碘等离子体受激辐射产生的可行性

针对目前碘激光用化学能作为泵浦源,体积大,易产生有毒物质,且运行时间短,影响其应用范围等问题,本文提出利用碘等离子体产生激光辐射的设想.建立了碘1315 nm受激辐射的等离子体产生模型;通过对泵浦光功率密度与离化电子数密度、自由电子温度等的理论计算,确定了本实验条件下的最优实验参数范围;然后在理论计算的参数范围内,用N...     

等离子体吸收对飞秒激光烧蚀绝缘材料的影响

以自由电子运动的速率方程模型为基础,研究了飞秒脉冲激光对绝缘材料的烧蚀机理,考虑了等离子体对激光能量的吸收效应,建立了激光强度与电子数密度及等离子体吸收系数三者相互耦合的数学模型,计算出飞秒激光烧蚀绝缘材料时的烧蚀阈值,分析了考虑等离子体吸收效应对烧蚀阈值的影响,通过与不考虑等离子体吸收所得结果相比较说明该效应是影响烧蚀阈值的一个重要因素.     

大功率激光焊接光致等离子体的光谱分析

大功率激光焊接过程中,光致等离子体的粒子密度及温度对入射激光能量的传输效率及焊缝的熔深都有很大影响。采用光谱诊断、分析方法,利用谱线相对强度法对激光光致等离子体的温度及电子密度进行了测量与计算,给出了实验条件下光致等离子体电子密度与激光焊接能量及焊接熔深的量化关系。     

基于金属阵列等离子体共振增强的太赫兹光电导天线设计

针对传统太赫兹光电导天线输出功率较低的问题,设计了一种基于金属阵列等离子体共振增强的太赫兹光电导天线,以提高太赫兹光电导天线的输出功率。通过对电磁波和半导体的物理场进行了理论分析,并建立了太赫兹光电导天线模型,利用COMSOL多物理场有限元软件进行了仿真实验研究。仿真计算了金属阵列等离子体共振增强结构不同周期宽度与高度下半导体基底对800 nm激光的光吸收量,得到了一种优化的金属阵列等离子体共振增强结构,然后计算该结构的太赫兹光电导天线的光电流,同时仿真计算了传统太赫兹光电导天线的光电流。研究结果表明:设计得到的金属阵列等离子体共振增强太赫兹光电导天线比传统太赫兹光电导天线光电流增强了约20倍,为等离子体共振增强的太赫兹光电导天线提供了依据。     

CO2激光深熔焊接光致等离子体吸收及其控制

研究高功率密度ＣＯ２激光焊接过程中光致等离子体对入射激光的吸收以及侧吹辅助气体对等离子体控制的影响。彩和准基模ＣＯ２激光束在１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢表面进行扫描焊缝,通过光谱检测装置检测等离子体辐射谱线强度。从而计算等离子体对激光的吸收系数;采和侧吹喷嘴分别通ＣＯ２、Ｎ２、Ａｒ、Ｈｅ４种气体压缩等离子体。研究结果表明,光致等离子体对入射激光能量的吸收损失高达２０％;随着侧吹辅助气体流量的增加,焊     

基于三次样条函数算法的逆阿贝尔变换

等离子体有关参数的径向分布,在等离子体研究中十分有意义的.只要等离子体具有轴对称和光性薄的性质,那么利用Abel逆变换便可以从所测量得到的某种物理量,沿测量方向的积分求出径向分布值.激光等离子体实验中的轴对称的X光体发射强度分布及通过多通道方法可测量电子密度和温度分布,需要采用逆阿贝尔(Abel)变换.本文采用三次样条函数近似方法计算逆Abel变换,并对两种有代表性的分布进行了计算,数值模拟结果表明:此方法反演的精度高,计算也比较简便,程序实现很容易.     

纳秒级激光脉冲展宽系统的分析及应用

建立了一种纳秒级多腔式激光脉冲扩展系统.通过激光脉冲展宽,该系统可以有效降低脉冲激光的峰值功率,从而在激光燃烧诊断实验中避免激光诱导等离子体的产生,减少背景干扰,有效提高信噪比.建立了理论模型,对影响脉冲展宽的分束比、腔长以及光学腔个数等几个主要参数进行了分析,并通过数值计算实现了各参数的优化.利用建立的多腔串联式激光...     

CO_2激光深熔焊接光致等离子体吸收及其控制

研究高功率密度 CO2 激光焊接过程中光致等离子体对入射激光的吸收以及侧吹辅助气体对等离子体控制的影响。采用准基模 CO2 激光束在 1 Cr1 8Ni9Ti不锈钢表面进行扫描焊缝 ,通过光谱检测装置检测等离子体辐射谱线强度 ,从而计算等离子体对激光的吸收系数 ;采用侧吹喷嘴分别通CO2 、N2 、Ar、He4种气体压缩等离子体。研究结果表明 ,光致等离子体对入射激光能量的吸收损失高达 2 0 % ;随着侧吹辅助气体流量的增加 ,焊缝呈现3个区间 :当气体压力低于金属蒸汽压力时 ,焊缝为“酒杯”状 ,深宽比很小 ;当辅助气体操作压力稍高于金属蒸汽压力 ,等离子体可被有效控制从而获得最佳焊缝。     

A304不锈钢薄板激光焊接的光谱分析

为了进一步分析不同焊接参数对A304不锈钢薄板激光焊接效果的影响,该文在不同的焊接参数和激光输出方式下,采用AvaSpec-2048型光纤光谱仪对A304不锈钢薄板激光焊接的电弧进行了光谱分析。研究结果表明,激光功率、焊接速度和激光输出方式对激发出特征谱线的元素的种类和激光等离子体中元素的含量有一定的影响。     

电弧等离子体折射率的理论计算

从等离子体物理方程出发,推导出了折射率与电弧等离子体各种组分和温度之间的关系,并以氩电弧等离子体为例进行了实际的数值计算。这一关系的确立,为基于折射率效应的激光干涉法电弧等离子体诊断技术提供了理论基础,因此可以采用单波长激光干涉法(包括全息法)同时确定电弧等离子体的各种组分和温度,从而避免了采用双波长法时的缺点,这对发展电弧等离子体诊断及其加工技术有重要意义。计算结果表明,在波长给定时折射率是原子密度和电子密度的单值函数;温度小于6 000 K时,电子对折射率几乎没有什么影响,当温度高于17 000 K后,折射率则完全由电子决定。     

FDM analysis for MHD flow of a non-Newtonian fluid for blood flow in stenosed arteries

A computational model is developed to analyze the effects of magnetic field in a pulsatile flow of blood through narrow arteries with mild stenosis, treating blood as Casson fluid model. Finite difference method is employed to solve the simplified nonlinear partial differential equation and an explicit finite difference scheme is obtained for velocity and subsequently the finite difference formula for the flow rate, skin friction and longitudinal impedance are also derived. The effects of various parameters associated with this flow problem such as stenosis height, yield stress, magnetic field and amplitude of the pressure gradient on the physiologically important flow quantities namely velocity distribution, flow rate, skin friction and longitudinal impedance to flow are analyzed by plotting the graphs for the variation of these flow quantities for different values of the aforesaid parameters. It is found that the velocity and flow rate decrease with the increase of the Hartmann number and the reverse behavior is noticed for the wall shear stress and longitudinal impedance of the flow. It is noted that flow rate increases and skin friction decreases with the increase of the pressure gradient. It is also observed that the skin friction and longitudinal impedance increase with the increase of the amplitude parameter of the artery radius. It is also found that the skin friction and longitudinal impedance increases with the increase of the stenosis depth. It is recorded that the estimates of the increase in the skin friction and longitudinal impedance to flow increase considerably with the increase of the Hartmann number.     

Characteristic analysis of shunt for high voltage direct current measurement

The resistive shunt is generally used as a sensor in the high voltage direct current (HVDC) system. The high frequency alternating current has an impact on the performance of the shunt owing to the skin effect and proximity effect causing DC measuring errors and even leading to protective system false operation. The impact of skin and proximity effects on the squirrel cage shunt is discussed in the paper. Numerical evaluation of the two effects is applied. The calculation results show that the value of the shunt resistance is dependent on the current frequency. Adequate selection of the radius of the conductors and the distances between conductors can greatly reduce the influence of the two effects on DC measurement accuracy. The field data of practical shunts during nominal operation and transient process confirm the results.     

Modeling magnetic fields measured by surface probes embedded in a cylindrical flux conserver

Calculating magnetic fields at the surface of a flux conserver, perfect conductor, for displaced plasma currents is useful for understanding modes of a Z-pinch. The magnetic fields measured at the flux conserver are a sum of the magnetic fields from the plasma current and the eddy currents which form in the walls to keep the flux constant. While the magnetic field at the wall from the plasma current alone is easily calculated using the Biot-Savart law, finding the eddy currents in the flux conserver which satisfy the boundary conditions can be a tedious process. A simple method of calculating the surface magnetic field for a given Z-pinch displacement off-axis is derived for a cylindrical flux conserver. This relationship does not require the explicit calculation of the eddy currents, saving time when analyzing surface magnetic probe measurements. Analytic expressions can be used to describe the surface magnetic field which increase the understanding of the magnetic probe measurements.     

电流变减振器用于铣床振动控制的试验研究

试验研究了电流变减振器在铣床颤振控制中的应用。试验发现，电流变减振器的刚度及阻尼随外加电场强度的增加而增大，主振系统的振幅随电场强度的增加而减小。试验表明电流变减振器具有控振效果明显、结构简单的特点。只要场强选取适当，采用电流变减振装置可以控制铣床刀杆系统的颤振。     

A 3D Monte Carlo code for the modeling of plasma dynamics and beam formation mechanism in electron cyclotron resonance ion sources

The code here presented is the first part of a Monte Carlo (MC) self-consistent 3D plasma simulator. It is yet able to solve the equation of motion for thousands of independent charged particles. The procedure allows to understand the consequences of each phenomenon introduced in the evolution steps of the code. MC random selection of starting parameters is used for each particles; the environmental conditions enclosed in the simulation are ECRIS magnetic field, resonant electromagnetic wave, initial plasma density distribution and MC calculation of Spitzer collision. The results of the first simulations explain some typical effects as the hollow beam formation and the main plasma deconfinement mechanism.     

惯性圆锥破碎机多体动力学分析及试验验证

惯性圆锥破碎机存在整机振幅大且能耗高等问题，制约了其在工业领域的进一步发展，其多体动力学求解可以为明确各主要动力学参数与整机振幅和能耗的关系提供理论计算方法。采用绝对坐标法建模，将动锥的纯滚动约束等效为完整和线性非完整约束，得到了含一阶线性非完整约束的微分代数方程组,提出了基于隐式Runge-Kutta积分变步长的LU状态空间法。在稳定工况下，对定锥各测量点动态响应的仿真结果和工业现场试验结果进行对比分析，验证了模型和数值算法的有效性。计算结果表明：驱动转速、定锥质量、阻尼系数和动锥质量对振幅的影响较大，刚度系数对振幅几乎没有影响；增加定锥的质量可以有效降低单位能耗；在一定范围内，增加阻尼系数会造成阻尼耗散增大，使单位能耗升高。     

一种新的离子引出方法——射频共振法

在传统的静电场离子引出中,由于等离子体屏蔽的存在,限制离子引出时间,降低了离子引出率。为了削弱静电场方法中等离子体屏蔽对离子引出的影响,提出了射频共振的方法。射频共振法是利用等离子体回路阻抗与外加射频电场频率之间的相互关系,通过调节射频电场频率,使射频电场与等离子体达到共振状态。当达到共振时,等离子体阻抗最小,电场可以穿透等离子体,提高了离子引出效率。共振法缩短了离子引出时间,提高了离子引出效率,并且可以通过对外加磁场的调节来控制等离子体密度。本文介绍了目前射频共振理论的模拟计算和实验研究情况。     

底盘构件多轴随机载荷下高周疲劳准则研究

为探明汽车底盘构件在随机载荷下多轴高周疲劳准则的应用方法与寿命预测规律,以某品牌B级轿车为研究对象,通过采集试验场强化路轮心六分力信号,建立了整车多体动力学模型,应用虚拟迭代法获取转向节与其他零件连接点的载荷时间历程;建立转向节有限元模型,通过模态仿真与试验验证了有限元模型的准确性;提取了von Mises应力下寿命值最小节点的应力分量时间历程;研究了8种高周疲劳准则所基于的3种类型临界平面的计算方法,通过多轴循环计数提取临界面上正应力幅与剪应力幅,并计算不同准则对应的等效应力幅,总结幅值分布与寿命预测规律。研究结果表明,在幅值分布与寿命预测方面,Zhang-Yao准则的等效剪应力幅值整体偏大,预测寿命为1.09×105周次,较其他准则偏于保守;McDiarmid准则的大应力幅仅占3.4%,预测寿命为1.25×106周次,明显大于其他准则的预测寿命值,而改进的McDiarmid准则预测寿命值明显减小。在计算成本方面,von Mises准则无需提取临界面与多轴循环计数,应用最为便捷;Findley准则提取临界面过程需要计算所有平面的正应力与剪应力数据,故计算成本最高。     

结晶器振动状态在线检测系统的研制

根据板坯连铸机结晶器的特点,设计并实现了结晶器振动状态在线检测系统。系统实现了三维振动动画模型仿真、振动频率辨识与计算、振动相位计算、振动幅值及偏差计算和相关工艺参数计算。在炼钢厂现场应用表明,系统的软硬件设计满足工业现场的使用要求,能精确地测量结晶器的振动幅值、频率、相位和相关工艺参数,为结晶器的安全生产提供了科学的依据,有较好的工程应用价值。     

Calculation on cylinder pressure fluctuation by using the wave equation in KIVA program

Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and knock.The current studies are based on cylinder pressure test to obtain ...