A Newton-Schur alternative to the consistent tangent approach in computational plasticity

We introduce a Newton-Schur alternative to the consistent tangent approach in plasticity computations and show that the structure of the consistent tangent approach is preserved in the new Newton-Schur approach. However, the local constitutive iterations used in the conventional computational plasticity analyses are eliminated when using the Newton-Schur approach. Two numerical examples are presented which illustrate the efficiencies gained by the new approach.     

Mean tangent rotational angles and curvature integration

Stationary values of mean tangent rotation angles are used in the intrinsic-curve design method which defines curves for CAD by specifying curvature and/or torsion profiles. This paper discusses these mean angles ($\text{ψ}$ and $\text{φ}$) and makes use of $\text{ψ}$ to derive approximate formulas for fast integration of curvature profiles.     

Indefinite integration as term rewriting: Integrals containing tangent

We describe the development of a term-rewriting system for indefinite integration; it is also called a rule-based evaluation system. The development is separated into modules, and we describe the module for a wide class of integrands containing the tangent function.     

Generating efficient derivative code with TAF: Adjoint and tangent linear Euler flow around an airfoil

FastOpt’s new automatic differentiation tool TAF is applied to the two-dimensional Navier–Stokes solver NSC2KE. For a configuration that simulates the Euler flow around an NACA airfoil, TAF has generated the tangent linear and adjoint models as well as the second derivative (Hessian) code. Owing to TAF’s capability of generating efficient adjoints of iterative solvers, the derivative code has a high performance: running both the solver and its adjoint requires 3.4 times as long as running the solver only. Further examples of highly efficient tangent linear, adjoint, and Hessian codes for large and complex three-dimensional Fortran 77-90 climate models are listed. These examples suggest that the performance of the NSC2KE adjoint may well be generalised to more complex three-dimensional CFD codes. We also sketch how TAF can improve the adjoint’s performance by exploiting self-adjointness, which is a common feature of CFD codes.     

四元数与欧拉角刚体动力学数值积分算法及其比较

为推广四元数保辛积分在工程中的应用,对欧拉角表示的状态方程数值积分与四元数的保辛积分进行比较.重陀螺的数值仿真结果表明四元数保辛积分的数值结果明显优于欧拉角状态方程积分.与欧拉角状态方程积分相比,四元数保辛积分在刚体动力学的数值仿真中更具优势.     

四元数与欧拉角刚体动力学数值积分算法及其比较

为推广四元数保辛积分在工程中的应用,对欧拉角表示的状态方程数值积分与四元数的保辛积分进行比较.重陀螺的数值仿真结果表明四元数保辛积分的数值结果明显优于欧拉角状态方程积分.与欧拉角状态方程积分相比,四元数保辛积分在刚体动力学的数值仿真中更具优势.     

Studies on generalized midpoint integration in rate-independent plasticity with reference to plane stress J2-flow theory

Issues related to use of the generalized midpoint integration in rate-independent plasticity are investigated restricting attention to plane stress J₂-flow theory. Accuracy analysis is performed by developing the iso-error maps for a representative range of loading conditions and -values utilized in the midpoint integration rule. Consequences of the discrete enforcement of the consistency condition on the numerical resolution of the boundary value problem are discussed. A numerical example is presented to test the influence of the choice of -value on a global accuracy and effectiveness of the solution scheme.     

NICE h : a higher-order explicit numerical scheme for integration of constitutive models in plasticity

The article introduces, as a result of further development of the first-order scheme NICE, a simple and efficient higher-order explicit numerical scheme for the integration of a system of ordinary differential equations which is constrained by an algebraic condition (DAE). The scheme is based on the truncated Taylor expansion of the constraint equation with order h of the scheme being determined by the highest exponent in the truncated Taylor series. The integration scheme thus conceived will be named NICE ^h , considering both principal premises of its construction. In conjunction with a direct solution technique used to solve the boundary value problem, the NICE ^h scheme is very convenient for integrating constitutive models in plasticity. The plasticity models are defined mostly by a system of algebraic and differential equations in which the yield criterion represents the constraint condition. To study the properties of the new integration scheme, which, like the forward-Euler scheme, is characterised by its implementation simplicity due to the explicitness of its formulations, a damage constitutive model (Gurson–Tvergaard–Needleman model) is considered. The general opinion that the implicit backward-Euler scheme is much more accurate than the thus-far known explicit schemes is challenged by the introduction of the NICE ^h scheme. The accuracy of the higher-order explicit scheme in the studied cases is significantly higher than the accuracy of the classical backward-Euler scheme, if we compare them under the condition of a similar CPU time consumption.     

The discrete null space method for the energy consistent integration of constrained mechanical systems: Part I: Holonomic constraints

The present work deals with energy consistent time stepping schemes for finite-dimensional mechanical systems with holonomic constraints. The proposed procedure is essentially based upon the following steps: Firstly, the index three differential-algebraic equations corresponding to the constrained mechanical system are directly discretized. Secondly, the discrete Lagrange multipliers are eliminated by using a discrete null space matrix. In many cases it is feasible to further reduce the number of unknowns by employing specific reparametrizations. The proposed method entails a number of advantageous features such as size-reduction and improved conditioning of the resulting system of algebraic equations. It is shown that the newly developed method is well-suited for both open-loop and closed-loop multibody systems.     

On near equivalence of assumed stress and reduced integration formulations of the bilinear plane stress finite element

It is now well known that displacement finite elements in which reduced integration is used tend to exhibit similar performance to that of finite elements formulated on a stress basis. The bilinear displacement element for plane stress provides a useful example of this equivalence; as when selective one point integration is used for the shearing energy, the resulting stiffness matrix is identical to that obtained for the equivalent assumed stress element when Poisson's ratio is zero.     

Nesting in Euler Diagrams: syntax,semantics and construction

This paper considers the notion of nesting in Euler diagrams, and how nesting affects the interpretation and construction of such diagrams. After setting up the necessary definitions for concrete Euler diagrams (drawn in the plane) and abstract diagrams (having just formal structure), the notion of nestedness is defined at both concrete and abstract levels. The concept of a dual graph is used to give an alternative condition for a drawable abstract Euler diagram to be nested. The natural progression to the diagram semantics is explored and we present a nested form for diagram semantics. We describe how this work supports tool-building for diagrams, and how effective we might expect this support to be in terms of the proportion of nested diagrams.     

Euler index of uncertain random graph: concepts and properties

We are usually in the state of indeterminacy. Uncertainty and randomness are two basic types of indeterminacy. In many cases, uncertainty and randomness exist simultaneously in a complex system. This paper considers the Euler tour of an uncertain random graph, in which some edges exist with some degrees in uncertain measure and others exist with some degrees in probability measure. In order to show how likely an uncertain random graph is Eulerian, an Euler index of an uncertain random graph is proposed first. Then a method to calculate the Euler index of an uncertain random graph is given. In addition, some properties of the Euler index are discussed.     

Elastic SI-Cache: consistent and scalable caching in multi-tier architectures

The new vision of cloud computing demands scalable, available and autonomic software platforms in order to deploy applications and services accessible anywhere and anytime. Multi-tier architectures are an important building block for many applications that are deployed in the cloud. This paper presents a novel caching and replication infrastructure that facilitates the scalable and elastic deployment of multi-tier architectures. Our Elastic SI-Cache is a novel multi-version cache that attains high performance and consistency in multi-tier systems. In contrast to most existing caches, Elastic SI-Cache provides snapshot isolation coherently across all tiers. Furthermore, Elastic SI-Cache supports scalable replication of the different tiers where replicas can be added or removed dynamically as needed, making the cache amenable for cloud computing environments. Elastic SI-Cache has been implemented and integrated into an open source JEE application server and its performance evaluated with the industrial benchmark SPECjAppServer.     

Class consistent k-means: Application to face and action recognition

A class-consistent k-means clustering algorithm (CCKM) and its hierarchical extension (Hierarchical CCKM) are presented for generating discriminative visual words for recognition problems. In addition to using the labels of training data themselves, we associate a class label with each cluster center to enforce discriminability in the resulting visual words. Our algorithms encourage data points from the same class to be assigned to the same visual word, and those from different classes to be assigned to different visual words. More specifically, we introduce a class consistency term in the clustering process which penalizes assignment of data points from different classes to the same cluster. The optimization process is efficient and bounded by the complexity of k-means clustering. A very efficient and discriminative tree classifier can be learned for various recognition tasks via the Hierarchical CCKM. The effectiveness of the proposed algorithms is validated on two public face datasets and four benchmark action datasets.     

Concurrent Pascal with backward error recovery: Language features and examples

The programming language Concurrent Pascal has been extended to include some language features that facilitate the writing of fault-tolerant software. As a result, it is possible now to (1) write operating systems with a measure of fault-tolerance, and (2) for such an operating system to support fault-tolerant user programs. The paper describes these language features and illustrates their use with the help of a few working examples.     

Rhythms and plasticity: television temporality at home

Digital technologies have enabled new temporalities of media consumption in the home. Through a field study of home television viewing practices, we investigated temporal orderings of television watching. In contrast to traditional pictures of television use, our evidence suggests that rhythms across households play an important role in shaping television watching. Further, we found a flexibility and openness within the patterns of television viewing that we refer to as “plasticity.” Our data suggest that plasticity and rhythms co-exist and together compose the qualitative experience of domestic television time; an understanding of both aspects of temporality suggests an approach for the design of future television technologies.     

Out-of-Order Execution in Sequentially Consistent Shared-Memory Systems:Theory and Experiments

Traditional implementation of sequential consistency in shared-memory systems requires memory accesses to be globally performed in program order.Based on an event ordering model for correct executions in shared-memory systems,this paper proposes and proves that out-of-order execution does not influence the correctness of an execution providing certain condition is met.Simulation results show that out-of-order execution proposed in this paper is an effective way to improve the performance of a sequentially consistent shared-memory system.     

CIMOSA: enterprise engineering and integration

Enterprises are rather complex systems which have to be managed for their internal affairs, but more importantly for the many relations to the different environments in which they are operating. Today, these environments are changing much more rapidly and the need for relevant information becomes of paramount importance in the decision making processes at all levels of enterprise management. Fluctuations in market demands, technology evolution and changing regulations require very flexible enterprise operations, capable of reacting to those changes. These reactions must be based on relevant and up-to-date information which must be supported by new decision support technology. The challenges in decision support concern the identification of relevant information, easy access and intelligent use of this information. Building and maintaining the enterprise knowledge base and enabling its efficient use for decision support are major tasks of enterprise engineering. Enterprise integration and its subsequent operation in the global environment of customers, suppliers and regulatory bodies will heavily depend on the availability and the continuous extension of this knowledge base. Enterprise modelling will play an important role in creating the knowledge base and in using it for enterprise integration and operational decision support. The paper discusses enterprise engineering as an enterprise life-cycle oriented discipline for identification, design, and implementation of enterprises and their continuous evolution. Current problems in the field are identified and initiatives are presented.