Wind-induced vibration of a long span space truss structure
In this paper, characteristic of wind-induced vibration of a a long span space truss structure was studied. Wind tunnel test was conducted in a boundary wind tunnel, based on which displacement along Z direction under all wind directions are discussed, and vibrations of typical nodals are emphasized. It is shown that the upwards corner of the roof may course greater peak displacement in this area than that in other areas. On the other hand, modal vibration of part area may be much greater than that of others, which may enhance the danger of local wind induced structural damage of these areas.
Fluctuating and mean pressure measurements on a stadium covering in wind tunnel
Abstract This paper describes a wind-tunnel research of surface pressure distribution on a football stadium covering. A full-depth atmospheric boundary layer simulation with barrier, elliptic wedge and surface roughness corresponding to a sub-urban terrain was used, with a scale factor of 250. Mean pressure coefficients over the covering were determined. Likewise, maximum and minimum peak pressure coefficients were determined at areas of interest, using the area-averaged pressure measurement technique and applying the extreme-value method. On the other hand, a comparison between quasi-static and extreme-value assessment methods was made.
Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose
Abstract Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1–1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.