scholarly journals DYNAMIC ANALYSIS AND FORMULATION OF THE SOLUTION FOR COMPLEX PROBLEM OF DURABILITY INCREASE FOR STRUCTURAL ELEMENTS IN A TURBULENT FLOW OF THE MEDIUM

2021 ◽  
pp. 36-45
Author(s):  
Saveliy Kaplunov ◽  
Natalia Valles ◽  
Denis Toporov
Keyword(s):  
Frequency Tuning ◽  
Experimental Studies ◽  
Natural Oscillation ◽  
Complex Problem ◽  
Optimal Choice ◽  
Structural Elements ◽  
General Plan ◽  
Resource Requirements ◽  
Oscillation Frequencies ◽  
Intense Vibration

When designing the structures of modern hydroelastic systems in power engineering, namely heat exchangers for various purposes, effective frequency tuning should be purposefully carried out to prevent intense vibration of individual elements. To do this, it is necessary, in accordance with the specified resource requirements, to provide reasonably defined ratios of various values of the natural oscillation frequencies of the structural elements and the characteristic nearest excitation frequencies in the flow. The optimal choice of the values of the frequency tuning coefficients is realized taking into account the characteristic known factors of hydroelastic systems, such as the effects of attached masses and the significant influence of damping on the intensity of vibrations of the structure in the fluid flow. The article provides a description and a general plan for solving the set complex problem based on the results of numerical and experimental studies known in this direction.

scholarly journals Collective Losses of Low Power Cage Induction Motors—A New Approach

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1749
Author(s):  
Elzbieta Szychta ◽  
Leszek Szychta
Keyword(s):  
Control System ◽  
Experimental Studies ◽  
Complex Problem ◽  
Accurate Estimation ◽  
New Approach ◽  
Water Pumping ◽  
Efficiency Control ◽  
Interacting Systems ◽  
Cage Induction Motor ◽  
Selection Of

Energy efficiency of systems of water pumping is a complex problem since efficiency of two distinct interacting systems needs to be combined: water and power supply. This paper introduces a non-intrusive method of calculating the so-called “collective losses” of a cage induction motor. The term “collective losses”, which the authors define, allows for accurate estimation of motor efficiency. Control system of a pump determines operating point of a pumping station, and thus its efficiency. General estimated performance characteristics of a motor, components of a control system, are assumed to serve selection of a range of pumping speed variations. Rotational speed has a direct effect on motor load torque, pump power and head, and thus on motor performance. Hellwig’s statistical method was used to specify characteristics of estimated collective losses on the basis of experimental studies of 21 motors rated at up to 2.2 kW. The results of simulations and experiments are used to verify validity and efficiency of the suggested method. The method is non-intrusive, simple to use, and requires minimum data.

scholarly journals A study of two-dimensional flow past an oscillating cylinder

1999 ◽  
Vol 385 ◽  
pp. 255-286 ◽  
Author(s):  
H. M. BLACKBURN ◽  
R. D. HENDERSON
Keyword(s):  
Experimental Studies ◽  
Cross Flow ◽  
Relaxation Oscillator ◽  
Two Dimensional ◽  
Flow State ◽  
Long Time ◽  
Two Dimensional Flow ◽  
Vorticity Production ◽  
Oscillation Frequencies ◽  
Motion Amplitude

In this paper we describe a detailed study of the wake structures and flow dynamics associated with simulated two-dimensional flows past a circular cylinder that is either stationary or in simple harmonic cross-flow oscillation. Results are examined for Re=500 and a fixed motion amplitude of ymax/D=0.25. The study concentrates on a domain of oscillation frequencies near the natural shedding frequency of the fixed cylinder. In addition to the change in phase of vortex shedding with respect to cylinder motion observed in previous experimental studies, we note a central band of frequencies for which the wake exhibits long-time-scale relaxation oscillator behaviour. Time-periodic states with asymmetric wake structures and non-zero mean lift were also observed for oscillation frequencies near the lower edge of the relaxation oscillator band. In this regime we compute a number of bifurcations between different wake configurations and show that the flow state is not a unique function of the oscillation frequency. Results are interpreted using an analysis of vorticity generation and transport in the base region of the cylinder. We suggest that the dynamics of the change in phase of shedding arise from a competition between two different mechanisms of vorticity production.

SEM Study of Fatigue Crack Propagation in Chromium Martensitic Steel after LCF

2017 ◽  
Vol 754 ◽  
pp. 15-18 ◽  
Author(s):  
Tamaz Eterashvili ◽  
G. Abuladze ◽  
L. Kotiashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
Complex Problem ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Sem Study ◽  
Deformation Tests ◽  
Microstructure Of The Material

Crack propagation after low-cycle fatigue (LCF) deformation has been studied in the chromium martensitic structural steel. Although the study of a fundamental mechanism of fatigue crack growth has received much attention over the last decade, it still remains a sufficiently complex problem and needs full understanding. Moreover, the recent studies show that the cracks propagate discontinuously even on the millisecond timescale, and their growth rate significantly depends on a microstructure of the material. In the present work the boundaries of the former austenitic grains were revealed on the polished surfaces of the thermally treated samples, which subsequently were undergone low-cycle fatigue tests. The experimental studies show that fatigue macrocracks mainly grow along the boundaries of the former austenitic grains, and changetheir propagation direction when crossing the grain boundary, however, remain within 45 ̊ interval with regard the cycling axis. In particular cases, when the boundaries of a martensite packets and those of the former austenite grains lay along the length of a packet, the macrocrack is better formed and with regular borders. After a macrocrack reaches a definite length ~30-50μ, a microcrack is nucleated ahead of the macrocrack tip, and is oriented along the substructure element of the steel. Further deformation tests provide an increase in the length of the main crack via aggregation of microcracks initiated ahead of it during the LCF. In the cases when the macrocrack is deviated, slip bands are formed in martensitic structures along the boundaries of martensite packets (laths). A correlation is revealed between the microcrack components and the substructure elements of the steel as well. The same results were obtained by fractography of the tested and fractured samples. However, in the latter case correlation was established between the cleavage facets and the dimensions of packets.

Effect of Tow Sheet Composite Wrap Architecture on Strengthening of Concrete Due to Confinement: I—Experimental Studies

1995 ◽  
Vol 14 (9) ◽  
pp. 1008-1030 ◽  
Author(s):  
Ian Howie ◽  
Vistasp M. Karbhari
Keyword(s):  
Concrete Strength ◽  
Experimental Studies ◽  
Load Carrying Capacity ◽  
Structural Elements ◽  
New Techniques ◽  
Column Type ◽  
Load Carrying ◽  
Concrete Shell ◽  
Original Construction ◽  
Stub Columns

Worldwide there is a need for the renewal of infrastructure because of age, deterioration, misuse, lack of timely repair and maintenance, use of improper materials and/or techniques in the original construction, and even changing needs. Notwithstanding the need for retrofit and repair methods for column-type structural elements, there is also a need for new techniques that would increase the confining action of concrete, as well as enhance the load-carrying capacity and ductility of such structures from a strengthening, rather than a seismic, viewpoint. This study investigates the use of carbon-fiber-reinforced jackets applied to concrete stub columns through the use of tow-sheet-type fabric forms. The primary emphasis is on the investigation of orientation and thickness effects of the composite wraps on the load-carrying efficiency and enhanced ductility of the new structural elements. It was seen that the predominant use of hoop reinforcement provides significant enhancement in concrete strength through confining action and also offers the potential for fabrication of concrete shell-type elements that would enable reinforcing action without the use of steel and the attending problems of corrosion.

scholarly journals NUMERICAL ANALYSIS OF STRUCTURAL ELEMENTS BETWEEN 3D CAD SOLIDWORKS AND CODE_ASTER

2020 ◽  
Vol 7 (10) ◽  
pp. 458-470
Author(s):  
Benício de Morais Lacerda ◽  
Alex Gomes Pereira
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Complex Problem ◽  
Numerical Results ◽  
Good Precision ◽  
Institutional Research ◽  
Structural Elements ◽  
The Finite Element Method ◽  
Numerical Application ◽  
Element Method

This study aimed to investigate numerically the validation of the use of the free license program Code_ Aster, with numerical results of the SolidWorks program. For this, four metal elements were modeled, all of them subjected to the tensile stress, they are: a cylindrical bar, two plates with a hole and a metal console. The objective is to validate the use of a free program for analysis of structural elements in engineering office projects and institutional research to verify if the results obtained from the free program show significant differences in the numerical application of a commercial program. All programs have in their design of analysis the use of the finite element method (FEM). The finite element method (FEM) consists to divide a continuous object into a finite number of parts. This allows a complex problem to be transformed into a set of simple problems (finite element) in addition to solving a set of finite elements by approximations with good precision of the results and to model the problem in a real physical way. It was observed that the numerical results between the SolidWorks program and the free program Code_ Aster were close with differences of less than 5%, which indicates the reliability of the use of Code_ Aster for numerical analyzes of structural elements of engineering projects and also in institutional research.

scholarly journals When failure fails to be productive: probing the effectiveness of productive failure for learning beyond STEM domains

2020 ◽  
Vol 48 (6) ◽  
pp. 651-697
Author(s):  
Valentina Nachtigall ◽  
Katja Serova ◽  
Nikol Rummel
Keyword(s):  
Problem Solving ◽  
Social Science ◽  
Research Methods ◽  
Social Science Research ◽  
Experimental Studies ◽  
Science Research ◽  
Complex Problem ◽  
Productive Failure ◽  
Stem Learning ◽  
Beneficial Effects

AbstractThe current work builds on research demonstrating the effectiveness of Productive Failure (PF) for learning. While the effectiveness of PF has been demonstrated for STEM learning, it has not yet been investigated whether PF is also beneficial for learning in non-STEM domains. Given this need to test PF for learning in domains other than mathematics or science, and the assumption that features embodied in a PF design are domain-independent, we investigated the effect of PF on learning social science research methods. We conducted two quasi-experimental studies with 212 and 152 10th graders. Following the paradigm of typical PF studies, we implemented two conditions: PF, in which students try to solve a complex problem prior to instruction, and Direct Instruction (DI), in which students first receive instruction followed by problem solving. In PF, students usually learn from their failure. Failing to solve a complex problem is assumed to prepare students for deeper learning from subsequent instruction. In DI, students usually learn through practice. Practicing and applying a given problem-solving procedure is assumed to help students to learn from previous instruction. In contrast to several studies demonstrating beneficial effects of PF on learning mathematics and science, in the present two studies, PF students did not outperform DI students on learning social science research methods. Thus, the findings did not replicate the PF effect on learning in a non-STEM domain. The results are discussed in light of mechanisms assumed to underlie the benefits of PF.

Composite Polymer Mesh For Masonry

2019 ◽  
pp. 15-19
Keyword(s):  
Strain State ◽  
Mechanical Characteristics ◽  
Experimental Studies ◽  
Structural Elements ◽  
Composite Polymer ◽  
Performance Technology ◽  
Different Types ◽  
Composite Grids ◽  
And Performance ◽  
Physical And Mechanical Characteristics

With the development and introduction of technologies for the production of composite materials for construction purposes in Russia appeared composite flexible ties, anchors, fittings, etc. These materials and products are not fundamentally new and have previously been studied for use for reinforcing concrete or structural elements. However, for increasing the bearing capacity of stone structures as masonry meshes they were practically not used, while masonry mesh is one of the most demanded materials in construction. The article presents experimental studies of composite meshes of different types and performance technology used in masonry. Experimentally substantiated and normalized values of physical and mechanical characteristics of rods for composite polymer grids are obtained. The evaluation of efficiency of composite meshes in masonry is made, the values of crack forming and rupture loads are determined, the peculiarities of the stress-strain state of composite grids as flexible ties are revealed, the fields of application are formulated.

The Parametric IR Lasers with High Radiation Efficiency Over the Entirerange of Frequency Tuning

2013 ◽  
Vol 8 (4) ◽  
pp. 6-10
Author(s):  
Valerik Airapetyan ◽  
Tamara Shirokova ◽  
Petr Pasko
Keyword(s):  
Optical Parametric Oscillator ◽  
Tuning Range ◽  
Frequency Tuning ◽  
Nonlinear Crystal ◽  
Experimental Studies ◽  
Parametric Oscillator ◽  
High Radiation ◽  
Pump Frequency ◽  
Parametric Generation ◽  
Optical Parametric

Computational and experimental studies of the lasing characteristics of IR optical parametric oscillator (OPO) on the nonlinear crystal LiNbO3 were performed. Implemented outside the cavity ring scheme OPO with replaceable output mirrors allows the conversion of the pump frequency in parametric generation to 30 % over the tuning range from 1.41 to 4.24 microns

Geomechanical justification of room-and-pillar dimensions for rock salt and polymineral salt mining

2021 ◽  
pp. 37-43
Author(s):  
V. A. Eremenko ◽  
◽  
M. A. Kosyreva ◽  
N. G. Vysotin ◽  
Ch. V. Khazhy-ylai ◽  
...  
Keyword(s):  
Rock Salt ◽  
Experimental Studies ◽  
Structural Elements ◽  
Structural Components ◽  
Underground Structures ◽  
Russian Science ◽  
Strain Behavior ◽  
Analytical Estimation ◽  
Pillar Mining ◽  
External Loads

The key target of room-and-pillar planning for mining rock salt, polymineral salt and polyhalite at the minimized loss of minerals in pillars is optimization of the dimensions of rooms and rib pillars. The authors compare some variants of mining with rooms and rib pillars, as well as with honeycomb mine structure. The theoretical and experimental studies prove efficiency of room-and-pillar dimension optimization by combination of analytical estimation with numerical analysis and physical modeling of the stress–strain behavior of underground structures (honeycomb mine structures). It is found that the honeycomb mine structures feature higher resistability of structural components to external loads. The research into secondary stress field generation and influence on structural elements of the roomand- pillar mining systems made it possible to calculate stable parameters for the conventional and innovative mining systems. The study was supported by the Russian Science Foundation, Project No. 19-17-00034.

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