某型船钢拉应力与磁场关系试验

舰船磁场包括固定磁场和感应磁场,固定磁场是现有消磁勤务的主要目标.通过对船钢的拉伸试验,在船钢弹性形变范围内,研究其总磁场强度随拉应力的变化关系.由试验结果确定船钢的磁场强度初次发生显著变化时的拉力幅值.施力之前,通过试验从船钢的原始磁场中分离出感应磁场,然后任意选择一船钢总磁场发生显著变化的状态,在同样条件下做感应磁...     

一种计算内外域声场的简单源方法

使用赫尔霍兹积分方程计算声压的一个缺陷是积分变量过多导致的计算量过大."简单源"法将内域和外域的赫尔霍兹积分方程相互耦合,消去了多余积分变量.然而经典简单源法只能用于静止介质.为此,利用格林函数、势理论和运动介质波动方程,得到了求均匀流动介质条件下声压辐射的"简单源"边界积分式.与利用变换域中的赫尔霍兹积分方程求运动介质条件下声压的方法相比,新方法边界积分方程更加简洁和易于数值求解.基于新方法推导了有限长导管声场的预报模型.通过与标准问题的比较验证了新方法的有效性.     

隧道扩建合理开挖步序的研究

目前隧道的扩建施工技术仍然是借鉴新修隧道的施工方法,没有专门针对隧道扩建的施工方法,因此,需要积极探索适用于隧道扩建的新施工方法.以重庆市机场路拓宽改造工程的渝州隧道扩建为依托,从合理拱轴线的角度出发,确定隧道扩建的合理断面形式,再根据不同的拱跨和拱高来确定隧道扩挖合理施工步序,证明是一种可行的办法.它适用于类似重庆地...     

基于舰艇基线及DGPS的雷达实时标校方法

针对舰载雷达标校真值测量困难、精度不高的问题,设计了一种利用舰艇基线数据和高精度差分GPS测量信息进行基线修正、坐标变换,实时计算雷达真值并标校的方法,给出了真值计算模型。测试验证结果表明,该方法得到的真值精度高,使用方便、快捷,不受环境制约,且可同时对多部舰载雷达进行标校,有效提高了舰载雷达标校效率。     

基于弱多径覆盖的虚电路恢复策略研究

虚电路技术可以为Ad Hoc网络中的节点提供面向连接的服务。然而,由于拓扑动态性等特征,Ad Hoc网络中的虚电路容易断开,从而导致业务时延、时延抖动增大甚至通信中断等问题。为此文章提出了一种基于弱多径覆盖的虚电路恢复策略,通过将虚电路机制与弱多径覆盖多径策略相结合,可以有效地减少虚电路恢复时间和需要重新预约资源的节点的数量。理论分析和仿真结果表明了该方法的有效性。     

基于双谱切片小波包的雷达体制识别技术

根据机械扫描雷达、一维相控阵雷达和二维相控阵雷达扫描方式的差异,通过对3种体制雷达进行双谱分析、切片化处理以及小波包分解,提出了双谱切片小波包的概念,并根据此特征用支持向量机对不同体制的雷达进行识别.仿真结果表明:该方法在噪声占比为0～20％时,可分性好,并且在噪声占比增大时,通过该特征仍能对不同体制的雷达进行有效识别.     

Gas metal arc welding of high nitrogen stainless steel with Ar-N2-O2 ternary shielding gas

High nitrogen stainless steel with nitrogen content of 0.75％was welded by gas metal arc welding with Ar—N2-O2 ternary shielding gas. The effect of the ternary shielding gas on the retention and improvement of nitrogen content in the weld was identified. Surfacing test was conducted first to compare the ability of O2 and CO2 in prompting nitrogen dissolution. The nitrogen content of the surfacing metal with O2 is slightly higher than CO2. And then Ar—N2-O2 shielding gas was applied to weld high nitrogen stainless steel. After using N2-containing shielding gas, the nitrogen content of the weld was improved by 0.1 wt％. As N2 continued to increase, the increment of nitrogen content was not obvious, but the ferrite decreased from the top to the bottom. When the proportion of N2 reached 20％, a full austenitic weld was obtained and the tensile strength was improved by 8.7％. Combined with the results of surfacing test and welding test, it is concluded that the main effect of N2 is to inhibit the escape of nitrogen and suppress the ni-trogen diffusion from bottom to the top in the molten pool.     

Force chains based mesoscale simulation on the dynamic response of Al-PTFE granular composites

Force chains based mesoscale simulation is conducted to investigate the response behavior of aluminum-polytetrafluoroethylene (Al-PTFE) granular composites under a low-velocity impact. A two-dimensional model followed the randomly normal distribution of real Al particles size is developed. The dynamic compressive process of Al-PTFE composites with varied Al mass fraction is simulated and validated against the experiments. The results indicate that, force chains behavior governed by the number and the size of agglomerated Al particles, significantly affects the impact response of the material. The failure mode of the material evolves from shear failure of matrix to debonding failure of particles with increasing density. A high crack area of the material is critical mechanism to arouse the initiation re-action. The damage maintained by force chains during large plastic strain builds up more local stresses concentration to enhance a possible reaction performance. In addition, simulation is performed with identical mass fraction but various Al size distribution to explore the effects of size centralization and dispersion on the mechanical properties of materials. It is found that smaller sized Al particle of com-posites are more preferred than its bulky material in ultimate strength. Increasing dispersed degree is facilitated to create stable force chains in samples with comparable particle number. The simulation studies provide further insights into the plastic deformation, failure mechanism, and possible energy release capacity for Al-PTFE composites, which is helpful for further design and application of reactive materials.     

二次型极小化问题带误差的迭代算法

证明了二次型极小化问题带误差的迭代算法的有效性,所得结果推广了关于二次型极小化问题迭代的收敛性。     

论工程款和民工工资拖欠问题产生的原因及对策

文章就工程款和民工工资拖欠问题产生的原因及对策作了系统分析,认为从源头上抓起和管起、从环节上把关控制、从全过程监督和防范、从企业自身规避和降低风险、从法律上寻求保障和途径,来有效解决工程款和农民工工资的拖欠问题。