Three-dimensional transient numerical simulation for gas exchange process in a four-stroke motorcycle engine

Three-dimensional transient numerical simulation of gas exchange process in a four-stroke motorcycle engine with a semi-spherical combustion chamber with two tilt valves was studied. Combination of the grid re-meshing method and the snapper technique made the valves move smoothly. The flow structure and pattern in a complete engine cycle were described in detail. Tumble ratios around the x-axis and y-axis were analyzed. Comparison of computed pressure with experimental pressure under motored condition revealed that the simulation had high calculation precision; CFD simulation can be regarded as an im-portant tool for resolving the complex aerodynamic behavior in motorcycle engines.

秦岭物种多样性宣传海报的多模态话语分析

本研究以一张秦岭物种多样性的宣传海报为对象,从图像、语言、字体、色彩和模态间关系等角度研究了海报意义的多模态建构。研究发现,海报模态不仅各自参与意义建构,还相互协同,共同传递海报物种多样性的主旨。字体模态作为社会符号,不仅参与意义建构,还丰富了海报内涵。此外,生态视角的运用也揭示出海报背后人类优于动植物的生态观。从多模态话语分析的视角研究海报意义的建构,不仅丰富了当前领域的研究成果,也促进了人们对人与自然关系的深入思考,还拓宽了汉字传播与研究的视角。