We report a linear-scaling random Green's function(rGF) method for large-scale electronic structure calculation. In this method, the rGF is defined on a set of random states and is efficiently calculated by projec...We report a linear-scaling random Green's function(rGF) method for large-scale electronic structure calculation. In this method, the rGF is defined on a set of random states and is efficiently calculated by projecting onto Krylov subspace. With the rGF method, the Fermi–Dirac operator can be obtained directly, avoiding the polynomial expansion to Fermi–Dirac function. To demonstrate the applicability, we implement the rGF method with the density-functional tight-binding method. It is shown that the Krylov subspace can maintain at small size for materials with different gaps at zero temperature, including H_(2)O and Si clusters. We find with a simple deflation technique that the rGF self-consistent calculation of H_(2)O clusters at T = 0 K can reach an error of~ 1 me V per H_(2)O molecule in total energy, compared to deterministic calculations. The rGF method provides an effective stochastic method for large-scale electronic structure simulation.展开更多
The resistivity difference between oil and gas layers and the water layers in low contrast tight sandstone reservoirs is subtle. Fluid identification and saturation calculation based on conventional logging methods ar...The resistivity difference between oil and gas layers and the water layers in low contrast tight sandstone reservoirs is subtle. Fluid identification and saturation calculation based on conventional logging methods are facing challenges in such reservoirs. In this paper, a new method is proposed for fluid identification and saturation calculation in low contrast tight sandstone reservoirs. First, a model for calculating apparent formation water resistivity is constructed, which takes into account the influence of shale on the resistivity calculation and avoids apparent formation water resistivity abnormal values.Based on the distribution of the apparent formation water resistivity obtained by the new model, the water spectrum is determined for fluid identification in low contrast tight sandstone reservoirs.Following this, according to the average, standard deviation, and endpoints of the water spectrum, a new four-parameter model for calculating reservoir oil and gas saturation is built. The methods proposed in this paper are applied to the low contrast tight sandstone reservoirs in the Q4 formation of the X53 block and X70 block in the south of Songliao Basin, China. The results show that the water spectrum method can effectively distinguish oil-water layers and water layers in the study area. The standard deviation of the water spectrum in the oil-water layer is generally greater than that in the water layer. The new four-parameter model yields more accurate oil and gas saturation. These findings verify the effectiveness of the proposed methods.展开更多
The method of two-dimensional viscous space-time conservation element and solution element (CE/SE) can be used to calculate the gas-liquid two-phase interior flow field in pulse detonation engine (PDE). In this paper,...The method of two-dimensional viscous space-time conservation element and solution element (CE/SE) can be used to calculate the gas-liquid two-phase interior flow field in pulse detonation engine (PDE). In this paper, the evolution of the detonation wave and the distribution of its physical parameters were analyzed. The numerical results show that the change of axial velocity of gas is the same as that of detonation pressure. The larger the liquid droplet radius is, the longer the time to get stable detonation wave is. The calculated results coincide with the experimented results better.展开更多
For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low vo...For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low voltage problems were highlighted in the rural power grid due to the characteristics of rural power grid. Using the distribution network flow calculation method, we evaluated the low voltage problems of the rural power grid which belongs to Chongqing Jiangbei Power Company. In addition, we collected the data of distribution transformers in electricity consumption peak period. Some practical management strategies were proposed by the analysis and evaluation of potential and appeared low voltage problems.展开更多
A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especia...A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a 3D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.展开更多
The origin and substance of the tlywheel moment calculation method of inertia mo ment of crane mechanism are set forth comprehensively and systematically in this paper, that is, the nucleus or the focus ofmoment of in...The origin and substance of the tlywheel moment calculation method of inertia mo ment of crane mechanism are set forth comprehensively and systematically in this paper, that is, the nucleus or the focus ofmoment of inertia calculation is the problem of calculating convertible tlywheelmoment. It is much better for the calculation of flywheel moment of loading move mass of lifting, traveling and rotating mechanism using the low of conservation of energy, the theorem of kinetic energyfor that of radius - changing mechanism, and the law of conservation of energy for that of all parts of gearing mechanism.展开更多
The bearing beams and the supporting beams under low velocity impact may be in four different strain stages of deformation depending on the impact intensity and beam structure strength.Based on the different judging c...The bearing beams and the supporting beams under low velocity impact may be in four different strain stages of deformation depending on the impact intensity and beam structure strength.Based on the different judging conditions of deformation stages,the corresponding calculation models are proposed,the calculation formulae for the determination of the impact force and the beam's lateral displacement are obtained.Calculation shows that the beam's total deflection is small when the flexibility of the supporting component is high and the effect of diminishing deflection disappears almost when the stiffness of the supporting component is high.展开更多
In order to implement the optimal design of the indoor thermal comfort based on the numerical modeling method, the numerical calculation platform is combined seamlessly with the data-processing platform, and an intera...In order to implement the optimal design of the indoor thermal comfort based on the numerical modeling method, the numerical calculation platform is combined seamlessly with the data-processing platform, and an interactive numerical calculation platform which includes the functions of numerical simulation and optimization is established. The artificial neural network （ANN） and the greedy strategy are introduced into the hill-climbing pattern heuristic search process, and the optimizing search direction can be predicted by using small samples; when searching along the direction using the greedy strategy, the optimal values can be quickly approached. Therefore, excessive external calling of the numerical modeling process can be avoided, and the optimization time is decreased obviously. The experimental results indicate that the satisfied output parameters of air conditioning can be quickly given out based on the interactive numerical calculation platform and the improved search method, and the optimization for indoor thermal comfort can be completed.展开更多
Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augment...Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augmented plane wave （FP-LAPW） method. The exchange correlation effects are included through the local density approximation （LDA ）, generalized gradient approximation （GGA） and modified Becke-Johnson （mBJ） exchange potential The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young＇s modulus and Poisson＇s ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states （DOS） and charge density show that this compound has an indirect energy band gap （M-F） with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of O-40eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.展开更多
Neutral particle energy spectra in the HT-7 tokamak are calculated by using the Monte Carlo method. It can reproduce the spectra measured in experiment. Differences of neutral particle energy spectra in higher and low...Neutral particle energy spectra in the HT-7 tokamak are calculated by using the Monte Carlo method. It can reproduce the spectra measured in experiment. Differences of neutral particle energy spectra in higher and lower electron density plasma are discussed. Results show that the ion temperature given by neutral particle energy spectra is lower than the real ion temperature, but the deviation is within 10% if the ion temperature is less than 800 eV and thecentral chord-averaged electron density does not exceed 3 ×1013 cm-3. But for ion temperature higher than 1000 eV at the central chord-averaged density limit up to 5 ×1013 cm-3, the neutral particle energy spectra can still give the ion temperature within 10% deviation.展开更多
To perform nuclear reactor simulations in a more realistic manner,the coupling scheme between neutronics and thermal-hydraulics was implemented in the HNET program for both steady-state and transient conditions.For si...To perform nuclear reactor simulations in a more realistic manner,the coupling scheme between neutronics and thermal-hydraulics was implemented in the HNET program for both steady-state and transient conditions.For simplicity,efficiency,and robustness,the matrixfree Newton/Krylov(MFNK)method was applied to the steady-state coupling calculation.In addition,the optimal perturbation size was adopted to further improve the convergence behavior of the MFNK.For the transient coupling simulation,the operator splitting method with a staggered time mesh was utilized to balance the computational cost and accuracy.Finally,VERA Problem 6 with power and boron perturbation and the NEACRP transient benchmark were simulated for analysis.The numerical results show that the MFNK method can outperform Picard iteration in terms of both efficiency and robustness for a wide range of problems.Furthermore,the reasonable agreement between the simulation results and the reference results for the NEACRP transient benchmark verifies the capability of predicting the behavior of the nuclear reactor.展开更多
In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre e...In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre expansion is widely used in discrete ordinates transport codes because of algebraic simplifications with spherical harmonics for the scattering source.However,negative cross sections caused by the finitely truncated expansion may give rise to a negative source and flux.A simple method is adopted,based on integrating functions of scattering moments,to evaluate anisotropy and convergence of expanded functions.A series of problems were designed with angular fluxes of different anisotropy,and numerical simulations were performed using the ARES transport code to study different treatments and algorithms for scattering.Results show that the diagonal transport approximation is more stable and obtains a similar accuracy with the extended approximation.A conservative fixup for the negative source could ensure particle balance and improve computational accuracy significantly for photon transport.The effect of anisotropic scattering is problem-dependent,and no distinct differences among various methods are observed for volume source problems with a continuous energy source.For beam source problems,flux results are sensitive to negative scattering functions,and strictly nonnegative cross sections need to be implemented.展开更多
By analyzing the existing average skidding distance formulac and the shape of the landing area, theauthors put forward that the average skidding distance is the shortest when the ratio of length and width is 1, and th...By analyzing the existing average skidding distance formulac and the shape of the landing area, theauthors put forward that the average skidding distance is the shortest when the ratio of length and width is 1, and the landing collectioll area is in proportion to of average geometrical skidding distance. The new models of calculating average distance are presented.展开更多
The paper presents a formal and practical approach to dependable algorithm development.First,starting from a formal specification based on the Eindhoven quantifier notation,a problem is regularly reduced to subproblem...The paper presents a formal and practical approach to dependable algorithm development.First,starting from a formal specification based on the Eindhoven quantifier notation,a problem is regularly reduced to subproblems with less complexity by using a concise set of calculation rules,the result of which establishes a recurrence-based algorithm.Second,a loop invariant is derived from the problem specification and recurrence,which certifies the transformation from the recurrence-based algorithm to one or more iterative programs.We demonstrate that our approach covers a number of classical algorithm design tactics,develops algorithmic programs together with their proof of correctness,and thus contributes fundamentally to the dependability of computer software.展开更多
The crystal structural parameters of Nd ^3＋-doped rare earth orthotantalate Gd x Lu 1 x TaO 4（x = 0.85） are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation sp...The crystal structural parameters of Nd ^3＋-doped rare earth orthotantalate Gd x Lu 1 x TaO 4（x = 0.85） are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation spectra at 77 K are analysed.The relativistic model of ab initio self-consistent DV-Xα method,which is applied to the cluster NdO 8 in Gd x Lu 1 x TaO 4,and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters.The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm 1.According to the crystal-field calculations,96 levels of Nd ^3＋ are assigned.Finally,the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd ^3＋：YAlO 3.The results indicate that the free-ion parameters are similar to those of the Nd3＋ in Gdx Lu1-x TaO4 and YAlO 3 hosts,and the crystal-field interaction of Nd^3＋ in Gdx Lu1-x TaO4 is stronger than that in YAlO 3.展开更多
According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears...According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears is researched, and computing formulas of power and rotation speed for equivalent gears are deduced. A numerical simulation of contact stress for non-circular gears has also been conducted based on the finite element method. By the comparison of fitting curves, the feasibility of using equivalent gears instead of non-circular gears to calculate the contact stress is testified.展开更多
A semi-relativistic distorted wave method has been developed to calculate the differential cross section(DCS)and Stokes parameters for electron impacting excitation of gold atom at 30 eV.At large angle(≥60°)our ...A semi-relativistic distorted wave method has been developed to calculate the differential cross section(DCS)and Stokes parameters for electron impacting excitation of gold atom at 30 eV.At large angle(≥60°)our DCS results are within the experimental error limit.At small angle(≤60°)our DCS results deviate a little from the experimental data.In the whole range our DCS data are roughly the same as those of complete relativistic distorted wave(RDW)method.The P1 and P2 calculated from our semi-relativistic method both in structure and tendency are similar to those of the complete RDW method.In particularly,-P3 calculated from two kinds of relativistic methods are almost the same in magnitude and structure.The difference between our results and those of complete RDW method may come from the neglecting direct relativistic of incident electron in our calculation.By comparing the results with those of experiment and complete RDW method it is deduced that the semi-relativistic distorted wave is a convenient and reliable method.展开更多
Parameter calculation and result storage, as two necessary steps in phase-field simulation play an important role in ensuring the accuracy of simulation results. A strategy of parameter calculation and result storage ...Parameter calculation and result storage, as two necessary steps in phase-field simulation play an important role in ensuring the accuracy of simulation results. A strategy of parameter calculation and result storage is presented for phase-field simulation in α-Mg dendrite growth of Mg-5-wt% Zn alloy under isothermal solidification. Based on the phase diagram and empirical formulas, key parameters of the phase-field model, such as equilibrium partition coefficient k, liquidus slope m, solutal diffusion coefficient in liquid Dl, and solutal diffusion coefficient in solid Ds, can be obtained.Both structured grid method and structured point method can be used to store simulation results, but using the latter method will reduce about 60% storage space and 37.5% storage time compared with the former. Finally, convergent simulation results of α-Mg dendrite growth are obtained and they are in good agreement with the experimental results about optical micrograph, which verify the accuracy of parameters and stability of storage method.展开更多
We investigate the geometries and energies of seven electronic states X-1A1, A1B1, a-3B1, B-1A2,b-3A2, C1B2 and c-3B2 of CF2 carbene using internally contracted multireference configuration interaction methods includi...We investigate the geometries and energies of seven electronic states X-1A1, A1B1, a-3B1, B-1A2,b-3A2, C1B2 and c-3B2 of CF2 carbene using internally contracted multireference configuration interaction methods including Davidson correction （icMRCIq-Q） with different basis sets aug-cc-pVXZ （X=T, Q, 5）. For the first time, the potential energy curves of electronic states of CF2 related icMRCI＋Q/aug-cc-pVTZ level. The ab initio results will and dynamics of electronic states of CF2 radical. to the lowest dissociation limit are calculated at the further increase our understanding of the structures展开更多
The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation....The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys,16-atom supercells with the 2 × 2 × 2 dimensions are used and the dependency of the lattice parameter, bulk modulus,electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary Tl_xGa_（1-x） As alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys.展开更多
基金financial support from the National Natural Science Foundation of China (Grant No. 12227901)the financial support from the National Natural Science Foundation of China (Grant Nos. 11974263 and 12174291)。
文摘We report a linear-scaling random Green's function(rGF) method for large-scale electronic structure calculation. In this method, the rGF is defined on a set of random states and is efficiently calculated by projecting onto Krylov subspace. With the rGF method, the Fermi–Dirac operator can be obtained directly, avoiding the polynomial expansion to Fermi–Dirac function. To demonstrate the applicability, we implement the rGF method with the density-functional tight-binding method. It is shown that the Krylov subspace can maintain at small size for materials with different gaps at zero temperature, including H_(2)O and Si clusters. We find with a simple deflation technique that the rGF self-consistent calculation of H_(2)O clusters at T = 0 K can reach an error of~ 1 me V per H_(2)O molecule in total energy, compared to deterministic calculations. The rGF method provides an effective stochastic method for large-scale electronic structure simulation.
基金funded by the National Natural Science Foundation of China (42174131)。
文摘The resistivity difference between oil and gas layers and the water layers in low contrast tight sandstone reservoirs is subtle. Fluid identification and saturation calculation based on conventional logging methods are facing challenges in such reservoirs. In this paper, a new method is proposed for fluid identification and saturation calculation in low contrast tight sandstone reservoirs. First, a model for calculating apparent formation water resistivity is constructed, which takes into account the influence of shale on the resistivity calculation and avoids apparent formation water resistivity abnormal values.Based on the distribution of the apparent formation water resistivity obtained by the new model, the water spectrum is determined for fluid identification in low contrast tight sandstone reservoirs.Following this, according to the average, standard deviation, and endpoints of the water spectrum, a new four-parameter model for calculating reservoir oil and gas saturation is built. The methods proposed in this paper are applied to the low contrast tight sandstone reservoirs in the Q4 formation of the X53 block and X70 block in the south of Songliao Basin, China. The results show that the water spectrum method can effectively distinguish oil-water layers and water layers in the study area. The standard deviation of the water spectrum in the oil-water layer is generally greater than that in the water layer. The new four-parameter model yields more accurate oil and gas saturation. These findings verify the effectiveness of the proposed methods.
基金Sponsored by the National Natural Science Foundation of China (10672080)
文摘The method of two-dimensional viscous space-time conservation element and solution element (CE/SE) can be used to calculate the gas-liquid two-phase interior flow field in pulse detonation engine (PDE). In this paper, the evolution of the detonation wave and the distribution of its physical parameters were analyzed. The numerical results show that the change of axial velocity of gas is the same as that of detonation pressure. The larger the liquid droplet radius is, the longer the time to get stable detonation wave is. The calculated results coincide with the experimented results better.
文摘For a long time, because of the lack of investment capital and enough attentions, the overall constructions of rural power grid were far behind than the urban power grid in Chongqing Jiangbei Power Company. The low voltage problems were highlighted in the rural power grid due to the characteristics of rural power grid. Using the distribution network flow calculation method, we evaluated the low voltage problems of the rural power grid which belongs to Chongqing Jiangbei Power Company. In addition, we collected the data of distribution transformers in electricity consumption peak period. Some practical management strategies were proposed by the analysis and evaluation of potential and appeared low voltage problems.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51137004,61427806 and 51577184the Equipment Development Project of Chinese Academy of Sciences under Grant No YZ201507
文摘A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a 3D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.
文摘The origin and substance of the tlywheel moment calculation method of inertia mo ment of crane mechanism are set forth comprehensively and systematically in this paper, that is, the nucleus or the focus ofmoment of inertia calculation is the problem of calculating convertible tlywheelmoment. It is much better for the calculation of flywheel moment of loading move mass of lifting, traveling and rotating mechanism using the low of conservation of energy, the theorem of kinetic energyfor that of radius - changing mechanism, and the law of conservation of energy for that of all parts of gearing mechanism.
基金the National Science Foundation of China(50578158)
文摘The bearing beams and the supporting beams under low velocity impact may be in four different strain stages of deformation depending on the impact intensity and beam structure strength.Based on the different judging conditions of deformation stages,the corresponding calculation models are proposed,the calculation formulae for the determination of the impact force and the beam's lateral displacement are obtained.Calculation shows that the beam's total deflection is small when the flexibility of the supporting component is high and the effect of diminishing deflection disappears almost when the stiffness of the supporting component is high.
基金Sponsored by the National Program"973"Project (2005CB623906)
文摘In order to implement the optimal design of the indoor thermal comfort based on the numerical modeling method, the numerical calculation platform is combined seamlessly with the data-processing platform, and an interactive numerical calculation platform which includes the functions of numerical simulation and optimization is established. The artificial neural network （ANN） and the greedy strategy are introduced into the hill-climbing pattern heuristic search process, and the optimizing search direction can be predicted by using small samples; when searching along the direction using the greedy strategy, the optimal values can be quickly approached. Therefore, excessive external calling of the numerical modeling process can be avoided, and the optimization time is decreased obviously. The experimental results indicate that the satisfied output parameters of air conditioning can be quickly given out based on the interactive numerical calculation platform and the improved search method, and the optimization for indoor thermal comfort can be completed.
基金Supported by UGC,New Delhi through UGC-BSR(JRF)fellowships
文摘Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augmented plane wave （FP-LAPW） method. The exchange correlation effects are included through the local density approximation （LDA ）, generalized gradient approximation （GGA） and modified Becke-Johnson （mBJ） exchange potential The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young＇s modulus and Poisson＇s ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states （DOS） and charge density show that this compound has an indirect energy band gap （M-F） with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of O-40eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.
文摘Neutral particle energy spectra in the HT-7 tokamak are calculated by using the Monte Carlo method. It can reproduce the spectra measured in experiment. Differences of neutral particle energy spectra in higher and lower electron density plasma are discussed. Results show that the ion temperature given by neutral particle energy spectra is lower than the real ion temperature, but the deviation is within 10% if the ion temperature is less than 800 eV and thecentral chord-averaged electron density does not exceed 3 ×1013 cm-3. But for ion temperature higher than 1000 eV at the central chord-averaged density limit up to 5 ×1013 cm-3, the neutral particle energy spectra can still give the ion temperature within 10% deviation.
基金supported by the China Postdoctoral Science Foundation(No.2021M703045)the National Natural Science Foundation of China(No.12075067)the National Key R&D Program of China(No.2018YFE0180900).
文摘To perform nuclear reactor simulations in a more realistic manner,the coupling scheme between neutronics and thermal-hydraulics was implemented in the HNET program for both steady-state and transient conditions.For simplicity,efficiency,and robustness,the matrixfree Newton/Krylov(MFNK)method was applied to the steady-state coupling calculation.In addition,the optimal perturbation size was adopted to further improve the convergence behavior of the MFNK.For the transient coupling simulation,the operator splitting method with a staggered time mesh was utilized to balance the computational cost and accuracy.Finally,VERA Problem 6 with power and boron perturbation and the NEACRP transient benchmark were simulated for analysis.The numerical results show that the MFNK method can outperform Picard iteration in terms of both efficiency and robustness for a wide range of problems.Furthermore,the reasonable agreement between the simulation results and the reference results for the NEACRP transient benchmark verifies the capability of predicting the behavior of the nuclear reactor.
基金supported by the National Natural Science Foundation of China(Nos.11505059,11575061)the Fundamental Research Funds for Central Universities(No.2017XS087)
文摘In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre expansion is widely used in discrete ordinates transport codes because of algebraic simplifications with spherical harmonics for the scattering source.However,negative cross sections caused by the finitely truncated expansion may give rise to a negative source and flux.A simple method is adopted,based on integrating functions of scattering moments,to evaluate anisotropy and convergence of expanded functions.A series of problems were designed with angular fluxes of different anisotropy,and numerical simulations were performed using the ARES transport code to study different treatments and algorithms for scattering.Results show that the diagonal transport approximation is more stable and obtains a similar accuracy with the extended approximation.A conservative fixup for the negative source could ensure particle balance and improve computational accuracy significantly for photon transport.The effect of anisotropic scattering is problem-dependent,and no distinct differences among various methods are observed for volume source problems with a continuous energy source.For beam source problems,flux results are sensitive to negative scattering functions,and strictly nonnegative cross sections need to be implemented.
文摘By analyzing the existing average skidding distance formulac and the shape of the landing area, theauthors put forward that the average skidding distance is the shortest when the ratio of length and width is 1, and the landing collectioll area is in proportion to of average geometrical skidding distance. The new models of calculating average distance are presented.
基金National Natural Science Foundation of China under Grant No. 60773054,60870002 and 61020106009Zhejiang Provincial Natural Science Foundation of China under Grant No. R1110679
文摘The paper presents a formal and practical approach to dependable algorithm development.First,starting from a formal specification based on the Eindhoven quantifier notation,a problem is regularly reduced to subproblems with less complexity by using a concise set of calculation rules,the result of which establishes a recurrence-based algorithm.Second,a loop invariant is derived from the problem specification and recurrence,which certifies the transformation from the recurrence-based algorithm to one or more iterative programs.We demonstrate that our approach covers a number of classical algorithm design tactics,develops algorithmic programs together with their proof of correctness,and thus contributes fundamentally to the dependability of computer software.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 90922003,51172236,and 50872135)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. YYYJ-1002)
文摘The crystal structural parameters of Nd ^3＋-doped rare earth orthotantalate Gd x Lu 1 x TaO 4（x = 0.85） are determined by applying the Rietveld refinement to its X-ray diffraction,and its emission and excitation spectra at 77 K are analysed.The relativistic model of ab initio self-consistent DV-Xα method,which is applied to the cluster NdO 8 in Gd x Lu 1 x TaO 4,and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters.The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm 1.According to the crystal-field calculations,96 levels of Nd ^3＋ are assigned.Finally,the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd ^3＋：YAlO 3.The results indicate that the free-ion parameters are similar to those of the Nd3＋ in Gdx Lu1-x TaO4 and YAlO 3 hosts,and the crystal-field interaction of Nd^3＋ in Gdx Lu1-x TaO4 is stronger than that in YAlO 3.
文摘According to Hertz theory, the difference of contact stress for non-circular gears and equivalent gears is compared in the paper, a calculating method of contact stress for non-circular gears by using equivalent gears is researched, and computing formulas of power and rotation speed for equivalent gears are deduced. A numerical simulation of contact stress for non-circular gears has also been conducted based on the finite element method. By the comparison of fitting curves, the feasibility of using equivalent gears instead of non-circular gears to calculate the contact stress is testified.
基金the National Natural Science Foundation of China under Grant No.19874037.
文摘A semi-relativistic distorted wave method has been developed to calculate the differential cross section(DCS)and Stokes parameters for electron impacting excitation of gold atom at 30 eV.At large angle(≥60°)our DCS results are within the experimental error limit.At small angle(≤60°)our DCS results deviate a little from the experimental data.In the whole range our DCS data are roughly the same as those of complete relativistic distorted wave(RDW)method.The P1 and P2 calculated from our semi-relativistic method both in structure and tendency are similar to those of the complete RDW method.In particularly,-P3 calculated from two kinds of relativistic methods are almost the same in magnitude and structure.The difference between our results and those of complete RDW method may come from the neglecting direct relativistic of incident electron in our calculation.By comparing the results with those of experiment and complete RDW method it is deduced that the semi-relativistic distorted wave is a convenient and reliable method.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 52074246, 52275390, 52205429, and 52201146)the National Defense Basic Scientific Research Program of China (Grant Nos. JCKY2020408B002 and WDZC2022-12)+1 种基金the Science and Technology Major Project of Shanxi Province, China (Grant Nos. 20191102008 and 20191102007)the Guiding Local Science and Technology Development Projects by the Central Government, China (Grant Nos. YDZJSX2022A025 and YDZJSX2021A027)。
文摘Parameter calculation and result storage, as two necessary steps in phase-field simulation play an important role in ensuring the accuracy of simulation results. A strategy of parameter calculation and result storage is presented for phase-field simulation in α-Mg dendrite growth of Mg-5-wt% Zn alloy under isothermal solidification. Based on the phase diagram and empirical formulas, key parameters of the phase-field model, such as equilibrium partition coefficient k, liquidus slope m, solutal diffusion coefficient in liquid Dl, and solutal diffusion coefficient in solid Ds, can be obtained.Both structured grid method and structured point method can be used to store simulation results, but using the latter method will reduce about 60% storage space and 37.5% storage time compared with the former. Finally, convergent simulation results of α-Mg dendrite growth are obtained and they are in good agreement with the experimental results about optical micrograph, which verify the accuracy of parameters and stability of storage method.
基金Supported by the 2014 Postdoctoral Sustentation Fund of Qingdao under Grant No 01020120517the Natural Science Foundation of Shandong Province under Grant No ZR2014AP001+1 种基金the National Natural Science Foundation of China under Grant No11447226the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents under Grant No 2015RCJJ015
文摘We investigate the geometries and energies of seven electronic states X-1A1, A1B1, a-3B1, B-1A2,b-3A2, C1B2 and c-3B2 of CF2 carbene using internally contracted multireference configuration interaction methods including Davidson correction （icMRCIq-Q） with different basis sets aug-cc-pVXZ （X=T, Q, 5）. For the first time, the potential energy curves of electronic states of CF2 related icMRCI＋Q/aug-cc-pVTZ level. The ab initio results will and dynamics of electronic states of CF2 radical. to the lowest dissociation limit are calculated at the further increase our understanding of the structures
文摘The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys,16-atom supercells with the 2 × 2 × 2 dimensions are used and the dependency of the lattice parameter, bulk modulus,electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary Tl_xGa_（1-x） As alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys.
