共查询到19条相似文献,搜索用时 156 毫秒
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在详细分析反射式激光多普勒原理的基础上,研究了高g值加速度传感器的冲击校准方法。该方法利用Hopkinson杆作为加载手段,利用差动式激光多普勒干涉仪来绝对复现冲击加速度的量值。针对高g值压阻加速度传感器SIMIT-AYZ-60k进行了一系列的校准试验,利用积分运算法和最小二乘法的组合从准动态条件下的校准数据得到了准静态条件下的传感器冲击灵敏度。试验表明,这种方法实现了利用脉宽有限的激励脉冲对固有频率在20kHz以上的高g值加速度传感器的校准,校准的不确定度可以满足冲击测试的工程需求。 相似文献
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精密仪器对工作环境的振动要求通常有微振、低频等特点,因此准确预测分析列车振动对精密仪器的影响具有一定的难度。结合北京地铁16号线规划通过北京大学西门的工程案例,首次在频域内采用两位校准法进行了远场低频微振动的定量预测研究。研究过程中,利用实测钢轨振动加速度时程计算得到模拟地铁列车荷载;建立北京地铁4号线校准模型,利用实测隧道壁和地表的振动响应对输入荷载、模型参数选择进行校核,确保了模型的预测精度;最后采用校核过的建模方法建立地铁16号线预测模型进行低频振动预测。结果表明:利用该方法得到的地铁列车振动荷载及振动预测模型可以较准确的进行远场低频振动响应预测;地铁16号线地铁采用钢弹簧浮置板后,北大新建实验楼外预测点10~20 Hz频段的振动满足仪器振动要求,但10 Hz以下频段的振动仅满足VC-C标准,需进行实验室或仪器隔振处理。 相似文献
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针对地震模拟试验常采用的开环迭代控制存在控制精度差的缺点,提出一种用于地震模拟的自适应控制方法。该方法不断识别系统的传递函数,来克服液压系统的时变性,获得较高的地震模拟波形复现精度。在此基础上,通过分析控制方法中预试验步骤存在的不足,实现试验方法改进,使得无需预试验步骤能直接进行正式试验,且首帧试验中的参考时域信号和控制时域信号相关系数较高。在浙江大学构建的振动台上进行若干典型地震波试验表明:改进后的试验方法在不进行预试验的情况下,首帧地震模拟试验获得75%以上的输入输出信号时域相关系数,同时能缩短试验时间;多帧地震模拟试验后,通过更新系统传递函数,地震模拟输入输出信号时域相关系数能稳定在95%以上。 相似文献
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在土木工程领域,GPS作为一种新的结构振动健康监测方法正受到广泛关注.以在建的广州新电视塔(塔高610 m)为研究背景,利用RTK-GPS测量技术对其在台风以及一般风荷载作用下的动态特性进行了监测试验,获得了电视塔核心筒顶部一个测点沿其短轴和长轴方向的动位移时程曲线,位移曲线的谱分析结果表明,利用动态GPS观测能精确地识别出高耸结构物的低阶振动频率,其识别结果同加速度计识别结果以及有限元模型分析结果吻合很好.研究结果表明,在高耸结构施工监控和健康监测中,应用动态GPS技术进行环境激励动态特性监控是一种有效的方法. 相似文献
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自由边界条件在计算方法中的数值表征是地震波模拟中的一个重要内容,表征的有效性直接关系到所得波场能否代表地表介质特性的真实响应。该文评估了交错网格有限差分法中5 种常用自由边界处理方法:直接法、应力镜像法、改进应力镜像法、横向各向同性介质替换法和声学边界替换法,并与有限元法模拟结果进行了对比,波形曲线直观比较及波幅比与相关系数定量比较显示横向各向同性介质替换法与有限法模拟结果一致性最好。进一步的层状介质模型弹性波数值模拟结果表明:横向各向同性介质替换法的精度和可靠性最高,能真实表征地表介质中的地震波传播。 相似文献
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为了研究挤淤爆破规律以及爆破地震波的传播特性,结合连云港连云新城示范区填海造地及基础设施建设项目的挤淤爆破工程实例,对挤淤爆破的全过程进行高速摄影录像和爆破地震波监测与分析。高速摄影再现了挤淤爆破过程中"水—淤泥—围堰"系统相互作用的运动过程,有效解释了挤淤爆破过程中预埋石料与淤泥置换的作用机理。利用实测的爆破地震波数据修正与地形地质条件有关的系数K和衰减系数α,获得了适于挤淤爆破过程中计算质点振动速度随距离衰减的Sadovsk计算公式,为有效预测类似工程中爆破地震波的传播规律特征提供了一种方法参考。挤淤爆破过程中测得的爆破地震波主振频率范围在8~50 Hz之内,说明淤泥介质对爆破地震波不同频率成分的传播具有选择性:高频地震波通过淤泥时产生大幅度的衰减,低频地震波通过淤泥后对建(构)筑物造成破坏。 相似文献
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非比例阻尼线性体系基于规范反应谱的CCQC法 总被引:5,自引:0,他引:5
根据平稳随机过程理论和抗震设计反应谱,对具有非比例阻尼特性的线性体系,给出了实数形式的复振型反应谱叠加法和复振型完全平方组合(CCQC)计算公式。式中除了包含一般CQC方法中振型间的位移相关系数以外,还包含了新的速度相关系数和位移-速度相关系数。公式推导按照与一般CQC法同样的原理和假定,形式也同样简洁、明了,易于工程设计人员掌握和使用。用实例分析对比了基于设计反应谱的CCQC法、CSRSS法及强迫解耦法,并以人工地震波作为地震输入,用逐步积分法对计算结果进行了验证。结果表明:提出的CCQC法比CSRSS法具有更好的精度。实例分析还表明,对于一般的强非比例阻尼结构,抗震设计规范中采用的强迫解耦方法也具有较好的精度。 相似文献
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We present a method for the independent calibration of Raman backscatter water-vapor lidar systems. Particular attention is given to the resolution of instrumental changes in the short and the long terms. The method reposes on the decomposition of the instrument function, which allows the lidar calibration coefficient to be re-expressed as the product of two terms, one describing the instrumental transmission and detection efficiency and the other describing the wavelength-dependent convolution of the Raman backscatter cross sections with the instrument function. The origins of changes in instrument response necessitate the experimental determination of the system detection efficiency. Two external light sources for calibration are assessed: zenith observation of diffuse sunlight and a xenon arc lamp. The results favor use of the diffuse-sunlight measurement but highlight the need for simultaneous sunphotometer measurements to constrain modeled aerosol optical properties. Quantum mechanical models of the Raman cross sections are described, and errors in determining the cross sections and their convolution with the instrument function are discussed in detail. The calibration coefficients deduced by using the independent method are compared with coefficients deduced from Vaisala H-Humicap radiosonde measurements. These results agree to within current calibration errors (15%, unconstrained aerosol parameters), and a change in calibration coefficient following instrument modification is reproduced satisfactorily. Results from modeling and intercomparison studies are extended to estimate the calibration accuracy and the precision of the diffuse-sunlight method with constrained modeled aerosol parameters. Changes in the calibration coefficient in the short and the long terms should be resolved to 4(6)% and 6(9)%, respectively, which is comparable or better than the precision of existing dependent methods of calibration. The reduction of the absolute calibration error remains an outstanding issue for all calibration methods. 相似文献
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提出一种快捷、高效且可靠的方法来确定海洋平台结构多维地震反应分析中地震动的最不利输入方向。该方法利用MATLAB中的小波分析工具箱可以方便且形象地显示地震动的局部时频特性,并根据平台结构的模态信息提取所关心响应的重要小波系数曲线从而获得地震动的有效输入能量时间过程,并判别地震动的最不利输入方向。以某一实际海洋平台为例,采用所提出的方法对四类场地的十组实际地震动不同角度输入情况进行了计算,同时利用ANSYS软件对平台的各种工况进行了时程反应分析以校核该方法的有效性;同时采用相同的方案对一组单自由度系统在某一地震动作用下进行了计算与校核。计算结果均表明:当结构对地震动方向较敏感时,在地震动以不同角度输入情况下,地震动有效输入能量最大的方向正是结构响应最大的方向,小波变换系数法在多维地震反应分析中具有很好的应用前景。 相似文献
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This paper describes a calibration method for acoustic emission and ultrasonic sensors that is effective from 1 kHz to 1 MHz. The method combines generalized ray theory and finite element analysis to model wave propagation at higher and lower frequencies, respectively. A ball impact is used as a calibration source, a thick aluminum plate is used as the test block, and hot glue is used as the couplant. We demonstrate this method on five commercial piezoelectric sensors: Physical Acoustics (PAC) R15a, PAC WSa, Panametrics V101, Panametrics V103, and Valpey-Fisher Pinducer. Our calibration results show that reflections and other wave phases can be more clearly identified with the less-resonant Panametrics sensors. The PAC sensors have the greatest sensitivity and are able to detect surface normal displacements at least down to 1 pm amplitude in the 100s of kHz frequency band. Aperture effect is minimized by the small size of the Pinducer. Our method focuses on the amplitude response of the sensors (phase is ignored) and extends the calibration to a frequency band that is lower than typical analyses. Low frequency information is useful for determining the seismic moment of a seismic source (analogous to the magnitude of an earthquake) and can increase the amount of information acquired in a single recording. 相似文献
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Two methods of particle sizing using an acoustic method are presented. The technique relies on the detection and measurement of elastic waves arising from impact of the particles with a small target plate. The acoustic impact signal, as measured from a high fidelity piezoelectric transducer, is characterised by the first wave arrival (compression wave) amplitude and risetime. A theoretical approach, based upon Hertzian impact theory and elastic wave propagation theory, is developed and used to determine the relationship between the impact dynamics of the particle and the acoustic signal. The first method of particle sizing relies upon amplitude measurements alone but requires accurate system calibration and full knowledge of the particle impact velocity, incident angle and coefficient of restitution. The velocity measurements were determined using a laser Doppler technique. The second approach for particle sizing incorporates risetime measurement and only depends very weakly upon the compression wave amplitude, thus minimizing the need for accurate absolute calibration. Knowledge of the impact velocity, incident angle, and coefficient of restitution were not required.Spherical particles of glass in the size range 35 to 140 µm diameter were dropped onto an aluminium target plate at an incident velocity of 8.1 m/s and angle to the surface normal of 0°, 40°, and 61°. The two acoustic methods were used to size the particles, and the results were compared to the particle size distributions obtained from video microscope measurements. The first sizing method undersized the smaller particles by 20% to 30% and oversized the larger ones by 5% to 10%. However, the second approach gave much smaller errors and consistently undersized all sizes of particle by just a few percent. This undersizing was understood in terms of some plasticity in the target that occurred during particle impact. 相似文献