scholarly journals Reduced order model of a two-phase loop thermosyphon by modal identification method

2018 ◽  
Vol 123 ◽  
pp. 637-654 ◽  
Author(s):  
Serge Bodjona ◽  
Manuel Girault ◽  
Etienne Videcoq ◽  
Yves Bertin
Keyword(s):  
Reduced Order Model ◽  
Modal Identification ◽  
Order Model ◽  
Two Phase ◽  
Reduced Order ◽  
Identification Method ◽  
Phase Loop

scholarly journals Identification and influence factors analysis of blade crack mistuning in hard-coated blisk based on modified component mode mistuning reduced-order model

2020 ◽  
pp. 146134842097138
Author(s):  
Kunpeng Xu ◽  
Xianfei Yan ◽  
Dongxu Du ◽  
Wei Sun
Keyword(s):  
Crack Length ◽  
Influence Factors ◽  
Reduced Order Model ◽  
Order Model ◽  
Reduced Order ◽  
Crack Location ◽  
Vibration Localization ◽  
Identification Method ◽  
Bending Modes ◽  
Blade Crack

Blade crack will cause severe mistuning of hard-coated blisks, which will lead to vibration localization. To identify crack mistuning and analyze influence factors, in this study, a mistuning identification method of blade cracks in hard-coated blisks is presented based on modified component mode mistuning reduced-order model, in which the hard-coated blisk with blade crack is decomposed into a substructure of tuned hard-coated blisk and a substructure of coated blade with cracks. Crack mistuning of each coated blade can be obtained by a single identification calculation. After verifying the rationality of this identification method, the influence factors of blade crack mistuning are analyzed. The influence factors include the crack location on the coated blade (cracks occurring only in coating or only in blade substrate or both in blade substrate and coating), crack length, crack position in the radial direction of the blisk, and modal data type of coated blisk used for mistuning identification calculation. The research results show that, with the increase of crack length, the mistuning of crack occurring only in the coating does not increase continuously but decreases firstly and then increases. For the first bending modes, the closer the blade crack is to the blade root, the larger the mistuning is. For the second bending modes, the blade crack located at the position of maximum modal displacement will produce large mistuning. For hard-coated blisk with blade crack, these crack mistuning variation rules are of great significance to the dynamic analysis and the determination of the crack location.

scholarly journals Reduced-Order Model of Rotor Cage in Multiphase Induction Machines: Application on the Prediction of Torque Pulsations

2020 ◽  
Vol 25 (1) ◽  
pp. 11 ◽  
Author(s):  
Abdelhak Mekahlia ◽  
Eric Semail ◽  
Franck Scuiller ◽  
Hussein Zahr
Keyword(s):  
Induction Machine ◽  
Induction Machines ◽  
Reduced Order Model ◽  
Order Model ◽  
Two Phase ◽  
Reduced Order ◽  
Three Phase ◽  
Torque Pulsations ◽  
Sinusoidal Current ◽  
Rotor Cage

For three-phase induction machines supplied by sinusoidal current, it is usual to model the n-bar squirrel-cage by an equivalent two-phase circuit. For a multiphase induction machine which can be supplied with different harmonics of current, the reduced-order model of the rotor must be more carefully chosen in order to predict the pulsations of torque. The proposed analysis allows to avoid a wrong design with non-sinusoidal magnetomotive forces. An analytical approach is proposed and confirmed by Finite-Element modelling at first for a three-phase induction machine and secondly for a five-phase induction machine.

Advanced Natural Circulation Reduced Order Model With Inclined Channel for Low Pressure Conditions

2018 ◽  
Author(s):  
René Manthey ◽  
Alexander Knospe ◽  
Carsten Lange ◽  
Christoph Schuster ◽  
Antonio Hurtado
Keyword(s):  
Reference Model ◽  
Nonlinear Dynamical Systems ◽  
Natural Circulation ◽  
Dynamical Behavior ◽  
Low Pressure ◽  
Reduced Order Model ◽  
Circulation System ◽  
Order Model ◽  
Two Phase ◽  
Reduced Order

Natural circulation with two-phase flow is a nonlinear dynamical systems, which can show a very complex and strange behavior under specific conditions. The application of stability analysis requires a large computational effort and is cumbersome in case of prediction the dynamical behavior by system codes alone. Therefore, model order reduction techniques are used to compensate this disadvantage by coupling with a bifurcation code such as MatCont. A reduced order model is derived by employing the POD-method to analyze the stability landscape of a low pressure natural circulation system representing passive safety systems such as the containment cooling condenser. The required full order model contains a classical natural circulation loop with a heated section and a riser. The two-phase region is modeled by a drift-flux mixture model. The reliability of the FOM is investigated by comparison with a reference model by the validated system code ATHLET.

Advanced Natural Circulation Reduced-Order Model With Inclined Channel for Low Pressure Conditions

2020 ◽  
Vol 6 (2) ◽  
Author(s):  
René Manthey ◽  
Alexander Knospe ◽  
Carsten Lange ◽  
Christoph Schuster ◽  
Antonio Hurtado
Keyword(s):  
Reference Model ◽  
Nonlinear Dynamical Systems ◽  
Natural Circulation ◽  
Dynamical Behavior ◽  
Low Pressure ◽  
Reduced Order Model ◽  
Circulation System ◽  
Order Model ◽  
Two Phase ◽  
Reduced Order

Abstract Natural circulation with two-phase flow is a nonlinear dynamical systems, which can show a very complex and strange behavior under specific conditions. The application of stability analysis requires a large computational effort and is cumbersome in case of prediction the dynamical behavior by system codes alone. Therefore, model-order reduction techniques are used to compensate this disadvantage by coupling with a bifurcation code such as MatCont. A reduced-order model is derived by employing the proper orthogonal decomposition (POD) to analyze the stability landscape of a low pressure natural circulation system representing passive safety systems such as the containment cooling condenser. The required full-order model contains a classical natural circulation loop with a heated section and a riser. The two-phase region is modeled by a drift–flux mixture model. The reliability of the full-order model is investigated by comparison with a reference model by the validated system code ATHLET.

Nodalized Reduced Ordered Model for Stability Analysis of Supercritical Fluid in Heated Channel

2018 ◽  
Author(s):  
Munendra Pal Singh ◽  
Md. Emadur Rahman ◽  
Suneet Singh
Keyword(s):  
Stability Analysis ◽  
Stability Boundary ◽  
External Pressure ◽  
Reduced Order Model ◽  
Nonlinear Stability Analysis ◽  
Weighted Residual Method ◽  
Order Model ◽  
Two Phase ◽  
Reduced Order ◽  
Heated Channel

In this paper, a novel nodalized reduced order model (NROM) has been developed to analyze the linear stability in a heated channel using supercritical water (SCW) as a coolant. The presented reduced order model is developed based on the two-phase flow system approach. The model is much simplified, which reduced the requirement of computational efforts and resources. In the heated channel, the SCW’s density shows a dramatic downfall near the pseudo-critical temperature, based on which it has been divided into n number of nodes. The one-dimension partial differentiation conservation equations of energy, mass and momentum are used and have been linearized by a small perturbation applied on its steady-state solution. These PDEs are converted into the corresponding time-dependent, nonlinear ordinary differential equations (ODEs) by using weighted residual method applied under some appropriate assumptions and approximations. These sets of ODEs (n+1 equations) are then solved analytically by using a state space approach to capture the stability boundary (SB) in terms of trans-pseudo-critical phase change number (Ntpc), pseudo-subcooling number (Nspc) by applying a constant external pressure drop (ΔPtpc) condition across the channel. The NROM results are found to be in good agreement with the methodology and have been verified by numerical simulation. To extend this as a nonlinear stability analysis, the different types of the Hopf Bifurcation regime are also reported.

scholarly journals Numerical investigation of the POD reduced-order model for fast predictions of two-phase flows in porous media

2019 ◽  
Vol 29 (11) ◽  
pp. 4167-4204 ◽  
Author(s):  
Jingfa Li ◽  
Tao Zhang ◽  
Shuyu Sun ◽  
Bo Yu
Keyword(s):  
Projection Methods ◽  
Reduced Order Model ◽  
Governing Equations ◽  
Order Model ◽  
Numerical Accuracy ◽  
Two Phase ◽  
Content Type ◽  
Reduced Order ◽  
Computational Speed ◽  
Speed Up

Purpose This paper aims to present an efficient IMPES algorithm based on a global model order reduction method, proper orthogonal decomposition (POD), to achieve the fast solution and prediction of two-phase flows in porous media. Design/methodology/approach The key point of the proposed algorithm is to establish an accurate POD reduced-order model (ROM) for two-phase porous flows. To this end, two projection methods including projecting the original governing equations (Method I) and projecting the discrete form of original governing equations (Method II) are respectively applied to construct the POD-ROM, and their distinctions are compared and analyzed in detail. It is found the POD-ROM established by Method I is inapplicable to multiphase porous flows due to its failed introduction of fluid saturation and permeability that locate on the edge of grid cell, which would lead to unphysical results. Findings By using Method II, an efficient IMPES algorithm that can substantially speed up the simulation of two-phase porous flows is developed based on the POD-ROM. The computational efficiency and numerical accuracy of the proposed algorithm are validated through three numerical examples, and simulation results illustrate that the proposed algorithm displays satisfactory computational speed-up (one to two orders of magnitude) without sacrificing numerical accuracy obviously when comparing to the standard IMPES algorithm that without any acceleration technique. In addition, the determination of POD modes number, the relative errors of wetting phase pressure and saturation, and the influence of POD modes number on the overall performances of the proposed algorithm, are investigated. Originality/value 1. Two projection methods are applied to establish the POD-ROM for two-phase porous flows and their distinctions are analyzed. The reason why POD-ROM is difficult to be applied to multiphase porous flows is clarified firstly in this study. 2. A highly efficient IMPES algorithm based on the POD-ROM is proposed to accelerate the simulation of two-phase porous flows. 3. Satisfactory computational speed-up (one to two orders of magnitude) and prediction accuracy of the proposed algorithm are observed under different conditions.

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