In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 50 No. 1 March 2001


Editorial; 3–4

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Agent-based software design; 5–21

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Margus OJA, Boris TAMM, and Kuldar TAVETER

Abstract. This paper introduces an agent-based software development method. It defines a limited number of components of an agent-based software system and shows the possibility of designing and implementing actual software. Starting points in developing agent-based software are the business rules and the basic agent-based concepts as defined in the paper. A notation for visualizing the defined concepts is introduced. The notation of the unified modelling language UML is used. The possibility to define rules for mapping agent model elements onto source code is shown using the JADE agent platform.

Key words: software agents, software design, software engineering, UML, JADE.

Characterization of powder particle morphology; 22–34

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Valdek MIKLI, Helmo KÄERDI, Priit KULU, and Michal BESTERCI

Abstract. Technological properties of powders depend on their granulometry and particle morphology. Most of the image analysis methods provide only average size parameters (diameter, area, perimeter, etc.) which are often inadequate for characterizing the morphology of the particles. For particle abrasivity characterization, angularity factors are more sensitive. This paper studies different parameters for describing the hardmetal powder granulometry and morphology. The main aim is to find numerical descriptors for the shape factors that adequately characterize the hardmetal powders produced by the mechanical method – milling in a disintegrator. For the characterization of the powder particle morphology, irregularity parameter IP (relation of the diameters of the maximum inscribed and minimum circumscribed circles) suits best, taking into account the ellipticity and irregularity of the particle form. For describing the angularity of ground powders, the so-called “spike parameter – quadratic fit” can be used.

Key words: hardmetal powder, granulometry, morphology, shape factor, angularity

Anisotropy of moderate and strong winds in the Baltic Proper; 35–49

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Abstract. It is shown that directional distribution of moderate and strong winds in the Baltic Sea area is highly anisotropic. The dominating wind direction is south-west and a secondary peak corresponds to north winds. North-west storms are relatively infrequent and north-east storms are extremely rare. Angular distributions of moderate and strong winds are identical on both sides of the Baltic Sea. The specific wind regime does not penetrate into mainland.

Key words: wind directions, wind speed, wind energy, Baltic Sea meteorology.

Periodical component of the West-Estonian wind; 50–57

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Abstract. Characteristics of the periodical component of the daily wind on the Estonian western coast have been established using the correlation analysis. The named component is known as coastal breeze occurring only in summer and it is always directed from the sea towards the land with the peak at 2 PM local time, independent from the cyclonic wind. Interrelation between the components of the wind, blowing parallel and crosswise to the coastline, decreases monotonously towards inland. Thus the breeze has no natural boundary and it is replaced smoothly by the local periodical wind of the same velocity while the prevailing direction of the latter is not transverse to the coast any more.

Key words: periodical wind, coastal breeze, correlation analysis.

Investigation of turbulence in a plunging breaking wave; 58–78

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Toomas LIIV

Abstract.  The velocity field created by a plunging breaking wave on a smooth bottom with slope 1 : 17 was studied experimentally in a wave flume. Laser Doppler anemometry was used to investigate the flow field above the bottom boundary and below the trough level of the wave. Turbulence intensities, Reynolds stresses, and turbulent kinetic energy were examined. The results show that large-scale motions dominate in turbulence under the plunging breaker. The flow has characteristic features of an outer surf zone. It is found that turbulent quantities in the zone close to the bottom depend on the nature of the flow acceleration. During the deceleration phase, all turbulent quantities reach their maximum values. In the layers close to the wave trough, turbulent quantities depend on the wave parameters. Turbulent kinetic energy reaches its maximum value under the wave crest and decreases rapidly to a constant value under the wave trough. Turbulence is generated on the surface during the breaking process and it diffuses towards the bottom. The energy level first decreases downward and then increases again close to the bottom due to the bottom boundary layer turbulence. Kinetic energy is transported landward in the upper layers of the flow and seaward near the bottom.

Key words: plunging breaking wave, turbulence, Laser Doppler anemometry.




Estonian Academy of Sciences: Meeting the challenges for 2000–2004. Framework of activities; 79–80