Physical decoupling of the GOES daytime 3.9 µ m channel thermal emission and solar reflection components using total solar eclipse data

A new satellite‐based technique has recently been proposed which seems suitable for an automatic detection of volcanic clouds in daytime conditions. In this paper the robustness of such a new approach, in particular in detecting early eruptive clouds, is evaluated, on several eruptive events at Mt Etna, by using five years of Advanced Very High Resolution Radiometer (AVHRR) data. The detection scheme is discussed together with its possible extension to night‐time monitoring and the improvements expected by its application to the next generation of satellite sensors (in particular Spinning Enhanced Visible and Infrared Imager (SEVIRI)) with enhanced spectral and temporal resolution. The proposed approach seems to overcome the limitations related to other proposed methods which, in some conditions (very fresh eruptive clouds, cold‐backgrounds, etc.), give false or missed detection and will no longer be applicable to the next generation of Geostationary Operational Environmental Satellites (GOES) due to the planned reduction of their thermal infrared channels until 2010.     

Conservative global gyrokinetic toroidal full-f five-dimensional Vlasov simulation

A new conservative global gyrokinetic toroidal full-f five-dimensional Vlasov simulation (GT5D) is developed using a novel non-dissipative conservative finite difference scheme. The scheme guarantees numerical stability by satisfying relevant first principles in the modern gyrokinetic theory, and enables robust and accurate simulations of tokamak micro-turbulence. GT5D is verified through comparisons of zonal flow damping tests, linear analyses of ion temperature gradient driven (ITG) modes, and nonlinear ITG turbulence simulations against a global gyrokinetic toroidal δf particle code. In the comparison, global solutions of the ITG turbulence are identified quantitatively by using two gyrokinetic codes based on particle and mesh approaches.     

低高径比气升式环流反应器Realizable k-ε模型数值模拟分析

气升式反应器因其结构简单,有良好的混合传热性能,便于操作等优点已广泛用于化工、生物化工等行业。本文利用商用计算流体力学软件Fluent,利用Euler-Euler双流体模型,重点针对好氧反应的特点,对一种具有低高径比(H/D=1.67)的环流气升式反应器内的气液两相流动及混合性能进行研究,描述出反应器内气含率和环流液速等参数的详细分布,分析模拟结果,气液速度分布和气含率分布等与实际情况基本吻合,从而证实了计算结果的有效性,为工业实际应用提供一定参考。     

An adaptive scheme for fault-tolerant scheduling of soft real-time tasks in multiprocessor systems

The scheduling of real-time tasks with primary-backup-based fault-tolerant requirements has been an important problem for several years. Most of the known scheduling schemes are non-adaptive in nature meaning that they do not adapt to the dynamics of faults and task's parameters in the system. In this paper, we propose an adaptive fault-tolerant scheduling scheme that has a mechanism to control the overlap interval between the primary and backup versions of tasks such that the overall performance of the system is improved. The overlap interval is determined based on the observed fault rate and task's soft laxity. We also propose a new performance index, called SR index, that integrates schedulability (S) and reliability (R) into a single metric. To evaluate the proposed scheme, we have conducted analytical and simulation studies under different fault and deadline scenarios, and found that the proposed adaptive scheme adapts to system dynamics and offers better SR index than that of the non-adaptive schemes.     

TOUGH+CO2: A multiphase fluid-flow simulator for CO2 geologic sequestration in saline aquifers

TOUGH+CO₂ is a new simulator for modeling of CO₂ geologic sequestration in saline aquifers. It is a member of TOUGH+, the successor to the TOUGH2 family of codes for multicomponent, multiphase fluid and heat flow simulation. The code accounts for heat and up to 3 mass components, which are partitioned into three possible phases. In the code, the thermodynamics and thermophysical properties of H₂O-NaCl-CO₂ mixtures are determined based on system status and subdivided into six different phase combinations. By solving coupled mass and heat balance equations, TOUGH+CO₂ can model non-isothermal or isothermal CO₂ injection, phase behavior and flow of fluids and heat under typical conditions of temperature, pressure and salinity in CO₂ geologic storage projects. The code takes into account effects of salt precipitation on porosity and permeability changes, and the wettability phenomena. The new simulator inherits all capabilities of TOUGH2 in handling fractured media and using unstructured meshes for complex simulation domains. The code adds additional relative permeability and capillary pressure functions. The FORTRAN 95 OOP architecture and other new language features have been extensively used to enhance memory use and computing efficiency. In addition, a domain decomposition approach has been implemented for parallel simulation. All these features lead to increased computational efficiency, and allow applicability of the code to multi-core/processor parallel computing platforms with excellent scalability.     

Three-dimensional simulation of magneto-hydrodynamic implosion of multi-wire cylindrical liners by the FLUX-3D code

A three-dimensional magneto-hydrodynamic model of conductive radiating plasma, underlying the Euler (in the cylindrical coordinates r-φ-z) program code FLUX-3D, developed at the Russian Federal Nuclear Center VNIIEF, is presented. Finite-difference methods for solving the equations of the model on a stationary regular spatial grid are described. Results of numerical 3D simulation of a multi-wire Z-pinch in conditions of the Shot-51 experiment on electrophysical facility Z (USA) in the full (2π) azimuth angle are presented. The computation geometry has been approximated to the real experimental configuration, in which the electromagnetic energy was supplied to the chamber by a vacuum coaxial transmission line. In the numerical simulation, the dynamics of the acceleration of plasma ablated from tungsten wires as a function of the number of wires in the initial cylindrical assembly was studied. In addition, results of 3D calculations of the current implosion of multi-wire Z-pinch for two kinds of artificial perturbations on the plasma ablation intensity are presented. The reasons of the difference in the soft X-ray radiation pulses generated in these cases are discussed.     

Physis语言框架在WENO高阶数值格式异构计算中的应用

WENO(weighted essentially non-oscillatory)是计算流体力学中广泛采用的一种高阶数值格式。由于算法本身和异构计算编程的复杂性,需要开展异构计算代码自动生成的研究,以加速更多的应用。本文基于Physis这一领域编程语言框架,针对三维五阶WENO计算的天文应用,实现了其异构代码的自动生成。在超级计算机"元"上的测试结果表明,自动生成的异构计算代码具有良好的可扩展性,计算性能达到手工优化异构代码的72%,可为相关流体计算的异构代码生成提供借鉴。     

The 3-D gravity inversion package GROWTH2.0 and its application to Tenerife Island, Spain

We present the gravity inversion software GROWTH2.0 and its application to recently obtained gravity data from the volcanic island of Tenerife (Canary Islands, Spain) to inform on its subsurface density structure. GROWTH2.0 is an inversion tool which enables the user to obtain, in a nearly automatic and nonsubjective mode, a 3D model of the subsurface density anomalies based on observed gravity anomaly data. The package is composed of three parts: (a) GRID3D to generate a 3D partition of the subsurface volume into parallelepiped elements, (b) GROWTH to perform the inversion routine and to obtain a 3D anomalous density model, and (c) VIEW for visual representation of the input data, the inversion model, and modeling residuals. The current version of the tool has been developed from an earlier code (Camacho et al., 2002) and now incorporates several novelties: (1) a Graphical User Interface (GUI), (2) an optional automated routine for determination of parameter λ, which controls the balance between model fitness and smoothness, (3) optional determination of values for minimum density contrast, (4) a robust handling of outlier data, and (5) improved automated data reduction for terrain effects based on anticorrelation with topographic data. The new capabilities and applicability of GROWTH2.0 for 3-D gravity inversion are demonstrated by a case example using new gravity data from the volcanic island of Tenerife. In a nearly automatic approach, the software provides a 3-D model informing on the location and shape of the main structural building blocks of the island. Our model results allow us to shed light on the low-density structure of the islands dominant Pico Viejo-Pico Teide (PV-PT) volcanic complex and the identification of an intrusive structure (the east bulge volcano) embedded in Teide's east flank. A low-density body located at around 5.8 km depth beneath PT's summit may represent a current magma or hybrid reservoir.     

An open source, parallel DSMC code for rarefied gas flows in arbitrary geometries

This paper presents the results of validation of an open source Direct Simulation Monte Carlo (DSMC) code for general application to rarefied gas flows. The new DSMC code, called dsmcFoam, has been written within the framework of the open source C++ CFD toolbox OpenFOAM. The main features of dsmcFoam code include the capability to perform both steady and transient solutions, to model arbitrary 2D/3D geometries, and unlimited parallel processing. Test cases have been selected to cover a wide range of benchmark examples from 1D to 3D. These include relaxation to equilibrium, 2D flow over a flat plate and a cylinder, and 3D supersonic flows over complex geometries. In all cases, dsmcFoam shows very good agreement with data provided by both analytical solutions and other contemporary DSMC codes.     

A global collisionless PIC code in magnetic coordinates

A global plasma turbulence simulation code, ORB5, is presented. It solves the gyrokinetic electrostatic equations including zonal flows in axisymmetric magnetic geometry. The present version of the code assumes a Boltzmann electron response on magnetic surfaces. It uses a Particle-In-Cell (PIC), δf scheme, 3D cubic B-splines finite elements for the field solver and several numerical noise reduction techniques. A particular feature is the use of straight-field-line magnetic coordinates and a field-aligned Fourier filtering technique that dramatically improves the performance of the code in terms of both the numerical noise reduction and the maximum time step allowed. Another feature is the capability to treat arbitrary axisymmetric ideal MHD equilibrium configurations. The code is heavily parallelized, with scalability demonstrated up to 4096 processors and 10⁹ marker particles. Various numerical convergence tests are performed. The code is validated against an analytical theory of zonal flow residual, geodesic acoustic oscillations and damping, and against other codes for a selection of linear and nonlinear tests.     

Robust roll motion control of a vehicle using integrated control strategy

This paper presents an electrically actuated roll motion control of a vehicle using simulation and experimental analysis. The controller is designed with an H_∞ control scheme based on the 3 DOF vehicle model considering parameter variations, which affect the roll dynamics. To investigate the feasibility of the active roll control system, its performance is evaluated by simulation in a full vehicle model under various conditions. The Hil setup with the electrically actuated roll control system was devised and its performance was investigated through experimental works. Finally, to enhance the performance in a transient region, an integrated control strategy is presented.     

Accelerating dissipative particle dynamics simulations on GPUs: Algorithms,numerics and applications

We present a scalable dissipative particle dynamics simulation code, fully implemented on the Graphics Processing Units (GPUs) using a hybrid CUDA/MPI programming model, which achieves 10–30 times speedup on a single GPU over 16 CPU cores and almost linear weak scaling across a thousand nodes. A unified framework is developed within which the efficient generation of the neighbor list and maintaining particle data locality are addressed. Our algorithm generates strictly ordered neighbor lists in parallel, while the construction is deterministic and makes no use of atomic operations or sorting. Such neighbor list leads to optimal data loading efficiency when combined with a two-level particle reordering scheme. A faster in situ generation scheme for Gaussian random numbers is proposed using precomputed binary signatures. We designed custom transcendental functions that are fast and accurate for evaluating the pairwise interaction. The correctness and accuracy of the code is verified through a set of test cases simulating Poiseuille flow and spontaneous vesicle formation. Computer benchmarks demonstrate the speedup of our implementation over the CPU implementation as well as strong and weak scalability. A large-scale simulation of spontaneous vesicle formation consisting of 128 million particles was conducted to further illustrate the practicality of our code in real-world applications.     

Weak consistency of the cell-centered Lagrangian GLACE scheme on general meshes in any dimension

We study the consistency in the weak sense of the cell-centered Lagrangian scheme GLACE. The main result is that GLACE is weakly consistent on general meshes in any dimension. The proof relies on a new formula for some geometric vectors defined at the corners of the cell, and which are basic Lagrangian objects. It validates theoretically the use of isoparametric elements (based on Q¹ integration) for 3D Lagrangian compressible gas dynamics calculations. Finally we give the result of a simple convergence test in 2D.     

Rich-information watermarking scheme for 3D models of oblique photography

The security issues of copyright information arise rapidly along with the widely application of 3D models of oblique photography. In this paper, a reversible watermarking scheme is proposed for 3D models of oblique photography, aiming at robustness enhancing and rich-information watermark embedding. To realize the goal of rich-information watermark embedding, an encoding method of original copyright information is designed based on QR code, which can shorten significantly the length of the final watermark data without affecting the copyright expression. A 3D point grouping method is designed and both watermark embedding and extraction are completed group by group, so that the robustness of this scheme under certain attacks can be enhanced, e.g., model segmentation, data compression, point randomly deleting, etc. Moreover, watermarks are embedded into spherical coordinates of 3D points so that the ability of the proposed scheme in resisting geometric transformation can be improved. Results of simulation experiments have demonstrated that the proposed scheme can support rich-information watermark embedding, and it has a satisfying robustness under common geometric and non-geometric attacks.

     

O(N) parallel tight binding molecular dynamics simulation of carbon nanotubes

We report an O(N) parallel tight binding molecular dynamics simulation study of (10×10) structured carbon nanotubes (CNT) at 300 K. We converted a sequential O(N³) TBMD simulation program into an O(N) parallel code, utilizing the concept of parallel virtual machines (PVM). The code is tested in a distributed memory system consisting of a cluster with 8 PC's that run under Linux (Slackware 2.2.13 kernel). Our results on the speed up, efficiency and system size are given.     

A scalable parallel Poisson solver for three-dimensional problems with one periodic direction

A code for the direct numerical simulation (DNS) of incompressible flows with one periodic direction has been developed. It provides a fairly good performance on both Beowulf clusters and supercomputers. Since the code is fully explicit, from a parallel point-of-view, the main bottleneck is the Poisson equation. To solve it, a Fourier diagonalization is applied in the periodic direction to decompose the original 3D system into a set of mutually independent 2D systems. Then, different strategies can be used to solved them. In the previous version of the code, that was conceived for low-cost PC clusters with poor network performance, a Direct Schur-complement Decomposition (DSD) algorithm was used to solve them. Such a method, that is very efficient for PC clusters, cannot be used with an arbitrarily large number of processors and mesh sizes, mainly due to the RAM memory requirements. To do so, a new version of the solver is presented in this paper. It is based on the DSD algorithm that is used as a preconditioner for a Conjugate Gradient method. Numerical experiments showing the scalability and the flexibility of the method on both the MareNostrum supercomputer and a PC cluster with a conventional 100 Mbits/s network are presented and discussed. Finally, illustrative DNS results of an air-filled differentially heated cavity at Ra = 10¹¹ are also presented.     

Modeling shear-induced diffusion force in particulate flows

In this paper, a novel approach is presented to mechanistically model the dispersion of solid particles due to shear-induced diffusion effect. The model is based on the interfacial force concept, so that it is compatible with the ensemble averaged multifield model of multicomponent flows. Although the new model has been developed with membrane filtration processes in mind, the proposed shear-induced diffusion force formulation can be utilized to model a variety of industrial processes where particulates are present. The model has been verified against the other phenomenological models currently in use.The first part of this paper is concerned with theoretical aspects of model derivation. Then, a numerical analysis is presented to illustrate the application of the new model to dilute liquid/particle two-phase flows in tube membrane systems similar to those that are used for micro- and nano-filtration processes. The numerical simulations have been performed using a state of the art multiphase/multicomponent CFD code, NPHASE [Antal SP, Ettorre SM, Kunz RF, Podowski MZ. Development of a next generation computer code for the prediction of multicomponent multiphase flows. In: International meeting on trends in numerical and physical modeling for industrial multiphase flow, Cargese, France; 2000; Kunz RF, Yu WS, Antal SP, Ettorre SM. An unstructured two-fluid method based on the coupled phasic exchange algorithm. AIAA Paper 2001; 2001:2672]. The numerical consistency of the results of computer calculations have been verified against simplified semi-analytical approximations.     

A new 3D parallel SPH scheme for free surface flows

We propose a new robust and accurate SPH scheme, able to track correctly complex three-dimensional non-hydrostatic free surface flows and, even more important, also able to compute an accurate and little oscillatory pressure field. It uses the explicit third order TVD Runge-Kutta scheme in time, following Shu and Osher [Shu C-W, Osher S. Efficient implementation of essentially non-oscillatory shock-capturing schemes. J Comput Phys 1988;89:439-71], together with the new key idea of introducing a monotone upwind flux for the density equation, thus removing any artificial viscosity term. For the discretization of the velocity equation, the non-diffusive central flux has been used. A new flexible approach to impose the boundary conditions at solid walls is also proposed. It can handle any moving rigid body with arbitrarily irregular geometry. It does neither produce oscillations in the fluid pressure in proximity of the interfaces, nor does it have a restrictive impact on the stability condition of the explicit time stepping method, unlike the repellent boundary forces of Monaghan [Monaghan JJ. Simulating free surface flows with SPH. J Comput Phys 1994;110:399-406]. To asses the accuracy of the new SPH scheme, a 3D mesh-convergence study is performed for the strongly deforming free surface in a 3D dam-break and impact-wave test problem providing very good results.Moreover, the parallelization of the new 3D SPH scheme has been carried out using the message passing interface (MPI) standard, together with a dynamic load balancing strategy to improve the computational efficiency of the scheme. Thus, simulations involving millions of particles can be run on modern massively parallel supercomputers, obtaining a very good performance, as confirmed by a speed-up analysis. The 3D applications consist of environmental flow problems, such as dam-break flows and impact flows against a wall. The numerical solutions obtained with our new 3D SPH code have been compared with either experimental results or with other numerical reference solutions, obtaining in all cases a very satisfactory agreement.