爆炸荷载作用下防护门反弹效应的影响因素分析

防护门在常规武器爆炸荷载作用下将发生反弹效应,门体将承受反弹所引起的较大反向应力,反弹力达到一定程度,铰页和闭锁在反弹力的作用下就会先于门扇主体发生破坏。该文推导了爆炸荷载作用下防护门反弹力的解析计算公式,分析了各种因素,包括：边长比、荷载作用时间、阻尼比、荷载形式以及冲击波负压等对反弹效应的影响规律,结果表明：随着边...     

冲击波负压对防护门反弹效应的影响分析

本文对冲击波负压作用下防护门的反弹效应进行了研究,采用合理的荷载假定形式,推导了考虑负压影响的防护门反弹力的精确解析公式,评价了负压对防护门反弹效应的影响规律：即随着比例爆距的增大,负压峰值相对于正压峰值逐渐增大,反弹增大效应也较明显,但这样一个响应可能仅对比较小的超压值才出现,由于正压、负压峰值都较小,防护门刚度较大,故增大的反弹力不足以对防护门造成破坏,设计中可以不考虑负压的影响。     

温压弹爆炸冲击波作用下防护门破坏模式研究

为研究温压弹爆炸冲击波作用下防护门的破坏模式,利用ANSYS/LS-DYNA软件建立了考虑材料应变率效应的分离式钢筋混凝土防护门数值计算模型。对防护门加载温压弹爆炸冲击波波形,分析了防护门的挠度、转角和剪应力,并与TNT的作用结果进行了对比。结果表明:温压弹爆炸冲击波作用下,随着距爆炸源距离的增加,防护门的破坏模式由直剪破坏、弯剪耦合破坏逐渐变为弯曲破坏;防护门的响应与温压弹爆炸冲击波的高冲量有关,温压弹爆炸冲击波作用下防护门的破坏程度大于TNT的作用结果;防护门跨中速度值可以用来快速评估防护门的破坏模式。     

水下和空中爆炸时混凝土重力坝动态响应对比分析

由于水和空气的物理属性差异以及与爆炸产物的界面作用效应不同,使得水下和空中爆炸冲击波传播特性及其荷载作用下的大坝结构动态响应存在较大的差异。通过构建混凝土重力坝水下爆炸和空中爆炸的全耦合数值仿真模型,考虑炸药起爆、冲击波传播、冲击波与结构的相互作用以及结构的动态响应等复杂过程,在对比分析爆炸冲击波在水下和空中传播特性的基础上研究了水下和空中爆炸冲击波对大坝动态响应及损伤程度的影响。研究表明,水下爆炸冲击荷载作用下混凝土重力坝动态响应及损伤程度均较同等炸药量下空中爆炸冲击荷载作用时大;在研究水工大坝抗爆性能时,应重点关注水下爆炸冲击波传播的特性及大坝在水下爆炸荷载作用下的动态响应。     

长坑道中化爆冲击波压力传播规律的数值模拟

为了对坑道中的防护门抗化爆冲击波效果进行有效的设计,首先需要确切知道通道中自由场压力的传播规律.基于Hopkinson比例定律,用LS-Dyna动力有限元软件模拟了常规炸药在坑道入口外爆炸情况下,长坑道中冲击波峰值压力的衰减规律.模拟结果与其它经验方法的预测结果进行了比较,可为进一步研究确定坑道中防护门上的化爆冲击波荷载及其防护技术提供依据.     

隧道内爆炸冲击波传播特性及爆炸荷载分布规律研究

隧道内爆炸产生复杂的爆炸冲击波流场,作用于隧道衬砌上的冲击波荷载分析十分困难.采用三维有限元计算方法,对带端墙隧道内爆炸空气冲击波的传播过程进行了数值模拟,给出了内爆炸产生的隧道内冲击波流场,并与双向开口隧道内爆炸流场进行了对比,分析了炸药装药形状、炸药引爆位置对爆炸荷载分布的影响,研究了作用于隧道衬砌上的反射冲击波荷载峰值分布规律,给出了估计衬砌上反射超压峰值的公式.     

平板防护门不同约束形式下的动力响应

防护门是许多防护工程的重要组成部份,是重要防护设备,在保障防护工程战时的整体安全方面具有重要的作用。爆炸荷载作用下防护门一般假设为四边简支板,用等效静力法计算。而防护门还受到铰页和闭锁的约束,在实际工程中由于安装和施工工艺等因素影响,防护门受约束程度无法得知,因此需要充分了解铰页和闭锁以及周围支撑条件对防护门变形响应的影响。利用LS-DYNA模拟冲击荷载作用下防护门受不同约束条件下的动力响应。分析结果表明:铰页和闭锁的存在使得防护门门扇局部区域的内力和损伤有变大的趋势,而总体上防护门钢筋设计按四边简支计算是偏于保守的。     

港口水下爆炸荷载冲击特性研究

采用数值仿真方法研究港口水下爆炸荷载的冲击特性,并与经验公式及实验结果比较验证数值模拟方法的正确性;分析水下爆炸冲击波传播过程与气泡膨胀规律。研究表明,港口水下爆炸气泡膨胀荷载不可忽略,由比冲量知,大部分区域气泡膨胀荷载大于冲击波荷载;自由水面对冲击波荷载与气泡膨胀荷载均影响较大,越接近水面二者比冲量越小,气泡膨胀荷载衰减越快,在水面附近其冲量甚至会小于冲击波荷载。水底对气泡膨胀荷载影响不大,而对冲击波荷载影响较大。受水底反射波影响,冲击波作用时间缩短,导致比冲量迅速减小。水底有淤泥层时,冲击波在泥层与水体交界面反射不显著,水底反射冲击波主要来自泥层底部与岩石层分界面。     

包覆泡沫铝钢梁动态位移的计算及影响因素

为考察运用FSI(流固耦合效应)能否考虑包覆泡沫铝对钢梁在爆炸荷载作用下最大动位移的影响及分析包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移的影响因素,运用理论及数值模拟方法分析了包覆泡沫铝钢梁在爆炸荷载作用下的动态位移变化情况。在验证理论及数值模拟结果可靠的基础上,对比理论结果与数值模拟计算结果的优缺点,并运用数值模拟分析影响包覆泡沫铝衰减钢梁在爆炸荷载作用下动位移的因素。结果表明:FSI可以考虑包覆材料对爆炸冲击波的衰减作用,但不能反映材料本身变化的影响(如材料厚度、屈服强度等);在计算包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移时,泡沫铝的厚度、屈服强度均具有最优解;增加刚性面板会放大包覆泡沫铝钢梁在爆炸荷载作用下的最大动位移。     

爆炸冲击荷载作用下框架柱简化分析模型研究

爆炸冲击荷载作用下结构的反应分析属于典型的动力学问题，由于爆炸冲击荷载作用位置的局部性和作用时间非常短暂，结构构件的抗爆分析与地震荷载作用下的动力分析有显著不同，结构构件抗爆分析具有明显的局部性，结构构件在爆炸冲击波荷载作用下的受力与整体结构关系不大，只与受力构件周围一定范围内的结构构件刚度有关，在爆炸冲击荷载作用下，可以把结构构件简化为考虑端部约束条件的单根杆件进行分析。本文以理论分析为基础、以ANSYS通用大型有限元分析软件为工具，研究了柱端约束条件对框架柱在爆炸空气冲击波作用下分析结果的影响，提出了一种框架柱抗爆分析计算的简化模型，对结构抗爆分析研究和设计具有指导意义。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...