Comparison of average radial expansion velocity from impacted liquid filled cylinders

In this paper, the average radial expansion velocity of an impacted fluid filled cylindrical target is investigated. Theoretical and numerical predictions of the radial expansion velocity are compared to the experimentally measured radial expansion velocity. The primary objective of this work is to assess the ability of these theoretical and numerical techniques to predict the radial expansion velocity. A secondary objective of this work is to quantify the effect of changes in dimensional scale on the radial expansion velocity and to construct a simple physics based model which incorporates these scaling effects. Two-dimensional numerical hydrocode simulations accurately predict the measured ejection velocity for tests with low projectile–target misalignment. However, three-dimensional numerical calculations, which account for this misalignment, accurately predict all experimental tests. A theoretical formulation, based on a simple conservation of energy principle, yields a zero-dimensional model which accurately predicts the two-dimensional hydrocode simulations. Thus for experimental simulations which have low projectile–target misalignment, the simple theoretical model developed here accurately predicts the average radial expansion velocity. A dimensional analysis of this theoretical formulation yields a scaling relationship which accurately predicts the effect of dimensional scale between two different experimental test series.     

Formation and expansion of the plasma column under electron beam-metal interaction

The process of expansion of low-energy electrons and ions produced from electron beam evaporation of a metal target in the technological vacuum chamber of an electron beam welding machine is studied. Analyzing the spatial distribution of the particle density that is measured, the radial collisionless plasma motion from the beam region is shown to be prevailing. A model of the free plasma expansion out of the cylindrical source is developed. The relative distribution of the electron density and the electrostatic potential obtained are compared with the experimental results. The knowledge of the plasma parameter distributions in the technological vacuum chamber can be used for remote diagnostics and control of the technology process.     

CAVITY MODELS FOR SOLID AND HOLLOW PROJECTILES

Two analytical models for the crater size generated by long-rod and thick-walled tube projectiles are presented. The first is based on energy; in a steady-state penetration, the kinetic energy loss of a projectile is related to the total energy deposited in the target. This simple approach provides an upper bound for the crater size. The second approach is based on the observation that two mechanisms are involved in cavity growth due to long projectiles: flow of projectile erosion products, which exerts radial stress on the target and opens a cavity, and radial momentum of the target as it flows around the projectile nose (cavitation). This analysis includes the centrifugal force exerted by the projectile, radial momentum of the target, and the strength of the target. Thus, it can estimate the extent of cavity growth due to projectile mushrooming, which cannot be predicted by other analyses. This model is shown to be in good agreement with experimental data.     

Oblique penetration of a rigid projectile into an elastic-plastic target

The main objective of the present work is to develop an approximate solution of the problem of oblique penetration of a rigid projectile into an elastic-plastic target of finite thickness. This is accomplished by generalizing the work on normal penetration reported in [1]. Here, an irrotational isochoric velocity field is considered that consists of three parts, each of which together satisfy the condition of impenetrability at the projectile's surface. The first part is associated with the longitudinal motion of the projectile, the second part with the transverse motion, and the third part with the projectile rotation in the plane defined by the initial longitudinal projectile velocity and the normal to the target surface. The target material is assumed to be incompressible and the target region is subdivided into an elastic region ahead of the projectile, and a rigid-plastic region near the projectile. Using the above potential velocity field, inertia effects are included and the linear momentum equation is solved exactly in the elastic region. In the plastic region, the linear momentum equation is integrated numerically along the instantaneous streamlines to determine the pressure field on the projectile surface. Then the decelerating force and moment applied to the projectile are solved numerically. The model developed here predicts the residual velocity, the ballistic limit, as well as the residual angle of obliquity. Moreover, this model is able to describe the phenomenon of ricochet. It is shown that the agreement of the theory with experiments is good even though no adjustable parameters are used. Also, a user-friendly computer program has been developed that is available for distribution along with a Users' Manual.     

Modeling the characteristic types and heat release of stretched premixed impinging flames

 A numerical code has been developed for the simulation of the impingement of a turbulent jet on a plane surface. The performance of three turbulence models is assessed under isothermal conditions. Predictions are compared with experimental data from the literature. Based on the results an appropriate turbulence model is selected to model a premixed jet flame impinging on a solid surface. Mass transfer and combustion are modeled with a two-equation model simulating volumetric and kinetically controlled chemical reaction rates. Modeling of heat transfer accounts for convection and radiation effects. Results show that under high pressure environment turbulent premixed flames are of wrinkled-thickened type near the outlet of the nozzle (free jet region) and of wrinkled reaction sheets in the area near the surface (impingement region and radial wall jet). The results establish that appropriate choice of turbulence and combustion models can lead to accurate prediction of the flow characteristics.     

Impact damage in layered glass

High-velocity impact onto a layered glass target produces a very extensive damage pattern exhibiting many distinct morphologies. Material around the penetration cavity is finely comminuted. Under the arrested projectile, the glass is largely intact with spoke-like fracture regions. Around the projectile cavity, needle fragments are formed; they are radial in outer layers and circumferential in inner layers. Extensive radial cracks occur in all layers, but the spacing and frequency of transverse fractures change in each layer. Damage from radial cracks also progresses from being hoop-stress-induced to flexural-induced through the depth of the target. Fan and dicing cracks occur near the periphery of the target. Mesoscale damage features include conventional mist and hackle markings indicating very fast cracks. The map of damage presented herein should be a valuable reference for attempts to model impact damage of glass.     

内压荷载下安全壳1:10模型结构非线性有限元分析

对先进核电厂预应力混凝土安全壳1:10模型结构进行了内压作用下的非线性有限元分析。径向位移计算值与实验值的比较说明了计算模型和计算参数基本合理;由于预应力的作用,内压加至0.6MPa,模型结构仍处于受压状态,满足使用要求;1.5m至3.0m高范围内的径向位移大于其它高度的径向位移,标高2.0m左右的径向位移最大;沿模型结构环向,63.24o附近的径向位移大于其它位置的径向位移;极限内压为1.34MPa,为设计内压的3.35倍。分析表明,新开发的先进核电厂安全壳结构在内压作用下是安全的。     

Optimum Design of Warehouses Having Radial Aisles1

A warehouse design model is developed for the case of a radial aisle structure within a warehouse having a single dock. It is shown that approximate straight movement efficiencies may be achieved by using a small number of radial aisles. Item movement is assumed to be rectilinear to the nearest radial aisle and Euclidean along the aisle to the dock.     

Radiation transport calculations for 50 MV photon therapy beam using the Monte Carlo code GEANT4

A new thin transmission target technique for fast dose delivery using narrow scanned photon beams has been developed. High-energy, 50-100 MeV, electron beams of low emittance incident on thin low-Z targets produce narrow and intense high-energy bremsstrahlung beams. However, electrons transmitted through the target are bent from the therapeutic beam by a purging magnet and have to be effectively absorbed in a dedicated electron collector. The electron-photon transport through a treatment head has been studied using the Monte Carlo simulation toolkit Geant4. The Geant4 electromagnetic physics processes have been compared with experimental data of radial dose profiles. The differences between calculated and measured radial dose distributions are approximately 2-10%. Preliminary investigations of the collector design have been carried out in order to minimise secondary electron and photon contamination of the therapeutic beam. The toolkit presented here is promising for further development of narrow photon beam therapy.     

一种基于综合泄漏流机制的涡轮转子流固耦合模型

针对涡轮转子Alford力模型的固有缺陷,综合考虑涡轮径向和轴向动静转子间隙变化对泄漏流的影响,研究了既包括涡轮径向偏心又涉及涡轮轴向偏斜的综合泄漏流机制,并以此为基础建立了能够同时反映涡轮径向偏心和轴向偏斜,同时还能体现涡轮平均径向和轴向间隙的非线性流体激振力模型。通过MATLAB进行数值积分和图形处理,得到了反映流体激振力与涡轮径向偏心距和轴向偏斜角关系的一组图形。最后还讨论了涡轮平均径向和轴向间隙以及涡轮偏心与偏斜相位差对流体激振力的影响。理论分析结果与现有实验数据比较证明,该模型是有效的,对建立考虑流固耦合的涡轮转子动力学模型具有实际意义。     

A general geometrical model of scroll compressors based on discretional initial angles of involute

Based on discretional initial angles of involute of scroll compressors, a general mathematical representation of scroll wraps, working chamber volume and leakage areas is presented. The scroll wraps' geometrical expressions, including interaction arc, of the involute angle with discretional initial angles of involute are developed. By using it, a new calculation formula of working chamber volume without restriction to special involute initial angles is set up and the expression of the volume during all the suction, compression and discharge processes in a general subsection function style is given. A geometrical model of leakage areas, including flank in, flank out, radial in and radial out, is also developed based on the discretional initial angles condition. Finally, this geometrical model is applied in a thermodynamic model and the simulation results are compared with some former experimental results. It is found that this model has a satisfactory accuracy and is easy to be used in thermodynamic simulation.     

刚性尖头弹侵彻圆柱形金属厚靶分析模型

考虑金属厚靶侧面自由边界的影响,研究了刚性尖头弹侵彻有限平面尺寸金属厚靶问题。基于有限柱形空腔膨胀理论和线性硬化材料模型,得到了空腔壁径向压力的解析式,建立了刚性尖头弹侵彻有限直径圆柱形金属厚靶工程模型。与试验和数值模拟比较表明,该文工程模型计算精度很好。基于所建立的工程模型,研究了靶板半径对侵彻深度和侵彻阻力的影响,结果表明:当靶板与弹丸半径比值小于20时,靶板半径对侵彻阻力和侵彻深度有显著影响,不能按无限尺寸靶板计算;当靶板与弹丸半径比值大于20时,靶板半径对侵彻阻力和侵彻深度影响较小,可近似按无限尺寸靶计算。     

Process tolerance allocation in angular tolerance charting

The paper deals with the process tolerance allocation problem for manufacturing a product with angular features in two-dimensional angular tolerance charting. First, a discrete interval cost–tolerance model is investigated to represent the relationship between manufacturing cost and tolerance. Then a multichoice knapsack model is formulated to allocate systematically the best tolerance to each individual machining dimension in both radial and axial directions with the objective of minimizing the total manufacturing cost. Furthermore, a genetic algorithm is developed to obtain the optimal solution to the multichoice knapsack model. Finally, a numerical example is presented to illustrate the model and the approach developed.     

New analytical model of expansion of spherical cavity in brittle material based on the concepts of mechanics of compressible porous and powder materials

In this paper, the concepts of mechanics of porous and powder media are applied for development of new analytical model of expansion of spherical cavity in brittle materials. The model is based on the approach that recognizes the existence of three regions with different rheology: region of comminuted and compacted material; region of pore formation formed by radial cracks; elastically deformed region. Strain–stress state in each region is determined and analyzed. Cavity expansion pressure is determined. Energy losses on elastic deformation, fracture and compaction of material are calculated and compared for a number of ceramic materials. It is shown that the contribution of compaction and fracture in total energy losses is considerable. The presented model avoids the use of rheological characteristics that are difficult to determine and uses instead the porosity of the material.     

半主动式激光导引头跟踪角误差的分析与测试

根据半主动式激光导引头的目标探测原理,提出了四象限光电探测器的目标位置解算偏差模型,以及由探测器信号测量一致性引起的测量误差模型,据此进行了数值分析计算和试验验证.数值分析与试验结果表明,目标位于跟踪区外侧时,电路的目标位置解算偏差起决定作用,目标位于跟踪区中心时,探测器测量一致性误差起决定作用.利用本文的分析方法,可在激光导引头跟踪性能试验中,对其跟踪性能指标进行深入的分析与评价.     

Automatic target tracking in FLIR image sequences using intensity variation function and template modeling

A novel automatic target tracking (ATT) algorithm for tracking targets in forward-looking infrared (FLIR) image sequences is proposed in this paper. The proposed algorithm efficiently utilizes the target intensity feature, surrounding background, and shape information for tracking purposes. This algorithm involves the selection of a suitable subframe and a target window based on the intensity and shape of the known reference target. The subframe size is determined from the region of interest and is constrained by target size, target motion, and camera movement. Then, an intensity variation function (IVF) is developed to model the target intensity profile. The IVF model generates the maximum peak value where the reference target intensity variation is similar to the candidate target intensity variation. In the proposed algorithm, a control module has been incorporated to evaluate IVF results and to detect a false alarm (missed target). Upon detecting a false alarm, the controller triggers another algorithm, called template model (TM), which is based on the shape knowledge of the reference target. By evaluating the outputs from the IVF and TM techniques, the tracker determines the real coordinates of one or more targets. The proposed technique also alleviates the detrimental effects of camera motion, by appropriately adjusting the subframe size. Experimental results using real-life long-wave and medium-wave infrared image sequences are shown to validate the robustness of the proposed technique.     

非均质表皮层径向双层承压井流数学模型的半解析解

考虑表皮层和未扰动承压层的非均质性、各向异性以及竖向越流补给作用,建立了径向双层承压三维井流的数学模型,采用Laplace变换和矩阵理论求得表皮层和未扰动承压层的水头降以及井壁流量的半解析解.应用所求解编制计算程序,分析了表皮层沿竖向随机变化的渗透性对承压层井流的影响,结果表明:表皮层非均质变化形态决定了表皮层内和其附近处的水头降以及井壁流量的竖向分布规律,表皮层对承压层渗流产生的影响范围与承压层的竖向渗透系数大小有关;改善井周岩土介质渗透性或增大"负表皮层"厚度可提高抽水井产量;表皮层径向渗透系数较小时,承压层的水头降幅度主要取决于承压层径向渗透系数的大小,而当表皮层径向渗透系数较大时,承压层径向渗透系数和竖向渗透系数均对承压层水头降有较大影响.     

Disk-and-washer cavities for an accelerator

Studied is the behavior of disk-and-washer accelerator cavities, in which the single radial stem support is adopted. The support leads about 70% larger and 20% smaller rf power loss than that of the calculated value in the normal cell and in the end cell, respectively. The distortion of the field is limited in the region of the so-called coupling cells. The properties of the coupled cavities, as the dispersion curve or the effect of tuners on the relative axial field is measured and well explained by the biperiodic coupled resonator model. The manufacturing of the actual cavity is also described, in which electroplating and welding methods are developed. The transverse coupling impedance calculated for a multiple-cell cavity are comparable with the instability experiments made in the TRISTAN accumulation ring.     

纵径耦合振动管形振子的特性研究

对纵径耦合振动的管形振子进行了研究,给出了管形振子的频率方程,并利用有限元和边界元软件对管形振子的振动模态和辐射的声场特性进行了分析。对于管形振子,由于振子各部分的振动幅度和相位不同,因而在振子径向位移较大的水平区域声场加强,较小的水平区域声场减弱。通过实验验证了分析结果的正确性。     

Assessment of Analytical Models of Pure Bending of Sheet Materials Using the Digital Image Correlation Method

Bending of sheet materials is a common forming mode for shaping sheet components. Although many numerical models of bending, both analytical and numerical simulations based, are available in the literature, extensive experimental validations have been rather limited. A new bend test method and complementary three‐dimensional finite element (FE) simulation of the experiments are employed to assess the predictions from an advanced analytical and FE model of pure bending of aluminium sheet materials. The experimental set‐up developed and utilised is an open concept design that allows access to the tensile surface and through‐thickness region in the vicinity of the specimen bend line to continuously record images of the deforming specimen with two cameras. The specimen images are analysed for strains using an online strain mapping system based on digital image correction method. Tangential strain distribution results from the models in terms of material thinning in the bend region are compared with those from the experiments on AA2024 aluminium sheet material by considering the responses from the specimen edges and mid‐width regions at the bend line. Furthermore, the tangential and radial stress distributions on the through‐thickness section of the specimen from the analytical model are compared with those from the FE model. The results from experiments, FE model and analytical model are compared and discussed in the light of the experimental data and the assumptions involved in the development of the models.