HHT法识别结构模态频率和阻尼比的改进

在应用EMD方法分解信号时,可能造成固有模态函数中不同的振动模态混合,从而淹没能量较小的振动模态而导致无法识别其模态参数。为了提高结构模态参数识别的精度和比较精确地识别低频模态及能量较小模态的参数,文章对结构响应信号进行带通滤波后再应用EMD方法进行分解,最后得到结构的各阶模态频率和阻尼比;仿真结果表明,该方法可以有效提高结构模态频率和阻尼比的识别精度。     

约束阻尼结构的振动分析及结构参数优化研究

为了准确获取约束阻尼复合结构(CLD)的振动特性,依据模态应变能(MSE)理论,针对黏弹性材料的温变和频变特性,基于大型通用有限元软件ANSYS及MATLAB进行了联合仿真,研究了CLD矩形薄板的振动特性。通过分析环境温度和阻尼层厚度等设计参数对结构固有频率和模态损耗因子的影响,建立了CLD设计参数的多目标优化模型,利用遗传优化算法对CLD结构参数进行了优化。分析结果表明:随着温度的升高,CLD结构的固有频率下降并趋于稳定;存在最佳温度点,使得CLD结构的模态损耗因子最大;在固有频率改变较小的情况下,通过结构参数的优化能够保证CLD结构具有低成本、高模态损耗因子等特性;联合仿真方法适用于阻尼复合结构振动特性研究,在阻尼减振技术中具有一定的理论和实用意义。     

考虑定子各向异性的永磁同步电机振动噪声优化

为了有效降低永磁同步电机的振动和噪声,在考虑定子各向异性建模的基础上,提出了一种通过定子结构模态规划来优化振动噪声的方法。首先分析了对定子模态频率较为敏感的各向异性材料参数,通过定子铁芯和总成的模态试验进行了参数识别;随后分析了电机在额定工况下的振动和噪声峰值来源,并且在电磁力二维分解的基础上提出了降低电机噪声的模态规划目标;最后分析了主要结构参数对定子模态频率的灵敏度,最终选择定子轭部厚度作为优化参数来实现模态频率的规划。研究结果表明:通过考虑定子材料的各向异性可以建立较为准确的定子模型,模态频率计算值与实测结果的误差都在4%以内;仿真优化后的电机振动峰值下降了58%,总体噪声功率级(A)降低了4.3dB。     

联合经验模态分解与二次时频分布的参数识别方法

提出了联合经验模态分解和二次时频分布进行模态参数识别的方法.将多自由度系统的响应信号用经验模态分解法分解为单频率响应的振动信号,进而计算模态频率和阻尼;由单频率响应信号的二次时频分布及其与其它质点响应信号的互二次时频分布的比值来识别模态振型,并对一多自由度的线性系统进行了计算,结果表明该方法能较好地识别结构的模态参数,且抗噪声强.     

卫星振动频率漂移现象与非线性参数识别

针对卫星振动实验中的频率漂移现象进行了分析.通过实验数据对比、等效线性化模拟和单自由度非线性模拟计算,对随振动实验载荷烈度增加而导致的频率降低、模态阻尼增大的现象作了定性解释,并对铝蜂窝板的非线性特性进行了振动实验及分析.根据谐波平衡法原理,对各级等效线性系统进行模态参数识别,进一步基于Duffing假设,对非线性刚度、阻尼系数进行了识别,并基于多自由度非线性系统理论进行了仿真检验.证明了实验现象与理论仿真的一致性.     

基于视觉测量的微陀螺振动系统线性度测试研究

为了测试分析微陀螺驱动模态振动系统的线性度,使驱动模态在静电驱动信号激励下产生稳定的线性振动,采用计算机视觉测量方法,使用高速摄像机获取微陀螺驱动模态在频率固定的调幅驱动电压信号激励下的振动位移响应视频图像;通过对运动时序图像的处理、目标识别与运动参数测量,获得振动位移的时变曲线.进一步得到驱动电压幅值变化与振动位移幅值的变化关系,分析结果表明,该方法便于对微陀螺振动系统的线性度进行测试分析.     

基于HVD和RDT的工作模态识别

应用希尔伯特振动分解(HVD)和随机减量技术(RDT)建立了环境激励下结构工作模态参数的识别方法。基于环境激励下结构的单点振动响应信号作为分析信号,应用希尔伯特振动分解将分析信号分解为若干个包含结构模态信息的信号,再利用随机减量技术提取自由衰减信号,应用最小二乘复指数法获得各阶模态频率和阻尼比。应用该方法对5自由度剪切模型以及12层混凝土框架地震台模型的顶点地震响应作为分析信号进行了结构工作模态参数的识别,并将识别结果与其他方法识别结果进行对比。结果表明该方法识别模态频率是可靠的;对平稳结构响应信号模态阻尼比的识别有好的精度,而对非平稳响应信号有较满意的精度。     

微谐振器纵向振动热弹性耦合分析

对微谐振器在纵向振动时的热弹性耦合进行分析,以悬臂梁为基础,在环境温度为300 K时,对热弹性本构方程进行数值求解,对在纵向振动过程中产生的温度、受热弹性耦合的影响产生的频率漂移、热弹性阻尼进行分析.分析结果发现,在纵向振动过程中,悬臂梁在前3阶振动模态下,温度变化量随着振动模态的升高而增大,在3阶振动模态时,温度变化量约为1.5 K;受热弹性耦合影响,频率漂移比首先随着梁长的增加而迅速增加,然后稳定在1.67×10-4附近;热弹性阻尼最大值约为1.0×10-4.然后,使用COMSOL Multiphysics软件对悬臂梁进行热弹性耦合仿真,并对数值结果进行验证.结果表明,仿真结果与理论计算结果相吻合.      

模态参数识别的LMD-BPF方法及其应用（英文）

鉴于准确识别结构模态参数存在的问题,提出了一种局部均值分解(LMD)-带通滤波(BPF)的模态参数识别方法。首先,将LMD方法用于位移仿真信号和压气机导向叶片测频信号的分解,分解得到的PF分量存在模态混叠现象;然后,使用LMD-BPF方法对位移仿真信号和导向叶片测频信号进行分解,成功实现了对各模态频率的准确分离;最后,使用LMD-BPF模态参数识别方法对位移仿真信号和导向叶片测频信号进行模态参数识别。识别的位移仿真信号4个模态频率和阻尼比与相应的理论值之间的最大误差分别为0.205%和2.387%,识别导向叶片的3种模态频率与测试模态频率之间的最大差别小于1.0%,识别的导向叶片的3种模态阻尼比与半功率带宽法识别的阻尼比,最大差别小于0.65%。模态参数识别的仿真分析和实验研究验证了该方法的有效性。     

一种利用起车过程瞬态振动响应的转子动力学参数识别方法

在分析转子系统起动过程的振动响应组成和振动响应信号中出现拍振现象成因的基础上,提出了一种基于起车过程瞬态振动响应的转子动力学参数时域识别方法。以转子系统起动过程中的失衡振动响应信号替代频域参数识别法中的正弦扫描激振响应信号,来识别转子系统固有频率和阻尼参数的时域信号,同时给出了参数估计原理,并利用仿真信号和实验测试的起车过程振动响应信号对转子系统的一阶固有频率和阻尼进行了计算。结果表明:所提出方法利用了转子起动过程的振动响应信号,其参数识别仅在时域内进行,不需要复杂的激振设备,具有计算简单、应用前景广阔等特点。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

橡胶颗粒沥青混合料低温抗裂性试验研究

以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

Quantitative trait loci （QTLs） for quality traits related to protein and starch in wheat

Quality traits in wheat （Triticum aestirum L.） were studied by quantitative trait locus （QTL） analysis in a recombinant inbred line （RIL） population, a set of 131 lines derived from Chuan 35050 × Shannong 483 cross （ChSh）. Grains from RILs were assayed for 21 quality traits related to protein and starch. A total of 35 putative QTLs for 19 traits with a single QTL explaining 7.99-40.52% of phenotypic variations were detected on 10 chromosomes, 1D, 2A, 2D, 3B, 3D, 5A, 6A, 6B, 6D, and 7B. The additive effects of 30 QTLs were positive, contributed by Chuan 35050, the remaining 5 QTLs were negative with the additive effect contributed by Shannong 483. For protein traits, 15 QTLs were obtained and most of them were located on chromosomes 1 D, 3B and 6D, while 20 QTLs for starch traits were detected and most of them were located on chromosomes 3D, 6B and 7B. Only 7 QTLs for protein and starch traits were co-located in three regions on chromosomes 1D, 2A and 2D. These protein and starch trait QTLs showed a distinct distribution pattern in certain regions and chromosomes. Twenty-two QTLs were clustered in 6 regions of 5 chromosomes. Two QTL clusters for protein traits were located on chromosomes 1D and 3B, respectively, three clusters for starch traits on chromosomes 3D, 6B and 7B, and one cluster including protein and starch traits on chromosome 1D.