首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
提出了一种适合于确定框架结构可靠性计算方法.利用模态变换,把系统变为模态独立的振动方程,根据Field提出的假设,先定义阈值,假设控制后系统响应对阚值的穿阚率服从泊松分布,然后根据各模态的控制结果确定相应的可靠性.最后根据Veneziano提出的方法给出系统的可靠性。本文提出针对框架重点部位的控制输出来确定系统可靠性概念。考虑到实际情况,在控制方法选择针对系统不确定性具有较好控制效果的广义预测控制并考虑时滞影响。本文最后给出了计算实例。  相似文献   

2.
振动控制系统的可靠性可以反映出主动控制的效果,本文提出了一种适合于确定框架结构控制系统可靠性的计算方法。该方法利用模态变换,把系统变为模态独立的振动方程,根据Field提出的假设,先定义阈值,假设控制后系统响应对阈值的穿阈率服从泊松分布,然后根据各模态的控制结果确定相应的可靠性,最后根据Veneziano提出的方法给出系统的可靠性。文中提出针对框架最大位移的控制输出来确定系统可靠性概念;此外,在系统降阶和控制方法方面,选择了基于系统可控性的平衡降阶法和针对系统不确定性具有较好控制效果的广义预测控制,最后给出了计算实例,算例表明这一方法是有效的。  相似文献   

3.
为了发展可用于各种岩土工程及工程地质问题的一般的位移反分析系统方法, 本文在边界控制方法的基础上进行了改进。其目的是对于其各种复杂的系统问题确定最重要的力学参数。  相似文献   

4.
Localised arc filament plasma actuators are modelled with a validated technique to examine asymmetric control of a perfectly expanded round free jet to deflect its downstream trajectory. The nominal Mach and Reynolds numbers are 1.3 and 1 million, respectively. No-control, symmetrically controlled, and under-expanded jets are also simulated for comparison purposes. Parametric variation of actuation frequency and duty cycle indicate that asymmetric control can alter the trajectory, and, within the confines of the parameters investigated, the optimal forcing scheme was found to correspond to the jet's column-mode frequency and a duty cycle of approximately 60%. Increasing frequency and duty cycle beyond these values have a detrimental effect on control, which is consistent with experimental findings. Asymmetric actuation resulted in significant mixing enhancement on the actuated side, as evidenced by the increased growth rate of the non-dimensional momentum thickness. The effectiveness of control is reduced for under-expanded jet conditions.  相似文献   

5.
In this study, a fuzzy-based automatic slip control system was developed for agricultural tractors. The developed system continuously measures the amount of slip that occurs during the tillage activities and automatically changes the operation depth of tillage equipment according to the amount of increase in the slip value. The amount of slip occurring on the driving wheels was applied as a separate input to the designed fuzzy control system (FCS) and at the fuzzy rule base, it was decided how much the depth of tillage would be reduced. The system was mounted on an agricultural tractor and trials were carried out in actual field conditions. The results of the tillage trials performed with the developed FCS were compared separately with the results of the tillage trials performed with an operator control (OC) without using any automatic control system. As a result of the trials, compared to the operator control, it was determined that in the tillage activities carried out with FCS, there were 42% decreases in slip values, 30% decreases in draft force values, 44% decreases in fuel consumption values and 5% increases in field work performance values. It was also observed that there were 10% changes in tillage depth.  相似文献   

6.
针对基于磁流变液阻尼器的半主动控制系统中存在的时滞问题, 采用了一种将可控的时滞变量引入半主动控制切换条件的控制策略, 研究了考虑时滞的天棚阻尼控制切换条件对半主动阻尼减振系统的影响, 分析了含有分数阶Bingham模型的线性刚度系统在基础激励下的振动特性. 利用平均法得到了系统在含时滞半主动控制策略下主共振响应的近似解析解, 根据Lyapunov理论分析了系统的稳定性. 通过数值解验证了近似解析解的准确性, 二者具有较好的一致性. 利用近似解析解分析了固定激励频率下时滞对系统幅频响应特性的影响, 以及主共振峰值响应和共振频率随时滞变化的特性规律. 结果表明, 含时滞的半主动控制系统存在一个小时滞区间, 使得系统的振幅在主共振峰对应的频率附近低于不考虑时滞时系统的振幅, 且存在最优时滞使得系统的振幅大幅度降低; 而大时滞的引入会加剧系统的振动, 导致系统的颤振. 确定了基于分数阶Bingham模型的线性刚度系统在天棚阻尼半主动控制下的时滞选取原则, 为振动系统半主动阻尼控制中的时滞选取提供了参考.   相似文献   

7.
研究了亚音速气流下非线性二维薄板结构在横向周期载荷作用下的混沌运动及控制问题.基于von Karman板理论和分离变量法,建立了亚音速下薄板结构的运动控制方程.对于未控系统,采用Melnikov方法判断其混沌运动阈值,并用Runge-Kutta法进行数值验证.对处于混沌运动状态的系统,采用时滞反馈控制方法对混沌运动进行控制.结果表明,Melnikov方法可以有效地预测系统的混沌运动行为,时滞反馈控制方法可以有效地将系统的混沌运动转化为周期运动.  相似文献   

8.
Periodic solutions for parametrically excited system under state feedback control with a time delay are investigated. Using the asymptotic perturbation method, two slow-flow equations for the amplitude and phase of the parametric resonance response are derived. Their fixed points correspond to limit cycles (phase-locked periodic solutions) for the starting system. In the system without control, periodic solutions (if any) exist only for fixed values of amplitude and phase and depend on the system parameters and excitation amplitude. In many cases, the amplitudes of periodic solutions do not correspond to the technical requirements. On the contrary, it is demonstrated that, if the vibration control terms are added, stable periodic solutions with arbitrarily chosen amplitude and phase can be accomplished. Therefore, an effective vibration control is possible if appropriate time delay and feedback gains are chosen.  相似文献   

9.
针对带非线性摩擦力矩和负载扰动的高精度猎雷声纳基阵姿态稳定系统,提出了一种基于神经网络的自适应反步法控制方法。其中神经网络用于估计未知非线性摩擦力矩,进而设计反步法控制器和参数自适应律来对神经网络估计误差和负载扰动进行补偿。最后应用Lyapunov方法证明了所提出的自适应控制器能保证闭环系统的稳定性,并且可以通过选择适当的控制器参数来调整收敛率。仿真结果表明,基于神经网络的自适应反步法控制方法与PID控制相比,系统的动、静态性能指标及鲁棒性得到了全面的改善,与双闭环PID控制相比,跟踪精度提高了3倍多。  相似文献   

10.
地震作用下主-从结构的被动优化控制研究   总被引:5,自引:1,他引:4  
提出了一种利用主-从结构间的相互作用来减少在地震作用下结构响应的控制方法。该方法通过优化设计主-从结构间的被动耗能单元,最大限度地耗散结构的相对振动能量能减小主、从结构的整体振动水平,或最大限度地吸收主结构的相对振动能量以减小主结构的振动。文章首先导出了在平稳白噪声激励下被动耗能单元优化刚度和阻尼的一般表达式,并分析了不同结构参数对控制效果的影响,比较了在不同的平稳过滤白噪声激励下主-从结构相对位  相似文献   

11.
主动约束层阻尼振动控制研究进展   总被引:4,自引:0,他引:4  
主动约束层阻尼(Active Constrained Layer Damping, ACLD)是以可控的压电材料代替被动约束层中不可控的约束层,通过可控的约束层主动地控制黏弹性材料的剪切变形以进一步增大其对振动能量耗散的主动阻尼形式,它充分结合了主动控制与被动阻尼作用各自的优势,使得其在结构振动控制方面显示出极好的应用价值.本文首先解释了ACLD的基本结构和阻尼机理,然后综述了最近几年有关ACLD在结构建模,控制方案及结构优化等方面的最新研究进展,最后指出了应用前景并总结了进一步研究的问题.   相似文献   

12.
针对带不匹配不确定非线性干扰的惯性平台稳定回路跟踪控制问题,提出了基于backstepping的动态滑模控制方法。首先,建立了惯性平台稳定回路的等价模型,该模型由一个线性模型加上一个不确定的非线性函数组成。然后,基于backstepping方法设计了带渐近稳定滑模面的动态滑模控制器,解决了模型不匹配的问题,并提高了系统的鲁棒性。进而应用Lyapunov稳定性理论证明了所设计的控制器不仅能保证闭环系统的稳定性,而且可以通过选择适当的控制器参数来调整跟踪误差的收敛率。最后,仿真结果表明,基于backstepping的动态滑模控制方法与PID控制方法相比,提高了系统的跟踪精度,增强了鲁棒性。  相似文献   

13.
In order to use the optimal control techniques in models of geophysical flow circulation, an application to a 1D advection–diffusion equation, the so-called Burgers' equation, is described. The aim of optimal control is to find the best parameters of the model which ensure the closest simulation to the observed values. In a more general case, the continuous problem and the corresponding discrete form are formulated. Three kinds of simulation are realized to validate the method. Optimal control processes by initial and boundary conditions require an implicit discretization scheme on the first time step and a decentered one for the non-linear advection term on boundaries. The robustness of the method is tested with a noised dataset and random values of the initial controls. The optimization process of the viscosity coefficient as a time- and space-dependent variable is more difficult. A numerical study of the model sensitivity is carried out. Finally, the numerical application of the simultaneous control by the initial conditions, the boundary conditions and the viscosity coefficient allows a possible influence between controls to be taken into account. These numerical experiments give methodological rules for applications to more complex situations. © 1998 John Wiley & Sons, Ltd.  相似文献   

14.
易中贵  戈新生 《力学学报》2016,48(6):1390-1397
研究猫自由下落时的转体运动对探索宇航员在太空失重状态下的空间运动规律具有重要的参考价值.针对猫自由下落时四肢先着地现象的姿态最优控制问题,提出一种由Gauss伪谱法求解可行解与直接打靶法求解最优精确解相结合的混合优化策略.首先,根据猫在自由下落过程中的角动量守恒原理,推导出简化后的两对称刚体系统的非完整姿态运动方程;然后基于Gauss伪谱法将此无漂移系统的姿态非完整运动规划问题离散为非线性规划问题,并在不考虑实际性能指标函数的条件下利用序列二次规划算法求解此非线性规划问题在较少节点时对应的控制变量可行解,再通过三次样条插值获取较多节点时的控制变量值;最后基于直接打靶法将插值得到的控制值作为序列二次规划算法的初始猜测值,从而求解得到最优的控制输入,再代入系统姿态运动方程,通过数值积分得到落体猫的转体姿态运动曲线.通过数值仿真,求解得到的姿态运动曲线是光滑的,能以较高的精度到达预定的目标姿态;最优控制输入也能满足预先设计的零边界控制要求以及最大控制要求;结果表明了此混合优化策略具有较强的鲁棒性和有效性.  相似文献   

15.
Abstract

The purpose of this research is to numerically study a drag reduction method—passive control of shock/boundary layer interaction, which is applied to the boattail portion of a secant-ogive-cylinder-boattail projectile in turbulent transonic flows. The flow pattern and the components of aerodynamic drag computed from numerical data are analyzed. The effectiveness of this method is studied by varying the values of parameters such as porosity distribution, maximum porosity factor and size of porous region. The conditions for optimal drag reduction are investigated and reported. The present results show that the use of this passive control method can not only reduce the boattail drag but also the base drag, and results in an additional 8% total drag reduction compared to that without the passive control technique. This passive control method can be an effective approach for the design of high-performance projectiles in the transonic regime.  相似文献   

16.
高层建筑TMD风振控制优化设计   总被引:10,自引:0,他引:10  
本文探讨了高层建筑TMD风振控制优化设计方法,研究了高层建筑TMD风振控制最优参数取值问题,给出了高层建筑TMD风振控制设计步骤,最后给出了算例说明及其应用。  相似文献   

17.
IntroductionIntheactivitiessuchastheaerospaceengineeringheatprotection[1,2 ],thelarge_scaleconcretepouring ,thechemicalproduction ,thepowdermetallurgyandthefiresafetyengineering[3,4],thereisonekindofnonlinearparabolicdistributedparametercontrolsystemwithmovi…  相似文献   

18.
In this work, it is investigated how classical techniques of linear feedback control design can be applied to the problem of the reduction of acoustic radiation from vibrating structures for cases where the disturbance is broadband and where no reference is available. Much of the work carried out to date in the field of active noise and vibration control has concentrated on applications where either the disturbance to be cancelled is periodic (propeller noise in aircraft,...) or a reference signal, highly correlated with the disturbance, is available (air conditioning duct noise,...) such that a feedforward control approach can be used. When the disturbance is broadband and where no reference is available, feedforward control cannot be used and feedback control must instead be used. Feedback control theory is well established and a vast amount of analytical tools are available to the feedback control designer. However, due to the inherent delays associated with the propagation of sound waves, feedback control of acoustic fields is prone to being unstable. In this paper, a controller is presented which feeds back a measure of the structural response (vibration) of the system in order to determine the control force that needs to be applied to the vibrating structure in order to reduce the total acoustic energy radiated by the vibrating structure. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
包覆电磁场激活板的圆柱尾迹的数值研究   总被引:19,自引:3,他引:19  
陈志华  范宝春 《力学学报》2002,34(6):978-983
利用电磁场作用于电介质溶液的Lorentz力可以控制溶液的流动.对置于弱电介质溶液中,包覆电磁场激活板的圆柱周围的绕流进行数值研究,讨论了电磁场激活板的安装位置,激活方式等对圆柱尾迹的影响.  相似文献   

20.
运用被动连接单元减小相邻结构的振动被证明是一种行之有效的手段。将两相邻结构简化为两单自由度体系,用Maxwell模型模拟连接两相邻结构的流体阻尼器,分别导出了在地面白噪声激励下主结构平均振动能量最小或两相邻结构总平均振动能量最小这两个控制目标下流体阻尼器优化参数的一般表达式,该优化参数仅与两相邻结构的相对自振频率和相对质量有关,也讨论了两相邻结构的相对自振频率和相对质量对控制效果的影响。最后,运用具有不同相对参数的三类相邻结构在El Centro 1940 NS地震波作用下时域响应的数值结果说明了这种被动优化流体阻尼器能够非常有效地减小在地震作用下两相邻结构的振动响应。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号