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Modelling thermo-mechanical cyclic behavior of P91 steel

INTERNATIONAL JOURNAL OF PLASTICITY 2020年 135卷 102820-102820页

作者： Egner, Wladyslaw Sulich, Piotr Mrozinski, Stanislaw Egner, Halina Cracow Univ Technol Fac Mech Engn Inst Appl Mech Al Jana Pawla II 37 PL-31864 Krakow Poland UTP Univ Sci & Technol Fac Mech Engn Al Prof Kaliskiego 7 PL-85796 Bydgoszcz Poland

In this paper, the analysis of the low cycle fatigue behavior of P91 steel is presented. First, experimental tests are performed to recognize different aspects of material behavior. Then an appropriate constitutive model is developed within the framework of thermodynamics of irreversible processes with internal state variables. Two different approaches to fatigue damage modeling are applied comparatively to describe the final stage of material cyclic softening. The material parameters are identified, and the model is validated based on the available experimental data.

关键词： Fatigue Constitutive behavior Mechanical testing numerical algorithms

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Diffusion Map-based Algorithm for Gain Function Approximation in the Feedback Particle Filter

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SIAM-ASA JOURNAL ON UNCERTAINTY QUANTIFICATION 2020年第3期8卷 1090-1117页

作者： Taghvaei, Amirhossein Mehta, Prashant G. Meyn, Sean P. Univ Illinois Dept Mech Sci & Engn MechSe Coordinated Sci Lab CSL Urbana IL 61801 USA Univ Illinois Mech Engn Urbana IL 61801 USA Univ Florida Elect & Comp Engn Gainesville FL 32611 USA

Feedback particle filter (FPF) is a numerical algorithm to approximate the solution of the nonlinear filtering problem in continuous-time settings. In any numerical implementation of the FPF algorithm, the main challenge is to numerically approximate the so-called gain function. A numerical algorithm for gain function approximation is the subject of this paper. The exact gain function is the solution of a Poisson equation involving a probability-weighted Laplacian Delta(rho). The numerical problem is to approximate this solution using only finitely many particles sampled from the probability distribution rho. A diffusion map-based algorithm was proposed by the authors in prior works [A. Taghvaei and P. G. Mehta, Gain function approximation in the feedback particle filter, in 2016 IEEE 55th Conference on Decision and Control (CDC), IEEE, 2016, pp. 5446-5452], [A. Taghvaei, P. G. Mehta, and S. P. Meyn, Error estimates for the kernel gain function approximation in the feedback particle filter, in American Control Conference (ACC), IEEE, 2017, pp. 4576-4582] to solve this problem. The algorithm is named as such because it involves, as an intermediate step, a diffusion map approximation of the exact semigroup e(Delta rho). The original contribution of this paper is to carry out a rigorous error analysis of the diffusion map-based algorithm. The error is shown to include two components: bias and variance. The bias results from the diffusion map approximation of the exact semigroup. The variance arises because of finite sample size. Scalings and upper bounds are derived for bias and variance. These bounds are then illustrated with numerical experiments that serve to emphasize the effects of problem dimension and sample size. The proposed algorithm is applied to two filtering examples and comparisons provided with the sequential importance resampling (SIR) particle filter.

关键词： nonlinear filtering stochastic processes Poisson equation ensemble Kalman filter numerical algorithms error analysis

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Multilevel Algorithm for Obtaining the Proper Orthogonal Decomposition

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AIAA JOURNAL 2018年第11期56卷 4423-4436页

作者： Behzad, Fariduddin Helenbrook, Brian T. Ahmadi, Goodarz Clarkson Univ Dept Mech & Aeronaut Engn 8 Clarkson Ave Potsdam NY 13699 USA Clarkson Univ Dept Mech & Aeronaut Engn Engn Sci Simulat 8 Clarkson Ave Potsdam NY 13699 USA Clarkson Univ Dept Mech & Aeronaut Engn Mech & Aeronaut Engn 8 Clarkson Ave Potsdam NY 13699 USA

A multilevel proper orthogonal decomposition (mPOD) is introduced for obtaining the proper orthogonal decomposition (POD) of data sets with a large number of snapshots without requiring the solution of an equally large eigenvalue problem. mPOD works by producing the PODs for subsets of data first and then applying the POD again to the modes obtained from these subsets. A proof is given that mPOD reproduces identically the modes that would be obtained with the standard POD. mPOD also provides a systematic way to combine POD modes obtained from different simulations and to update POD modes using new data. A numerical algorithm based on mPOD is developed that shows a factor of 10 reduction in computation time compared to snapshot POD. The method is applied to data for fluid flow over a NACA 0015 at Re = 1000 with an actuator jet on the top surface of the airfoil, and results are compared to methods such as subsampling, double proper orthogonal decomposition, sequential mode generation methods, recursive singular value decomposition (R-SVD), and partitioned R-SVD. The examples demonstrate that mPOD provides more accurate eigenvalues, requires fewer disk accesses, and generates modes that create more reliable reduced-order models and have better orthogonality properties than any of the other methods.

关键词： Singular Value Decomposition NACA 0015 Velocity Profiles Actuators numerical algorithms Vortex Shedding Direct numerical Simulation Incompressible Viscous Flow MATLAB Finite Element Method

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A conservative scheme for parallel interval narrowing

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INFORMATION PROCESSING LETTERS 2000年第3-4期74卷 141-146页

作者： Granvilliers, L Hains, G Univ Orleans LIFO F-45067 Orleans 2 France Univ Nantes IRIN F-44322 Nantes France

An efficient parallel interval narrowing algorithm for solving numerical problems is designed, implemented and tested. Differences with the corresponding sequential algorithm are clearly stated. The algorithm's performance is analyzed in the Bulk-Synchronous Parallel (BSP) cost model which suggests speed-ups on high-bandwidth architectures. Experimental results on a massively parallel machine Gray T3E-1200 validate the model and show the parallel algorithm's efficiency as well as its limitations. (C) 2000 Elsevier Science B.V. All rights reserved.

关键词： parallel algorithms numerical algorithms interval narrowing constraint propagation BSP model

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Multiprocessing ocean circulation: Modeling, implementation, and performance on the Intel Paragon

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JOURNAL OF SUPERCOMPUTING 1997年第4期10卷 349-369页

作者： Ahmad, I Leung, KC Hsu, HM NATL CTR ATMOSPHER RES BOULDERCO 80307

In this paper we present the modeling and implementation of a grand challenge problem in the field of scientific computation: the primitive-equation numerical ocean circulation model. We present the mathematical formulation of the model and propose a scheme for its parallel implementation. Optimizations are made through collective communications and various partitioning schemes. In our experiments, which use up to 100 processors on the Intel Paragon parallel computer, the proposed strategy yields an encouraging speedup and exhibits a sustained scalability with increasing problem and machine sizes. We consider barotropic continental shelf waves in a periodic channel as a test problem. The model has numerous applications in environmental studies and ocean sciences.

关键词： high-performance computing parallel applications partial differential equations partitioning numerical algorithms numerical ocean circulation scientific computation

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Fracture Cross Extension Arithmetic Research Based on Non-continuum Theory

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WIRELESS PERSONAL COMMUNICATIONS 2018年第1期103卷 41-53页

作者： Wang, Suling Jiang, Minzheng Dong, Kangxing Chen, Mingzhan Northeast Petr Univ Mech Sci & Engn Coll Daqing 163318 Heilongjiang Peoples R China Daqing Oilfield Co LTD Daqing 163300 Heilongjiang Peoples R China

The cross extension of hydraulic fracture and natural fracture is the key to realize the volume fracture in unconventional reservoir. Based on the non-continuum theory, with the help of numerical simulation algorithm, a mathematical model for in-situ stress about fracturing expansion when the hydraulic fracture intersects with a natural fracture is presented. Then, using two-dimensional linear elastic theory verify the validity of degenerate in-situ stress mode. So it makes the natural fissure error about natural fracture surface pressure less than 1%. As a result, the accuracy of the model was proved. On the basis of the above, considering fluid-structure coupling effect, the stress change rules on natural fracture surface are obtained during hydraulic fracture extension process. The calculation results are as follows: In the process of hydraulic fracture approaching natural fracture, the surface of natural fracture occurs shear deformation first, and then turns into open deformation. Under the influence of shear deformation, the direction of the maximum principal stress on natural fracture surface is the same as initial horizontal maximum principal geostress. Due to the expansion of hydraulic fracture and fracture tip concentration effect, the maximum principal stress appears in the hydraulic fracture tip, this two points may induce the natural fracture begin to extend. And for initial ground stress in a stratum, the smaller the difference, the greater the pressure required to open the natural fracture. At this time, the maximum principal stress on the surface of the natural fracture is less concentrated;multiple fracture initiations are easily formed. Under high pressure, when the approaching angle between natural fracture and hydraulic fracture closes to 45 degrees hydraulic fracture is easier to activate natural fracture, the formed hydraulic fracture shape is more complicated.

关键词： numerical algorithms Natural fracture Shear slip Fracture diverting Initial ground stress difference Approaching angle

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Objective molecular dynamics

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2007年第10期55卷 2206-2236页

作者： Dumitrica, Traian James, Richard D. Univ Minnesota Dept Mech Engn Minneapolis MN 55455 USA Univ Minnesota Dept Aerosp Engn & Mech Minneapolis MN 55455 USA

We introduce a generalization of periodic molecular dynamics that we term objective molecular dynamics. It is a method of doing molecular dynamics for a restricted set of atoms, nonperiodically mapping the time-dependent displacements of this small set of atoms onto the full, typically infinite structure, such that the full structure satisfies exactly the full, unconstrained set of equations of molecular dynamics subject to certain group-invariant initial conditions. The method is applicable to a wide variety of interesting molecular structures including the tails, capsids and other parts of many viruses, carbon nanotubes, many of the common proteins, C-60 and many other nanostructures now being synthesized, especially via the process of self-assembly. The method is illustrated by simulations of carbon nanotubes. (c) 2007 Elsevier Ltd. All rights reserved.

关键词： atomistic structures numerical algorithms buckling structures dynamics

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Concurrent atomistic-continuum simulations of dislocation-void interactions in fcc crystals

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INTERNATIONAL JOURNAL OF PLASTICITY 2015年 65卷 33-42页

作者： Xiong, Liming Xu, Shuozhi McDowell, David L. Chen, Youping Iowa State Univ Dept Aerosp Engn Ames IA 50011 USA Georgia Inst Technol Sch Mat Sci & Engn Atlanta GA 30332 USA Georgia Inst Technol Woodruff Sch Mech Engn Atlanta GA 30332 USA Univ Florida Dept Mech & Aerosp Engn Gainesville FL 32611 USA

Dislocation interactions with distributed condensed vacancy clusters in fcc metals were simulated via a concurrent atomistic-continuum method. Due to void strengthening, the dislocation lines are found to bow as a result of pinning on the original glide plane and undergo depinning through drawing out screw dipoles and forming prismatic loops on the secondary slip plane. We discovered an inertia-induced transition between Hirsch looping and void shearing mechanisms as the void spacing ranges from the scale of nm to hundreds of nm. Contrary to prior understanding, simulations suggest that large voids nm in diameter) can behave as weak barriers to dislocation motions under high strain-rate dynamic conditions. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Dislocations Strengthening mechanisms Metallic material Finite elements numerical algorithms

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Modeling of coupled phase transformation and reorientation in shape memory alloys under non-proportional thermomechanical loading

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INTERNATIONAL JOURNAL OF PLASTICITY 2016年 82卷 192-224页

作者： Chatziathanasiou, Dimitris Chemisky, Yves Chatzigeorgiou, George Meraghni, Fodil Arts & Metiers ParisTech CNRS LEM3 UMR 7239 4 Rue Augustin Fresnel F-57078 Metz 01 France

In the present study, a new 3D thermodynamic coupled model is proposed for SMAs. The behavior of SMA structures is described through several strain mechanisms, each associated with its proper internal variables. This model is built to capture the particular behavior of SMAs when subjected to complex loading, namely non-proportional thermomechanical loading. To achieve this task, a new approach to describe the martensitic reorientation mechanism has been introduced in conjuction with a new method to account for forward and reverse transformation. Thermomechanical coupling, related to dissipation and latent heat is fully implemented. The validity of the model is demonstrated by comparing experimental results of complex thermomechanical loading paths of SMA structures with numerical simulations. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Phase transformation Thermomechanical processes Constitutive behaviour Martensitic reorientation numerical algorithms

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Assessing the impact of the new Athens airport to urban air quality with contemporary air pollution models

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ATMOSPHERIC ENVIRONMENT 1997年第10期31卷 1497-1511页

作者： Moussiopoulos, N Sahm, P Karatzas, K Papalexiou, S Karagiannidis, A ARISTOTELIAN UNIV THESSALONIKI LAB HEAT TRANSFER & ENVIRONM ENGN THESSALONIKI 54006 GREECE

The new airport of Athens will be constructed in the Spata area to the east of the Athens basin. In an attempt to study how the airport operation influences air quality in Athens, the wind how and pollutant transport in the Athens basin and the Spata area are studied by applying a set of contemporary models, all constituents of the EUMAC Zooming Model (EZM): (1) the nonhydrostatic prognostic mesoscale model MEMO for simulating air flow and the dispersion of inert pollutants, and (2) two photochemical dispersion models, the three-dimensional model MARS and the three-layer model MUSE for describing the dispersion of reactive pollutants. Simulations were performed for meteorological conditions favouring the occurrence of air pollution episodes. Emphasis is put on the influence of the airport emissions on air quality assuming that the airport is operating either at its old location (Hellenikon) or at Spata Comparison of simulation results for one selected scenario achieved with all three models reveals similar diurnal variation's of nitrogen oxides in the Athens basin and the Spata area. The model results show that under conditions favoring air mass penetration from Athens to the Spata area the resulting pollutant transport causes an increase in air pollution levels without, however, leading to the exceedance of air quality standards. In the opposite case, the pollutant transport cannot have a noticeable adverse influence on the Athens air quality because of both the relatively high urban air pollution levels and the fact that the penetration depth is small. (C) 1997 Elsevier Science Ltd.

关键词： air pollution modeling numerical algorithms airport emissions comparison with measurements

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