科创中国

Direct drive servovalves are mostly restricted to low flow rate and low bandwidth applications due to the considerable flow forces.Current studies mainly focus on enhancing the driving force,which in turn is limited to the development of the magnetic material.Aiming at reducing the flow forces,a novel rotary direct drive servovalve(RDDV)is introduced in this paper.This RDDV servovalve is designed in a rotating structure and its axially symmetric spool rotates within a certain angle range in the valve chamber.The servovalve orifices are formed by the matching between the square wave shaped land on the spool and the rectangular ports on the sleeve.In order to study the RDDV servovalve performance,flow rate model and mechanical model are established,wherein flow rates and flow induced torques at different spool rotation angles or spool radiuses are obtained.The model analysis shows that the driving torque can be alleviated due to the proposed valve structure.Computational fluid dynamics(CFD)analysis using ANSYS/FLUENT is applied to evaluate and validate the theoretical analysis.In addition,experiments on the flow rate and the mechanical characteristic of the RDDV servovalve are carried out.Both simulation and experimental results conform to the results of the theoretical model analysis,which proves that this novel and innovative structure for direct drive servovalves can reduce the flow force on the spool and improve valve frequency response characteristics.This research proposes a novel rotary direct drive servovalve,which can reduce the flow forces effectively.

DC-inverter split air-conditioner is widely used in Chinese homes as a result of its high-efficiency and energy-saving. Recently, the researches on its outdoor unit have focused on the influence of surrounding structures upon the aerodynamic and acoustic performance, however they are only limited to the influence of a few parameters on the performance, and practical design of the unit requires more detailed parametric analysis. Three-dimensional computational fluid dynamics(CFD) and computational aerodynamic acoustics(CAA) simulation based on FLUENT solver is used to study the influence of surrounding structures upon the aforementioned properties of the unit. The flow rate and sound pressure level are predicted for different rotating speed, and agree well with the experimental results. The parametric influence of three main surrounding structures(i.e. the heat sink, the bell-mouth type shroud and the outlet grille) upon the aerodynamic performance of the unit is analyzed thoroughly. The results demonstrate that the tip vortex plays a major role in the flow fields near the blade tip and has a great effect on the flow field of the unit. The inlet ring's size and throat's depth of the bell-mouth type shroud, and the through-flow area and configuration of upwind and downwind sections of the outlet grille are the most important factors that affect the aerodynamic performance of the unit. Furthermore, two improved schemes against the existing prototype of the unit are developed, which both can significantly increase the flow rate more than 6 %(i.e. 100 m3·h-1) at given rotating speeds. The inevitable increase of flow noise level when flow rate is increased and the advantage of keeping a lower rotating speed are also discussed. The presented work could be a useful guideline in designing the aerodynamic and acoustic performance of the split air-conditioner in engineering practice.

In piezoceramic ultrasonic devices,the piezoceramic stacks may fail permanently or function improperly if their working temperatures overstep the Curie temperature of the piezoceramic material.While the end of the horn usually serves near the melting point of the molten metal and is enclosed in an airtight chamber,so that it is difficult to experimentally measure the temperature of the transducer and its variation with time,which bring heavy difficulty to the design of the ultrasonic molten metal treatment system.To find a way out,conjugate heat transfer analysis of an ultrasonic molten metal treatment system is performed with coupled fluid and heat transfer finite element method.In modeling of the system,the RNG model and the SIMPLE algorithm are adopted for turbulence and nonlinear coupling between the momentum equation and the energy equation.Forced air cooling as well as natural air cooling is analyzed to compare the difference of temperature evolution.Numerical results show that,after about 350 s of working time,temperatures in the surface of the ceramic stacks in forced air cooling drop about 7 K compared with that in natural cooling.At 240 s,The molten metal surface emits heat radiation with a maximum rate of about 19 036 W/m2,while the heat insulation disc absorbs heat radiation at a maximum rate of about 7922 W/m2,which indicates the effectiveness of heat insulation of the asbestos pad.Transient heat transfer film coefficient and its distribution,which are difficult to be measured experimentally are also obtained through numerical simulation.At 240 s,the heat transfer film coefficient in the surface of the transducer ranges from–17.86 to 20.17 W/(m2?K).Compared with the trial and error method based on the test,the proposed research provides a more effective way in the design and analysis of the temperature control of the molten metal treatment system.

传统的二代压水反应堆主要是采取鼓风机鼓风的方式对控制棒驱动机构(Control Rod Drive Mechanism,CRDM)进行强制通风冷却,该冷却方式耗能较大且无法保证绝对安全可靠.本文针对于大亚湾核电站中CRDM群的布置方式,采用中广核新型的EMC-B型控制棒驱动机构的结构及材料物性参数,运用了计算流体力学(Computational Fluid Dynamics,CFD)分析方法,研究了当采用空气自然循环冷却方式时,CRDM群及各线圈的温度分布,探索对CRDM群采用空气自然循环冷却方式的可行性.模拟分析结果表明:总体来看,处于外围和中心位置处的CRDM的线圈温度,要比中间区域的CRDM线圈温度高;对于给定计算工况,各线圈的最高温度为198°C,低于限制温度(200°C),表明对于所研究的CRDM群,依靠空气的自然对流,可以对CRDM进行有效冷却.计算结果可为新型CRDM群分布设计提供参考.

利用计算流体力学(CFD)方法建立了一个耦合低温水气变换反应的多孔介质二维拟均相反应器模型.采用FLUENT缺省的单温度模型进行模拟,无法得到气固相两相的温度,而且温度场与实际不符.通过用户自定义标量(UDS)添加固相能量方程,将多孔介质的单温度模型修正为气固相耦合传热两温度模型,以源项的形式添加化学反应,将化学反应热添加到气固相能量方程.湍流模型采用Spalart.Allmaras方程,动力学模型采用Langmuir-Hinshelwood方程,催化剂的性质及操作条件以Wei.HsinChen等的实验为基础.采用有限体积法对模型进行非稳态模拟,对反应器内组分浓度、速度场及温度进行了可视化分析.最后列出了非稳态两温度模型在3个时间点的轴向温度曲线,并且与FLUENT缺省的单温度模型进行了对比,两温度模型的结果与实际更相符.

冷凝系数为冷凝流率与碰撞流率之比,是气体冷凝过程的重要性质.本文采用分子动力学方法,探讨了不同温度(95.5、104-3、113-3、123.2)K下,氩流体气液两相平衡体系中气相的冷凝过程.模拟得到了氩流体气液相主体范围、Gibbs界面位置及界面厚度;并分别以气相主体与界面区的分界面|z8|及Gibbs界面作为碰撞界面,统计得到了氩流体的冷凝系数,并与文献值进行了比较.模拟结果表明,在相同温度条件下,以Gibbs界面为碰撞界面得到的碰撞粒子数目明显高于以|z8|为碰撞界面得到的碰撞粒子数目.当采用|z8|界面作为碰撞界面时,冷凝系数出随着温度的变化规律与文献值一致,均随着温度的升高而降低,变化范围在0.822与0.596之间;但以Gibbs界面作为碰撞界面时,所得冷凝系数口,基本上与温度无关,其值在0.335左右,且a2明显小于a1.

The large and complex structures are divided into hundreds of thousands or millions degrees of freedom(DOF) when they are calculated which will spend a lot of time and the efficiency will be extremely low. The classical component modal synthesis method(CMSM) are used extensively, but for many structures in the engineering of high-rise buildings, aerospace systemic engineerings, marine oil platforms etc, a large amount of calculation is still needed. An improved hybrid interface substructural component modal synthesis method(HISCMSM) is proposed. The parametric model of the mistuned blisk is built by the improved HISCMSM. The double coordinating conditions of the displacement and the force are introduced to ensure the computational accuracy. Compared with the overall structure finite element model method(FEMM), the computational time is shortened by 23.86%–31.56% and the modal deviation is 0.002%–0.157% which meets the requirement of the computational accuracy. It is faster 4.46%–10.57% than the classical HISCMSM. So the improved HISCMSM is better than the classical HISCMSM and the overall structure FEMM. Meanwhile, the frequency and the modal shape are researched, considering the factors including rotational speed, gas temperature and geometry size. The strong localization phenomenon of the modal shape's the maximum displacement and the maximum stress is observed in the second frequency band and it is the most sensitive in the frequency veering. But the localization phenomenon is relatively weak in 1st and the 3d frequency band. The localization of the modal shape is more serious under the condition of the geometric dimensioning mistuned. An improved HISCMSM is proposed, the computational efficiency of the mistuned blisk can be increased observably by this method.

在CFD离散误差和不确定度估计问题中,为研究计算得到的观测精度对仿真计算结果的影响,消除GCI离散不确定度估计法中当观测精度大于格式精度时出现的不合理的小不确定度,提出了1种改进的CFD离散不确定度估计方法,即用加权平均的数值解代替细网格数值解来估计离散误差及不确定度.针对低雷诺数二维非轴对称圆柱绕流模型进行数值计算,划分5套网格,用二阶迎风格式计算圆柱绕流的阻力系数和升力系数,分别给出了GCI和改进方法的离散不确定度估计结果,并与文献参考值进行比较,结果表明改进的方法对离散不确定估计要优于GCI方法,且置信度更高.

The existing research of the active suspension system(ASS) mainly focuses on the different evaluation indexes and control strategies. Among the different components, the nonlinear characteristics of practical systems and control are usually not considered for vehicle lateral dynamics. But the vehicle model has some shortages on tyre model with side-slip angle, road adhesion coefficient, vertical load and velocity. In this paper, the nonlinear dynamic model of lateral system is considered and also the adaptive neural network of tire is introduced. By nonlinear analysis methods, such as the bifurcation diagram and Lyapunov exponent, it has shown that the lateral dynamics exhibits complicated motions with the forward speed. Then, a fuzzy control method is applied to the lateral system aiming to convert chaos into periodic motion using the linear-state feedback of an available lateral force with changing tire load. Finally, the rapid control prototyping is built to conduct the real vehicle test. By comparison of time response diagram, phase portraits and Lyapunov exponents at different work conditions, the results on step input and S-shaped road indicate that the slip angle and yaw velocity of lateral dynamics enter into stable domain and the results of test are consistent to the simulation and verified the correctness of simulation. And the Lyapunov exponents of the closed-loop system are becoming from positive to negative. This research proposes a fuzzy control method which has sufficient suppress chaotic motions as an effective active suspension system.

The existing research of the integrated chassis control mainly focuses on the different evaluation indexes and control strategy. Among the different evaluation indexes, the comprehensive properties are usually not considered based on the non-linear superposition principle. But, the control strategy has some shortages on tyre model with side-slip angle, road adhesion coefficient, vertical load and velocity. In this paper, based on belief, desire and intention(BDI)-agent model framework, the TYRE agent, electric power steering(EPS) agent and active suspension system(ASS) agent are proposed. In the system(SYS) agent, the coordination mechanism is employed to manage interdependences and conflicts among other agents, so as to improve the flexibility, adaptability, and robustness of the global control system. Due to the existence of the simulation demand of dynamic performance, the vehicle multi-body dynamics model is established by SIMPACK. And then the co-simulation analysis is conducted to evaluate the proposed multi-agent system(MAS) controller. The simulation results demonstrate that the MAS has good effect on the performance of EPS and ASS. Meantime, the better road feeling for the driver is provided considering the multiple and complex driving traffic. Finally, the MAS rapid control prototyping is built to conduct the real vehicle test. The test results are consistent to the simulation results, which verifies the correctness of simulation. The proposed research ensures the driving safety, enhances the handling stability, and improves the ride comfort.