided only by the melt s...
Article
Full-text available
An open-source library called EOF which provides efficient two-way coupling between the finite element multi-physics simulation software Elmer and computational fluid dynamics software OpenFOAM is presented. Library controls interpolation and communication of fields between two codes. The main focus of this code is industrial magnetohydrodynamics w...
Conference Paper
Full-text available
The paper presents the transient distributions of physical fields for turbulent nitrogen bubbles flow through Wood-metal in rectangle bubble reactor (RBR), which is placed in the external uniform magnetic field. For multiphase flow LES (Large Eddy Simulation) study the experimentally verified (without magnetic field) Euler-Euler approach is used, w...
Conference Paper
Full-text available
A numerical study which is based on a lattice-Boltzmann model of two-phase flows has been performed to investigate the characteristics of bubble flow in vertical channel with electroconducting liquid under the action of homogeneous external magnetic field. The bubble driven flows have found wide applications in industrial technologies with liquid m...
Article
Full-text available
A numerical approach based on a lattice-Boltzmann model of two-phase flows has been developed to investigate the characteristics of bubble flow in an electroconducting liquid in a vertical channel under the action of an external magnetic field. Bubble driven flows have found wide applications in industrial technologies, such as mixing of metals and...
Article
This paper presents qualitative and quantitative characterization of two-phase liquid metal flows agitated by the stirrer on rotating permanent magnets. The stirrer was designed to fulfil various eddy flows, which may have different rate of solid particle entrapment from the liquid surface and their homogenization. The flow was characterized by vis...
Article
Purpose The purpose of this paper is to the study the multiphase bubbles flow motion in a vertical channel with an electroconducting liquid without and under the influence of a magnetic field. Design/methodology/approach For numerical calculations, the lattice Boltzmann method (LBM) is used, which is based on the kinetic theory for solving fluid m...
Article
The paper discusses transient distributions of physical fields computed with LES for a turbulent bubbles flow through an electrically conducting liquid in a cylindrical bubble reactor which is placed in an external uniform transversal or a longitudinal magnetic field. The experimentally verified (without magnetic field) Euler-Euler approach, realiz...