电阻网膜型石膏吸波天花板的制备与特性研究

根据电磁波吸收理论,基于电阻网膜设计制备了一种宽频吸波天花板。实验表明,采用厚度为1.2 cm厚的石膏板,格子型电阻网膜(3格),电阻条线宽为24 mm,在S带(2~4 GHz),-10 dB以下吸收带宽达到92%,在3 GHz附近有最大吸量-17 dB;随着入射角度的增大,吸收峰逐渐向低频方向移动,带宽逐渐增大。新材料可用于建筑室内电磁污染控制。     

石膏填充蜂窝结构吸波材料的吸波性能

通过在浸渍乙炔炭黑的蜂窝结构中填充石膏,制备了具有蜂窝结构的石膏基吸波材料,采用弓形反射法研究了该吸波材料在2~18GHz的吸波性能.结果表明:蜂窝结构的孔格边长和高度对材料的吸波性能有一定影响;当石膏填充单层蜂窝结构吸波材料在2~18GHz频宽,蜂窝结构孔格边长为6mm,高度为8mm时,反射率低于-10dB的吸收频宽为10.4GHz;石膏填充双层蜂窝结构吸波材料,由于匹配层和吸收层形成了阻抗梯度结构,在一定程度上改善了其吸波性能,故能够在2~18GHz频宽内获得小于-8dB的吸波效率,反射率曲线存在5个吸收峰,在2.2GHz附近的吸收峰可达-20.3dB.     

三维界面特性双层水泥基材料的吸波性能研究

设计并制备了具有三维界面结构的双层水泥基吸波材料,利用弓形反射法研究了其在2～18 GHz频率范围内的电磁波吸收性能,研究了覆盖三维结构界面的透波层性质对吸波性能的影响.结果表明,三维界面结构设计能够显著提高水泥基材料的吸波性能、拓宽有效吸波带宽,具有尖劈界面结构的双层水泥基材料在2～18 GHz频率范围内电磁波反射率...     

石墨粒径对防电磁辐射纸面石膏板的影响研究

随着科技的发展,电器的普及越来越广泛,随之而来的电磁污染对人类的身体健康造成了越来越严重的伤害。实验将不同粒径的鳞片石墨掺加到石膏粉中,制备出具有防电磁辐射功能的纸面石膏板,通过万能试验机、N5234A型网络分析仪测试其抗压抗折强度及吸波性能。研究结果表明,随着石墨粒径的减小,石膏板的有效吸收频率带宽逐渐增大,由0提高到了7.2GHz,但是石膏板的抗压和抗折强度则随着粒径减小逐渐降低;相比于粒径单一的石墨,混合粒径石墨的试样抗压和抗折强度均是最大,但是吸波效果一般;考虑石膏板强度、吸波性能和成本,选择0.15mm粒径的石墨作为吸波材料是比较合适的。同时,石墨对石膏板护面纸的粘结性能具有一定负面影响。     

防电磁辐射纸面石膏板的吸波性能

电磁辐射作为第四大污染源,对人体身心健康带来了巨大的威胁,为了保护环境和人类健康,必须对电磁辐射加以防护。本文研究以石墨、铁氧体作为吸波材料制备防电磁辐射纸面石膏板及其吸波性能。实验结果表明,石膏板的吸波性能随石墨掺量增加而提高;在8GHz~18GHz范围内,掺8%宁海产石墨的板材吸波效果最好,具有8GHz以上的连续有效吸收带宽;在2GHz~18GHz范围内,掺8%青岛产石墨的板材,有效吸收带宽超过10GHz,同时在低频2.7GHz~3.9GHz内也具有一定的吸波效果。     

S带电磁污染控制用珍珠岩泡沫水泥吸波板的设计与制备

根据电磁波吸收原理,对建筑隔热材料进行功能化改造,通过λ/4模型设计和理论模拟分析,成功制备出珍珠岩泡沫水泥电磁波吸收板材。实验表明,2~4GHz频段,电阻膜采用380Ω/□,厚度为1.20cm的吸波板材,在3GHz附近有最大吸量-25dB,反射率在-10dB以下带宽达到65%;同样采用380Ω/□电阻膜,厚度为1.50cm的材料,成功实现了2.45GHz吸波材料的制备。新材料可用于无线局域网的电磁干扰防护及建筑室内电磁辐射污染控制。     

水泥混凝土加铺层的分缝机理研究

本文通过现场试验和冷冻试验,对不同结合类型双层道面的实际效果进行了观测,提出了部分结合式和隔离式双层道面的分缝要求.利用有限元理论编制了考虑结合面状况的双层道面有限元分析程序,并用室内试验和理论对比分析了程序的正确性.利用有限元程序分析了不对缝加铺层的荷载应力状态,提供了不对缝加铺层设计诺模图和计算方法.     

基于阻抗匹配原则多层吸波材料研究进展

基于隐身技术在武器系统中的运用,针对阻抗匹配原理提出并设计了多层吸波材料,分别计算了单层、双层及多层结构吸波材料其自由空间与介质材料界面上的反射率,阐述了吸波材料的匹配特性及其对复合吸波材料吸波性能的影响,并介绍了多层吸波材料的研究进展。     

网格布增强硫氧镁发泡水泥力学性能和吸波特性研究

采用物理发泡法制备了玻纤网格布增强硫氧镁发泡水泥,对其力学性能和吸波性能进行了研究。结果表明:对于干密度在800~850 kg/m3的硫氧镁发泡水泥,玻纤网格布可有效提高材料的抗折强度,而抗压强度基本保持不变;当玻纤网格布为3层/cm时,材料的电磁波吸收效果较好,而厚度的增加可进一步改善材料的吸波性能。对材料进行双层夹膜结构设计,当总厚度为8 mm,夹膜阻值为400Ω/时,在2.6~18 GHz的吸收量均低于-10 d B。通过玻纤网格布的增强和双层夹膜设计,实现了硫氧镁发泡水泥在保持较好力学性能的同时对吸波性能的改善。     

大面积双层纸面石膏板吊顶施工技术

本文结合教学科研楼等4项东南区综合楼、集体宿舍楼项目装饰装修施工过程,研究了大面积双层纸面石膏板吊顶安装工艺,通过总结形成大面积双层纸面石膏板吊顶防开裂的关键技术,有效解决了大面积纸面石膏板吊顶开裂的质量控制难题.     

Numerical simulation of transient flow development in a naturally ventilated room

Numerical simulations were conducted to model the transient flow development in a naturally ventilated space containing a centrally located localized source of heat. The simulations were compared with a series of small-scale laboratory experiments and existing theoretical models. The aim of the work was to benchmark CFD models for time-dependent buoyancy-driven natural ventilation against previously published experimental results and theoretical models. The simulations agree well with experimental results during the initial development of the room stratification. The CFD results accurately predict the maximum depth of the hot buoyant layer at the top of the room as well as the steady-state interface height which separates the warm upper buoyant layer from the cooler air below. The simulations also predict well the time taken for the buoyant upper layer to reach its maximum depth. However, at longer times the results diverge. This may be due to thermal diffusion and mixing at the interface between the upper and lower layers due to the inflow from the floor level vents.     

电压谐波对MOA泄漏电流检测方法影响分析

电网电压谐波不仅对MOA泄漏电流中的容性分量带来干扰,而且对阻性分量也带来干扰。分析了电压谐波对两种基本方法-补偿法与谐波分析法的影响,并对补偿法进行了仿真计算,补偿法必须考虑容性谐波的干扰,谐波分析法避开了容性谐波的干扰,两种方法都不能消除阻性电流中直接来自电压谐波中的分量,综述目前已有消除电压谐波影响的方法,可根据阻性电流基波分量计算出阻性电流值及谐波分量,阻性电流中来自系统电压谐波干扰部分的消除还需进一步分析。     

避雷器阻性电流测试新方法

供电可靠性的要求使设备试验由原来的停电预试为主转为带电测试为主的模式,带电测试工作得到加强.在进行避雷器带电测试的过程中,由于受避雷器的安装排列方式等的影响,经常出现阻性电流负值,三相阻性电流值相差很大的情况,导致判断困难.笔者通过大量的现场测试经验,总结了一套测量氧化锌避雷器阻性电流的新方法——实际相角法,该方法使运...     

电导率线性变化高密度电法有限元正演模拟

本文从点电流源的边值问题出发,推导了相应的变分问题,采用矩形网格剖分、双线性插值的有限元法,给出了完整的电导率线性变化的高密度电法正演算法,进而编制了相应的正演程序。利用该程序对一个水平层状的地电模型进行计算,将有限元解与解析解对比分析,验证了该算法的正确性和有效性;然后以电导率线性变化的层状模型、对称高阻体、对称低阻体典型模型进行正演计算,得到了相应的视电阻率断面图,结果表明其模拟效果良好。     

A theoretical strain transfer model between optical fiber sensors and monitored substrates

This study proposed an analytical model to investigate strain transfer mechanism between FBG sensor and measured geogrid. Both geometric and mechanical parameters (bonding length, bonding thickness, bonding width, and Young's modulus) of interaction interface can be taken into account in this model. Both laboratory tensile tests of geogrid and experimental data in published literatures were used to verify the developed model. Validation study shows that the maximum relative error between experimental values and theoretical values is 8.2%, indicating that this theoretical model can be used to reflect geogrid deformation. Parametric study indicates that bonding length, bonding thickness, bonding width, Young's modulus of adhesive layer, and substrate layer have significant influence on strain transfer coefficient. Grey Relational Analysis (GRA) method was used to analyze influencing sensitivity of different parameters. GRA parameter values of bonding width and length are higher than 0.72, indicating that bonding width and bonding length are relatively dominant factors affecting average strain transfer coefficient in comparison with bonding thickness, Young's moduli of substrate and adhesive layers (their related GRA values are all lower than 0.692).     

Hydraulic performance of percolating biological filters and consideration of oxygen transfer

A distinct difference exists between the experimentally measured and theoretically calculated values of residence time in percolating biological filters. From existing information it was shown that the measured values are usually at least three times higher than those calculated theoretically. Based on several premises, it was concluded that two liquid film layers should be distinguished. One “free” liquid film flowing on top of the biofilm, the second “captured” flowing through the biofilm.From experimentally measured residence time, it becomes evident that the total liquid film depth will be in the region of 150–550 μm for a hydraulic load range of 0.02–5 m³m⁻²m⁻¹. It can be proved that oxygen cannot penetrate up to such a depth, especially when the captured liquid film thickness is in the region of 110–380 μm. The largely anoxic conditions in the captured liquid film are in drastic contrast with the prevailing conditions close to oxygen saturation in the free flowing liquid layer. Due to the large developed surface the outflowing liquid can be saturated with oxygen. The measured oxygen concentration in filter effluent does not reflect the aerobic conditions neither in the captured liquid film nor in the biofilm as such.     

高层隔震结构提离摇摆耦合理论模型及振动台试验验证

基于受力及变形方程的微分求解给出高层隔震结构考虑支座水平及竖向刚度衰减规律和结构摇摆效应的耦合动力理论模型,并给出摇摆角、压应力及剪应变对隔震层水平及竖向的力学性质影响规律。对高宽比为5及25的隔震结构进行振动台试验研究,试验结果表明大高宽比隔震结构动力特性出现明显振型二阶效应,地震动作用下大高宽比结构隔震层摇摆角响应比小高宽比结构大,在输入地震动峰值06g时两者差值达到5倍以上,且大高宽比结构出现明显的支座受拉现象。对隔震层水平、竖向及摇摆响应的理论计算值和试验实测值进行对比,结果表明理论和试验结果较为一致。进一步分析4种高宽比隔震结构的摇摆角响应,得到摇摆角随高宽比增加而增大的结果。大高宽比隔震结构更易产生摇摆响应,隔震层的摇摆角不可忽视,因此高层结构在隔震设计中应考虑隔震层的摇摆响应和支座受拉的情况。     

考虑多孔介质迂回曲折效应的幂律流体柱形渗透注浆机制

多孔介质的迂回曲折效应对浆液在其中的渗透扩散与注浆效果具有非常重要的影响.采用理论分析,研究考虑多孔介质迂回曲折效应的幂律流体渗流运动方程,推导考虑多孔介质迂回曲折效应的幂律流体柱形渗透注浆机制;基于计算机编程技术,依托COMSOL Multiphysics平台与达西定律,二次开发得到考虑多孔介质迂回曲折效应的幂律流体...     

Growth of organic films on indoor surfaces

We present a model for the growth of organic films on impermeable indoor surfaces. The model couples transport through a gas‐side boundary layer adjacent to the surface with equilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas phase and the surface film. Model predictions indicate that film growth would primarily be influenced by the gas‐phase concentration of SVOCs with octanol‐air partitioning (K_oa) values in the approximate range 10≤log K_oa≤13. Within the relevant range, SVOCs with lower values will equilibrate with the surface film more rapidly. Over time, the film becomes relatively enriched in species with higher log K_oa values, while the proportion of gas‐phase SVOCs not in equilibrium with the film decreases. Given stable airborne SVOC concentrations, films grow at faster rates initially and then subsequently diminish to an almost steady growth rate. Once an SVOC is equilibrated with the film, its mass per unit film volume remains constant, while its mass per unit area increases in proportion to overall film thickness. The predictions of the conceptual model and its mathematical embodiment are generally consistent with results reported in the peer‐reviewed literature.     

水中养护两年高性能混凝土的自干燥研究

通过测定高性能混凝土（ＨＰＣ）中不同层面上（外层、中层和内层）的相对湿度ｈｒ，研究了在水中养护两年后ＨＰＣ的自干燥问题。同时，对影响ｈｒ的诸多因素，如水灰比、硅灰和含气量进行了调查。结果表明：内层和中层混凝土的ｈｒ值随着水灰比降低和硅灰掺量的增加而降低，其中硅灰的影响更显著，但它们对外层混凝土的ｈｒ的影响很小；含气量对ＨＰＣ的ｈｒ值影响很小；理论计算表明，混凝土中可溶离子的浓度增大，以及层间水、吸附水和凝胶孔水在总可蒸发水量中的比例增大，是引起ＨＰＣ中ｈｒ值降低或者是所谓自干燥现象产生的主要原因。