Reentry Attitude Tracking Control for Hypersonic Vehicle with Reaction Control Systems via Improved Model Predictive Control Approach

This paper studies the reentry attitude tracking control problem for hypersonic vehicles(HSV)equipped with reaction control systems(RCS)and aerodynamic surfaces.The attitude dynamical model of the hypersonic vehicles is established,and the simplified longitudinal and lateral dynamic models are obtained,respectively.Then,the compound control allocation strategy is provided and the model predictive controller is designed for the pitch channel.Furthermore,considering the complicated jet interaction effect of HSV during RCS is working,an improved model predictive control approach is presented by introducing the online parameter estimation of the jet interaction coefficient for dealing with the uncertainty and disturbance.Moreover,considering the strong coupling effect between the yaw channel and roll channel,a coupled model predictive controller is designed by introducing the feedback of sideslip angle into the roll control channel to eliminate the coupling effect.Finally,the comparison simulations using the classical control method,MPC and IMPC approach are given to demonstrate the effectiveness and efficiency of the presented IMPC scheme.

Experimental studies of water hammer in propellant feed system of reaction control system

Water hammer pressure transient produces large dynamic forces which can damage the pipes and other assemblies in the feed line of a reaction control system(RCS).It has led to the failure of pressure transducers monitoring the manifold pressure in the feed line of RCS.Therefore,water hammer studies have been carried out to understand its effect in feed line.Feedline system has been simplified to develop a mathematical model and experiments have been carried out at extensive levels.The mathematical model was developed considering pipe of uniform c/s and moving liquid-gas interface.The experimental studies have been done using water as working medium instead of actual propellant.The studies showed that rate of pressurization have a very critical role on the water hammer amplitude.Sensitivity studies have been also carried out to study the effect of density,friction and initial liquid column length on water hammer amplitude.

Precisely Controlled Synthesis of Pt-Pd Octahedral Nanoframes as a Superior Catalyst towards Oxygen Reduction Reaction

Pt-based nanoframes represent a class of promising catalysts towards oxygen reduction reaction. Herein, we, for the first time, successfully prepared Pt-Pd octahedral nanoframes with ultrathin ridges less than 2 nm in thickness. The Pt-Pd octahedral nanoframes were obtained through site-selected deposition of Pt atoms onto the edge sites of Pd octahedral seeds, followed by selective removal of the Pd octahedral cores via chemical etching. Due to that a combination of three-dimensional opens geometrical structure and Pt-skin surface compositional structure, the Pt-Pd octahedral nanoframes/C catalyst shows a mass activity of 1.15 A/mgPt towards oxygen reduction reaction, 5.8 times enhancement in mass activity relative to commercial Pt/C catalyst （0.20 A/mgPt）. Moreover, even after 8000 cycles of accelerated durability test, the Pt-Pd octahedral nanoframes/C catalyst still exhibits a mass activity which is more than three times higher than that of pristine Pt/C catalyst.

Operational feasibility study of stagnation pressure reaction control for a mid-caliber non-spinning projectile

Controlled,guided munitions can reduce dispersion in the shot,while providing the capability of engaging both stationary and maneuvering targets.The Netherlands Organisation for Applied Scientific Research has developed a fin-less control technology called Stagnation Pressure Reaction Control(SPRC)that takes stagnation pressure air and directs it sideways to control non-spinning projectiles.In a previous study,this technology was demonstrated at Mach 2 wind-tunnel conditions to achieve up to 1.5°controllable angle of incidence for a non-spinning,aerodynamically unstable projectile-like test object.In an operational scenario,the decelerating projectile will experience a decline in control force while the simultaneous forward shift of the center of pressure increases the need for control force.Furthermore,angles of incidence exceeding 1.5°will be experienced under realistic flight conditions,especially against maneuvering targets.This work addresses these challenges and presents an operational feasibility study for a practical application of SPRC in a non-spinning mid-caliber gun-launched projectile,using experiment data on control latency and force of the earlier study.It illustrates the combined effect of the control-and stability dynamics and underlines the potential of an SPRC projectile as a precisionoperation ammunition.This research revealed that SPRC technology can stabilize and control the hypothesized projectile in a direct fire scenario against stationary and maneuvering targets.

THE SOLID STATE CONTROLLED PHOTOCHEMICAL REACTION OF NITROBENZALDEHYDE WITH INDOLE

The solid state photochemical reaction of nitrobenzaldehyde with indole was investigated. Seven hey products were identified by IR, MS,^(1)H HMR and elemental analysis.

Active disturbance rejected predictive functional control for space vehicles with RCS

Reaction control system(RCS) is a powerful and efficient actuator for space vehicles attitude control, which is typically characterized as a pulsed unilateral effector only with two states(off/on). Along with inevitable internal uncertainties and external disturbances in practice, this inherent nonlinear character always hinders space vehicles autopilot from pursuing precise tracking performance. Compared to most of pre-existing methodologies that passively suppress the uncertainties and disturbances, a design based on predictive functional control(PFC) and generalized extended state observer(GESO) is firstly proposed for three-axis RCS control system to actively reject that with no requirement for additional fuel consumption. To obtain a high fidelity predictive model on which the performance of PFC greatly depends, the nonlinear coupling multiple-input multiple-output(MIMO) flight dynamics model is parameterized as a state-dependent coefficient form. And based on that, a MIMO PFC algorithm in state space domain for a plant of arbitrary orders is deduced in this paper.The internal uncertainties and external disturbances are lumped as a total disturbance, which is estimated and cancelled timely to further enhance the robustness. The continuous control command synthesised by above controller-rejector tandem is finally modulated by pulse width pulse frequency modulator(PWPF) to on-off signals to meet RCS requirement. The robustness and feasibility of the proposed design are validated by a series of performance comparison simulations with some prominent methods in the presence of significant perturbations and disturbances, as well as measurement noise.

Robust controller design for compound control missile with fixed bounded convergence time

A robust controller for bank to turn(BTT) missiles with aerodynamic fins and reaction jet control system(RCS) is developed based on nonlinear control dynamic models comprising couplings and aerodynamic uncertainties. The fixed time convergence theory is incorporated with the sliding mode control technique to ensure that the system tracks the desired command within uniform bounded time under different initial conditions. Unlike previous terminal sliding mode approaches, the bound of settling time is independent of the initial state, which means performance metrics like convergence rate can be predicted beforehand. To reduce the burden of control design in terms of robustness, extended state observer(ESO) is introduced for uncertainty estimation with the output substituted into the controller as feedforward compensation. Cascade control structure is employed with the proposed control law and therein the compound control signal is obtained.Afterwards, control inputs for two kinds of actuators are allocated on the basis of their inherent characteristics. Finally, a number of simulations are carried out and demonstrate the effectiveness of the designed controller.

Robust cobalt oxide catalysts for controllable hydrogenation of carboxylic acids to alcohols

The selective catalytic hydrogenation of carboxylic acids is an important process for alcohol production,while efficient heterogeneous catalyst systems are still being explored.Here,we report the selective hydrogenation of carboxylic acids using earth‐abundant cobalt oxides through a reaction‐controlled catalysis process.The further reaction of the alcohols is completely hindered by the presence of carboxylic acids in the reaction system.The partial reduction of cobalt oxides by hydrogen at designated temperatures can dramatically enhance the catalytic activity of pristine samples.A wide range of carboxylic acids with a variety of functional groups can be converted to the corresponding alcohols at a yield level applicable to large‐scale production.Cobalt monoxide was established as the preferred active phase for the selective hydrogenation of carboxylic acids.

NOVEL HYPERBRANCHED POLY(PHENYLENE OXIDE)S WITH PHENOLIC TERMINAL GROUPS: EFFECTS OF REACTION TIME AND CORE MOLECULES ON THE MOLECULAR WEIGHT AND POLYDISPERSITY

A novel hyperbranched poly（phenylene oxide） （HPPO） with phenolic terminal groups was prepared from 4-bromo-4＇,4＂-dihydroxytriphenylmethane as AB2 monomer in dimethylsulfoxide （DMSO） via a modified Ullmann reaction. The molecular weight and polydispersity （PD） of the resulting polymers increased with increasing reaction time. In the presence of core molecules （bisphenol A and 1,3,5-trihydroxybenzene）, which have the similar molecular backbones to the reactive monomer, the molecular weight could be controlled by varying the core-to-monomer ratio. Incorporation of a very small amount of core molecules could lead to a higher molecular weight as compared with that without the addition of core molecules. However, when the core content reached certain extent, the molecular weight would decrease with the further increase in the core content. A new similar behavior of control over the PD was also obtained. The resulting polymers were characterized by ^1H-NMR, ^13C-NMR, FT-IR, and GPC.

Robust sliding mode control with ESO for dual-control missile

This paper proposes a novel composite dual-control bycombing the integral sliding mode control （ISMC） method basedon the finite time convergence theory with extended state observer（ESO） for a tracking problem of a missile with tail fins and reactionjetcontrol system （RCS）. First, the ISMC method based on finitetime convergence is utilized to design the control law of tail fins andthe pulse control of RCS for the dual-control system, ensuring thesystem with rapid response and high accuracy of tracking. Then,ESO is employed for the estimation of aerodynamic disturbancesinfluenced by the airflow of thruster jets. With the characteristicof high accuracy estimation of ESO, the chattering free trackingperformance of the attack angle command and the robustnessof the control law are achieved. Meanwhile, the stability of thedual-control system is analyzed based on finite time convergencestability theorem and Lyapunov’s theorem. Finally, numerical simulationsdemonstrate the effectiveness of the proposed design.

Nested case-control study of multiple serological indexes and Brighton pediatric early warming score in predicting death of children with sepsis

BACKGROUND Currently, it is difficult to predict the complications of children at the early stage of sepsis. Brighton pediatric early warning score(PEWS) is a disease risk assessment system that is simple and easy to operate, which has good sensitivity and specificity in disease recognition among children. Because detection indicators vary widely in children, a single indicator is difficult to assess the posttreatment status of children with sepsis.AIM To investigate the relationship between serological markers, Brighton PEWS, and death in children with sepsis after treatment.METHODS A total of 205 children diagnosed with sepsis at our hospital were enrolled. The baseline data, serum scores, and PEWS scores were recorded. In the nested casecontrol study, children who died during the study period were included in an observation group. According to the matching principle, the children who were not dead in the same cohort were included in a control group. The influencing factors of death in children with sepsis after treatment and the value of each evaluation index in predicting the prognosis of children were analyzed.RESULTS A total of 96 children were enrolled in the study, including 48 each in the observation group and the control group. Multivariate logistic regression analysis indicated that antibacterial treatments within 1 h(P = 0.017), shock(P = 0.044),multiple organ dysfunction syndrome(MODS)(P = 0.027), serum procalcitonin(PCT)(P = 0.047), serum albumin(ALB)(P = 0.024), and PEWS(P = 0.012) were independent risk factors for the death of children with sepsis. The area under the curve of the combination of ALB, PCT, and PEWS to predict the death in children with sepsis was the highest(0.908).CONCLUSION Antibacterial treatments within 1 h, shock, MODS, PCT, ALB, and PEWS are independent risk factors for the death of children with sepsis. The predictive accuracy of the combination of PCT, ALB, and PEWS for the prognosis of children with sepsis is the best.

基于嵌入式ARM的微流控PCR检测系统设计

为了实现微流控设备功能的集成化、提高交互系统的可操作性,提出一种基于嵌入式ARM的微流控聚合酶链式反应(PCR)控制系统及上位机软件的设计方案。系统硬件采用多个嵌入式ARM控制器与功能模块相互协调,制定可扩展的通信机制和协议,实现微流控PCR检测过程中的流路运动、温度控制、荧光信号采集等功能的集成控制。采用Qt结合SQLite数据库设计了上位机软件,利用多线程和节点映射,实现对硬件模块的协调控制以及检测信息存储。实验表明:该系统运行稳定,人机交互效果好,可操作性高,满足微流控PCR的集成功能需求。

磺化工艺过程控制方案

以多管膜式磺化反应工艺为例,描述了磺化反应的制取方法、生产过程及控制流程。详细介绍了反应过程中对温度、压力、流量等反应条件的控制方案。

Fenton法预处理合成革废水的去除研究

合成革废水中含有大量的二甲基甲酰胺(DMF)等有机污染物,对生物具有毒性危害。采用单因素试验方法,获得Fenton反应对DMF处理最佳工艺参数为pH=3、过氧化氢(H_(2)O_(2))与化学需氧量(COD_(Cr))的质量比m=6.69、H2O2与亚铁离子的摩尔比n=8及反应时间t=120 min, DMF的平均去除率达96.18%。在此基础上,利用Design-Expert软件中的响应面实验设计原理,设计三因素三水平共17组实验,进一步研究确定上述参数对Fenton法预处理合成革废水COD_(Cr)的去除效果。设计并制作针对DMF皮革废水有良好降解效果的Fenton一体化、H_(2)O_(2)和FeSO_(4)精准投加、pH精准调控的自动控制系统及集成反应设备,合成革废水的COD_(Cr)和DMF的平均去除率为71.87%和95.78%。

Boundary Control for a Class of Reaction-diffusion Systems

Boundary control for a class of partial integro-differential systems with space and time dependent coefficients is consid- ered. A control law is derived via the partial differential equation （PDE） backstepping. The existence of kernel equations is proved. Exponential stability of the closed-loop system is achieved. Simulation results are presented through figures.

石油催化裂化分馏系统的自控化设计及仪表选型分析

按照“化工装置自控工程设计规定”,根据工艺提出的检测及控制要求,对催化裂化分馏装置的分馏塔、反应-再生系统、回炼油罐、汽提塔的液位、温度、压力等进行控制和检测,并对流程做了简单的介绍。根据催化裂化分馏装置的特点选择了合适的仪表和DCS系统。

基于反作用发动机推力的空天飞行器再入姿态飞行控制

研究了空天飞行器(ASV)再入跨大气层飞行时的姿态控制问题。在ASV跨大气层再入飞行时,通过反作用控制系统(RCS)中的反作用发动机推力产生控制力矩来控制ASV的姿态,以补偿气动舵面操纵失效或者部分失效而引起的控制力矩不足;随着空气密度的增加,气动舵面逐步介入控制系统,RCS随之逐步退出.由于快回路控制器产生进行姿态控制所需要的控制力矩,其通过相应的控制分配将控制力矩映射到作动器,为了减轻作动器的抖振,提出了利用基于区域模型的T-S模糊多模型控制方法设计快回路控制器,在跟踪期望角速度的同时,柔化控制信号.最后通过仿真验证了所提方法的有效性.

空天飞行器概念设计再入数学建模研究

研究了空天飞行器(ASV)再入飞行条件下6自由度数学建模问题,所建数学模型包含完整的6自由度动力学方程和运动方程。气动力和力矩系数是迎角、马赫数、高度及控制舵面偏角的函数,反作用控制系统(RCS)推进器属于开关型的,控制量可近似为常值开关型的量。开环特性分析说明整个模型能够体现出ASV复杂的非线性、耦合性以及快时变性等特点,可满足新一代高超声速飞行器轨迹优化、姿态控制等问题的概念设计和仿真研究。

跨大气层飞行器再入段RCS控制特性

以航天飞机为例,论述了跨大气层飞行器反推力控制系统(R eaction Con trol System,RCS)的工作原理,并给出了RCS推进器的控制模型。同时分析了RCS在回路中的各种工作模式和多推进器的系统冗余及其组合方式。最后在对RCS系统操作的基础上,研究了航天飞机在再入段飞行时的RCS控制问题。