다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

A thermo-viscoelastic approach for the characterization and modeling of the bending behavior of thermoplastic composites – Part II Part A Applied science and manufacturing

This paper presents the computational investigation of air flow over an aircraft at realistic speeds while demonstrating the importance of extending the existing analysis to the complete airplane and how pivotal it is in improving its in-flight performance. The study is done for F16 and F22 aircraft using ANSYS Fluent (19.2) to obtain pressure distribution, shear stress distribution and temperature variation on the complete surface of the aircraft. Since the front section of the aircraft is prone to direct initial impact of surrounding environment, this portion is also examined. Here, as the speed is doubled from Mach 1 to Mach 2, a rise in the value of all the three variables is noticed for the F16 aircraft, whereas the pressure distribution for F22 aircraft shows strange behaviour for the highest speed (Mach 2). On comparing the results over the whole surface, it is seen that F16 experiences smaller pressure (29% lower for Mach 1 and 30% for Mach 2), temperature (9.5% lower for Mach 1 and 30% for Mach 2) and shear stress relative to F22 and the stress shows a huge change (90% lower for Mach 1 and 83% for Mach 2). Results of the present study imply that the design of the aircraft highly influences its performance as the parameters discussed touch their limits.

https://publications.drdo.gov.in/ojs/index.php/dsj/article/download/15762/7514

Comparative Analysis of Aerodynamic Characteristics of F16 and F22 Combat Aircraft using Computational Fluid Dynamics

Thermoplastic towpregs are convenient and scalable raw materials for the fabrication of continuous fiber-reinforced thermoplastic matrix composites. In this paper, the potential to employ epoxy and styrene-acrylic sizing agents was evaluated for the making of carbon fiber thermoplastic towpregs via a powder-coating method. The protective effects and thermal stability of these sizing agents were investigated by single fiber tensile test and differential scanning calorimetry (DSC) measurement. The results indicate that the epoxy sizing agent provides better protection to carbon fibers, but it cannot be used for thermoplastic towpreg processing due to its poor chemical stability at high temperature. The bending rigidity of the tows and towpregs with two styrene-acrylic sizing agents was measured by cantilever and Kawabata methods. The styrene-acrylic sized towpregs show low torque values, and are suitable for further processing, such as weaving, preforming, and winding. Finally, composite panels were fabricated directly from the towpregs by hot compression molding. Both of the composite panels show superior flexural strength (>400 MPa), flexural modulus (>63 GPa), and interlaminar shear strength (>27 MPa), indicating the applicability of these two styrene-acrylic sizing agents for carbon fiber thermoplastic towpregs.

https://www.mdpi.com/1420-3049/23/3/547/pdf

Effects of Styrene-Acrylic Sizing on the Mechanical Properties of Carbon Fiber Thermoplastic Towpregs and Their Composites

The paper presents an example of the practical application of the previously proposed analytical method for the analysis of electromagnetic circuits of active magnetic bearings to search for force characteristics taking into account control laws. It consists in introducing detailed equivalent circuit substitution schemes and applying the contour flux method. These schemes contain all elements of active magnetic bearings (AMBs), such as air gaps under poles, sections of stator and rotor pressure lines, grooves filled with copper windings, and others. Magnetic resistances of circuit sections included in the expressions are determined by schematizing the magnetic flux paths. Validation of the method, methodology and calculation software is performed for an axial active magnetic bearing. This bearing is a part of a designed and technically implemented rotor laboratory rig in a complete combined passive-active magnetic suspension. The variant calculation results for various parameters of the axial AMB control system are presented. Comparison of these results with experimental data confirms approach accuracy and practical applicability. The advantage of the proposed analytical method is high accuracy with low dimensionality and resource consumption. This enables the AMB optimal design with a large number of variable geometric and physical parameters, as well as the control law parameters. The approach avoids a large number of field experiments.

Practical Application of the Analytical Method of Electromagnetic Circuit Analysis for Determining Magnetic Forces in Active Magnetic Bearings

The method for an identification of accident causes of turbine-generator sets is suggested. The accident causes can be factors, which are related to the failure of an equipment, and technological factors. For example, a deviation of the structural components from design values is related to these technological factors. The suggested approach is interdisciplinary as a gas dynamic behavior, thermal fields and a dynamic stress-strain state of the bladed disk are analyzed jointly. The approach is based on numerical methods of a gas dynamics and a dynamic strength. The vapor flow through the turbo machine blade lattice is calculated using the viscous compressible gas model. For a numerical integration of the structure a nonlinear finite element model is applied to analyze forced vibrations of the bladed disk under an action of aerodynamic loads.

Detection of Accident Causes on Turbine-Generator Sets by Means of Numerical Simulations

The paper discusses an approach to the analysis of the dynamic behavior of turbine rotors and a generator of an energy gas turbine unit with active magnetic bearings as supports. This unit is a part of the gas turbine cogeneration plant (GT CP). The problem of modeling the phenomena of rotor dynamics is solved with full consideration of controlled electromagnetic processes in active magnetic bearing (AMB) circuits. In order to analyze them, the method of contour flows similar to the method of contour currents for the analysis of electrical circuits is used. To describe the electromagnetic circuits of the AMB, detailed substitution schemes are introduced which take into account almost all the elements of the magnetic circuit (air gaps, sections of magnetic cores, grooves with windings, coils and other parts). Description of the considered mechatronic system requires constructing a mathematical model on the basis of application of the magnetomechanical Lagrange-Maxwell equations. The resulting system of differential equations relates to the generalized mechanical coordinates and flux linkages of the electric circuits of the AMB coils. The calculation results have the form of Cambell diagrams and amplitude-frequency characteristics of rotating rotors. Verification of the proposed approach to the modeling of dynamic phenomena in a rotary mechatronic system involves comparison with known calculation data. A comparative analysis reveals the advantages of the proposed approach for numerical simulation of the dynamics of rotors of controlled mechatronic systems and industrial electromechanical machines.

Modeling of the Dynamics of Rotors of an Energy Gas Turbine Installation Using an Analytical Method for Analyzing Active Magnetic Bearing Circuits

The paper presents a technique for designing and investigating the strength of a composite blade on an example of a mine ore ventilation fan, considering aerodynamic loads acting on a blade airfoil surface. The technique is based on the use of the finite element method in a combination with the theory of multilayer shells to determine the dynamics and strength of the composite airfoil, as well as the methods of the computational fluid dynamics, namely the Reynolds equations, for modeling an air movement in a fan passage to determine aerodynamic loads. A static strength estimation is based on an application of the Hashin strength criterion. An analysis of the results of strength calculations considering aerodynamic forces indicates a necessity of accounting them for thin-walled composite elements. A possibility of varying a thickness of the shell and taking it into account using the presented method allows to achieve an optimal ratio of strength and weight indices. A buckling analysis of the composite shell under an action of complex loading, based on methods of the linear stability theory, as well as calculations of natural frequencies and natural frequencies with regard to a prestressed state from an action of static loads, completes the technique. The results of the research allow to conclude on an applicability of the presented methodology for analyzing the strength of composite blades and an efficiency of the proposed design of the airfoil, as well as a possibility of its use to create real rotary machines.

Technique for Evaluating the Strength of Composite Blades

The paper presents a numerical technique for an evaluation of effective viscoelastic properties of fiber reinforced composite materials based on known mechanical properties of fibers and matrix. Th...

Numerical prediction of temperature-dependent anisotropic viscoelastic properties of fiber reinforced composite

The paper proposes a technique for a numerical determination of power characteristics of active magnetic bearings (AMBs), taking into account control laws. It is based on an application of the finite element method for analyzing static electromagnetic fields. Electromagnetic forces are calculated using the Maxwell's stress tensor. As an example, two types of bearings are considered with the given control laws. These are an axial AMB of a bilateral action with stators in the form of pot cores and a radial AMB with an eight-pole stator. The results of computational studies for a determination of the dependences of forces and stiffness coefficients on a rotor displacement for various control parameters are given. A practical applicability of the methodology for calculating the base force and stiffness characteristics of AMBs is proved by comparison with experimental data. The technique can be used for a selection of rational or optimal AMB parameters and parameters of the control laws for them.

Volodymyr Martynenko

Papers

Detection of Accident Causes on Turbine-Generator Sets by Means of Numerical Simulations

Modeling of the Dynamics of Rotors of an Energy Gas Turbine Installation Using an Analytical Method for Analyzing Active Magnetic Bearing Circuits

Technique for Evaluating the Strength of Composite Blades

Numerical prediction of temperature-dependent anisotropic viscoelastic properties of fiber reinforced composite

Numerical Determination of Active Magnetic Bearings Force Characteristics Taking into Account Control Laws Based on Parametric Modeling