In this work it presents a strategy to obtain the ozone solubility in water by gradient step method. In this methodology, the ozone in mixture with oxygen is bubbling in a reactor with distilled water at 21℃ and pH 7...In this work it presents a strategy to obtain the ozone solubility in water by gradient step method. In this methodology, the ozone in mixture with oxygen is bubbling in a reactor with distilled water at 21℃ and pH 7. The ozone concentration on gas phase is continually increased after the saturation is reached. The method proposed is faster than conventional method （isocratic method）. The solubility from the gradient method is compared with that values obtained from correlations founded in the literature.展开更多
In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the elec...In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the electrical performances measured.The obtained results show that compared with untreated and single treated samples,the samples treated by step gradient modification significantly improve the flashover performance.According to experiment and simulation,the mechanism explanations are summarized as follows.First,it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode.Then,step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform.Furthermore,it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region.All these results can restrain surface discharge and increase the flashover voltage.The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.展开更多
M stepJacobi预处理共轭梯度法被用于求解源于自共轭椭圆偏微分方程的有限元或有限差分逼近的大型稀疏线性系统。这种方法的应用基础是相应的Jacobi迭代收敛。研究结果表明:偶数步的Jacobi预处理共轭梯度法较相邻奇数步的Jacobi预处理...M stepJacobi预处理共轭梯度法被用于求解源于自共轭椭圆偏微分方程的有限元或有限差分逼近的大型稀疏线性系统。这种方法的应用基础是相应的Jacobi迭代收敛。研究结果表明:偶数步的Jacobi预处理共轭梯度法较相邻奇数步的Jacobi预处理共轭梯度法更有效,步数越多,收敛速度越快。展开更多
Phononic materials with specific band-gap characteristics at desired frequency ranges are in great demand for vibration and noise isolation, elastic wave filters, and acoustic devices. The attenuation coefficient curv...Phononic materials with specific band-gap characteristics at desired frequency ranges are in great demand for vibration and noise isolation, elastic wave filters, and acoustic devices. The attenuation coefficient curve depicts both the frequency range of band gap and the attenuation of elastic wave, where the frequency ranges corresponding to the none-zero attenuation coefficients are band gaps. Therefore, the band-gap characteristics can be achieved through maximizing the attenuation coefficient at the corresponding frequency or within the corresponding frequency range. Because the attenuation coefficient curve is not smooth in the frequency domain, the gradient-based optimization methods cannot be directly used in the design optimization of phononic band-gap materials to achieve the maximum attenuation within the desired frequency range. To overcome this difficulty, the objective of maximizing the attenuation coefficient is transformed into maximizing its Cosine, and in this way, the objective function is smoothed and becomes differentiable. Based on this objective function, a novel gradient-based optimization approach is proposed to open the band gap at a prescribed frequency range and to further maximize the attenuation efficiency of the elastic wave at a specific frequency or within a prescribed frequency range. Numerical results demonstrate the effectiveness of the proposed gradient-based optimization method for enhancing the wave attenuation properties.展开更多
In this paper, multi-scale modeling for nanobeams with large deflection is conducted in the framework of the nonlocal strain gradient theory and the Euler-Bernoulli beam theory with exact bending curvature. The propos...In this paper, multi-scale modeling for nanobeams with large deflection is conducted in the framework of the nonlocal strain gradient theory and the Euler-Bernoulli beam theory with exact bending curvature. The proposed size-dependent nonlinear beam model incorporates structure-foundation interaction along with two small scale parameters which describe the stiffness-softening and stiffness-hardening size effects of nanomaterials, respectively. By applying Hamilton's principle, the motion equation and the associated boundary condition are derived. A two-step perturbation method is introduced to handle the deep postbuckling and nonlinear bending problems of nanobeams analytically. Afterwards, the influence of geometrical, material, and elastic foundation parameters on the nonlinear mechanical behaviors of nanobeams is discussed. Numerical results show that the stability and precision of the perturbation solutions can be guaranteed, and the two types of size effects become increasingly important as the slenderness ratio increases. Moreover, the in-plane conditions and the high-order nonlinear terms appearing in the bending curvature expression play an important role in the nonlinear behaviors of nanobeams as the maximum deflection increases.展开更多
为拓宽吸波频段,获得高效吸波材料,以纤维素纳米纤维(CNF)为骨架、二维过渡金属碳化物(Ti_(3)C_(2)T_(x))为导电填料,制备了三维多孔气凝胶吸波材料。通过扫描电镜及透射电镜、红外光谱仪、X射线光电子能谱及衍射仪、矢量网络分析仪表...为拓宽吸波频段,获得高效吸波材料,以纤维素纳米纤维(CNF)为骨架、二维过渡金属碳化物(Ti_(3)C_(2)T_(x))为导电填料,制备了三维多孔气凝胶吸波材料。通过扫描电镜及透射电镜、红外光谱仪、X射线光电子能谱及衍射仪、矢量网络分析仪表征了其结构与各项性能。结果表明:基于气凝胶的多孔结构及Ti_(3)C_(2)T_(x)的导电损耗,使得CNF/Ti_(3)C_(2)T_(x)复合气凝胶具有吸波效能,改变Ti_(3)C_(2)T_(x)含量及气凝胶厚度可调节吸波带宽和峰值。根据三维电磁仿真软件CST STUDIO SUITE仿真模拟结果,制备Ti_(3)C_(2)T_(x)质量分数依次为1%、25%、50%的CNF/Ti_(3)C_(2)T_(x)复合气凝胶,在电磁波入射方向按照特征阻抗从大到小叠层构建阻抗阶跃渐变的多层复合结构吸波材料,该材料具有更好的阻抗匹配和衰减损耗性能,反射损耗最小可达-15.9 dB,有效吸收带宽覆盖整个X波段。展开更多
文摘In this work it presents a strategy to obtain the ozone solubility in water by gradient step method. In this methodology, the ozone in mixture with oxygen is bubbling in a reactor with distilled water at 21℃ and pH 7. The ozone concentration on gas phase is continually increased after the saturation is reached. The method proposed is faster than conventional method （isocratic method）. The solubility from the gradient method is compared with that values obtained from correlations founded in the literature.
基金supported by National Natural Science Foundation of China(No.51777076)the Self-topic Fund of State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources(No.LAPS2019-21)。
文摘In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the electrical performances measured.The obtained results show that compared with untreated and single treated samples,the samples treated by step gradient modification significantly improve the flashover performance.According to experiment and simulation,the mechanism explanations are summarized as follows.First,it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode.Then,step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform.Furthermore,it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region.All these results can restrain surface discharge and increase the flashover voltage.The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.
基金Project supported by the National Natural Science Foundation of China(Nos.11502043,11332004 and 11402046)the Fundamental Research Funds for the Central Universities Of China(DUT15ZD101)the 111 Project(B14013)
文摘Phononic materials with specific band-gap characteristics at desired frequency ranges are in great demand for vibration and noise isolation, elastic wave filters, and acoustic devices. The attenuation coefficient curve depicts both the frequency range of band gap and the attenuation of elastic wave, where the frequency ranges corresponding to the none-zero attenuation coefficients are band gaps. Therefore, the band-gap characteristics can be achieved through maximizing the attenuation coefficient at the corresponding frequency or within the corresponding frequency range. Because the attenuation coefficient curve is not smooth in the frequency domain, the gradient-based optimization methods cannot be directly used in the design optimization of phononic band-gap materials to achieve the maximum attenuation within the desired frequency range. To overcome this difficulty, the objective of maximizing the attenuation coefficient is transformed into maximizing its Cosine, and in this way, the objective function is smoothed and becomes differentiable. Based on this objective function, a novel gradient-based optimization approach is proposed to open the band gap at a prescribed frequency range and to further maximize the attenuation efficiency of the elastic wave at a specific frequency or within a prescribed frequency range. Numerical results demonstrate the effectiveness of the proposed gradient-based optimization method for enhancing the wave attenuation properties.
基金supported by the National Natural Science Foundation of China(Nos.11672252 and11602204)the Fundamental Research Funds for the Central Universities,Southwest Jiaotong University(No.2682016CX096)
文摘In this paper, multi-scale modeling for nanobeams with large deflection is conducted in the framework of the nonlocal strain gradient theory and the Euler-Bernoulli beam theory with exact bending curvature. The proposed size-dependent nonlinear beam model incorporates structure-foundation interaction along with two small scale parameters which describe the stiffness-softening and stiffness-hardening size effects of nanomaterials, respectively. By applying Hamilton's principle, the motion equation and the associated boundary condition are derived. A two-step perturbation method is introduced to handle the deep postbuckling and nonlinear bending problems of nanobeams analytically. Afterwards, the influence of geometrical, material, and elastic foundation parameters on the nonlinear mechanical behaviors of nanobeams is discussed. Numerical results show that the stability and precision of the perturbation solutions can be guaranteed, and the two types of size effects become increasingly important as the slenderness ratio increases. Moreover, the in-plane conditions and the high-order nonlinear terms appearing in the bending curvature expression play an important role in the nonlinear behaviors of nanobeams as the maximum deflection increases.
文摘为拓宽吸波频段,获得高效吸波材料,以纤维素纳米纤维(CNF)为骨架、二维过渡金属碳化物(Ti_(3)C_(2)T_(x))为导电填料,制备了三维多孔气凝胶吸波材料。通过扫描电镜及透射电镜、红外光谱仪、X射线光电子能谱及衍射仪、矢量网络分析仪表征了其结构与各项性能。结果表明:基于气凝胶的多孔结构及Ti_(3)C_(2)T_(x)的导电损耗,使得CNF/Ti_(3)C_(2)T_(x)复合气凝胶具有吸波效能,改变Ti_(3)C_(2)T_(x)含量及气凝胶厚度可调节吸波带宽和峰值。根据三维电磁仿真软件CST STUDIO SUITE仿真模拟结果,制备Ti_(3)C_(2)T_(x)质量分数依次为1%、25%、50%的CNF/Ti_(3)C_(2)T_(x)复合气凝胶,在电磁波入射方向按照特征阻抗从大到小叠层构建阻抗阶跃渐变的多层复合结构吸波材料,该材料具有更好的阻抗匹配和衰减损耗性能,反射损耗最小可达-15.9 dB,有效吸收带宽覆盖整个X波段。
