Development of a Novel Parallel-spool Pilot Operated High-pressure Solenoid Valve with High Flow Rate and High Speed

High-pressure solenoid valve with high flow rate and high speed is a key component in an underwater driving system.However,traditional single spool pilot operated valve cannot meet the demands of both high flow rate and high speed simultaneously.A new structure for a high pressure solenoid valve is needed to meet the demand of the underwater driving system.A novel parallel-spool pilot operated high-pressure solenoid valve is proposed to overcome the drawback of the current single spool design.Mathematical models of the opening process and flow rate of the valve are established.Opening response time of the valve is subdivided into 4 parts to analyze the properties of the opening response.Corresponding formulas to solve 4 parts of the response time are derived.Key factors that influence the opening response time are analyzed.According to the mathematical model of the valve,a simulation of the opening process is carried out by MATLAB.Parameters are chosen based on theoretical analysis to design the test prototype of the new type of valve.Opening response time of the designed valve is tested by verifying response of the current in the coil and displacement of the main valve spool.The experimental results are in agreement with the simulated results,therefore the validity of the theoretical analysis is verified.Experimental opening response time of the valve is 48.3 ms at working pressure of 10 MPa.The flow capacity test shows that the largest effective area is 126 mm2 and the largest air flow rate is 2320 L/s.According to the result of the load driving test,the valve can meet the demands of the driving system.The proposed valve with parallel spools provides a new method for the design of a high-pressure valve with fast response and large flow rate.

Effects of impeller speed and aeration rate on flotation performance of sulphide ore

The effects of aeration rate and impeller speed on the concentrate sulfur grade and recovery for batch flotation of a complex sulphide ore were investigated. The relationships between the water recovery and solid entrainment were discussed. It is found that the solid entrainment is linearly related to the water recovery regardless of aeration rate and impeller speed, and the higher sulfur recovery at the aeration rate of 2 and 4 L/min for the impeller speed of 1 500 r/min is considered to be the contribution of true flotation. Finally, the sulfur recovery flux is correlated with the bubble surface area flux based on the froth image at the different aeration rates and impeller speeds.

电动叶菜收获机速度协同控制系统设计与试验

针对电动叶菜收获机切割、输送和行走三者速度不协调导致的叶菜损伤率高、功耗大和收获效率低等问题,开发了一种电动叶菜收获机速度协同控制系统。系统以可编程逻辑控制器为核心,利用信息传感模块对割刀电机的电流、电压和转速进行数据采集;主控模块根据速度协同控制算法对采集信号进行处理,得到负载信息并协同切割、输送和行走三者速度。田间试验结果表明:系统稳定可靠,能够根据收获情况动态协同各部件速度参数,叶菜损伤率为8.88%;与传统定速控制方法相比,收获机功耗降低了13.1%,收获效率提升了33.4%。

Variation in cross-shore wind speeds influenced by the morphology of nourished beach

The cross-shore variation in wind speeds influenced by beach nourishment,especially the dramatic changes at the nourished berm,is important for understanding the aeolian sand transport processes that occur after beach nourishment,which will contribute to better beach nourishment project design on windy coasts.In this paper,the influencing factors and potential mechanism of wind speed variation at the edge of a nourished berm were studied.Field observations,together with the Duna model,were used to study the cross-shore wind speed distribution for different nourishment schemes.The results show that the nourished berm elevation and beachface slope are the main factors controlling the increase in wind speed at the berm edge.When the upper beach slope is constant,the wind speed at the berm edge has a positive linear correlation with the berm elevation.When the berm elevation remains constant,the wind speed at the berm edge is also proportional to the upper beach slope.Considering the coupling effects of nourished berm elevation and beachface slope,a model for predicting the wind speed amplification rate at the nourished berm edge was established,and the underlying coupling mechanism was illustrated.

Effect of high shear rate on solidification microstructure of semisolid AZ91D alloy

To investigate the effects of rotation speed and shearing time on morphology of semisolid AZ91D alloy,experimental work was undertaken using a twin-screw slurry maker.The results show that increasing the rotation speed and reasonable time can give rise to substantial grain refinement during continuous shearing stage,which can be attributed to the increasing of effective nucleation rate caused by the extremely uniform temperature due to high shear rate and high degree of turbulence.Comparing with low rotation speed at the same thermal condition,the analysis indicates that the microstructures obtained at high rotation speed are homogenous spherical and fine grains instead of dendritic or rosette and exhibits uniform distribution in the eutectic matrix.

电动汽车行驶稳定性模型预测控制仿真研究

为了提高电动汽车行驶的稳定性,提出了一种集成的汽车和车轮稳定性控制系统,并对汽车行驶的稳定性控制效果进行仿真。创建电动汽车模型简图,给出电动汽车动力学方程式。采用模型预测控制技术,设计了一种集成的汽车和车轮稳定性控制器。采用MATLAB软件对电动汽车横摆角速度、行驶速度和侧滑角进行仿真,与无模型预测控制器输出结果进行对比。结果显示:采用无模型预测控制器,电动汽车横摆角速度、行驶速度跟踪误差较大,振动幅度较大,产生的侧滑角较大。采用模型预测控制器,电动汽车横摆角速度、行驶速度跟踪误差较小,振动幅度较小,产生的侧滑角较小。采用模型预测控制器,能够提高电动汽车行驶的稳定性,避免汽车在突然转弯时发生侧翻现象。

南方籼稻热风干燥特性及其工艺参数优化

水稻是全球重要的粮食作物之一,籼稻是中国南方主要种植品种。收获的新鲜水稻含水率较高,不适合长期储存。针对南方籼稻在热风干燥过程中容易产生爆腰等问题,选择了中早35和玉针香2个典型品种,通过单因素试验和Box-Behnken Design试验,分析了热风干燥工艺条件下的影响因素(包括干燥温度、干燥缓苏比和初始含水率)与水稻的干燥爆腰增率和干燥速率之间的关系。结果显示,干燥温度对干燥速率和爆腰增率的影响最显著,其次是缓苏时间占比和初始含水率。在符合国家标准的爆腰增率要求下进行试验,得到了2个水稻品种的最佳干燥温度、缓苏时间占比和初始含水率参数组合:中早35的最佳参数为49.48℃、0.67、26%;玉针香的最佳参数为45.00℃、0.698、26%。在最佳参数下进行干燥试验,测得2种水稻品种的干燥速率分别为0.02280%·min^(-1)和0.02461%·min^(-1),爆腰增率分别为2.87%和2.80%,均低于国家标准的3.00%。优化后的干燥工艺参数可为生产实践和稻谷品质变化机理的深入研究提供理论基础。

DNS Analysis on the Indirect Relationship between the Local Burning Velocity and the Flame Displacement Speed of Turbulent Premixed Flames

The local burning velocity and the flame displacement speed are the dominant properties in the mechanism of turbulent premixed combustion. The flame displacement speed and the local burning velocity have been investigated separately, because the flame displacement speed can be used for the discussion of flame-turbulence interactions and the local burning velocity can be used for the discussion of the inner structure of turbulent premixed flames. In this study, to establish the basis for the discussion on the effects of turbulence on the inner structure of turbulent premixed flames, the indirect relationship between the flame displacement speed and the local burning velocity was investigated by the flame stretch, the flame curvature, and the tangential strain rate using DNS database with different density ratios. It was found that for the local tangential strain rate and the local flame curvature, the local burning velocity and the flame displacement speed had the opposite correlations in each density ratio case. Therefore, it is considered that the local burning velocity and the flame displacement speed have a negative correlation.

Study on Rheological Characteristics of a Grease Used in High Speed Bearing

On a self-made super-high shear strain rate rheometer, the rheological characteristics and apparent viscosity curves of a high-speed bearing grease were obtained under different working conditions. A new grease rheological model suited to a shear strain rate range of 0—3.5×10~6s^(-1) was presented. The results showed that the shear stress increased linearly at first and then increased nonlinearly with the increase in shear strain rate up to 1.5×10~6s^(-1), and finally the shear stress decreased slightly with the successive increase in shear strain rate. The shear stress increased with a decreasing rolling speed and an increasing contact pressure. The apparent viscosity decreased rapidly with the increase of shear strain rate at beginning and could approach the viscosity of the base oil if the shear strain rate surpassed 1.5×10~6s^(-1). The fits between the test data and the predicted values by the new model were fairly good.

抽水蓄能电站单机容量与机组转速选择

通过分析国内外已建抽水蓄能电站机组主要技术参数,研究抽蓄电站定转速混流式水泵水轮机水头与单机容量、参数水平的关系,提出了不同水头段抽水蓄能电站单机容量和比速系数选择原则,推荐了合适的机组额定转速范围,可提高抽水蓄能电站水泵水轮机选型设计的工作效率和成果质量。

纳米划擦速度对单晶硅去除行为的影响

单晶硅作为典型的硬脆材料在不同的划擦速度下会有不同的应变率,进而产生不同的材料去除行为,采用分子动力学从应变率角度研究不同划擦速度下材料的变形与去除过程。结果表明:划擦过程中随划擦速度由25 m/s增加到250 m/s,单晶硅的应变率从1.25×10^(10) s^(−1)提高至1.25×10^(11) s^(−1),其划擦力、剪切应力和摩擦系数减小,划擦温度升高,且划擦表面的轮廓精度和粗糙度随划擦速度的增大而改善。划擦过程中的非晶化和相变是单晶硅纳米尺度变形的主要发生机制,剪切应力减小造成其亚表面损伤层深度由2.24 nm减小到1.89 nm,划擦温度升高导致其表面非晶层深度增加。

卧式厨余垃圾搅拌器搅拌影响因素仿真分析

卧式厨余垃圾搅拌器的转速和填充率对其搅拌均匀性的影响较大,为了提高搅拌效率及搅拌均匀性,建立卧式搅拌器及物料固体参数化模型,颗粒接触模型采用JKR模型,运用EDEM(Engineering Discrete Element Method)模拟搅拌过程。采用控制变量法设置对比仿真实验,并采用标准偏差法处理实验数据,通过分别控制填充率、转速的改变,对比得出最合适的搅拌环境以及各因素对搅拌效率、搅拌均匀性的影响趋势。结果表明:60%的填充率时搅拌均匀性最好,较大的填充率可以获得更好的搅拌效率,但填充率过大搅拌均匀性会下降;在转速为(48~72)rpm的范围内,转速越大搅拌效率、搅拌均匀性越好,但转速在(60~72)rpm时搅拌均匀性提升不明显且颗粒发生离析,继续增加转速对搅拌无明显增益且增加功耗。研究成果对卧式搅拌器的设计与应用提供了一定的参考。

模拟海水对Q235钢腐蚀性能的影响分析

以Q235碳素钢为研究对象,借助旋转式挂片腐蚀试验仪,考察转速、温度、酸碱度等因素对其在模拟海水中腐蚀性能的作用。结果表明,腐蚀速度随温度的变化呈现两个阶段:第一阶段,当温度小于45℃时,腐蚀速度随温度的增大而不断升高;第二阶段,在温度大于45℃时,曲线斜率最大,腐蚀速度达到最大值;腐蚀速度随转速的变化呈现两个阶段:第一阶段,当转速小于60 r/min时,腐蚀速度基本保持不变,维持恒定;第二阶段,当转速大于60 r/min时,曲线斜率增大,腐蚀速度急剧升高,腐蚀速度随转速的增大而不断升高,并出现60 r/min的临界值;腐蚀速度随酸碱度的增大而不断降低。所得结论对Q235钢在海洋环境中的腐蚀和防护具有一定的参考价值。

叶顶间隙对低比转数小流量泵性能的影响

为建立叶顶间隙对低比转速小流量泵性能的影响关系,采用数值计算的方法,以叶顶间隙宽s和叶轮出口宽b的比值(s/b)表征间隙大小,对不同间隙下泵的性能展开对比分析。分析发现,随着间隙的增加,泵的扬程和效率均逐渐降低,最大和最小间隙下的扬程和效率差分别达15.4%,5.5%。当间隙较小即s/b<0.2时,扬程曲线在小流量工况会出现不稳定的“驼峰”现象,在s/b>0.3后,设计工况附近效率的降幅显著增大。从流动特性来看,随着叶顶间隙的增大,间隙泄漏流对叶轮内主流区影响加剧,会诱导严重的二次流和旋涡的产生,同时间隙内不稳定流动也会产生能量损失,造成扬程和效率下降。为低比转数小流量泵的设计与优化提供借鉴意义。

西北地区红层泥岩崩解特性试验研究

针对西北地区红层泥岩设计了一套自由浸水崩解装置,对不同质量的红层泥岩试块进行自由浸水试验。考虑试块的吸水过程,将试块吸水率作为崩解试验结果的补偿,研究不同质量红层泥岩试块的崩解率、崩解速率随时间变化规律。结果表明,测试红层泥岩膨胀性矿物含量较少,其崩解的前30%时间内崩解率可达45%~75%,前50%时间内崩解率可达68%~90%,崩解总时间T与试块质量m满足T=a*(1-e^(-b*m)) 关系。随着试块质量增加,试块崩解速率越大,且崩解的前50%时间内崩解率增加显著。

Impact of Pedestrian Traffic on Saturation Rate of Protected Left-Turn at Urban Intersections

Heavily congested intersections in metropolitan areas in China are facing unique problems due to high travel demand and a high degree of traffic law violations. Based on a study conducted by the authors of this paper, 93% of left-turn vehicles turning left in these areas were slowed in order to avoid conflict with pedestrians. Intertwined pedestrian and vehicular flows can significantly reduce the capacity of exclusive left-turn lane group through reducing saturation flow rate, which increases the congestion at intersections. This paper investigates how the saturation flow rate of exclusive left-turn lane group is affected by the characteristics of pedestrian flow. By analyzing the imagery data collected by video cameras installed at intersections, the research team is able to obtain the characteristics of both vehicular and pedestrian flows, such as speed and spatial locations. The average operating speed at the saturation flow rate with and without pedestrian traffic is used as a direct measurement to evaluate the effect of pedestrians. Based on the statistical analysis, the paper concludes that saturation flow rate is mainly affected by the position of pedestrian in the crosswalk (inside or outside of left-turn vehicle’s trajectory), and the distance between the vehicle and pedestrians. In general, when the distance is less than four meters, the smaller the distance between vehicle and pedestrians, the larger the impact. However, there is no significant impact when the distance is larger than four meters. To accurately quantify the effect, the degree of pedestrian-vehicle impact is defined in four levels. The results show that the difference in the saturation flow rate between the best and the worst level could be 15.7%, which clearly indicates how important it is to enforce pedestrian crossing behavior.

基于RTK测速的油菜直播机随速可控可调排种控制系统研究

针对油菜精量直播机连续作业过程中设定作业速度条件下,作业速度波动导致排种量与目标播量不一致的问题,设计了一种基于“RTK测速+落种检测+电机实时调控”的油菜精量直播机随速可控可调排种控制系统,确定了影响调速性能的关键参数,构建了步进电机调速模型;运用GNSSToolKitLite上位机开展ZED-F9P GNSS模块静态速度漂移试验,得到该模块静态速度漂移量服从均值为0.054 m/s、方差为0.029 m^(2)/s^(2)的正态分布。利用自动数粒仪与JPZS-16型排种性能试验台进行试验,得到正负气压组合式排种器转速为5~60 r/min时,落料计数器播种量检测值与实际值平均绝对误差小于10%;通过台架试验确定了不同排种器调速模型,得到不同排种器最佳工作转速、电机转速与目标播量的函数关系。不同排种器随速控制适应性台架试验结果表明:当作业速度为3~12 km/h时,系统搭载高速机械离心式与油麦兼用气送式排种器总排量稳定性变异系数小于1.21%。田间试验结果表明:当作业速度为5~12 km/h时,本系统搭载高速机械离心式与窝眼轮式排种器总排量稳定性变异系数小于9.7%,满足随速播种要求,可为油菜精量播种控制系统结构改进提供参考。

基于智能逆变技术的玉米精播机性能优化

为进一步提升我国玉米精播机的综合作业效率,以性能优化提升作为研究目标,基于智能逆变技术的深度应用展开分析。以电控逆变处理与调速机制相融合为出发点,建立正确的电控模块逆变应用数学模型,通过控制分析与硬件优化,进行整机作业试验。结果表明:基于智能逆变技术应用的玉米精播机性能优化效果明显,排种精准率与播深合格率分别可提升至94.46%与94.05%,满足精量播种机的设计要求;同时,种子的重播率与漏播率可降低至3.83%与3.06%,整机作业运行稳定,各零部件指令执行协同性好,综合效率相对提升了5.88%,充分体现了智能逆变应用的准确性与适应性,可为类似农机播种装备优化提供参考。

螺旋卸船机颗粒回流分析

为了研究螺旋卸船机在不同倾角下输送物料时颗粒在螺旋槽中的回流问题,文中通过离散元对物料输送过程进行模拟,分析颗粒的运动状态、波动程度和回流情况以及不同几何参数和物理参数对颗粒回流的影响。结果表明:螺旋转速对物料在螺旋槽中的波动程度与螺旋卸船机的倾角相关,螺旋转速的选取应与倾斜角度相匹配以达到降低回流率的目的;增加进料量和减小螺距均可减小颗粒的回流率但不会降低发生回流现象的频率;无论改变螺旋转速、进料量还是螺距,颗粒在稳定输送时间内回流率对主流量影响较小,故回流现象不会影响卸船机的输送效率。

声呐流量计技术综述

声呐流量计是一种基于声呐阵列波束形成技术的新型高端流量测量仪表,本文阐述了声呐流量计的测量原理和应用场景。首先,介绍了声呐流量计的发展现状;其次,阐述了测量介质流速的对流技术,主要包括湍流漩涡的移动速度和校准公式,以及测量介质声速的声学技术主要包括管道一维声波、GVF含气率和管道声速衰减公式,重点是在波数-频率(k-ω)域所形成的“对流脊”和“声学脊”;然后,与传统流量计比较分析了声呐流量计在衬里、HDPE、积垢、铁磁矿方面的应用优势和不足;最后,从纸浆和油砂行业应用列举了声呐流量计的技术特点。声呐流量计在准确度和可靠性方面有显著的技术优势,具有广阔的市场应用前景。