Numerical simulation of deformations and forces of a floating fish cage collar in waves

The dynamic behavior of a fish cage collar in waves was investigated using a numerical model based on the finite element method. The floating collar and mooring system were divided into a series of line segments modeled by straight massless model segments with a node at each end. To verify the validity of the numerical model, research data from other authors were cited and compared with the simulated results, the comparison of results showed a good agreement. The numerical model was then applied to a dynamic simulation of a floating cage collar in waves to analyze its elastic deformation and mooring line tension. The simulated results indicated that the greatest deformation of the collar taken place in the position of the mooring line connection point when incident waves were in the same direction. An increase in the length of mooring line would help to decrease the mooring line tension of the collar. Furthermore, the effects of collar dimension, including collar circumference, pipe diameter in cross-section, and pipe thickness, on the dynamic behavior of the floating collar were discussed. The results of this study provided a better understanding of the dynamic behavior of the fish cage collar.     

An investigation of the veld problems of the Molopo area: I. early findings

Factors mainly responsible for limiting animal production in the Molopo ranching area are the poor grass species composition of the veld, bush encroachment, droughts and the poor fertility status of the soil. Data illustrating the extent to which grass species composition and grass production are affected by these factors are presented and discussed. Data from earlier attempts to .solve these problems reveal that several different directions of pasture research have possibilities in such semi‐arid areas.     

木材表面非极性化原理的研究 Ⅱ.木材与苯乙烯接枝共聚过程中化学官能团和表面极性的变化

通过对杉木、杨木木材及其主要成分在与苯乙烯接枝共聚反应过程中化学官能团及临界表面张力变化的研究,探讨了木材各化学组成在接枝共聚过程中的反应性能和对木材表面极性的影响。研究表明:木材可与苯乙烯发生接枝共聚反应,反应只在木素和苯乙烯之间进行。木材与苯乙烯接枝共聚可降低木材临界表面张力,即降低木材表面自由能,从而有效地改善木材的极性。     

后期热固化处理对竹基纤维复合材料性能的影响

对竹基纤维复合材料进行两种条件(80℃处理8h和50℃处理24 h)的热固化处理后,观测其表观形貌,并进行拉伸、压缩、水平剪切性能以及疲劳性能检测.结果表明:经过热固化处理后,竹基纤维复合材料表面有不连续的微小裂纹产生,其拉伸、压缩、水平剪切性能略有提高,疲劳性能则无显著变化.     

木工适张带锯条的振动分析

应用振动理论,对经过适张处理后的木工带锯条进行研究,确定张紧力与系统固有频率之间的关系,提出将带锯条的振动简化为弦的振动与受拉伸的梁振动.用电测法测应变换算张紧力,用频谱分析法测量系统的固有频率,理论解得到试验支持,同时计算张紧力和张紧应力.     

无粘结预应力混凝土的应用

本文详细介绍了无粘结预应力混凝土的抗震性、耐久性及施工中应注意的事项以及对材料的要求。     

木材渗透性可控制原理研究

本文研究了木材渗透性可控制机制,探寻了渗透性可控制原理。结果表明,影响渗透性高低的最主要因素为纹孔膜微孔半径和数量,微孔大而多者,渗透性高;微孔愈小,微孔里气-液界面上毛细管张力愈高,对液体流动的影响愈大,浸注愈难,欲使浸注液深注入木材,必须施一与此微孔半径相应足以克服此张力的压力。若欲改善低渗透树种木材的难浸注性,似应从纹孔入手,用化学的、物理的和生物的等方法增大和增多有效纹孔膜微孔半径和数量,以减小毛细管张力,降低使用压力,增大流量率,提高渗透性。     

无粘结预应力混凝土结构施工质量控制

本文从施工角度阐述了无粘结预应力砼结构的施工质量控制及施工工艺。     

Critical discussion of perpendicular to grain tension testing of structural timber – case study on the European hardwoods ash,beech and maple

ABSTRACT

Knowledge about perpendicular to grain tension behavior of wood is essential, since in construction tension stresses perpendicular to grain cannot be avoided completely. Especially for hardwoods, the data basis is scarce. EN 338 design values are with 0.6 N/mm² characteristic strength set very low. The US-American National Design Specifications even set this value to zero and make local reinforcements mandatory. This paper compares strength and stiffness values attained with newly-designed, little, prismatic specimens and EN 408 structural timber specimens to evaluate the current European design values. Little specimen’s characteristic strength values range from 7.2 to 10.6?N/mm² and are assumed to be real material properties. EN 408 specimen values are with approximately 4.0?N/mm² lower. These lower values are mainly due to stress peaks introduced by the force introduction. Strength values attained for the medium-dense European hardwoods beech, ash and maple exceed EN 338 design values by a factor of six to seven. Adaptation of the EN 338 design value is not recommended, though. The abundance of influencing factors makes clear that the design value and the ensuing design code have to be synchronized carefully by tedious testing in order to make use of the perpendicular to grain tension strength potential of the selected hardwoods.