Fluid flow and heat transfer in an optical fiber coating process

The optical fiber coating process, using a die and applicator system, was numerically simulated. The coupled partial differential equations, governing the fluid flow and heat transfer, were solved on a transformed, non-uniform, staggered grid. A finite volume method, with conjugate heat transfer, boundary-fitted grid, and variable transport properties, was employed. The pressure was calculated using a SIMPLE-based algorithm. An isothermal case was first modeled, where the effect of the Reynolds number (Re) was studied for different geometries. Different coating fluids were considered. A conjugate boundary condition was employed at the fiber–fluid interface for the non-isothermal flow. A free surface boundary condition was used at the fiber entry into the coating fluid. The meniscus was prescribed on the basis of prior experimental work. Regardless of fiber speed, a circulating flow was observed in the applicator. High shear rates at the dynamic contact point suggest that air can be entrained with a fast moving fiber. It was also found that pressures at the coating fluid inlet did not play a major role, for typical fiber speeds, whereas the thermal conditions that affect the properties of the fluid, such as viscosity, made a significant impact on both the flow and the thermal field. This work could be used to determine the parameters that are critical for improving the quality of the coating, particularly its uniformity, and the production rate.     

Research on better use of wood for sustainable development: Quantitative evaluation of good tactile warmth of wood

Wood is a prospective material against the problems of mineral resource shortage and global warming from the viewpoint of sustainable development. The continuous cycle of felling, planting and growing of trees is essential prerequisite for sustainability. The engineering evaluation of advantages of wood can increase its use more widely as a substitute for other industrial materials and save the finite mineral resources. The increase of wood use can support the continuous cycle for the sustainable forestry as an industry. This paper treats good tactile warmth of wood as one of its advantages. The relationship between contact surface temperature and thermal effusivity is derived from the theoretical analysis of governing heat transfer phenomenon on tactile warmth. Some knowledge on tactile warmth of wood is reviewed with these physical properties. The sensory tactile warmth of wood has a high and positive linear correlation with the logarithm of the contact surface temperature. The materials with lower thermal effusivity feel warmer than the ones with higher thermal effusivity. The relationship between contact surface temperature and thermal effusivity explains rationally why each wood has a large difference of tactile warmth in spite of their small difference of material properties. It also explains the reason why wood has good tactile warmth regardless of seasons against metals, which feel too hot in summer and too cold in winter to touch. The contact surface temperature and the thermal effusivity are proposed as engineering measures to evaluate the tactile warmth of wood and other materials.     

Fiber–fiber interactions in carbon mat thermoplastics

Carbon mat thermoplastics (CMT) consisting of 12.7 mm long, chopped carbon fibers in a polypropylene matrix were manufactured using the wetlay technique at fiber volume fractions (FVF) from 10% to 25%, and tests simulating the compression molding process were conducted. The packing stress of the CMT followed a power law relation with FVF. A single fiber pull-out fixture was used to measure the frictional and hydrodynamic lubrication coefficients at fiber–fiber touch points, and results were fit with an existing relation for glass mat thermoplastics. In isothermal squeeze flow the load–displacement behavior for the 10% FVF CMT was similar in shape to that for a fluid with a yield stress. However, for FVFs of 15–25%, the load–displacement curves showed a load spike at the beginning of the flow, then followed the curve for a fluid with a yield stress. The spike was attributed to fiber breakage that increased with increasing FVF of the sample.     

Effect of Magnetic Interaction on Thermally Activated Reversal in a Magnet With a Distribution of Energy Barriers

The time dependence of magnetization is usually expressed as M(t)=M₀-SInt [see Proc. Phys. Soc. 62, 562 (1949)] for magnetic viscosity experiments. Considering magnetic interaction during the thermal activation process, a form as M(t)=M₀-SIn(t+t₀) is deduced. The dipolar interaction and exchange coupling in a magnet can lead to positive and nonpositive t₀, respectively. In the experiments of the magnetic viscosity for nanocrystalline Pr₂Fe₁₄B ribbons, the existence of positive t₀ is confirmed.     

高速列车浮式地板振动响应有限元分析

针对采用试验方法开发高速列车浮式地板耗时耗力,且试验规模小,不能反映整车的振动效果的问题,基于有限元法进行高速列车振动响应分析.对三明治夹芯理论、蜂窝板理论和等效板理论进行比较,确定采用等效板理论数值模拟某浮式地板中的蜂窝板;利用橡胶材料的超弹性理论拟合橡胶材料参数;建立完整模型模拟实际工况下浮式地板的振动响应,得到浮式地板的隔振效果.结果表明此浮式地板的隔振效果约为90%,满足设计要求.     

A method for robot placement optimization based on two-dimensional manifold in joint space

This article addresses a method for placement determination of robotic drilling system on two-dimensional manifold in robot joint space. It has been proved that the feasibility of positioning error compensation on two-dimensional manifold, and that the continuity of the robot parameters in the two-dimensional space is the prerequisite to perform the compensation in previous study. It appears that there are bifurcations which might break the continuity of the robot parameters on the two-dimensional manifold due to improper placement. To avoid bifurcations, a performance index and a set of optimization procedure are proposed to achieve proper placement of robotic machining system. Experiments conducted on a KUKA robot have verified the effectiveness of the proposed placement optimization method. Experiment results indicated that positioning errors were significantly improved with the proposed method, which is beneficial for robotic machining accuracy.     

基于1553B和外部FLASH实现星上FPGA配置

太阳辐射监测仪作为某卫星载荷之一,其控制系统主要由DSP+FPGA组成,文章利用1553B和外部Flash实现了系统上电后自动配置FPGA;首先,利用1553B通讯芯片上传FPGA和DSP代码到外部RAM,并通过DSP烧写程序分别烧写到Flash的合理区域;系统上电后,DSP从Flash 0x0地址运行,初始化后运行FPGA配置程序,实现FPGA的动态配置;避免了FPGA跑飞后需要重新上电和归零,提高了系统的可靠性;省去了FPGA专用配置EPROM芯片,简化结构,降低了系统成本;实践证明,FPGA加载时间约2分钟,可定时加载或命令控制加载,该方法简单实用,适合星上载荷使用。