共查询到19条相似文献,搜索用时 390 毫秒
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研究浅层土壤中声波耦合的地震波的传播特性, 用于声波探雷技术的机理分析. 根据浅层土壤具有孔隙度和可压缩性的特点, 利用非饱和三相孔隙介质中的地震波模型, 研究了土壤孔隙度、含水饱和度等参数对地震波传播特性的影响. 计算结果显示: 在给定的参数条件下, 地震波的传播速度和衰减系数均随频率的增加而增加; 纵波的传播速度随孔隙度的增加而减小, 横波的传播速度随孔隙度的增加而增加; 地震波的传播特性随含水饱和度的增加变化比较复杂. 通过对计算结果与已发表实验结果的比较分析, 讨论了解析方法的可行性, 为声-地震耦合机理及其在声波探雷研究中的应用提供了一定的理论基础.
关键词:
声-地震耦合
地震波
孔隙度
声波探雷 相似文献
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针对高中物理教科书中共振现象的演示实验装置存在着纰缪,在大学物理实验弹簧振子的受迫振动仪的基础上改进了共振实验演示装置。装置由T形支架下的弹簧和小球组成振动系统,通过比较浸没在水中的小球的固有周期和转动圆盘出现最大振幅时的周期,进而得到二者频率的关系,即共振产生的条件. 相似文献
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以往的研究大多考虑线性谐振子模型受频率涨落噪声的影响, 而当布朗粒子处于具有吸附能力的复杂环境时, 粒子质量也存在随机涨落. 因此, 本文研究具有质量及频率涨落两项噪声的二阶欠阻尼线性谐振子模型的随机共振现象. 利用Shapiro-Loginov公式和Laplace变换, 推导了系统响应一阶稳态矩及稳态响应振幅的解析表达式. 并根据稳态响应振幅的解析表达式, 建立了稳态响应振幅关于质量涨落噪声及频率涨落噪声各自的噪声强度能够诱导随机共振现象产生的充分必要条件. 仿真实验表明, 当系统参数满足本文所给出的充分必要条件要求时, 系统稳态响应振幅关于噪声强度的变化曲线具有明显的共振峰, 即此选定参数组合能够诱导系统产生随机共振现象. 相似文献
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法诺共振是物理体系中普遍存在的一种非对称共振现象,它最早起源于量子物理,其微观图像是原子谱线中窄的分离态与宽的连续态之间的相干干涉.本文利用经典力学体系中两个弹簧振子的耦合,使其中一个弹簧振子受到周期性外力的驱动,成功类比了量子力学中的法诺共振现象.通过分析每个弹簧振子的动力学方程,严格求解它们的振动公式,从而得到每个弹簧振子的振幅和位相与外部驱动力频率之间的关系.结果表明,耦合体系中受外力驱动的那个弹簧振子既可以发生非对称的法诺共振,又可以发生对称的洛仑兹共振,而另一个弹簧振子只能发生洛仑兹共振.本文的推导与分析能够使读者更好地理解法诺共振现象及其激发条件. 相似文献
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Brown运动中,环境分子的吸附能力使Brown粒子的质量存在涨落. 本文将这一质量涨落建模为对称双态噪声, 以考察其对系统共振行为的影响. 首先,利用Shapiro-Loginov公式和Laplace变换推导系统稳态响应振幅的解析表达式, 并根据相应数值结果, 研究系统的共振行为; 然后, 通过仿真实验对理论与实际的符合情况进行对比分析, 验证理论结果的可靠性及其对实际应用的指导意义. 理论结果和仿真实验均表明: 1) 系统稳态响应为频率与外部驱动相同的简谐振动; 2) 稳态响应振幅随外部驱动频率、振子质量、噪声强度及相关率的变化分别相应出现真实共振、参数诱导共振、随机共振现象; 3) 质量涨落噪声导致系统共振形式出现多样化现象, 包括单峰共振、单峰单谷共振、双峰共振等.
关键词:
质量涨落噪声
随机共振
双峰共振 相似文献
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A fluid-type floating vibration isolation system was developed based on anti-resonance mechanism. The mathematical model was derived for theoretical analysis. The system enables completely isolate vibration at any specific frequency, when the frequency of anti-resonance of the floating vibration isolation system is adjusted to the vibration frequency by tuning the added mass of flowing fluid. Since the approach only alters the inertial force of added mass rather than changing the entire system stiffness, the robustness of the system’s static stability remains during a tuning process, and the system can perform vibration isolation superbly at very low frequencies. A prototype of fluid-type floating vibration isolation system was designed, built and tested to validate the mathematical model. The experimental results illustrated a good agreement with the theoretical analysis. 相似文献
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研究了一种锥形剖面径向复合超声换能器。该换能器由一个等截面内金属圆环、一个轴向极化的压电陶瓷圆环和一个锥形剖面外金属圆环沿径向复合而成,且换能器的径向尺寸远大于高度。锥形剖面外金属圆环满足关系式h=h0r,h0为厚度变化常数。基于平面应力径向振动理论,推导了换能器的机电等效电路,得到了共振频率方程和反共振频率方程,进而研究了换能器的振动特性。并将理论计算的第1阶、第2阶径向共振频率和反共振频率与数值仿真结果相比较,二者结果一致。研究表明:锥形剖面换能器第1阶、第2阶径向共振频率、反共振频率、有效机电耦合系数不仅与换能器各部分的材料、径向几何尺寸有关,还与h0有关。h0越大,第1阶径向共振频率、反共振频率越大,有效机电耦合系数先增大后减小。与等截面相比,锥形剖面换能器沿径向向外辐射声波,辐射面积更大,辐射声功率更高,指向性更好。 相似文献
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The piezotransducers employed in high power ultrasound are composed of piezoelectric ceramics and metallic pieces. These transducers are mechanically pre-stressed in order to avoid the ceramic fractures when high voltage is applied under resonance. The resonance and anti-resonance frequencies are shifted depending on the level of applied mechanical pre-stressing. This paper discusses some causes of this shifting on a experimental study. The discussion takes into account the variations on characteristic parameters of the ceramics and the acoustic coupling between parts of the transducer. 相似文献
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提出了一种阶梯圆环径向振动压电超声换能器,根据力电类比原理建立了阶梯圆环及阶梯圆环换能器的径向振动等效电路,推导了阶梯圆环的径向共振频率方程和位移放大系数,在此基础上进一步推导了换能器的径向共振和反共振频率方程。通过理论推导和有限元仿真模拟分析了阶梯圆环压电超声换能器的径向振动性能。结果表明,增大阶梯圆环中内外环的径向厚度之比K1或减小轴向厚度之比K2,阶梯圆环的一阶径向共振频率减小,二阶径向共振频率增大;在二阶径向共振模式下,K1、K2值在一定范围内阶梯圆环可实现由内向外的径向位移振幅放大;随着压电陶瓷圆环的内半径增大,阶梯圆环压电超声换能器的一阶、二阶径向共振和反共振频率减小,二阶径向共振下的有效机电转换系数趋于零;增大阶梯圆环内环的外半径,换能器的一阶径向共振和反共振频率减小,二阶径向共振和反共振频率先增大后减小,理论推导与仿真模拟结果符合良好。本文研究结果为阶梯圆环压电超声换能器的工程应用提供理论参考。 相似文献
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The mechanical interaction between the induced seismic waves and landmines was analyzed according to acoustic-to-seismic coupling theory. And a geophone array based experimental system for landmine detection was developed. By modeling a compliant mine and the soil on top of the mine as a mass-spring system, analytic method was adopted to study the resonance mechanism of the system. A loudspeaker was employed as energy source to excite a swept sine tone over the soil. We also used a geophone array to measure the vibration velocity of the ground surface. In order to analysis the landmine effect on the surface vibration, the magnitude spectra curves of the measured velocity values on-and-off mine were plotted. The results showed that the data measured on mine is much bigger than that off target and the proposed system can be applied to further investigation of acoustic landmines detection. 相似文献
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本文对轴向极化压电陶瓷薄圆环的径向振动进行了研究,推出了其机电等效电路,得出了振子的共振和反共振频率方程并进行了实验验证。探讨了振子的共振和反共振频率与其材料和几何尺寸之间的依赖关系。 相似文献
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Jiang Du 《Applied Acoustics》2010,71(7):597-606
The compressed air experiments are conducted to investigate the whistle noise radiated from the oil separator component of refrigerant cycle system. Two types of insert edge and a height-adjustable oil separator model are adopted. The acoustic characteristic of flow through plain top insert edge is more likely to be broadband. Flow through ramp top insert edge would induce whistle peaks at Mach number higher than 0.1197 and the oil separator model works like an acoustic amplifier. Moreover, the Strouhal number jumps are captured inside oil separator model and two mechanisms are presented to clarify the phenomena. First, the whistle noise at Modes A1, A3, B1 and B3 is regarded as coupling of shear layer instability with resonance acoustic modes of oil separator model. Second, the whistle noise at Modes A2 and B2 is regarded to be the feedback loop of flow-acoustic interaction in fluctuated shear layer and defined as jet-cavity interaction tones. 相似文献
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The effect of self-induced acoustic transparency for transverse-longitudinal pulses propagating along an external magnetic field in a system of resonance paramagnetic impurities with the effective spin S=1/2 is theoretically investigated. In this case, the short-wave transverse component of the pulse causes quantum transitions, and the longitudinal long-wave component dynamically shifts the frequency of those transitions. When the speeds of the longitudinal and transverse acoustic waves in the crystal matrix are close to each other, both components interact in the mode of the long-short-wave resonance, which is described by a system of nonlinear integro-differential equations. It is shown that this interaction results, in particular, in the modulation of the carrier frequency of the circular-polarized component of the pulse. More precisely, the frequency in the neighborhood of the signal’s maximum is less than in the vicinity of its edges. Solutions in the form of traveling 2π-pulses are analyzed analytically and numerically. It is shown that there exist solutions that include a longitudinal component and cannot be reduced to well-known transverse solitons of the sinus-Gordon equation. 相似文献