Quantitative assessment of offshore wind speed variability using fractal analysis

Z.R. Shu,P.W. Chan,Q.S. Li,Y.C. He,B.W. Yan 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.31 No.4

Proper understanding of offshore wind speed variability is of essential importance in practice, which provides useful information to a wide range of coastal and marine activities. In this paper, long-term wind speed data recorded at various offshore stations are analyzed in the framework of fractal dimension analysis. Fractal analysis is a well-established data analysis tool, which is particularly suitable to determine the complexity in time series from a quantitative point of view. The fractal dimension is estimated using the conventional box-counting method. The results suggest that the wind speed data are generally fractals, which are likely to exhibit a persistent nature. The mean fractal dimension varies from 1.31 at an offshore weather station to 1.43 at an urban station, which is mainly associated with surface roughness condition. Monthly variability of fractal dimension at offshore stations is well-defined, which often possess larger values during hotter months and lower values during winter. This is partly attributed to the effect of thermal instability. In addition, with an increase in measurement interval, the mean and minimum fractal dimension decrease, whereas the maximum and coefficient of variation increase in parallel.

Numerical investigation on residual stress in photovoltaic laminates after lamination

Q. Z. Zhang,B. F. Shu,M. B. Chen,Q. B. Liang,C. Fan,Z. Q. Feng,P. J. Verlinden 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

A series of simulations were carried out to investigate the residual stress induced in the photovoltaic laminate during the cooling processafter lamination with a global model and several submodels. The simulations focus separately on the effects of the cooling rate, thecell layout and anisotropy on the residual stress and deformation of the photovoltaic laminate in a comparative manner with the finiteelement method. The results have shown that significant stress concentration and twist occurs in the interconnection region in the cell. Inaddition, different cooling rates, cell layouts and anisotropy only influence the largest stress rather than the stress distribution and deformation. Therefore, the results of a uniform stationary isotropic model with fewer cells can provide enough insight into the stress distributionin real photovoltaic laminates and the modified largest first principal stress can be used for design and verification.

Semi-Empirical Study on the Yield Energy-Dependence of the ^(235) U + n Fission

N.-C Shu,Y. -J Chen,T. -J Liu,Z. -J Sun,X. -Z Wu,J. Qian,R. -R Xu 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

The yield dependence on energy of ^(235)U+n fission was studied with semi-empirical mode based upon the basic idea of Brosa model, wherein the macro energy and the shell effects were taken into account at scission. And the yield could be expressed with a five-gaussian formula formally with 11 parameters, which were determined by fitting experimental data. The results showed it could well describe the yield mass distributions and the yield energy-dependance of part fragments in the incident energy range 0 - 20 MeV.

INFLUENCE OF THE ACCELERATING OPERATION MECHANISM ON THE COMBUSTION NOISE IN DI-DIESEL ENGINES

H. WEI,Z. LI,X. LIANG,G. SHU 한국자동차공학회 2012 International journal of automotive technology Vol.13 No.3

This paper focuses on the mechanisms of combustion noise during the accelerating operation of multi-cylinder diesel engines using testing technology for the transient conditions of IC engines. Based on impact factors, such as the gas dynamic load and cylinder pressure oscillations, tests and analysis of the combustion noise during transient and steady-state conditions for different loads are made on four-cylinder naturally aspirated engines, turbocharged engines, EGR-introduced engines, and high pressure common rail engines. The laws of combustion noise difference for the same engine speed and load are researched during transient and steady-state conditions. It is found that during transient conditions, the maximum pressure rise rate and the high frequency oscillation amplitude of the cylinder pressure are all higher than those observed during steadystate conditions for the same engine speed and load. With their joint action, the combustion noise during transient conditions is greater than that during steady-state conditions. Turbocharging is useful in reducing the combustion noise during transient conditions. Turbocharging has a better effect on the control over the combustion noise during transient conditions with a constant engine speed and an increasing torque than in conditions with a constant torque and an increasing engine speed. One of the main reasons for different control effects on the combustion noise is that turbocharging causes different wall temperatures inside combustion chambers. The introduction of the appropriate EGR is helpful in the reduction of the combustion noise during transient conditions. The key to the control of combustion noise with EGR during transient conditions is whether a real-time adjustment to the EGR rate can be made to achieve the optimization of the EGR rates for different transient conditions. By means of analyzing the differences in the combustion noise between the transient and steady-state conditions for different pilot injection controls, we obtain a strategy for controlling the combustion noise during transient conditions with a pilot injection. Compared with the steady-state conditions, a larger pilot injection quantity and a longer interval between the main injection and pilot injection should be selected for transient conditions, and this is verified through tests.

LOAD-CARRYING CAPACITIES FOR CIRCULAR METAL FOAM CORE SANDWICH PANELS AT LARGE DEFLECTION

W. HOU,Z. WANG,L. ZHAO,G. LU,D. SHU 한국소성가공학회 2008 한국소성가공학회 컨퍼런스 Vol.2008 No.10

Structural Stability of Characteristic Interface for NiTi/Nb Nanowire: First-Principle Study

G. F. Li,H. Z. Zheng,X. Y. Shu,P. Peng 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.1

Compared with some other conventional interface models, the interface of NiTi(211)/Nb(220) in NiTiNb metal nanocomposite had been simulated and analyzed carefully. Results show that only several interface models, i.e., NiTi(100)/Nb(100)(Ni↔Nb), NiTi(110)/Nb(110) and NiTi(211)/Nb(220), can be formed accordingly with their negative formation enthalpy. Therein the cohesive energy ΔE and Griffith rupture work W of NiTi(211)/ Nb(220) interface model are the lowest among them. Density of states shows that there exists only one electronic bonding peak for NiTi(211)/Nb(220) interface model at -2.5 eV. Electron density difference of NiTi(211)/ Nb(220) shows that the Nb-Nb, Nb-Ti and Nb-Ni bonding characters seem like so peaceful as a fabric twisting every atom, which is different from conventional metallic bonding performance. Such appearance can be deduced that the metallic bonding between Nb-Nb, Nb-Ti and Nb-Ni in NiTi(211)/Nb(220) may be affected by its nanostructure called nanometer size effect. Thus, our findings open an avenue for detailed and comprehensive studies of nanocomposite.

Plastic / Superplastic Forming : MODELLING OF SUPERPLASTIC FORMING UNDER A HYDROSTATIC PRESSURE

Song Yu Quan,Z . C . Wang,Kou Shu Qing 대한금속재료학회 ( 구 대한금속학회 ) 1995 Advanced Material and Processing Vol.1 No.-

SIMULATION OF UNIT CELL PERFORMANCE IN THE POLYMER ELECTROLYTE MEMBRANE FUEL CELL

Kim, H.G.,Kim, Y.S.,Shu, Z. The Korean Society of Automotive Engineers 2006 International journal of automotive technology Vol.7 No.7

Fuel cells are devices that convert chemical energy directly into electrical energy. Owing to the high efficiency of the fuel cells, a large number of research work have been done during these years. Among many kinds of the fuel cells, a polymer electrolyte membrane fuel cell is such kind of thing which works under low temperature. Because of the specialty, it stimulated intense global R&D competition. Most of the major world automakers are racing to develop polymer electrolyte membrane fuel cell passenger vehicles. Unfortunately, there are still many problems to be solved in order to make them into the commercial use, such as the thermal and water management in working process of PEMFCs. To solve the difficulites facing the researcher, the analysis of the inner mechanism of PEMFC should be implemented as much as possible and mathematical modeling is an important tool for the research of the fuel cell especially with the combination of experiment. By regarding some of the assumptions and simplifications, using the finite element technique, a two-dimensional electrochemical mode is presented in this paper for the further comparison with experimental data. Based on the principals of the problem, the equations of electronic charge conservation equation, gas-phase continuity equation, and mass balance equation are used in calculating. Finally, modeling results indicate some of the phenomenon in a unit cell, and the relationships between potential and current density.

SIMULATION OF UNIT CELL PERFORMANCE IN THE POLYMER ELECTROLYTE MEMBRANE FUEL CELL

H. G. KIM,Y. S. KIM,Z. SHU 한국자동차공학회 2006 International journal of automotive technology Vol.7 No.7

Fuel cells are devices that convert chemical energy directly into electrical energy. Owing to the high efficiency of the fuel cells, a large number of research work have been done during these years. Among many kinds of the fuel cells, a polymer electrolyte membrane fuel cell is such kind of thing which works under low temperature. Because of the specialty, it stimulated intense global R&D competition. Most of the major world automakers are racing to develop polymer electrolyte membrane fuel cell passenger vehicles. Unfortunately, there are still many problems to be solved in order to make them into the commercial use, such as the thermal and water management in working process of PEMFCs. To solve the difficulites facing the researcher, the analysis of the inner mechanism of PEMFC should be implemented as much as possible and mathematical modeling is an important tool for the research of the fuel cell especially with the combination of experiment. By regarding some of the assumptions and simplifications, using the finite element technique, a two-dimensional electrochemical mode is presented in this paper for the further comparison with experimental data. Based on the principals of the problem, the equations of electronic charge conservation equation, gas-phase continuity equation, and mass balance equation are used in calculating. Finally, modeling results indicate some of the phenomenon in a unit cell, and the relationships between potential and current density.

Optical Nanostructures Fabricated by SU-8 based Nanoimprint Lithography

R. Liu,B.-R. Lu,S.-Q. Xie,J. Wan,Z. Shu,X.-P. Qu,Y. Chen 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3

The high resolution low-cost and high-volume nano-pattering capability of the nanoimprint lithography (NIL) and the high optical transmittance of SU-8 in the infrared, the visible and the near-UV light ranges have enabled us to apply the SU-8 based NIL to produce various optical nanostructures. We fabricated dielectric and metallic gratings of various groove density (1000 – 5000 lines/mm) in a relatively large area (10 mm × 10 mm) and planar chiral photonic meta-material structure in SU-8 with periods of both 600 nm and 4 μm. We also designed and successfully fabricated distributed Bragg reflectors (DBRs) with Si/SiO2/SU8/air structures Optical measurements of the SU-8 based nanostructures showed good optical performance and interesting properties, and the experimental data agree reasonably well with simulation results. The high resolution low-cost and high-volume nano-pattering capability of the nanoimprint lithography (NIL) and the high optical transmittance of SU-8 in the infrared, the visible and the near-UV light ranges have enabled us to apply the SU-8 based NIL to produce various optical nanostructures. We fabricated dielectric and metallic gratings of various groove density (1000 – 5000 lines/mm) in a relatively large area (10 mm × 10 mm) and planar chiral photonic meta-material structure in SU-8 with periods of both 600 nm and 4 μm. We also designed and successfully fabricated distributed Bragg reflectors (DBRs) with Si/SiO2/SU8/air structures Optical measurements of the SU-8 based nanostructures showed good optical performance and interesting properties, and the experimental data agree reasonably well with simulation results.