Experimental investigation on the influence of different grades of wood chips on screw feeding performance

Although basic investigations on wood chip material properties haven been carried out, only few studies deal with transport of wood chips, despite the fact that significant problems are commonly observed when feeding biomass in industrial applications. Within the work presented, basic bulk material properties were measured and experiments carried out with a system consisting of a hopper, agitator and a screw conveyor. The aim of this study was to investigate how three different wood chip grades and two blends of wood chips influence typical design parameters, such as mass flow and driving torque, of a biomass feeding system. The measured basic bulk properties are in good overall agreement with the literature. However, discrepancies were discovered between two standardized methods for determination of the bulk density. The results for the driving torque, mass flow and mass-related energy consumption showed that different grades of wood chips can alter these values considerably. Between two wood chip grades, a twice as high torque was recorded, while a third grade could not be fed due to jamming. One of the major findings of this study is that mixing a rather small amount of a high-fine content grade with the non-feedable grade of wood chips resulted in a blend which inhibited jamming during the screw feeding process.     

Mechanical performances and stress states of rock bolts under varying loading conditions

A comprehensive study including laboratory tests and numerical modeling was performed to investigate factors of rock bolt fracture. Experimental tests were performed to evaluate the mechanical performances of bolt ends including the thread and adjacent. The effects of installation angle, pretension and accessories (plate, washer and nut) were evaluated. It is found that a bolt installed with an oblique angle to roadway surface suffers a complex stress combination of tensioning, bending and twisting on the bolt. This complex stress is much greater than the tensile stress, leading to cracking and growth at the location of bending causing the thread to fail even though the tensile stress is less than the yield strength. Bolt thread is more vulnerable to fracture than rebar.     

Mechanics and dynamics of thread milling process

This paper presents the mechanics and dynamics of thread milling operations. The tool follows a helical path around the wall of the pre-machined hole in thread milling, which has varying tool-part engagement and cut area during one threading cycle. The variation of cut area that reflects the kinematics of threading as well as structural vibrations is modeled along the helical, threading path. The mechanics of the process are first experimentally proven, followed by the formulation of dynamic thread milling which is periodic in threading cycle, in a semi-discrete time domain. The stability of the operation is predicted as a function of spindle speed, axial depth of cut, cutter path and tool geometry. The mechanics and stability models are experimentally proven in opening M16×2 threads with a five-fluted helical tool on a Steel AISI1045 workpiece.     

钢模板专用液压冲孔机设计

针对钢模板行业专用设备缺乏而影响产品质量和生产效率的现状,通过分析冲孔机机械结构和液压控制系统的原理,设计了满足行业需要的钢模板专用液压冲孔机,为解决钢模板行业的质量、成本和效益问题提供了装备上的保证。     

Effect of cycle time and duty cycle on psychophysically determined acceptable levels in a highly repetitive task

Psychophysical methodology has been used to develop guidelines for lifting and more recently similar methods have been applied to repetitive upper limb movements. While a range of cycle times are usually used, there is often no control for duty cycle. The purpose of this paper is to present psychophysically determined acceptable torques for a common upper limb task, with both cycle time and duty cycle conditions set by the researcher. Eight female participants, sitting at adjustable workstations, performed a simulated in-line screw running task. A computer-controlled torque motor applied a torque every 3, 6, 12 or 20?s with a duty cycle of 25, 50 or 83%. The participants worked with one set of conditions each day and self-selected the highest torque that they felt was acceptable without developing undue pain and discomfort. Duty cycle was found to significantly affect the amount of torque selected. With duty cycle controlled, cycle time was no longer found to have any significant effect on selected torque. Acceptable torques for 25, 50 and 83% duty cycles were 1.09, 0.9 and 0.73 Nm. Discomfort and stiffness were concentrated on the back of the hand and on the thumb web. These findings suggest that increased perception of discomfort with increased frequency (decreased cycle time) may be related to decreased rest/recovery time for muscles.     

Stochastic rotational response of a parametric pendulum coupled with an SDOF system

In this paper, parametric excitation of a lumped mass pendulum is investigated when having its pivot point vertically excited. Such a system is described by a sinus type nonlinear Mathieu equation and attention is drawn to the rotational motion of the mass. A single-degree-of-freedom (SDOF) system is used as a base for the pendulum, floating on ocean waves and being externally excited by them thus falling into the subclass of autoparametric systems. Due to the random nature of waves, a narrow-band stochastic process is used to model the environmental excitation. The effect of dry friction is considered and the interaction between the pendulum's rotational response and the base is studied.     

基于RT Thread的便携式健康监测仪的设计

随着社会的发展、生活水平的不断提高,人们对自身健康问题更为重视,而传统的健康监测设备缺乏有效的健康管理功能。为此,介绍了一种便携式健康监测仪的软硬件设计,该设计采用基于Cortex M4内核的32位低功耗处理器作为系统的控制核心,采用RT Thread实时操作系统作为系统的软件平台。系统可实现心率测量、额温测量、计步与能耗监测、健康任务管理等功能。进而通过健康检测—干预方案生成—干预方案执行监测—干预效果评估（健康再检测）的闭环管理模式,不断改善和促进健康。     

LNG接收站卸料管道保冷层厚度优化模拟

国内LNG接收站卸料管道保冷层多为组合式保冷,保冷层普遍存在着材料浪费的问题。为此,应用Ansys Workbench(AWE)工作平台分别建立了LNG接收站典型的外径为40 in、10 in(1 in=25.4 mm)卸料管道保冷层传热及优化模型。在满足使用要求及设计标准的前提下,对保冷层组合厚度进行优化模拟,并分析了保冷材料热导率受温度变化影响时,其对管道保冷性能的影响。结果表明:优化后,40 in管道每1 000 m可节省投资156万元,10 in管道每1 000 m可节省投资25.62万元;在设计时,如不考虑保冷层热导率随温度变化而采用平均热导率计算,保冷层厚度设计偏保守。对组合保冷材料交接点处温度及各类输入参数敏感性进行分析后得出结论:优化后管道各类指标性能均满足使用要求;内层保冷材料厚度对总投资及热流密度影响最大,大气温度对交接点处温度影响最大。该优化模拟结果及基于AWE工作平台流程化设计优化方法可为LNG管道保冷设计提供参考。     

地下水对引水式电站隧洞围岩稳定性影响的研究

基于大型通用有限元软件ANSYS对引水式水电站引水隧洞开挖与衬砌过程进行数值模拟。隧洞开挖与衬砌采用ANSYS软件中的生死单元来实现。通过模拟隧洞的开挖与衬砌,改变地下水水位,进而对各水位对应下的引水隧洞洞身段围岩及衬砌稳定进行评价。故在计算结果的基础上．结合工程实际情况和经验．研究地下水水位对隧洞围岩稳定性的影响,并得出几点有益的结论,以期为实际隧洞工程施工及设计提供依据。     

基于有限元分析的压机用螺纹的比较

通过有限元软件对压机用锯齿形螺纹和潘克螺纹的齿面应力和齿根应力进行分析比较,阐明了潘克螺纹较锯齿形螺纹具有明显的优势,表现为应力在每一牙上分布的均匀程度高,齿根应力高应力分布范围窄。锯齿形螺纹已经阻碍了现代压机的技术进步,急需一种新型螺纹来代替。期望本文对压机用螺纹技术进步起到积极的推进作用。