Numerical Simulation of the Shaped Charge Jet Velocity Effected by Warhead Shell

The numerical simulation for the process of shaped charge jet produced with the shell of explosives is performed by means of the ANSYS/LS-DYNA 3D software. The effect of warhead shell on shaped charge jet velocity has been analyzed qualitatively in this paper. The numerical simulation results are creditable and in agreement well with that of the corresponding experiment. The research results show that the jet velocity of explosive with metal shell is higher than that without shell; when the shell thickness increases, jet＇ s head speed also increases; when the shell thickness increased to certain value, the jet velocity will not change any longer; with the same shell thickness, the bigger material density the higher jet＇s head velocity.

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.

Numerical Simulation Study on the Surface Deflection of Cylindrical Shallow Shell

The increasing applications of new materials such as high strength low alloy (HSAL) steels and aluminum alloy sheets have lead to greater focus on the surface deflections of auto body panels in the automobile industry in recent years.The finite element models of cylindrical shallow shell that can represent auto body panels are established.Numerical simulations of forming and unloading of cylindrical shallow shell are carried out.And a measurement and evaluation method of the surface deflection is introduced.The simulations of surface deflections with various blank homing forces (BHF) show great agreement with the experi- mental results.The influence laws of sheet thickness and material properties such as yield strengthσs,strain-hardening exponent n,anisotropy parameter r and strength coefficient k on the surface deflection are achieved by simulations,which give a basic refer- ence for controlling surface deflections.

Numerical simulation on thixoforging of electronic packaging shell with SiC_p/A356 composites

Based on the research of modem electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell. The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed. The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation. The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.

Numerical Simulation of Continuous Tension Leveling Process of Thin Strip Steel and Its Application

Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti-cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were clone with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross-section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti-cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.

Numerical study on the dynamic fracture of explosively driven cylindrical shells

Research on the expansion and fracture of explosively driven metal shells has been a key issue in weapon development and structural protection.It is important to study and predict the failure mode,fracture mechanism,and fragment distribution characteristics of explosively driven metal shells.In this study,we used the finite element-smoothed particle hydrodynamics(FE-SPH)adaptive method and the fluid-structure interaction method to perform a three-dimensional numerical simulation of the expansion and fracture of a metal cylindrical shell.Our method combined the advantages of the FEM and SPH,avoiding system mass loss,energy loss,and element distortion;in addition,the proposed method had a good simulation effect on the interaction between detonation waves and the cylindrical shell.The simulated detonation wave propagation,shell damage morphology,and fragment velocity distribution were in good agreement with theoretical and experimental results.We divided the fragments into three regions based on their shape characteristics.We analyzed the failure mode and formation process of fragments in different regions.The numerical results reproduced the phenomenon in which cracks initiated from the inner surface and extended to the outer surface of the cylindrical shell along the 45°or 135°shear direction.In addition,fragments composed of elements are identified,and the mass and characteristic lengths of typical fragments at a stable time are provided.Furthermore,the mass and size distribution characteristics of the fragments were explored,and the variation in the fitting results of the classical distribution function under different explosion pressures was examined.Finally,based on mathematical derivation,the distribution formula of fragment velocity was improved.The improved formula provided higher accuracy and could be used to analyze any metal cylindrical shells with different length-to-diameter ratios.

3D simulation on the unit duct in the shell side of the ROD baffle heat exchanger

The ROD baffle heat exchanger can slightly enhance the shell side heat transfer coefficient with the significant reduction of pressure, loss due to the shell side fluid flowing longitudinally through tube bundle, which leads to the reduction of the manufacture and running cost and in some cases to the dimensions reduction of the heat exchangers. Because of the complexities of fluid dynamics equations and the structure of heat exchangers, few theoretical researches have been accomplished to specify the shell side characteristics of the ROD baffle heat exchanger. A unit duct model in the shell side of the longitudinal flow type heat exchanger has been developed based on suitable simplification. A numerical analysis on shell side of the ROD baffle heat exchanger has been carried out at constant wall temperature to obtain the characteristics of heat transfer and pressure drop. The numerical results show that the ROD baffles placed vertically and horizontally in the unit duct continue to shear and comminute the streamline flow when the fluid crosses over the ROD-baffles, and change the fluid flow directions, and then the continuity and stability of the fluid axe destroyed. The effect of disturbing flow can promote fluid turbulent intensity and effectively enhance heat transfer. The numerical analyses can provide the theoretical bases for optimizing the structure of ROD baffle heat exchanger and improving its performance.

Finite Difference Simulation of Implosive Collapsing for Aluminum Spherical Shell

Implosive collapsing for spherical metal shells is a kind of dynamic compressing method, in which high pressure and high compression degree of materials can be attained. In present work, the dynamic process of implosive collapsing for spherical metal shells was regard as spherical symmetry ideally, so one-dimensional spherical symmetric fluid dynamics conservation equations were established, and the finite difference schemes for solving these equations were given. An aluminum spherical shell was assumed, whose inner radius is 4cm and thickness is 2 cm. In numerical simulation, initial centripetal velocities (800, 1000 and 1200 m/s) were used to make aluminum spherical shell collapse. The simulation results show that during the process of implosive collapsing, the material exhibits a compression-expansion-compression pulsation process, and the internal pressure changes and distribution are consistent with the theoretical expectations. The simulation results can be used as a reference for relevant analysis.

Numerical analysis of applying special pavements to solve the frost heave diseases of high-speed railway roadbeds in seasonally frozen ground regions

The Haerbin-Dalian Passenger Dedicated Line is the first high-speed railway constructed in the seasonally frozen ground regions of northeastern China. Frost heave diseases occurred in the first winter of its operation （between October 2012 and January 2013）, and frost heave was observed mainly in the roadbed fills that were considered not susceptible to frost heave. This paper proposes applying two special pavements -- black pavement and insulation-black pavement -- to improve the thermal regime of the roadbed. Three numerical models of the roadbed temperature field were built based on the field con- ditions of the Changchun section （D3K692＋840 to D3K692＋860）. The results show that： （1） Compared with cement pave- ment, black pavement and insulation-black pavement could reduce the freezing index at the roadbed surface by 37% and 64%, respectively, which could influence the maximum frozen depth; （2） the maximum frozen depths under the black pavement and insulation-black pavement were respectively 1.3-1.4 m and 1 m. Compared with cement pavement, they could reduce the maximum frozen depth by 0.4 m and 0.7-0.8 m, respectively, which would reduce the permitted amount of frost heave by 4 mm and 7-8 ram, which would meet the deformation limit established by the Code for Design on Special Subgrade of Railway; （3） the freezing periods of the black pavement and the insulation-black pavement were, respectively, approximately four months and two months. Compared with cement pavement, they could reduce the freezing period by approximately 19 days and 40 days, respectively, and delay the initial freezing time by 9 days and 18 days; and （4） compared with cement pavement, black pavement and black-insulation pavement could reduce the frozen areas of roadbeds in the cold season, which suggests that these two special pavements could provide better thermal stability for roadbeds.

Numerical investigation of grooves effects on the thermal performance of helically grooved shell and coil tube heat exchanger

Heat exchangers are integral parts of important industrial units such as petrochemicals,medicine and power plants.Due to the importance of systems energy consumption,different modifications have been applied on heat exchangers in terms of size and structure.In this study,a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical simulation.Helically grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat exchanger.In the first section,thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical grooves.At the second section,helically grooves created on both outer and inner wall of the annulus shell with different groove depths.The results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20%compared to the heat exchanger with grooves on only outer shell wall.The highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

基于Flow Simulation的管壳式换热器水与R134a热交换模态分析

换热器是工业中重要的换热组件之一,换热性能的良好与否直接影响整个机组的运行性能。本文采用数值模拟方法,使用Flow Simulation对管壳式换热器壳侧水与管侧R134a的两相流动及相变传热进行了模拟计算。根据流体流动特点,合适的湍流模型,选定水流在壳程中进行换热,并根据水的进出口温度来校核热交换;选定R134a冷媒在壳程中进行换热,并根据冷媒特性设置进出口温度及管程内部压力来校核热交换。通过对管壳式换热器壳侧的流体介质与管侧的流体介质发生的热交换进行模拟研究,得到了管壳式换热器壳程与管程的速度场、温度场、压力场的分布情况,并进行了分析。对当下壳管式换热器结构设计起到参考、指导、验证作用。

考虑物性变化及壳体传热的新型板壳式换热器板程流动传热数值模拟

板壳式换热器以优越的换热性能和耐温耐压性在化工生产等领域有着广阔的应用前景。本文采用可实现k⁃ε湍流模型结合增强壁面函数,对一种新型板壳式换热器板程流动与传热特性进行数值模拟研究,讨论了介质物性变化及壳体传热的影响,并与已有实验进行验证。重点分析了不同波纹高度在不同入口流速下的流动传热特性,基于场协同理论揭示了速度场与温度场及压强场协同分布规律。结果表明:流动传热计算不能忽略流体介质物性变化及壳体传热的影响;增大波纹高度流态由曲折流向十字交叉流转变,板间流体分布趋于均匀,换热性能增大;沿沟槽形成连续的涡结构,在触点周围形成具有周期性和中心对称的高剪切涡量集中区,垂直于流动方向场协同呈现周期性变化,波纹高度越高周期性越明显;在波纹核心流域内因流动与热流相似,其协同程度变差。

大跨度装配式单层网壳十字形半刚性螺栓连接节点抗弯性能研究

装配式连接节点是大跨度装配式单层空间网壳结构体系的关键。提出一种适用于大跨度单层网壳结构的十字形板装配式节点。该节点由圆钢管、十字形钢板、角钢、矩形连接盖板、圆盖板和高强螺栓组成,其中圆钢管、盖板、十字形钢板在工厂焊接,现场将十字形板和角钢、矩形盖板用高强螺栓连接。该节点通过设置角钢、矩形连接盖板和十字形钢板螺栓连接,在节点受到弯曲荷载时,角钢和矩形连接盖板可以首先承受弯曲荷载,从而减少节点内侧的十字形钢板塑性损伤,并且提高节点的抗弯性能。利用有限元模拟方法,构建新型连接节点有限元模型,分析了十字形钢板和角钢厚度等变量如何影响节点在平面内外的抗弯性能。通过对各组成部分尺寸的参数化研究,得到了这些因素对所提出的连接节点平面内外抗弯性能的影响规律。研究结果表明,采用角钢与矩形盖板相连接形成的十字形节点,在抗弯刚度和承载力方面表现出了优异的性能。通过调节十字形板厚度、螺栓个数、角钢和盖板厚度可调控节点的初始抗弯刚度和抗弯承载力。基于刚性节点设计方法,对该半刚性节点进行尺寸理论设计,结果表明该方法可以保证节点弯矩设计值基本达到圆钢管的屈服弯矩,满足设计要求,提高节点安全。

基于ALE方法的加筋圆柱壳水下接触爆炸计算研究

随着水下制导技术的发展,接触爆炸对水下结构的毁伤问题越加受到关注。为研究加筋圆柱壳结构水下接触爆炸毁伤特性,采用LS-DYNA软件的任意拉格朗日-欧拉(ALE)方法模拟爆炸冲击波的形成、传播及其对圆柱壳结构的毁伤过程,探讨水下接触爆炸作用下单、双层加筋圆柱壳的毁伤响应特性,并分析不同药量和爆距条件下加筋圆柱壳的破坏模式。研究结果表明:在不同药量和爆距的水下接触爆炸条件下,加筋圆柱壳呈现多种破坏模式,加筋和加肋位置处易出现撕裂状破口,板壳结构的破坏主要表现为凹陷变形及沿着加筋位置处扩展的裂纹,其中爆距对破坏模式的影响更明显。本文结果可为水下接触爆炸冲击波作用下水下航行体结构强度分析和防护设计提供参考。

铝合金变速箱后壳压铸工艺设计与数值模拟优化

以某汽车变速箱后壳为研究对象,选择合适的压铸工艺参数并设计了浇注系统。应用MAGMAsoft软件对其充型过程、凝固过程进行数值模拟。结果表明,金属液充型过程平稳,但凝固时间顺序不合理,产生缩松缩孔缺陷。根据铸件凝固时间顺序添加冷却系统。通过对优化后的工艺方案进行数值模拟分析、产品试制,最终得到了合理可行的压铸工艺方案,提高了压铸件的产品质量。

型壳加热温度对单晶高温合金显微组织及“雀斑”形成的影响

利用所设计的阶梯试样进行定向凝固试验和模拟,研究定向凝固过程型壳加热温度对单晶高温合金铸件显微组织和“雀斑”形成的影响。分析糊状区的温度场及形貌。结果表明,升高型壳加热温度,一次和二次枝晶间距减小,糊状区液相的渗透率和对流通道的宽度降低,“雀斑”形成倾向性降低,“雀斑”宽度减小,“雀斑”区域枝晶碎片减少。此外,随着型壳加热温度的升高,糊状区液相冷却速率增加,糊状区熔体的冷却时间减少,液体流动对枝晶的破碎程度得到削弱,这进一步降低单晶高温合金铸件“雀斑”形成的倾向性。

基于中低温相变材料的管壳式储热单元传热性能数值分析

针对管壳式相变储热单元换热效率低的问题,设计一种带有径向矩形翅片的复合盐管壳式相变储热单元,进行数值模拟并与实验研究对比验证,然后选择适当的性能指标分析模拟结果。采用ANSYS FLUENT进行三维瞬态仿真,改变换热流体入口温度及储热单元翅片间距进行储热过程的数值计算,对相变材料温度变化、传热过程及熔化情况进行对比分析。结果表明:提高换热流体温度和缩小翅片间距是有效强化换热的手段。在本工作中,换热流体与相变材料复合盐CH_(3)COONa·3H_(2)O-KCl相变温差每增加5℃,相变材料熔化速率分别提升54.98%、 34.67%、 23.92%、 18.13%、 14.45%,潜热储热速率分别提升61.56%、 45.79%、 35.15%、27.04%、22.31%,速率提升效果均逐渐减弱。翅片间距每缩短10 mm,相变材料熔化速率分别提升32.37%、41.26%、38.66%,储热量随之减少6.40%、11.95%、6.55%,储能密度降低0.53%、10.97%、1.57%,实际应用中需综合换热能力、成本等方面问题选择合适的翅片间距。本工作可为实际工程中储热单元的设计优化提供理论支持。

基于内管移动的卧式管壳式相变储热器储热性能优化研究

相变储热技术能够实现对固态储放氢过程热量的回收和供给,实现固态储氢罐内的自热平衡,提高储放氢性能。研究针对卧式管壳式相变储热器,提出了一种新型的内管偏心放置绕中心轴线旋转的运动方式,采用Fluent数值模拟软件,基于动网格技术编写了用户自定义函数UDF,重点研究了内管偏心距离与旋转速度对储热性能的影响。结果表明:与传统中心内管静止布置相比,偏心内管的旋转运动能够显著提高储热性能,当偏心距离为9 mm,旋转速度为0.10 r/min时,储热时间达到最小值,储热时间减少了92.16%,时间平均储热速率是内管静止布置的11.51倍;当偏心距离为9 mm,旋转速度由0.30 r/min减少至0.10 r/min时,储热时间减少了13.57%;当旋转速度为0.10 r/min,偏心距离由3 mm增至9 mm时,储热时间减少了70.48%。该研究结果可为卧式管壳式相变储热器在储氢领域的性能优化研究提供新思路。

爆炸动载下金属柱壳破片速度场分布研究

针对格尼(Gurney)公式无法描述破片速度场沿圆柱壳体轴向变化的问题,该文通过AUTODYN软件建立仿真模型,分析了长径比和壳体壁厚对破片速度场分布的影响。考虑爆炸加载下壳体断裂过程,修正了Gurney公式。基于上述研究,将壳体长径比和相对壁厚引入指数形式的修正因子中,建立了破片速度场轴向分布模型。通过实验验证了该模型的合理性。研究结果表明:对于圆柱形战斗部,相对壁厚为常数,长径比越大,战斗部形成破片速度越接近v 0;长径比为常数,壳体相对壁厚越小,战斗部形成破片速度越接近v 0。将该文理论结果与Gurney理论结果以及实验结果进行对比,该文理论结果误差均在7%以内,大部分误差小于3%,与实验结果更加吻合,验证了该文建立的破片速度场轴向分布模型的合理性。该文理论模型可为杀伤战斗部破片参数精准设计提供参考。

通孔球壳胞元结构压缩力学性能

球壳胞元结构作为一种新型轻质功能材料,在航空航天、交通运输等领域有着广阔的应用前景。本工作通过实验和数值模拟的方法对简单堆积的通孔球壳胞元结构受压缩时的力学性能进行了研究,得出其名义应力-应变曲线,分析了结构的有效弹性模量、屈服极限、平台应力、比吸能等性能随球壳壁厚和球心距变化的规律。结果表明,部分球壳胞元结构在压缩过程中出现屈曲现象,并翻转形成塑性铰,从而增强结构的承载能力。球壳胞元结构的有效弹性模量、屈服极限随着球心距增大呈先增加后减小的规律,其平台应力和比吸能随着球心距增大而增加。综合各项数据可得,球壳胞元结构的球心距大于等于18.0 mm是更理想的结构形式。