圆筒型加热炉管壁最高热强度点计算模型

以底部烧气单侧立管圆筒型加热炉为研究对象,建立了燃烧区内高温火焰对炉管外壁的辐射热流强度的数学模型,并且给出计算实例,分别采用复形调优法和对分法解出炉管外壁向火面上最高热强度点的大小及其位置,两种计算方法的结果一致。最后对炉管在加热炉内的优化布置作了一定的探讨;对于多管程的圆筒炉,各管程的出口炉管不应该布置在来自高温焰烟的辐射热流强度较高的区域空间内。其计算实例为分析其它炉型提供了方法。     

简谐SH波作用下管桩的振动特性

在一维波动模型的基础上得到了简谐SH波作用下桩周土和桩芯土的位移。在三维轴对称的情况下,运用势函数和分离变量法求解了简谐水平集中荷载和SH波引起的管桩桩周土和桩芯土的振动问题,得到了桩周土和桩芯土的径向位移和环向位移。考虑管桩土动力相互作用和管桩土的连续性边界条件对简谐水平集中荷载和SH波作用下管桩的振动进行了研究,得到了管桩桩顶的动力放大因子。通过数值算例分析可知,简谐SH波作用下管桩存在共振现象;管桩管壁过薄宜导致桩基失稳;相同外径情况下采用管桩要比实芯桩的抗震性能更好。     

预警机雷达对海目标探测能力评估方法

为准确评估预警机预警雷达在对海探测模式下的实际探测能力,分析了预警机实际作战运用时的探测盲区问题;基于建立的目标位置实时动态估算模型,提出了一种考虑实际探测盲区的预警机雷达对海目标探测能力评估模型,并给出了具体的评估算法流程,进行了仿真分析.仿真结果表明：该评估方法能够在考虑下视探测盲区条件下,对实际作战运用时预警机雷达不同海况下的对海目标探测能力进行有效准确评估.     

A new analytical algorithm for computing probability distribution of project completion time

An analytical algorithm was presented for the exact computation of the probability distribution of the project completion time in stochastic networks, where the activity durations are mutually independent and continuously distributed random variables. Firstly, stochastic activity networks were modeled as continuous-time Markov process with a single absorbing state by the well-know method of supplementary variables and the time changed from the initial state to absorbing state is equal to the project completion time. Then, the Markov process was regarded as a special case of Markov skeleton process. By taking advantage of the backward equations of Markov skeleton processes, a backward algorithm was proposed to compute the probability distribution of the project completion time. Finally, a numerical example was solved to demonstrate the performance of the proposed methodology. The results show that the proposed algorithm is capable of computing the exact distribution function of the project completion time, and the expectation and variance are obtained.     

Numerical investigation of piled raft foundation in mitigating embankment vibrations induced by high-speed trains

A three-dimensional dynamic finite element model of track-ballast-embankment and piled raft foundation system is established. Dynamic response of a railway embankment to a high-speed train is simulated for two cases: soft ground improved by piled raft foundation, and untreated soft ground. The obtained results are compared both in time domain and frequency domain to evaluate the effectiveness of the ground improvement in mitigating the embankment vibrations induced by high-speed trains. The results show that ground improving methods can significantly reduce the embankment vibrations at all considered train speeds(36-432 km/h). The ground response to a moving load is dictated largely by the relationship between load speed and characteristic value of wave velocities of the ground medium. At low speeds, the ground response from a moving load is essentially quasi-static. That is, the displacements fields are essential the static fields under the load simply moving with it. For the soft ground, the displacement on the ballast surface is large at all observed train speeds. For the model case where the ground is improved by piled raft foundation, the peak displacement is reduced at all considered train speeds compared with the case without ground improvement. Based on the effect of energy-dissipating of ballast-embankment-ground system with damping, the train-induced vibration waves moving in ballast and embankment are trapped and dissipated, and thus the vibration amplitudes of dynamic displacement outside the embankment are significantly reduced. But for the vibration amplitude of dynamic velocity, the vibration waves in embankment are absorbed or reflected back, and the velocity amplitudes at the ballast and embankment surface are enhanced. For the change of the vibration character of embankment and ballast, the bearing capacity and dynamic character are improved. Therefore, both of the static and dynamic displacements are reduced by ground improvement; the dynamic velocity of ballast and embankment increases with the increase of train speed and its vibration noise is another issue of concern that should be carefully evaluated because it is associated with the running safety and comfort of high-speed trains.     

中部进刀单向割煤采面煤壁瓦斯涌出量模型

煤壁瓦斯涌出是采面瓦斯涌出的重要组成部分,但实践中难以直接测量;准确估算煤壁瓦斯涌出量,对采面瓦斯治理具有重要意义.为掌握采面煤壁瓦斯涌出量的变化规律,针对中部进刀单向割煤作业循环,推导并建立了采面煤壁瓦斯涌出量关于割煤机位置的分段函数模型.利用该模型绘制出了割煤循环过程中煤壁瓦斯涌出量的时间变化曲线,并推导出了煤壁峰值瓦斯涌出量的计算公式.与已有成果相比,本文所建立的计算模型更具体地考虑了采煤工艺流程的特点,因此更加合理.通过算例分析发现,在进刀位置位于采面中点附近时,已有计算式与本文的计算模型相比,可能会使采面煤壁最大瓦斯涌出量被高估12%左右.     

多因素影响下基于Bagging-NSGAII的数控铣削稳定性预测与优化研究

数控机床铣削过程中出现的颤振失稳,是限制数控机床加工效率和加工质量的关键因素。铣削稳定性与工艺参数、工艺系统动力学特性密切相关,而工艺系统动力学特性又随加工位置、刀具悬伸量的变化或刀具的更换而变化。因此,针对多因素影响下的铣削稳定性预测和无颤振工艺参数选择问题,本文以数控机床各向移动部件位置、刀具直径、刀具悬伸量和切削参数为变量,提出一种基于引导聚集算法(Bagging)与带精英策略的快速非支配排序遗传算法(NSGA-II)的切削稳定性预测与工艺参数优化方法。该方法首先采用正交实验设计离散数控机床的工作空间,在每个加工位置对不同悬伸量下的刀具进行锤击实验,由此得到各把铣刀对应的刀尖点频率响应函数;然后,在不同工艺参数方案下进行铣削稳定性理论预测,进而引入Bagging算法建立以各向运动部件位置(x, y, z)、刀具直径(d)、刀具悬伸量(h)、主轴转速(n)、切削宽度(ae)、每齿进给量(fz)为输入的极限切削深度(aplim)预测模型;在此基础上,采用该Bagging模型作为铣削稳定性约束,以加工位置和工艺参数{x, y, z, d, h, n, ap, ae, fz}为优化变量,建立最大材料切除率和刀具寿命的多目标优化模型,采用NSGA-II算法求解该模型得到Pareto最优解集,并结合熵权法和优劣解距离法(TOPSIS)选出Pareto解集中的最佳解。以一台三轴立式加工中心展开实例分析,所建极限切削深度Bagging模型的预测误差为2.99%,且铣削加工实验表明获取的{x, y, z, d, h, n, ap, ae, fz}最优配置可实现稳定铣削,验证所提方法的可行性和有效性。     

聚氨酯泡沫发泡位置监视跟踪装置研制

本文主要论述了聚氨酯泡沫发泡位置监视跟踪装置的设计原理、结构特点和在生产中的应用．其工作过程是将被检部位的透射电磁波转换成监视器荧光屏上的视频信号，然后通过调整控制系统以达到应用一步法制造钢管道黑夹克聚氨酯泡沫防腐保温管的目的．     

Sharp convergence rates of stochastic approximation for degenerate roots

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一种基于单程波方程的转换波模拟方法

采用脉冲或子波作为震源,利用纵波方程将炮点向地下延拓,再利用横波方程将检波点向地下延拓,每延拓一个深度步长对二波场进行相关处理,并乘以相关点处的反射系数即得反射波场值,与此同时计算出两波场的时间之和,再根据等时叠加原理,将前面计算的反射波场值在对应的时间和空间位置处进行叠加,即可实现P～S转换波资料的共炮记录正演模拟,若采用横波方程延拓炮点,采用纵波方程延拓检波点,则可以实现S—P转换波资料的共炮记录模拟,由于该模拟方法在处理过程中无需估算转换点位置,因此模拟资料更客观真实。通过该方法模拟的转换波具有无直达波、多次反射干扰等优点,且具有较强的动力学特征,是复杂构造模拟、多波多分量模拟等的首选方法。     

Dynamic modeling and simulation for the rigid flexible coupling system with a non-tip mass

The rigid flexible coupling system with a mass at non-tip position of the flexible beam is studied in this paper. Using the theory about mechanics problems in a non-inertial coordinate system, the dynamic equations of the rigid flexible coupling system with dynamic stiffening are established. It is clearly elucidated for the first time that, dynamic stiffening is produced by the coupling effect of the centrifugal inertial load distributed on the beam and the transverse vibration deformation of the beam. The modeling approach in this paper successfully solves problems of popular modeling methods nowadays: the derivation process is too complex by using only one dynamic principle; a clearly theoretical mechanism for dynamic stiffening can't be offered. First, the mass at non-tip position is incorporated into the continuous dynamic equations of the system by use of the Dirac function and the Heaviside function. Then, based on the conclusions of orthogonalization about the normal constrained modes, the finite dimensional state space equations suitable for controller design are obtained. The numerical simulation results show that: dynamic stiffening is included in the first-order model established in this paper, which indicates the dynamic responses of the rigid flexible coupling system with large overall motion accurately. The results also show that the mass has a softening effect on the dynamic behavior of the flexible beam, and the effect would be more obvious when the mass has a larger mass, or lies closer to the tip of the beam.     

扭转模态导波检测管道纵向缺陷的数值模拟

为了评价超声扭转模态导波对管道纵向缺陷的检测能力,采用有限元方法进行了数值模拟研究.建立了带有纵向缺陷的管道有限元模型,激励和接收了扭转模态的T(0,1)导波,获得了缺陷长度与反射系数之间的关系曲线和回波信号在管道圆周方向的分布规律,并提出了采用T(0,1)模态导波检测时,对纵向缺陷进行周向和纵向定位的方法.结果表明,32.6 kHz的T(0,1)模态导波对管道上的纵向缺陷比较敏感,在缺陷所对应的圆周位置上,导波的回波幅度最大,而且,纵向缺陷对T(0,1)模态导波的反射系数呈单调增大、然后减小的趋势.     

Manufacturing cost optimization and estimation combined computer of composite-stiffened panels

The primary goal of this study is to fully grasp the production flow of the new processing technologies for manufacturing composite stiffened panels incorporating cost as one of the design variables early in the design process. An approach is presented to determine the optimum process for cost as objective function. A cost estimation model is established based on the integrally molding process. In the model,the cost drivers which are related to the manufacture processes in terms of material,labor,tool and equipment costs are taken into account. At the same time,estimation software combined computer is developed to aid optimization design. A case of manufacturing composite stiffened panels with T-shaped stiffeners is examined. Excellent agreement shows the optimum process for cost is obtained for the composite stiffened panel with cocuring. It is also revealed that the estimation software combined computer is efficient. The estimation methodology is valid to guide design of the manufacturing process for the composite-stiffened panel.     

卡尔曼滤波用于变压器数字式差动保护的研究

本文用变压器数字式差动保护的仿真模型,求得变压器的涌流和故障电流波形,并以此为依据,研究在变压器差动保护中用卡尔曼滤波算法时,其滤波方程中各参数的选择原则及滤波的状态方程数,分析了卡尔曼滤波在时间常数设定不精确情况下和频率变化时的滤波性能,并指出文献[1]计算结果的局限性。文中提出的结论,均经过大量计算,对卡尔曼滤波在数字保护中的应用有普遍意义。     

高分子反应Markov过程的渐近性质分析

以存在凝胶化现象的高分子反应模型为背景,定义了高分子反应所对应的可逆M arkov过程,给出了过程的稳定分布及配分函数,推导出了分子间协方差的表达式.通过对该过程在下临界、临界、上临界状态下的渐近性质的分析,证明了仅在临界状态下系统存在长程相关性.     

A Model for Capacity Considering the Interference by Pedestrian Traffic at Signal Intersections

The capacity is impacted badly by pedestrians’ violation behavior at signal intersections. In order to quantify the impact, the time-headway and the vehicular speed from start-up to reach the stable saturation flow with and without pedestrian traffic are used as the direct measurements. Using the statistical analysis, the time-headway of saturation flow is mainly affected by the position of pedestrians and the degree of pedestrians’ influence is classified into four levels. Then the speed-time profile for the vehicular acceleration at each level is fitted by Curve Fitting Software. Based on the effect to the time-headway and acceleration time, the model of capacity influenced by pedestrians is established and the influence is quantified, which enriches the fundamental theory of traffic engineering. The result shows that the vehicular capacity can be decreased by 14% at the worst case (level I ). The conclusions obtained in this paper are valuable for better management of the signal intersection.     

Unsteady transverse injection of kerosene into a supersonic flow

A shadowgraph and a new fuel injection system were used to study kerosene transversely injected into a supersonic flow. High pressure and velocity of injection can be attained. The pressure time histories were detected in oil-line and the shadowgraphs of the flow field were obtained at different time-delays. The inflow stagnation pressure was varied to change the local flow speed in test section. The results indicate that kerosene jet exhibits deep penetration and four regimes appear clearly during the fuel jet atomization in a high-speed flow. The jet disintegration is caused by surface waves propagating along the jet surface, and the breakup point is located at the wave trough. The surface waves are dominantly generated by aerodynamic force. The jet shock is close to windward surface of the jet. The shock reflects on and transmits in duct boundary layers. In the case of unsteady injection, the shock structure is very complicated and different from that of hydrogen injection. The results of kerosene inj     

Energy flux characteristics of seismic waves at the interface between soil layers with different saturations

Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics.     

应力盘面形变化量与驱动器策动力间的多元统计模型

为了保证应力盘与非球面光学元件在不同位置上实时吻合研磨,将回归分析法应用于应力盘盘面面形变化量与驱动器策动力间变化规律的分析,建立磨盘面形变化量关于驱动器策动力的多元回归分析模型。该模型将分别以面形变化、策动力为因变量和自变量建立多元回归分析模型,并根据最小二乘原理求得回归方程系数,从而对于任意的驱动器策动力可以快速地求得与其对应的磨盘面形变化量。此外,还建立了驱动器策动力关于磨盘面形变化量的多元回归分析模型,对任意目标曲面可以快速求得与其对应的各驱动器策动力大小。这两个模型互逆,建模过程类似,能实时地为能动磨盘控制系统提供合理的输入。针对有效变形口径为420 mm,包含12个驱动器和60个微位移阵列传感器的能动磨盘,建立的应力盘面形变化量与驱动器策动力间的多元回归分析模型计算结果与试验值极为接近,验证了模型的精确性和可行性。     

浪流共同作用下隔水管涡激动力响应分析

隔水管是海洋浮式生产系统中的重要附属设备.为了探讨在波浪海流共同作用下隔水管的动力响应及进行涡激振动分析,文中给出了三维空间中隔水管运动的控制方程,其中以Matteoluca改进的Vanderpol尾流振子模型为基础计算涡激振动时隔水管与流体之间的相互作用.利用Hermite插值函数对隔水管的运动方程进行有限元离散,采用Newmark方法求解隔水管的动力响应.同时绘出了不同外界条件下相应的位移分布的包络线以及横向涡激振动响应曲线.计算结果表明,所采用的方法正确、有效,可以为隔水管的生产设计及理论分析提供依据.