ATMOSPHERIC DISPERSION OF LARGE SCALE SPILLS

Large scale spills of volatile cryogenic or pressurized ambient temperature liquids often produce denser-than-air clouds which disperse in the atmosphere in a manner that is different than trace gases. These differences are due to density or gravity-induced effects such as turbulence damping from the stable density stratification, alteration of the ambient velocity field due to gravity flow, and the source momentum flux. Also important are thermodynamic effects such as aerosol formation and flash vaporization upon release, evaporative cooling, or heat transfer from the ground modifying cloud buoyancy and turbulence. In addition, chemical reaction effects such as hydrolysis with atmospheric water vapor, polymerization, or decomposition which also affects cloud density and thermodynamics can be important. These effects are very important close to the release point but also can have dramatic effects on the cloud as it disperses downwind.

Large scale tests involving releases of heavy gases have been conducted since the early 1970's. These tests have resulted in the discovery of previously unknown and important effects, the accumulation of data for model validation, as well as accident simulation and evaluation of accident mitigation equipment and techniques. A review of recent tests and some of the important results will be presented and examples from recent test series will be used in a review of our current understanding of dense gas dispersion.

The status of computer modeling in this field will also be reviewed with an emphasis on the problems associated with Gaussian models and recent progress in intermediate and 3D conservation equation models. Two of these models, FEM3 and SLAB will be compared to data so that the observed phenomena can be understood and so that predictions can be made regarding the consequences of accidental spills of sizes of concern to industry. FEM3 simulates the dispersion of the released gas by solving the time-dependent, three-dimensional conversion equations of mass, momentum, energy, and species. This model is used as a research tool and is designed to simulate as closely as possible the physics and thermodynamics governing the dispersion process. Steady-State SLAB is based on the crosswind-averaged form of the conservation equations, using similarity profiles to determine the crosswind dependence. It also conserves mass, momentum, energy and species, but is inherently one-dimensional, and is computationally simple and fast to use.     

Some cautions in large-scale system design and implementation

Virtually all large-scale system implementations will benefit from the application of certain management techniques. Awareness (and avoidance) of erroneous assumptions as to system requirements and objectives, data reliability, human interface, and testing methods is important. Strategies such as phased implementation, use of pilots and packaged software, and categorizing and reducing risks are useful. Knowledgeable selection of applicable developments in computer architecture and serious use of planning and control techniques are advocated.Today's trends include well-informed users, better hardware and networking facilities, analysis and study of alternatives, and heavy user involvement in the entire system design and implementation process.     

Effect of shallow-angled skins on the structural performance of the large-scale wind turbine blade

Two shallow-angled symmetric and asymmetric skins, with off-axis fiber angles of less than 45°, were proposed and employed to a 5 MW wind turbine blade. For the symmetric configuration, shallow-angled skins were applied to both the pressure and suction sides of the blade, while, for the asymmetric configuration, only the pressure side was implemented with a shallow-angled skin, keeping the conventional 45-degree-angled skin for the suction side. The blade tip deflection, modal frequencies, buckling stability, and failure index were computed for off-axis fiber angles of 45°, 35°, and 25°. The use of shallow-angled skins improved blade bending stiffness and strength. The buckling resistance decreased for symmetric skins and remained unchanged for asymmetric skins; the former case was compensated for by increasing the core thickness. For both skin configurations, a reduction in the blade failure index of up to 18% and 38%, and mass reductions of up to 8% and 13% were demonstrated for the 35° and 25° shallow-angled skins, respectively.     

近年国外大停电事故概述及分析

国外近年发生多起大规模停电事故,对当地社会经济及日常生活造成巨大影响,虽然事故起因、发展各有不同,但分析其主要原因集中在自然灾害、电网投资不足、调度模式及管理理念不适应大电网运行等。国外停电事故的教训,对我国高速发展的电网安全带来警示作用,我们应该吸取其教训,对电网的安全运行给予充分重视。     

产业集聚形成原因探析

产业集聚是当今世界经济中颇具特色的经济组织形式,特别集中在高新技术产业领域。集聚区内的企业通过合作与交流可以发挥规模经济效应,同时可产生强大的溢出效应。集聚区的形式多种多样,产生原因由以资源禀斌为主日益转变为以高等生产要素特别是创新体系为主。以高新技术产业为代表的集聚区将会成为区域经济和世界经济发展的重要力量。     

日本能源政策新动向

日本政府10月3日正式讨论福岛能源政策。野田佳彦认为安全措施如果到位的话,核电是可以有效利用的。可以预计,相对于菅直人而言,野田佳彦将采取现实的能源政策路径。最后决定日本能源政策的因素是经济问题。