横向扰动对超声速混合层被动标量混合影响分析

采用大涡模拟数值计算二维空间发展的超声速混合层,重点分析横向扰动对混合层的标量结构、标量厚度以及标量体积卷吸率的影响。采用理论模型验证了数值方法在计算标量混合特性方面的准确性。结果表明,横向扰动频率和振幅明显影响着混合层的标量增长率和卷吸率。高频扰动增大了混合层近场标量增长率和卷吸率,但是低频扰动改善了混合层远场标量增长率。大尺度涡卷吸过程对混合层标量卷吸率起决定作用。多频扰动有效地增强了超声速混合层的标量混合。     

函数变换提高灰色预测模型精度的条件

指出选择函数变换来提高模型精度主要与三个方面的因素有关：提高数据序列的光滑比、调整数据序列的级比和确保凸凹性。在调整级比方面，扩充了级比压缩变换的相关定理，并讨论了几种常用的函数变换在上述三个方面的关系。最后结合实例提出，对于变换后的数据序列若不满足这三方面的要求可以再进行函数变换以达到提高模型精度的目的。     

应用改进的LP算法构建虚拟阵的精确定向方法

为了克服传统LP(Linear Predecition)算法在构建虚拟阵过程中存在预测误差容易累积的弊端,提出了一种能够更充分利用实阵信息量的改进LP算法来构建虚拟阵。采用实际基阵方法、传统LP虚拟阵方法和改进LP虚拟阵方法分别对假定基阵的波束性能进行计算机仿真及对湖试数据进行处理成像,研究结果表明,与传统LP方法相比,改进的LP方法能够有效地抑制波束旁瓣,进一步提高了基阵的角度分辨力和阵增益,将其运用于特定试验背景下的实际湖底目标探测,方向分辨精度可提高75%。     

多子带雷达信号融合噪声抑制方法

全极点模型对信号构建线性模型,通过对模型进行定阶和计算可以得到估计信号的各个参数,从而实现信号预测。子带融合之前需要进行相干处理,可以通过相干函数等方式解决。root-MUSIC算法在低信噪比环境中极点选择并不稳健,会导致模型在阶数上判断错误。为解决全极点模型方法中子带融合在信噪比低时模型阶数估计不准的问题,提出一种噪声抑制方法。对信号Hankel矩阵的主对角奇异值矩阵加权处理,以消除噪声分量,并利用整体前向预测矩阵得到整体频段极点值与极点幅值,由此估计出低信噪比时的多子带融合信号。结果表明所提方法在仿真环境下,在信噪比-20 dB至10 dB时,相较于传统极点模型方案具有更好的估计结果。     

Driving force coordinated control of an 8 ×8 in-wheel motor drive vehicle with tire-road friction coefficient identification

Because of the complexities of tire-road interaction,the wheels of a multi-wheel distributed electric drive vehicle can easily slip under certain working conditions.As wheel slip affects the dynamic per-formance and stability of the vehicle,it is crucial to control it and coordinate the driving force.With this aim,this paper presents a driving force coordination control strategy with road identification for eight-wheeled electric vehicles equipped with an in-wheel motor for each wheel.In the proposed control strategy,the road identification module estimates tire-road forces using an unscented Kalman filter al-gorithm and recognizes the road adhesion coefficient by employing the recursive least-square method.According to road identification,the optimal slip ratio under the current driving condition is obtained,and a controller based on sliding mode control with a conditional integrator uses this value for accel-eration slip regulation.The anti-slip controller obtains the adjusting torque,which is integrated with the driver-command-based feedforward control torque to implement driving force coordination control.The results of hardware-in-loop simulation show that this control strategy can accurately estimate tire-road forces as well as the friction coefficient,and thus,can effectively fulfill the purpose of driving force coordinated control under different driving conditions.     

Optimization of process parameters of the activated tungsten inert gas welding for aspect ratio of UNS S32205 duplex stainless steel welds

The activated TIG (ATIG) welding process mainly focuses on increasing the depth of penetration and the reduction in the width of weld bead has not been paid much attention. The shape of a weld in terms of its width-to-depth ratio known as aspect ratio has a marked influence on its solidification cracking tendency. The major influencing ATIG welding parameters, such as electrode gap, travel speed, current and voltage, that aid in controlling the aspect ratio of DSS joints, must be optimized to obtain desirable aspect ratio for DSS joints. Hence in this study, the above parameters of ATIG welding for aspect ratio of ASTM/UNS S32205 DSS welds are optimized by using Taguchi orthogonal array (OA) experimental design and other statistical tools such as Analysis of Variance (ANOVA) and Pooled ANOVA techniques. The optimum process parameters are found to be 1 mm electrode gap, 130 mm/min travel speed, 140 A current and 12 V voltage. The aspect ratio and the ferrite content for the DSS joints fabricated using the optimized ATIG parameters are found to be well within the acceptable range and there is no macroscopically evident solidification cracking.     

一种鱼雷自导信号频率检测方法研究

靶场在进行智能鱼雷鉴定试验任务时,实时准确地检测出鱼雷自导信号的频率成分是靶标信号处理中的重要环节,谱线比值法便是靶标进行信号处理时检测信号频率的一种有效方法。本文介绍了谱线比值法的基本原理,针对目前鱼雷自导信号特点,对该方法提出了改进方案并进行了仿真。仿真结果表明,经改进的谱线比值法能够满足靶标检测复杂鱼雷自导信号体制下信号频率的使用要求。     

数值模拟气/气喷嘴速度比对燃烧性能的影响

为研究应用于全流量补燃循环发动机的不同气/气喷嘴得到的燃烧流场,通过求解NavierStokes方程组,对不同燃料与氧化剂速度比下的流动燃烧过程进行了数值计算,计算结果与实验结果吻合。仿真结果表明:增加速度比能使燃烧火焰面提前,燃烧效率变大。如果发动机的长度受到限制,可以适当增加速度比以实现高效燃烧。     

绳系拖曳离轨过程中的摆动抑制策略

以周向常值连续小推力作用下的绳系拖曳离轨为背景,针对离轨过程中的系绳摆动抑制问题,建立了系统质心轨道动力学方程及系绳摆动动力学方程,分析了无系绳收放控制时的系绳摆动特性以及系绳收放对系绳摆动的作用效果,构造了使系绳摆动衰减的期望绳长收放速率并设计了系绳张力控制律。仿真结果表明:无系绳收放控制时,系绳摆动表现为平衡位置附近的周期性往复运动;张力控制连续平滑,很好地实现了系绳实际长度对期望长度的跟踪,同时有效地抑制了离轨过程中的系绳摆动。     

基于非合作雷达辐射源的无源雷达目标检测方法

主要研究了基于非合作雷达辐射源的非相参体制无源雷达目标检测问题。对目标回波通道中的直达波干扰,利用一种基于三元传感器对消的方法来进行抑制。然后采用周期间相关检测的处理方法对目标进行检测。仿真分析表明,该方法在辐射源信号未知的情况下,能够有效抑制目标回波通道中的直达波干扰,得到优于传统的确知信号的相关检测性能。