The analysis of flutter characteristics based on generalized parameters of eigen modes of vibrations

Flutter numerical analysis of a dynamically scaled model (DSM) of a high aspect ratio wing was performed using experimentally obtained generalized parameters of eigen modes of vibrations. The DSM is made of polymer composite materials and is designed for aeroelastic studies in a high-speed wind tunnel. As a result of the analysis, safe operation conditions (flutter limits) of the DSM were determined. The input data to develop the flutter mathematical model are DSM modal test results, i.e. eigen frequencies, mode shapes, modal damping coefficients, and generalized masses obtained from the experiment. The known methods to determine generalized masses have experimental errors. In this work some of the most practical methods to get generalized masses are used: mechanical loading, quadrature component addition and the complex power method. Errors of the above methods were analyzed, and the most reliable methods were selected for flutter analysis. Comparison was made between the flutter analysis using generalized parameters and a pure theoretical one based on developing the mathematical model from the DSM design specifications. According to the design specifications, the mathematical model utilizes the beam-like schematization of the wing. The analysis was performed for Mach numbers from 0.2 to 0.8 and relative air densities of 0.5, 1, 1.5. Comparison of the two methods showed the difference in critical flutter dynamic pressure no more than 6%, which indicates good prospects of the flutter analysis based on generalized parameters of eigen modes.

Optimum transfer characteristics of the Tesla transformer on the first and second half-waves of output voltage

The elements of the theory of the Tesla transformer are stated, the exact solution of the equations of the dynamics of currents and voltages in the transformer circuits through the generalized parameters of the circuits (Q-factors of the primary and secondary circuits, the coupling coefficient of the circuits and mismatching factor of the natural resonance frequencies of the circuits) is given, under the assumption of their constancy. The optimal transfer characteristics of the processes of charging the capacitive storage of the secondary circuit of the transformer on the first and second half-waves are given, demonstrating the capabilities of the Tesla transformer.

MONITORING AND PREDICTION OF TECHNICAL CONDITION OF STRUCTURAL UNITS OF BUILDINGS AND STRUCTURES

Рассмотрены вопросы анализа существующих подходов к мониторингу технического состояния строительных конструкций эксплуатируемых зданий и сооружений, описанные в нормативно-технической литературе. Рассмотрены и проанализированы типы мониторинга технического состояния зданий, особенности их проведения, имеющиеся несогласованности и разница в подходах к выполнению разных типов мониторинга. Проведено уточнение схемы мониторинга технического состояния строительных конструкций зданий и сооружений. Рассмотрены основные контролируемые параметры и их предельные значения с точки зрения проведения мониторинга, а также прогноза технического состояния несущих и ограждающих строительных конструкций зданий и сооружений различного назначения. Проведен анализ возможности использования предусмотренных в действующих нормативно-технических документах динамических испытаний строительных конструкций в условиях отсутствия объективных результатов при прогнозировании технического состояния конструкций по результатам вибрационных испытаний зданий. Выявлены значительные расхождения в подходах к проведению процедуры мониторинга технического состояния и мониторинга технического состояния зданий и сооружений, находящихся в ограниченно работоспособном или аварийном состоянии. Сделана попытка провести увязку требований и рекомендаций действующего ГОСТ 31937-2011 по проведению мониторинга, для обеспечения плавного перехода по ключевым контролируемым параметрам от общего мониторинга к мониторингу зданий, находящихся в ограниченно работоспособном или аварийном техническом состоянии. Рассмотрены пути прогнозирования дальнейшего развития технического состояния строительных конструкций зданий, с использованием обобщенных параметров, характеризующих текущее фактическое техническое состояние строительных конструкций, с использованием методов параметрического прогнозирования и экспертных методов. We considered the issues of analysis for existing approaches to monitoring technical condition of structural units of operated buildings and structures that are described in the normative and technical literature. We considered and analyzed different types of monitoring technical condition of buildings, features of their implementation, existing inconsistencies and difference in approaches to performing different types of monitoring. As a result we clarified the scheme of monitoring technical condition of structural units of buildings and structures. The main controlled parameters and their limit values are considered from the point of view of monitoring, as well as prediction of the technical condition of load-bearing and enclosing structural units of buildings and structures for various purposes. We carried out the analysis of the possibility of using dynamic tests of structural units provided in the current regulatory and technical documents in the absence of objective results when predicting the technical condition of structures based on the results of vibration tests of buildings. Significant discrepancies were revealed in the approaches to the procedure of monitoring technical condition of buildings and structures that are in a limited operational or emergency condition. We made an attempt to link the requirements and recommendations of the current GOST 31937-2011 for monitoring, to ensure a smooth transition in key controlled parameters from general monitoring to monitoring of buildings that are in a limited operational or emergency technical condition. The ways of predicting further development of the technical condition of structural units of buildings are considered, using generalized parameters that characterize the current technical condition of structural units, using parametric prediction and expert methods.

Design of compositions and types of structures of injection molded dispersed filled thermoplastics with good processability and high strength

The issues on the assessment of rheological properties of dispersed filled polymer composite materials (DFPCM) in terms of generalized parameters of disperse structure are considered. The dependences of pressure loss during injection molding of thin-walled DFPСM products with different types of disperse structure: dilute, low-filled, medium-filled and high-filled systems are given for the first time. It has been established that to obtain DFPCM based on thermoplastics with good processing properties and products with high strength, it is necessary to create materials having medium-filled type of structure and the generalized parameter Θ ≈ 0.5-0.6 vol/vol. The algorithm for calculating the dispersed filler content with known basic properties to provide a given type of DFPCM structure is proposed.

Rheological properties of dispersion-filled thermoplastics with different types of structures at various processing temperatures

The article presents the results of a study of the rheological characteristics of dispersion-fi lled polymer composite materials (DFPCM) based on LDPE and glass balls of the ШСО-30 brand in a wide range of processing temperatures. For the fi rst time, the rheological properties of dispersion-fi lled polymer composite materials are considered from the standpoint of the formation of the dispersed phase with diff erent types of lattices, functional division of the polymer matrix (φp = Θ + В + М) and the construction of dispersed systems with diff erent types of structures (DS, LFS, MFS, HFS) in terms of generalized parameters (Θ, amid/d). This approach allows us to predict and describe the rheological properties for all DFPCMs with diff erent types of dispersed structures, using a dispersed phase (fi ller) with known geometric dimensions (d), packing density (parameter kpacking and φm) based on this polymer matrix. The infl uence of temperature on the processing technology of DFPCM with diff erent types of structures into products by injection molding has been established.

Porous materials: microporosity induced by the shape and length of the pores

There are insufficient parameters to explain the appearance of microporosity in porous materials. One of the parameters associated with micropores is the generalized pore shape factor F, which includes, as special cases, the known slit, circular and spherical model pore shapes. F covers the shapes between the slit (F = 2000) and spherical (F = 6000), as well as beyond. For the intermediate shape, one can estimate proportions of model motifs. The transition of the shape from one model to another is accompanied by the appearance of micropores (or vice versa); corresponding dependencies are given. Nanotechnologies, such as self-assembly of ordered mesoporous materials (OMMs), the production of carbon OMMs as replicas of silica matrixes, supercapacitors made of carbon nanofibres (CNF), a hybrid CNF/MWCNT for use in lithium-ion batteries, carbon xerogels with Ni additive for storage of H2, catalysis and others are discussed; they cover materials with F in the range 1,100 ÷ 32,600. A pore surface length index Lsi is proposed for any pore shape; it supplements the generalized parameters causing stresses, deformations and micropores. Using F and Lsi, it was discovered, that activated carbon, obtained as a replica of non-circular matrix of silica, behaves like a compressed spring, which, after removal of silica, expands and its pores become circular. A concept of molecular sieving based on the shape of molecules is proposed and demonstrated by the example of lipase immobilization. Application of the proposed parameters improves understanding of many published and new results.