scholarly journals The Effects of Grid Accuracy on Flow Simulations: A Numerical Assessment

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 110 ◽  
Author(s):  
Majid Allahyari ◽  
Vahid Esfahanian ◽  
Kianoosh Yousefi
Keyword(s):  
Fourth Order ◽  
Computational Simulation ◽  
Fluid Flows ◽  
Grid Generation ◽  
Linearization Method ◽  
Flow Simulations ◽  
Numerical Assessment ◽  
Fourth Order Compact Scheme ◽  
Naca 0012

High-quality, accurate grid generation is a critical challenge in the computational simulation of fluid flows around complex geometries. In particular, the accuracy of the grids is an effective factor in order to achieve a successful numerical simulation. In the current study, we present a series of systematic numerical simulations for fluid flows around a NACA 0012 airfoil using different computational grid generation techniques, including the standard second-order, fourth-order compact, and Theodorsen transformation approaches, to assess the effects of grid accuracy on the flow solutions. The flow solvers are based on the second- and fourth-order schemes for spatial discretizations and Beam-Warming linearization method for time advancement. The obtained grids, as well as the metrics and the corresponding numerical flow solution for each grid generation technique, are compared and studied in detail. It is demonstrated that the quality and orthogonality of the grids is improved by using the fourth-order compact scheme. Moreover, the numerical assessment showed that the accuracy and the quality of the grids directly influence the numerical flow solutions. Finally, the higher-order accurate flow solvers are found to be more sensitive to the accuracy of the generated grid.

scholarly journals Hybrid Grid Generation for Viscous Flow Simulations in Complex Geometries

2020 ◽  
Author(s):  
Hongfei Ye ◽  
Yang Liu ◽  
Bo Chen ◽  
Zhiwei Liu ◽  
Jianjing Zheng ◽  
...  
Keyword(s):  
Viscous Flow ◽  
Grid Generation ◽  
Complex Geometries ◽  
Fast Detection ◽  
Flow Simulations ◽  
Surface Triangulation ◽  
Front Shape ◽  
Hybrid Grid ◽  
Different Levels

Abstract In this paper, we present a hybrid grid generation approach for viscous flow simulations by marching a surface triangulation on viscous walls along certain directions. Focuses are on the computing strategies used to determine the marching directions and distances since these strategies determine the quality of the resulting elements and the reliability of the meshing procedure to a large extent. With respect to marching direction, three strategies featured with different levels of efficiencies and robustness performance are combined to compute the initial normals at front nodes to balance the trade-off between efficiency and robustness. A novel weighted strategy is used in the normal smoothing scheme, which evidently reduce the possibility of early stop of front generation at complex corners. With respect to marching distances, the distance settings at concave and/or convex corners are locally adjusted to smooth the front shape at first; a further adjustment is then conducted for front nodes in the neighbourhood of gaps between opposite viscous boundaries. These efforts, plus other special treatments such as multi-normal generation and fast detection of local/global intersection, as a whole enable the setup of a hybrid mesher that could generate qualitied viscous grids for geometries with industry-level complexities.

scholarly journals Effect of the turning characteristics of underfloor wheel lathes on the evolution of wheel polygonisation

2018 ◽  
Vol 233 (5) ◽  
pp. 479-488 ◽  
Author(s):  
Dabin Cui ◽  
Boyang An ◽  
Paul Allen ◽  
Ruichen Wang ◽  
Ping Wang ◽  
...  
Keyword(s):  
Fourth Order ◽  
High Speed ◽  
Higher Order ◽  
Ride Quality ◽  
Sustained Use ◽  
High Speed Trains ◽  
Cut Quality ◽  
Multiple Unit ◽  
Component Failures

During both running and wheel cut operations, wheels of railway vehicles and the friction rollers that support and drive the wheelset on a typical wheel cut lathe are subject to wear and hence are likely to develop out-of-round characteristics after sustained use. The resulting out-of-round wheels can significantly affect the ride quality and can potentially increase the incidence of fatigue-related component failures due to the resulting higher intensity loading cycles. Furthermore, the corresponding out-of-round characteristics of the lathe's friction rollers will continue to degrade the subsequent cut quality of wheels. For the analysis of the out-of-round characteristics caused by an underfloor wheel lathe used for the high-speed trains in China, a mathematical model based on a typical electric multiple unit (EMU) vehicle's wheelsets and their interactions with the wheel lathe friction rollers was established. Factors influencing the cut quality of the wheels, including the number of cuts, eccentricity forms of the friction rollers and the longitudinal spacing of the two rollers, have been analysed. The results show that two cuts can effectively remove the higher order polygon on the wheel surface. The eccentricity and phase angle of the friction rollers have no influence on the cut quality of higher order polygons, whereas they are the primary cause for the fourth-order polygons. The severity of the fourth-order polygon depends on the level and the phase of the eccentricity of the friction rollers. The space of the two rollers can also significantly affect the cut quality. Obtaining the theoretical and practical value for the maintenance of polygonised wheels using the underfloor lathe is the main outcome of this study.

FOURTH-ORDER COMPACT SCHEME FOR OPTION PRICING UNDER THE MERTON’S AND KOU’S JUMP-DIFFUSION MODELS

2018 ◽  
Vol 21 (04) ◽  
pp. 1850027 ◽  
Author(s):  
KULDIP SINGH PATEL ◽  
MANI MEHRA
Keyword(s):  
Fourth Order ◽  
Initial Conditions ◽  
Linear Equations ◽  
Jump Diffusion ◽  
Diffusion Models ◽  
Compact Scheme ◽  
Discrete Problem ◽  
Option Prices ◽  
Fully Discrete ◽  
Fourth Order Compact Scheme

In this paper, a compact scheme with three time levels is proposed to solve the partial integro-differential equation that governs the option prices in jump-diffusion models. In the proposed compact scheme, the second derivative approximation of the unknowns is approximated using the value of these unknowns and their first derivative approximations, thereby allowing us to obtain a tridiagonal system of linear equations for a fully discrete problem. Moreover, the consistency and stability of the proposed compact scheme are proved. Owing to the low regularity of typical initial conditions, a smoothing operator is employed to ensure the fourth-order convergence rate. Numerical illustrations concerning the pricing of European options under the Merton’s and Kou’s jump-diffusion models are presented to validate the theoretical results.

Application of the Finite Element Method (FEM) through GFAS Software to the study of a tunnel

2021 ◽  
Vol 4 (2) ◽  
pp. 001
Author(s):  
Maurizio Ponte ◽  
◽  
Filippo Catanzariti ◽  
Gloria Campilongo
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Computational Simulation ◽  
Theoretical Method ◽  
The Finite Element Method ◽  
Tunnel Excavation ◽  
Analysis System ◽  
Quality Of Products ◽  
Element Method

Computational simulation is widely used in companies to perform analysis and improve the quality of products and projects. Most of these analyses are carried out using software that uses the Finite Element Method, which allows to obtain answers to numerous engineering problems. In this study, two examples of application to the study of tunnels of the Finite Element Method using the Geostru Software "GFAS - Geotechnical F.E.M. Analysis System" are proposed. The case of a tunnel excavated inside a granite rock massif was analyzed, first determining the state of stresses in the cavity contour through a theoretical method and comparing these results with those obtained in the software. Then, by means of finite element modeling, the settlements induced by the excavation were determined. Finally, the problem of tunnel excavation in a viscoplastic rock mass is presented and the authors propose a comparison of the analytical and numerical method.

Method of numerical estimating aerial images indicators quality for mapping purposes

2021 ◽  
Vol 968 (2) ◽  
pp. 29-37
Author(s):  
I.A. Anikeeva
Keyword(s):  
Random Noise ◽  
Experimental Studies ◽  
Aerial Images ◽  
Practical Application ◽  
Correct Color ◽  
Numerical Assessment ◽  
Airborne Imaging ◽  
Imaging Sensors ◽  
Color Rendering

The task of assessing the quality of aerial imagery, obtained for mapping, in terms of vision properties, is very ambiguous due to the lack of objective criteria and evaluation methods. A system of indicators for aerial images quality and methods of their numerical assessment is presented. The fine aerial image’s quality is characterized by a set of its structural and gradation properties. The structural properties of the image are determined by the actual spatial resolution and photographic sharpness. Gradation properties of an image are characterized by the correct color rendering, the level of random noise and information completeness indicators – haze, radiometric resolution and the percentage of information loss in illumination and shadows.Methods of evaluating these indicators are formulated, and their recommended and acceptable numerical values are determined analytically. To clarify and correct the obtained analytical recommended and acceptable numerical values of the image quality indicators of their practical application possibility and further experimental studies are necessary with materials, obtained through various airborne imaging sensors for mapping.

STUDY OF PERIODIC PROCESSES TAKING INTO ACCOUNT THE UNCERTAINTY STATE FACTOR OF THE ANALYZED PARAMETER

2021 ◽  
Vol 1 (7) ◽  
pp. 5-15
Author(s):  
V.L. Lazarev ◽  
Keyword(s):  
Adaptive Control ◽  
Control System ◽  
Practical Implementation ◽  
Periodic Processes ◽  
Numerical Assessment ◽  
State Factor

The paper describes the approach and methodology for the numerical assessment of the quality of periodic processes. With regard to their particular case the processes of selfoscillations, on the basis of the proposed approach, the problem of optimization of the control system is formulated and possible ways of solving it are shown. The practical implementation of the approach is possible when synthesizing a control system, as well as in the variant of automatic adaptive control during its operation. The proposed solutions are based on the use of methods of the theory of entropy potentials. The implementation of the proposed solutions will improve the quality of monitoring of periodic processes and the efficiency of regulation systems in selfoscillation modes.

Higher‐order moveout spectra

Geophysics ◽  
1979 ◽  
Vol 44 (7) ◽  
pp. 1193-1207 ◽  
Author(s):  
Bruce T. May ◽  
Donald K. Straley
Keyword(s):  
Fourth Order ◽  
Seismic Reflection ◽  
Order Term ◽  
Higher Order ◽  
Second Order ◽  
Equation Modeling ◽  
Fourth Order Term ◽  
Higher Order Terms ◽  
Velocity Spectra

Higher‐order terms in the generalized seismic reflection moveout equation are usually neglected, resulting in the familiar second‐order, or hyperbolic, moveout equation. Modeling studies show that the higher‐order terms are often significant, and their neglect produces sizable traveltime residuals after correction for moveout in such cases as kinked‐ray models. Taner and Koehler (1969) introduced velocity spectra for estimating stacking velocity defined on the basis of second‐order moveout. Through the use of orthogonal polynomials, an iterative procedure is defined that permits computation of fourth‐order moveout spectra while simultaneously upgrading the previously computed, second‐order spectra. Emphasis is placed on the fourth‐order term, but the procedure is general and can be expanded to higher orders. When used with synthetic and field recorded common‐midpoint (CMP) trace data, this technique produces significant improvements in moveout determination affecting three areas: (1) resolution and interpretability of moveout spectra, (2) quality of CMP stacked sections, and (3) computation of velocity and depth for inverse modeling.

Design Optimisation of Casing Grooves Using the Zipper Layer Meshing Method

2011 ◽  
Author(s):  
Greg Carnie ◽  
Yibin Wang ◽  
Ning Qin ◽  
Shahrokh Shahpar
Keyword(s):  
Response Surface ◽  
Computational Simulation ◽  
Surface Model ◽  
Stall Margin ◽  
Layer Method ◽  
Gap Ratio ◽  
Structured Meshes ◽  
Leave One Out ◽  
Solution Behaviour

In an earlier paper by the authors [1], a buffer layer method for linking two non-matching structured meshes was introduced for computational simulation of multi-component geometries, each requiring high quality structured meshes. Based on the work, a new algorithm, named the zipper layer method [2], has been developed to link multi-block meshes for gas turbine applications. Numerical results for a turbomachinery rotor flow case are included to demonstrate the solution behaviour across the zipper layer. In the present paper, we will report our work on the optimisation of the casing groove geometries in relation to stall margin and efficiency of a transonic rotor using this new meshing methodology. Six grooves are parameterised by their independent depths and a width to gap ratio. An advanced response surface method based on Sobol Design of Experiment (DoE) and Krigging Response Surface Model (RSM) are used for the optimisation. A leave-one-out cross-validation (LOOCV) method is used to calculate the quality of the response surface metric. The final optimized groove configuration was obtained through an optimisation cycle using the Rolls-Royce SOPHY (SOFT-PADRAM-HYDRA) software [3], which not only improves the Stall Margin (SM) of the rotor but also maintains its peak efficiency. The optimized grooves on the casing side show large variations in their depth from upstream to downstream of the rotor.

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