The Fourier transform is very important to numerous applications in science and engineering. However, its usefulness is hampered by its computational expense. In this paper, in an attempt to develop a faster method fo...The Fourier transform is very important to numerous applications in science and engineering. However, its usefulness is hampered by its computational expense. In this paper, in an attempt to develop a faster method for computing Fourier transforms, the authors present parallel implementations of two new algorithms developed for the type IV Discrete Cosine Transform （DCT-IV） which support the new interleaved fast Fourier transform method. The authors discuss the realizations of their implementations using two paradigms. The first involved commodity equipment and the Message-Passing Interface （MPI） library. The second utilized the RapidMind development platform and the Cell Broadband Engine （BE） processor. These experiments indicate that the authors＇ rotation-based algorithm is preferable to their lifting-based algorithm on the platforms tested, with increased efficiency demonstrated by their MPI implementation for large data sets. Finally, the authors outline future work by discussing an architecture-oriented method for computing DCT-IVs which promises further optimization. The results indicate a promising fresh direction in the search for efficient ways to compute Fourier transforms.展开更多
Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive p...Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.展开更多
In order to provide power quality monitoring activities with metrological certification, a DAS （data acquisition system） has been designed, realized and characterized. The system allows acquisition on tri-phases plu...In order to provide power quality monitoring activities with metrological certification, a DAS （data acquisition system） has been designed, realized and characterized. The system allows acquisition on tri-phases plus neutral lines picking up 499 samples per period of the fundamental at 50 Hz. To ensure certified measurements, the system gets external certified time and voltage references. The system uses a FTDI Virtual Com Port Driver to communicate data over High Speed RS232 virtual interface and it does not need any advanced programming skill. The choice to use a virtual serial communication makes the data acquisition software portable over many platforms, regardless by the development environment and by the programming language. To test the proposed device some custom software have been written in many programming language （C^#, VB6, LabView, MatLab）, moreover in order to characterize the device the most common ADC （analog to digital converter） performing test have been applied.展开更多
With the intermediate flow states predicted by local two phase Riemann problem,the modified ghost fluid method(MGFM)and its variant(r GFM)have been widely employed to resolve the interface condition in the simulation ...With the intermediate flow states predicted by local two phase Riemann problem,the modified ghost fluid method(MGFM)and its variant(r GFM)have been widely employed to resolve the interface condition in the simulation of compressible multi-medium flows.In this work,the drawback of the construction procedure of local two phase Riemann problem in r GFM was investigated in detail,and a refined version of the construction procedure was specially developed to make the simulation of underwater explosion bubbles more accurate and robust.Beside the refined r GFM,the fast and accurate particle level set method was also adopted to achieve a more effective and computationally efficient capture of the evolving multi-medium interfaces during the simulation.To demonstrate the improvement brought by current refinement,several typical numerical examples of underwater explosion bubbles were performed with original r GFM and refined r GFM,respectively.The results indicate that,when compared with original r GFM,numerical oscillations were effectively removed with the proposed refinement.Accordingly,with present refined treatment of interface condition,a more accurate and robust simulation of underwater explosion bubbles was accomplished in this work.展开更多
We extend the recent formulation of the Ewald sum for electrostatics in a two-dimensionally periodic three-dimensional multi- atom layer or two-dimensional single-atom layer system with a rectangular periodic boundary...We extend the recent formulation of the Ewald sum for electrostatics in a two-dimensionally periodic three-dimensional multi- atom layer or two-dimensional single-atom layer system with a rectangular periodic boundary condition （J Chem Theory, Comput, 2014, 10： 534-542） to that with a parallelogrammic periodic boundary condition in general. Following the discussion of an efficient implementation of the formula, we suggest a simple setup of parameters using a relatively smaller screening factor and the associated larger real space cutoff distance to reach an optimized algorithm of an order N computational cost. The connection between the previous application of the Ewald sum to ionic crystal systems and the future application to mo- lecular self-assembly or disassembly systems on solid surfaces or at liquid-liquid interfaces ate illustrated to demonstrate the applicability of the present work to simulate the self-assembly process and to produce dynamical, structural and thermody- namic properties of experimental self-assembly systems of interest.展开更多
Measurements of topography at the segment of bifurcation between the South Channel and North Channel in the Yangtze Estuary were conducted, and a new type of subaqueous dune was discovered. This structure, newly defin...Measurements of topography at the segment of bifurcation between the South Channel and North Channel in the Yangtze Estuary were conducted, and a new type of subaqueous dune was discovered. This structure, newly defined as a catenary-bead dune, consists of a catenary dune and its associated elliptical pit bedform. Based on this finding, the nomenclature of "morphology of dune associated with accompanying bedform" is first proposed. The measured data indicate a mean height and wavelength of 1.29 m and 31.89 m, respectively; wavelength/height ratio(L/H) of 14 to 56; and elliptical pits of mean and maximum depth 0.98 m and 1.98 m, respectively. Flow information was obtained using an Acoustic Doppler Current Profile(ADCP), and the bed material components were gathered with a bottom sampler. The results show mean flood and ebb velocities of 0.27 and 0.78 m s?1, respectively, with shorter duration of flood tide than ebb tide. The silt, very fine sand, and fine sand fractions were within the ranges 21.6–23.4%, 28.2–32.2%, and 39.7–41.6%, respectively, revealing complex bed material composition. Water depth at the study site varies from 13 to 17 m. This finding will enrich the study of dunes and provide important data for geomorphological research. Moreover, the results are significant for engineering applications to estuaries.展开更多
Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dy...Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dynamics can be modeled by an interface motion. This paper is devoted to exhaustive analysis of the invariant solutions for a modified Kuramoto-Sivashinsky equation in two spatial and one temporal dimensions is presented. This nonlinear partial differential equation asymptotically characterizes near planar interfaces, which are marginally long-wave unstable. For this purpose, by applying the classical symmetry method for this model the classical symmetry operators are attained.Moreover, the structure of the Lie algebra of symmetries is discussed and the optimal system of subalgebras, which yields the preliminary classification of group invariant solutions is constructed. Mainly, the Lie invariants corresponding to the infinitesimal symmetry generators as well as associated similarity reduced equations are also pointed out. Furthermore,the nonclassical symmetries of this nonlinear PDE are also comprehensively investigated.展开更多
文摘The Fourier transform is very important to numerous applications in science and engineering. However, its usefulness is hampered by its computational expense. In this paper, in an attempt to develop a faster method for computing Fourier transforms, the authors present parallel implementations of two new algorithms developed for the type IV Discrete Cosine Transform （DCT-IV） which support the new interleaved fast Fourier transform method. The authors discuss the realizations of their implementations using two paradigms. The first involved commodity equipment and the Message-Passing Interface （MPI） library. The second utilized the RapidMind development platform and the Cell Broadband Engine （BE） processor. These experiments indicate that the authors＇ rotation-based algorithm is preferable to their lifting-based algorithm on the platforms tested, with increased efficiency demonstrated by their MPI implementation for large data sets. Finally, the authors outline future work by discussing an architecture-oriented method for computing DCT-IVs which promises further optimization. The results indicate a promising fresh direction in the search for efficient ways to compute Fourier transforms.
文摘Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.
文摘In order to provide power quality monitoring activities with metrological certification, a DAS （data acquisition system） has been designed, realized and characterized. The system allows acquisition on tri-phases plus neutral lines picking up 499 samples per period of the fundamental at 50 Hz. To ensure certified measurements, the system gets external certified time and voltage references. The system uses a FTDI Virtual Com Port Driver to communicate data over High Speed RS232 virtual interface and it does not need any advanced programming skill. The choice to use a virtual serial communication makes the data acquisition software portable over many platforms, regardless by the development environment and by the programming language. To test the proposed device some custom software have been written in many programming language （C^#, VB6, LabView, MatLab）, moreover in order to characterize the device the most common ADC （analog to digital converter） performing test have been applied.
基金supported by the National Natural Science Foundation of China(Grant Nos.041322062 and 51075004)the Foundation of Zhejiang Educational Committee(Grant No.529003+G21144)
文摘With the intermediate flow states predicted by local two phase Riemann problem,the modified ghost fluid method(MGFM)and its variant(r GFM)have been widely employed to resolve the interface condition in the simulation of compressible multi-medium flows.In this work,the drawback of the construction procedure of local two phase Riemann problem in r GFM was investigated in detail,and a refined version of the construction procedure was specially developed to make the simulation of underwater explosion bubbles more accurate and robust.Beside the refined r GFM,the fast and accurate particle level set method was also adopted to achieve a more effective and computationally efficient capture of the evolving multi-medium interfaces during the simulation.To demonstrate the improvement brought by current refinement,several typical numerical examples of underwater explosion bubbles were performed with original r GFM and refined r GFM,respectively.The results indicate that,when compared with original r GFM,numerical oscillations were effectively removed with the proposed refinement.Accordingly,with present refined treatment of interface condition,a more accurate and robust simulation of underwater explosion bubbles was accomplished in this work.
基金supported by the National Natural Science Foundation of China(91127015,21103063(Z.H.))
文摘We extend the recent formulation of the Ewald sum for electrostatics in a two-dimensionally periodic three-dimensional multi- atom layer or two-dimensional single-atom layer system with a rectangular periodic boundary condition （J Chem Theory, Comput, 2014, 10： 534-542） to that with a parallelogrammic periodic boundary condition in general. Following the discussion of an efficient implementation of the formula, we suggest a simple setup of parameters using a relatively smaller screening factor and the associated larger real space cutoff distance to reach an optimized algorithm of an order N computational cost. The connection between the previous application of the Ewald sum to ionic crystal systems and the future application to mo- lecular self-assembly or disassembly systems on solid surfaces or at liquid-liquid interfaces ate illustrated to demonstrate the applicability of the present work to simulate the self-assembly process and to produce dynamical, structural and thermody- namic properties of experimental self-assembly systems of interest.
基金the National Natural Science Foundation of China (Grant No. 41476075)
文摘Measurements of topography at the segment of bifurcation between the South Channel and North Channel in the Yangtze Estuary were conducted, and a new type of subaqueous dune was discovered. This structure, newly defined as a catenary-bead dune, consists of a catenary dune and its associated elliptical pit bedform. Based on this finding, the nomenclature of "morphology of dune associated with accompanying bedform" is first proposed. The measured data indicate a mean height and wavelength of 1.29 m and 31.89 m, respectively; wavelength/height ratio(L/H) of 14 to 56; and elliptical pits of mean and maximum depth 0.98 m and 1.98 m, respectively. Flow information was obtained using an Acoustic Doppler Current Profile(ADCP), and the bed material components were gathered with a bottom sampler. The results show mean flood and ebb velocities of 0.27 and 0.78 m s?1, respectively, with shorter duration of flood tide than ebb tide. The silt, very fine sand, and fine sand fractions were within the ranges 21.6–23.4%, 28.2–32.2%, and 39.7–41.6%, respectively, revealing complex bed material composition. Water depth at the study site varies from 13 to 17 m. This finding will enrich the study of dunes and provide important data for geomorphological research. Moreover, the results are significant for engineering applications to estuaries.
文摘Problems of thermodynamic phase transition originate inherently in solidification, combustion and various other significant fields. If the transition region among two locally stable phases is adequately narrow, the dynamics can be modeled by an interface motion. This paper is devoted to exhaustive analysis of the invariant solutions for a modified Kuramoto-Sivashinsky equation in two spatial and one temporal dimensions is presented. This nonlinear partial differential equation asymptotically characterizes near planar interfaces, which are marginally long-wave unstable. For this purpose, by applying the classical symmetry method for this model the classical symmetry operators are attained.Moreover, the structure of the Lie algebra of symmetries is discussed and the optimal system of subalgebras, which yields the preliminary classification of group invariant solutions is constructed. Mainly, the Lie invariants corresponding to the infinitesimal symmetry generators as well as associated similarity reduced equations are also pointed out. Furthermore,the nonclassical symmetries of this nonlinear PDE are also comprehensively investigated.
