物理模拟虚功和余虚功原理及它们在金属成形工艺中的应用

在文[1]的基础上,本文建立了金属成形工艺非耦联系统和相似非耦联系统的物理模拟虚功原理及余虚功原理,并从该两原理出发导出了文[1]所建立的物理模拟变分原理。上述诸原理共同组成物理模拟能量原理。而物理模拟虚功原理及余虚功原理是物理模拟能量原理的统一理论。同时,给出了模拟虚功原理的应用。     

Sequential Monte Carlo-based fidelity selection in dynamic-data-driven adaptive multi-scale simulations

In a simulation-based planning and control framework, timely monitoring, analysis, and control is important not to disrupt a dynamically changing system. To meet this temporal requirement, a dynamic-data-driven adaptive multi-scale simulation (DDDAMS) paradigm was proposed earlier, where the fidelity of a complex simulation model adapts to available computational resources by incorporating dynamic data into the executing model, which then steers the measurement process for selective data update. In this work, a sequential Monte Carlo method (sequential Bayesian inference technique) is proposed and embedded into the simulation to enable its ideal fidelity selection given massive datasets under the DDDAMS framework. As dynamic information becomes available, the proposed method makes efficient inferences to determine the sources of abnormality in the system (a shop floor in this paper). A parallelisation framework is also discussed to further reduce the number of data accesses while maintaining the accuracy of parameter estimates. A prototype DDDAMS involving the proposed algorithm has been implemented successfully for preventive maintenance scheduling and part routing scheduling in a semiconductor manufacturing supply chain, reducing the average waiting time of batches and increasing the machine utilisation significantly.     

A Backscatter Radiography Simulation Study

Backscatter radiography has become a well known inspection technique for the cases where the inspection is to be carried out only for one sided configurations. Compared to the conventional projection radiography, the backscatter radiography has more parameters to be adjusted for a well implemented inspection procedure. The interrogating beam and detector collimation, beam and detector orientation and the distance to the target surface are among those parameters that need to be adjusted. The adjustment of these parameters is not straightforward. A simulation based approach can provide good insight into adjusting the parameters. In this article, we show how simulations can be used for understanding the impact of various parameters. In doing that, we also document how the deterministic methods can prove to be very beneficial since the computations can be done only once and the scattered flux can be computed for various detector configurations without going back to transport computations. Some computational results are provided.     

Reversible scaling: Optimized free-energy determination using atomistic simulation techniques

We present a new simulation technique that allows accurate and very efficient determination of free energies as a function of temperature using a single constant temperature molecular dynamics or Monte Carlo simulation. The method is based on the dynamical reversible scaling of the potential energy function of the system of interest and is implemented using the adiabatic switching method. Application to the calculation of the free energy of crystalline silicon using a semi-empirical interatomic potential demonstrates that the reversible-scaling method provides an accurate and very efficient tool for the calculation of free energies over a wide temperature interval. This revised version was published online in July 2006 with corrections to the Cover Date.     

PINO—a tool for simulating neutron spectra resulting from the Li(p,n) reaction

The ⁷Li(p,n) reaction in combination with a 3.7 MV Van de Graaff accelerator was routinely used at FZK to perform activation as well as time-of-flight measurements with neutrons in the keV-region. Planned new setups with much higher proton currents like SARAF and FRANZ and the availability of liquid-lithium target technology will trigger a renaissance of this method. A detailed understanding of the neutron spectrum is not only important during the planning phase of an experiment, but also for the analysis of activation experiments. Therefore, the Monte-Carlo based program PINO (Protons In Neutrons Out) was developed, which allows the simulation of neutron spectra considering the geometry of the setup and the proton-energy distribution.     

Radiochemical approaches for formation of endohedral fullerenes and MD simulation

The formation of atom-doped fullerenes has been investigated by using several types of radionuclides produced by nuclear reactions. From the trace of the radioactivities after a high performance liquid chromatography, it was found that formation of endohedral fullerenes (or heterofullerenes) of small atoms (Be, Li), noble-gas atoms (Kr, Xe) and 4B–6B elements (Ge, As, Se, Sb, Te, etc.) is possible by a recoil process following the nuclear reaction. In order to show the possibility of creating endohedral fullerenes with a suitably high kinetic energy of foreign atoms, we have carried out large-scale ab initio molecular dynamics simulations on the basis of the all-electron mixed-basis approach with atomic orbitals and plane waves for several atoms.     

Radiochemical approaches for formation of endohedral fullerenes and MD simulation

The formation of atom-doped fullerenes has been investigated by using several types of radionuclides produced by nuclear reactions. From the trace of the radioactivities after a high performance liquid chromatography, it was found that formation of endohedral fullerenes (or heterofullerenes) of small atoms (Be, Li), noble-gas atoms (Kr, Xe) and 4B–6B elements (Ge, As, Se, Sb, Te, etc.) is possible by a recoil process following the nuclear reaction. In order to show the possibility of creating endohedral fullerenes with a suitably high kinetic energy of foreign atoms, we have carried out large-scale ab initio molecular dynamics simulations on the basis of the all-electron mixed-basis approach with atomic orbitals and plane waves for several atoms.     

卫星尾迹带电数值模拟研究

基于运行于低轨道"冷稠"等离子体环境中的卫星可以在其尾部形成电子和离子浓度不等量的尾迹,尾迹效应可严重影响卫星的表面不等量带电。因此,在分析卫星尾迹效应物理机制的基础上,建立了尾迹效应的二维简单计算模型,利用PIC(particle-in-cell)方法编制二维模拟程序,计算了不同尺寸卫星的尾迹电位分布和高能电子注入下的卫星尾迹电位分布,从而得到了卫星尾迹带电和卫星尺寸及高能电子注入之间的关系。     

声学仿真软件在噪声预测和评价中的应用

本文对声学仿真软件RAYNOISE的功能、结构及特点作了简单介绍。并对其在环境噪声及车间噪声预测中的应用作了探讨，可以看出RAYNOISE仿真软件在环境噪声预测，室内噪声预测，建声设计，电声设计方面都有广泛的应用。     

A molecular dynamics approach in simulations of fluid-solid particles flow

In the paper a discrete system of particles carried by fluid is considered in a planar motion. The volumetric density of particles is assumed to be small enough such that they can be treated within the framework of a molecular dynamics model. The fluid is then considered as a carrier of particles. The Landau-Lifshitz concept of turbulence is used to describe the fluctuating part of fluid velocity. This approach is applied to simulate different regimes (laminar and turbulent) and various states of particle motion (moving bed, heterogeneous flow, and homogeneous flow) using only two parameters, which have to be determined experimentally. These two parameters, found for a particular pipe and for a particular velocity from a simple experiment, then can be used for other pipe diameters and different velocities. The computer simulations performed for the flow of particles in pipes at different flow velocities and different pipe diameters agree favorably with experimental observations of the type of flow and critical velocities identifying transitions from one type to another. Received: 8 January 1999     

Preliminary dust-impact risk study for the “Solar Probe” spacecraft

Solar Probe is a mission currently under study, funded by the NASA's Office of Space Science—Sun–Earth Connection theme. This mission seeks to achieve the first visit to the Sun to explore the physical phenomenon that occurs at close proximity to our star. The mission requires the spacecraft to follow a polar orbit around the Sun with a perihelion of four (4) solar radii. A flyby at this close distance from the Sun will put the spacecraft under extraordinary environmental loads. One of the concerns is the effect that interplanetary and interstellar dust will have on the integrity of the spacecraft. The maximum dust impact velocity is expected to be around 500 km/s. This velocity is well above current experimental capabilities—more than an order of magnitude higher. For this reason, numerical simulations appear to be the best tool to determine the expected level of damage generated by the solar dust on the structural components and instruments of the Solar Probe spacecraft. Presented here are the results of the analysis of the dust environment to be experienced by the spacecraft and the shielding design parameters for different components. The design parameters of various structural components and instruments were used to conduct computer simulations using CTH to study shielding concepts.     

3D-analysis of the effect of interfacial debonding on the plastic behaviour of two-phase composites

The present paper deals with the interfacial debonding processes in Al/SiC metal matrix composites, by using 3D finite element calculations on representative cells. The reinforcements are considered as elastic, while the behaviour of the matrix is described by an elastoviscoplastic law. The debonding of the reinforcement is allowed for by using a non-linear elastic dependence between the stress vector and the separation vector at the interface. The results obtained show that the macroscopic behaviour of the composite depends to a large extent on the ratio between the the normal and tangential strength of the interface and the characteristic lengths defining the geometry of the reinforcements.     

Interparticle Collision of Particle Composites—Finite and Discrete Element Simulations

Three different cases of interparticle collisions were simulated to observe the fragmentation mechanisms of composite particles. It was found that the cracking mechanism in interparticle collisions is different from that observed in particle-wall collisions. By means of DEM simulations, it was observed that the primary interparticle bonds break in both tension and shear. Depending on the type of interparticle collisions, cracks and fragments are generated. In general, finer fragments are generated around the impact site of the particles and are surrounded by larger fragments. From DEM simulations, it was found for the most part that the impacting particles exhibit more damage than the stationary particles. The symmetrical loading showed almost the same amount of damage to both types of particles. The discontinuous nature of the material and the unsymmetrical loading caused unsymmetrical damages (crack patterns). In unsymmetrical loadings, the impacting particle was more damaged and had more cracks than the stationary particle.     

Studies on sputtering process of multicomponent Zr-Ti-Cu-Ni-Be alloy thin films

Sputter deposition process of a multicomponent Zr-Ti-Cu-Ni-Be metallic alloy has been studied experimentally and by numerical simulations. Monte-Carlo simulations were performed using a model based on thermalization and diffusion of sputtered atoms. Incident energy and angle of sputtered atoms on substrate were obtained from simulations. The incident angular distribution was observed to be a normal distribution at all sputtering pressures. Average incident kinetic energy of the condensing atoms on the substrate was observed to be 0.2-0.3 eV indicating most of them are thermalized. Simulations were extended to predict compositional variations in films prepared at various process conditions. These results were compared with composition of films determined experimentally using Rutherford Backscattering Spectrometry (RBS). Contents of Zr, Ti, Cu and Ni quantified using RBS were in moderate agreement with the simulated composition. Be could not be quantified accurately by RBS largely due to very low energy peak of Be in the spectrum. These studies are shown to be useful in understanding the complexities in multicomponent sputtering.