民用建筑配电系统谐波防治技术初探

简述了民用建筑配电系统中谐波源设备的主要类型及其谐波形成机理：分析了一些容易被设计人员忽视的谐波对配电系统的负面影响;探讨了工程设计中一些与谐波有关的计算问题;简单介绍了一些谐波预防和治理的有效方法。     

浅析分布式光伏发电并网谐波影响及治理

并网逆变器谐波的治理对分布式光伏发电并网的推广具有重大的意义。本文介绍了电力谐波的定义,危害;阐述了谐波的产生机理;分析了传统谐波治理措施的优缺点;并简述了部分新的治理策略,具有一定的指导意义。     

民用建筑中的谐波及其抑制

民用建筑中的谐波污染日趋严重.通过简述各类谐波源;利用傅里叶级数分析谐波的特性;阐述谐波的各种危害及其机理;提出谐波的抑制和防治方法等内容,为设计人员在工程设计中,将谐波控制在规范规定的范围内提供帮助与对策.最后论述了谐波抑制与无功补偿的关系.     

谐波电能追责警示指标及实例分析

谐波会对计量产生影响,但是影响的严重程度如何衡量,以及什么时候需要考虑谐波对计量的影响,以往的文献没有进行过系统的讨论。为了弥补这一缺陷,提出了谐波电能追责警示指标即谐波有功功率含有率的概念,用于判断是否需要对非线性用户实行谐波电能计费。首先,在计量点建立谐波分析的等效模型;然后,通过理论推导计算了谐波在不超标时的谐波有功功率含有率的最大取值,并结合实际案例分析验证了所得到的结论;最后,简单讨论了在谐波超标情况下的电能计量问题。研究结果表明:在母线或公共连接点谐波符合国标情况下,谐波电能带来的计量收费偏差低且可以忽略;但对于谐波超标、污染严重的系统或负荷,谐波电能可能会严重影响计费结果;此时需结合实际工况对计量对象进行测试评估,从而对谐波电能收费做出合理的调整。     

电力系统谐波的危害与治理

本文阐述了谐波电流的产生对在供配电系统所造成的影响危害;谐波电流产生的主要因素;谐波电流的抑制方法。     

对电梯电气系统谐波电流发射的研究

主要分析电梯电气系统的谐波电流。首先介绍了国内外相关标准对电气设备谐波电流发射限值的规定及其试验方法,以及谐波的相关概念;通过对实测数据的分析,得出在用电梯电气系统的主要谐波源是调速用变频器;针对变频器主要产生5次和7次谐波规律,提出用装设谐波补偿装置（LC滤波器）的方式来抑制谐波电流。     

扬声器辐射体旋转薄壳的谐波失真

研究了扬声器辐射体旋转薄壳几何非线性引起的谐波失真。采用摄动法和有限元法确定了2次和3次谐波振型,计算了薄壳材料参数和几何参数对谐波失真的影响。结果表明扬声器薄壳谐波失真的机制是分割振动模态的基波共振和超谐波共振,以基波共振为主。采用高阻尼、大杨氏模量和低密度的振膜材料可以降低振膜谐波失真;厚度对谐波失真的峰值影响不大;锥壳半顶角过大,可使3次谐波明显增大。     

谐波治理的方法(一)

总结了治理谐波的一些基本方法,列出了变频器、UPS及各种家用电器的谐波实测数据,介绍了谐波治理方案确定的步骤:首先对谐波源设备进行评估,初步确定参数或实际测量谐波值。然后根据谐波源设备分布的情况确定补偿位置、容量及相关参数,最终选定较完整的补偿方案。较详细地介绍了:①补偿位置的确定原则;②补偿容量确定的两种方法:估算法和计算法;③有源滤波器的三相三线或三相四线的确定和性能比较;④有源滤波器的主要技术参数及与无源滤波器的比较;⑤串行通信问题。     

第3讲 公用电网谐波标准

介绍谐波的基本概念、谐波的危害;对现行国家标准GB/T 14549- 93《电能质量 公用电网谐波》中不同谐波源的叠加计算、用户注入电网的谐波电流允许值等几个基本问题进行了说明:指出现行国标中存在的主要问题,以及标准修订中正在考虑的几个问题:提出减少谐波危害应优先对谐波源本身或在其附近采取适当的技术措施.     

一种分类估算信息中心谐波的方法

简介信息中心的谐波源及其特点;结合实际案例介绍分类评估和估算谐波源谐波数据的方法;分析计算信息中心谐波限值,为新建或改造项目的配电系统谐波治理提供依据。     

钢筋混凝土双肢柱抗震加固与震后修复的试验研究

本文结合我国双肢柱厂房和太钢工程实际,在钢筋混凝土双肢柱试验研究的基础上:①对4榀已发生压肢破坏的双肢柱采用外包钢方法重新进行修复加固和水平加荷试验;②对比了外包钢双肢柱与钢筋混凝土双肢柱每一加载阶段荷载——位移及外包钢钢板箍应变关系;③在刚度、强度、变形方面,探讨了钢筋混凝土双肢柱采用外包钢加固和震后修复效果及抗震性能;④分析了外包钢双肢柱在水平力作用下裂缝出现、屈服时拉肢与压肢的刚度分配关系。     

Terrain-dependence of longitudinal R.M.S. velocities in the neutral atmosphere

Values of the ratio of the longitudinal r.m.s. velocity σ to the friction velocity $\text{u}{}_{\mathrm{★}}$ are compared for a number of sites for which these quantities are adequately defined. Conflicting hypotheses concerning the variation of this ratio with terrain are examined in the light of some recent roughness-change measurements and theoretical results. Although the results of this re-examination are not conclusive, they tend to favour the traditional view that $\text{σ/u}{}_{\mathrm{★}}$ is constant in fully developed equilibrium flows which are not affected by roughness changes.     

Residual bond strength between steel bars and concrete after elevated temperatures

The effects of elevated temperatures and cooling regimes on the residual (after cooling) bond strength between concrete and steel bars are investigated. For this study, ribbed steel bars of 8 mm diameter are embedded in to C20 and C35 concrete blocks with embedment lengths of 6, 10 and 12 cm. Unsealed specimens are heated to 12 different temperatures ranging between 50 and 700 °C and then cooled in water or in air. Pull-out tests are carried out on the specimens, and the effects of elevated temperatures on the residual bond strength are investigated by comparing the results against unheated specimens.     

Seismic Performance Evaluation of SSMF with Simple Beam–Column Connections Under the Base Level

Simple beam–column connections are simpler and cheaper in construction than rigid beam–column connections, moreover, beams under the base level are only carrying gravity loads because of high rigidity of basement walls; therefore, seismic performance of special steel moment frame with basement wall is investigated in two cases in this paper. First, as the normal case of design, rigid beam–column connections are used under the base level, then all of the beam–column connections under the base level are changed to simple connections. The seismic performance of these two types is evaluated by FEMA P695 method. For predicting the collapse capacity of each archetype, adjusted collapse margin ratios are evaluated based on several nonlinear analyses and compared to acceptance criteria. Finally, seismic performance of these two kinds of structures is compared with each other. Despite the structural system’s change in height, seismic performance factors of special steel moment frames are considered for designing whole of the structures. Finally all two types of structures pass the acceptability checks and all the initial assumption are proved.     

The elements of forming traditional Turkish cities: Examination of houses and streets in historical city of Erzurum

When the historical parts of cities—which are the cultural mosaics and which reflect the feelings, thoughts, tendencies, life experiences and the accumulations of the periods in which they were built—begin to disappear, it affects the historical identities of the cities negatively. Investigating, learning, documenting and transferring to the future the values of these spaces, which are bridges between past and future, are vitally important for the maintenance of the cities. This analytical study carried out in Üç Kümbetler and its vicinity in the historical city of Erzurum—where historical and traditional urban elements such as religious buildings, traditional houses, streets, and fountains are intense—aimed at fulfilling these ends.     

On the concept of earthquake resistant hybrid steel frames

The concept of hybrid steel frame system is presented in which mixtures of fully-rigid and semi-rigid steel connections are used in the 9 and 20-story SAC frames. Several different patterns and locations of semi-rigid connection replacements within the frame are examined in order to identify the hybrid frames with most energy dissipation capabilities. Inelastic dynamic analyses are conducted on the proposed selected frames by subjecting them to the Los Angeles earthquake records characterized as those with 10% probabilities of exceedance in 50 years and 2% probabilities of exceedance in 50 years. The maximum story drift for the hybrid frames are determined and compared to the “life safety” and “collapse prevention” limits as recommended by the FEMA 356. The roof-displacement time history, story drift, and member forces for the hybrid frames are reported and compared with those of conventional SAC frames without semi-rigid connections.     

Experimental and finite element analysis on the steel fiber-reinforced concrete (SFRC) beams ultimate behavior

Steel fiber-added reinforced concrete (SFRC) applications have become widespread in areas such as higher upper layers, tunnel shells, concrete sewer pipes, and slabs of large industrial buildings. Usage of SFRC in load-carrying members of buildings having conventional reinforced concrete (RC) frames is also gaining popularity recently because of its positive contribution to both energy absorption capacity and concrete strength.This paper presents experimental and finite element analysis of three SFRC beams. For this purpose, three SFRC beams with 250 × 350 × 2000 mm dimensions are produced using a concrete class of C20 with 30 kg/m³ dosage of steel fibers and steel class S420 with shear stirrups. SFRC beams are subjected to bending by a four-point loading setup in certified beam-loading frame, exactly after having been moist-cured for 28 days. The tests are with control of loads. The beams are loaded until they are broken and the loadings are stopped when the tensile steel bars are broken into two pieces. Applied loads and mid-section deflections are carefully recorded at every 5 kN load increment from the beginning till the ultimate failure.One of the SFRC beams modeled by using nonlinear material properties adopted from experimental study is analyzed till the ultimate failure cracks by ANSYS. Eight-noded solid brick elements are used to model the concrete. Internal reinforcement is modeled by using 3D spar elements. A quarter of the full beam is taken into account in the modeling process.The results obtained from the finite element and experimental analyses are compared to each other. It is seen from the results that the finite element failure behavior indicates a good agreement with the experimental failure behavior.     

Linear and non-linear stability analyses of thin-walled beams with monosymmetric I sections

The paper investigates beam lateral buckling stability according to linear and non-linear models. First, the classical linear stability solutions are derived from the stability equation in the case of monosymmetric cross-sections. Bending distribution, load height parameter and Wagner's coefficient effects are taken into account. In the second step, they are extended to non-linear stability by considering pre-buckling deformation and improved solutions are then obtained. Based on a finite element model developed for large torsion of thin-walled beams with open sections, the stability of beams under gradient moments (M₀, ψM₀, ?1≤ψ≤1) is particularly investigated. It is then concluded that beam lateral buckling resistance depends not only on pre-buckling deformation but also on section shape and load distribution. For bisymmetric I beam, closed form solutions are possible and pre-buckling deformations have an incidence. In the case of beams with monosymmetric I and Tee sections, effects of pre-buckling deflections are important only when the largest flange is in compression under M₀ and positive gradient moment. Analytical solutions are possible. For negative gradient moments all available solutions fail and numerical solutions are more powerful. Effect of gradient moments on stability of redundant beams is investigated at the end. Under such boundary conditions, important axial forces are present due to non-linear beam deformation. These forces, omitted in literature, have an incidence on stability. The element is then concerned with beam-column behaviour rather than beam stability.     

Aerodynamic stability of the downstream of two tandem square-section cylinders

The work reported in the present paper consists of three parts. In part one, the velocity distribution in the wake of a square cylinder at different distances from it (2⩽x/D⩽12) are measured and reported. Analytical expressions for the wake velocity distribution and for the correlation between wake half-width and downstream distance are obtained. The above expressions make it possible to estimate the wake velocity distribution without the availability of the actual experimental data. In part two, the lift and drag acting on the downstream of two cylinders are measured. The results are found to be in reasonable agreement (except in the range L/D=3–4 and T/D=2–3) with previous measurements, and are presented as contours of constant quantities, which make them useful to other researchers for quick information retrieval or estimation. Based on these steady flow results, the region where the downstream cylinder will become unstable to transverse galloping (static instability) are estimated and reported. In the next part, data are acquired with the downstream cylinder undergoing transverse oscillation. From the measurement of the phase angle between the body frequency component of the lift force and the cylinder displacement, the region where the downstream cylinder will be (dynamically) unstable to transverse galloping is estimated, and is found to be in good agreement with the estimation based on the steady flow results in the range L/D⩽4. The variations of the mean drag as well as the Strouhal number and fluctuating lift and drag of the downstream cylinder with reduced velocity are also measured at different L/D and A/D, and possible explanations for the behaviour of the data are offered.     

Time-dependent tests on intact rocks in uniaxial compression

The influence of strain history on rock specimen deformation during multi-level loading and unloading cyclic uniaxial compression creep tests is studied with a creep testing machine. An experimental data processing method for such creep tests is suggested. The correction formulas to determine the rheological model parameters are derived for the case when load relaxation is considered. Creep and relaxation tests under uniaxial compression on four types of rocks are conducted using an electronic hydraulic servo-controlled stiff testing machine. The creep and relaxation laws of the different rocks are compared. The complete stress–strain curves for red sandstone specimens are obtained at nine strain rates from 2.43×10⁻⁶ to 4.38×10⁻³/s. The effects of strain rates on rock strength and limit strain are discussed. Empirical equations to evaluate the strain rate dependence of rock mechanical properties are presented.