Precise measurement and control of the pressure-driven flows for microfluidic systems

The pressure-driven device is designed and the flow rates of the microfluidic systems can be supplied by the pressure-driven flows, which can significantly reduce the flow-rate fluctuations coming from the pump source. For pressure-driven flows, the flow rates of the fluids can be predicted by measuring the pressure drop along a polytetrafluoroethylene (PTFE) tubing. Especially, by varying the geometrical parameters of the PTFE tubing, the predicted flow rates of the fluids are compared with the experimental measurements, and the testing precision of the pressure-driven flows can be obtained. Meanwhile, the dynamic characteristics of the open-loop and closed-loop control pressure-driven device are comparatively studied. Particularly, a proportional and integral (PI) controller is integrated with the closed-loop control pressure-driven device, and the effects of the parameters of the PI controller on the dynamic characteristics of the pressure-driven devices are mainly discussed. Most importantly, by improving the dynamic characteristics of the pressure-driven devices, precise measurement and control of the pressure-driven flows can be achieved for microfluidic systems.     

Optimal spectral phase control of femtosecond laser-induced up-conversion luminescence in Sm^3+:NaYF4 glass

The spectral phase of the femtosecond laser field is an important parameter that affects the up-conversion(UC)luminescence efficiency of dopant lanthanide ions.In this work,we report an experi-mental study on controlling the UC lmiiinescence efficiency in Sm^3+:NaYF4 glass by 800-nm femtosec-ond laser pulse shaping using spectral phase modulation.The optimal phase control strategy efficiently enhances or suppresses the UC luminescence intensity.Based on the laser-power dependence of the UC luminescence intensity and its comparison with the luminescence spectrum under direct 266-nm fem-tosecond lciser irradiation,we propose herein an excitation model combining non-resonant two-photon absorption with resonance-media ted three-photon absorption to explain the experimental observations.     

接地式三要素型动力吸振器性能分析

利用固定点理论优化接地类型的动力吸振器得到的结果可能不是全局最优参数,在选择其他参数时主系统可以获得更小的振幅, 接地类型动力吸振器的优化问题值得进一步研究. 因此,以一种接地式三要素型动力吸振器为对象,通过研究系统参数变化对固 定点位置与主系统最大振幅的影响,得到了此吸振器的局部最优参数并分析了它的性能. 首先建立了此系统模型的运动微分方程, 得到了主系统振幅放大因子,发现系统存在3个与阻尼无关的固定点. 固定点中幅值较大点随系统参数变化的趋势可以代表最大振 幅随系统参数变化的趋势,因此利用盛金公式得到了固定点幅值的表达式. 为了更加精确,进一步使用数值算法得到了最大振幅与 系统参数的关系图,发现系统中存在局部最优参数. 通过对比接地式吸振器与接地三要素型吸振器的最大振幅随系统参数变化的趋 势,得到了接地式三要素型吸振器的局部最优参数,并发现当固有频率比小于局部最优频率比时,接地式三要素型吸振器模型主系 统的最大振幅要远小于接地式动力吸振器模型.      

主动射流控制水翼空化的数值模拟与分析

为了改善高速流动工况下水翼吸力面上流场的空化特性,提出了水翼表面主动射流对绕水翼周围流动加以控制的方法.基于密度分域滤波的FBDCM混合湍流模型联合Zwart-Gerber-Belamri空化模型,分析了来流空化数为0.83,来流攻角为8°,射流位置距水翼前缘为x=0.19c时,主动射流对于水翼吸力面上流动的空化特性和水动力特性影响.对回射流的强度进行了量化分析,以探究回射流与流场空化特性的关系.数值分析结果表明,在射流水翼吸力面上的时均空泡体积为原始水翼的1/15,使得流场内空化流动由云空化状态转变为较为稳定的片空化状态,显著地削弱了云空化的发展.此外,射流极大地改善了水翼的水动力性能,使得水翼的升阻比较原始水翼提高了22.9%,空泡的脱落频率减少了26.2%,空泡脱落所引起的振幅减小了9.1%.射流大幅降低了水翼吸力面上低压区面积,水翼吸力面上流体的逆向压力减小,回射流强度降低;同时,射流使水翼吸力面上的边界层减薄,增强了流动的抗逆压梯度能力,一定程度上阻挡了回射流向水翼前缘的流动,这也从机理上分析了主动射流抑制空化的原因.      

空间机器人捕获航天器后基于无源性理论的鲁棒镇定控制

研究了漂浮基空间机器人捕获非合作航天器过程对系统产生的冲击效应及其后联合体系统镇定运动的控制问题。为此,利用拉格朗日方法及牛顿-欧拉法分别获得了捕获前空间机器人及目标航天器的动力学模型;结合动量守恒定律、系统运动几何关系及力的传递规律,分析了捕获过程相互碰撞所产生的冲击效应,建立了捕获完成后两者联合体的系统动力学模型。在此基础上,针对同时存在不确定参数及外部扰动的联合体系统,设计了基于无源性理论的镇定运动神经网络H_∞鲁棒控制算法。本文提出的基于无源性理论设计的鲁棒控制算法具有良好的动态特性及较强的鲁棒性,可快速完成系统的镇定控制,实现轨迹的精确跟踪。系统数值模拟仿真验证了本文控制方案的正确性。     

PDα‐type distributed learning control for nonlinear fractional‐order multiagent systems

This paper considers the consensus tacking problem for nonlinear fractional‐order multiagent systems by presenting a PD^α‐type iterative learning control update law with initial learning mechanisms. The asymptotical convergence of the proposed distributed learning algorithm is strictly proved by using the properties of fractional calculus. A sufficient condition is derived to guarantee the whole multiagent system achieving an asymptotic output consensus. An illustrative example is given to verify the theoretical results.     

An improved generalized predictive control algorithm based on the difference equation CARIMA model for the SISO system with known strong interference

ABSTRACT

The single input single output (SISO) system with known strong interference is widely used in various occasions. Due to its strong interference, the control accuracy is hard to guarantee. To solve this problem, an improved generalized predictive control (IGPC) algorithm is developed. The IGPC firstly builds the difference equation CARIMA (Controlled Auto-Regressive Integrated Moving-Average) model of the SISO system and then treats the system as a two input single output (TISO) system and calculates its predictive vector, then transforms it into a SISO system and uses the TISO system predictive vector to calculate the SISO system control increment. A new parameter called phase coefficient is added to inhibit the control lag. Simulations are performed to make the comparison among the traditional GPC, PID control, velocity synchronization control (VSC), fuzzy adaptive PID control (FAPID), model-based robust PID control (BPID) and the IGPC. Results show that IGPC has best performance compared to the others. Finally, experiments are developed which proved that the IGPC algorithm has a higher accuracy in the SISO system with known strong interference than that of VSC.     

Coexistence and harvesting control policy in a food chain model with mutual defense of prey

A model is proposed to understand the dynamics in a food chain (one predator‐two prey). Unlike many approaches, we consider mutualism (for defense against predators) between the two groups of prey. We investigate the conditions for coexistence and exclusion. Unlike Elettreby's (2009) results, we show that prey can coexist in the absence of predators (as expected since there is no competition between prey). We also show the existence of Hopf bifurcation and limit cycle in the model, and numerically present bifurcation diagrams in terms of mutualism and harvesting. When the harvest is practiced for profit making, we provide the threshold effort value that determines the profitability of the harvest. We show that there is zero profit when the constant effort is applied. Below (resp. above) , there will always be gain (resp. loss). In the case of gain, we provide the optimal effort and optimal steady states that produce maximum profit and ensure coexistence. Recommendations for resource managers As a result of our investigation, we bring the following to the attention of management:

• 1. In the absence of predators, different groups of prey can coexist if they mutually help each other (no competition among them).
• 2. There is a maximal effort to invest in order to gain profit from the harvest. Above , the investment will result in a loss.
• 3. In the case of profit from harvest, policy makers should recommend the optimal effort to be applied and the optimal stock to harvest. This will guarantee maximum profit while ensuring sustainability of all species.

     

Free boundary problem for a fully nonlinear and degenerate parabolic equation in an angular domain

This paper concerns with the problem of how to running an insurance company to maximize his total discounted expected dividends. In our model, the dividend rate is limited in $[0,M]$ and the company is allowed to transfer any proportion of risk by reinsuring. So there are two strategies which we call dividend strategy and reinsurance strategy. The objective function and the corresponding optimal two strategies are the solution and the two free boundaries of the following Barenblatt parabolic equation

$v_t?\underset{0\le a\le 1}{\max }?(\frac{1}{2}{a}^2{\sigma }^2{v}_{xx}+a\mu v_x)+cv?\underset{0\le l\le M}{\max }?[(1?v_x)l]=0$

under certain boundary conditions on an angular domain

$Q_T=\{(x,t)|0<x<Mt,0<t\le T\}.$

The main effort is to analyze the properties of the solution and the free boundaries to show the optimal decision for the insurance company.