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Improvement of the prediction of surface ozone concentration over conterminous US by a computationally efficient second-order Rosenbrock solver in CAM4-Chem

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JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2017年第1期9卷 482-500页

作者： Sun, Jian Fu, Joshua S. Drake, John Lamarque, Jean-Francois Tilmes, Simone Vitt, Francis Univ Tennessee Dept Civil & Environm Engn Knoxville TN 37996 USA Oak Ridge Natl Lab Climate Change Sci Inst Oak Ridge TN 37830 USA Oak Ridge Natl Lab Comp Sci & Math Div Oak Ridge TN 37830 USA Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA

The global chemistry-climate model (CAM4-Chem) overestimates the surface ozone concentration over the conterminous U.S. (CONUS). Reasons for this positive bias include emission, meteorology, chemical mechanism, and solver. In this study, we explore the last possibility by examining the sensitivity to the numerical methods for solving the chemistry equations. A second-order Rosenbrock (ROS-2) solver is implemented in CAM4-Chem to examine its influence on the surface ozone concentration and the computational performance of the chemistry program. Results show that under the same time step size (1800 s), statistically significant reduction of positive bias is achieved by the ROS-2 solver. The improvement is as large as 5.2 ppb in Eastern U.S. during summer season. The ROS-2 solver is shown to reduce the positive bias in Europe and Asia as well, indicating the lower surface ozone concentration over the CONUS predicted by the ROS-2 solver is not a trade-off consequence with increasing the ozone concentration at other global regions. In addition, by refining the time step size to 180 s, the first-order implicit solver does not provide statistically significant improvement of surface ozone concentration. It reveals that the better prediction from the ROS-2 solver is not only due to its accuracy but also due to its suitability for stiff chemistry equations. As an added benefit, the computation cost of the ROS-2 solver is almost half of first-order implicit solver. The improved computational efficiency of the ROS-2 solver is due to the reuse of the Jacobian matrix and lower upper (LU) factorization during its multistage calculation.

关键词： second-order Rosenbrock solver first-order implicit solver time step ozone computational performance

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Limitations on gas turbine performance imposed by large turbine cooling flows

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JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 2001年第3期123卷 487-494页

作者： Horlock, JH Watson, DT Jones, TV Univ Cambridge Dept Engn Whittle Lab Cambridge CB2 ODY England Rolls Royce PLC Derby DE2 8BJ England Univ Oxford Osney Lab Dept Engn Sci Oxford England

Calculations of the performance of modern gas turbines usually include allowance for cooling airflow rate;assumptions are made for the amount of the cooling air bled from the compressor, as a fraction of the mainstream flow, but this fractional figure is often set in relatively arbitrary fashion. There are two essential effects of turbine blade cooling: (i) the reduction of the gas stagnation temperature at exit from the combustion chamber (entry to the first nozzle row) to a lower stagnation temperature at entry to the first rotor and (ii) a pressure loss resulting from mixing the cooling air with the mainstream. Similar effects occur in the following cooled blade rows. The paper reviews established methods for determining the amount of cooling air required and semi-empirical relations, for film cooled binding with thermal barrier coatings, are derived. Similarly, the pressure losses related to elements of cooling air leaving at various points round the blade surface are integrated over the whole blade. This gives another semi-empirical expression, this time for the complete mixing pressure loss in the blade row, as a function of the total cooling air used. These two relationships are then used in comprehensive calculations of the performance of a simple open-cycle gas turbine, for varying combustion temperature and pressure ratio. These calculations suggest that for maximum plant efficiency there may be a limiting combustion temperature (below that which would tie set by stoichiometric combustion). For a given combustion temperature, the optimum pressure ratio is reduced by the effect of cooling air.

关键词： air cooling combustion temperature PRESSURE LOSS plant efficiency Turbine performance Blades computational performance PresRto stagnation temperature

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Hydraulic transient guidelines for protecting water distribution systems

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JOURNAL AMERICAN WATER WORKS ASSOCIATION 2005年第5期97卷 111-124页

作者： Boulos, PF Karney, BW Wood, DJ Lingireddy, S MWH Soft Inc Broomfield CO USA Univ Toronto Dept Civil Engn Toronto ON Canada Univ Kentucky Dept Civil Engn Lexington KY 40506 USA

Transients can introduce large pressure forces and rapid fluid accelerations into a water distribution system. These disturbances may result in pump and device failures, system fatigue or pipe ruptures, and even the backflow/intrusion of dirty water. Many transient events can lead to water column separation, which can result in catastrophic pipeline failures. Thus, transient events cause health risks and can lead to increased leakage or decreased reliability. Transient flow simulation has become an essential requirement for ensuring safety and the safe operation of drinking water distribution systems. This article provides a basic understanding of the physical phenomena and context of transient conditions, presents practical guidelines for their suppression and control, and compares the formulation and computational performance of widely used hydraulic transient simulation schemes. Such capabilities greatly enhance the ability of water utilities to conceive and evaluate cost-effective and reliable water supply protection and management strategies and safeguard public health.

关键词： Water distribution networks Safe handling WATER HAMMER computational performance System management Sound velocity Water distribution systems Hydraulic system control systems Transient conditions Operating systems Hydraulic transients

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Long-term symbolic learning

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COGNITIVE SYSTEMS RESEARCH 2007年第3期8卷 237-247页

作者： Kennedy, William G. Trafton, J. Gregory USN Res Lab Washington DC 20375 USA

What are the characteristics of long-term learning? We investigated the characteristics of long-term, symbolic learning using the Soar and ACT-R cognitive architectures running cognitive models of two simple tasks. Long sequences of problems were run collecting data to answer fundamental questions about long-term, symbolic learning. We examined whether symbolic learning continues inde. finitely, how the learned knowledge is used, and whether computational performance degrades over the long term. We report three. findings. First, in both systems, symbolic learning eventually stopped. Second, learned knowledge was used diff. erently in different stages but the resulting production knowledge was used uniformly. Finally, both Soar and ACT-R do eventually suffer from degraded computational performance with long-term continuous learning. We also discuss ACT-R implementation and theoretic causes of ACT-R's computational performance problems and settings that appear to avoid the performance problems in ACT-R. Published by Elsevier B. V.

关键词： long-term learning symbolic learning computational cognitive modeling ACT-R soar computational performance utility problem

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HYBRID HIGH-ORDER AND WEAK GALERKIN METHODS FOR THE BIHARMONIC PROBLEM

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SIAM JOURNAL ON NUMERICAL ANALYSIS 2022年第5期60卷 2626-2656页

作者： Dong, Zhaonan Ern, Alexandre INRIA 2 Rue Simone Iff F-75589 Paris France CERMICS Ecole Ponts F-77455 Marne La Vallee France

We devise and analyze two hybrid high-order (HHO) methods for the numerical approximation of the biharmonic problem. The methods support polyhedral meshes, rely on the primal formulation of the problem, and deliver O(h(k+1)) H-2-error estimates when using polynomials of order k >= 0 to approximate the normal derivative on the mesh (inter)faces. Both HHO methods hinge on a stabilization in the spirit of Lehrenfeld and Schoberl for second-order PDEs. The cell unknowns are polynomials of order (k + 2) that can be eliminated locally by means of static condensation. The face unknowns approximating the trace of the solution on the mesh (inter)faces are polynomials of order (k + 1) in the first HHO method, which is valid in dimension two and uses an original stabilization involving the canonical hybrid finite element, and they are of order (k + 2) for the second HHO method, which is valid in arbitrary dimension and uses only L-2-orthogonal projections in the stabilization. A comparative discussion with the weak Galerkin methods from the literature is provided, highlighting the close connections and the improvements proposed herein. Additionally, we show how the two HHO methods can be combined with a Nitsche-like boundary-penalty technique to weakly enforce the boundary conditions. An originality in the devised Nitsche's technique is to avoid any penalty parameter that must be large enough. Finally, numerical results showcase the efficiency of the proposed methods and indicate that the HHO methods can generally outperform discontinuous Galerkin methods and even be competitive with C-0-interior penalty methods on triangular meshes.

关键词： biharmonic problem fourth-order PDEs hybrid high-order method weak Galerkin method stability error analysis computational performance

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performance and Accuracy Implications of Parallel Split Physics-Dynamics Coupling in the Energy Exascale Earth System Atmosphere Model

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JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2020年第7期12卷 e2020MS002080-e2020MS002080页

作者： Donahue, Aaron S. Caldwell, Peter M. Lawrence Livermore Natl Lab Livermore CA 94550 USA

Simultaneous calculation of atmospheric processes is faster than calculating processes one at a time. This type of parallelism is beneficial or perhaps even necessary to provide good performance on modern supercomputers, which achieve faster performance through increased processor count rather than improved clock speed. The scalability of the Energy Exascale Earth System Model (E3SM) Atmosphere Model (EAM) is limited by the fluid dynamics which scales up to the number of mesh cells in the global mesh. In contrast, the suite of physics parameterizations in EAM is scalable up to the total number of physics columns, which is an order of magnitude greater than the number of mesh cells. A proposed solution to unlocking the greater potential performance from the physics suite is to solve the physics and dynamics in parallel. This work represents a first attempt at parallel splitting of the grid-scale fluid dynamics model and the subgrid-scale physics parameterizations in a global atmosphere model. We will demonstrate that switching to parallel physics-dynamics coupling extends the scalability of the EAM to up to 3 times the previous peak scalability limit and is up to 20% faster than the sequentially split coupling at the highest core counts and the same time step. Decadal simulations of both coupling approaches show very little impact to the model climate. This improved performance does not come without drawbacks, however. Parallel splitting requires a shorter time step and other modifications which largely offset performance gains. A mass fixer is required for conservation. Techniques for mitigating these issues are also discussed.

关键词： computational performance parallel splitting physics-dynamics coupling global atmosphere modeling time stepping numerical stability

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IEEE MICRO 2018年第6期38卷 46-55页

作者： Alcaide, Sergi Kosmidis, Leonidas Tabani, Hamid Hernandez, Carles Abella, Jaume Cazorla, Francisco J. Univ Politecn Cataluna Barcelona Spain Barcelona Supercomp Ctr Barcelona Spain Barcelona Supercomp Ctr CAOS Res Grp Barcelona Spain IIIA CSIC Barcelona Spain

GPUs have been shown to cover the computing performance needs of autonomous driving (AD) ***, since the GPUs used for AD build on designs for the mainstream market, they may lack fundamental properties for correct operation under automotive's safety regulations. In this paper, we analyze some of the main challenges in hardware and software design to embrace GPUs as the reference computing solution for AD, with the emphasis in ISO 26262 functional safety requirement.

关键词： Safety ISO Standards Graphics processing units Hardware acceleration Automotive engineering Redundancy Unmanned autonomous vehicles automotive engineering Software design computational performance AD safety requirements redundancy ISO standard Graphics Processing Unit

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The neutronics scheme adopted for the HELIOS irradiation experiment in the High Flux Reactor Petten

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ANNALS OF NUCLEAR ENERGY 2017年第Mar.期101卷 312-321页

作者： D'Agata, E. Doderlein, C. Tsige-Tamirat, H. Oettingen, M. Mutnuru, R. European Commiss Inst Energy & Transport JRC IET Joint Res Ctr POB 2 NL-1755 ZG Petten Netherlands AGH Univ Sci & Technol Al A Mickiewicza 30 PL-30059 Krakow Poland Nucl Res & Consultancy Grp NRG POB 25 NL-1755 ZG Petten Netherlands

A dedicated neutronics computational scheme is a crucial tool in the preparation and the post-analysis of an irradiation experiment, as it defines the key parameters of the experiment. The complex and very dynamic environment of a Materials Testing Reactor (MTR) core, on the other hand, represents a challenging object for neutronics calculations. Within the framework of the HELIOS experiment conducted at the High Flux Reactor (HFR) in Petten (The Netherlands) in 2009 under the European Project EUROTRANS, a new neutronics scheme has been developed with the objective of finding the optimum balance between accuracy and calculation performance. This scheme is based on the Monte-Carlo technique and employs a two-level approach by separating the problem into overlapping spatial and temporal domains. The underlying physical phenomena are presented, together with elements of validation which gives a further insight into the effects governing the neutron fluxes in the core. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://***/licenses/by-nc-nd/4.0/).

关键词： Neutron flux computational performance Scheme HFR REACTOR Irradiation

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Reliability-constrained robust expansion planning of active distribution networks

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IET GENERATION TRANSMISSION & DISTRIBUTION 2022年第1期16卷 27-40页

作者： Pinto, Rafael S. Unsihuay-Vila, Clodomiro Tabarro, Fabricio H. Univ Fed Parana Elect Engn Dept BR-80050370 Curitiba Parana Brazil COPEL Dept Serv Channels Technol & Qual Curitiba Parana Brazil

Power distribution systems have become more complex in recent years due to the integration of new technologies. Motivated by these challenges, this paper describes a model to solve the multi-period expansion planning problem of active distribution systems, considering uncertainty, reliability, distributed generation, self-healing, reactive power support, switches, and energy storage devices. The objective is to determine the best installation times and locations of new components, minimizing the total cost, and ensuring desired reliability levels. The approach consists of a three-level decomposition. The first level identifies expansion proposals, the second level finds the worst-case scenario using adaptive robust optimization, and the third level performs a Monte Carlo Simulation to compute reliability indexes. The main contributions are the introduction of a novel reliability sensitivity matrix to improve computational performance and the representation of the hours of the day inside the expansion planning formulation. The proposed method is illustrated using the IEEE 123-bus test system. The analyses show high computational efficiency as compared with similar works. The impacts on the number of expansion components placed in the system and on the total cost are presented and discussed using cases varying the uncertainty budget and not considering some of these components.

关键词： installation times distributed power generation reliability indexes power distribution planning expansion proposals reliability sensitivity matrix multiperiod expansion planning problem expansion components reactive power support Monte Carlo Simulation three-level decomposition Monte Carlo methods distributed generation adaptive robust optimization power distribution systems active distribution networks reliability levels worst-case scenario expansion planning formulation reliability-constrained robust expansion planning power distribution reliability IEEE 123-bus test system high computational efficiency energy storage devices computational performance

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Postbuckling performance of the TRIC natural mode triangular element for isotropic and laminated composite shells

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COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 1998年第3-4期166卷 211-231页

作者： Argyris, J Tenek, L Papadrakakis, M Apostolopoulou, C Natl Tech Univ Athens Inst Struct Anal & Seism Res GR-15773 Athens Greece Univ Stuttgart Inst Comp Applicat D-70579 Stuttgart 80 Germany

We present the computational performance and the achieved accuracy of the TRIC flat triangular shell element for nonlinear postbuckling analysis of arbitrary isotropic and composite shells. The element is based on the natural mode finite element method, which allows a convenient description of the current position of the structure. These natural modes are assigned to a convective coordinate system which follows the element during deformation within the framework of an Eulerian motion. With respect to this coordinate system the natural modes are additive. Numerical examples verify the accuracy, computational efficiency and the potential of the TRIC element in predicting the postbuckling behaviour of shells. Natural energy measures inform us about the energy allocation during nonlinear deformation and the interplay of the separate energy components. (C) 1998 Elsevier Science S.A.

关键词： computational performance triangular element natural MARVEL Domain Containing 2 Protein Elements Current Position laminate composite Isotropic shell element

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