How to Select the Optimized Time Step and Mesh Size for FEM Thermal Transients Simulations of PWR Vessels and Nozzles by Means of Artificial Neural Networks

2019 ◽  
Author(s):  
Nicolas Santucho ◽  
Martin Chimenti ◽  
Jose Duo
Keyword(s):  
Data Base ◽  
Structural Integrity ◽  
Mesh Size ◽  
Time Step ◽  
Thermal Transients ◽  
Element Size ◽  
Mechanical Models ◽  
Allowable Error ◽  
Artificial Neural ◽  
Definition Of

Abstract This paper describes the development of a data base and associated interpolation tool used to perform the validation of FEA thermo-mechanical models designed to verify the structural integrity of a self-pressurized modular Reactor Pressure Vessel (RPV) and its nozzles under service transient thermal loads. The main goal is to assess the element’s size and time steps that provide a confidence level on the obtained solutions. The validation process implies the definition of the geometry under study, its material’s properties, thermal load conditions and type of mesh element. With all this information, the program gives the user a set of curves for maximum time steps vs. temperature change rates for each typical thickness section in the modeled geometry for a chosen element size. Any point located below those curves assures a solution underneath a user specified allowable error (e.g.: 5%). All calculations are processed using dimensionless variables in order to create a universal data base enabling the analysis of many different situations of geometries, materials and loads. To improve performance, an Artificial Neural Network algorithm was developed. The resulting application significantly reduces the convergence study time and efforts.

Dynamics Simulations of a Graphite Block Under Longitudinal Impact

2010 ◽  
Author(s):  
Gyeongho Kim ◽  
DongOk Kim ◽  
Woo-Seok Choi ◽  
Ji Ho Kang ◽  
Jae Man Noh
Keyword(s):  
Structural Integrity ◽  
Seismic Analysis ◽  
Mesh Size ◽  
Contact Dynamics ◽  
Longitudinal Impact ◽  
Graphite Block ◽  
Time Step ◽  
Core Components ◽  
Dynamics Simulations ◽  
Step Contact

Graphite blocks are important core components of the high temperature gas-cooled reactor. As these blocks are simply stacked in array, collisions among neighboring components may occur during earthquakes or accidents. Thus, it is important to develop a reliable seismic model of the stacked graphite blocks and have them designed to maintain their structural integrity during the anticipated occurrences. Various aspects involved in modeling and calculating impact-contact dynamics can affect the resulting behavior of the graphite block. These include mesh size, time step, contact behavior, mechanical constraint formulation of impact-contact analysis, etc. This work is dedicated to perform comparative studies and the effects of these parameters will be identified. The insights obtained through these studies will help build a realistic impact-contact model of the graphite block, from which a lumped or reduced dynamics model will be developed for the seismic analysis of the reactor including these graphite components.

Dynamics Simulations of a Graphite Block Under Longitudinal Impact

2010 ◽  
Vol 133 (5) ◽  
Author(s):  
Gyeongho Kim ◽  
Dong Ok Kim ◽  
Woo-Seok Choi ◽  
Ji Ho Kang ◽  
Jae Man Noh
Keyword(s):  
Structural Integrity ◽  
Seismic Analysis ◽  
Mesh Size ◽  
Contact Dynamics ◽  
Longitudinal Impact ◽  
Graphite Block ◽  
Time Step ◽  
Core Components ◽  
Dynamics Simulations ◽  
Step Contact

Graphite blocks are important core components of the high temperature gas-cooled reactor. As these blocks are simply stacked in array, collisions among neighboring components may occur during earthquakes or accidents. Thus, it is important to develop a reliable seismic model of the stacked graphite blocks and have them designed to maintain their structural integrity during the anticipated occurrences. Various aspects involved in modeling and calculating impact-contact dynamics can affect the resulting behavior of the graphite block. These include mesh size, time step, contact behavior, mechanical constraint formulation of impact-contact analysis, etc. This work is dedicated to perform comparative studies and the effects of these parameters will be identified. The insights obtained through these studies will help build a realistic impact-contact model of the graphite block from which a lumped or reduced dynamics model will be developed for the seismic analysis of the reactor including these graphite components.

scholarly journals 3D-Based Transition hpq/hp-Adaptive Finite Elements for Analysis of Piezoelectrics

2021 ◽  
Vol 11 (9) ◽  
pp. 4062
Author(s):  
Grzegorz Zboiński ◽  
Magdalena Zielińska
Keyword(s):  
Finite Elements ◽  
Numerical Solutions ◽  
High Stress ◽  
Continuous Change ◽  
Transition Elements ◽  
Finite Element Approximations ◽  
Element Size ◽  
Piezoelectric Elements ◽  
Mechanical Models ◽  
Transition Models

This paper concerns the algorithm of transition piezoelectric elements for adaptive analysis of electro-mechanical systems. In addition, effectivity of the proposed elements in such an analysis is presented. The elements under consideration are assigned for joining basic elements which correspond to the mechanical models of either the first or higher order, while the electric model is of arbitrary order. In this work, three variants of the transition models are applied. The first one assures continuity of displacements between the basic models and continuity of electric potential between these models, as well. The second transition piezoelectric model guarantees additional continuity of the stress field between the basic models. The third transition model additionally enables continuous change of the strain state between the basic models. Based on the mentioned models, three types of the corresponding transition finite elements are introduced. The applied finite element approximations are hpq/hp-adaptive ones, which allows element-wise changes of the element size parameter h, and the element longitudinal and transverse orders of approximation, respectively, p and q, depending on the error level. Numerical effectiveness of the models and their approximations is investigated in the contexts of: ability to remove high stress gradients between the basic and transition models, and convergence of the numerical solutions for the model problems of piezoelectrics with and without the proposed transition elements.

scholarly journals Mesh size sensitivity analysis for interlaminar fracture of the fiber-reinforced laminated composites

2019 ◽  
Vol 14 ◽  
pp. 155892501988346 ◽  
Author(s):  
Fatih Daricik
Keyword(s):  
Crack Closure ◽  
Strain Energy ◽  
Three Dimensional ◽  
Laminated Composite ◽  
Mesh Size ◽  
Strain Energy Release ◽  
Virtual Crack Closure Technique ◽  
Closure Technique ◽  
Interlaminar Fracture ◽  
Element Size

The virtual crack closure technique is a well-known finite element–based numerical method used to simulate fractures and it suits well to both of two-dimensional and three-dimensional interlaminar fracture analysis. In particular, strain energy release rate during a three-dimensional interlaminar fracture of laminated composite materials can successfully be computed using the virtual crack closure technique. However, the element size of a numerical model is an important concern for the success of the computation. The virtual crack closure technique analysis with a finer mesh converges the numerical results to experimental ones although such a model may need excessive modeling and computing times. Since, the finer element size through a crack path causes oscillation of the stresses at the free ends of the model, the plies in the delaminated zone may overlap. To eliminate this problem, the element size for the virtual crack closure technique should be adjusted to ascertain converged yet not oscillating results with an admissible processing time. In this study, mesh size sensitivity of the virtual crack closure technique is widely investigated for mode I and mode II interlaminar fracture analyses of laminated composite material models by considering experimental force and displacement responses of the specimens. Optimum sizes of the finite elements are determined in terms of the force, the displacement, and the strain energy release rate distribution along the width of the model.

Influence of Clearances and Thermal Effects on the Dynamic Behavior of Gear-Hydrodynamic Journal Bearing Systems

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
R. Fargère ◽  
P. Velex
Keyword(s):  
Degrees Of Freedom ◽  
Integration Scheme ◽  
Time Step ◽  
Specific Element ◽  
Normal Contact ◽  
Contact Algorithm ◽  
Gear Teeth ◽  
Proposed Model ◽  
Elastic Couplings ◽  
Definition Of

A global model of mechanical transmissions is introduced which deals with most of the possible interactions between gears, shafts, and hydrodynamic journal bearings. A specific element for wide-faced gears with nonlinear time-varying mesh stiffness and tooth shape deviations is combined with shaft finite elements, whereas the bearing contributions are introduced based on the direct solution of Reynolds' equation. Because of the large bearing clearances, particular attention has been paid to the definition of the degrees-of-freedom and their datum. Solutions are derived by combining a time step integration scheme, a Newton–Raphson method, and a normal contact algorithm in such a way that the contact conditions in the bearings and on the gear teeth are simultaneously dealt with. A series of comparisons with the experimental results obtained on a test rig are given which prove that the proposed model is sound. Finally, a number of results are presented which show that parameters often discarded in global models such as the location of the oil inlet area, the oil temperature in the bearings, the clearance/elastic couplings interactions, etc. can be influential on static and dynamic tooth loading.

Fractal Characteristics of Sandstone Cutting Fracture under Mechanical Shock Loading Conditions

2012 ◽  
Vol 226-228 ◽  
pp. 1789-1794 ◽  
Author(s):  
Shu Ren Wang ◽  
Paul Hagan ◽  
Yan Cheng
Keyword(s):  
Fractal Dimension ◽  
Size Distribution ◽  
Structural Integrity ◽  
Theoretical Calculations ◽  
Mesh Size ◽  
Rock Cutting ◽  
Weight Percent ◽  
Rock Breaking ◽  
Engineering Practice ◽  
Mechanical Shock

It is the key to guide rock-breaking design and engineering practice for how to obtain a reasonable test indicator to assess the cuttability of the rock. Some sandstone samples were tested by using the linear rock cutting machine in the school of mining engineering, University of New South Wales (UNSW), Australia. The curves characteristics for the weight percent of the broken debris with the mesh size distribution were obtained through the screening statistics. Furthermore, the fractal dimension of the specimen broken debris was derived through theoretical calculations and statistical analysis. The results showed that the rock cutting fragmentation is of significant fractal features under the mechanical shock loads. The broken debris fractal dimension of the structural integrity specimens is bigger, the range of the fractal dimension is smaller and the broken debris size distribution is more even than that of the poor structural integrity specimens. The fractal dimension is the ideal test indicator to assess and analysis the rock-breaking degree.

Definition of an Architecture to Configure Artificial Neural Networks Topologies Using Partial Reconfiguraton in FPGA

2015 ◽  
Vol 13 (7) ◽  
pp. 2094-2100 ◽  
Author(s):  
Carlos Alberto de Albuquerque Silva ◽  
Adriao Duarte Doria Neto ◽  
Jose Alberto Nicolau Oliveira ◽  
Jorge Dantas Melo ◽  
David Simonetti Barbalho ◽  
...  
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Artificial Neural ◽  
Definition Of

Data Base Requirements for Concurrent Design Systems

1991 ◽  
Author(s):  
Ranko Vujosevic ◽  
Andrew Kusiak
Keyword(s):  
Data Base ◽  
Data Model ◽  
Object Oriented ◽  
Concurrent Design ◽  
Complex Objects ◽  
Maintenance System ◽  
Design And Manufacturing ◽  
Design Systems ◽  
Truth Maintenance ◽  
Definition Of

Abstract The data base requirements for concurrent design systems are discussed. An object-oriented data base, which allows for definition of complex objects, specification of relationships between objects, and modular expandability without affecting the existing information is defined. The data base is developed based on the object-oriented data model implemented in Smalltalk-80. An assumption-based truth maintenance system for maintaining the dependency relationships between design and manufacturing information is described.

scholarly journals Numerical Method of Fabric Dynamics Using Front Tracking and Spring Model

2013 ◽  
Vol 14 (5) ◽  
pp. 1228-1251 ◽  
Author(s):  
Yan Li ◽  
I-Liang Chern ◽  
Joung-Dong Kim ◽  
Xiaolin Li
Keyword(s):  
Upper Bound ◽  
Mesh Size ◽  
Front Tracking ◽  
Time Step ◽  
Mass System ◽  
Ode System ◽  
Spring System ◽  
Fabric Surface ◽  
Mass Spring ◽  
Eigen Frequency

AbstractWe use front tracking data structures and functions to model the dynamic evolution of fabric surface. We represent the fabric surface by a triangulated mesh with preset equilibrium side length. The stretching and wrinkling of the surface are modeled by the mass-spring system. The external driving force is added to the fabric motion through the “Impulse method” which computes the velocity of the point mass by superposition of momentum. The mass-spring system is a nonlinear ODE system. Added by the numerical and computational analysis, we show that the spring system has an upper bound of the eigen frequency. We analyzed the system by considering two spring models and we proved in one case that all eigenvalues are imaginary and there exists an upper bound for the eigen-frequency This upper bound plays an important role in determining the numerical stability and accuracy of the ODE system. Based on this analysis, we analyzed the numerical accuracy and stability of the nonlinear spring mass system for fabric surface and its tangential and normal motion. We used the fourth order Runge-Kutta method to solve the ODE system and showed that the time step is linearly dependent on the mesh size for the system.

scholarly journals An orthogonal terrain-following coordinate and its preliminary tests using 2-D idealized advection experiments

2014 ◽  
Vol 7 (4) ◽  
pp. 1767-1778 ◽  
Author(s):  
Y. Li ◽  
B. Wang ◽  
D. Wang ◽  
J. Li ◽  
L. Dong
Keyword(s):  
Rotation Angle ◽  
Computational Grids ◽  
Time Step ◽  
Numerical Errors ◽  
Terrain Following ◽  
Steep Terrain ◽  
Definition Of ◽  
Σ Coordinate ◽  
Basis Vectors ◽  
Better Than

Abstract. We have designed an orthogonal curvilinear terrain-following coordinate (the orthogonal σ coordinate, or the OS coordinate) to reduce the advection errors in the classic σ coordinate. First, we rotate the basis vectors of the z coordinate in a specific way in order to obtain the orthogonal, terrain-following basis vectors of the OS coordinate, and then add a rotation parameter b to each rotation angle to create the smoother vertical levels of the OS coordinate with increasing height. Second, we solve the corresponding definition of each OS coordinate through its basis vectors; and then solve the 3-D coordinate surfaces of the OS coordinate numerically, therefore the computational grids created by the OS coordinate are not exactly orthogonal and its orthogonality is dependent on the accuracy of a numerical method. Third, through choosing a proper b, we can significantly smooth the vertical levels of the OS coordinate over a steep terrain, and, more importantly, we can create the orthogonal, terrain-following computational grids in the vertical through the orthogonal basis vectors of the OS coordinate, which can reduce the advection errors better than the corresponding hybrid σ coordinate. However, the convergence of the grid lines in the OS coordinate over orography restricts the time step and increases the numerical errors. We demonstrate the advantages and the drawbacks of the OS coordinate relative to the hybrid σ coordinate using two sets of 2-D linear advection experiments.

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