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用有限场(FF)方法在4-31G+2p2d水平上研究了外加电场强度对尿素分子的偶极矩,极化率,一阶超极化率,二阶超极化率的影响。计算发现,要获得上述性质的稳定计算结果,电场强度需确定在0.001-0.004a.u.范围内。在此电强度范围内,与耦合微扰Hartree-Fork(CPHF)法的计算结果符合较好,且可有效地利用二级微扰方法(MP2)进行电子相关计算。 相似文献
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利用有限元程序ANSYS,开展潘宁离子俘获装置的电场模拟计算。基于电场数据,结合Runge_Kutta_Fehlberg方法进行潘宁装置在多种模式下的离子俘获过程模拟工作,得到了准确的离子俘获结果。并对实际条件下具有偏离理想情况电极分布的俘获装置进行了优化计算及电场分析,同样实现了离子俘获过程的准确模拟。有限元方法用于离子俘获装置的电场计算以及后续离子俘获过程模拟流程的建立,为类似的电势阱离子俘获装置建造运行提供有效的技术支持。 相似文献
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Effective response of nonlinear cylindrical coated composites under external AC and DC electric field 下载免费PDF全文
This paper uses the perturbation method to study effective response
of nonlinear cylindrical coated composites. Under the external AC
and DC electric field Ea(1 + sinωt), the
local potentials of composites at all harmonic frequencies are
induced. An effective nonlinear response to composite is given for
the cylindrical coated inclusions in the dilute limit. 相似文献
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为了提高对光学仪器中光机结构分析的精度,引入了非线性分析方法,用非线性有限元法研究了某平行光管主镜组件存在的非线性问题。介绍了产生结构非线性的主要来源,并在接触理论的基础上对主反射镜组件进行了合理的有限元建模。采用接触非线性分析方法对螺钉预紧时反射镜的响应及在自重和温度载荷作用下反射镜的变形进行了分析。将线性和非线性分析结果与实际结果进行了对比,结果表明,采用接触非线性分析方法对反射镜组件进行工程分析减小了分析误差。因此,在工程分析中,对某些接触部位采用非线性分析方法可以提高分析精度,得到的结果更加符合实际。 相似文献
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为了提高对光学仪器中光机结构分析的精度,引入了非线性分析方法,用非线性有限元法研究了某平行光管主镜组件存在的非线性问题。介绍了产生结构非线性的主要来源,并在接触理论的基础上对主反射镜组件进行了合理的有限元建模。采用接触非线性分析方法对螺钉预紧时反射镜的响应及在自重和温度载荷作用下反射镜的变形进行了分析。将线性和非线性分析结果与实际结果进行了对比,结果表明,采用接触非线性分析方法对反射镜组件进行工程分析减小了分析误差。因此,在工程分析中,对某些接触部位采用非线性分析方法可以提高分析精度,得到的结果更加符合实际。 相似文献
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针对具有多丝、多条带结构特征的用于核物理实验的气体探测器,采用节点组合法并利用有限元程序实现电场的计算。该方法构建宏观几何模型,去除了丝状、条带状结构,能够获得准确的计算结果。基于对该方法的验证,以MSU研制的SRIT-TPC为研究对象,获得了该装置的二维电场分布以及电子在探测器中的漂移模拟结果。计算结果与GARFIELD程序得到的结果一致。采用节点组合法的有限元方法可用于复杂探测器结构的电场计算,并用于后续的探测器模拟计算,能够极大提高探测器的模拟效率。该方法也可适用于复杂结构的三维电场计算。 相似文献
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We incorporated a cell-wise acoustic pressure gradient smoothing operation into the standard compatible finite element method and extended the smoothed finite element method (SFEM) for 2D acoustic problems. This enhancement was especially useful for dealing with the problem of an arbitrary shape with violent distortion elements. In this method, the domain integrals that involve shape function gradients can be converted into boundary integrals that involve only shape functions. Restrictions on the shape elements can be removed, and the problem domain can be discretized in more flexible ways. Numerical results showed that the proposed method achieved more accurate results and higher convergence rates than the corresponding finite element methods, even for violently distorted meshes. The most promising feature of SFEM is its insensitivity to mesh distortion. The superiority of the method is remarkable, especially when solving problems that have high wave numbers. Hence, SFEM can be beneficially applied in solving two-dimensional acoustic problems with severely distorted elements, which, in practice, have more foreground than regularity mesh. 相似文献
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A reduced surface electric field in an AlGaN/GaN high electron mobility transistor(HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas(2-DEG) channel as an electric field shaping layer.The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions.Compared with the HEMTs with conventional sourceconnected field plates and double field plates,the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge.By optimizing both the length of Mg-doped layer,L m,and the doping concentration,a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure,respectively.In a device with V GS = -5 V,L m = 1.5 μm,a peak Mg doping concentration of 8×10 17cm-3 and a drift region length of 10 μm,the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty. 相似文献
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A helix type slow wave structure filled with plasma is immersed in a strong
longitudinal magnetic field. Taking into account the effect of the plasma and the
dielectric, the system is separated radially into three regions. By means of
the sheath model and Maxwell equation, the distribution of the electromagnetic
field is established. Using the boundary conditions of each region, the dispersion
relation of the slow wave structure is derived. The trend of change for the radial
profile of the axial electric field is analysed respectively in different plasma
densities, plasma column radius and dielectric constant by numerical computation.
Some useful results are obtained on the basis of the discussion. 相似文献
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We have theoretically investigated the electronic properties and nonlinear optical rectification spectra of GaAs/AlGaAs anisotropic quantum ring, modelled by an outer ellipsis and an inner circle, in connection to the presence of a donor off-centre impurity, structural distortions and in-plane electric field. The one-electron energy spectrum and wave functions are found using the adiabatic approximation and the finite element method within the effective-mass model. The energy spectrum of concentric ring reveals an anomalous oscillatory behaviour in the region of relatively small values of the electric field (< 12?kV/cm) followed by linear Stark effect at higher field values. We showed that this unusual behaviour is strongly affected by the ratio of the outer/inner ring radii, the displacement of the inner circle (eccentricity) along the x or y axis and the impurity presence. The related nonlinear optical rectification spectra present maxima whose positions mirror this oscillatory behaviour and consequently can be used as an excellent tool to distinguish the presence of an impurity or the direction of the eccentricity. 相似文献
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A semi-analytical finite element method (SAFE) has been widely used for calculating dispersion curves and mode shapes of guided waves as well as transient waves in a bar like structures. Although guided wave inspection is often conducted for water-loaded plates and pipes, most of the SAFE techniques have not been extended to a plate with leaky media. This study describes leaky Lamb wave calculation with the SAFE. We formulated a new solution using a feature that a single Lamb wave mode generates a harmonic plane wave in leaky media. Dispersion curves obtained with the SAFE agreed well with the previous theoretical studies, which represents that the SAFE calculation was conducted with sufficient accuracy. Moreover, we discussed dispersion curves, attenuation curves, and displacement distributions for total transmission modes and leaky plate modes in a single side and both two side water-loaded plate. 相似文献
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In this paper a modifed continuous energy law was explored to investigate transport behavior in a gas metal arc welding(GMAW)system.The energy law equality at a discrete level for the GMAW system was derived by using the finite element scheme.The mass conservation and current density continuous equation with the penalty scheme was applied 10 improve the stability.According to the phase-field model coupled with the energy law preserving method,the GMAW model was discretized and a metal transfer process with a pulse current was simulated.It was found that the numerical solution agrees well with the data of the metal transfer process obtained by high-speed photography.Compared with the numerical solution of the volume of fuid model,which was widely studied in the GMAW system based on the finite element method Euler scheme,the energy law preserving method can provide better accuracy in predicting the shape evolution of the droplet and with a greater computing efficiency. 相似文献
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The authors studied the electric field behavior in the vicinity of a triple junction, composed by metal, vacuum and dielectric parts, using computational simulations. A bi-dimensional model was constructed using ANSYS MAXWELL to analyze the magnitude of the electric field as a function of the contact angles of the materials. The results showed that a field enhancement or reduction could occur in vacuum for certain contact angles. The influence of the dielectric permittivity was also investigated, and the conclusions showed that the maximum electric field enhancement is proportional to the dielectric permittivity. 相似文献
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超导块材和永磁铁相互作用形成悬浮系统。讨论了对超导块材进行网格划分的方法,利用矢量电位法建立了Nd-FeB永磁铁和超导体相互作用的电磁场数学方程。利用伽辽金法形成有限元线性方程组。求解过程中采用Kim模型作为迭代条件,解出超导体电流密度分布,并进行受力分析。 相似文献
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用有效折射率法和有限元法分析多量子阱条形光波导 总被引:3,自引:2,他引:3
本文提出了一种快速和精确分析多量子阱(MQW)条形光波导的新算法。它基于有效折射率法和有限元法的结合。首先,由等效的平面波导替换多量子阱条形结构,用有效折射率法从原来问题得到平面波导的折射率分布;然后,用有限元法计算等效结构中E_(mn)~x模和E_(mn)~y模的传播常数和场强分布。文中给出了任意阱数和不同宽度多量子阱的对称结构和不对称结构的结果。 相似文献