Layer-oriented adaptive optics for solar telescopes

First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80?arc sec in diameter. We propose to implement the layer-oriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems.     

Modular simulation tool for modelling JIT manufacturing

Since quantitative information is very helpful in implementing JIT production techniques, computer simulation can be a valuable tool in designing, implementing or changing JIT practices in a production system. Nowadays, existing simulation software incorporates modular programming and enhanced graphic systems for output representation. It enables users to generate modules that represent partial aspects of a JIT system. These modules, adequately modified and integrated, give researchers and practitioners the possibility to create complex models that can be applied to a variety of JIT systems or JIT production environments. A modular simulation tool, based on the modular capabilities of Witness, is introduced in this paper. As a module example, the feeder double-kanban line module is presented, which represents one of the core aspects of a JIT manufacturing system. Finally, module integration is illustrated by modelling a U-Shaped line. The experimentation and evaluation of the U-line allow one to appreciate how modular simulation can be a powerful tool in decision making, by enabling users to analyse systems configurations and operation rules before implementing them.     

MPiSIM: Massively parallel simulation tool for metallic system

We report a domain decomposition molecular dynamics (MD) for simulation on metallic systems based on distributed parallel computers. The method is a development of a spatial decomposition in 3-D space with the combination of link-cell and neighbor list techniques for enhanced efficiency. The algorithm has been successfully implemented on the Origin2000, Wolf, HP Examplar etc. various platforms. The scaling performance on these platforms will be discussed and several applications in metallic systems will also be given in the paper. This revised version was published online in June 2006 with corrections to the Cover Date.     

Three dimensional simulation of microstructure evolution for ceramic tool materials

The observation and scientific quantitative characterization of three dimensional microstructure evolution during sintering process of ceramic tool materials is important to investigate the influence of nano-particles on mechanical properties. The relationship between microstructure and mechanical properties of ceramic tool materials can be established to direct the development of nano-composite ceramic tool materials by the research of the grain growth, grain boundary migration, distribution of nano-particles and microstructure densification at the different sintering temperature and pressure. In this paper, a 3D Monte Carlo model of three-phase nano-composite ceramic tool material is built and applied to simulate the microstructure evolution during sintering process. In this model, the grain boundary energy of each phase and interfacial energy between two phases are taken into consideration as the driving forces for grain growth. The sintering temperature and pressure are successfully coupled into the Monte Carlo simulation model. The microstructure evolution of defect free three-phase nano-composite ceramic tool materials is successfully simulated at different sintering temperature and pressure. The simulation results show that the higher the sintering temperature is, the faster the grain growth. However, the sintering pressure has little effect on the grain growth.     

A simulation tool for virtual laboratory experiments in a WWWenvironment

Virtual instruments and distributed systems are of great interest to create advanced and flexible teaching and experimentation environments for measurement technologies at limited costs. Availability of simple and efficient technological supports to dissemination and remote use of virtual systems becomes attractive to increase the access to experimental practice without regard to the number of students and their location as well as the variety of instruments and measurement procedures directly available for experimentation     

Emergency department operations: The basis for developing a simulation tool

In recent years, hospitals have been vigorously searching for ways to reduce costs and improve productivity. One tool, simulation, is now widely accepted as an effective method to assist management in evaluating different operational alternatives. It can help improve existing Emergency Departments (EDs) and assist in planning and designing new EDs. In order to increase the acceptance of simulation in healthcare systems in general and EDs in particular, hospital management should be directly involved in the development of these projects. Such involvement will also bolster the simulation's credibility. In addition, it is important to simplify simulation processes as much as is reasonably possible and use visual aids or animation that will heighten users' confidence in the model's ability. This study lays the foundation for the development of a simulation tool which is general, flexible, intuitive, simple to use and contains default values for most of the system's parameters.     

Application of defect simulation as a tool for more efficient failure analysis

In modern VLSI processes, increasing process complexity has resulted in an exponential rise in the costs of thorough failure analysis. In this paper, we present a defect simulation-based failure analysis methodology, which can be used to significantly reduce both costs and turn-around time for failure analyses. The methodology is based on the ability to generate a defect dictionary, which can relate defect characteristics to some easily measurable symptoms of defect occurrence.     

Numerical simulation and design optimisation of an integrally-heated tool for composite manufacturing

Tooling design is crucial for the production of cost-effective and durable composite products. As part of the current search for cost reduction, integrally-heated tooling is one of the technologies available for ‘out-of-autoclave’ processing of advanced thermoset polymer composites. Despite their advantages, integrally-heated tools can suffer from uneven distribution of temperature, variability in heat flow rate and inconsistency in heating/cooling time. This research, therefore, investigates a number of design variables such as shape and layout of heating channels in order to improve the thermal performance of an integrally-heated tool. Design of Experiments (DoE) has been carried out using Taguchi’s Orthogonal Array (OA) method to set several combinations of design parameters. Each of these design combinations has been evaluated through numerical simulation to investigate heating time and mould surface temperature variation. The simulation results suggest that the layout of the channels and their separation play a vital role in the thermal performance. Signal-to-Noise (S/N) ratio and analysis of variance (ANOVA) have been applied to the results obtained to identify the optimal design combination of the integrally-heated tool. Statistical analysis reveals that the heating performance of an integrally-heated tool can be significantly improved when the channels’ layout is parallel. The shape of the channels has negligible effect and the distance between the channels should be determined based on the production requirement.     

CoilDesigner: a general-purpose simulation and design tool for air-to-refrigerant heat exchangers

A simulation and design tool to improve effectiveness and efficiency in design, and analysis of air to refrigerant heat exchangers, CoilDesigner, is introduced. A network viewpoint was adopted to establish the general-purpose solver and allow for analysis of arbitrary tube circuitry and mal-distribution of fluid flow inside the tube circuits. A segment-by-segment approach within each tube was implemented, to account for two-dimensional non-uniformity of air distribution across the heat exchanger, and heterogeneous refrigerant flow patterns through a tube. Coupled heat exchangers with multiple fluids inside different subsets of tubes can be modeled and analyzed simultaneously. A further sub-dividing-segment model was developed in order to address the significant change of properties and heat transfer coefficients in the single-phase and two-phase regime when a segment experiences flow regime change. Object-oriented programming techniques were applied in developing the program to facilitate a modular, highly flexible and customizable design platform and in building a graphic user-friendly interface. A wide variety of working fluids and correlations of heat transfer and pressure drop are available at the user's choice. The model prediction with CoilDesigner was verified against experimentally determined data collected from a number of sources.     

Numerical study of contact conditions in press hardening for tool wear simulation

In the press hardening industry, industrial and academic efforts are being directed toward predicting tool wear to realize an economical manufacturing process. Tool wear in press hardening is a tribological response to contact conditions such as pressure and sliding motion. However, these contact conditions are difficult to measure in-situ. Furthermore, press hardening involves high temperatures, and this increases the complexity of the tribo system. The present work investigated the contact conditions of press hardening with a commercial FE code (LS-DYNA) as a base for tool wear simulation. A press hardening experiment was established in industrial environments and evaluated through FE simulations. The numerical model was set up so as to approximate the manufacturing conditions as closely as possible, and the sensitivity with respect to the friction coefficients was examined. The influence of numerical factors such as the penalty value and mesh size on the contact conditions is discussed. The implementation of a modified Archard’s wear model in the FE simulation proved the possibility of tool wear simulation in press hardening. Finally, a comparison between the tool wear simulation and the measured wear depth is presented.     

Integrated simulation tool for quality support in the low-volume high-complexity electronics manufacturing domain

Low-volume high-complexity printed circuit board manufacturing is a highly dynamic domain because of prevailing global pressures. In such an evolving environment, quality issues caused by manufacturing defects are the major concern. The generation, detection and elimination of those defects further impact customer requirements and demands. Current practices in terms of identification and solution of quality issues have three major drawbacks: (i) the metrics used are not meaningful; (ii) several manual operations are involved; and (iii) there is no significant decision support. A novel integrated simulation tool for quality support in low-volume electronics manufacturing that overcomes these weaknesses is presented in this paper. The simulation tool supports current needs in the domain, i.e. knowledge capitalisation, waste reduction, right-first-time performance and agility, as well as the domain customer requirements, i.e. lead time, cost, quality and reliability. Quantitative results from a case study are presented as evidence of the usefulness of the tool in a real context. The results show that the approximately 80% non-value-added cost for the product studied is due to just two types of manufacturing defects. This outcome is key for root cause analysis based not only on defect quantity.     

The simplex simulation as a tool to reveal publication strategies and citation factors

Scientometrics - Scientists’ evaluations are commonly made by h-index calculated from citation levels of published papers. Although single index way is simple, synthetic, rapid and popular,...     

A simulation tool for the AC-DC transfer difference of thermalconverters at low frequencies

To find the reason for the AC-DC transfer differences of the planar multijunction thermal converter (PMJTC) at low frequencies, where temperature oscillation is present due to the lack of integration of the oscillating Joule heat, the coupled electro-thermal mathematical problem has been solved. The dynamic nonlinear model includes the temperature dependence of all material parameters, of heat conduction through the air and radiation losses. The results of the simulation are compared with those of measurements using a sampling voltmeter with special software as a reference. A new design is proposed to improve the performance of the PMJTC at low frequencies     

A new approach for the simulation of skeletal muscles using the tool of statistical mechanics

The structure of a skeletal muscle is dominated by its hierarchical architecture in which thousands of muscle fibres are arranged within a connective tissue network. The single muscle fibres consist of many force‐producing cells, known as sarcomeres. These micro biological engines are part of a motor unit and contribute to the contraction of the whole muscle. There are a lot of questions concerning the optimisation of muscle strength and agility. Standard experimental investigations are not sufficient to answer these questions because they do not supply enough information. Additionally, these methods are limited because not enough material for testing is accessible. To overcome these problems, numerical testing tools can be an adequate alternative. From the mechanical point of view the material behaviour of muscles is highly non‐linear. They undergo large deformations in space, thereby changing their shape significantly, so that geometrical nonlinearity has to be considered. Many authors use continuum‐based approaches in combination with the finite element method to describe such material behaviour. However, models of this kind require realistic constitutive relations between stress and strain which are difficult to determine in an inhomogeneous material. Furthermore, biomechanical information cannot be fully exploited in these models. The present approach is crucially based on the use of the finite element method. The material behaviour of the muscle is split into a so‐called active and a passive part. To describe the passive part special unit cells consisting of one tetrahedral element and six truss elements have been derived. Embedded into these unit cells are further truss elements which represent bundles of muscle fibres. Depending on the discretisation it is possible to simulate the material behaviour of e.g. artery walls characterised by oriented fibres or soft tissue including only non‐oriented fibres. In summary, the present concept has the advantage that a three‐dimensional model is developed which allows us take into account many physiological processes at the micro level.     

Development of tool for physical simulation of skin formation during investment casting of nickel-based superalloys

Development of investment casting process has been always a challenge for manufacturers of complex shape parts with thin elements. Particularly, misruns often occur in the as-cast complex shape parts due to the formation of solid skin by freezing of melt in contact with colder ceramic mould. This work presents a new tool for physical simulation of skin formation during investment casting. Special ceramic tubes are designed and fabricated from the material used for the manufacturing of ceramic moulds for investment casting. Melting/solidification experiments are carried out in the thermo-mechanical simulator, where the melt is contained in the ceramic tube, which is heated to the temperature of ceramic mould in investment casting. Detailed microstructural characterization of the solidified specimens is performed; the obtained results predict the thickness of skin and its microstructure. This concept is applied to investment casting of complex shape nozzle guide vanes from the Mar-M247 Ni-based superalloy. Experimental casting trials are performed, and the outcomes of physical simulation tool are validated against experimental results.     

A system dynamics-based decision-making tool and strategy optimization simulation of green building development in China

Clean Technologies and Environmental Policy - Green building has emerged as a new type of building to mitigate the conflict between the rapid expansion of buildings and the deteriorating ecological...     

Application of DQM as an effective simulation tool for buckling response of delaminated composite plates

The application of differential quadrature method (DQM), as an effective and robust numerical method, for the analysis of buckling of delaminated composite plates is introduced. The analysis investigated the response of laminated composite plates hosting a circular or an elliptical delamination. The delaminations were assumed to be fairly thinner than the plate hosting them, and thus, they could be treated as plates with clamped edges. Several case studies were used to verify the integrity of DQM in predicting the buckling strain of the plates. The investigation included the examination of several parameters influencing the buckling strength. The results obtained from DQM were compared with those obtained by the Rayleigh–Ritz and finite element solutions of other workers.     

Numerical simulation tool for paving block structures assessed by means of full-scale accelerated pavement tests

Block pavements are an attractive alternative to asphalt and concrete pavements, especially in communal areas. Architects and urban planners would like to take advantage of various shapes, colours and textures of paving blocks in order to achieve a higher quality of urban space if the performance of block pavements could be better predicted to avoid large horizontal displacements of chipped stone corners and rutting. Unfortunately, the computational performance prediction of paving block structures is more complex than that for flexible pavements with homogeneous surface layers of asphalt concrete. The influence of the large number of vertical joints between paving blocks on the overall mechanical performance has not been considered sufficiently within computational tools yet. The proposed numerical simulation tool is able to take into account the complex mechanical behaviour of sand-filled joints as well as the non-linear mechanical behaviour of the underlying base courses. Joints are modelled using a Mohr–Coulomb-type friction model with the normal stresses non-linearly related with joint opening. Three different experimental set-ups were developed for the identification of the model parameters. The base behaviour was modelled using the Drucker–Prager cap model. The paper shows that the proposed tool predicts reasonable deformations and stresses in block pavements. The results of the simulations were compared with measured stresses from the full-scale accelerated pavement testing and a good agreement was observed.