Discrete Lagrangian mechanics for nonseparable nonsmooth systems

We consider event‐driven schemes for the simulation of nonseparable mechanical systems subject to holonomic unilateral constraints. Systems are modeled in discrete time using variational integrator (VI) theory, by which equations of motion follow from discrete variational principles. For smooth dynamics, VIs are known to exactly conserve a discrete symplectic form and a modified Hamiltonian function. The latter of these conservation laws can play a pivotal role in stabilizing the energy behavior of collision simulations. Previous efforts to leverage modified Hamiltonian conservation have been limited to integrators using the Störmer–Verlet method on separable, nonsmooth Hamiltonian mechanical systems. We generalize the existing approach to the family of all VIs applied to nonseparable, potentially nonconservative Lagrangian mechanical systems. We examine the properties of the resulting integrators relative to other structured collision simulation methods in terms of conserved quantities, trajectory errors as a function of initial condition, and required computation time. Interestingly, we find that the modified collision Verlet algorithm (MCVA) using the Störmer–Verlet integrator defined as a composition method leads to the best accuracy. Although relative to this method, the VI‐based generalized MCVA method offers computational savings when collisions are particularly sparse. Copyright © 2015 John Wiley & Sons, Ltd.     

Contact bridging dampers for back-up on automated highways

Automated Highway Systems (AHS) are under development to address congestion, inefficient energy use and inadequate safety margins. As more intelligence is applied to highway and vehicles, the system increasingly relies on secure communications and control, with potentially hazardous consequences in the event of technical failure. The authors propose an active, intelligently controlled extended fender which permits vehicles to operate in lengthy, stable platoons in direct but 'soft' contact, allowing fault support for an AHS. Simulation studies have indicated that stable operation may be retained with only a simple 'leader' broadcast signal and that good longitudinal ride quality is also retained, providing results similar to the fully co-operative system. The device also provides potential for additional safety in the event of a collision and for selective power reduction for a co-operative system at steady speed     

A Dynamic Multi-ary Query Tree Protocol for Passive RFID Anti-collision

In this paper, a dynamic multi-ary query tree (DMQT) anti-collision protocol for Radio Frequency Identification (RFID) systems is proposed for large scale passive RFID tag identification. The proposed DMQT protocol is based on an iterative process between the reader and tags which identifies the position of collision bits through map commands and dynamically encodes them to optimize slots allocation through query commands. In this way, the DMQT completely eliminates empty slots and greatly reduces collision slots, which in turn reduces the identification time and energy costs. In addition and differently to other known protocols, the DMQT does not need to estimate the number of tags, reducing the protocol implementation complexity and eliminating the uncertainty caused by the estimation algorithm. A numerical analysis shows that DMQT has better performance than other algorithms for a number of tags larger than 300. Meanwhile, when the number of tags is 2000 and the tag identity (ID) length is 128 bits, the total identification time is 2.58 s and the average energy cost for a tag identification is 1.2 mJ, which are 16.9% and 10.4% less than those of state-of-the-art algorithms, respectively. In addition, a DMQT extension based on ACK command has also been presented to deal with capture effect and avoid missing identification.

     

Case specific prediction intervals for tri-PLS1: The full local linearisation

A new method to estimate case specific prediction uncertainty for univariate trilinear partial least squares (tri-PLS1) regression is introduced. This method is, from a theoretical point of view, the most exact finite sample approximation to true prediction uncertainty that has been reported up till now. Using the new method, different error sources can be propagated, which is an advantage that cannot be offered by data driven approaches such as the bootstrap. In a concise example, it is illustrated how the method can be applied. In the Appendix, efficient algorithms are presented to compute the estimates required.     

DEM Simulation of Abrasion of Nonspherical Particles in Tumbling Mill

Abrasion is a surface breakage event where irregular surfaces of particles are removed. Abrasion produces rounded particles by comminuting irregular edges. Extensive experimental work has been performed to study abrasion events and their process parameters. Very few studies have used the discrete element method (DEM) to study the abrasion behavior of particles. In this regard, the research work uses the DEM simulation of abrasion of nonspherical particles to study the process parameters in a tumbling mill environment. A 1.1 m diameter and 0.2 m length mill with square-shaped lifters of 30 mm cross section has been simulated. Particle trajectories, collision force, collision energy, and energy spectra are evaluated to understand the effect of surface roughness on abrasion. It was observed that as the asperities of the particle decreases, the rate of abrasion decreases. Based on the energy analysis, it was found that the normal collision force (average 0.4 kN) is larger than the tangential collision force (average 0.09 kN) for the considered case, and hence the former maybe more responsible for the abrasion of particles.     

柱形八叉树模型的运算规则及应用

八叉树模型是计算机科学中常用的一种非线性数据结构。它在工程中有广泛的应用。笔者选用柱形坐标空间作为八叉树模型的根结点，提出了一个由三维实体的CSG模型按递归方式生成实体八叉模型的算法，找出了八叉树中的平移、旋转、镜像等运算规则，并给出了八叉树模型求并、交、差的算法。文后给出了八叉树模型在空间物体碰撞方面的应用实例。     

Contact algorithms for the material point method in impact and penetration simulation

The inherent no‐slip contact constraint in the standard material point method (MPM) creates a greater penetration resistance. Therefore, the standard MPM was not able to treat the problems involving impact and penetration very well. To overcome these deficiencies, two contact methods for MPM are presented and implemented in our 3D explicit MPM code, MPM3D. In MPM, the impenetrability condition may not satisfied on the redefined regular grid at the beginning of each time step, even if it has been imposed on the deformed grid at the end of last time step. The impenetrability condition between bodies is only imposed on the deformed grid in the first contact method, while it is imposed both on the deformed grid and redefined regular grid in the second contact method. Furthermore, three methods are proposed for impact and penetration simulation to determine the surface normal vectors that satisfy the collinearity conditions at the contact surface. The contact algorithms are verified by modeling the collision of two elastic rings and sphere rolling problems, and then applied to the simulation of penetration of steel ball and perforation of thick plate with a particle failure model. In the simulation of elastic ring collision, the first contact algorithm introduces significant disturbance into the total energy, but the second contact algorithm can obtain the stable solution by using much larger time step. It seems that both contact algorithms give good results for other problems, such as the sphere rolling and the projectile penetration. Copyright © 2010 John Wiley & Sons, Ltd.     

Linear scaling methods for electronic structure calculations and quantum molecular dynamics simulations

In the past five years, notable advances in the field of electronic structure calculations have been made, by the development of linear scaling methods for total energy calculations and quantum molecular dynamics simulations. These are methods implying a computational workload which grows linearly with th system-size,in contrast to standard algorithms where the workload scales as the cube of the system-size. Therefore the use of linear scaling methods can considerably widen the class of systems and type of problems being tackled with quantum simulations. At present, linear scaling methods using semi-empirical Hamiltonians allow one to perform simulations involving up to a thousand atoms on small workstations, and up to ten thousand atoms for tens of picoseconds when using supercomputers. This has made it possible to study problems such as large organic molecules in water, thin film growth on a surface and extended defects in semiconductors. Although the implementation of first-principles linear scaling methods is less advanced than that of semi-empirical methods, promising results regarding organic molecules and metal-alloys have already appeared in the literature.     

Analysis of cushion systems for impact protection design of bridges against overheight vehicle collision

Based on several theoretical models of elastic and elastic–plastic impact as well as energy method, a systematic methodology for design analysis of cushion structures for impact protection of bridges against overheight vehicle collision is presented with consideration of the shear-off effect of projectiles and the nonlinear crushing behavior of sandwich cores. Three design criteria based on contact force, deflection, and energy are proposed, and the theoretical models for elastic, elastic–plastic, and after-densification impact including the shear-off effect of projectile are developed to improve the analysis and design of cushion structures against overheight vehicle impact. Realistic analysis of cushion structures is resulted from the above models, and it can be applied to design of cushion structures for the sake of bridge protection from overheight vehicle collision.     

Collision between mass–spring systems

As an effective simplification of beam-on-beam collision problems, a mass–spring model is proposed and analyzed. The energy partitioning between the two beams predicted by the mass–spring model very well approximates the rigid–plastic complete solution. Moreover, due to its simplicity and analytical solvability, the mass–spring model serves as a simplest collision system that provides the fundamental features of a structural collision event. In general, a structural response to impact can be divided into two stages: a very brief collision stage, followed by the structural deformation stage. The first stage starts with a severe velocity discontinuity in the contact region, and characterized by the local velocity change and the local contact dissipation. In the second stage, a restoring instant exists at which the stronger structure transfers from an energy dissipation state to a non-dissipation state and the total energy dissipated by this structure is termed the restoring energy. The remaining kinetic energy after this restoring instant will completely be dissipated by the weaker structure, if it exhibits no deformation-hardening. For the structure with constant load-carrying capacity during its large plastic deformation, the initial velocity will not affect the energy partitioning; while the increase of the relative mass of the impinging structure will make the energy-partitioning pattern closer to an elementary static estimate, that is, the structure with lower strength will dissipate all the input energy.     

A new understanding of near-threshold damage for 200 keV irradiation in silicon

Recently we reported room temperature point defect creation and subsequent extended defect nucleation in nitrogen-doped silicon during 200 kV electron irradiation, while identical irradiation of nitrogen-free silicon produced no effect. In this paper, first principles calculations are combined with new transmission electron microscope (TEM) observations to support a new model for elastic electron-silicon interactions in the TEM, which encompasses both nitrogen doped and nitrogen free silicon. Specifically, the nudged elastic band method was used to study the energetics along the diffusion path during an electron collision event in the vicinity of a nitrogen pair. It was found that the 0 K estimate for the energy barrier of a knock-on event is lowered from ∼ 12 to 6.2 eV. However, this is still inadequate to explain the observations. We therefore propose an increase in the energy barrier for Frenkel pair recombination associated with N₂-V bonding. Concerning pure silicon, stacking fault formation near irradiation-induced holes demonstrates the participation of bulk processes. In low oxygen float zone material, 2–5 nm voids were formed, while oxygen precipitation in Czochralski Si has been verified by electron energy-loss spectroscopy. Models of irradiation-induced point defect aggregation are presented and it is concluded that these must be bulk and not surface mediated phenomena.     

Modelling the energy-loss mechanism of charged particles in organic solids

The present study examines the energy-loss mechanism of charged particles in organic solids as determined by the inelastic interactions with the electronic sub-system of the target. The dielectric approach was applied to non-conducting valence electrons while an appropriate binary collision theory was used for core-electron transitions. The development of energy-loss models based on optical data (i.e. at zero momentum transfer) and appropriate extension algorithms (to non-zero momentum transfer) is discussed. The optical absorption spectrum is now available for a variety of organic compounds and allows for the inclusion of phase effects by incorporating pertinent experimental information. The dispersion of the optical functions is based on an analysis of the general properties of the Bethe-surface. Calculations are presented for the case of liquid water as a model substance for other condensed organic materials with very similar absorption characteristics.     

Design and Implementation of a Fuzzy Area-Based Image-Scaling Technique

In this paper, we propose the design and implementation of an interpolation scheme for performing image scaling by utilizing a dynamic mask combined with a sophisticated neighborhood averaging fuzzy algorithm. The functions that contribute to the final interpolated image are the areas of the input pixels, overlapped by a dynamic mask, and the difference in intensity between the input pixels. Fuzzy if–then rules for these two functions are presented to carry out the interpolation task. Simulation results have shown a fine high-frequency response and a low interpolation error, in comparison with other widely used algorithms. The interpolation can be applied to both gray-scale and color images for any scaling factor. The proposed hardware structure is implemented in a field-programmable gate array (FPGA) chip and is based on a sequence of pipeline stages and parallel processing to minimize computation times. The fuzzy image interpolation implementation combines a fuzzy inference system and an image-interpolation technique in one hardware system. Its main features are the ability to accurately approximate the Gaussian membership functions used by the fuzzy inference system with very few memory requirements and its high-frequency performance of 65 MHz, making it appropriate for real-time imaging applications. The system can magnify gray-scale images of up to 10-bit resolution. The maximum input image size is 1024 $times$ 1024 pixels for a maximum of 800% magnification.      

构件跌落碰撞的数值模拟研究

针对构件跌落碰撞问题,将Hertz-damp模型与有限元方法结合,给出了结构碰撞位移突加约束条件,建立了碰撞结构体系的动力方程。该方法能考虑碰撞体质量分布对碰撞过程的影响,同时可描述结构碰撞过程中的刚度非线性和能量损失。建立了构件跌落碰撞模型,初步分析了跌落构件质量、质量分布以及跌落高度等参数对碰撞过程的影响。研究表明:结构碰撞模拟中碰撞体质量沿接触面法线轴向不对称时应考虑其质量分布,否则会高估碰撞反应;碰撞荷载峰值和单次碰撞持续时间与跌落构件质量和跌落高度均成指数关系,碰撞荷载峰值随跌落构件质量和跌落高度增大而增大,而单次碰撞持续时间则随跌落构件质量增大而增大,随跌落高度增大而减小。这些规律能为减轻结构碰撞破坏研究提供参考。     

Thermal-gradient-induced interaction energy ramp and actuation of relative axial motion in short-sleeved double-walled carbon nanotubes

We investigate the phenomenon of actuation of relative linear motion in double-walled carbon nanotubes (DWNTs) resulting from a temperature gradient. Molecular dynamics simulations of DWNTs with short outer tube reveal that the outer tube is driven towards the cold end of the long inner tube. It is also found that the terminal velocity of the sleeve roughly depends linearly on the applied thermal gradient. We calculate the inter-tube interaction energy surface which is revealed to have a gradient depending upon the applied thermal gradient. Consequently, it is proposed that the origin of the thermophoretic motion of the outer tube may be attributed partially to the existence of such an energy gradient. A simple analytical model is presented accounting for the gradient in energy profile as well as the effect of biased thermal noise. It is shown that the proposed model predicts the dynamical behaviour of the long-time performance reasonably well.     

Physical scale modeling to verify energy storage inductor parameters

In the pulse charging and discharging of energy storage inductors, the influence of I²R heating, magnetic diffusion skin depth, and eddy current losses must be evaluated. These effects are not easily treated analytically. To address these problems, the system can be constructed according to governing scaling laws. The performance of the model can then be evaluated and scaled up to predict actual system performance. The scaling laws as applied to a 1O-MJ homopolar generator charging a 2-MJ cryogenic aluminum Brooks coil are presented in this paper. System parameters measured on the scale model are compared to parameters subsequently measured on the full-size equipment.     

一种集成空间分解与占用的精确碰撞检测算法及其在建筑工程中的应用

碰撞检测是建筑工程三维CAD中行之有效的辅助手段, 现代建筑形式复杂、规模庞大, 对碰撞检测算法的效率提出了更高的需求。该文基于空间分解和空间占用这两种应用最为广泛的预处理方法, 提出了一种集成、高效的精确碰撞检测算法。通过工程实例的测试和分析, 该集成算法的检测效率优于其他几种算法, 且模型量越大, 效率优势越明显。该文还针对建筑工程的实际应用需求, 对集成算法进行改进, 并应用于实际工程, 验证了算法的有效性和鲁棒性。实际应用表明, 该集成算法适用于建筑、结构、机电、幕墙等专业设计之间的碰撞检测。     

船-桥梁浮式钢套箱碰撞数值模拟中的流场处理方法对比研究

本文采用Ansys/Ls-dyna对1000吨级船舶与浮式桥梁钢套箱的碰撞过程进行了数值仿真,为了较精确地分析流场处理方法对于数值计算结果的影响,分别采用了流固耦合方法和附加质量系数法来模拟碰撞过程中流场的作用,并对比分析了两种方法下浮式钢套箱的碰撞力、撞深、竖向位移、内能变化等计算结果。研究结果表明,与采用附加质量系数法的结果相比,考虑流固耦合时防撞钢套箱的最大撞深较小而最大撞击力较大,且随着碰撞能量的增加,最大撞击力明显大于采用附加质量系数法的结果。因此对于桥梁的防撞钢套箱设计,常规附加质量系数法偏于危险,有必要用流固耦合方法来考虑流场的作用。另外,船体的撞击能量越大时,浮式钢套箱的竖向位移约束也越重要,可以通过设计浮式钢套箱的压载水,减小钢套箱在碰撞过程中的竖向位移,以提高其吸能效果。     

船桥碰撞过程引发的冲击动力学论题

对船桥撞击过程引发的几个冲击动力学论题进行了分析。研究表明:1为降低船撞力,应采用柔性(低的结构动态广义波阻抗)防撞装置;2撞击力所做的功,通过应力波传播转化为内能(变形能)与动能之和;而变形能中的不可逆部分愈高,防撞装置发挥的整体作用愈大,则愈有利于防撞装置发挥缓冲耗能作用。并且如何让船舶尽早结束撞击并带走尽量多的剩余动能,应是防撞装置设计的关键点;3黏性耗能可缓冲撞击过程、延长撞击历时,有利于防撞装置发挥整体作用,进而为船舶在低应力下转向滑离、从而带走尽可能多的剩余动能创造条件。因此,船撞桥防护装置的设计应该建立在如下的科学设计理念上:ⅰ低波阻抗意义上的冲击柔性,ⅱ缓冲撞击过程意义上的粘性耗能,ⅲ防撞装置能及早发挥整体作用,化撞击集中力为分布载荷,以及ⅳ让船尽早滑离而带走尽量多的剩余动能。以钢丝绳防撞圈为主要元件的柔性耗能防撞装置是这一防撞理念的工程应用实例,其有效性已为工程实践和实船撞击试验证实。     

Photovoltaic Models Parameters Estimation Based on Weighted Mean of Vectors

Renewable energy sources are gaining popularity, particularly photovoltaic energy as a clean energy source. This is evident in the advancement of scientific research aimed at improving solar cell performance. Due to the non-linear nature of the photovoltaic cell, modeling solar cells and extracting their parameters is one of the most important challenges in this discipline. As a result, the use of optimization algorithms to solve this problem is expanding and evolving at a rapid rate. In this paper, a weIghted meaN oF vectOrs algorithm (INFO) that calculates the weighted mean for a set of vectors in the search space has been applied to estimate the parameters of solar cells in an efficient and precise way. In each generation, the INFO utilizes three operations to update the vectors’ locations: updating rules, vector merging, and local search. The INFO is applied to estimate the parameters of static models such as single and double diodes, as well as dynamic models such as integral and fractional models. The outcomes of all applications are examined and compared to several recent algorithms. As well as the results are evaluated through statistical analysis. The results analyzed supported the proposed algorithm’s efficiency, accuracy, and durability when compared to recent optimization algorithms.