Simple force expressions for idealized saturable poles and wedges

Force expressions are presented for simple idealized magnetic pole geometries with (a) infinitely permeable pole material, (b) “square B/H” saturable pole material, and (c) “square M/H” saturable material, the third being the most realistic. The simplicity of the force expressions with saturation is surprising, and important conclusions can be drawn about the role of saturation, the effects of different iron saturation models, and details of the field. For example, for the fundamentally important saturable overlapping rectangular pole configuration, with saturable poles modeled as highly nonlinear, “square M/H” iron, the useful transverse force for positive overlaps is F=μ₀M_sF, twice a comparable value for infinitely permeable poles. This paper is an exploration of how far one can go, using a variety of analytical nonnumerical techniques, in determining fields and forces when saturation effects predominate. The results give useful insights not easily obtained from numerical solutions and provide exact results in certain cases     

Evaluating safety risk of locating above ground utility structures in the highway right-of-way

Roadside safety has been a concern for highway engineers and designers for many decades. A significant part of this concern is related to collisions with utility poles. Current practices and standards for placing utility poles are based on a combination of qualitative guidelines/heuristics and relatively outdated findings. Accordingly, there is a need to study the safety level associated with placing utility poles at different lateral offsets from the edge of the travel-way. In this paper a Safety Performance Function (SPF) is developed to relate roadway and roadside variables to utility pole collision frequency. It was found that increasing the poles offset has a more significant effect on reducing the frequency of utility pole collisions compared to increasing poles spacing. Based on the developed utility pole-SPF, design charts were provided to facilitate calculations and decision-making process. The developed utility pole-SPF was compared to a widely-used utility pole collisions model and the differences in the type of data and the development methodology were highlighted.     

Transient dynamic analysis of tapered FRP composite transmission poles using finite element method

Power transmission poles are subjected to dynamic cantilever bending due to wind gusts and cable unilateral failure, or may also be subjected to vehicle impacts. In this paper, transient dynamic analysis of tapered fiber-reinforced polymer (FRP) composite transmission poles with circular thin-walled cross-section subjected to dynamic cable tension and vehicle impacts is investigated by combination of tapered beam finite element and precise time integration method. It is assumed that the material behavior is linearly elastic and the laminate of the cross-section of the wall is symmetric or antisymmetric angle-ply. The effect of fiber type and orientation, the pole geometry, and the concentrated mass at the pole tip are evaluated by performing the dynamic analysis of FRP poles under step, triangular and sine pulses. There is a good agreement between the results of the present method and those obtained from the poles modeled by ANSYS commercial finite element software and existed literatures. Also, there is a significant shorter run-time in the present method. It is concluded that beyond 10 layers for the laminate with constant thickness of the wall, the pole tip deflection does not change.     

Fault-tolerant homopolar magnetic bearings

This paper summarizes the development of a novel magnetic suspension that improves reliability via fault-tolerant operation. The suspension is suitable for flywheels used in satellites and space stations for attitude control and energy storage. Specifically, we show that flux coupling between poles of a homopolar magnetic bearing can deliver desired forces even after termination of coil currents to a subset of "failed poles". Linear, coordinate-decoupled force-voltage relations are also maintained before and after failure by bias linearization. We determined current distribution matrices that adjust the currents and fluxes following a pole set failure for many faulted pole combinations. We used one-dimensional magnetic circuit models with fringe and leakage factors derived from detailed, three-dimensional finite-element field models to obtain the current distribution matrices and the system response. Reliability is based on the success criterion that catcher bearing-shaft contact does not occur after pole failures. The magnetic bearing reliability is improved by increasing the number of the radial poles. An advantage of our method over other redundant approaches is a significantly reduced requirement for backup hardware such as additional actuators or power amplifiers.     

离心成型预应力钢纤维混凝土电杆设计试验研究

对研制的呼称高27m离心成型预应力钢纤维混凝土电杆进行了受力性能试验研究。结果表明,在断线工况荷载作用下,电杆的受力表现出良好的整体性,各项性能均满足设计要求;杆身采用预应力和钢纤维双重增强作用,使电杆的抗裂能力提高,变形减小;一旦发生超载运行出现裂缝,裂缝细短且非贯通,卸载后变形回复能力强,残余变形很小;在极限承载时,整杆变形明显,具有良好的延性破坏预兆。同时,预应力钢纤维混凝土电杆在预应力筋放张和杆段对焊组装过程中,避免了普通预应力混凝土电杆在预应力筋挂板和杆段连接钢圈附近混凝土起皮爆裂现象。根据试验结果对比分析,建立了预应力钢纤维混凝土电杆抗裂度、裂缝宽度、挠度和正截面承载力设计计算方法。研究成果为河南省漯河~淮阳220kV线路工程建设提供了重要科研依据,为钢纤维混凝土在预应力电杆中的应用提供了重要参考。     

Exact field calculations for asymmetrical finite-pole-tip ring heads

An exact solution is given for the fields of an infinitely permeable asymmetrical finite-pole-tip ring head. The solution is obtained by conformal mapping and is expressed in terms of elliptic integrals and elementary functions. Using the method of undetermined coefficients, it is shown how to decompose the Schwarz-Christoffel integral into elementary functions and elliptic integrals. For each given pole geometry, the constants appearing in the Schwarz-Christoffel formula are calculated once. Then the fields at various points in the poles domain are calculated using Newton's method and the formulas for the decomposition of the Schwarz-Christoffel integral.<>     

Record characteristics of tape heads with CoZr and NiFe poles

Overwrite and recorded signal are compared for tape heads with Co ₉₁Zr₉ and Ni₈₁Fe₁₉ poles as a function of throat height. The effects of throat height variation on performance are discussed for constant current recording with and without pole saturation. The impact of pole saturation on throat height tolerance is also discussed. Co₉₁Zr₉ and Ni₈₁ Fe₁₉ tape heads have equivalent record performance as long as their poles are not saturated. When pole saturation does affect head performance, it has less impact on CoZr heads, and they record and overwrite better than NiFe heads. In a system that requires at least 25-dB 2f/1f overwrite at 2362 fc/mm (60 kFCI), for example, both CoZr and NiFe heads would perform well on oxide tape over a wide range of throat heights. On metal particle tape the overwrite falls below 25 dB at a throat height of 4.4 μm for the CoZr heads and 2.3 μm for the NiFe heads. These throat height limits could be extended with thicker poles or, in the case of NiFe, plated poles that maintain a uniform thickness on sloped areas of the underlying films. Nonetheless, for the conditions described here CoZr heads had nearly twice the throat height tolerance of otherwise identical NiFe heads     

Geometry and Stacking Sequence Effect on Composite Spinnaker Pole's Stiffness: Experimental and Numerical Analysis

Composite materials are widely employed in sailing sports, a possible application is for the mast pole or other sail poles. In the paper the attention is focused on the spinnaker poles mechanical performances; in particular the focus is on axial and ring compressive properties of three different carbon fibre/epoxy resin spinnaker poles, to investigate both the diameter and stacking sequence effect on the mechanical performance of the structure. Starting from the stacking sequence used in the production of a particular spinnaker pole, the effect of a lamina at 0° in the middle of wall thickness is investigated with the purpose to obtain a more stiff structure. Moreover to test the proposed stacking sequence on different size products, a prototype with lower diameter is realized. To properly evaluate axial and ring stiffness, axial compression test and ring stiffness one are performed. Then a numerical model is developed to support the design of the finished product: A simple and versatile numerical analysis (FEA with software ANSYS), by simulating ring stiffness and pull-direction compression tests, is carried out in elastic regime. Such model should be suitable for designing and/or verifying the mechanical performance of pole structures, even though differing from those above described, for materials, geometry and stacking sequence.     

On the nature of the fourth sound

The density-density correlation function of He II bounded by solid walls is calculated in the hydrodynamic region. The migration of its poles as a function of the resistance parameter is investigated, and it is found that the fourth-sound pole can only be related to the first-sound pole far enough (_s0/₀>1/9) from the critical temperature. Otherwise, it arises from a mixture of the first- and second-sound poles. The contributions of poles to the sum rules are also discussed.     

A General Expression for the Electrometer Transfer Impedance

An expression for the electrometer transfer impedance Z21 is derived which describes the high-gain amplifier and the feedback network as general functions of the Laplace operator s. The equation derived is in the form of the general feedback equation, enabling the designer to employ the many tools of feedback analysis, such as root locus, Nyquist or Routh stability criteria, and Bode plots. Previous analyses have been limited to a constant forward transfer function and a feedback network employing a simple pole. Using this general analysis, the electrometer designer can take into consideration the unavoidable poles and zeros which are found in the forward transfer and feedback network. Furthermore, he can use this analysis to synthesize different desirable transform characteristics, thus optimizing electrometer design for a particular application.     

Pole assignment using state feedback with time delay in friction-induced vibration problems

The dynamic behavior of friction-induced vibration problems is governed by second-order differential equations having asymmetric matrices, due to the coupling of structures and external loads, which are functions of some parameters. Asymmetric systems are prone to unstable vibration (flutter) as a parameter reaches a critical value. Placement of these unstable poles to the left-hand half of the complex pole plane for stabilization can be achieved by active (feedback control) and passive means (structural modification). Moreover, placement of poles is also done to achieve the desirable dynamic response and system performance. However, such active pole assignment control introduces inherent time delays in the feedback control loop. This paper presents a method for assigning complex poles to second-order damped asymmetric systems by using state-feedback control while considering a constant time-delay in the feedback control loop. The control strategy is based on receptances of the symmetric part of the asymmetric open-loop system (without time delay), which can be easily obtained from transfer function measurements. This method does not require the knowledge of mass, damping and stiffness matrices, and hence circumvents the modeling errors (finite element or reduced order). In this research, with numerical examples, it is shown that by means of active state feedback control and by using a relatively small number of available receptances, open-loop poles of the asymmetric system can be assigned precisely. The stability of the closed-loop system is analyzed by computing primary closed-loop poles and the associated critical time delay.     

An improved method using factor division algorithm for reducing the order of linear dynamical system

An improved method is proposed to determine the reduced order model of large scale linear time invariant system. The dominant poles of the low order system are calculated by clustering method. The selection of pole to the cluster point is based on the contributions of each pole in redefining time moment and redefining Markov parameters. The coefficients of the numerator polynomial for reduced model are obtained using a factor division algorithm. This method is computationally efficient and keeps up the stability and input output characteristic of the original arrangement.     

Performance improvement of permanent magnet machines by modular poles

Modular permanent magnet poles have recently been proposed to enhance the performance of permanent magnet machines and improve the exploitation of used magnet materials. An optimisation method for these poles is proposed for use in linear permanent magnet synchronous machines. The main objective of the optimisation is to select proper dimensions and material properties of modular permanent magnet poles to enhance the machine developed thrust. The optimisation is carried out based on a mathematical model of the machine obtained analytically. In particular, the developed thrust of linear permanent synchronous machines with modular poles is given by the model. Genetic algorithm is then employed to optimise pole parameters where the ratio of thrust ripples to average thrust is chosen as an objective function. Extensive investigations carried out by analytical and finite element methods confirm that substantial lower thrust ripples are produced with almost the same average thrust.     

A study on failure mechanism of self-supported electric poles through full-scale field testing

Self-supported single poles are widely used for transmission of electricity in rural areas of India. Recently, in Unnao District of Uttar Pradesh, India, a large number self-supported poles was found to suffer extensive tilting during wind storms. This incident has raised safety concerns for the Government as well as the company in charge of the construction and installation of the poles. These prestressed concrete poles of about 8.5m height were embedded in the ground by 1.5m as per standard practice. From visual inspection of the failure sites and a detailed geotechnical investigation of soil from 24 nearby boreholes, it seemed that the failures caused primarily due to inadequate resistance from the soft soil of Indo-Gangetic plain, resulting bearing and overturning failures. In order to understand further, a test setup was created at the Institute of Technology Kanpur, where the full-scale poles had been brought from Unnao and were erected in a specifically prepared soil pit to match the in-situ soil condition of the Unnao case-study sites. The poles were erected on compacted silty clay soil deposit by adopting standard procedure of back-filling as used in site. The poles were then subjected to lateral loading and unloading through a specially designed frame. The load capacities of the poles have been found to be in the range of 0.95 to 1.48 times the design wind load for the chosen sites. It is noted that by increasing the footing dimension by only 20%, the capacity of the pole is improved by about 54%. Further, it is also found that by replacing a concrete footing by a compacted brick-stone aggregate grouted footing (a common practice in rural India), no significant alteration in the load capacity or force-deformation behavior is observed. A numerical study was also conducted to understand the experimentally observed behavior. It is found from this study that the analytical model considering nonlinear soil–pole interaction (Case II) showed better prediction of experimental behavior than the fixed base model (Case I). Finally, a sensitivity analysis using First-Order-Second-Moment (FOSM) method indicated that cohesion influences the load capacity of the poles most significantly compared to other soil parameters such as friction angle, unit weight and shear modulus for the chosen soil type and available soil exploration data.     

Environmental and economic assessment of utility poles using life cycle approach

Due to increasing demand for utility poles and the banning of native forests logging in Australia, it is necessary to find sustainable alternatives to roundwood utility poles. Currently, steel and concrete are the most common alternatives. Veneer-based composite (VBC) is a newly developed product made from hardwood plantation mid-thinning. To assess the viability of VBC, comparative life cycle assessment (LCA) and life cycle costing (LCC) analysis were conducted. Two end-of-life scenarios for VBC pole were assessed: incineration with energy recovery and landfilling. Five impact categories were considered: global warming (GWP); acidification (AP); eutrophication (EP); fossil depletion (FDP) and human toxicity (HTP). VBC pole with incineration showed the best environmental performance, particularly on GWP (63.22 kg-CO₂-eq), AP (0.29 kg-SO₂-eq), FDP (30.78 kg-Oil-eq) and HTP (2.27 kg-1,4-DB-eq), which are less than half of concrete and steel poles. However, VBC had higher EP than concrete and steel due to use of adhesives and preservatives. VBC pole also had the lowest LCC ($1529), due to use of low-value materials and lower manufacturing cost. The LCC showed that both VBC scenarios performed equally on economic grounds. Sensitivity analysis showed that service life was the most sensitive parameter affecting both environmental and economic results, especially the VBC. Transportation distances and fossil fuel consumption also had significant effects on LCA result. Monte Carlo analysis further revealed that despite the high levels of uncertainties in the input parameters, the overall ranking of the options remained the same with VBC being the best performer and concrete the least.     

Power density improvement of three phase flux reversal machine with distributed winding

The three phase flux reversal machine (FRM) is a doubly salient permanent magnet machine with concentrated windings. This study proposes the distributed winding for this machine. This winding (i.e. full pitch winding) offers high-power density and improves the efficiency. The permanent magnet (PM) flux linking the stator winding has effectively two or four pole flux pattern, which depends on the number of stator poles and independent of number of rotor poles. Finite element method (FEM) analysis is performed on the concentrated stator pole winding FRM (CSPFRM) and proposed full pitch winding FRM (FPFRM) to obtain induced EMF, flux linkages and inductance of the winding. The inductance of both machines is also obtained using winding function approach and compared with FEM results. The effect of armature reaction is compensated by capacitive series compensation to improve the voltage regulation. FEM analysis is also carried out on both the compensated generators to evaluate the power density. Speed of the flux pattern and that of the rotor is different in FRM. The ratio of these two speeds is termed as fictitious 'electrical gear'. FRM and permanent magnet synchronous machine (PMSM) have sinusoidal terminal voltage and surface mounted PMs. The power density of both machines is compared using the concept of fictitious `electrical gear?. To verify the above analysis, a 6/14 pole FRM with distributed and concentrated winding is designed and fabricated. The experimental results are in close agreement with simulated results.     

一般振动系统的多输入状态反馈部分极点配置

本文讨论具有非对称阻尼、刚度矩阵的一般振动系统多输入部分极点配置问题。基于系统的矩阵二阶微分方程而非一阶状态方程形式,采用多输入状态反馈控制,使系统的部分极点得以配置,同时使其它的极点保持不变。对于该配置问题,本文给出了控制增益矩阵的一种显式解,最后用一个算例说明本文方法。     

结构振动的电磁驱动AMD系统控制策略与试验

提出了结构振动的新型电磁驱动AM／）控制系统，基于极点配置控制算法的控制策略，进行了结构模型地震响应控制的小型振动台试验，验证了所提控制策略的有效性。首先，研究了振动台试验对象结构无控建模的相关问题，分析比较了AMD系统摩擦等效处理为线性粘滞阻尼的影响，以系统无控三自由度模型为例，结合正弦扫频试验进行了参数验证。其次，提出了基于极点配置控制算法的电磁驱动AMD系统控制策略，给出了理想的极点配置控制区域。最后，以El Centro地震波输入为例，试验比较了极点配置参数对结构振动控制效果的影响，结果表明恰当的控制策略及其参数是成功实现应用电磁驱动AMD系统控制结构振动的前提和基础。     

直流电机复合定位控制系统性能分析及系统优化

在直流电机复合定位控制系统(CPCS)设计过程中,发现电机速度等动态响应曲线发生振荡,表现出一定程度的不稳定性.为探究这一振荡与控制系统内在结构之间的关联性,使用MATLAB对PID及CPCS系统动态响应、根轨迹及频率特性等进行分析、比较.结果显示：高阶控制系统的传递函数总可以通过降阶等方式简化为具有1个实数零点、1个实数极点和2对复共轭极点的基本形式.其中离原点位置较近处的一对复共轭极点的移除是造成CPCS系统稳定性下降,产生振荡的根本原因.该振荡可通过增大另一对复共轭极点实部或减小虚部的方法予以降低或消除.这一结论对提高控制系统的定位精度和稳定性具有重要的参考意义.     

The automated analysis of prestressed concrete poles for street lighting

Different countries have produced codes for prestressed concrete poles for street lighting. An attempt is made to present an automated analysis to calculate the safety factors, resultant stresses, ultimate loads and forces against cracking in prestressed pole. Based on these results one can bring about a unified analysis in which a provision is made for a comparative study of all these codes.