基于小波分解的颅脑动态电阻抗监测中体动干扰实时处理方法研究

目的:为抑制临床颅脑电阻抗动态监测中体动干扰导致的图像伪影,提出一种基于小波分解的体动干扰实时处理方法。方法:首先,使用混合高斯模型描述颅脑电阻抗信号小波分解系数分布特征,对体动干扰和正常信号进行区分并加以处理;其次,采用垒墙式的计算策略,实现小波分解的实时化处理;最后,开展仿真实验与人体实测数据实验验证提出方法的有效性。结果:实验结果表明,该方法可以有效抑制尖峰类型的体动干扰,恢复信号的连续性,并显著减少图像上的重构伪影,恢复正常的图像监测。结论:基于小波分解的体动干扰实时处理方法能够有效抑制临床颅脑电阻抗动态监测中的体动干扰,特别适用于多通道数据采集的应用场景。

基于小波包分解的脑部EIT测量干扰分析与抑制方法研究

目的:为了抑制脑部电阻抗断层成像(electrical impedance tomography,EIT)在临床使用过程中因人为或自身体动造成的干扰,提出一种基于小波包分解的抑制方法。方法:首先分析正常与受体动干扰信号的频谱差异,并采用皮尔逊相关系数作为判断受干扰数据的依据。其次基于数据频谱特征,应用小波包分解与重建的方法对体动所造成的偏置性干扰进行抑制。最后选取5名健康志愿者进行临床试验,通过对比处理前后原始电压信号特征以及重构图像结果验证干扰抑制效果。结果:提出的方法可以有效地修正EIT原始电压信号等效时间采样中存在的体动干扰,改善了采样信号的频谱质量,提高了EIT成像效果。结论:提出的方法能初步实现对正常与干扰信号的识别,并对存在干扰的信号进行抑制,对脑部EIT的临床应用具有重要意义。

Hydrodynamic interactions between two bodies in waves in 3D time domain

In this paper, a 3D time domain technique is adopted to calculate the coupled hydrodynamic interaction between two bodies without flare in waves. For verifying the code, two same cylinders are selected to calculate coupled hydrodynamic effects by comparison with the results obtained by 3D frequency method which has been proved to be efficient for solving such problems. In order to improve efficiency of calculation, the effect of history time has been discussed, and an improved method is presented. Moreover, the effect of lateral separation distance is also discussed in detail. The technique developed here may serve as a more rigorous tool to analyze the related transient problems of two ships doing underway replenishment in waves.

Dynamics of mechanical system for electromechanical integrated toroidal drive under electric disturbance

Based on electromagnetics and mechanics, electromechanical coupled dynamic equations for the drive were developed. Using method of perturbation, free vibrations of the mechanical system under electric disturbance were investigated. The forced responses of the mechanical system to mechanical excitation under electric disturbance were also presented. It is known that for the system with electric disturbance, as time grows, beat occurs. When electric disturbing frequency is near to the natural frequencies of the mechanical system or their integer multiple, resonance vibrations occur. The forced responses of the mechanical system to mechanical excitation under electric disturbance are compound vibrations decided by mechanical excitation, electric disturbance and parameters of the system. The coupled resonance vibration caused by electric disturbance and mechanical excitation was discussed as well. The conditions under which above coupled resonance occurs were presented. The results show that when the difference of the excitation frequency and the perturbation frequency is equal to some order of natural frequency, coupled resonance vibrations occur.

A hypersonic lift mechanism with decoupled lift and drag surfaces

In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.

Hypersonic flow control of shock wave/turbulent boundary layer interactions using magnetohydrodynamic plasma actuators

The effect of magnetohydrodynamic(MHD)plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation.A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma.Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected.On the basis of the relative position of control area and separation point,MHD control can be divided into four types and so effects and mechanisms might be different.Amongst these,D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region.A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied.The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.

Mechanism of perturbation-combined active control technique for asymmetric vortex flow over slender body at high angle of attack

Based on the determinability of asymmetric vortices flow over slender body under changeless round grain at high angle of attack,the effect of microblowing set in special position on the behaviors of asymmetric flow is discussed in this paper,including blowing momentum and circumferential locations of the microblowing hole of 0.5 mm in diameter on nose tip.A new kind of active control technique,named perturbation-combined active control technique,which combines the micro-grain and micro-blowing perturbation,was proposed on the basis of the above.This control technique can not only change the sign of side force of slender body arbitrarily through changing the vortices positions between yaw-left and yaw-right configuration,but also can make the magnitude of side force variable gradually even at bistable state of asymmetric vortex.Finally,the interferential mechanism of the perturbation-combined active control technique has also been concluded from this paper.The tests have been conducted at low speed wind tunnel with subcritical Reynolds number of 1.05×10~5 at angle of attack α=50° in Beihang University,Beijing,China.