GPU accelerated online multi-particle beam dynamics simulator for ion linear particle accelerators

An online beam dynamics simulator is being developed for use in the operation of an ion linear particle accelerator. By employing Graphics Processing Unit (GPU) technology, the performance of the simulator has been significantly increased over that of a single CPU and is therefore viable in the demanding accelerator operations environment. Once connected to the accelerator control system, it can rapidly respond to any control set point changes and predict beam properties along an ion linear accelerator in pseudo-real time. This simulator will be a virtual beam diagnostic tool which is especially useful when direct beam measurements are not available. Details about the code structure design, physics algorithms, GPU implementations, and performance are presented.     

Molecular dynamics for long-range interacting systems on graphic processing units

We present implementations of the numerical integration of systems with long-range interactions on graphic processing units for three N$N$-body models with long-range interactions of general interest: the Hamiltonian Mean Field, Ring and two-dimensional self-gravitating models. We discuss the algorithms, speedups and errors using one and two GPU units. Speedups can be as high as 140 compared to a serial code, and the overall relative error in the total energy is of the same order of magnitude as for the CPU code. The number of particles used in the tests range from 10,000 to 50,000,000 depending on the model.     

An analysis method for atomistic abrasion simulations featuring rough surfaces and multiple abrasive particles

We present a molecular dynamics (MD) model system to quantitatively study nanoscopic wear of rough surfaces under two-body and three-body contact conditions with multiple abrasive particles. We describe how to generate a surface with a pseudo-random Gaussian topography which is periodically replicable, and we discuss the constraints on the abrasive particles that lead to certain wear conditions. We propose a post-processing scheme which, based on advection velocity, dynamically identifies the atoms in the simulation as either part of a wear particle, the substrate, or the sheared zone in-between. This scheme is then justified from a crystallographic order point of view. We apply a distance-based contact zone identification scheme and outline a clustering algorithm which can associate each contact atom with the abrasive particle causing the respective contact zone. Finally, we show how the knowledge of each atom’s zone affiliation and a time-resolved evaluation of the substrate topography leads to a break-down of the asperity volume reduction into its components: the pit fill-up volume, the individual wear particles, the shear zone, and the sub-surface substrate compression. As an example, we analyze the time and pressure dependence of the wear volume contributions for two-body and three-body wear processes of a rough iron surface with rigid spherical and cubic abrasive particles.     

Interpretation of quasi-elastic light scattering data for flexible chains: model dependence

The autocorrelation functions and corresponding relaxation times obtained from the forward depolarized quasi-elastic light scattering experiment are exhibited for two quite similar models of flexible polymer chains in solution. A very small change in the chain dynamics is found to be sufficient to change the relaxation time from a relatively short time independent of chain length, with an autocorrelation function suggestive of an unweighted sum of contributions from all the relaxation times in the spectrum of chain motion, to a long time with an autocorrelation function identical with that for the end-to-end vector, strongly dependent upon chain length and dominated by the longest relaxation time in the spectrum. These results raise the question whether widely-used models in which information about short-range chain structure and motion is deliberately omitted can be expected to be appropriate for the interpretation of depolarized scattering experiments.     

Security concepts for the dynamics of autonomous vehicle networks

The secure operation of autonomous vehicle networks in the presence of adversarial observation is examined, in the context of a canonical double-integrator-network (DIN) model. Specifically, we study the ability of a sentient adversary to estimate the full network’s state, from noisy local measurements of vehicle motions. Algebraic, spectral, and graphical characterizations are provided, which indicate the critical role of the inter-vehicle communication topology and control scheme in achieving security.     

Development of a system‐based water balance model to assess interrelated physical and anthropogenic constraints in lake and reservoir watersheds,applied to Coeur d'Alene Lake,Idaho, USA

This study presents a methodology for the development of a water balance model that uses publicly available data in a manner useful to water scientists and managers who manage complex lake and reservoir watersheds. The approach was applied to Coeur d'Alene Lake, a naturally occurring lake that is controlled by a dam located on its outlet (Spokane River) in North Idaho, USA. As in many other areas, the region surrounding Coeur d'Alene Lake has experienced high rates of population growth in recent years, and there is concern that, as consumptive water use increases, the lake will eventually not be able to be managed to simultaneously maintain the federally mandated minimum flow requirements in the Spokane River and also maintain the target summertime elevation of 2128 feet (648.6 m) for recreation and hydropower purposes. The complexity caused by the competing uses at Coeur d'Alene Lake makes it an excellent case study for similarly characterized watersheds. Both a natural flow model and regulated elevation model were developed, and sensitivity analysis was conducted on both models to evaluate which lake processes have the greatest effects on lake elevation, thereby requiring the most attention. A ‘low‐flow’ scenario was modelled to demonstrate the usefulness of the model and to inform Coeur d'Alene Lake regional stakeholders regarding the interrelationship between current water policy and the lake's physical behaviour under stressed conditions that could result from climate change. Model result indicates that, while lake elevation may be maintained at the summertime elevation of 2128 feet (648.6 m) under a low‐flow scenario, the outflows in the Spokane River start to approach the minimum flow requirements in the month of August. The developed approach is useful where publicly available data exist and allows for economic, yet rigorous, water resources systems evaluation without requiring significant field data collection.     

THE EFFECT OF OPERATING VARIABLES ON THE DYNAMICS OF CATALYTIC CRACKING PROCESSES

The dynamic Characteristics of a Fluidized Catalytic Cracking Process are examined over a wide range of operating conditions. A novel Order of Magnitude Approach is introduced to successfully provide physical insight into the cause and effect relationship between operating conditions and dynamic characteristics. It is shown that the original five-dimensional dynamic model is characterized by three fast time constants and two slow ones that dominate the dynamic responses. The two most important time constants are expressed as explicit functions of the operating conditions. These formulas correctly indicate in which parameter regions the open loop response is oscillatory (underdamped) or nonoscillatory (overdamped). Extensive process variables, that are either flow or capacity, related are defined in order to provide an approximate physical meaning for the dynamic modes of the system. It is shown that the two slow modes of the process are related to the enthalpy content of the regenerator and the sensible heat content of the catalyst phase in both the reactor and regenerator.     

Planar and axially symmetric slow shearing granular flows: a comparative evaluation of assembly evolution incorporating wavelet transforms

We demonstrate the enhanced capacities of our analysis toolset for three-dimensional data. In particular, we provide supporting evidence for some of the conclusions reached in our previous studies of two-dimensional avalanching heaps. Segregation by self-diffusion is shown to take place in three-dimensional assemblies and self-diffusion velocities are shown to be of a comparable order of magnitude to those found in plane-strain situations. The effect on assembly evolution by discrete avalanching of the availability of a third dimension for translation is investigated. The discrete wavelet transform is again shown to be a useful component of the toolset in coupling process variables in the context of the discrete defining events associated with assembly evolution. In particular, we move towards the determination of time constants by correlating wavelet coefficients with a time shift.     

凸轮磨恒线速加工过程曲线优化

为了提高凸轮轴的加工效率和加工精度,开发可用于凸轮轴磨削修整系统的动态优化模块。根据凸轮轴恒线速磨削原理,在Matlab中完成了数学模型的建模,采用三次样条曲线拟合插值法对加工过程曲线进行了优化,从而得到了波动更小的速度曲线并减少了恒线速度磨削所引起的联动轴响应问题。实验表明,该方法很好地实现了在二次磨削中对凸轮轴表面轮廓的修整,提高了凸轮轴的表面质量。     

四元数与欧拉角刚体动力学数值积分算法及其比较

为推广四元数保辛积分在工程中的应用,对欧拉角表示的状态方程数值积分与四元数的保辛积分进行比较.重陀螺的数值仿真结果表明四元数保辛积分的数值结果明显优于欧拉角状态方程积分.与欧拉角状态方程积分相比,四元数保辛积分在刚体动力学的数值仿真中更具优势.