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A dynamic-mode-decomposition-based acceleration method for unsteady adjoint equations at low Reynolds numbers

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Theoretical & Applied Mechanics Letters 2023年第5期13卷 353-356页

作者： Wengang Chen Jiaqing Kou Wenkai Yang Changzhou Institute of Technology Changzhou 213032China Institute of Aerodynamics RWTH Aachen UniversityWüllnerstraße 5a52062 AachenGermany

The computational cost of unsteady adjoint equations remains high in adjoint-based unsteady aerodynamic op-timization.In this letter,the solution of unsteady adjoint equations is accelerated by dynamic mode decomposi-tion(DMD).The pseudo-time marching of every real-time step is approximated as an infinite-dimensional linear dynamical system.Thereafter,DMD is utilized to analyze the adjoint vectors sampled from these pseudo-time marching.First-order zero frequency mode is selected to accelerate the pseudo-time marching of unsteady adjoint equations in every real-time step.Through flow past a stationary circular cylinder and an unsteady aerodynamic shape optimization example,the efficiency of solving unsteady adjoint equations is significantly improved.Re-sults show that one hundred adjoint vectors contains enough information about the pseudo-time dynamics,and the adjoint dominant mode can be precisely predicted only by five snapshots produced from the adjoint vectors,which indicates DMD analysis for pseudo-time marching of unsteady adjoint equations is efficient.

关键词： Acceleration method Unsteady adjoint dynamic mode decomposition Optimization efficiency

Practical Implementation and Operational Experience of dynamic mode decomposition in Wide-area Monitoring Systems of Italian Power System

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Journal of modern Power Systems and Clean Energy 2023年第3期11卷 793-802页

作者： Andrea Vicario Alberto Berizzi Giorgio Maria Giannuzzi Cosimo Pisani Department of Energy at Politecnico di Milano MilanItaly Terna S.p.A. RomeItaly

This study presents the assumptions and strategies for the practical implementation of the dynamic mode decomposition approach in the wide-area monitoring system of the Italian transmission system operator,Terna.The procedure setup aims to detect poorly damped interarea oscillations of power systems.dynamic mode decomposition is a data-driven technique that has gained increasing attention in different fields;the proposed implementation can both characterize the oscillatory modes and identify the most influenced areas.This study presents the results of its practical implementation and operational experience in power system monitoring.It focuses on the main characteristics and solutions identified to reliably monitor the interarea electromechanical modes of the interconnected European power system.Moreover,conditions to issue an appropriate alarm in case of critical operating conditions are described.The effectiveness of the proposed approach is validated by its application in three case studies:a critical oscillatory event and a short-circuit event that occurred in the Italian power system in the previous years,and a 15-min time interval of normal grid operation recorded in March 2021.

关键词： Power system control power system dynamics wide-area monitoring system(WAMS) dynamic mode decomposition

Application of Hankel dynamic mode decomposition for Wide Area Monitoring of Subsynchronous Resonance

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Energy Engineering 2023年第4期120卷 851-867页

作者： Lei Wang Tiecheng Li Hui Fan Xuekai Hu Lin Yang Xiaomei Yang State Grid Hebei Electric Power Research Institute Shijiazhuang050021China State Grid Hebei Electric Power Company Shijiazhuang050021China The College of Electrical Engineering Sichuan UniversityChengdu610065China

In recent years,subsynchronous resonance(SSR)has frequently occurred in DFIG-connected series-compensated systems.For the analysis and prevention,it is of great importance to achieve wide area monitoring of the incident.This paper presents a Hankel dynamic mode decomposition(DMD)method to identify SSR parameters using synchrophasor data.The basic idea is to employ the DMD technique to explore the subspace of Hankel matrices constructed by synchrophasors.It is analytically demonstrated that the subspace of these Hankel matrices is a combination of fundamental and SSR modes.Therefore,the SSR parameters can be calculated once the modal parameter is extracted.Compared with the existing method,the presented work has better dynamic performances as it requires much less data.Thus,it is more suitable for practical cases in which the SSR characteristics are timevarying.The effectiveness and superiority of the proposed method have been verified by both simulations and field data.

关键词： Hankel dynamic mode decomposition time-varying sub-synchronous oscillation synchrophasor

Stability analysis for flow past a cylinder via lattice Boltzmann method and dynamic mode decomposition

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Chinese Physics B 2015年第6期24卷 378-384页

作者：张伟王勇钱跃竑 Department of Mechanical Enignneering National University of Singapore Department of Mechanical and Aerospace Engineering University of California Shanghai Institute of Applied Math and Mechanics Shanghai University

A combination of the lattice Boltzmann method and the most recently developed dynamic mode decomposition is proposed for stability analysis. The simulations are performed on a graphical processing unit. Stability of the flow past a cylinder at supercritical state, Re = 50, is studied by the combination for both the exponential growing and the limit cycle regimes. The Ritz values, energy spectrum, and modes for both regimes are presented and compared with the Koopman eigenvalues. For harmonic-like periodic flow in the limit cycle, global analysis from the combination gives the same results as those from the Koopman analysis. For transient flow as in the exponential growth regime, the combination can provide more reasonable results. It is demonstrated that the combination of the lattice Boltzmann method and the dynamic mode decomposition is powerful and can be used for stability analysis for more complex flows.

关键词： lattice Boltzmann dynamic mode decomposition stability analysis graphical processing unit

Visualization and selection of dynamic mode decomposition components for unsteady flow

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Visual Informatics 2021年第3期5卷 15-27页

作者： T.Krake S.Reinhardt M.Hlawatsch B.Eberhardt D.Weiskopf Visualization Research Center(VISUS) Allmandring 1970569 StuttgartGermany Hochschule der Medien Nobelstraße 1070569 StuttgartGermany

dynamic mode decomposition(DMD)is a data-driven and model-free decomposition technique.It is suitable for revealing spatio-temporal features of both numerically and experimentally acquired data.Conceptually,DMD performs a low-dimensional spectral decomposition of the data into the following components:the modes,called DMD modes,encode the spatial contribution of the decomposition,whereas the DMD amplitudes specify their impact.Each associated eigenvalue,referred to as DMD eigenvalue,characterizes the frequency and growth rate of the DMD mode.In this paper,we demonstrate how the components of DMD can be utilized to obtain temporal and spatial information from time-dependent flow fields.We begin with the theoretical background of DMD and its application to unsteady flow.Next,we examine the conventional process with DMD mathematically and put it in relationship to the discrete Fourier transform.Our analysis shows that the current use of DMD components has several drawbacks.To resolve these problems we adjust the components and provide new and meaningful insights into the decomposition:we show that our improved components capture the spatio-temporal patterns of the flow better.Moreover,we remove redundancies in the decomposition and clarify the interplay between components,allowing users to understand the impact of components.These new representations,which respect the spatio-temporal character of DMD,enable two clustering methods that segment the flow into physically relevant sections and can therefore be used for the selection of DMD components.With a number of typical examples,we demonstrate that the combination of these techniques allows new insights with DMD for unsteady flow.

关键词： dynamic mode decomposition Spectral decomposition

Automatic detection and assessment of crack development in ultra-high performance concrete in the spatial and Fourier domains

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Frontiers of Structural and Civil Engineering 2024年第3期18卷 350-364页

作者： Jixing CAO Yao ZHANG Haijie HE Weibing PENG Weigang ZHAO Zhiguo YAN Hehua ZHU School of Safety Engineering and Emergency Management Shijiazhuang Tiedao UniversityShijiazhuang 050043China College of Civil Engineering and Architecture Zhejiang UniversityHangzhou 310058China College of Civil and Architectural Engineering Taizhou UniversityTaizhou 318000China College of Civil Engineering and Architecture Zhejiang University of TechnologyHangzhou 310014China Department of Geotechnical Engineering Tongji UniversityShanghai 200092China

Automatic detection and assessment of surface cracks are beneficial for understanding the mechanical performance of ultra-high performance concrete(UHPC).This study detects crack evolution using a novel dynamic mode decomposition(DMD)method.In this method,the sparse matrix‘determined’from images is used to reconstruct the foreground that contains cracks,and the global threshold method is adopted to extract the crack patterns.The application of the DMD method to the three-point bending test demonstrates the efficiency in inspecting cracks with high accuracy.Accordingly,the geometric features,including the area and its projection in two major directions,are evaluated over time.The relationship between the geometric properties of cracks and load-displacement curves of UHPC is discussed.Due to the irregular shape of cracks in the spatial domain,the cracks are then transformed into the Fourier domain to assess their development.Results indicate that crack patterns in the Fourier domain exhibit a distinct concentration around a central position.Moreover,the power spectral density of cracks exhibits an increasing trend over time.The investigation into crack evolution in both the spatial and Fourier domains contributes significantly to elucidating the mechanical behavior of UHPC.

关键词： dynamic mode decomposition ultra-high performance concrete crack detection geometric features Fourier domain

Numerical analysis of the correlation between fluid dynamic modes and hydrodynamic noise in flows around a three-dimensional circular cylinder

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Journal of Hydrodynamics 2024年第1期36卷 119-129页

作者： Jia-jia Qin Ming-xin Zou Yuan Zhuang De-cheng Wan Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Wuhan Second Ship Design and Research Institute Wuhan430205China

The flow around a circular cylinder for Re=1000 is characterized by flow separation and Karman vortex street.The typical flow features can be captured to study the correlation between fluid fields and sound fields.In this paper,the three-dimensional circular cylinder is taken as the research object,and the probes of surface fluctuating pressure and far field sound pressure are arranged every 10°.The directional diagram and the coherence of fluctuating pressure and sound pressure are analyzed.The relationship between the flow mode and hydrodynamic noise is studied by using dynamic mode decomposition(DMD).The characteristics of the dipole and quadrupole sound source term of a long span cylinder are studied.The results show that at the angles between 30°–120°and 190°–350°,the fluctuating pressure contributes more to the generation of dipole sounds.The quadrupole sound source shows three-dimensional effects,which is more obvious in a cylinder with large spanwise length.

关键词： Pressure coherence dynamic mode decomposition flow-sound correlation circular cylinder

Soft Sensors for Property‑Controlled Multi‑Stage Press Hardening of 22MnB5

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Automotive Innovation 2023年第3期6卷 352-363页

作者： Juri Martschin Malte Wrobel Joshua Grodotzki Thomas Meurer A.Erman Tekkaya Institute of Forming Technology and Lightweight Components TU Dortmund UniversityBaroper Str.30344227 DortmundGermany Institute of Mechanical Process Engineering and Mechanics Karlsruhe Institute of Technology(KIT)Hertzstr.1676187 KarlsruheGermany

In multi-stage press hardening,the product properties are determined by the thermo-mechanical history during the sequence of heat treatment and forming steps.To measure these properties and finally to control them by feedback,two soft sensors are developed in this work.The press hardening of 22MnB5 sheet material in a progressive die,where the material is first rapidly austenitized,then pre-cooled,stretch-formed,and finally die bent,serves as the framework for the development of these sensors.To provide feedback on the temporal and spatial temperature distribution,a soft sensor based on a model derived from the dynamic mode decomposition(DMD)is presented.The model is extended to a parametric DMD and combined with a Kalman filter to estimate the temperature(-distribution)as a function of all process-relevant control vari-ables.The soft sensor can estimate the temperature distribution based on local thermocouple measurements with an error of less than 10°C during the process-relevant time steps.For the online prediction of the final microstructure,an artificial neural network(ANN)-based microstructure soft sensor is developed.As part of this,a transferable framework for deriving input parameters for the ANN based on the process route in multi-stage press hardening is presented,along with a method for developing a training database using a 1-element model implemented with LS-Dyna and utilizing the material model Mat248(PHS_BMW).The developed ANN-based microstructure soft sensor can predict the final microstructure for specific regions of the formed and hardened sheet in a time span of far less than 1 s with a maximum deviation of a phase fraction of 1.8%to a reference simulation.

关键词： Press hardening Property control Soft sensor Artificial neuronal network dynamic mode decomposition

Modal Analysis of Axial Compressor Tip Rotating Instability under Varying Operating Conditions

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Journal of Thermal Science 2023年第4期32卷 1345-1356页

作者： LI Tao WU Yadong TIAN Jie OUYANG Hua School of Mechanical Engineering Shanghai Jiao Tong UniversityShanghai200240China Engineering Research Centre of Gas Turbine and Civil Aero Engine Ministry of EducationShanghai Jiao Tong UniversityShanghai200240China

The full annulus numerical research was performed on a low-speed compressor rotor to investigate the rotating instability in the tip region.The frequency spectra show the existence of rotating instability at narrow stable operating range.With the decrease of flow rate,31 cells of flow disturbance can be found in the instantaneous flow field.The distribution of vortex suggests that the circumferential propagation of the interaction between tip leakage vortex and adjacent blade brings about these cells.The dynamic mode decomposition(DMD)method and spatial discrete Fourier transform(SDFT)were applied to obtain the circumferential mode features,and the results indicate that the rotating instability is associated with the 31 cells of flow disturbance.Then the DMD method was further applied on the pressure data from a circle and an annulus domain,so as to extract different mode components with the corresponding spatial structures,frequencies and amplitudes.The results suggest that DMD modes can display the flow feature and explore the evolution of each instability source in the tip flow field.

关键词： axial compressor rotating instability flow structure circumferential mode dynamic mode decomposition