Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power systemtomaintain reliable operation.With equal conductor spacing grounding grid design,the distribution of the current in the grid is not uniform.Hence,unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing.This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors:the least-square curve fitting technique and the compression ratio techniquewith equal grid configuration for both square and rectangular grids.Particle Swarm Optimization(PSO)is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids.Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration.Simulation results are obtained by theMATLAB software developed.Percentage of improvement in ground potential rise,step voltage,touch voltage,and grid resistancewith variation in compression ratios are plotted.

Study of HCP→FCC phase transformation mechanism under different hot compression rates of AZ31 magnesium alloy

At present,there are few studies on the phase transition during the thermocompression plastic deformation of magnesium alloy.In this study,the evolution model of thermal compression plastic of AZ31 magnesium alloy was constructed by molecular dynamics,and the phase transition relationship between HCP and FCC at different thermal compression rates was studied.By combining GLEEBLE thermal compression experiment with transmission electron microscopy experiment,high-resolution transmission electron microscopy images were taken to analyze the transition rules between HCP and FCC during plastic deformation at different thermal compression rates,and the accuracy of molecular dynamics analysis was verified.It is found that the slip of Shockley’s incomplete dislocation produces obvious HCP→FCC phase transition at low strain rate and base plane dislocation at high strain rate,which makes the amorphous phase transition of HCP→OTHER more obvious,which provides theoretical guidance for the formulation of forming mechanism and preparation process of magnesium alloy.

Quantitative Comparative Study of the Performance of Lossless Compression Methods Based on a Text Data Model

Data compression plays a key role in optimizing the use of memory storage space and also reducing latency in data transmission. In this paper, we are interested in lossless compression techniques because their performance is exploited with lossy compression techniques for images and videos generally using a mixed approach. To achieve our intended objective, which is to study the performance of lossless compression methods, we first carried out a literature review, a summary of which enabled us to select the most relevant, namely the following: arithmetic coding, LZW, Tunstall’s algorithm, RLE, BWT, Huffman coding and Shannon-Fano. Secondly, we designed a purposive text dataset with a repeating pattern in order to test the behavior and effectiveness of the selected compression techniques. Thirdly, we designed the compression algorithms and developed the programs (scripts) in Matlab in order to test their performance. Finally, following the tests conducted on relevant data that we constructed according to a deliberate model, the results show that these methods presented in order of performance are very satisfactory:- LZW- Arithmetic coding- Tunstall algorithm- BWT + RLELikewise, it appears that on the one hand, the performance of certain techniques relative to others is strongly linked to the sequencing and/or recurrence of symbols that make up the message, and on the other hand, to the cumulative time of encoding and decoding.

Effect of compression ratio on microstructure evolution of Mg−10%Al−1%Zn−1%Si alloy prepared by SIMA process

A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated.The results indicate that the average size ofα-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%.In addition,the eutectic Mg2Si phase in the Mg−10%Al−1%Zn−1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process.With the increasing of compression ratio,the morphology and average size of Mg2Si phases do not change obviously.The morphology modification mechanism of Mg2Si phase in Mg−10%Al−1%Zn−1%Si alloy by SIMA process was also studied.

Simulation Research on the Effect of Cooled EGR, Supercharging and Compression Ratio on Downsized SI Engine Knock

Knock in spark-ignition（SI） engines severely limits engine performance and thermal efficiency. The researches on knock of downsized SI engine have mainly focused on structural design, performance optimization and advanced combustion modes, however there is little for simulation study on the effect of cooled exhaust gas recirculation（EGR） combined with downsizing technologies on SI engine performance. On the basis of mean pressure and oscillating pressure during combustion process, the effect of different levels of cooled EGR ratio, supercharging and compression ratio on engine dynamic and knock characteristic is researched with three- dimensional KIVA-3V program coupled with pressure wave equation. The cylinder pressure, combustion temperature, ignition delay timing, combustion duration, maximum mean pressure, and maximum oscillating pressure at different initial conditions are discussed and analyzed to investigate potential approaches to inhibiting engine knock while improving power output. The calculation results of the effect of just cooled EGR on knock characteristic show that appropriate levels of cooled EGR ratio can effectively suppress cylinder high-frequency pressure oscillations without obvious decrease in mean pressure. Analysis of the synergistic effect of cooled EGR, supercharging and compression ratio on knock characteristic indicates that under the condition of high supercharging and compression ratio, several times more cooled EGR ratio than that under the original condition is necessarily utilized to suppress knock occurrence effectively. The proposed method of synergistic effect of cooled EGR and downsizing technologies on knock characteristic, analyzed from the aspects of mean pressure and oscillating pressure, is an effective way to study downsized SI engine knock and provides knock inhibition approaches in practical engineering.

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ratios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm （Nos. 7, 6 and 5 according to JIS A 5001） were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

A SPARSITY AND COMPRESSION RATIO JOINT ADJUSTMENT METHOD FOR COLLABORATIVE SPECTRUM SENSING

Spectrum sensing is the fundamental task for Cognitive Radio (CR). To overcome the challenge of high sampling rate in traditional spectral estimation methods, Compressed Sensing (CS) theory is developed. A sparsity and compression ratio joint adjustment algorithm for compressed spectrum sensing in CR network is investigated, with the hypothesis that the sparsity level is unknown as priori knowledge at CR terminals. As perfect spectrum reconstruction is not necessarily required during spectrum detection process, the proposed algorithm only performs a rough estimate of sparsity level. Meanwhile, in order to further reduce the sensing measurement, different compression ratios for CR terminals with varying Signal-to-Noise Ratio (SNR) are considered. The proposed algorithm, which optimizes the compression ratio as well as the estimated sparsity level, can greatly reduce the sensing measurement without degrading the detection performance. It also requires less steps of iteration for convergence. Corroborating simulation results are presented to testify the effectiveness of the proposed algorithm for collaborative spectrum sensing.

Specimen aspect ratio and progressive field strain development of sandstone under uniaxial compression by three-dimensional digital image correlation

The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in specimens with different aspect ratios was also examined.Peak stress,post-peak portion of stress-strain,brittleness,characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio.Strain patterns of the rocks were obtained by applying three-dimensional(3D) digital image correlation(DIC) technique.Unlike conventional strain measurement using strain gauges attached to specimen,3D DIC allowed not only measuring large strains,but more importantly,mapping the development of field strain throughout the compression test,i.e.in pre-and post-peak regimes.Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime.However,in post-peak regime,strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone.The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation.Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.

Radial Compressive Property of Nerve Regeneration Conduit with PGLA Biodegradable Fibers

Radial compressive property greatly influences nerve regeneration and functional recovery. In this study,four types of braided bioabsorbable nerve regeneration conduits made from poly(glycolide-co-L-lactide)(PGLA) were produced. The aim is to test the radial compressive force and elastic recovery ratio of nerve regeneration conduits. The results indicated that radial compressive force was closely related to the inner diameter and length of tubes and elastic recovery ratio was nearly unaffected by these two factors.

短切玄武岩纤维对混凝土力学性能的影响

为了提高混凝土的力学性能,研究短切玄武岩纤维对混凝土力学性能的影响规律。把不同体积掺量(0.25%、0.5%、0.75%、1.0%、1.25%)、不同长度(6 mm、12 mm)的短切玄武岩纤维掺入以C40混凝土为主的不同基体强度等级的混凝土中,进行立方体抗压强度、劈裂抗拉强度、抗弯强度试验,分析短切玄武岩纤维对混凝土力学性能产生的影响,并拟合出C40混凝土抗弯强度与短切玄武岩纤维体积掺量的数量关系。结果表明:同一掺量下,12 mm短切玄武岩纤维比6 mm短切玄武岩纤维提升混凝土力学性能效果更佳;C40混凝土在12 mm短切玄武岩纤维掺量为1%时,其立方体抗压强度、劈裂抗拉强度、拉压比和抗弯强度对比未掺入玄武岩纤维的混凝土分别提高7.11%、30.00%、21.34%和24.89%,此时混凝土力学性能提升效果最佳。

Equal Volumes of Sand and Gravel Concrete Mix Ratios in Cameroon and Its Effect on Concrete Compressive Strength

In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm2 for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m3 of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.

配筋PVA-钢混杂纤维增强水泥基复合材料梁柱边节点抗震性能试验研究

改善工程材料韧性和耐久性,提高框架梁柱节点抵抗变形和破坏的能力,是提高框架结构抗震韧性的有效途径之一。采用PVA-钢混杂纤维增强水泥基复合材料代替普通混凝土应用到梁柱边节点,考虑轴压比和加密区体积配箍率的影响,设计6个配筋PVA-钢混杂纤维增强水泥基复合材料、1个配筋单掺PVA纤维增强水泥基复合材料和1个钢筋混凝土梁柱边节点试件进行拟静力试验,分析其破坏形态、滞回曲线、骨架曲线、延性、耗能能力、钢筋应变和梁端塑性铰区转角,探讨混杂纤维的加入对梁柱边节点抗震性能的影响。结果表明:与钢筋混凝土节点和单掺PVA纤维增强水泥基复合材料节点相比,PVA-钢混杂纤维增强水泥基复合材料节点的承载力高、变形能力大、延性好、耗能能力强,抗震性能显著提升。当试验轴压比从0.12增加到0.24,梁端塑性铰区产生一定的外移,塑性性能发挥更充分,同时试件的变形能力、延性、耗能能力增加。在加密区体积配箍率减小的情况下,试件仍表现出良好的抗震性能。

水泥基材料用原位增韧材料研究现状

原位增韧材料可以从微纳观层次改善水泥水化产物的特性以及水泥基材料的微观结构,从而提升水泥基材料的韧性。通过整理国内外学者关于原位增韧材料增强水泥基材料宏观性能的研究,比较了纳米材料、聚合物材料和功能性微晶这三类增韧材料对水泥基材料力学性能的影响,包括抗压强度、抗折强度、劈裂抗拉强度以及韧性。此外,分别从水化产物特性、水化产物微结构以及界面过渡区这三个方面出发,对原位增韧材料增强水泥基材料韧性的机理进行了系统地阐述。为后续水泥基材料用原位增韧材料的研发和混凝土韧性提升提供参考。

两级液环压缩机内流场及外特性

采用数值模拟与试验相结合的方法,以2SY-6两级液环压缩机为研究对象,对多级液环压缩机在不同工况、不同叶轮宽度比下内流场及性能进行对比分析,结果表明:二级叶轮叶片载荷小于一级叶轮,其排气口区域锯齿形气液交界面较一级叶轮更为光滑.一级叶轮吸气口区域回流强度相对于二级叶轮吸气口区域更强,一级叶轮吸气口区域湍动能明显大于二级叶轮.等外径设计的二级叶轮进出口压缩比远小于一级叶轮,二级叶轮的做功能力小于一级叶轮.由于一级叶轮的进出口压缩比较大且均位于效率极值点的右侧,一级叶轮效率随泵的压缩比增大而逐渐下降,而二级叶轮压缩比范围包含极值点,所以其效率先增后减.液环压缩机随着二级叶轮宽度的增大,其吸气能力越强,各个工况下的流量均逐渐增大.低压缩比工况下的效率随k值减小逐渐增大,高压缩比工况下的效率随k值减小先增后减.随首次级叶轮宽度比k值的减小,二级叶轮的压缩比曲线逐渐向上平移,而一级叶轮的压缩比曲线逐渐向下平移.随泵出口压力的增大,首次级叶轮压缩比的比值曲线下降趋于平缓,k值为2.2时两级叶轮压缩比的比值趋于1.1.

改性干粉型聚合物水泥砂浆试验研究

本文研究两种不同的可再分散乳胶粉(醋酸乙烯-乙烯共聚物和醋酸乙烯/叔碳酸乙烯酯共聚物)对干粉型聚合物水泥砂浆力学性能、粘结强度、吸水率、干燥收缩的性能影响。结果表明,可再分散乳胶粉的掺量、类型对聚合物水泥砂浆的性能影响较大,力学性能较普通水泥砂浆有明显的提升和改善。可再分散乳胶粉的加入虽然降低了砂浆的抗压强度,但显著提高了抗折强度和折压比,改善了砂浆的柔韧性和抗裂能力;砂浆的干燥收缩、粘结强度和吸水率等性能均有较为明显的改善。

不同压缩比螺旋翅片对相变储能罐蓄热的影响机制

在传统螺旋翅片基础上提出3种不同压缩比的螺旋翅片结构。首先数值模拟不同压缩比的螺旋翅片储能罐相变材料的熔化过程;其次,讨论4个储能罐中温度场和固液界面的演变情况;再次,分析液相分数、平均温度和平均努塞尔数的变化趋势;最后,对比不同压缩比下相变材料的总蓄热量、熔化时间和平均蓄热速率。结果表明:设计压缩比合适的螺旋翅片可有效促进储能装置相变材料的熔化,减轻下部温度垂直分层现象,增强相变材料的自然对流,提升相变储能罐的蓄热性能;随着压缩比的增加,蓄热速率呈先增加后减小的趋势,而完全熔化时间则先减少后增加;与无压缩螺旋翅片的储能罐相比,当压缩比为3时,石蜡完全熔化时间缩短27.27%,平均蓄热速率提升33.33%,但当压缩比增加到7时,平均蓄热速率反而下降25%,完全熔化时间增加34.67%。

高强页岩轻骨料混凝土制备及微观结构研究

基于最紧密堆积理论和最小需水量法进行高强页岩轻骨料混凝土配合比设计与制备,研究了水胶比对抗压及劈裂抗拉强度影响,并借助SEM/EDS进行微观测试分析。结果表明:当粗细骨料体积分数比为5.5:4.5时,粗细骨料达到最紧密堆积状态;当硅灰、粉煤灰和水泥质量比为0.8:3.2:6时,需水量最少,粉体材料密实度最佳;依据优化配比所配混凝土的抗压强度和劈裂抗拉强度均随龄期增加而增加;随着水胶比增加,抗压强度和劈裂抗拉强度呈先增后减的趋势,且当水胶比为0.24时达到最大,分别为70.9、5.83MPa;硅灰和粉煤灰特有的形态效应和火山灰效应有效改善了浆体与骨料间界面的密实程度,微观结果显示浆体与骨料界面区域结构致密,陶粒区域为富Si、Al相,浆体一侧为富Ca相。

进气歧管喷水对发动机燃烧性能的试验研究

为研究进气歧管喷水技术对汽油发动机热效率的提升潜力,基于一台研究型单缸汽油发动机,采用试验的手段对比研究了不同的喷水比例、不同的负荷工况及不同的压缩比下进气歧管喷水对发动机燃烧性能的影响。结果表明,采用进气歧管喷水技术可有效降低发动机的爆震趋势,随着喷水比例的增加,CA50逐渐提前,燃料的滞燃期及燃烧持续期增加,同时伴随着传热损失逐渐增加。相比于无喷水(w/o PWI)的结果,喷水的引入虽然导致未燃损失增加,但有利于排气能量损失大幅降低,最终反应到经济性的表现为热效率随着喷水比例的增大呈先增加后降低的趋势,油耗率的表现同热效率的结果相反;此时最佳的净指示热效率(GITE)为43.1%,相比于w/o PWI的结果升高了2.5%;最佳的净指示油耗率(GISFC)为197.9 g/(kW·h),相比于w/o PWI的结果降低了11.8 g/(kW·h)。高负荷运用喷水技术将达到更显著的热效率改善及油耗改善效果;同时,喷水技术的引入使得发动机高压缩比的应用成为可能。

煤矸石机制砂C20混凝土力学性能研究

为探究煤矸石机制砂对低强度等级C20混凝土力学性能的影响,调控煤矸石机制砂掺量和水灰比浇筑混凝土试块,开展抗压和抗折强度试验。结果表明:相同水灰比下,随煤矸石机制砂掺量增加,混凝土的抗压强度先增强后降低;相同取代率下,混凝土的抗压和抗折强度随水灰比增大而降低。相较于煤矸石机制砂取代率,水灰比对混凝土抗折强度的影响更大。取代率不超过30%时,对混凝土的抗压和抗折强度均有利,水灰比为0.55、取代率为25%时,混凝土抗压和抗折强度提高最多。

超高压缩比混动专用发动机的爆震控制研究

为抑制混动发动机爆震现象,基于超高压缩比混动发动机,建立计算流体力学(CFD)模型,通过台架试验分析发动机子系统及控制参数对爆震的影响。结果表明:提高进气道滚流比可实现快速燃烧;提升燃烧室加工精度可改善燃烧一致性;缸体、缸盖分离式冷却可实现分区温度智能调节;增加挡水板可降低金属温度;对于该发动机最大有效热效率点,降低废气再循环(EGR)系统压损,可使EGR率达到25%;高温环境下,需对发动机有效压缩比及出水温度进行精确控制。