Systems design of high performance stainless steels I. Conceptual and computational design

Application of a systems approach to the computational materials design led to the development of a high performance stainless steel. The systems approach highlighted the integration of processing/structure/property/ performance relations with mechanistic models to achieve desired quantitative property objectives. The mechanistic models applied to the martensitic transformation behavior included the Olson–Cohen model for heterogeneous nucleation and the Ghosh–Olson solid-solution strengthening model for interfacial mobility. Strengthening theory employed modeling of the coherent M₂C precipitation in a BCC matrix, which is initially in a paraequilibrium with cementite condition. The calibration of the M₂C coherency used available small-angle neutron scattering (SANS) data to determine a composition-dependent strain energy and a composition-independent interfacial energy. Multicomponent pH-potential diagrams provided an effective tool for evaluating oxide stability. Constrained equilibrium calculations correlated oxide stability to Cr enrichment in the metastable spinel film, allowing more efficient use of alloy Cr content. The composition constraints acquired from multicomponent solidification simulations improved castability. Then integration of the models, using multicomponent thermodynamic and diffusion software programs, enabled the design of a carburizable, secondary-hardening martensitic stainless steel for advanced bearing applications. This revised version was published online in June 2006 with corrections to the Cover Date.     

Digital system simulation based on a computational model

Simulation in digital system design is primarily used for validating the design and predicting performance. While the simulation model of an operational system can be validated by comparing the simulated behaviour with that of the actual system, particular care is required in the representation in the case of design simulation. System design simulation implies that the design and simulation models be the same or be derivable from one another. Digital systems carry out computations. In this paper, a powerful operational semantic model for computation, referred to as aQ-sequence, is introduced and used as the formal basis for design and simulation. TheQ-sequence is a multilevel model capable of representing the system design at any one of several levels of detail and is powerful enough to represent procedural or non-procedural and synchronous or asynchronous computations. TheQ-sequence enforces a structured approach to system design, the design beginning at the top and proceeding through successive levels of detail. Design problems such as register clashes and timing hazards are formally modelled using theQ-sequence.     

Towards a taxonomy for multiscale methods in computational mechanics: building blocks of existing methods

Existing multiscale methods in computational mechanics are analyzed with respect to their computational building blocks, considering methods in both solid and fluid mechanics. From this analysis, a step towards a taxonomy for multiscale methods in computational mechanics is taken. The present article is not intended as a closed story; it is rather hoped that it may provide some basis for future discussions. Moreover, it might even provide a point of view to more clearly identify differences and similarities in the variety of multiscale methods currently existing or being developed in the future. The methods or their building blocks, respectively, are investigated with a view on their multiscale features regarding the underlying problem, spatial scale processing, and temporal scale processing. As expected, it turns out that the mechanics of the underlying problem strongly influences the necessary building blocks of an adequate multiscale method.     

Effects of connecting sequences of building blocks on reticular synthesis of covalent organic frameworks

The principle of reticular chemistry has been widely used to guide the design of crystalline porous materials such as metal organic frameworks(MOFs)and covalent organic frameworks(COFs).While in the early strategies only the symmetries of the building blocks were considered for reticular synthesis of COFs,recently a few researches on COFs with hierarchical porosities indicate that connecting sequence of building blocks also plays a crucial role in determining crystalline structures of COFs.However,this important phenomenon has not been systematically investigated yet.In this article,a model system has been established to demonstrate how different connecting sequences of two C_2v-symmetric building blocks lead to the formation of four two-dimensional(2D)COFs with distinct framework structures.To verify this concept,target synthesis was conducted to produce three COFs,whose structures were confirmed by powder X-ray diffraction and pore size distribution analysis.     

Fundamental building blocks for molecular biowire based forward error-correcting biosensors

This paper describes the fabrication, characterization and modeling of fundamental logic gates that can be used for designing biosensors with embedded forward error-correction (FEC). The proposed logic gates (AND and OR) are constructed by patterning antibodies at different spatial locations along the substrate of a lateral flow immunosensor assay. The logic gates operate by converting binding events between an antigen and an antibody into a measurable electrical signal using polyaniline nanowires as the transducer. In this study, B.?cereus and E.?coli have been chosen as model pathogens. The functionality of the AND and OR logic gates has been validated using conductance measurements with different pathogen concentrations. Experimental results show that the change in conductance across the gates can be modeled as a log-linear response with respect to varying pathogen concentration. Equivalent circuits models for AND and OR logic gates have been derived based on measured results.     

Supporting product architecture design using computational design synthesis with network structure constraints

A product’s architecture can affect many aspects of product and process quality, from technical performance to the design effort required, production costs and satisfaction of later lifecycle requirements. This paper explores how computational tools can augment creative methods in product architecture design. Based on an empirical study aiming to understand the context of product architecture design, a new computational method is proposed to support this activity. In the method, product architectures—networks of components linked by connections—can be synthesised using constraints on the structure of the network to define the set of ‘realisable’ architectures for a product. An example illustrates how the method might be used on a real design problem, including the construction of an appropriate set of network structure constraints and the identification of promising architectures from the synthesis results. Preliminary evaluation of the method’s usability, assessed through a laboratory experiment, and its utility, assessed through application to a real historical design problem, supported by initial validation by an engineer from the case study company, suggests that the method has value for engineering design practice.     

Conceptual design and the simulation of final cooling section for a muon collider

The scheme of final cooling for muon beams, based on using current-carrying liquid-lithium rods, is discussed. The dynamics of particles in the course of cooling taking into account the non-paraxial motion has been studied with the help of computer simulation. It is suggested to minimize the effective increase of the longitudinal emittance caused by fluctuations of ionization losses and large angular spread, by the rotation of the longitudinal phase-space portrait for arranging self-action. We have considered the non-dissipative multiple successive full emittance redistribution from the longitudinal dimension to transverse one, necessary for cooling of all degrees of freedom. This redistribution is based on special rotations of the particle six-dimensional phase space by the beam division in several streams and their consequent merging with the minimum increment of full emittance and minimal beam losses taking into account their local phase-space density. Some of the basic technical parameters of the cooling system elements have been estimated.     

Ultrasound simulation of complex flow velocity fields based on computational fluid dynamics

In this work, a simulation environment for the development of flow-related ultrasound algorithms is presented. Ultrasound simulations of realistic Doppler signals require accurate modeling of blood flow. Instead of using analytically described flow behavior, complex blood movement can be derived from velocity fields obtained with computational fluid dynamics (CFD). By further modeling blood as a collection of point scatterers, resulting RF-signals can be efficiently retrieved using an existing ultrasound simulation model. The main aim of this paper is to elaborate on creating CFD-based phantoms for ultrasound simulations. The coupling of a computed flow field with an ultrasound model offers flexible control of flow and ultrasound imaging parameters, beneficial for improving and developing imaging algorithms. The proposed method was validated in a straight tube with a stationary parabolic velocity profile and further demonstrated by an eccentrically stenosis carotid bifurcation. The estimated flow velocities are in good agreement with the CFD reference, both for color flow imaging and pulsed-wave doppler simulations. The presented method can also be extended to include wall mechanics simulations in future work.     

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production (>1,000 T·year^–1) of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics (CFD) calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor.

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Conceptual and computational advances in multiple-scattering electronic-structure calculations

A physically transparent transformation of the Korringa-Kohn-Rostoker (KKR or multiple-scattering) method into a tightbinding form is described. The transformation replaces the complicated, slowly decaying, traditional KKR structure constants by exponentially decaying “tight-binding” parameters. The main computational effort consists in the inversion of sparse matrices and scales for surfaces and interfaces, i.e. for systems with two-dimensional periodicity, linearly with the number of layers. This gives the opportunity to treat high-indexed surfaces as an approximation for almost isolated surface steps. Additional adatoms on surfaces and at steps can also be treated and it is discussed that reliable atomic forces and geometric arrangements can be obtained.     

Quantification of margins and uncertainties: Conceptual and computational basis

In 2001, the National Nuclear Security Administration of the U.S. Department of Energy in conjunction with the national security laboratories (i.e., Los Alamos National Laboratory, Lawrence Livermore National Laboratory and Sandia National Laboratories) initiated development of a process designated Quantification of Margins and Uncertainties (QMU) for the use of risk assessment methodologies in the certification of the reliability and safety of the nation's nuclear weapons stockpile. This presentation discusses and illustrates the conceptual and computational basis of QMU in analyses that use computational models to predict the behavior of complex systems. The following topics are considered: (i) the role of aleatory and epistemic uncertainty in QMU, (ii) the representation of uncertainty with probability, (iii) the probabilistic representation of uncertainty in QMU analyses involving only epistemic uncertainty, and (iv) the probabilistic representation of uncertainty in QMU analyses involving aleatory and epistemic uncertainty.     

双锥流量计实验研究与计算模拟

提出的双锥流量计是一种新型的差压式流量计.采用CFD软件Fluent模拟计算管内流体绕流双锥节流件结构时的流动情况,得到流量与差压信号之间的关系.对几种特定直径比β为0.4,0.5,0.6的双锥流量计进行实验研究.结果表明,实验与模拟基本一致,并且具有量程比大,直管段要求短,压损小等优点.     

基于压电陶瓷的引信物理电源的建模与设计

压电陶瓷能将弹药发射环境中的机械能转换为电能,压电电源就是基于此特性为引信供电的环境能源。提出一种压电发电建模方法,利用其对引信压电电源的发电特性进行了理论研究。共包括两个步骤:利用总能量求偏导法推导出并联压电叠堆产生的电压、电荷及电能公式;将压电结构发电模型等效为电路形式,利用电路知识分析得到压电电源的电能输出表达式。然后利用MATLAB软件进行了数值仿真分析,最后以所得理论模型为指导、以最大化提高发电量为目的进行压电电源的设计。     

Monodispersed spherical colloids of Se@CdSe: synthesis and use as building blocks in fabricating photonic crystals

Monodispersed spherical core-shell colloids of Se@Ag(2)Se have been exploited as a chemical template to synthesize Se@CdSe core-shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag(+) by Cd(2+) in methanol at 50 degrees C to complete the conversion within 150 min. The orthorhombic structure of beta-Ag(2)Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to beta-Ag(2)Se by reacting with AgNO(3) in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core-shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.     

Novel bioinorganic nanostructures based on mesolamellar intercalation or single-molecule wrapping of DNA using organoclay building blocks

Nanosheets or nanoclusters of aminopropyl-functionalized magnesium phyllosilicate (AMP) were prepared in water by exfoliation and used as structural building blocks for the preparation of DNA-based hybrid nanostructures in the form of ordered mesolamellar nanocomposites or highly elongated nanowires, respectively. The former consisted of alternating layers of single sheets of AMP interspaced with intercalated monolayers of intact double-stranded DNA molecules of relatively short length ( approximately 700 base pairs) that were accessible to small molecules such as ethidium bromide. In contrast, the nanowires comprised isolated micrometer-long molecules of lambda-DNA or plasmid DNA that were sheathed in an ultrathin organoclay layer and which were either protected from or remained accessible to endonuclease-mediated clipping depending on the extent of biomolecule wrapping. Both types of hybrid nanostructures showed a marked increase in the DNA melting (denaturation) temperature, indicating significant thermal stabilization of the confined biomolecules. Our results suggest that nanoscale building blocks derived from organically modified inorganic clays could be useful agents for enhancing the chemical, thermal, and mechanical stability of isolated molecules or ensembles of DNA. Such constructs should have increased potential as functional components in bionanotechnology and nonviral gene transfection.     

An efficient evolutionary structural optimization method with smooth edges based on the game of building blocks

Although bi-directional evolutionary structural optimization (BESO) has the advantages of a simple concept and clear-cut solutions, the edges of the optimal solution are normally non-smooth. This article proposes an approach that directly represents the smooth structure using finite elements. The pseudo-auxiliary line is introduced to make the staggered boundary approach a smooth one, and a rule is presented to make the boundary element deformable to describe the structure’s edges. To improve the efficiency, the game of building blocks is incorporated into the classical BESO algorithm. A set of basic blocks is predefined and is positioned in a suitable location to assemble the optimal structure. In this way, the optimal structure has better mechanical performance and smooth edges with acceptable computational cost. The roundness of corners is easily controlled by adjusting the configuration of the basic blocks. Several two- and three-dimensional numerical examples investigate the effects of the parameters of auxiliary lines and the shape of basic blocks on the boundary smoothness and optimization performance. The efficiency of the proposed method is justified through these examples.     

MIDAS/Building双塔大跨度连体建筑抗震设计

双塔大跨度连体建筑结构形式及受力较为复杂,其结构安全性设计特别是抗震设计尤为重要。以某双塔大跨度连体建筑为例,基于MIDAS/Building结构分析设计系统及SATWE对整体结构进行小震反应谱分析,考虑施工模拟及P-delta影响,计算其水平及竖向地震作用,得到整体结构受力与位移参数,并进行设计验算。通过比较两种软件计算结果,可以看出该工程各项指标均符合规范要求,具有良好的抗震性能。基于计算结果,提出一些改进措施,为类似结构的计算与抗震性能分析提供参考。