多回路串级控制系统开环传递函数的分析

由于多回路串级控制系统结构上存在两个以上的反馈通道,在进行结构图化简时采用不同的变换思路,可以得到相同的闭环传递函数和不同的开环传递函数。以带测速发电机局部反馈的位置随动系统为例,根据开环传递函数的定义和结构图等效变换原则,对多回路串级控制系统的开环传递函数进行了分析,得出了求解复杂多回路串级控制系统开环传递函数的方法。     

被动式单级弹簧隔振系统模型分析

基于弹簧的被动式隔振系统通过等效换算可以简化为悬挂式弹簧振子模型,根据动力学方程求得传递函数,建立数学模型。通过给所建立模型输入典型信号——阶跃信号、脉冲信号、正弦信号,进行系统仿真,在系统固有频率两端频段均有隔振效果,随着系统固有频率的降低,系统在高频段的隔振性能有所提高,但是对低频段干扰信号有放大作用。     

短周期气压波对青岛台体应变的影响分析

利用相关分析、回归分析和交叉小波变换等方法，研究青岛台短周期（小于128 min）气压波和体应变的相关系数、气压系数和时频谱。结果表明，影响青岛台体应变的短周期气压波的优势周期为16~128 min。周期小于16 min（高频段）时，相关系数较小，随周期增大而增大；周期大于16 min（低频段）时，相关系数较大，趋于稳定。在相关系数较大且稳定的周期，气压系数为（3.5~3.6）×10-9/hPa，其中周期为16~64 min的气压系数随时间波动最小。交叉小波变换能更细致地揭示不同周期气压波和体应变在时频域的相关关系。     

反馈地震计低频扩展方法研究

根据反馈地震计的反馈模型推导传递函数,并将其频率特征分解为低频端和高频端两部分。基于反馈模型中低频端频率特性的二阶高通滤波器传递函数,提出低频截止频率扩展的方法,包括降低机械固有角频率ω0、增加摆的质量m、降低灵敏度Sv、增大反馈线圈阻值或减少线径、选用更高电阻率的线圈材料、使用更弱的磁场。通过井下反馈地震计实验,验证了其低频端扩展与理论推导的一致性。     

绝对重力仪中几种隔振系统的对比测试

介绍目前绝对重力仪中几种常用的隔振系统及其研究进展,并利用FG5-112绝对重力仪中的Super Spring以及现有的几种隔振系统,在相同的环境下进行对比测试。通过对测试结果的分析,给出各种隔振系统的隔振效果。该项工作的开展为下步自主研制隔振系统、提高隔振性能积累经验。     

基于低轨星座增强的北斗系统RAIM可用性分析

介绍基于残差的RAIM模型及基于单故障假设的保护水平计算方法,分析信号波束角与低轨信号高度遮蔽角之间的关系,提出以保护水平改善值和保护水平改善比作为低轨星座完好性增强的评价指标。同时,基于北斗系统与低轨星座的仿真数据,分析高度遮蔽角和等效误差水平对低轨星座增强的北斗系统保护水平和RAIM可用性的影响。结果表明,低轨星座的高度遮蔽角和等效误差水平越低,对导航系统保护水平和RAIM可用性的增强效果越好。     

基于2014年康定6.3级地震震后形变分析区域介质特征

以2014年康定6.3级地震震后InSAR形变资料为约束,采用三层粘弹性地震周期模型及遗传算法反演鲜水河断裂南东段的康定地震震区深部介质粘弹性层厚度及粘滞系数。最优拟合结果表明：1）该区域下地壳粘弹性层厚度为5 km,粘滞系数为9.9×10¹⁷ Pa·s,且断层两侧下地壳流变存在显著的横向不均一性。2）将断层两侧分别反演,显示断层南西盘下地壳粘滞系数（8.7×10¹⁷ Pa·s）略小于断层北东盘下地壳粘滞系数（1.2×10¹⁸ Pa·s）。     

闭环极点与开环零极点的一种关系式

根据控制系统的特征方程和开环传递函数的关系 ,推导出闭环极点与开环零极点之间的关系式 ,并举例说明其应用 ,该公式简单且具有通用性和实用性。     

拉普拉斯变换的两个新运算法则

推导出了拉普拉斯变换乘法运算法则和除法运算法则,进一步给出了线性系统增加闭环零点或闭环极点时时间响应的计算式,应用这些计算公式,分析了闭环零点和闭环极点对时间响应的影响。分析结果表明:增加闭环零点或实数闭环极点不会改变时间响应的振荡性,在线性系统中,离虚轴越远的闭环零点和闭环极点对时间响应影响越小。     

四翼混沌吸引子系统控制

分析具有四翼混沌吸引子系统(An系统)的动力学性质,得出系统存在9个不稳定平衡态,导致系统形成复杂的四翼吸引子结构.数值计算得出系统随参数变化的倍周期分岔图,通过单输入和多输入方式,采用线性反馈方法控制混沌态.结果表明:当控制参数选择适当的范围时,可以将混沌运动控制为规则的周期运动或稳定平衡态;不同初始条件的控制结果存...     

中国食管癌与土壤环境中元素的相关性

利用土壤元素资料 2 0 6 94 4 8个数据 ,食管癌死亡调查资料 1750 80例 ,研究了食管癌死亡率与人群生存的土壤环境中元素的相关性。结果表明 ,铅、硒、铷、铯、镁、钙、镓、铊、钍、铀、锡、铪、铋、钼、溴、碘元素与食管癌死亡率有相关性     

天然地基强迫振动测试与分析

在试验块体分别为明置与埋置情形时,利用激振器对某工程场地天然地基分别进行竖向、水平回转及扭转稳态强迫振动试验。试验结果表明,埋置情形试验的动力特性参数值均大于明置情形试验相应值;同种试验情形下,地基第一振型共振频率竖向最大,水平回转向其次,扭转向最小;土的参振质量均远大于基础本身质量。     

Synergetic Analysis and Possible Control of Vortex-Induced Vibrations in a Fluid-Conveying Steel Catenary Riser

This work aimed to demonstrate possibilities for both active and passive control of the vortex-induced vibration and fatigue life of steel catenary risers via an analysis of the self-organization and evolution of the structural vibration based on synergetic theory. An analysis of the complex interrelated and synergistic relationship between the order parameter and the fast variable was performed, and the master equation of the nodal displacements was established as the order parameter for the evolution of the riser’s structural vibration. Passive control methods include modifying the structure’s elastic modulus, the internal fluid velocity, the top tension and the structural damping ratio, while an active control involves adjusting the external flow rate. Optimized parameters were obtained by analyzing the non-steady state solution of the master equation. The results show that the fatigue life greatly increases as the riser’s elastic modulus decreases. In contrast, the fatigue life decreases with an increase of the internal fluid velocity. With an increase of the top tension, the vibration amplitudes and the number of modes may decrease, resulting in fewer bending stress cycles and a longer fatigue life. Furthermore, the structural damping ratio should be as large as possible. Finally, an active and passive control of the riser structure’s response to vortex-induced vibration and its fatigue life can be achieved by carefully modifying the parameters mentioned above. The results may provide a theoretical framework for engineering practice concerning the design and control of steel catenary riser structures which are affected by vortex-induced vibration.     

论折叠摆对地壳振动的响应特性

通过简化的折叠摆模型，深入研究了折叠摆对地壳振动的响应特性。理论分析表明，折叠摆不仅对地倾斜固体潮的响应非常灵敏，而且具有明显的抗外界振动干扰的能力。如果采用精密红外位移传感和负反馈控制技术，折叠摆测量倾斜潮的灵敏度可望达到１０－１０ｒａｄ。最后给出了折叠摆倾斜仪的实验设计     

A nonlinear vortex induced vibration model of marine risers

With the exploitation of oil and gas in deep water, the traditional vortex induced vibration (VIV) theory is challenged by the unprecedented flexibility of risers. A nonlinear time-dependent VIV model is developed in this paper based on a VIV lift force model and the Morison equation. Both the inline vibration induced by the flow due to vortex shedding and the fluid-structure interaction in the transverse direction are included in the model. One of the characteristics of the model is the response-dependent lift force with nonlinear damping, which is different from other VIV models. The calculations show that the model can well describe the VIV of deepwater risers with the results agreeing with those calculated by other models.     

Study on dynamic characteristics of coupled model for deep-water lifting system

The underwater installation of marine equipment in deep-water development requires safe lifting and accurate positioning. The heave compensation system is an important technology to ensure normal operation and improve work accuracy. To provide a theoretical basis for the heave compensation system, in this paper, the continuous modeling method is employed to build up a coupled model of deep-water lifting systems in vertical direction. The response characteristics of dynamic movement are investigated. The simulation results show that the resonance problem appears in the process of the whole releasing load, the lifting system generates resonance and the displacement response of the lifting load is maximal when the sinking depth is about 2000 m. This paper also analyzes the main influencing factors on the dynamic response of load including cable stiffness, damping coefficient of the lifting system, mass and added mass of lifting load, among which cable stiffness and damping coefficient of the lifting system have the greatest influence on dynamic response of lifting load when installation load is determined. So the vertical dynamic movement response of the load is reduced by installing a damper on the lifting cable and selecting the appropriate cable stiffness.     

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基于Nevanlinna-Pick插值的时滞系统鲁棒控制器设计

针对时滞系统,提出一种基于Nevanlinna-Pick插值的鲁棒控制器设计方法.它首先通过互质分解得到控制器和灵敏度函数的参数化形式,将控制器的设计转化为灵敏度函数成型;然后利用同伦法求解具有阶次约束的Nevanlin-na-Pick插值问题,从而求得控制器和灵敏度函数.仿真实验结果表明,闭环系统的灵敏度函数由被控对象的非最小相位零点和不稳定极点决定.