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Homogenization for Periodic Heterogeneous Materials with Arbitrary Position-Dependent Material Properties

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Communications in Theoretical Physics 2012年第8期58卷 189-194页

作者：徐志杰 energy Resource recovery & management Idaho National Laboratory Idaho Falls

We present a rigorous homogenization approach for elcient computation of a class of physical problems in a one-dimensional periodic heterogeneous material. This material is represented by a spatially periodic array of unit cells with a length of More specifically, the method is applied to the diffusion, heat conduction, and wave propagation problems. Heterogeneous materials can have arbitrary position-dependent continuous or discontinuous materials properties （for example heat conductivity） within the unit cell. The final effective model includes both effective properties at the leading order and high-order contributions due to the microscopic heterogeneity. A dimensionless heterogeneity parameter ~ is defined to represent high-order contributions, shown to be in the range of [-1/12, 0], and has a universal expression for all three problems. Both effective properties and heterogeneity parameter 13 are independent oft, the microscopic scale of heterogeneity. The homogenized solution describing macroscopic variations can be obtained from the effective model. Solution with sub-unit-cell accuracy can be constructed based on the homogenized solution and its spatial derivatives. The paper represents a general approach to obtain the effective model for arbitrary periodic heterogeneous materials with position-dependent properties.

关键词： diffusion conduction wave homogenization multi-scale upscaling dispersive

Homogenization and Upscaling for Diffusion,Heat Conduction,and Wave Propagation in Heterogeneous Materials

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Communications in Theoretical Physics 2012年第3期57卷 348-354页

作者：徐志杰 energy Resource recovery&management Idaho National Laboratory Computational Mathematics Group Fundamental and Computational Sciences DirectoratePacific Northwest National Laboratory

We present a general homogenization method a periodic heterogeneous material with piecewise constants for diffusion, heat conduction, and wave propagation in The method is relevant to the frequently encountered upscaling issues for heterogeneous materials. The dispersion relation for each problem is first expressed in the general form where the frequency co （or wavenumber k） is expanded in terms of the wavenumber k （or frequency ω）. A general homogenization model can be directly obtained with any given dispersion relation. Next step we study the unit cell of the heterogeneous material and derive the exact dispersion relation. The final homogenized equations include both leading order terms （effective properties） and high order contributions that represent the effect of the microscopic heterogeneity on the macroscopic behavior. That effect can be lumped into a single dimensionless heterogeneity parameter β, which is bounded between -1/12≤β≤ 0 and has a universal expression for all three problems. Numerical examples validate the proposed method and demonstrate a significant computational saving.

关键词： diffusion conduction wave homogenization multi-scale dispersion upscaling heterogeneous

Aerodynamic Performances of wind Turbine Airfoils Using a Panel Method

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Journal of Environmental Science and Engineering 2011年第9期5卷 1175-1182页

作者： M.M. Oueslati A.W. Dahmouni M. Ben Salah F. Askri C. Kerkeni S. Ben Nasrallah laboratory of wind energy management and waste energy recovery Research and Technology Center of Energy Hammam Lif 2050 Tunisia laboratory of Thermal Process Research and Technology Center of Energy Hammam Lif 2050 Tunisia laboratory of Studies of Thermal and energy Systems National Engineering School of Monastir Monastir 5019 Tunisia

One of the key features of Laplace＇s Equation is the property that allows the equation governing the flow field to be converted from a 3D problem throughout the field to a 2D problem for finding the potential on the surface. The solution is then found using this property by distributing ＂singularities＂ of unknown strength over discretized portions of the surface： panels. Hence the flow field solution is found by representing the surface by a number of panels, and solving a linear set of algebraic equations to determine the unknown strengths of the singularities. In this paper a Hess-Smith Panel Method is then used to examine the aerodynamics of NACA 4412 and NACA 23015 wind turbine airfoils. The lift coefficient and the pressure distribution are predicted and compared with experimental result for low Reynolds number. Results show a good agreement with experimental data.

关键词： Panel method wind turbine airfoils incompressible potential flow pressure distribution

Practical consideration for design and optimization of the step feed process

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Frontiers of Environmental Science & Engineering 2013年第1期7卷 135-142页

作者： Shijian GE Yongzhen PENG Congcong LU Shuying WANG College of Environmental and energy Engineering Key Laboratory of Beijing Water Quality Science and Water Environment Recovery Engineering Beijing University of Technology Beijing 100124 China

Based on the anoxic/oxic (A/O) step feed process, a modified University of Cape Town (UCT) step feed process was developed by adding an anaerobic zone and adjusting sludge return pipeline. Performance evaluation of these two types of processes was investigated by optimizing operational parameters, such as the anaerobic/anoxic/oxic volumes, internal recycle ratios, and sludge retention times, for removal of chemical oxygen demanding (COD), nitrogen, and phosphorus. Results showed high removal efficiencies of COD of (85.0±1.7)%, ammonium of (99.7±0.2)%, total nitrogen (TN) of (85.5±1.7)%, phosphorus of (95.1±3.3)%, as well as excellent sludge settleability with average sludge volume index of (83.7±9.5) L·mg in the modified UCT process. Moreover, (61.5±6.0)% of influent COD was efficiently involved in denitrification or phosphorus release process. As much as 35.3% of TN was eliminated through simultaneous nitrification and denitrification process in aerobic zones. In addition, the presence of denitrifying phosphorus accumulating organisms (DNPAOs), accounting for approximately 39.2% of PAOs, was also greatly beneficial to the nitrogen and phosphorus removal. Consequently, the modified UCT step feed process was more attractive for the wastewater treatment plant, because it had extremely competitive advantages such as higher nutrient removal efficiencies, lower energy and dosages consumption, excellent settling sludge and operational assurance.

关键词： step feed anoxic/oxic (A/O) University of Cape Town (UCT) simultaneous nitrification and denitrification (SND) denitrifying phosphorus removal biological nutrient removal (BNR)

Transient Characteristics and Quantitative Analysis of Electromotive Force for DFIG-based wind Turbines during Grid Faults

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Chinese Journal of Electrical Engineering 2022年第2期8卷 3-12页

作者： Yumei Ma Donghai Zhu Xudong Zou Yong Kang Josep M.Guerrero Key laboratory of Power Electronics and energy management for Ministry of Education of China Huazhong University of Science and TechnologyWuhan 430074China Department of energy Technology Aalborg UniversityAalborg 9220Denmark

For doubly-fed induction generator(DFIG)-based wind turbines(WTs),various advanced control schemes have been proposed to achieve the low voltage ride through(LVRT)capability,whose parameters design is significantly reliant on the rotor electromotive force(EMF)of DFIG-based ***,the influence of the rotor current on EMF is usually ignored in existing studies,which cannot fully reflect the transient characteristics of *** tackle with this issue,this study presents a comprehensive and quantitative analysis of EMF during grid faults considering various control ***,the DFIG model under grid faults is ***,the transient characteristics of EMF are analyzed under different control modes(that is,rotor open-circuit and connected to converter).Furthermore,the EMF transient eigenvolumes(that is,accessorial resistance item,transient decay time constant,and frequency offset)are quantitatively analyzed with the typical parameters of MW-level DFIG-based *** analysis results contribute to the design of the LVRT control ***,the analysis is validated by the hardware-in-the-loop experiments.

关键词： Doubly-fed induction generator(DFIG) electromotive force(EMF) quantitative analysis transient characteristics wind turbines(WTs) grid faults

Analysis of Near-Wake Deflection Characteristics of Horizontal Axis wind Turbine Tower under Yaw State

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energy Engineering 2021年第6期118卷 1627-1640页

作者： Zhen Liu Jianwen Wang Fuzhong Bai Caifeng Wen Yunchao Du School of energy and Power Engineering Inner Mongolia University of TechnologyHohhot010051China Key laboratory of wind energy and Solar energy Utilization Technology Ministry of EducationInner Mongolia University of TechnologyHohhot010051China School of Mechanical Engineering Inner Mongolia University of TechnologyHohhot010051China

The yaw of the horizontal axis wind turbine results in the deflection of the wake flow field of the *** reasonable layout of wind farm can reduce the power loss of the downstream wind turbine generators due to the blocking effect of the upstream wake flow and increase the output power of the whole wind ***,there is still much space for further *** this paper,experimental research is conducted on the near-wake deflection characteristics of wind turbine tower under yaw state,expecting the effect of throwing away a brick in order to get a *** the low-turbulence wind tunnel test,regarding the most unfavorable position where the rotating blades coincide with the tower,Particle image velocimetry(PIV)technology is used to test the instantaneous velocity field and output power and analyze experimental data at four different yaw angles,different inflow velocities and ***,in order to quantitatively analyze the laws on wake deflection,the radon transformation is used to analyze the velocity contour for calculating the wake direction angle,and the results show high *** comprehensive experimental results indicate that the near-wake flow field of the tower obviously deflects towards a side in the horizontal *** the increase of the yaw angle,the deflection angle of the wake flow field further increases,and the recovery of wake velocity *** closer to the blade root,the more complex the flow is,and the influence of the blade on the near wake of the tower is gradually *** change laws on the wake direction angle with the yaw angle and the blade spanwise direction are *** experiment in this paper can provide guidance for layout optimization of wind farm,and the obtained data can provide a scientific basis for the research on performance prediction of horizontal axis wind turbine.

关键词： Horizontal axis wind turbine yaw tower near-wake

The Effects of Turbulence Intensity and Tip Speed Ratio on the Coherent Structure of Horizontal-Axis wind Turbine Wake:A wind Tunnel Experiment

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energy Engineering 2022年第6期119卷 2297-2317页

作者： Yuxia Han Jianwen Wang Xin Li Xueqing Dong Caifeng Wen School of energy and Power Engineering Inner Mongolia University of TechnologyHohhot010051China Key laboratory of wind energy and Solar energy Utilization Technology Ministry of EducationInner Mongolia University of TechnologyHohhot010051China Power Research Institute Inner Mongolia Electric Power Group Co.Ltd.Hohhot010020China

The evolution laws of the large-eddy coherent structure of the wind turbine wake have been evaluated via wind tunnel experiments under uniform and turbulent inflow *** spatial correlation coefficients,the turbulence integral scales and power spectrum are obtained at different tip speed ratios(TSRs)based on the time-resolved particle image velocity(TR-PIV)*** results indicate that the large-eddy coherent structures are more likely to dissipate with an increase in turbulence intensity and ***,the spatial correlation of the longitudinal pulsation velocity is greater than its axial counterpart,resulting into a wake turbulence dominated by the longitudinal *** an increase of turbulence intensity,the integral scale of the axial turbulence increases,meanwhile,its longitudinal counterpart *** to an increase in TSR,the integral scale of axial turbulence decreases,whereas,that of the longitudinal turbulence *** analyzing the wake power spectrum,it is found that the turbulent pulsation kinetic energy of the wake structure is mainly concentrated in the low-frequency vortex *** dissipation rate of turbulent kinetic energy increases with an increase of turbulence intensity and the turbulence is transported and dissipated on a smaller scale vortex,thus promoting the recovery of wake.

关键词： Horizontal axis wind turbine coherent structure turbulence integral scale TR-PIV spatial correlation

Thermal Property Enhancement of a Novel Shape-Stabilized Sodium Acetate Trihydrate-Acetamide/Expanded Graphite-Based Composite Phase Change Material

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Journal of Thermal Science 2024年第4期33卷 1564-1576页

作者： AN Zhoujian HOU Wenjie DU Xiaoze HUANG Zhongzheng MOMBEKI PEA Hamir Johan ZHANG Dong LIU Xiaomin College of energy and Power Engineering Lanzhou University of TechnologyLanzhou730050China Key laboratory of Multi-supply System with Solar energy and Biomass of Gansu Province Lanzhou730050China Gansu Natural energy Research Institute Lanzhou730046China

Phase change materials(PCMs)are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings,waste heat recovery,battery thermal management and so *** inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and ***,inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature,liquid phase leakage,large supercooling and severe phase separation in the application *** this work,sodium acetate trihydrate was selected as the basic inorganic PCM,and a novel shape-stabilized composite phase change material(CPCM)with good thermal properties was prepared by adding various functional *** first,the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using *** the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized *** thermophysical properties of the resultant shape-stabilized CPCM were systematically *** microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and *** experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate *** obtained shape-stabilized CPCM modified with additional 18%(mass fraction)acetamide and 12%(mass fraction)expanded graphite exhibited good shape stability and thermophysical characteristics:a low supercooling degree of 1.75℃and an appropriate melting temperature of 40.77℃were obtained;the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K)were also ***,after 50accelerated melting-freezing cycles,the obtained shape-stabilized CPCM represented good thermal reliability.

关键词： sodium acetate trihydrate melting point modification agent expanded graphite shape stability thermal conductivity enhancement

Modification of k-ω Turbulence Model for Predicting Airfoil Aerodynamic Performance

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Journal of Thermal Science 2015年第3期24卷 221-228页

作者： PENG Bo YAN Hao FANG Hong WANG Ming School of Economics and management Beihang University National Key laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power Engineering Beihang University Shenyang Aeroengine Research Institute

Predicting wind turbine S825 airfoil＇s aerodynamic performance is crucial to improving its energy efficiency and reducing its environmental impact. In this paper, a numerical simulation on the wind turbine S825 airfoil is con- ducted with k-to turbulence model at different attack angles. By comparing with experimental data, a new method of modifying k-to model is proposed. A modifying function is proposed to limit the production term in ω equation based on fluid rotation and deformation. This method improves turbulent viscosity and decreases separating re- gion when the airfoil works at large separating conditions. The predictive accuracy could be improved by using the modified k-to turbulence model.

关键词： S825 airfoil separation k-ω model aerodynamic performance non-equilibrium