The implementation of low-energy construction includes aspects related to technological and material research regarding thermal insulation. New solutions are sought, firstly, to reduce heat losses and, secondly, to improve the environment conditions in isolated rooms. The effective heat resistance of insulating materials is inversely proportional to temperature and humidity. Cement composites filled with lightweight artificial aggregates may be a suitable material. Selecting a proper method for measuring the thermal conductivity of concrete is important to achieve accurate values for calculating the energy consumption of buildings. The steady state and transient methods are considered the two main thermal conductivity measurement approaches. Steady state is a constant heat transfer, whereby the temperature or heat flow is time independent. In the transient method, temperature changes over time. Most researchers have measured the conductivity of cement-based materials based on transient methods. The availability and cost of equipment, time for experimental measurements and measurement ability for moist specimens may be some of the reasons for using this method. However, considering the accuracy of the measurements, the steady state methods are more reliable, especially for testing dry materials. Four types of composites were investigated that differed in filler: natural aggregate, sintered fly ash filler, sintered clay and granular foam glass aggregate. The method of preparing the samples for testing is especially important for the obtained results. The samples, with a specific surface roughness, will show a lower coefficient of thermal conductivity by 20–30%; therefore, the selection of the type of contact layer between the plate of the measuring device and the sample is of particular importance.

Considered here is the effect of multistage coupling on the dynamics of an aircraft engine rotor with eight mistuned bladed discs on a drum-disc shaft. Each disc had a different number of rotor blades. Free and forced vibrations were examined using finite element models of single rotating blades, bladed discs, and an entire rotor. Calculations of the global rotating mode shapes of flexible mistuned bladed discs-shaft assemblies took into account the excitation of the turbine bladed disc with 0EO, 1EO and 2EO forces. The thus obtained maximal stress values of all of the rotor blades were carefully examined and compared with a tuned system to discover resonance conditions and coupling effects. Mistuning changes the stress distribution in individual rotor blades and the level of maximum stress increases or decreases as compared to bladed discs which are analyzed without the shaft.

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The powders of electrical-engineering periclase obtained from natural brucite mainly meet the specifications of the second and the third classes according to GOST 13236-83. The reason for the poor quality of the powders is their high calcium oxide content and this owes to its presence in large quantities in the original brucite (exceeds 2.0~ in the calcined substance). This fact made it necessary to carry out additional and more detailed studies on the properties of the periclase powders having a high calcium oxide content.Moisture (water) absorption is one of the most important parameters determining the service characteristics of the periclase powders in TEN [i, 2]. Calcium oxide has a considerable hydration ability [3] and, consequently, it can make periclase powders highly prone to moisture absorption.It was established [4] that the change in the weight content of calcium oxide in a periclase powder from 0.75 up to 2.20~ does not have a significant effect on its moisture absorption. We note that in these experimental powders, calcium oxide was present in the form of silicate compounds.However, in periclase powders, calcium oxide can be present in free state (besides calcium silicates).This paper deals with a study of the aspects concerning the hydration activity of a periclase powder, pure magnesium and calcium oxides, and the calcium-containing compounds present in periclase in the form of additional (impurity) phases. Imported periclase powders were also studied for the purpose of comparison.The granulometric composition of the experimental periclase powders that were obtained from brucite met the specifications concerning the 'fine grade' according to GOST 13236-83. Pure magnesium and calcium oxides and silicate compounds (monticellite CaO'MgO'SiO 2, mervinite 3CaO-MgO'2SiO2, and dicalcium silicate 2CaO'SiOe) had a grain (particle) size less than 0.063 mm.The powders were calcined at 1000~ and were held in the medium of air having a humidity of 97-98~ at 20-25~The duration of holding varied from i up to 50 days. Hydration activity of the powders was evaluated on the basis of the change in their weight during calcination at 1000~In view of the fact that the processes of moisture adsorption and subsequent hydration occur mainly at the surface of the grains, it is necessary to take the specific surface of the powders into account. The data presented in Table I show that the powders of calcium and magnesium oxides and the impurity-phase are characterized by uncomparable (widely differing) values of the specific surface. Therefore, in order to evaluate their hydration activity, we used the parameter of weight change during calcination (recalculated) per unit surface area (Table 2).It was established that the hydration activity (ability to hydrate) of calcium oxide exceeds that of magnesium oxide by approximately 8 times. Monticellite, mervinite, and dicalcium silicate hydrate very strongly as compared to pure calcium oxide.Thus, calcium oxide present in the periclase powders in free state must have a signific...

Considered here was the effect of multistage coupling on the dynamics of a rotor consisting of eight mistuned bladed discs on a solid shaft. Each bladed disc had a different number of rotor blades. Free vibrations were examined using finite element representations of rotating single blades, bladed discs, and the entire rotor. In this study the global rotating mode shapes of eight flexible mistuned bladed discs on shaft assemblies were calculated, taking into account rotational effects such as centrifugal stiffening. The thus obtained natural frequencies of the blade, shaft, bladed disc and entire shaft with discs were carefully examined to discover resonance conditions and coupling effects. This study found that mistuned systems cause far more intensive multistage coupling than tuned ones. The greater the mistuning, the more intense the multistage coupling.

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During the exploitation of a commercial LP steam turbine, self-excitation occurred in the last stage of slender blades, inducing high vibration amplitudes. These problems were solved by changing the geometry of certain blades (feathering) and arranging them in a specific order (alternating mistuning). This paper presents free and forced vibrations of various mistuned steam turbine bladed discs. The natural frequencies and mode shapes of the steam turbine bladed discs were calculated using FEM models. Two different approaches to mistuning were applied: either the blade geometry or the Young’s Modulus were changed. Next, the results were compared. This showed that blade geometry mistuning gave the best results for long blades in the case of higher mistuning. The forced vibration analysis showed that the maximal blade stress location differed, depending on the kind of mistuning. The application feathering and alternating mistuning showed lower stress levels than the tip-timing measured standard mistuning pattern.

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