Dynamic testing of Krasnoyarskgrazhdanproekt office building in Krasnoyarsk

Introduction. Experimental methods for studying vibrations of buildings and structures (dynamic tests) make it possible to determine an individual set of parameters of dynamic characteristics of natural vibrations inherent in each building and structure. The method of standing waves was chosen to determine dynamic characteristics; it allows to obtain detailed (with the required degree of detail) and, most importantly, reliable data on the technical condition of the building. Materials and methods. Mobile diagnostic unit “Standing Wave Method” (MSW) recorded the micro-seismic vibrations of building constructions. The layout of sensors with a single reference point was chosen. The standing wave method was applied to develop the software package in order to process the micro-seismic vibrations of the building. Vibration cohe­rence spectra were analyzed to identify the natural frequencies of the building. A GIS model was developed to demonstrate the amplitudes and phases of vibrations in the building. Results. Eigenfrequencies, peak amplitudes, and phase characteristics of the building’s wave field were determined. Patterns of distribution of amplitudes and maps of vibration phases were constructed. Areas, accommodating destructive processes in the brickwork of the building’s bearing walls, were identified and the reasons for their occurrence were established. Conclusions. The dynamic characteristics of the building were obtained in reliance upon the results of dynamic tests of the office building. The analysis of the distribution of these parameters allowed to assess the technical condition of the building and to make recommendations towards its strengthening. The author suggests that the mobile diagnostic system, employing the standing wave method, can be used to resolve a wide range of problems.

Thermal Insulation and Sound Absorption Properties of Open-Cell Polyurethane Foams Modified with Bio-Polyol Based on Used Cooking Oil

The main goal of this work was to evaluate the thermal insulation and sound absorption properties of open-cell rigid polyurethane foams synthesized with different contents of cooking oil-based polyol. The content of the applied bio-polyol as well as flame retardant (triethyl phosphate) in the foam formulation had a significant influence on the cellular structures of the materials. The open-cell polyurethane foams were characterized by apparent densities in the range 16–30 kg/m3. The sound absorption coefficients of the polyurethanes with various contents of bio-polyol were determined using the standing wave method (Kundt’s tube) in the frequency range of 100–6300 Hz. The effect of the content of the bio-polyol and flame retardant on the coefficient of thermal conductivity (at average temperatures of 0, 10 and 20 °C) as well as the compressive strength (at 20 and −10 °C) was analyzed. Different trends were observed in terms of the thermal insulation properties and sound absorption ability of the open-cell polyurethanes due to the addition of bio-polyol. In conclusion, it is necessary to use systems containing both petrochemical and bio-based raw materials.

Methods of detectiоn a voids under concrete slabs of water faces of the dam of Novosibirsk hydrostation by the standing wave method

Using the example of the Novosibirsk hydrostation, the capabilities of the standing wave method to identify defects in the fastenings of water faces of dams of hydraulic structures are demonstrated. The accumulation of amplitude spectra of acoustic noise records allows one to determine the frequencies of the few first modes of standing compression waves generated by noise in concrete slabs. A sharp increase in the frequency of the lowest mode of standing waves is an indicator of the appearance of voids under the slabs or decompression of the base soil.

STANDING WAVES IN ENGINEERING OBJECTS OF COMPLEX CONSTRUCTIONS

According to the results of research on complex engineering objects, results were obtained that demonstrate significant deviations from the models of buildings and structures adopted as the basis for calculating seismic resistance and structural stability. First, it is the existence of reflecting seismic oscillations of the boundaries inside the building, when standing waves form a common field for the building as a whole and a local field for a part of the object. Secondly, a block structure of the object, when there are natural oscillations of different magnification with a different area of the object's coverage, when some blocks independently oscillate, they unite into one system. Thirdly, the existence of walls with double reflecting properties, which changes the field of standing waves. Fourthly, the complex geometry of the object causes fields of standing waves, e is described by two wave numbers. Experimental data show that in the theory of buildings, it is necessary to move to the models of nested resonators, models of coupled resonators, and the verification of models should be entrusted to the standing wave method.

Effect of the Separation Distance on the Aeroacoustic Source of Multiple Shallow Cavities

Flow over ducted shallow cavities can excite fluid resonant oscillations. A common industrial application is the flow in corrugated pipes that can be modeled as a series of consecutive shallow cavities. In the current study, the effect of the separation distance on the aeroacoustic source of multiple shallow cavities is investigated. The standing wave method (SWM) is used to measure the source, where multiple microphones reconstruct the acoustic standing wave upstream and downstream of the cavities. The effect of the ratio between the separation distance to cavity length is investigated for a practical range from 0.5 to 1.375 for two- and three-cavity configurations. At low and intermediate sound levels, constructive hydrodynamic interference, resulting in a strong source, is observed for the extremum spacing ratios of 0.5 and 1.375. However, at high excitation levels, 10% and higher, the source, slightly but consistently, decreases upon increasing the separation ratio. These trends persist for both the double- and triple-cavity configurations. On the other hand, the separation distance of destructive interference is found to depend on the number of cavities of the tested configuration. Particle image velocimetry (PIV) measurements of the constructive interference cases show strong synchronized vorticity shedding in all cavities. Each cavity contribution to the total aeroacoustic source is then examined by means of Howe's analogy, and the percentage contribution of each cavity is found to depend on the excitation level.