基于Hilbert—Huang变换的振动信号特征提取

采用Hilbert-Huang变换,提取高压齿轮泵泵壳振动信号故障特征.该方法先对信号进行EMD分析和Hilbert变换,再提取信号Hilbert谱及谱熵.Hilbert谱刻画了信号的能量随时间和频率的变化规律,而谱熵刻画了信号能量分布的复杂性.分析结果表明,提取的特征有效地刻画了故障信号,为故障模式的识别奠定了基础.     

基于时频分析的CO2焊接电弧信息提取

利用Choi-Williams分布二次型时频分析方法研究CO2焊接过程所采集的电弧电压信号,获得信号的时频分布图。通过时频图像信息提取,进一步获得焊接过程特征信息,即信号的能量谱密度和瞬时频率估计。结果表明,利用Choi-Williams分布可以描述弧焊过程中电弧电压信号的时频能量分布。在时频分析基础上进行电弧信息提取,可以得到短路、断弧等物理现象的时间特征及瞬时频率信息。电弧特征信息的奇异点表现出明显不同的瞬时频率特性,以此界定电弧物理过程。     

基于零空间追踪算法的铣削功率信号分析

功率信号因获取简便、成本低等特点被广泛应用在切削过程监控中,因此对功率信号的特征进行深入分析非常必要。利用零空间追踪算法(Null Space Pursuit,NSP)分解铣削功率信号,分析分量及其能量分布的特征;通过计算能量分布与相关系数的相关程度,探究NSP的自适应性。分析结果表明,铣削功率信号的NSP分量包含大量有关铣削过程的信息,分量能量集中在前4阶;铣削参数恒定时,功率信号可分为静态分量和动态分量两部分;NSP分解铣削功率信号的自适应性良好。     

基于CEEMD的冲击回波分析方法研究

冲击回波法检测混凝土结构缺陷过程中由于存在面波和噪声干扰，反射层纵波难以从频谱特征直接识别出来。针对该问题，本研究将完备集成经验模态分解（CEEMD）方法引入冲击回波检测信号分析中，提出基于CEEMD冲击回波信号分析方法。通过对模拟和实验的冲击回波信号分析和研究，结果表明:CEEMD方法从冲击回波信号分解出的特征模态函数IMF1~IMF10，中间模态IMF5、IMF6的频谱反映出混凝土内部缺陷位置和板厚信息，据此频谱能准确确定内部夹层缺陷位置和混凝土板厚。CEEMD方法能分离面波和噪声干扰，可作为处理冲击回波信号的一种常规方法。     

高温后陶瓷纤维增强地聚物混凝土性能与声学损伤的关系

以矿渣和粉煤灰为原料,制备了陶瓷纤维增强地质聚合物混凝土(CFRGC)。通过抗压强度试验、超声波测试和裂缝宽度检测,引入小波变换理论,研究了不同温度、不同纤维掺量下CFRGC强度、波速、频谱特征的变化规律以及温度裂缝的开展演化情况。结果表明,高温后CFRGC内部结构受损,导致抗压强度降低,纵波波速和声阻抗减小,温度裂缝宽度增大;声波测试信号经小波分解后在各频段内的功率谱密度分布及能量随损伤的增大有较为明显的变化,某一频段内的信号能量对损伤比波速更敏感;纤维体积掺量为0.3%时,陶瓷纤维对地质聚合物混凝土的高温性能具有良好的改善效果。     

基于声信号处理的窨井盖盗毁检测方法

为遏制偷盗和毁坏窨井盖行为,提出一种利用声信号对窨井盖偷盗和毁坏进行检测的方法。因不同声信号的能量基于频率的分布存在差异,将窨井盖产生的振动声信号进行FFT变换,将变换后的频谱转化为能量谱,利用统计方法确定窨井盖振动声信号能量在频率上的特征分布区间和分布阈值,计算其他干扰声信号的20个最大能量点在该特征区间的概率分布数并与阈值对比,判断窨井盖的振动声是否是遭受盗毁时敲击引起的。实验结果显示:窨井盖敲击声的能量分布与其他声信号具有明显不同,其能量分布的特征频率为48～504 Hz,分布阈值为85%。该方法能够有效识别盗毁窨井盖声音,且在一定信噪比环境下具有较强鲁棒性。     

基于声发射信号能量衰减的混凝土材料损伤检测

混凝土结构受载损伤破裂过程伴随着声发射(AE)现象，其损伤的积累会影响AE信号能量的衰减效应。为进一步探究材料损伤和AE信号能量衰减之间的关联模式，进而利用能量衰减规律对混凝土损伤程度进行量化表征，对钢筋混凝土梁三点弯曲破坏的全过程进行了AE监测，并根据损伤定位结果实时计算了能量衰减系数，通过衰减系数的时程变化确定了混凝土损伤发展的三个阶段，提出了基于AE能量衰减系数的混凝土损伤评估方法。试验结果表明，该方法可实时量化评估混凝土试件的损伤状态，并对试件宏观裂纹出现后承载模式的转变进行预警。     

基于HHT的预应力钢筋混凝土梁断裂AE信号分析

针对混凝土材料损伤所产生的声发射信号复杂的特点,提出了基于Hilbert—Huang变换的分析混凝土声发射信号的新方法。利用全波形声发射技术记录了预应力混凝土梁在三点弯曲荷载试验下整个破坏过程的声发射信号,研究了声发射累计能量随时间变化的关系曲线,分析了梁在不同破坏阶段产生的实测声发射信号,获得了信号的Hilbert谱。通过与小波分析结果进行比较,显示出该方法具有处理精度高、自适应性强的特点,能有效地提取声发射信号中损伤的主要特征,为声发射信号处理提出了一种新的途径。     

电梯钢丝绳拉伸过程中的声发射特征

采用声发射技术对电梯钢丝绳拉伸过程进行监测,获取钢丝绳断丝信号,并对断丝信号进行参数分析和波形分析。试验结果表明:声发射检测技术能很好地定性辨识断丝信号。断丝信号具有高幅值高能量的特点,信号幅值在80~100 dB之间或绝对能量在2×10~6 mV·s以上的信号可定性认定为断丝信号。通过对具有这些特征的信号进行统计,可对钢丝绳断丝情况定量计算,从而推断出钢丝绳的剩余强度。钢丝绳断丝信号为突发型信号,对信号进行快速傅里叶变换可得知断丝信号的频率主要分布在0~220 kHz之间,且在25~50 kHz之间有明显的能量峰值。     

基于EEMD＿SVM的波纹管压浆超声检测

采用超声方法检测接收波纹管模型的回波信号,利用总体平均经验模态分解(EEMD)方法将信号分解成多个频带的本征模态分量(IMF);当波纹管内部出现脱浆缺陷时,回波信号在不同IMF内的能量分布会发生变化,将主要IMF分量的能量熵特征作为支持向量机(SVM)的输入向量,建立分类机制来区分波纹管结构。试验结果表明,文中提出的方法能有效地判断波纹管是否出现严重脱浆。     

Time–energy density analysis based on wavelet transform

Energy is an important physical variable in signal analysis. The distribution of energy with the change of time and frequency can show the characteristics of a signal. A time–energy density analysis approach based on wavelet transform is proposed in this paper. This method can analyze the energy distribution of signal with the change of time in different frequency bands. Simulation and practical application of the proposed method to roller bearing with faults show that the time–energy density analysis approach can extract the fault characteristics from vibration signal efficiently.     

Energy distribution and effective components analysis of 2n sequence pseudo-random signal

In order to extract usable harmonics from real 2ⁿ sequence pseudo-random data, a technical method is proposed. An equation for predicting the average amplitude of the main frequencies is proposed to guide the choice of signal type for different exploration tasks. By the threshold of the amplitude of the transmitted signal, a set of candidate frequencies are first selected. Then, by operating a spectrum envelope method at these candidate frequencies on received data, effective components in data are extracted. A frequency density calculation method is proposed based on a logical number summation method, to reasonably characterize the frequency density in different frequency bands. By applying this method to real data in Sichuan, China, with signal Type 13, 75 effective components are extracted, including both main frequencies and harmonics. The result suggests that the number of effective frequencies in the 2ⁿ sequence pseudo-random signal can be increased by extracting usable harmonics, without any additional fieldwork.     

钢丝绳声发射信号传播特性分析

针对钢丝绳断丝缺陷的在役动态监测需要,提出采用COMSOL软件对钢丝绳的声发射检测信号传播特性进行研究。首先建立钢丝绳结构模型,然后模拟不同频率、不同位置的断丝声发射信号在结构中的传播过程,获得不同位置的信号位移场及能量变化,最后根据导波理论,采用模态特征曲线结合小波变换分析不同类型声发射源的特征频率与模态成分。结果表明:声发射信号传播过程中,对于不同频率和激发方向的声发射源,其主要模态成分和特征频率的差异较大,可根据不同位置的时频分析结果,结合理论频散曲线判别声发射源信号的主要模态特征,并确定结构中声发射源的不同振动方向与中心频率。该研究结果可为钢丝绳损伤声发射检测提供理论参考依据。     

Stack imaging of spectral amplitudes based on impact-echo for flaw detection

The impact-echo method recently has drawn a remarkable amount of attention for nondestructive evaluation of defects in concrete structures. Extracting resonance frequencies responsible for the locations of reflectors, the depth and the presence of defects are estimated. So far, however, the technique has some limitations for practical applications. This is because there exist unresolved problems in the application of the impact-echo to concrete structures in service. Consequently, the method is studied theoretically on the basis of the elastodynamics and the signal analysis. In order to circumvent the difficulty to identify peak frequencies in the conventional procedure, a new procedure to evaluate defects in concrete is investigated, applying an imaging procedure. Thus, stack imaging of spectral amplitudes based on the impact-echo is developed. This procedure is applied to a prestressed concrete beam to classify a grouted duct and an ungrouted duct. The location and the presence of the ungrouted duct can be visually identified.     

谱峭度和Vold-kalman阶比跟踪在风电机组齿轮箱故障诊断中的应用

针对风电机组齿轮箱在时变工况下的振动信号具有非平稳特性,提出一种谱峭度和Vold-kalman阶比跟踪(Vold-Kalman Filter Based Order Tracking,VKF-OT)相结合的故障特征提取方法。以转频和啮合频率作为VKF-OT的提取频率,获得随转速变化的阶比信号,通过阶比信号复包络直接求两种频率分量的幅值、相位,经实验分析这种方法能保留齿轮箱的瞬变信息。而后计算两种频率分量的谱峭度,以最大谱峭度对应的频率带能量与原阶比信号总能量之比作为故障特征,最后采用高斯混合模型对风电机组齿轮箱在不同工况下的150组振动信号进行特征描述,运用最大贝叶斯分类器实现故障识别。故障识别率表明该方法可有效地识别任意时变工况下的齿轮早期局部微弱故障。     

基于小波的金属材料裂纹声发射信号特征

为对车载CNG气瓶因裂纹引起的安全事故进行控制,研究了气瓶裂纹声发射信号的特征。分析了气瓶失效的机理,提出在实验室条件下拉伸金属试件的方法,并对之进行模拟与声发射信号采集。通过对信号的分析显示出其时域与频域分析在特征分析时所具有的局限性,从而引出小波分析的信号分析方法,结果得出不同类型的声发射信号在相同频率段内所占的能量比例系数不同的结论。因此利用信号能量比例作为该信号的特征值,并在此基础上进行神经网络识别,取得了理想的结果,表明基于小波的金属材料信号特征能够对信号进行较好地表征。     

Non-destructive testing of high strength concrete using spectral analysis of surface waves

Non-destructive testing is essential in the inspection of alteration, repair and new construction in construction industry. Researchers are exploring the performance of non-destructive testing method using spectral analysis of surface waves (SASW) in concrete structures. The method consists of the generation, measurement and processing of dispersive surface waves. In SASW test, the surface of the media under consideration is subject to an impact using, for example, a 12-mm steel ball, to generate surface wave energy at various frequencies. Two vertical accelerometer receivers detect the energy transmitted through the testing media. By recording signals in digitized form using a data acquisition system and processing them, surface wave velocity can be obtained using a dispersion curve. This study is to focus on understanding of the applicability and limitations of the SASW method in a high strength concrete. This study is also to characterize the material property of early age high strength concrete emphasizing compressive strength using non-destructive testing methods. Three high strength concrete slabs of 600, 850 and 1100 kg/cm² compressive strengths were prepared together with cylinders from same batches. Cylinder tests were performed at the ages of 7, 14, 21 and 28 days after pouring concrete. Using the impact-echo method, the compression wave velocities were obtained based on different high strength concrete ages and compressive strengths. The equation to obtain the compressive strengths of high strength concrete has been developed using the obtained compression wave velocities (f′_c=1.083V_p−3816.1143). Using the method, the equation has also been developed to obtain the compressive strengths of high strength concrete based on the surface wave velocities (f′_c=0.253V_p+16.271). This study can be utilized in examining structural elements of high strength concrete structures and be applied in the integrity analysis of high strength concrete structures with a finite thickness.     

电弧故障信号的小波检测与分析

焊缝质量受多种因素影响,电弧的稳定性就是其中重要的因素之一。当电弧信号发生异常时,电弧能量就会发生变化,这种能量的变化将会给焊缝成形带来影响。为了分析电弧能量变化,采用小波变换技术,这种有别于传统的信号分析方法能够对信号的局部进行放大和缩小,适合于非平稳信号的分析,尤其是对信号故障点的分析,通过调节时间或频率轴的比例,可获得满意的信号分辨率。实验表明,小波分析法不仅能够判断信号质量,也为焊缝故障的诊断提供了一种新的方法。