Level Of Detail In Models Research Articles

A guide for building hospital simulation models

Healthcare systems aspire to offer an effective and efficient provision of health service without compromising on quality. Hospitals are important links in the healthcare service chain, and Operational Research/Management Science methods have an essential role to play in helping to improve the planning and management of hospitals. In particular, simulation methods have been widely used by healthcare researchers and practitioners. This paper is written as a guide for building hospital simulation models and is based on the author's experience and the published literature. Two points of view emerge in this paper supporting each other: a conceptual view and a technical view. Initially, conceptual issues are discussed, including topics such as framing and specification, level of model detail, and data requirements. Second, a technical point of view buttresses the discussion from the methodological side and three simulation methods are evaluated, namely: Discrete Event Simulation, System Dynamics, and Agent-Based Simulation.

Analysis on Using Average Curvature Algorithm to Simplify the Mapping of Large-Scale Battlefield Terrain Space Grids with LOD and its Errors

When mapping large-scale battlefield terrain, in order to make a real-time show it on the computer it is required to keep the vector data (points, lines, areas) at the high curvature and delete the vector data at the low curvature as much as possible. This article puts forward a simplified algorithm to calculate the average curvature of the space mesh points with level of detail (LOD) model technique as well as the visualization implementation of this algorithm. Then according to this algorithm, work out the curvature value of the mesh points, delete the center points of the low curvature and triangularize the cavity left so as to simplify LOD model and reduce dramatically the number of the vector data (points, lines, areas) in the field of view of the large-scale battlefield terrain. Experiments show the average curvature algorithm put forward in this article can better solve the contradiction between the big vector data and the limited real-time processing capacity of the computer. As a result, it can meet the requirements of mapping great number of real-time data of the large-scale battlefield terrain by 3 D visualization.

Automatic simplification and visualization of 3D urban building models

A high-fidelity and real-time rendering urban building model was implemented through the simplification of 3D building groups. An approach to simplify a single 3D building has been addressed for generating a levels-of-detail (LOD) building model in nearby urban regions. In farther regions, a single-chain cluster was used to collect footprints of neighboring building groups. To effectively merge footprints, the Delaunay triangulation and line simplification were employed. As a result, a coarse LOD model was created based on generalized footprints and building heights. Our approach not only preserved urban legibility (Lynch, 1960), which is effective for viewers visually navigating through an urban environment, but also implemented dynamic visualization of 3D city models.

An Efficient Point Cloud Management Method Based on a 3D R-Tree

Vehicle-borne laser-scanned point clouds have become increasingly important 3D data sources in fields such as digital city modeling and emergency response management. Aiming at reducing the technical bottlenecks of management and visualization of very large point cloud data sets, this paper proposes a new spatial organization method called 3DOR-Tree, which integrates Octree and 3D R-Tree data structures. This method utilizes Octree's rapid convergence to generate R - T ree leaf nodes, which are inserted directly into the R - T ree, thus avoiding time-consuming point-by-point insertion operations. Furthermore, this paper extends the R - T ree structure to support LOD (level of detail) models. Based on the extended structure, a practical data management method is presented. Finally, an adaptive control method for LODS of point clouds is illustrated. Typical experimental results show that our method possesses quasi-real-time index construction speed, a good storage utilization rate, and efficient visualization performance.

Multi-objective optimization of design and testing of safety instrumented systems with MooN voting architectures using a genetic algorithm

This paper presents the optimization of design and test policies of safety instrumented systems using MooN voting redundancies by a multi-objective genetic algorithm. The objectives to optimize are the Average Probability of Dangerous Failure on Demand, which represents the system safety integrity, the Spurious Trip Rate and the Lifecycle Cost. In this way safety, reliability and cost are included. This is done by using novel models of time-dependent probability of failure on demand and spurious trip rate, recently published by the authors. These models are capable of delivering the level of modeling detail required by the standard IEC 61508. Modeling includes common cause failure and diagnostic coverage. The Probability of Failure on Demand model also permits to quantify results with changing testing strategies. The optimization is performed using the multi-objective Genetic Algorithm NSGA-II. This allows weighting of the trade-offs between the three objectives and, thus, implementation of safety systems that keep a good balance between safety, reliability and cost. The complete methodology is applied to two separate case studies, one for optimization of system design with redundancy allocation and component selection and another for optimization of testing policies. Both optimization cases are performed for both systems with MooN redundancies and systems with only parallel redundancies. Their results are compared, demonstrating how introducing MooN architectures presents a significant improvement for the optimization process.

Multidimensional analysis of fission gas transport following fuel element failure in sodium fast reactor

Abstract Significant progress in several areas will have to be made to achieve the required technological and safety standards for future Gen. IV reactors, including both novel experimental methods (starting with separate-effect, then followed by integral experiments) and high performance computational models characterized by the necessary level of modeling detail and high accuracy of predictions. Furthermore, it is important that the experimental and theoretical/computational research complement each other, so that the results of measurements could be directly used for model validation purposes, whereas the results of simulations should provide input to identify modeling uncertainties and provide guidelines for prioritizing future experiments. The purpose of this paper is to present the modeling concept for mechanistic computer simulations of the injection of a jet of gaseous fission products into a partially blocked SFR coolant channel following localized cladding overheat and breach. A three-dimensional model of gas/liquid-sodium interaction has been developed based on a multifield modeling framework implemented in the NPHASE-CMFD code. The boundary conditions used as input to NPHASE-CMFD have been obtained by averaging the results of direct numerical simulations (DNS) performed using the PHASTA code. The novel aspects of the results discussed in the paper include the demonstration of advantages of using a multiscale approach to model local phenomena governing gas/liquid-sodium two-phase flow inside reactor coolant channels following cladding breach, as well as the observations about areas where future experiments are needed to improve the predictive capabilities of two-phase flow models.

Large-scale forest rendering: Real-time, realistic, and progressive

Real-time rendering of large-scale forest landscape scenes is important in many applications, such as video games, Internet graphics, and landscape and cityscape scene design and visualization. One challenge in the field of virtual reality is transferring a large-scale forest environment containing plant models with rich geometric detail through the network and rendering them in real time. We present a new framework for rendering large-scale forest scenes realistically and quickly that integrates extracting level of detail (LOD) tree models, rendering real-time shadows for large-scale forests, and transmitting forest data for network applications. We construct a series of LOD tree models to compress the overall complexity of the forest in view-dependent forest navigation. A new leaf phyllotaxy LOD modeling method is presented to match leaf models with textures, balancing the visual effect and model complexity. To progressively render the scene from coarse to fine, sequences of LOD models are transferred from simple to complex. The forest can be rendered after obtaining a simple model of each tree, allowing users to quickly see a sketch of the scene. To improve client performance, we also adopt a LOD strategy for shadow maps. Smoothing filters are implemented entirely on the graphics processing unit (GPU) to reduce the shadows' aliasing artifacts, which creates a soft shadowing effect. We also present a hardware instancing method to render more levels of LOD models, which overcomes the limitation of the latest GPU that emits primitives into only a limited number of separate vertex streams. Experiments show that large-scale forest scenes can be rendered with smooth shadows and in real time.

Quantitative models of signal transduction networks

Receptor-mediated signal transduction networks, comprised of multiple biochemical pathways, control cell responses and are therefore central to normal and aberrant physiological processes. An appreciation for the inherent complexities of these networks has matured in recent years, to the point where it is now apparent that experimental measurements will need to be combined with computational modeling and analysis to best interpret and predict how individual mechanisms (protein-protein interactions, enzymatic reactions, etc.) are integrated at the network level. To progress along these lines, there is a major barrier to overcome: although a deep mechanistic understanding of signal transduction has been achieved, data sets of a suitably quantitative nature are still lacking. Based on our efforts to systematically acquire and analyze such measurements, we contend that the level of detail in models of signaling networks ought to be limited by the availability of quantitative data, rather than by the much greater availability of qualitative information about signaling interactions. Although this approach is sensible from a data-driven modeling perspective, it is controversial because it gives the false impression that molecular-level details are being ignored.

Black-box decomposition approach for computational hemodynamics: One-dimensional models

Increasing efforts exist in integrating different levels of detail in models of the cardiovascular system. For instance, one-dimensional representations are employed to model the systemic circulation. In this context, effective and black-box-type decomposition strategies for one-dimensional networks are needed, so as to: (i) employ domain decomposition strategies for large systemic models (1D–1D coupling) and (ii) provide the conceptual basis for dimensionally-heterogeneous representations (1D–3D coupling, among various possibilities). The strategy proposed in this article works for both of these two scenarios, though the several applications shown to illustrate its performance focus on the 1D–1D coupling case. A one-dimensional network is decomposed in such a way that each coupling point connects two (and not more) of the sub-networks. At each of the M connection points two unknowns are defined: the flow rate and pressure. These 2 M unknowns are determined by 2 M equations, since each sub-network provides one (non-linear) equation per coupling point. It is shown how to build the 2 M × 2 M non-linear system with arbitrary and independent choice of boundary conditions for each of the sub-networks. The idea is then to solve this non-linear system until convergence, which guarantees strong coupling of the complete network. In other words, if the non-linear solver converges at each time step, the solution coincides with what would be obtained by monolithically modeling the whole network. The decomposition thus imposes no stability restriction on the choice of the time step size. Effective iterative strategies for the non-linear system that preserve the black-box character of the decomposition are then explored. Several variants of matrix-free Broyden’s and Newton-GMRES algorithms are assessed as numerical solvers by comparing their performance on sub-critical wave propagation problems which range from academic test cases to realistic cardiovascular applications. A specific variant of Broyden’s algorithm is identified and recommended on the basis of its computer cost and reliability.

Modeling safety instrumented systems with Moo N voting architectures addressing system reconfiguration for testing

This paper addresses the modeling of probability of dangerous failure on demand and spurious trip rate of safety instrumented systems that include Moo N voting redundancies in their architecture. Moo N systems are a special case of k-out-of- n systems. The first part of the article is devoted to the development of a time-dependent probability of dangerous failure on demand model with capability of handling Moo N systems. The model is able to model explicitly common cause failure and diagnostic coverage, as well as different test frequencies and strategies. It includes quantification of both detected and undetected failures, and puts emphasis on the quantification of common cause failure to the system probability of dangerous failure on demand as an additional component. In order to be able to accommodate changes in testing strategies, special treatment is devoted to the analysis of system reconfiguration (including common cause failure) during test of one of its components, what is then included in the model. Another model for spurious trip rate is also analyzed and extended under the same methodology in order to empower it with similar capabilities. These two models are powerful enough, but at the same time simple, to be suitable for handling of dependability measures in multi-objective optimization of both system design and test strategies for safety instrumented systems. The level of modeling detail considered permits compliance with the requirements of the standard IEC 61508. The two models are applied to brief case studies to demonstrate their effectiveness. The results obtained demonstrated that the first model is adequate to quantify time-dependent PFD of Moo N systems during different system states (i.e. full operation, test and repair) and different Moo N configurations, which values are averaged to obtain the PFD avg . Also, it was demonstrated that the second model is adequate to quantify STR including spurious trips induced by internal component failure and by test itself. Both models were tested for different architectures with 1≤ N≤5 and 2≤ M≤5 subject to uniform staggered test. The results obtained also showed the effects that modifying M and N has on both PFD avg and STR, and also demonstrated the conflicting nature of these two measures with respect to one another.

Feature Aware Multiresolution Animation Models Generation

In computer graphics, investigation has been made in many years in LOD (Level of Detail) models generation to alleviate the workload of visualization processing. However, most of the existing algorithms only focus on static models , and very little works are to deal with animation models. In this paper, we propose a feature aware method for generating multiresolution animation models. By the method we first use a normal deviation based quadric error metric to generate a base hierarchy , and then update the edge contraction order progressively from the first frame to the last one . Thus, we can get the simplified versions for each frame in the animation sequence . Finally , a mesh optimization method is proposed to allow visual distortion of the simplified models to be further alleviated. We demonstrate that our method works efficiently and can generate better approximations with well-preserved features for each frame than previous methods.

3D 문화재 데이터의 LOD 기반 상세정보 브라우징 기술

본 논문에서는 건조물 문화재의 대용량 3D 데이터를 LOD(Level of Detail) 모델로 가공하고, 이를 기반으로 시스템의 메모리 제약을 완화시켜 사용자에게 3D모델에 대해 정밀한 상세정보를 제공하는 방법을 제안한다. 제안한 방법은 먼저 변형한 AOSP 알고리즘으로 3D 데이터에 대한 계층적 공간구조를 생성하고, 생성된 공간구조에 대한 표면 간략화를 수행하여 LOD 모델을 생성한다. 다음으로 간략화 된 LOD 모델에서 사용자의 관심 영역을 추출하고, 추출된 영역에 대하여 국부 상세화를 수행한 후 최종적으로 관심영역에 원 모델과 동일한 표면의 상세정보를 형성하여 렌더링 한다. 제안한 방법의 성능 평가를 위하여 정밀하게 실측된 건조물 문화재의 3D 스캔 데이터들로 실험을 진행하였다. 제안한 방법은 간략화 된 LOD 모델의 메쉬(mesh) 구조를 기반으로 관심 영역에서만 원 모델과 동일한 메쉬 구조를 형성함으로써, 기존의 모든 데이터를 메모리에 적재하여 렌더링을 하는 방법과 동일한 상세정보를 제공하면서도 메모리의 사용량을 평균적으로 45% 절감하여, 제원이 낮은 보급형 PC 환경에서도 대용량의 건조물 문화재를 정밀하게 관찰할 수 있었다. In this paper, we propose the new method that offer detailed-information through relax the system memory limitation about 3D model to user. That method based on making LOD(Level of Detail) model from huge 3D data of structure cultural assets. In our method as transformed AOSP algorithm, first of all it create the hierarchical structure space about 3D data, and create the LOD model by surface simplification. Then it extract the ROI(Region of Interest) of user in simplified LOD model, and then do rendering by original model and same surface detailed-information after process the local detailed in extracted region. To evaluate the proposed method, we have some experiment by using the precise 3D scan data of structure cultural assets. Our method can offer the detailed-information same as exist method, and moreover 45% reduced consumption of memory experimentally by forming mesh structure same as ROI of simplified LOD model. So we can check the huge structure cultural assets particularly in general computer environment.

3D streaming based on multi-LOD models for networked collaborative design

This paper presents a method of 3D streaming for collaborative design in networked environment. It is derived from the concept of multiple levels of detail (LODs) in product information. A CAD model is decomposed into triangular meshes grouped by its design features. Aggregating the mesh data in different manners produces models at various LODs. The method allows incremental transmission of 3D model from a coarse representation to a finer one through a sequence of LODs specified by the sender. Each transmission only consists of the mesh difference between two LOD models. A prototyping platform with a proprietary client–server framework is developed using Java™ technologies to demonstrate the effectiveness of the method. A lightweight client can progressively receive the streaming data while rendering the corresponding model without implementing complex CAD functions. A scenario of sharing product information among multiple participants in collaborative design illustrates the streaming process. This work provides a useful mechanism that improves the efficiency, effectiveness, as well as security in sharing large CAD files over the network.

Multi-agent collaborative 3D design with geometric model at different levels of detail

This paper presents a scheme for collaborative 3D design using product model at various levels of detail (LODs). Design features are selectively hidden at each level from certain participants, depending on their actual needs and individual accessibility in the collaboration. A tree data structure represents the feature hierarchy of CAD construction, the link between feature and LOD, and 2D mesh data for display control of each feature. An XML/XSLT-based approach is proposed to enable real-time visualization of different LOD models in distributed environment. A collaborative design system is implemented using multi-agent technologies, which focuses on function design of each agent, interactions among agents, the client–server structure, and generation of the LOD data using the XML/XSLT approach. A scenario of synchronous 3D mold assembly demonstrates that geometric categorization of product model provides an operational mechanism for assuring security of information sharing in engineering collaborations over the Internet. It also validates the effectiveness of the agent technologies for automating complex engineering activities.

Reliability of building embodied energy modelling: an analysis of 30 Melbourne case studies

Building design decisions are commonly based on issues pertaining to construction cost, and consideration of energy performance is made only within the context of the initial project budget. Even where energy is elevated to more importance, operating energy is seen as the focus and embodied energy is nearly always ignored. For the first time, a large sample of buildings has been assembled and analysed in a single study to improve the understanding of the relationship between energy and cost performance over their full life cycle. Thirty recently completed buildings in Melbourne, Australia have been studied to explore the accuracy of initial embodied energy prediction based on capital cost at various levels of model detail. The embodied energy of projects, elemental groups, elements and selected items of work are correlated against capital cost and the strength of the relationship is computed. The relationship between initial embodied energy and capital cost generally declines as the predictive model assumes more detail, although elemental modelling may provide the best solution on balance.

The application of the water resources modeling platform from strategic planning through to operational control

The concepts of a water resources modeling approach which caters for the varying levels of modeling detail required for broad strategic planning through to the short-term operation of reservoirs have been described by Mallory and van Vuuren [Mallory, S.J.L., van Vuuren, S.J., 2007. Integration of water resources modelling approaches for varying levels of decision-making. In: Fourth International Conference on Water Resources Management. WITPress, Wessex, UK]. This paper addresses the application of this approach in practice on South Africa’s Algoa system, a complex and strategically important catchment within South Africa. The Algoa system was modeled, firstly in reconnaissance mode to gain a broad understanding of the water requirements and the available water resource, then in systems analysis mode to take into account the actual operating rules applied in the catchment, and thirdly in short-term operation mode, to determine when restrictions should be imposed in order to avoid catastrophic failure of the system. The conclusion reached in this paper that this multi-tiered modeling approach is a useful tool for enhancing the understanding of decision makers and stakeholders of how the water resources in a catchment are managed and offers a considerable improvement in terms of the time and effort expended on setting up, running and maintaining several models each supporting it own niche in the decision-making framework.

Methodology for the Design of Man-Portable Power Generation Devices

An overview of a comprehensive methodology for the design of microfabricated fuel cell systems for portable power generation is presented. The methodology is based on a decomposition into three levels of modeling detail: (i) system-level models for process synthesis, (ii) intermediate-fidelity models for optimization of sizes and operation, and (iii) detailed computational fluid dynamics (CFD) models for geometry improvement. Process synthesis, heat integration, and layout considerations are addressed simultaneously through the use of lumped algebraic models, general enough to be independent of detailed design choices, such as reactor configuration and catalyst choice. At the intermediate-fidelity level, space-distributed models are used, which allow optimization of unit sizes and operation for a given process structure without the need to specify a detailed geometry. Finally, the use of detailed CFD facilitates geometrical improvements as well as the derivation and validation of modeling assumptions that are used in the system-level and intermediate-fidelity models.

Multi-objective genetic algorithm for optimization of system safety and reliability based on IEC 61508 requirements: A practical approach

This paper presents a practical approach for optimization by evolutionary computation of safety instrumented system design, based on safety and reliability measures, plus life cycle cost. The standard IEC 61508 establishes the necessity of this kind of systems to meet specific safety integrity requirements, expressed in terms of safety integrity levels (SIL). The SIL is determined in terms of average probability of failure on demand (PFDavg) for control systems that operate in demand mode. The optimization executed takes into account the level of modelling detail contemplated by the standard, including multiple failure modes, diagnostic coverage, and common cause failures. This study addresses the case of series-parallel systems. Optimization is approached by treating the problem as one of redundancy and reliability allocation, together with testing intervals specifications. Modelling is made through fault tree analysis with house events. The multi-objective genetic algorithm proposed by Fonseca and Fleming is used as the optimization technique.

Wind Turbine Modelling for Power System Stability Analysis—A System Operator Perspective

In recent years, computer models of wind turbines for power system stability studies have been developed and supplied to power system operators worldwide. The development of such models is of particular significance for stability studies on systems experiencing very large penetrations of wind energy such as the electricity system in the Republic of Ireland. There is a large variation in the complexity of models developed and no widespread agreement on the level of modelling detail required. The use of multiple wind turbine models for large-scale stability studies is also proving difficult. In addition, the majority of models have not been validated. This paper will examine model development and use from the perspective of the Irish grid operator. The validation of developed models will be discussed, and a generic modelling approach will be proposed for large-scale power system stability investigations.

Low-voltage ride-through of a full converter wind turbine with permanent magnet generator

The low-voltage ride-through capability of a 2 MW full converter wind turbine with permanent magnet synchronous generator is investigated herein. A detailed description of the system, its controller options and its behaviour when subjected to a severe voltage dip, is presented. A control scheme for the turbine that allows it to withstand severe voltage dips is designed and simulated. This control scheme emphasises the regulation of the dc‐link voltage and minimisation of the drive train torque surplus. Also, the level of modelling detail required for stability analysis is analysed and discussed.