福州正大广场深基坑支护施工技术

本文结合福州正大广场工程实例，总结了深基坑支护的施工工艺、监测及处理一些常见问题的技术措施，可供广大工程技术人员参考。     

矿物掺合料混凝土力学性能与耐久性试验研究

在混凝土中添加矿物掺合料,可有效改善混凝土的力学性能和耐久性。以掺复合型掺合料混凝土的性能为主要研究对象,试验研究了掺复合型掺合料混凝土力学性能、耐久性的发展规律,并与基准混凝土各性能进行比较     

重庆地产大厦双塔连体结构设计

重庆地产大厦的主要功能为办公区及配套服务设施用房。主体分为南北两个塔楼,底部通过裙房连为整体,裙房楼板由于建筑功能要求多处开洞;层16以上通过一个5层的钢结构连廊连为一体。工程属于平面不规则,竖向不规则,复杂连接的超限高层建筑。重庆地产大厦工程采用框架-剪力墙结构体系,主体结构高度为92m。根据工程的特点,对重要结构构件制定了相应的性能目标。通过对多种计算程序分析结果的比对,依照结构的抗震性能目标,对结构薄弱部位采取了相应的抗震构造加强措施。同时对局部重要部位进行了补充验算,进一步验证了相应加强措施的效果。     

Surface topography and roughness in hole-making by helical milling

Helical milling is used to generate holes with a cutting tool traveling on a helical path into the workpiece in which the diameter of the hole can be adjusted through that of the helical path. Based on an improved Z-map model, a 3D surface topography simulation model is established to simulate the surface finish profile generated after a helical milling operation using a cylindrical end mill. The surface topography simulation model incorporates the effects of the relative motion between the cutting tool and the workpiece, in which the effect of the insert runout error of the cutting tool is considered. Furthermore, the roughness parameters are deduced from simulations of the 3D surface topography. The experimental result shows that the proposed simulation algorithm can predict well the surface roughness in a helical milling operation. The surface topography simulation model is used to study the effects of cutting conditions such as the tangential feedrate, the diameter of the cutting tool and the hole, the insert runout error of the cutting tool, as well as the revolution of the cutting tool around the axis of the hole on the surface finish profile. It is found that the surface quality can be improved by optimization of the cutting conditions. As a result, the proposed model will be helpful in determining the cutting conditions to meet surface finish requirements in helical milling operation.     

中国涂料用树脂的技术进展

中国涂料用树脂产销量快速发展，技术进步非常迅速，但在许多领域与国外企业差距明显，本文从人才、装置、技术趋势等方面讨论我国的涂料用树脂的现状与发展。     

基于频响函数的高速铣削颤振稳定域快速分析与研究

基于经典铣削加工颤振稳定域分析解,提出了直接使用刀尖点频响函数快速构建稳定域图形的方法,构造出的稳定域图形与经典分析解的仿真结果基本一致,而构造速度却提高了2—3数量级。使用该方法对一台装有三种不同刀具的加工中心的加工性能进行了评估并给出了优化的切削参数。     

Fast prediction of chatter stability lobe diagram for milling process using frequency response function or modal parameters

Prediction of chatter stability is important for planning and optimization of machining process in order to improve machining efficiency and reduce machining damage. Based on the classical analytical solution of chatter stability for milling process and in-depth analysis of the impact of modal parameters on the stability lobe diagram, a straight forward procedure for fast predicting stability lobe diagram directly using modal parameters of machining system was put forward. In consideration of the fact that the modal parameters of milling system can be estimated directly from the frequency response function using single DOF modal parameter estimation method, stability lobe diagram can be plotted directly using the tool tip’s frequency response function. The machining performances of a machining center with three different cutting tools were evaluated and the corresponding optimized cutting conditions were determined. The correctness of the proposed method was validated by good agreement of the predicted stability lobe diagram with that using the classical analytical method, and simulation results show that its calculation speed had been improved by 2–3 orders of magnitude. As a result, the proposed method of plotting stability lobe diagram using frequency response function can be utilized as an effective tool to select chatter-free cutting conditions in shop floor applications.     

L1-norm based null space discriminant analysis

Multimedia Tools and Applications - Null space based linear discriminant analysis (NSLDA) is a well-known feature extraction method, which can make use of the most discriminant information in the...     

综放面区段小煤柱合理尺寸确定研究

为了解决五阳煤矿综放面区段煤柱宽度过大问题,基于7803综放面工程地质条件,运用极限强度理论和弹塑性理论计算出了煤柱合理宽度分别为7.9,7.6 m;采用FLAC^3D软件模拟分析了7803综放面侧向支承压力,并确定其峰值在距离巷道16 m处,分析了不同煤柱宽度塑性区分布规律。综合考虑巷道支护难度、安全系数、资源采出率等客观因素,确定7803综放面合理煤柱宽度为8~10 m。     

基于GRA-SVM方法的煤与瓦斯突出预测模型研究

通过分析煤与瓦斯突出的主要影响因素,采取灰熵关联分析法进行关联度排序及特征向量的提取,利用支持向量机强大的模式识别能力,提出基于支持向量机的煤与瓦斯突出预测方法。以典型的煤与瓦斯突出样本为训练实例,利用Matlab平台下的Libsvm工具包建立预测模型,通过测试样本对模型进行验证,表明此模型具有较高的分类精度,适合于解决小样本的突出预测问题。