初始体积分数法在爆炸模拟中的应用

为避免因采用实际装药结构导致网格精度难以保证,同时为减少因简化装药形状而造成模拟误差,针对LS-DYNA软件中的初始体积分数法展开研究。首先对初始体积分数法进行了详细的介绍,接着通过两个典型的算例对该方法在多物质ALE算法和流固耦合算法上应用的可行性进行了验证,最后将模拟值与传统方法及实测结果进行了对比。结果表明:用初始体积分数法模拟不同炸药形状对水中爆炸冲击波超压峰值的影响,圆柱形和球形时的模拟结果互为接近,正方体模拟的结果相对偏大,其差距会随着比例距离的增加而逐渐减小;该方法能够建立爆炸模拟中常见的1/2,1/4甚至1/8球形或圆柱形装药模型,求解的结果精度较高;对于需要考虑炸药不同埋深的情况,建模时可先对炸药预定埋深的区域网格进行细化,再采用初始体积分数法调整炸药的位置,这样可减少重复建模的繁琐过程,且能保证较高的求解精度。     

混合气体氧体积分数检测自动报警控制系统设计

采用KY-2F型氧传感器、ZBWJ-90型气体流量计和西门子S7-300PLC等设备,设计并搭建了混合气体氧体积分数自动检测、报警与控制系统,详细介绍了该系统的软件设计、硬件组成和工作原理.该系统可根据生产工艺实际情况和计算的极限氧体积分数值,设定氧体积分数的报警阈值和电动调节阀的控制阈值,通过PLC软件设计,检测化工反应釜中混合气体的极限氧体积分数,实现生产过程的检测、报警与控制功能,为化工生产工艺的安全防护提供可靠的技术支撑.     

黄土中爆炸空腔体积规律的数值模拟

黄土中爆炸成腔的大小与黄土参数具有密不可分的关系,其中黄土的天然密度和含水率是主要影响因素。利用ANSYS/LS-DYNA软件进行三维建模,模拟黄土中爆炸成腔的过程,与黄土中爆炸试验结果进行对比,从空腔体积、峰值应力、爆后土体密度3个方面验证数值模拟的可行性。以土体天然密度和含水率作为影响因素,对黄土中爆炸空腔的体积规律进行数值模拟研究,得到三维拟合规律,发现天然密度对爆后空腔体积影响较大,含水率对其影响较小。     

爆炸荷载作用下不同抗剪连接件组合梁动力响应及破坏模拟分析

桥梁结构多采用含有抗剪连接件的组合梁,由于意外事故可能导致汽车爆炸冲击对桥梁结构造成损伤,同时一些废弃桥梁有必要进行爆破拆除.基于此背景,有必要对含有抗剪连接件的桥梁结构进行爆炸分析.首先应用ABAQUS参照已有文献的爆炸试验验证了考虑高应变率相关混凝土本构、钢材本构的流固耦合模型的合理性,然后对爆炸荷载作用下波形钢板...     

拱顶钢储罐内部蒸气云爆炸冲击荷载的数值模拟

利用TNT当量模型模拟储罐内部的蒸气云爆炸,对拱顶钢储罐内部爆炸流场和壁面爆炸冲击荷载进行数值模拟。首先将储罐壁面视为刚性,系统考察拱顶罐在各种不同工况下的爆炸流场及壁面反射冲击荷载分布情况;然后进一步考察爆炸流场与罐壁之间的耦合效应对爆炸冲击荷载的影响。研究表明：储罐壁面爆炸冲击荷载最大值出现在顶盖中心区域,且往往出现在第2个波形峰值位置,而壁面其他位置的冲击荷载最大值一般出现在第1个反射超压峰值位置;爆炸流场和容器壁面间的耦合效应对内部爆炸冲击荷载的影响不大,计算分析时可近似采用非耦合模型。     

钢奥氏体分解转变体积分数计算方法研究进展

概述了杠杆法计算钢奥氏体分解转变体积分数的基本原理及其局限性,并介绍了通过考虑多相组织中各相比容差异、碳在奥氏体中的富集及膨胀各向异性的影响等改进工作研究进展,同时指出了改进方法自身的不足之处。     

耦合有限元物质点法及其在流固耦合问题中的应用

有限元法在求解大变形问题时会遇到网格畸变和时间步长严重减小的问题。物质点法在大变形问题中无网格扭曲问题,且粒子代表了物质流动,无需界面追踪算法。但在小变形问题中,物质点法的精度和效率均低于有限元法。该课题组针对冲击侵彻问题提出的耦合有限元物质点法分别采用有限元法和物质点法模拟小变形和大变形物体,物体间的相互作用通过接触算法实现,既保留了有限元针对小变形问题高精度高效率的特点,又避免了材料大变形给有限元法带来的网格扭曲和时间步长严重减小的问题,还可以自动追踪界面。在流固耦合问题中,固体变形较小而流体变形较大,因此也适合用耦合有限元物质点法求解。该文简要介绍了耦合有限元物质点法的基本原理,并将其应用于流固耦合问题中,取得了较好的效果,表明耦合有限元物质点法是分析流固耦合问题的一种有效的方法。     

高体积分数SiC_p/Al复合材料中界面现象研究

利用 XRD及 TEM方法测定了真空气压渗流法制备的四种基体复合材料及其界面区域的相组成。结果表明 ,复合材料中界面处出现了新相 ,认为新相的出现是界面反应的结果。应用热力学及动力学方法分析讨论了界面反应及其产物的形成过程。指出 ,通过控制基体中的添加元素含量便可控制复合材料中界面反应及出现的相 ,界面反应对材料的制备过程及其性能有重要的影响。     

圆柱壳在水下爆炸载荷下的流-固耦合响应分析

研究了无限域流场中两端简支圆柱壳受球形炸药爆炸冲击载荷作用的响应特性。运用Hamilton变分原理,推导出了考虑流固耦合作用圆柱壳受水下爆炸冲击载荷作用的运动方程,并分别展开成Fourier级数的形式,最后在时域上差分离散,用Galerkin方法求解,得到了在水下爆炸冲击载荷下圆柱壳的响应分析。文章着重就圆柱壳在迎爆面和背爆面的不同位置的变形位移和变形速度进行了对比分析,同时还比较了流体动压力对结构响应的影响。并将分析结果与有限元计算软件MSC.DYTRAN计算结果比较,验证了算法的可靠性。     

油品计量中体积-重量法的基本原理在实际中的应用

本文通过从理论计算入手,对油品计量中体积-重量法的基本原理进行了分析及在实际中的具体应用进行了说明。     

Finite volume method for simulation of extrusion processes

In this paper, the development of a finite volume method for prediction of plastic flow of metals during cold and hot extrusion processes is described. The method solves the equations governing mass, momentum and heat balance in their integral form, using discretization elements of an arbitrary polyhedral shape. Comparisons of the numerical and experimental results show a very good agreement, implying that the proposed numerical method can be used as a useful tool in designing extrusion processes. Copyright © 2005 John Wiley & Sons, Ltd.     

Utilizing prior information in the estimation of volume fraction distribution

For many industrial processes the bulk volume fraction of one phase such as gas or solid can be of considerable importance. For this reason it is often controlled within certain limits and therefore is known at least vaguely. Tomographic imaging of volume fraction can provide very valuable information not only on the bulk volume fraction but also on the spatial distribution of the phase of interest. Prior information on the bulk volume fraction can assist in tomographic inversion, even if this information is not precise. In this paper we propose an electrical impedance tomography approach for imaging volume fraction distribution. A vague bulk volume fraction prior is utilized in the estimation. Two‐dimensional numerical examples are used to demonstrate the proposed method. Copyright © 2005 John Wiley & Sons, Ltd.     

Interlaminar stress distribution of composite laminated plates with functionally graded fiber volume fraction

Various functionally graded design methods have been proposed recently for fiber reinforced composite plates. The laminates with variable fiber spacing along the thickness direction are focused on in this paper. Fiber volume ratio distribution functions are defined separately in each single layer. Classic state space method as well as differential quadrature state space method are utilized here for different boundary and plied conditions. For the latter method, a sub-layer based scheme, which has both high accuracy and less numerical capacity, is suggested for functionally graded plates. Numerical examples indicate that the non-uniform distribution of fibers rearranges the stress field, of which the in-plane stresses are sensitive to the fibers’ distribution, while the transverse stresses are not affected so much. In-plane stresses near interfaces would decrease if the fiber ratio reduces in this region, which provides a method to resolve the interfacial stress concentration problems.     

爆炸复合接头剪切强度测试方法研究

参照正交各向异性层压复合板层间剪切强度的测试方法，提出了用于测试爆炸复合接头复合界面剪切强度的3种方法；并建立三雏有限元模型，分别对3种测试方法进行模拟；最后分别对3种方法进行了测试试验．结果表明，3种试验方法均能有效测试爆炸复合接头的剪切强度，其中对称试件双切口拉伸法最适合实际应用．     

水泥基复合材料界面过渡区体积分数的定量计算

借助邻近函数公式, 给出了水泥基复合材料集料与浆体间界面过渡区体积分数的定量计算公式, 并采用随机点采样方法验证采用该定量公式计算水泥基复合材料界面过渡区体积分数的可行性。在此基础上, 预测了由符合Fuller 分布的集料制备的混凝土中界面过渡区体积分数随集料体积分数和集料粒径范围的变化曲线。讨论了界面厚度变化、集料体积分数变化以及集料粒径分布变化对界面过渡区体积分数影响的差别, 并给出了衡量界面过渡区重叠程度的定性和定量方法。结果表明: 在常规集料体积分数下, 三者中对界面过渡区体积分数以及界面过渡区重叠程度影响的主次顺序均为: 界面过渡区厚度变化带来的影响> 集料体积分数变化带来的影响> 集料细度变化带来的影响。      

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0⁷.0 m)都较缓,而进入远场(>7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

TNT炸药爆炸场中三波点的数值模拟

准确预测三波点的位置和揭示三波点的规律,对工程防护和实现弹药的高效损伤有着重要作用。基于LS-DYNA有限元软件,利用数值模拟方法研究了TNT炸药在混凝土地面上形成爆炸冲击波的三波点运动轨迹,并初步揭示了炸高、药量和炸药形状等因素对三波点高度的影响。研究表明:在爆炸场中,爆炸冲击波以炸药为中心向四周传播,三波点轨迹的高度均呈现逐渐增高的变化趋势。不论改变炸药的药量还是炸高,三波点高度的增速在中场(4.0~7.0 m)都较缓,而进入远场(7.0 m)增速骤增。当炸药的炸高和药量相同,炸药形状不同时,圆柱状炸药在中场爆炸形成的三波点高度比长方体炸药略高,且高度增速都较缓;而在远场三波点的高度基本相等,且增速急剧上升,趋于定值。与炸药形状的影响相比,炸高和药量对TNT炸药爆炸冲击波的三波点高度的影响较大。     

The effect of martensite volume fraction and particle size on the tensile properties of a surface-carburized AISI 8620 steel with a dual-phase core microstructure

This study is focused on the production of a dual-phase steel structure in the core of a surface-carburized AISI 8620 cementation steel and the effect of martensite volume fraction (MVF) and martensite particle size (MPS) on tensile properties. Experimental results showed that, compared with specimens with a fully martensitic microstructure in the core, those with a dual-phase microstructure in the core exhibited slightly lower tensile and yield strength but superior ductility without sacrificing surface hardness. In specimens with a dual-phase microstructure in the core, the tensile strength increased and ductility decreased with increasing MVF. Both the tensile strength and the ductility increased with decreasing MPS at constant MVF. The best combination of tensile strength and ductility was obtained with a fine MPS at a constant MVF of 25%.     

Numerical simulation of 3D unsteady aluminium extrusion process using finite volume method based on non-orthogonal block structured grids

Abstract

The mathematic model of three-dimensional aluminium profile extrusion processes using the finite volume method was established in the present paper. Basic theories and key technologies of the Simple method using the collocated arrangement strategy based on boundary fitted non-orthogonal block structured grids were studied. The governing equations were directly discretised on boundary fitted non-orthogonal grids. The coordinate transformation between the Cartesian rectangular coordinateand the curvilinear coordinate was avoided. The negative effects of grids' non-orthogonality, such as the dislocation between the lines connecting the centre points of adjacent elements and the centre of their interface, were compensated. The volume of fluid (VOF) scheme was used to capture the free surface of the deforming material. A program was written according to the above theories and equations. A typical three-dimensional aluminium profile extrusion process was simulated by use of the program developed in the present paper. The simulation results were also compared with that simulated by Deform-3D in the same process, material and die conditions. The feasibility of the mathematic model built in the present paper was demonstrated by the simulation results and the comparison.