燃烧室部件传热时间非均匀性对柴油机整体性能影响的研究

将所有燃烧室部件(气缸盖-气缸套-活塞组-润滑油膜)作为一个耦合体,在对耦合体进行瞬态传热数值模拟的基础上,利用分区求解、边界耦合法建立缸内工作过程与燃烧室部件的耦合传热计算模型,从而实现缸内工作过程与燃烧室部件的耦合仿真模拟,以此考察燃烧室部件传热时间非均匀性对发动机性能的影响。结果表明:燃烧室部件表面的非均匀温度分布对常规金属柴油机的动力性、经济性和排放性能的影响十分微小,对传热性能有一定影响,但幅度也小于1%。因此在常规柴油机整体性能的准维模拟预测中,可以忽略燃烧室部件传热时间非均匀性的影响。

燃气管网运行工况非均匀时间间隔的宏观分析

对燃气输配管网供气调度所需要的管网运行工况分析方法进行了详细讨论，提出了用非均匀时间间隔法对燃气管网运行工况进行宏观分析，克服了均匀时间间隔宏观模型分析燃气管网运行工况产生的误差。建立了完整的数学模型，进行了仿真计算，计算结果满足供气调度要求。

概率密度演化方程TVD格式的自适应时间步长技术及其初值条件改进

随机性普遍存在于实际工程问题中,而复杂结构的非线性随机响应分析是其中的一个难点,近年发展的概率密度演化方法为此类问题的求解提供了新的途径.由于实际问题的复杂性,概率密度演化方程通常采用数值方法求解,因此提高计算效率和求解精度对实际应用具有重要意义.本文基于变网格技术,推导了概率密度演化方程在非均匀时间步长上的总变差减小(total variation diminishing,TVD)差分格式,算例结果表明通过自适应插值可将迭代次数减少为原来的43.4%,当随机过程样本持续时间增大时均值估计的平均误差基本不变,而标准差估计的平均误差不断增大,但增大幅度不断减小;计算耗时随样本持续时间的增大也呈增大趋势,而由于使用了时间步长自适应插值算法导致有些情况下长持时样本的计算耗时反而比短持时样本的计算耗时短;在传统的脉冲函数型初值条件基础上,提出了一种高阶导数更稳定的余弦函数型初值条件形式.结果表明,脉冲函数型的初值条件是余弦函数型初值条件的一个特例,当参数取值适当时,余弦函数型初值条件的数值求解结果具有更高的精度.本文的工作进一步完善了概率密度演化方程的求解方法,为其在实际工程中的应用提供了基础.

一种高速并行采样实时校正方法研究

并行交替采样带来的非均匀误差严重影响采集性能。本文建立了并行交替采集系统的数学模型,实现了一种幅度非均匀误差校正的归一化算法,在误差校正系统中引入可程控参考校正源,再利用查表法同时校正系统的偏置和增益失配误差,然后对时间非均匀性参数进行估计,并通过高精度可编程时钟延时网络对其修正。实验结果表明,该校正方法实时性好,降低了硬件设计难度和成本,提高了系统性能。

基于FPGA的TIADC并行采样系统设计

介绍一种基于多片ADC的时间交替并行采样设计方法以及在FPGA平台上的实现。着重阐述TIADC并行采样的增益误差、时间误差校正算法及实现。实验结果表明,TIADC并行数据采集系统的结构设计和预处理算法,能较好抑制因相位偏移、时钟抖动等造成的非均匀误差。

天文光变周期提取算法综述

随着大量巡天项目的开展和完成,天文领域积累了大量的光变数据。这些数据中蕴含了许多有重要价值的物理参数,如光变周期,它对研究光变的物理机制、爆发预测和天体质量估算等有很大的帮助。但受到天体自身动力学过程、观测条件和仪器状态等客观因素的影响,光变数据往往是非均匀采样的,并且都不同程度地受到噪声的影响。因此,非常有必要研究基于非均匀采样信号的光变周期提取算法。综述了基于频域、时域和时-频域分析的三大类光变周期提取算法,主要包括Lomb-Scargle周期图法、Jurkevich算法和加权小波Z变换算法等,着重分析和比较了这些算法的性能,同时分析了它们的优缺点,最后总结与展望了光变周期算法。

Time-temperature-property curves for quench sensitivity of 6063 aluminum alloy

The quench sensitivity of 6063 alloy was investigated via constructing time-temperature-property（TTP） curves by interrupted quenching technique and transmission electron microscopy（TEM） analysis.The results show that the quench sensitivity of 6063 alloy is lower than that of 6061 or 6082 alloy,and the critical temperature ranges from 300 to 410℃ with the nose temperature of about 360℃.From TEM analysis,heterogeneous precipitate β-Mg2Si is prior to nucleate on the（AlxFeySiz） dispersoids in the critical temperature range,and grows up most rapidly at the nose temperature of 360℃.The heterogeneous precipitation leads to a low concentration of solute,which consequently reduces the amount of the strengthening phase β＇＇ after aging.In the large-scale industrial production of 6063 alloy,the cooling rate during quenching should be enhanced as high as possible in the quenching sensitive temperature range（410-300℃） to suppress the heterogeneous precipitation to get optimal mechanical properties,and it should be slowed down properly from the solution temperature to 410℃ and below 300℃ to reduce the residual stress.

局部惯性系的优越性

对于任意一个计算系统，在一般情况下，“时—空”是不均匀的，空间也不是各向同性的，因而应在黎曼空间中去描述这一弯曲的“时—空”特性．即在自然界中，由于引力的不可屏蔽性，因而在有引力存在的“时—空”中去研究物质的运动规律时，应在黎曼空间中去描述．本文采用“消除”外力的局部惯性系（文中称ｇ坐标系）来进行观测．这样，将一个“非均匀时空”的黎曼空间，转换为一个“均匀时空”的“平直”的闵可夫斯基空间．“消除”了引力场的作用，从动力学中的加速效应和“静力学”中的形变效应两个方面都得到了满意的结果。

Quenching sensitivity and heterogeneous precipitation behavior of AA7136 alloy

The quenching sensitivity of AA7136 alloy was investigated by time−temperature−property(TTP)diagrams,and the heterogeneous precipitation behavior during isothermal holding was investigated using scanning electron microscopy,scanning transmission electron microscopy and high resolution transmission electron microscopy.Based on 99.5%TTP diagram,the nose temperature is determined to be about 346℃ with the transformation time of about 0.245 s.The precipitation ofη(MgZn_(2)),T(Al_(2)Zn_(3)Mg_(3)),S(Al_(2)CuMg)or Cu−Zn-rich Y phases can be found depending on isothermal holding temperature and time,and it is described in a time−temperature−precipitation diagram.The size and area fraction of isothermal holding induced phase particles increase,which results in the decrease of hardness of samples after aging.The quantitative contribution to loss of hardness by grain boundaries/subgrain boundaries and dispersoids in the matrix is discussed based on the amount of heterogeneous precipitation related to them.

Effect of heat transfer space non-uniformity of combustion chamber components on in-cylinder soot emission formation in diesel engine

Combustion chamber components （cylinder head, cylinder liner, piston assembly and oil film） are treated as a coupled body. Based on the three-dimensional numerical simulation of heat transfer of the coupled body, a coupled three-dimensional calculation model for the in-cylinder working process and the combustion chamber components was built with domain decomposition and boundary coupling method, in which the coupled three-dimensional simulation of in-cylindcr working process and the combustion chamber components was adopted. The simulation was applied in the influence investigation of the space non-uniformity in heat transfer among combustion chamber components on the generation of in-cylinder emissions. The results show that the space non-uniformity in heat transfer among the combustion chamber components has great influence on the generation of in-cylinder NOx emissions. The heat transfer space non-uniformity of combustion chamber components has little effect on soot formation, and far less effect on soot formation than on NOx. Under two situations of different wall temperature distributions, the soot in cylinder is different by 1.3% when exhaust valves are open.

基于TIADC的信号频谱分析系统设计

为实现宽带信号的高速高精度采样以及频谱分析,采用TIADC并行采样技术,基于FPGA完成了信号采集、时间非均匀误差校正以及快速傅里叶变换等模块的设计。利用12位的多路ADC完成时间交替并行采样,设计Farrow结构的分数时延滤波器实现时间非均匀误差校正能够提高有效位数和采样后信号无杂散动态范围,能同时满足高精度与高速度的要求。实验结果表明,TIADC并行采样的结构设计和预处理算法能够较好抑制因相位偏移、时钟抖动等造成的非均匀误差。系统实现了基于FPGA的TIADC并行数据采集、误差校正与频谱分析等功能,系统稳定可靠。

Time-stepping finite element analysis on the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors

To study the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors,a 5.5-kW motor was taken as an example and the multi-sliced field-circuit coupled time stepping finite element method(T-S FEM)was used to analyze the axially non-uniform fundamental and harmonic field distribution characteristics at typical locations in the stator and rotor cores.The major conclusions are:firstly the skewed rotor exhibits a decrease in the harmonic copper losses caused by slot harmonic currents in the stator winding and rotor bars.Secondly,the skewed rotor shifts the non-uniform distribution of field in the axial direction,which leads to more severe saturation and an increase in iron losses.The heavier the load,the more pronounced the increase in iron losses.Furthermore,the influences of different skew angles on motor losses are studied systematically,with skew angles from 0.5 to 1.5 stator tooth pitch.It is found that the lowest total loss occurs at 0.8 stator tooth pitch,and the slot harmonics can be decreased effectively.