双塔脱丙烷工艺技术

对扬子乙烯装置双塔脱丙烷系统低压塔液泛、高压塔再沸器堵塞等问题进行了技术分析,提出了工艺流程修改方案,完善了双塔脱丙烷技术,对同类装置有参考价值。     

The Danish Twin Apartment Study – Part II: Mathematical modeling of the relative strength of sources of indoor air pollution

Abstract This study deals with the modeling of air pollution in apartments from laboratory measurements of source strengths, using formaldehyde and Total Volatile Organic Compounds (TVOCs) as model pollutants. The sources in two test apartments were grouped into two: building-related sources and occupant-related sources. The measured source strengths and ventilation rates were used for the prediction of concentrations expected in the apartments. These predictions were compared to measurements in the apartment over 12 months. The conclusions were that the model predictions based on emission rates measured in the laboratory can be used to predict the long-term concentration of the two model pollutants in the apartments. Considering the measured differences in ventilation between the apartments, an occupant emission rate of between 0.2 and 0.3 mg/h/kg body weight could be estimated. Based on previous suggested limits of acceptable exposures of humans to VOCs, an acceptable average emission rate of VOCs from building materials in general was estimated to be about 30 (μ/m²/h. The modeling showed that during the first 200 days, building materials dominated the emissions. After this, sources relating to the occupants dominated. On average about half of the VOC pollution originated from the building materials.     

Digital Twin Enhanced Dynamic Job-Shop Scheduling

For dynamic scheduling, which is daily decision-making in a job-shop, machine availability prediction, disturbance detection and performance evaluation are always common bottlenecks. Previous research efforts on addressing the bottlenecks primarily emphasize on the analysis of data from the physical job-shop, but with little connection and convergence with its virtual models and simulated data. By introducing digital twin (DT), further convergence between physical and virtual spaces of the job-shop can be achieved, which greatly enables dynamic scheduling. DT fuses both real and simulated data to provide more information for the prediction of machine availability on one hand; and on the other hand, it helps to detect disturbances through comparing the physical machine with its continuously updated digital counterpart in real time, triggering timely rescheduling when needed. It also enables comprehensive performance evaluation for rescheduling using multiple-dimension models, which can describe geometric properties, physics parameters and behaviors of the machines. In the paper, a five-dimension DT for a machine in the job-shop is introduced first, then the DT-based machine availability prediction, disturbance detection and performance evaluation methods are explored. Based on this, a DT-enhanced dynamic scheduling methodology is proposed. A scheduling process of making hydraulic valves in a machining job-shop is taken as a case study to illustrate the effectiveness and advantages of the proposed method.     

Digital Twin-driven machining process for thin-walled part manufacturing

Thin-walled parts are widely used in the aerospace, shipbuilding, and automotive industry, but due to its unique structure and high accuracy requirements, which leads to an increase in scrapped parts, high cost in production, and a more extended period in the trial machining process. However, to adapt to fast production cycles and increase the efficiency of thin-walled parts machining, this paper presents a Digital Twin-driven thin-walled part manufacturing framework to allow the machine operator to manage the product changes, make the start-up phases faster and more accurate. The framework has three parts: preparation, machining, and measurement, driven by Digital Twin technologies in detail. By establishing and updating the workpiece Digital Twin under a different status, various manufacturing information and data can be integrated and available to machine operators and other Digital Twins. It can serve as a guideline for establishing the machine tool and workpiece Digital Twin and integrating them into the machining process. It provides the machine operator opportunities to interact with both the physical manufacturing process and its digital data in real-time. The digital representation of the physical process can support them to manage the trial machining from different aspects. In addition, a demonstrative case study is presented to explain the implementation of this framework in a real manufacturing environment.     

超大长径比双螺杆挤出机制备聚丙烯腈初生纤维

采用自主研发的超大长径比(136)双螺杆挤出机实现了PAN初生纤维的纺丝制备,研究了PAN粉料质量分数(16%、20%、24%)、双螺杆挤出机机筒温度(50、60、70℃)、循环挤出次数(0、1、2)对PAN初生纤维力学性能及表面形貌的影响。结果表明,PAN初生纤维的拉伸强度随质量分数、机筒温度和循环挤出次数的增加而增大;PAN初生纤维的断裂伸长率随质量分数和循环挤出次数的增加而减小,随机筒温度的升高而增大;随着循环挤出次数增加,纤维表面越来越规整,缺陷逐渐减少。研究结果为利用超大长径比双螺杆挤出机制备出性能更好的PAN初生纤维奠定了基础。     

啮合型同向旋转双螺杆挤塑机熔体输送机理研究

本文提出了描述啮合型同向旋转双螺杆挤塑机中非等温三维熔体输送流场的理论模型。借助罚函数有限无及边界无法对该流场进行了求解。此后计算和分析了熔体输送段的重要工作特性参数。计算结果和实验结果的良好吻合证明所采用的模型合理、计算方法可行、计算结果可靠。     

改进TD3算法在四旋翼无人机避障中的应用

为了提高无人机（Unmanned Aerial Vehicle,UAV）系统的智能避障性能,提出了一种基于双延迟深度确定性策略梯度（Twin Delayed Deep Deterministic Policy Gradient,TD3）的改进算法（Improved Twin Delayed Deep Deterministic Policy Gradient,I-TD3）。该算法通过设置两个经验缓存池分离成功飞行经验和失败飞行经验,并根据两个经验缓存池的不同使用目的分别结合优先经验回放（Prioritized Experience Replay）方法和经验回放（Experience Replay）方法,提高有效经验的采样效率,缓解因无效经验过高导致的训练效率低问题。改进奖励函数,解决因奖励设置不合理导致的训练效果差问题。在AirSim平台上实现仿真实验,结果表明在四旋翼无人机的避障问题上,I-TD3算法的避障效果优于TD3算法和深度确定性策略梯度（Deep Deterministic Policy Gradient,DDPG）算法。     

Fatigue crack growth behavior of laser-processed 304 stainless steel in air and gaseous hydrogen

Fatigue crack growth test was performed to evaluate fatigue behavior of 304 stainless steel specimens with or without laser processing (welding and surface treatment) in air and gaseous hydrogen. As the crack propagation normal to the laser welding or scan direction, the laser-processed specimens exhibited a higher resistance to crack growth in the low stress intensity factor range (ΔK) than the as-received steel plates regardless of testing environments. However, the marked retardation of crack growth behavior vanished for welded specimens subjected to a 850 °C/h stress relief treatment or with a shorter distance from notch tip to the weld centerline in the test.Fatigue-fractured appearance of the steel plate tested in air was composed of mainly transgranular fatigue fracture and some flat facets, along with a small amount of intergranular fracture. While quasi-cleavage fracture and few twin boundary separations were observed for the same specimen in hydrogen. On the other hand, the lower crack growth rate of laser-processed specimens in both air and hydrogen was accompanied with rubbed areas on the fracture surfaces. It was found that the extent of quasi-cleavage fracture was related to the formation of strain-induced martensite, which would contribute to an increased fatigue crack growth rate of all specimens in gaseous hydrogen.     

Additional bending moment analysis of the trigeminal universal joint installed by single or twin radial bearing北大核心CSCD

To find out the causes of vibration and noise of the trigeminal universal joint which appeared in the installation and use process, the additional moment distribution with the varies of the input shaft angular and the deflection angle was analyzed. Kinematics diagrams of the trigeminal universal joint when the output shaft installed by single radial bearing or twin radial bearing were established. The system coordinates were established under the two installation ways, and the motion equations were established by the direction cosine matrix tools. It indicated that the trigeminal universal joint installed by the single radial bearing was an approximately isometric speed transmission, and was a constant velocity transmission with twin radial bearing installed. Furthermore, the additional moment component on the input shaft and the output shaft was analyzed under the two installation ways. According to the virtual displacement principle, the additional moment on the tripod universal joint when the output shaft installed by twin radial bearing and single radial bearing were determined. When installed by single radial bearing, the deflection moment exists and the vibration frequency of additional moment was three times of the input shaft as a sine curve. The variation trend of the additional moment was straight up with the increase of deflection angle. When installed by twin radial bearing, the deflection moment was zero and the additional moment increased gradually with the increase of deflection angle but did not fluctuate. The analysis revealed that additional moment existed in the trigeminal universal joint system under both installation ways would produce bending vibration. This study is of great significance to study the causes of vibration and determine the nonlinear dynamics of the system.     

基于双支持向量回归机的增量学习算法

提出了一种基于双支持向量回归机的增量学习算法。将获取到的新样本加入训练数据集后,该算法无需在整个新的数据集上重新训练双支持向量回归机,而是充分利用增量前的计算信息,从而大大减少了模型更新中逆矩阵的计算量,提高了算法的执行效率。在人工数据集、时间序列预测和UCI数据集上的数值实验表明,该算法快速有效。