Circumferential Component Research Articles

Компьютерное моделирование сварки давлением образцов из гетерофазных никелевых сплавов через прослойку

Computer simulation of pressure welding of cylindrical workpieces through an interlayer was carried out using the DEFORM-2D software package in a two-dimensional formulation (axisymmetric deformation). Two combinations of materials to weld were considered: sample I — cylinders of heterophase nickel-based deformable superalloy EP975 in a coarse-grained state were welded through an interlayer of EP975 with a fine-grained microduplex structure; sample II — cylinders of dissimilar nickel-based alloys, one the deformable alloy EP975 in a coarse-grained state and the other an intermetallic alloy VKNA-25 with a single-crystal structure, were welded through an interlayer of EP975 alloy with a fine-grained microduplex structure. The welding process was carried out under isothermal conditions at a temperature of 1125°C and an initial strain rate of 10−4 s−1. The material characteristics were described by experimental curves obtained under uniaxial compression tests of alloys at the welding temperature. The Siebel friction model was used to describe the contact conditions on the surfaces to be welded. The friction coefficient was taken equal to 0.3. The distribution of equivalent, axial, radial, circumferential and shear components of stress and strain in the samples have been investigated. Analysis of the simulation results allowed one to conclude that, in comparison to welding of similar materials, during welding of dissimilar materials the values of the radial, axial and circumferential stresses increase. Radial and circumferential stresses in the material of the cylinders are tensile, while compressive stresses prevail in the material of the interlayer. Area with the maximum values of shear stresses in the region of contact between the cylinders and the interlayer also increases. In this case, axial, radial and circumferential strains decrease in a cylinder made from a material with higher strength, the overall level of shear strain does not change, and on the reciprocal contact surface of the interlayer, the region of extension of maximum shear strain extends to the entire contact zone. Such a combination of factors allows one to conclude on more favorable pressure welding conditions for welding of dissimilar alloys in comparison with similar materials.

Recovery of radial-axial velocity in axisymmetric swirling flows of a viscous incompressible fluid in the Lagrangian consideration of vorticity evolution

Swirling laminar axisymmetric flows of viscous incompressible fluids in a potential field of body forces are considered. The study of flows is carried out in a cylindrical coordinate system. In the flows, the regions in which the axial derivative of the circumferential velocity cannot take on zero value in some open neighborhood (essentially swirling flows) and the regions in which this derivative is equal to zero (the region with layered swirl) are considered separately. It is shown that a well-known method (the method of viscous vortex domains) developed for non-swirling flows can be used for regions with layered swirling. For substantially swirling flows, a formula is obtained for calculating the radial-axial velocity of an imaginary fluid through the circumferential vorticity component, the circumferential circulation of a real fluid, and the partial derivatives of these functions. The particles of this imaginary fluid “transfer” vortex tubes of the radial-axial vorticity component while maintaining the intensity of these tubes, and also “transfer” the circumferential circulation and the product of the circular vorticity component by some function of the distance to the axis of symmetry. A non-integral method for reconstructing the velocity field from the vorticity field is proposed. It is reduced to solving a system of linear algebraic equations in two variables. The obtained result is proposed to be used to extend the method of viscous vortex domains to swirling axisymmetric flows.

A machine-learning approach to predicting the energy conversion performance of centrifugal pump impeller influenced by blade profile

Centrifugal pump is a kind of energy conversion machine for fluid delivering. It transfers the mechanical energy of impeller to the potential and kinetic energy of fluid. As a key factor in influencing the energy conversion performance of centrifugal pump, blade profile design is crucial. Traditional design concepts have ideal assumptions. To have a better design guidance, machine-learning based on neural network is used in this study. A typical centrifugal pump with simplified blade profile is numerically studied with experimental validation for a better discussion. Statistical results show that, for the high dimensional nonlinear relationship between blade angle and performance of centrifugal pump, neural network can adapt to this complex correlation better. The blade installation angle at leading-edge ( βLE′) and trailing-edge ( βTE′) and the wrap angle (Δ θ′) has significant correlation with the performance including pump head H, pump efficiency η, impeller head Himp, impeller efficiency ηimp and volute loss Δ Hvol. The influence level of blade angle follows the high-to-low order of Δ θ′, βLE′ and βTE′. Determination of blade profile can be done for improving the energy conversion efficiency. Optimal blade profiles have higher βLE′ and Δ θ′ with better flow-control ability. Compared with the blade parameters of the initial pump, the blade profile with the best centrifugal pump efficiency is the best βLE′ increased by 1.926°, Δ θ′ increased by 9.858°, Optimization of impeller efficiency βLE′ increased by 1.855°, Δ θ′ increased by 9.421°. Computational fluid dynamics indicate the elimination of vortex in impeller after optimal selection. Then, βTE′ and Δ θ′ are found influential in aggravating the circumferential flow component in this special circular-volute with generating higher loss. βTE′ has a positive correlation with impeller head which suits traditional theory. In general, the machine-learning using neural network is effective in determining blade profiles for enhancing the performance of centrifugal pump.

Global and regional right ventricular mechanics in repaired tetralogy of Fallot with chronic severe pulmonary regurgitation: a three-dimensional echocardiography study

BackgroundData about the right ventricular (RV) mechanics adaptation to volume overload in patients with repaired tetralogy of Fallot (rToF) are limited. Accordingly, we sought to assess the mechanics of the functional remodeling occurring in the RV of rToF with severe pulmonary regurgitation.MethodsWe used three-dimensional transthoracic echocardiography (3DTE) to obtain RV data sets from 33 rToF patients and 30 age- and sex- matched controls. A 3D mesh model of the RV was generated, and RV global and regional longitudinal (LS) and circumferential (CS) strain components, and the relative contribution of longitudinal (LEF), radial (REF) and anteroposterior (AEF) wall motion to global RV ejection fraction (RVEF) were computed using the ReVISION method.ResultsCorresponding to decreased global RVEF (45 ± 6% vs 55 ± 5%, p < 0.0001), rToF patients demonstrated lower absolute values of LEF (17 ± 4 vs 28 ± 4), REF (20 ± 5 vs 25 ± 4) and AEF (17 ± 5 vs 21 ± 4) than controls (p < 0.01). However, only the relative contribution of LEF to global RVEF (0.39 ± 0.09 vs 0.52 ± 0.05, p < 0.0001) was significantly decreased in rToF, whereas the contribution of REF (0.45 ± 0.08 vs 0.46 ± 0.04, p > 0.05) and AEF (0.38 ± 0.09 vs 0.39 ± 0.04, p > 0.05) to global RVEF was similar to controls. Accordingly, rToF patients showed lower 3D RV global LS (-16.94 ± 2.9 vs -23.22 ± 2.9, p < 0.0001) and CS (-19.79 ± 3.3 vs -22.81 ± 3.5, p < 0.01) than controls. However, looking at the regional RV deformation, the 3D CS was lower in rToF than in controls only in the basal RV free-wall segment (p < 0.01). 3D RV LS was reduced in all RV free-wall segments in rToF (p < 0.0001), but similar to controls in the septum (p > 0.05).Conclusions3DTE allows a quantitative evaluation of the mechanics of global RVEF. In rToF with chronic volume overload, the relative contribution of the longitudinal shortening to global RVEF is affected more than either the radial or the anteroposterior components.

A comprehensive comparison between shortest-path HARP refinement, SinMod, and DENSEanalysis processing tools applied to CSPAMM and DENSE images

We addressed comprehensively the performance of Shortest-Path HARP Refinement (SP-HR), SinMod, and DENSEanalysis using 2D slices of synthetic CSPAMM and DENSE images with realistic contrasts obtained from 3D phantoms. The three motion estimation techniques were interrogated under ideal and no-ideal conditions (with MR induced artifacts, noise, and through-plane motion), considering several resolutions and noise levels. Under noisy conditions, and for isotropic pixel sizes of 1.5 mm and 3.0 mm in CSPAMM and DENSE images respectively, the nRMSE obtained for the circumferential and radial strain components were 10.7 ± 10.8% and 25.5 ± 14.8% using SP-HR, 11.9 ± 2.5% and 29.3 ± 6.5% using SinMod, and 6.4 ± 2.0% and 18.2 ± 4.6% using DENSEanalysis. Overall, the results showed that SP-HR tends to fail for large tissue motions, whereas SinMod and DENSEanalysis gave accurate displacement and strain field estimations, being the last which performed the best.

Bifurcation analysis of elastic residually-stressed circular cylindrical tubes

The theory of superimposed incremental elastic deformations is applied to a deformed configuration of a residually-stressed circular cylindrical tube. The tube is subject to internal or external pressure and an axial load that maintain its circular cylindrical shape, and then bifurcations from this shape are analysed. Detailed governing equations and boundary conditions are provided for axisymmetric, prismatic and asymmetric bifurcations for a general form of strain–energy function that incorporates radial and circumferential residual stress components. The theory is applied to a simple model strain–energy function with two material parameters and a parameter that reflects the magnitude of the residual stress. Numerical computations are used to illustrate the dependence of the results of the bifurcation analysis on these parameters and the axial and radial underlying deformation. It is shown that in general the presence of residual stress has a significant effect compared with the corresponding results without residual stress.

Design of a 10 MVA Fully HTS Synchronous Generator With Dual Field Windings and 4 Poles Spanned Armature Windings

We have proposed a fully high temperature superconducting (HTS) synchronous generator with dual field windings to reduce the circumferential component of the magnetic field on the HTS tape in the armature. In this paper, we suggested a design of a 10 MVA fully HTS synchronous generator with dual field windings. We varied the distance between inner and outer field windings, the shape of the cross-sections of the fields, and the height of the armature windings to find the structure with minimum losses. The structure of the HTS armature windings should be different from the one of the copper armature windings because the overhang of the HTS armature windings in cryostats cannot be bent. So, we also proposed 4 poles spanned 3 phase armature windings. Normally one set of 3 phase copper armature windings is installed in 2 poles span with the structure of double layer winding, but the proposed 3 phase HTS armature windings are installed in 4 poles span in single layer. We analyzed AC losses of various designs of the fully HTS machines and suggested the de-sign parameters with minimum AC loss.

Quantitative study on the triaxial characteristics of weak magnetic stress internal detection signals of pipelines based on the theory of magnetoelectric coupling

The quantitative analysis of stress concentration zone in pipelines using weak magnetic stress internal detection is quite challenging. In this study, magneto-mechanical calculations are introduced into Maxwell’s equations, and a mathematical model is established for triaxial weak magnetic stress detection. This model is used to calculate and analyze the variation trend of triaxial weak magnetic signal with stress and propagation distance in the pipeline. The results indicate that weak magnetic signal has a linear relationship with the stress. As the stress increases, the weak magnetic signal is reversed, where the tensile capacity of the pipeline begins to weaken and the magneto-mechanical sensitivity decreases, but the signal recognition rate increases. The weak magnetic signal exhibits an exponential decaying trend during propagation. The axial component of weak magnetic signal has the highest signal recognition rate. The circumferential and radial components exhibit strong abilities of avoiding false detection and avoiding missed detection, respectively.

Discontinuous solutions of the unsteady boundary-layer equations for a rotating disk of finite radius

Abstract

A model of the time-harmonic torsional response of piled plates using an IBEM-FEM coupling

This article presents a model of the response of rigid circular plates supported by embedded elastic pile foundations under time-harmonic torsional excitation. The contact tractions at the pile-soil and plate-soil interfaces are resolved into circumferential components, which are then approximated by piece-wise constant distributions. The dynamic stress-displacement relation for the soil part, here modeled as a homogeneous, transversely isotropic half-space, is obtained by numerical integration of that medium’s Green’s functions. The pile is modeled as a series of interconnected one-dimensional circular shafts, and the plate is modeled by imposing rigid-body rotation conditions throughout the portion of the surface of the soil that it occupies. A tangential Winkler-type layer is incorporated between the plate and the soil, in order to represent potential imperfect bonding contact that may occur in engineering practice. This article presents an analysis of the influence of geometric and constitutive parameters of the system in its time-harmonic torsional response, as well as a study on the wave propagation from the piled plate system through the soil.

Experimental Studies into the Effect that the Rotor Rotation and Flow Swirling Upstream of Seals Have on the Leakage Flowrate

The results from experiments for studying the effect of rotor rotation on the leakage through different types of seals are presented. It is shown from a comparative study of models involving a stalled rotor and rotor rotating with a 50 Hz frequency that the rotor rotation has hardly any effect on the leakage flowrate, so that the rotation may not be taken into account in calculations of leakage flowrate through the steam turbine end and diaphragm seals. The article presents results from experiments for studying the dependence of leakage flowrate on the flow parameters, namely, the change of the velocity vector axial and circumferential components in the annular inlet channel upstream of a single annular throttle orifice. During the experiments, the velocity axial and circumferential components were varied independently and in a very significant range. The accomplished studies have shown that the change of both the axial and circumferential velocity components has hardly any effect on the leakage flowrate. It can be concluded from an analysis of the obtained results that the influence of flow parameters upstream of the seal on the leakage flowrate is so insignificant that its neglect in the previously developed calculation procedures for determining the leakage flowrate in the steam turbine seals, which are still in use at present, is quite substantiated and justified. At present, studies are being carried out that allow the flow structure in different places of turbine machinery flow paths, including the turbine seals, to be analyzed by calculation. It should be noted that it is possible by using the modern calculation methods not only to determine the vortex structure in the seal neighborhood but also to estimate the leakage flowrate, leakage losses, and even the stage efficiency for different configurations of the chamber upstream of the seal. Nonetheless, care should be taken in dealing with practical recommendations on changing the seal configurations that are based solely on the calculation results. The soundness of such recommendations must be confirmed by the relevant experimental investigations.

Measurement and Analysis of Deformation Behavior of Polyethylene Tube Subjected to Biaxial Tensile Stress with Large Strain

A material testing apparatus for measuring the biaxial deformation behavior of a polymer tube is developed to quantitatively evaluate the deformation behavior of polymeric materials. The testing apparatus can apply axial force and internal pressure to a tubular specimen. A noncontact strain measurement system is also developed, and the biaxial strain components and the radius of curvature in the axial direction of the specimen are continuously measured to control the stress path applied to the specimen. Polyethylene tubes with an outer diameter of 17 mm and a thickness of 2 mm are used as test specimens, that are subjected to linear stress paths with stress ratios of σφ :σθ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where σφ and σθ are the axial and circumferential stress components applied to the center of the bulging specimen, respectively. Biaxial stress-strain curves are successfully measured for every linear stress path at a nearly constant logarithmic strain rate of 1×10-3 s-1. A maximum equivalent strain of up to 0.71 is achieved for a specimen with a stress path of σφ :σθ =2:1. The contours of equal work plotted in the principal stress space show a significant anisotropy of the test material.

A Mathematical Model of the Wall of a Rat Cerebral Resistance Vessel

A mathematical model of the mechanical properties of the rat small cerebral artery wall is presented. It is assumed that the active component of the stress has a circumferential direction and is a function of the concentration of the activator of smooth muscle cell contractions and circumferential and radial stretch ratios; longitudinal stretching is not considered. Calculations showed a significant decrease in both the circumferential stress and circumferential stretch ratios in the vascular wall after activation; the distribution of these values in the transmural direction became more uniform. The active component has a predominant effect on the formation of the total stress. The circumferential stress component was several times higher than the radial and longitudinal ones. The modulus of the ratio of the radial stress component to the circumferential one increased as a result of activation, and a tendency to a decrease in its value with increasing circumferential stretching was observed. Numerical analysis revealed a high sensitivity of both the radius and stress to even a small change in the values of the parameters included in the functional dependence of the stress on the concentration of the smooth muscle contraction activator.

ВЛИЯНИЕ ТУРБУЛЕНТНЫХ ПУЛЬСАЦИЙ НА ПРОЦЕСС ФРАКЦИОННОГО РАЗДЕЛЕНИЯ МЕЛКОДИСПЕРСНЫХ ПОРОШКОВ НИТРИДОВ МЕТАЛЛОВ

This paper presents a numerical study of a two-phase swirling turbulent flow in a separation element of a vortex chamber. The paper considers a process of fractional separation in the separation chamber with three particular features in its design. The main feature is the separation mobile element located at the outlet of the separation area. Changes in the position of this element can affect the boundary size and the sharpness of the separation. The second feature of the considered separation chamber is the presence of a rotating element along the vertical axis. This element helps to align the field of the circumferential velocity component. The third feature of this chamber is the presence of a branch pipe for the auxiliary gas flow supply intended to push the particles away from the chamber wall and to blow the separated particles in order to prevent them from agglomeration. In this work, the trajectories of the motion of fine nitride particles are calculated taking into account the turbulent diffusion effect. A possibility to control the boundary size of the particles, when moving the separation element located at the outlet of the vortex chamber, is demonstrated. Numerical study results show that the turbulent pulsations cause significant changes in the separation process and affect the boundary size and the sharpness of the separation.

Numerical Simulation of Double Surface Liquid Ejector with Flow Swirl for Centrifugal Pump

Many systems with liquid ejectors and centrifugal pump are known. Often, jet pumps are used to provide a self-priming mode, as well as an acceptable pressure level for cavitation-free operation. The main disadvantage of such systems is the relatively low efficiency associated with the peculiarities of energy transfer in ejector. To increase efficiency double surface jet pump with driving and suction flow swirl (with circumferential component of velocity) is proposed. The active flow swirling is ensured by using of multi-nozzle tangential nozzle inlet and passive flow part by a special blade system. Combination of these factors makes it possible to improve the efficiency of energy conversion process. In comparison with the known design increases pump efficiency by 10 % – 15 %. Flow swirl also permits to reduce horizontal overall size by increasing the diffuser angle and reducing the mixing chamber length. These positive effects can be achieved by using methods and recommendations given in this paper. The paper also includes ANSYS CFX numerical simulation study results of double surface jet pump and analysis of the impact of nozzle position, length of the mixing chamber and other geometry parameters on pump performance. The results allow optimize the constructive solutions.

The numerical simulation of the rope vortex creation and the possibilities of its control

The rope vortex is a phenomena which can be observed in many hydraulic machines, especially turbines and pump–turbines. Its creation is based on a non uniform velocity profile characterized by high value of the circumferential component. This phenomena limits the range of operating conditions, which results in reduction of the energy production. The article presents the flow analysis of the hydraulic Francis turbine, where the rope vortex was observed. The structure of the vortex was identify and some solutions were analysed to prevent or reduce the size of multiphase flow.

Prospects for production of viscous fluid by electric shaft-driven vane pumps (ESP)

The article deals with the prospects of developing significant world reserves of high-viscosity oil. Its production requires specific equipment and technologies, selection of efficient equipment, as well as a special approach in its operation. At the same time it is necessary to take into account the influence of high viscosity on the main characteristics of pumps and on the operating conditions of the equipment in the well. The reasons for unstable operation of the ESP at start-up after long stops are described. The methods of recalculation of characteristics of pumps for oil production of common design are offered. Some results of researches of such pumps on viscous liquid and recommendations on calculation of a flowing part are provided. The possibilities of pumps with open impeller stages and with increased shaft speeds are determined. Additional reasons for decreasing the characteristics of the pump on the viscous fluid, results of the test of stage assembly with measurement of average circumferential components of flow rates at different viscosity of the pumped fluid are given. The possibility of using helico-axial pumps is also considered. Application of modern programs and methods of equipment selection and operation, ESP rotor speed regulation, liquid temperature regulation in tubing and automation of the whole oil production process is recommended. Possible design changes of the ESP in the process of tubing production for the purpose of increasing their efficiency in comparison with the serial pumps are specified. The article can be useful for specialists in design, selection and operation of equipment for high-viscosity oil production.

The method of reconstruction of residual stresses and plastic deformations in thin-walled pipelines in the delivery state and after bilateral vibro-shock surface hardening with a shot

We suggest the phenomenological method of reconstructing the fields of residual stresses and plastic deformations in thin-walled cylindrical tubes made of Х18N10Т steel in the delivery state and after a simultaneous bilateral surface plastic hardening by the vibration-shot blasting of the surface with beads on a special vibrating stand. A cylindrical container filled with three-millimeter beads was attached to it. The tubes were 50 % filled with one-millimeter beads, and they were placed inside the container. The axis of the tube and the container coincided. The space between the tube and the container was 80 % filled with beads. The vibrational frequency of the stand was 18.5 KHz, the hardening time was 20 minutes. The tube in the container was rotated to ensure uniform hardening. We determined the experimental values of residual stresses σθ and σ z in the surface layers using the method of rings and strips with the procedure of the layer-by-layer electrochemical picking of the hardened layers. For this purpose, the experimentally measured values of the beam-strip deflection and the angular opening of the cut ring (changing the diameter) were used. The hardening anisotropy parameter which relates the axial and circumferential components of plastic deformation was introduced into the mathematical model. In solving the stated problems the hypotheses of plastic incompressibility of the material, the absence of secondary plastic deformations of the material in the compression region of the surface layer, as well as the hypothesis of flat sections and straight radii were used. We described the method aimed at solving this type of boundary value problems of reconstructing stress-strain states, which makes it possible to determine the missing component σ r and all the components of the tensor of residual plastic deformations (off-diagonal components of the tensors of stresses and deformations were not considered). The method of reconstructing the stress-strain state is universal, because it has shown its operability both in determining the technological fields of residual stresses, as well as the irreversible strains in the samples in the delivered state after mechanical operations, and after bilateral surface plastic deformation. The adequacy of the calculated data was verified, which was obtained using the phenomenological method of reconstructing the stress and strain fields of the experimental data for the samples in the delivery state and after hardening. The correspondence of the calculated and experimental data was matched. The numerical values are given for the anisotropy parameter connecting the circumferential and axial irreversible strains, for samples, in the delivery state, its numerical value is 0.1, and, for the hardened samples, it is 4.2. This indicates a significant anisotropy of the distribution of the axial and circumferential components of the residual strain tensor. It has been established that the compressive residual stresses are observed in the delivery state in the region adjacent to the inner surface, and the tensile stresses are observed in the layer on the outer surface. Only compressive stresses are observed in both regions after hardening, which significantly exceed in module similar stresses for the samples in the delivery state. The main results are illustrated by the tabular data and the corresponding diagrams of the distribution of residual stresses along the depth of the hardened layer.

Research of high-speed high-performance and small-sized screw conveyors-grain loaders

Currently, agricultural enterprises are offered many conveyors of various typesfor the mechanization of loading and unloading works during cropmovement. The article presents studies of a method of increasing performance of a screw type conveyor allowing to create a small-sized design by increasing its revolutions. It investigates workmechanism, describesoperational technology of conveyors-grain and work disadvantages, namely, problematicgrain transportation over long distances along a spatial route or complication of technological scheme. Loading directly from pile may require manual labor or additional equipment. It is noted that increase in performance with increase in rotor revolutions (from 400 to 1100 rpm) occurs up to a point, after which revolutions increase, and performance decreases. In order to increase screw performance, it is necessary to accelerate material axial advance, i.e. to stretch ascending and, especially, falling material trajectorybranches at high speeds, with bulky material (grain), cast by centrifugal force to inner pipe surface, filling the grooves. Since their locationis close to each other (at 30°), surface braking layer is formed, which decreases circumferential speed component of absolute movement of grain andincreases the axial one. In order to increase screw performance, it is necessary to accelerate material axial advance, i.e. stretch ascending and, especially, falling material trajectorybranches. Further studies will contribute to finding new ways to increase speed coefficient K υ and coefficient ψ and create high-speed, high-performance, and small-sized screw conveyors-grain loaders.

Analysis of Local Damages Effect on Mechanical Responses of Underwater Shield Tunnel via Field Testing and Numerical Simulation

The investigation of concrete structural performance is crucial to maintain the stability of infrastructure. In order to assess structural stability, this work focuses on the development of an integrated framework to detect damaged conditions in the field and analyze their effect on mechanical performance through nondestructive testing (NDT) technology and numerical models. First, a ground penetrating radar (GPR) and an infrared camera work collaboratively to identify the damaged positions of the concrete structure, with parameters calibrated by laboratory experiments. Then, a finite element model is established to study structural mechanical performance based on field conditions and detected results. In addition, the influenced regions induced by local damage are studied under different boundary conditions. As a case study, the devised method was employed in the Nanjing Yangtze River tunnel for stability assessment and disaster prevention. The detected results of the damaged conditions agree well with the actual conditions in the field. Numerical results show that the circumferential stress component is more significant than that observed longitudinally. The effect of local damage on stress implies a positive correlation with the rise of water pressure, in which the maximum stress response to the variation of water level is 45KPa per meter.