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Numerical study of the turbulent channel flow under space-dependent electromagnetic force control at different Reynolds numbers

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Applied Mathematics and Mechanics(English Edition) 2019年第4期40卷 435-448页

作者： Daiwen JIANG Hui ZHANG Baochun FAN Zijie ZHAO Jian LI Mingyue GUI Science and Technology on Transient Physics Laboratory Nanjing University of Science and Technology Department of Mathematics Imperial College London

In this paper, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with the direct numerical simulation(DNS) methods for different Reynolds numbers. A formulation is derived to express the relation between the drag and the Reynolds shear stress. With the application of optimal electromagnetic force, the in-depth relations among characteristic structures in the flow field, mean Reynolds shear stress, and the effect of drag reduction for different Reynolds numbers are discussed. The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers. The regular quasi-streamwise vortex structures, which appear in the flow field, have the same period with that of the electromagnetic *** structures suppress the random velocity fluctuations, which leads to the absolute value of mean Reynolds shear stress decreasing and the distribution of that moving away from the wall. Moreover, the wave number of optimal electromagnetic force increases,and the scale of the regular quasi-streamwise vortex structures decreases as the Reynolds number increases. Therefore, the rate of drag reduction decreases with the increase in the Reynolds number since the scale of the regular quasi-streamwise vortex structures decreases.

关键词： flow control drag reduction electromagnetic force turbulent channel flow

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Numerical simulation for high speed oblique water entry of different density projectiles 2

Numerical simulation for high speed oblique water entry of d...

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2nd Spring International Conference on Defence technology, ICDT 2020

作者： Mu, Q. Xiong, T.H. Wang, K.J. Yi, W.J. Jun, G. National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China

To explore the effects of material density on the cavitation flow field of a projectile entering water at an oblique angle at 300m/s, numerical simulations were conducted. The model was based on the finite volume method, VOF (Volume Of Fluid) multiphase model, Schnerr-Sauer cavity model, SST(Shear Stress Transfer) k-ω turbulence model and dynamic mesh method. The evolution laws of cavity shape, motion characteristics and hydrodynamic characteristics of water entry are analyzed. The research results show that the numerical calculation method can effectively simulate the change of cavity shape during the water entry of the projectile. The larger the density is, the smaller the diameter of the cavity formed after entering water is;the longer the cavity is, and the smaller the diameter of the cavity opening is;The peak value of pressure on the surface of projectile with different density is the same at the moment of entering water, but the projectile with larger density experiences a slower rate of the surface pressure decline;Moreover, the larger the density, the smaller the acceleration peak value of the projectile at the moment of entering the water, the slower the velocity decay after entering the water, and the deeper underwater at the same time. © Published under licence by IOP Publishing Ltd.

关键词： Projectiles

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D-shaped terahertz microstructured fiber biosensor based on plasmon resonance on graphene surface

D-shaped terahertz microstructured fiber biosensor based on ...

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International Conference on Optical Communications and Networks (ICOCN)

作者： Yani Zhang Jia Xue Yunxia Zhang Ting Miao Yiming Yao Qiuyang Wang Jiaqin Gong State Key Laboratory of Transient Optics and Photonics Xi’an Institute of Optics and Precision Mechanics of CAS Xi’an Shaanxi Department of Physics School of Arts & Sciences Shaanxi University of Science & Technology Xi’an Shaanxi China

This paper designs a D-shaped microstructured fiber optic biosensing model based on surface plasmon resonance of graphene, which is dedicated to the terahertz frequency band. Improving optical fiber sensing performance by adjusting graphene thickness and graphene chemical potential to increase peak spectral loss. The optimization results show that the resonance peak decreases with increasing excitation layer thickness and graphene chemical potential. Moreover, the higher the graphene chemical potential, the more the resonance spectrum is shifted towards the higher frequency band. The maximum frequency sensitivity is 1300 GHz/RIU over a refractive index sensing range of 1.1-1.5, corresponding to a quality factor of $1.0\times 10^{4}$ RIU. In conclusion, the proposed D-type microstructured optical fiber has a novel and ingenious structure with high detection accuracy. With graphene as the excitation medium, the microstructured optical fiber operating band is successfully extended to the terahertz band, opening up a broader application prospect for the microstructured optical fiber structure in the THz sensing field.

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Prediction of three-dimensional elastic behavior of filament-wound composites based on the bridging model 2

Prediction of three-dimensional elastic behavior of filament...

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2nd Spring International Conference on Defence technology, ICDT 2020

作者： Yin, D.M. Li, B.M. Ch Xiao, H. National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China

With the high specific stiffness, specific strength and designable ability, filament-wound composites have been widely applied in many industries, such as aerospace, energy and transportation, and they are also the one of more ideal choices for the lightweight structural design of weapon system. However, their complex structures, which including the cross-overs, undulations, and overlaps between different winding passages of the fiber bundles, make it difficult to obtain their macro mechanical properties. And this work will provide a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle. The representative volume element (RVE) in the meso-scale is defined on the basis of the filament winding pattern, which characterizes all the micro-architecture details of the filament wound composites, such as fiber undulation, winding angle and lamination arrangement. Referring to the principle of volume average in the analysis method of braided composites, a theoretical prediction model for the three-dimensional equivalent elastic constants of the filament wound composites is established by adopting the bridging model. Through this method, the results obtained for the previous experimental model are in good agreement with the experimental ones, which verifies the reliability of this model. In addition, the effects of some winding parameters, such as winding angle, on the equivalent elastic behavior of the filament-wound composites are analyzed. And the rules gained can provide a theoretical reference for the optimum design of filament-wound composites. The full version of this extended abstract will appear in Defence technology in 2020. © Published under licence by IOP Publishing Ltd.

关键词： Filament winding

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Incubation Temperature Effect on Bacterial Self-Healing Capabilities of Cementitious Mortar Cracks: Deep Learning Based Crack Sealing Rates Evaluations

SSRN

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SSRN 2024年

作者： Sun, Xichen Huang, Jingnan Sun, Weiwei Chen, Bingcheng Shen, Huiming Wang, Yang Feng, Jun National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China School of Safety Science and Engineering Nanjing University of Science and Technology Nanjing210094 China Institute of Structural Engineering Zhejiang University Hangzhou310058 China Xi’an Research Institute of Hi-tech Shaanxi 710024 China School of Environmental and Biological Engineering Nanjing University of Science and Technology Nanjing210094 China

Successful implementation of microbial self-healing cementitious materials requires the provision of a suitable incubation environment, which activates the bacteria to produce calcium carbonate sealing the cracks. Affecting microbial mineralization, incubation temperature determines the self-healing efficiency of microbial cement which limits its widespread application. To investigate the effect of incubation temperature on the self-healing abilities, laboratory experiments were conducted on polyvinyl alcohol (PVA) fiber reinforced cement mortar impregnated with Sporosarcina pasteurii. The mortar specimens were initially cracked by three point bending to generate 0.4 mm width cracks at the bottom and then incubated for 30 days at ambient temperatures of 20 ◦C, 25 ◦C, 30 ◦C, and 35 ◦C. The cracks were inspected regularly which were further analyzed via deep learning to evaluate the crack healing ratio and sealing rate. The cracks failed to completely repair at 20 ◦C, while cracks at 30 ◦C requires only 4 days to seal. The crack healing rate accelerated with increasing temperature from 20 ◦C to 30 ◦C, exhibiting a trend of initial increase followed by decrease across all temperatures. The bacterial-repaired mortar specimens exhibited a recovery in flexural strength, with a regained strength ratio of approximately 7.184% at 30 ◦C. Supported by Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD), the results revealed that the higher temperature actives larger particle CaCO3 with mainly vaterite and some calcite morphology. The interaction mechanism of temperature effect on bacterial self-healing capabilities was revealed by the comprehensive assessment between the microbial activity, crack width evolution and mechanical performance. This paper may shed some light on the engineering application of microbial cementitious material resilient infrastructures with desirable healing efficiency under real ambient temperatures during service. © 2024, The Authors. A

关键词： Scanning electron microscopy

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Study on shock initiation of the charge covered by metal plate with penetrated notch 2

Study on shock initiation of the charge covered by metal pla...

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2nd Spring International Conference on Defence technology, ICDT 2020

作者： Chen, X.W. Wang, J.X. Tang, K. Wang, H.F. Li, Y.B. National Key Laboratory of Transient Physics Nanjing University of Science and Technology Jiangsu Nanjing210094 China

To analyze the coupling damage effect of high-speed fragments and near-field strong shock wave on the covered charge, a theoretical model of the shock initiation of the charge covered by metal plate with defects was established. The defect of the covered plate was simplified as a penetration notch, and the evolution characteristics of the shock wave in the notch were analyzed theoretically. The critical condition of the explosive detonation was determined by combining the explosive initiation criterion and the shock wave evolution characteristics. Take TNT covered by steel plate with a penetrated notch as an example, the nonlinear finite element program was used to simulate the shock initiation process of pressed charge, and the validity of the numerical simulation was verified by experimental results. The influence of the intensity of the shock wave, the thickness of the covered metal plate as well as the geometrical characteristics of the penetrated notch on the shock initiation of the pressed charge were analyzed by combining the theoretical model and numerical simulation results. The relationship of the notch size of the covered plate and the detonation distance was obtained by fitting, and the parameters n and K of the critical initiation criterion were obtained by least squares method. The theoretical calculation results and the numerical simulation results are agree with each other well and show that, the covered metal plate is beneficial for the protection of the charge. The existence of notch will weaken the protective performance of the covered plate, and the shape and size of the notch are also important factors that will affect the critical detonation distance of the charge. For the pressed TNT with and without 45# steel covered plate with the thickness 3 millimeters, the critical detonation distance of non-contact explosion was 13 millimeters and 81 millimeters, respectively. For the covered plate with a cylindrical notch, the critical detonation distan

关键词： Detonation

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Comparative study on longitudinal momentum characteristics of L-type and I-type breech in railgun 2

Comparative study on longitudinal momentum characteristics o...

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2nd Spring International Conference on Defence technology, ICDT 2020

作者： Xu, Y.T. Li, B.M. National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing Jiangsu210094 China

The position and magnitude of the longitudinal force during launch are very important to the design of electromagnetic railgun. This problem has become a hot topic of research for a long time. Previous experiments showed that most of the recoil force of the electromagnetic railgun locates at the breech. In order to study the stress distribution and momentum characteristics of the breech during launch. Based on Maxwell's stress tensor, the momentum conservation equations for electromagnetic railgun were derived. Depending on whether the direction of the source current is perpendicular to the current direction in the rails, the breech is simplified and summarized into I-type and L-type structures. Then, the 3-d models of the two breeches were established and the launch process was simulated by finite element method. Some results such as the current density, magnetic field intensity and electromagnetic stress of the current injector plates and coaxial power connector under both models were obtained. The simulation results show that the longitudinal force on the breech is concentrated on the current injector plates. The longitudinal force on the power connector of L-type breech is much bigger than that of the I-type breech, up to nine times. Besides, different structures of the breech will not affect the launch performance of the railgun. © Published under licence by IOP Publishing Ltd.

关键词： Plates (structural components)

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Research on Electromagnetic Launch Control System Based on ARM and FPGA Architecture

Research on Electromagnetic Launch Control System Based on A...

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Computational Modeling, Simulation and Data Analysis (CMSDA), International Conference on

作者： Xiaodong Zhao Wantong Li Haiyuan Li National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing China Unmanned System Research Institute Northwestern Polytechnical University Xi'an China

Aiming at the high reliability design problem of electromagnetic launch control system, this paper proposes a control system design method based on ARM and FPGA architecture. The overall structure of the control system is divided into three parts: box control, subsystem control and module control. Among them, the subsystem controller is composed of a control motherboard and a pulse power management board. The control motherboard is designed based on the architecture of ARM and FPGA. ARM runs logic related processing, and FPGA processes timing control, synchronous feedback and other functions that require high time accuracy. Based on the host computer software, the current curves of specific discharge energy and discharge time sequence are analyzed. The verification results show that the discharge current waveform can be controlled by controlling the discharge sequence of Pulse Forming Network (PFN) through the control system. Under the condition of long equal interval discharge sequence, the peak current decreases and the wave pattern changes gently. The electromagnetic launch control system realized in this paper has high scalability, can monitor more than twenty pulse power units, and can achieve highly reliable control of the launch system based on single shot and continuous shot operation mode.

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Response of underwater cylindrical shell subjected to supercavitating projectile trans-medium penetration: Experiment and simulation

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Defence technology 2025年

作者： Ma, Yiming Tang, Kui Kong, Lingquan Gong, Hanxin Gu, Minhui Cao, Chao Wang, Jinxiang National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China

To investigate the dynamic response of the cylindrical shell targets to supercavitating projectile trans-medium penetration and the penetration mechanism, experiments and numerical simulations were conducted. Simulations examined the effects of entry water velocity and impact angle on penetration behavior. The results indicate that, upon water entry, the supercavitating projectile transfers its kinetic energy to the surrounding water medium, causing a sudden rise in local pressure. This creates an approximately hemispherical pressure field in the water medium ahead of the nose of the projectile, where the pressure distribution and magnitude are positively correlated with the velocity of the projectile. As the pressure field approaches the cylindrical shell, the area around the impact point experiences pre-stress and deformation due to the hydrodynamic pressure, which is known as the hydrodynamic ram effect. The deformation of the cylindrical shell caused by the hydrodynamic ram effect increases with increasing velocity of the projectile and exhibits a non-linear relationship with the impact angle, first decreasing and then increasing as the impact angle rises. Additionally, the hydrodynamic ram effect leads to greater local deformation and higher peak stresses in the cylindrical shell, which reduces the penetration drag force faced by the projectile in water compared to air, indicating a lower ballistic limit for underwater targets. During the penetration process, as the impact angle increases, the supercavitating projectile undergoes repetitive bending deformation and even brittle fracture, while the failure mode of the target is characterized by ductile hole expansion. Furthermore, the critical penetration velocity required to perforate the cylindrical shell target increases with increasing impact angle. © 2025 China Ordnance Society

关键词： Brittle fracture

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Soliton microcombs in optical microresonators with perfect spectral envelopes

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Opto-Electronic Advances 2025年第3期8卷 60-68页

作者： Mulong Liu Ziqi Wei Haotong Zhu Hongwei Wang Xiao Yu Xilin Han Wei Zhao Guangwei Hu Peng Xie School of Science Northwest A&F UniversityYangling 712100China School of physics Peking UniversityBeijing 100871China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore 308232Singapore Qiguang Research and Innovation Center Aerospace Laser Technology and System DepartmentShanghai Institute of Optics and Fine MechanicsChinese Academy of ScienceShanghai 201800China State Key Laboratory of Transient Optics and Photonics Xi’an Institute of Optics and Precision Mechanics(XIOPM)Chinese Academy of Sciences(CAS)Xi’an 710119China

We theoretically and experimentally investigate thermal dynamics involved soliton microcomb generation in silicon oxynitride microresonators. Importantly, auxiliary laser heat balance scheme with flexible thermal manipulation is introduced to circumvent thermal instability and the intra-cavity temperature can be tuned from 60 ℃ to 41.5 ℃ via the commercial thermoelectric controller. As a result, various perfect soliton states with ultra-smooth spectral envelopes are observed on a well-designed and fabricated microresonator with homogeneous sidewall and thickness where spatial modes interaction and distortion are eliminated. The pre-reported spectral abrupt jumps due to mode hybridization are completely avoided and solitons tail oscillation vanishes simultaneously. This reported ideal coherent comb source without residual temporal and spectral noise will facilitate practical applications such as spectroscopy, ranging and astrocomb calibration.

关键词： perfect solitons thermal dynamics auxiliary laser heat balance Raman effect

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