建筑节能初期设计阶段的能耗模拟与分析

针对建筑节能初期设计阶段,采用建筑环境设计软件Ecotect对某节能示范楼外窗遮阳情况进行模拟分析,得到各朝向外窗的遮阳形式以及大小设计范围,为下一阶段包括外遮阳形式,构造尺寸和各朝向房间的窗墙比、外窗材料选择提供了设计参考.     

污水中重金属离子浓度软测量的BP算法

在重金属离子检测仪器及其工作原理研究的基础上,对污水中重金属离子浓度测量方法进行了分析研究,分析了采用软测量技术的可行性和必要性,针对水质测量具有非线性、大时变和多滞后的特点,提出了基于BP神经网络的污水中重金属离子浓度软测量建模方法,建立了软测量模型,并通过仿真分析和实验验证了该方法的实用性.     

计及开关抖动特性的低压复合开关仿真分析

为了改进复合开关特性,准确评估复合开关中电力电子器件的发热水平,以低压复合开关为研究对象,建立了开关的抖动仿真模型,并在此基础上分析了负载条件下复合开关中双向可控硅本身及其考虑底板散热影响后的温升特性.通过加入散热片,大大减少了复合开关的发热量.研究结果为可靠地控制复合开关、延长其寿命提供了条件,并为进一步开发多路集成...     

元器件性能退化信息的系统性能可靠性评估

性能可靠性方法为解决现代工程实际中的高可靠、长寿命、小子样产品的可靠性建模分析提供了途径.目前的性能可靠性研究主要是针对元器件开展的,对系统性能可靠性进行研究时通常需要将其看作一个元器件,需要得到系统的性能退化数据,在某些情况下,得到系统的性能退化数据比较困难.实际上,由于元器件的性能退化导致系统性能的变化,因而可以利...     

重力势能锁止型外骨骼设计及其效能评价

现存的被动式外骨骼存在助力效果不明显等缺陷。基于人体步态特征,提出了将人体行走过程中的重力势能转化为人体抬腿过程中动能的原理,通过弹簧、曲柄滑块机构、棘轮棘爪机构以及链传动机构的组合,设计了一款被动式下肢机械外骨骼,并通过外骨骼动力学分析和生理消耗指数实验测试的方法进行了外骨骼性能评价。动力学分析结果表明,穿戴外骨骼后髋关节峰力矩总量降低了23.43%,髋关节做功总量降低了30.59%,初步验证了外骨骼的有效性。生理消耗指数实验测试结果表明, 穿戴外骨骼对于短距离动作转换未产生显著效果,但在长距离行走和上坡行走中分别降低了8.1%和10.4%的能量消耗。因此,该下肢外骨骼助力性能得到了验证,为相关领域的研究提供了实例化参考。     

Survey and technological analysis of laser and its defense applications

The laser technology has made remarkable progress over the past couple of decades.It is being widely employed in diverse domains,such as holography,space sciences,spectroscopy,medical sciences,micro and power electronics,industrial engineering,and most distinctively,as directed energy military weapons.Owing to their active transmissions,laser systems are similar to microwave radars to some extent;however,unlike conventional radars,the laser operates at very high frequencies thus making it a potent enabler of narrow-beam and high energy aerial deployments,both in offensive and defensive roles.In modern avionics systems,laser target indicators and beam riders are the most common devices that are used to direct the Laser Guided Weapons(LGW)accurately to the ground targets.Additionally,compact size and outstanding angular resolution of laser-based systems motivate their use for drones and unmanned aerial applications.Moreover,the narrow-beam divergence of laser emissions offers a low probability of intercept,making it a suitable contender for secure transmissions and safety-critical operations.Furthermore,the developments in space sciences and laser technology have given syner-gistic potential outcomes to use laser systems in space operations.This paper comprehensively reviews laser applications and projects for strategic defense actions on the ground or in space.Additionally,a detailed analysis has been done on recent advancements of the laser technology for target indicators and range-finders.It also reviews the advancements in the field of laser communications for surveillance,its earlier state of the art,and ongoing scientific research and ad-vancements in the domain of high energy directed laser weapons that have revolutionized the evolving military battlefield.Besides offering a comprehensive taxonomy,the paper also critically analyzes some of the recent contributions in the associated domains.     

Damage mechanics and energy absorption capabilities of naturalfiber reinforced elastomeric based bio composite for sacrificial structural applications

The present study deals with the experimental, finite element (FE) and analytical assessment of low ballistic impact response of proposedflexible'green' composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute (JRJ), jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ). Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime. The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism. Results revealed that inclusion of natural rubber aids in better energy ab-sorption and mitigating the failure of the proposed composite. Among the three different stacking se-quences of flexible composites considered, JRJRJ provides better ballistic performance compared to its counterparts. The damage study reveals that the main mechanism of failure involved in flexible com-posites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposedflexible composites are free from catastrophic failure. Results obtained from experimental, FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other. The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.     

Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites

The mechanical, thermal and ablation properties of carbon phenolic (C-Ph) composites (Type-I) rein-forced with different weight percentages of organo-modified montmorillonite (o-MMT) nanoclay have been studied experimentally. Ball milling was used to disperse different weight (wt) percentages (0, 1,2,4,6 wt.％) of nanoclay into phenolic resin. Viscosity changes to resin due to nanoclay was studied. On the other hand, nanoclay added phenolic matrix composites (Type-II) were prepared to study the dispersion of nanoclay in phenolic matrix by small angle X-ray scattering and thermal stability changes to the matrix by thermogravimetric analyser (TGA). This data was used to understand the mechanical, thermal and ablation properties of Type-I composites. Inter laminar shear strength (ILSS), flexural strength and flexural modulus of Type I composites increased by about 29％, 12％and 7％respectively at 2 wt.％ addition of nanoclay beyond which these properties decreased. This was attributed to reduced fiber volume fraction (％Vf) of Type-I composites due to nanoclay addition at such high loadings. Mass ablation rate of Type-I composites was evaluated using oxy acetylene torch test at low heat flux (125 W/cm2) and high heat flux levels (500 W/cm2). Mass ablation rates have increased at both flux levels marginally up to 2 wt.％ addition of nanoclay beyond which it has increased significantly. This is in contrast to increased thermal stability observed for Type-I and Type-Ⅱ composites up to 2 wt.％addition of nanoclay. Increased ablation rates due to nanoclay addition was attributed to higher insulation effi-ciency of nanolcay, which accumulates more heat energy in limited area behind the ablation front and self-propagating ablation mechanisms triggered by thermal decomposition of organic part of nanoclay.     

Fullerene bisadduct stabilizers: The effect of different addition positions on inhibiting the autocatalytic decomposition of nitrocellulose absorbed nitroglycerin

To explore the effect of different positions and number of pyrrolidine bound to the carbon cage on the stabilization effect of fulleropyrrolidine derivatives to nitrocellulose (NC)/nitroglycerine (NG), we synthesized N-(4-methoxy) phenylpyrrolidine-C₆₀ and four different of bis(N-(4-methoxy) phenylpyrrolidine)-C₆₀ compounds through Prato reaction. Their structures were characterized by UV–vis, ¹H NMR, ¹³C NMR, high-resolution mass spectroscopy, and single-crystal X-ray diffraction. Their stabilization effect to NC/NG were investigated using differential scanning calorimetry, methyl violet, vacuum stabilization effect, weight loss, and accelerating rate calorimeter tests. The results indicated these compounds had excellent stabilization effect to NC/NG. The stabilization effect of the fulleropyrrolidine bisadducts to NC/NG is significantly better than that of fulleropyrrolidine monoadduct and C₆₀. Moreover, the position where pyrrolidine binds to fullerene in fulleropyrrolidine bisadducts is different, and its stabilization effect to NC is also different. The stabilization effect order of different bisadduct isomers to nitrocellulose is as follows: e-edge > trans-2> cis-2> trans-3. Electron paramagnetic resonance (EPR) and FT-IR were used to study the stabilization mechanism of fulleropyrrolidine derivatives to NC/NG. The EPR results also show that fulleropyrrolidine bisadducts with different addition sites have different abilities to absorb nitroxide, and their ability is better than that of the monoadduct and C₆₀, which is consistent with the results of stabilization effect performance test.     

An interface shear damage model of chromium coating/steel substrate under thermal erosion load

The Cr-plated coating inside a gun barrel can effectively improve the barrel's erosion resistance and thus increase the service life.However,due to the cyclic thermal load caused by high-temperature gun-powder,micro-element damage tends to occur within the Cr coating/steel substrate interface,leading to a gradual deterioration in macro-mechanical properties for the material in the related region.In order to mimic this cyclic thermal load and,thereby,study the thermal erosion behavior of the Cr coating on the barrel's inner wall,a laser emitter is utilized in the current study.With the help of in-situ tensile test and finite element simulation results,a shear stress distribution law of the Cr coating/steel substrate and a change law of the interface ultimate shear strength are identified.Studies have shown that the Cr coating/steel substrate interface's ultimate shear strength has a significant weakening effect due to increasing temperature.In this study,the interfacial ultimate shear strength decreases from 2.57 GPa(no erosion)to 1.02 GPa(laser power is 160 W).The data from this experiment is employed to establish a Cr coating/steel substrate interface shear damage model.And this model is used to predict the flaking process of Cr coating by finite element method.The simulation results show that the increase of coating crack spacing and coating thickness will increase the service life of gun barrel.