Effects of the pump-circuit acoustic coupling on the blade-passing frequency perturbations

Centrifugal pumps are a source of pressure and flow rate perturbations in hydraulic pumping systems. In particular, a significant excitation is usually induced at the blade-passing frequency and harmonics as a consequence of the fluid-dynamic interaction between the rotor and the stator. The magnitude of this excitation is very dependent on the internal geometry of the pump and on its point of operation, but it depends also on the acoustic response of the hydraulic network to the perturbations. The induced and transmitted perturbations can be either amplified or reduced depending on the pump-circuit acoustic coupling, and thus they can lead to excessive levels of noise and vibration under certain conditions. The purpose of the present investigation is the theoretical and experimental characterization of the perturbations induced in a laboratory pumping system, as a function of the acoustic impedance of the pipelines. For different points of operation, the blade-passing frequency impedance is changed by varying the speed of rotation and, additionally, by modifying a closed side branch of the hydraulic system (that is, in the absence of net flow through it). For the theoretical calculations an acoustic model, based on matrix formulation, is applied to obtain the influence of different acoustic impedances of the suction side on the pressure fluctuations at the pump. Test measurements with a fast-response piezoelectric pressure transducer situated at the tongue region of the pump under the same system configurations confirm the significant effect of the pump-circuit acoustic coupling on the pressure perturbations.     

Self-excited transverse combustion instabilities in a high pressure lean premixed jet flame

An experimental investigation of self-excited combustion instabilities in a high pressure, lean premixed natural gas jet flame is presented. The combustor is designed with optical access and is instrumented with high frequency pressure transducers at multiple axial and circumferential locations. OH*-chemiluminescence measurements performed at a frequency of 50 kHz were temporally synchronized with the acoustic measurements recorded from the pressure transducer array during the test. Two representative test conditions are analyzed in detail: Flame 1 (F1) that presents longitudinal mode dynamics $(p^{\prime }/p_c=3\%)$ and Flame 2 (F2) that presents high amplitude transverse instabilities $(p^{\prime }/p_c=15\%)$. Singular Spectrum Analysis (SSA) and Dynamic Mode Decomposition (DMD) analysis indicate a strong correlation of both instabilities to flame-vortex interactions. Longitudinal mode instabilities are correlated with axisymmetric vortex shedding about the combustor axis that result in periodic axial variations in heat release at the 1L frequency. Transverse mode instabilities correspond to asymmetric vortex shedding pattern that drive transverse variations in heat release at the fundamental 1T frequency of the combustion chamber. The phase relationship of the flame emission intensity and the chamber head-end pressure measurement at the 1T frequency indicates presence of a non-stationary transverse mode that rotates about the chamber axis at 55 Hz.     

一种低频大功率调频声波束扫描发射系统

本文介绍一种中心工作频率在４．５ｋＨｚ发射电功率８ｋＷ的１６基元线列阵发射系统，并介绍了使用ＤＳＰ５６００１数字信号处理产生线性调频扫描波束发射信号及接收信号的频域处理和和一些测试结果。     

Measurement of temperature fluctuations and anomalous transport in the SINP tokamak

Temperature fluctuations have been measured in the edge region of the SINP tokamak. We find that these fluctuations have a comparatively high level (30–40%) and a broad spectrum. The temperature fluctuations show a quite high coherence with density and potential fluctuations and contribute considerably to the anomalous particle flux.     

高频聚焦超声声场和温度场的仿真研究*

为探究临床常用的7 MHz高频聚焦超声在多层生物组织中的声传播以及毫秒级时间内的生物传热规律问题,基于Westervelt方程和Pennes传热方程,使用有限元方法建立高频聚焦超声辐照多层组织的非线性热黏性声传播及传热模型。首先分析了线性模型和非线性模型之间的差异,然后在非线性模型下探究换能器的参数对声场和温度场的影响。仿真结果显示：在7 MHz频率下,当换能器输出声功率超过5 W时,声波传播的非线性效应不可忽视(p <0.05);当声功率从5 W增大到15 W时,非线性模型与线性模型预测的温度偏差从20%增加到34.703%;高频聚焦超声波的非线性行为比低频更加显著,基频能量向高次谐波转移的程度增大,声功率为10 W和15 W时4次谐波与基波之比分别达到7.33%和12.12%;高频换能器参数的改变对组织中声场和温度场分布的影响较大,换能器焦距从12 mm减小到11.2 mm,焦点处最高温度增加了77%。结果表明,7 MHz聚焦超声的非线性声传播需要考虑到4次谐波的影响。该文提出的多层组织非线性仿真模型可为高频聚焦超声换能器参数优化及制定安全、有效的术前治疗方案提供理论参考。     

Effect of coupling between passenger compartment and trunk of a car on coupled system natural frequencies using acoustic frequency response function

Conventional numerical techniques, used to study the acoustics of a car passenger cabin, treat the cabin as an isolated cavity excited by the cavity boundaries. Realistically, other cavity volumes such as the trunk communicate with the cabin through the holes in the parcel shelf of the car. An extended acoustic model of a car is formed by the cavity volumes of the passenger compartment and the trunk as well as air leakages through the holes provided for electrical devices and ventilation on the parcel shelf. In this study, the dynamic influence of air leakages between the passenger and trunk compartments on the first and second coupled system modes was investigated experimentally using acoustic frequency response function. The response to the acoustic excitation was measured for four different configurations of trim and holes of the parcel shelf. The natural frequencies of the first and second coupled system modes increased with increasing holes size with and without the trim of the parcel shelf. The experimental results were in good agreement with the reported results of coupling effects of double cavities connected by a neck. In the low frequency region since the wavelength is longer compared to the holes dimension, these holes act as point sources.     

高频聚焦换能器声场的激光测量法

本文描述了一种使用激光测振技术测量高频聚焦换能器声场布的方法，并给出了使用该方法对一种高频聚换能器进行测量的结果，通过理论计算对结果的正确性进行了验证。     

高频噪声干扰器对抗声自导鱼雷效果分析*

为提高潜艇对抗声自导鱼雷时机动方案的合理性,在高频噪声干扰器对抗声自导鱼雷原理分析的基础上,探讨了基于方位和能量的干扰效果分析方法。仿真分析了典型态势下噪声干扰器对主被动声自导鱼雷的干扰区域,给出了干扰扇面和自导距离缩减率随雷目距离的变化规律。结果表明,干扰噪声谱级比潜艇辐射噪声高出一定值(如15 dB)时,对被动声自导鱼雷具有较好的干扰效果,将宽带噪声功率集中到窄带中进行频率瞄准干扰,可大幅提高对抗主动声自导鱼雷的效果。该文的研究方法可为潜艇规避声自导鱼雷的机动方案提供依据。     

Analytical and numerical calculations of optimum design frequency for focused ultrasound therapy and acoustic radiation force

Focused ultrasound therapy relies on acoustic power absorption by tissue. The stronger the absorption the higher the temperature increase is. However, strong acoustic absorption also means faster attenuation and limited penetration depth. Hence, there is a trade-off between heat generation efficacy and penetration depth. In this paper, we formulated the acoustic power absorption as a function of frequency and attenuation coefficient, and defined two figures of merit to measure the power absorption: spatial peak of the acoustic power absorption density, and the acoustic power absorbed within the focal area. Then, we derived “rule of thumb” expressions for the optimum frequencies that maximized these figures of merit given the target depth and homogeneous tissue type. We also formulated a method to calculate the optimum frequency for inhomogeneous tissue given the tissue composition for situations where the tissue structure can be assumed to be made of parallel layers of homogeneous tissue. We checked the validity of the rules using linear acoustic field simulations. For a one-dimensional array of 4 cm acoustic aperture, and for a two-dimensional array of 4 × 4 cm² acoustic aperture, we found that the power absorbed within the focal area is maximized at 0.86 MHz, and 0.79 MHz, respectively, when the target depth is 4 cm in muscle tissue. The rules on the other hand predicted the optimum frequencies for acoustic power absorption as 0.9 MHz and 0.86 MHz, respectively for the 1D and 2D array case, which are within 6% and 9% of the field simulation results. Because radiation force generated by an acoustic wave in a lossy propagation medium is approximately proportional to the acoustic power absorption, these rules can be used to maximize acoustic radiation force generated in tissue as well.     

高频调制电弧的声学特性及其细化焊缝组织的应用

以等离子体电弧作为声源,利用高频电流进行调制,激发电弧可以产生超声波。研究了高频调制电弧的激发特性和声场特征,发现调制电弧所发射超声波在激励频段内呈现平坦的幅频特性,激励电流是影响电弧超声强度的主要因素,声压幅值与电弧等离子体流力的变化量成正比,声场呈现轴向强两侧弱的特征。同时介绍了利用电弧激发超声波在改善焊缝组织性能方面的应用。     

A new method of flame temperature measurement utilizing the acoustic emissions from laser-induced plasmas

The optical emissions from laser-induced plasmas have been successfully exploited for elemental composition measurements in flames; however, the information from the accompanying plasma-generated acoustic emissions has not been well utilized. In this study, we investigated the influence of flame temperature and composition on the acoustic emissions from laser-induced plasmas in an ethylene-air premixed flame. The acoustic emissions are sensitive to temperature, and a negative correlation can be established. The effect of composition on acoustic emissions was found to be second order compared to that of temperature. Based on these findings, we introduce acoustic-based laser-induced breakdown thermometry (LIBT). A statistical analysis was performed to mitigate the bias introduced by anomalous extreme values. The spatial and temporal resolution of LIBT were also analyzed to demonstrate its potential to perform simultaneous composition and temperature measurements when used along with laser induced breakdown spectroscopy (LIBS). Finally, the temperature distribution in an ethylene-air counter-flow diffusion flame was measured; and the results compared favorably with numerical results.     

铑铁电阻温度计低温性能测试

针对一种商用铑铁电阻温度计进行了低温下的工作性能研究。对传感器进行了常温和液氮温度下的两点校正,校正结果验证了厂商提供的电阻温度拟合关系式。另外,还对该铑铁传感器连续进行了三次热循环实验。实验前,传感器的液氮温度稳定性优于20mK,而在实验后其温度稳定性优于30mK,满足工程应用的要求。所有实验结果表明,该铑铁电阻温度计性能可靠稳定,为其在超导磁体系统中的进一步应用提供了基础。     

高频线阵的研制

本文描述了一种用于侧扫声纳的高频线列阵，该阵由中心频率分别为１００ＫＨｚ和５００ＫＨｚ的两部分构成。由于采用阵元加权排列和充分利用有效工作面积，该阵具有尖锐的主瓣，较高的主、副瓣比和较高的发射、接受灵敏度（１００ＫＨｚ时分别为１７４ｄＢ，５００ＫＨｚ时分另为１７４ｄＢ、－１８３ｄＢ），技术指标达到国外同类高频线阵的水平。满足侧扫声呐的尖波束、低副瓣、大功率、高灵敏度，深水（１００ｍ）使用的要求，本     

Numerical investigation of the effect of dual frequency sonication on stable bubble dynamics

A computational study aiming to simulate an oxygen single acoustic bubble oscillation under a dual-frequency sonication was presented in this paper. The non-linear response of the bubble to the superposition of two fields of ultrasonic waves was investigated through dynamics parameters, collapse ratios and average velocities. The main goal of this analyze is to link the properties of the wave resulting from the dual-frequency excitation to the dynamics behavior of the bubble. The obtained results prove that, in contrast with the mono-frequency, coupling a wave to lower frequencies enhances the collapse duration and raises the compression ratio in the case of 35 kHz, while associating any of the studied waves to a higher frequency elevates the number of bubble oscillations during a time interval as compared to mono-frequency. The total sonochemical production has been investigated in accordance with the dynamics results, as well as the proportions of the three predominant free radicals, that show a dependency on the value of the basic frequency.     

基于相位调控的超高透射声学超表面及其应用*

声学超表面可以灵活有效地对声波进行调控,实现多种新颖的现象和功能,在诸多声波调控领域有潜在的应用前景。该文引入了一种镀膜型迷宫结构单元,可以提供全范围(0~2π)的突变相位,具有高效的透射率(~100%)和较好的鲁棒性。基于相位调控,可利用镀膜型迷宫结构单元构建出超高透射超表面,实现异常声折射、声聚焦、声束沿任意凸轨迹弯曲传播以及声成像等应用。     

弱耦合封闭声腔的声辐射模态理论与计算

有源结构声控制是耦合封闭声腔的声辐射控制的有效方法。在此前的研究中有学者提出了\     

Thermal effect on the acoustic behavior of an axisymmetric lined duct

This paper deals with the effect of the temperature and the frequency on the acoustic behavior of lined duct partially treated with usual material used in acoustic insulation.First, the effect of frequencies and temperature on the acoustic impedance of usual materials used in lined duct such as glass or rock wools in order to reduce acoustic level is investigated.Secondly, the variational formulation of the acoustic duct problem taking into account velocity and temperature effects is established. Then, a numerical model is derived which permits to compute the reflection and the transmission coefficients of such duct for different temperatures and several flow velocities. The acoustic power attenuation is then computed from these coefficients and the effect of the temperature and flow velocities on this energetic quantity is evaluated.The numerical results are obtained for three configurations of a lined duct treated for different temperature ranges and several velocities. Numerical coefficients of transmission and reflection as well as the acoustic power attenuation show the relative influence of temperature.     

简单体系温度涨落的发散问题

平衡体系热力学推导涨落的前提是涨落必须很小，如果得到一个发散的结果说明这一涨落是不可靠的.对一些体系温度涨落的热力学结果，在温度趋于绝对零度时是发散的，这时必须用统计物理来处理.对这些体系进行统计物理处理的结果表明，涨落在温度趋于绝对零度时是趋于零的. 关键词： 热力学与统计物理 涨落     

非均匀三腔谐振腔高频特性的数值分析

 用SUPERFISH程序对非均匀三腔谐振腔的高频特性进行了数值分析。分析了各腔长度的变化对类TM₀₁₀ 2π/3模式及其频率、各腔纵向场分量Ez大小及Ez径向分布的影响。结果表明：当各腔长度变化时，该模式只在一定范围内存在，且频率变化不大，频率的最大值和最小值相差小于4%；当该模式存在时，第一腔长度越小，则第一腔的纵向场分量越大；当第一腔长度不变时，第三腔的纵向场分量随着第二腔长度的增大而增大，而第一，二腔纵向场分量则随之变小；各腔长度变化对纵向场分量的径向分布影响很小。     

磁绝缘线振荡器谐振腔的高频特性研究

 利用数值方法计算了磁绝缘线振荡器(MILO)主慢波结构谐振腔和扼流腔的谐振频率和场分布。结果表明：当主慢波结构腔内半径为4.6 cm,扼流腔内半径为4.2 cm,阴极半径为3 cm时,MILO工作在3.6~4.4 GHz频率范围,扼流片可以阻止微波功率向脉冲功率源泄漏,这有利于提高器件微波输出的功率;4.5~4.9GHz频段为慢波结构的阻带,微波在该频段截止。计算了C波段MILO开放腔的谐振频率,当模式分别为3π/8,π/2,5π/8,3π/4时,其谐振频率分别为3.18,3.76,4.00,4.11 GHz;并通过实验测出了开放腔的谐振频率,其相应的值分别为3.80,3.94,4.08.4.18 GHz, Q分别为194,143,231,468。数值计算的谐振频率与实验测出的频率基本一致。