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The Instability Marsh Phenomenon and Marginal Stability Boundary Distortion of Density Wave Oscillation in Parallel Channels

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SSRN 2024年

作者： Sun, Ducheng Ma, Zaiyong Lu, Q. Liu, C.W. Pan, L.M. School of Energy and Power Engineering Shandong University No. 17923 Jingshi Road Jinan250061 China Key Laboratory of Low-grade Energy Utilization Technologies and Systems Ministry of Education Chongqing400044 China Department of Nuclear Engineering and Technology Chongqing University Chongqing400044 China Science and Technology on Reactor System Design Technology Laboratory Chengdu610041 China

Density wave oscillation (DWO) in parallel channels is an important problem that has been widely studied. The marginal stability boundary (MSB) is often found to be "L " shaped on the N pch -N sub plane, but some very different shapes were also reported. In this paper, the instability marsh region which could occur in the traditional instable region but having both instability and stability sections was presented and discussed, which is found to be an explanation of the distortion of MSB. The analysis of the instability marsh region showed that the evolution of instability marsh should be due to the stability change when operation condition changes, which can be estimated with the analysis of the two-phase and single phase pressure drop variation, as well as Ma’s stability criterion for different heat flux profiles. Variation of instability marsh with different heat flux profile, inlet and outlet resistance coefficient, mass flow and pressure were obtained and analyzed, and the effects of these parameters on instability marsh variation were found to be well interpreted with stability change. The calculation and analysis of instability marsh showed a clear evolution figure of the distortion of MSB under different conditions, and related research could be helpful in better understanding the flow instability in parallel channels. © 2024, The Authors. All rights reserved.

关键词： Stability criteria

Modal Analysis of Lead-Bismuth Eutectic Flow in a Single Wire-Wrap Rod Channel

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SSRN 2022年

作者： Zhao, Xielin Cheng, Qian Yu, Xiaofei Huang, Qian Zhang, Ke Feng, Zhipeng Zhou, Jinxiong State Key Laboratory for Strength and Vibration of Mechanical Structures School of Aerospace Xi'an Jiaotong University Xi'An710049 China Key Laboratory of Science and Technology on Reactor System Design Technology Nuclear Power Institute of China Chengdu610200 China

The thermal-hydraulics as well as flow-induced vibration of wire-wrapped rod bundles calls for accurate and efficient liquid metal flow simulation and prediction, yet it remains a challenge due to the complex geometries and high Reynolds number flow in wire-wrapped rod channel. Previous efforts towards this goal exclusively adopts full-order modeling (FOM), which is prohibitively computation-intensive. This work reports the first reference on modal analysis of the turbulent lead-bismuth eutectic (LBE) flow in a single wire-wrapped rod channel by a data-driven dynamic mode decomposition (DMD) method. The spatio-temporal data of fluid velocities and pressure were modelled and collected by using the Reynolds-averaged NavierStokes equations (RANS) approach with stress-omega RSM turbulence model. Model analysis was performed over the snapshot matrices and DMD modes and corresponding eigenvalues were calculated. The DMD modes and eigenvalues were then used to construct a reducedorder modeling (ROM) system for fast fluid field reconstruction and short-term forecasting. The correctness and feasibility of the method was demonstrated and compared with groundtruth CFD simulation results. Our method offers a fast and reliable approach for ROM of turbulent flow in wire-wrapped rod fuel assemblies. We publicize all the data and codes via https://***/XJTU-Zhou-group/Wire-wrapped-fuel-pin-CFD-DMD. © 2022, The Authors. All rights reserved.

关键词： Dynamic mode decomposition

Study on the Load Following Control of SMR with Flexible Load 5th

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Study on the Load Following Control of SMR with Flexible Loa...

5th International Symposium on Software Reliability, Industrial Safety, Cyber Security and Physical Protection of Nuclear Power Plant, ISNPP 2020

作者： Liu, Ming-Ming Sun, Ao-Di Qiu, Lei-Lei Zhang, Ru Wei, Xin-Yu Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610041 China Key Laboratory of Advanced Nuclear Energy and Technology and Shaanxi Engineering Research Center of Advanced Nuclear Energy Xi’an Jiaotong University Xi’an710049 China

ISBN: (纸本)9789811634550

The load following requirement will be increased greatly while the Small Modular reactor (SMR) is used for isolated island operation mode. In order to improve the load following ability of the system, the flexible load (FL) is presented in this study to follow the electricity load during load follow. The definition of FL is a type of power consuming system that can change the needed power discretionary. For example, the hydrogen manufacture plant, the desalination facility, the district heating system, and other industrial process heat supply system are all FLs. In order to analyze the dynamic characters of the system, pressurized water reactor (PWR) type SMR (comprised with reactor core and once-through steam generator), balance of plant (BOP), and FL are modeled first. Based on these dynamic models, a SMR-FL dynamic simulation program is built in MATLAB/Simulink environment. According to different system characteristics, two types of FL are considered, and the related load allocation control systems are designed. A typical electricity load is used to verify the designed control systems for the two types of FL. The simulation results show that the designed control systems can achieve load following by adjusting the power consuming of FL and maintaining a constant or moderate changing output of SMR. Obviously, this character can make the SMR-FL system more flexible and efficiency. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Control systems

An Adaptive Bionic Sensor: Enhancing Ankle Joint Tracking with High Sensitivity and Superior Cushioning Performance

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SSRN 2024年

作者： Jin, Jianqiao Zhang, Chen Zhao, Jianyuan Yu, Minghan Lei, Ming Jin, Chun Yin, Rui Zhao, Weiwei Sauvage Laboratory for Smart Materials The School of Integrated Circuit Harbin Institute of Technology Shenzhen518055 China Shenzhen Key Laboratory of Flexible Printed Electronics Technology Harbin Institute of Technology Shenzhen518055 China State Key Laboratory of Advanced Welding & Joining Harbin Institute of Technology Harbin150001 China Human-Computer Interaction Design Lab School of System Design and Intelligent Manufacturing Southern University of Science and Technology Shenzhen518055 China

Flexible sensors are renowned for their rapid responsiveness, high flexibility, and outstanding mechanical properties, making them ideal for applications in wearable devices, sports and health monitoring, and human-machine interfaces. To enhance the sensing performance of these flexible sensors, researchers have drawn inspiration from nature, creating various bionic microstructures. However, these structures often manifest in the macroscopic form of thin films, which do little to improve impact resistance and joint protection. In response, this work achieves a highly sensitive and impact-resistant pressure sensor by integrating bionic principles at both micro and macro levels. Specifically, at the micro level, a muscle-like hydrogel system consisting of MXene nanosheets incorporated into the double network of polyvinyl alcohol and sodium alginate matrix is selected. At the macro level, the bionic prototypes of mimosa leaves and durian spikes with good energy absorption structure, together with octopus’ sucker with good adsorption capacity are selected, and the synergistic construction of the three structures is realized through 3D printing methods. The obtained sensor has an appropriate response range, sensitivity and stability. More importantly, the displacement deformation of the hydrogel can be reduced by 91.22%, while its adhesion strength can be increased by 57.5% compared to the unstructured hydrogel. As a proof-of-concept, the proposed bionic flexible sensor can be used to monitor the motion status of the human ankle joint in real-time, thereby assisting users in making real-time judgments on gait health. © 2024, The Authors. All rights reserved.

关键词： Sodium alginate

Characterization of High-Performance Nanostructured Wick for Heat Pipes

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SSRN 2023年

作者： Sun, Qishi Han, Ruiyu Guo, Kailun Wang, Chenglong Zhang, Jing He, Xiaoqiang Qiu, Suizheng Su, Guanghui Tian, Wenxi Department of Nuclear Science and Technology State Key Lab. of Multiphase Flow in Power Engineering Shaanxi Key Lab. of Advanced Nuclear Energy and Technology Xi’an Jiaotong University Xi’an710049 China Key Lab. of Nuclear Reactor System Design Technology China Nuclear Power Research and Design Institute Chengdu610213 China

To investigate the best performance wick forms to support the design and fabrication of high-performance heat pipes, in this paper, two kinds of nanostructured wick were prepared by the oxidation-reduction method. The effect of surface nanostructure on the wick performance was investigated by comparing the surface characteristics, capillary properties, permeability, and evaporation properties. The result shows that the nanostructured wick presented excellent super hydrophilic properties. A liquid-lift visualization experimental method for measuring the capillary performance factor M was proposed, and it was verified to be correct by the separation effect of the capillary pumping experiment under a vacuum environment. With the increasing oxidized degree, the densification of nanoparticles on the wick surface increased the capillary performance factor M from 8.68 μm to 13.81 μm, with a maximum enhancement of 59.1%. The effective capillary radius decreased from 4.70×10-5 m to 4.01×10-5 m, with a maximum reduction of 14.9%. The permeability increased from 4.33×10-10 m2 to 5.83×10-10 m2, with a maximum enhancement of 34.7%. The increase in porosity made the effective capillary radius dominate the competition for permeability, and the capillary performance factor decreased by 17.1%. The thermal resistance of the wick decreased with the enhancement of the capillary performance factor, which fell from 2.03×10-3 m2·K/W to 1.26×10-3 m2·K/W. The current study provides a reference for the future design and preparation of high-performance heat pipe wicks. © 2023, The Authors. All rights reserved.

关键词： Heat resistance

Natural antibacterial membranes prepared using Schisandra chinensis extracts and polyvinyl alcohol in an environment-friendly manner

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Chemosphere 2024年 346卷 140524页

作者： Jia, Wenting Jiang, Shanxue Wang, Fang Li, Jing Wang, Zeru Yao, Zhiliang School of Ecology and Environment Beijing Technology and Business University Beijing100048 China State Environmental Protection Key Laboratory of Food Chain Pollution Control Beijing Technology and Business University Beijing100048 China School of System Design and Intelligent Manufacturing Southern University of Science and Technology Shenzhen518055 China

Foodborne pathogens can cause food spoilage and lead to food safety issues. In recent years, food packaging has received a lot of attention. Traditional packaging membranes are non-biodegradable and remain in the environment for a long time. In this study, natural antimicrobial substances were extracted from Schisandra chinensis by a green extraction process using distilled water as the solvent, and the effects of different treatment on the antimicrobial activity of the extract were compared. At the same time, four types of Schisandra chinensis antimicrobial membranes were prepared using polyvinyl alcohol (PVA) as the substrate. The whole extraction and membrane preparation process did not involve organic solvents, making the process green and environment friendly. Material characterization included inverted biological microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), tensile strength test, pore size measurement, water uptake test, etc. Among them, no extract particles were observed with the naked eye on the surfaces of MⅡ and MⅣ. MⅡ has a uniformly transparent, nearly colorless morphology and is the most tensile. MⅣ surface is flat and smooth, the microstructure is dense and uniform. At the same time, the four types of membranes were tested against common pathogenic bacteria for 12 h, and the OD600 trend revealed the excellent antimicrobial activity of the membranes against S. aureus, MRSA, E. coli, and L. monocytogenes. The membranes could also be reused at least once. This study provides a new idea for preparing natural plant-based antimicrobial membranes. © 2023 Elsevier Ltd

关键词： Food safety

Joint Beamforming and Offloading design for Integrated Sensing, Communication and Computation system

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arXiv

arXiv 2024年

作者： Liu, Peng Fei, Zesong Wang, Xinyi Zhou, Yiqing Zhang, Yan Liu, Fan The School of Information and Electronics Beijing Institute of Technology Beijing100081 China The State Key Laboratory of Processors The Beijing Key Laboratory of Mobile Computing and Pervasive Device Institute of Computing Technology Chinese Academy of Sciences Beijing100190 China The School of System Design and Intelligent Manufacturing Southern University of Science and Technology Shenzhen518055 China

Mobile edge computing (MEC) is powerful to alleviate the heavy computing tasks in integrated sensing and communication (ISAC) systems. In this paper, we investigate joint beamforming and offloading design in a three-tier integrated sensing, communication and computation (ISCC) framework comprising one cloud server, multiple mobile edge servers, and multiple terminals. While executing sensing tasks, the user terminals can optionally offload sensing data to either MEC server or cloud servers. To minimize the execution latency, we jointly optimize the transmit beamforming matrices and offloading decision variables under the constraint of sensing performance. An alternating optimization algorithm based on multidimensional fractional programming is proposed to tackle the non-convex problem. Simulation results demonstrates the superiority of the proposed mechanism in terms of convergence and task execution latency reduction, compared with the state-of-the-art two-tier ISCC framework. Copyright © 2024, The Authors. All rights reserved.

关键词： Beamforming

Uncovering a Sintering Mechanism of Nanoparticulate Sic by a Molecular Dynamics Simulation

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SSRN 2024年

作者： Li, Jia Liu, Wentao Peng, Jing Liu, Jiajun Liu, Bin Fang, Qihong Key Laboratory of Fabrication Technology of Reactor Irradiation Special Target Baotou014035 China State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body College of Mechanical and Vehicle Engineering Hunan University Changsha410082 China State Key Laboratory of Powder Metallurgy Central South University Changsha410083 China China North Nuclear Fuel Co. Ltd. Baotou014035 China

Sintering is a valuable processing technique utilized to create bulk materials from powder compacts. In recent years, sintering has garnered significant attention in the research community due to its versatility and applicability in various fields, including additive manufacturing. Herein, we investigate the sintering kinetics and mechanism of SiC particulates using molecular dynamics simulation. The surface morphology evolution, microstructure evolution, radial distribution function, mean square displacement, atomic displacement distribution, structural transformation, and diffusion coefficient are analyzed in detail. The free surfaces surrounding the neck region undergo a process of evolution and reconstruction to eventually reach an equilibrium dihedral angle. The neck rapidly grows and aligns with the surface of the particles, causing the SiC material to transform from its original spherical form into a pebble-like shape. The concentration of shear stress results in a change in the local lattice structure from face-centered cubic to an amorphous phase. With increasing sintering time, the dominant diffusion mechanism gradually shifts from surface diffusion to volume diffusion and interface diffusion. This leads to a rise in the intensity of atomic migration, the consumption of interface energy, and the degree of particle fusion. Ultimately, this results in the formation of sintered SiC particles that are spherical in shape, possess lower surface energy, and have more stable structures. Additionally, the high mobility of melted SiC atoms causes the gradual dissolution of SiC particles into larger particles from the surface towards the interior. This process creates high-altitude concentration structures that facilitate atomic migration. These results shed light on an atomic sintering mechanism in nanoparticulate SiC for applications in the preparation of nanostructured materials, and additive manufacturing. © 2024, The Authors. All rights reserved.

关键词： Shear stress

Convergence Analysis and Latency Minimization for Retransmission-Based Semi-Federated Learning

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Convergence Analysis and Latency Minimization for Retransmis...

IEEE Conference on Global Communications (GLOBECOM)

作者： Jingheng Zheng Wanli Ni Hui Tian Wenchao Jiang Tony Q. S. Quek State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications Beijing China Department of Electronic Engineering Tsinghua University Beijing China Information System Technology and Design Pillar Singapore University of Technology and Design Singapore

In this paper, we propose a semi-federated learning (SemiFL) framework to ameliorate the performance of conventional federated learning. The base station and devices are coordinated to collaboratively train a shared model. However, due to the rapidly fluctuating channels and irrationally assigned local learning workloads, SemiFL encounters excessive latency. To overcome the challenges, we propose a retransmission-based over-the-air computation mechanism to facilitate model aggregation and data mixing over quasi-static channels. The closed-form probability of successful aggregation is derived, while the communication latency is modeled based on the Pascal distribution. Further, we establish an optimality gap to characterize the convergence performance of SemiFL, wherein the minimum number of iterations for attaining a specific local target accuracy is identified. Next, a joint resource allocation and local target accuracy assignment problem is formulated to minimize the latency of each round, subject to the decay rate, central processing unit (CPU) frequency, and transmit power. To address this non-convex problem, we develop an algorithm using the closed-form solutions for the normalizing factors and CPU frequencies. Simulation results on two real-world datasets confirm the superiority of SemiFL over benchmarks in terms of latency and learning performance.

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