共查询到16条相似文献,搜索用时 339 毫秒
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以液体中光击穿所激发声场为研究对象,在等离子体椭球模型的基础上,为方便理论计算,简化等离子体椭球模型,提出了等离子体椭圆盘模型,对光击穿所激发声场进行了理论研究.得到了等离子体椭圆盘辐射声场的声压规律,并利用椭圆坐标变换,依据马修函数特性和模态的正交性,求得了等离子体椭圆盘振动位移的解析表达式. 相似文献
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A method to generate a pulse sound source for acoustic tests based on nanosecond laser ablation with a plasma plume is discussed. Irradiating a solid surface with a laser beam expands a high-temperature plasma plume composed of free electrons, ionized atoms, etc. at a high velocity throughout ambient air. The shockwave generated by the plasma plume becomes the pulse sound source. A laser ablation sound source has two features. Because laser ablation is induced when the laser fluence reaches 1012–1014 W/m2, which is less than that for laser-induced breakdown (1015 W/m2), laser ablation can generate a lower sound pressure, and the sound source has a hemispherical radiation pattern on the surface where laser ablation is generated. Additionally, another feature is that laser-induced breakdown sound sources can fluctuate, whereas laser ablation sound sources do not because laser ablation is produced at a laser beam–irradiation point. We validate this laser ablation method for acoustic tests by comparing the measured and theoretical resonant frequencies of an impedance tube. 相似文献
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Summary The two-fluid model of liquid helium is generalized to the case that the superfluid fraction has a small entropy content.
We present theoretical arguments in favour of such a small superfluid entropy. In the generalized two-fluid model various
sound modes of He II are investigated. In a superleak carrying a persistent current the superfluid entropy leads to a new
sound mode which we call sixth sound. The relation between the sixth sound and the superfluid entropy is discussed in detail. 相似文献
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In this paper we present a simple theoretical model of how pulsed ultrasound is attenuated by the particles in a solid/liquid flow. The theoretical model is then used to predict the attenuation of sound, given the mass fraction, the density, and the size distribution of the solid particles. The model is verified experimentally for suspensions of 0-10% (by mass) Dolomite ((Ca,Mg)CO3) particles and water. The experimental results show that the attenuation of sound due to particles varies linearly with mass fraction, and that the proposed theoretical model can be used to predict this attenuation. In all experiments the transmitter and receiver array were clamped onto the pipe wall, thus providing a completely non-invasive and non-intrusive measurement technique. 相似文献
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N. F. Bunkin A. M. Lomonosov G. A. Lyakhov N. V. Suyazov S. I. Bakum L. M. Dorozhkin 《Acoustical Physics》2005,51(3):246-254
It is demonstrated that, in the case of optically probing the breakdown region, a pulsed signal is formed due to the acoustic pulses produced by the breakdown and collapse of the cavitation cavity. The measured dependence of the delay time of the second pulse on the hydrostatic pressure in the liquid and the pressure of saturated vapor agrees well with the theoretical dependence corresponding to the hydrodynamic model of the cavity. On the basis of the optical cavitation effect, a technique is proposed for a noncontact measurement of hydrostatic pressure in a liquid enclosed in a sealed cell. The range of applicability of the technique is evaluated. 相似文献
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This report presents a theoretical model of development of the post-arc gap breakdown in vacuum as a result of surface processes following cathode bombardment by energetic ions flowing from residual plasma after zero arc current. The most important surface processes for this model are sputtering and secondary electron emission. For a considerable group of metals, the sputtering yield Sr and secondary electron emission ?c can assume relatively high values when the ions have a high energy. Based on the ion flux from the plasma and the time of its flow as well as the ionization of sputtered atoms, a quantitative criterion for a breakdown will be derived. It has been proven that breakdown will occur if there is at least a minimum ion charge Qi which is dependent on the product of Sr · ?c. Qualitative consistency was also demonstrated between experimental results and the conclusion derived from our breakdown criterion. 相似文献