Test and Calculation Model of Thermal Conductivity of Concrete

In order to study the influence of water content and hydration degree on the thermal conductivity of concrete, based on the steady-state plate method, the influence of water content, temperature, hydration degree and other factors on the thermal conductivity of early concrete was studied, and the calculation model of thermal conductivity of early concrete was established according to the test results and influence rules. The results show that there is a linear relationship between the thermal conductivity and water content at 28d, the higher the hydration degree is, the lower the thermal conductivity of concrete is; the difference between the measured value and the calculated model value is small, and the calculation formula can meet the requirements of engineering calculation.

Direct SN2 or SN2X Manifold – Mechanistic Study of Ion-Pair Catalyzed Carbon(sp3)-Carbon(sp3) Bond Formation

Density functional theory (DFT) is used in this work to predict the mechanism for constructing congested quaternary-quaternary carbon(sp3)–carbon(sp3) bonds in a pentanidium catalyzed substitution reaction. Computational mechanistic studies were carried out to investigate the proposed SN2X manifold, which consists of two primary elementary steps: halogen atom transfer (XAT) and subsequent SN2. For the first calculated model on original experimental substrates, XAT reaction barriers were more kinetically competitive than an SN2 pathway and connects to thermodynamically stable intermediates. Extensive computational screening-modelling were then done on various substrate combinations designed to study steric influence and to understand the mechanistic rationale, and calculations reveal that sterically congested substrates prefer the SN2X manifold over SN2. Different halides as leaving groups were also screened and it was found that the reactivity increases in order of Br > Cl > F in agreement of the strength of C–X bonds. However, DFT modelling suggests that chlorides can be a viable substrate for the SN2X process which should be further explored experimentally. Finally, ONIOM calculations on the full catalyst model were carried out to rationalize the stereoselectivity which corroborates with experimental results.

Design of metal casting mold for ADC 12 aluminium alloy with assistance of 20 kHz ultrasonic vibration

Metal mold casting is widely used in industry because of higher accuracy than sand casting and lower cost than diecasting. Metal mold casting can yield products with complex shapes and adjustable cooling rate. In this work, designing and fabrication of 20 kHz ultrasonic assisted mold casting using 20Cr steel are studied. Some major components such as motor, heater power, melting chamber are selected and calculated. Model for heating and pouring the ADC 12 alloy is designed. Samples with and without ultrasonic vibration are investigated using 3D laser scan.

Calculated Model of Endurance Limit Estimation Based on Structural-Strain Analysis of the Critical Condition of Ferrite-Perlite Steels with Macrocracks in Ship Structures

In this study, a structural-deformation analysis of the process of crack development is performed, on the basis of which an engineering methodology is developed for assessing the endurance limit and resource of large-sized structures. A simple analytical dependence (correlation аналитическая зависимость) was obtained, which allows one to determine the critical size of macrocracks for ferritic-pearlitic steels without using the well-known Griffith formula. The results of calculating the cracks critical lengths of various steels depending on their yield strength are presented. The analytical dependence of the calculation of the fatigue limit for the most dangerous symmetric loading cycle according to the standard set of mechanical characteristics of ferrite-pearlite steel is presented. The obtained results make it possible to calculate the endurance limit of structural elements of marine equipment and other structures subject to cyclic loads

Seismic performance analysis of a wind turbine tower subjected to earthquake and ice actions

Sea ice is one of the main loads acting on a wind turbine tower in areas prone to icing, and this threatens safe working life of the wind turbine tower. In our study, a simplified calculated model of ice, wind turbine tower, and water dynamic interaction under earthquake action was proposed, which could avoid to solve a large number of nonlinear equations. Then, the seismic behaviour of the wind turbine tower with and without the influence of sea ice was investigated, and we found that the influence of the greater mass of the sea ice on the seismic response of a wind turbine tower should be considered when the wind turbine tower is designed in an area with thick ice. With the influence of the most unfavourable ice mass, the deformation and energy dissipation capacity of the wind turbine tower are decreased, and the wall thickness or stiffening rib thickness should be increased to improve the seismic performance and ductility of the wind turbine tower; the shear force and bending moment increased significantly on the wind turbine tower, and the shear force changes at the bottom of the wind turbine tower and position of action of the sea ice: attention should be paid to the wind turbine tower design at these positions. Finally, we conducted the shaking table test, and verified the rationality of our proposed simplified model.

Identification of Factors Determining Winning in Men’s and Women’s Beach Volleyball: a Logistical Regression Approach

The purpose of this study was to find the factors responsible for winning in the men’s and women’s beach volleyball championship. Materials and methods. The study sample consisted of a total of 212 matches for men and 214 matches for women of the 2017 & 2019 FIVB Men and Women Beach Volleyball World Championships held at Vienna & Hamburg from 28 July to 6 Aug 2017 and 28 June to 7 July 2019. The matches were played by 192 teams (both men and women combined) consisting of 384 numbers (both men and women combined) of players from different nations. The data were analyzed using Binary Logistic Regression (Forward: LR Method) with the result of the game as the dependent variable and predictor variables as covariates. β, standard error β, Wald’s χ2, odds ratio with 95% confidence interval were calculated. Model evaluation was conducted using the likelihood ratio test, Cox & Snell (R2), and Nagelkerke (R2) tests. The goodness of fit test for the models was conducted using the Hosmer & Lemeshow test. Results. The analysis revealed seven factors related to winning in men’s and women’s competition. While in league rounds, six factors in men’s and seven factors in women’s competition were related to winning. Besides, in knockout rounds, four factors in men’s and six factors in women’s competition were related to winning. Conclusion. The study shows that there is a significant association of important factors with respect to winning a match in an elite beach volleyball championship. The coaches and players can take note of the important factors responsible for winning in the elite beach volleyball championship, with different factors playing an important role in men’s and women’s competition during league and knockout rounds as well.

Determination and verification of the calculated model parameters of salt rocks taking into account softening and plastic flow

The article suggests using a combination of the modified Burgers model and the Mohr – Coulomb model with the degradation of the adhesion coefficient and the increase in the friction coefficient to determine the parameters of salt rocks. A comparative analysis of long-term laboratory tests and field observations in underground mine workings with the results obtained using a calculated model with certain parameters is carried out. The parameters of the Mohr – Coulomb model with the degradation of the adhesion coefficient and the increase in the friction coefficient were obtained from the statistically processed data of laboratory tests, and the parameters of the modified Burgers model were determined. Using numerical methods, virtual (computer) axisymmetric triaxial tests, both instantaneous and long-term, were performed on the basis of the proposed model with selected parameters. A model problem is solved for comparing the behavior of the model with the data of observation stations in underground mine workings obtained from borehole rod extensometers and contour deformation marks. The analytically obtained coefficients of the nonlinear viscous element of the modified Burgers model for all the analyzed salt rocks did not need to be corrected based on the monitoring results. At the same time, optimization was required for the viscoelastic element coefficients for all the considered rocks. The analysis of the model studies showed a satisfactory convergence with the data on the observation stations. The comparative analysis carried out on the models based on laboratory tests and observations in the workings indicates the correct determination of the parameters for salt rocks and the verification of the model in general.

Semantic Changes in the Meaning of the Word Istinnyj (True) in Scientific Texts

The article deals with the semantics of the adjective istinnyj (true) in scientific texts. Semantic changes of this lexeme were identified in various verified contexts. It is shown that in contexts describing a statement, istinnyj is a metacharacteristic of mathematical, not linguistic, statements (inequalities, functions, etc.). This adjective can have two meanings in contexts describing reality. The first meaning characterizes situations in which the true is hidden consciously or as a result of an error. This use contains an implicit assumption of the existence of some untrue knowledge. The second meaning indicates hidden features, characteristics that need to be made explicit. It is shown that the second meaning in scientific texts can change semantically: such contexts contain an implicit juxtaposition of the true and the calculated/model/averaged. We need to make an implicit assumption about the equality of the true and the empirical in order to properly understand such contexts. This change in the semantics of the lexeme istinnyj takes place as late as in the 1960s. There is no opposition between the calculated and the true in earlier texts. Moreover, there is a juxtaposition of the true and the empirical in some of the earlier contexts. We have to accept the presupposition of the equality of the empirical and the false in order to interpret such contexts properly.

DETERMINATION OF VIBRATION POWER OF VIBRATION SOURCES OF SPINDLE UNITS OF METAL CUTTING MACHINES

Monitoring the state of spindle assemblies of modern metal-cutting machines using CIP methods implies the possibility of installing control sensors in places with maximum vibration information content. In this regard, the assessment of the informativeness of the vibration field of the spindle assembly, which can be carried out in advance, taking into account the design features, geometric and dimensional characteristics, is an urgent task. Based on the energy approach, using the example of the spindle assembly of a universal lathe, a computational model is proposed, built along the median planes of the walls. On the basis of the calculated model, the equations of the energy balance were compiled taking into account the conditions for the transfer of vibration power between the walls of the housing. The method for determining the vibration power of the main sources in the spindle assemblies is given: a spindle with residual unbalance, a drive gear and bearings. It has been established that the most significant factors determining the vibration power introduced into the spindle unit housing are the operation of the bearings, the weight of the spindle and the location of its center of mass. The result obtained makes it possible to detect incipient defects in the bearings, which, as practice shows, are the defining elements of the parametric reliability of spindle assemblies. The resulting model of the vibration field can be used to determine the reference values of vibration velocities that are formed from sources in the absence of defects.

Numerical calibration of railway bridge based on measurement data

<p>Bridges rarely behave precisely according to design assumptions. In most cases, they have some hidden reserves and behave preferable under traffic loads. To take these benefits into consideration numerical models can be calibrated based on measured structural response. The case study presented herein shows the calibration process for a railway truss bridge in Austria and the comparison of calibration results obtained by two individual teams. Each team did an individual and independent calibration based on different finite element models based on measured train passages. Both calibrations improved the precision of the calculated model response compared to the initial model, but also showed that the calibration parameters must be chosen with care to ensure plausibility of the results.</p>