静子尾缘喷气后尾迹与动叶干涉噪声研究

尾缘喷气技术已经广泛地用于航空发动机和多级压缩机等领域,用以降低动静叶片间的相互干涉作用以提高透平机械的气动性能,并降低动静干涉噪声.本文对尾缘喷气用于低压轴流风机进行了详细的研究,对轴流风机的上游静叶实施尾缘喷气,通过实验测量,尾缘喷气使静叶尾迹达到无动量亏损尾迹状态能够降低风机噪声,文章还提出了基于CFD数值模拟的尾迹与动叶相互干涉的噪声预测模型,预测结果和实验结果比较接近.     

EFFECTS OF COLOURED NOISE IN A TWO-MODE LASER SYSTEM

A homogeneously broadened two-mode laser system with multiplicative coloured noise is investigated when the mode coupling constant ξ=2. An analytical result is obtained when two-dimensional decoupling theory is applied to the system. The intensity auto-correlation function and effective eigenvalue of the laser system are calculated when the difference of pump parameters, multiplicative noise strength and noise correlation time are varied. It is shown that the multiplicative noise can enhance the fluctuations while the noise colour can reduce the fluctuations in the laser system.     

ANALYSIS OF DISC BRAKE NOISE USING A TWO-DEGREE-OF-FREEDOM MODEL

Although a brake pad and disc have many modes of vibration, when it is unstable and hence noisy then frequently only a single mode of the complete system contributes to the vibration. In this condition, only a few modes are required to model the system. In this paper, a two-degree-of-freedom model is adopted where the disc and the pad are modelled as single modes connected by a sliding friction interface. Using this model, the interaction between the pad and the disc is investigated. Stability analysis is performed to show under what parametric conditions the system becomes unstable, assuming that the existence of a limit cycle represents the noisy state of the disc brake system. The results of this analysis show that the damping of the disc is as important as that of the pad. Non-linear analysis is also performed to demonstrate various limit cycles in the phase space. The results show that the addition of damping to either the disc or the pad alone may make the system more unstable, and hence noisy.     

31P核磁共振谱应用数则

用³¹P对烷基膦酸二烷基酯,乙酰丙烯磷酸二烷基酯的组成进行了分析,为寻找反应条件和产品纯化方法提供了有益的数据。并对几种腺嘌呤核苷酸磷酸酯及磷酰胺不同的立体异构体进行了测定,平展式较直立式在高场约2ppm处共振。     

喷流噪声预测中小尺度湍流声源模型

本文在Tam & Auriault提出的喷流噪声预测方法的基础上,导得计算轴对称喷管伴随格林函数的方程以及声源谱、伴随格林函数与噪声谱密度函数之间的关系,比较了几种典型的声源模型,并且采用了一种随频率变化的长度尺度.验证结果表明,TA预测模型中随频率变化长度尺度与Harper-Bourne提出的声源模型的结合能给出更好的预测结果.     

GENERALIZATION OF AN INVERTIBLE TRANSFORMATION AND EXAMPLES OF ITS APPLICATIONS

Recently we highlighted the remarkable nature of an explicitly invertible transformation, we reported some generalizations of it and examples of its expediency in several mathematical contexts: algebraic and Diophantine equations, dynamical systems (with continuous and discrete time), nonlinear PDEs, analytical geometry, functional equations. In this paper we report a significant generalization of this approach and we again illustrate via some analogous examples its expediency to identify problems which appear far from trivial but are in fact explicitly solvable.     

二维等离子体粒子模拟程序介绍

对研制的激光等离子体相互作用二维粒子模拟程序作了剖析,着重介绍了该程序具有的特点     

ACTIVE CONTROL OF A MOVING NOISE SOURCE—EFFECT OF OFF-AXIS SOURCE POSITION

An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary noise source. When the primary noise source moves, the active control of the noise becomes much more difficult, as the primary noise field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving source also causes difficulties from an acoustical perspective. A moving source not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active noise control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving source, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary source moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary source moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary source.     

PREDICTION OF NON-CAVITATING UNDERWATER PROPELLER NOISE

Non-cavitation noise of underwater propeller is numerically investigated. The main purpose is to analyze non-cavitation noise in various operating conditions with different configurations. The noise is predicted using time-domain acoustic analogy and boundary element method. The flow field is analyzed with potential-based panel method, and then the time-dependent pressure data are used as the input for Ffowcs Williams-Hawkings formulation to predict the farfield acoustics. Boundary integral equation method is also considered to investigate the effect of ducted propeller. Sound deflection and scattering effect on the duct is considered with the BEM. The governing equations are based on the assumption that all acoustic pressure is linear. A scattering approach is applied in which the acoustic pressure field is split into the known incident component and the unknown scattered component. Noise prediction results are presented for single propeller and ducted propeller in non-uniform flow conditions similar to real situation. The investigation reveals that the effect of a duct on the acoustic performance propeller is small in the far field under non-cavitating situations since the noise directivities of single and ducted propellers are almost the same. Only the high order BPFs are influenced by the existence of the duct.     

超导磁通量子比特低频磁通噪声的测量

在极低温下,我们对基于Nb／AlOx／Nb约瑟夫森结构成的超导磁通量子比特进行了测量,从粒子在双势阱的分布率和磁通的关系曲线中,分析得到了低频磁通噪声强度SФ（1Hz）．进一步我们测量了在不同温度下的SФ（1Hz）,结果表明在49．4mK到400mK温度区间,SФ（1Hz）随温度呈平方关系增长．     

INVESTIGATION OF AUTOMOTIVE CREEP GROAN NOISE WITH A DISTRIBUTED-SOURCE EXCITATION TECHNIQUE

Creep groan is a high-intensity, low-frequency noise and vibration problem that affects road vehicles at very low speeds. It usually persists for short periods of time, but a “skilled” driver can deliberately make it last several seconds by tuning the force exerted on the brake pedal. The original cause is considered to be a self-induced vibration of the brake components, due to the friction material characteristics that make the system prone to a stick-slip behaviour. No clear evidence upon the creep groan and how it is perceived inside the passenger cockpit has yet been analyzed in the literature and no formal methods are yet available for its analysis. The present study focuses on the transmission of the vibration from the brake component regions to the ears of the vehicle occupants. Characterization of the calliper acceleration and noise inside the cockpit are described for a test vehicle. Distributed-source noise excitation via the standard vehicle hi-fi system is proposed as a practical but less rigorous particular application of the exact reciprocity method. Virtual groan (in which sound power is delivered by means of a loudspeaker) dismisses the airbone path and shows that the phenomenon is structure-borne. On the examined vehicle, front brakes contribute more strongly than rear. Groan frequency close to cavity acoustic resonance constitutes the worst case scenario, and has to be avoided.     

激光与蛋白质孤子的非线性相互作用研究

在蛋白质分子一维分子链模型的基础上,引入了激光与蛋白质的相互作用项.讨论了激光对蛋白质分子孤立子的作用.表明在弱激光作用下蛋白质分子的集体振荡可能进入浑沌状态.     

SOME EXAMPLES OF ALGEBRAIC GEODESICS ON QUADRICS. II

In this note we give new examples of algebraic geodesics on some two-dimensional quadrics, namely, on ellipsoids, one-sheet hyperboloids, and hyperbolic paraboloids. It appears that in all considered cases, such geodesics are rational space curves.     

LARGE-SIGNAL SIMULATIONS OF A GYROTRON TRAVELING-WAVE AMPLIFIER WITH A MODE-SELECTIVE INTERACTION CIRCUIT

A self-consistent nonlinear theory is used to analyze the saturated performances of a Ka-band gyrotron traveling wave amplifier (gyro-TWA) operating at the fundamental with a mode-selective interaction circuit involving a tapered vane-slot mode converter. The amplifier is predicted to generate 140 kW saturated output power with 33.3% efficiency, a saturated gain of 33dB, and a 3dB bandwidth of 2.7 GHz (8%) for a 70 kV, 6A electron beam with a velocity ratio of 1.0 and an axial velocity spread of 5%.     

STUDY ON ENVIRONMENTAL NOISE EXPOSURE OF RESIDENCE

Survey on environmental noise was carried out in Beijing from April to August,1986.The data ofL_(eq) and L_(50) for every 10 minutes in all day were obtained.The reactions of inhabitants on noise and the in-formations related to noise environment were also collected.The results concerning.environmental noise ex-posure and reactions of inhabitants are mainly stated in this paper.     

THE CORRELATION AND RELAXATION OF A MULTIDIMENSIONAL SYSTEM DRIVEN BY QUADRATIC NOISE

We discuss a multidimensional system driven by a non-Markovian quadratic a}oise.Using the MSR formalism and Novikov theorem, we derive approximately a lot of moments equations,the correlation functions and the relaxation times. As an illustration of our results we make con- Crete calculations for a Brownian bound oscillator system and for a liquid crystal model.     

INTERACTION OF A SPHERICAL SHOCK WAVE AND A SUBMERGED FLUID-FILLED CIRCULAR CYLINDRICAL SHELL

The complete three-dimensional interaction between a spherical shock wave and a submerged fluid-filled elastic circular cylindrical shell is considered. A hybrid analytical-numerical solving procedure is established. An exact analytical solution in the form of double Fourier series with time-depending coefficients is obtained for the hydrodynamic pressure. Displacements of a shell are approached analytically to reduce the problem to a set of systems of ordinary differential equations, which are treated numerically. Detailed analysis of the interaction is performed with emphasis given to the stress-strain state. A few important features of the interaction process have been found. In particular, it has been shown that the interior fluid not only substantially affects the magnitude of displacements and stresses, but also dramatically changes the nature of the interaction. It has been found that the absolute maximum of stresses can neither be caused by a direct action of a shock wave nor by a constructive superpose of elastic waves in the shell, but by the pressure wave propagating in the interior fluid. This fact seems to be of essential importance for engineering applications, especially when safety is a primary design concern. Another important result is that the maximum stresses are attained at large times, which makes use of early time asymptotics leading to incorrect results. The proposed semi-analytical approach seems to be computationally attractive and suitable for extensive numerical simulations.     

用光电倍增管测量微光像增强器噪声

在微光像增强器成像中，迭加在图像上的时空域噪声，不仅限制系统的可工作最低照度，而且使显示图像有随机蠕动颗粒闪烁的外观。随着低噪声、高增益的光电倍增管的出现，比较精确地测量微弱光信号成为可能。在此基础上提出了采用光电倍增管来测试像增强器信噪比的方法。实验中发现，这种方法能比较准确并直观地反映像增强器噪声的大小。