Optimal allocation method of electric/air braking force of high-speed train considering axle load transfer

Reasonable distribution of braking force is a factor for a smooth,safe,and comfortable braking of trains.A dynamic optimal allocation strategy of electric-air braking force is proposed in this paper to solve the problem of the lack of consideration of adhesion difference of train wheelsets in the existing high-speed train electric-air braking force optimal allocation strategies.In this method,the braking strategy gives priority to the use of electric braking force.The force model of a single train in the braking process is analyzed to calculate the change of adhesion between the wheel and rail of each wheelset after axle load transfer,and then the adhesion of the train is estimated in real time.Next,with the goal of maximizing the total adhesion utilization ratio of trailer/motor vehicles,a linear programming distribution function is constructed.The proportional coefficient of adhesion utilization ratio of each train and the application upper limit of braking force in the function is updated according to the change time point of wheelset adhesion.Finally,the braking force is dynamically allocated.The simulation results of Matlab/Simulink show that the proposed algorithm not only uses the different adhesion limits of each trailer to reduce the total amount of braking force undertaken by the motor vehicle,but also considers the adhesion difference of each wheelset.The strategy can effectively reduce the risk and time of motor vehicles during the braking process and improve the stability of the train braking.

INFLUENCE OF PHASE RATIO ON PACKING EFFICIENCY IN COLUMNS FOR MASS TRANSFER PROCESSES

The phase ratio has been found to affect the packing efficiency in packed columns.To ac-count for the effect,a model is set up to correlate the height of a mass transfer unit with the phaseratio with reasonable accuracy.Proposed also is a correlation that allows to predict the efficiency inquestion at any given liquid-gas ratio using the knowledge of other efficiency values at other liquid-gas ratios.

Optimal selection of annulus radius ratio to enhance heat transfer with minimum entropy generation in developing laminar forced convection of water-Al2O3 nanofluid flow

Heat transfer and entropy generation of developing laminar forced convection flow of water-Al_2O_3 nanofluid in a concentric annulus with constant heat flux on the walls is investigated numerically. In order to determine entropy generation of fully developed flow, two approaches are employed and it is shown that only one of these methods can provide appropriate results for flow inside annuli. The effects of concentration of nanoparticles, Reynolds number and thermal boundaries on heat transfer enhancement and entropy generation of developing laminar flow inside annuli with different radius ratios and same cross sectional areas are studied. The results show that radius ratio is a very important decision parameter of an annular heat exchanger such that in each Re, there is an optimum radius ratio to maximize Nu and minimize entropy generation. Moreover, the effect of nanoparticles concentration on heat transfer enhancement and minimizing entropy generation is stronger at higher Reynolds.

The Effect of the Gap Ratio on the Flow and Heat Transfer over a Bluff Body in Near-Wall Conditions

In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been conducted.The former were carried out using an open circulating water tank experimental platform and a single cylinder and square column as geometrical models(their characteristic length being D).The latter were based on the well-known SIMPLE algorithm for incompressible flow.The results show that the gap ratio is an important factor affecting the wake characteristics of near-wall bluff bodies.When the gap ratio is small,the influence of the wall on the bluff body wake is large.With an increase in the gap extension,periodic vortex shedding is enabled and heat transfer is strengthened accordingly;in addition,the vortex shedding period is larger for the square column.The square column displays hysteresis compared with the cylinder at the same gap ratio(the critical gap ratio of cylinder is 0.2~0.4,while that of square column is 0.4
0.6).

Puff-by-puff Transfer Ratios of Some Added Flavors in Cigarettes

[Objecdve] The aim was to observe the puff-by-puff transfer ratios of some flavors in cigarettes. [Method] Based on national stand- ards, the puff-by-puff transfer of tobacco of carbonyl flavors was analyzed. In the meantime, by dint of simultaneous distillation and extraction equip- ment coupled to GC and GC/MS, the puff-by-puff transfer ratios to TPM of smoke were expounded and compared. [ Result] The puff-by-puff deliv- ery profiles of NFDPT,nicotine and carbon monoxide increased with increasing puff number. This trend was similar to that of particulate matters. The transfer ratio of flavored tobacco was increasing in general, but partial flavors augmented to the maximum value and then decreased slowly. [ Conclusion] The study provided reference for the application of carbonyl compounds in tobacco.

Augmentation of Heat Transfer in Pipe Flow Using Plain Twisted Tape Inserts for Different Twist Ratios

The heat transfer augmentation of plain twisted tape inserts for different twist ratios has been studied in this study. The data are conducted using the plain twisted tape insert with five different twist ratios respectively. The range of Reynolds number is considered under a uniform heat flux condition. In the case of simulation, the tapes are made from a stainless steel strip with a thickness of 2 mm. A tubular pipe with 850mm U-loop length and twist length of 800 mm each is considered in our study for simulation. Water is used as working fluids inside the tube for our simulation. The simulation results demonstrate that the important heat transfer parameters including Nusselt number (Nu), friction factor (f) and thermal performance index (η) are gradually increased with the increment of the twist ratio and reached at the saturated level while twist ratio is 3.5,?afterward the thermal properties are decreased.

Effect of Hole Configuration on Heat Transfer through a Hollow Block Subjected to Solar Flux

In this paper,some effort is provided to optimize the geometry of a concrete hollow brick(used in the construction of building roofs)in order to increase the related thermal resistance,thereby reducing energy consumption.The analysis is conducted for three different configurations of the hollow concrete bricks.Coupling of conduction,natural convection and thermal radiation phenomena is considered.Moreover,the flows are assumed to be laminar and two-dimensional for the whole range of parameters examined.The conservation equations are solved by a finite difference method based on the control volumes approach and the SIMPLE algorithm for velocity-pressure coupling.The results show that the aspect ratio affects neither the nature of the fluid flow nor the number of convective cells.However,the extension of the circulation cells increases with this parameter.Moreover,the cavities with a large aspect ratio lead to significant reductions in the heat transfer through the hollow block,these reductions reaching approximately 14%.

REACTIVITY RATIOS FOR COPOLYMERIZATION WITH THE PARTICIPATION OF A CHARGE-TRANSFER COMPLEX

The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by H-1-NMR spectroscopy, and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50 degrees C was determined to be 0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions for copolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios is presented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained. They are r(12) = 0.034, r(21) = 0.012, r(1C) = 0.0030, r(2C) = 0.0034, and k(1C)/k(12) = 11.34, k(2C)/k(21) = 3.42.

子宫内膜癌增强MRI定量参数变化与临床特征的关系及对预后的预测价值分析

目的 探究子宫内膜癌(EC)增强MRI定量参数变化与临床特征关系,分析其对预后的预测价值。方法 选取2019年3月~2022年3月本院收治的EC患者98例作为研究组,另选同期子宫内膜良性病变患者98例作为对照组。比较两组增强MRI定量参数[速率常数(K_(ep))、容量转移常数(K^(trans))、血管外细胞外间隙容积比(V_(e))]。比较研究组不同临床特征患者增强MRI定量参数,分析其与临床特征相关性。比较研究组不同预后患者增强MRI定量参数,分析其对预后的预测价值。结果 研究组K_(ep)、K^(trans)、V_(e)高于对照组(P<0.05);K_(ep)、K^(trans)、V_(e)病理分期、淋巴结转移、宫颈间质累及情况、子宫肌层浸润深度呈正相关,而与分化程度呈负相关(p<0.05)预后不良者K_(ep)、K^(trans)、V_(e)高于预后良好者,且与预后不良显著相关(P<0.05);K_(ep)、K^(trans)、V_(e)联合预测预后不良的AUC大于各参数独独预测(P<0.05)。结论 EC患者增强MRI定量参数K_(ep)、K^(trans)、V_(e)升高,且与临床特征、预后密切相关,联合检测各参数对预后不良具有一定预测价值。

中心性肥胖对不孕女性体外受精-胚胎移植妊娠结局的影响

目的探讨中心性肥胖对不孕女性接受体外受精-胚胎移植后的妊娠结局的影响。方法回顾性选取2017年10月至2019年9月在温州医科大学附属第一医院生殖医学中心首次接受体外受精-胚胎移植的2801例不孕女性为研究对象。根据进入治疗周期时的BMI和腰臀比(WHR)分为正常BMI非中心性肥胖组1659例、正常BMI中心性肥胖组654例、肥胖非中心性肥胖组146例和肥胖中心性肥胖组342例,比较4组治疗过程中促性腺激素使用剂量、促排时间、获卵数、可用胚胎数及新鲜胚胎移植妊娠结局。采用多元线性回归分析中心性肥胖对促排周期获得可用胚胎数的影响,多因素logistic回归分析影响患者新鲜胚胎移植能否获得活产的相关因素。应用Kaplan-Meier生存曲线绘制各组单个取卵周期累积活产率。结果与正常BMI非中心性肥胖组相比,肥胖中心性肥胖组促性腺激素使用剂量增加,获卵数和可用胚胎数减少,新鲜胚胎移植后活产率下降,妊娠丢失率增加,单个取卵周期累积活产率下降,差异均有统计学意义(均P<0.05)。多元线性回归分析提示WHR≥0.85显著降低患者促排周期获得的可用胚胎数。不论BMI是否提示肥胖,WHR≥0.85的中心性肥胖女性,其单个取卵周期累积活产率较正常BMI非中心性肥胖组女性下降(均P<0.05)。多因素logistic回归分析发现腰围的增加会使新鲜胚胎移植后活产率降低(OR=0.978,95%CI:0.963~0.992,P=0.003)。Kaplan-Meier生存曲线显示随着胚胎移植周期数增多,4组患者单个取卵周期累积活产率比较差异有统计学意义(P<0.05)。结论中心性肥胖对女性体外受精-胚胎移植的妊娠结局造成不良影响。

高接触比螺旋锥齿面修形方法及动态特性研究

为抑制高接触比螺旋锥齿轮传动的振动,提出一种新的高阶齿面修形方法。根据高接触比螺旋锥齿轮的啮合特点,提出一种新的修形曲线,采用辅助齿面修形方法生成高阶修形螺旋锥齿轮。在考虑齿变形的情况下,计算了高阶修正弧齿锥齿轮传动的载荷传递误差和啮合冲击,在此基础上建立了降低高接触比螺旋锥齿轮传动的载荷传递误差和啮合冲击的优化模型。仿真结果表明:与二阶修形弧齿锥齿轮相比,高阶齿面修形方法不仅可以有效降低高接触比螺旋锥齿的载荷传递误差、啮合冲击和动态负载系数,而且可以提高其在全速范围内的动态性能。

南海高温高压凝析气藏凝析水产出机理及产量预测方法

针对南海高温高压凝析气藏中凝析水产出量上升的问题,以东方气田为研究对象,采用地层水蒸发实验方法,分别在地层条件下的PVT筒和长岩心中进行水气比测试,并提出了高温高压凝析气藏凝析水产量计算方法,预测东方气田凝析水产出程度。研究表明:高温高压凝析气藏中的流体受多孔介质微小孔径以及临界性质偏移的影响,饱和蒸气压发生变化,导致凝析水产出大幅度增加。考虑水、气相间传质的数值模拟方法可以准确预测高温高压凝析气藏中凝析水产出变化。对东方气田的日产水进行模拟,设置井底流压限制为1.5 MPa,预测时间为5 a,历史产水量拟合精度大于90%,能够很好地模拟凝析水产出情况。研究成果对高温高压凝析气藏制订合理开发方案,改善油藏开发效果具有重要指导意义。

基于工程应用的CW-GMAW熔滴过渡形态表征

综述了涉及工程应用的冷丝熔化极气体保护焊(Cold wire gas metal arc welding,CW-GMAW)熔滴过渡形态特征。结果表明,在大电流、强规范、富氩混合气体保护下,CW-GMAW工艺的熔滴过渡形态呈喷射过渡;当电流较小、电弧电压较低时,可能为滴状过渡,甚至在弧压很低时,呈现短路过渡形态。该工艺电弧发生偏向冷丝的位移,弧长变短甚至发生短路,与冷丝送进速率比增高及冷丝在电弧中产生大量金属蒸气时弧柱电阻下降有关。在具有富氩混合保护气体的相同工艺参数下,CWGMAW转变电流比GMAW降低了4%~7%。焊接工艺参数对CW-GMAW和GMAW工艺熔滴过渡形态的影响规律大致相近,但前者因涉及冷丝送进速率比和电极焊丝送进速度,以及它们的匹配等,使焊接电流的影响更为复杂。

低载波比牵引系统的感应电机特征根离散化模型研究

在大功率和高速电机驱动领域,电机控制系统将运行于低载波比工况。传统的一阶欧拉、二阶双线性等降阶离散化模型在低载波比下由于离散化误差过大,对应的状态观测将出现幅值和相位的稳态误差,严重时甚至出现发散不收敛现象。针对上述问题,该文提出了感应电机特征根离散化模型。通过构建感应电机的复矢量模型状态空间方程,将满秩的状态转移矩阵进行对角化,得到状态转移矩阵的精确离散化结果,该模型在低载波比时仍具有较高的离散化精度。同时,提出了一种基于伯德图的离散化误差定量分析方法,通过定量对比不同离散化模型和连续域模型之间观测变量的幅值和相位误差,从理论上证明了提出方法的优越性。最后,通过仿真和实验验证了上述感应电机特征根离散化模型在低载波比下均具有良好的稳态精度与暂态跟随性能。

气膜孔堵塞对凹槽叶顶冷却传热性能的影响

采用数值方法,研究了燃气透平叶片气膜孔堵塞条件下凹槽叶顶的冷却传热性能,获得了3种吹风比M=0.5, 1.0, 1.5和不同堵塞比B=0, 0.2, 0.4, 0.6, 0.8条件下的凹槽叶顶的气膜冷却效率和传热系数分布。研究表明:气膜孔堵塞会导致凹槽叶顶气膜冷却性能下降、热负荷升高,堵塞比越大,凹槽叶顶的冷却传热性能越差。气膜孔堵塞显著改变了叶顶区域的流场结构,加剧冷气的抬升效应,导致冷气过早离开凹槽。吹风比是影响堵塞工况下凹槽叶顶冷却传热性能的重要因素,吹风比为1.0、堵塞比为0.8时,凹槽叶顶的面积平均气膜冷却效率相比于未堵塞时下降了64.88%、传热系数上升了13.01%。减小吹风比可以改善小堵塞比工况下的叶顶气膜冷却性能,吹风比为0.5、堵塞比为0.4时,叶顶平均气膜冷却效率仅下降了6.82%,但小吹风比会导致大堵塞比工况下的气膜冷却性能恶化严重,吹风比为0.5、堵塞比为0.8时,平均气膜冷却效率下降了82.09%。增大吹风比,可改善大堵塞比工况下的叶顶气膜冷却性能,吹风比为1.5、堵塞比为0.8条件下叶顶平均气膜冷却效率下降了51.34%、传热系数上升了11.52%。

燃料分级对贫预混多喷嘴燃烧器火焰动态响应特性影响的实验研究

贫预混多喷嘴燃料分级技术可以有效降低局部热负荷,从而降低NOx排放并拓宽工况范围,是现代重型燃气轮机低排放燃烧室的主要燃烧方式。本文开展了燃料分级及当量比变化对贫预混多喷嘴燃烧火焰动态响应的影响研究。利用扬声器产生火焰的受迫振荡,利用压力脉动传感器与光电倍增管完成了多喷嘴火焰响应特性的试验分析。试验表明,燃烧室内压力波动与热释放率波动随扰动频率同步变化。当量比低于0.53时,多喷嘴火焰传递函数呈现单峰的特征。当量比大于0.64时,多喷嘴火焰传递函数呈现双峰特征,且火焰响应增强。延迟时间τ随着当量比的增大而减小。燃料分级将使得火焰动态响应特征频率发生偏移。增加喷嘴数量使得火焰传递函数幅值上升,火焰响应增强,峰值频率增大,延迟时间偏短。对于采用多喷嘴燃料分级技术的燃烧室,负荷上升将导致火焰趋于不稳定。

单晶多级孔ZSM-5分子筛酸性质对正庚烷催化裂解反应传质性能的影响

采用L-赖氨酸作为介孔模板剂,通过调控铝源(偏铝酸钠)添加量改变分子筛硅铝比,在单晶分子筛内部引入晶内介孔,成功地合成了一系列具有不同硅铝比的单晶多级孔ZSM-5分子筛,研究了其酸性质对正庚烷催化裂解反应传质性能的影响。利用X射线衍射(XRD)、N2物理吸附、氨气程序升温脱附(NH_(3)-TPD)、吡啶红外(Py-IR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等表征了单晶多级孔ZSM-5分子筛的物理结构、酸性质和微观形貌。同时,利用零长柱(ZLC)装置测试获取了正庚烷在单晶多级孔ZSM-5分子筛中的表观扩散系数,用于反映其传质性能。研究结果表明,随着硅铝比的提高,单晶多级孔ZSM-5分子筛的物理结构基本保持一致;传质性能随酸量的减少而提升,催化裂解性能随酸量的增加而提高。当单晶多级孔ZSM-5分子筛的Si/Al从80提高至140,正庚烷的表观扩散系数提升了87%以上;当单晶多级孔ZSM-5分子筛的Si/Al=80时,正庚烷的转化率最高可达97.5%,乙烯和丙烯的选择性分别为24.3%和35.1%。

基于能量传递效率的煤冲击倾向性评价指标

冲击地压与煤体能量的积聚和释放密切相关,能量传递是评价冲击倾向性的关键参数之一。通过构建能量源扰动条件下的能量传递模型,关联冲击能量指数与弹性能量指数,提出能量释放比例φ,基于传递过程中的能量耗散模型提出了能量传递效率β,建立了包含2种参数的冲击倾向性评价方法。对煤矿11个煤层分层进行冲击倾向性鉴定试验,引用79个煤矿分层的冲击倾向性鉴定结果进行可靠性验证。结果表明:能量释放比例φ具有冲击地压边界条件的意义;能量传递效率β与泊松比具有负相关性,取值范围可以由模型边界条件推导获得;能量传递指数η的计算结果,与冲击倾向性鉴定的结果具有较高的一致性(88.61%),能够反映煤体的冲击倾向性,并且可以成为“*”结果的评价依据,是一种适用于现有冲击倾向性评价体系的有效指标。

基于平衡分布自适应迁移学习的多风电机组运行状态监测方法

风电机组状态的准确监测对风电机组安全稳定运行和经济效益提升至关重要。但是,受不同风电机组运行数据分布差异的影响,现有状态监测方法在多风电机组应用场景下存在精度和效率难以兼顾的问题,而平衡分布自适应迁移学习(BDA)可以拉近数据距离,同化数据分布。因此,文章提出了一种基于BDA的多风电机组状态监测方法。首先,基于Copula熵的互信息法挖掘风电机组运行状态关键影响参量;然后,构建基于门控循环单元模型(GRU)和序贯概率比检验(SPRT)方法的单风电机组状态监测模型;最后,构建基于BDA的多风电机组运行数据分布同化模型,并用于多风电机组运行状态监测。算例结果表明,所提方法可以有效节省建模成本和计算成本,能够在保障多风电机组运行状态监测精度的前提下,显著提升监测效率。

氩气保护电渣重熔脱硫预测研究

在工业级氩气保护电渣重熔过程中,钢中脱除的硫在渣中积累,会影响脱硫反应效率,造成重熔锭中硫含量分布不均。目前,电渣脱硫研究主要是基于规格较小的实验级,与大规格的工业级电渣脱硫动力学条件差别明显,故相关研究成果在工业应用中存在局限性。因此,本研究建立了工业级电渣重熔过程脱硫反应模型,经3吨氩气保护电渣实验验证,模型计算结果与实验结果基本一致。研究结果表明,降低电极和渣中初始硫含量、增加渣量、提高硫容量、降低电极下降速度均有利于提高脱硫率。基于研究结果推导出模型简化公式,可直接近似求解重熔锭不同质量处的硫含量。