多国荷载规范中阵风荷载因子的比较研究

将我国的《建筑结构荷载规范》(GB5009-2001)与美国(ASCE7-98)、日本(RLB-AIJ2004)、加拿大(NBC1990)和澳大利亚(AS1170.2)几国规范进行了比较研究.首先总结了各国规范所采用的Davenport提出的经典抗风设计方法——阵风荷载因子法(GLF),然后对包括平均风速剖面、湍流强度、脉动风速谱类型进行了比较.美日加澳都将GLF取为一个恒量,相当于"位移风振系数",中国规范中的风振系数却是随高度变化的量,相当于"惯性力风振系数".

利用HHT方法对非平稳风力的时频分析

非平稳信号的分析方法是信号分析领域中的一个重要问题。以风洞试验获得的非平稳风压信号和升力系数信号为研究对象,采用HHT方法对信号进行时频分析。HHT(Hilbert-Huang transform)方法可以获得有意义的瞬时频率,从而给出频率随时间变化的精确表达;信号最终被表示为时频平面上的能量分布,成为Hilbert谱;该方法适用于分析生活中普遍存在的大量频率随时间变化的非线性、非平稳信号,可将复杂的信号直接分离成从高频到低频的若干阶固有模态函数。分析结果虽然没有表现出明显的频谱分布特性,但与以往HHT分析结果提取的固有模态函数不同,如果对该试验获得的非平稳信号提取的固有模态是低频部分的残余信号,忽略其他高频信号,则风压时程和升力系数时程的残余信号曲线就可以分别回归为一个线性函数和一个正弦函数。这也说明,该非平稳信号的主成分仍然是由平稳信号组成的,可以用分析平稳信号的方法进行时程分析。

几种非平稳分析方法对非平稳风力时程的比较分析

非平稳信号的分析方法是信号分析领域中的一个重要问题。本文以风洞试验获得的非平稳风压信号和升力系数信号为研究对象,分别采用短时傅里叶变换、Wigner-Ville分布,小波变换方法和Hilbert-Huang变换(HHT)方法对信号进行时频分析。分析结果表明,由于短时傅里叶变换、Wigner-Ville分布,小波变换方法都是基于傅里叶变换,因此,得到的频谱特性都大致相同,只是在分析的精细程度上有所差异;HHT方法可以获得有意义的瞬时频率,从而给出频率随时间变化的精确表达,信号最终被表示为时频平面上的能量分布,成为Hilbert谱,该方法适用于分析生活中普遍存在的大量频率随时间变化的非线性、非平稳信号,可将复杂的信号直接分离成从高频到低频的若干阶固有模态函数。另一方面,无论用哪一种分析方法都可以看出,风速和风压信号的能量大多分布在低频部分,高频部分所占比例很少,而升力信号的能量大多分布在高频部分,低频部分所占比例很少。本文采用HHT方法提取起控制作用的信号主成分。

雷暴冲击风模拟及其荷载的风洞试验研究

为了研究在突变气流作用下结构的空气动力特性,介绍了利用主动控制风洞模拟突变气流的试验研究。首先通过该风洞模拟出了雷暴冲击风阵风剖面;然后,采用"阶跃流法"模拟了风速突变的时程;最后将高层结构模型置于该突变气流中,观测在特殊气流中结构表面风压以及结构空气动力学参数的变化特征。试验结果表明,利用主动控制风洞模拟出的雷暴冲击风阵风剖面同理论的相似性达到90%以上,突变气流会使高层结构整体产生较大的非定常升力,并且在结构表面产生较大的非定常风压。

Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Physical and Electrolytic Properties of Monofluorinated Ethyl Acetates and Their Application to Lithium Secondary Batteries

Ethyl acetate (EA) shows low viscosity for its relative permittivity. Monofluorinated organic solvents exert the polar effect on the various properties. We have investigated the effect of position isomerism on the physical and electrochemical properties of two monofluorinated carboxylates: 2-fluoroethyl acetate (2FEA) and ethyl fluoroacetate (EFA). Relative permittivity of 2FEA was lower than that of EFA, whereas viscosity of 2FEA was higher. Electrolytic conductivity of a LiPF6 solution in 2FEA was lower than that in EFA, but higher than that in EA at high temperatures. The use of 2FEA as a co-solvent improved cycling efficiency and suppressed fading of discharge capacity of a Li|LiCoO2 coin cell at high cycle numbers.

Feasible Development of a Carbon-Based MEMS Using a MEMS Fabrication Process

We aimed to develop a process technology for constructing a carbon-based micro-electromechanical system that does not require a high-temperature and high-energy process. A HOPG （highly oriented pyrolytic graphite） crystal microsheet was prepared by exfoliation. Cantilevers and doubly clamped beams were patterned using a photoresist. The HOPG microsheet was attached by using a tantalum layer. We fabricated cantilevers and a doubly clamped beam by controlling the thickness of the HOPG microsheet and then measured the first resonance frequency. The measurements suggest a need to improve the stiffness of the beam.

Development of a Notion of Limit as Proximity From Discourse Analysis in Secondary-School Function Classes

Mathematical teaching and learning of an introductory calculus conception of limit in secondary school before students learn the formal definition of limit in higher education are discussed.In this study,applications of the theory of instruction based on“Formalizing Introductory Notions(FIN)”(Nagle,2013),in which a theory incorporating new pedagogical approaches was introduced to describe static notions of limit,without ignoring dynamic notions of limit,are presented to help foster an informal limit conception better aligned with the formal definition.A qualitative discourse analysis based on students’utterances,including students’drawing pictures on graphs,was done.In the results of the investigation,it was found that the students’utterances drawings on a graph of the secants(segments)used static notions of limit supported by dynamic notions of limit according to the operating activities.There were learning activities in which students developed a notion of limit as the proximity of the predicted tangent line of a function.Consequently,students’discussions changed focus to the validation of limit candidates with static notions of limit.To overcome the contradiction of their explanations of the operating activities with dynamic notions of limit,the students changed to an explanation with static notions of limit.In light of the findings,this study suggests adapting the pedagogical approach used by the Nagle(2013).

Airflow Distribution Measurements around the Human Body Using a Thermal Manikin by Particle Image Velocimetry

The human body is a heat source in a room. As the human body has a complex shape, it is difficult to accurately measure the airflow distribution around the human body using a conventional anemometer. This study measured the airflow distribution around a thermal manikin acting as a human body by visualization and particle image velocimetry (PIV). The thermal manikin was 1700 mm in height, and its surface temperature was set to 30oC. The experiments were performed in the conditions when the manikin was seated on a chair. The ambient air temperature and wind velocity were experimental variables. The airflow distribution around the manikin was reported by considering the relationships between convection and ambient wind velocity. There were no differences in the airflow distribution around the manikin due to the ambient air temperature when the wind velocity in the chamber was set as 1.0 m/s. Hence, it was assumed that the ambient wind velocity was dominant in this condition. Various airflow distributions were formed around the manikin due to the difference between the body surface temperature and the ambient air temperature in the case where the wind velocity in the chamber was set to approximately equal to 0.0 m/s.

Shape Optimization and Assessment of Wind Induced Stresses in Domes

Domes are popularly used for column free areas. They are employed as covers to reservoirs and treatment units and also as containment in nuclear reactors. Inverted domes are popular as foundations. Structures are built with an intended end use for a specified utility period. The functional requirement is to serve the purpose and the structural requirement constitutes stability, strength, safety, serviceability and durability. Satisfaction of these requirements at affordable costs is the goal of structural optimization. This paper demonstrates the need and scope for optimization of domes by formulating and solving the problem by use of calculus （volume of material is the objective function being minimized using first principles of calculus）. A simple but elegant method is suggested for determination of wind stresses by statics which compares very well with that obtained by rigorous method.

IR Spectroscopic Study of Silicon Nitride Films Grown at a Low Substrate Temperature Using Very High Frequency Plasma-Enhanced Chemical Vapor Deposition

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been grown from a SiH4–N2 gas mixture through very high frequency (VHF) plasma-enhanced chemical vapor deposition (PECVD) at 50℃. The films are dense and transparent in the visible region. The peak frequency of the Si–N stretching mode in the IR absorption spectrum increases with increasing N–H bond density, which is similar to the behavior of a-SiNx:H films grown from SiH4–NH3 gas. During storage in a dry air atmosphere, the Si–O absorption increases. A large shift in the peak frequency of the Si–N stretching mode in the initial stage of oxidation, which is higher than the shift expected from the increase in the N–H bond density, is mainly caused by the change in the sum of electronegativity of nearest neighbors around the Si–N bond due to the increase in the Si–O bond density.

From the Voices in the Narratives of After-School Support Advisors: Support for Children’s After-School Support Advisors in Japan

This paper examines how advisors perceive the voices made by Mr.A(pseudonym),the founder of after-school support for children(Initiative Z:pseudonym)in Japan,to advisors who support children.Furthermore,the purpose of this study is to find out how advisors think about the voices and that the voices have led or not advisors to support children,if to do so,what points are key to continuing support for children.Therefore,in Initiative Z,I conducted a survey of two advisors who were approached by Mr.A,who is involved in supporting children as an advisor.As a result of analyzing the narratives obtained from interviews with the two advisors,it was found that the advisor had a sense of being recognized by Mr.A because Mr.A acknowledged the advisor’s way of life.This feeling on the part of the advisor led to trust in Mr.A,and the advisor was in tune with Mr.A’s thoughts on after-school support,suggesting that the advisor was providing support to the child.

Effective improvement of a local thermal environment using multi-vent module-based adaptive ventilation

Indoor thermal comfort is essential as it improves living standards.Activity scenarios of personnel are in the process of a dynamic change.In most interior spaces with fixed working stations,people directly blown by cold air have a poor thermal experience.Therefore,to meet the differentiated environmental demands,one challenge is to explore novel ventilation strategies to satisfy the changing environmental needs.An adaptive strategy,multi-vent module-based adaptive ventilation(MAV),was designed to increase the adjustability of air distribution and better adapt to variable demands.A classroom was chosen as a representative model with multiple scenarios during its use.Simulations were conducted to verify the three-level control effect of MAV on improving the thermal environment.The results revealed that different vent solutions create different airflow patterns and thermal environments,which can be matched to the scenarios.The scale for ventilation efficiency No.4,which measured the influence scope of supply air,was used to evaluate the zoning division control in MAV.The space under the charge of a concerned MAV module showed a higher SVE4 than that at other zones.This implied that the zoning division can be effectively implemented.Thermal comfort measured using the air diffusion performance index,predicted mean vote,and draught rate showed that the application of MAV is better than that of the fixed MV mode,and the discomfort experienced when exposed to cold air can be avoided.It is believed that these results will help extend the research of adaptive ventilation strategies.

A prototype online database-enabled design framework for wind analysis/design of low-rise buildings

This study presents a development of an advanced cyberbased database-enabled design module for low- rise buildings （DEDM-LR） which provides estimation of the wind-induced responses for main wind force resisting frames by making direct use of pressure time histories measured at a large number of pressure taps over a suite of building models. These responses may be considered in lieu of code-specified load effects in which the overall accuracy may be influenced by the inherent simplifications in codes. In addition, this new automated approach is particularly attractive and advantageous as it allows a web-based online analysis/design via intuitive user-friendly interfaces for both the input and output in terms of familiar web-style forms that are nowadays very common in most of web-based services. Presently, the DEDM-LR hosts an aerodynamic database developed by the Tokyo Polytechnic University （TPU）, Japan for a variety of building configurations like flat, gable, and hip roofs under suburban terrain flow condition with immediate application to other databases. The paper shows the efficacy and validity of the DEDM-LR by walking through its details and examples on selected gable-roofed buildings. The architecture of DEDM-LR platform offers the ability to pool resources by hosting other databases that may become available in the near future.

Review and development of the contribution ratio of indoor climate(CRI)

An indoor thermal environment is affected by various heat elements,such as heat transfer through walls,solar radiation,and heat emissions from people,lighting and equipment.To promote both local thermal comfort and building energy efficiency,demand-oriented ventilation(such as personalized ventilation)has been developed.When using this method,a good understanding on indoor temperature distribution becomes necessary.For this purpose,an index known as Contribution Ratio of Indoor Climate(CRI)has been developed through extraction from the calculation results of Computational Fluid Dynamics(CFD).This index can be used to analyze the independent contribution of each heat element to indoor temperature distribution.In this paper,a complete and detailed introduction of the CRI is given,including its basic premises,definitions,and mathematical meaning.Particularly,calculation method of the CRI in natural convection airflow fields is further developed.Two cases(forced and natural convection airflow fields)have been carried out in different scenarios,with results showing that the CRI of a heat source had higher values in the area around itself.Also,it had a larger influence range in forced convection airflow field because of the convective airflow,while relatively larger CRI values only appear in the area above the heat source in the natural convection airflow field because of the heat plume.As a useful index for understanding the form of indoor temperature field,the CRI has guiding significance for regulating air-conditioning/ventilation systems to build better indoor thermal environment.