Research on the Stress of the Oxide Scales on the Superheater Tubes under Uneven Circumferential Loading

2013 ◽  
Vol 860-863 ◽  
pp. 1398-1401
Author(s):  
Qing Wei Li
Keyword(s):  
Growth Temperature ◽  
Axial Stress ◽  
Circumferential Stress ◽  
Circumferential Direction ◽  
Oxide Scales ◽  
Negative Effects ◽  
Superheater Tube ◽  
Simulated Temperature ◽  
Simulation Results ◽  
Volume Method

Oxide scales have negative effects on the security and economy of supercritical and ultra-supercritical units.The finite volume method was exploited to simulate oxide scales growth temperature on the inside of superheater tube,then the appropriate time and spatial intervals were selected to calculate oxide scales thickness along the circumferential direction with the correspond growth temperature.At last,the stress response of the oxides was simulated with finite element method.The simulated temperature is closed to the analytical temperature, confirming that the simulation results are credible.The results show that the growth temperature rises fast at the beginning and drops in the circumferential direction,which changes rapidly at the 90°. Oxide scales thickness is thinner and thinner in the circumferential direction and changes fast at approximately 90°.Though the magnitude of circumferential stress and axial stress is different, but the trend same.The simulation results can provides a theoretical basis for the failure research of the oxide scales.

Stress and Strain Distribution in Hypertensive and Normotensive Rat Aorta Considering Residual Strain

1996 ◽  
Vol 118 (1) ◽  
pp. 62-73 ◽  
Author(s):  
Takeo Matsumoto ◽  
Kozaburo Hayashi
Keyword(s):  
Residual Stresses ◽  
Wall Thickness ◽  
Axial Stress ◽  
Circumferential Stress ◽  
Circumferential Direction ◽  
Wall Thickening ◽  
Left Renal Artery ◽  
Stress And Strain ◽  
Stress Distributions ◽  
Cross Sectional

The effects of hypertension on the stress and strain distributions through the wall thickness were studied in the rat thoracic aorta. Goldblatt hypertension was induced by constricting the left renal artery for 8 weeks. Static pressure-diameter-axial force relations were determined on excised tubular segments. The segments were then sliced into thin ring specimens. Circumferential strain distributions were determined from the cross-sectional shape of the ring specimens observed before and after releasing residual stresses by radial cutting. Stress distributions were calculated using a logarithmic type of strain energy density function. The wall thickness at the systolic blood pressure, Psys, significantly correlated with Psys. The mean stress and strain developed by Psys in the circumferential direction were not significantly different between the hypertensive and control aortas, while those in the axial direction were significantly smaller in the hypertensive aorta than in the control. The opening angles of the stress-free ring specimens correlated well with Psys. The stress concentration factor in the circumferential direction was almost constant and independent of Psys, although the stress distributions were not uniform through the wall thickness. Histological observation showed that the wall thickening caused by hypertension is mainly due to the hypertrophy of the lamellar units of the media, especially in the subintimal layer where the stress increase developed by hypertension is larger than in the other layers. These results indicate that: (a) the aortic wall adapts itself to the mechanical field by changing not only the wall dimensions but also the residual stresses, (b) this adaptation is primarily related to the circumferential stress but not to the axial stress, and (c) the aortic smooth muscle cells seem to change their morphology in response to the mechanical stress.

scholarly journals Thermoelastic analysis of FGM hollow cylinder for variable parameters and temperature distributions using FEM

2020 ◽  
Vol 9 (1) ◽  
pp. 256-264
Author(s):  
Dinkar Sharma ◽  
Ramandeep Kaur
Keyword(s):  
Stress Field ◽  
Hollow Cylinder ◽  
Numerical Study ◽  
Axial Stress ◽  
Circumferential Stress ◽  
Functionally Graded ◽  
Gradient Index ◽  
Variable Parameters ◽  
Graded Material ◽  
Governing Differential Equation

AbstractThis paper presents, numerical study of stress field in functionally graded material (FGM) hollow cylinder by using finite element method (FEM). The FGM cylinder is subjected to internal pressure and uniform heat generation. Thermoelastic material properties of FGM cylinder are assumed to vary along radius of cylinder as an exponential function of radius. The governing differential equation is solved numerically by FEM for isotropic and anistropic hollow cylinder. Additionally, the effect of material gradient index (β) on normalized radial stresses, normalized circumferential stress and normalized axial stress are evaluated and shown graphically. The behaviour of stress versus normalized radius of cylinder is plotted for different values of Poisson’s ratio and temperature. The graphical results shown that stress field in FGM cylinder is influenced by some of above mentioned parameters.

scholarly journals How May Virtual Communication Shape Cooperation in a Work Team?

2004 ◽  
Vol 26 (1) ◽  
Author(s):  
Andreas Flache
Keyword(s):  
Social Relationships ◽  
Work Teams ◽  
Work Team ◽  
Online Interaction ◽  
Negative Effects ◽  
Virtual Communication ◽  
Team Members ◽  
Face To Face ◽  
Interaction Task ◽  
Simulation Results

AbstractThis paper addresses theoretically the question how virtual communication may affect cooperation in work teams. The degree of team virtualization, i.e. the extent to which interaction between team members occurs online, is related to parameters of the exchange. First, it is assumed that in online interaction task uncertainties are higher than in face-to-face contacts. Second, the gratifying value of peer rewards is assumed to be lower in online contacts. Thirdly, it is assumed that teams are different in the extent to which members depend on their peers for positive affections, operationalized by the extent to which team members are interested in social relationships for their own sake, independently from their work interactions. Simulation results suggest both positive and negative effects of team virtualization on work-cooperation.

Entropy generation optimization for MHD natural convection of a nanofluid in porous media-filled enclosure with active parts and viscous dissipation

2017 ◽  
Vol 27 (2) ◽  
pp. 379-399 ◽  
Author(s):  
M.A. Mansour ◽  
Sameh Elsayed Ahmed ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Flow ◽  
Negative Effects ◽  
Content Type ◽  
Volume Method

Purpose This paper aims to investigate the entropy generation due to magnetohydrodynamic natural convection flow and heat transfer in a porous enclosure filled with Cu-water nanofluid in the presence of viscous dissipation effect. The left and right walls of the cavity are thermally insulated. There are heated and cold parts, and these are placed on the bottom and top wall, respectively, whereas the remaining parts are thermally insulated. Design/methodology/approach The finite volume method is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published woks is presented and is found to be in an excellent agreement. Findings The minimization of entropy generation and local heat transfer according to different values of the governing parameters are presented in details. It is found that the presence of magnetic field has negative effects on the local entropy generation because of heat transfer and the local total entropy generation. Also, the increase in the heated part length leads to a decrease in the local Nusselt number. Originality/value This problem is original, as it has not been considered previously.

Modeling of Aluminum Extrusion Process Using Non-Orthogonal Block Structured Grids Based FVM

2011 ◽  
Vol 189-193 ◽  
pp. 1749-1752
Author(s):  
Rui Wang ◽  
Hong Zhong Li
Keyword(s):  
Mathematic Model ◽  
Extrusion Process ◽  
Special Treatment ◽  
Aluminum Extrusion ◽  
Rigid Plastic ◽  
Structured Grids ◽  
Simulation Results ◽  
Flow Theories ◽  
Volume Method ◽  
Die Extrusion

The mathematic model of 3D aluminum extrusion processes using finite volume method (FVM) was established in this paper. The basic theories and rigid-plastic flow theories of this model were researched and built. Non-orthogonal structured grids were used to match complex geometric boundaries and local refinement of grids was also realized. The collocated arrangement is used to discretize the governing equations on non-orthogonal grids directly, pressure oscillations bring by this arrangement and error caused by grid’s non-orthogonality is eliminated by special treatment. A pocket die extrusion process was simulated using the program developed in this paper. The simulation results were also compared with that simulated by FEM software Deform in the same process, material and die conditions. The feasibility and efficiency of the mathematic model built in this paper was demonstrated by the simulation results and the comparison.

X-ray residual stress analysis of cylindrically curved surfaces—estimation of circumferential distributions of residual stresses

2003 ◽  
Vol 38 (5) ◽  
pp. 459-468 ◽  
Author(s):  
T Oguri ◽  
K Murata ◽  
Y Sato
Keyword(s):  
Residual Stresses ◽  
Least Squares Method ◽  
Stress Measurement ◽  
Incident Angle ◽  
Axial Stress ◽  
Circumferential Stress ◽  
Distribution Functions ◽  
Scanning Method ◽  
X Ray ◽  
Reference Axis

A new measuring technique utilizing X-ray diffraction is proposed in order to estimate the circumferential distributions of residual stresses on convex/concave cylindrical surfaces. This technique requires neither tilting X-ray beams in the circumferential direction in which the X-ray incident angle tends to be limited nor adjusting the normal of the irradiation area to the reference axis of the ψ angle. The circumferential distributions of the circumferential stress and of the axial stress are estimated from the diffraction angles at ψ = 0° and the axial stresses obtained by the stress measurement on multiple inclined areas on the cylindrical surfaces under the configuration of the axial stress measurement using the iso-inclination scanning method. This estimate technique was applied to two round bars of steel, one with circumferential distributions of the residual stresses and the other with almost uniform stresses. The distribution functions of the residual stresses were expanded to a couple of Fourier series, and the coefficients of them were determined by the least-squares method. The estimated distributions of the residual stresses were in good agreement with the actual ones.

scholarly journals Numerical study of a case of the free discharge of water through the turbine with a braked runner

2021 ◽  
Vol 2119 (1) ◽  
pp. 012152
Author(s):  
D V Platonov ◽  
A V Minakov ◽  
A V Sentyabov
Keyword(s):  
Finite Volume Method ◽  
Finite Volume ◽  
Numerical Study ◽  
Francis Turbine ◽  
Flow Structures ◽  
Pressure Pulsations ◽  
Integral Characteristics ◽  
Free Discharge ◽  
Simulation Results ◽  
Volume Method

Abstract The paper presents a numerical study of the free discharge of water through the turbine with a braked runner. The simulation was carried out for a unit of a full-scale Francis turbine. The finite volume method was employed for unstructured meshes using the DES method. The simulation results show the flow structures, integral characteristics, and pressure pulsations in the flow path. The analysis of the applicability of this approach to real conditions is carried out.

Experimental and Numerical Investigation of High-Temperature Multi-Axial Fatigue

2021 ◽  
Author(s):  
Harish Ramesh Babu ◽  
Marco Böcker ◽  
Mario Raddatz ◽  
Sebastian Henkel ◽  
Horst Biermann ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Biaxial Loading ◽  
Complex Geometry ◽  
Low Cycle Fatigue ◽  
Axial Stress ◽  
Equivalent Stress ◽  
Turbine Blades ◽  
Damage Development ◽  
Simulation Results ◽  
Axial Fatigue

Abstract Gas turbines and aircraft engines are dominated by cyclic operating modes with fatigue-related loads. This may result in the acceleration of damage development on the components. Critical components of turbine blades and discs are exposed to cyclic thermal and mechanical multi-axial fatigue. In the current work, planar-biaxial Low-Cycle-Fatigue tests are conducted using cruciform specimens at different test temperatures. The influence on the deformation and lifetime behaviour of the nickel-base disk alloy IN718 is investigated at selected cyclic proportional loading cases. The calculation of the stress and strain distribution of the cruciform specimens from the experimental data is difficult to obtain due to complex geometry and temperature gradients. Therefore, there is a need for Finite Element Simulations. A viscoplastic material model is considered to simulate the material behaviour subjected to uniaxial and the selected planar-biaxial loading conditions. At first, uniaxial simulation results are compared with the uniaxial experiment results for both batches of IN718. Then, the same material parameters are used for simulating the biaxial loading cases. The prediction of FE simulation results is in good agreement with the experimental LCF test for proportional loadings. The equivalent stress amplitude results of the biaxial simulation are compared with the uniaxial results. Furthermore, the lifetime is calculated from the simulation and by using Crossland and Sines multi-axial stress-based approaches. The Crossland model predicts fatigue life significantly better than the Sines model. Finally, the simulated lifetime results are compared with the experimental lifetime

Simulation on Multi-Oil-Cavity and Multi-Oil-Pad Hydrostatic Bearings

2013 ◽  
Vol 274 ◽  
pp. 274-277 ◽  
Author(s):  
Xiao Qiu Xu ◽  
Jun Peng Shao ◽  
Xiao Dong Yang ◽  
Yan Qin Zhang ◽  
Xiao Dong Yu ◽  
...  
Keyword(s):  
Hydraulic System ◽  
Thrust Bearing ◽  
Three Dimensional ◽  
Structure Design ◽  
Analysis Software ◽  
Hydrostatic Bearing ◽  
Hydrostatic Bearings ◽  
Simulation Results ◽  
Three Dimensional Models ◽  
Volume Method

Taking multi-oil-cavity and multi-oil-pad hydrostatic bearings as studied projects, firstly make brief instructions for structure characteristics and working principal of hydraulic system; Then, build three-dimensional models of multi-oil-cavity and multi-oil-pad hydrostatic bearings respectively. Adopting finite volume method, oil film mesh is generated by universal finite analysis software CFD; then, carry on numerical simulations for pressure distribution and temperature distribution of the two studied hydrostatic thrust bearing under various viscosity, and make comparative analysis for difference between the two studied hydrostatic thrust bearing. Based on the analysis of numerical simulation results, the conclusions whether oil-return groove is set for hydrostatic bearing could be received. Simulation results reveal truly the influence of setting oil-return groove or not on hydrostatic thrust bearing, and improve structure design for hydrostatic thrust bearing.

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