计算机辅助加工工件变形分析方法研究

为迅速、准确、合理地确定切削加工的工艺参数 ,将有限元方法、人工神经网络和遗传算法运用于计算机辅助加工工件变形分析中。通过合理的系统设计 ,实现了对工件切削加工变形量的准确预报和对加工参数的正确优化。实际生产证明 ,采用本方法优化确定加工参数 ,达到了预期的迅速、准确、合理的目标 ,有效地降低生产成本 ,提高生产率     

监测位移趋势分析确定滑坡稳定状态研究

针对滑坡预报缺少公认的临界速率,同时由于普遍存在的位移突变现象,易于造成大量误报的问题,提出了基于监测位移趋势分析的滑坡预报新思路。通过分析某工程滑坡的位移监测数据,得出了选取关键断面、观测预报点的一般规律。采用FLAC3D计算考虑流变状况下,不同安全系数所对应的滑坡位移趋势曲线,通过对比分析相应关键点监测位移趋势曲线,定量、全过程判定滑坡所处的稳定状态,为工程项目提供决策参考,避免了滑坡进一步发展,验证了滑坡观测预报点选择规律和对比监测、计算位移趋势曲线进行滑坡预报的可行性。     

Initiating a cooperative denuclearization effort with North Korea

ABSTRACT

As the United States and North Korea pursue negotiations on a “denuclearization” agreement, the two countries should consider initiating cooperative measures as a way to build confidence and encourage finalization of a complete agreement. Based on lessons from the initial engagements carried out under the Cooperative Threat Reduction (CTR) program in states of the former Soviet Union (FSU), initial cooperation should focus on safety and security, training, and infrastructure elimination. By offering to implement these initiatives now while negotiations are underway, the United States could gain additional insights into North Korean intentions. These early initiatives could be proposed without compromising the US maximum-pressure campaign on North Korea by using the current authorities of the CTR program and carefully designing specific exemptions that may be required for any agreed measures. If North Korea is truly interested in pursuing disarmament efforts, the initial cooperative projects would enable them to begin reaping potential benefits while negotiations continue with sanctions still in place. These initial proposals could also be expanded to include additional international partners such as Russia, China, South Korea, and Japan. Such programs and initiatives would support and supplement longer-term strategies to address North Korean weapons-of-mass-destruction challenges.     

超空泡体结构响应问题的有限元分析

超空泡体在水下高速航行时要受到冲击载荷的作用,这对其结构是不利的。用有限元方法分析计算了冲击载荷作用下超空泡体的结构响应,数值计算结果表明,超空泡体在一定频率下引起的结构响应非常显著,且随着频率的升高响应幅值有减小的趋势。     

Effect of silicon carbide and wire-mesh reinforcements in dissimilar grade aluminium explosive clad composites

Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight, superior corrosion resistance and higher specific properties. These composites reduce the weight of the aircraft, improve the fuel efficiency and enhance the maintenance duration. This study proposes the development of dissimilar grade aluminium (aluminium 1100-aluminium 5052) composites with different reinforcement’s viz., stainless steel wire-mesh, silicon carbide (SiC) powders and SiC powder interspersed wire-mesh, by explosive cladding technique. Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad, while SiC particles form a band on the interface. Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement. The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength, which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.     

低频域结构噪声问题数值解法

对形体不规则的物体 ,数值计算其结构噪声问题是获得解答的直接办法 .文中综述了结构噪声问题数值解法的基本思路 .首先介绍了数值求解的两个基本方法 :有限元法和边界元法的基本数学原理、操作方法及各自的局限性 ;其后描述了结构噪声耦合问题的数值计算公式的构造及运用不同数值方法构造求解公式的特点 ;针对边界元法构造的公式分析特征值问题的不足 ,给出了几种边界元法结构噪声特征值分析的方法 .文章结尾 ,提出了目前商业有限元软件分析噪声问题的不足及改进方向