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Physics-informed deep Koopman operator for Lagrangian dynamic systems

Science China(Information Sciences) 2024年第9期67卷 146-163页

作者： Xuefeng WANG Yang CAO Shaofeng CHEN yu KANG Department of Automation University of Science and Technology of China State Key Laboratory of Fire Science University of Science and Technology of China Institute of Advanced Technology University of Science and Technology of China

Accurate mechanical system models are crucial for safe and stable control. Unlike linear systems,Lagrangian systems are highly nonlinear and difficult to optimize because of their unknown system *** research thus used deep neural networks to generate linear models of original systems by mapping nonlinear dynamic systems into a linear space with a Koopman observable function encoder. The controller then relies on the Koopman linear model. However, without physical information constraints, ensuring control consistency between the original nonlinear system and the Koopman system is tough, as the learning process of the Koopman observation function is unsupervised. This paper thus proposes a two-stage learning algorithm that uses structural subnetworks to build a physics-informed network topology to simultaneously learn the Koopman observable functions and the system energy representation. In the Koopman matrix learning session, a quadratic-constrained optimization problem is solved to ensure that the Koopman representation satisfies the energy difference matching hard constraint. The proposed energy-preserving deep Lagrangian Koopman(EPDLK) framework effectively represents the dynamics of the Lagrangian system while ensuring control consistency. The effectiveness of EPDLK is compared with those of various Koopman observable function construction methods in multistep prediction and trajectory tracking tasks. EPDLK achieves better control consistency by guaranteeing energy difference matching, which facilitates the application of the control law generated on the Koopman system directly to the original nonlinear Lagrangian system.

关键词： Koopman operator Lagrangian physics-informed nonlinear model predictive control (MPC)

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Large eddy simulation of turbulent premixed and stratified combustion using flame surface density model coupled with tabulation method

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Applied Mathematics and Mechanics(English Edition) 2018年第12期39卷 1719-1736页

作者： Zhou yu Hongda ZHANG Taohong YE Minming ZHU Department of Thermal Science and Energy Engineering University of Science and Technology of China Shenyang Engine Research Institute Aero Engine (Group) Corporation of China

Large eddy simulations(LESs) are performed to investigate the Cambridge premixed and stratified flames, SwB1 and SwB5, respectively. The flame surface density(FSD) model incorporated with two different wrinkling factor models, i.e., the Muppala and Charlette2 wrinkling factor models, is used to describe combustion/turbulence interaction, and the flamelet generated manifolds(FGM) method is employed to determine major scalars. This coupled sub-grid scale(SGS) combustion model is named as the FSD-FGM model. The FGM method can provide the detailed species in the flame which cannot be obtained from the origin FSD model. The LES results show that the FSD-FGM model has the ability of describing flame propagation, especially for stratified flames. The Charlette2 wrinkling factor model performs better than the Muppala wrinkling factor model in predicting the flame surface area change by the *** combustion characteristics are analyzed in detail by the flame index and probability distributions of the equivalence ratio and the orientation angle, which confirms that for the investigated stratified flame, the dominant combustion modes in the upstream and downstream regions are the premixed mode and the back-supported mode, respectively.

关键词： large eddy simulation(LES) flame surface density(FSD) model tabulation premixed combustion stratified combustion

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NUMERICAL MODELLING OF PROGRESSIVE FAILURE IN PARTICULATE COMPOSITES LIKE SANDSTONE

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中国有色金属学会会刊：英文版 1999年第1期9卷 167-173页

作者： Xing, Jibo yu, Liangqun Zhang, Ruifeng Wang, Yongjia Yantai Univ Yantai China

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｎｕｍｅｒｉｃａｌｍｏｄｅｌｉｎｇｏｆｐｒｏｇｒｅｓｉｖｅｆａｉｌｕｒｅｉｎｐａｒｔｉｃｕｌａｔｅｃｏｍｐｏｓｉｔｅｓｉｓｉｍｐｏｒｔａｎｔｉｎｕｎｄｅｒｓｔａｎｄｉｎｇｔｈｅｍｅ... 详细信息

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｎｕｍｅｒｉｃａｌｍｏｄｅｌｉｎｇｏｆｐｒｏｇｒｅｓｉｖｅｆａｉｌｕｒｅｉｎｐａｒｔｉｃｕｌａｔｅｃｏｍｐｏｓｉｔｅｓｉｓｉｍｐｏｒｔａｎｔｉｎｕｎｄｅｒｓｔａｎｄｉｎｇｔｈｅｍｅｃｈａｎｉｓｍｓｆｏｒｔｈｅｇｅｎ...

关键词： beam particle model particulate composites progressive failure meso structure

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Orthogonalized lattice enumeration for solving SVP

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Science China(Information Sciences) 2018年第3期61卷 191-205页

作者： Zhongxiang ZHENG Xiaoyun WANG Guangwu XU Yang yu Department of Computer Science and Technology Tsinghua University Institute for Advanced Study Tsinghua University Key Laboratory of Cryptologic Technology and Information Security Ministry of EducationShandong Universtiy

The orthogonalized integer representation was independently proposed by Ding et al. using genetic algorithm and Fukase et al. using sampling technique to solve shortest vector problem(SVP). Their results are promising. In this paper, we consider sparse orthogonalized integer representations for shortest vectors and propose a new enumeration method, called orthognalized enumeration, by integrating such a representation. Furthermore, we present a mixed BKZ method, called MBKZ, by alternately applying orthognalized enumeration and other existing enumeration methods. Compared to the existing ones, our methods have greater efficiency and achieve exponential speedups both in theory and in practice for solving SVP. Implementations of our algorithms have been tested to be effective in solving challenging lattice problems.

关键词： lattice-based SVP sparse representations enumeration BKZ

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Measuring spatio-temporal autocorrelation in time series data of collective human mobility

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Geo-Spatial Information Science 2019年第3期22卷 166-173页

作者： Yong Gao Jing Cheng Haohan Meng yu Liu Institute of Remote Sensing and Geographic Information System School of Earth and Space SciencesPeking UniversityBeijingChina

Massive spatio-temporal big data about human mobility have become increasingly *** underlying dynamic patterns from these data is essential for understanding people’s behavior and urban ***-temporal autocorrelation analysis is an exploratory approach to recognizing data distribution in space and *** most widely used spatial autocorrelation measurements,such as Moran’s I and local indicators of spatial association(LISA),only apply to static data,so are powerless to spatio-temporal big data about human ***,we proposed a new method by extending Moran’s I to measure the spatial autocorrelation of time series *** the method was applied to taxi ride data in Beijing,China to reveal the spatial pattern of collective human *** result shows that there is strong positive spatio-temporal autocorrelation within the 5th Ring Road,weak negative spatio-temporal autocorrelation nearby the Sixth Ring Road,and almost no spatiotemporal autocorrelation between the *** spatial patterns of taxi travel were also *** method is useful for discovering underlying patterns from spatio-temporal big data to understand human mobility.

关键词： Taxi rides human mobility spatio-temporal autocorrelation Moran index

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A Soft Robotic Fish with Variable-stiffness Decoupled Mechanisms

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Journal of Bionic Engineering 2018年第4期15卷 599-609页

作者： Kangkang Li Hongzhou Jiang Siyu Wang Jianmin yu School of Mechatronics Engineering Harbin Institute of Technology Harbin 150001 China

A Body and/or Caudal Fin （BCF） fish modulate its body stiffness by mechanisms consisting of antagonistic muscles. The mecha- nisms can be considered as Redundant Planar Rotational Parallel Mechanisms （RPRPM） with antagonistic flexible elements. For a typical RPRPM, its stiffness consists of the adjustable stiffness resulting from internal forces and the inherent stiffness caused by inherent com- pliances of flexible elements. In order to decouple the adjustable stiffness from the inherent stiffness and expand the range of stiffness variation, a variable-stiffness decoupled mechanism based on the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator （MACCEPA） is presented and used to construct a soft robotic fish with large stiffness variation. According to the analysis of the evolution from RPRPM to MACCEPA, it can be found that MACCEPA is just a special type of RPRPM with only an adjustable stiffness. In addition, MACCEPA existed before RPRPM mechanism. The prototype of the soft robotic fish with variable- stiffness decoupled mechanisms is built to explore the relationships between the body stiffness and the swimming performance. It is validated experimentally that the stiffness variation multiple of the robotic fish is raised, the swimming performance of the robotic fish is improved when the stiffness is modulated to match the driving frequency.

关键词： bionic soft robotic fish variable stiffness decoupled MACCEPA pretension

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A high-performance and endurable SSD cache for parity-based RAID

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Frontiers of Computer Science 2019年第1期13卷 16-34页

作者： Chu LI Dan FENG yu HUA Fang WANG Wuhan National Lab for Optoelectronics Key Laboratory of Information Storage System(School of Computer Science and TechnologyHuazhong University of Science and Technology) Ministry of Education of ChinaWuhan 430074China

Solid-state drives (SSDs)have been widely used as caching tier for disk-based RAID systems to speed up dataintensive ***,traditional cache schemes fail to effectively boost the parity-based RAID storage sys- tems (e.g.,RAID-5/6),which have poor random write performance due to the small-write ***'s worse,intensive cache writes can wear out the SSD quickly,which causes performance degradation and cost *** this article,we present the design and implementation of KDD, an efficient SSD-based caching system which Keeps Data and Deltas in *** write requests hit in the cache, KDD dispatches the data to the RAID storage without updating the parity blocks to mitigate the small write penalty, and compactly stores the compressed deltas in SSD to reduce the cache write traffic while guaranteeing reliability in case of disk *** addition,KDD organizes the metadata partition on SSD as a circular log to make the cache persistent with low *** evaluate the performance of KDD via both simulations and prototype *** results show that KDD effectively reduces the small write penalty while extending the lifetime of the SSD-based cache by up to 6.85 times.

关键词： solid-state drive (SSD) parity-based RAID small write problem write endurance

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Design of Compliant Straight-line Mechanisms Using Flexural Joints

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Chinese Journal of Mechanical Engineering 2014年第1期27卷 146-153页

作者： PEI Xu yu Jingjun ZONG Guanghua BI Shusheng School of Mechanical Engineering and Automation Beihang University

Straight-line compliant mechanisms are important building blocks to design a linear-motion stage, which is very useful in precision applications. However, only a few configurations of straight-line compliant mechanisms are applicable. To construct more kinds of them, an approach to design large-displacement straight-line flexural mechanisms with rotational flexural joints is proposed, which is based on a viewpoint that the straight-line motion is regarded as a compromise of rigid and compliant parasitic motion of a rotational flexural joint. An analytical design method based on the Taylor series expansion is proposed to quickly obtain an approximate solution. To illustrate and verify the proposed method, two kinds of flexural joints, cross-axis hinge and leaf-type isosceles-trapezoidal flexural（LITF） pivot are used to reconstruct straight-line flexural mechanisms. Their performances are obtained by analytic and FEA method respectively. The comparisons of the results show the accuracy of the approach. Both examples show that the proposed approach can convert a large-deflection flexural joint into approximate straight-line mechanism with a high linearity that is higher than 5 000 within 5 man displacement. This can lead to a new way to design, analyze or optimize straight-line flexure mechanisms.

关键词： flexure mechanism straight-line mechanism flexural joint center-shift

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Key processes of carbon cycle and sink enhancement paths in natural wetland ecosystems in China

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Science China Earth Sciences 2024年第8期67卷 2444-2459页

作者： Jinshuai LI Tianxiang HAO Meng YANG Guirui yu Key Laboratory of Ecosystem Network Observation and Modeling Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijing 100101China College of Resources and Environment University of Chinese Academy of SciencesBeijing 100049China

Wetland ecosystems have become one of the long-term solutions for mitigating global climate change due to their strong carbon sequestration ***,the key carbon cycle processes in wetland ecosystems still lack a systematic *** the context of wetland protection and restoration,there is still a lack of consensus on the technical pathways to realize carbon sink multiplication in wetland *** this paper,the key processes of carbon cycle,such as photosynthetic carbon uptake,microbial carbon decomposition and carbon deposition and burial,are sorted out and summarized in four major wetland types,namely,swamp and peat wetlands,river and riparian wetlands,lake and lakeshore wetlands,and estuarine and coastal *** on the key processes of carbon cycle,three technological pathways for carbon sink multiplication are proposed,including,vegetation carbon sequestration and sink enhancement technology,soil carbon emission reduction technology and carbon deposition and burial *** key technologies under each pathway are further *** the carbon sink effects of the carbon sink technologies in different wetland types are qualitatively ***,wetland protection and restoration methods in corresponding regions are given in the light of the regional characteristics of wetlands in *** will provide a scientific basis for the strategy of doubling the carbon sinks of China′s wetland ecosystems.

关键词： Wetlands Carbon cycle Carbon sinks Technology pathways Conservation and restoration

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The impact of industrial transformation on green economic efficiency:New evidence based on energy use

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Petroleum Science 2024年第5期21卷 3644-3655页

作者： Jin-Xing Jiang Jing-Jing Wang yu Cheng Institute for Carbon Neutrality Shandong Normal UniversityJinan250014ShandongChina School of Public Administration Shandong Normal UniversityJinan250014ShandongChina College of Geography and Environment Shandong Normal UniversityJinan250238ShandongChina

Developing a green economy is key to achieving the 2030 Sustainable Development Goals. This paper uses the SBM-GML index, which includes non-desired outputs, to measure the trend of regional green economic efficiency changes and analyze the impact mechanism and realization path of industrial transformation on green economic efficiency. The research results show that advanced industrial structure has a positive influence on green economic efficiency nationwide, while energy utilization structure and energy utilization efficiency have positive partial intermediary effects in the influence path;industrial structure rationalization is also significantly positively related to green economic efficiency nationwide, and the mediating effect of energy utilization is positive. The impact of industrial transformation on green economic efficiency has regional heterogeneity, and the mediating effect of energy use also differs. Among them, the impact effect in the eastern region is basically consistent with the national sample, but is negative in the central and western regions. This paper proposes countermeasures in terms of adjusting the industrial structure, improving energy efficiency, and perfecting industrial and energy policies, which can provide theoretical and practical references for promoting the transformation and upgrading of regional industrial structure, optimizing energy utilization, and advancing the efficiency of the national and regional green economy.

关键词： Industrial transformation Energy use Green economic efficiency The SBM-GML model Mediating effect model

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