In-situ magnetic inspection of the part fixture and the residual stress in micromilled hot-work tool steel

A magnetic method for the in-situ inspection of the combined effects of both, clamping force (CF) and the distribution of the surface residual stress (RS) on a face milled workpiece are presented. FE simulations have been conducted and evaluated, illustrating the impact of clamping on the workpiece surface deflection and thus, the machining accuracy. Furthermore, magnetic Barkhausen noise (MBN) signals were acquired on a hot-work tool steel workpiece after three different milling procedures: Face milling, one pass of micro-milling and 38 passes of micro-milling. Finally, the MBN signal on the unclamped workpiece was obtained. The MBN signal energy MBN_energy presented the highest values with the probe oriented in the pick (clamping) direction for all stages of milling process where the CF was applied. After unclamping the workpiece, the higher value of the MBN_energy was obtained with the probe oriented in feed direction of the milling processes revealing the true effect of the RS. These results were in agreement with the literature and confirmed by numerical simulations and X-ray diffraction based residual stress measurements.     

Particle swarm optimization based nonlinear active noise control under saturation nonlinearity

In this paper, a method is proposed to overcome the saturation non-linearity linked to the microphones and loudspeakers of active noise control (ANC) system. The reference microphone gets saturated when the acoustic noise at the source increases beyond the dynamic limits of the microphone. When the controller tries to drive the loudspeaker system beyond its dynamic limits, the saturation nonlinearity is also introduced into the system. The secondary path which is generally estimated with a low level auxiliary noise by a linear transfer function does not model such saturation nonlinearity. Therefore, the filtered-x least mean square (FXLMS) algorithm fails to perform when the noise level is increased. For alleviating the saturation nonlinearity effect a nonlinear functional expansion based ANC algorithm is proposed where the particle swarm optimization (PSO) algorithm is suitably applied to tune the parameters of a filter bank based functional link artificial neural network (FLANN) structure, named as PSO based nonlinear structure (PSO-NLS) algorithm. The proposed algorithm does not require any computation of secondary path estimate filtering unlike other conventional gradient based algorithms and hence has got computational advantage. The computer simulation experiments show its superior performance compared to the FXLMS, filtered-s LMS and genetic algorithms under saturation present at both at secondary and reference paths. The paper also includes a sensitivity analysis to study the effect of different parameters on ANC performance.     

Improving bit error rate under burst noise in OFDM power line communications

Noise in Power Line Communications is typically impulsive, with impulses being a fraction of the OFDM symbol length. Because of their large duration the impulse can also be called bursts. The short duration of the burst compared with the OFDM symbol length implies that there is a strong correlation between the noise at different carriers, given a determined burst position. The position can be determined using an estimate of the noise after a first demodulation. The high correlation is used to develop demodulators with a reduced bit error rate in comparison with conventional demodulators, so increasing the capacity. The demodulators use a smoothed estimate of the noise signal or a new metric for the distance based on the new correlation matrix. About half of the bit errors can be corrected in this way, corresponding to a 1 dB improvement in Signal Noise Ratio (SNR). How to split the OFDM symbol without increasing the overhead due to the circular prefix is also shown. Noise measurements in power lines are presented. These measurements are used in the simulations.     

居住区声环境调研分析--以上海市铁岭路28弄馨怡花园为例

噪声作为一种环境污染，与人们的日常生活质量息息相关。然而越来越多的噪声源，也带来了愈加严重的噪声问题。本文以居住区声音环境为出发点，结合实际调研，剖析出了住区内的噪声问题。并从建筑科学技术的角度，提出了一定的可行措施。     

Investigations for indications of deliberate blasting on the front bulkhead of the ro-ro ferry MV ESTONIA

The roll-on-roll-off passenger ferry MV ESTONIA sank during the night of 28 September 1994 in the Baltic Sea. In October 2000, divers recovered two palm-sized test pieces from the front bulkhead of the wreck. The investigators analysed these specimens to determine whether there were any indications of deliberate blasting. Since the wreck had been submerged for almost six years, it was clear that chemical traces would not be present on the surfaces of the test pieces. Therefore, the investigators performed comparative tests on shipbuilding steel to find a microstructural criterion that exclusively characterises a blast. The shipyard Jos. L. Meyer, Germany, had built the ESTONIA and supplied shipbuilding steel plates similar to that used for building the vessel in 1979/1980. The comparative tests comprised mechanical tests, shot peening tests and blasting tests using different explosives. Testing demonstrated that blasting always formed twinned ferrite grains in the microstructure over the whole cross-section of each of the 8 mm thick comparative plates. Although one of the original test pieces of the ESTONIA showed deformation twins, this was only confined up to 0.4 mm underneath the surfaces and not spread over the whole cross-section. Comparative shot peening tests produced the very same pattern of subsurface deformation twins. Therefore, the twins detected in the microsection of the test pieces of the ESTONIA wreck traced back to the shot peening process performed by the shipyard in 1979/1980 and not to a deliberate blast.     

基于Android系统的船舶行业移动办公的研究实现

基于现代网络技术的发展和移动终端的发展前景,为了更好地发展船舶行业,从而实现移动办公,本文采用了智能移动终端开发了一款查询软件,主要从用户的角度进行功能分析、权限设计、接口设计和测试。通过测试,可以看出该软件可以实现远程访问数据库,查询信息和收发信息。在一定程度上,这一功能的实现推进了移动办公的速度,同时加速了船舶行业的数字化进程,如果把该软件推广到其他行业,依然可以完成相似的功能,有更广阔的发展前景。     

A novel clipping technique for filtering FM signals embedded in intensive noise

A novel adaptive clipping technique for filtering a constant amplitude frequency modulated (FM) signal embedded in non-Gaussian noise is proposed. It is based on the analysis and processing of the estimate of probability density function of a FM signal realization. As a result, modifications of two robust estimators of FM signal amplitude are proposed. It is shown that these estimators can be used for Gaussian and non-Gaussian heavy-tail environments. The proposed clipping technique can exploit one or another obtained robust estimate of the signal amplitude for adaptive setting a threshold. Analysis of signal estimate accuracy for different noise environments is carried out. Comparative analysis of the obtained methods and known approaches based on scanning window nonlinear filtering and optimal robust L-DFT form is performed. It is demonstrated that the usage of clipping-based technique leads to the considerable improvement of the FM signal filtering efficiency in comparison to the aforementioned known approaches for different noise environments and a wide range of input SNR values.     

提高50Mn-C材质船用锻件质量的措施

本文主要介绍了50Mn-C材质船用锻件在生产过程中,有效控制了锻件草状波、性能不合格等问题的发生,提高了锻件一次探伤及性能的合格率。     

一种基于北斗信号的星载双站SAR成像频率同步的方法

针对基于北斗信号的星载双站SAR成像频率同步误差,提出一种在高噪声情况下新的频率同步方法。以北斗卫星直达波信号为同步信号源建立同步通道,使用单周期积累的扩频信号优化时频捕获算法得到较精确伪码时延,在码同步后使用已知时延的多周期积累的时频捕获算法获到频率误差。连续10次计算机仿真在SNR=-50db的高噪声环境下频率误差均不超过1.5Hz。     

一种Ka波段低相噪GaAs HBT压控振荡器

本文研究了一种采用GaAs HBT工艺实现的工作在Ka波段的压控振荡器。该振荡器采用共射级组态和对称式电容电感谐振腔结构以降低其相位噪声,采用π型反馈网络补偿180°相移。在片测试结果表明：偏离中心频率1 MHz处相位噪声为-96.47dBc/Hz,调谐范围为28.312到28.695GHz,在-6V电源电压下该振荡器直流功耗为18mA,振荡器芯片面积为0.7mm×0.7mm。