Natural convection heat transfer of molten salt in a single energy storage tank

Heat transfer in molten salt in a cylinder tank is studied via simulation and experiment to obtain its natural convection heat transfer in a single energy storage tank. Simulation and experimental results show that the natural convection heat transfer of water in a cylinder tank fits well with Garon's correlation. However, significant deviations occur when Garon's correlation is used to predict the natural convection heat transfer of molten salt because of its high viscosity and low thermal conductivity. However, the simulated data of the natural convection heat transfer of molten salt fit well with those of the experimental results. Thus, a correlation that considers the effect of variable physical properties is proposed in this study to predict the natural convection heat transfer of molten salt. The deviation of the present data from the proposed correlation is less than ±20%. The results of this study can serve as a basis for the design of single energy storage tanks.     

Analysis of the Relationship Between the Meshing Stiffness and the Inherent Characteristics of Planetary Gear Transmission Mechanism

According to the relationship between the meshing stiffness and the inherent characteristics of a seven-speed three-row coupled planetary transmission mechanism, a equivalent concentrated mass dynamics model of the planetary transmission mechanism is established. The natural frequency of the planetary gear train at a specific gear is calculated and extracted. The relationship between the meshing stiffness of each row and the natural frequency of the system is analyzed, thereby avoiding possible resonance behavior by changing the meshing stiffness. These results show that the meshing stiffness, in its range of possible values, has nearly no effect on the low order natural frequency (<4.000.Hz), and that the time-varying meshing stiffness mainly affects the natural frequencies of the higher- and middle-order parts of the system. Changes of the natural frequencies lead to the change of the system''s corresponding vibration mode, which will change the vibration situation of the system.     

Basic dynamic characteristics and seismic design of anchorage system

Based on some assumptions, the dynamic governing equation of anchorage system is established. The calculation formula of natural frequency and the corresponding vibration mode are deduced. Besides, the feasibility of the theoretical method is verified by using a specific example combined with other methods. It is found that the low-order natural frequency corresponds to the first mode of vibration, and the high-order natural frequency corresponds to the second mode of vibration, while the third mode happens only when the physical and mechanical parameters of anchorage system meet certain conditions. With the increasing of the order of natural frequency, the influence on the dynamic mechanical response of anchorage system decreases gradually. Additionally, a calculating method, which can find the dangerous area of anchorage engineering in different construction sites and avoid the unreasonable design of anchor that may cause resonance, is proposed to meet the seismic precautionary requirements. This method is verified to be feasible and effective by being applied to an actual project. The study of basic dynamic features of anchorage system can provide a theoretical guidance for anchor seismic design and fast evaluation of anchor design scheme.     

Stabilization of Chaotic Time Series by Proportional Pulse in the System Variable Based on Genetic Algorithm

The PPSV (Proportional Pulse in the System Variable) algorithm is a convenient method for the stabilization of the chaotic time series. It does not require any previous knowledge of the system. The PPSV method also has a shortcoming, that is, the determination off. is a procedure by trial and error, since it lacks of optimization. In order to overcome the blindness, GA (Genetic Algorithm), a search algorithm based on the mechanics of natural selection and natural genetics, is used to optimize the λi The new method is named as GAPPSV algorithm. The simulation results show that GAPPSV algorithm is very efficient because the control process is short and the steady-state error is small.     

Thermo-hydraulic experimental validation of an integrated modular small reactor operating in full power natural circulation

Small reactors have become a new hotspot of international nuclear energy research.The nuclear heating reactor(NHR)technology developed by Tsinghua University is an important multipurpose small reactor solution with features such as high integration,modular design and full power natural circulation.A new small reactor based on the existing NHR-200 reactor was developed by the Institute of Nuclear and New Energy Technology of Tsinghua University.A full-scale natural circulation test loop with the same operating parameters as the actual reactor was built in order to experimentally validate the natural circulation ability of the reactor primary loop and heat-transfer ability of fuel assemblies and heat exchangers.Corresponding results are given in detail,including parameter validation of the reactor primary loop,flow rules of the natural circulation and heat-transfer coefficients of heaters and heat exchangers,which can be directly used in the actual reactor as a reference for optimization design.Finally,a characteristic parameter k is proposed to represent the natural circulation ability of a system.By using the new data arrangement method in the form of parameter k,comprehensive experimental results of the natural circulation can be represented by a simple integrated expression.The work in this paper is of importance in broadening application fields and pushing forward commercialization of the NHR type reactors.     

A review of engine application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas

The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this paper.Discussions include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas,visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel,and the fundamental study of turbulent premixed combustion of hydrogen enriched natural gas.The effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.     

Optimal Design of Two-Chamber Gas Distributor with CFD Approach

Computational fluid dynamics( CFD) is used to investigate a new type of two-chamber natural gas distributor,which has a natural gas inlet and nine nozzle outlets. The uniformity at the outlet of distributor is practice proven to have significant degree influence on its comprehensive performance. To improve the uniformity at the nozzles of the gas distributor,CFD modeling with the RNG k-ε turbulence model is undertaken to understand the mass flow rate of nozzles with reference to different length of chambers and the most optimal length is obtained. The internal flow pattern of the natural gas distributor is analyzed. It is found that the local maximum deviation of the nozzle outflow rate increases with the increase of chambers length when the length is more than 64 mm. The results provide useful suggestions for the optimal design of two-chamber natural gas distributor.     

Design and Analysis of a Horizontal Quasi-Zero Stiffness Vibration Isolator by Combining Rolling-Ball and Disk Springs in Parallel

Combining disk springs having negative stiffness with a rolling-ball in parallel is proposed in this paper.It is used to reduce the system stiffness and the positioning error in a non-ideal environment.The characteristics of a disk spring are analyzed.The dynamic equation of its motion has been obtained based on Newton's second law.After definition of a error margin,the dynamic equation of the motion can be treated as a Duffimg oscillator,and the influences of non-dimensional parameters on the stiffness and transmissibility are studied.The natural frequency and transmissibility are achieved in a linearization range,where the ratio of linear to nonlinear items is small enough.The influence of mass ratio and non-dimensional parameters on natural frequency are analyzed.Finally,a comparison of numerical example demonstrates that the QZS system can realize a lower stiffness within an increased range.     

活性钙溶解度初探

0 Introduction Activated Ca is a white natural powder material made and refined with special technique from the shell of a marineorganism oyster. It is the only kind of new Ca preparation which can be easily absorbed by human body at present. It is known as "natural food "," natural Ca preparation ", "product of times ", worth exploreing and applying. But the shortcoming is low solubility in water, only 884m~3/ 1000ml (at 25C). This article studies how to increase its sclubility so as to increase greatly the efficiency of the usage of activated Ca.     

Study on the Optimization for Design of Indoor Natural Ventilation and Lighting Based on Passive Design Measurements

Based on the current indoor natural ventilation and lighting in the space of traditional residential buildings, this paper starts from the passive-design optimization of the spatial natural ventilation and lighting, and makes quantitative evaluation on the quality of current interior natural ventilation and lighting for two typical residential buildings by three indexes, including wind speed, static wind area ratio and satisfaction ratio about minimum lighting coefficient. Based on that, this paper conducts the passive design optimization, and establishes the quantitative association and reevaluation among the passive reformation design, natural ventilation, and lighting environmental quality, proposing the general strategy for the existing residential buildings to respond to the passive reformation design of the natural ventilation and lighting. The special reconstruction of core functionary space of integration of “the living room+dining room+partial space” is researched, and the redesign for the optimization and replacement of both indoor and outdoor enclosure parts is explored, which is expected to provide practical exploration on the strategies for passive construction of spatial natural environmental quality within a large number of highly-energy-consumed residential buildings in China, as well as the green design of residential buildings.     

Adaptive robust control for electrical cylinder with friction compensation using modified LuGre model

The position tracking control problem of an electrical cylinder in the presence of dynamic friction nonlinearities in its transmission process is addressed in this paper. First, a torque decou- piing approach is proposed to formulate the dynamic model. Secondly, to compensate the friction in the case of servo motion, a modified LuGre model is designed to make a continuous transition be- tween a static model at a high speed and a LuGre model at a low speed to avoid instability due to dis- cretization with a finite sampling rate. To accelerate the speed of estimating time-varying parame- ters, a fast adaption law is proposed by designing an attraction domain around a rough value related to the load force. Finally, a discontinuous projection based adaptive robust controller is synthesized to effectively handle parametric uncertainties for ensuring a guaranteed robust performance. A Lya- punov stability analysis demonstrates that all signals including tracking errors have the guaranteed convergent and bounded performance. Extensive comparative simulations with sinusoidal and point- point tracks are obtained respectively in low and high speeds. The results show the effectiveness and the achievable control performance of the proposed control strategy.     

QFT在航空发动机MIMO鲁棒控制中的应用

利用QFT理论推导出非对角控制器控制律的求解公式,并提供了一个评价最优非对角控制律的工程指标,给出MIMO航空发动机控制系统设计方法和步骤,保证所设计的控制系统具有所要求的鲁棒稳定性和跟踪性能要求。将该方法应用于某型涡扇发动机控制系统设计,仿真验证表明,控制效果良好满足设计要求。     

基于随机牵制控制器的复杂网络系统的镇定

主要研究一类具有连续线性耦合节点的复杂动态网络系统的牵制控制问题, 提出了一种基于随机变 量的随机牵制控制方法。通过对部分节点施加带有随机变量的状态反馈牵制控制器, 可以实现整个复杂网络系统 的稳定。可以看出, 虽然随机牵制方法不要求控制器一直作用在选定的节点上, 但同样能使得复杂网络系统稳定。 运用鲁棒思想首次讨论了系统耦合矩阵发生变化时所设计的随机牵制控制器的有效性问题, 给出了所设计控制器 仍然能保证系统的稳定性的充分条件。基于所得结果, 进一步讨论了所含随机变量的期望值含有不确定性和未知 时的牵制控制问题。最后通过数值仿真进一步验证了所提方法的正确性和有效性。     

数量反馈理论在导弹攻角鲁棒控制系统中的应用

对简化的弹体动力学模型，应用数量反馈理论方法对导弹攻角控制系统进行了鲁棒校正，设计了一个不变的鲁棒控制器Ｇ（Ｓ），使导弹在整个飞行过程中，攻角对俯仰舵偏角的传递函数的频率响应满足设计期望要求，改善了弹体的动力学特性。设计导弹控制系统时，能用它计算出理想控制器的参数     

基于鲁棒控制理论的卫星姿态控制

对于三轴角动量飞轮式卫星的姿态控制提出了一种鲁棒控制设计方法.针对挠性卫星中存在的未建模动态以及参数不确定性问题,基于H∞控制理论对姿态控制器进行了设计,通过选取合适的加权函数将姿态控制问题转化为标准H∞控制问题,进而获得所需控制器.并与PID控制器进行了仿真实验对比,仿真结果表明,对于系统中存在的干扰和参数不确定性,H∞控制具有良好的鲁棒稳定性与动态性能.     

不确定性扰动下双足机器人动态步行的自适应鲁棒控制

针对不确定性扰动下双足机器人动态步行的鲁棒控制问题,建立不确定性扰动下双足机器人的动力学模型. 将特定庞卡莱映射方法拓展到不确定性扰动下双足机器人的稳定性分析,将机器人随机系统的稳定性分析转化为确定性周期系统的稳定性分析. 基于滑模控制方法,提出自适应滑模控制器. 与以往滑模控制器相比,该控制器无需外部扰动的准确幅值信息. 考虑到双足机器人在实际应用中常会遭遇非平整路面,进一步将该自适应滑模控制器拓展到非平整路面的鲁棒控制：提出碰撞速度不变性条件,基于落地速度控制进行在线轨迹规划,基于自适应滑模控制器对机器人进行反馈控制. 基于三维（3-D）五杆双足机器人进行仿真实验,结果表明,所设计的控制器能有效实现机器人在不确定性扰动下的鲁棒控制.     

重复控制系统中低通滤波器与输出反馈控制器同时设计

针对具有时变范数有界不确定性的线性系统,为了有效地抑制周期性扰动和跟踪周期性参考输入信号,提出一种同时设计重复控制器中的低通滤波器和输出反馈控制器的方法。首先,将重复控制系统转化为时滞系统;采用 lyapunov稳定性理论得到该时滞系统的鲁棒稳定性条件。基于此条件,将设计低通滤波器和输出反馈控制器的问题转换成一个非线性矩阵不等式求解问题,利用线性矩阵不等式方法(LMI)、锥补线性化方法(CCL),通过所提出的迭代算法计算低通滤波器最大的剪切频率及其对应的输出反馈控制器参数。仿真示例验证了所提出方法的有效性。     

基于遗传算法的鲁棒PID控制器设计

从分析控制系统的性能指标入手,从抗干扰性能和鲁棒性能两方面综合考虑控制器的设计,得到一种鲁棒 PID 控制器的设计思路,把 PID 控制器的设计问题转化为求解一个带鲁棒性能约束的绝对误差积分指标 (IAE) 优化问题。鉴于问题是非凸的,用常规优方法无法得到最优解,采用遗传算法来求解该问题。分别对一阶加纯迟延(FOPDT)和非线性对象进行了仿真,结果表明了方法的有效性,不仅控制系统性能优良,而且抗干扰能力和鲁棒性能也很好。     

基于H_∞控制的多变量系统PID控制器设计

研究了基于环路成形Ｈ∞控制的多变量系统ＰＩＤ控制器设计。为了能方便地在实际工程中实现复杂的控制，提出了采用多变量ＰＩＤ控制器逼近所得高阶控制器的方法，并给出了如何选择影响闭环系统性能的预补偿器方法。这种设计方法的主要特点是，只通过调整反映闭环系统的鲁棒稳定性与时域性能的一个设计参数，便可以得到ＰＩＤ控制器。仿真结果表明，所得的多变量ＰＩＤ控制器具有较好的鲁棒稳定性和鲁棒性能。     

燃烧控制系统H_∞鲁棒控制器设计

针对火电厂燃烧控制系统传统控制策略的不足,给出了以辐射能信号为串级控制的中间被调量的H∞鲁棒控制燃烧系统。介绍了设计控制器的过程,通过仿真分析了该控制器的稳定性和鲁棒性,并与采用参数自调整的辐射能信号的模糊PI复合控制系统进行了比较。仿真结果显示:该控制器有良好的鲁棒控制稳定性和鲁棒控制性能。