A new particular solution method is proposed to indirectly calculate the strong singular integrals and free terms in conventional Helmholtz boundary integral equation (CBIE) and hyper-strong singular integrals in Burton-Miller boundary integral equation (BMBIE).For the acoustic problem of interior field,the particular solution satisfying Helmholtz governing equation is given,and the strong singular integral and free terms in CBIE are obtained indirectly.For an exterior field problem,however,calculation of its Cauchy principal value (CPV) for hyper-strong singular integral needs higher-order approximation of the kernel function through Taylor series expansion,which makes numerical implementation quite complex.In this paper,the particular solution satisfying Helmholtz governing equation and Sommerfeld radiation condition is given,and the hyper-strong singular integrals are obtained using a proposed new particular solution method.Also,the CPV of the strongly singular integral for an axisymmetric structure is derived.The high efficiency of the method is demonstrated with axisymmetric examples.The numerical results show that for the interior domain problem,the accuracy obtained by the proposed particular solution method is superior to that of directly calculating the strongly singular integral and the free term coefficient.Furthermore,the particular solution method can avoid calculating the free term with consideration of specific geometric information,and thus is of more general applicability.For an exterior domain problem,both methods provide almost the same accuracy,however,the proposed particular method can avoid expanding the kernel function to higher order and is easier to implement numerically. © 2019, Editorial Office of Chinese Journal of Computational Mechanics. All right reserved.

The dual reciprocity method(DRM) is extended to study the eigenvalue and eigenmode of thin-walled axisymmetric structures. First the displacement in the domain integral can be approximated by a set of radial basis functions and the domain integral can be converted to the boundary using DRM. Then the displacement and the traction can be expanded as Fourier series and integrate along the circumferential direction. The obtained boundary integral equation can be used for analysis of elastostatics of axisymmetric structure distributed body force and elastodynamics subject to asymmetric loading. The special case of the source point on the axis of symmetry is discussed in detail. New schemes are suggested for dealing with singular matrices for cases with and without body force respectively according to the degenerate form of the fundamental solution and the particular solution. For the thin walled structure, the sinh transformation is applied to improve the accuracy of evaluation of the nearly singular integrals. The developed project has been used to analyze elastostatics with body force and the free vibration of the thin axisymmetric structures. Numerical results indicate that the proposed method for dealing with singular matrices can effectively deal with the situation where the source point is on the axis of symmetry. and when the thickness ratio reaches 10-3, the relative error of the results can approach 10-3, which is better than those of FEM. © 2019, Chinese Journal of Theoretical and Applied Mechanics Press. All right reserved.

Personalized recommendation has important implications in raising online shopping efficiency and increasing product sales. There has been wide interest in finding ways to provide more efficient personalized recommendations. Most existing studies focus on how to improve the accuracy of the recommendation algorithms, or are more concerned on ways to increase consumer satisfaction. Unlike these studies, our study focuses on the process of decision-making, using long tail theory as a basis, to reveal the mechanisms involved in consumers' adoption of recommendations. This paper analyzes the effect of personalized recommendations from two angles: product sales and ratings, and tries to point out differences in consumer preferences between mainstream products and niche products, high rating products and low rating products, search products and experience products. The study verifies that consumers demand diversity in the recommended content, and also provides suggestions on how to better plan and operate a personalized recommendation system. © 2019 IEEE Computer Society. All rights reserved.

Task type may have influence on driving behavior in disasters, while personality trait may have moderating effects on driving behavior in different task types, there are few studies focus on it. In this paper, the research method of laboratory experiment and questionnaires is used to investigate the impact of altruistic task and self-interest task on driving behavior. And the personality trait is taken as the moderating variable to research the moderating effect of personality trait on driving behavior in different task types. The results show that, (1) Compared with self-interest task, altruistic task has critically significant influence on average acceleration, which indicates driver will improve the driving performance in altruistic task. (2) Personality trait of emotional stability has a moderating effect in the influence mechanism of task type on driving behavior. The results of this paper may provide scientific support to traffic evacuation and emergency management in disasters. © 2019 ACM.

Since communities are the basic units for public safety management, community risk prevention is of great significance. Community risk prevention must first identify community risks for people, things and management. This study analyzed the characteristics and causes of community risk to identify community risk prevention methods and how to monitor, control, predict, quickly detect and prevent community risk. Current international development trends for community risk prevention are reviewed to show that big data platforms are the key technology for community risk prevention. Finally, this paper describes the function, structure and construction of a large data platform for community risk prevention. This research on community risk prevention and big data platforms provides theoretical and technical support for community safety and security. © 2019, Tsinghua University Press. All right reserved.

Community risk prevention is the basis of urban safety. Research on the basic theoretical model for community risk prevention has important theoretical and practical significance. First of all, based on the triangle theory of public safety and security, this paper deeply analyzes the main factors of community risk prevention, including community risk bearing carrier, types of community risks and community emergency management. Then, according to safety management theory, this paper puts forward a triangle model for community risk prevention on the basis of analyzing the connotation of community risk prevention by theoretical thinking method. Finally, the connotation of triangle model is expounded in detail from three aspects: monitoring and control, forecasting and warning, comprehensive prevention, and this triangle model is verified with an instance. The study found that, the triangle model for community safety risk prevention emphasizes that, the community safety construction should be carried out comprehensively based on the whole cycle and the whole system of community risk response. Moreover, the model will provide effective guidance and support to understand community risk prevention and community safety construction. © 2019, Editorial Board of Journal of Systems Engineering Society of China. All right reserved.

This paper presents a scheme to evaluate the element integration accuracy for the boundary element method based on a singular geometric index to improve the accuracy of the final solution. The singular geometric index is defined as the ratio of the shortest distance from the source point to the integral element to the element length. For a discretized boundary mesh, the upper bound of the quadrature error is used to obtain the relationship between the singular geometric index and the element integration accuracy with the integrated accuracies of all the elements estimated from the node geometries. Furthermore, the maximum relative error of the solution which is a global precision index is estimated from the matrix error transfer formula. If the index is larger than a threshold, some of the element integrals are not accurate and should be corrected to improve the solution accuracy. This method uses the sinh transformation method to correct the element integrals of low accuracy elements. Numerical results show that this method can guarantee the accuracy of the overall stiffness matrix coefficient of the boundary element method and the final solution accuracy using only the geometric node information. This scheme does not need to change the original calculation, requires little additional computational cost, and can be easily implemented. © 2019, Tsinghua University Press. All right reserved.

提出了间接求解传统Helmholtz边界积分方程CBIE的强奇异积分和自由项系数,以及Burton-Miller边界积分方程BMBIE中的超强奇异积分的特解法。对于声场的内域问题,给出了满足Helmholtz控制方程的特解,间接求出了CBIE中的强奇异积分和自由项系数。对于声场外域对应的BMBIE中的超强奇异积分,按Guiggiani方法计算其柯西主值积分需要进行泰勒级数展开的高阶近似,公式繁复,实施困难。本文给出了满足Helmholtz控制方程和Sommerfeld散射条件的特解,提出了间接求出超强奇异积分的方法。推导了轴对称结构外场问题的强奇异积分中的柯西主值积分表达式,并通过轴对称问题算例证明了本文方法的高效性。数值结果表明,对于内域问题,采用本文特解法的计算结果优于直接求解强奇异积分和自由项系数的结果,且本文的特解法可避免针对具体几何信息计算自由项系数,因而具有更好的适用性。对于外域问题,两者精度相当,但本文的特解法可避免对核函数进行高阶泰勒级数展开,更易于数值实施。

该文提出基于几何指标来评估边界元法单元积分精度并对其进行修正来改善求解精度的方法。奇异性几何指标定义为源点到被积单元的最短距离与单元长度的比值。对于离散后的边界元法网格，利用求积误差上界公式得到各单元奇异性几何指标与积分精度的关系，通过该网格节点几何信息估算出全部单元的积分精度。通过矩阵的误差传递公式估算代数方程组求解结果的最大相对误差，将其作为全局精度指标。若该指标大于指定值，说明存在局部单元积分精度不足而影响结果精度的情况，必须对单元积分精度进行修正和提高。提出采用sinh变换法对精度不满足要求的单元积分进行修正。数值结果表明：该方法可以仅基于网格的几何信息，在不改变原计算流程和几乎不增加计算量的条件下，保证边界元法整体刚度矩阵系数精度和最终求解精度，且易于数值实施。

采用双互易法分析薄壁轴对称结构自由振动的特征频率以及特征模态.首先,采用径向基函数插值域积分里的位移,利用双互易法将域积分转化为子午面边界的积分.然后,将边界物理量、基本解和特解展开为傅里叶级数,沿环向积分后得到的边界积分方程可用于轴对称结构带体积力问题和受非对称载荷的动力学分析,其积分域为轴对称结构子午面边界上的线积分,进一步降低了问题的维度和离散的难度.文章详细探讨了源点处于对称轴的特殊情况,根据基本解和特解的退化形式,针对无体积力和有体积力分别给出了处理奇异矩阵的方案.对于薄壁结构,采用双曲正弦变换处理近奇异积分有效提高积分精度.最后将双互易法和双曲正弦变化应用于薄壁轴对称结构带体积力的静力学和自由振动分析.数值结果表明,文章提出的处理奇异矩阵的方法能够有效处理源点处于对称轴的情况;当圆筒厚高比为10~(-3),边界元计算的特征频率的相对误差为10~(-3),且优于有限元的结果.Free vibration analysis of thin-walled axisymmetric structures with Boundary Element Method The Dual Reciprocity Method(DRM) is extended to study the eigenvalue and eigenmode of thin-walled axisymmetric structures. First the displacement in the domain integral can be approximated by a set of radial basis functions and the domain integral can be converted to the boundary using DRM. Then the displacement and the traction can be expanded as Fourier series and integrate along the circumferential direction. The obtained boundary integral equation can be used for analysis of elastostatics of axisymmetric structure distributed body force and elastodynamics subject to asymmetric loading. The special case of the source point on the axis of symmetry is discussed in detail. New schemes are suggested for dealing with singular matrices for cases with and without body force respectively according to the degenerate form of the fundamental solution and the particular solution. For the thin walled structure, the sinh transformation is applied to improve the accuracy of evaluation of the nearly singular integrals. The developed project has been used to analyze elastostatics with body force and the free vibration of the thin axisymmetric structures. Numerical results indicate that the proposed method for dealing with singular matrices can effectively deal with the situation where the source point is on the axis of symmetry. and when the thickness ratio reaches 10^(-3), the relative error of the results can approach 10^(-3), which is better than those of FEM .