scholarly journals Flow-Induced Vibration of a Candu Fuel String

2021 ◽  
Author(s):  
Mohammad Fadaee
Keyword(s):  
Finite Elements ◽  
Frictional Contact ◽  
Nuclear Industry ◽  
Contact Forces ◽  
Pressure Tube ◽  
Integration Scheme ◽  
Fluid Forces ◽  
Highly Nonlinear ◽  
Mixed Beam ◽  
Unsteady Fluid

A comprehensive vibration model is developed in this thesis to simulate the dynamical behaviour of a string of CANDU fuel bundles subjected to unsteady flow of coolant inside a pressure tube. The large-scale dynamical system of interest consists of several hundreds of solid and deformable components interacting with the coolant flow, with each other and with the pressure tube through frictional contact at various interfaces. In the first stage of this thesis, the three-node higher-order mixed beam finite elements and the nine-node thick plate finite elements are employed to model the fuel bundles. The equations of motion of the fuel string system are discretised in the time domain using the Newmark integration scheme. The CANDU fuel string behaviour is highly nonlinear and the total number of potential frictional contact exceeds thousand sets. In the second stage, a numerical scheme for efficiently handling three-dimensional friction and contact is developed. The incremental displacement is used to relate gaps with contact forces and the problem is formulated to be a linear complementarity problem (LCP). The accuracy and robustness of the presented method is tested against several numerical simulations and experimental results available in the literature. To find the unsteady fluid forces acting on the fuel string two comprehensive computational fluid dynamic (CFD) models that include endcaps and spacer pads are developed. The models are solved using the large eddy simulation (LES) scheme. The coolant unsteady pressure is integrated over fuel rods surfaces and unsteady fluid forces are found and used as the excitation sources for fuel string vibration. The power spectral density (PSD) of unsteady fluid forces are obtained and peak frequencies are identified. A FORTRAN code consisting of approximately 13000 lines is developed and validated at different stages for use in Canadian nuclear industry to simulate the vibrational behaviour of a 12-bundle fuel string and the material loss during reactor normal operations. Free vibration analyses of a CANDU fuel string are also performed and natural frequencies of the system are obtained.

scholarly journals Flow-Induced Vibration of a Candu Fuel String

2021 ◽  
Author(s):  
Mohammad Fadaee
Keyword(s):  
Finite Elements ◽  
Frictional Contact ◽  
Nuclear Industry ◽  
Contact Forces ◽  
Pressure Tube ◽  
Integration Scheme ◽  
Fluid Forces ◽  
Highly Nonlinear ◽  
Mixed Beam ◽  
Unsteady Fluid

A comprehensive vibration model is developed in this thesis to simulate the dynamical behaviour of a string of CANDU fuel bundles subjected to unsteady flow of coolant inside a pressure tube. The large-scale dynamical system of interest consists of several hundreds of solid and deformable components interacting with the coolant flow, with each other and with the pressure tube through frictional contact at various interfaces. In the first stage of this thesis, the three-node higher-order mixed beam finite elements and the nine-node thick plate finite elements are employed to model the fuel bundles. The equations of motion of the fuel string system are discretised in the time domain using the Newmark integration scheme. The CANDU fuel string behaviour is highly nonlinear and the total number of potential frictional contact exceeds thousand sets. In the second stage, a numerical scheme for efficiently handling three-dimensional friction and contact is developed. The incremental displacement is used to relate gaps with contact forces and the problem is formulated to be a linear complementarity problem (LCP). The accuracy and robustness of the presented method is tested against several numerical simulations and experimental results available in the literature. To find the unsteady fluid forces acting on the fuel string two comprehensive computational fluid dynamic (CFD) models that include endcaps and spacer pads are developed. The models are solved using the large eddy simulation (LES) scheme. The coolant unsteady pressure is integrated over fuel rods surfaces and unsteady fluid forces are found and used as the excitation sources for fuel string vibration. The power spectral density (PSD) of unsteady fluid forces are obtained and peak frequencies are identified. A FORTRAN code consisting of approximately 13000 lines is developed and validated at different stages for use in Canadian nuclear industry to simulate the vibrational behaviour of a 12-bundle fuel string and the material loss during reactor normal operations. Free vibration analyses of a CANDU fuel string are also performed and natural frequencies of the system are obtained.

scholarly journals Wavelet analysis of poorly-focused ultrasonic signal of pressure tube inspection in nuclear industry

2018 ◽  
Author(s):  
Huan Zhao ◽  
Anthony Gachagan ◽  
Gordon Dobie ◽  
Timothy Lardner
Keyword(s):  
Wavelet Analysis ◽  
Ultrasonic Signal ◽  
Nuclear Industry ◽  
Pressure Tube

Three-Dimensional Solid Brick Element Using Slopes in the Absolute Nodal Coordinate Formulation

2013 ◽  
Vol 9 (2) ◽  
Author(s):  
Alexander Olshevskiy ◽  
Oleg Dmitrochenko ◽  
Chang-Wan Kim
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Absolute Nodal Coordinate Formulation ◽  
Mass Matrix ◽  
Equations Of Motion ◽  
Test Problems ◽  
Absolute Nodal Coordinate ◽  
Highly Nonlinear ◽  
Brick Element ◽  
The Absolute

The present paper contributes to the field of flexible multibody systems dynamics. Two new solid finite elements employing the absolute nodal coordinate formulation are presented. In this formulation, the equations of motion contain a constant mass matrix and a vector of generalized gravity forces, but the vector of elastic forces is highly nonlinear. The proposed solid eight node brick element with 96 degrees of freedom uses translations of nodes and finite slopes as sets of nodal coordinates. The displacement field is interpolated using incomplete cubic polynomials providing the absence of shear locking effect. The use of finite slopes describes the deformed shape of the finite element more exactly and, therefore, minimizes the number of finite elements required for accurate simulations. Accuracy and convergence of the finite element is demonstrated in nonlinear test problems of statics and dynamics.

Unilateral Impact and Contact of Elastic Structures Using Lagrangian Multipliers

2011 ◽  
Author(s):  
Sebastian Tatzko
Keyword(s):  
Equations Of Motion ◽  
Structural Equations ◽  
Contact Forces ◽  
Integration Scheme ◽  
Lagrangian Multiplier ◽  
Elastic Structures ◽  
Lagrangian Multipliers ◽  
Linear Elastic ◽  
Time Stepping ◽  
Numerical Effort

This paper deals with linear elastic structures exposed to impact and contact phenomena. Within a time stepping integration scheme contact forces are computed with a Lagrangian multiplier approach. The main focus is turned on a simplified solving method of the linear complementarity problem for the frictionless contact. Numerical effort is reduced by applying a Craig-Bampton transformation to the structural equations of motion.

A Method for Extracting the Time Delay From the Unsteady and Quasi-Steady Fluidelastic Forces in Two-Phase Flow

2013 ◽  
Author(s):  
Teguewinde Sawadogo ◽  
Njuki Mureithi
Keyword(s):  
Time Delay ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Fluid Forces ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Measured Time ◽  
Unsteady Fluid ◽  
Theoretical Results

The time delay is a key parameter for modeling fluidelastic instability, especially the damping controlled mechanism. It can be determined experimentally by measuring directly the time lag between the tube motion and the induced fluid forces. The fluid forces may be obtained by integrating the pressure field around the moving tube. However, this method faces certain difficulties in two-phase flow since the high turbulence and the non-uniformity of the flow may increase the randomness of the measured force. To overcome this difficulty, an innovative method for extracting the time delay inherent to the quasi-steady model for fluidelastic instability is proposed in this study. Firstly, experimental measurements of unsteady and quasi-static fluid forces (in the lift direction) acting on a tube subject to two-phase flow were conducted. The unsteady fluid forces were measured by exciting the tube using a linear motor. These forces were measured for a wide range of void fraction, flow velocities and excitation frequencies. The experimental results showed that the unsteady fluid forces could be represented as single valued function of the reduced velocity (flow velocity reduced by the excitation frequency and the tube diameter). The time delay was determined by equating the unsteady fluid forces with the quasi-static forces. The results given by this innovative method of measuring the time delay in two-phase flow were consistent with theoretical expectations. The time delay could be expressed as a linear function of the convection time and the time delay parameter was determined for void fractions ranging from 60% to 90%. Fluidelastic instability calculations were also performed using the quasi-steady model with the newly measured time delay parameter. Previously conducted stability tests provided the experimental data necessary to validate the theoretical results of the quasi-steady model. The validity of the quasi-steady model for two-phase flow was confirmed by the good agreement between its results and the experimental data. The newly measured time delay parameter has improved significantly the theoretical results, especially for high void fractions (90%). However, the model could not be verified for void fractions lower or equal to 50% due to the limitation of the current experimental setup. Further studies are consequently required to clarify this point. Nevertheless, this model can be used to simulate the flow induced vibrations in steam generators’ tube bundles as their most critical parts operate at high void fractions (≥ 60%).

scholarly journals Some Unsteady Fluid Forces on Pump Impellers

1992 ◽  
Vol 114 (4) ◽  
pp. 632-637 ◽  
Author(s):  
R. S. Miskovish ◽  
C. E. Brennen
Keyword(s):  
Fluid Flow ◽  
Centrifugal Pump ◽  
Bending Moments ◽  
Pump Impeller ◽  
Spectral Analyses ◽  
Fluid Forces ◽  
Radial Forces ◽  
Unsteady Fluid ◽  
Rotordynamic Forces ◽  
Centrifugal Pump Impeller

Spectral analyses of all the forces and moments acting on a typical centrifugal pump impeller/volute combination are presented. These exhibit shaft frequencies, blade passing frequencies, and beat frequencies associated with a whirl motion imposed on the shaft in order to measure rotordynamic forces. Among other features the unsteady thrust was found to contain a surprisingly large blade passing harmonic. While previous studies have explored the magnitudes of the steady fluid-induced radial forces and the fluid-induced rotordynamic forces for this typical centrifugal pump impeller/volute combination, this paper presents information on the steady bending moments and rotordynamic moments due to the fluid flow. These imply certain axial locations for the lines of action of the radial and rotordynamic forces. Data on the lines of action are presented and allow inferences on the sources of the forces.

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