The morphological distribution of absorbent in composites is equally important with absorbents for the overall electromagnetic properties,but it is often ignored.Herein,a comprehensive consideration including electrom...The morphological distribution of absorbent in composites is equally important with absorbents for the overall electromagnetic properties,but it is often ignored.Herein,a comprehensive consideration including electromagnetic component regulation,layered arrangement structure,and gradient concentration distribution was used to optimize impedance matching and enhance electromagnetic loss.On the microscale,the incorporation of magnetic Ni nanoparticles into MXene nanosheets(Ni@MXene)endows suitable intrinsic permittivity and permeability.On the macroscale,the layered arrangement of Ni@MXene increases the effective interaction area with electromagnetic waves,inducing multiple reflection/scattering effects.On this basis,according to the analysis of absorption,reflection,and transmission(A-R-T)power coefficients of layered composites,the gradient concentration distribution was constructed to realize the impedance matching at low-concentration surface layer,electromagnetic loss at middle concentration interlayer and microwave reflection at high-concentration bottom layer.Consequently,the layered gradient composite(LG5-10-15)achieves complete absorption coverage of X-band at thickness of 2.00-2.20 mm with RL_(min) of-68.67 dB at 9.85 GHz in 2.05 mm,which is 199.0%,12.6%,and 50.6%higher than non-layered,layered and layered descending gradient composites,respectively.Therefore,this work confirms the importance of layered gradient structure in improving absorption performance and broadens the design of high-performance microwave absorption materials.展开更多
The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an ...The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an exception of a few operating in wind tunnels. This study proposes for a comprehensive reevaluation of Betz’s derivation, aiming to establish the gap between a theoretical power limit and a practical limit for realization. There are two common expressions for power coefficient giving the same optimal value of 59%, but they generate different power-coefficient curves when plotted against velocity ratios. This paper presents a new method being referred as “Direct Multiplication Fractional Change” (DMFC) for deriving power-coefficient curves in wind energy, and compares its generated curve with established models. Discrepancies in power-coefficient expressions are identified and harmonized. Three approaches, namely EVAM, LVM, and DMFCM, were used for the numerical derivation of cp in the study, with their evaluation summarized in a table. The study collaborates its findings with a formulated velocity-distance curve, commonly presented as a hypothetical velocity profile in some publications. The results from DMFCM indicate two distinct maxima for the power coefficient. On the front side of the disc, a maximum of 0.5 is achievable in practice, although it is not the highest theoretically. On the rear side, a theoretical maximum of 0.59 is observed, but this value is not attainable in practice. These maxima are separated by their positions along the line of flow relative to the disc. However, this approximation is limited to a streamlined flow model of the rotor disc.展开更多
Characters of head of low head pump station and the pump shaft power areanalyzed. Influence of each single factor on pump shaft power is expressed as change of specificshaft power. (non-dimensional) and the probabilit...Characters of head of low head pump station and the pump shaft power areanalyzed. Influence of each single factor on pump shaft power is expressed as change of specificshaft power. (non-dimensional) and the probability density function is determined. Influences ofmultiple factors on pump shaft power are analyzed. Method of calculating none over-loadedprobability of motor by integration by successive reductions is put forward and then relationbetween power spare coefficient and none over-loaded reliability of electric motor is established.Influences of all factors on pump shaft power being considered completely; power spare coefficientsof motor are calculated in three kinds of heads (changing and unchanging), two kinds of dirty-outconditions. Electrical motor power spare coefficients should be chosen as 1.20 approx 1.44, 1.11approx 1.19, 1.09 approx.14 respectively when pump heads are 4, 7, 9.5 m. The results mean much toreasonable choose of electrical motors in large pump stations, increasing reliability of pump unitsand saving equipment investment.展开更多
The basic theory of the purchasing power at par refers to the rate of one country＇s currency to U.S. dollar while purchasing ＂a basket＂ goods and services in the same quantity and quality respectively in this count...The basic theory of the purchasing power at par refers to the rate of one country＇s currency to U.S. dollar while purchasing ＂a basket＂ goods and services in the same quantity and quality respectively in this country and U.S.A. This paper gives out calculation method of purchasing power conversion coefficient at par and how to calculate the non-base year purchasing power at par.展开更多
Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especia...Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.展开更多
To improve the power-extraction performance of the Savonius vertical-axis wind turbine(S-VAWT),additional cylinders,which are used to control the fluid flow around the wind turbine blade,were introduced into the blade...To improve the power-extraction performance of the Savonius vertical-axis wind turbine(S-VAWT),additional cylinders,which are used to control the fluid flow around the wind turbine blade,were introduced into the blade design.In contrast to the traditional numerical method,a mathematical model in the form of a dynamical system was used in this study.A numerical calculation program that could effectively solve the equations of wind-induced rotation of S-VAWT was developed,and combined with the Taguchi experimental method to investigate the influence of additional cylinders on the power-extraction characteristics of the S-VAWT.The results showed that the additional cylinders have a significant impact on the power-extraction performance of the S-VAWT.At 4-m/s wind speed,the average power coefficient of the S-VAWT with additional cylinders is 15%higher than that of the conventional S-VAWT.After construction of the wind turbine prototype and power-extraction tests,the results showed that compared with a conventional S-VAWT,the output power was 29%higher for the S-VAWT with additional cylinders under the same particular conditions.展开更多
Here we report a regulation about power conversion in fuel cells. This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the \{...Here we report a regulation about power conversion in fuel cells. This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the \{equilibrium\} potential and work potential. With this regulation we deduced fuel cell performance equation which can describe the potential vs.the current performance curves, namely, polarization curves of fuel cells with three power source parameters: equilibrium potential E_0; internal resistance R; and power conversion coefficient K. The concept of the power conversion coefficient is a new criterion to evaluate and compare the characteristics and capacity of different fuel cells. The calculated values obtained with this equation agree with practical performance of different types of fuel cells.展开更多
In order to describe pavement roughness more intuitively and effectively, a method of pavement roughness simulation, i.e., the stochastic sinusoidal wave, is introduced. The method is based on the primary idea that pa...In order to describe pavement roughness more intuitively and effectively, a method of pavement roughness simulation, i.e., the stochastic sinusoidal wave, is introduced. The method is based on the primary idea that pavement roughness is denoted as the sum of numerous sines or cosines with stochastic phases, and uses the discrete spectrum to approach the target stochastic process. It is a discrete numerical method used to simulate pavement roughness. According to a given pavement power spectral density （PSD） coefficient, under the condition that the character of displacement frequency based on the time domain model is in accordance with the given pavement surface spectrum, the pavement roughness is optimized to stochastic equivalent vibrations by computer simulation, and the curves that describe pavement roughness under each grade are obtained. The results show that the stochastic sinusoidal wave is suitable for simulation of measured pavement surface spectra based on the time domain model. The method of the stochastic sinusoidal wave is important to the research on vehicle ride comfort due to its rigorous mathematical derivation, extensive application range and intuitive simulation curve. Finally, a roughness index defined as the nominal roughness index （NRI） is introduced, and it has correlation with the PSD coefficient.展开更多
Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct...Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.展开更多
The Savonius rotor is a vertical axis-wind machine composed of two half cylindrical blades presenting a central gap. It is a slow velocity machine compared with horizontal wind machines. Its efficiency is about twenty...The Savonius rotor is a vertical axis-wind machine composed of two half cylindrical blades presenting a central gap. It is a slow velocity machine compared with horizontal wind machines. Its efficiency is about twenty per cent. In this work experimental tests are presented using two kind of deflectors placed in front of the resistive blade. Such disposition allows to hide the resistant blade and to guide the flow toward the motrice blade. Two deflectors have been used： a short one and a long one. The results obtained in wind tunnel have shown that the long deflector is the more efficient, essentially for high values of the tip speed ratio. One has been interested, using a numerical approach, in the study of the influence of a wall on the aerodynamical field near the rotor.展开更多
In this paper, the radiation losses of impurity on HL-2A have been simulated by assuming the profiles electron temperature and density and solving ionization rate equation under conditions of non-coronal radiation. Th...In this paper, the radiation losses of impurity on HL-2A have been simulated by assuming the profiles electron temperature and density and solving ionization rate equation under conditions of non-coronal radiation. The time required for an impurity species to establish equilibrium is proved to be sensitively dependent on the plasma electron temperature, and it is strongly correlated with the ionization state distribution during equilibrium establishment of impurity species, It is found from simulation results that the residence parameter plays an important role in the enhancement of radiation losses of plasma.展开更多
With the background of offshore wind energy projects, this paper studies aerodynamic performance and geometric characteristics of large capacity wind turbine rotors （1 to 10 MW）, and the main characteristic paramete...With the background of offshore wind energy projects, this paper studies aerodynamic performance and geometric characteristics of large capacity wind turbine rotors （1 to 10 MW）, and the main characteristic parameters such as the rated wind speed, blade tip speed, and rotor solidity. We show that the essential criterion of a high- performance wind turbine is a highest possible annual usable energy pattern factor and a smallest possible dimension, capturing the maximum wind energy and producing the maximum annual power. The influence of the above-mentioned three parameters on the pattern factor and rotor geometry of wind turbine operated in China＇s offshore meteoro- logical environment is investigated. The variation patterns of aerodynamic and geometric parameters are obtained, analyzed, and compared with each other. The present method for aerodynamic analysis and its results can form a basis for evaluating aerodynamic performance of large-scale offshore wind turbine rotors.展开更多
Abstract Tidal current energy is renewable and sustainable, which is a promising altemative energy resource for the future elec- tricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool t...Abstract Tidal current energy is renewable and sustainable, which is a promising altemative energy resource for the future elec- tricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool to capture the tidal current energy especially under low-speed conditions. A 2D unsteady numerical model based on Ansys-Fluent 12.0 is established to conduct the numerical simulation, which is validated by the corresponding experimental data. For the unsteady calculations, the SST model, 2x 105 and 0.01 s are se- lected as the proper turbulence model, mesh number, and time step, respectively. Detailed contours of the velocity distributions around the rotor blade foils have been provided for a flow field analysis. The tip speed ratio （TSR） determines the azimuth angle of the appearance of the torque peak, which occurs once for a blade in a single revolution. It is also found that simply increasing the incident flow velocity could not improve the turbine performance accordingly. The peaks of the averaged power and torque coeffi- cients appear at TSRs of 2.1 and 1.8, respectively. Furthermore, several shapes of the duct augmentation are proposed to improve the turbine performance by contracting the flow path gradually from the open mouth of the duct to the rotor. The duct augmentation can significantly enhance the power and torque output. Furthermore, the elliptic shape enables the best performance of the turbine. The numerical results prove the capability of the present 2D model for the unsteady hydrodynamics and an operating performance analy- sis of the vertical tidal stream turbine.展开更多
In this paper, the Geometric Optics (GO) method using the approximate ray paths coupled with the Computer Aided Tri-dimensional Interface Application (CATIA) meshing modeling are implemented to analyze the performance...In this paper, the Geometric Optics (GO) method using the approximate ray paths coupled with the Computer Aided Tri-dimensional Interface Application (CATIA) meshing modeling are implemented to analyze the performance of electric large three-dimensional dielectric radome-enclosed antenna of arbitrary contour shape. The surfaces of the radome are approximated by planar triangular patches, the influences of various number of patches on power transmission coefficient and Insertion Phase Delay (IPD) via an ogive and a conical radome are discussed by the hybrid method. The simulation results indicate that computational error from planar triangular patches can limit in one percent, meeting the engineering application requirements.展开更多
Utilization of tidal current is becoming a focus of marine energy research and development field. In this paper, a new type of tidal current power generating device which was called flexible blade turbine was put forw...Utilization of tidal current is becoming a focus of marine energy research and development field. In this paper, a new type of tidal current power generating device which was called flexible blade turbine was put forward. A scale model testing was carried out, and results show that the models performed as expected with good hydrodynamic characteristics. Based on analysis of the results, a scale model turbine with a rated power of 5 kW was constructed, which was an optimal scheme of the flexible blade turbine having higher coefficient of power and power generation capacity. Sea trials were carried out in the Zhaitang Island Channel to evaluate the performance of the turbine. Results show that the turbine performed well, generating the power predicted.展开更多
Due to the presence of non-stationarities and discontinuities in the audio signal, segmentation and classification of audio signal is a really challenging task. Automatic music classification and annotation is still c...Due to the presence of non-stationarities and discontinuities in the audio signal, segmentation and classification of audio signal is a really challenging task. Automatic music classification and annotation is still considered as a challenging task due to the difficulty of extracting and selecting the optimal audio features. Hence, this paper proposes an efficient approach for segmentation, feature extraction and classification of audio signals. Enhanced Mel Frequency Cepstral Coefficient (EMFCC)-Enhanced Power Normalized Cepstral Coefficients (EPNCC) based feature extraction is applied for the extraction of features from the audio signal. Then, multi-level classification is done to classify the audio signal as a musical or non-musical signal. The proposed approach achieves better performance in terms of precision, Normalized Mutual Information (NMI), F-score and entropy. The PNN classifier shows high False Rejection Rate (FRR), False Acceptance Rate (FAR), Genuine Acceptance rate (GAR), sensitivity, specificity and accuracy with respect to the number of classes.展开更多
This research explores the potential of wind energy as a sustainable solution to environmental challenges by focussing on the deployment of vertical axis wind turbines in confined spaces,such as urban rooftops,ship de...This research explores the potential of wind energy as a sustainable solution to environmental challenges by focussing on the deployment of vertical axis wind turbines in confined spaces,such as urban rooftops,ship decks,gas stations,etc.It aims to identify the optimal configuration for a cluster of three rotors by varying geometric parameters,assessing the omnidirectionality of the rotors,and using an artificial neural network as an optimization tool.The methodology involves 2D unsteady Reynolds-averaged Navier-Stokes computational fluid dynamics simulations followed by building and training an artificial neural network.The results indicate that the best cluster configuration,achieving a power coefficient of 0.2517,consists of a horizontal distance of 0.08D,vertical distance of 0.1D,and wind direction of 232°.The accuracy of the neural network is demonstrated by a mere 1.206%discrepancy with the computational analysis,thus highlighting its potential as a time-saving tool in the optimization process.Additionally,the average power coefficient across all wind directions was found to be 0.194,thus confirming the strong omnidirectional characteristics of the cluster.The study also notes a significant speed-up region between the rotors,which creates a low-pressure area,enhancing the power coefficient of the downstream rotor and demonstrating the advantages of this pressure-based turbine configuration.This comprehensive study establishes the efficacy of neural networks in optimizing wind turbine clusters,thus significantly expediting their design and development process.展开更多
The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based ...The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based on an in-house solver.This solver is developed on an in-house platform HRAPIF based on the finite volume method(FVM)with the elemental velocity vector transformation(EVVT)approach.The present solver adopts the density-based method with a low Mach preconditioning technique.The turbulence models are the Spalart-Allmaras(SA)model and the k-ωshear stress transport(SST)model.The inviscid spatial discretization schemes are the third-order monotone upstream-centered schemes for conservation laws(MUSCL)scheme and the fifth-order modified weighted essentially non-oscillatory(WENO-Z)scheme.The power coefficient,instantaneous torque of blades,blade wake,and turbine wake are compared and analyzed at different tip speed ratios.The extensive analysis reveals that the density-based method can be applied in VAWT numerical simulation;the SST models perform better than the SA models in power coefficient prediction;the rotation-curvature correction is not necessary and the third-order MUSCL is enough for power coefficient prediction,the high-order WENO-Z scheme can capture more flow field details,the rotation-curvature correction and high-order WENO-Z scheme reduce the length of the velocity deficit region in the turbine wake.展开更多
The aerodynamic forces and vortex characteristics of an H-type Vertical Axis Wind Turbine(VAWT)become complicated because of dynamic stall,particularly in the three-dimensional impact on the blade spanwise direction.T...The aerodynamic forces and vortex characteristics of an H-type Vertical Axis Wind Turbine(VAWT)become complicated because of dynamic stall,particularly in the three-dimensional impact on the blade spanwise direction.This study focused on the evaluation of the aerodynamic performance and vortex characteristics of an H-type VAWT in the spanwise direction by numerical simulations and wind tunnel experiments.Pressure acting on the blade surface was obtained from multiport pressure measurement devices by wind tunnel.Meanwhile,the vortex field around different blade sections was investigated through numerical simulations.The stall behavior was analysed by comparing the results of numerical simulations and experiments.As a result,the tangential force of single blade was mainly contributed at the chordwise position of x/c≤0.4 c and the power of single blade was mainly contributed at the azimuthal angle range of 60°≤θ≤150°in the blade section position region of 0≤z/(H/2)≤0.7.At the section position of z/(H/2)=0.5,the initial flow separation was found at the suction side and progressed forward to the leading edge.With the increase of the tip speed ratios,the decreasing position of the averaged local power coefficient of each section was closer to the middle section of z/(H/2)=0,and the attenuation speed became faster.The power coefficient reductions at the blade section position of z/(H/2)=0.9 were 38.29%,46.78%and 56.42%when the tip speed ratios were 1.38,2.19 and 2.58,respectively.The results of this study provided a better understanding of the development of the performance characteristics and vortex characteristics of H-type VAWT.展开更多
Ocean current energy is a promising and reliable resource that offers sustainability and predictability in realizing green future needs.A diffuser-augmented horizontal-axis turbine is utilized to generate ocean curren...Ocean current energy is a promising and reliable resource that offers sustainability and predictability in realizing green future needs.A diffuser-augmented horizontal-axis turbine is utilized to generate ocean current energy.A numerical study on the impact of diffuser angle variations on the power coefficient has been carried out in the previous research.To elucidate the fluid dynamics aspects and further validation of previous computational results,the experimental investigation on the optimal design of tidal turbine with 20.04°diffuser augmentation is presented in this study.The study was conducted in a flowing tank with a current velocity of 0.7 m/s.The maximum power coefficient of 20.04°is 0.436 experimentally,which is a little smaller than the numerical value.Moreover,to reinforce the 20.04°result,a diffuser with an angle of 10.43°was also manufactured and tested experimentally.The maximum power coefficient of 10.43°is 0.303 experimentally,which is 3%smaller than the numerical value.It was concluded that the numerical approach might be considered satisfactory and represent similar phenomena to the experimental investigation in an application for modelling of multi-objective optimization.展开更多
基金support for this work by Key Research and Development Project of Henan Province(Grant.No.241111232300)the National Natural Science Foundation of China(Grant.No.52273085 and 52303113)the Open Fund of Yaoshan Laboratory(Grant.No.2024003).
文摘The morphological distribution of absorbent in composites is equally important with absorbents for the overall electromagnetic properties,but it is often ignored.Herein,a comprehensive consideration including electromagnetic component regulation,layered arrangement structure,and gradient concentration distribution was used to optimize impedance matching and enhance electromagnetic loss.On the microscale,the incorporation of magnetic Ni nanoparticles into MXene nanosheets(Ni@MXene)endows suitable intrinsic permittivity and permeability.On the macroscale,the layered arrangement of Ni@MXene increases the effective interaction area with electromagnetic waves,inducing multiple reflection/scattering effects.On this basis,according to the analysis of absorption,reflection,and transmission(A-R-T)power coefficients of layered composites,the gradient concentration distribution was constructed to realize the impedance matching at low-concentration surface layer,electromagnetic loss at middle concentration interlayer and microwave reflection at high-concentration bottom layer.Consequently,the layered gradient composite(LG5-10-15)achieves complete absorption coverage of X-band at thickness of 2.00-2.20 mm with RL_(min) of-68.67 dB at 9.85 GHz in 2.05 mm,which is 199.0%,12.6%,and 50.6%higher than non-layered,layered and layered descending gradient composites,respectively.Therefore,this work confirms the importance of layered gradient structure in improving absorption performance and broadens the design of high-performance microwave absorption materials.
文摘The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an exception of a few operating in wind tunnels. This study proposes for a comprehensive reevaluation of Betz’s derivation, aiming to establish the gap between a theoretical power limit and a practical limit for realization. There are two common expressions for power coefficient giving the same optimal value of 59%, but they generate different power-coefficient curves when plotted against velocity ratios. This paper presents a new method being referred as “Direct Multiplication Fractional Change” (DMFC) for deriving power-coefficient curves in wind energy, and compares its generated curve with established models. Discrepancies in power-coefficient expressions are identified and harmonized. Three approaches, namely EVAM, LVM, and DMFCM, were used for the numerical derivation of cp in the study, with their evaluation summarized in a table. The study collaborates its findings with a formulated velocity-distance curve, commonly presented as a hypothetical velocity profile in some publications. The results from DMFCM indicate two distinct maxima for the power coefficient. On the front side of the disc, a maximum of 0.5 is achievable in practice, although it is not the highest theoretically. On the rear side, a theoretical maximum of 0.59 is observed, but this value is not attainable in practice. These maxima are separated by their positions along the line of flow relative to the disc. However, this approximation is limited to a streamlined flow model of the rotor disc.
文摘Characters of head of low head pump station and the pump shaft power areanalyzed. Influence of each single factor on pump shaft power is expressed as change of specificshaft power. (non-dimensional) and the probability density function is determined. Influences ofmultiple factors on pump shaft power are analyzed. Method of calculating none over-loadedprobability of motor by integration by successive reductions is put forward and then relationbetween power spare coefficient and none over-loaded reliability of electric motor is established.Influences of all factors on pump shaft power being considered completely; power spare coefficientsof motor are calculated in three kinds of heads (changing and unchanging), two kinds of dirty-outconditions. Electrical motor power spare coefficients should be chosen as 1.20 approx 1.44, 1.11approx 1.19, 1.09 approx.14 respectively when pump heads are 4, 7, 9.5 m. The results mean much toreasonable choose of electrical motors in large pump stations, increasing reliability of pump unitsand saving equipment investment.
文摘The basic theory of the purchasing power at par refers to the rate of one country＇s currency to U.S. dollar while purchasing ＂a basket＂ goods and services in the same quantity and quality respectively in this country and U.S.A. This paper gives out calculation method of purchasing power conversion coefficient at par and how to calculate the non-base year purchasing power at par.
文摘Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.
基金This work is supported by the National Natural Science Foundation of China(No.51975429).
文摘To improve the power-extraction performance of the Savonius vertical-axis wind turbine(S-VAWT),additional cylinders,which are used to control the fluid flow around the wind turbine blade,were introduced into the blade design.In contrast to the traditional numerical method,a mathematical model in the form of a dynamical system was used in this study.A numerical calculation program that could effectively solve the equations of wind-induced rotation of S-VAWT was developed,and combined with the Taguchi experimental method to investigate the influence of additional cylinders on the power-extraction characteristics of the S-VAWT.The results showed that the additional cylinders have a significant impact on the power-extraction performance of the S-VAWT.At 4-m/s wind speed,the average power coefficient of the S-VAWT with additional cylinders is 15%higher than that of the conventional S-VAWT.After construction of the wind turbine prototype and power-extraction tests,the results showed that compared with a conventional S-VAWT,the output power was 29%higher for the S-VAWT with additional cylinders under the same particular conditions.
基金Supported by EPSRC Funds(No.GR/ R5 0 4 17) and an EPSRC/ HEFCF J.I.F Award(No.JIF4 NESCEQ )
文摘Here we report a regulation about power conversion in fuel cells. This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the \{equilibrium\} potential and work potential. With this regulation we deduced fuel cell performance equation which can describe the potential vs.the current performance curves, namely, polarization curves of fuel cells with three power source parameters: equilibrium potential E_0; internal resistance R; and power conversion coefficient K. The concept of the power conversion coefficient is a new criterion to evaluate and compare the characteristics and capacity of different fuel cells. The calculated values obtained with this equation agree with practical performance of different types of fuel cells.
文摘In order to describe pavement roughness more intuitively and effectively, a method of pavement roughness simulation, i.e., the stochastic sinusoidal wave, is introduced. The method is based on the primary idea that pavement roughness is denoted as the sum of numerous sines or cosines with stochastic phases, and uses the discrete spectrum to approach the target stochastic process. It is a discrete numerical method used to simulate pavement roughness. According to a given pavement power spectral density （PSD） coefficient, under the condition that the character of displacement frequency based on the time domain model is in accordance with the given pavement surface spectrum, the pavement roughness is optimized to stochastic equivalent vibrations by computer simulation, and the curves that describe pavement roughness under each grade are obtained. The results show that the stochastic sinusoidal wave is suitable for simulation of measured pavement surface spectra based on the time domain model. The method of the stochastic sinusoidal wave is important to the research on vehicle ride comfort due to its rigorous mathematical derivation, extensive application range and intuitive simulation curve. Finally, a roughness index defined as the nominal roughness index （NRI） is introduced, and it has correlation with the PSD coefficient.
基金Project(HEUCF110707)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(E201216)supported by Heilongjiang Natural Science Fund,China
文摘Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.
文摘The Savonius rotor is a vertical axis-wind machine composed of two half cylindrical blades presenting a central gap. It is a slow velocity machine compared with horizontal wind machines. Its efficiency is about twenty per cent. In this work experimental tests are presented using two kind of deflectors placed in front of the resistive blade. Such disposition allows to hide the resistant blade and to guide the flow toward the motrice blade. Two deflectors have been used： a short one and a long one. The results obtained in wind tunnel have shown that the long deflector is the more efficient, essentially for high values of the tip speed ratio. One has been interested, using a numerical approach, in the study of the influence of a wall on the aerodynamical field near the rotor.
文摘In this paper, the radiation losses of impurity on HL-2A have been simulated by assuming the profiles electron temperature and density and solving ionization rate equation under conditions of non-coronal radiation. The time required for an impurity species to establish equilibrium is proved to be sensitively dependent on the plasma electron temperature, and it is strongly correlated with the ionization state distribution during equilibrium establishment of impurity species, It is found from simulation results that the residence parameter plays an important role in the enhancement of radiation losses of plasma.
基金supported by the National Basic Research Program of China (973 Program) (No. 2007CB714605)
文摘With the background of offshore wind energy projects, this paper studies aerodynamic performance and geometric characteristics of large capacity wind turbine rotors （1 to 10 MW）, and the main characteristic parameters such as the rated wind speed, blade tip speed, and rotor solidity. We show that the essential criterion of a high- performance wind turbine is a highest possible annual usable energy pattern factor and a smallest possible dimension, capturing the maximum wind energy and producing the maximum annual power. The influence of the above-mentioned three parameters on the pattern factor and rotor geometry of wind turbine operated in China＇s offshore meteoro- logical environment is investigated. The variation patterns of aerodynamic and geometric parameters are obtained, analyzed, and compared with each other. The present method for aerodynamic analysis and its results can form a basis for evaluating aerodynamic performance of large-scale offshore wind turbine rotors.
基金the financial support provided by the National Natural Science Foundation of China (51279190 and 51311140259)National High Technology Research and Development Program of China (863 Project,2012AA052601)+2 种基金Shandong Natural Science Funds for Distinguished Young Scholar (JQ201314)Qingdao Municipal Science & Technology Program (13-4-1-38hy and 14-9-1-5-hy)the Program of Introducing Talents of Discipline to Universities (111 Project,B14028)
文摘Abstract Tidal current energy is renewable and sustainable, which is a promising altemative energy resource for the future elec- tricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool to capture the tidal current energy especially under low-speed conditions. A 2D unsteady numerical model based on Ansys-Fluent 12.0 is established to conduct the numerical simulation, which is validated by the corresponding experimental data. For the unsteady calculations, the SST model, 2x 105 and 0.01 s are se- lected as the proper turbulence model, mesh number, and time step, respectively. Detailed contours of the velocity distributions around the rotor blade foils have been provided for a flow field analysis. The tip speed ratio （TSR） determines the azimuth angle of the appearance of the torque peak, which occurs once for a blade in a single revolution. It is also found that simply increasing the incident flow velocity could not improve the turbine performance accordingly. The peaks of the averaged power and torque coeffi- cients appear at TSRs of 2.1 and 1.8, respectively. Furthermore, several shapes of the duct augmentation are proposed to improve the turbine performance by contracting the flow path gradually from the open mouth of the duct to the rotor. The duct augmentation can significantly enhance the power and torque output. Furthermore, the elliptic shape enables the best performance of the turbine. The numerical results prove the capability of the present 2D model for the unsteady hydrodynamics and an operating performance analy- sis of the vertical tidal stream turbine.
基金Supported by the National Natural Science Foundation of China (No. 61172024)
文摘In this paper, the Geometric Optics (GO) method using the approximate ray paths coupled with the Computer Aided Tri-dimensional Interface Application (CATIA) meshing modeling are implemented to analyze the performance of electric large three-dimensional dielectric radome-enclosed antenna of arbitrary contour shape. The surfaces of the radome are approximated by planar triangular patches, the influences of various number of patches on power transmission coefficient and Insertion Phase Delay (IPD) via an ogive and a conical radome are discussed by the hybrid method. The simulation results indicate that computational error from planar triangular patches can limit in one percent, meeting the engineering application requirements.
基金the National Natural Science Foundation of China(No. 50979101)Shandong Province Natural Science Foundation (No. Q2008F05)
文摘Utilization of tidal current is becoming a focus of marine energy research and development field. In this paper, a new type of tidal current power generating device which was called flexible blade turbine was put forward. A scale model testing was carried out, and results show that the models performed as expected with good hydrodynamic characteristics. Based on analysis of the results, a scale model turbine with a rated power of 5 kW was constructed, which was an optimal scheme of the flexible blade turbine having higher coefficient of power and power generation capacity. Sea trials were carried out in the Zhaitang Island Channel to evaluate the performance of the turbine. Results show that the turbine performed well, generating the power predicted.
文摘Due to the presence of non-stationarities and discontinuities in the audio signal, segmentation and classification of audio signal is a really challenging task. Automatic music classification and annotation is still considered as a challenging task due to the difficulty of extracting and selecting the optimal audio features. Hence, this paper proposes an efficient approach for segmentation, feature extraction and classification of audio signals. Enhanced Mel Frequency Cepstral Coefficient (EMFCC)-Enhanced Power Normalized Cepstral Coefficients (EPNCC) based feature extraction is applied for the extraction of features from the audio signal. Then, multi-level classification is done to classify the audio signal as a musical or non-musical signal. The proposed approach achieves better performance in terms of precision, Normalized Mutual Information (NMI), F-score and entropy. The PNN classifier shows high False Rejection Rate (FRR), False Acceptance Rate (FAR), Genuine Acceptance rate (GAR), sensitivity, specificity and accuracy with respect to the number of classes.
文摘This research explores the potential of wind energy as a sustainable solution to environmental challenges by focussing on the deployment of vertical axis wind turbines in confined spaces,such as urban rooftops,ship decks,gas stations,etc.It aims to identify the optimal configuration for a cluster of three rotors by varying geometric parameters,assessing the omnidirectionality of the rotors,and using an artificial neural network as an optimization tool.The methodology involves 2D unsteady Reynolds-averaged Navier-Stokes computational fluid dynamics simulations followed by building and training an artificial neural network.The results indicate that the best cluster configuration,achieving a power coefficient of 0.2517,consists of a horizontal distance of 0.08D,vertical distance of 0.1D,and wind direction of 232°.The accuracy of the neural network is demonstrated by a mere 1.206%discrepancy with the computational analysis,thus highlighting its potential as a time-saving tool in the optimization process.Additionally,the average power coefficient across all wind directions was found to be 0.194,thus confirming the strong omnidirectional characteristics of the cluster.The study also notes a significant speed-up region between the rotors,which creates a low-pressure area,enhancing the power coefficient of the downstream rotor and demonstrating the advantages of this pressure-based turbine configuration.This comprehensive study establishes the efficacy of neural networks in optimizing wind turbine clusters,thus significantly expediting their design and development process.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2806300).
文摘The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based on an in-house solver.This solver is developed on an in-house platform HRAPIF based on the finite volume method(FVM)with the elemental velocity vector transformation(EVVT)approach.The present solver adopts the density-based method with a low Mach preconditioning technique.The turbulence models are the Spalart-Allmaras(SA)model and the k-ωshear stress transport(SST)model.The inviscid spatial discretization schemes are the third-order monotone upstream-centered schemes for conservation laws(MUSCL)scheme and the fifth-order modified weighted essentially non-oscillatory(WENO-Z)scheme.The power coefficient,instantaneous torque of blades,blade wake,and turbine wake are compared and analyzed at different tip speed ratios.The extensive analysis reveals that the density-based method can be applied in VAWT numerical simulation;the SST models perform better than the SA models in power coefficient prediction;the rotation-curvature correction is not necessary and the third-order MUSCL is enough for power coefficient prediction,the high-order WENO-Z scheme can capture more flow field details,the rotation-curvature correction and high-order WENO-Z scheme reduce the length of the velocity deficit region in the turbine wake.
基金financial support of the National Natural Science Foundation of China(Grant No.51765050)support from Inner Mongolia University of Technology+1 种基金Chinese Academy of SciencesHarbin University of technology。
文摘The aerodynamic forces and vortex characteristics of an H-type Vertical Axis Wind Turbine(VAWT)become complicated because of dynamic stall,particularly in the three-dimensional impact on the blade spanwise direction.This study focused on the evaluation of the aerodynamic performance and vortex characteristics of an H-type VAWT in the spanwise direction by numerical simulations and wind tunnel experiments.Pressure acting on the blade surface was obtained from multiport pressure measurement devices by wind tunnel.Meanwhile,the vortex field around different blade sections was investigated through numerical simulations.The stall behavior was analysed by comparing the results of numerical simulations and experiments.As a result,the tangential force of single blade was mainly contributed at the chordwise position of x/c≤0.4 c and the power of single blade was mainly contributed at the azimuthal angle range of 60°≤θ≤150°in the blade section position region of 0≤z/(H/2)≤0.7.At the section position of z/(H/2)=0.5,the initial flow separation was found at the suction side and progressed forward to the leading edge.With the increase of the tip speed ratios,the decreasing position of the averaged local power coefficient of each section was closer to the middle section of z/(H/2)=0,and the attenuation speed became faster.The power coefficient reductions at the blade section position of z/(H/2)=0.9 were 38.29%,46.78%and 56.42%when the tip speed ratios were 1.38,2.19 and 2.58,respectively.The results of this study provided a better understanding of the development of the performance characteristics and vortex characteristics of H-type VAWT.
基金This research was funded by Kementerian Riset dan Teknologi/Badan Riset dan Inovasi Nasional(Kemenristek/BRIN)through Publikasi Dasar Unggul Perguruan Tinggi(PDUPT)grant program,grant number NKB-197/UN2.RST/HKP.05.00/2021.
文摘Ocean current energy is a promising and reliable resource that offers sustainability and predictability in realizing green future needs.A diffuser-augmented horizontal-axis turbine is utilized to generate ocean current energy.A numerical study on the impact of diffuser angle variations on the power coefficient has been carried out in the previous research.To elucidate the fluid dynamics aspects and further validation of previous computational results,the experimental investigation on the optimal design of tidal turbine with 20.04°diffuser augmentation is presented in this study.The study was conducted in a flowing tank with a current velocity of 0.7 m/s.The maximum power coefficient of 20.04°is 0.436 experimentally,which is a little smaller than the numerical value.Moreover,to reinforce the 20.04°result,a diffuser with an angle of 10.43°was also manufactured and tested experimentally.The maximum power coefficient of 10.43°is 0.303 experimentally,which is 3%smaller than the numerical value.It was concluded that the numerical approach might be considered satisfactory and represent similar phenomena to the experimental investigation in an application for modelling of multi-objective optimization.
