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Journal Details
Format
Journal
eISSN
2255-8896
First Published
18 Mar 2008
Publication timeframe
6 times per year
Languages
English

Search

Volume 53 (2016): Issue 3 (June 2016)

Journal Details
Format
Journal
eISSN
2255-8896
First Published
18 Mar 2008
Publication timeframe
6 times per year
Languages
English

Search

7 Articles
Open Access

Investigations of Wind Shear Distribution on the Baltic Shore of Latvia

Published Online: 27 Jul 2016
Page range: 3 - 10

Abstract

Abstract

The paper presents a review of wind parameter measurement complexes and investigation methods used for potential wind energy evaluation. Based on results of long-term investigations of wind shear distribution regularities are shown up to 160 m height on the Baltic Sea shore. Distribution of potential wind energy in Latvia is shown as a map and table of average and average cubic wind speed values. Database of wind parameter measurements is available at a public website.

Keywords

  • website
  • wind map
  • wind shear
  • wind speed measurement
Open Access

Theoretical and Experimental Investigations of Cylindrical Air-Heating Solar Collector

Published Online: 27 Jul 2016
Page range: 11 - 21

Abstract

Abstract

Solar energy is used not only at low latitudes, where it is available at large amounts, but also at higher latitudes, where height of sun and irradiance are significantly lower. On the other hand, the length of day at higher latitudes is longer in summer than at low latitudes, and also the path of the sun is longer.

The present research deals with seeking for new shapes of solar collectors capable of receiving more solar energy.

For designing and evaluating new shapes of solar collectors, it is necessary to have new methods for simple calculations of energy received from the sun by surface of any shape and direction. Such a method is explained in the present paper.

Based on calculations by the proposed method, a new form of solar collector – a cylindrical collector – has been worked out. This collector is intended for air heating, but main principles can also be used for water heating, and even for photovoltaics.

A cylindrical collector receives more energy in the morning and evening than a flat one, but at midday power of both collectors is equal, if effective areas are equal. Daily energy sum of the cylindrical solar collector is 1.5 times greater than that of the flat one.

Keywords

  • air heating
  • collector
  • cylindrical
  • solar energy
Open Access

Wave Energy Potential in the Latvian EEZ

Published Online: 27 Jul 2016
Page range: 22 - 33

Abstract

Abstract

The present article deals with one of the alternative forms of energy – sea wave energy potential in the Latvian Exclusice Economic Zone (EEZ). Results have been achieved using a new method – VEVPP. Calculations have been performed using the data on wave parameters over the past five years (2010–2014). We have also considered wave energy potential in the Gulf of Riga. The conclusions have been drawn on the recommended methodology for the sea wave potential and power calculations for wave-power plant pre-design stage.

Keywords

  • Latvian EEZ
  • renewable energy
  • sea wave potential
  • wave energy
  • wave energy distribution of time wave energy directional distribution
Open Access

Invariant Control of the Technological Plants to Compensate an Impact of Main Disturbances Preemptively

Published Online: 27 Jul 2016
Page range: 34 - 44

Abstract

Abstract

The paper considers a survey of the research procedures and results due to invariant control method application perspective for operation quality advancement in several technological plants (wastewater biological treatment tanks and water steam production boilers), which operate under influence of organised and random disturbances. A specified subject of research is the simulation model of the multi-link invariant control system for steam pressure stabilisation in a steam boiler by preemptive compensation of steam load and feed water flow impact on output parameter (steam pressure), developed in MATLAB/SIMULINK. Simulation block-diagram of the steam boiler invariant control system, containing closed loop PID control circuit and open loop DPC circuit, has been composed on the basis of the designed mathematical model of the system components, disturbance compensation algorithms, and operational equation of the invariant control system. Comparative response of the steam boiler, operating under influence of fluctuating disturbances, with conventional PID control and using PID-DPC control with disturbance compensation controller DPC, has been investigated. Simulation results of invariant PID – DPC control system show that output parameter of the steam boiler - pressure remains practically constant under fluctuating disturbances due to a high-speed response of DPC controller.

Keywords

  • controller
  • disturbance
  • invariant control
  • simulation model
  • steam boiler
  • technological plant
  • wastewater aeration
Open Access

Influence of Voltage Dips on the Operation of Brushless Exciter System of Synchronous Machines

Published Online: 27 Jul 2016
Page range: 45 - 56

Abstract

Abstract

This paper presents a mathematical model with continuous variables for brushless exciter system of synchronous machines, containing the thyristor elements. Discrete Laplace transform is used for transition from a mathematical model of a system with variable structure in continuous variables to equation finite difference with permanent structure. Then inverse transition is made to a mathematical model in continuous variables with permanent structure.

Keywords

  • discrete transformation
  • exciter system
  • mathematical model
  • semiconductor thyristor
  • synchronous motor
Open Access

Production of ZnO and CdO-ZnO thin Films by Extraction–Pyrolytic Method

Published Online: 27 Jul 2016
Page range: 57 - 66

Abstract

Abstract

The extraction-pyrolytic method has been applied to produce the ZnO and CdO-ZnO thin films on glass and quartz glass substrates. According to X-ray diffraction measurements, the ZnO and CdO phases have been produced with an average size of crystallites about 8–42 nm in the films. The thickness of the layers measured by a profilometer has been up to 150 nm. The surface morphology measurements show that the surface of the films may be rough and non-continuous. The SEM results confirm the dependence between the preparation procedure and the quality of the thin film.

Keywords

  • CdO-ZnO thin films
  • extraction-pyrolytic method
  • surface morphology
  • X-ray diffraction
Open Access

Impact of the Former Salaspils Nuclear Reactor on the Surrounding Territory

Published Online: 27 Jul 2016
Page range: 67 - 76

Abstract

Abstract

The paper presents results of the long-term environment radioactivity monitoring in the vicinity of the decommissioned Salaspils Nuclear Reactor. Data include Cs-137 contamination levels of soils, H-3 concentration in ground waters, as well as gross beta activity of sewage and rainwater drainage of SNR. Special attention is devoted to the radioactive pollution of water due to leakage from the special wastewater basin detected in December 2014.

Keywords

  • artificial radionuclides: Cs-137, H-3
  • beta-activity
  • environment radioactivity monitoring
  • nuclear reactor
7 Articles
Open Access

Investigations of Wind Shear Distribution on the Baltic Shore of Latvia

Published Online: 27 Jul 2016
Page range: 3 - 10

Abstract

Abstract

The paper presents a review of wind parameter measurement complexes and investigation methods used for potential wind energy evaluation. Based on results of long-term investigations of wind shear distribution regularities are shown up to 160 m height on the Baltic Sea shore. Distribution of potential wind energy in Latvia is shown as a map and table of average and average cubic wind speed values. Database of wind parameter measurements is available at a public website.

Keywords

  • website
  • wind map
  • wind shear
  • wind speed measurement
Open Access

Theoretical and Experimental Investigations of Cylindrical Air-Heating Solar Collector

Published Online: 27 Jul 2016
Page range: 11 - 21

Abstract

Abstract

Solar energy is used not only at low latitudes, where it is available at large amounts, but also at higher latitudes, where height of sun and irradiance are significantly lower. On the other hand, the length of day at higher latitudes is longer in summer than at low latitudes, and also the path of the sun is longer.

The present research deals with seeking for new shapes of solar collectors capable of receiving more solar energy.

For designing and evaluating new shapes of solar collectors, it is necessary to have new methods for simple calculations of energy received from the sun by surface of any shape and direction. Such a method is explained in the present paper.

Based on calculations by the proposed method, a new form of solar collector – a cylindrical collector – has been worked out. This collector is intended for air heating, but main principles can also be used for water heating, and even for photovoltaics.

A cylindrical collector receives more energy in the morning and evening than a flat one, but at midday power of both collectors is equal, if effective areas are equal. Daily energy sum of the cylindrical solar collector is 1.5 times greater than that of the flat one.

Keywords

  • air heating
  • collector
  • cylindrical
  • solar energy
Open Access

Wave Energy Potential in the Latvian EEZ

Published Online: 27 Jul 2016
Page range: 22 - 33

Abstract

Abstract

The present article deals with one of the alternative forms of energy – sea wave energy potential in the Latvian Exclusice Economic Zone (EEZ). Results have been achieved using a new method – VEVPP. Calculations have been performed using the data on wave parameters over the past five years (2010–2014). We have also considered wave energy potential in the Gulf of Riga. The conclusions have been drawn on the recommended methodology for the sea wave potential and power calculations for wave-power plant pre-design stage.

Keywords

  • Latvian EEZ
  • renewable energy
  • sea wave potential
  • wave energy
  • wave energy distribution of time wave energy directional distribution
Open Access

Invariant Control of the Technological Plants to Compensate an Impact of Main Disturbances Preemptively

Published Online: 27 Jul 2016
Page range: 34 - 44

Abstract

Abstract

The paper considers a survey of the research procedures and results due to invariant control method application perspective for operation quality advancement in several technological plants (wastewater biological treatment tanks and water steam production boilers), which operate under influence of organised and random disturbances. A specified subject of research is the simulation model of the multi-link invariant control system for steam pressure stabilisation in a steam boiler by preemptive compensation of steam load and feed water flow impact on output parameter (steam pressure), developed in MATLAB/SIMULINK. Simulation block-diagram of the steam boiler invariant control system, containing closed loop PID control circuit and open loop DPC circuit, has been composed on the basis of the designed mathematical model of the system components, disturbance compensation algorithms, and operational equation of the invariant control system. Comparative response of the steam boiler, operating under influence of fluctuating disturbances, with conventional PID control and using PID-DPC control with disturbance compensation controller DPC, has been investigated. Simulation results of invariant PID – DPC control system show that output parameter of the steam boiler - pressure remains practically constant under fluctuating disturbances due to a high-speed response of DPC controller.

Keywords

  • controller
  • disturbance
  • invariant control
  • simulation model
  • steam boiler
  • technological plant
  • wastewater aeration
Open Access

Influence of Voltage Dips on the Operation of Brushless Exciter System of Synchronous Machines

Published Online: 27 Jul 2016
Page range: 45 - 56

Abstract

Abstract

This paper presents a mathematical model with continuous variables for brushless exciter system of synchronous machines, containing the thyristor elements. Discrete Laplace transform is used for transition from a mathematical model of a system with variable structure in continuous variables to equation finite difference with permanent structure. Then inverse transition is made to a mathematical model in continuous variables with permanent structure.

Keywords

  • discrete transformation
  • exciter system
  • mathematical model
  • semiconductor thyristor
  • synchronous motor
Open Access

Production of ZnO and CdO-ZnO thin Films by Extraction–Pyrolytic Method

Published Online: 27 Jul 2016
Page range: 57 - 66

Abstract

Abstract

The extraction-pyrolytic method has been applied to produce the ZnO and CdO-ZnO thin films on glass and quartz glass substrates. According to X-ray diffraction measurements, the ZnO and CdO phases have been produced with an average size of crystallites about 8–42 nm in the films. The thickness of the layers measured by a profilometer has been up to 150 nm. The surface morphology measurements show that the surface of the films may be rough and non-continuous. The SEM results confirm the dependence between the preparation procedure and the quality of the thin film.

Keywords

  • CdO-ZnO thin films
  • extraction-pyrolytic method
  • surface morphology
  • X-ray diffraction
Open Access

Impact of the Former Salaspils Nuclear Reactor on the Surrounding Territory

Published Online: 27 Jul 2016
Page range: 67 - 76

Abstract

Abstract

The paper presents results of the long-term environment radioactivity monitoring in the vicinity of the decommissioned Salaspils Nuclear Reactor. Data include Cs-137 contamination levels of soils, H-3 concentration in ground waters, as well as gross beta activity of sewage and rainwater drainage of SNR. Special attention is devoted to the radioactive pollution of water due to leakage from the special wastewater basin detected in December 2014.

Keywords

  • artificial radionuclides: Cs-137, H-3
  • beta-activity
  • environment radioactivity monitoring
  • nuclear reactor

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