Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Engineering

Volume 9 No. 1 March 2003

Exploring irregular vibrations and chaos by the wavelet method; 3–24

Ülo Lepik

Abstract. The paper cosiders possibilities of exploring nonlinear structural vibrations and detecting chaos by the wavelet method. The signal is decomposed into several lower resolution components. Some numerical quantities for characterizing the signal (wavelet energy distribution, Shannon and threshold entropy, similarity index, self-similarity) are introduced. Noisy systems are discussed. An example, in which the noise transfers chaotic motion to regular vibrations, is described. The wavelet packet method is applied; it is shown that such an approach allows to decrease the width of the frequency bands and gives the possibility to distinguish chaotic vibrations from random motion.

Key words: non-linear vibrations, chaos, wavelet method, entropy, noisy systems.

A parametric optimization technique for model-predictive control simulation; 25–33

Ingmar Randvee

Abstract. A parametrization technique, which has been introduced in the 1980s in the context of multilevel systems, is revisited. It is shown that a version of this optimization technique (which skips the introduction of co-states and the solution of the two-point boundary value problem) may be applicable in the numerical simulation of one-step ahead unconstrained model-predictive control strategies and other suboptimal real-time dynamic systems that use predicted closed-loop system trajectories. The representation is given in discrete-time setting using state-space models.

Key words: predictive control, parametric optimization.

On the crawl space moisture control in buildings; 34–58

Miimu Airaksinen, Jarek Kurnitski, and Olli Seppänen

Abstract. This study considers transient effects of the moisture capacity and other properties of ground covers and base floor on relative humidity in cold-climate outdoor-air-ventilated crawl spaces. The objectives of the study were to find out how relative humidity can be reduced by optimal selection of ground covers and air change rates, and to evaluate the acceptability of achieved moisture conditions by means of mould growth analyses. Two buildings, one with a relatively warm and another with a relatively cold crawl space, were studied with the resistance-capacity network model including the heat and moisture transfer in crawl spaces. Thermal and moisture buffering effects of various ground covers and air change rates were simulated. In a relatively warm crawl space the moisture problems were easy to avoid – all ground covers gave clearly acceptable conditions at an air change rate of 0.5–2.0 ach. In the cold crawl space, the moisture conditions were much more critical. The acceptability of conditions was evaluated by calculating the mould growth index. To achieve acceptable moisture conditions, 15–30 cm lightweight expanded clay aggregate or 5–10 cm expanded polystyrene ground cover must be used. An air change rate of 0.5–1.0 ach provided the lowest relative humidity conditions during the heating season, and in the summer it was necessary to use an air change rate of 2.0–5.0 ach to warm up the crawl space. In critical conditions, thermal insulation and moisture capacity proved to be important properties of the ground cover allowing to achieve acceptable conditions.

Key words: crawl space, air change rate, relative humidity, mould growth.

Thermal performance of typical residental buildings; 59–66

Teet-Andrus Kõiv and Kadi Kusnetsov

Abstract. This paper describes indoor temperature forming in typical panel apartment buildings. Using average free heat gain data, balance temperatures in different months of the heating period are determined. Based on average external temperatures of the years 1971–2000 in Tallinn and balance temperatures, the number of corrected heating degree-days in different months is obtained.

Key words: free heat gains, heat losses, balance temperature, corrected heating degree-days.

Instructions to authors; 67–69