检索结果-内蒙古大学图书馆

ON THE REPRESENTATION OF OPERATORS IN BASES OF COMPACTLY SUPPORTED WAVELETS

SIAM JOURNAL ON numerical ANALYSIS 1992年第6期29卷 1716-1740页

作者： BEYLKIN, G SCHLUMBERGER DOLL RES CTR RIDGEFIELDCT 06877

This paper describes exact and explicit representations of the differential operators, d(n)/dx(n), n = 1,2,..., in orthonormal bases of compactly supported wavelets as well as the representations of the Hilbert transform and fractional derivatives. The method of computing these representations is directly applicable to multidimensional convolution operators. Also, sparse representations of shift operators in orthonormal bases of compactly supported wavelets are discussed and a fast algorithm requiring O(N log N) operations for computing the wavelet coefficients of all N circulant shifts of a vector of the length N = 2n is constructed. As an example of an application of this algorithm, it is shown that the storage requirements of the fast algorithm for applying the standard form of a pseudodifferential operator to a vector (see [G. Beylkin, R. R. Coifman, and V. Rokhlin, Comm. Pure. Appl. Math., 44 (1991), pp. 141-183]) may be reduced from O(N) to O(log2 N) significant entries.

关键词： WAVELETS DIFFERENTIAL OPERATORS HILBERT TRANSFORM FRACTIONAL DERIVATIVES PSEUDODIFFERENTIAL OPERATORS SHIFT OPERATORS numerical algorithms

来源：评论

学校读者我要写书评

暂无评论

Parallel Sparse Approximate Inverse Preconditioning on Graphic Processing Units

引用

IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 2013年第9期24卷 1852-1862页

作者： Dehnavi, Maryam Mehri Fernandez, David M. Gaudiot, Jean-Luc Giannacopoulos, Dennis D. MIT Cambridge MA 02139 USA McGill Univ Montreal PQ H3A 0E9 Canada Univ Calif Irvine Dept Elect Engn & Comp Sci Irvine CA 92697 USA

Accelerating numerical algorithms for solving sparse linear systems on parallel architectures has attracted the attention of many researchers due to their applicability to many engineering and scientific problems. The solution of sparse systems often dominates the overall execution time of such problems and is mainly solved by iterative methods. Preconditioners are used to accelerate the convergence rate of these solvers and reduce the total execution time. Sparse approximate inverse (SAI) preconditioners are a popular class of preconditioners designed to improve the condition number of large sparse matrices. We propose a GPU accelerated SAI preconditioning technique called GSAI, which parallelizes the computation of this preconditioner on NVIDIA graphic cards. The preconditioner is then used to enhance the convergence rate of the BiConjugate Gradient Stabilized (BiCGStab) iterative solver on the GPU. The SAI preconditioner is generated on average 28 and 23 times faster on the NVIDIA GTX480 and TESLA M2070 graphic cards, respectively, compared to ParaSails (a popular implementation of SAI preconditioners on CPU) single processor/core results. The proposed GSAI technique computes the SAI preconditioner in approximately the same time as ParaSails generates the same preconditioner on 16 AMD Opteron 252 processors.

关键词： numerical algorithms parallel algorithms graphics processors parallel programming conditioning

来源：评论

学校读者我要写书评

暂无评论

Unified Method for Field-of-View-Limited Homing Guidance

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2022年第8期45卷 1415-1434页

作者： Dong, Wei Wang, Chunyan Wang, Jianan Son, Hungsun Xin, Ming Beijing Inst Technol Sch Aerosp Engn Beijing 100081 Peoples R China Ulsan Natl Inst Sci & Technol Dept Mech Engn Ulsan 44919 South Korea Univ Missouri Dept Mech & Aerosp Engn Columbia MO 65211 USA

Homing guidance requires maintaining the target lock-on condition within the seeker's field of view (FOV). This paper aims at developing a unified FOV-limited guidance framework from which a variety of two-dimensional (2D) and three-dimensional (3D) guidance laws can be derived. First, the unified method for 2D homing guidance is established by augmenting an arbitrary baseline guidance law with a biased command. To mitigate the effect on the baseline guidance law, this biased command is designed in the admissible range that respects the FOV limit and only takes effect when the lead angle approaches the FOV bound. For more practical relevance, the autopilot dynamic of any order is further considered explicitly in the design with a recursive approach. Then, the unified method for 3D homing guidance with coupling nonlinearity is developed by exploiting the geometric relation among space angles. Unlike existing similar results, the proposed design requires neither switch logic nor numerical algorithms, which allows for continuous guidance command and convenient implementation. With the proposed method, various illustrative guidance laws are derived to demonstrate the significance of the unified framework. Finally, numerical simulations with comparative study are conducted to support the analytical findings and show the superiority of the proposed method.

关键词： Homing Guidance Control Guidance Autopilot numerical Simulation numerical algorithms Rudder Flight Path Angle Optimal Control State Dependent Riccati Equation Terminal Sliding Mode

来源：评论

学校读者我要写书评

暂无评论

Ontology-Enabled Generation of Simulation Software for a Complex Dynamic System

引用

JOURNAL OF AEROSPACE INFORMATION SYSTEMS 2018年第7期15卷 462-470页

作者： Sankari, S. S. Uma Kumar, P. Sreenivasa Geethaikrishnan, C. Indian Inst Technol Madras Dept Comp Sci & Engn Artificial Intelligence & Database Res Lab Chennai 600036 Tamil Nadu India Indian Space Res Org Vikram Sarabhai Space Ctr Qual Assurance Mission Div Thiruvananthapuram 695022 Kerala India

来源：评论

学校读者我要写书评

暂无评论

Anisotropic and asymmetrical yielding and its distorted evolution: Modeling and applications

引用

INTERNATIONAL JOURNAL OF PLASTICITY 2016年 82卷 127-158页

作者： Li, H. Hu, X. Yang, H. Li, L. Northwestern Polytech Univ State Key Lab Solidificat Proc Sch Mat Sci & Engn Xian 710072 Peoples R China Res Inst Baosteel Automobile Steel Res Inst Shanghai 201900 Peoples R China

Characterizing the anisotropy/asymmetry-induced distortional yielding and subsequent evolution is still a challenge for potential usages of hard-to-deform materials. From perspective of multiple mechanisms, two types of yield functions are classified, viz., the principal shear stress-based models (SSM) and the stress invariants-based models (SIM);then a unified continuum-based discontinuous (CBD) framework is constructed, in which SSM and SIM are introduced to capture the distorted shape of the yielding, and an interpolation approach is adopted to smoothly present the nonlinear evolution of the distorted plasticity in the full stress space. Taking the CPB06 (Cazacu et al., 2006) and Yoon's criteria (Yoon et al., 2014) as typical SSM and SIM, the CBD framework is implemented in the explicit 3D-FE platform for practical usages by combining implicit algorithm and interpolation approach, and the Nelder-Mead (N-M) method and the genetic algorithm (GA) approach are evaluated for calibrating of CBD related to convergence, overlapping and accuracy. The evaluation proves that the GA-based method is suitable for CBD, and the SIM seems to be feasible for embedding into the CBD framework because of its solid physical basis and numerical robustness. Taking high strength titanium alloy tube (HSTC) as a case, the distorted plasticity evolution of the HSTT with six typical initial textures are characterized, then the correlations among initial textures, distorted behaviors and inhomogeneous deformation are quantitatively established to improve the multi-defect constrained formability in uniaxial tension/compression and mandrel bending. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Yield condition Anisotropic material Constitutive behaviour Finite elements numerical algorithms

来源：评论

学校读者我要写书评

暂无评论

Experimental and Visco-Plastic Self-Consistent evaluation of forming limit diagrams for anisotropic sheet metals: An efficient and robust implementation of the M-K model

引用

INTERNATIONAL JOURNAL OF PLASTICITY 2015年 73卷 62-99页

作者： Schwindt, C. Schlosser, F. Bertinetti, M. A. Stout, M. Signorelli, J. W. UNS CONICET Dept Engn Buenos Aires DF Argentina IFIR UNR CONICET Rosario Santa Fe Argentina

In the present work, an efficient formulation for the prediction of forming-limit diagrams (FLDs) based on the well-known Marciniak and Kuczynski (M-K) theory using a Visco-Plastic Self-Consistent (VPSC) crystal-plasticity model has been detailed. The present model extends the previous MK-VPSC implementation (Signorelli et al., Predictions of forming limit diagrams using a rate-dependent polycrystal self-consistent plasticity model, International Journal of Plasticity 25 (2009) 1-25) based on the Newton Raphson (N-R) method, which gives no guarantee of a robust iterative procedure. In order to avoid convergence problems and to reduce the computational cost of the coupled MK-VPSC scheme, a direct approach (DA) is proposed. The DA eliminates the need of the Jacobian evaluation associated with the N-R method as well as the iterative procedure tied to other possible minimization techniques. Moreover, the mechanical states outside and inside the groove are solved in the sample reference frame, avoiding the need to rotate the crystallographic orientations and the internal variables to the current band reference frame at each increment. In this way, only two calls to the material law are required per M-K increment, obtaining a more robust numerical procedure with a significant computational cost reduction. Interestingly, the requirement of more complex boundary conditions does not substantially increase the number of internal VPSC iterations to achieve a given tolerance. Simulation results show that the direct MK-VPSC approach is consistent with that based on the N-R method. The generalized boundary conditions in the polycrystal model allowed us to calculate either strain-rate ratio or stress ratio based FLDs. The effect of using either strain-rate ratio or stress ratio paths on the FLDs has been investigated by imposing three types of pre-straining on the sheet metals. Formability predictions for a randomly-textured FCC material and for textured FCC, BCC and HCP polycryst

关键词： Ductility Polycrystalline material Viscoplastic material numerical algorithms Forming limit

来源：评论

学校读者我要写书评

暂无评论

Vibration mode localization in two-dimensional systems

引用

AIAA JOURNAL 1997年第10期35卷 1653-1659页

作者： Xie, WC Wang, X University of Waterloo Waterloo Ontario N2L 3G1 Canada

The method of regular perturbation is applied to study vibration mode localization in randomly disordered weakly coupled two-dimensional cantilever-spring arrays. Localization factors, which characterize the average exponential rates of decay or growth of the amplitudes of vibration, are defined in terms of the angles of orientation. First-order approximate results of the localization factor are obtained using a combined analytical-numerical approach. The localization factors are symmetric about the cantilever and the horizontal and vertical axes passing through the cantilever at which vibration is originated. For the systems under consideration, the direction in which vibration is originated corresponds to the smallest localization factor;whereas the diagonal directions correspond to the largest rate of decay or growth of the amplitudes of vibration. When plotted in the logarithmic scale, the vibration modes are of a hill shape with the amplitudes of vibration decaying linearly away from the cantilever at which vibration is originated.

关键词： Cantilever Bending Stiffness Structural Dynamics Linear Vibrations Green's Function numerical algorithms Computer Memory Kinetic Energy

来源：评论

学校读者我要写书评

暂无评论

DESIGNING REDUCED-ORDER LINEAR-MULTIVARIABLE CONTROLLERS USING EXPERIMENTALLY DERIVED PLANT-DATA

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1993年第1期16卷 53-58页

作者： FRAZIER, WG IRWIN, RD Ohio University Athens Ohio 45701

An iterative numerical algorithm for simultaneously improving multiple performance and stability robustness criteria for multivariable feedback systems is developed. The unsatisfied design criteria are improved by updating the free parameters of an initial, stabilizing controller's state-space matrices. Analytical expressions for the gradients of the design criteria are employed to determine a parameter correction that improves all of the feasible, unsatisfied design criteria al each iteration. A controller design is performed using the algorithm with experimentally derived data from a large space structure test facility. Experimental results of the controller's performance at the facility are presented.

关键词： Large Space Structures numerical algorithms Open Loop Controller Linear Quadratic Gaussian Mathematical Models Control System Design Algorithm Performance Frequency Domain NASA Marshall Space Flight Center Search Algorithm

来源：评论

学校读者我要写书评

暂无评论

OPTIMAL REENTRY MANEUVERS WITH BOUNDED LIFT CONTROL

引用

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1987年第4期10卷 321-329页

作者： BEINER, L Tel Aviv University Ramat Aviv Israel

Green’s theorem is employed to find the optimal lift control that transfers a hypervelocity vehicle between prescribed initial and final values of the altitude and flight-path angle when maximum lift coefficient is bounded. Payoffs to be extremized are either final velocity, range, time, or heat input. Problem formulation leads to linear control, and the optimal maneuvers consist of either max-lift/min-lift or itnin-lift/max-lift nonsingular paths. Conditions for the final state to be reachable by such sequences are derived. Only descending or ascending trajectories are considered. Analytical solutions are derived, and order of subarcs and locations of switching points are determined. Results of parametric studies in nondimensional form are presented graphically. © 1987 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Flight Path Angle Lift Coefficient Zero Lift Drag Coefficient Lift to Drag Ratio Optimal Control numerical algorithms Heat Transfer Earth

来源：评论

学校读者我要写书评

暂无评论

A quasistatic implementation of the concurrent atomistic-continuum method for FCC crystals

引用

INTERNATIONAL JOURNAL OF PLASTICITY 2015年 72卷 91-126页

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

In recent years, numerous partitioned-domain methods have been developed to describe dislocation behavior at length scales that are usually inaccessible to most classical atomistic methods. These methods retain full atomistic detail in regions of interest while using a continuum description to reduce the computational burden elsewhere. In most of these methods, however, lattice defects in the continuum are either implemented via constitutive relations, lattice elasticity with dislocation field interactions, or are not permitted at all. In such approaches, the transit of dislocations across the atomistic/continuum interface appeals to approximate heuristics intended to minimize the effects of the interface due to the change from atomistic to continuum degrees of freedom. The concurrent atomistic-continuum (CAC) method, originally developed for addressing dynamic dislocation behavior by Xiong et al. (2011), permits dislocations to propagate in a continuum domain that employs a piecewise continuous finite element description with interelement displacement discontinuities. The method avoids ghost forces at interfate between atomistically resolved and coarse-grained domains. CAC has subsequently been used to investigate complex dislocation behavior in face-centered cubic (FCC) metals (Xiong et al., 2012b,a,c, 2015). In this paper, we propose a quasistatic 3-D method to carry out sequential energy-minimized simulations at 0 K. This facilitates study of structure evolution along minimum energy pathways, avoiding over-driven conditions of high rate molecular dynamics. Parallelization steps in code implementation are described. Applications are presented for the quasistatic CAC method in FCC metal plasticity. Comparisons are made with a fully-resolved atomistic method for generalized stacking fault energy, core structure and stress field of a single 60 mixed type dislocation, surface indentation, and 60 mixed type dislocation migration through the interface between atomistic

关键词： Concurrent atomistic-continuum method Dislocations Metallic material Finite elements numerical algorithms

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：