DNB Oscillatory Temperature and Thermal Stress Responses for Evaporator Tubes Based on Rivulet Model

1978 ◽  
Vol 100 (3) ◽  
pp. 424-431 ◽  
Author(s):  
C. L. Chu ◽  
J. M. Roberts ◽  
A. W. Dalcher
Keyword(s):  
Finite Element ◽  
Thermal Stress ◽  
Temperature Variation ◽  
Stress Responses ◽  
Thermal Model ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Computer Codes ◽  
Oscillatory Temperature

Experiment evidence and observations have shown that the DNB oscillation phenomena can best be characterized by water rivulets motion with temperature variation in the circumferential direction. This paper presents the rivulet thermal model that directly corresponds to these observations. Finite element computer codes were used to evaluate temperature and thermal stress behavior of the steam tube under the condition where water rivulets appear and disappear along the tube inside circumference. An inherently complicated three-dimensional problem can reasonably be reduced to a two-dimensional analysis with relative simplicity.

An asymptotic procedure and numerical study for the analysis of an elastic body with a thin sub-surface crack

1995 ◽  
Vol 6 (1) ◽  
pp. 1-23
Author(s):  
A. B. Movchan ◽  
J. R. Willis
Keyword(s):  
Finite Element ◽  
Numerical Study ◽  
Three Dimensional ◽  
Internal Crack ◽  
Numerical Implementation ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Crack Problems ◽  
Finite Element Calculations ◽  
Good Agreement

A class of three-dimensional crack problems is considered, of which a prototype example is provided by a half-space containing a long internal crack, located in a plane perpendicular to the boundary. By means of an asymptotic procedure, the original three-dimensional problem is split up into a sequence of two-dimensional formulations. Results of its numerical implementation are in good agreement with results of more computer-intensive finite-element calculations.

Thermal Stress in Discretely Layered Structures with Functional Graded Materials

2008 ◽  
Vol 24 (4) ◽  
pp. 297-300 ◽  
Author(s):  
S.-F. Hwang ◽  
W.-T. Liao
Keyword(s):  
Finite Element ◽  
Thermal Stress ◽  
Three Dimensional ◽  
Stress Singularity ◽  
Layered Structures ◽  
Two Dimensional ◽  
Element Analysis ◽  
Graded Materials ◽  
Dimensional Finite Element ◽  
Graded Material

AbstractFunctional graded materials are generally provided in discretely layered structures to reduce the abrupt mismatch and to improve failure performance. To investigate the thermal stress singularity occurring at the intersection of an interface and a free end, two-dimensional and three-dimensional finite element analyses are performed for titanium and aluminum layers with or without functional graded materials. The results indicate that once the functional graded material is added, the stress singularity around the intersection of an interface and a free end could be significantly relieved. If more FGM layers are used, the stress singularity could be further reduced to a very small value. If the longitudinal normal stresses and interlaminar shear stress are considered, two-dimensional finite element analysis may be enough, while three-dimensional analysis is necessary for the interlaminar normal stress. Otherwise, one may underestimate its stress singularity.

Inclusion of Local Shell Behavior of Tubes Into a Two-Dimensional Beam Approximation of Deformation in Nuclear Fuel Channels

2002 ◽  
Author(s):  
S. Khajehpour ◽  
R. G. Sauve´ ◽  
N. Badie
Keyword(s):  
Finite Element ◽  
Contact Stiffness ◽  
Three Dimensional ◽  
Local Deformation ◽  
Beam Model ◽  
Two Dimensional ◽  
Dimensional Modeling ◽  
Dimensional Finite Element ◽  
Nonlinear Force ◽  
Three Dimensional Finite Element

A method has been developed to incorporate the local three-dimensional shell behavior of two concentric tubes in the two-dimensional beam modeling of the problem. The two dimensional modeling of fuel channels in CANDU pressurized heavy water nuclear reactors is used in lieu of a more accurate three dimensional finite element approach in order to reduce the on-line simulation time which greatly affects the SLAR (Spacer Location And Repositioning) maintenance operation cost during outage. However, effort must be made to include the three-dimensional shell behavior of these channels into the two-dimensional modeling. In recent studies a nonlinear force-dependent model for contact stiffness between the calandria tube and pressure tube has been developed. However, local deformation of calandria the tube at spacer locations due to in-reactor creep leads to settling of the spacer into the calandria tube that consequently reduces the gap between the two tubes. In this work, the effect of local deformation (elastic and creep) of calandria tubes on modeling of contact at spacer locations is assessed using a three dimensional finite element code. The result is incorporated into a two-dimensional beam model of the problem as a reduction in size of the spacers that separate the two tubes. It is shown that the proposed method increases the accuracy of prediction of contact time and the spacer. In general, the method described in this paper suggests a way to incorporate local shell deformation into beam models of slender shell structure.

Preliminary Ship Design Using One and Two-Dimensional Models

1999 ◽  
Vol 36 (02) ◽  
pp. 102-112
Author(s):  
Michael D. A. Mackney ◽  
Carl T. F. Ross
Keyword(s):  
Finite Element ◽  
Dimensional Analysis ◽  
Three Dimensional ◽  
Two Dimensional ◽  
One Dimensional ◽  
Dimensional Finite Element ◽  
Dimensional Models ◽  
Support Conditions ◽  
The One ◽  
Three Dimensional Finite Element

Computational studies of hull-superstructure interaction were carried out using one-, two-and three-dimensional finite element analyses. Simplification of the original three-dimensional cases to one- and two-dimensional ones was undertaken to reduce the data preparation and computer solution times in an extensive parametric study. Both the one- and two-dimensional models were evaluated from numerical and experimental studies of the three-dimensional arrangements of hull and superstructure. One-dimensional analysis used a simple beam finite element with appropriately changed sections properties at stations where superstructures existed. Two-dimensional analysis used a four node, first order quadrilateral, isoparametric plane elasticity finite element, with a corresponding increase in the grid domain where the superstructure existed. Changes in the thickness property reflected deck stiffness. This model was essentially a multi-flanged beam with the shear webs representing the hull and superstructure sides, and the flanges representing the decks One-dimensional models consistently and uniformly underestimated the three-dimensional behaviour, but were fast to create and run. Two-dimensional models were also consistent in their assessment, and considerably closer in predicting the actual behaviours. These models took longer to create than the one-dimensional, but ran in very much less time than the refined three-dimensional finite element models Parametric insights were accomplished quickly and effectively with the simplest model and processor, but two-dimensional analyses achieved closer absolute measure of the displacement behaviours. Although only static analysis with simple loading and support conditions were presented, it is believed that similar benefits would be found for other loadings and support conditions. Other engineering components and structures may benefit from similarly judged simplification using one- and two-dimensional models to reduce the time and cost of preliminary design.

scholarly journals Membrane analogy for multi-material bars under torsion

2019 ◽  
Vol 475 (2225) ◽  
pp. 20190124 ◽  
Author(s):  
Laura Galuppi ◽  
Gianni Royer-Carfagni
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Cross Sections ◽  
Three Dimensional ◽  
Element Model ◽  
Elastic Problem ◽  
Two Dimensional ◽  
Torsion Problem ◽  
Linear Elastic ◽  
Physical Apparatus

Prandtl's membrane analogy for the torsion problem of prismatic homogeneous bars is extended to multi-material cross sections. The linear elastic problem is governed by the same equations describing the deformation of an inflated membrane, differently tensioned in regions that correspond to the domains hosting different materials in the bar cross section, in a way proportional to the inverse of the material shear modulus. Multi-connected cross sections correspond to materials with vanishing stiffness inside the holes, implying infinite tension in the corresponding portions of the membrane. To define the interface constrains that allow to apply such a state of prestress to the membrane, a physical apparatus is proposed, which can be numerically modelled with a two-dimensional mesh implementable in commercial finite-element model codes. This approach presents noteworthy advantages with respect to the three-dimensional modelling of the twisted bar.

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