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61.
Stephen Wornom Hilde Ouvrard Maria Vittoria Salvetti Bruno Koobus Alain Dervieux 《Computers & Fluids》2011,47(1):44-50
Variational multiscale large-eddy simulations (VMS–LES) of the flow around a circular cylinder are carried out at different Reynolds numbers in the subcritical regime, viz. Re = 3900, 10,000 and 20,000, based on the cylinder diameter. A mixed finite-element/finite-volume discretization on unstructured grids is used. The separation between the largest and the smallest resolved scales is obtained through a variational projection operator and finite-volume cell agglomeration. The WALE subgrid scale model is used to account for the effects of the unresolved scales; in the VMS approach, it is only added to the smallest resolved ones. The capability of this methodology to accurately predict the aerodynamic forces acting on the cylinder and in capturing the flow features are evaluated for the different Reynolds numbers considered. The sensitivity of the results to different simulation parameters, viz. agglomeration level and numerical viscosity, is also investigated at Re = 20,000. 相似文献
62.
Karim JaballiAuthor Vitae Alain BellaciccoAuthor VitaeJamel LouatiAuthor Vitae Alain RiviereAuthor VitaeMohamed HaddarAuthor Vitae 《Computers in Industry》2011,62(5):541-554
During the production of new part in an industrial environment, it results in a high percentage of scrap if manufacturing planning is not carried out properly. One of the major factors responsible for this phenomenon is tolerance synthesis. In this paper, we deal with tolerance synthesis, and especially tolerance type identified after transfer. An algorithmic Rational method for 3D Manufacturing Tolerancing Synthesis (R3DMTSyn), which is based on the use of the Technologically and Topologically Related Surface (TTRS) rules, is developed. The TTRS concept helps to generate only the necessary manufacturing specification needed to guarantee the respect of the functional specification studied.The manufacturing project is modeled by a graphical representation called the SPIDER GRAPH. With the SPIDER GRAPH, all active surfaces can be detected (machined and positioning surfaces), so it is possible to identify the location of the functional surfaces used in each functional specification. The construction or the determination of the tolerancing torsor, belonging to each active surface, contributes to the selection of the adequate case of associations. A semantic study is already done to identify all possible combinations or associations needed to locate surfaces during each phases.Finally, referring to the developed TTRS_Cars_Process and in every phase, one or more manufacturing specifications are generated until finishing the treatment of all surfaces (surface belonging to the functional condition, or intermediate surfaces). 相似文献
63.
A snap-stabilizing protocol, starting from any configuration, always behaves according to its specification. In this paper, we are interested in the message forwarding problem in a message-switched network in which the system resources must be managed in order to deliver messages to any processor of the network. To this end, we use the information provided by a routing algorithm. In the context of an arbitrary initialization (due to stabilization), this information may be corrupted. In Cournier et al. (2009) [1], we show that there exist snap-stabilizing algorithms for this problem (in the state model). This implies that we can request the system to begin forwarding messages without losses even if routing information is initially corrupted.In this paper, we propose another snap-stabilizing algorithm for this problem which improves the space complexity of the one in Cournier et al. (2009) [1]. 相似文献
64.
We show that for some special functions (called k-multigrid equidistributed functions), we can compute the limit of the frequency of patterns in the discretization of their graph, when the resolution tends to zero. This result is applied to parabolas. We deduce also that local length estimators almost never converge to the length for the parabolas. 相似文献
65.
The idea of decomposed software pipelining is to decouple the software pipelining problem into a cyclic scheduling problem without resource constraints and an acyclic scheduling problem with resource constraints. In terms of loop transformation and code motion, the technique can be formulated as a combination of loop shifting and loop compaction. Loop shifting amounts to moving statements between iterations thereby changing some loop independent dependences into loop carried dependences and vice versa. Then, loop compaction schedules the body of the loop considering only loop independent dependences, but taking into account the details of the target architecture. In this paper, we show how loop shifting can be optimized so as to minimize both the length of the critical path and the number of dependences for loop compaction. The first problem is well-known and can be solved by an algorithm due to Leiserson and Saxe. We show that the second optimization (and the combination with the first one) is also polynomially solvable with a fast graph algorithm, variant of minimum-cost flow algorithms. Finally, we analyze the improvements obtained on loop compaction by experiments on random graphs. 相似文献
66.
Sébastien Bardin Alain Finkel Jérôme Leroux Laure Petrucci 《International Journal on Software Tools for Technology Transfer (STTT)》2008,10(5):401-424
Fast acceleration of symbolic transition systems (Fast) is a tool for the analysis of systems manipulating unbounded integer variables. We check safety properties by computing
the reachability set of the system under study. Even if this reachability set is not necessarily recursive, we use innovative
techniques, namely symbolic representation, acceleration and circuit selection, to increase convergence. Fast has proved to perform very well on case studies. This paper describes the tool, from the underlying theory to the architecture
choices. Finally, Fast capabilities are compared with those of other tools. A range of case studies from the literature is investigated.
This paper is mainly based on results presented at CAV 2003, TACAS 2004 and ATVA 2005. 相似文献
67.
The contribution of this paper is threefold. First, we present the paradigm of snap-stabilization. A snap- stabilizing protocol guarantees that, starting from an arbitrary system configuration, the protocol always behaves
according to its specification. So, a snap-stabilizing protocol is a time optimal self-stabilizing protocol (because it stabilizes
in 0 rounds). Second, we propose a new Propagation of Information with Feedback (PIF) cycle, called Propagation of Information with Feedback and Cleaning (). We show three different implementations of this new PIF. The first one is a basic cycle which is inherently snap-stabilizing. However, the first PIF cycle can be delayed O(h
2) rounds (where h is the height of the tree) due to some undesirable local states. The second algorithm improves the worst delay of the basic
algorithm from O(h
2) to 1 round. The state requirement for the above two algorithms is 3 states per processor, except for the root and leaf processors
that use only 2 states. Also, they work on oriented trees. We then propose a third snap-stabilizing PIF algorithm on un-oriented
tree networks. The state requirement of the third algorithm depends on the degree of the processors, and the delay is at most
h rounds. Next, we analyze the maximum waiting time before a PIF cycle can be initiated whether the PIF cycle is infinitely
and sequentially repeated or launch as an isolated PIF cycle. The analysis is made for both oriented and un-oriented trees.
We show or conjecture that the two best of the above algorithms produce optimal waiting time. Finally, we compute the minimal
number of states the processors require to implement a single PIF cycle, and show that both algorithms for oriented trees
are also (in addition to being time optimal) optimal in terms of the number of states.
WARNING: The concept of snap-stabilization was first introduced in [12]. The concept evolved over the last eight years. We
take this evolution in consideration in this paper, which includes the early results published in [10] and [12]. In particular,
infinite repetition of computation cycles is a requirement of self-stabilizing systems. This is not required in snap-stabilization because snap-stabilization ensures that the first completed computation cycle is executed according to the
specification of the problem. The correctness proofs conform to this basic property. 相似文献
68.
Anne Berry Jean-Paul Bordat Alain Sigayret 《Annals of Mathematics and Artificial Intelligence》2007,49(1-4):117-136
Generating concepts defined by a binary relation between a set of properties and a set of objects is one of the important current problems encountered in Data Mining and Knowledge Discovery in Databases. We present
a new algorithmic process which computes all the concepts, without requiring an exponential-size data structure, and with
a good worst-time complexity analysis, which makes it competitive with the best existing algorithms for this problem. Our
algorithm can be used to compute the edges of the lattice as well at no extra cost.
相似文献
69.
Different analytical expressions for the membrane potential distribution of membranes subject to synaptic noise have been proposed and can be very helpful in analyzing experimental data. However, all of these expressions are either approximations or limit cases, and it is not clear how they compare and which expression should be used in a given situation. In this note, we provide a comparison of the different approximations available, with an aim of delineating which expression is most suitable for analyzing experimental data. 相似文献
70.
The main aim of this study is to examine the factors that affect Chinese consumers’ intention to adopt 3G. This study has extended the Technology Acceptance Model (TAM) by incorporating the determinants of perceived usefulness, cost, trust, and demographic profiles of Chinese consumers. Data is collected from Chinese consumers via self-administered questionnaire. Structural equation modeling was applied to examine the research model proposed. Our result showed that social influence, service quality and perceived ease of use have a direct and significant relationship with perceived usefulness of 3G, and this in turn affects the consumers’ decision to adopt 3G. Contrary to existing TAM research, perceived ease of use was not found to have a direct and significant influence with Chinese consumers’ intention to adopt 3G. Our study also revealed that those with higher educational level are more likely to adopt 3G. Based on the findings, this research is able to propose several practical recommendations to 3G providers in China, such as enhancing the variety of services provided through collaborations with mobile software and content developers. Furthermore, 3G providers can focus on promoting 3G through services such as “Friends and Family” packages as Chinese consumers’ 3G adoption decisions is influenced by their social network. In terms of theoretical contributions, this study has answered many calls from past researchers to investigate the determinants of perceived usefulness. This research was also conducted in China, which is one of the largest telecommunication markets in the world. 相似文献