scholarly journals Algebraic method for efficient adaption of structured grids to fluctuating geometries

2005 ◽  
Vol 219 (4) ◽  
pp. 303-314 ◽  
Author(s):  
D E Bohn ◽  
N Moritz
Keyword(s):  
Algebraic Method ◽  
Numerical Code ◽  
Aerodynamic Load ◽  
Deformation Model ◽  
Test Cases ◽  
Structured Grid ◽  
Grid Adaption ◽  
Simple Deformation ◽  
The Stability ◽  
Rotational Load

An efficient method for adaption of a structured grid to fluctuating turbine blade geometry is presented based on an algebraic algorithm. The objective of the application of this method is to analyse the aerodynamic, thermal and rotational load of rotating and cooled blades with a conjugate approach. The grid adaption method is validated with two test cases by using a simple deformation model considering the blade as a torsion spring. This model ensures a strong coupling between aerodynamic load and deformation of the blades. Thus, the stability of the numerical code can be analysed. The calculations show that convergence for the blade deformation is reached very soon. Even for great blade deformation the algebraic grid adaption method generates no negative cell volumes although this cannot be guaranteed by an algebraic algorithm.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

1994 ◽  
Vol 144 ◽  
pp. 503-505
Author(s):  
R. Erdélyi ◽  
M. Goossens ◽  
S. Poedts
Keyword(s):  
Resonant Absorption ◽  
Numerical Code ◽  
Mhd Waves ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Element Discretization ◽  
Flux Tubes ◽  
Magnetohydrodynamic Waves ◽  
Viscosity Coefficients ◽  
Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

Adhesion of Partially and Fully Collapsed Nanotubes

2018 ◽  
Vol 86 (1) ◽  
Author(s):  
Ming Li ◽  
Hao Li ◽  
Fengwei Li ◽  
Zhan Kang
Keyword(s):  
Finite Deformation ◽  
Adhesion Energy ◽  
Van Der Waals Interactions ◽  
Critical Conditions ◽  
Nano Composites ◽  
Deformation Model ◽  
Analysis And Design ◽  
Structural Rigidity ◽  
Multiwall Nanotubes ◽  
The Stability

The competition between the structural rigidity and the van der Waals interactions may lead to collapsing of aligned nanotubes, and the resulting changes of both configurations and properties promise the applications of nanotubes in nano-composites and nano-electronics. In this paper, a finite-deformation model is applied to study the adhesion of parallel multiwall nanotubes with both partial and full collapsing, in which the noncontact adhesion energy is analytically determined. The analytical solutions of both configurations and energies of collapsed nanotubes are consistent with the molecular dynamics (MD) results, demonstrating the effectiveness of the finite-deformation model. To study the critical conditions of generating the partially and fully collapsed multiwall nanotubes, our analytical model gives the predictions for both the geometry- and energy-related critical diameters, which are helpful for the stability analysis and design of nanotube-based nano-devices.

Instability of Heated Panels in Supersonic Air Flow

2008 ◽  
Vol 33-37 ◽  
pp. 1101-1108
Author(s):  
Zhi Chun Yang ◽  
Wei Xia
Keyword(s):  
Stability Analysis ◽  
Stability Boundary ◽  
Boundary Curve ◽  
Static Stability ◽  
Static Deformation ◽  
Limit Cycle Oscillation ◽  
Aerodynamic Load ◽  
Aeroelastic System ◽  
Aerodynamic Pressure ◽  
The Stability

An investigation on the stability of heated panels in supersonic airflow is performed. The nonlinear aeroelastic model for a two-dimensional panel is established using Galerkin method and the thermal effect on the panel stiffness is also considered. The quasi-steady piston theory is employed to calculate the aerodynamic load on the panel. The static and dynamic stabilities for flat panels are studied using Lyapunov indirect method and the stability boundary curve is obtained. The static deformation of a post-buckled panel is then calculated and the local stability of the post-buckling equilibrium is analyzed. The limit cycle oscillation of the post-buckled panel is simulated in time domain. The results show that a two-mode model is suitable for panel static stability analysis and static deformation calculation; but more than four modes are required for dynamic stability analysis. The effects of temperature elevation and dimensionless parameters related to panel length/thickness ratio, material density and Mach number on the stability of heated panel are studied. It is found that panel flutter may occur at relatively low aerodynamic pressure when several stable equilibria exist for the aeroelastic system of heated panel.

Predictive estimates of subsidence of the earth’s surface during the development of the Yamburgskoye oil and gas condensate field

2021 ◽  
pp. 9-22
Author(s):  
Yu. V. Vasiliev ◽  
M. S. Mimeev ◽  
D. A. Misyurev
Keyword(s):  
Oil And Gas ◽  
Active Faults ◽  
Physical And Mechanical Properties ◽  
Deformation Model ◽  
Reservoir Pressure ◽  
Gas Reservoirs ◽  
Field Development ◽  
Geodynamic Processes ◽  
Deformation Processes ◽  
The Stability

The production of hydrocarbons is associated with a change in the physical and mechanical properties of oil and gas reservoirs under the influence of rock and reservoir pressures. Deformation of the reservoir due to a drop in reservoir pressure leads to the formation of various natural and man-made geodynamic and geomechanical phenomena, one of which is the formation of a subsidence trough of the earth's surface, which leads to a violation of the stability of field technological objects.In order to ensure geodynamic safety, a set of works is used, which includes analysis of geological and field indicators and geological and tectonic models of the field, interpretation of aerospace photographs, identification of active faults, construction of a predictive model of subsidence of the earth's surface of the field with identification of zones of geodynamic risk.This work was carried out to assess the predicted parameters of rock displacement processes during field development; even insignificant disturbances in the operation of technological equipment caused by deformation processes can cause significant damage.Prediction of rock displacements is possible only on the basis of a reservoir deformation model that adequately reflects the geomechanical and geodynamic processes occurring in the subsoil. The article presents a model of reservoir deformation with a drop in reservoir pressure, describes its numerical implementation, and performs calculations of schemes for typical development conditions.

scholarly journals Galloping Stability and Aerodynamic Characteristic of Iced Transmission Line Based on 3-DOF

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Xiaohui Liu ◽  
Ming Zou ◽  
Chuan Wu ◽  
Bo Yan ◽  
Mengqi Cai
Keyword(s):  
Wind Speed ◽  
Transmission Line ◽  
Angle Of Attack ◽  
Wind Tunnel Test ◽  
Simulation Method ◽  
Theoretical Formula ◽  
Aerodynamic Load ◽  
Line System ◽  
Critical Wind Speed ◽  
The Stability

A new calculation method of critical wind speed based on three degrees of freedom (3-DOF) is proposed for galloping problem of iced transmission line. Based on the quasistatic theory, the aerodynamic load of iced transmission line is obtained, which considers the influence of transverse and torsional motion on the relative wind angle of attack. Finally, the equivalent galloping model of 3-DOF iced transmission line is established. At the initial angle of attack, the aerodynamic load is expanded by Taylor, and the unsymmetrical linear aerodynamic coefficient matrix is obtained. The Routh–Hurwitz criterion is used to judge the stability of iced transmission line system, and then the critical wind speed is calculated. The in-plane and out-plane frequencies corresponding to the first-order mode of the transmission line are solved by the analytical method and numerical simulation method. The results obtained by the two methods are compared and verified. The influence of dimensionless transmission line parameter λ on the in-plane and out-of-plane frequencies is discussed. The aerodynamic coefficients of the iced transmission line are measured by wind tunnel test and the aerodynamic characteristics are analyzed. According to the theoretical formula, the critical wind speed is calculated by MATLAB. The critical wind speed determined in this paper is compared with the critical wind speed determined by Den Hartog and Nigol theory. The influences of torsional vibration frequency, ice thickness, and ice shape on critical wind speed are analyzed. The research results of this paper have important theoretical significance for the stability judgment of iced transmission lines.

Numerical Simulation on Failure Mechanism of Rock Slope Using RFPA

2011 ◽  
Vol 50-51 ◽  
pp. 568-572 ◽  
Author(s):  
Nu Wen Xu ◽  
Chu Nan Tang ◽  
Chun Sha ◽  
Ru Lin Zhang
Keyword(s):  
Rock Slope ◽  
Slip Surface ◽  
Process Analysis ◽  
Failure Process ◽  
Numerical Code ◽  
Natural State ◽  
Left Bank ◽  
Good Tool ◽  
Deep Rock ◽  
The Stability

This research applied a numerical code, RFPA2D (Realistic Failure Process Analysis) to evaluate the stability and investigate the failure mode of the high rock slope during excavations based on Strength Reduction Method (SRM). The corresponding shapes and positions of the potential slip surfaces are rationally simulated in different stages, and the related safety coefficients are obtained, which agrees well with the allowable minimum safety factors of the slope. The numerical results show that the safety coefficient drops from 1.25 at the natural state to 1.09 after excavation, and then increases to 1.35 after slope reinforcement. Moreover, the potential slip surface of the left bank moves into deep rock mass after taking support measures, which demonstrates the reinforcement is reasonable and efficient. The study shows that cracks and faults will cause crucial influences on the slope stability, and RFPA2D is a good tool to directly display the potential slip surface of the slope, which will offer valuable guidance for bolt support.

scholarly journals Stochastic perturbations for parametrisation tendencies in a convection-permitting ensemble

2018 ◽  
Author(s):  
Clemens Wastl ◽  
Yong Wang ◽  
Aitor Atencia ◽  
Christoph Wittman
Keyword(s):  
Ensemble Forecasting ◽  
Limited Area ◽  
Test Cases ◽  
Shallow Convection ◽  
Stochastic Perturbations ◽  
Forecasting System ◽  
The Stability ◽  
Positive Effect ◽  
Total Model ◽  
Stochastic Physics

Abstract. A modification of the widely used SPPT (Stochastically Perturbed Parametrisation Tendencies) scheme is proposed and tested in a Convection-permitting – Limited Area Ensemble Forecasting system (C-LAEF) developed at ZAMG (Zentralanstalt für Meteorologie und Geodynamik). The tendencies from four physical parametrisation schemes are perturbed: radiation, shallow convection, turbulence and microphysics. Whereas in SPPT the total model tendencies are perturbed, in the present approach (pSPPT hereinafter) the partial tendencies of the physics parametrisation schemes are sequentially perturbed. Thus, in pSPPT an interaction between the uncertainties of the different physics parametrisation schemes is sustained and a more physically consistent relationship between the processes is kept. Two configurations of pSPPT are evaluated over two months (one of summer and another of winter). Both schemes increase the stability of the model and lead to statistically significant improvements in the probabilistic performance compared to the original SPPT. An evaluation of selected test cases shows that the positive effect of stochastic physics is much more pronounced on days with high convective activity. Small discrepancies in the humidity analysis can be dedicated to the use of a very simple supersaturation adjustment. This and other adjustments are discussed to provide some suggestions for future investigations.

Hyperbolic Runge–Kutta Method Using Evolutionary Algorithm

2018 ◽  
Vol 13 (10) ◽  
Author(s):  
A. Arun Govind Neelan ◽  
Manoj T. Nair
Keyword(s):  
Evolutionary Algorithm ◽  
Stability Region ◽  
Strong Stability ◽  
Higher Order ◽  
Test Cases ◽  
Runge Kutta Method ◽  
Higher Order Terms ◽  
Runge Kutta ◽  
The Stability ◽  
Classical Optimization

A family of Runge–Kutta (RK) methods designed for better stability is proposed. Authors have optimized the stability of RK method by increasing the stability region by trading some of the higher order terms in the Taylor series. For flow involving shocks, compromising a few higher order terms will not affect convergence rate that is justified with an example. Though this kind of analysis began about three decades ago, most of the papers dealt with classical optimization and ended up in relatively nonoptimal values. Here, authors have overcome that by using evolutionary algorithm (EA), the result is refined using multisection method (MSM). The schemes designed based on this procedure have better stability than the classical RK methods, strong stability RK methods (SSPRK), and low dispersive and dissipative RK methods (LDDRK) of the same number of stages. Authors have tested the schemes on a variety of test cases and found some significant improvement.

On the synthesis of a polynomial controller for enlarging the stability domain for nonlinear discrete system

2020 ◽  
Vol 42 (10) ◽  
pp. 1834-1839 ◽  
Author(s):  
Bedoui Sabrine ◽  
Belhadj Brahim Anis ◽  
Elloumi Salwa ◽  
Benhadj Braiek Naceur
Keyword(s):  
Stability Region ◽  
Algebraic Method ◽  
Discrete Systems ◽  
Stability Domain ◽  
Attraction Domain ◽  
Initial Stability ◽  
Polynomial Controller ◽  
The Stability ◽  
Nonlinear Discrete System ◽  
Nonlinear Discrete Systems

This paper aims to propose an algebraic method for estimating the stability region for nonlinear discrete systems. The main contribution is the improvement of an existing technique to enlarge the initial stability region in which the asymptotic stability is guaranteed. To deal with the maximization issue, a state feedback controller is proposed to extend the largest estimation of attraction domain of nonlinear polynomial discrete systems. The proposed approach is illustrated and validated on an isothermal stirred tank reactor.

scholarly journals Mass of dusty clumps with temperature and density structure

2019 ◽  
Vol 631 ◽  
pp. A65 ◽  
Author(s):  
R. Cesaroni
Keyword(s):  
Flux Density ◽  
Cylindrical Symmetry ◽  
Numerical Code ◽  
Effect Of Temperature ◽  
Density Gradients ◽  
Density Structure ◽  
The Stability ◽  
Spherical And Cylindrical Symmetry ◽  
Account Temperature ◽  
Approximate Expressions

We consider a dusty clump in two cases of spherical and cylindrical symmetry to investigate the effect of temperature and density gradients on the observed flux density. Conversely, we evaluate how the presence of these gradients affects the calculation of the clump mass from the observed flux. We provide approximate expressions relating flux density and mass in the optically thick and thin limits and in the Rayleigh-Jeans regime, and we discuss the reliability of these expressions by comparing them to the outcome of a numerical code. Finally, we present the application of our calculations to three examples taken from the literature, which shows how the correction introduced after taking into account temperature and density gradients may affect our conclusions on the stability of the clumps.

Sign in / Sign up

Export Citation Format

Share Document