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Numerical Study of Dam-Break Induced Tsunami-Like Bore with A Hump of Different Slopes

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China Ocean Engineering 2017年第6期31卷 683-692页

作者： CHENG Du zhao xi-zeng ZHANG Da-ke CHEN Yong Ocean College Zhejiang University Zhoushan 316021 China

Numerical simulation of dam-break wave, as an imitation of tsunami hydraulic bore, with a hump of different slopes is performed in this paper using an in-house code, named a Constrained Interpolation Profile （CIP）-based model. The model is built on a Cartesian grid system with the Navier Stokes equations using a CIP method for the flow solver, and employs an immersed boundary method （IBM） for the treatment of solid body boundary. A more accurate interface capturing scheme, the Tangent of hyperbola for interface capturing/Slope weighting （THINC/SW） scheme, is adopted as the interface capturing method. Then, the CIP-based model is applied to simulate the dam break flow problem in a bumpy channel. Considerable attention is paid to the spilling type reflected bore, the following spilling type wave breaking, free surface profiles and water level variations over time. Computations are compared with available experimental data and other numerical results quantitatively and qualitatively. Further investigation is conducted to analyze the influence of variable slopes on the flow features of the tsunami-like bore.

关键词： dam break tsunami-like bore CIP method VOF method immersed boundary method

Numerical Study of the Impact of Climate Change on Irregular Wave Run-up Over Reef-Fringed Coasts

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China Ocean Engineering 2020年第2期34卷 162-171页

作者： LIU Wei-jie SHAO Ke-qi NING Yue zhao xi-zeng Ocean College Zhejiang UniversityZhoushan 316021China Key Laboratory of Port Waterway&Sedimentation EngineeringMinistry of CommunicationsNanjing 210029China

Wave hydrodynamics over fringing reefs is largely controlled by the reef surface roughness and hydrodynamic forcing.It is believed that climate change will result in a net increase in the water depth over the reef flat,a degrading of the surface roughness of coral reefs and changes in extreme incident wave heights.For an accurate assessment of how climate change affects the safety of reef-fringed coasts,a numerical study of the impact of climate change on irregular wave run-up over reef-fringed coasts was carried out based on a Boussinesq wave model,FUNWAVE-TVD.Validated with experimental data,the present model shows reasonable prediction of irregular wave evolution and run-up height over fringing reefs.Numerical experiments were then implemented based on the anticipated effects of climate change and carried out to investigate the effects of sea level rise,degrading of the reef surface roughness and increase of extreme incident wave height on the irregular wave run-up height over the backreef beach respectively.Variations of run-up components(i.e.,spectral characteristics of run-up and mean water level)were examined specifically and discussed to better understand the influencing mechanism of each climate change-related effect on the run-up.

关键词： fringing reefs irregular waves climate change infragravity run-up height

Experimental and Numerical Study on the Hydrodynamic Characteristics of Solitary Waves Passing Over A Submerged Breakwater

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China Ocean Engineering 2019年第3期33卷 253-267页

作者： zhao xi-zeng CHENG Du ZHANG Yi-fei LI Meng-yu Ocean College Zhejiang University Zhoushan 316021 China Troops Zhoushan 316021 China Troops Ningbo 315171 China

In this study, solitary waves passing over a submerged breakwater are investigated both experimentally and numerically. A total of 9 experimental conditions are carried out, including different incident wave heights and water depths. Numerical simulations are performed using a high-order finite-difference model solving Navier–Stokes (N–S) equations. The predicted water wave elevation, velocity and pressure show good agreement with experimental data, verifying the accuracy and capacity of the numerical model. Furthermore, parametric studies are conducted by numerical modelling to examine the effects of the geometrical features of submerged dike on hydrodynamic characteristics around the breakwater.

关键词： submerged breakwater solitary wave CIP method Navier-Stokes model VOF method

Numerical Simulation of Water Entry of Wedges in Waves Using A CIPBased Model

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China Ocean Engineering 2021年第1期35卷 48-60页

作者： HU Zi-jun zhao xi-zeng LI Meng-yu zhao xin YAO Wen-wei SHAO Jie Zhejiang Institute of Hydraulic and Estuary Hangzhou 310020China Ocean College Zhejiang UniversityZhoushan 316021China

In this study,the water entry of wedges in regular waves is numerically investigated by a two-dimensional in-house numerical code.The numerical model based on the viscous Navier−Stokes(N−S)equations employs a high-order different method—the constrained interpolation profile(CIP)method to discretize the convection term.A Volume of Fluid(VOF)-type method,the tangent of hyperbola for interface capturing/slope weighting(THINC/SW)is employed to capture the free surface/interface,and an immersed boundary method is adopted to treat the motion of wedges.The momentum source function derived from the Boussinesq equation is applied as an internal wavemaker to generate regular waves.The accuracy of the numerical model is validated in comparison with experimental results in the literature.The results of water entry in waves are provided in terms of the impact force of wedge,velocity and pressure distributions of fluid.Considerable attention is paid to the effects of wave parameters and the position of wedge impacting the water surface.It is found that the existence of waves significantly influences the velocity and pressure field of fluid and impact force on the wedges.

关键词： Water entry water wave wedge internal wave maker CIP method VOF method

Experimental Study on Flow past A Rotationally Oscillating Cylinder

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China Ocean Engineering 2017年第4期31卷 495-503页

作者： GAO Yang-yang YIN Chang-shan YANG Kang zhao xi-zeng TAN Soon Keat Ocean College Zhejiang University Nanyang Environment and Water Research Institute and School of Civil and Environmental Engineering Nanyang Technological University

A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number （Re=300） placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise- and- counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry （PIV） technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and time-averaged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed. The effects of four rotation angle and frequency ratios Fr （Fr=fn/fv, the ratio of the forcing frequency fn to the natural vortex shedding frequency fv） on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤Fr≤1.0.

关键词： rotational oscillation cylinder PIV frequency ratio wake flow pattern time-averaged flow field

A NUMERICAL METHOD FOR NONLINEAR WATER WAVES

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Journal of Hydrodynamics 2009年第3期21卷 401-407页

作者： zhao xi-zeng SUN zhao-chen LIANG Shu-xiu HU Chang-hong State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China RIAM Kyushu University 6-1 Kasuga-koen Kasuga Fukuoka 816-8580 Japan

This article presents a numerical method for modeling nonlinear water waves based on the High Order Spectral （HOS） method proposed by Dommermuth and Yue and West et al., involving Taylor expansion of the Dirichlet problem and the Fast Fourier Transform （FFT） algorithm. The validation and efficiency of the numerical scheme is illustrated by a number of case studies on wave and wave train configuration including the evolution of fifth-order Stokes waves, wave dispersive focusing and the instability of Stokes wave with finite slope. The results agree well with those obtained by other studies.

关键词： high order spectral method wave focusing wave instability fifth-order Stokes wave Fast Fourier Transform （FFT）

Numerical simulation of violent impact flow using a CIP-based model

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Numerical simulation of violent impact flow using a CIP-base...

Homological Transfer between Additive Categories and Higher Differential Additive Categories

第十六届中国海洋（岸）工程学术讨论会

作者： zhao xi-zeng Ocean College Zhejiang University

A three dimensional(3D) Constrained Interpolation Profile(ClP)-based model is developed,capable of capturing correctly complex three-dimensional free surface flows and,even more important,also capable of predicting an accurate impact pressure force.The flow is represented by one set of governing equations,which are solved numerically on a non-uniform,staggered Cartesian grid by a high-order finite difference method.The governing equations are divided into an advection step and two non-advection steps by making use of a time splitting method.The CIP method is adopted to calculate the hyperbolic equation for velocity at the advection step.The free surface is immersed in the computation domain and expressed by a one-fluid density function. With this treatment the dynamic conditions at the free surface are automatically satisfied.The validity and utility of the numerical model are demonstrated by applying it to a 3D dam-breaking problem and compared with a performed experiment.Three free surface capturing methods-VOF(Volume of Fluid),CIP and THINC(Tangent of Hyperbola for Interface Capturing )-are used for the interface capturing.Main attention is paid to the free surface and impact pressure.Numerical results show that the present CFD model is capable of simulating violent impact free-surface flow.

关键词： CIP method VOF method Distorted free surface flow Wave breaking Water impact

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Acta Mathematica Sinica,English Series 2024年第5期40卷 1325-1344页

作者： xi TANG zhao Yong HUANG School of Science Guilin University of Aerospace TechnologyGuilin 541004P.R.China Department of Mathematics Nanjing UniversityNanjing 210093P.R.China

Given an additive category C and an integer n≥2.The higher differential additive category consists of objects X in C equipped with an endomorphism ϵ_(X)satisfying ϵ_(X)^(n).Let R be a,finite-dimensional basic algebra over an algebraically closed field and T the augmenting functor from the category of finitely generated left R-modules to that of finitely generated left R/(t^(n))-modules.It is proved that a finitely generated left R-module M isτ-rigid(respectively,(support)τ-tilting,almost completeτ-tilting)if and only if so is T(M)as a left R[t]/(t^(n))-module.Moreover,R isτm-selfinjective if and only if so is R[t]/(t^(n)).

关键词： Higher differential objects Wakamatsu tilting subcategories G_(ω)-projective modules sup-portτ-tilting modules τ_(m)-selfinjective algebras precluster tilting subcategories

Automatic Generation Control in a Distributed Power Grid Based on Multi-step Reinforcement Learning

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Protection and Control of Modern Power Systems 2024年第4期9卷 39-50页

作者： Wenmeng zhao Tuo zeng Zhihong Liu Lihui xie Lei xi Hui Ma the Electric Power Research Institute Southern Power GridGuangzhou 510663China the Heyuan Power Supply Bureau Guang-dong Power Grid Co.Ltd.Heyuan 517000China the College of Electrical Engineering&New Energy China Three Gorges UniversityYichang 443002China the College of Electrical Engineering&New Energy and Hubei Provincial Key Laboratory for Operation and Control of Cascaded Hydropower Station China Three Gorges UniversityYichang 443002China IEEE

The increasing use of renewable energy in the power system results in strong stochastic disturbances and degrades the control performance of the distributed power grids.In this paper,a novel multi-agent collaborative reinforcement learning algorithm is proposed with automatic optimization,namely,Dyna-DQL,to quickly achieve an optimal coordination solution for the multi-area distributed power grids.The proposed Dyna framework is combined with double Q-learning to collect and store the environmental samples.This can iteratively update the agents through buffer replay and real-time data.Thus the environmental data can be fully used to enhance the learning speed of the agents.This mitigates the negative impact of heavy stochastic disturbances caused by the integration of renewable energy on the control performance.Simulations are conducted on two different models to validate the effectiveness of the proposed algorithm.The results demonstrate that the proposed Dyna-DQL algorithm exhibits superior stability and robustness compared to other reinforcement learning algorithms.

关键词： Automatic generation control Dyna framework distributed power grid multi-agent mod-el-based reinforcement learning