In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 9 No. 2 June 2003


Directional and extreme wind properties in the Gulf of Finland; 73–90

Tarmo Soomere and Sirje Keevallik

Abstract. The wind regime of the Gulf of Finland, Baltic Sea,  combines consists of SWgloballydominating  and north winds dominating in the whole Baltic Sea basin with and of local east and west winds blowing along the axis of the gulf. The angular structure of strong winds does not match the structure of all winds since they sometimes. Strong winds  blow from directions where winds generally are infrequent. Extreme wind speeds are estimated on the basis of the parameters of the Weibull distribution. The 3-hour mean wind speed in the most severe south and SW storms, estimated on the basis of the Weibull distribution, is about 24 m/s once in a century, thus by 2–3 m/s less than in the Baltic Propermay reach. The mean wind speed in the strongest east and north storms may reach 21–23 m/s or 19–22 m/s once in a century, respectively. The frequency and intensity the maximum speed of east and north winds decrease is relatively small in the eastern directionpart of the gulf. SE winds are infrequent and weak.

Key words: wind climate, extreme wind speed, Baltic Sea meteorology, marine winds.

Observed thermohaline fields and low-frequency currents in the Narva Bay; 91–106

Janek Laanearu and Urmas Lips

Abstract. This article analyses hydrophysical processes in the Narva Bay, a sub-basin of the Gulf of Finland, on the basis of measurements collected during April–August 2001. The fields of temperature and salinity are determined from the measurement data, and the progressive-vector diagrams are constructed for the currents. Surface-water characteristics and spreading of the Narva River water were affected by the winds. Large vertical displacements of the coastal waters associated with the Ekman transport away from the shore were observed in the western part of the bay. The currents at the buoy stations revealed the signals of near-inertial fluctuations in the surface layer. Theoretical analysis of low-frequency motions is based on the integrated Ekman equations, which use the wind stress and include the Rayleigh friction. The bursts of the inertial oscillations in the mixed layer observed in the open-sea side of the bay during strong winds are qualitatively well reproduced by numerical calculations.

Key words: Gulf of Finland, Narva Bay, temperature, salinity, Ekman transport, inertial oscillation.

A sea ice dynamics model for the Gulf of Riga; 107–125

Keguang Wang, Matti Leppäranta, and Tarmo Kõuts

Abstract. A model for simulating and forecasting the drift of sea ice in the Gulf of Riga, Baltic Sea, is presented. The basin size and ice thickness scale to 100 km and 30 cm, respectively. The model is based on the conservation and momentum laws of ice with a three-level ice state and viscous-plastic rheology. The steady-state momentum equation is employed; the ice state levels are open water, undeformed ice, and deformed (ridged) ice, together with a dynamic constraint controlling the redistribution process. The model parameters have been estimated by comparing the model outcome with the database of ice charts. Ridging was allowed for ice thicker than 10 cm and thinner ice rafting in compression.

Key words: sea ice dynamics, model, ice thickness distribution, constitutive law, Gulf of Riga.

Microstructural effects on wear of non-homogeneous hardmetal materials; 126–136

Irina Hussainova and Mart Viljus

Abstract. Microstructure and composition of ceramic–metal alloys have been investigated using scanning electron microscope and energy-dispersive X-ray analysis. It is shown that microstructural variables play even more important role in the tribological performance of multiphase materials than the measured mechanical properties.

Key words: non-homogeneous materials, microstructure, tribology, SEM, X-ray analysis.

Formation of aerosol particles by low-frequency sound-stimulated combustion; 137–147

Veera Dushenko, Medhat Hussainov, Igor Shcheglov, and Toomas Tiikma

Abstract. This paper presents the results of an experimental study of the formation of aerosol particles at the outlet of a flue gas duct of power equipment under the influence of low-frequency sound fluctuations (acoustic field) by burning a gaseous fuel. To measure the concentration and velocities of the aerosol particles in the flue gas, a laser Doppler anemometer, adapted to the conditions of the test rig, was used. The applied technique allowed to detect signals of solid aerosol particles with a size of 4–70 μm directly in a flue gas duct. In our experiments the existence of particles with a size over 40 μm was not detected. That is, there were no large agglomerates of aerosol particles in the flow. Besides, the study of aerosol particles enabled us to explain the increased content of CO because of the CO2 decay. Thus, monitoring of aerosol particles allowed to receive additional information about the combustion process.

Key words: combustion, low-frequency sound fluctuations, aerosol particles, LDA.

Instructions to authors; 148–150

Copyright Transfer Agreement; 151